12 Guaymas Basin and Gulf of California Subsurface Systems and Energy Applications

This session will present subsurface research in the Gulf of California, especially IODP Expedition 385 to Guaymas Basin that explored the linkages between tectonics, magmatism, sedimentation, hydrothermalism, carbon cycling, and microbial life. Merged sessions: Subsurface Research  in Guaymas Basin and the Gulf of California and Energy Resources and Economic Development in Baja California: Fossil, Renewable, and Transition Minerals.

Wednesday, 22 April 2026
1:30 PM - 5:30 PM
LMH, Isla Carmen

Trace metal enrichments as a biosignature of modern and ancient hypersaline microbial mats

Paper number: 12-9
Program: Technical Sessions
Time: 3:35 PM – 3:50 PM

Authors

Abstract

The fossil record indicates that microbial mats represent some of the earliest ecosystems on Earth, persisting for roughly 3.7 billion years, leaving characteristic sedimentary structures behind. A major challenge in confirming the biological origin of apparently biogenic sedimentary structures is the definition of robust biosignatures through comparisons between modern microbial mats and fossil stromatolites. Geochemical biosignatures, in particular, trace metal enrichments has been proposed as evidence of biological activity in both ancient and modern hypersaline microbial mats. However, it remains unclear whether these metal enrichments primarily result from seawater evapoconcentration or from biogeochemical processes intrinsic to the mats. In this study, we analyze a sedimentary core from the pristine hypersaline lagoon of Punta Cardón, Baja California, Mexico, which contained interstratified layers of microbial mats and sediments. Total metal concentrations (Metot) of Al, As, Ca, Cu, Fe, Mn, Mo, Pb, S, Sr, and Zn were measured using portable X-ray fluorescence analyzer, and Me/Al ratios, authigenic fractions, and enrichment factors (EFMe) were calculated using global shale and regional soil background values. Microbial mats were geochemically distinguished from the sediments by: (1) high Catot and low Altot; (2) Mn depletion, with EFMn values exceeding those of sediments; (3) EFFe and EFCu values comparable to background levels; and (4) substantial enrichments of Mo and Sr, with moderate enrichments of As and Pb. Mass balance calculations indicated that metals enter the lagoon through compensatory inflow from the Gulf of California, offsetting evaporative losses, and through episodic mobilization of lithogenic material during extreme rainfall events. Evapoconcentration promotes metal transport to the mat-water interface, whereas early diagenetic and biogeochemical processes regulate metal fixation in authigenic minerals phases within the microbial mats. We propose that EFMe, together with Catot concentrations, constitutes a robust geochemical biosignature capable of distinguishing microbial mats from sediments in modern hypersaline, oxic, anoxic, and anoxic-sulfidic environments, as well as differentiating microbially induced sedimentary structures from ancient sedimentary rocks. This biosignature may also contribute to the interpretation of metal-enriched sedimentary structures reported on the surface of Mars.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-411024

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