Late Quaternary periplatform sediments and environments on the northeastern Nicaragua Rise, Caribbean Sea
Glaser, Karen Sullivan
Droxler, Andre W.
Doctor of Philosophy
Four main factors control the accumulation of periplatform sediment on the northeastern Nicaragua Rise: (1) input of carbonate sediment; (2) input of siliciclastic sediment; (3) physical redistribution of sediment; and (4) partial dissolution of carbonate phases (aragonite and magnesian calcite). The intensity of these factors is directly influenced by climatic variations and associated sea-level fluctuations, creating the cyclic glacial/interglacial pattern characteristic of late Quaternary high resolution stratigraphy in periplatform sediments. During interglacial stages, the bank/shelf tops of the Nicaragua Rise were submerged. The northwestward flowing Caribbean Current swept neritic sediments off-bank to the periplatform environment where they accumulated, by settling through the water column or by sediment gravity flow, preferentially in downcurrent areas. These neritic sediments along with pelagic carbonates, form a thick wedge of highstand sediment on the upper slopes. Carbonate input was locally augmented by siliciclastic sediment input from Jamaica during peak sea-level highstands. Finally, neritic aragonite deposited in water depths below 1100 m was subject to partial dissolution. Glacial sea-level lowstands were characterized by bank/shelf top exposure and lower production, therefore, neritic carbonate input to the periplatform environment was reduced. Nannoplankton productivity shows little glacial/interglacial variation, while glacial foraminifer productivity was only half interglacial levels. Consequently, bulk sediment accumulation rates and turbidite frequencies are lower during glacial stages than in interglacial stages. Bank-top exposure restricted flow of the Caribbean Current to seaways between the banks and shelves. This flow constriction considerably increased flow rates, winnowing sediments in areas of Walton Basin with water depths shallower than 600 m today. Partial dissolution of aragonite may be associated with the formation of magnesian calcite cements in current winnowed sediments. The geometry of the late Quaternary sedimentary bodies, displayed on 3.5 kHz seismic lines, can be interpreted in a sequence stratigraphic framework for periplatform carbonate sediments. Lowstands are thin and overlain by thick accumulations of highstand sediments, all of which lap out on the steep bank/shelf margins. Transgressive systems tracts are too thin to be resolved on seismic data, but are revealed by subtle changes in interglacial sediment mineralogy.