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Pdf/104/4/409/3381416/I0016-7606-104-4-409.Pdf by Guest on 27 September 2021 410 RIECK and OTHERS Magnetostratigraphy and tephrochronology of an upper Pliocene to Holocene record in lake sediments at Tulelake, northern California HUGH J. RIECK* U.S. Geological Survey, Flagstaff, Arizona 86001 ANDREI M. SARNA-WOJCICKI \ CHARLES E. MEYER 1 U.S. Geological Survey, Menlo Park, California 94025 DAVID P. ADAM j ABSTRACT correlation. Most of the tephra at Tulelake records eruptions from the nearby southern and central Cascade Range of Oregon and northern Combined paleomagnetic and tephra chronologies of one of the California, and the Medicine Lake Highland of northern California. most complete middle Pliocene through Holocene stratigraphic rec- Deposition took place during most of the past 3 m.y. within the Tule- ords yet recovered in western North America provide a reference lake basin; notable periods of slow or sporadic accumulation, or ero- section for much of northwestern North America and adjacent Pacific sion, occurred between about 620,000 and 200,000 yr B.P. and Ocean. Five long drill cores of lacustrine sediments at Tulelake, north- between about 2.5 and 2.1 Ma. Rapid deposition occurred during ern California, recovered a nearly continuous 331-m-thick record marine oxygen-isotope stage 6, between about 170 and 125 ka. Re- spanning the past 3 m.y. The Brunhes Normal-Polarity, Matuyama gional volcanism during the past 3 m.y. was markedly episodic, with Reversed-Polarity, and Gauss Normal-Polarity Chronozones are rec- notable volcanic activity from about 2.1 to 1.9 Ma and from 0.4 Ma to ognized; within these, the Jaramillo, Olduvai, Reunion(?), and the present. Kaena(?) Subchronozones are present. Six short stratigraphic inter- vals exhibit anomalous remanent inclinations that may record excur- INTRODUCTION sions and brief subchrons within the Brunhes and Matuyama Chronozones. Age estimates suggest correlation of five of the anoma- Detailed geologic records of late Neogene paleoclimates and past lous intervals with (1) one of the Biwa excursions at about 18,000 yr volcanic activity are becoming increasingly important to earth scientists B.P., (2) the Mono Lake excursion at about 27,000 yr B.P., (3) the attempting to determine the history and natural variability of climate Blake Reversed-Polarity Subchron at about 114,000 yr B.P., (4) the systems. Late Neogene climatic reconstructions and global-circulation Kamikatsura Normal-Polarity Subchron at about 850,000 yr B.P., and models are being developed to predict the timing and extent of climate (5) the Cobb Mountain Normal-Polarity Subchron at about 1.10 Ma. changes that may be anticipated in the near future. Concurrently, the Age of the sixth interval of anomalous inclination is broadly con- possible relation of volcanic activity and climatic response is being investi- strained between 117,000 and 180,000 yr B.P. gated. The predictive models must rely heavily on inferences drawn from Sixty-three individual tephra layers were characterized by geologic records. Viable attempts to reconstruct ancient ocean and electron-microprobe and X-ray fluorescence analyses of volcanic glass atmosphere-circulation patterns during climatic episodes significantly shards. Identified tephra of relatively well known age include (1) the warmer than any during the late Pleistocene must be based on an extensive basal airfall pumice at Llao Rock, 7015 yr B.P.; (2) the Trego Hot paleoclimatic data base from both marine and continental records. De- Springs Bed, 23,400 yr B.P.; (3) the Olema ash bed, between 55,000 tailed age control and precise correlation are essential for meaningful and 75,000 yr B.P.; (4) the airfall pumice at Goudcap Road ("Pumice interpretation of such records. Castle-like tephra 2"), about 120,000 yr B.P.; (5) the Rockland ash Five cores were drilled by the U.S. Geological Survey in a thick bed, about 410,000 yr B.P.; (6) the Lava Creek-B ash bed, 620,000 yr sequence of lacustrine sediments at Tulelake, northern California (Fig. 1). B.P.; (7) the Rio Dell ash bed, about 1.45 Ma; and (8) the Bear Gulch The objectives of drilling were to (1) provide a terrestrial record of late ash bed, about 1.9 Ma. A sedimentation-rate curve based on inde- Pliocene, Pleistocene, and Holocene climate change, (2) obtain a record of pendently dated tephra and polarity reversals is used to infer age late Cenozoic volcanic activity, and (3) establish a regional chronostrati- estimates of undated or previously unidentified ash beds. Some of graphic reference framework through which other, shorter or less complete these ash beds are found over large areas of the western United States terrestrial and marine records of paleoclimatic and volcanological events and eastern Pacific Ocean basin and provide widespread horizons for could be placed into temporal context. This temporal framework, together with geochemical, paleontological, and other studies (for example, Adam and others, 1986a, 1986b, 1987,1989), provides a basis for evaluation of * Present address: U.S. Geological Survey, M.S. 913, Box 25046, Federal large ancient lake systems, remnants of which are preserved over much of Center, Denver, Colorado 80025-0046. the western United States. The 331-m-thick record recovered at Tulelake Additional material for this article (Table A) may be secured free of charge by requesting Supplementary Data 9209 from the GSA Documents Secretary. Geological Society of America Bulletin, v. 104, p. 409-428, 8 figs., 4 tables, April 1992. 409 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/409/3381416/i0016-7606-104-4-409.pdf by guest on 27 September 2021 410 RIECK AND OTHERS 121 30 W OREGON Figure 1. Location of Tulelake LU drill site. Dashed line indicates ap- CD proximate limit of untilted lake sed- < iments. Solid lines and hachured < O CALIFORNIA < line mark traces of prominent > UJ north-northwest normal faults. QC Note that the Clear Lake shown here is not the same as the Clear LÜ Lake mentioned in the text, which is in Lake County, about 350 km to O < the south-southwest of Tulelake. OREGON O 42° N CO TULELAKE CALIFORNIA < • DRILL , , SITE i \ o CLEAR LAKE LAVA BEDS NAT'L. MON. (Quoternary basalts) 0 10 20 km offsets (McKee and others, 1983). Development of fault-scarp ridges, ^^ | MEDICINE coupled with damming of southward drainage by volcanic deposits, is LAKE thought to be responsible for the accumulation of at least 550 m of lake HIGHLANDS sediment in the Tulelake basin (Adam and others, 1986a, 1986b, 1987). The sedimentary record of this basin probably extends back to about the is one of the longest and most complete late Neogene stratigraphie records Miocene-Pliocene boundary. Deposition continued in the basin into his- from the western United States. toric time, when the lake was drained for fanning. We present here integrated paleomagnetic and tephrostratigraphic Five cores were drilled within about 30 m of each other in the town chronologies for the 3-m.y. record of events preserved in the Tulelake of Tulelake, at an elevation of about 1,220 m (Fig. 1). The drill site was section. The combined chronologies aid in deciphering late Neogene basin located close to the center of the Tulelake basin, near the Tulelake munici- development in the region, facilitate correlation of paleoclimatic informa- pal water well, for which the driller's log showed an ~500-m-thick se- tion among numerous terrestrial basins in the western United States, and quence of lake sediments. Overall, about 90% of the depositional sequence link contemporaneous deposits of the western coterminous United States was recovered. Short stratigraphic intervals from which core could not be and eastern Pacific Ocean. Results allow us to provide age estimates and recovered in one hole were often recovered in another; recovery was identify probable eruptive source areas for several tens of previously un- virtually complete for the multiple, overlapping cores in the upper 80 m identified tephra layers that may be widespread chronostratigraphic (Fig. 2). Bedding at the surface is horizontal, and consistent paleomagnetic markers and also provide a history of volcanism in the northwestern inclinations at depth, similar to those expected from horizontal beds, sug- United States for this time interval. gest that no appreciable tilting has taken place in the lower part of the cored section. GEOLOGIC SETTING Most of the cored section consists of mud and diatomite, although marl and a few slightly sandy and tuffaceous intervals also were noted Tulelake lies near the western margin of the Modoc Plateau (Mac- (Fig. 3). Regional volcanism, particularly in the southern and central donald, 1966), a region physiographically transitional between the Cascade Range of northern California and Oregon and in the Medicine southern Cascade Range to the west and the Basin and Range province to Lake Highland of northern California, has resulted in numerous tephra the east. A thick and little known sequence of interbedded upper Miocene layers throughout much of the section. A number of these are widespread to lower Pliocene basalt flows and sedimentary deposits underlies much of silicic tephra layers identified and independently dated at other sites, and the region. The overlying Pliocene through Holocene volcanic and sedi- they thus provide age control that serves to calibrate the magnetostrati- mentary rocks are widely exposed (McKee and others, 1983). Crustal graphic record at Tulelake. Conversely, the magnetostratigraphy and thinning by extension since middle Miocene time has produced numerous correlated dated tephra layers provide age constraints for previously un- north-northwest-trending normal faults with relatively small vertical dated tephra layers within the sediments of Tulelake. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/4/409/3381416/i0016-7606-104-4-409.pdf by guest on 27 September 2021 RECORD IN LAKE SEDIMENTS, TULELAKE, CALIFORNIA 411 Depth Dominant Lilhology Cm) O- Olive grciy clay — and silly clay • -WS-S • -¿¿k" •'••^gfji -lì 30- R « - ; ^ .
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