Alternative Diagenetic Models for Cretaceous Talus Deposits, Deep Sea Drilling Project Site 536, Gulf of Mexico

Abstract

Talus deposits recovered from Site 536 show evidence of aragonite dissolution, secondary porosity development, and calcite cementation. Although freshwater diagenesis could account for the petrographic features of the altered talus deposits, it does not uniquely account for isotopic or trace-element characteristics. Also, the hydrologic setting required for freshwater alteration is not easily demonstrated for the Campeche Bank. A mixing-zone model does not account for the available trace-element data, but does require somewhat less drastic assumptions about the size of the freshwater lens. Although a seawater (bottom-water) alteration model requires no hydrologic difficulties, unusual circumstances are required to account for the geochemical characteristics of the talus deposits using this model.

Site 634: Northwest Providence Channel

“…The type B clasts in Unit IV are similar to those at the foot of the Campeche Escarpment reported by Halley et al (1984). They interpreted the moldic porosity to have formed in deep wa ter by selective leaching of aragonite.…”

Interactions between the Laramide Foreland and the passive margin of the Gulf of Mexico: Tectonics and sedimentation in the Golden Lane area, Veracruz State, Mexico

“…The best data for this stratigraphic level comes from the DSDP site 538A and EXXON well 3, both of which indicate evidence of clay, silts and calcareous muds Halley et al, 1984).…”

Evolution of pore space in the Poza Rica trend (Mid‐Cretaceous), Mexico

“…This is a potential petroleum prospect several tens of kilometres wide and many thousands of kilometres long. Prolific production is established in the Poza Rica and Reforma trends (Enos, 1985;Viniegra, 1981 ;Aguayo et al, 1985) and secondary porosity is reported from the slope east of the Yucatan shelf (Halley et al, 1984). All portions of this trend will clearly not be equally prospective, but if zones of former discharge of meteoric water into the sea can be identified, these should be explored with particular care.…”

“…The Tamabra Limestone (Mid-Cretaceous, Albian and Cenomanian) of the Poza Rica trend, Mexico, will ultimately produce more than 2.3 x lo9 barrels of oil, largely from secondary porosity in probable basinmargin mass-flow deposits (Enos, 1977a(Enos, , 1985. Clarifying and quantifying the evolution of pore space in this type of reservoir has implications for development of this trend and other comparable deposits (Cook & Mullins 1983;Enos & Moore 1983;Halley, Pierson & Schlager, 1984;Hobson, Caldwell & Toomey, 1985;Crevello & Harris, 1985;Enos, 1977b).…”

“…Secondary porosity through aragonite dissolution accompanied by calcite precipitation, very reminiscent of Tamabra diagenesis, was recently reported from a basin-margin setting in the southeastern Gulf of Mexico (Hal1eyet ai., 1984). These Early Cretaceous (Aptian-Albian) rocks formed from shallow-water skeletal debris deposited 5 km east of the Campeche Escarpment at an estimated paleodepth of 1700 m. Halley et al (1984) considered alteration in seawater, fresh (meteoric) water, and mixed water as alternative hypotheses for the observed diagenetic effects. They concluded that available data do not allow a clear choice among the hypotheses; each encountered problems with the bulk geochemistry of the rocks or the inferred hydrologic setting.…”