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DOGAMI Bulletin 83, Eocene Stratigraphy of Southwestern Oregon

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DOGAMI Bulletin 83, Eocene Stratigraphy of Southwestern Oregon EOCENE STRATIGRAPHY OF SOUTHWESTERN OREGON 1974 STATE OF OREGON DEPARTMENT OF GEOLOGY AND MI NERAL INDUSTRIES l 069 State Office Building , Portland, Oregon 97201 BULLETIN 83 EOCENE STRATIGRAPHY OF SOUTHWEST ERN OREGON Ew art M. Baldwin Department of Geology University of Oregon GOVERNING BOARD R. W. deWeese, Chairman, Port land Wil liam E. Mil ler Bend H. Lyle Van Gordon Grants Pass STATE GEOLOGIST R. E. Corcoran 1974 FOREWORD So uthwestern Oregon has had a long history of mineral production dating back to the 1850's. Coal was discovered in Eocene marine sediments of the southern Coast Ra nge near Coos Bay in 1854. By 1880, when records were first kept, production was about 40, 000 tons a year, and for 15 years annua I production ranged between 30, 000 and 75, 000 tons. Sh ortly after th e turn of the century , pe troleum discoveries in Cal­ ifornia caused most rai lroad and steamship lines on the West Coast to switch to fuel oil, and coalmining at Coos Bay declined rapidly. The first detai I ed survey of the Coos County coo Is was made in 1896 for the U.S. Geological Su rvey by J. S. Dil ler. In the course of his studies, Dil ler compi led sev­ eral geologic maps and reports showing the exten t of the Eocene rocks and named and described many of the stratigraph ic units. His work forms the basis of all subsequent investigations on the Tertiary stratigraphy of the Coast Range and encouraged subse­ quent search for oi I and gas in western Oregon . In more recent years, Dr . E. M. Ba ldwin and severa l of his graduate students in the Departm ent of Geology at the University of Oregon have remapped in greater detail most of Coos County and adjoining parts of Doug las, Josephine, and Curry Counties . The origina l formations proposed by Diller have been revised and redefined so as to provide a clearer understanding of th E( Cenozoi c; structure and stratigraphy of the southern Coast Range. Their report comes at an especially appropriate time now that there is renewed interest in the Coos Bay coals and th e petroleum po tential of these marine sediments. R. E. Corcoran State Geologist July 1974 ii CONTENTS FOREWORD ii INTRODUCTION ------------------------------- 1 -- Location and access ------------------------- 1 -- - Previous work ------ -------------------- -- 1 Acknowledgments ---- -- --- - --- ----- ----- ----- 3 STRATIGRAPHY ----------------- ---- ----------- 5 Genera I discu ssion 5 - Pre Tertiary forma tions ---------- --------- ----- 6 Roseburg Forma tion ------- -------------------- 6 Description ------------------- -- -------- 6 Age and correlation --- - - - ------- -------- -- 8 Deformation -- - ---------·---- --- ---------- 10 Size and shape of the basin ------------------- 12 ----- - Lookingglass Formation ------------------- 12 Description ----- ------------------- ----- 12 Bushnell Rock Member -- -------- ------------ 12 T enm i I e Mem ber - ------------------------- 14 OlallaCreek Member ------- -------------- - 14 Age and correlation -- ---- - -- --------------- 16 Size and sh ape of the basin ---- - --- ----- ----- 16 Flournoy Forma tion ------------------------ --- 18 Description ------------ ----- --- -- ------- 18 White Tail Ridge Mem ber --- ----------------- 18 Camas Valley Member - - ------------ -------- 19 Age and correlati -- -------- - --- -- - on ------ - 19 Size ---- - - - - and shape of the basin - ---- ----- 19 Tyee Formation -------- ------- ------- - ------- 20 Description -- ------ - - ------------------- 20 Tyee Mountain Member ------------------ --- 22 Hubbard Creek Member ----- -- -------------- 22 Baughman Member ----- -------------------- 22 Age and correlation ---------------- - - ------ 22 Size and shape of the basin -- -- -- ----------- -- 23 Elkton Formation -- ------ ------------------- -- 25 Description ------ ---- -- ---- ------------- 25 Age and correlation ------------------ -- --- 25 Size -- ------- --- a nd sh ape of th e ba sin --- ---- 27 iii ST RATIGRAPHY, continued Bateman Formati on -- ------------------------ 27 Description ---------- ------------------ 27 Ag e and correlation ---------------------- 28 Si ze and shape ofthe basin -------------- --- 2 8 Coa l edo Formation -------------------------- 28 Description - --------------------- - - --- 28 Ag e and corre lation ----------------------- 30 Si ze and shape of the basin --------- --------- 30 Sp encer Formation 30 Celestin Forma tion 30 Bastendorff Formation 32 Description ------ ---------------------­ 32 Age and Correlation ---------------------­ 33 Si ze and shape of the basin ----- ------- ----- 33 In trusive Ig neous ro cks 33 Post- Eocene Formations 33 TECTONIC HIST ORY --------------------------- I 34 SOME REMAIN ING PROBLEMS --------------------- 36 ------- BIB LIOGRAPHY ------------------------ 3 7 iv ILL USTRATIONS Figures 1. Index map of areas geo logica lly mapped ---- ----------- - 2 2. Stratigraph ic chart for southwestern Oregon ------------- 4 3. Roseburg Formation; low -dipping beds near axis of syncline ---- 7 4. Contorted beds of Roseburg Formation along Umpqua River 11 5. Steeply tilted Roseburg strata at Coos Bay Wagon Road and Burnt Ridge Road - - -------- - - ---- - - - - - - --- 11 6. Pa l eogeographic map of Roseburg, Lookingglass, and Flournoy Formations ------- ---------- - - - - ----- 13 7. Contact between Roseburg and Lookingglass Formations --- --- 15 8. Bushnell Rock Mem ber unconformably overlying Roseburg stra ta - 15 9. Lookingglass strata of the Tenmile Member along Rock Creek Road 17 1 D. Tyee escarpm ent, and Camas Valley and White Ta il Ridge Members of Flournoy Formation ------------------- 17 11. Base of th e Tyee Formation upon Lookingglass strata -------- 21 - 12. Tyee Formation at Golden Falls ------ ------ - ------- 21 13. Pal eogeographic map of Tyee, Elkton, and Bateman Formations - 24 14. Sacchi Beach and va lley of Fivemile Creek underlain by Elkton Formation --------- - - ----- --- ---- ---- - 26 15. Coaledo Formation crops out from Cape Arago Ligh thouse to Cape A raga ------------ -- - --- ----- - - - - - - 29 16. Pa l eogeographic map of Coa ledo, Celestin , Spencer, and Bastendorff Formations ------------------------ 31 17. Conglomerate in Celestin Formation on Whiterock Road 32 Geologic Map Eocene stratigraphy of sou thwestern Oregon; in pocket inc luding cross sections v EOCENE STRAT I GRAPHY OF SOUTHWESTERN OREGON Ewart M. Baldwin I NTRODUCTI ON Geologic in terest in southwestern Oregon stemmed from early discoveries of gold and oth er metals in lode and placer deposits in and along the northern margin of the Klamath Mountains. Coal was dis­ covered in the Coos Ba y are a about 1854 , and later a se arch for co mmercia l deposit s of oil and gas fo cused intere st on the early Ce nozoic strata. Geo logic mapping accompanied by studies of the mega- and micro­ fau nas aided in determining the distribution and age of the stratigraphic units. The process of refin ing our knowledge of the geology of the area has co ntinued and the revised stratigraphy presented here is a further attempt to explain geologic events. Locati on and Acce ss The area mapped lies largely at the south end of the Oregon Coa st Range, where it borders the pre-Te rtiary formations of the Klamath Mountains and, in addition, the broad UmpCjua Va lley to the foot hil ls of the Ca scade Range. Although the Klamath pre-Te rtiar y strata occupy only a sma ll part of the area (see Geologic Map), they acted as a major source of sediments, and their Ce nozoic tectonic history is interwoven with that of the se dimentary basins that reached northward from the Klamath Mountains into Washington . Exposures in the Coast Range are largely a long government and pr ivate timber access roads and along the streams. Exposures vary in accessibility and usefu lness. The region is covered in most places by brush and a thick man tie of weath ered rock . Annual rainfa ll ranges from an average of 55 inches at Coos Bay to more than 100 inch es in parts of the Coa st Range and th en diminishes to approximately 32 inches at Roseburg . Previous Wo rk Pioneer geologic work was done in this area by Dil ler (1898, 1899 , 1901, 1903�who named and described many of the st ratigraphic units. Turner ( 1938) described se lected stratigraphic se ctions and the Eocene megafaunas. His work has been very usefu l in this st udy. Al len and Baldwin (1944) mapped the Co os Bay co al field. Weaver and others (1944) zoned the West Coast Ce nozoic formations, and We aver (1945) descr ibed the coastal exposure s and listed megafaunas. Microfaunas of the Coa ledo Formation were descr ibed by Detling (194 6) and Cu shman, Stewart and Stewart (1947). Other microfaunas have been identified by Stewart (1957), Thoms (1965), Bird (1967) , and Ra u (w ritten communication). Hoover (1963) described the geology of the Drain and Anlauf Cjuadrangles in the northeast co rner of the area mapped. His co ntacts are little changed but the Umpq ua strata are reassigned. Baldwin (1964, 1965, and 1966) discussed aspects of early Cenozoic revisions leading up to this report. Pr evious mapping in the area includes studies on the Elkton, Scottsburg, and Reedsport quadrangles in the northern edge (Baldwin 1961 ), the Myrtle Point, Coos County area (Baldwin 1969), and the Pow ers quadrang le (Bal dwin and Hess 1971 ). Dott (1965) discussed the tectonic history o f the Klamat h Mountains, and Dott (1966) described the Co aledo Formation, it s pe trograph y and environment of deposition. Dott (1971) summarized the re sults of a Univer­ sity of Wisconsin mapping
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