SEQUENCE STRATIGRAPHY, BIOSTRATIGRAPHY, AND TAPHONOMY IN SHALLOW MARINE ENVIRONMENTS

Sequence stratigraphy provides an integrated framework within which to examine historical patterns of paleontological phenomena. Depositiona l sequences are the stratigraphic record of fluctuations of sea level and sedimentation, environmental parameters that also exert critical c ontrols on the distribution of shallow marine organisms, and the prese rvation. and accumulation of their skeletal remains. As such, stratigr aphic paleontology and sequence stratigraphy share multiple associatio ns. Biostratigraphy is a critical tool for relative age-dating and cor relation. of depositional sequences; in. turn, sedimentological and de pth-related variables exert a primary control on. the occurrence of zo nally significant fossils. The most readily dated portions of many seq uences are offshore condensed facies. Correlation of a hierarchy of di scontinuity surfaces, however, permits extension of biostratigraphic d ating into less fossiliferous facies. In turn, mingling of fossils of distinct zones provides a key to recognition of condensed sections, an d truncation of zones points to significant unconformities such as seq uence boundaries. The combination of refined graphic biostratigraphy, cycle-based ecostratigraphy, and sequence stratigraphy, sequence biost ratigraphy, will ultimately permit extremely precise stratigraphic cor relation and dating of marine strata. Taphonomic attributes of fossil assemblages also relate closely to sequence stratigraphy. Taphofacies vary predictably in depositional sequences because of the dependence o f fossil preservation upon rates of burial and environmental energy. A spectrum of preservation should exist from highly corroded, fragmente d remains, typical of erosive lowstand or early transgressive conditio ns, to intact multielement skeletons, characteristic of rapid backgrou nd sedimentation during mid-highstand progradation; geochemically stab le lags of corroded fossils (e.g., bone beds) typify many highly conde nsed sections. Skeletal accumulations develop during interval of low s ediment input. Sediment-starved accumulations overlying marine floodin g surfaces occur at bases of parasequences, winnowed shell beds at par asequence tops. At a larger scale, thin, sheet-like skeletal deposits may form transgressive systems tracts of third order sequences. Fossil Lagerstatten (typically involving rapid burial and/or anoxia) are cha racteristic of the transgressive to early highstand interval. Although higher background sedimentation rates typify the later highstand, fos sil event beds are commonly less recognizable due to dilution and biot urbation effects. Close integration of paleontologic and sequence stra tigraphic data should foster a greatly improved understanding of biase s and relationships of biotic and abiotic processes in the accumulatio n of the stratigraphic record.