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213-5 Signals from the Seep: Foraminiferal Assemblages and δ¹³C Insights from the Chilean Margin

Session: Cushman Symposium: Microfossils of Extremophiles: Living in the Danger Zone

Presenting Author:

Gracie Babineaux

Authors:

Babineaux, Gracie¹, Oppo, Davide², Skarke, Adam³, Beeson, Jeffrey⁴, Thirumalai, Kaustubh⁵

(1) School of Geosciences, University of Louisiana at Lafayette, Lafayette, LA, USA, (2) University of Louisiana at Lafayette, School of Geosciences, Lafayette, LA, USA, (3) Mississippi State University, Starkville, Mississippi, USA, (4) Oregon State University, Cooperative Institute for Marine Ecosystem and Resource Studies (CIMERS), Corvalis, Oregon, USA; NOAA Pacific Marine Environmental Laboratory (PMEL), Newport, Oregon, USA, (5) University of Arizona, Tucson, Arizona, USA,

Abstract:

Benthic foraminifera are widely used in palaeoceanographic and paleoclimate reconstructions due to their ability to record environmental δ¹³C and δ¹⁸O signals during test calcification. However, most stable isotope studies focus on foraminifera from conventional marine settings, leaving a knowledge gap in extreme environments such as deep-sea methane seeps, where geochemical conditions differ significantly.

In this study, we use Individual Foraminiferal Analysis (IFA) to assess the intra- and inter-genus δ¹³C variability among living and dead calcareous benthic foraminifera and investigate their occurrence within microoxic, methane-influenced sediments. Push core samples were collected from two methane seep sites along the Chilean Margin—El Quisco (350 m water depth) and Mocha Island (~2500 m), the latter representing one of the deepest known active seeps in the region.

The samples are dominated by infaunal rotaliids such as Uvigerina spp., Bolivina spp., and Nonionoides spp., with low abundances of Miliolids, most of which are Quinqueloculina spp. Despite challenging conditions—including high alkalinity, low oxygen, and methane flux—live foraminifera are present at both sites. Rose Bengal staining indicates low living foraminiferal densities (∼3–5 individuals/cm³) with stained specimens primarily comprising Bolivina, Chilostomella, Nonionoides, and Uvigerina spp., suggesting tolerance for high-organic, microoxic microhabitats.

Preliminary IFA of Bolivina, Bulimina, Cibicidoides, Melonis, Pyrgo, Quinqueloculina, and Uvigerina individuals reveal distinct negative δ¹³C excursions across all analyzed genera, with values as low as -23‰ VPDB, indicating a strong methane influence on the sediments. Bulimina spp. are the most negative overall, with an average of -11.09 ‰, VPDB.

This work contributes to refining the application of benthic foraminifera as geochemical archives in methane-rich environments, provides information on the foraminiferal ecology of methane seeps, and informs paleoclimate reconstructions that rely on δ¹³C signatures from deep-sea seep settings.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7357

Signals from the Seep: Foraminiferal Assemblages and δ¹³C Insights from the Chilean Margin

Description

Session Format: Oral

Presentation Date: 10/21/2025

Presentation Start Time: 02:40 PM

Presentation Room: HBGCC, 303C

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