Sedimentology and diagenesis of the basinal facies of the Dimple Limestone, Marathon Basin, West Texas

Abstract

The Dimple Limestone (Morrowan?-Atokan), Marathon Basin, Texas, represents a break in the Ouachita clastic flysch sequence. Carbonate material was transported from the present northwest into the Ouachita trough, an abrupt change from influx of clastic flysch derived from a southern source. The basinal facies of the Dimple Limestone was deposited in the mid- to lower portions of a submarine fan system, and is represented by allodapic limestones, turbidite and hemipelagic shales, and thin black chert beds, also interpreted as turbidites.

The basinal facies may be divided into sedimentary packages, reflecting the ^ode of deposition. A package consists of a thick, coarse-grained, basal member with an overlying mudstone, followed by thinner interbedded limestones, shales, and cherts. The thick basal members of the oobiolithoclastic packstone and spiculiferous packstone lithofacies, show evidence of scouring. They represent the main locus cf the turbidity flows, channelized areas, or perhaps stronger flows with disturbance in shelf environments. Thick basal units typically fine upward into mudstones of the spiculiferous shale lithofacies. All sediments from the base through the mudstone were deposited by one continuously decelerating turbidity current. The thinner, interbedded turbidites within each sedimentary package represent weaker currents, with instability in upper slope, spicule-rich environments. They represent shifting of the main locus of the flows within the submarine fan system. Pelagic shales represent periods of relative quiescence, during which normel marine deposition resumed.

At least seven stages of diagenesis have altered the basinal Dimple sediments. These include: 1) post-burial diagenesis, 2) fresh-water diagenesis, 3) dolomitization, 4) precipitation of siderite, 5) precipitation of celbar, 6) fresh-water diagenesis, and 7) ferroan dolomitization. Virtually all effective porosity has been occluded, with no remaining reservoir potential. Potential as a hydrocarbon source is possible due to abundant organic matter, and depending on the burial history.