ESCHARD, REMI, BERNARD CARPENTIER, GUY DESAUBLIAUX, and BRIGITTE DOLIGEZ, Institute Francais du PEtrole, Rueil Malmaison, France

ABSTRACT: Facies Partitioning and Reservoir Architecture of a Transgressive Systems Tract from Outcrop and Subsurface Data (Campanian, San Juan basin, Colorado, and New Mexico)

The architecture of a major Transgressive Systems Tract has been studied in large outcrops and correlated with subsurface data in the Campanian series of the San Juan basin (Colorado and New Mexico). The TST shows a landward stepping pattern of seven units of shoreface and foreshore sediments. Each unit is 20 to 40m thick, and extends over 3 to 5 km in a dip direction, pinches out seaward in offshore shales and landward in coastal-plain sediments. Each unit is bounded by ravinement surfaces and has been deposited during a IVth order transgressive-regressive cycle.

The transgressive phase was recorded by a ravinement surface, by transgressive deposits reworked seaward and by thick coastal-plain and estuarine sediments aggrading landward. The coastal-plain series was shale-rich, and showed marsh sediments alternating with coal beds and t-de-influenced meandering channels. The estuarine complexes were very thick (up to 20m) and consisted of stacked tidal channels, sand flats and wave-influenced shoals.

The regressive phase consisted of a prograding wedge of storm-dominated shoreface, foreshore and coastal-plain sediments. This wedge showed a seaward stepping pattern of prograding units, related to the superimposition of several Vth order transgressive-regressive cycles. Each Vth order transgressive phase induced a landward shift of the facies associations and a minor ravinement surface. Then the progradation of a shingle of shoreface, foreshore and coastal-plain sediments occurred during the regressive phase.

The turn around between the transgressive and regressive phase of the IVth order cycle was marked by the vertical stacking of thick shoreface, foreshore back-barrier and coastal-plain deposits.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.