THE EFFECT OF DEPOSITIONAL SEQUENCE ASYMMETRY ON ORIGINATION AND EXTINCTION RATES: INSIGHTS FROM MODELING

Gap-bound rock packages are fundamental stratigraphic units. Macrostratigraphy characterizes the rock record on the basis of the stratigraphic ranges of such gap-bound packages. From these, area-weighted rates of stratigraphic origination (expansion) and extinction (contraction), among other parameters, can be measured in ways that, at least in principle, permit underlying forcing mechanisms to be readily detected and quantified.

Here we explore this possibility by using a physics-based, process model of sedimentary dynamics (SedFlux) to simulate basin fills with known and realistic subsidence, sedimentation, and sea level histories. The resultant basin fills were then sampled and macrostratigraphic parameters calculated for the recovered gap-bound packages. Preliminary results suggest that sea level and other forcing mechanisms are readily detectable and quantifiable using macrostratigraphic parameters calculated for a range of temporal resolutions and binning strategies. Further, we find that in a wide range of simulated conditions, there is a fundamental asymmetry in depositional sequences such that rates of stratigraphic extinction have greater volatility than rates of stratigraphic origination. Thus, truncations in the sedimentary record tend to be more synchronous and more widely distributed than expansions. Accordingly, variation in the area of depositional sequences is more strongly correlated with variation in rates of stratigraphic extinction than with rates of origination. These results mirror some aspects of the macroevolutionary history of marine animal genera, suggesting that a combination of sampling bias and common cause mechanisms might drive similar quantitative patterns in sedimentary successions and among marine animals.