14 Lake Sedimentary Records of Past Climate and Environment

This session will focus on lacustrine archives and reconstructions of past environmental changes through the use of geochemical, biological, and sedimentological proxies. Both modern and paleo proxy datasets are welcome.

Sunday, 22 March 2026
1:30 PM - 5:30 PM
CCC, Room 27

Detrital Contributions to Lake Junín (Peru) During Glacial Periods Revealed by Clumped Isotopes: Application of a Two-Point Δ47 Mixing Model to Mixed-Source Carbonate and Implications for Isotope-Based Paleoclimate Reconstructions

Paper number: 14-8
Program: Technical Sessions
Time: 3:50 PM – 4:10 PM

Authors

Abstract

Lacustrine carbonate oxygen isotope records are a powerful tool for reconstructing terrestrial hydroclimate. However, this approach often assumes lake carbonates are entirely authigenic, which is not always valid, especially if the lake catchment contains sources of detrital carbonate (e.g., carbonate bedrock). Although detrital carbonates in lake sediment records hinder isotope-based paleoclimate interpretations, it can be difficult to physically separate or screen for these contaminants using mineralogical or sedimentological means. Therefore, detrital carbonate is unaccounted for in many studies. Here, we demonstrate an approach to screen for detrital carbonate using carbonate clumped isotopes (Δ47) and a two-endmember mixing model which accounts for non-linear Δ47 mixing. We validate the model using a synthetic dataset and show that the proportion of bedrock within a bulk sample can be accurately estimated from bulk Δ47 values. Further, in some cases (e.g., when bedrock fraction is low and bedrock δ18O is precisely known), it may be possible to estimate the δ18O value of authigenic carbonate from the bulk δ18O value.

 

We then apply this approach to cores from Lake Junín, Peru. At Lake Junín, the clastic abundance within the bulk sediment is highest during glacial periods and minimal during interglacial periods. This implies that carbonates within the glacial intervals may be partially derived from limestone bedrock in the catchment. Local bedrock has an average Δ47 value of 0.484 ‰ (ICDES90), corresponding to a formation temperature of ~71°C, while modern authigenic carbonate from Lake Junín and other nearby lakes have average Δ47 and temperature values of 0.638 ‰ and ~11°C, respectively. We use these values to represent model endmember conditions for Lake Junín. For Lake Junín glacial sediments (e.g., Last Glacial, MIS 14, MIS 16), some samples have cooler Δ47-derived temperatures than modern lake carbonates, which we interpret as a primary climate signal. However, other glacial samples reflect warmer Δ47-derived temperatures (~20-50°C), which contradicts our expectations of local temperatures at the time. We interpret these anomalously warm samples as a mixture of authigenic and detrital carbonate, with the latter comprising up to ~60% of the total carbonate in the sample. Beyond application of this approach at Lake Junín, this framework can be readily adapted to evaluate detrital contaminants and improve the accuracy of paleoclimate reconstructions in other modern and ancient lake systems.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411164

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