THE IMPORTANCE OF MICROBIAL BINDING IN NEOGENE-QUATERNARY STEEP SLOPES

摘要

The geometry and inclination of carbonate-platform slopes are typically described as the result of the sediment texture, components, and grain size occurring in the slope. Three carbonate slopes from the Holocene of the Tongue of the Ocean (Bahamas) and three slopes from an upper Miocene carbonate platform in SE Spain are investigated to identify the factors controlling dip angles. Although platforms differ in size and elevation with regard to the surrounding basin, both locations present slopes with linear profiles and steep angles over 35 degrees. The slope facies in both locations are very similar, with the matrix and some bioclasts presenting microfabrics that evidence microbial activity during deposition. These include (1) clotted micrite patches locally connecting bioclasts or infilling primary pores, (2) porostromate structures in the micrite, (3) dense micritic masses, (4) binding structures, (5) micritic crusts, and (6) peloidal textures. The Holocene and Miocene depositional geometries and facies distribution are the response to various sedimentary processes including rockfalls, gravity flows, and in situ carbonate production. Extensive microbial binding is identified as the controlling factor for early stabilization of the slope, which in combination with subsequent rapid cementation produces and maintains the steep slope angles. Consequently, microbial-induced stabilization of modern and Neogene slopes is as significant as in Paleozoic and Triassic examples.