Monday, December 28, 2015

A Link Between the Cooler, Drier Aptian Cretaceous Climate and Carbonate Production Ending?

Cool episode and platform demise in the Early Aptian: New insights on the links between climate and carbonate production


Bonin et al


The Early Aptian encountered several crises in neritic and pelagic carbonate production, major perturbations in the carbon cycle, and an Oceanic Anoxic Event (OAE1a). Yet the causal links between these perturbations and climate changes remain poorly understood, partly because temperature records spanning the Early Aptian interval are still scant. We present new δ18O data from well-preserved bivalves from a carbonate platform of the Galve sub-Basin (Spain) that document a major cooling event postdating most of OAE1a. Our data show that cooling postdates the global platform demise and cannot have triggered this event that occurred during the warmest interval. The warmest temperatures coincide with the time-equivalent of OAE1a and with platform biotic assemblages dominated by microbialites at Aliaga as well as on other tethyan platforms. Coral-dominated assemblages then replace microbialites during the subsequent cooling. Nannoconids are absent during most of the time-equivalent of the OAE1a, probably related to the well-known crisis affecting this group. Yet they present a transient recovery in the upper part of this interval with an increase in both size and abundance during the cool interval portion that postdates OAE1a. An evolution toward cooler and drier climatic conditions may have induced the regional change from microbial to coral assemblages as well as Nannoconids size and abundance increase by limiting continent derived input of nutrients.

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