I !I" W

W,» .5!!! 1‘ I”:
:JIIE} *1 f9" {[0 .....

WM 9

     
 

__-.m
-I Om ~—
A..-

0-
“—

I "If?”
WI. W

I J

 
     
 
   
 

     
 

I.

m , I
a...
\fE =m:
. 9-h-
_ ,_._..-,
3
< . .

.
a gap-"1'
“ 4»;- -< .
.. -a‘c' -
- ; ":v .-
«. . ...Tf.a -
- _ ' - :...:‘,'
. ‘_.’_..=:P.'!
, ‘- -— 3....
-.,..
.__.
—..

 
     
   
   
  
  
       
      
   
 
 
   

 

   

    
 
  
  
 

 

éfl‘ m:

g1," 'Ofii‘zfi'
‘W

4. 5‘1???
"3:33;, _

 

2;!“

   
  

  

  
    

‘ I I .
.I W I ' 2 13‘1”“? jib}
. I4? 1:. I?!” III‘ :7, 3:3 A «“é‘fi f»:
., «1-3.; 1 Igii 512. f”! .
‘ .I ; " ‘ I. 31 ‘t :5.
I::§‘{1:I'. 1&3 'I 2 1W“ "5’!“ “74' 1 I13”! I.
v; 5,! r - Il’Is‘i "‘5
I; .1

   
 

”r {33.8”
L. J,“
lid” ’4!

          
  

phdql- 31‘ NW?!

fi'gqg “H'-
f’ ‘5r

‘1 ' ' L'21.d."!!

 

    
   

‘ 1b): 2*“ :Ajii'y “4 ‘ ‘
';I;:L‘;E?%?¥!§{?‘I"“ '! It: 95:". III:

' "12:7?!le ‘I‘zf. W Wu. “I:
'UJ 1'

”It! vlqglth-Frr
staff 3'“ j 1 E, L

...
"
In.

 
   
 
 

O
!I!U.W

{U 5W3?!”

       
  
 

           
   
     
   

- ‘.
..’." A .
-' v4 .

's‘iff‘ l
I II ". -‘
w I'll” ' '1'! u “If!“ .3wa H
:3‘;:II I. ;-.- :g :Ij; ' ;

  

~
- ‘a
u...“
<~...
-c‘-

~43
‘

     
  

w
v
£1.

   
 
 
   

Wk?“ 2;: ‘T‘QHI‘

WW Jo]j $§§Ifil§ewgw ,2]

" l "‘9’! 'IUII: ‘
,l’H‘Lfldsz‘ II :Iig-l. .I "III:

If??? !l}.v1{,¢; '5, I?
54 L7 f". I

. [i'fil “1‘" fr 1,”. 'EJE‘EII} if;
M; l!’ iffy“ L TI IJIWLWWIIQ?
fI ‘Ifi'II’fu'II'III'r »? I'm“ 1;: !
J}:H!i:, :[Lf

I W I“
{I 1st EM!!!"

III!L

rm?) flu,
I") I!

u-

  

_.-.__
-~:,‘I..__
......_
m.—

   

   

_,.:;;r

-q_

 
     
 

I
i:
,.
I. J
.3
I'.
'1

lg:
. M,

r:

 

’54

IllllIIIHIHHIIIIIIHIHIHIIllllWllfllilllllllllllllllllll

3 1293 10421 9856

.»-—W

  
  

- A-....h-M~‘¥"‘

Liam fiY
Ecmmn £3533“:
University

A
\

 

 

This is to certify that the

thesis entitled

The Origin and Geochemistry of Carbonate Concretions,

Antrim Sha1e(Devonian, Michigan Basin)

presented by

Mel issa S . Wardlaw

has been accepted towards fulfillment
of the requirements for

M- S - degree in J9 01 08)’ ,

‘9
< " Mi

Major professor

0-7 639

’...

 

MSU
LIBRARIES
“

 

 

 

RETURNING MATERIALS:

 

Place in book drop to
remove this checkout from
your record. FINES will
be charged if book is
returned after the date
stamped below.

 

4; e014"

 

 

 

ORIGIN AND GEOCHEMISTRY OF CARBONAIE CONCRETIONS
ANTRIM SHALE (DEVONIAN, MICHIGAN BASIN)

by

Helissa Wardlaw
A Thesis
submitted to .
Michigan State University

in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Geology

1981

ABSTRACT

Concretions may record diagenetic pore fluid reactions because they
grow during sediment compaction. Diagenetic concretions from the Antrim
Shale were studied to determine their origin, nature of growth and if they
record pore fluid changes that occur during compaction. Detailed
chemical, mineralogical and isotopic analyses revealed inconsistencies in
interpretations of concretion origin and nature of growth that were not
found in previous, less detailed, studies. The dolomite encased in
pyrite, lack of chemical trends across the diameters, high porosity,
uncrushed fossils and light 6180 values were interpreted to indicate
that the concretions were precompaction, not deeply buried, the carbon
source was organic, the pore fluid was isotopically (oxygen) light and the
system.was open. The concretions originated as a result of bacterial
activity and were early diagenetic; thus, they did not record and pore

fluid changes that occurred during compaction.

ACKNOWLEDGEMENTS
I wish to thank David T. Long for his support, guidance and
friendship during this thesis. I would also like to express my
appreciation to Drs. Robert Anstey, Duncan Sibley and James Trow for
their criticisms of the manuscript.
Funding for this research came from Sigma Xi, The Scientific
Research Society and the Geological Socity of America. Their

support was greatly appreciated.

ii

TABLE OF CONTENTS

Purpose
Nature of Problem
Zonal Theory of Shale Diagnesis
Summary of Concretion Research
Physical Interpretation from Previous Concretion Research
Description of Antrim Shale and Its Concretions
Research Goals
Methods
Collection
Descriptions of Two Concretions Analyzed
Preparation Methods
Thin Sections
Electron MicrOprobe Analysis
Atomic Absorption
Bulk Geochemistry
Carbonate Geochemistry
Porosity

X-ray Diffraction

iii

page

13
14
19
20
20
21
24
26
26
27
27
27
28

29

TABLE OF CONTENTS, continued

Organic Carbon

Carbon and Oxygen Isotopes
Results and Interpretation

Mineralogy

Physical Setting

Chemical Trends

Oxygen Isotopes

Carbon Isotopes

Discussion
Comparison of the Antrim Concretions to Other carbonate
Concretions in Black Shales
Inconsistencies in Data Interpretation
Speculations on Inconsistencies
Concretions as Chemical Tape Recorders

Conclusions

iv

Page
28
29
29
33
36
43
55
58
61
63
64
67
71
76

77

Figure
Figure
Figure
Figure

Figure
Figure
Figure

Figure

Figure
Figure
Figure
Figure
Figure
Figure

Figure

2.
30
4.

5.

6.

7.

8.

LIST OF FIGURES

Location Map.
Concretion 3.
Devonian algal structure inside concretion 3.
Concretion 7.

Photomicrograph of radial ferroan dolomite
crystals in concretion 3.

Antrim Shale compacted around carbonate
concretions, Kettle Point, Ontario.

Typical sphere-shaped carbonate concretion,
Kettle Point, Ontario

Uhcrushed Tasmanites in concretion 3.

9a,b,c,d. Plot of percent carbonate in samples across

concretion 3 and 7.

10a,b,c,d. Plot of total organic carbon content in

samples across concretions 3 and 7.

lla,b,c,d. Plot of Ca/Mg ratio in carbonate samples

across concretions 3 and 7.

12a,b,c,d. Plot of sodium concentration in carbonate

samples across concretions 3 and 7.

13a,b,c,d. Plot of K concentration in carbonate samples

across concretions 3 and 7.

14a,b,c,d. Plot of Fe concentration in carbonate

samples across concretions 3 and 7.

15a,b. Plot of stable carbon and oxygen isotopes across

the horizontal core from concretion 3.

\

Page
18

22

25

37

38

41,42

44,45

48

49,50

51,52

53,54

57

LIST OF FIGURES, Cont.
Figure 16. Mixtures of carbonate carbon reduction (SR),
bacterial fermentation (F) and marine origin (M)
which give total 5130 values of 110/00 FDB. 60

Figure 17. Interpretations made from geochemical and physical
data. 62

vi

1.

LIST OF TABLES

Name

Diagenetic zones within compacting marine mudstone sequences

(from Curtis, 1978).

Summary of the research on carbonate concretions.

List of references used in constructing Table 2.

Carbonate geochemistry (atomic absorption data).

Carbon and oxygen isotope values for two Antrim concretions.

vii

page

46

56

PURPOSE

The purpose of this research is to determine the origin and
nature of growth of the carbonate concretions in the Antrim Shale
(Devonian, Michigan Basin). A working hypothesis for this research
is that the trace element and stable isotope geochemistry of the
concretions can be used to make interpretations about their origin
and nature of growth. The approach is to study the bulk and three
dhmensional geochemistry and mineralogy of the concretions.
Additionally, the geochemical study may shed some light on the
chemical changes that occurred in the pore fluid and the surrounding
sediment during compaction and lithification of the sediment in the

basin.

NATURE OF PROBLEM

During the evolution of a compacting sedimentary basin, chemical
diagenetic processes occur that affect both the sediment and the pore
water. Laboratory, theoretical and field studies have demonstrated
these changes in modern systems. Laboratory squeezing studies of
kaolinite and montmorillonite by Engelhardt and Gaida (1963), for
example, show that the salinity of released pore water changes during
compaction. They found decreasing salinity up to 800 atm compaction
pressure followed by increased salinity up to 3200 atm of overburden
pressure.

Samples from the Deep Sea Drilling Project also show that

diagenetic processes occur that affect pore fluid chemistry in recent

1

2

sediments. There are significant changes in specific ion
concentrations with depth, and concomitant compaction and diagenesis,
in some pore fluid samples from the DSDP. According to a summary by
Sayles and Manheim (1975) Ca, Sr, and H003 are generally enriched,
while Mg and 504 are depleted in the pore fluid with increasing
depth. Chemical changes in sediment during compaction have been
reported also. In the samples studied the amount of illite increases
with depth of burial at the expense of mixed layer illite-smectites.
This is accompanied by increases in temperature and decreases in the
sediment porosity (Perry, 1970; Bower, et al., 1976). Carrels and
MacKenzie (1974) have used these results to interpret the chemical
diagenetic history of rocks; however, this interpretation is as yet
unequivocal.

An understanding of diagenetic processes in ancient rocks is
important because these processes are in part responsible for the
generation and migration of petroleum and the origin of low temperature
are deposits (e.g., the Mississippi Valley lead and zinc deposits).

The rationale for the present study is that concretions may
provide a record of the chemical changes that occur in the pore waters
of the sediment during burial and compaction. Concretions grow in
various types of sedimentary rocks (Coleman and Raiswell, 1981; Sass
and Koladny, 1975; Tarr, 1920). Their origin is either syngenetic
(formed at the time of deposition of the enclosing sediments),
diagenetic (formed in the enclosing sediments while they are still
soft and unconsolidated) or epigenetic (formed after consolidation of
the enclosing sediments)(Raiswell, 1971). This study infers a

diagenetic origin for the carbonate concretions in the Antrim.

Diagenetic concretions presumably grow during compaction, below
the sediment-sea water interface (Raiswell, 1971). The precipitating
carbonate material incorporates trace elements such as Na, Sr, Zn,
Mn, and K, during growth. The concentration of the trace elements in
the precipitated mineral will be a function of their concentration in
the solution and their partitioning coefficient. If the
concentration of a trace element in solution changes during
concretion growth, then its concentration in the precipitating
mineral should change accordingly. Thus the concretion may be a sort
of chemical "tape recorder", recording chemical changes in the pore
fluid that occured as the shale was compacted.

In order to determine if concretions are chemical "tape
recorders”, however, a better understanding of their origin and
nature of growth is needed. This can be accomplished in part by
detailed geochemical, petrographic and isotopic investigations of

carbonate concretions found in black shales.

ZONAL THEORY OF SHALE DIAGENESIS

With increasing burial depth, diagenetic reactions are known to
occur that affect the sediment and the pore fluid. A sequence of
diagenetic reaction zones in compacting marine mudstones was
originally defined by Curtis (1978). Diagenetic concretions have
been subsequently analyzed in light of these reaction zones (Coleman
and Raiswell, 1981; Irwin, 1980; Curtis, 1978). In this study the
Antrim concretions will be analyzed in order to determine if their

origin and nature of growth can be predicted by the zonal theory.

4

According to Curtis (1978), Zone I is represented by a thin top
layer of sediment that is well oxygenated by the depositional waters
(Table 1). Bacterial oxidation of organic material takes place in
this zone and diagenetic mineral precipitation does not occur because
the ions diffuse into the overlying water. Below the sediment
surface, in Zone II, reducing conditions are set up and bacterial
sulfate reduction occurs. The source of the sulfate is the overlying
water. Pyrite and iron-poor carbonates with isotopically light
carbonate carbon, due to the sulfate reducing bacteria, are
precipitated in this zone. Zone II merges into Zone III at the depth
of approximately 10 m where 30'4 diffusion from the depositional
waters into the sediment stOps.

Bacterial fermentation of organic matter producing isotopically
light methane and carbonate containing heavy carbon isotopes typifies
Zone III. In this zone the ferrous material from unstable iron
compounds precipitates as isotopically heavy, iron—rich carbonate
mineral. The lower boundary of Zone III is inferred to be the lower
limit of organic activity in the sediment.

In zone IV bicarbonate is produced by thermal decarboxylation
and oxidized iron compounds continue to be reduced. These processes
increase as temperature increases and stop when the reactants are
used up. Isotopically light, iron-rich carbonates precipitate but
their exact composition depends upon the composition of the original
sediment.

There is not much organically derived bicarbonate in Zones V and
VI, according to Curtis. Dissolution, reprecipitation or replacement

occur in these zones involving unstable primary carbonates. The

mucous—Com 0:325... madame woauomaaoo c.3053 mason oauozommfin

. 33a .2980 son:

. H manna.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.330; 3.239.: “ouuunuuuo entices-.0:
..ao.gu sea—use . o
.o 2:332: 2:. to at .8. a... a r.
soc: n:.ocsmoc ausn_us n e..:aaau
wetlcoaosoa au.: lean emu
. o..uuo.n sea-nu
o..Io—oa coats-u
s._.__ o..so_oa son-ue‘ so..ssecoo
3 3:6 :2 2 on. no... coat-2:2: a
ue_m¢_um> 9.30.4
nan-u ssh-J new.! I I c l I i I I
o..usm.u
o..eo._.uos.eox wo..e.~o-a so was. a. an o-.«.« to..s.>wonuauoa a.
s-.Io_oa a
or..usa< scouts.
cox '7\ sh a..s.uomno . souunaeelhah
on . o on eaoeoouou 0.. on on o. —_.
a u u .50. o
seamen.» e ensues 0.0 usacaaos< eu‘uuau n .a u a
enouueu
.u ..< .s: .0. n9.o._ou at .em sea so..usoom
3...... 3- 3 no 2 322:... :
_.0u so so..u:u.nam v.sq¢ s..u.au .n.uo.onm
as..cs nus..- .aeo...noceo me.».usao co..ns.no
..eautc .o eo..us~..oo .s..ssa o.e. ue.:.0o .o so.n:._.m unvox a«- a. o «w. .n..s.ua- _
.0. e.asa
s::..so...=0f .sstt.’ €0....a.osum 90....a.usam 9.0::asnu a..uobe; U h szsn co..m.uuuso aces
s.ssoc.f assoc no.1:csumu oqvca;Un_. cussesx o . one” oneness

 

 

 

 

 

 

 

cation compositions are determined by silicate transformation in
these zones.

Several processes are responsible for the carbon isotope
distribution in carbonate minerals; l) assimilation of dissolved
primary carbonate; and the degradation of organic material by 2)
bacterial fermentation, 3) sulfate reduction, and 4) decarboxylation
(Coleman and Raiswell, 1981; Irwin, 1980).

Bacterial fermentation processes produce carbon dioxide with a
«513C value of +150/oo(PDB) and methane with values of -750/oo
(Irwin, 1980). Sulfate reduction produces carbon dioxide with

613C values of -10 to -ZSo/oo and carbonate precipitated due to
assimilation of dissolved primary carbonate results ind l~30
values equal to 00/00 (Irwin, 1980). Decarboxylation, the removal of
a molecule of carbon dioxide from amino acids and proteins by
bacterial action, produces 513C values of -ZOo/oo (Coleman and
Raiswell, 1981).

Each process of carbon dioxide production occurs in a different
burial depth zone (Curtis, 1978). The depth zones overlap; thus
carbon dioxide production by two or more processes can occur
simultaneously in certain zones in the sediment resulting in
carbonate containing intermediate 13C values (Irwin, 1980;

Coleman and Raiswell, 1981).

SUMMARY OF CONCRETION RESEARCH

Table 2 summarizes the current research on the nature and origin

of carbonate concretions. (References are listed on Table 3; numbers

:oumomou venomoua ousu scum mcoauapuuunooe

AoNaAV mama an mcouuouucoo new coaumuuuammmeo

own no woman .usoauvum weavesouusm cu uooamou so“: suaouw acquouonoo no one o>aumaou u
nouuouocoo no amoaouoowa acnman

momhammm momma can save noon mcouuouocoo co some muooaouzmmoa Hooaeosom

hmoaouocwa
~3.a.a.e.n.~

monouomu m
ms

monououw o
«.ma.~a.aa.a.o.n

monouomu o
4.H~.a.a.ma.~a.e.m.n.a

mucosa oomph

  

 

 

 

a.oH.~H

N -.m.~.m um

aquoeowaao ouuuoeuu a.oa.o.o.n
a:

a.-.w.n.~
a.~a.m.m< om

couuomaaou ouuonowmue ouusoaoo emonuou «.o~.~.o.~

a.m~.-.w.o

«gave: as

.e.m.~.a «.Nfl.oa.m.a.e
some» «.na.e.a.e ca.aa.na.~a.o.m.o.e co

NH.¢. .n oouuommsoooua ouuocommuv some use souoamo , e.oH.owbuc.N.H

h oaon no: immm¢ o>uumaom A odouoofix monogamowauouoa amowaono

monHumozco ma¢zonm<u ZDHQA¢U zo IUM<Mmma HIE ho Nm<225m “N man<a

TABLE 3: List of References used in constructing Table 2.

KEY REFERENCE

1 Galimov, E. M. and Girin, Y. P. (1968)

2 Girin, Y. P. (1970)

3 Bbefs, J. (1970)

4 Raiswell, R. (1971)

5 Curtis, C. D., Petrowski, C. and Oertel, G.
(1972)

6 Sass, E. and Kolodny, Y. (1972)

7 Curtis, C. D., Pearson, M. J. and Somogyi, V. A.
(1975)

8 Raiswell, R. (1976)

9 Irwin, H. and Curtis, C. D. (1977)

10 Dickson, J. A. and Barber, C. (1976)

11 Hudson, J. D. (1978) and Friedman, I. (1976)

12 Irwin, H. (1980)

13a 13 Coleman, M. L. and Raiswell, R. (1980)

13b Coleman, M. L. and Raiswell, R. (1981)

used on Table 3 are also used in this section in order to facilitate
referencing),

These studies have given some insights into the chemical nature
of the associated pore waters during concretion growth, and can be
summarized as interpretations on the nature of the pore water in
terms of pH (1,2,6); Eh(2,6,7,9); bulk chemistry(1,2,3,7,9,ll,12);
isotopic chemistry(3,ll,12,13); state of the system (i.e., open or
closed)(3,l3a); source of pore water (i.e., meteoric or
marine)(3,ll,12,13b); and source of dissolved ions (1,2,6,7,ll,12).
Interpretation of pH trends in concretions from center to edge have
revealed a sequence of alkaline-acid-alkaline pore water conditions
(1,2) and acid-alkaline conditions (6). Eh conditions were anoxic
(2,6,7,9). Bulk chemical analyses reveal predominantly carbonate
mineralogies including calcite, siderite and ferroan dolomite.
Pyrite, marcasite, quartz and apatite are present in smaller
quantities (1,2,3,7,9,ll,12). Stable oxygen isotopic ratios
indicated generally a freshening of the pore fluid during or after
concretion growth, and stable carbon isotOpic ratios indicated an
organic source of carbonate carbon (3,11,12,13). The state of the
system was open for some and closed for others (3,13a). The
unaminously agreed upon source of pore fluid was seawater, but with
later fresh water infiltration in some examples (3,11,12,13b).
Various sources of dissolved ions were indicated by the studies:
Ca-exchange sites of clays, calcite, seawater, feldspar;
Mg--exchange sites of clays, organic matter, seawater, high Mg
calcites; Mn-detrita1 oxides; Sr--primary carbonate, seawater;

Fe--hydrated ferric oxides, clays; CO3-organic matter;

10

804+i-seawater (l,2,6,6,11,12). It is clear from these studies
that chemical trends are found within carbonate concretions and that
they may reflect the changing chemistry of the surrounding pore
waters.

There is debate, however, as to the significance of these
trends because effects other than changes in pore water composition
during the formation of the concretions could cause chemical trends

in the concretions. These include:

(1) Changes in the mineralogy of the concretion (Girin, 1970; Curtis
et al., 1975; Irwin and Curtis, 1977). A change in mineralogy across
the concretion could change the bulk chemistry and chemical trend
analyses would not reflect original composition. However, a
mineralogic change could possibly be used to interpret the pore fluid
chemical changes.

(2) Recrystallization (Dickson and Barber, 1976). Although it would
depend on the nature of recrystallization that had occurred, the bulk
chemistry of the concretion including 61.30 and 813C might be
unaffected. Trends in elements like Sr would need careful
interpretation.

(3) Formation in a closed system (Coleman and Raiswell, 1979). If a
concretion grew in a closed geochemical system, then the manner in
which a component would be depleted from the pore solution would
depend on its partitioning coefficient. A coefficient other than 1
would create a chemical trend across the concretion. This process
would affect most trace components in the concretion forming minerals

including 6180 and 613C. Since many partitioning coefficients

11
are known or can be estimated for carbonate minerals, predictions can
be made as to what type of trends can be expected if the concretion
formed in a closed system. If a variety of components are measured,
each with a different partitioning coefficient, then it may be
possible to determine whether the concretion formed in a closed or
open geochemical system.
(4) Nature of concretion growth (Raiswell, 1976; Curtis et al.,
1975). During this process the microbial action surrounding some
concretions creates a unique local geochemical environment unrelated
to the chemistry of the surrounding pore waters. This would affect
the distribution of components such as 8003, 8, Fe, C, etc.;
however, most of the bulk distributions of the non-major mineral
forming elements should be unaffected.
(5) Post lithification reequilibration with meteoric waters (Hoefs,
1970). Most researchers recognize that the chemistry of marine
deposited carbonates can be affected during the chemical
reequilibration of the concretion with meteoric waters. This is
particularly true for oxygen isotopes.

In order to make meaningful interpretations from the chemistry
of concretions the above effects must be considered. Unfortunately
only a few investigators have done the relatively detailed work on
the chemistry and mineralogy of the concretions necessary to address
the problems (Raiswell, 1976, ; Coleman and Raiswell, 1979, 1981, E3;
and Irwin, 1980).

However, a few conclusions on the nature of the geochemistry of
the concretions that to characterize most of the past work. They

are:

12

l. The source of C appears to be mainly degradation of organic
matter (1,2,3,5,6,7,8,9,lO,ll,12,l3). This conclusion is based
on the light (negative) 6130 values found in the

concretions.

2. The p130 values (may) reflect the type of microbial
activity and possibly the depth of the formation of the
concretion (8,9,12,13b). In many of the carbonate concretions
analyzed listed in Table 2, 5130 values were found to change
along the radius of the concretion. Since &13 values do not
appear to be affected by diagenetic reactions, the trends
indicated across the concretion could indicate changes in the
pore waters (chemical or biological) during the course of
carbonate precipitation. Early interpretations were that the
change from negative¢513C values to positive values

indicated a change in the source of C from organic (microbial
activity) to inorganic (dissolved bicarbonate in
seawater)(Ga1imov and Girin, 1970). More recent interpretations
on the trends in d‘1‘3c values are that the source of C

remains organic matter, but the organic matter is degraded by
different chemical processes operating at various depths during
burial diagenesis (Coleman and Raiswell, 1981; Irwin, 1980).
These different processes (sulfate reduction, fermentation, and
thermally-induced decarboxylation) would each produce a unique
5130 value.

3. The 6430 values, when a trend is indicated usually

become lighter from center to edge (3,9,11,12,13b). This change

in 5180 has been attributed to the influence of meteoric

13
water during the formation of the concretion, and growth of the
concretion in a closed system. There is not enough data
available to make a definitive statement as to which of these is
more important. Although there is a strong indication that
contact with meteoric waters during the growth of some
concretions has influenced the 6180 values (11,13b),
measurement of independent chemical indicators for the source of
the water is needed to support these conclusions.
4. The absolute 6130 values of the concretions are lighter
than what would be expected if the concretions precipitated form
modern seawater (3,11,12,13b). The light values have been
attributed to a high temperature of precipitation, the influence
of meteoric water during concretion formation, an overall
lighter 5180 value of Devonian seawater, and local effects
due to microbiological activity or the fractionation of the
isotope as the carbonate minerals precipitate directly from the
pore fluid. A geochemical analysis of a variety of concretions

may help to eliminate some of these alternatives.
PHYSICAL INTERFRETATIONS FROM PREVIOUS CONCRETION RESEARCH

From previous work several physical indicators of the nature of
concretion growth have been used to interpret the time of concretion
growth relative to shale compaction. For example, concretions that
are covered with boring or encrusting organisms have been interpreted
to have grown exposed at the sediment-seawater interface (Pantin,

1958), and represent paleoecologic hardgrounds. These are

14

syngenetic concretions and thus have a precompaction origin.

The presence of uncrushed fossils at the center of concretions
also indicates that concretion growth began before compaction of the
sediment crushed the fossils (weeks, 1953).

The nature of the sediment layers within and surrounding the
concretions can be used to interpret the timing of concretion growth
relative to compaction. According to Clifton (1957), horizontal
bedding lines in a concretion indicate concretion growth after shale
deposition but before shale compaction. Beds that curve around the
concretion indicate that concretion growth occurred before sediment
compaction (Raiswell, 1971).

The shape of a concretion is in part related to vertically
continuing pressure, and therefore, the compactional history of a
basin. During early pre—compaction growth concretion shape should be
spherical, indicating that the rate of growth was equal in all
directions (Pantin, 1958). As vertical compaction increases, lateral
growth would exceed vertical growth and a flattened, oblate

concretion would result (Clifton, 1957).

DESCRIPTION OF THE ANTRIM SHALE AND ITS CONCRETIONS

The Antrim Shale was first recorded in the geological literature
by state geologist Douglass Houghton in 1838 and 1841 respectively
(Rep. Inv. 22, 1979). The formation was given its present name in
1901 by A. C. Lane who named it after the northern Michigan county
that contains its type section. The unit was variously named before

1901 as the Enron Shale and the St. Clair Shale.

15

' The Antrim Shale is dark brown to black, highly carbonaceous,
pyritic, finely laminated, fissile and hard (Lane, 1902). The total
organic carbon content, determined by the dry combustion method,
ranges from 5 to 10 percent in the shale (Beers, 1945). Lenses of
light gray shale or limestone are located at the base of the Antrim
followed by uniform black beds in the middle and lighter beds at the
top (Tarbell, 1941).

Fossils found in the shale include Faleoniscids, Ligggla and

other brachiopods, fossil wood, including Callixylon newberry,

 

conodonts and several types of spores (LeMone, 1964; Winslow, 1962).

The fossil spores of floating plants (Protosalvinia huronensis),

 

disc-like objects with thick walls, are inferred to be a source of
the carbonaceous material in the shale (Mozola, 1955). The spore
cases are scattered throughout the carbonate concretions as well as
through the shale.

The Antrim encompasses the Upper DevonianvLower Mississippian
boundary. It was initially classified as exclusively Devonian,
however, Mississippian fossils were found in the upper part of the
shale (Newcombe, 1933).

The Antrim Shale ranges from 100 to 450 feet in thickness in
Michigan (Newcombe, 1928). It thins from east to west with the
thickest part located in the Saginaw Bay region. Outcrops of the
shale are located in the northern part of the southern peninsula, in
Antrim, Charlevoix, Emmet, Cheboygan and Alpena counties. The Antrim
also outcrops in Oakland county in southeastern Michigan (Newcombe,
1928).

The Squaw Bay Limestone, the upper member of the Middle and

16

Upper Devonian Traverse Group, underlies the Antrim (Kelly and Smith,
1947). The Squaw Bay Limestone is a 10 foot thick bed of brown
crystalline limestone that contains Upper Devonian cephalopods. The
nature of the Squaw Bay-Antrim contact is unknown because the base of
the Antrim has not been identified in outcrop (Rep. luv. 22, 1979).

Overlying the Antrim in eastern Michigan is the Mississippian
Redford Shale and in western Michigan the Upper Devonian Ellsworth
Shale (Rep. luv. 22, 1979). In western Michigan the upper two-thirds
of the Antrim interfinger with the lower half of the Ellsworth
(Tarbell, 1941). A facies relationship is inferred between the
Antrim of eastern Michigan and the Ellsworth of western Michigan
(Rep. Inv. 22, 1979).

' The Antrim is stratigraphically equivalent to the Ohio, Sunbury,
New Albany, Chattanooga, Maple Mill, Mountain Glen, Kettle Point, and
Sweetland Creek Shales (Conant and Swanson, 1961). There are two
major hypotheses regarding the environment of deposition of these
black shales. According to Conant and Swanson (1961), the black
shales were deposited in the mid—continent region by an
epicontinental sea. Such a sea would have poor circulation creating
anoxic conditions in both the bottom water and sediments (Heckel,
1977).

An alternative to the restricted-epicontinental sea environment
is the shallow lagoon model (Merrill, 1975). According to this
model, the sediment is deposited in shallow, plankton—covered
lagoons. The migration of the lagoonal environment across the
continent as the sea transgressed would account for the widespread

nature of the Devonian black shales.

17

For the Antrim, reducing conditions are indicated by the
presence of abundant pyrite framboids and vegetal material and a lack
of fossils in the shale. However, the environment of deposition of
the Antrim, epicontinental sea or shallow lagoon, is as yet an
unresolved issue.

The area of study for this research is located at the Paxton
Quarry near Alpena, Michigan (Figure]_). The occurrence of the
concretions in the Antrim Shale is similar to what has been reported
for the stragigraphically equivalent black shales of the Ohio Shale
and the Kettle Point Formation, Ontario (Daly, 1900; Bownocker, 1911;
Clifton, 1957; MacDonald, 1960); however, the occurrence of the
carbonate concretions in the Antrim has not been reported in detail
in the literature.

Two major types of concretions are common in the shale and are
differentiated by mineralogy. Large iron carbonate concretions,
roughly spherical in shape and ranging from eight inches to six feet
in diameter, occur in the lower part of the formation. Smaller
pyrite or marcasite concretions range in size from one to three
inches in diameter, are shaped like flattened spheres and lie
parallel to the bedding planes in the lower part of the shale.

Little work has been done on the geochemistry of the concretions
from either the Antrim or its stratigraphic equivalents. Recently
Hathon (1979) studied the origin of the quartz in the Antrim Shale.
The Antrim has a uniquely large quartz content (502 quartz by weight
in the less than 500 mesh size fraction).

Hathon (1979) measured the oxygen isotopes of the quartz and

carbonate phases and the carbon isotopes of the carbonate phase of

H'

7

 

Z-mzonm-E

18

LAKE SUPERIOR

 

 

      
 

M
I
Q
o
.3, mron 4'
by QUARRY
a
z ’ N
v 1"
9 A
3; n
- I
a D
m KETTLE
x POINT
<
0““
J
I
I.
L
I
N
0 IN a I A N A o HID
I
s .
J

 

 

 

Figure 1. Location Map

 

19

the shale, including one concretion. The oxygen isotope values were
highly variable in both the quartz and carbonate phases.

This would suggest that post lithification isotopic reequilibration
with meteoric waters had not taken place or had been of minor
importance in determining the isotope values in the concretions.
Hathon concluded that a gradual isotopic lightening of the pore
fluids took place during the formation of the authigenic quartz and
carbonate phases of the Antrim. This was also indicated in the
lightening of the oxygen isotopes of the concretions from center to
edge. His results, which will be discussed in detail in later
sections, stimulated my interest to study the geochemistry of the

Antrim concretions in more detail.
RESEARCH GOALS

Black shales have frequently been reported to contain carbonate
concretions (Irwin, 1980; Hudson, 1978; Curtis, et al., 1975;
Raiswell, 1971; Hoefs, 1970; Girin, 1970; Tarr, 1920). These
concretions are important because they form during shale diagenesis,
at the same time that petroleum and low temperature ores are
generated. Thus the presence and chemistry of carbonate concretions
in black shales may indicate similar chemical and physical stages of
diagenesis among the various host shales. The major questions

addressed by this study, therefore, are:

I. Can the origin and evolution of the carbonate concretions in the

Antrim Shale be interpreted in light of the "zonal theory of black

20

shale diagenesis” proposed by Curtis (1978)?

II. Are the carbonate concretions in the Antrim Shale similar in
terms of their geochemistry to similar concretions from Europe
(Raiswell, 1971; Curtis, et al., 1975; Hudson, 1978; Irwin, 1980)?
If so, does this suggest a commonality of origin and growth of

carbonate concretions in black shales?

111. Can the Antrim cencretions (and other carbonate concretions in
black shales) be used to interpret changes in pore fluid chemistry

during the diagenesis of black shale?
METHODS

Both shale and concretions were studied by means of thin
sections, atomic absorption, x-ray diffraction, and electron
microprobe analysis. Components measured were mineral content,
carbon and oxygen isotope values, and concentrations of Ca, Mg, Na,

Sr, K, Fe, Mn, Pb, Cu, Zn and organic carbon.

Collection

Concretions were collected from the Paxton Quarry, Alpena,
Michigan (Figure 1). The Antrim is presumably 96 feet thick in the
vicinity of the quarry; however, only a 50 foot section is exposed.
The exposure in the quarry is about one half mile in length and
concretions are exposed along the full length of the exposure. Only

whole, unweathered, uncracked concretions composed of the iron

21

carbonate were taken from the quarry. The sheer size and weight of
the larger concretions prevented i3 gigg collection, thereby making
it necessary to take some of the smaller machine‘quarried
concretions.

A total of nine concretions were collected and numbered randomly
Close examination of the whole concretions in the lab revealed
weathering and cracks in several of the nine concretions; however,
two, #3 and #7, were uncracked and therefore, seemed relatively
unaffected by weathering. Thus, these two concretions were used for
the chemical analyses. In addition, randomly located shale samples

were collected from the quarry floor for chemical analysis.

Descriptions of Two Concretions Analyzed
I. Concretion #3 is roughly spherical. Its vertical diameter is 30
cm, somewhat smaller than its horizontal diameter of 38 cm (Figure 2).
It is composed of iron carbonate (see mineralogy section) and encased
in a 2 cm outer layer of iron sulfide. The crystals of both the iron
carbonate and the iron sulfide radiate outward from.the middle of the
concretion. At its center the concretions contains very well
preserved Devonian algae (Figure 3). The algae are preserved as a
kelp-like structure roughly two cm. wide and 10-13 cm long. The
structure is filled with the iron carbonate in some areas and
microcrystalline quartz in others. Solution cavities 1/2 to 1 cm in
diameter, filled with coarse white calcite and dolomite crystals, are

located 8-10 cm from the center of the concretion.

22

 

 

Figure 2. Concretion 3.

 

Figure 3. Devonian algal structure inside concretion 3.
Scale bar - 0.1mm.

24

II. Concretion #7 is more irregular in shape than #3 and comprises
two interpenetrating spheres (Figure 4). The vertical diameter is 32
cm and horizontal diameter is 35 to 40 cm. It is composed of iron
carbonate crystals that radiate outward from the center with an outer
layer of pyrite 1 cm.wide. No fossils have been found in the center
of the concretion. As in #3, solution cavities lined with coarse,
white calcite or dolomite crystals are located 7.5-10 cm from the

~middle of the cores.

Preparation Methods

Because the concretions were too large and heavy to saw apart,
they were instead cored in two directions through their centers,
vertically and horizontally relative to the bedding planes. A hand
Operated water-cooled corer was used. Distilled water was used as
the coolant in order to avoid sample contamination as much as
possible.

The cores were sawed in half lengthwise on a distilled water
cooled saw and one half was polished with 600 mesh grit for
macroscopic examination. The other half was again sawed in half
lengthwise and one quarter was used for thin section preparation and
the other subsampled and powdered for chemical and x—ray analysis.
The subsample chips were cleaned in distilled water for 10 minutes in
an ultrasonic cleaner, than each sample was powdered for 10 minutes
(300 mesh) in a titanium ball mill.

Each powdered sample and thin section was assigned an
alphanumeric code such as 3-v-l. The first digit denotes the

concretion sampled. The v or h digit indicates which core in each

25

 

 

Figure 4. Concretion 7.

26

concretion, vertical or horizontal, the sample was taken from, and
the second digit indicates the subsample location along the
particular core. Each successive second digit assigned to the
powdered samples from concretions #3 and #7 indicates a 1 to 2 cm

increment from the center of the concretion.

Thin Sections

Thin sections were prepared along the full length of the six
cores for petrographic and microprobe analysis. Each thin section
was polished and carbon coated for the microprobe analysis. After
microprobing, the thin sections were etched and stained to aid in
mineral identification utilizing the method of Bouma (1969).

The best results were obtained when the slides were first etched
for 20 seconds in 10! cold HCl and then immersed in the staining

solution for five minutes.

Electron Microprobe Analysis

The mole percent of CaCO3, MgC03 and FeCO3 in
the concretions was determined using electron microprobe analysis.
Points spaced 1 cm apart along the full length of the cores were
probed. To avoid burning holes in the thin sections, the probe was
set at 10 KV and 1.5 MA. Five ten second readings were taken for
each point and the results averaged to minimize instrumental error.
The data was reduced to mole percent carbonates using a computer

program.by Bence and Albee (1967).

27

Atomic Absorption

Bulk Geochemistry

The bulk geochemistry of the subsamples was determined using
atomic absorption analysis. The powdered samples were prepared using
the fusion method of Perkin-Elmer (1980). Powdered rock (0.2 g) were
mixed with l g of lithium metaborate and fused at 1000°C for 20
minutes. After fusion, the samples were dissolved in 50 ml of 10%
cold HCl and diluted to 100ml. The samples were analyzed for Na, Zn,
Mn, Sr, Pb and Cu.

Carbonate Geochemistry

In order to determine the chemistry of the carbonate material
in the concretions and the shale, 0.5 g of each sample was dissolved
in 252 acetic acid solution by the method of Barber (1974). The
samples were analyzed for Fe, Ca, Mg, Na, Zn, K and Sr. In order to
bring the concentration of Mn down within the working range of the
instrument, the sample solutions were diluted 10 times. Ca, Mg and
Fe required dilution of 100 times.

The solution samples from the bulk chemistry and carbonate
chemistry dissolutions were analyzed in an air-acetylene flame on a
Perkianlmer Atomic Absorption Photospectrometer Model 306 using
single and multi-element hollow cathode tubes and a 4-inch single
slot burner head.

The standards used for each element were prepared with the same
background solution as the unknown samples. The standards used with .
the fused samples were prepared with a blank lithium metaborate
solution just as thse used with the dissolved samples were prepared

with a 251 acetic acid solution. This was done in order to achieve

28
maximum accuracy of measurement. Appropriate procedures were used to
eliminate chemical and physical interference (Perkin-Elmer Methods

Manual, 1980).

Porosity

The volume of carbonate mineral in the concretions, represents
the porosity of the sediment in which the concretions grew (Lippman,
1955). It was estimated by measuring the percent of the material

dissolved in the 252 acetic acid dissolutions.

Xéray Diffraction

Pellets of the powdered samples, some of the insoluble residue
from the acetic acid dissolutions and powdered shale samples were
x-rayed from 5° to 65° 20 on a General Electric x-ray machine using
Cu Kralpha radiation. The instrument was set at 50 RV and 10 MA and
the best results were obtained at 500 CPS peak intensity.

The insoluble residue from the acetic acid dissolutions was
x-rayed in order to determine if all the carbonate material was
dissolved. Because the amount of insoluble residue left from the
dissolutions was extremely small, only three samples could be x—rayed
Of these three, one showed a small peak while the others showed only
quartz peaks. Thus, the weight percent dissolved carbonate material

discussed in a later section, are minimum values at best.

Organic Carbon

The total organic carbon content of both the concentric zones in

29

the concretions and the shale was determined using the titration

method of Gaudette et al., (1974)(Appendix A).

Carbon and Oxygen Isotopes

Stable carbon and oxygen isotOpe analyses were performed by
Geochron Laboratories, Cambridge, Mass. Before sending the samples
out for the analysis, the organic carbon was removed from the
powdered samples. This was done by soaking 0.5 g of sample in 5.25%
sodium hypochlorite solution (Chlorox) overnight (Barber, 1974).
After soaking, the samples were filtered and washed and then dried in

a cool oven.

RESULTS AND INTERPRETATION

From the consideraton of the past work on concretions, four
aspects of concretion growth have been defined from which
interpretations on the nature and origin of concretions can be
organized. These are (1) the state of the system during growth
(i.e., open or closed), (2) how the data can be interpreted in terms
of the zonal theory of shale diagenesis, (3) the time of concretion
growth relative to shale compaction, and (4) the temperature and
salinity of the local pore waters during growth. These aspects can
be summarized as follows:

1. State of the systemr- In the discussion of concretions the state
of the system refers to the nature of the environment in which the
concretion grew: whether it was open or closed to seawater

circulation or diffusion. Raiswell (1971) used three indicators to

30

determine whether the system in which the calcite concretions from
the Upper Lias black shales of NE England precipitated was open or
closed to seawater during growth: 1) porosity, 2) Sr++, and 3)
mineralogy. A high porosity, 80-902, indicates an open system and a
low porosity, 402, indicates a closed system. Sr++

concentrations of 1000-1500 ppm indicate an open system and Sr++
concentrations of 600 ppm or less indicate a closed system according
to Raiswell (1971). An open system is indicated by pyritiferous
margins and a closed system by siderite concretions.

According to Raiswell (1971) the porosity of the sediment in
which carbonate concretions grow can be determined by measuring the
volume of the carbonate mineral in the concretions. The assumption
is that as the concretions grow the carbonate precipitates in the
open pore space in the sediment. Therefore, the percent carbonate
that is in the concetions roughly represents the original pore space
of the sediment. A problem with this type of interpretation clearly
is that the crystals of carbonate could disrupt the sediment as they
grow and thus the amount of carbonate would not be representative of
the sediment pore space.

However, evidence that supports the hypotheses that the amount
of carbonate in a concretion represents the original pore space of
the sediment for Raiswell's (1971) concretions, is that the amount of
carbonate in the centers of the concretions (80-902) is near to or
equal to the amount of pore space in uncompacted clays (Muller,
1967).

According to Raiswell (1971) pyritiferous margins on a

concretion indicate tht the concretion was in contact with a steady

31

supply of 804' that was in turn reduced and precipitated as the
iron sulfide. The likely source of 804' is seawater (Berner,
1964); thus, pyritiferous margins on a concretion are evidence for an
environment open to seawater circulation or diffusion through
the sediment. If there was no source of seawater the reduced iron
would precipitate as a carbonate mineral and the concretions would
contain siderite instead of pyrite (Curtis, 25 El}, 1975; Raiswell,
1971).

The amount of Sr++ in calcite in a system open to seawater
circulation, thus providing a source of Sr++, is higher
(1000-1500 ppm) than in a system closed to seawater (0-6000)
(Raiswell, 1971). The use of Sr++ content as evidence of an open
or closed system may not be valid, however, for the Antrim
concretions because they are composed of ferroan dolomite and the
sr++ limits in ferroan dolomite have not been determined (Land,

1980).

Zonal Theory- While it is difficult to prove the origin of carbonate
concretions, it is possible to gain some insights by making
interpretations of the data in terms of the zonal theory (Coleman and
Raiswell, 1981; Irwin, 1980; Curtis, 1978). Results from this study
will be compared to the model for the theory as discussed in the
introduction. Three aspects of the theory will be studied (1) the
nature of the reaction causing the local supersaturation of the
carbonate (i.e. inorganic or organic), (2) the source for the carbon

(fermentation), and (3) depth of burial.

32

Time of growth-- The time of concretion growth relative to compaction
history can be determined by the ovservation of the physical nature
of the concretions in the outcrops as discussed earlier in the

summary of concretion research.

Temperature/Salinity-- The oxygen isotope ratio of carbonate material
is a function of the temperature and the salinity of the
precipitating pore solution (Craig, 1953). Thus the 6180 values

of the Antrim concretions can be used to make interpretations on the
temperature and the salinity of the pore fluid.

Some trace elements in dolomite also may be indicative of the
pore fluid salinity. The Na and K concentrations in dolomite have
been used as indicators by Fritz and Katz (1972) and Land (1980).

The use of trace elements to predict exact salinity of the pore fluid
is as yet unreliable; however, trace elments have been used to make
interpretations on pore fluid salinity (Land, 1980). Acccording to
Fritz and Katz (1972) supratidal dolomites contain 200-900 ppm Na and
“600-2000 ppm K. Early diagenetic dolomites contain 70-200 ppm Na and
(1500 ppm K, while late diagenetic dolomites contain (150 ppm Na and

(800 ppm K.

These aspects of the nature of concretion growth will now be
interpreted in light of the data collected. Prior to interpretation,

the results of each type of data collected are summarized.

33

MINERALOGY

The carbonate concretions in the Antrim Shale are composed of
ferroan dolomite with little change in mineralogy from the center to
the edge of the concretions. The carbonate turns blue upon staining
and does not react with HCl unless powdered, thus indicating
dolomite. In thin section the crystals are long and slender,
feathery-like in appearance, have curved edges and sweeping
'extinction, similar to what has been reported by Choquette (1971)
(Figure 5).

Z-ray diffraction and microprobe analysis both confirmed the
carbonate as ferroan dolomite. A typical x-ray pattern is shown in
Appendix B. Quartz was the only other mineral indicated by a major
peak. Brown (1961) established characteristic d spacings for common
carbonate minerals and found that for dolomite d - 2.88 A. Irwin
(1980) found that ferroan dolomite in concretions produced d spacings
of 2.89-2.90 A. All of the Antrim concretion samples had peaks at
2.89 A. .

According to Howie and Broadhurst (1958 ) dolomites with a MC:Fe
ratio less than or equal to 4:1 should be classified as ankerite.
Microprobe analysis revealed an average of 582 CaC03, 352 MgCO3
and 82 FeCO3 in the Antrim concretions. Because the Antrim
concretions contain a higher ratio of Mg:Fe than 4:1 and d - 2.89 A
when xrrayed, they are identified as ferroan dolomite rather than
ankerite as previously identified by Hathon (1979).

Pyrite is also present in the concretions. It is scattered as

rare euhedral crystals throughout the concretions and forms a 0.5 -

34

, ' ."
“.- 5 .431"! , 07'

.'.

 

Figure 5. Photomicrograph of radial ferroan dolomite
crystals in concretion 3. Scale bar - 0.1mm.

35

2 cm layer around the concretions.

Authigenic quartz fills many of the spores scattered throughout
the concretion (Hathon, 1979). It also lines parts of the fossil
algae in the center of concretion #3. A small number of detrital
quartz grains are present in both of the analyzed concretions.

Calcite and dolomite, identified by staining, are present as

white crystals lining the solution cavities in the concretions.

State of the systemr- The pyritiferous concretion margins and the
absence of siderite in both the Antrim concretions and the shale
indicate an open system during concretion growth according to
Raiswell (1971). Reduced iron precipitated with reduced sulfate to
form pyrite, instead of with.carbonmte.produced'in the sediment by
microorganic activity (Curtis, et al., 1975; Raiswell, 1971). This
indicates a seawater source because sulfate is derived primarily from

seawater .

Zonal theory- According to Raiswell (1971) sulfate reduction takes
place in the top 3 meters of the sediment through which there is a
steady supply of 80'4 provided by the overlying water. The
concretions studied by him are encased in pyrite and were thus
interpreted by him to have formed in the upper 3 meters of the
sediment. because the Antrim concretions are encased in pyrite, in
light of Raiswell's interpretation, they accordingly should have
formed in the upper 3 meters of sediment.

The carbonate mineralogy does not suggest that local reactions

were organic or inorganic. The carbon source cannot be identified

36

via the mineralogy. The presence of pyrite is indicative of sulfate

reduction with the most likely mechanism being an organic reaction.

Time of growth-- The mineralogy of the Antrim concretions as studied
does not provide any inference on the temperature or salinity of the
pore fluids during concretion growth. Future work should be
designed to interpret salinity based on Fe-S concentration by the

method of Berner, ssng£., (1979).

PHYSICAL SETTING

Field observations-- The carbonate concretions in the Antrim Shale
are located in the lower part of the formation and are not limited to
any particular horizon in the shale. The shale beds are compacted
around the concretions, equally above and below (Figure 6). The
shale beds can be traced through some of the concretions, near their
outer edges. Most of the carbonate concretions are spherical or
nearly spherical in shape (Figure 7). Some have slightly larger

horizontal than vertical diameters.

Textural observations-- The centers of many of the carbonate
concretions are composed of massive mudstone cemented with ferroan
dolomites. Outward from the mudstone are the bladed ferroan dolomite
crystals which are encased with pyrite. The body of the concretions
extends a few inches outward from the pyrite and it is in this outer
zone that the shale beds can be traced through the concretions. Some

of the carbonate concretions do not contain the

37

 

Figure 6. Antrim Shale compacted around carbonate concretions,
Kettle Point, Ontario.

38

 

Figure 7. Typical sphere-shaped carbonate concretion,
Kettle Point, Ontario.

39

I

massively-textured center; rather, they contain only the bladed
crystals. Others do not have the outer shale layers and are encased
only in pyrite. Uncrushed Tasmanites, are scattered thoughout the
concretions also (Hathon, 1979)(Fig. 8). The carbonate content of
the Antrim concretions ranges from 50 to 90%. There is a trend to
decreasing porosity from the center to the edge of #3 and no clear
trend across #7. The porosity results are plotted on Figures

9 a,b,c,d.

State of the system-- The carbonate content of Antrim concretions
indicates a porosity which can be classified as an open system
according to Raiswell's (1971) criteria. The trend of decreasing
porosity from the center to the edge of #3 is expected in a

compacting clay.

Zonal theory- The depth of burial indicated by the porosity of the
Antrim concretions is a maximum of 10 m accrding to Curtis (1978)
zones (Table 1). The absence of boring or encrusting organisms on
the Antrim concretions can be interpreted to indicate that the
concretions were buried and not exposed at the sediment-seawater
interface during growth (Pantin, 1958), or were quickly buried or
were formed at the surface on an anoxic bottom which excluded benthic

organisms.

Time of growth-- The presence of uncrushed fossils at the center of
# 3 and uncrushed Tasmanites throughout both analyzed concretions

indicates that growth occurred before compaction of the shale (Weeks,

40

 

Figure 8. Uncrushed Tasmanites in concretion 3.
Scale bar - 0.1 mm.

41

90* 3 horizontal
80‘

70‘

60‘

$4Corbonois
on .a
9‘?

N
0

<3

 

 

M
o:
4.
0H

00“

“—4

3 vertical
90 ‘

80"
70‘
60‘
50‘

40"

94 Carbonate

30‘
20"

mi

 

 

abiaiz'a‘i Zr? 45' S
0 c 0

Figure 9a,b. Plot of percent carbonate in samples across
concretions 3 and 7. (See text for explanation). Samples
analyzed were approximately 3/4 inch apart across the
concretions (c - concretion center; e - concretion edge).

42

90‘
80‘
70‘

60‘

40"

% Corbonolo

7 vertical
30 1

20‘

IO*

 

sciosazoizézs
C c

90 ‘ 7 horizontal
80 -

70‘
sol
50%
ml

94 Carbonate

we
20‘

IO‘

 

 

0—l
N«
on
.b
a.
on

o-w

Figure 9c,d. Plot of total organic carbon content in
samples across concretions 3 and 7.

ll

43

1953). The nature of the shale beds around the Antrim concretions
and the spherical shape of the concretions also indicates that growth

took place before and during compaction of the shale.

CHEMICAL TRENDS

The results of the atomic absorption analysis are listed in
Table 4. The major element (Ca, Mg, Fe) and the 'trace' element (Sr,
Zn, Cu, Pb, Na, K, Mn) concentrations vary somewhat but do not show
any specific trends across concretions #3 and #7.

The total organic carbon content of the concretions ranges from
0.92 in #3 to 2.41 in #7 (Figure 10a,b,c,d) as compared to about 52
in the shale (Beers, 1945). There is no trend in the total organic
carbon content across the concretions. The organic carbon value
determined by Beers (1945) is inferred to be more representative of
the Antrim Shale as a whole than the mx values because in the present

study the sampling design is crude at best.

State of the system--The lack of chemical trends in the Antrim
concretions can be interpreted as evidence of an open system during
concretion growth. If a concretion grew in a closed system the
manner in which a component would be depleted from the pore solution
would depend on its partitioning coefficient. A coefficient other
than one would create a chemical trend across the concretions. Thus
trends in trace elments would be expected in a closed geochemical
system. Because there are no trends in the trace element

geochemistry across the Antrim concretions, it has been inferred that

44

 

 

i 3horizontol
051
C
o
8
a «I
t:
4: 44
.3:
cl 4
Si
.17.
o i i 3 4 f5 6
0
§ .68« 3vsrlicol
8 .
<5
.2
g .511
S
C> .
3e
.344

 

 

0H
h.
01
em.

éoéos'az'aié
s c

Figure 10a,b. Plot of total organic carbon content in samples
across concretions 3 and 7.

45

 

 

 

 

'854 Thorizontol
.
S
e 68‘
O
0
a 1
'2
O
3 .SP
0
a! .
.344
l 2 3 4 5 s 'F
C O
7vsrticol
so
3
g as
Q
.2 '
C
O
8 an
0
g I
.34-
5o433'4227 i345§

Figure 10c,d. Plot of total organic carbon content in samples
across concretions 3 and 7.

TABLE 4:
3 vertical
edge 5a
4a
3a
2a
center 1
2
3
4
edge 5
3 horizontal
center 1
2
3
l;
5
edge 6
(pyrite)
Shale
light
dark
7 vertical
6
5
4
3
2
1
2a
3a
4a
5a

7 horizontal

NO‘UID‘UDNH

46

Carbonate Geochemisty (atomic

K

356
458
493
268
451
211
238
140
403

1014
932
893
925

1183

4553

2603
11250

283
491
647
692
617
728
750
613
777
857

2154
1229
791
1247
1131
524
760

Sr

146
191
272
203
204
174
226
165
180

Sr
179
206
186
178
169

0

293
304
316
292
289
265
178
495
282
279

266
269
304
299
297
303
289

Zn

17
20
109
14
25

80
11
87

Zn
14
13
12
14
14
16

218
99

11
13
14
14
13
13

9
24
14
15

14
15
14
14
15
17
14

Mn

6551
11054
9881
5635

8878'

5726
6342
4815
6039

5522
8200
9612
10156
5645
160

1095

5983
5351

M8

101395
94904
285214
113207
84818
94712
127613
133350
87321

“8
75546

87307
85179
96148
90781
16821

47,143
4941

78634
91345

6375 100458

5358
6301
6301
5343

95305
86149
86149
79175

12390 182739

4827
6378

6951
8210
7790
8278
6744
7439
6406

83676
93553

89850
84783
94148

102708

93036
88444
81593

absorption data).

Fe

43981
28252
39893
26439
30309
22470
30460
22987
27784

Fe
26636
33355
28395
28041
28024
81805

23175
0

22642
25785
27173
25105
23141
23141
18261
47425
27558
27918

29970
18641
23455
23639
25943
25279
25476

Ca

298985
304458
637536
303177
316087
414767
335457
270444
303725

Ca
294051
204666
305944
308203
297012
244649

116175
0

280723
303365
311790
300183
270196
270196
169749
509000
303970
309380

303413
295549
281067
267863
277320
284152
267817

Na

462
568
537
613
924
427
522
395
434

Ne
598
625
430
439
392

1262

3079
7960

353
438
653
453
417
356
356
710
586
475

626
449
528
720
473
617
713

47

the concretions grew in an open system.

Zonal theory-- the trace element geochemistry of the concretions
yields no information as to the time of growth of the concretions
relative to compaction of the shale, the carbon source or the nature

of the reactions.

Temperature/Salinity- No information on the temperature of the pore
fluid can be gained from the concretion geochemistry. However,
according to Land and Hoops (1973) the Na and K content of a dolomite
can represent the salinity of the most recent solution with which the
dolomite has come in contact if no recrystallization or
post-lithification reequilibration has occurred.

In thin sections there is no evidence of recrystallization in
progress in the Antrim concretions; therefore, either none has taken
place or the entire body of the concretion has been recrystallized
leaving no trace of the original fabric. The oxygen isotope ratio in
concretion #3 differs from those of the shale. This observation
supports the hypothesis that no recrystallization or reequilibration
with meteoric water has taken place in the Antrim concretions
(Hathon, 1979). Thus the Na content of the Antrim concretions may be
representative of the salinity of the pore fluid. According to Fritz
and Katz (1972) the low concentration of Na and K in the Antrim
concretions may indicate that the concretions formed in pore fluid of
relatively low salinity. The lack of a monotonic gradient in sodium
across the concretion can be interpreted as evidence that no change
in pore fluid salinity occurred during concretion growth (Fig.

11,12,13,14).

48

.5 one m accuuouoeoo emouoe oodmeoe ouodooueu.ew canon wz\eo we mean .o.o.o.om~ museum

h
D
p
D
D

 

 

3233.. n

I.
p
b

I...”

 

 

 

 

o\o\o\o/o/o\o .

2.3.3.. t.

o
o a co on
i a a a. m a a. .n r .
5Y0
hYO
IN;
rN._ Ma Mg
.m. /
.9. w M
b 1¢.~
LYN
.nYm
ea.»
33...? n. fi
o o
o o c m N am am .ow om.
.OAU .mAu
rm; Mo am.—
a.
‘ e o
1m.—V m — /
a 3 w
4d . o
.O;m
.O.m _oo_to>h

 

 

.u one m «coauonoooo enouoo «cameos oueeoouoo cu eouuouucooeoo Bowman mo oodm .o .eua seamen

 

 

 

 

37:2:
0 o o o o
mmwmm._ mo¢n~.o~.u.no.¢o.n
.OOM .OOn
M. .Oov .Qrov
M econ m .00... N
9 .03 . o.
4 . .000
d M
roasm .00» m
.000 .000
.00m .00m
.000. . . .000.
.00: , _
32:: n .00:
.2523...» .OON. .. .OON.
.oom.

 

 

 

50

 

 

800‘ ThorizoMol
- 700i
2.
Q_ 60(3‘
500‘
+
O
z 400‘
300‘
200‘
I i 3 4 5 s 7
c e
800 a 7 VOfIiCO'
TOCD‘
SIJO'
E .
5} 5C)O
+ 400‘
O
'z
300‘
2C>O'
saioioz'3I i 54 5%

Figure 12c,d. Plot of Na concentration in carbonate samples
across concretions 3 and 7.

51

l500‘

1400* ShorizonIol

l200‘

(ppm)

I 100‘
1000‘

K+

900q

800‘

 

 

a...
”1
0h
.5.
UI

.0)

3 vertical

 

 

Figure l3a,b. Plot of K concentration in carbonate samples
across concretions 3 and 7. (Sample 3-horizontal-6

is pyrite.)

(ppm)

K+

Figure l3c,d.

2200‘
2000‘

I800J
l600‘
“N30‘

1200‘

(ppm)

l000‘

K+

800‘

600‘

400‘

 

soo-
soo«
root
soo-
500'
400-
soo-

200‘

 

7hoflzufld

7 vertical

 

54 4o 54 2o

iééIéE

Plot of K concentration in carbonate samples

across concretions 3 and 7.
is pyrite.)

(Sample 3-horizonta1—6

Figure 14a,b.

53

901 3 horizontal
80‘
70<
SCI

50‘

(x1000 ppm)

40‘

Fe

30‘

20..

 

 

a...
N1
u
a.
u

no:

90'
80‘
7°. 3 vertlcd
60-

50‘

(xlOOO ppm)

401

Fe

301

20‘

 

 

r I’

5343333ai254 5
0 c

Plot of Fe concentration in carbonate samples
across concretions 3 and 7.

(II 1000 ppm)

Fe

Fe (xlOOOppm)

Figure l4c,d.

30‘

50‘
4o-
30'
20‘

IO‘

 

54

7 horizontal

 

50‘

40‘

20

IO‘

 

0—1

7 vertical

W

£4 44 3o 2o l 2
e c

.1

on
45
an

Om.

Plot of Fe concentration in carbonate samples
across concretions 3 and 7.

55

OXYGEN ISOTOPES

The stable oxygen isotope ratios were determined for a group of
samples traversing Antrim concretion #3 and for three samples across
an Antrim carbonate concretion studied by Hathon (1979)(Table 5)(Fig.
15). There is no trend across concretion #3 except for a slightly
heavier value at the edge of the concretion. There is a trend of
lightening 6180 values across the concretion studied by Hathon.

THe Antrim Shale sample contains a somewhat lighter 6180 value
than concretion #3. The oxygen isotope values reveal no information

on the time of growth of the concretions.

State of system-- The lack of a trend in the 6130 values across

the Antrim concretions can be interpreted as evidence that the system
in which the concretions grew was open. If the system were closed,
then an increase of lighter 5180 values toward the edge of the
concretion would be expected, because the 180 will precipitate

in the solid before the 160, thus concentrating the 16O in

the pore solution and raising the 160/130 ratio in the
later-precipitated carbonate. If the system had been open to
seawater, then no trend would be expected because there would be a

constant source of 18O to precipitate in the carbonate mineral.

Temperature/Salinity-- The oxygen isotope ratio of carbonate material
is a function of the temperature and the salinity of the
precipitating pore solution (Craig, 1953). Using the equation for

dolomite-seawater fractionation by Matthews and Katz (1977):

56

TABLE 5: Carbon and Oxygen Isotope Values for Two
Antrim Concretions

#3.

Center 3-v-l
3-v-2
3-v-3
3-v-4

Edge 3-v-5

Shale

Hathon (1979)
inner
middle

outer

-11.8
-12.0
-11.7
-ll.3
-10.2

-901

-1103
‘1202

-10.1

PDB - -30.37 + SMOW

 

1.03

6136(PDB)

+20.8
+20.8
+20.8
+20.8
+20.0

+20.0

+23.9
+23.3

+22.6

4180(suom 5 180091313}

-9.29
-9.29
-9.29
-9.29
-9.10

-6028
-6086

-2.54

57

.n eomuouocoo Eoum ouoo moucouuuon osu moouoo eooououu eomhxo.oee eooueo omoeuu no uo~m .o .om~ ouommm

 

 

 

 

 

o o o
m .4 m N . m ¢ m N .
LT .
.. m/o .N_I M.w/o
.o... 9.. . 9..
08 32
D . mum .2. mm
O\O|IIQ C. 0 m m
rm- . l.
.25th m . _ .0...
323.3; m e

58

1n n - (3.06 x 106 x 1'2 - 3.24)]1000,

and assuming that the 6180 solution - 00/00, a temperature of
approximately 83°C can be calculated from the 5130 values of
concretion #3.

The trend in «5180 values can also be interpreted as
evidence for a change in pore fluid salinity as the concretion grew.
However, there are inconsistencies in the data because concretion #3
indicates an increase in salinity by its increase in heavier isotopes
toward the concretion edge, whereas the concretion studied by Hathon
,(1979) indicates a lightening of the water by the increase of lighter
isotopes toward the concretion edge. These inconsistencies will be

discussed in a later section.

Zonal theory-- the 6 18O values of concretion #3 indicate a pore
fluid temperature of 83°C. According to the zonal theory (Curtis,
1978; Table l), 83°C would occur in the pore fluid at a burial depth

of approximately 2500 meters.

CARBON ISOTOPES

Stable carbon isotope ratios were determined for the same
samples as the oxygen isotope ratios. The results are listed on
Table 5 (Fig. 15). In both concretions analyzed, there is a gradual
gradient in theI513C value across the concretions.

The carbon isotope values do not reveal any information on the
state of the system, the time of growth or the temperature or

salinity of the pore fluid.

59

Zonal theory-- The carbon isotopes can give information on the carbon
source and the depth of burial of the concretions during growth. The
513 values of the concretions are intermediate values, caused by
a combination of either bacterial sulfate reduction (613C -
-250/oo) and bacterial fermentation(613C - +15p/ppPDB), or
bacterial fermentation and decarboxylation (613C -
-200/ooPDB)(Curtis, l978)(Table 1). According to Curtis (1978) the
Antrim concretions can be interpreted to have grown either at a
burial depth of approximately 10-100 meters between zone 11 and zone
III or at a burial depth of 1000-2500 meters, between zone III and
zone IV.

However, Coleman and Raiswell (1981) determined that the
613C value from carbonate concretions from Upper Lias black shale
of northeastern England was the result of a mixture of three carbon
sources: 1) bacterial fermentation, 2) sulfate reduction and 3)
marine derived carbonate (skeletal or dissolved). They plotted the
possible range of mixtures of these three sources that would result
in a513C value of -14o/ooPDB. If no fermentation occured, then
432 of the carbon must have come from a marine source in order to
achieve the -l4o/oo 513C value (Coleman and Raiswell, 1981).
Because there was only a small amount of skeletal material in the
shale, Coleman and Raiswell (1981) suggested that bacterial
fermentation was a probable source of carbonate carbon in the
concretions. The average 5130 value of the Antrim concretions is
approximately llo/oo(PDB) and as there is little skeletal material in
the shale, these interpretations can be applied to the Antrim

concretions also (Fig. 16).

60

. 3 3:3...

one EycofimueoEuou :«uouuoo .Ammvcowuonoou enough scum coouoo 323930 «0 monsoon“:
4

 

  

.nnm oo\o.: no 333, can dmuou o3». sou—.5 Canaan—o oozes

:.
d 4 4 10401 ‘4 4 4.4 4 v. I 4 a 4 o“.404Q4.J4 40- 404 454 404 4.40.04OQ 4.4 4 O
4.94%.... age.seaeaeaeeEEea....
0.142.344.4934“. .. .. A. a.3......amqeméuwfifiww.a... . $2..
3...... e...\%.®@ www.meweewaaMammy... 0....
0...... . .0... .4... .. . .0. .h. .

4 a... aaafigmeeeewa

1 4 s

yfia®¢£¥®w 1.35%.
a...

 

mm

                 

4.4.4 . It.
save...
-\ .

       

. float... a... a. a...
.. 4...: 4 t. .
. Cm.» on... to o . an.
0%.. «329%wa.momm.mwholvfiww.fiooofimw .46 5.... a... ..
.
... fie§§fi$¢
a.

. a .. .
. “was. av...o.m...o..axes»....fimmo
. sit}: new». . o.

5.. am...” new“? tweeme. 4 . ..

.4 -.........e as as sees.

t9 kwwaukwmgfi «Roulmny .. 1mm. . imam. .. .
. 4.. a. .0 owwoowmwomoafiovwwwofifivm

skinny. .4.

. QR o 4&5...) 4.2.4.4....5....H..o.m4...me a.
.. WV . o X 3 .1. I.
. .49. . xgwmwdmdmwgwfi may .wwow .mowamiv. mammowwww owe“. a
. 4o. 04 0404 o 404 4 . 4 00 4 o 4» 040 404
s fixagw. e. a. e. . gen... :a. 4.1%
.mp9. . :v a.\ a...» hwmafiwmomawwwmz. WWW”? «mm. «amiaowovamv. . a
4 4 4044404 4040 40 0044 04440 4 4 44 04 o p 4. 40404 40 44
. 243.2:53 .0: an 3... «ovfiww w.%
4w... . .. wag... .e.
.o a. gmlfiwfifio .. $03.3 “$1.315. fig
a“ 4%. .«zmwwwwwwoum.w.w€ .£.wmmmwo%owwwamomww. am“...
1 ‘0‘ 1 0“0( ‘04 '0‘9‘ Q i 4 1 ‘ ‘ H% ”Ho—.0 o ‘
o 0.... . a...» .. {.30 0
ea...» maew..%m
2:4. : :o. the...” . .
afield»?mo.m.mm%4.w%mfiféwhomage?“ 0%
. . . s.%..w.w.w.m.fi%w «w. .“mewwo.
22:. 3. . 5.0 we...
{momanfiwwwamoo

4..
p e%h°>e.4- 4» s4. .4 >
day...“ how“. omega. .
o 3.»... 0.0.3... Manama».
. .. . 53...: 2..
a Foowoloawwfiwwo

    
        

 

        

 

 

 

    

      

   
 

alum...“ F»... . ..
.. 0. ... .. a. . a...
$wmoofiu.m%.ow¢.... .

4 b. . .40. 543.19 2.9%...

..o... o ..
2.20.0.1: .
fimwyfi yoomflovu . . .
. .% vowmgommw.

a. . .0 .

o». a avowww...t sumo”.
.9 3.4.4.4.

4o a.” .

     

             

d.
9.0.0.030. . .
a...

  

    

61

Thus from the carbon isotope data alone, the Antrim concretions
can be interpreted to have grown at either a shallow depth (lo-100 m)
as a result of sulfate reduction, bacterial fermentation and marine
derived carbonate, or they could have grown at a deeper depth
(1000-2500 m) as a result of bacterial fermentation and

decarboxylation.

DISCUSSION

The interpretations made from the geochemical data collected
from the Antrim concretions have been tabulated on Figure 17 and are

summarized below.

State of systemr- The mineralogy, porosity and lack of monotonic

gradients all indicate an open system during concretion growth.

Zonal theory- The mineralogy and stable carbon isotope values can be

interpreted to indicate sulfate reduction, bacterial fermentation and

marine derived carbonate as sources of carbonate carbon in the Antrim

concretions. However, the carbon isotOpe values can also be

interpreted to indicate a combined carbonate carbon source of

bacterial fermentation and decarboxylatin in the Antrim concretions.
The depth of burial is indicated to be shallow according to

the mineralogy, physical characteristics and the carbonate carbon

source of bacterial fermentation, sulfate reduction and marine

4 derived carbonate. But the temperature indicated by the

oxygen isotopes and the carbonate carbon source of bacterial

62

.auwv Hwoamunn van dungeonuomm scum mvms muoaunumuaumuaH .n~ wuswwm

 

acuuudhuonuaoov

aoomuncocd A--:uuuu .auou .oan

 

HO

 

huq>quua unquaa_.aumu mumoaoma
cucumuo soooauoa Auu.oua a.eau ouauaaa zomm<o
Aa.:osuumv .ocou
yonuocu :« :mmum
menusou vcouu
a can An*v
.uaoo 0:0 nu Awnma
o.mm «adduu «you .aquusov a ocmu mmmoeomH
avuwsou vaoua ouuaudvcu comm zumo zmumxo
sysop»
auguse Amazmmav
«mango oz zumo auamuzmmo
aouuuaa
Iaououm aways: ammo moHamHmuso<m<=o
auquouom Adonamm
Auauusov
mmuameoH
Hovom
adamauuqmv coauuavuu madman»
Aouauhav huq>uuu¢ manna: n mouuouvaa «aqua;
unm<m ouaomuo magnum mo ooaoaoum zmmo wooqddmsz
«usuauogama huucuaum nusouo ouauwuc suave Huuusn auuacm cognac amuahm
mo u> mo and: no «aha
«may oucuwuoca ououm \aouuuuouauouaH

 

amomma Adzon

63

fermentation and decarboxylation can be interpreted to indicate a

much deeper burial depth between 1000 and 2500 meters.

Time of growthr- The mineralogy and physical characteristics of
the concretions in surface exposures indicate an early, precompaction

time of growth.

Salinity- The salinity of the pore fluid is not clearly indicated by
the analyses performed on the Antrim concretions. A lack of a
gradient in the sodium concentration may indicate that no salinity
change occurred during concretion growth. The low concentrations of
potassium and sodium in the concretions can be interpreted to
indicate that the pore fluid salinity was low. The trends in the
oxygen isotopes can be interpreted to indicate that a change in

salinity did occur during concretion growth.

Temperature-- The oxygen isotope values indicate a pore fluid
temperature of approximately 83°C. It is apparent that there are
some inconsistencies in the data interpretation. These will be

discussed below.

COMPARISONS OF THE ANTRIM CONCRETIONS TO OTHER CARBONAIE

CONCRETIONS IN BLACK SHALES

Comparing the results of studies on carbonate concretions from
various black shales may suggest a commonality in their origin and

nature of growth. These comparisons can also be used to

64

Time of growth-- The mineralogy and physical characteristics of
the concretions in surface exposures indicate an early, precompaction

time of growth.

Salinity- The salinity of the pore fluid is not clearly indicated by
the analyses performed on the Antrim concretions. A lack of a
gradient in the sodium concentration may indicate that no salinity
change occurred during concretion growth. The low concentrations of
potassium and sodium in the concretions can be interpreted to
indicate that the pore fluid salinity was low. The trends in the
oxygen isotopes can be interpreted to indicate that a change in

salinity did occur during concretion growth.

Temperature-- The oxygen isotope values indicate a pore fluid
temperature of approximately 83°C. It is apparent that there are
some inconsistencies in the data interpretation. These will be

discussed below.

COMPARISONS OF THE ANIREM CONCRETIONS TO OTHER CARBONAIE

CONCRETIONS IN BLACK SHALES

Comparing the results of studies on carbonate concretions from
various black shales may suggest a commonality in their origin and
nature of growth. These comparisons can also be used to
gain insights into the nature of black shale diagenesis. Earlier,
four aspects that seem to characterize the nature of the geochemistry

of concretions were summarized from past work. The results of this

65

study on the concretions 0f the Antrim compare favorably to that

summary in terms of bulk chemistry, of chemical trends from the

center to the edge of the concretions and of their physical and

geochemical relationship with their host shale. The following is a

comparison of data:

Carbon isotopes--

Irwin (1980) edge: +20/00 PDB; center; +9o/oo; edge: -20/oo

Hudson (1978) edge; -14.lo/00; heavier toward edges

Galimov and Girin edge: -960/00; center: -2.27o/00

(1968)
Hoefs (1970) Cretaceous concretion: -3.3 to -43.20/00
Cretaceous shale: 0.9 to -5.30/00
Devonian concretion: 2.0 to -7.00/00
Devonian shale: -0.3 to ~6.20/00
Curtis, g£_gl. edge: -2.00/00; center: 8.00/00; edge: -l.00/00
(1975)

Sass and Kolodny edge: -7.20/00; center: -7.60/00

(1975)

Coleman

and UA:edge: - 120/00; center: ~130/00

Raiswell (1981) UB:edge: - 130/00; center: -lSo/00

Oxygen isotopes--

center

edge

Coleman and Hudson and Irwin Hoefs Antrim Hathon (1979)

Raiswell Friedman #3
203 -809 .007 -1056 -900 -902 -6040/00 PDB
-408 -909 -307 ‘4046 ’1203 ”901 “706

66

Porosity changes--

Coleman and Irwin Hudson and Curtis g£_213 Antrim

Raiswell Friedman #3 #7
center 77-872 80-952 78-952 73.22 812 812
edge decrease 63-762 10.22 602

691

Nature of system?-
Irwin: closed
Hoefs: closed

Raiswell: open

Physical relationship with the surrounding shale--The Antrim
concretions are similar to those studied by Raiswell (1971) in that
in both cases the shale beds can be traced through the outer zones of

the concretions and they bend around the concretions.

Black shale carbon isotopes--Similar to the Antrim, the concretions
studied by Coleman and Raiswell (1981) and Hoefs (1970) contained
carbon isotopes that were heavier than the values determined for
the surrounding shales.

From the results of studies on carbonate concretions in black
shales several conclusions as to the origin and nature of growth can
be drawn:

1. The carbonate carbon source is a result of organic reactions in
the shale.

2. The variable 6136 values suggest different sources of

67

carbonate carbon among the concretions studied.

3. The porosity indicates early growth in uncompacted sediment.

4. The state of the system in which concretions grow can be open or
closed.

5. The oxygen isotopes are lighter than what would be expected in
carbonate precipitating from.modern seawater.

6. The oxygen isotopes indicate a lightening of the pore fluid as
concretion growth occurred.

7. The physical relationship between the shale and the concretions
indicates early, precompaction concretion growth.

8. The oxygen isotopes of the shales are lighter than those of the
concretions.

9. Pyrite was present throughout the concretions in one study
(Hudson, 1976), and formed rims on concretions in another
study (Coleman and Raiswell, 1981).

The data from the Antrim concretions and the previous studies
can be interpreted to indicate that carbonate concretions in black
shale are an early diagenetic phenomenon. They originate as a result
of varying organic reactions in uncompacted sediment in a system open
or closed to seawater, and as they grow the oxygen isotopes of the

pore fluid are lightened.

INCONSISTENCIES IN DAIA.INTERPRETAIION

Zonal theory-For the Antrim, interpretations as to the source of
carbon from carbon isotopes is difficult. Since the 613 C values

become heavier towards the edge (Tables, FigurelS), in line with

68

interpretations of 513C isotope trends in other concretions

(Coleman and Raiswell, 1981; Hudson, 1976; Sass and Kolodny, 1975;
Galimov and Girin, 1968), increasing contributions to the carbon pool
are needed from either the process of bacterial fermentation or
assimilation of primary marine carbonate material. However, sources
of carbon from these processes may be inconsistent with the
mineralogy of the concretion and the surrounding shale. Pyrite rims
on the Antrim concretions indicate that sulfate reduction was a
significant source of carbonate carbon in the concretions. However,
the 613C values of carbonate formed as a result of sulfate
reduction is -250/oo PDB (Irwin, 1980) and the 5130 values in the
Antrim concretions average approximately -130/oo. Thus, if sulfate
reduction was the source of carbonate carbon, then the 513C

values should be lighter and they should not become more positive
toward the edge of the concretions. The 5130 values should

remain constant all the way across the concretions if sulfate
reduction was the steady source, or the 513C value should become
lighter if sulfate reduction was in increasing source of carbonate
carbon in the concretions.

In order to achieve the absolute 6130 values of the Antrim
concretions there must have been another process besides sulfate
reduction contributing carbonate carbon to bring the 6130 value
up from -250/oo to -130/00. Both bacterial fermentation and the
assimilation of primary marine carbonate could mix with sulfate
reduction and cause the 513C values found in the Antrim
concretions. Possible mixtures of these three sources to give a

613C value of -llo/oo, as in the Antrim concretions, are plotted

69

on Figure 18. It is impossible to determine exactly how much
carbonate carbon each process contributed to the Antrim concretions.
The association of pyrite with the ferroan dolomite is also
inconsistent with the zonal theory. If sulfate reduction were the
major source of carbonate carbon in the shale, as indicated by the
pyrite and the 513C values, then the iron in the pore fluid
should have been bonded with the reduced sulfur to form pyrite and
not with the carbonate to form ferroan dolomite. The iron should not
bond with the carbonate until the sulfur is depleted in the pore
fluid. Thus, the Antrim concretions are mineralogically ”inside out"
with the ferroan dolomite on the inside and the pyrite forming rims

on the concretions.

Temperature/Salinity-There are two inconsistencies in

the interpretation of the oxygen isotope data: 1) the 6180

values of the Antrim concretions are much lighter than would be
expected of carbonate minerals precipitating form modern marine
water, and 2) assuming normal seawater salinity and using the
equation of Matthews and Katz (1977), the temperature of the pore
fluid was calculated to be approximately 83°C. However, Hathon
(1979) used vitronite reflectance and the burial depth of the Antrim
Shale to determine a maximum temperature of 60°C for the Antrim
Shale. Thus the temperature indicated by the oxygen isotopes is
inconsistent with the independent data on the temperature of the pore

fluids in the Antrim Shale.

70

Depth Sediment/water i_nte gate

 

2i

 

 

 

Oxidation by bacteria cazo + 02'
and molecular oxygen
10“
Anaerpoie oxidation “3320)“! ) 4. an; .
J
by a, D2
6coz+6lzo+2lz+ln3+loe
latterial eaiphata 2(cn20) + 30' - a 2’ + zuto‘
3
reduction .
1° 2(ca20)+soI-as“"+zmo3+u
2(0
Santeria! fematatioo O+Egzg + H

Iiogenit deearbaylatioa _ ’
a-coza+azo-sa+m03+a

10

 

Abiotit reactions
(deearbaylatioa and Gee-ratioa of hydrocarbons
ther-i tracking)

Figure 18. Expanded version of diagenetic zones within compacting
marine mudstone sequences (Irwin, 1980).

71

SPECULAIIONS ON INCONSISTENCIES

A model of concretion growth is needed that accounts for the
origin, the nature of growth and the inconsistencies in the data
between the Antrim concretions and the zonal theory of black shale
diagenesis. The physical characteristics and the pyrite rims on
the Antrim concretions indicate early concretion growth at a shallow
burial depth in the sediment. The stable carbon and oxygen isotope
ratios can be interpreted to indicate later, more deeply buried

conditions.

Oxygen isotope values--Any interpretation of the 8180 values of

the concretions must account for the trends in thed 180 values

and for the overall lightness of the 6180 values of the Antrim
concretions. There are several factors that can affect the isotope
values, thus caution must be exercised when conclusions are drawn
using the 5180 values.

Speculations:

1. The experimental oxygen isotope values could be wrong. This
speculation can be eliminated because the 6130 values of

concretion #3 are consistent with the values determined previously
for an Antrim concretion (Hathon, 1979) and they are consistent with
6130 values determined for carbonate concretions in other black
shales (Coleman and Raiswell, 1981; Hoefs, 1970).

2. The trend of light oxygen isotopes towards the edges of the
concretions has been attributed to an influx of meteoric water

through the shales. The values may be primary (Hudson, 1976), so

72

that as the concretions grew, the 5130 of the pore fluid changed,

as suggested by Hathon (1979) for the Antrim. However, a meteoric
influx is unlikely through sediment as impermeable as shale (Coleman
and Raiswell, 1981). The 6180 values also could be secondary, as

a result of reequilibration with the meteoric water in the shale.
This possibility can be eliminated for the Antrim because there is no
evidence of recrystallization in the Antrim concretions (D. F.
Sibley, 1981, pers. comm.).

3. The trend of light oxygen isotopes towards the edges of the
concretions could be due to diagenetic reactions in the shale with
depth as evidenced by samples from the Deep Sea Drilling Project
(Sayles and Hanheim, 1975). However, the mineralogy of the Antrim is
different than the sediment from the DSDP which contains abundant
volcanic material. Therefore, the diagenetic reactions caused

by burial in the Antrim Shale probably would not be the same as those
in the samples from the DSDP.

4. Local microenvironmental factors could effect the 6180 values

in the Antrim concretions. The precipitation of ferroan dolomite in
a closed system could cause a gradient; however, the experimental
data on the Antrim concretions has been interpreted to indicate that
the system was open during concretion growth. Bacterial activity has
been inferred to affect the local environment surrounding the
concretions and thus affect the 6430 values in the precipitated
carbonate mineral (Coleman and Raiswell, 1981). There is no evidence
as yet to eliminate this possibility.

5. The temperature of the pore fluid could have been 83°C, thus

causing the light 6180 values. This is unlikely because evidence

73

from the burial depth of the Antrim Shale and vitronite reflectance
indicate a maximum temperature of 60°C for the shale. However, the
Antrim is believed to be a source of natural gas in the Michigan
Basin and unless the gas was generated biogenically, the temperature
would need to have reached 150°C (J. H. Fisher, 1981, pers. comm.).
6. The Devonian seawater may have been isotopically lighter than
modern seawater causing the overall lightness of the Antrim.6130
values as suggested by K. C. Lohmann (1981, pers. comm.). The
6130 values of the Antrim concretions indicate a 5130 value of
seawater of approximately -9.00/oo PDB.
7. The overall light<5180 values of the Antrim Shale and
concretions may very likely indicate that the shale was deposited in
a brackish to fresh water environment similar to the modern Florida
coastline (D. T. Long, 1981, pers. comm.) instead of in a normal
marine salinity environment.

Although various factors can affect the 6180 values in
the Antrhm concretions, several can be eliminated using independent
evidence. The possibilities that cannot be eliminated are local
bacterial activity, the overall isotopic lightnes of the Devonian
seawater and the possibility that the shale was deposited in a
brackish water environment as opposed to a saline environment.
Zonal theory-It is difficult to formulate a geochemical model of
concretion growth that accounts for the carbon source, the 6180
values, the ferroan dolomite and the pyrite rims around the Antrim
concretions. In the formulation of a model it can be assumed that
either no recrystallization occurred or that recrystallization did

occur in the Antrim concretions. There is no apparent evidence of

74

recrystallization in the Antrim concretions (D. F. Sibley, 1981,
pers. comm.); therefore, speculations assuming recrystallization are
not discussed. 2

If no recrystallization occurred, then two possible models can
be constructed. The first assumes that as the concretion grew,
changes in the sediment and pore fluid surrounding the concretion
caused changes in the concretion geochemistry according to the zonal
theory of shale diagenesis (Curtis, 1978).

The zonal theory accounts for the characteristics of the Antrim
concretions and the carbonate concretions in black shales in Europe
studied prevously (Coleman and Raiswell, 1981; Irwin, 1980; Hudson,
1976) if concretion growth occurred at a shallow burial depth and
during very early diagenesis of the shale. The physical
characteristics of the Antrim concretions and the pyrite rims around
the concretions are indicative of early diagenetic concretion growth
at a shallow burial depth, according to the zonal theory. The
presence of the pyrite strongly suggests that sulfate reduction
played an important role in the concretion precipitation. The
613C vaues, however, indicate a mixture of carbon sources that can .
be interpreted to indicate a deeper burial depth than the physical
characteristics imply according to the zonal theory. If the:513c
values were controlled by sulfate reduction and primary
primary marine-derived carbonate then the early diagenetic shallow
burial model might be a good model for carbonate concretion growth.
An expanded version of the zonal theory is depicted in Figure 18
‘(Irwin, 1980). This version details the shallow zones in the model

of Curtis (1978; Table 1). According to the early diagenetic shallow

75

burial model, concretion growth would begin in the anaerobic
oxidation zone above the zone of bacterial sulfate reduction, and
continue until further burial occurred causing sulfate reduction,
pyrite precipitation and, thus, the end of concretion growth.

The second model, constructed by Coleman and Raiswell (1981),
also assumes that no recrystallization occurred in the concretions.
They suggested that the carbonate concretions in the Upper Lias black
shale of northeastern England originated and grew due to sulfate
reduction in the sediment. After growth the concretions were later
infilled by carbonate derived from bacterial fermentation so that the
concretions attained the heavier 6 13C values towards their edges.

The assumption in this model is that the concretions retained some
porosity that could be later infilled by heavier carbonate.

This model could help to explain the variations in 6 180
values found in the Antrim concretions. Each concretion might have
experienced different amounts of infilling by later bacterial
fermentation carbonate so that the early carbonate (with its unique
oxygen isotope ratio) will be combined with the later carbonate (with
its unique oxygen isotope ratio) in different proportions in each
concretion, and will create the observed trends in each concretion.
However, it is difficult to prove the assumption that the concretions
retained pore space that could be later infilled with heavier
carbonate.

Further study is needed. Carbon and oxygen isotopes are needed
from a variety of carbonate concretions from the Antrim Shale.
Samples to be analyzed should include portions of the massively

textured and the bladed crystals in the concretions along with the

76

samples of the surrounding shale. Paleosalinity analyses using the
pyrite in the concretions and in the shale using the method of Berner
(1979) would be useful in the determination of the original pore

fluid salinity.

CONCRETIONS AS CHEMICAL TAPE RECORDBRS

Possible gradients across the concretions from the center to
the outer edge include an increase or decrease in a specific ion
concentration across the concretion or an increase or decrease in
ionic ratios such as Ca:Mg across the concretion. Chemical trends
could be due to changes in pore fluid composition during concretion
growth.

Trends previously discussed are the increase in the 6130
value, and the decreasing porosity and change in mineralogy from
ferroan dolomite to pyrite across the concretions. These trends have
been interpreted to show that the contribution of different sources
of carbonate carbon changes, that the sediment porosity decreases and
that an open system existed during concretion growth.

Because the Antrim concretions grew in an open system, any
trends across them could be interpreted as changes in the chemical
environment surrounding the concretions during concretion growth, as
opposed to the effect of the partitioning coefficient of the
particular component.

However, as discussed, the Antrim concretions analyzed, #3 and
#7, do not contain any trends in carbonate geochemistry across their
diameters. Thus, either no changes in pore fluid chemistry occurred

during concretion growth, or changes in pore fluid chemistry were not

77

recorded in the concretion geochemistry.

Physical evidence indicates that the concretions formed during
the early diagenesis of the shale. Because the concretions were
early diagenetic and grew in an open system, it is likely that no
major changes in pore fluid chemistry occurred during concretion
growth. Thus, although the concretions might have been able to
record pore fluid changes in their geochemistry, no changes occurred
for them to record as they grew. If the concretions were
recrystallized after deep burial and compaction, anything they had

recorded would have been wiped out by recrystallization.
CONCLUSIONS

1. The carbonate concretions in the Antrim Shale are composed of
ferroan dolomite and contain quartz and pyrite. The pyrite forms
rims around the concretions, approximately 1 to 2 cm thick. The
shale beds bend around the concretions, equally above and below, and
the concretions are spherical or nearly spherical in shape. The
weight percent of ferroan dolomite in the concretions ranges from
50-902 and decreases across the concretions from center to edge.
There are no trends in the major or trace elements or the total
organic content across the concretions. The oxygen isotope values of
are approximately -9.lo/oo PDB and they do not vary systematically
across the concretion. The carbon isotope values range from.-lO to
-l3o/oo PDB, and they increase from the center to the edge of
concretion #3.

2. The experimental data have been interpreted to indicate that the

78

concretions grew in a system open to seawater, and buried in the top
10 meters of the sediment. The carbonate contributing reactions were
organic in nature. The concretions apparently grew before compaction
occurred in the shale.

3. The geochemistry of the Antrim concretions is not consistent with
the zonal thory of shale diagenesis. The carbon source is difficult
to interpret from the carbon isotope values. The trend of
increasingly positive<513c values towards the edge of concretion

#3 is inconsistent with the pyrite rims on the concretion. The
association of pyrite and ferroan dolomite is thermodynamically
inconsistent. The«5130 values of concretion #3 are lighter than
what would be expected if the concretions precipitated from modern
seawater.

The carbon isotope values can be explained the concretions
formed at a very shallow burial depth in the sediment and gradually
became buried until sulfate reduction caused pyrite precipitation.

On the other hand, the<513C values could have been controlled by
local microbiological activity.

The Devonian seawater could have been isotopically lighter than
modern seawater producing the light 5 18O values in the
concretions. Another possibility is that the Antrim Shale was not
deposited in a marine environment, but in a brackish water, mangrove
swamp-type or lagoonal environment.

4. The carbonate concretions in the Antrim Shale are similar in
terms of their geochemistry to the concretions that have been studied
in Europe. The concretions studied and the Antrim concretions have

similar carbonate mineralogies; all were early diagenetic,

79

precompaction phenomena and they have similar trends in porosity and
carbon and oxygen isotopes. The state of the system in which the
concretions grew was not interpreted to be open, as interpreted in
the Antrim concretions, in all cases, however. Although the other
concretions studied also compared favorably to the zonal theory, they
shared the same inconsistencies with the theory as the Antrim
concretions.

5. The Antrim concretions were not used to interpret changes in pore
fluid trace element chemistry during diagenesis of the shale because
no trace element trends were present across the concretions. The
concretions were used to interpret changes in the stable isotopic

chemistry of the pore fluid during diagenesis of the shale.

APPENDIX A

80

APPENDIX A
Titration method for organic carbon (Gaudette, et al., 1974)
2 Organic Carbon - 10(1-T/S)(0.336N)(0.003)(100/W)

T . Sample titration, ml ferrous solution

8 - Standardization blank titration, ml ferrus solution
0.003 - 12/14,000 - meq weight of carbon

N - Normality of K2Cr207

10 - Volume of KZCr207 in ml

W - weight of sediment sample in grams

Reagents:
852 H3P04
Solid NaF
concentrated H2804

Standard 0.336N K20r207 solution: Dissolve 49.4 g
K2Cr207 in water; dilute to 1 liter.

0.5 N Ferrous solution: Dissolve 196.1 g of
Fe(NH4)(804)2'H20 in 800 ml water containing
20 ml concentrated H2804; dilute to 1 liter.

Dipehylamine Indicator: Dissolve approximately 0.5 g
of reagent grade diphenylamine in 20 ml of water
and 100 ml of concentrated H2804

Procedure:

1. Place a 0.2 to 0.5g dried and sieved (10 mesh, ASTM)
sediment sample in a 500 ml Eelenmeyer flask.

2. Exactly 10 ml of 0.336N K20r207 solution is added by
buret and mixed by swirling the flask.

3. Twenty ml of cone. H2804 are added (by buret) and are mixed
for about 1 minute.

4. Allow mixture to stand for 30 minutes.

5. Run a standardization blank with each set of samples.

6. After 30 minutes, dilute the solution to 200 ml with distilled
water.

7. Add 10 ml 852 H3PO4, 0.2 g NaF and 15 drops diphenylamine
indicator to the flask.

8. Titrate solution with 0.5 N ferrous ammonium sulfate solution.
The color will progress from an opaque green-brown to green upon
the addition of approximately 10 ml of ferrous solution. The
color will continue to change upon titration to a bluish-black
grey; at this point the addition of 10-20 drops of ferrous
solution will shift the color to a brilliant green giving a
one-drop endpoint.

APPENDIX B

81

 

Appendix B. X-ray diffractionopattern of dolomite (30.86020)
and quartz (26.67 20) in Antrim concretion 7.

REFERENCES

82

REFERENCES

Beers, R. F. (1945) Radioactivity and organic content of some
Paleozoic shales. AAPG Bull 29, 1-22.

Bence, A. E. and Albee, A. L. (1968) Empirical correction factors

for the electron microanalysis of silicates and oxides. Jour. Geol.
76, 382-403.

Berner, R. A. (1964) Distribution and diagenesis of sulphur in some
sediments from the Gulf of California. Marine Geology 1, 117-140.

Berner, R. A., Baldwin, T. and Haldren, R., Jr. (1979) Authigenic
iron sulfides as paleosalinity indicators. Jour. Sed. Pet. 49,
1345-1350.

Bouma, A. H. (1969) Methods for the Study of Sedimentary Structures.
Wiley-Interscience. John Wiley and Son, New York.

Bownocker, J. A. and Stauffer,'C. R. (1911) Geology of the Columbus
Quadrangle. Ohio Geol. Surv. (4) B 14:133pp.

Brown, G. (1961) Other Minerals, Chap 13 in the X-ray identification
and crystal structures of clay minerals, 2nd edition: London, Min.
Soc. p393-445.

Chilingarian, G. V. and Rieke, H. H. (1974) Compaction of
Argillaceous Sediments. Elsevier Scientific Pub. Co. Amsterdam. 424 pp.

Choquette, P. W. (1971) Late ferroan dolomite cement, Mississippian
carbonates, Illinois Basin, 0.8.A. In Carbonate Cements. The Johns
Hopkins University Studies in Geology, number 19, 339-345.

 

Clifton, H. E. (1957) The carbonate concretions of the Ohio Shale.
The Ohio Jounal of Science 2, 114-124.

Coleman, M. L. and Raiswell, R. (1978). C, O, and S isotope
investigations of lower Jurassic carbonate concretions. In Fourth
International Conference on Geochronology, Cosmochronology an Isotope
Geology. 0808 Open-File Services Sechon, Report No. 78-0701, 74-77.

Conant, L. C. and Swanson, V. E. (1961) Chattanooga Shales and
related rocks of central Tennessee and nearby areas. 0. Geological
Survey Prof. Pap. 357, 0.8. Government Printing Office.

Coleman, M. L. and Raiswell, R. (1981) Carbon, oxygen and sulfur
isotope variation in concretions from the Upper Lies of N. E.
England. Geochim. Cosmochim Acta 45, 329-340.

83

Curtis, C. D., Petrowski, C. and Oertel, G. (1972). Stable carbon
isot0pe ratios within carbonate concretions: a clue to place time of
formation. Nature 235, 98-100.

Curtis, C. D., Pearson, M. J. and Somagyi, V. A. (1975):
Mineralogy, chemistry and origin of a concretionary siderite sheet
(clay-ironstone band) in the westphalian of Yorkshre Min. Mag. 40,

Curtis, C. D. (1978). Possible links between sandstone diagenesis
and depth-related geochemical reactions occurring in enclosing
mudstones: Jour. Geol. Sco., v. 135, p. 107-118.

Daly, R. A. (1900). The calcareous concretions of Kettle Point,
Lambton County, Ontario. Journal of Geology 8, 135-151.

Dickson, J. A. D. and Barber, C. (1976). Petrography, chemistry and
origin of early diagenetic concretions in the Lower Carboniferous of
the Isle of Man. Sedimentology 23, l89-21;l.

Engelhardt, W. V. and Gaida, (1963). Concentration changes of pore
solutions during the compaction of clay sediment. Jour. Sed. Pet.
33, 919-930.

Friedman, G. M. (1968). the fabric of carbonate cement and matrix
and its dependence on the salinity of water, in recent developments
in carbonate sedimentology in Central Europe (G. Muller and G. M.
Friedman, eds.). New York, Springer-Verlag, p. 11-20.

Fritz, P. and Katz, A. (1972). The sodium distribution of dolomite
crystals. Chemical Geology 10, 237-244.

Galimov, E. M. and Girin, Y. P. (1968). Variation in the isotopic
composition of carbon during the formation of carbonate concretions.
Geochem. Int. 5, 178-182.

Carrels, R.M. and Mackenzie, F. T. (1974). Chemical history of the
oceans deduced from post-depositional changes in sedimentary rocks.
In Studies in Paleo-oceanography (ed. w. W. Hay) SEPMN Spec. Pub.

Gaudett, H. E., Flight, W. E., Toner, L. and Folger, D W. (1979) An
inexpensive titration method for the determination of organic carbon
in recent sediments. Jour. Sed. Pet. 44, 249-253.

Girin, Y. P. (1970) Geochemical stages during diagenesis of Middle
Jurassic sediments of the High Caucasus. Geochem. Int. 7,

Hathon, C. P. (1979) The origin of the quartz in the Antrim Shale.
M. S. Thesis, Michigan State University.

Heckel, P. P. (1977) Origin of phosphatic black shale facies in
Pennsylvanian cyclotherms of mid-continent North America. AAPG Bull.
‘61, 1045-1068.

84

Hoefs, J. (1970) Hohlenstaff and Saverstoff-Isotopenuntersuchungen on
karbonatkonkrehonen und umgebendem gestein. Centr. Mineral. and
Petrol. 27, 66-79.

Howie, R. A. and Boradhurst, F. M. (1958) X-ray data for dolomite
and ankerite. Am. Min. 43, 12101

Hudson, J. D. (1978) Concretions, isotopes and the diagenetic history
of the Oxford Clay (Jurassic) of central England. Sedimentology.

Hudson, J. D. and Friedman, I. (1976) Carbon and oxygen isotopes in
concretions: relationship to pore-water changes during diagenesis.
In: Proceedings of the International Symposium on water-Rock
Interaction, Czechoslovakia, 1974 (ed. by J. Cadek and T. Paces)
pp331-339, Geol. Surv., Prague.

Irwin, H. (1980) Early diagenetic carbonate precipitation and pore
fluid migration in the Kimmerage Clay of Dorset, England.
Sedimentology 27, 577-591.

Irwin, H., Coleman, M. L. and Curtis, C. R. (1978) Isotopic evidence
for souce of diagenetic carbonates formed during burial of
organic-rich sediments. Nature 269, 209-213.

Kelly, W. A. and Smith, CE. W. (1947) Stratigraphy and structure of
Traverse Group in Afton-Onaway area, Michigan. AAPG Bull. 31,
447-469.

Land, L. S. (1980) The isotopic and trace element geochemistry of
dolomite: the state of the art. SEPM Spec. Pub. No. 28, 87-110.

Land, L. S. and Hoops, G. K. (1973) Sodium in carbonate sediments
and rocks: a possible index to the salinity of diagenetic solutions.
Jour. Sed. Pet. 43, 614-617.

Lane, A. C. (1902) Michgan Geological Survey Annual Report, 1901

LeMbne, D. (1964) The Upper Devonian and Lower Mississippian
sediments of the Michigan Basin and Bay County, Michigan. Unpublished
Ph.D. dissertation, Michigan State Univ. East Lansing, Michigan.

MacDonald, W. D. (1960) The Upper Devonian Kettle Point formation of
Ontario. Canadian Mining and Metallurgy Bulletin 63, 568-571.

Manheim, F. T. (1976) Interstitial waters in marine sediments. In:
Chemical Oceanography, Vol 6 (Ed. J. P. Riley and R. Chester), ppp.
115-186. Academic Press, London.

Matthews, A., and Katz, A. (1977), Oxygen isotope fractionation
during the dolomitization of calcium carbonate: Geochim. Cosmochim.
Acta, 241,1431-1438.

85

MbGregor, D. J. (1954) Stratigraphic analysis of Uper Devonian and
Mississippian rocks in the Michigan Basin. AAPG Bull. 38,
2324-2356.

Merrill, G. K. (1975) Pennsylvanian conodont biostratigraphy and
paleoecology of northwestern Illinois. G.S.A. Microfilm Publ. 3,
130p.

Mozola, (1955) Michigan Geological Survey Pub. 48,part 2.

Neglia, S. (1979) Migration of fluids in sedimentary basing. AAPG
Bull. 63, 573-596.

Newcombe, (1929) Michigan Geological Survey Pub. 38.

Pantin, H. M. (1958) Rate of formation of a diagenetic calcareous
concretion. Journal of Sed. Pet. 28, 366-371.

Perkin-Elmer (1980) Methods Manual.

Perry, E. A. and Hower, J. (1972) Late-stage dehydration in deeply
buried pelitic sediments. AAPG Bull. 56, 2013-2021.

Raiswell, R. (1971) The growth of Cambrian and Liassic concretions.
Sedimentology 17, 147-171.

Raiswell, R. (1976) The microbiological formation of carbonate
concretions in the Upper Lias of N. E. England. Chemical Geology 18,
227-244.

Report of Investigation #22 (1979) Stratigraphic cross sections
extending from Devonian Antrim Shale to MIssissippian Sunbury Shale
in the Michigan Basin. Mich. Dept. of Nat. Res., Geo Survey
Division.

Sass, E. and Kolodny, Y. (1972) Stable isotopes, chemistry and
petrology of carbonate concretions. (Mishash formation, Israel).
chemical Geology 10, 261-286.

Sayles, F. L. and Hanheim , F. T. 91975) Interstitial solutions and
diagenesis in deeply buried marine sediments: results from the Deep
Sea Drilling Project. G. C. A. 39, 103-111.

Siever, R. et a1. (1965) Comparison of interstitial waters of modern
sediments. Journal of Geology 73, 39-73.

Tarbell, E. (1941) Antrim-Ellsworth-Coldwater Shale formations in

Tarr, W. A. (1921) Syngenetic origin of concretions in shale.
geological Society of America Bull. 32, 373-384.

86

Vine, J. D. and Tourtelot, E. B. (1970) Geochemistry of black shales
- A summary report. Economic Geology 65, 253-272.

Winslow, M. R. (1962) Plant spores and other microfossils from Upper
Devonian and Lower Mississippian rocks of Ohio. USGS Prof. Pat. 364,
93 pp.

"7'11?@2‘22’2‘2‘72'2222