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Revisions to the Cenozoic Stratigraphy of Harney Basin, Southeastern Oregon

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Revisions to the Cenozoic Stratigraphy of Harney Basin, Southeastern Oregon Revisions to the Cenozoic Stratigraphy of Harney Basin, Southeastern Oregon *s GEOLOGICAL SURVEY BULLETIN 1475 'if Revisions to the Cenozoic Stratigraphy of Harney Basin, Southeastern Oregon By GEORGE W. WALKER GEOLOGICAL SURVEY BULLETIN 1475 A formal designation and description of three major units of volcanic rocks with extensive regional correlations throughout southeastern Oregon UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1979 UNITED STATES DEPARTMENT OF THE INTERIOR CECIL D. ANDRUS, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Catalog in Publication Data Walker, George Walton, 1921- Revisions to the Cenozoic stratigraphy of Harney basin, southeastern Oregon. (Geological Survey bulletin ; 1475) Bibliography: p. 33-35. 1. Geology, Stratigraphic-Cenozoic. 2. Geology-Oregon. I. Title. II. Series: United States. Geological Survey. Bulletin ; 1475. QE75.B9 "no. 1475 [QE690] 557.3'08s [551.7'8'0979595] 79-23867 For sale by the Superintendent of Documents, U. S. Government Printing OfRce Washington, D. C. 20402 Stock Number 024-001-03249-0 CONTENTS Page Abstract _____________________-_-_-___ _. 1 Introduction ____________________________ ______ 1 The depositional basin______-_______________ - _ _ 5 Stratigraphy ______________________________ _ _ 6 Miocene rocks_________________________ ________ 7 Intrusive and extrusive silicic rocks 7 Basalt and andesite ________________________________ 9 Volcaniclastic and sedimentary rocks ___ _______- _ . 12 Ash-flow tuffs and related rocks ___________ _ _ 12 Devine Canyon Ash-flow Tuff _ _____._____ _ ____ 15 Prater Creek Ash-flow Tuff ________________________ 20 Rattlesnake Ash-flow Tuff _______________________ 23 Pliocene Rocks __________________________________ 27 Regional correlations ____________________________________ 31 References cited __________________________________ 33 ILLUSTRATIONS PLATE 1. Stratigraphic columns showing regional correlation of middle and late Cenozoic units of Harney Basin and adjacent areas _ In pocket FIGURE 1. Index map of Harney Basin, Oregon, and adjacent areas _______ 2 2. Diagram showing Cenozoic lithologic units of Harney Basin ____ 2 3. Map showing distribution and potassium-argon ages of rhyolite domes 8 4. Photograph of Keg Springs Valley ___________________ 14 5. Map showing distribution of the Devine Canyon Ash-flow Tuff ___ 16 6. Photograph showing welded columnar part of the Devine Canyon Ash-flow Tuff exposed in Devine Canyon _ __________ _ 17 7. Plot of potassium-argon ages, including analytical errors ______ 19 8. Map showing approximate distribution of Prater Creek Ash-flow Tuff _______________________________ 21 9. Photographic view north along Poison Creek Canyon near its junction with Devine Canyon, showing the Prater Creek Ash-flow Tuff ____________________ 22 10. Map showing distribution of the Rattlesnake Ash-flow Tuff _____ 24 11. Photograph showing type locality of the Rattlesnake Ash-flow Tuff _ 26 TABLES Page TABLE 1. Potassium-argon ages on selected volcanic units of Harney Basin and adjacent areas ______________________ _ ____ 18 2. Average chemical composition of the Devine Canyon, Prater Creek, and Rattlesnake Ash-flow Tuffs ____________________ 19 3. Revisions to stratigraphic nomenclature _______ ____________ 28 ill REVISIONS TO THE CENOZOIC STRATIGRAPHY OF HARNEY BASIN, SOUTHEASTERN OREGON By GEORGE W. WALKER ABSTRACT Harney Basin in southeastern Oregon has persisted as a site of deposition during essentially all of late Cenozoic time; the basin is filled with a sequence of continental volcanic, volcaniclastic, and tuffaceous sedimentary rocks derived from voluminous and widespread basaltic and rhyolitic volcanism. Many rock units are confined to small areas of Harney Basin, whereas others extend beyond the limits of the basin. Included among the latter are a few thick prisms of basalt and related palagonite tuffs, and several late Miocene ash-flow tuffs that cover tens of thousands of square kilometers in eastern Oregon. The ash-flow tuffs, which represent unique time-stratigraphic marker horizons, occur in lithologic sequences within a number of neighboring depositional basins, where they have been given various formal and informal formational names. In order to clarify the stratigraphic nomenclature of Harney Basin and adjacent regions, three of the ash-flow tuffs the Devine Canyon Ash-flow Tuff, the Prater Creek Ash-flow Tuff, and the Rattlesnake Ash-flow Tuff are redefined as formations. In this report their distribution and relations to other stratigraphic units are described, and the terminology of other formational units of which they formerly were a part is revised. INTRODUCTION Geologic mapping, petrographic studies, and potassium-argon dat­ ing of the Cenozoic rocks in and adjacent to Harney Basin, southeast­ ern Oregon, in the 1960's and early 1970's, provide a basis for estab­ lishing a late Cenozoic stratigraphic sequence of the region (fig. 1) in greater detail and precision than heretofore possible. This work also permits clarification and simplification of the current regional stratigraphic nomenclature, particularly where identical units of east-central Oregon have been given several different formal or in­ formal formational names. In this report the terminology of silicic volcanic rocks in Harney Basin is updated, and some minor modifications are made in subdivi­ sion of the stratigraphic column into formational units. Potassium- argon ages have been obtained on some units, and several new names are applied to regionally extensive and distinctive lithologic units within the stratigraphic section (see comparison of old and new names in fig. 2). However, I do not intend to give a complete and CENOZOIC STRATIGRAPHY OF HARNEY BASIN, OREGON 120° 119° 118° 44° 43° APPROXIMATE LIMIT OF BC QC Frenchglen HARNEY BASIN JHARNEY COUNTY /; ,AKE CO BJ I v O CV \V/.<£ u til WV I & GS HM 0 10 20 30 40 KILOMETERS 0 10 20 MILES FIGURE 1. Index map of Harney Basin, Oregon, and adjacent areas. AL, Alkali Lake; AM, Alsup Mountain; BC, Bacon Camp; BV, Bear Valley; BJ, Blue Joint Lake; BB, Burns Butte; BZ, Buzzard Creek; CB, Calamity Butte; CR, Castle Rock; CV, Catlow Valley; CP, Coffee Pot Creek; CM, Coleman Mountain; CH, Crowcamp Hills; DC, Devine Canyon; DG, Dog Mountain; DO, Double O Ranch; DM, Dry Mountain; DB, Duck Butte; ER, Egli Ridge; FF, Follyfarm; GB, Glass Buttes; GS, Guano Slough; HM, Hart Mountain; IM, Iron Mountain; JM, Jackass Mountain; KS, Keg Springs Valley; LV, Logan Valley; MB, Mackey Butte; OC, Orijana Canyon; PB, Palomino Buttes; PV, Paulina Valley; PC, Poison Creek; PR, Prater Creek; RC, Rattlesnake Creek; RM, Riddle Mountain; SH, Sagehen Hills; ShM, Sheep Mountain; SC, Soldier Creek; SM, Snow Mountain; SW, Stinking Water Mountain (Pass); WM, Wagontire Mountain; WV, Warner Valley; WP, Wrights Point. INTRODUCTION A. B. Epoch 1 Generalized stratigraphic Recommended lithologic section K-Ar dates section from Piper, Robinson, bound­ n millions and Park (1939, p. 25 - 26) aries for Harney Basin 2 of years c f. Valley fill and comtem- Alluvium, fanglomerate, and 0) g poraneous basalt near § c ___du£e and playa deposits iasalt andTracp^- - ^_ mental ejects- «=.*" . ^- c Diamond Sl­ Lacustrine and 01 Basalt and basaltic ot C fluviatile -^ ^=--^~ 0) ejectamenta near Voltage o _ _ _ _ ^pHimPnt"=^2livme bas ^ lt * 1.8 o and near Mines seoirncni - L-_ ^ ~" '5 Terrace deposits Wrights Point Member ~ 2.4-2.6 a. 1 01 i vine basa_U__S 0) a ^_s ^==~' C o> oTuTfaceous and palagonitic.sed- <B Harney Formation o c o <U > iments; includes lenses of ba- 8 °- E saltic vent ejecta, fanglomer- Fanglomerate near 0. 1 ate, and minor conglomerate Coffeepot Creek NUnconformity?/ Rattlesnake Ash-flow Tuff __ _ -5.4-6.8 Tuffaceous sediments__^= and tuffs; .^sSSl^and andesite (D c _ locally altered and zeolitized~ O) 8 Danforth Formation Basalt and andesittu^' a. ' PrateTCree^k^sh-IiayvIIint -8.2-8.6 Tuffaceous sedimentary rocks __ De^vTne~Cany^on Ash-fljw Tuff _ _ 8.5-10.0 VolcaniclastTc^-s^ostly dikty^ Unconformity -^, 01 c rocks (ashy and g~Easalt 8 ^-^-^-^jumiceous ) ?"^-? I ~-^~' _ ___ _ Basalt and andesite. lncluois~ 7 01 c Steens Basalt and probably 12.1 0) '' Steens Basalt parts of Steens Mountain Volcanic Series of Fuller (1931); also, unnamed 14.5-15.5 igneous complex of Haddock (1967) and of Kittleman and 7 others (1965, 1967). 19.4 Unconformity- 7 * ^^\. 7 r^. ____ 0) ~v ^Tjjff . sedimen « 22.5 Older siliceous C c a> Intrusive and extrusive"" ~~^ 8 extrusive rocks 5 m~ silicic rocks _^_ Unconformity - -> ->7777? 7 Pre:Ter'tiary rocks' Pre-Tertiary rocks> 1 From Berggren and Van Couvering (1974). undifferentiated 2 Does not include post-early Miocene intru­ sive and near-vent extrusive accumulations FIGURE 2. Cenozoic lithologic units of Harney Basin. comprehensive summary of the lithologic and stratigraphic succes­ sion of Cenozoic rocks in Harney Basin, inasmuch as many of the available data are of a reconnaissance nature only. Cenozoic units exposed in and marginal to Harney Basin consist of continental volcanic, volcaniclastic, and sedimentary rocks of late 4 CENOZOIC STRATIGRAPHY OF HARNEY BASIN, OREGON Oligocene and younger age,1 several of which are traceable into adja­ cent depositional basins where they have been given various forma- tional names. Some units, particularly late Miocene ash-flow tuffs that formed during a brief interval, can be traced over many thousands of square kilometers and are sufficiently distinctive lithologically to be useful as key time-stratigraphic
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