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.