Paleoenvironmental and temporal significance of variably colored Paleozoic orthoconic nautiloid cephalopod accumulations

摘要

Accumulations of orthoconic nautiloid cephalopods occur throughout the Lower Paleozoic from the Ordovician to the Carboniferous. Studies focused on unraveling the nature of their formation tend to be restricted both spatially and temporally to localized investigations of either the constituent faunas or the lithological successions within which they occur. Herein, an innovative approach to determining common factors among these particular fossil rich beds is utilized whereby different color and taphonomic groupings are identified and classified for known world occurrences of orthoconic nautiloid cephalopod concentrations. These groupings are related to inferred paleosettings and paleoenvironmental gradients. Those horizons with a predominantly black to gray color generally represent event beds and were frequently deposited together with black shales while those ranging from red-brown-green-beige are prevalently accumulations associated with condensed sequences and discontinuity surfaces. The findings are further used to identify time-specific changes in orthoconic nautiloid accumulation processes.