The Missing Early Miocene: Evidence for a major hiatus in the Early Miocene marine sedimentary record

Abstract:

The largest known extinction event in open ocean sharks, as traced by their denticles (dermal scales) preserved in sediment cores, occurs in the Early Miocene, around 19 Ma, with over 70% of shark denticle types disappearing suddenly within a 100 kyr interval. The timing of such a dramatic extinction is enigmatic, as it coincides with no known climatic or oceanographic event, although there are fossilization gaps and significant evolutionary turnover in whales and other large marine tetrapods, as well as other marine and terrestrial vertebrate groups between the Late Oligocene and the Middle Miocene. Here I present evidence for a widespread hiatus, or series of hiatuses, through Early Miocene aged deep-sea sediment cores, using a broad survey of shipboard and post-cruise age models from sites drilled by the International Ocean Discovery Program and its predecessors. Of the 461 Sites which reach deeper than Early Miocene in age and have sufficiently continuous coring to make a determination that a stratigraphic gap likely not due to coring disturbance, 377 (82%) have a hiatus that spans at least some of the Early Miocene. Of the remaining 84 Sites (18%) only 36 (7.6%) have what appears to be a biostratigraphically complete Early Miocene section and the remaining 48 (10.4%) likely contain most of the Early Miocene. Together, this dataset, along with evidence for a major extinction in some marine groups, suggests that the Early Miocene, and particularly the interval between 20 and 18 Ma, may have been a time of significant and rapid transition in the open ocean that is largely missing from the stratigraphic record.