Planktonic foraminiferal biostratigraphy of the Middle America Trench region, Deep Sea Drilling Project Leg 84.

Abstract

Planktonic foraminifers are variable preserved but generally common in all holes, except within several highly dissolved intervals. Both quantitative and semiquantitative analyses of planktonic foraminifers, in addition to the first and last occurrences of index species, were used to establish the biostratigraphy for Leg 84 sites. Biostratigraphic analysis of the planktonic foraminifers provides useful data for reconstructing the tectonostratigraphic history of the S Guatemalan segment of the Middle America Trench. The Leg 84 stratigraphic record is fragmentary. The poorly represented Paleogene section is interrupted by several unconformities, and one major Neogene unconformity occurs between the upper lower Miocene and the upper Pliocene. The Neogene unconformity can be related to tectonic activity in the Middle America Trench region associated with a major pulse in volcanic activity between 1 and 4 Ma (peaking from 1 to 2 Ma) and a minor pulse between 14 and 16 Ma. Despite the fragmentary nature of the sedimentary record, the sequences are not repeated or reversed, and evidence of imbrication of oceanic sequences is lacking. Gravity-induced downslope transport and reworking of older sediments into younger deposits, however, are apparent through analysis of benthic and planktonic foraminifers, suggesting that a slope- trench environment similar to the present one existed during the Cenozoic.-from Authors