Micrometer-scale porosity as a biosignature in carbonate crusts
- 1California Institute of Technology, MC 100-23, 1200 East California Boulevard, Pasadena, California 91125, USA
- 2Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089, USA
- 3California Institute of Technology, MC 100-23, 1200 East California Boulevard, Pasadena, California 91125, USA
Abstract
We formed calcite crusts in the presence and absence of the heterotrophic bacterium Desulfovibrio desulfuricans strain G20 to investigate microbial morphological signatures in fast-accreting carbonate precipitates. Submicrometer- to micrometer-sized pores (micropores) were present and ubiquitous in the G20 crusts but absent in abiotically precipitated crusts. Bacterial micropores resemble inclusions under transmitted light, but have distinct size, biological shapes and patterns (swirling or dendritic) and are distributed differently from common fluid inclusions. We observed similar porosity in both modern and ancient carbonate crusts of putative biotic origin. Our experiments support the microbial origin of micropores and help define specific criteria whereby to recognize these features as biosignatures in the rock record.
Footnotes
-
↵*Present address: Souza-Egipsy—Centro de Astrobiología CSIC-INTA, Ctra. Torrejón a Ajalvir Km 4, Torrejón de Ardoz 28850, Madrid, Spain. Newman—dkngps.caltech.edu
-
↵GSA Data Repository item 2004133, Figures DR1, larger-scale backscattered SEM image of 4-day old crusts (vertical cross section), DR2, confocal image of G20 cells on top of 3-day old crusts, and DR3, transmitted-light image of pore-filling carbonate cement within a cavity of Mount Dunfee stromatolite, is available online at www.geosociety.org/pubs/ft2004.htm, or on request from editinggeosociety.org or Documents Secretary, GSA, P.O. Box 9140, Boulder, CO 80301-9140, USA.
-
- Accepted May 18, 2004.
- Received March 18, 2004.
- Revision received May 17, 2004.
- Geological Society of America
