fl -‘__.__._._‘_‘ __ _.A _.u_ .9-.-.-o‘.‘.l(‘v.99 0.....5- 0.- «co-.«“.V" — ." y“"-'.- '1 A GRAVITATIONAL. INVESTIGATION OF ERACTURE zones m DEVONIAN ROCKS m PORTI-ONS‘OF Q ~ ARENAC AND BAY coumtEs. MlCHIGAN Thesis for the Degree “of M. S MiCl-HGAN STATE UNIVERSHY John N. Roth 1965 _ T I :i.‘ ' -"I‘-‘- .‘ . . , . - o o . .' ' t 3' .p 9'! v ‘.. ' - . ...-. “-3.0.000oq'?|.“00““3” - ...... .r. '1’ '.:.a:.:-..' .~ .. .I‘“ l n \v I Y '3 ‘54.. Lbl 3 1 93 1 1 Michiga U ' n mversistta y N 4‘ 7 1W a, t 0‘ 1995 MW MICHIGAN STATE UNI'. [mm DEPARTMENT GEOLOG! um unsmc, MICHIGAN ABSTRACT A GRAVITATIONAL INVESTIGATION OF FRACTURE ZONES IN DEVONIAN ROCKS IN PORTIONS OF ARENAC AND BAY COUNTIES, MICHIGAN by John N. Roth The gravity exploration method is capable of detecting fracture zones buried at depths of 2800 feet, if the frac- ture zone is of sufficient width and if there is a density differential produced between the fracture zone and the surrounding country rock of 0.10 gm/cc or greater. Three known fracture zones occurring in the Rogers City-Dundee interval of Devonian age, the North Adams, Deep River and Pinconning, are studied by the gravity method using graphical, statistical and analytical tech- niques of interpretation. The characteristics of the fracture zones and their associated anomalies are studied, and the optimum methods of isolation are discussed. Theoretical calculations indicate that the anomalies associated with the fracture zones are positive and may have a magnitude as great as 0.27 mgals. The source of the fracture zone anomalies is lateral variations in the density of the porous dolomitized fracture zone and the surrounding tight limestone. JOHN N. ROTH The North Adams fracture zone has a positive anomaly associated with it that has a mean amplitude of 0.15 mgals. The Deep River and Pinconning fractures do not have anom— alies correlative with them. There are negative anomalies due to buried bedrock valleys that are capable of masking the fracture zone anomalies. In areas where the bedrock topography is known, the effects of the bedrock valleys can be deter- mined and eliminated from the interpretation. Theoretical calculations using the configuration of the bedrock valleys show that the valleys can produce gravity effects equal to those observed. There is no correlation, either positive or negative, between the gravity maps and the Paleozoic structures, that are present in the area. Graphical and statistical methods isolate the anomalies associated with the fracture zones. A limited study of the application of upward continu— ation, downward continuation, and second derivative methods to isolating fracture zone anomalies indicates that these techniques have no advantage over the statistical methods in this investigation. A GRAVITATIONAL INVESTIGATION OF FRACTURE ZONES IN DEVONIAN ROCKS IN PORTIONS OF ARENAC AND BAY COUNTIES, MICHIGAN By John N. Roth A THESIS Submitted to Michigan State University in partial fulfillment of the requirements MASTER OF SCIENCE Department of Geology 1965 ACKNOWLEDGMENTS The author wishes to express his sincere thanks to the following individuals and organizations. To Dr. w. J. Hinze for his sincere interest, guidance, and helpful criticism during the study and preparation of this manuscript. To Dr. C. E. Prouty for reviewing the manuscript and for his helpful suggestions. To Mr. C. K. Dean for making available the data and well samples for this study, and for his aid during the study. To Mr. D. W. Merritt for his assistance in preparing the data for the computer and for the use of several of his programs. To Michigan State University for free use of the C.D.C. 3600 computer. ii TABLE OF CONTENTS ACKNOWLEDGMENTS LIST OF FIGURES Chapter I. II. III. IV. VI. VII. INTRODUCTION GEOGRAPHY OF THE AREA GEOLOGY OF THE AREA. Stratigraphy . Regional Geology - Local Structure and Geology Porosity by Dolomitization. Relation of Fracture Zones to Regional Geology REDUCTION OF DATA Introduction Observed Gravity Latitude Correction Free Air Correction Mass Correction Terrain Correction ACCURACY OF BOUGUER REDUCTIONS REGIONAL GRAVITY ANOMALY INTERPRETATIONAL METHODS Introduction Cross— Profiles Graphical Technique Three Dimensional Least Squares Method. Analytical Techniques Theoretical Techniques iii Page ii TABLE OF CONTENTS ACKNOWLEDGMENTS LIST OF FIGURES Chapter I. II. HI. IV. VI. VII. INTRODUCTION GEOGRAPHY OF THE AREA GEOLOGY OF THE AREA. Stratigraphy Regional Geology Local Structure and Geology Porosity by Dolomitization. Relation of Fracture Zones to Regional Geology REDUCTION OF DATA Introduction Observed Gravity Latitude Correction Free Air Correction Mass Correction Terrain Correction ACCURACY OF BOUGUER REDUCTIONS REGIONAL GRAVITY ANOMALY INTERPRETATIONAL METHODS Introduction Cross- Profiles Graphical Technique Three Dimensional Least Squares Method. Analytical Techniques Theoretical Techniques iii Page ii Chapter Page VIII. INTERPRETATION . . . . . . . . . . A6 Gravity Effects of Bedrock Valleys . . . A6 Gravity Effects of Fracture Zones . . . 56 Gravity Effects of Regional Structures. . 63 Bouguer Gravity Anomaly Map . . . . 6A Least Squares Residual Anomaly Map . . . 65 Upward, Downward and Second Vertical Derivative Methods. . . . . . . . 68 IX. CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY . . . . . . . . 72 Conclusions . . . . 72 Recommendations for Further Study . . . 72 BIBLIOGRAPHY . . . . . . . . . . . . . 74 APPENDIX. . . . . . . . . . . . . . . 77 iv Figure \0 . 00 N 0\ U1 .1: LA) 10. ll. 12. 13. IA. 15. l6. 17. LIST OF FIGURES Location of Area Location of Oil Fields Stratigraphic Succession of Michigan. Bedrock Geology of the Area. Deep River Area Structure Contour Map Pinconning Area Structure Contour Map Deep River Area Bouguer Gravity Anomaly. Pinconning Area Bouguer Gravity Anomaly. Portion of Regional Gravity Map of Michigan Elements for Talwani's 2D Computations Deep River Area Least Squares Residual O-Sth Degree Pinconning Area Least Squares Residual 0-5th Degree Deep River Area Bedrock Topography Pinconning Area Bedrock Topography Typical Bedrock Valley with Observed and Theoretical Anomalies . . . . Density and Porosity Relationships of Dolomite and Limestone. . . . . . . . . Theoretical Anomalies for Various Width Fracture Zones 2800 Feet Below the Surface Page 12 15 17 20 3o 31 32 A3 147 A8 50 52 5A 58 61 Figure Page 18. Theoretical Anomalies for Various Width Fracture Zones 2800 Feet Below the Surface . 62 19. Profiles of Analytical Methods. . . . . . 69 20. Profiles of Analytical Methods Over the North Adams Fracture Zone . . . . . . 70 vi CHAPTER I INTRODUCTION There are several fracture zones in the central area of the Michigan Basin that are important petroleum reser- voirs. It has been extremely difficult to locate these zones of porous dolomite. The masking of the bedrock by the glacial drift and the depths to the Devonian reservoir rocks near the center of the Basin have been handicaps to exploration. Since the late 1930's and early 19A0's, when these zones were first being discovered, the only successful method of locating them has been by wildcat drilling. To date, there has been no method described for delineating these features by the gravity exploration method. It is therefore the purpose of this study to determine if known fracture zones give rise to gravity anomalies, and if so, what are the optimum methods for isolating the anomalies. The area of investigation located in the southwest portion of Arenac County and the northern portion of Bay County, Michigan, has been penetrated by a large number of wells. The majority of them are located in the l northern half of the study area (Arenac County). The geology is known quite well and is used with the at an overall geological and geophysical the area. The southern half of the area (Bay small number of drilled wells. They are geophysics to arrive interpretation of County) has only a concentrated in two fields, the Mt. Forest and Pinconning. There are also a few scattered test wells in the area. Due to lack of geological control, this area is interpreted with the methods found best for interpreting the northern half of the study area. CHAPTER II GEOGRAPHY OF THE AREA The area under investigation, shown by the diagonal parallel lines in Figure 1, is located in Arenac and Bay counties, Michigan. Townships 16 and 17 north, Range 4 east comprise the majority of the area in Bay County. Parts of Townships l5, 16, 17, and 18 north, Range 3 east and Township 15 north, Range 4 east are also included. This portion of the study area is referred to as the Pinconning area or the southern. half of the study area. In Arenac County, Townships l8 and 19 north, Range 3 east, cover most of the area. Parts of Townships 18 and 19 north, Range 5 east, and three sections in Township 20 north, Range 4 east, make up the remainder of the study area in Arenac County. This area is referred as the Deep River or northern half of the study area. The area as a whole is a flat glacial lake bed. The area slopes in a southeast direction toward Saginaw Bay, and Lake Huron. The only relief encountered is that of the major river beds in the area. They are the Rifle River and three branches of the Pine River in the northern half of the study area, and the Pinconning and Kawkawlin Rivers in the southern half of the study area. 3 \ \ V l. / \ / / \ / // 1 m / r/ m / / //. / / / A .UIIy— / \I _ IL ‘ / “A W// . J .fi if 7/ , a r¢VV éWV/A / _ ll L. Lllz 7 e I... 4 TOWNSHIP INVESTIGATION AREA OF FIGURE I [It‘ll III‘ [ IIILII LII Geographically the area lies wholly within a physio- graphic subdivision known as the Saginaw Lowland (Newcombe, 1933). Of major interest to the investigation are the known oil fields in the area. Their names and locations are shown in Figure 2. The largest is the Deep River Field. It is located in the northern half of Township 19 north, Range A east, and extends for 5 1/A miles in a northwest direction. It is about 1 1/A miles northeast of the town of Sterling and approximately 30 miles north of Bay City, Michigan. The North and South Adams Fields are located in Township 19 north, Range 3 east. The North Adams Field trends northeast for three miles, approximately at right angles to the Deep River Field. The South Adams Field is approximately one mile east of the southern end of the North Adams field. One mile south of the South Adams field is the Adams Detroit River Field. Another field of importance in the northern half of the study area is the Sterling Field. It is located one half mile south of the Deep River Field and produces from the same structure. There are two fields of importance in the Pinconning portion of the study area. These are the Pinconning and Mt. Forest Fields. The Pinconning Field is located in the southeast quarter of Township 17 north, Range A east. It extends about two miles in a northeast direction and is 1—:«2104 3 _| '0! I l >l RI 2 > )\ \ - _-~ 3y 3 —_l—- .1..— OT- ‘ —$ .L I —:_ L—_- I—-I 4 .A-.--..-:. ----- w “J - ------------ - m... s...“ -.__ A- A a“ A nah-x: E 5 .II’. “’ I—d “. "v‘v‘v“‘-“v‘v‘v‘v‘ v‘v‘v‘vnv‘v‘v‘v‘v‘v V‘s—avAvg‘ovr‘;‘v“|:;A ‘. #V‘ ‘V‘MV‘V‘V‘AV‘. - :3 GRAND ’ ' 3 MERAMECIAN “9,05 m | F H .A: LESLILLI LIL. we... -- -LLELLZLWJL , “A. u A A a , ). OSAGIAN . Na anSa. ‘ 3 Marshall 50. pa. 0 “‘ KINDERHOOKIAN Goldwater Sh. '6 MlSSISSIPPIAN-DEVONIAN Unaulqnad Sunbury su. N Baraa SO. 0 u BadI'ord 3h. - I“ = II- —————— J——————————————————T a! .4 CHAUTAUOUAN AMTIITI 8b. a, I'- SENECAN Squaw Bay La. Thunder Bay La. Poflar Farm Fm z z . mumm- .. 5 ‘25 our ' 0 am m. g g TRAVERSE AIPONO L.- I In “1 ER'AN Newton Crack a. a O 3 Ferran o M m. a n g Ball Sh. Regan City La. Dundaa La. M2".— Fm DETROIT ULSTERIAN RIVER m OrI r vana Ly - 1:“ A A--- .3 ......... - ijumgmv nix; I," STRATIGRAPHIC SUCCESSION OF MICHIGAN FROM RECENT THROUGH MAJOR PRODUCING ZONES OF THE AREA (MODIFIED ONO! MICHIGAN DEPARTMENT OF CONSERVATION, I964) FIGURE 3 H is} Most likely, the Kankakee and Findlay Arches were developed in Ordovician time. These changes in structural character are inferred by the great unconformity between the Ordovician-Black River rocks and the under— lying strata, and the slight thinning of these rocks over the Kankakee Arch suggests its development at this time (Ver Wiebe, 1952). The thickening of the above mentioned sediments toward the center of the Basin, suggests that it was sub— siding then. Subsidence continued in early and middle Silurian time, but the Basin appears to have tilted as well. This is evidenced by the Cataract and Niagara rocks thickening to the north (Ver Wiebe, 1952). There was rapid subsidence in late Silurian time as suggested by the thick Salina group. The Salina has a great amount of salt within it, indicating an arid climate. Subsidence continued through Devonian time but the center of the basin shifted some 50 miles eastward. To— gether, the Silurian and Devonian periods account for the majority of subsidence in the Michigan Basin, amounting to more than 7000 feet. Rocks of Silurian age crop out along the northern edges of the Findlay and Kankakee Arches. Rocks of Ordovician age crop out to She west and northwest through Wisconsin and the Northern Peninsula of Michigan. In southwest Ontario, rocks of Devonian age are at the surface. Further northeast along the Algonquin axis rocks of Ordovician and Silurian age are exposed. As one travels from the outcrop areas around the margin of the Basin, the beds occur in rings and become progres—i sively younger toward the center of the Basin, where rocks of Pennsylvanian age generally are beneath the glacial drift. Within the Basin itself, definite structural trends are noted. The dominant trend near the center of the Basin is northwest-Southeast, as exhibited by the largest structure in the Basin, the Howell Anticline. Figure A is a map of the bedrock geology of the study area. In the northern portion of the area, northwest—southeast trends are also noted. Around the margins of the basin, other trends are noted. In the southwestern portion of the Basin, there appears to be no dominant structural trend. According to Ver Wiebe, this portion of the Basin shows many local depressions, which he attributes to a collapse phenomena due to leaching of the salt of the Salina group. His evidence for this is the abnormal rapid thinning of salt in that part of the Basin. Local Structure and Geology Figure A shows a northwest—southeast trending anti- cline in the center of the northern half of the area. The older Michigan formation surrounded by the younger Pennsyl— vanian Parma Sandstone of the Saginaw group indicate its presence at the bedrock surface. This is a reflection .lllal.Illll II!" I I. 15 g I— wl‘rI II N I I 3 .1 I I.‘ ’ -J Pa P 6L I '4 Lui- _--_.r--" .L I4: BAY L... / 4 l, I I..__..._..I/ / / / . FIGURE 4 \ \ \ \ \ MICHIGAN / / / / / / / / .1 _‘._i / LEGEND Pa — Saginaw Famaflan Pp - Pama Sands!” Mb- Bayport letana Mlcflgan FOI’MNOII Mm- Momma Seaman. MC - Goldwater Shala BEDROCK GEOLOGY OF THE AREA (aftar MARTIN. l936) m- f .3; of the deeper feature responsible for some of the oil accumulation in that area. At the very top of the figure, another similar feature can be seen. It is a more pronounced feature as shown by the older Mississippian Goldwater Shale cropping out in the northern half of Township 20 north, Range A east. An interesting fact, although not pertinent to this study, is the fact that Figure A is part of a bed— rock geology map published in 1936. The fields on the southern most of the two trends were not discovered until after 1936, Figure 5 is a structure contour map on the base of the Traverse group, covering the Deep River area in Arenac County. Again local northwest-southeast struc— tural trends are noted. The Deep River Anticline, covering most of the northwest quarter and central portion of Township 19 north, Range A east, is the largest feature in the area. Although the closure on a major anticline in the central area of the Michigan Basin, such as this one, is often greater than 100 feet, oil production is generally obtained from the upper A0 to 60 feet. In fields where porosity is due to dolomitization, production may be found on the flanks of the structure and not on the crest. The Deep River Field actually was found after the development of the Deep River gas field had determined the presence of DEEP RIVER AREA TF/ \\ I I _ Av -~- ~71’. ’ . , \ . I], ‘ .2100 -_/ 1 o ._ \-. \I N ._L \ __ __ l/ ARENAC COUNTY, MIC HIGAN 5 FIGURE STRUCTURE CONTOUR MAP ON THE BASE OF THE TRAVERSE GROUP CONTOUR INTERVAL - Io' nil“ DEPARTMENT 0' “.va IICMOAN STATE UNIVUIS'TW ‘905 «goo .000 um .,T______-_j a .. coo . I , mu 2000 a I I‘m 1.8 an anticline (Landes, 1956). The discovery well was the Werblo well in the south 1/2 of the NW l/A, NW l/A of section 1. The well was drilled off the dome and some 50 feet structurally lower. Its total depth is 28A6 feet, penetrating 8 feet of the Rogers City Dolomite. Had the operator not drilled some 1200 feet below the base of the Berea gas zone, the field might not have been discovered. The Deep River oil Field is parallel to the regional trends of the area, but its production is due to a fracture zone with porosity due to dolomitization. The North and South Adams Fields are located on a northwest—southeast trending nose. The North Adams Field also is due to porosity by dolomitization. The South Adams Field is structurally high on the nose. The Adams Detroit River Field is located on a small anticline in the extreme southeast portion of Township 19 north, Range 3 east. A small field, the Standish, located at the south— west corner of the City of Standish is also on a north- west—southeast trending structural high. The closure here is not nearly as great as that of the Deep River Anticline. This may account for the lower amount of production of oil. In the extreme southwest corner of Figure 5, three wells have been drilled and are producing. No name has been given to this field as far as the writer knows. It again, is situated on a structure conforming to the regional trend. Figure 6 is a structure contour map on the base of the Traverse group. The contour interval is 10 feet. The map covers the southern half of the study area or the Pinconning area. The same structural trends are noted again. The Mt. Forest Field is located on a northwest— southeast trending high running through the southern half of Township 17 north, Range A east. The small field located in section 29 also is on a northwest-southeast trending high. It is paralleled in sections 27 and 28 by a similarly aligned trough. A saddle separates this small field from the Mt. Forest Field. The Pinconning Field located in the extreme southeast portion of Township 17 north, Range A east, cuts perpendicu— larly across the trends of the area. A fault shown in the southern end of the field may well run the entire length, but is not shown due to lack of control. A large structural trough shown by dashed contour lines is located in the northwest corner of Township 16 north, Range A east. The contours are dashed in this area due to the sparseness of wells. The extreme southern portion of the map shows the start of another northwest-southeast trending high. If this map were continued a few miles south, it would include, on this high, the large Kawkawlin oil field. 2O m a N . n w .. m T w T \\\\\ \\\ \ \ + \\\ \\\ \\\\\ x xxx \ \\\\\ \\ ~\ : \ M I I . _ m ... u PINCONNING AREA an m. mum V”! O STRLETURE CONTOUR MAP ON THE BASE C!" THE TRAVERSE GROUP w mt, Porosity by Dolomitization Oil has accumulated in the Deep River, North Adams and Pinconning Fields in dolomitized fracture zones, where the porosity is much greater than the surrounding tight limestones. It is thought that these fracture zones have allowed circulating ground waters, rich in magnesia, derived from older primary dolomites, to ascend to the surface. Through a process of solution and precipatation, the dolomite was deposited. Landes (19A6) states that solution and precipitation usually occur at the same rate, but if the waters were moving fairly rapidly, solution may exceed precipitation. He feels that the waters were part of an artesian system, there— fore, assumed to be moving fairly rapidly. Landes (1958) states that the dolomitization porosity may be younger than the immediately overlying rock. His evidence for this is the greater width of pOrosity near the top of the producing zone. This is due to the Bell Shale acting as a partial dam, restricting the vertically ascending waters. In this case the water would move laterally at the contact of the producing zone and the Bell shale, thus producing a wider zone of porosity. An alternative thebry, also by Landes, is that dolomitization occurred prior to the Bell Shale sedimenta— tion.' The greater width of dolomite at the top of the ..... producing Rogers City formation is due to the greater development of weathering porosity, on either side of the major fracture, at that level. No well in any of the three fields was even drilled completely through the fracture zone. This tends to dis- agree with Landes' wider zone of porosity at the top of the formation, but supports the fact that the fractures are nearly vertical. Since no well has ever penetrated the fracture zone, the depth to its bottom can only be estimated. Relation to Fracture Zones to Regional Geology The structural trends and fractures in the study area have been explained, in terms of the regional geology, by several different theories. Lockett (19A7) states that during the Paleozoic era, three sides of the Michigan structural basin remained more or less stationary while the southeast end continued to subside in the Chatham Sag area. He further states, that under these conditions, a system of fractures or lines of weakness developed in the basal complex, radiating from the unsupported end. These fractures trending northwest- southeast have thus developed from simple subsidence. Pirtle (1932) states that there is some indication of cross folding near the center of the basin. The forces that caused these folds, perpendicular to the general structural trend, were less intense. This may account for the fact that the northeast—southwest trending North Adams and Pinconning fractures are less developed than the Deep River fracture zone. Pirtle attributes the major trends to regional diastrophism which was active during several periods but was probably most intense during the Mississippian period. Lockett states that it seems highly improbable that deformational stresses could have been transmitted through the basin even if it had been appreciably com- pressed. Orogenic forces imply mountain building activity. He further states, "anticlinal folds with relief of approximately 1000 feet, such as the Howell Anticline, when considered in their true relation to the extent of the basin seem hardly of sufficient proportion to warrant the assumption of crumpling orogenic forces to account for their formation.” CHAPTER IV REDUCTION OF DATA Introduction Observed gravity values must be corrected for the effect of station elevation, latitude, and terrain, before they are useful in geophysical studies. These corrections are applied to each station and the resulting value is called the Bouguer gravity anomaly. The complete Bouguer gravity anomaly was calculated on a digital computer aCCOrding to the following formula: Gbga = go - gl + ge - gm + gt where Gbga = complete Bouguer gravity anomaly gO = observed gravity g1 : latitude correction ge = free-air correction gm = mass correction gt = terrain correction Observed Gravity The observed gravity values were measured by a con- tract geophysical crew and made available for this study. Briefly, the observed gravity is calculated as follows: 2A The meter readings collected in the field are corrected for time variations or drift, and the values are multi- plied by the calibration constant of the meter. The amount of drift is determined from graphs of base- check readings. Latitude Correction The latitude correction takes into account the increase in gravity from the equator to the poles. In this case latitude corrections were made from latitude A3°A0', which was arbitrarily selected as the base lati— tude. Latitude corrections are made from the base latitude by multiplying the distance of each station from this latitude by a constant, K. Nettleton (l9A0) determined K to be 1.307 sin 29 mgal per mile, where 0 is the mean latitude of the survey. In this study the mean latitude is A3°50', and K was determined to be 0.0002A7A mgals per foot. Free—Air Correction The free-air correction takes into account the decrease in gravity with an increase in elevation. This correction was calculated by multiplying the vertical gradient of gravity, 0.09A06 mgals per foot, by the elevation differential between the gravity station and the datum. D.) O\ Mass Correction The mass correction takes into account the increase in gravity due to the attraction of material between the datum and the individual stations. The formula to deter— mine the mass correction is 0.01276ph mgals per foot, where p = density (2.1 gm/cc), and h = the elevation difference between individual stations and the datum. The datum to which the gravity values were reduced is 650.0 feet, approximately the mean elevation of the survey area. The determination of the correct density of the near surface material is extremely important. In this area a density of 2.1 gm/cc was employed. This value was determined by using the Nettleton density profile method. Klasner (196A) determined a density of 2.15 gm/cc for the near surface material in southwestern Michigan, and Servos (1965) determined a density of 2.1 gm/cc for material near the surface in southeastern Michigan. Terrain Correction The relief in the area was low enough so that no terrain corrections were needed. Where local variations, such as stream beds were encountered, the stations were placed far enough away so that the effect of the feature was negligible upon the gravity reading. CHAPTER V ACCURACY OF BOUGUER REDUCTIONS There are several factors that cause error in the computed Bouguer gravity anomaly. These are: 1. Errors in observed gravity 2. Errors in elevation 3. Errors in latitude A. Errors in the assumed density of near surface material An estimate of the accuracy of the gravimeter readings and drift control can be obtained by re-observing previ— ously occupied stations. The standard deviation for these repeated gravity observations is 0.0A mgals. Errors in station elevation can cause considerable error in the Bouguer gravity anomaly. Errors can be determined by closing survey elevation loops. The allow— able error of closure in this case was 0.5 feet. By combining the free-air and mass effects, an error of 0.03A mgals would occur for a station 0.5 feet in error at a density of 2.1 gm/cc. Errors in the latitude correction depend on the accuracy of the latitude measurements. Latitude cOrrections were made to an accuracy of 200 feet or better on the base maps used in this study. An error in 27 so latitude of 200 feet would result in an error of 0.0A9 mgals. at 0.0002A7A mgals per foot. An incorrectly chosen density value of 0.1 gm/cc with a change in elevation between two stations of 20 feet will cause an error of 0.025 mgal. The formula for calculating this error is: Error = 0.00128ph where 0.00128 = magnitude of error in mgals per foot for each 0.1 gm/cc error in density p = error in density in units of 0.1 gm./c.c. h = maximum relief in feet In areas of no relief an error in choosing the density would result in a constant error for each station and would not affect the results of the survey. A combination of possible errors in observed gravity, elevation, mass, and latitude corrections could result in a maximum error of 0.15 mgals. It is however, unlikely that the signs of each possible error would coincide at any station. CHAPTER VI REGIONAL GRAVITY ANOMALY The Bouguer gravity anomaly maps shown in Figures 7 and 8 show the results of combining the previously mentioned data reductions to each gravity station. The two maps show-a decrease in regional gravity from 78.50: mgals. in the south to 66.50 mgals. in the north. The northern portion of-Figure 8 and the southern portion of Figure 7 show the gravity decreasing in a regular manner. Two large.anomalous areas that interrupt the regional picture are readily apparent. One is the complex gravity in the northwest portion of Figure 7, and the other area occupies the southern portion of Figure 8. I These maps show excellent agreement with Figure 9, the regional gravity map of Michigan (Hinze, 1963). The area lies partially on the southeast flank of a regional gravity minimum that has a closure of 6 mgals. The southern portion of the study area lies in an area of slightly complicated regional gravity. Besides the two large anomalous areas, there are several other smaller anomalous areas that can be seen in Figures 7 and 8. 29 ”005‘ TIQN Al'oo' TISN ‘3'35 DEEP RIVER AREA u- 00' ARENAC COUNTY, MICHIGAN FIGURE 1' BOUGUER GRAVITY ANOMALY (ll-010mg DENSITY - Ugh/ct o 2000 a900,!" cow “I“: Iaooo DEuRYHE ‘T or GEOLOGV I MICMCAN STATE L'NIVU’SITV I I1 0" T ION TIIN Ti?)- II K “I PINCONNING AREA IAY m, m O WEB GRAIITY AMMALY E3 37x" M W 3/4 9% - % WILL: V A” \ 4/ / is ? J §g <27 \3 s6: % is LL % 5:1 /1 I Ffi I~\ I / I \,\\~ \f/\_‘ //g /““p ' :%r 5—, \‘ < A E \fi\ 31 _/\_/_\4 d f . ~11“ 71 T / A a? \ I) ”l 3%. é/ I Viz—f \ .QL :13 My fx-U‘V :,";’.‘———— 7C; l 00' seas . as... as .... - .eee:22e%%wstsso sessile seas/MEWW WWW- t PM AW//W . W/f WWW e //. + I 32 PORTION OF REGIONAL GRAVITY MAP OF MICHIGAN (oImHINZE,I963I FIGURE 9 The Bouguer gravity anomaly values of Figures 7 and 8 differ from the magnitude of those shown in Figure 9. This is due to the fact that the two surveys were not corrected to the same datum. CHAPTER VII INTERPRETATIONAL METHODS Introduction The gravity exploration method has been used for a number of years, but the confidence placed in it has been limited. The lack of confidence is due mostly to an inherent problem in gravity interpretation, that of ambiguity of results. I Skeels (1950) has shown that any gravity anomaly produced by one mass can be reproduced by another mass at a shallower depth. Studies in the last decade have helped to defeat this problem by defining the various types of anomalies produced by different features in many geological situations. Digital computers have been a great help in advancing the status of the gravity exploration method. They now allow many new and older techniques to be used that were once impractical due to the involved mathematics and time consuming arithmetic. In this study, analytical and statistical methods of interpretation were used much more than graphical methods. Graphical methods were used only to serve as a check of the statistical methods. 3A Cross—Profiles Graphical Technique The cross—profile method fOr the approximation of the regional gravity is a graphical method and is subject to personal bias. _This method consists of drawing a smooth curve of the estimated regional gravity gradient along the profile. Sets of profiles are constructed perpendicu- lar to each other. Where one profile crosses another the value of the regional must be the same on each of the perpendicular profiles. Thus, the procedure is to adjust the rbgional by trial and error until a suitable fit is ob- tained. The residual gravity values are obtained by subtracting the regional gravity from the value of the Bouguer gravity anomaly at each intersection of the profiles. This method has the advantage of being a simple way to determine the residual gravity and it permits any knowledge of the area to be used. 'The method is limited if the residual anomalies are low in magnitude of if the regional gradients are complex. Three Dimensional Least Squares Statistical Analysis The least squares method consists of fitting a polynomial equation to a three dimensional surface. In this case the surface consists of X, Y coordinate points and a gravity value at each point giving the third dimension in the Z direction. The polynomial equation is fitted to the surface to a degree where the regional UN LA) gravity is adequately defined. In general, the higher the degree of the equation, the better the three dimensional surface is defined. A high degree equation may fit the surface so well that there is no residual anomaly left, while on the other hand, a low degree equation may not adequately define the regional gravity. It is possible that the regional gravity of an area may be so complex that a polynomial equation cannot accurately define it. If this should happen, the least squares method would not be valid. The principle of the least squares method states that the coefficients of the polynomial equation must be such as to make the sum of the errors a minimum, where the error in this case is the residual gravity or that portion of the surface not fitted by the equation. The basic polynomial equation used is: .... p q OIOO + leX + leY + +dqu Y A¢ Regional = where a's = the coefficients of the equation. The expression can be solved easily by matrices on a digital computer and the resulting gravity value is subtracted from the Bouguer gravity anomaly to give the residual gravity at any point. LA) “‘4 Analytical Techniques Often it is desireable to study the original gravi- tational field on some plane other than the true plane of observation. The upward continuation method moves the original observation plane farther above the source of the anomalies. Small sharp gradient anomalies that originate near the surface, due to features such as bed- rock valleys, may be eliminated while broad lower gradient anomalies due to deeper features are retained. The down- ward continuation method allows the plane of observation to be brought closer to the source of the anomalies, thus both enhancement and resolution of the anomalies are increased. Henderson (1960) developed a practical method of approximation for evaluating both the upward and downward continuation equations. This method is outlined in the following paragraphs. Basically, the problem is to compute the gravity value A¢ (X, Y, Z) above and below the plane of observation. The origin of the right-handed system of coordinates is taken at a point where the field is to be computed, with the Z axis positive vertically downward. The integral solving the Dirichlet problem for a plane in polar co-ordinates is: «*m maAT(r) rdr A¢ (‘ma) = 2 2)3/2 o '(r +m2q m e l, 2, 3, . . . ., n (the upward continuation integral) where (a) is the interval between points, m equals the number of units above the original surface in multiples of (a), and where 2n. — - l. M - 2“ {CM (r,e) de (2) is the average value of AD on circles of radius r about the point. Experimentally it was found that radii of r = 0, a, a/E, a/—, a/8, a/I—, a5, a/5U, a/I36, a/§7_, and a25 ade- quately sample the field. The number of mesh points falling on these radii is respectively 1, A, A, 8, A, 8, l2, l2, 8, 8, and 12. Next a Lagrange interpolation polynomial is fitted to A¢ (O) and the n values A¢ (-ma) computed from (1) to obtain the approximation formula A¢(Z) = I ('§)m ZL/ \\\\' ‘ >— / I-———-I ./ FRACTURE ZONE _— /' ' | I ' I I I 0 2000 4000 6000 \N~—/ PROFILES OF ANALYTICAL METHODS OVER THE NORTH ADAMS FRACTURE ZONE FIGURE 20 These profiles, although of only limited extent, indicate that these analytical techniques do not enhance the detection or isolation of the anomalies associated with the fracture zones. CHAPTER IX CONCLUSIONS AND RECOMMENDATIONS FOR FURTHER STUDY Conclusions The North Adams fracture zone produces a positive anomaly of over 0.10 mgals and is detected by the methods employed in this study. The Deep River fracture zone, although it is longer and broader than the North Adams fracture zone,does not have a detectable anomaly associ» ated with it.» It_is felt that this is due to the in- creased porosity of this zone over that of the North Adams fracture zone. Theoretical calculations indicate that the Pinconning fracture zone does not have an anomu:y of detectable magnitude associated with it. There is no relation between the Bouguer gravity anomaly or the least squares residual gravity with the regional geological structures of the area. Recommendations for Further Study It is recom.ended that a greater station density be used over and adjacent to the fracture zones. ghis would eliminate having to interpolate gravity values in areas of H sparse geophysical control. It is a.so strongly recommendec that various combinations of downward continuing upward 72 73 continued gravity surfaces be studied to see if these methods enhance or isolate the anomalies due to fracture zones. B" lBLIOGRAPHY 74 BIBLIOGRAPHY Cohee, George V., and Landes, Kenneth K. (1958) Oil in the Michigan Basin, in Habitat of Oil, a symposium, A.A.P.G., p. 473—494. Enlers, G. M., and Radabaugh, R. W. (1938) The Rogers City Limestone, a new Devonian formation in Michigan: Papers of the Mich. Acad. of Science, Arts and Letters, vol. 23, p. 441—446. Goldich, Samual S., and Parmelee, E. Bruce. (1947) Physical and chemical properties of Ellenburger rocks, Llano County, Texas: Bull., A.A.P.G., vol. 3l,pp. 1982—2020. Henderson, R. G. (1960) A comprehensive system of automatic computation in magnetic and gravity interpretation: Geophysics, vol. 25, no. 3, p. 569— 585. Hinze, W. J. (1963) Regional gravity and_magnetic maps of the Southern Peninsula of Michigan: Michigan Dept. of Conservation, Geological Survey Division, Report of Investigation 1. Hubbert, M. K. (1948) Gr avitaticn ts rrain effects of twc- dimensional ton'lraphir features: Geophysics, VOI 13, no. 2, pp 226 2EWI. Klasner, J. S. (1964) A study of buried bedrock valleys near South Haven, Michigan by the gravity method: Masters Thesis, Michigan State University. Landes, K. K. (146) Porosity through dolomitization: Bull., A.A.P.G., Vol. 30, p. 305. Landes, K. K. ”9 6) Petroleum Geo logy: John Wiley and Sons, Inc. , New York, pp 29(8— Lockett, J. R. (1947) Development of structures in basin areas of Northeastern United States, Bull , A.A.P.G , v61. 31, pp. 441—443. Martin, Helen M. (1936) Geological map of th» Southern 1 s Peninsula of Michigan: Michigan Geol. Survey Pub. 39, geol. ser. 33, Ann. Rept. 75 76 Nettleton, L. L. (19AO) Geophysical Prospecting for Oil: McGraw—Hill, New York. Newcombe, R. B. (1933) Oil and gas development in Michigan: Mich. Geol. Survey Pub. 37, Series 31. Pirtle, G. W. (132) Michigan structural basin and its relationship to surrounding areas: Bull., A.A P.G., vol. 16, pp. 105-152. Servos, Gary Gordon (1965) A gravitational investigation of Niagaran reefs in southeastern Michigan: PhD. Thesis, Michigan State University. Skeels, D. C. (1947) Ambiguity in gravity interpretation: Geophysics, vol. 12, pp. AB—Sb. Talwani, M., Worzel, J. Lamer, and Landisman, M. (1959) Rapid gravity computations for twowdimensional bodies with application to the Mendocino submarine fracture zone: Jour. Geophys. Res., Vol. 6A, pp. A9» 590 9‘”) North American Petroleum: Edwaris 3 Ver Wiebe, W. A. '2 Ann Arbor, Michigan, pp. 58-72. (1 Brothers, Inc. 78 The following is a list of wells from the Deep River and Pinconning areas that were used in this study. Their locations and permit numbers are given. They are listed.) according to Township, Range and section number. The wells have been divided into two groups, those of the Deep River area and those of the Pinconning area. Deep River Area Township 18 north, Range 3 east Location Section Permit No. NW6 Nw6 NW6 1 13670 SE6 sw6 SW6 1 16382 C SW6 NE6 1 10176 NW6 Sw6 NW6 1 14868 NW6 SW6 SW6 1 16283 NW6 Nw6 NE6 1 154uu SW6 sw6 sw6 1 16052 SE6 Nw6 SE6 2 16303 NW6 NE6 NE6 2 1532: NW6 NW6 NE6 2 15627 SE' SE6 SE6 2 15836 SE NE6 NE6 2 16867 NW6 NE6 SE6 2 15135 SW6 SE6 SW6 2 786 SE6 SE6 WE6 2 2670 SW6 sw6 NM6 12 3123 NW6 NW6 NW6 12 16098 WE6 Nw6 Nw6 12 16302 NW6 NE6 Nw6 12 16383 c sw6 NE6 21 1126 Township 18 north, Range 3 east SE6 SE6 sw6 1 1699? NE6 NE6 SE6 1 163A2 SW6 SW6 sw6 1 17273 NW6 NE6 SW6 1 16502 SW6 SW6 NE6 3 16679 SE6 NE6 SE6 6 17867 SE6 SE6 Nw6 A 1653? ection Permit No. 5341 15535 15654 9602 u I L ./ PV- H m N 16E; $1311.34 N [111,4 N In“; N N 33' N 1413 Ing Ifihg 383% 86 M86 SE1 NE% SE% NW' N76 GEL c~ E .9. Ki) KO CI)“\1 0‘. 0‘. 868A . '4 to 1.: '4 L) .1 % 6 9332 0‘1 30% n_% 10 13859 h 6 \ -l 1” 21A6O 886 M66 N“ 10 16251 4 836 MW6 W2» 10 16212 Nifi NEH—"a Nfilg 10 21239 stg W86 SW6 11 14199 SW6 SE4 N56 12 1665 NW1 NW6 8‘6 13 10770 1 N16 816 19 16678 NW6 N86 NW6 14 13718 8B6 ME6 JW6 16 10121 S6 M36 SW6 16 8000 NW6 NW6 WW9 16 6796 NE6 886 NW6 17 13706 8M6 SE6 NE6 18 19720 NW6 NM6 NW6 19 16359 0 NW6 066 19 10285 SE6 NE6 386 20 18549 NW6 NW6 SW6 2: 13262 86 SE6 SE6 ' 23 16891 NE6 NE6 8M6 24 18726 1:.“ LI ,1. 1‘11, ‘~_ I112: 1171/15“; DEM L L4 7“ I: fitfid SIM; 533% ME6 NW9 SE6 NW6 33% NW6 ‘Ln SW% NW% Xhfiilflifi SE6 iiiiia £6683; P3606; (LI—z y—IC‘) N 11 . 4-— .f‘ . 006 NW6 N66 23 10755 886 8M6 SW6 :6 18367 0 NE6 8:6 28 .359 NM6 8M6 NW6 . 99 052 '1‘.” .‘Y.’ 1 . "r n11 EIE :19 , :90 ,—5 7-— \‘IL' 33 J: C“ R) Ln ‘. "r‘ _‘. 11.. rUR>H+Ar'H LA: LA} Uu' LA) U.) 'uo O‘Iw D H U": J . 00 H 0 Township 18 north, Rango 5 east C NW6 NE6 5 9733 W86 N56 S“1 6 22:90 N86 NE6 SE6 6 21817 NW9 3W6 Sig 9 10939 886 816 SE6 17 16839 816 Mwa SN6 18 12665 835 SE6 ME6 19 15021 R65 SE6 3N6 {W1 16501 , v—y 4—1. 2' \t— \ 1A) "3 8M6 NW6 17956 80 Township 19 north, Range 3 east Location Section Permit No. SE2 WE2 NW2 1 11073 WW2 SW2 NW2 1 12879 SE2 NE2 NE2 2 6203 NW2 SW2 NW2 2 10628 NE2 NE2 SE2 2 16686 NW2 SW2 NE2 3 25102 SE2 SE2 N“2 9 8666 SW2 SW2 NE2 10 13655 NE2 NE2 SW2 11 12702 NE2 SE2 SW2 11 12022 SE2 NE2 SW2 11 12219 SW2 NW2 SE2 11 12327 NW2 NW2 SE2 11 12328 SW2 SW2 NE2 11 12695 SE2 SE2 SW2 11 .11819 SE2 SW2 NE2 11 18810 NW2 SW2 SE2 11 11363 SW2 NE2 NE2 11 11269 SW2 NE2 NW2 12 16837 C SW2 SW2 13 9711 NW2 NW2 NE2 16 11318 SW2 SW2 SW2 16 7880 NE2 NW2 SW2 16 10702 NW2 SW2 SW2 1 10198 SW2 NE2 NW2 1' 11115 SW2 SE2 NW2 16 10821 NW2 NE2 NW2 16 11685 NW2 SE2 NW2 16 10987 SE2 SW2 WW2 16 10776 SE2 NW2 NW2 16 11036 NW2 SE2 WW2 16 10765 NW2 SW2 NE2 16 10855 SW2 SW2 NW2 16 10572 WW2 SE2 SE2 16 11306 WE2 SE2 SE2 15 10697 SE2 SE2 SW2 15 7872 SW2 SE2 SE2 15 8988 SE2 SE2 SE2 15 9158 SE2 NE2 SE2 15 12608 SW2 SW2 SE2 2 0568 NW2 SW2 SE2 22 8773 NE2 NE2 NE2 22 8880 NE2 SE2 SW2 22 8969 SE2 NE2 NW2 22 8382 NE2 SW2 SW2 22 10671 SW2 NW2 SE2 22 9009 NW2 SE2 NE2 22 7895 SE2 SE2 NW2 22 8560 NW2 SW2 NE2 22 8087 Location Section Permit No. SE2 NW2 NE2 22 7907 SW2 NE2 NE2 22 7908 NW2 NW2 SE2 22 8300 NE2 SW2 SE2 2 9008 SE2 SE2 SW2 22 10569 NE2 SW2 NW2 22 9821 NW2 SE2 SE2 22 9289 SW2 SW2 NE2 22 8661 NE2 NW2 NE2 22 9296 SE2 NE2 SW2 22 9169 SE2 NE2 NE2 22 9290 NE2 NW2 SE2 22 8672 SE2 SW2 NE2 22 8365 NE2 SE2 NW2 22 8063 SE2 NW2 SE2 22 9207 NW2 SW2 NW2 23 8680 SW2 SE2 SE2 23 7837 SE2 SE2 SW2 23 7876 SW6 NW2 NW2 23 7875 SE2 SE2 SE2 23 8576 SE2 SW2 SE2 23 8215 NW2 SE2 SE2 23 8192 SW2 SW2 SE2 23 227 NW2 NW2 NW2 23 9216 SW2 NW2 NE2 ' 23 7926 SE2 SW2 SW2 26 8576 SW2 MW2 SW2 26 8656 SW2 SW2 SW2 26 8366 SW2 SE2 SW2 26 6806 SW2 NW2 SW2 26 16855 SE2 NW2 NE2 25 5117 SW2 NE2 W2 25 23696 c NE2 SE2 25 9637 SW2 NW2 NE2 25 6755 c SE2 NW2 25 9696 WW2 NW2 NW2 25 8335 SW2 SE2 NE2 25 18538 SW2 SW2 NW2 25 16010 NW2 NW2 SW2 25 6365 C SE2 SE2 25 9501 SE2 NE2 NW2 26 6901 c SW2 SE2 26 20126 NW2 NW2 SE2 26 6387 NE2 NW2 NE2 26 13373 NW2 NE2 NE2 26 8266 SW2 NE2 NW2 26 13122 SE2 SW2 NE2 26 6855 SE2 E2 NE2 26 6787 SW2 E2 NE2 26 6718 N82 NE2 SW2 26 6508 82 Locgtion Section Permit No. NE2 SE2 SE2 26 6696 SW2 NW2 NE2 26 5523 NW2 322 N22 26 5160 SE2 N22 322 26 6190 NE2 NE2 NW2 26 6665 N22 NE2 N22 26 9102 NE2 NW2 SE2 26 8911 sw2 SE2 N22 26 16966 C2 SE2 822 26 9565 SE2 NE2 NE2 26 15729 NE2 SE2 NE2 26 15236 0 NW2 SE2 27 9701 NE2 NE2 NW2 27 9377 SW2 sw2 SE2 27 17316 c SE2 NW2 27 9866 S2 NE2 NW2 27 10567 C 322 SW2 28 10390 NW2 SW2 NW2 36 ~26207 SE2 SE2 SE2 36 715629 SE2 SW2 N22 36 16669 SE2 SE2 N22 36 16300 NW2 SW2 SE2 35 15656 C SE6 NW2 35 9705 SW2 Nw2 NE2 35 15311 sw2 SW2 NE2 35 15691 SE2 NE2 SW2 35 15521 NE2 NE2 SW2 35 15690 SE2 SE2 SW2 35 15321 822 Nw2 SW2 35 15610 NW2 NW2 SE2 35 15605 322 SW2 NW2 35 16798 NW2 NW2 SW2 35 15857 SE2 NW2 SE2 35 16301 0 N22 822 35 9520 SE2 SE2 NE2 35 12867 NW2 SE2 SW2 35 15862 NE2 NE2 NE2 35 6618 SE2 SE2 SE2 35 15222 SW2 NW2 NW2 35 16766 322 SW2 SE2 35 15218 NE6 SE6 SE2 35 13705 SE2 SE2 NW2 36 15622 SE2 SW2 SW2 3 16885 C SW2 SW2 36 9638 C SE2 NE2 36 9636 C NW2 NE2 36 9500 SE2 NE2 NE2 36 18593 922 SE2 SW2 36 15590 622 SW2 SW2 36 15576 Location Section Permit No. SE2 SW2 36 10056 N2 NW2 SW2 36 16686 SE2 NW2 SW2 36 15616 NE2 NE2 NE2 36 9293 N2 NE2 NE2 36 21855 Township 19 north, Range 6 east SE2 NW2 SW2 1 21256 % SW6 SW6 5 10593 2 SW2 SE2 6 10662 SE2 SW2 SE2 6 10960 SE2 SW2 N22 6 11268 SE NE2 SWL 0“ SN: SE2 SE2 2 11572 N52 322 SW2 6 13561 2 N22 sw2 6 11268 SE2 SE2 SE2 6 11292 SE2 822 N22 7 10869 NE2 822 N82 .7 11650 SW2 SW2 SW2 7 11787 NE2 NE2 NE2 7 12360 0 SW2 7 10331 3: N22 N22 7 10617 NW2 N22 7 10672 N22 N22 7 11387 NE2 NW2 N22 7 11285 632 SE2 SE2 7 17669 NE2 NE2 SW2 8 11071 322 N22 822 8 11107 172 SW2 NW2 8 11577 2 822 322 8 9506 2 SW2 NW2 8 10620 2 NW2 NW2 8 10633 ’6 35% NE% 3 11578 “22 N72 822 ll 58 .:2 N22 322 8 11357 22 822 NW2 8 11226 N22 SW2 NW2 8 11668 2 NW2 SE2 8 10925 2 SW2 N22 8 10839 NE2 NW2 NW2 8 12619 2 NW2 NW2 8 12339 SW2 E2 NW2 8 12178 SW2 SW2 NE2 8 11862 NE2 SW2 N22 8 11958 2 SW2 N22 8 10691 ”2 N22 NW2 8 11575 2 SW2 SW2 9 11861 Location Seer13« Permit No. SW2 562 SW2 9 12869 NW2 NW2 SW2 9 10926 SW2 SE2 SW2 9 11863 SW2 SE2 SE2 9 11383 882 NW2 SW2 9 11157 882 Sw2 SW2 9 10965 NW2 862 $62 9 11109 Sw2 ng swg 9 '11838 SE2 SE2 SW2 9 11232 SW2 SW2 SE2 9 11259 SW2 NW2 NW2 9 11651 882 NE2 SW2 9 11233 NW2 NW2 SE2 9 11062 E2 NE2 SE2 9 8676 SW2 NW2 N82 9 11373 Nw2 SW2 NW2 10 10867 1.4 1:- H , !--1‘ CB -& .3: N62 NE2 SW2 SW2 322 SW2 16 12029 SW2 SW2 Nw2 16 11753 822 SE2 SW2 16 12030 SW2 sW2 SW2 16 19768 822 SW2 SW2 16 12038 SW2 SW2 SE2 16 11951 SW2 NW2 322 16 20155 322 392 SE2 16 121:6 NW2 SW2 SW2 16 11952 SW2 SW2 SW2 15 19299 022 SW2 822 15 11989 802 922 SE2 15 12276 982 N52 SW2 15 11872 882 652 SE2 -5 12689 652 SW2 NW2 15 12062 822 SW2 NW2 5 11956 N36 SE2 SE2 15 11886 092 NE2 SW2 15 12037 602 SW2 522 15 11997 962 NE2 SW2 15 11619 202 NE2 SW2 15 11613 8M2 NW2 NW2 15 11502 SE2 SW2 NW2 15 11500 NW2 502 NW2 15 11379 NW2 SE2 322 15 11782 862 NW2 SE2 15 11756 N22 N82 SW2 :5 11715 SW2 NW2 SE2 15 11708 862 SE2 N02 15 11661 662 NW2 SW2 15 11660 822 $22 NW2 15 11907 N22 822 SW2 15 12061 85 LOCation Seetion Permit No. SE2 NW2 NW2 15 12167 NW2 NW2 NW2 15 11362 NW2 NW2 SW2 15 11262 sw2 SW2 SE2 15 20235 SW2 NW2 SW2 15 19657 NW2 NE2 NW2 16 10956 NW2 SE2 NW2 16 10976 SW2 SW2 SW2 16 16693 SW2 NE2 SE2 16 3619 SW2 SE2 NE2 16 12168 322 NW2 NW2 16 16398 sw2 SW2 SE2 16 18293 SW2 NE2 SW2 16 19612 SE2 SE2 NE2 16 11871 Sw2 NE2 NE2 16 11926 SW2 NW2 NE2 16 12003 NE2 NE2 NE2 16 12002 SE2 NE2 NE2 ‘ 16 11536 NE2 SE2 N22 16 11501 Nw2 SE2 NE2 16 11626 NW2 NE2 NE2 16 11382 NE2 NE2 NW2 16 11376 SE2 NW2 N22 16 11261 NW2 NW2 N22 16 11118 SE2 SW2 SW2 17 16517 NW2 NW2 SW2 17 13866 NE2 SE2 SE2 17 16133 NW2 SW2 SW2 17 13812 SW2 sw2 SE2 17 16567 SW2 NW2 NW2 17 15971 c SE2 18 10280 C NE2 18 10216 NE2 SE2 SE2 18 13728 s 2 NE2 822 18 13665 SW2 SE2 NE2 18 16108 NE2 SE2 NE2 18 16386 822 N22 N22 18 15730 NW2 SE2 NE2 18 16387 NW6 83% SE2 18 13771 SW2 N22 N22 18 16650 NE2 NE2 322 18 13766 NW2 NE2 SE2 18 16109 SW2 N22 322 18 13776 SE2 SE2 322 18 19705 SE2 NE2 NE2 20 17639 NW2 NE2 NW2 20 16996 NW2 NE2 SE2 20 16805 sw2 NE2 NE2 20 20349 SE2 SW35 NW1; 20 191463 86 Location Section Permit No. SW2 SW2 NW2 21 19557 sw2 NW2 NE2 21 19353 sw2 NE2 NW2 21 19615 SW2 NW2 NW2 21 17632 sw2 NW2 NW2 21 18705 SW2 NE2 NE2 21 19030 SW2 NW2 SW2 22 ‘ 19536 SW2 NE2 NE2 22 * 19676 SW2 SE2 NW2 22 19356 SW2 NW2 NW2 22 19171 sw2 sw2 NE2 22 19623 NW2 NE2 NW2 22 11263 NE6 SW2 NE2 23 16596 NW2 NE2 NE2 23 12073 NW2 NW2 NE2 23 11896 NE2 SE2 NW2 23 12563 NW2 NE2 NW2 23 12060 NE2 NW2 NE2 234 11970 SE2 SE2 NE2 23 12206 SE2 NE2 NW2 23 12603 SW2 Nw2 NE2 ~ 23 12362 SW2 NE2 NW2 23 12679 SW2 NW2 822 23 18526 SW6 SE2 NW2 23 19903 NW2 NW2 SE2 23 11531 SE2 SE2 NW2 26 12398 NW2 NW2 SW2 26 12090 NE2 NE2 SW2 26 17186 'W% SE2 NW2 26 13755 NW2 SW2 NW2 26 12166 SW2 SW2 NW2 26 12300 SW2 NE2 NW2 26 12120 522 NW2 NW2 26 12133 SW2 NW2 NW2 25 11620 SE NE2 NE2 25 16010 SW NE2 NW2 25 19973 SW2 NW2 NE2 26 23799 NE2 SE2 SW2 . 27 2612 NW2 SW2 NE2 27 11781 NE2 SW2 NW2 27 10986 NW2 NW2 SW2 27 16926 SW2 NE2 NW2 28 17361 NE2 SW2 SW2 28 11867 NE2 NE2 NW2 29 16772 SE2 SW2 NW2 29 21665 NW2 sw2 NE2 29 11988 c NW2 NW2 31 9502 NE2 NW2 SE2 32 6096 SE% NW2 SW2 36 - 9288 Location SE% SEk SWk NW8 666 NE6; SE6 Nwlg SE% SW% NW% SWk NW& NE% NW% NE% NWk ka NWk SW% SW% SW% SW% SW% SW% E8 SW% SW% SW% SW% NE% SE% SW% SW% NW% NWk NEk SMk swa swa NW% SW% NW% SW% SW% NW% NW% SW8 SE% SWk SE% NW% NE% NE% NW% SWk SE% SE% SW% NE% SWk NW% SEk SWk NWk NW% SWk SW% NW% NE% NW6; SWk W 14 NW% NW%, N W15 N E $3 NE% NW% N E 3‘3 NW% NE% NW% SE% SW% SW% NE% SE% NE% SE% SE% 87 Township 19 north, R Section 8 10 17 l9 29 3O 31 32 y“ " I 111- {3‘ t2) Pinconning Area 10 2O 23 35 NNRJNMMNIMNNNNN 7 13 13 13 13 13 D Township 15 north, Range Township 16 north, Range ToWnship 17 north, Range L~ . f 1‘ +- 1 E '13 t. / 1 1 ».v. '1 (7.173 (t 3 r 3 east Township 16 north, Range 6 cost Township 16 north, Range 5 east 3 List Permit No. 6905 6391 11812 12878 5971 11906 19172 21232 2056 8603 16160 3267 14767 12152 11966 14501 l37u5 12760 12216 12177 11192 11315 10966 13885 11138 6613 16608 12963 13509 13362 13367 Location Section Permit No. NE% SE% SE% 13 1516? NE6 NE% SE% 13 15203 NE% SW% NE% 26 13915 NE% NE% NW% 26 1f853 NE% NW% SE% 26 16152 SW6 NE% NE% 26 13795 NE% SE% N88 26 16002 NE% NE% SE% 29 16858 NEK NE% NE% 26 13295 m (’1' Township 17.north, Range 6 eat SW6 NN6 NE% 12 3690 SE8 3 6 NE% 16 12655 NW% N66 Nwa 17 2107 Sw% 666 Nwa 18 13338 SW% NW% SW8 1 13596 swa swa SE% 18 13658 swa 886 NE% 18 1369, SW% SW6 NW% 18 13491 SW1 SE6 SW% 18 13138 NEE S 6 SW8 18 13636 SW? SW8 SW% 18 13385 Sui NE6 SW% 18 13339 N72 N56 S16 18 18026 NE? 0 % SW% 18 17929 NE6 NW8 SE? 18 17938 NE% NW% SW% 18 17326 SW5 NW% NE% 1 L’LFO NE% CW8 SE8 1 17510 NE6 SE% SE% 1 17799 SE13 NEE; SW52; 18 17720 NE6 SE8 NE% 18 18101 SW? NE6 NW6 1' 13353 SW4 NW% NW% 19 19117 SW6 SW3 NW% 19 13761 SW% SE8 SW% 21 13737 SW% NW% 3‘3 25 11193 NE6 NW8 oE% 25 17093 SE6 SW% SW% 25 17495 NE% NE% SW% 25 23915 NE% ‘Wh SW% 25 17305 NE% NE% SW% 25 177:8 NW% SW% NE% 25 17985 NE% NW% SW8 25 17806 NW8 NW6 SE% 25 1837? S66 NE% SW% 25 17595 SE1 SW% SW% 27 2745 89 Location Section Permit No. NW8 NEk NW8 29 16510 NE8 SW8 NE8 29 ‘ 15297 SE8 NW8 NE% 29 16178 NE8 NE8 NE8 29 16585 SW8 NE8 NE8 29 16398 SW8 SW8 NE8_ 29 15220 SW8 SE8 NE8 29 15970 SW8 NW8 NE% 30 14859 SW8 8E8 NE8 33 15708 SW8 SE8 SW8 34 11106 SW8 NE8 SW8 35 11158 SW8 SW8 SE8 35 13578 SW8 SE8 NE% 35 13809 SW8 NW8 SW8 35 12224 SE8 NW8 SE8 35 13969 SE8 SW8 SE8 35 13811 SE8 SE8 SW8 35 12213 NE8 SE8 NE8 35 13919 NEk NE8 NE% 35 12615 SE8 SE8 SW8 35 12860 NW8 NEk SE8 35 13951 ng swa NW8 36 16954 SW8 NW8 NW8 36 14228 NEk NE8 NW8 6 21882 NE8 NW8 NW8 2 13838 HICHIGQN STQTE UNIV. LIBRQRIES llllllllllllllllllIllllllll1|||||l|||l|1|1111111IIIIIHHI 31293101165821