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

This session will assemble studies documenting microfossil presence and/or microfossil-generating taxa in extreme environments, widely defined present and past, and those elucidating adaptations employed by extremophiles, to inform interpretations of the geologic record.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 303C

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

Paper number: 213-5
Program: Technical Sessions
Time: 2:40 PM – 2:55 PM

Authors

  • Gracie Babineaux Presenting Author
    University of Louisiana at Lafayette, Lafayette, LA
  • Davide Oppo
    University of Louisiana at Lafayette, School of Geosciences, Lafayette, LA
  • Adam Skarke
    Mississippi State University, Starkville, Mississippi
  • Jeffrey Beeson
    Oregon State University, Cooperative Institute for Marine Ecosystem and Resource Studies (CIMERS), Corvalis, Oregon
  • Kaustubh Thirumalai
    University of Arizona, Tucson, Arizona

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 Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412676

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