AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Major Characteristics of Lacustrine Stromatolites
(1) Earth Science, University of California, Santa Barbara, CA.
(2) Earth and Biological Sciences, Loma Linda University, Loma Linda, CA.
Stromatolites dominate the lacustrine microbialites record, with thrombolites constituting a minor component. Lacustrine stromatolites often look different from their marine counterparts. Lacustrine stromatolites are often morphologically variable within a bioherm or biostrome, they frequently exhibit macrolamination, often have moderately sharp boundaries between light and dark laminae, dark and light laminae are usually composed of calci-/dolo-micrite and calci-/dolo-siltite, respectively, and light laminae can be composed fibrous carbonate. Domical, columnar, and columnar-layered shapes dominate; whereas the Phanerozoic marine record is rich in domical, columnar, and flat-laminated stromatolites while the pre-Phanerozoic marine record is morphologically more diverse with domes, columns, branching columns, cones, and flat-laminated shapes common. Lacustrine oncoids are often larger than their marine counterparts and show similar lamina patterns as lacustrine stromatolites.
No single characteristic listed above can be used to recognize a lacustrine stromatolite. There is no smoking gun. However, the combination of two or more of these features increases the confidence that the stromatolite in question is lacustrine. This can be a key to recognizing a lacustrine versus marine depositional settings when other, more conventional indicators are lacking, such as in core material.