Neogene/Quaternary Evolution of Pedro Channel, Northern Nicaragua Rise: The Strike-Slip Induced Breakup of a Carbonate Megabank in a Plate Boundary Zone

Andrew D. Cunningham, Andre W. Droxler, Albert C. Hine

Pedro Channel, averaging between 800 and 1200 m water depth, is the central and largest of the Northern Nicaragua Rise (NNR) seaways. The channel is interpreted to have formed in the middle Miocene by the partial demise of a carbonate megabank that had extended from the Honduran and Nicaraguan shelves to Jamaica. Pedro Channel is bounded to the east, south and west by isolated carbonate banks (25-35 m water depth) which are parts of the megabank that have kept up with subsidence and remained within the photic zone.

Examination of over 2800 km of high resolution seismic data reveals a basal seismic unit marked by irregular, high amplitude, sub-parallel reflectors which is interpreted as the foundered megabank. Analysis of nine dredge hauls from the outcropping megabank indicates an early Miocene age for the shallow-water facies. In several places, the edges and tops of the megabank have undergone significant submarine erosion related to flow of the Caribbean Current. A thick package of periplatform sediments, characterized by regular, relatively low amplitude, parallel reflectors, either overlies the megabank or onlaps the northern margin of the megabank and younger adjacent bank edges. An extensive, basement rooted fault system was likely initiated by a reorganization of the faults bordering the Cayman Trough, while another fault system is limited to the sedimentary cover. Both systems continue to displace surface sediments and influence sea floor morphology. Block faulting appears to have caused over 1200 m of subsidence in parts of the megabank.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995