ABSTRACT: Leeward Vs. Windward Effects on Glacial/Interglacial Periplatform Aragonite Cycles off Pedro Bank and Jamaica (Northern Nicaragua Rise)

Karen S. Glaser, Andre W. Droxler, Geoffrey A. Haddad

Fine (< 62 µm) aragonite content in periplatform sediment from the northern (leeward) and southern (windward) slopes of Pedro Bank shows late Quaternary climate-induced cyclic downcore variations. Intervals characterized by high aragonite content correspond to interglacial stages. The aragonite cycles are clearly developed despite significant windward/leeward differences in sediment sources and composition, pelagic productivity(?), and current regime.

Interglacial sedimentation rates on the leeward slope (LS) are nearly twice as high as those on the windward slope (WS), and twice as high as LS glacial sedimentation rates. Carbonate values (75-85%) in sediments deposited on the northern slope of Pedro Bank are higher than those (50-70%) on its southern slope. On both slopes, high carbonate values correspond to interglacial intervals. The lowest carbonate values occur during glacial intervals on the southern slope and are explained by an increase of siliciclastic input from Jamaica during sea level lowstands. This siliciclastic increase could compensate for the drop of bank-derived fine aragonite, and thus, could explain the constant glacial/interglacial sedimentation rates found on the southern slope. In addition, high pteropod abun ance during glacial stages along the southern slope may also indicate higher glacial pelagic productivity.

Winnowing effects are rather conspicuous in one core from the northern slope within Walton basin (600 m water depth) during glacial intervals, when values of the coarse (> 62 µm) fraction are the highest (the opposite is observed in the other cores). In this relatively shallow core, partial cementation during glacial intervals is also observed.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990