Facies belts of the Middle America Trench and forearc region, southern Mexico: results from Leg 66 DSDP

Abstract

The Middle America Trench SE of Acapulco is flanked by a steep canyon-incised slope and narrow shelf, showing one of a variety of sedimentary facies patterns possible at convergent margins. Piston and drill cores from this region define eight facies belts including: (1) a pelagic facies of brown clay, (2) an outer slope mud facies, (3) a trench sand facies, (4) a foraminiferan-free facies on the lower slope, (5) a foraminiferanbearing facies on the mid-slope, (6) a laminated mud facies on the upper slope, (7) a shelf facies of sand and mud, and (8) a canyon facies of sand and gravel. The superposition of trench and lower slope sediment during accretion results in a fining upward sequence reflecting a gradual uplift of the seafloor through the trench sediment-plume. The lower limit of the foraminiferan-bearing facies is defined by the absence of in situ calcareous foraminiferans and is controlled by the calcite compensation depth. The upper slope laminated mud facies probably reflects the depth range of the oxygen minimum zone.In the Leg 66 area sedimentation rates are high in the trench and on the outer and lower slope, decrease on the mid-slope, and increase again on the shelf. On the inner shelf, waves and currents concentrate sand which funnels through a prominent submarine canyon, bypassing the mud-dominated slope and accumulating in the trench. A terrigenous sediment-plume generated by trench turbidity flow causes accelerated sediment accumulation to about 500 m above and 40 km seaward of the trench. The volume of material transported by the trench sediment-plume is five or six times greater than that moved by the shelf sediment-plume which supplies detritus to the shelf, upper slope and mid-slope environments.

Sediment Accumulation Rates of the Lesser Antilles Intraoceanic Island Arc, Deep Sea Drilling Project Leg 78A

“…Crude sedimentation rates (in m/Ma) determined from biostratigraphic age-versus-depth information were calculated on board ship for each Leg 78A site and are published in Moore, Biju-Duval, et al (1982) and BijuDuval, Moore, et al (1981). Though these sedimentation rates are gross estimates at best and do not account for downhole porosity or density changes or tectonic tilting, they are surprisingly similar to the dip-corrected bulk sediment accumulation rates presented in this chapter.…”

Sediment Distribution and Depositional Processes Operating in the Lesser Antilles Intraoceanic Island Arc, Eastern Caribbean

“…This model differs from models developed both for continental convergent margins (Piper et al, 1973;Moore, Watkins, et al, 1982;Underwood and Bachman, 1982) and for intraoceanic convergent margins isolated from continental sediment sources (Lundberg, 1983). Data from continental convergent margins indicate that substantial amounts of terrigenous gravel, sand, and silt are eroded from the adjacent continental block and are deposited on the shelf, in intraslope basins, and in trench segments fed by major submarine canyons.…”

Petrogénesis ígnea de la Faja Volcánica Transmexicana

“…Los estudios de Manea et al (2003) permiten interpretar que la columna sedimentaria sobre la placa de Rivera no debe alcanzar más de 20 metros de espesor, y que este espesor se incrementa gradualmente hacia el SE. Por otra parte, el DSDP realizó varios sondeos sísmicos y perforaciones exploratorias en la trinchera mesoamericana, en la denominada Leg 66 (Moore et al, 1982). De todas ellas, la perforación realizada a unos 11 km de las costas de Guerrero, en el sitio 487 (15° 51.210' de latitud Norte y 99° 10.518' de longitud W), penetró completamente en la pila sedimentaria y alcanzó la corteza basáltica subyacente (Figuras 4 y 5).…”

“…La columna litológica de este sitio (Figura 5) ha sido descrita y estudiada con cierto detalle por varios autores (Moore et al, 1982;Plank y Langmuir, 1998;Verma, 2000a;LaGatta et al, 2003). Los sedimentos hemipelá-gicos tienen un carácter terrígeno y deben derivarse de la denudación de las rocas continentales de la margen pacífi ca mexicana.…”