Quantitative Multivariate Analytical Strategy for Paleoenvironmental Analysis of Mixed Benthic Foraminiferal Assemblages

Abstract

Fossil assemblages of benthic foraminifera commonly contain taxa that were not associated together during life. A variety of processes act to modify living assemblages during the transition to fossil assemblages-transport of tests by traction and gravity currents, taphonomic filtering, and rapid shifting of environments in response to sea level fluctuations, to name a few. Unraveling the nature of faunal mixing can provide insights into depositional processes and paleoenvironmental history of particular lithofacies. A quantitative multivariate analytical strategy is presented to address these problems, using the late Cenozoic Yakataga Formation, Gulf of Alaska as a specific example. A variety of lithofacies are present within the Yakataga Formation including normal marine mudstones, sandstones, coquinas and conglomerates and glaciomarine diamictites. Comparison of fossil assemblages with modern foraminiferal distributions indicates significant faunal mixing in most lithofacies, particularly the diamictites. Quantitative analysis includes cluster analysis to define broad patterns in faunal similarity, R-mode factor analysis to define species interrelationships, and Q-mode polytopic vector analysis to 'unmix' the assemblages into their component biofacies. Two broad patterns of faunal mixing are identified: (1) comprehensive mixing of all possible biofacies within a particular bathymetric range and (2) mixing of very shallow (innermost neritic) with deeper (upper bathyal) assemblages,more » bypassing environments from outer neritic areas. Diamictites are shown to form in a variety of water depths from inner neritic to upper bathyal.« less