\HI = —— = = = —— _—__-= _— —- _— —— —— —— g g I I. - ‘ I i.- 1 A. , ,. M. g 2 U r ,n 1'- Q I 9 f” 4 .4 ' 9 I - .-. ...i o' .'4‘I.'~. .‘ 0 ' MAhlA' ' .. m‘ . -.->1a'r-..- ’a‘tlia d’Vc'aoeu-qm __ ._ 9 I .4 l . arr. en'zmrglg’; 3.“ films 1 Malia-7“- This is to certify that the dissertation entitled A STRATIGRAPHIC AND STRUCTURAL STUDY OF COAL MINE BASIN, IDAHO 7.0REGON presented by Kyie Douglas Walden has been accepted towards fulfillment of the requirements for M 3- degreein 6;:QIQ%§2:QI Sciences Major professor Date W MS U is an Afl'trmative Action/Equal Opportunity Institution 0—12771 MSU LIBRARIES m 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. A STRATIGRAPHIC AND STRUCTURAL STUDY OF COAL MINE BASIN, IDAHO - OREGON By Kyle Douglas Walden A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Geological Sciences 1986 ABSTRACT A STRATIGRAPHIC AND STRUCTURAL STUDY OF COAL MINE BASIN, IDAHO - OREGON By Kyle Douglas Walden Coal Mine Basin, Idaho-Oregon, lies within a broad, block-faulted, gently plunging anticline or dome northwest of the Owyhee Mountains of southwestern Idaho. The major emphases of this study was the pre- paration of a measured stratigraphic section and a structural map of the basin. The composite stratigraphic section measured is comprised of 265 m of predominately volcaniclastic fluvial, lacustrine, and deltaic sediments of the Miocene Sucker Creek Formation. Reconnais- sance field observation lead to the suggestion of three tentative stratigraphic marker zones. Maar volcanism was widespread during Sucker Creek time, leaving local stratigraphic marker tuffs. Twenty- one plant and two animal fossil zones were precisely placed strat- igraphically. The rocks of Coal Mine Basin have been subdivided into five episodes during Sucker Creek time based on sediment source and depositional environment. ACKNOWLEDGEMENTS I would like to thank all that have contributed to this project. My thesis committee members contributed time and thought to the thesis. Special thanks go to Professors Aureal T. Cross and Ralph E. Taggart who provided field guidance and assistance, collected specimens, and discussed numerous ideas, and problems during field work, laboratory study and writing of the thesis. Dr. Lanny Fisk oriented me on my first day in the field and loaned a significant quantity of data and aerial photos. Pat Fields advised me on numerous points during the final revisions of the manuscript. Professor Robert Giegengack of the University of Pennsylvania supplied advice and encouragement in the field. Professor Alan Holman of Michigan State University and Professor Gerald Smith of the University of Michigan examined and discussed some of the vertebrate fossils found during field work. Winston Lancaster, of the Idaho Museum of Natural History, excavated and curated the oreodont jaws which I found and Dr. Greg McDonald, of the same institution, identified those fossils. Ted Weasma, Geologist, Bureau of Land Management, coordinated the removal of the oreodont remains. Howard and Darlene Emry of Boise pointed out several fossil localities. A very sincere thanks go to landowners, Dale and Ruth Gardner, and Mr. and Mrs. Bob Bruce for permission to do field work on their properties. The Chevron Corporation contributed generously to the project through its support of field-oriented theses. My grandparents George and Eda Walden, and my parents helped support this work. My brother Bryce accompanied me to several Quaternary volcanic areas. ii TABLE OF CONTENTS FIGURES AND TABLES INTRODUCTION METHODS AND PROCEDURES STRUCTURE, TECTONICS, AND VOLCANISM Structural Features Regional Tectonics and Volcanism Coal Mine Basin Volcanism The "Antler" Tuff; A Maar Deposit STRATIGRAPHY Introduction Nomenclature of Pyroclastic Sediments Oldest Sediments "Lakebeds" Unit "Delta" Unit "Antler" Tuff and "Antler" Unit "Schnabel" Unit "Youngest Sediments" Unit Lateral Stratigraphic Variations Southeastern Exposures Whiskey Creek McBride Creek CORRELATION PALEONTOLOGY 0F COAL MINE BASIN Paleobotany ‘ Vertebrates THE MIOCENE GEOLOGIC HISTORY OF COAL MINE BASIN Regional Overview Coal Mine Basin History Overview of Structural History SUMMARY AND CONCLUSIONS REFERENCES APPENDIX iii 11 12 14 17 17 20 21 22 24 25 27 29 31 31 32 32 34 38 38 4O 42 42 43 45 47 49 53 FIGURES AND TABLES Figure 1. Regional map showing location of study area Figure 2. Location map of Coal Mine Basin Figure 3. Structural map of Coal Mine Basin Figure 4. Relationship of the Sucker Creek Formation to other formations in the region Figure 5. Composite stratigraphic section of Coal Mine Basin, Idaho-Oregon Table 1. "Antler Tuff" Tree Molds and Casts, location 5, Figure 2 Figure 6. Symbols used in the stratigraphic sections Figure 7a-c. "Lakebeds" Unit Figure 8a-f. "Delta" Unit Figure 9a-b. "Antler" Unit Figure 103-b. "Schnabel" Unit Figure lla-c. "Youngest Sediments" Unit iv 18 19 27 50 51-53 54-59 60-61 62-63 64—66 INTRODUCTION Coal Mine Basin (Figures 1 and 2) is a drainage basin included in the northeastern quarter of the Sheaville Oregon-Idaho 7.5 minute topographic map (U. S. Geol. Survey, 1969). The Coal Mine Basin area includes extensive outcrops of the undifferentiated Sucker Creek Formation exposed by "badland" erosional dissection. No evidence of large-scale coal mining, past or present, is apparent in the area. ‘Early regional geological studies included all late Tertiary sedimentary rocks of the Succor Creek region within the Payette Formation (for example, Lindgren and Drake, 1904). The Sucker Creek Formation was differentiated from the Payette in 1962 (Corcoran, gt a}., 1962; Kittleman, 1962). The Coal Mine Basin area, however, has not been previously studied in detail. For an extensive review of the literature concerned with the Sucker Creek Formation see Fields, 1983. Objectives of this study are: 1) Construct a detailed composite stratigraphic section of the strata exposed in Coal Mine Basin; 2) Construct a large-scale structural map of Coal Mine Basin; 3) Identify key beds or fossil zones useful for correlation with other exposures of Sucker Creek strata; 4) Describe geological features of particular interest discovered during field work, such as extraordinary fossils or fossiliferous zones, or distinctive lithologic units. Interest in the Sucker Creek Formation stems from the excellent 1 :3 .2..- .......u .5 .33»- 5...:- ..o .33.- ...3..S :2- a.“ - .— ..oo «...—cu“ nun-acu- unnoukn .23; >02 agav— many «:62 song .Ammozv Hamzuamm as amaasam mm: m aaaamuoa mmouo was uumwwmh >3 nmcmwanaq ucm umwuzum coon m>mn n can .m .c .N mmwuwamuoq umxoam mnu mo auflamuoa ma>H on» ma N xufiamuoq .833 . COHUQEhOh xmth .mmum susum mnu mo coflumuoH wcflzocm awe Hmcoflmmm .H ouawflm . m- .-; . ‘ l. A :8 o 3...: .~ _ . .2 .2. I. a o _ a . .. . _ S . m ,— . N. . ...:z: :3... _ ...... ‘ .- fi. .. .. a. n... z .23.... I.- u. a 1.3;: .3- 83» .2- L ...-3.. c A. B a 0 x... E Figure 2. Location map of Coal Mine Basin. Key to localities shown in Figure 2: Numbered localities are locations of measured sections used to construct Figure 5, in ascending order, oldest to youngest: 1. mNO‘U‘#W o The base of the "Lakebeds" unit. Top of the "Lakebeds" unit, and the base of the "Delta" unit, and the location of fish and turtle fossils. Continuation of the "Delta" unit, fish fossils. Continuation of the "Delta" unit. Top of the "Delta" unit and base of the "Antler" unit. Top of the "Antler" unit. The "Schnabel" unit. The "Youngest sediments" unit. Localities depicted by a letter are other points of interest: WOWOZKFNFHEOWMUOW> "Centerline dike", a post-Miocene dike. Basalt exposed in the Succor Creek valley. "Delta" unit sandstones with a strike-slip fault component. Leaf-bearing fossil beds. Whiskey Creek section. Basalt dike. Closed drainage basin. "Lakebeds" unit exposed in the central basin. Gardner (formerly Fenwick) ranch. Basalt plug of the central basin, aligned with "centerline dike". "Lakebeds" unit exposed along U.S. Highway 95. Southeastern exposure (see "Lateral Variations"). Basalt plug or dike. Douglas fir leaf-bearing sediments. Arrowhead section (see "Lateral Variations"). Basalt plug or dike. Leaf-bearing shales. Drill hole. The area enclosed in hachures is the area depicted in Figure 3, "Structural map of the Coal Mine Basin area". mo //«-///_,_///'///V '4 "I -< I ////////y if?” B I ‘ .‘ m 19‘ ./ g, I . '2 If... .u’ Location up or Coal Mine Iasin Figure 2. V"! _;_A‘ I OREGON - IDAHO 15 MINUTE SERIES (TOPOORAPHIC) SHEAVILLE OUADRANOLE .(z) »/ U Jun; «2: / :7- human mp 01 the Coal Mine Basin area. Figure 2. 5 preservation of plant fossils representing an unusually high diversity of plant communities. Fossilization of land plants is ordinarily ' biased towards lowland, coastal, lacustrine and riparian taxa. However, rapid burial during volcanic ash eruptions in the region resulted in the preservation of taxa from inland and upland regions distant from usual preservational environments. These fossils may indicate communities in various successional stages of recovery after disturbance by volcanism, fire, or climatic change. Paleontologists working on the fossil deposits of the Sucker Creek Formation need detailed stratigraphic control to document changes in communities through time and to correlate from area to area in order to reconstruct paleolandscapes. ' Drs. A. T. Cross and R. E. Taggart are studying stratigraphic relationships and the geologic and vegetative history of the eastern Oregon-southwestern Idaho region (see Cross and Taggart, 1983). They are studying several fossil zones located in the Coal Mine Basin area. Correlation of the strata exposed in the basin with the fossil-bearing ash beds to the north and west is difficult because the few intervening outcrop exposures are thin and ambiguous, and because of complex faulting, localized diagenetic alteration of lithologic units, lateral facies changes, and anomalous fossil plant beds. The composite stratigraphic section and structural map resulting from this study should aid in some of these correlations and in the stratigraphic, and consequently temporal, placement of the fossil zones. Another study benefitting from this research is that of Prof. R. Giegengack, of the University of Pennsylvania. He collected organic- rich samples from Coal Mine Basin for use in experimental beryllium—10 6 age-dating studies. This isotope is concentrated in organic matter such as the lignites and organic shales from the Sucker Creek Formation. To check the experimental dates, Geigengack's research requires all samples to be accurately placed within stratigraphic sections and dated by fossils or other radiometric isotopes. Government, industry, and individuals may also benefit from the information contained in this study. Corporations which have shown an interest in the mineral potential of the Sucker Creek Formation include: Union Carbide, Norton, Occidental Minerals, Teague Minerals, Western Nuclear, and Amoco (Sheppard gt al., 1983; Fisk, oral comm., 1983; Weasma, oral comm., 1984). The Bureau of Land Management manages most of the Coal Mine Basin area and this study will help them appraise more accurately the scientific value of the land under their stewardship (Weasma, oral comm., 1984). Fossil collectors, and archeologists are also interested in this area as a source of silicified wood, leaf impressions in shales, and indian artifacts. Throughout this report location numbers and letters refer to Figure 2 unless another Figure is specified. The sites of measured sections used to compile the composite section are numbered in ascending order by age, beginning with the oldest. Letters indicate locations of other stratigraphic sections or points of interest such as fossil sites or reference points. METHODS AND PROCEDURES The primary source of information for this study was data collected in the field during the summers of 1983 and 1984. Field work concentrated on the measurement, description, and sampling of stratigraphic sections and mapping structural features. Faults and bed orientation were noted on a 7.5' topographic base map. Lineations apparent on stereo aerial photographs were field checked to determine if they were faults or other geological features. Satellite and high- altitude airborne imagery were found to be of regional help but were of too small a scale for extensive use in the study area. Field tools and supplies included a Brunton compass, a steel measuring tape and folding carpenter's rule, a mattock, rock hammer, rock color chart (Goddard, gt gl., 1951), sterile 6 oz. sample bags, and field notebook. The mattock was needed to dig through the severely-weathered zone to reach less-weathered sediments for descriptions and sampling. Lithologic descriptions included rock type, standardized color, grain size, bedding characteristics, inclusions such as fossils or concretions, mineralogy, character of contacts above and below, weathering characteristics, and topographic form, e.g., ledge- or slope-former. Ten weeks were spent in the field making observations, measuring stratigraphic sections and mapping structural features. Principal access to Coal Mine Basin is by a jeep trail which extends south from U. S. highway 95 at the Idaho-Oregon state line. STRUCTURE, TECTONICS, AND VOLCANISM Structural Features: Coal Mine Basin lies within the Owyhee Uplands physiographic province. The Columbia Plateau lies north and northwest of this area; the Basin and Range province to the south and west; the Mesozoic plutonic Owyhee Mountains to the southeast and the Snake River Graben to the northeast. The primary goal of the structural study was the construction of the large-scale structural map (Figure 3). This map aids in the cor— relation of the eight measured sections (Appendix) which comprise the composite measured section, Figure 5. The study area is part of a broad, gentle anticline or dome with its flanks complexly block- faulted. The dense faulting frustrates stratigraphic correlation. Displacements on the normal faults rarely exceed 50 m; most are a few meters in extent or less. Dips rarely exceed 16°. The north-south axis of the anticline or dome coincides with a basaltic dike, locality A-A, and a basaltic plug, locality J. The curvature of the anticline is best seen looking north from near BM 4650, about 300 m north— northwest of locality R. The hydrocarbon exploratory drill hole, locality R, appears to have been drilled near the apex of the struc- ture. A monocline is well-exposed at locality 1. At locality G is an 0.8 km long closed-basin typical of the Basin and Range province. Regional structural observations and conclusions of Kittleman (1962) for the Owyhee Reservoir district (Figure 1) are largely applic- Figure 3. ’ ..am Y ' Sun: I. flip M bedding I" Anurltne’. trace 0' "HI plane 7.. ' Honoclme VI. Puma! fault; {)1 dn‘vnvlhroum ‘.' slam u= uplhroun side. am a 01 hull plan-- _' ram snowing "mm hcrnonul "uiefi'fl‘ Dasuv' I‘m's Inmate inferred position Or can derived "om uric] photographs and "or Held confirmed. Structural map of ohb 'MALHEUR ()WYHES x I I. a I _ 1 ' [nubile yunu‘ ‘ . . 'nu » a u 1 l u D l‘ . o '1'; ,_L.__.._.,__..._. o w u Str‘nnulll :m. w-W IVA’, :3: “11' Mu'. um ‘Vnrr Locality nu-Mll "In to new. 2 Coal Mine Basin. lO able to the Coal Mine Basin area. He concluded from his regional studies that the dominant late Miocene faulting in the area may be localized within blocks bounded by widely spaced faults of the early and middle Pliocene Steens Mountain fault zone of the Basin and Range province, about 130 km southwest, and the Snake River Plain boundary faults, the nearest of which is about 16 km east of the Owyhee Reservoir District. He found that the faults of the Reservoir District were formed during at least four episodes of deformation corresponding to the major hiatuses in the stratigraphic sequence. In general Miocene faults were along northerly trends; Pliocene faulting along west-northwesterly and east-northeasterly trends. Most faults in the Reservoir District are normal faults with fault-plane dips usually over 85°. A few reverse faults or strike-slip faults were found. In Coal Mine Basin, all faults noted during this study are high-angle normal faults except a set of faults at locality C where nearly horizontal slickensides provide.evidence of a left-lateral, strike-slip component. In the study area, two east-west faults were mapped (Figure 3). Many faults evident on exposed slope faces were difficult to trace across vegetated land. Stereo aerial photographs were essential in some cases to confidently extend faults but in many cases the faults were either of short length, or were very subtle even on stereo aerial photos. Two different scales of aerial photographs were used. The few well-cemented sandstones and the late conglomerate show slickensides (e.g., Locality C) and fault surface "glazing", but the swelling clay that is a significant component of most of the rock in the area mantles the slopes with thick soils, covering evidence of faulting. Determin- ing the relative age or order of faulting was difficult in this area 11 for two main reasons. First,nearly vertical fault planes do not dra- matically offset earlier faults,and second.faults reactivate as evi- denced by Miocene rock showing greater displacement than the later conglomerate. However, judging by relative sharpness of fault traces on aerial photos, it appears that north-south faulting began first followed by northwest-southeast faulting and east-west faulting. The Plio-Pleistocene conglomerate shows evidence of all three directions of faulting. Regional Tectonics and Volcanism: Hart gt g}. (1984) provided some evidence that the western Idaho, eastern Oregon, northern Nevada region is an example of back-arc spreading. They conclude that high-angle normal faulting, associated with extension in the Basin and Range province, became an important factor about 7 Ma. These processes produced intense extensional tec- tonism which triggered fissure-controlled basalt eruptions. They ar- rived at these conclusions during their study of low-potassium, high alumina, olivine tholeiite (HOAT) basalts of the southeastern Oregon, southwestern Idaho, and northern California-Nevada region. Their data suggest three important pulses of magmatism in the northwestern Basin and Range during the late Cenozoic: O-2.S Ma, 3.5-6 Ma, and 7-10 Ma ago. Limited data suggest a fourth pulse at 13—16 Ma ago. Their study included the Cow Creek basalts of Jordan Craters (Figure 1) which include a Holocene basalt flow (Otto and Hutchison, 1977) about 35 km west-southwest of Coal Mine Basin. Armstrong (1978), in a review of the Cenozoic igneous history of the region, reported that the Miocene Columbia River flood basalts 12 buried a mature topography in western Idaho. He noted that within any particular area, volcanism followed a distinct gap in the sedimentary record. Large volumes of rhyolite were erupted as ash flows, lava flows, and air-fall tuffs, with associated minor volumes of basalt. Tuffaceous sediments and clastics derived from the erosion of older rocks were deposited simultaneously. Coal Mine Basin Volcanism: The strata of Coal Mine Basin, as in many parts of the Pacific Northwest, are comprised largely of Miocene or younger volcanic rocks. The three most obvious products of Miocene volcanism in the Coal Mine Basin area are tuffs, volcaniclastic sediments, and basaltic dike and plug intrusion. Lower Columbia River basalts immediately underlie the Sucker Creek Formation (Kittleman, gt gl., 1965, 1967; Ekrin, gt g;., 1981). A drill hole about 6.5 km south of Coal Mine Basin (locality R) pene- trated 148 m of the Sucker Creek Formation and 212 m of basalt before it was abandoned (Evenson, 1960). Basaltic volcanism is represented locally in Coal Mine Basin as plugs, dikes, and maar tuffs. Localities A-A, B, F, J, and M are volcanic plugs and dikes. Locality J is the site of an aphanitic basalt plug aligned with a north-south trending post-Miocene basaltic dike located at A-A. The dike is refered to in this study as "centerline dike" because it lies in the axial plane of the broad, gentle, anticline or dome. Both the dike and the plug are columnar-jointed. The basaltic dike contains zoned plagioclase laths up to 4 mm long and olivine phenocrysts which are being altered to iddingsite. The dike may be a later emplacement, 13 representing a northward propagation of the fracture conduit of the plug at locality J. In support of the age relationship, Corcoran and walker (1969) state that lower Pliocene to Pleistocene basaltic lavas are generally distinguished from Miocene lavas by their higher olivine content and, in some areas, by their coarser crystalline texture. The high-olivine, coarser-grained dike disrupted the Plio-Pleistocene stream channel conglomerate, whereas the youngest rocks intruded by the aphanitic plug, are "Delta" unit sandstones. The basalt of the plug shows slickensides from fault movement, possibly movement related to the later dike emplacement. The location of the volcanic centers for the thick ash deposits of the area are unknown. McKee, gt g}. (1975, in Laursen, and Hammond, 1978), found that the McDermitt Caldera, about 160 km south of the study area, was active between approximately 17.5 Ma and 13.7 Ma. Fields (1983, figure 9, after Kimmel, 1979) shows a silicic eruptive source along the eastern edge of the Owyhee Mountains approximately 15 Ma. The extensive, rhyolitic, Leslie Gulch Ash-Flow Tuff member, locally over 300 m thick, is found near the top of the Sucker Creek Formation; the feeder dike is probably in the Owyhee Reservoir District (Figure 1; Kittleman gt g;., 1965). The Leslie Gulch Ash-flow Tuff may have been accompanied by an airfall ash. Unfortunately this tuff has not been accurately placed stratigraphically. Other possible source conduits may be buried under the Pliocene Jump Creek Rhyolite or other deposits. The region is punctuated by volcanic necks of unknown age, such as "Three Fingers", a prominent landmark approximately 29 km north-northwest of the study area and aligned with the axis of the monocline in the southwestern basin area (monocline-locality 1). 14 The "Antler" tuff; a Maar Deposit: The "Antler" tuff, discussed in the stratigraphy chapter, is a key marker bed for correlations within the Coal Mine Basin vicinity. It appears to be the result of a maar explosion. Maars are associated with magma intruSion in or near bodies of water or water saturated sediments. Maar tuffs have also been found in the McBride Creek area (between localitys 6 and 7, Figure 1), in the Type section, and in the Devils Gate section. Maars are examined because their distinctive tuffs are important as local marker beds in the Sucker Creek Formation. A maar may explode when magma contacts sediments or rock contain— ing significant amounts of water. The water becomes superheated under the confining pressure of the rock or sediment overburden. When a critical temperature is reached, or when faulting opens up a conduit to the surface which lowers the pressure below a critical value, the superheated water flashes to steam, resulting in a series of explo- sions. Sediments and tephra on the crater rim slump into the crater, water reinvades, heats, and explosions continue until the system cools. Three tuff rings of Pleistocene and Holocene maar eruptions were examined in the Christmas Valley area of central Oregon as modern analogs to the "Antler" tuff. Hole-in-the-Ground exhibits the best preserved maar crater. It exploded between 13,500 and 18,000 years ago on the edge of a very large Pleistocene lake (Lorenz, 1971). Four major explosions have been documented at Hole-in-the-Ground (Peterson and Groh, 1961). A crater approximately 1.6 km in diameter remains, flanked by sediments of the old lake margin with blocks of basalt and bread-crust bombs over ten feet in diameter on the rim of the crater. 15 The tuff encircling a maar crater is displayed more clearly in Big Hole, another maar in the vicinity which erupted about 18,000 years ago. Fort Rock, a state park, is the third maar that was examined. Peterson and Groh (1963) described the composition and structure of the Pleistocene maar tuffs of central Oregon. Their descriptions of color, groundmass composition of accretionary lapilli, layering, struc- tures, and weathering characteristics generally apply to the "Antler" tuff of Coal Mine Basin. They observed that colors range from gray to dusky yellows and brown as a result of the sideromelane-palagonite composition of the accretionary lapilli which comprise the groundmass. The tuffs and breccias usually show layering from a few millimeters to several meters thick. Common structures include cross-bedding, chan- neling, impact sags from ballistic ejecta blocks, convolute bedding, and slumping. Weathering produces hoodoos, and pedestals. As the crater becomes more dissected and is obliterated, the layers of tuff commonly form low, curving, hogback ridges with a ring shape, or bold cliffs with a roughly circular shape. The "Antler" tuff of Coal Mine Basin, in addition, contains numerous standing tree casts at locality 5 (Table 1), and horizontal tree and branch molds indicating that trees were buried rapidly. There are several parameters which control the distribution of maar tuff ejecta: the fluid density and velocity of the eruption cloud, the size and density of the particles, and the drag coefficient. Lorenz (1970) mapped isopleths of large ballistic blocks ejected during the strongest explosion event at Big Hole maar. He calculated that Big Hole was a small maar, left a crater about 2.4 km across, and exploded with approximately the kinetic energy of 31.7 kilotons of TNT, compar- 16 able to a medium-sized nuclear event. Peterson and Groh (1963) state that this size is probably about the minimum. Where maars occur in clusters, such as along a fault line, they form much larger masses of tuff. Big Hole had a higher ejection cloud fluid velocity than Hole- In—The-Ground, but the apparent fluid density of the eruption cloud of Big Hole was only one-fourth that of Hole-In-The-Ground. Therefore, Big Hole has significantly smaller ejection blocks associated with its explosions. STRATIGRAPHY Introduction: The relationship of the Sucker Creek Formation to other formations in the area is illustrated in Figure 4. The strata exposed in Coal Mine Basin are discussed in this chapter and graphically illustrated at a small-scale in Figure 5, and at a large-scale in the appendix. The composite stratigraphic section was subdivided into six convenient units based on stratigraphic breaks, usually unconformities. The sub- division names are based on predominant depositional environments (e.g., "Lakebeds", "Delta") or distinctive lithologic units (e.g., "Antler", "Schnabel"); the youngest and oldest strata are named for their stratigraphic position. Some strata of surrounding areas are treated in the sections, "Oldest Sediments", "Lateral Variations", and in the chapter "Corre- lations". Localities 1, 2, and 3 of Figure 2 were not originally part of the study area but were added late in the 1983 field season because they allowed extension of the composite section to older strata. Time constraints prevented further expansion of the composite section to include the older sediments found south of Coal Mine Basin. Stand- ardized color references are from the Rock Color Chart (Goddard gt g;., 1951). Correlations between outcrop sections within Coal Mine Basin, localitys 1 through 7, were made by lateral tracing of marker beds, overlapping sequences of strata, or unconformities. The strata de- scribed in "Youngest Sediments" are separated from the composite sec- 17 18 .BNSmflggflnmog . 5. me 38... 3 BESS £883 3&3 9:. 688 was. 38 Mo umgfluoffiugt .5. 8 3 Spam 3232 .938» at ca mSBsfiou hate 3 83958 x86 668 05 «0 nEmcofiflum Am .mam .mmma .moamam saunas .c spawns 835 “.86 Hana W 83gb BEE EH03 cant I, uammmm “Mg cons-EON lIrIIl Bamboo 398 38 £I&w_._____u_am— nxx 58mg \ ..ldaam. Bums . ...... .mmm 43.4.21 IIJ 3qu W x88 38 , um Banana m. .finufln ...:- ..:.- 3:: ..nucual. ...... .22.. ~25...- ...... ..:.l ill '75 SNSDOIN ENSDOITd] 19 Glynn-Vin“: volcanic a. Figure 5. Composite stratigraphic section of Cbal Mine Basin, Idaho-Oregon. Paleontologic collections made during this study. "Pb" numbers indicate samples taken for palynologic analysis. ' Stratigra ,ic 51 ‘T‘ 167 {fits Lithologic Symbols f‘ t ‘ vitnc VOItNIflIC In "Youngest sediments"' 187 "“F: 612 100'“ "Schnabel" Vole-ll: shale as .... . ’ Ii 0 Pb 13945 Eiia (hum-nu w' Faun- FEE-‘1‘ 14245 ° N" "Schnabel" 13952 Mimic .- 14241 13948 'Wntler" 'Antler tuff Pb 13957 Pb 13944 "Lake beds" ~¢3> Pb 14244 ”9 all“: ) *‘ uni-xuuq 5% sun- dean m, "rand-I 735 ~— ‘5P Sub =3 m1- rm. .... ® Mia * inn-cu 20 tion by a stratigraphic interval of unknown thickness. The oldest sediments, not graphically presented in this report, are likewise separated from the overlying "Lakebeds" unit by an interval of unknown thickness, comprised predominantly of lake bed sediments. Several exposures, particularly west of locality K or in the vicinity of the "arrowhead" section, appear to include the strata which occupy the intervel between the oldest sediments and the base of the composite section shown in Figure 5. However, these outcrops were not studied in detail. Nomenclature of pyroclastic sediments: The pyroclastic sediments of the Sucker Creek Formation are come monly altered to clay minerals. Originally distinct, sand-sized grains have been consequently transformed into aggregates of silt- or clay- sized particles with more subtle grain boundaries. After studying the Type section, Kittleman gt g1. (1965) state that: "Sedimentary rocks of the Sucker Creek Formation are a varied assemblage dominated by yellowish-gray (5Y7/2), severely altered volcanic sandstones derived from andesine-bearing crystal-vitric ash. The vitric component usually is altered to montmorillonite minerals, but the original vitroclastic texture commonly is preserved. In some beds, glass shards are altered to pseudomorphs composed of heulandite or clinoptilolite. There are strata of slightly altered, crystal-poor vitric ash in which the shards are transparent and have an index of refraction of about 1.50. The arkosic rocks, which have a sparse volcanic component of montmorillonite, (authigenically derived from volcanic glass) glass shards, sanidine, and andesine, mainly contain quartz, plagioclase (probably oligoclase), biotite, and muscovite. These are believed to be derived from granitic rocks to the east. The sedimentary rocks of the Sucker Creek Formation probably are mainly fluviatile, but subordinate thinly laminated and carbonaceous strata suggest lacustrine deposition." The nomenclature of Kittleman gt gt (1965) for the sediments of the Sucker Creek Formation is used in this report with little modifica- 21 tion. The Sucker Creek Formation is predominantly a mixture of sed- iments of pyroclastic and arkosic origin. Most of the pyroclastic sediments have been reworked by wind or/and water. A special nomen- clature is desirable for this mixture of sediments, one which describes the origin, the distinctive mineralogical composition, and the two energy regimes of volcanic eruption and normal erosion and transport. Kittleman (1962) established a nomenclature for rocks and sed- iments of the Sucker Creek Formation based upon Hay's (1952) and Fisher's (1961) classifications for fine-grained detrital volcanic rocks. Later, Kittleman gt g}. (1965) further modified the terminol- ogy. Recent terminologies for purely pyroclastic deposits (Wright gt gl., 1980; Schmidt, 1981; Smith, 1986) are net used in this study because they do not adequately consider mixtures of epiclastic and reworked pyroclastics. Also, rock-type comparisons for correlations should be easier when original nomenclature is closely maintained. Oldest Sediments: The oldest rocks of the Sucker Creek Formation exposed near the study area lie to the sOuth of Coal Mine Basin, in the vicinity of localitys K, M, N, P, and Q. The strata of these outcrops have not been correlated with the Coal Mine Basin strata except to recognize that they are older than any exposed rocks in the basin. Stratigraphic correlation in the area surrounding Coal Mine Basin is difficult be- cause outcrops are limited and widely spaced. The sediments are pre- dominantly volcanic sandstones with some lignitic zones. An airfall ash, slightly reworked and locally altered by water, is present near the top of this section. Lake beds of the same lake as those of the 22 "Lakebeds" unit are exposed in a roadcut, locality K, but a correlation with the "Lakebeds" unit of locality 2, and therefore with the compos- ite stratigraphic section, was not established. A paleochannel boulder conglomerate is preserved within the lake beds at the north end of the highway road cut, locality K. This conglomerate contains angular, soft, bentonitic intraclasts ("rip-up" clasts) as large as 30 cm in length. The area south of Coal Mine Basin contains a number of features of geologic and paleontologic interest. Abundant fossil Douglas fir nee- dles with a few dicot leaves are found in an altered airfall ash at locality N. A variety of leaf types are found in shales at locality Q. Clinoptilolite (a zeolite derived from the alteration of volcanic ash) strip-mine pits are located at locality P, and extend northward about 0.6 km (Hays, 1978: Sheppard, 1983). Unstudied, leaf-bearing lignites outcrop below this zeolite unit. More zeolite strip pits are located less than 1.6 km east of locality N. "Lakebeds" Unit: The "Lakebeds" are the lowest unit of the composite stratigraphic sequence exposed in Coal Mine Basin (Figure 5). The unit totals 50.5 m of poorly consolidated, carbonaceous to lignitic, fine volcanic sands, silts and shales. Thin, parallel laminations, and articulated fish skeletons confirm that the depositional environment was lacustrine. Brown carbonaceous detritis and plant fossils, very thin hematitic siltstones, and clay partings accent the laminae. Sediments become_ more lignitic near the top of the unit with some clean, arkosic, vol- canic sand lenses intercalated. 23 The lake beds are well exposed in five places: locality 3 of Figure 1; and localitys 1, 2, H and K. The lake beds of localitys 1 and 2 were measured and sampled for this study. Cross and Taggart (1983) measured and sampled the lake beds exposed in the central basin (locality H) and identified 13 fossil leaf-zones in 45 m of deposits; however, neither the base nor the top of the lake beds are well exposed at locality H. The "Lakebeds" unit does not include the complete interval of lake bed sediments exposed in the area. Time prevented extending the unit to include the oldest lake bed sediments, therefore they are considered the top of the oldest sediments. The base of the "Lakebeds" unit is defined as the top of a distinctive grayishéyellow-green (5 GY 7/2), pumiceous, vitric, volcanic—shard sandstone lens about 30 m thick within the total sequence of lake bed sediments, exposed at locality 1. The sandstone lens is not included in the composite section, Figure 5. The paleocurrent direction at one point in the sandstone lens is 2550 based on the orientation of elongated bentonitic "rod" intraclasts and imbricated flat pebbles included in the sandstone. The top of the "Lakebeds" unit is defined by the unconformable base of a distinctive 1.2 m thick, ash-rich sand body that is well-exposed at locality 2. The correlation between the lake beds exposed at localitys 1 and 2, and those lake beds exposed at locality H, was based on a number of factors: 1) gross lithology, i.e. gray (volcanic-ash—rich) at the bottom becoming more organic (browner) towards the top; 2) a "fish kill" zone at the top of a distinctive gray sequence in which preserved fish skeletons and a turtle carapice at locality 2, 24 and fish skeletons at locality H, were observed, and; 3) several thin, distinctive and laterally persistent "chippy" shales, and zones of hematite-cemented laminae. "Delta" Unit: An angular unconformity separates the "Lakebeds" unit from the "Delta" unit. At locality 2, a 1.2 m thick volcanic sand lens lies immediately above the unconformity. This is overlain in turn by lig- nitic sands, deltaic bottomset beds, foreset beds, topset beds, and fine sands. The "Delta" unit is a sequence of arkosic volcanic sands, and interbedded volcanic sands, silts and shales. The unit was meas- ured in four sections, localitys 2, 3, 4, and 5, and composited for a total unit thickness of 80 m. The unit is referred to as the "Delta" unit because of the well-displayed, deltaic sand body, 12 m thick, which forms the base of this unit, best exposed at localities 2 and 3. The top of the unit is delimited by the unconformity which forms the base of the distinctive "Antler" maar-tuff in Coal Mine Basin. This unconformity and tuff may be a local features. The deltaic foreset beds at locality 3 strike 350° and dip at a maximum angle of 28.5°W. The deltaic foreset beds of locality C strike 316° and dip at 31°W. At locality C, the topset beds contain permineralized logs up to 1.5 m long and 15 cm in diameter; the undercut, well-cemented sandstone is currently used as a rookery by cliff-swallows. The "Delta" unit is also exposed just south of locality H. Ther- mally altered (baked) delta sands are present on the volcanic knob in the central Coal Mine Basin, locality J. On the east side of the knob formed of the metamorphosed sandstone, the sediments have altered to a 25 porcelanite. The heat source was a basalt intrusion. Other arkosic sands within the Sucker Creek Formation are thin, channel sands. The lower part of the "Delta" unit was the only deltaic sand unit observed in the Coal Mine Basin area. No other interval of the stratigraphic sequence exposed in Coal Mine Basin displays such thick arkosic sands as the "Delta" unit. Above the deltaic sand body is an interval of silts, lignites, and lake beds (locality 3) overlain by an interval of arkosic, volcanic sands displaying low-angle cross- bedding (locality 4). In the upper 18 m of the "Delta" unit (locality 5) less arkosic sub-units are found and a higher percentage of volcaniclastic fine sands and silts are present. These sediments commonly contain volcanic glass and diatoms. The skeletal remains of two oreodonts (Ticholeptis) and the tooth of a third were found near the top of this unit. These vertebrate fossils are described further in the section "Paleontology". "Antler" tuff and "Antler" unit: An unconformity separates this stratigraphic unit from the under- lying "Delta" unit. The "Antler" unit, 51 m thick measured at local- ities 5 and 6, represents an increase in volcanic activity. The unit is largely parallel-laminated or massive, fine-grained, altered volcan- iclastic sediments. There is a distinctive 30 cm-thick arkosic, vol- canic sandstone bed with basalt pebbles present at 30 m above the base of this unit. Near the top of the "Antler" unit there is a 2.1 m thick, cross-bedded, arkosic, volcaniclastic sand; the paleocurrent direction at one location is 5°N. The top 2 m of the unit is root- 26 mottled. Significant quantities of gypsum in the form of selenite are - found in several zones and are indicated on the measured sections in the Appendix. An unconformity was chosen as the top of the "Antler" unit. The "Antler" tuff forms the base of the "Antler" unit. The tuff is a major local marker bed for the Sucker Creek Formation exposed in the Coal_Mine Basin area. Correlation based on this tuff is discussed further in the section "Correlation". It is a dusky-yellow (5 Y 6/4), moderately indurated tuff of variable thickness with a sharp undulating base and a gradational top. The tuff is about 14 m thick at locality 5, where it was measured. Less than 3 km away, at locality 8, it was measured as less than 6 m in thickness. The unit is referred to as the "Antler" tuff because two permineralized tree branch casts at locality 6 superficially resembled antlers protruding from the rock. The "Antler" tuff is believed to have been produced by a maar eruption, as previously discussed, based on descriptions of maar tuffs (Peterson and Groh, 1961, 1963; Lorenz, 1970, 1971; Heiken gt g;., 1981) and compar- isons of maar tuffs of Pleistocene and Holocene eruptions in central Oregon. The "Antler" tuff is distinctive in a number of ways. The tuff is one of the most resistant units in the area and weathers to form high, angular, parallel-laminated, dusky—yellow cliffs, referred to as "hoodoos". Ballistically emplaced, angular diabase and basalt block clasts are found in several zones. The largest clasts are found in a zone about 12 m above the base. The clast size varies with location; clasts at locality 3, Figure 1, measured over 1.2 m in diameter, where- as clasts at locality 6 measured less than 1 m in diameter. "Bomb 27 sags", caused by the impact of these basaltic blocks, are an indication that the pyroclastic deposits were water-saturated (Thorpe and Brown, 1985). At locality 5 the tuff buried numerous standing trees that are now preserved in near vertical position as molds and casts (Table 1). Horizontal tree-branch molds located at the base of the tuff at local- ity 5 are lined with charcoal. The wood may have fusinized in place or the initial deposit of pyroclastic material was hot enough to burn the wood, leaving hollow molds. The tuff is mostly comprised of accretion- ary lapilli. Microscopic examination of grain mounts indicate that the main mineral constituent is a translucent anisotropic grain slightly orange in white light (probably palagonite), with minor amounts of accessory minerals including plagioclase, and calcite. TABLE 1 "Antler Tuff" Tree Molds and Casts locality 5, Figure 2. trend/ strike/dip of Specimen height diameter plunge antler tuff comments (m) (cm) 1 3 84 40°/35° 115’/8°N 2 3 40 322‘/81° 115°/8°N 3 3 -- 45°/70° 112°/15.5°N 4 4 46 18°/77° 52°/9°N 5 -- 92-112 12°/81° 52°/9°N elliptical trunk 6 - 25 115’/68° 52°/9°N "Schnabel" Unit: An unconformity overlain by a distinctive vitric volcanic sand- stone was chosen as a convenient stratigraphic break to define the base of the next unit. The "Schnabel" unit at locality 7 is 33 m thick and is concealed above by soil and vegetative cover. No correlation was made with strata above the top of the section measured. The unit 28 contains: three stump horizons, two root-mottled sections (all five may be local), a second unconformable surface overlain by a second airfall vitric volcanic sand, a 23 cm thick, poorly preserved basalt unit, several lignitic zones, and over 6 m of cross-bedded, quartzitic- arkosic sands at the top of the section measured. The unit is named after the sandstone which forms the base of the unit. The sandstone immediately overlying the unconformity at the top of the "Antler" unit is refered to as the "Schnabel" sandstone or ash, and may be a key stratigraphic marker within the Sucker Creek Formation. The "Schnabel" sandstone is composed of a clean, vitric, volcanic sand. Microscopic study of grain mounts reveal over 95% very angular, vol- canic glass shards. Cross—bedding suggests light reworking by both wind and water. This is an airfall ash about 6 m thick and is one of the thickest of its kind in the area. "Schnabel" became the field reference to this sandstone because "Schnabel 1904" had been carved in the soft stone of an undercut cliff at locality 6. Since this sand- stone is so distinctive, the name is further used to refer to the whole unit above the base of the "Schnabel" sandstone. The most likely sub-unit to be confused with the "Schnabel" sand- stone in the field would be the volcanic sandstone mined for zeolites south of Coal Mine Basin, which is stratigraphically below the "Lakebeds" unit and therefore significantly lower in the section than the "Schnabel". These volcanic ash-sand units apparently accumulated rapidly, clogging local drainages and probably created a landscape similar to that surrounding Mount St. Helens after the May, 1980, eruptions. The rock immediately underlying the basal unconformity is severely 29 altered, fine-grained and root-mottled. 0n the unconformable surface, lignitic lenses, leaf imprints and two horizontal tree molds were noted. The largest tree mold observed, found at locality 5, measured 79 cm in diameter, trended 48°, and forked at about 3 m. Trees grew on the newly deposited ash as indicated by permineralized roots locally present in the top of the ash, and lignitic sand containing permineral- ized stumps overlying the "Schnabel" sandstone. A similar, but thinner, sandstone appears about 9 m above the top of the thick, basal sand of this unit. These two vitric sandstones form a double, silver-gray band which has a distinctive weathering profile as seen from a distance on some slope faces. Locally, iron— stains discolor the cliff faces and weathering sculptures flutes, spires, and overhangs. The sandstones frequently form cliffs. The "Schnabel" is very friable but evaporation of mineralized water at exposed surfaces forms a cemented, thin crust. Locally present in the lower portions of this subunit are chert nodules, occasional leaf imprints, lignitic "rip—up" clasts, and laminated strata. "Youngest Sediments" Unit: The youngest Miocene sediments in Coal Mine Basin were observed only at locality 8. The section measures nearly 50 m thick. An angu- lar unconformity overlain by a Plio-Pleistocene boulder-cobble conglom- erate about 6 m thick (variable) caps the exposure. The section is composed of volcaniclastic sediments, arkosic sand units, and several lignitic zones. The most prominent unit in the section is a nearly white, gypsum-bearing, vitric, volcanic sandstone. The sharp base of this unit was used as a datum for this measured section. Lignitic 30 units lie below this vitric volcanic sandstone. Amber was collected from a lignitic zone 21 m below the datum; 27 m below the sandstone is a zone of lignitic wood. The lignites in this section contain several leaf zones that are illustrated in the appendix. Gypsum crystals, as selenite rosettes and tabular twins, are more common in this section than in any other part of Coal Mine Basin. No gypsum was noted above the prominent volcanic sandstone. Insect impressions were found in varved silts above this sandstone. The slope at locality 8 is crossed by a subtle northwest-trending fault (Figure 3), juxtaposing strata of the "Antler" unit with the "Youngest Sediments". At the west end of the volcanic sandstone marker is a small prominent knob. The northwest-trending fault separates the knob from the youngest sediments, forming a saddle. A white (N 9) ash caps the knob. Two fossil stump zones, 76 cm and 7.6 m below and two fossil wood zones, 5.2 m and 5.8 m below, outcrop below this knob. Lower in this section, the "Antler" tuff was measured as 6 m in thick- ness. The subtlety of the fault makes these fossil zones appear to be part of the "Youngest Sediments" section. No fossil wood or stump zones were found above the "Antler" at locality 6, 0.8 km east where this section was measured for the composite section, but a few stumps were noted at locality 5, illustrating the local nature of many of the fossil zones. The strata exposed are believed to be the youngest of the area studied because of its location in relation to the upper "Schnabel" unit. There is a fault, shown on Figure 3, with a displacement of approximately 2 m separating the slope which exposes these sediments from the adjacent slope to the east where the "Schnabel" unit is ex- 31 posed. The cover of soil and vegetation, which could conceal signif— icant faulting, make correlation of the sections uncertain. However, no faults of significant displacement are suspected to separate this exposure from the "Schnabel" unit; therefore these sediments are be- lieved to be the youngest sediments of the Sucker Creek Formation exposed in Coal Mine Basin. In addition, a small fault-wedge at local- ity 8 contains strata exposed nowhere else in the basin. These strata, because of the location are believed to be the youngest strata exposed in the basin. Two types of fern—leaf fossils are found in the strata of this small wedge; fern-leaf fossils have not been observed in any other sediments of the basin. Lateral Stratigraphic Variations: Southeastern Exposures: Two sections were measured for a composite total of 120 m of stratigraphic section (locality 2, Figure 1, local- itys L and 0, Figure 2). The lower section (locality 0, Figure 2; SE 1/4, SE 1/4, NW 1/4 Sec. 13, T. 38., R. 6W., Rooster Comb Peak 15' Quadrangle, Owyhee Co., Idaho), was called the "arrowhead" section since an indian arrowhead was found at the base of the section. Here the lake beds are well-exposed in 85 m of continuous section. The upper section, 0.6 km north of the arrowhead section (locality L, Figure 2; NW 1/4, SE 1/4, SW 1/4, Sec. 12, T. 38., R. 6W., Owyhee Co. Idaho; Rooster Comb Peak, Idaho 15' quadrangle), measured 81 m thick and was given the field name "southeastern exposure". The plural, "southeastern exposures" is used to refer to the two sections consid- ered together. The "southeastern exposures" range from within the "Lakebeds" unit to near the top of the "Delta" unit. At this location 32 two tree stump horizons are found within the "Delta" unit. The position of the unconformity at the base of the "Antler" tuff is believed to be less than 15 m stratigraphically above the top of the "southeastern exposure", but it was not located. The "Antler" tuff is exposed with basalt blocks as large as 1.2 m in diameter on the north- south trending ridge forming the eastern rim of the "southeastern exposure". The "southeastern exposure" contains two distinct fossil stump zones. The lower stump zone was laterally traced to the stump zone at the top of the "arrowhead" section to correlate the sections. Whiskey Creek: The thick basal volcanic sandstone of Whiskey Creek appears to contain water-reworked facies of the "Antler" tuff. The sandstone of the Whiskey Creek section (Cross and Taggart, 1983; Valley section of Taggart, 1973) contains large, angular, basalt clasts bal- listically emplaced in a coarse to fine-grained matrix closely resem- bling in gross appearance, the accretionary lapilli of the "Antler" tuff. Two exposures of the "Antler" tuff are massive with basalt blocks suspended in a fine grained matrix, specifically, in the first road-cut north of locality I, and at the mouth of Whiskey Creek. These deposits probably represent mud-flow deposits. Other exposures are cross-bedded indicating that some of the facies in the Whiskey Creek area were water-worked. McBride Creek: A second stratigraphic interval believed to be equivalent to the delta sands of the "Delta" unit is exposed southeast of the bridge over McBride Creek on U.S. Highway 95 (locality 6, Figure 1). The exposures, referred to in this study as the "McBride Creek" 33 section, are visible from U.S. Highway 95 atop the hill south of the McBride Creek bridge and are in part exposed in the first U.S. 95 road- cut south of McBride Creek. A 17 m section was measured up the lower part of the eastern face of locality 6, Figure 1. This measured sec- tion is not included in this report, however. An arkosic, deltaic sand forms the base of the section measured and is the basis for the pro— posed stratigraphic position. The "Delta" unit contains the only thick arkosic, deltaic sand body observed in the strata of Coal Mine Basin. Correlation of this sequence has not been confirmed. A tuff, similar in lithology and in gross microscopic detail to the "Antler" tuff, is exposed in two U.S. 95 road cuts north of McBride Creek (near locality 6, Figure 1). Ballistically emplaced basalt blocks are present but badly corroded. The largest blocks observed are 15 cm in diameter at the southern road cut, and 10 cm at the northern road cut. This section is between the McBride Creek section of this report, and the Shortcut section of Taggart (1973) and Cross and Taggart (1982). Thick vegetation cover and a thick soil here make it difficult to identify faulting which may intervene between these ex- posures. The McBride Creek "maar" tuff of the northern road cut is just north of the Dead Horse Creek road (SW 1/4, NE 1/4 section 17, T. 1 S., R. 6 W. Sands Basin, 15 minute quadrangle, Idaho). The sediments are comprised of accretionary lapilli with the characteristic dusky- yellow color (5 Y 6/4), and basalt blocks up to 10 cm in diameter. Maar eruptions would probably not eject material beyond several kilo- meters. Therefore this maar tuff is not equivalent to the "Antler" tuff. Similar tuffs are found as unit 7 of Kittleman gt gl. (1965) in the Type section, and in the Devils Gate section. CORRELATION Correlations of strata exposed in Coal Mine Basin to strata of other areas, including the Type section, may be possible by identifying distinctive marker beds, sequences of beds or fossil zones. Lateral tracing of beds for correlation is difficult in many places because exposures are widely spaced, limited in thickness and partially covered with soil and vegetation. Dense faulting in the region also compli- cates correlation. Faulting rarely prevents correlation however, since fault displacements in the area rarely exceed 60 m. Long-distance tracing of strata in such an extensive volcanic terrain may not be possible because: the sources of tephra may be attributed to a number of unidentified vents; the time and sequence of eruptions is unknown; sediments appear similar although they are from different volcanoes or they were distributed by different streams or rivers. Nonetheless, field observations made during this study indicate that there are some strata which may be potentially good marker beds locally. However, detailed analysis of fossil content, mineralogy, and stratigraphic position is required before correlations can be made. The Coal Mine Basin area contains the most extensive exposures of the Sucker Creek Formation south of the Type section. A thorough mega- fossil and microfossil analysis of the strata exposed in the Coal Mine Basin area would be one of the best ways to define the stratigraphic zones most persistent, and therefore most useful, for regional corre- lation within the Sucker Creek Formation. Dr. R.E. Taggart is actively 34 35 pursuing this objective as a part of his ongoing paleobotanical re— search of the Miocene strata of this region. Taggart has carried out an extensive palynologic study of the "Type" section, the "Shortcut" and "Rockville" sections, and the strata exposed along Whiskey Creek ("Valley" section), (locations 2, 7, 5, and 4 respectively, Figure 1). Satchell (1983) made a detailed palynologic study of the Devils Gate section (location 8, Figure 1). The only paleontological correlation made during this study involved the lateral tracing of fossil stumps between the "arrowhead" section and the "southeastern exposure" section. A horizon of fossilized fish skeleton ' nodules identified within the "Lakebeds" unit added to the evidence correlating the lake bed sediments of locality 2 with the sediments exposed at locality H. Some leaf impressions, fossil wood, insects, bones of land mammals, and fresh water fish, and turtles were noted and some rock samples were taken for palynologic and diatom studies. The measured sections of this report were correlated by tracing distinctive beds, sequences of beds or unconformities along well-exposed outcrops. The "Schnabel" sandstone, the "Antler" tuff and the Plio— Pleistocene boulder conglomerate are the most conspicuous cliff-forming units exposed in Coal Mine Basin. The "Antler" tuff may be used local- ly within the Coal Mine Basin area as a key marker bed. A detailed measured section is included in the Appendix (Figure 9-a). Some key characteristics of this tuff are: 1) The color and weathering profile are distinctive. The "Antler" tuff is resistant to weathering, forming castellated cliffs with relatively square-cornered vertical columns ("hoodoos"). This is one of the most resistant units in the Sucker Creek Formation. A 2) 3) 4) 36 distinctive dusky-yellow-green color (5 GY 6/2) is conspicuous from a distance. Parallel laminated bedding is well—developed. Some layers show cross-bedding, ripple marks, and ball and pillow structures. Some intrabeds are composed largely of pellets of accretionary lapilli, angular rock fragments, and scoriaceous basalt clasts. Ballistically emplaced, scoriaceous basalt pebbles and blocks are common in several layers. Between locations L and 0 the largest basalt block observed was over 1.2 m in diameter. The sediments were wet and cohesive when the basalt blocks dropped in, as evidenced by "bomb sags" (deformation) in beds below and "mud curling" over the top of some of the blocks. There were two major eruptions and several_smaller eruptions based on the repetition of horizons containing these ballistic basalt blocks. Standing trees were locally buried in the basal tuff of the "Antler" unit in the Coal Mine Basin area. Several tree casts were found in upright position (Table 1), the largest being 4 m tall, and the broadest was 1 m in diameter. Reconnaissance observations were made on beds in some previously described sections of the Succor Creek area. First, Unit 20 of Kittleman gt gl. (1965) in the Type section, 27 km north-northwest, might be equivalent to the "Schnabel" sandstone of Coal Mine Basin, based on field observations of gross appearance and thickness, strati- graphic position, and distinctive permineralized roots present in the upper portion of this zone both at the Type section and Coal Mine Basin. Leaf impressions, thin lignitic layers, and horizontal tree molds are found at the base of this distinctive air-fall ash in Coal 37 Mine Basin. Second, the "Rocky Ford" section (Cross and Taggart, 1983) might be equivalent to the top of the "Lakebeds" unit of Coal Mine Basin. The 1.2 m severely altered sandstone (base of section, Figure 8-a) forming the base of the "Delta" unit is similar in gross appear— ance and stratigraphic context to a sandstone in the "Rocky Ford" section. Likewise, the thick, arkosic, units 2 and 3 of the Type section (Kittleman gt g}. 1965) are in proper stratigraphic sequence to possibly be equivalent to some arkosic subunits of the "Delta" unit of Coal Mine Basin. Third, the sandstone bearing the Douglas fir needles of location I may be equivalent to conifer-needle bearing beds of the "Shortcut" or "Rockville" sections (locations 7 and 5 respectively, Figure 1). There are other beds in the Type section, measured and studied mineralogically by Kittleman gt gt. (1965) and palynologically by Cross and Taggart (1983), which have some similarities to certain units in Coal Mine Basin but demonstration of such correlations has not been accomplished. PALEONTOLOGY OF COAL MINE BASIN The Sucker Creek Formation is famous for well-preserved Miocene plant fossils. Leaf impressions in shales, and pollen have both been studied extensively from sections north and west of Coal Mine Basin. Permineralized and lignitized wood, though fairly common throughout the Succor Creek region, have been given only cursory study. Plant mega- fossils from the formation have been reported by Knowlton (i3, Lindgren and Drake 1904), Berry (1932), Brooks (1935), Arnold (1936a, 1936b, 1937), Smith (1938, 1939, 1940), Chaney and Axelrod (1959), Graham (1963, 1965), Taggart (1971, 1973), Cross and Taggart (1983), and Satchell (1983). Pollen and spore studies have been reported by Graham (1963, 1965), Taggart (1971, 1973), Taggart and Cross (1974, 1980, 1982), Cross and Taggart (1983), and Satchell (1983). Bradbury and Krebs (1982) made a brief report on the fresh-water diatoms. Eubanks (1966) lists 15 genera of fossilized wood from a location near Coal Mine Basin. Fields (1983) extensively reviewed the paleontologic literature and presented a table (ibid., Appendix II) listing all taxa identified in published reports on the Succor Creek flora. Terrestrial mammals have been reported by Scharf (1935) and Shotwell (1968). Fig- ure 5 summarizes the paleontologic data collected in Coal Mine Basin during field work for this study. Paleobotany In this study, several fossil plant zones are identified and placed stratigraphically. These include seven permineralized stump zones, one zone of tree casts and molds, one zone of tree molds only, a 38 39 zone of permineralized roots, and at least 17 leaf zones. Most of these fossil beds are discontinuous. Fourteen samples for palynologic analysis were macerated and microscope slides were made. Cross has macerated several more samples during ongoing research, thirteen in the "Lakebeds" at locality H; several in a small fault wedge at locality 8; and several associated with lignitic zones elsewhere in the basin. Metasequoia leaf and twig fossils have been found in Coal Mine Basin (Taggart, oral comm., 1983). Metasequoia was widely distributed in the Oligocene but is last known in North America from the Miocene Mascall flora of central Oregon. Its occurrence in Coal Mine Basin may indicate an earlier age for the strata or a later existence of Metasequoia in North America (Taggart, oral comm., 1983). Bradbury and Krebs (1982) identified an "apparently useful" bio- stratigraphic marker diatom in the Sucker Creek Type section and in the lower part of the Poison Creek Formation exposed in the upper Reynolds Creek area. This lacustrine diatom, Coscinodiscus (?) miocaenicus, is known from the western Snake River Basin and eastern Europe. Diatoms found in the Sucker Creek Formation represent cool, fresh-water species according to Bradbury (ig Cross and Taggart, 1983, p. 695). Bradbury and Krebs reported on only one sample from the Sucker Creek Formation and did not state the stratigraphic horizon from which it was collect- ed. They note that, in general, the diatom floras of these deposits are neither well-known nor have their ages been clearly defined by radiometric dates or paleontologic collections. The studies of Taggart and Cross (1980), Taggart gt gl. (1982), and Cross and Taggart (1983) and those of satchell (1983) have demon- strated the complex dynamics of the vegetation through repeated natural 40 disturbances, specifically fire, volcanism, and climatic oscillations. The Succor Creek Flora appears to represent a range of successional, sub-climax, and climax plant communities. Of other interest, fossil "mats" of Douglas fir needles were discovered at locality N, Figure 2, and localities 5 and 7, Figure 1. These fossils support the postu- lation that highlands existed in the vicinity as suggested by Cross and Taggart (1983). Vertebrates The remains of two oreodonts, genus Ticholeptus; several pieces of articulated skeletal remains of a fresh water fish, Archoplites; and the epidermal shield of a turtle, tentatively identified to cf. Clemmys were discovered during field studies. The "pond turtle" belongs to the family Testudinidae Gray 1825, sub-family Emydinae and ranges from the Eocene to Holocene (Dr. Alan Holman, oral comm., 1986). This omnivorous turtle probably lived in a vegetation-choked, low-energy environment with a water depth not over two meters. Dr. Gerald Smith (oral comm., 1983) of the University of Michigan identified fish fossils recovered from the ”Lakebeds" as Archoplites sp. During the Miocene and Pliocene this "sunfish" was a common lake fish ranging from Alaska to California-Nevada. Occasionally this genus appears to have comprised the whole fish fauna of a lake. According to Smith, the preservation of articulated skeletons may indicate a water temperature of less than 16° C; above this temperature dead fish float and are scavenged. The deep waters were probably anoxic since the skeletons are well-preserved. Dr. Smith infers from his study of Archoplites that the lake would have been at least 30 m. deep, the 41 local gradient was low, and the climate was not too variable. Based on comparative morphology, which is weak evidence, Archoplites would have lived below 150 m elevation. Smith points out, however, that trout, a stream or river fish of highlands or colder waters, is commonly as— sociated with Archoplites in Miocene lake deposits, yielding conflict- ing ecological signals. No trout fossils have yet been identified from the Sucker Creek Formation lake beds, however. The elevation of this region during Sucker Creek time is believed to have been higher than it is today (Cross and Taggart, 1983, p. 720). The skeletal remains of two Barstovian oreodonts, Ticholeptus, identified by Dr. Greg MacDonald, (oral comm., 1984), were recovered from 1.4 m below the erosional unconformity marking the base of the "Antler" tuff (locality 5). The mandibles had been gnawed by rodents after their death indicating that the carcasses probably had been exposed before being buried (MacDonald, oral comm., 1984). MacDonald noted that their worn teeth indicated that they were old individuals. The well-preserved tooth of a third, young, oreodont was also found. Oreodonts, popularly named "ruminating swine", were rather heavily built, sheep-sized grazers, somewhat pig-like in general appearance. Ticholeptus is a middle-Miocene genus of oreodont (Romer, 1966, p. 389). A portion of a skull of a Merychippus, a Miocene horse, was found several years earlier as a talus block just north of locality 4. The specimen was identified and curated at the Idaho Museum of Natural History in Pocatello. Another land mammal bone locality in the "Schnabel" unit of Coal Mine Basin was pointed out by Howard Emry of Denver, but has not been excavated. THE MIOCENE GEOLOGIC HISTORY OF COAL MINE BASIN In this section an attempt is made to deduce the geologic history of the Coal Mine Basin area from the sedimentologic, paleontologic, and structural data. Regional Overview: Taggart and Cross (1980), Taggart gt gl. (1982), and Cross and Taggart (1983), in discussing the history of the region during Sucker Creek time, synthesized original paleobotanical and geological data with the research results of others to concluded that: 1) area drainage gradients were low, 2) the climate was moist and cool but highly equa- ble, and 3) small thermal oscillations on the order of centuries to several thousand years probably occurred. Causes of the thermal oscil- lations include shifts in elevation, relief, continentality, albedo due to volcanic activity, and earth orbit mechanics. In addition, changes in edaphic conditions caused by fires and volcanic eruptions resulted in taxonomic changes in the local biota (Cross and Taggart 1983; Satchell, 1983). Two major problems are encountered in attempting to infer the time duration represented by the rocks of the Sucker Creek Formation. Cross and Taggart (1983) point out the difficulty in determining the time duration represented by rocks of different sedimentary environments. For example, fluvial sediments are usually deposited much faster than lake sediments and thus represent a longer time of accumulation for an equivalent stratigraphic thickness. Compounding the problem in the 42 43 study area is the fluctuating, but often considerable, air-fall volcanic-ash "rain" deposited directly into the basin. The second major problem is that no accurate way exists to determine the time intervals represented by the numerous unconformities and paraconform- ities in the formation. The absence of reliable and comparative radio- metric dates has also been a limiting factor. Coal Mine Basin History: Sediment sources and dominant depositional environments imply five major episodes in the geologic history of the area. These episodes roughly correspond to the units included in parentheses. Listed from earliest to latest, they are: 1. Volcanic-fluvial (oldest sediments) 2. Lacustrine ("Lakebeds" unit) 3. Arkosic-Deltaic-fluvial ("Delta" unit) 4. Volcanic-fluvial ("Antler" and "Schnabel" units) 5. Paludal ("Youngest sediments" unit) The episode breaks do not correspond exactly with the unit boundaries. The first episode (oldest sediments), only briefly examined during this study, includes volcanic ash-rich fluvial sediments located south of Coal Mine Basin. Interbedded, thin, localized, paludal sediments contain leaf fossils, lignites, and organic detritus in sands, silts, and clays. The second episode represents a sizeable paleolake as indicated by the total thickness and areal extent of the lake sediments and the thickness of the deltaic sands that follow. Sediments of the lacus- trine episode extend below the base of the "Lakebeds" unit. Because 44 the lake beds are significantly thicker than any observed fluvial channel, the paleolake is believed to have been an impoundment, due perhaps to volcanic eruptions, tectonic activity, or a combination of these, rather than an oxbow lake (see also Cross and Taggart, 1983). The possibility of a valley deep enough to contain a large lake is not inconsistent with the generally low slope gradients postulated for the region throughout most of Sucker Creek time. Two lines of evidence indicate that there was a shoreline south- east of Coal Mine Basin. First, the lake beds of the "arrowhead" section are less developed than those at localities 1, 2, H, and K, with more channel sands, possibly beach sands, and generally thinner sequences of lake beds. Second, Cross and Taggart (1983) report 13 leaf-fossil horizons throughout 45 m of lake beds at locality H. Accumulations of leaves are not usually found far from shore. Also the presence of a "pond turtle" at locality 2 suggests a shallow-water location at the time the turtle was entombed. Evidence for lakeshores in other directions were not found during this study, since the study area was of limited areal extent. It could be possible that the Owyhee Mountains to the east formed one shoreline while the Mahogany Mountains to the west would form a western shore. These north—south trending mountain ranges could have limited the width of the lake. The third episode ("Delta" unit) is characterized by thick sequences of arkosic deltaic and fluvial sediments with lesser thick- nesses of lacustrine beds and volcanic sediments (Figure 5). An angular unconformity at the base of the "Delta" unit may relate to the increase in gradient that supplied the arkosic sands from the Owyhee Mountains. No other interval contains such thick arkosic deposits. 45 Volcanic, ash-rich, fluvial deposits (fourth episode) dominate from approximately the upper 20 m of the "Delta" unit through the "Antler" and "Schnabel" units. Fossils of grazing land mammals (Merychippus), and browsers (Ticholeptus) come from this episode. The fifth episode ("Youngest sediments" unit) include lignitic sands second only to the lake bed sequences in total thickness. Plentiful clusters of gypsum crystals indicate that this paludal inter- val included evaporative basins. In general, the fluvial sediments examined support a theory of low slope gradients. Miocene channel sands are shallow and broad, and levees are poorly developed or absent. Fine-grained sediments predom- inate. The few conglomeratic sands seldom contain clasts larger than pebble size. The sediments include thick sequences of massive-bedded to parallel-laminated, fine sediments, frequently with root-mottling and organic-rich lenses, indicative of overbank floodplain deposits and mud flats. Fossil tree stumps outcrop locally in sediments deposited after the lacustrine episode. Overview of Structural History: Structural data collected for this project indicates that the area has been tectonically active since the Miocene. The oldest evidence for major tectonic activity is an angular unconformity found at local- ity 2. The "Lakebeds" below the deltaic sands dip northwest at about 16°. The overlying sediments dip westerly at about 9°. This uncon- formity may have been associated with tectonic activity which increased the gradient and resulted in the coarse sands that overlie the finer paleolake sediments. A second major angular unconformity exists between the Sucker Creek Formation and the overlying Plio-Pleistocene 46 cobble conglomerate. Development of this unconformity and most fault—' ing in the area are believed to have begun in post-Sucker Creek time (see Kittleman 1962). The area faulting is controlled by extension, and the individual blocks are generally bound by faults of three dif- ferent directions. North-south faulting appears to have begun the earliest while northwest—southeast and east-west faulting appear to have begun the latest. Reactivation of faults is known to occur in the area. The change in stress directions, and hence the change in dom- inant fault-plane trends, apparently involved overlapping of dominant direction of faulting rather than one episode ending before the next one began. The basaltic "centerline dike" is evidence of deep fractur- ing. The area remains tectonically active as is apparent from the closed basin at locality G, Figure 2. In conclusion, data collected during this study generally confirms the geologic interpretations of others. The rocks and fossils indicate a time of intense volcanism, broad shallow river valleys, localized lakes and swamps, and open woodlands or parklands. SUMMARY AND CONCLUSIONS Twelve sections totaling 580 m of stratigraphic section within the Coal Mine Basin area were measured, described, and sampled in detail. Eight of these sections were used to construct a composite stratigraphic section of 265 m (Figure 5 and Appendix) representing almost all the strata exposed along the north wall of Coal Mine Basin. The eight sections which form the composite section are graphically presented at large-scale in the Appendix and are disscussed in the section "Stratigraphy". In addition, a brief description is given of strata exposed outside of the Basin proper, in particular, the older rocks exposed south of Coal Mine Basin. Time constraints prevented expansion of the composite section to include these older rocks. The structural data collected during this study are summarized in Figure 3, a large-scale structural map. The area is gently and broadly folded or domed, with basaltic intrusions coincident with the north- south trending axis. The axis and flanks are severely block-faulted. Faulting, angular unconformities, and basaltic intrusions confirm that the area has been tectonically active since the Miocene. Locally useful marker beds in the Sucker Creek Formation include maar tuffs and volcanic sandstones. Further palynologic and mineralogic study must precede the identification of formation-wide marker beds or key fossil zones necessary for regional correlation. Detailed palynologic and mineralogic analyses have not been made. Local correlations are reliable; correlations to other areas of Sucker 47 48 Creek Formation exposures are only tentatively proposed. The eight stratigraphic sections of this study combined with those of the Type section and Devils Gate section should provide an excellent framework for future workers to establish intra-formational stratigraphic markers. Stratigraphic units or beds suspected of being useful for regional correlation have been suggested for further study. Features of interest discovered during field work include: maar tuffs; casts and molds of trees, permineralized tree stumps, and leaf impressions in shales; and turtle, oreodont, and fish fossils. Maar volcanism appears to have been common to the Coal Mine Basin, the McBride Creek area, the Type section, and the Devils Gate section during Sucker Creek time. The resultant tuffs formed locally useful marker beds and caused rapid burial of trees. REFERENCES Armstrong, R. L., 1978, Cenozoic igneous history of the U. S. Cordillera from latitude 42° to 49° N: in Smith, R. B., and Eaton, G. P., eds. , Cenozoic tectonics and regional geophysics of the western Cordillera: Geol. Soc. America Mem. 152, p. 1-31. Arnold, C.A., 1936a, The occurrence of Cedrela in the Miocene of western North America: Amer. Midl. Naturalist, v. 17, p.1018-1021. Arnold, C. A., 1936b, Some fossil species of Mahggig from the Tertiary of eastern and southeastern Oregon: Contr. Univ. Michigan Mus. Paleont., v. 5, p. 57-66. Arnold, C. A., 1937, Observations on the fossil flora of eastern and southeastern Oregon. Part 1: Contr. Univ. Michigan Mus. Paleont., v. 5, p. 79-102. Berry, E.W., 1932, A new Celtis from the western Miocene: Torreya v. 32, p. 40-42. Bradbury, J.P. and Krebs, W.N., 1982, Neogene and Quaternary lacustrine diatoms of the Snake River Basin, Idaho-Oregon, U.S.A: Acta Geologica Academiae Scientiarum Hungaricae, v. 25, p. 97-122. Brooks, B.W., 1935, Fossil plants from Sucker Creek, Idaho: Ann. Carnegie Museum, v. 24, p. 275-336. Chaney, R.W. and Axelrod, D.I., 1959, Miocene floras of the Columbia Plateau: Publ. Carnegie Inst. Washington, v. 617, 237 pp. Corcoran, R.E., Doak, R.A., Porter, P.W., Pritchert, F.I., and Privrasky, N.C. 1962, Geology of the Mitchell Butte quadrangle, Oregon: Geol. Map Series, GMS 2, Oregon Dept. Geol. Mineral Industries. Corcoran, R.E., and Walker, G.W., 1969, Geology of the Owyhee Upland Province, in Weissenborn, A.W. ed., Mineral and Water Resources of Oregon, Oregon Dept. Geol. and Mineral Industries Bull. 64. Cross, A.T. and Taggart, R.E., 1983, Causes of short-term sequential changes in fossil plant assemblages: some considerations based on a Miocene flora of the northwest United States: Ann. Missouri Bot. Garden, v. 69, p. 679-734. Ekren, E.B., McIntyre, D.H. Bennett, E.H., and Malde, H.E., 1981, Geologic map of Owyhee County, Idaho, west of longitude 116 degrees West: U.S.Geol. Survey Misc. Invest. Ser., Map I-1256. 49 50 Eubanks, W., 1966, Fossil woods supplement knowledge of the Succor Creek fossil flora: Ore Bin, v. 28, p. 173-181. Evenson, R.E., 1960, Hycalog well log of R.S. McKnight No. 1 wildcat, Sec. 23, T. 38., R. 6W, Owyhee Co., Idaho.: Core Drilling Inc. for Pan American Petrol. Corp., Oct. 5. Fields, P.F., 1983, A review of the Miocene stratigraphy of southwestern Idaho, with emphasis on the Fayette Formation and associated floras: MA Thesis (Paleont.), Univ. California, Berkeley, 363p. Fisher, R.V., 1961, Proposed classification of volcaniclastic sediments and rocks: Geol. Soc. America Bull., v. 72, p. 1409-1414. Goddard, E.N., Trask, P.D., Deford, R.K., Rove, O.N., Singewald, J.T., Jr. and Overbeck, R.M., 1951, Rock-Color Chart: Geol. Soc. America. Graham, A., 1963, Systematic revision of the Sucker Creek and Trout Creek Miocene floras of southeastern Oregon: Amer. J. Bot., v. 50, p 0 921-936 0 Graham, A., 1965, The Sucker Creek and Trout Creek Miocene floras of southeastern Oregon: Kent State Univ. Bull. Res. Ser., v. IX,53, 147p. Hart, W.K., Aronson, J.L., and Mertzman, S.A., 1984, Areal distribution and age of low-K, high-alumina olivine tholeiite magmatism in the northwestern Great Basin: Geol. Soc. America Bull., v. 95, p. 186- 195. Hay, R.L., 1952, The terminology of fine-grained detrital volcanic rocks: Jour. Sed. Petrology, v. 22, p. 119-120. Hay, R.L., 1978, Geologic occurrence of zeolites. pp. 135-143, t3 Sand, L.B.,and Mumpton, F.A., eds., Natural Zeolites: Occurrence Properties, Use, Pergamon Press, Ltd., Oxford, U.K., and New York, N.Y. Heiken, G.H., Fisher, R.V., and Peterson. N.V., 1981, A field trip to the maar volcanoes of the Fort Rock-Christmas Lake Valley Basin, Oregon; tg_Johnston, D.A., and Donnelly-Nolan, J., eds., Guides to some volcanic terranes in Washington, Idaho, Oregon,and Northern California: U.S. Geol. Survey Circ. 838, p. 119-137. Kittleman, L.R., 1962, Geology of the Owyhee Resevoir area, Oregon: Ph.D. Dissertation, Geology, Univ. of Oregon, Eugene, 174p. Kittleman, L.R., Green, A.R., Haddock, G.H., Hagood, A.R., Johnson, A.M., McMurray, J.M., Russell, R.G., Weeden, D.A., 1967, Geologic map of the Owyhee, region Malheur County, Oregon: Univ. Oregon Mus Nat. Hist. Bull. 8. 51 Kittleman, L.R., Green, A.R., Hagood, A.R, Johnson, A.M., McMurray, J.M., Russell, R.G. and Weeden, D.A., 1965, Cenozoic stratigraphy of the Owyhee region, southeastern Oregon: Univ. Oregon Mus. Nat. Hist. Bull., v. 1, 45p. Laursen, J.M. and Hammond, P.E., 1978, Summary of radiometric ages of Oregon, rocks supplement 1: July 1972 through December 1976: Isochron/West. no. 23, pp. 3, 18-19. Lindgren, W. and Drake, N.F., 1904, Description of the Silver City Quadrangle. Geologic Atlas of the U.S. Silver City, Idaho, Folio 104, U.S. Geol. Survey, p. 1-6, 3 maps. Lorenz, V., 1970, Some aspects of the eruption mechanism of the Big Hole maar, central Oregon: Geol. Soc. America Bull., v. 81, p. 1823-1830. Lorenz, V., 1971, An investigation of volcanic depressions. Part IV. Origin of Hole-in-the-ground, a maar in central Oregon: NASA Progress Report, NGR-38-OO3-012, 113p. Otto, B.R. and Hutchison, D.A., 1977, The geology of Jordan Craters, Malheur County, Oregon: Ore Bin, v. 39, p. 8. Peterson, N.V., and Groh, E.A., 1961, Hole-In-The-Ground, central Oregon, meteorite crater or volcanic explosion? Ore Bin, v. 23, p0 95-1000 Peterson, N.J., and Groh, E.A., 1963, Maars of south-central Oregon: Ore Bin, v. 25, p. 5. Romer, A.S., 1966, Vertebrate Paleontology, 3rd. ed., Univ. Chicago Press, p. 281, 389. Satchell, L.S., 1983, Patterns of disturbance and vegetation change in the Miocene Succor Creek flora (Oregon-Idaho): Ph,D. Dissert., Botany, Michigan State Univ., E. Lansing, 153 pp. Scharf, D.W., 1935, A Miocene mammalian fauna from Sucker Creek, southestern Oregon: Carnegie Inst. Wash. Publ., v. 453, p. 97-118. Schmidt, R., 1981, Descriptive nomenclature and classification of pyroclastic deposits and fragments: Recomendations of the IUGS Subcommission on the Systematics of Igneous rocks: Geology, v. 9, p. 41-43. Sheppard, R.A., Grude, A.J., Mumpton, F.A., 1983, An excursion to selected zeolite deposits in eastern Oregon, southwestern Idaho, and northwestern Nevada, and to the Tahoe-Truckee water reclamation plant, Truckee, California, July 7-10, 1983. in: Mumpton, F.A., ed. Zeo-trip '83., Intnl. Comm. on natural zeolites: State Univ. Coll., Brockport, N.Y., p. 25-31, 56-59. 52 Shotwell, J.A., 1968, Miocene mammalian faunas of southeastern Oregon: Univ. Oregon Mus. Nat. Hist. Bull., v. 14, p. 1-67. Smith, C.A., 1986, Coarse-grained nonmarine volcaniclastic sediment: terminology and depositional process: Geol. Soc. America Bull. V. 97, p. 1.10. Smith, H.V., 1938, Some new and interesting Late Tertiary plants from Sucker Creek, Idaho-Oregon boundary: Torrey Bot. Club Bull., V. 65, p0 557-5640 Smith, H.V., 1939, Additions to the fossil flora of Sucker Creek, Oregon: Papers Mich. Acad. Sci., Arts, Ltrs., v. 24, p. 107-120. Smith, H.V., 1940, Notes on the systematic and ecological relations of the Miocene flora of Sucker Creek, Oregon and Idaho: Amer. Midl. Naturalist, v. 24, p. 437-443. Taggart, R.E., 1971, Palynology and paleoecology of the Miocene Sucker Creek flora from the Oregon—Idaho boundary: PhD Dissert., Botany, Michigan State Univ., East Lansing, 196 pp. Taggart, R.E., 1973, Additions to the Miocene Sucker Creek flora of Oregon and Idaho: Amer. J. Bot., v. 60, p. 923-928. Taggart, R.E., and Cross, A.T., 1974, History of vegetation and paleoecology of upper Miocene Sucker Creek beds of eastern Oregon, 1g Sah, S.C.D. and A.T. Cross, A.T., eds., Symposium on Stratigraphic Palynology, Birbal Sahni Inst. Palaeobot. Spec. Publ. 3. Lucknow, India., p. 125-132. Taggart, R.E., and Cross, A.T., 1980, Vegetation change in the Miocene Succor Creek Flora of Oregon and Idaho: 6 case study in paleosuccession: in Dilcher, D.L. and Taylor, T.N., eds., Biostratigraphy of Fossil Plants: successional and paleoecological analyses: Dowden, Hutchinson & Ross, Stroudsburg, Penn., p. 185- 210. Taggart, R.E., Cross, A.T., Satchell, L., 1982, Effects of periodic volcanism on Miocene vegetation distribution in eastern Oregon and western Idaho: 3rd. N. Am. Paleont. Conv., Proc., v. 2, p. 535-540 Thorpe, R.S.,and Brown, G.C., 1985, The field description of igneous rocks: Open University Press, Milton Keynes, U.K., and Halsted Press, John Wiley & Sons, New York., 154 p. Wright, J.V., Smith, A.L., and Self, 8., 1980, A working terminology of pyroclastic deposits: Jour. Volcanology and Geothermal Regs, V. 8, p. 315-336. APPENDIX Figure 6. Symbols used in the stratigraphic sections. Lithologic Symbols jZ-Xttvf' .JZ__.'.'rr P ( -. . ' 3 ,{c v" I. . r‘“. I, \l Vitric volcanic ss Crystal-vitric volcanic ss Volcanic shale Conglcmerate Special Features Qiartzitic ss Arkosic ss Lignitic or carbonaceous Cross-bedding Parallel laminated Haatitic Gypsum (selenite) Mnned tabular crystals crystalline rosettes Cmtacts Sharp Unconfornable or irregular Fossils 12%) Root mottling Stumps Logs Branches leaves Manuals We Fish Turtle ,% Insects Rock Sample Collection Code: (MB = Coal Mine Basin Project 8-13-83 8 Morith-Day-Year I - Daily site ascensim number 3 8 Site sample ascension number Ebrample = (148 8-13-83 I 3 55 Figure 7-a."Iakebeds“unit. location 1, Figure 2. M Ft measured at locality 2, Figure 2. l treasured at locality 2, F' 2 igure resistant laminae - . measured at ‘7“ ‘ locality 1, ’ ‘ 2: - - _ Figure 2 ' 2 _ - l "' . v. ‘ sandstone carbol 1508005 I .. “ha-Ar? - 2" _“ volcanic m I, _"‘_—""l yellowish-gray ' __. T‘— (sure/1) when fresh H yellowish-gray (5Y7/2) when weathered (MB 8-25-83 I l . — a base of "takebeds' unit 56 FigureJ—b. 'Iakebeds'unit- Locality 2, Figure 2 ' ' sandstone, arkosic, volcanic channel lenses comm . us one, vitric-volcanic fine—gr amed grayish—yellow-green, (5917/2) well- indurated 5 an thick Exchert bed, "boamrk" ripples on-top, 4 on HF“— #conglanerate, pumice pebble, 4.5 an, white (N9) caxtinued Eran last page, Figure 7-a 57 ”Figure 7-c. "Lakebeds'unit. Locality 2, Figure 2. top of "lakebedsnunit (upper 22"= (MB 8-27-83 II 1) sandstone, arkosic, volcanic cross-bedded; dusky yellow (5Y6/4) continued below as Figure ‘7-b 58 Locality 2, Figure 2. "Delta" unit. Figure 8-a. continued above as n M m .....M m. ..m m. [P-PPnth _ "Delta"sandstoue sandstone, arkosic, bp_h.hp—.. a a . .- —-h-L l4 _ volcanic, del foresets 45' thi str' e = 350°, dip . 28.5°w o I C '1' sandstone, vol wp-p—_-..FPL._—.%PLL canic ly altered, tic, vol igni sandstone, l canic, severe thickness to 48" base of delta unit, Base of I — a d l- Eigure 8-b. "Delta" unit. locality 3, Figure 2. sandstone, arkosic, volcanic, massive .3, fine-grained, dusky-yellow (5Y6/4) _I‘d"- .31.- 048 8-22-84 II 1 sandstone, arkosic, volcanic, parallel-bedded, sane pebbles included g1 ..c "1:31 . ‘- a; e. ‘sf ‘ .’ I "‘ ’g '- J.,.s' ' . .Zf)"."‘;‘.’/ -‘ m)’ !: ...‘ .5463. ,t . .‘ . "‘-'."".“_'., ELI. ‘Iv‘ . A" ' sandstone, fine-grained, arkosic 3;-.. . volcanic, massive; noderate- -..~ .'_.j_. 311;: yellow-brown (lOYRS/B) ..‘7‘: "' ’v,‘ , ’ .’ QB 8-22-84 I 1 sandstone, volcanic, light-olive-brown (5Y5/6)above; upper grading down to pale-yellowish-brown (10YR6/2) sandstone, median-grained, quartzitic, white (N9) ‘”q“"‘-‘ _ sandstone, fine-grained, volcanic, greenish-'orange(lOYR7/4) as Figure B-a '3 I IIIII’IIUIIr'IUULlTUII‘IIIVVItIIUlT'UrTV'Ufi .L J A Figure 8-c. rU‘UflrrU'i‘YUUIr‘VU'II‘U‘ '71 (If (NB 8-14-83 I 2 60 "Delta" unit. locality 4, Figure 2. sandstone, arkosic,quar'tzitic, fine-to-medium-grained, white (N9): cross-beddded, with ironstone nodules J ~.. ...": sandstau. mm: ‘ ...; - volcanic; light-011V???” “VS/2’ 1““ W“ M" ,. -~ yeuw «ave/4) upper p... concretions sandstone, arkosic, quartzitic, fine- to coarse-grained, cross-bedded; white (N9); mafic grains near botton of cross- beds dusky-yellow (5Y6/4) :55? sandstone, volcanic, pale-olive (lOY6/2) when .- _-; fresh; grayish-yellow—green (5YG7/2) weathered '3' ’1’; lignites *3 (MB 8-14-83 I 1 weather to (lOYRB/ 2) sarxistme, arkosic, fine-grained volcanic, dusky-yellow when fresh, yellowish-gray (SW/2) weathered continued below as Figure g-b 61 'Figure 8-5. "Delta" unit. Locality 4, Figure 2. M F? shale, volcanic f‘ “22:15; pale-olive (10Y6/ 2) sandstone, quartzitic, ’é_ ’_ ~ , 17.3% 7'18‘33 I 4 fine-grained,grayish-yellow g ' ~ ‘ .‘ (MB 7-18-83 I 3 _,A If u I [frilliijlliv‘f'ltittlutrTlf'U'l'fi— I W _, semis, quartzitic, fine ' grained; grayish-yellow (5Y8/4) (MB 7-18-83 I 2 _ _ ’-" shale, volcanic, moderate-olive- ' 3' . brom (5114/4) ' ' (MB ‘7-18-83 I 1 _ sandstxme ~ - _ .._._.,£. . o arkosic, volcamc; 2,3- bimodal coarse quartz grains in ...;1:_,- volcanic sandstone matrix (fine -:.._: to silt size) ; light-olive- : bmvn <5v5/6) fresh: pale- . _-;; olive (lOY6/3) mathergj J A sandstone noderately canented quartz. fine to coarse, white (N9), cross-bedded I [—V'UIITr'TIUIUrl'UUrl'IrT'm'lf'Ir L grayish-yellow ( 5Y8/ 4 ) upper yellowish- gray ( 5Y7/2 ) lower sandstone, volcanic, continued below as Figure a-c 62 "Delta" unit. locality 5, Figure 2. Figure 8-e. continued above as Figure 8~f ‘ bl - E‘t 2‘.“x.; s3?" sandstone, volcanic, altered; if light-olive-brovm (sv5/6) ‘7’: on 7-19-83 I 2 ‘ m cross-bedded zones sandstone, volcanic, "f severely altered; grayish- _ yellow (SY8/4), moderately g; t; indurated :33." on 7-19-83 I 1 distinctive layer, sculpted ' sandstone, vitric-volcanic; weathered forms on slapes light-gray (N7) . o, (O. sandstcne, volcanic, moderate-yellow agglfz‘ (SW/6); bimodal: cobbles in sand matrix 4', sandstone, volcanic, grayish-yellow (5Y8/4) shale, volcanic, lt.-olive-brown (5Y5/6) dusky-yellow (5Y6/4) sandstone, volcanic, severely altered ..... moderate -yel low( SY‘I/ 6 ) ta ,’ - ' " ' sandstone, volcanic: grayish-yellow (5Y8/4) at locality 5, q _ I Figure 2 7 5’13".“ x“; CMB 7-18-83 I 5 LET-:33}: shale, volcanic, lt.-olive-brom (5175/6) ‘ ' - sandstone, quartzitic, fine-grained I— continued below as Figure 8-d 63 Figure 8-f. YDelta" unit. locality 5, Figure 2. top of "delta" unit sandstone, volcanic, severely altered moderate-greenish-yel low ( 10Y7/ 4 ) '5‘ ‘5 continued below as Figure a-e 64 Figure 9-a. "Antler" unit. localities 5 and 6, Figure 2. continued above as Figure 9‘b Z 3 sandstone, volcanic, fine- grained; 1t.-gray (N7) fresh; dusky-yellow (5Y6/4) weathered laminae 0.1-6 on thick I A I l ”llltlttlltfilrllltllllll'llTT 'lbp of "Antler" tuff above treasured at locality 6 upper acne of large angular basalt below measured at blocks over 50 on in diameter locality 5 "antler" tuff breccia lapillistone, dusky-y ellow (5Y6/4), moderately indurated, forms castella l 1.— "hoodoo" structures on _ weathering ,: angular basalt blocks to 10 an die. '— lower zone of large basalt blocks 4: J; angular basalt blocks to 8 on ‘2 tree molds and ._ casts, upright 4‘ and horizontal F at base of tuff is Base of section 9-a Base of "Antler” tuff 65 Figure 9‘b. "Antler" unit. locality 6, Figure 2. top of "antler" sandstone, volcanic fine-grained sandstone, volcanic, fine-gram aimed, yellowish-gray (5Y7/2) fresh sandstone, arkosic, volcanic sandstone, volcanic volcanic ash; 3 layers sandstone, volcanic selenite "rosettes" to * 6 on dia., lower 10' gyps'feruls 1 zone siltstcne, volcanic, basalt pebbles included sandstone, volcanic ' . shale, lcanic ,gypsiferous; twmned selenite dusky-yellow (SY6/4) crystals to 2 on / long continued from Figure 9-a. 66 Figure lO-a. "Sctmabel" unit. 2 localities 6 and 7, Figure 2. ..b 3 r l' -‘f‘;7,~~- L- sandstone, volcanic, inm 8-29-83 ‘. fine'grained :r.~ IV 2 : sardstone. volcanic, :~ ; ’ ' lt.-olive-gray (SYS/Z); git-“=23" saiflme. .. stileroidal was en . e'q'ft: vo canic L th ,I,‘~" _' 5Y8/1 ' .' ';.:-: _"0 ...:;‘:-¢;".: , sandstone. vitric-volcanic, 53:22::- gray (N8) . friable,- 5:553:33} weathers to SCUlptd 0. 4m»: {3.2.13.5 sandstme, volcanic, severely altered, I'U'UIVUUUIUUUUI'UUfi'UI'IUV' -~ l-".. v. fine-grained, 5%? - yellowish-gray (510/2) 3,-3.1: :5." 215:? .: . .12.:- sandstone, volcanic, fine- — =:"~"- «C. g§a}nali" BYE/1 um to .. A Isa-34R“ ofi 3&3 859i 1 .. fit" sandstone, vitric-volcanic, .— ' medium sand, light gray (N7). I F." . parallel lamina' ted upper _. -«"-. portions; cross-bedded lower, "_ gr}? ball and pillow structures .. 43‘§?. locally present; ‘r- .u%sh_- : fish—:17 "schnabel" ._ ”L r: sandstone '- ...—.n-u-‘I— :- ~ ~__~ ‘: ‘_ distinctive sandstone weathers ‘: .e - -' to form sculpted "knobs" and .. ..‘J—l- " overhangs : 3;:1—19"; occasional tree mold on basal J'- " “321%“ unconformity b ' ' m4£‘lh ° ottan of "schnabel" unit A 'iugure lo-b. "VVIVVVVIvafi I'U'V' IUD'U'T'UU'VUIVIUIIU 67 "Schnabel" unit. locality 7, Figure 2. ’e- :. o; . , arkosic, volcanic g-s‘cffi.‘ .‘ sandstone, quartzitic, 3% egg,” volcanic, arkosic, coarse- ,3». ""13, grained, basalt pebbles and 1n“?- .~ g" -.' gravel included, cross-bedded ‘3. g o. .. . -.32:-.'-;*~.-":.’:~ '2’:::.-‘:n>-..’.'- :-' 'o_.'.-U '. I I . 's-"J-r'. “21".?“- '-.' - - :o.'- ”" .--..‘.. ' s - .. a "'- {seer-4:5 shale, carbonaceous, lignitic sandstone, quartzitic, volcanic, medium-grained, cross-bedded dusky-yellow (516/ 4) sandstone, volcanic m . e, volcanic, indurated '31-;- .'?':§J." sandstme, volcanic, altered O ' . .. Etc. ' continued below as Figure 10 - a. 68 Figure 11- a. "Ymmgest sediments" unit. Locality 8, Figure 2. cmtinued above as Figure ll-b. M Ft - ‘ A sandstme, volcanic, v. fine-grained, a . n - . '._ yellowish-gray (SW/2), massive, mafic . . ‘- _‘ ., grain inclusions \4- .-. sardstaae, arkosic, volcanic, quartzitic, " X"; g.) lignitic, fine to median-grained, .._;5_-__.}...-_--* fines W ..4 '1‘: ... I. ' . . . ‘ . .' . .... sandstme, volcanic, lignitic, "ww' v. fine sand: yellowish-gray A . . . . ._:_- (SW/2’ I ' ' '31. a ' ' , ..X ' . ‘} sandstone, volcanic, "fair", . ‘ severely altered, : ’ N' ...m (MB 8‘28‘33 I 3: amber v. fine-grained, mssive- . '0, ,‘ ' A . - ~ "A or parallel-bedded, } I,-."_ R .. A" gypsuncrystals present " '. .-.° .?L{$a;fi '. l'yj' sandstone, volcanic, arkosic, . ...__ medium-grained, fines uward, TI" ’ mll—cetaxted near base; basal moanformity upper layers lignitic C143 8-28-83 I 2 sandstone, volcanic, severely altered, {L.,w :fzz'? base of ”youngest sediments" unit A A J— l Ullrliirt'vvvaIlII'YTII]UTII‘ITIIIIIIIIIIIUII 31, l l I’TrUT‘lUVU‘TlfiV'TUIUIIU'Ti'rl'TIUIIU'II 69 11 - b. "Yonmgest sediments“ unit. Location 8, Figure 2. continued above as Fig. ll-c sandstone, arkosic, volcanic, quartzitic, f ins-grained, sane muscovite sandstone, volcanic, f ine-grained, severely altered, sandstone, vitric-volcanic, Radian-grained“ white (N9), friable, gypsiferous, ledge-former, variable thickness 4'-8' (MB 8-29-83 I 2 sandstone, volcanic, v.-fine-grained, yellowish-gray (5Y7/2) , massive stone, quartzitic, well-cemented sandstone, volcanic, severely altered, v. fine-grained, yellowish-gray (5Y7/2), massive, mafic grains included; some lignitic zones continued fruu Figure 11 -a locality 8, Figure 2. 70 top of unit i w a m m Mic-Pleistocene sandstone, arkosic, volcanic, quartzitic, fine-grained "Youngest sediments" unit. Figure 11 - c. m M _ d L-n—P-nn—nnnb—hpnP—--.— bubblP dl q Pinb— J. Continued below as Figure ll-b