Reconstructing Paleogeography and Sea-level History of Western Puerto Rico Using High-resolution 2D Seismic Profiles

Hanzlik-Valentín, Martín¹, Paul Mann¹, Alejandro Escalona¹, Nancy Grindlay², Lewis Abrams² (1) Jackson School of Geosciences, The University of Texas at Austin, Austin, TX (2) University of North Carolina at Wilmington,

The island of Puerto Rico has gently-sloping carbonate shelves ranging in width from 2-26 km that were inundated by late Quaternary sea-level rise. High topographic elevations and large river systems on the island itself provided long-term point sources for siliciclastic sedimentation. We interpret 725 km of high-resolution, single-channel 2D seismic lines collected over the western insular shelf and slope to better understand the complex interplay between sedimentation and sea-level change. Sequence stratigraphic interpretation of the seismic data reveal four main units: Unit 1 (basement) - a gently folded and faulted basal section correlated to the Oligocene-early Pleistocene carbonate shelf of Puerto Rico, this unit was exposed to subaerial erosion during the Last Glacial Maximum about 20 ka; Unit 2 (Lowstand Systems Tract, LST) - chaotic channel fill deposits filling deep (~ 30 meter) incisions formed during the Last Glacial Maximum; Unit 3 (Transgressive System Tract, TST) – poorly stratified deposits produced by a siliciclastic sedimentary pulse truncating the top of Unit 2 and deposited during early Holocene transgression; Unit 4 (Highstand System Tract, HST) - late Holocene, highly stratified deposits related to aggradation as the Holocene transgression began to slow. East-northeast-striking faults are observed that offset late Quaternary units in three separate zones off the west coast of Puerto Rico and have activated a large 0.02 km³ slump. Age estimates for the four seismic units are based on correlations with sea-level curves derived from dated coral samples in the Caribbean and western Atlantic region.