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Weidhaas, Nicholas (2017) A 25,000-YEAR LAKE LEVEL HISTORY OF LAKE JUNÍN, PERU FROM STRATIGRAPHIC AND OXYGEN ISOTOPE STUDIES. Master's Thesis, University of Pittsburgh. (Unpublished)

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The 2015 NSF-ICDP Junín drilling project recovered multiple long sediment cores (~100 m depth) from Lake Junín, Peru (~300 km2; 4085 m.a.s.l.; 11.0°S, 76.1°W; zmax~12 m). These cores span multiple glacial-interglacial cycles and are anticipated to provide the longest independently-dated record of hydroclimate, glacier variability, and paleomagnetic variation for the tropical Andes. To aid in accurate interpretation of the drill core stratigraphy, we investigated spatial variations in sediment composition by collecting 9 cores (1-9 m length) from Lake Junín across a paleoglacier proximal-distal (NE-SW) transect. Each core extends into glacigenic sediments, indicating recovery of the complete postglacial sequence (past ~22.5 ka). Most cores exhibit a four-component stratigraphy: a lower unit of gray glacial flour and minerogenic material sourced from glacial outwash fans to the NE, a lower-middle unit of organic-rich sediments with abundant grass, an upper-middle unit of transitional organic to carbonate sediments, and an upper unit of non-glacial sediments composed primarily of beige marl. We interpret these facies changes to reflect major changes in depositional environment and hydrologic conditions. Spatial variations in the age, thickness, and transition character among these units reflect the complex stratigraphy of a lake with such shallow water depth and high sensitivity to regional changes in hydrologic balance. Additionally, we identified at least four erosional unconformities in the shallow-water cores to the NE, indicating substantial changes in lake level. These unconformities were radiocarbon dated to provide “benchmarks” constraining past lake level. We combined our reconstructed lake level history based on sedimentary changes in composite core C-15/D-15 with the benchmarks of past lake level from erosional unconformities identified and dated from the transect cores to create a comprehensive model for lake level over the past 25,000 years called Junín Lake Level Index (LLI). We compare our interpretation of past lake level with local, regional, and interhemispheric records of past hydroclimatic variability. The trends observed in LLI over the past 25,000 years are largely dependent on the mean annual latitudinal location of the Intertropical Convergence Zone and its impact on the strength of the South American Summer Monsoon.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Weidhaas, Nicholasniw29@pitt.eduniw29
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairAbbott, Markmabbott1@pitt.edumabbott1
Committee MemberHarbert, Williamharbert@pitt.eduharbert
Committee MemberWerne, Josefjwerne@pitt.edujwerne
Date: 15 June 2017
Date Type: Publication
Defense Date: 31 March 2017
Approval Date: 15 June 2017
Submission Date: 11 April 2017
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Number of Pages: 61
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Geology and Planetary Science
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: Paleoclimate, lake, sediment, Andes, Peru
Date Deposited: 16 Jun 2017 00:17
Last Modified: 15 Jun 2022 05:15


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