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The Comanche Series and associated rocks in the subsurface in central and south Florida

1965; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp447

2330-7102

Paul L. Applin, Esther English Richards Applin,

Geological Modeling and Analysis

The stratigraphy, structure, micropaleontology, and oil possibilities of a part of the Mesozoic sedimentary section in the subsurface of an area of more than 30,000 square miles in central and south Florida have been studied from the data provided by oil test wells drilled in the area.Microscopic examination of cores and samples of drill cuttings provide the basic stratigraphic data for this report.Electric logs aid in the correlation of the data.The primary purpose of the report is the integration of the data from the scattered test wells and the development from them of an interpretation of the regional geology.The Coastal Plain floor in the central and northern parts of the Florida peninsula is the truncated surface of a wide variety of igneous and sedimentary rocks that are chiefly Precambrian(?) and early Paleozoic in age.In the northern part of the peninsula, rocks of Late Triassic(?)age are evidently a part of the truncated floor.Highly altered igneous rocks of uncertain age have been penetrated only in a single well on the southeast coast of the peninsula.The depth below sea level to the Coastal Plain floor ranges from about 2,600 feet in northern Florida to more than 12,500 feet near Lake Okeechobee in the south-central part of the State.Oil test wells in south Florida have not been drilled sufficiently deep to penetrate the pre-Coastal Plain rocks.In south Florida, a stratigraphic unit of Late Jurassic (?) or earliest Cretaceous (?) age, the Fort Pierce Formation, is the oldest unit of the Coastal Plain rocks.The Fort Pierce Formation, the overlying units of the Comanche Series, and the basal rocks of the Gulf Series compose the part of the Coastal Plain rocks described in this report.This section of Mesozoic age forms a wedgelike mass that pinches out around an irregular-shaped area of lower Paleozoic strata in northern Florida and thickens gradually southeastward, southward, and southwestward toward the coast.On the Florida Keys about 8,000 feet of the section was penetrated in a well that stopped in the Fort Pierce Formation.The depth below sea level at the top of the Comanche rocks ranges from about 4,000 feet in central Florida to 8,582 feet in a well in Collier County on the southwest coast.The Comanche rocks in central Florida overlie with profound unconformity the truncated surface of the Coastal Plain floor.Most wells in south Florida terminated in the Comanche rocks, although six wells penetrated the underlying Fort Pierce Formation, the thickness and areal extent of which are largely unknown.Throughout the central and south parts of the peninsula, the Atkinson Formation of early Gulf age overlies the Comanche rocks.Irregularly interbedded carbonate rocks, evaporites, and a few thin lenses of dark shale compose the generally similar lithologic sequence of the Comanche rocks and of the underlying Fort Pierce Formation in the southern part of the peninsula.The carbonate rocks are separated into four major stratigraphic units, chiefly on the basis of distinctive microfaunas.The new central part of the peninsula was a stable area in contrast to the gradually subsiding southern and central parts.Beginning with the beds of middle Late Cretaceous age, the successively younger units of the Gulf Series and the units of Cenozoic age were deposited over most of the peninsula.82°.