A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA: II. Sedimentology, paleontology and geochemistry

Andrew Cohen, Manuel R. Palacios-Fest, Robert M. Negrini, Peter E. Wigand, Daniel B. Erbes

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

We have obtained a detailed paleoenvironmental record in the Summer Lake Basin, Oregon (northwestern Great Basin, US) spanning from 250 ka - 5 ka. This record is derived from core and outcrop sites extending from a proximal deltaic setting to near the modern depocenter. Lithostratigraphic, paleontologic (ostracodes and pollen) and geochemical indicators all provide evidence for hydroclimate and climate change over the study interval. Lithostratigraphic analysis of the Summer Lake deposits allows subdivision into a series of unconformity - or paraconformity-bound lithosomes. The unconformity and facies histories indicate that the lake underwent several major lake-level excursions through the Middle and Late Pleistocene. High stands occurred between-200 and-165 ka. between -89 and 50 ka and between -25 and 13 ka. Uppermost Pleistocene and Holocene sediments have been removed by deflation of the basin, with the exception of a thin veneer of late Holocene sediment. These high stands correspond closely with Marine Oxygen Isotope Stages 6, 4 and 2. within the margin of error associated with the Summer Lake age model. A major unconformity from -158 ka until -102 ka (duration varies between sites) interrupts the record at both core and outcrop sites. Lake level fluctuations, in turn are closely linked with TOC and salinity fluctuations, such that periods of lake high stands correlate with periods of relatively low productivity, fresher water and increased water inflow/evaporation ratios. Paleotemperature estimates based on palynology and geochemistry (Mg/Ca ratios in ostracodes) indicate an overall decrease in temperature from -236 ka-165 ka, with a brief interlude of warming and drying immediately after this (prior to the major uncomformity). This temperature decrease was superimposed on higher frequency variations in temperature that are not evident in the sediments deposited during the past 100 ka. Indicators disagree about temperatures immediately following the unconformity (-102-95 ka), but most suggest warmer temperatures between -100-89 ka, followed by a rapid and dramatic cooling event. Cooler conditions persisted throughout most of the remainder of the Pleistocene at Summer Lake, with the possible exception of brief warm intervals about 27-23 ka. Paleotemperature estimates for the proximal deltaic site are more erratic than for more distal sites, indicative of short term air temperature excursions that are buffered in deeper water. Estimates of paleotemperature from Mg/Ca ratios are generally in good agreement with evidence from upland palynology. However, there is a significant discordance between the upland pollen record and lake indicators with respect to paleoprecipitation for some parts of the record. Several possibilities may explain this discordance. We favor a direct link between lake level and salinity fluctuations and climate change, but we also recognize the possibility that some of these hydroclimate changes in the Summer Lake record may have resulted from episodic drainage captures of the Chewaucan River between the Summer Lake and Lake Abert basins.

Original languageEnglish (US)
Pages (from-to)151-182
Number of pages32
JournalJournal of Paleolimnology
Volume24
Issue number2
DOIs
StatePublished - 2000

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Sedimentology
paleontology
Geochemistry
geochemistry
sedimentology
paleoclimate
Lakes
lakes
summer
lake
unconformity
paleotemperature
lake level
Pleistocene
palynology
ostracod
temperature
outcrop
pollen
Catchments

Keywords

  • Great Basin
  • Ostracodes
  • Oxygen and carbon isotopes
  • Paleoclimate
  • Paleolimnology
  • Palynology
  • Pleistocene
  • Quaternary
  • Trace elements

ASJC Scopus subject areas

  • Aquatic Science
  • Environmental Science(all)
  • Environmental Chemistry

Cite this

A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA : II. Sedimentology, paleontology and geochemistry. / Cohen, Andrew; Palacios-Fest, Manuel R.; Negrini, Robert M.; Wigand, Peter E.; Erbes, Daniel B.

In: Journal of Paleolimnology, Vol. 24, No. 2, 2000, p. 151-182.

Research output: Contribution to journalArticle

Cohen, Andrew ; Palacios-Fest, Manuel R. ; Negrini, Robert M. ; Wigand, Peter E. ; Erbes, Daniel B. / A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA : II. Sedimentology, paleontology and geochemistry. In: Journal of Paleolimnology. 2000 ; Vol. 24, No. 2. pp. 151-182.
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N2 - We have obtained a detailed paleoenvironmental record in the Summer Lake Basin, Oregon (northwestern Great Basin, US) spanning from 250 ka - 5 ka. This record is derived from core and outcrop sites extending from a proximal deltaic setting to near the modern depocenter. Lithostratigraphic, paleontologic (ostracodes and pollen) and geochemical indicators all provide evidence for hydroclimate and climate change over the study interval. Lithostratigraphic analysis of the Summer Lake deposits allows subdivision into a series of unconformity - or paraconformity-bound lithosomes. The unconformity and facies histories indicate that the lake underwent several major lake-level excursions through the Middle and Late Pleistocene. High stands occurred between-200 and-165 ka. between -89 and 50 ka and between -25 and 13 ka. Uppermost Pleistocene and Holocene sediments have been removed by deflation of the basin, with the exception of a thin veneer of late Holocene sediment. These high stands correspond closely with Marine Oxygen Isotope Stages 6, 4 and 2. within the margin of error associated with the Summer Lake age model. A major unconformity from -158 ka until -102 ka (duration varies between sites) interrupts the record at both core and outcrop sites. Lake level fluctuations, in turn are closely linked with TOC and salinity fluctuations, such that periods of lake high stands correlate with periods of relatively low productivity, fresher water and increased water inflow/evaporation ratios. Paleotemperature estimates based on palynology and geochemistry (Mg/Ca ratios in ostracodes) indicate an overall decrease in temperature from -236 ka-165 ka, with a brief interlude of warming and drying immediately after this (prior to the major uncomformity). This temperature decrease was superimposed on higher frequency variations in temperature that are not evident in the sediments deposited during the past 100 ka. Indicators disagree about temperatures immediately following the unconformity (-102-95 ka), but most suggest warmer temperatures between -100-89 ka, followed by a rapid and dramatic cooling event. Cooler conditions persisted throughout most of the remainder of the Pleistocene at Summer Lake, with the possible exception of brief warm intervals about 27-23 ka. Paleotemperature estimates for the proximal deltaic site are more erratic than for more distal sites, indicative of short term air temperature excursions that are buffered in deeper water. Estimates of paleotemperature from Mg/Ca ratios are generally in good agreement with evidence from upland palynology. However, there is a significant discordance between the upland pollen record and lake indicators with respect to paleoprecipitation for some parts of the record. Several possibilities may explain this discordance. We favor a direct link between lake level and salinity fluctuations and climate change, but we also recognize the possibility that some of these hydroclimate changes in the Summer Lake record may have resulted from episodic drainage captures of the Chewaucan River between the Summer Lake and Lake Abert basins.

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