37-10 Reconstructing Aqueous Geochemistry and the Sedimentary Environment of Proglacial Paleolake Hitchcock using Carbonate Concretions

Session: Geoscience Research Poster Showcase by 2YC and 4YCU Undergraduate Students

Poster Booth No.: 133

Presenting Author:

Julio Melara

Authors:

Melara, Julio César¹, Piccione, Gavin², Edwards, Graham Harper³

(1) Earth & Environmental Geosciences, Trinity University, San Antonio, TX, USA, (2) Geology and Environmental Science, University of Pittsburgh, Pittsburgh, PA, USA, (3) Earth & Environmental Geosciences, Trinity University, San Antonio, TX, USA,

Abstract:

Modern climate warming has accelerated glacier retreat, resulting in the expansion of new proglacial lake systems that are highly sensitive to climatic and deglacial dynamics. Our work investigates the sedimentary and geochemical archives of an ancient proglacial lake to better understand these evolving environments. We focus on Glacial Lake Hitchcock (GLH), which occupied the Connecticut River Valley between approximately 18.2 and 12.5 ka, during the retreat of the Laurentide Ice Sheet after the last glacial maximum. While the sedimentary record has been well characterized by prior studies of the varved lake sediments, we examine carbonate concretions (which formed non-displacively within the varved sediments) to reconstruct the geochemical conditions of the proglacial sedimentary environment during and following deglaciation. 

We both used visual observations and energy-dispersive X-ray spectroscopy (EDS) to examine in situ geochemistry of concretions collected from varved GLH sediment outcrops in Connecticut and Vermont, representing earlier and later depositional periods, respectively. The Connecticut (southern) samples contain coarser-grained silicate and Fe-oxide detrital clasts as well as fine-grained, Fe- and Al-rich red clay minerals in a calcite-cemented matrix. The presence of coarse detrital grains indicates intermittent higher-energy depositional events capable of transporting larger clasts, or, more likely, transport and deposition of ice-rafted debris (IRD). In contrast, the Vermont (northern) samples are finer-grained and comprised of Al-rich clays in a calcite-cemented matrix, with concentric orange-brown growth rings that lack calcite cement, reflecting changes in redox chemistry in porewaters during concretion growth. 

The fine-grained clays cemented by the concretions reflect extensive chemical weathering and low-energy depositional conditions. The IRD in the Connecticut samples both suggest more ice-proximal conditions and may also have supported nucleation sites for concretion growth. In contrast, the concentric banding in the Vermont samples reflect noncontinuous concretion growth, likely regulated by changing redox conditions. Ongoing work includes U-series geochronology to better constrain the timescales of concretion growth following deposition of varved lake strata as well as carbon and oxygen isotope analyses of ostracod tests to infer lakewater compositions. These data will further develop our environmental and geochemical understanding of GLH.

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