CARBONATE FACIES CONTROL ON THE FIDELITY OF SURFACE-SUBSURFACE AGREEMENT IN BENTHIC FORAMINIFERAL COMMUNITIES – IMPLICATIONS FOR INDEX-BASED PALEOECOLOGY

Recent work on the paleoecology of mass extinctions and their aftermath has used mainly quantitative, index-based methods to examine patterns of extinction and subsequent recovery. Studies typically employ an equal area approach to calculate a variety of dominance, evenness and diversity indices through stratigraphic sections that include an extinction event and its immediate aftermath. However, many large-scale ecological crises, in particular the end-Permian event in Tethys, are recorded in carbonate-dominated environments and coincide with a dramatic change in sedimentary regime. The taphonomic biases associated with carbonate facies boundaries remain poorly explored and may have profound implications for the results of index-based studies.

In order to explore the reliability of bedding plane and thin section-based assemblages as indices of ecological change, the agreement between surface and subsurface benthic foraminiferal assemblages in a variety of carbonate depositional environments and energy settings was investigated. Sediment surface foraminiferal assemblages were compared with those recovered in cores at depths of 30 to 50 cm, simulating the transition from in situ living community to fossil assemblage. Good agreement was found for all samples in all environments, indicating minimal facies bias and facies influence on fossil communities. The results provide significant statistical support for the following assertions: 1. Different carbonate depositional settings host distinct communities, but preserve them with equal and high fidelity; 2. In both low- and high-energy carbonate settings, taphonomic processes involved in the transition from living assemblage to fossil record do not introduce significant biases that affect paleoecological indices. Thus quantitative paleoecological methods can be used through stratigraphic and facies boundaries without statistical correction. This work further demonstrates that benthic foraminifera are an ideal basis for studying rates and patterns of extinction and subsequent recovery.