On a new tectono-sedimentary model of the south-eastern margin of Hispaniola

Abstract

The San Pedro Basin (SPB) is an east-west elongated bathymetric depression in the south-eastern margin of Hispaniola Island. With an approximately extension of 6000 km2, SPB limits to the south with Muertos Thrust Belt (MTB) —an imbricate thrust system product of the southward transfer of the compressive stresses from the oblique collision/underthrusting between the continental crust of the North American Plate (i.e., the Carbonate Bahamas Banks) and the north-eastern segment of the island (i.e., Lower and Upper Cretaceous island arc terrains mainly consisting of volcanic and volcano-sedimentary sequences). Traditionally, SPB has been interpreted as a local “forearc basin” containing sediments from Middle Miocene to Present. However, this interpretation does not show clear connections with an overall geodynamic model of Hispaniola Island, and finally with the Greater Antilles Arc. From to the detailed revision and synthesis of the systematic geological mapping (SYSMIN I & II Programs) together with the integration of a large volume of sub-surface geophysical data we have obtained new tectonic and sedimentary constrains which led us to suggest a new geodynamic model for SPB. This new model may has important implications for the exploration in the area. Our study is based on:  The identification of major unconformities and seismic units which have been correlated with the exploration wells and the geological mapping. The new horizons identified are: Cenozoic Base, Oligocene Top and Miocene Top. This new correlation, in agreement with paleontological dating carried out in outcrop and well samples, sets the oldest sediments of the basin in Lower Paleogene, probably Lower to Middle Eocene.  The combined analysis and interpretation of gravity and magnetic anomaly data has allowed us to define the location, geometry and extension of the different Lower and Upper Cretaceous terrains. These terrains configure the northern limit of the basin and the control the accommodation space in SPB. Our new model suggests that the basement of the SPB is formed by the Cretaceous sedimentary and volcanic rocks, deposited in an intra/backarc context. A later change in the stress regime at the K/T limit led to the partial inversion of the basins and the volcanic arc. This is possibly related with the underthrusting of part of the North American continental crust, favored the creation of a deep trench with a NW-SE orientation in the backarc where sediments were deposited at least from Lower Eocene following a submerged foreland model. Due to the collision between the Carbonate Bahamas Platform and Hispaniola in Upper Eocene, compressional stresses were transferred to the south where Paleogene sediments were deformed yielding the MTB and generating a new configuration for SPB since Upper Eocene / Oligocene to Present and, in consequence the accommodation space of the basin. Although the architectural style of the SPB could be similar to a forearc basin of a subduction zone, the SPB should not be considered as one, due to its formation is not related with a subduction dynamic of the Caribbean Plate under the Island otherwise, it is the result of the inversion of the former Cretaceous and Paleogene arc-related basins and their thrusting over the Caribbean Plate. The revision of the geological maps available and the combined interpretation of the grav-mag anomaly maps have allowed us the identification of the following terrains or blocks which form the basement of the former basin: 1. Basalts, metasediments and serpentinized peridotites of Upper Jurassic to Lower Cretaceous age. 2. Volcanic rocks (interpreted as volcanic arc) and sediments from Lower Cretaceous. 3. Volcanic rocks (interpreted as volcanic arc) and sediments from Upper Cretaceous. 4. Basalts from Upper Cretaceous interpreted as part of the CLIP (Caribbean Large Igneous Province. 5. Intrusive to sub-volcanic bodies from Cretaceous to Eocene.

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018