Stratigraphic distribution of marine fossils in North America

Abstract

The stratigraphic distribution of fossils reflects a combination of physical and biological factors. Although many studies have addressed the distribution of fossils at a basin scale and within sedimentary sequences spanning 10 4 –10 6 yr, little is known about the distribution of fossils within longer duration sedimentary successions covering broad geographic regions. Here we combine a North American macrostratigraphic database with fossil occurrence data from the Paleobiology Database to quantify the stratigraphic distribution of fossils within hiatus-bound marine sedimentary rock packages that have a mean duration of 10 7 yr. We find that fossil collections and marine genera are, when averaged over all Phanerozoic sedimentary rock packages, more abundant than expected in the top 40% of package durations, and less common than expected in the bottom ∼25%. Generic first and last appearance datums (FADs and LADs) in North America are not randomly distributed among fossil collections. Instead, LADs are more common than expected in the top ∼20% of package durations, whereas FADs are more uniformly distributed. This result is not consistent with an unconformity-related sampling bias, but is indicative of greater congruence in the temporal scales over which genus extinction and regression occur than genus initiation and transgression. These results support the hypothesis that macroevolution, particularly genus extinction, and large-scale patterns of sedimentation share a common set of forcing mechanisms that are related to the formation and destruction of shallow-marine habitats.