Benthic foraminifera accumulation rate and benthic foraminiferal productivity proxies at ODP Site 165-999 in the Caribbean (Appendix A)

This study tests the hypothesis that the late Miocene to early Pliocene constriction and closure of the Central American Seaway (CAS), connecting the tropical Atlantic and East quatorial Pacific (EEP), caused a decrease in productivity in the Caribbean, due to decreased coastal upwelling and an end to the connection with high-productivity tropical Pacific waters. The present study compared paleoceanographic proxies for the interval between 8.3 and 2.5 Ma in 47 samples from south Caribbean ODP Site 999 with published data on EEP DSDP Site 503. Proxies for Site 999 include the relative abundance of benthic foraminiferal species representing bottom current velocity and the flux of organic matter to the sea floor, the ratio of infaunal/epifaunal benthic foraminiferal species and benthic foraminifer accumulation rates (BFARs). In addition, we calculated % resistant planktic foraminifers species and used the previously published % sand fraction and benthic carbon isotope values from Site 999. During early shoaling of the Isthmus (8.3-7.9 Ma) the Caribbean was under mesotrophic conditions, with little ventilation of bottom waters and low current velocity. The pre-closure interval (7.6-4.2 Ma) saw enhanced seasonal input of phytodetritus with even more reduced ventilation, and enhanced dissolution between 6.8 and 4.8 Ma. During the post-closure interval (4.2-2.5 Ma) in the Caribbean, paleoproductivity decreased, current velocity was reduced, and ventilation improved, while the seasonality of phytodetrital input was reduced dramatically, coinciding with the establishment of the Atlantic-Pacific salinity contrast at 4.2 Ma. Our data support the hypothesis that late Miocene constriction of the CAS at 7.9 Ma and its closure at 4.2 Ma caused a gradual decrease in paleoproductivity in the Caribbean, consistent with decreased current velocity and seasonality of the phytodetrital input.

Accumulation and composition of terrigenous material on Ceara rise over the past 55 Ma

Ceara Rise, located east the Amazon River mouth, is covered with a thick blanket of pelagic carbonate and hemipelagic terrigenous sediment. The terrigenous component has been extracted from 57 bulk sediment samples at Ocean Drilling Program (ODP) Sites 925 and 929 on Ceara Rise to obtain a Cenozoic record of riverine discharge from northern South America. From the early Eocene to early Miocene (55-20 Ma), terrigenous accumulation was dominated by moderate amounts of generally large-grained, gray to green sediment especially depleted in elements that are enriched in post-Archaean shale (e.g. Cs, Th, Yb). However, pulsed inputs of relatively small-grained, gray to green terrigenous sediment less depleted in the above elements occurred in the late Eocene and Oligocene. The accumulation of terrigenous sediment decreased significantly until 16.5 Ma. In the middle Miocene (16.5-13 Ma), terrigenous accumulation was dominated by small amounts of small-grained, tan sediment notably depleted in Na and heavy rare earth elements. The accumulation rate of terrigenous sediment increased markedly from the latest Miocene (10 Ma) to the present day, a change characterized by deposition of gray-green sediment enriched in elements that are enriched in post-Archaean shale. Observed changes in terrigenous sediment at Ceara Rise record tectonism and erosion in northern South America. The Brazil and Guyana shields supplied sediment to the eastern South American margin until the middle Miocene (20-16.5 Ma) when a period of thrusting, shortening and uplift changed the source region, probably first to highly weathered and proximal Phanerozoic sediments. By the late Miocene (9 Ma), there was a transcontinental connection between the Andes and eastern South America. Weathering products derived from the Andes have increasingly dominated terrigenous deposition at Ceara Rise since the Late Miocene and especially since the late Pliocene.