SHAPIRO, RUSSELL S.
Department of Geological Sciences, University of California, Santa Barbara, CA

Abstract: Microbialite Morphostratigraphy as a New Tool for Intrabasinal Correlation

Microbialite morphostratigraphy is a new, unique form of stratigraphy that utilizes the variability in microbialite (stromatolites, thrombolites, dendrolites, etc.) buildups to correlate time/rock sequences. Morphostratigraphy it is not simply lithostratigraphy or biostratigraphy, or even a marriage of the two. The model is based upon viewing each microbialitic buildup (=morphotype) as a unique recorder of the co-evolution of complex interactions that can be correlateable across large depositional realms. These factors include changes in the biota, sediments, and environmental parameters. The key point to the success of the model is that each of these factors varies through a defined time interval in either a linear, non-repetitive fashion or in a sigmoidal fashion that may or may not be repetitive. When viewed as a dynamic system, the multiple variations lead to a morphological succession that is non-repetitive over large temporal and spatial intervals (e.g., Phanerozoic stages and continental margins), thus the resultant multiple microbialite zonation is a linear, non-repetitive sequence.

As an illustration of the technique, six 'morphozones' and one 'morphosubzone' were segregated for the Late Cambrian and earliest Ordovician of the Great Basin, U.S.A. This zonation is a field-based approach and is defined on differences in the macro- and mesostructural attributes. The boundaries of the zones do not neccessarily follow major lithologic breaks. Morphostratigrapy can be a powerful tool in correlating Phanerozoic basins that contain abundant microbialites (e.g., Cambrian, Carboniferous) but lack other biostratigraphic control.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas