STRATIGRAPHY AND DEPOSITIONAL HISTORY OF THE UPPER CRETACEOUS STRATA IN SOUTHWESTERN

Volcanic/tectonic episodes followed by subsidence and relative sea-level rise in the Late Cretaceous resulted in deposition of 5 volcano-sedimentary cycles in southwestern Puerto Rico. Transgressive/highstand systems tracts resulted in deposition of rudist-bearing carbonates of Santonian, Campanian, and Maastrichtian age. The Cotui Lmst and the Bahia Fosforecente Mbr of the Parguera Lmst represents the Santonian age. These formations where deposited during a regional transgressive event that resulted in aggradation and progradation of the Cotui platform. Deposition ended by a volcano/tectonic event that exposed the platform developing a paleokarst. Santonian rudistids are Durania curasavica, Vaccinites sp. and Torreites tschoppi. The Peñones, Guaniguilla, and the Punta Papayo and Isla Magueyes members of the Parguera Lmsts, and the Monte Grande and Yauco Fms represents the Campanian age. The Peñones Lmst represents a small platform (LST) developed during exposure of the Santonian Lmsts. The TST is represented by the Monte Grande Fm, which is unconformably overlying the Cotui Lmst. Continued sea-level rise resulted in deposition of the Guaniquilla Lmst. The Punta Papayo and Isla Magueyes Mbrs of the Parguera Lmst and the Yauco Fm represents sediments deposited offshore the platform. Deposition was terminated by El Rayo volcanics extrusion. Campanian rudists are Macguillavryia nicholasi and several Barrettia species. The El Rayo Fm represent 3 volcano-sedimentary cycles. After volcanism, subsidence resulted in deposition of the lower limestone lens followed by aggradation and progradation of the platform margin. Deposition of the lower El Rayo lmst lens ended abruptly by a shift of volcanism and partial filling of the basin by volcanics. The middle limestone lens represents a ramp deposited across the volcanic surface in the Upper Maastrichtian. Deposition of the middle lens also ended by volcanism. The third limestone lens of El Rayo Fm was probably deposited in Paleocene time. The Maastrichtian is characterized by the rudistids Macguillavryia nicholasi, Parastroma treschmanni, and Titanosarcolites giganteous.The relative sea-level rises and falls of these carbonate platform and intervening volcanics correlate to similar carbonate platforms within the Caribbean.