TROPICAL CARBONATE SEQUENCES OF ALBIAN AGE DEPICT SEA LEVEL RISE OF REGIONAL EXTENT

Middle Cretaceous shallow water carbonate sequences present unique challenges to our understanding of the tropical ocean-climate system, as limestones are often recrystallized, and faulting of the sequences is pervasive in densely vegetated tropical regions. Here we present the integrated stratigraphy, sedimentology, paleoecology and geochemistry derived from three middle Cretaceous paleotropical carbonate sequences in Puerto Rico - the Aguas Buenas Limestone Member of the Torrecilla Breccia, 38m in stratigraphic thickness, the Barrancas Limestone Member of the Magueyes Formation, 73m thick, and the Rio Maton Member of the Robles Formation, 52m thick. Each member yields forams and macrofossils sufficiently preserved to indicate an Albian age. The Rio Maton, Barrancas and Aguas Buenas limestone members are dwarfed by thicker volcanic, volcaniclastic, and siliciclastic units, and the limestones are rarely free of volcaniclastic or siliciclastic input. The three limestone members were deposited in shallow water marine environments within inner to middle platform settings. Shales lying either directly under or over the carbonates yield carbon to sulfur ratios that allow for interpretation of fresh water and brackish water intervals within these three depositional sequences. Fluvial deposits occur more commonly in the lower parts of the stratigraphic sections, whereas sustained carbonate deposition with decreasing volcaniclastic and siliciclastic input, and thick-to massive-bedded packstones with moderately abundant gastropods and rudists, suggest a deepening trend upsection. Identification of fresh water units and transgressive system tracts allow for placement of sequence boundaries in these middle Cretaceous sections. This enhances future potential for correlation of tropical sequences to those of the well-studied temperate realms in the Gulf Coast and Western Interior Basin experiencing a similar sea level rise. Collectively these integrated data and interpretations will yield a greater understanding of the Cretaceous hydrologic cycle and the contribution of the tropics to Cretaceous ocean-climate system dynamics.