Abstract
Petrographic descriptions and stable oxygen and carbon isotope compositions of microsamples of Campanian-age sediment gravity-flow deposits from Northeast Providence Channel, Bahamas, indicate deep-marine cementation of shallow-marine skeletal grains that were transported to the channel during the Late Cretaceous. Shallow-marine compo nents are represented by mollusks, especially rudists, and shallow-water benthic foraminifers as well as sparse echino derm and algal grains. The sole evidence of diagenesis in shallow-marine environments consists of micrite envelopes around skeletal grains. Shallow-marine skeletal grains have mean stable isotope values of -3.1%o S180 and +2.6%o 513C. The 5180 values are consistent with precipitation in equilibrium with warm (20°-30°C), shallow-marine water. Deep-marine components are represented by equant calcite spar cements and rip-up clasts of slope sediments. Spar ce ments, exhibiting hexagonal morphology with scalenohedral terminations, most commonly occur as thin isopachous linings in the abundant porosity. Deep-marine cements have mean stable isotope values of - l.l%o S180 and +2.7%o 513C. Deep-marine cements are lsO-enriched relative to shallow-marine skeletal grains, consistent with precipitation in equilibrium with colder (10°-20°C), deep-marine waters. The cement .source during lithification appears to have been dissolution of aragonite and high-magnesium calcite skeletal grains, which made up part of the transported sediment. Interbedded periplatform ooze remains uncemented, or poorly cemented, probably because of lower permeability. Equant spar cements that occur in gravity-flow deposits recovered from Hole 634A have stable isotope compositions similar to spars in Lower and mid-Cretaceous shallow-water limestones exposed on the Bahama Escarpment, to Campanian-Paleocene deep-marine hardgrounds recovered during DSDP Leg 15 in the Caribbean, and to spars in AptianAlbian talus deposits at the base of the Campeche Escarpment recovered during DSDP Leg 77.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have