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Biostratigraphic data of the Middle America Trench indicate that the sediments decrease in age in the direction of the trench axis. Upper and middle slope sites (493 and 489) contain the oldest sediment (early Miocene above the basement), whereas sites in the accretionary and transitional zones contain middle Miocene through Pleistocene. This diachronous stratigraphic trend along the inner wall suggests accretion. Geophysical sedimentological and paleontologic evidence reveals a general uplift of the continental plate. The accretionary zone sites (488, 492, 491) and transitional zone site (490) reveal uplift of 500 to 200 m/m.y., whereas the sites at the continental plate indicate uplift of 100 to 80 m/m.y. These sediments were originally deposited in the trench environments and later uplifted. All the sites in the accretionary and transitional zones consist of three zones (A-C) with respect to abundance and preservation of planktonic foraminifers. Zone A is barren of calcareous fossils and was probably deposited below the CCD (calcite compensation depth) at 4000 to 5000 meters depth. Zone B contains rare and poorly preserved planktonic foraminifers. The facies indicate deposition near the CCD at a depth of perhaps 3000 to 4000 meters. Zone C contains abundant and well-preserved planktonic foraminifers, suggesting deposition above the CCD. Benthic foraminifers correspond to the present depth along the inner slope sites. Zones A to C suggest a marked uplift of the sites relative to the CCD. Some planktonic foraminifers in the basal core of Site 487 indicate a late Miocene data for the basaltic basement. Sites 486, 487, and 488 lie below the present CCD. However, the Quaternary cores contain well-preserved, smallsized planktonic foraminifers. They were transported by turbidity currents and rapidly buried with sand particles. In contrast to small-sized species the larger solution-resistant species such as Globorotalia menardii are poorly preserved. They represent productivity of the overlying water mass and slow deposition through the CCD. Furthermore, these foraminifers remain exposed for a longer time at the interface at the seafloor.

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Syndepositional Tectonics along the Middle America Trench, with Special Reference to Foraminiferal Bathymetry: Deep Sea Drilling Project Leg 66, offshore MexicoGeological Processes along an Active Margin

Syndepositional Tectonics along the Middle America Trench, with Special Reference to Foraminiferal Bathymetry: Deep Sea Drilling Project Leg 66, offshore MexicoGeological Processes along an Active Margin

Syndepositional Tectonics along the Middle America Trench, with Special Reference to Foraminiferal Bathymetry: Deep Sea Drilling Project Leg 66, offshore MexicoGeological Processes along an Active Margin