Niklas Hohmann

Stratigraphic changes in the clustering of first or last taxon occurrences are a joint
expression of evolutionary, ecological, taphonomic, and sedimentological processes.
Sedimentation rates control the degree of sedimentary dilution and condensation and thus
alter the time contained in a given thickness of sediment. However, it remains poorly
explored quantitatively how distinct the stratigraphic patterns in the first and last
occurrences can be under different deposition models with a constant thickness of
accumulated sediment. Here, I present an algorithm that translates ecological or
evolutionary signals between time and stratigraphic height. It is implemented for R
Software as the package DAIME and complemented by tools to quantify the uncertainties
associated with the construction of deposition models. By modeling the stratigraphic
expression of the K/Pg extinction and an earlier extinction pulse potentially linked to
Deccan volcanism on Seymour Island under varying sedimentation rates, I show that (1)
clustering of last occurrences ~ 250 kyr prior to the K/Pg boundary can be equally
explained by a stronger earlier extinction pulse or prolonged intervals with reduced
sediment accumulation rate, but (2) when the temporal variability in sedimentation rate is
known, the most plausible extinction dynamics can still be identified. The approach is
applicable for any type of information transported as a part of the sedimentary record (e.g.,
fossils or trace elements) or data derived from it (e.g., isotope ratios and rates of
morphological evolution).