Tectonic Controls on Pliocene Evaporite Facies, Enriquillo Basin, Dominican Republic
Well, seismic stratigraphic, and outcrop observations from the Enriquillo basin, Dominican Republic, are used to reconstruct Pliocene evaporite environments in a complex strike-slip basin. The 2,000-km2 floor of the Enriquillo basin is presently bounded by strike-slip, reverse, and thrust faults which form part of a 200 to 250-km wide zone of left-lateral, strike-slip motion between the North American and Caribbean plates. Convergent strike-slip displacement of bounding mountain blocks over the last 5 m.y. has depressed certain areas of the present valley floor to 80 m below sea level. In the deepest part of the basin, middle Miocene carbonate basement is overlain by up to 5 km of upper Miocene to Holocene clastic and evaporitic sedimentary rocks.
Surface and subsurface data indicate important tectonic controls on two distinct groups of Pliocene evaporite facies. (1) A shallow-water evaporite group occupies a 50-km2 anticlinal high defining the northern edge of the post-middle Miocene basin. This shallow-water group consists of four 1 to 9 m-thick gypsum horizons within an 860-m thick, coarsening-upward section of sandstone, siltstones, and conglomerate. Gypsum facies include nodular alabastrine gypsum, finely crystalline laminated gypsum, cavoli-type selenite with blades up to 40 cm in length, and gypsrudites. (2) A deep-water evaporite group occupies a 150-km2 synclinal low in the subsurface immediately to the south of the exposed shallow-water group. This deep-water group consists of approximately 1,700 m of 0.3 to 2-m thick beds of halite, gypsum, and anhydrite interbedded with euxinic black mudstones and siltstones. We interpret the deep-water evaporite group as forming within an actively subsiding synclinal axis, while the shallow-water evaporite group formed 10-20 km to the north on an actively growing anticline. This anticlinal high acted to shield the deep-water evaporite group from coarse clastic input.
AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.