T265 Lacustrine Systems across Space and Time (Posters)

Tuesday, 24 October 2017
9:00 AM - 6:30 PM
Halls 4EF

HOLOCENE HYDROCLIMATE AND SEDIMENTARY MAGNETISM FROM A GROUNDWATER FLOW-THROUGH LAKE, NORTHERN ROCKY MOUNTAINS, USA

Paper number: T265-9
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Sedimentary deposits in groundwater flow-through lakes can record important information about the interactions between regional hydroclimate, rates of groundwater recharge and discharge, and temporal changes in lake levels. The magnetic properties of lake sediments are particularly useful for reconstructions of environmental and climatic change due to the redox sensitivity of iron-bearing magnetic minerals that are deposited in lake basins (via erosion or eolian processes) or formed authigenically within lake sediments (e.g., magnetosomes from magnetotactic bacteria). Here, we present a sedimentary magnetic record from Jones Lake, Montana that reveals new insights about lake level changes and Holocene hydroclimate for the Northern Rocky Mountain region. Magnetic susceptibility, anhysteretic remanent magnetization (ARM), and isothermal remanent magnetization (IRM at 100 mT and saturating IRM, SIRM, at 1.5 T) reveal temporal trends in both the concentration of magnetic minerals (susceptibility, IRM, and SIRM) and the magnetic grain size (ARM/IRM ratio). There are two distinct intervals of fining magnetic grain size (increasing ARM/IRM ratio). The first, associated with relatively low concentrations of magnetic minerals (low susceptibility and IRM), begins near the onset of the Holocene (~11.5 kya) and continues until an abrupt coarsening in magnetic grain size (decrease in ARM/IRM) at 8.2 kya, a span including maximum Holocene aridity in the region. A second interval of fining magnetic grain size, this time associated with high concentrations of magnetic minerals (high susceptibility and IRM), begins ~ 3 kya and mostly persists to the present, coinciding with less-arid conditions in the region during the Neoglacial. We compare this magnetic record with a suite of geochemical, mineralogical, and isotopic data from Jones Lake to present a preliminary model for lake level fluctuations related to regional patterns of Holocene hydroclimate.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-306539

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