CALPIONELLID BIOSTRATIGRAPHY THROUGH THE JURASSIC/CRETACEOUS TRANSITION AT SIERRA DE LOS ORGANOS, PINAR DEL RIO PROVINCE, WESTERN CUBA

The current debate on Tithonian and Berriasian calpionellid zonations means that defining the Jurassic/Cretaceous boundary based on the stratigraphic records of species of this microfossil group remains uncertain. However, for our purposes we have chosen to use the standard calpionellid zonation scheme proposed by Reháková and Michalík (1997) for that boundary on the Tethyan Domain.

The Jurassic-Cretaceous transition marine carbonate deposits of the North America Mesozoic paleomargin in Sierra de Los Órganos, western Cuba consist of a sequence of partially dolomitized limestone facies represented by the Guasasa Formation. In this study, different microfossil groups, from which stand out the presence of calpionellids provided data that allowed us to further constrain the biostratigraphic position of these rocks.

Our stratigraphic section located at the Pinar del Río Province, consists at its base of typical facies of the top of the lowest unit of the Guasasa Formation, the San Vicente Member, indicative of a carbonate bank where sedimentation occurred in a protected, shallow marine lagoon-like environment.

By contrast, the base of the suprajacent El Americano Member displays wackestones with debris from the shallow environments, which also contain pelagic bioclasts from which stand out calpionellids and the crinoid Sacoccoma aracnoidea typical of the middle Tithonian Chitinoidella boneti Subzone.

These series of bioclastic wackestones initiated at the basal stratum of the El Americano Member, indicating that the environment became suddenly pelagic by the middle Tithonian.

A suprajacent set of wackestones, contains elements indicative of the three Subzones of the late Tithonian Crassicollaria Interval Zone, namely: Remanei, Brevis and Colomi Range Subzones; and the lowermost Berriasian Calpionella alpina (small forms) Acme Subzone, recording the Jurassic/Cretaceous boundary in our section of study.

Reháková, D., Michalík, J., 1997, Evolution and distribution of calpionellids – the most chacarteristic constituents of Lower Cretaceous Tethyan microplankton: Cretaceous Research, 18, 493-504.