Ichnologic Applications in Paleoceanographic, Paleoclimatic, and Sea-Level Studies

Abstract

Continued growth of ichnology over the last decade is reflected not only by an expanded realm of applications but also by the emergence of more holistic approaches involving the ichnofabric concept. Both of these trends are exemplified by recent ichnologic applications in paleoceanographic, paleoclimatologic, and sequence stratigraphic studies. Ichnofabrics and representative ichnocoenoses in pelagic/hemipelagic strata provide the basis for reconstructing benthic oxygenation histories of marine basins. Recent studies demonstrate that oxygen-related ichnocoenoses, when mapped within lithochronostratigraphic units, can help recognize spatial paleo-oxygenation gradients that reflect intrabasinal variations in circulation and govern organic matter accumulation. When cointerpreted with sedimentologic data, ichnology-based paleooxygenation histories also can be used to recognize and interpret paleoceanographic cycles and events, particularly those linked to climatic perturbations such as Milankovitch rhythms and El Nino-like phenomena. As demonstrated by recent investigations in the context of marine sequence stratigraphy, potential applications of ichnology in paleobathymetric studies extend well beyond the use of generalized ichnofacies models. Ichnofabric parameters can facilitate reconstructions of relative sea-level dynamics by providing supplementary or primary evidence used to delineate key sequence stratigraphic surfaces. Sequence boundaries and transgressive surfaces, which record erosional exhumation of underlying strata, typically are marked by well-expressed substrate-controlled ichnocoenoses (e.g., those representative of the firmground Glossifungites ichnofacies). Maximum flooding surfaces and other parasequence-bounding marine flooding surfaces can be recognized on the basis of abrupt to subtle vertical ichnofabric successions that signal sea-level-mediated paleoenvironmental change. INTRODUCTION