Taxonomy, biostratigraphy, and paleoecologic significance of calcareous-siliceous fades of the Neogene Montpelier Formation, northeastern Jamaica
Article
Maurrasse, FJMR. (1993). Taxonomy, biostratigraphy, and paleoecologic significance of calcareous-siliceous fades of the Neogene Montpelier Formation, northeastern Jamaica
. 182(1), 255-282. 10.1130/MEM182-p255
Rock sequences of the Montpelier Formation exposed on the northeastern coast of Jamaica east of Buff Bay include an interval of calcareous-siliceous facies composed of abundant sponge spicules with varying amounts of Radiolaria. Hexactinellid spicules of the Hyalospongea group (60 to 99%) dominate the biogenic silica components, whereas radiolarian assemblages vary from impoverished to well diversified. Liriospyris globosa, Calocycletta costata, and Dorcadospyris dentata occur at the base of the exposed outcrop, thus indicating a minimum age of late early Miocene (Calocycletta costata zone) for the onset of the calcareous-siliceous facies. This age is correlative with the Globigerinatella insueta zone as indicated by the co-occurrence of Globigerinatella insueta, Globorotalia peripheroronda, and Globigerinoides sicanus (without Praeorbulina glomerosa). Thus, the base of the silicabearing sequence lies within Zone N7 of Banner and Blow (1965). The upper limit of the calcareous-siliceous facies lies within the upper part of the Dorcadospyris alata zone, or early middle Miocene. This age is indicated by the presence of the nominate radiolarian taxon whose full range characterizes the zone, and the disappearance of distinctive taxa such as Didymocyrtis violina and Calocycletta costata, which occur up to the base of this zone. This radiolarian stratigraphic level corresponds to the Globorotalia fohsifohsi zone, as indicated by the presence of the nominate taxon and Sphaeroidinellopsis disjuncta and the absence of Praeorbulina glomerosa. These foraminifera are also indicative of Zones N10/N11 of Banner and Blow (1965). The overwhelming abundance of sponge spicules in the calcareous-siliceous facies at Buff Bay, Jamaica, implies that a significant subsurface current flowed through the area for more than four million years, between late early and middle Miocene time. Sponge spicule abundance remained continuous during that time while Radiolaria occurred with large variation in frequencies. Radiolarian recurrences are interpreted to indicate fluctuating productivity in relation to variations in climatic forcing superimposed on the long-lasting subsurface flow in the area. Physiographic and oceanic conditions that led to the calcareous-siliceous facies at Buff Bay are compared to environmental conditions in the Hatton/Rockall Bank area, in northeastern Atlantic. Sedimentation on the bank surface is strongly influenced by variations in the subsurface transport of North Atlantic Deep Water (NADW) over the bank. The subsurface flow may result in unusually high productivity of Hyalospongea similar to the Buff Bay sediments. Such a mechanism may apply to the Jamaican Miocene Series when paleophysiographic conditions in the northern Caribbean allowed the flow of NADW into the Caribbean basin through the incipient Jamaican island.
