Planktonic Foraminiferal Biostratigraphy of the Middle America Trench Region, Deep Sea Drilling Project Leg 84

TitlePlanktonic Foraminiferal Biostratigraphy of the Middle America Trench Region, Deep Sea Drilling Project Leg 84
Publication TypeBook Chapter
Year of Publication1985
AuthorsStone, SM, Keller, G
Book TitleInitial Reports of the Deep Sea Drilling Project
PublisherU.S. Government Printing Office

Eleven holes were drilled at six sites along a transect of the landward side of the Middle America Trench during DSDP Leg 84. Sites 566-570 are in the same area as DSDP Leg 67 sites offshore from Guatemala, and Site 565 is offshore from Costa Rica. Pleistocene and Pliocene sediments were recovered at Site 565; Pleistocene to upper Miocene sediments at Site 566; Pleistocene and Pliocene, lower Miocene, and Upper Cretaceous sediments at Site 567; Quaternary and middle and lower Miocene sediments at Site 568; Quaternary, lower Pliocene, middle Miocene to upper Oligocene, lower Oligocene and upper Eocene, and middle and lower Eocene sediments at Site 569; and Quaternary to middle Miocene and lower Eocene sediments at Site 570. Planktonic foraminifers are variably 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 southern 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.  PDF