ABSTRACT: Petrology of Platform and Slope Limestones: Bawihka Platform and Channel, Nicaraguan Rise, Western Caribbean Sea

TEDESCO, LENORE P., Indiana-Purdue University at Indianapolis, Indianapolis, IN, ALBERT C. HINE, University of South Florida, St. Petersburg, FL, A. CONRAD NEUMANN, University of North Carolina at Chapel Hill, Chapel Hill, NC, and PAMELA HALLOCK, University of South Florida, St. Petersburg, FL

Pleistocene to Recent platform and slope limestones of the Bawihka Channel--a shallow (220 m), open seaway within the tectonically active Nicaraguan Rise carbonate platform complex--have undergone a complex history of sediment infilling, cementation, and fracturing.

Seismic reflection and a 3.5 kHz profiles reveal low-relief platforms with steep, fault-controlled margins. Rock dredges of platform and slope limestones are dominated by Halimeda packstones. Halimeda bioherms form two deposits: (1) platform top meadows (40-60 m depth), and (2) a nearly continuous band of relict bioherms bordering the margins of Bawihka Channel (120-170 m depth).

Halimeda packstones have undergone multiple stages of void filling by at least two generations of sediment and one or two phases of cementation. Infilling sediments are skeletal grainstones that reflect associated benthic communities and pelagic foraminiferal packstones. Between phases of sediment filling was a phase of microcrystalline Mg-calcite precipitation.

Microcrystalline Mg-calcite occurs in voids in a sequence that grades from (1) amorphous micrite to (2) clotted and peloidal precipitates to (3) isopachous microspar rim cement.

Abundant microfractures cut both the Halimeda packstone primary sediment and infilling sediments and cements. Many fractures are partially filled with Mg-calcite cements indicating that fracturing occurred in the slope environment or during catastrophic downslope transport.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)