QUANTIFYING ICHNOGENERA DIVERSITY AND BIOTURBATION INTENSITY IN THE TERMINAL NEOPROTEROZOIC NAMA GROUP, NAMIBIA

The diversity and abundance of terminal Neoproterozoic trace fossils provide important insights into rates of early metazoan evolution leading up to the Cambrian explosion, and can help test between hypothesized drivers of the extinction of the Ediacaran biota (including ‘biotic replacement’). Over two weeks of field work, we review and re-examine the trace fossil record preserved in the terminal Ediacaran Nama Group of southern Namibia. We find that these trace fossil assemblages in both the Zaris and Witputs subbasins primarily record horizontal locomotion most likely related to matground feeding strategies, including Planolites and possible undermat mining traces. Although a number of vertical ichnogenera have also been reported, which would suggest the early evolution of metazoans with more diverse feeding behaviors, we have found that these represent a far less diverse group of ichnogenera, primarily Bergaueria and Conichnus. As well as analyzing the diversity of trace fossils, we quantify the intensity of metazoan activity using bedding plane point-counting methods in conjunction with bedding-plane bioturbation indices (BPBIs) and ichnofabric indices. We have thus far found that the intensity of bioturbation is low with BPBIs of 2 throughout the Nama Group until it increases to BPBIs up to 3 near the Ediacaran-Cambrian boundary. This quantification of diversity of ichnogenera and intensity of bioturbation in the Nama Group is part of a comprehensive new data set which will form the basis for performing the first robust test of ‘biotic replacement’ at the Ediacaran-Cambrian transition, as well as shed light on the role of metazoans in driving one of the most important geobiological revolutions in Earth history.