Print this pageCarbonate Sediment Gravity Flows of the Tertiary White Limestone of Jamaica: Platform to Basin Floor Model for Ancient Analogs
Contemporary allocthonous carbonate models are much less well described and modeled than those of their assumed terrigenous clastics analogues. Outcrop analysis using spectral gamma ray and constrained with petrography of the Tertiary White Limestone, along the northern coast of Jamaica, provide insights into the description of linked autochthonous and allocthonous carbonate deposits. The depositional systems are affected by both allocyclic and autocyclic processes, e.g. allocyclic tectonic Caribbean plate interactions and global eustatic changes in sea level and autocyclic carbonate platform sediment production.
Petrographic microfacies analysis reveals lateral changes in macrofaunal and foraminifera assemblages, which designate platform interior, platform margin, slope, and basin floor facies. For example, miliolids and robust Peneroplis sp. dominate the platform interior, rounded and robust Nummulites sp., Lepidocyclina sp., and red coralline algae the platform margin, elongate Lepidocyclina sp. along with allocthonous assemblages on the slope, and planktonic foraminifera, calcispheres, and coccoliths interspersed with transported assemblages on the basin floor.
Vertical excursions in total gamma ray, potassium, thorium, and uranium reveal changes which appear to be correlated to these autocyclic and allocyclic processes on the platform and basin floor. On the lagoonal platform, shoaling upward cycles are terminated with high uranium and thorium. On the basin floor, the gamma ray is diluted by less radioactive carbonates during highstands, and uranium is highest during times of condensed sections. In addition, the gamma ray changes reveal many cycles and sub cycles. The third order cycles are corroborated with broken and mixed allocthonous assemblages. Channel incision, debris flows, turbidites, and olistostromic mass transport blocks dominate during lowstands, while laterally continuous strata with increased neretic content dominate in pelagites and sediment gravity flows during highstands.
These observations emphasize the complexity yet potential vertical and lateral facies differentiation of platform to basin carbonate sediment gravity flows in comparison to terrigeneous clastics. Similar analysis can potentially provide important insight into the recognition and differentiation of carbonate autochthonous and allocthonous ancient analogues for oil and gas exploration, such as the Gulf Coast chalks, North Sea Ekofisk area, Delaware and Midland Basin, and Mexico's Poza Rica trend.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009