Sedimentology, petrology, and gas potential of the Brallier Formation: upper Devonian turbidite facies of the Central and Southern Appalachians
The Upper Devonian Brallier Formation of the central and southern Appalachian basin is a regressive sequence of siltstone turbidites interbedded with mudstones, claystones, and shales. It reaches 1000 meters in thickness and overlies basinal mudrocks and underlies deltaic sandstones and mudrocks. Facies and paleocurrent analyses indicate differences between the depositional system of the Brallier Formation and those of modern submarine fans and ancient Alpine flysch-type sequences. The Brallier system is of finer grain size and lower flow intensity. In addition, the stratigraphic transition from turbidites to deltaic sediments is gradual and differs in its facies succession from the deposits of the proximal parts of modern submarine fans. Such features as massive and pebbly sandstones, conglomerates, debris flows, and massive slump structures are absent from this transition. Paleocurrents are uniformly to the west at right angles to basin isopach, which is atypical of ancient turbidite systems. This suggests that turbidity currents had multiple point sources. The petrography and paleocurrents of the Brallier Formation indicate an eastern source of sedimentary and low-grade metasedimentary rocks with modern relief and rainfall. The depositional system of the Brallier Formation is interpreted as a series of small ephemeral turbidite lobes of low flow intensity which coalesced in time to produce a laterally extensive wedge. The lobes were fed by deltas rather than submarine canyons or upper fan channel systems. This study shows that the present-day turbidite facies model, based mainly on modern submarine fans and ancient Alpine flysch-type sequences, does not adequately describe prodeltaic turbidite systems such as the Brallier Formation. Thickly bedded siltstone bundles are common features of the Brallier Formation and are probably its best gas reservoir facies, especially when fracture porosity is well developed.
- Research Organization:
- Texas Univ., Austin (USA); Amoco Production Co., Houston, TX (USA); Cincinnati Univ., OH (USA). H.N. Fisk Lab. of Sedimentology
- OSTI ID:
- 5442102
- Report Number(s):
- DOE/METC/5201-5
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
030200* -- Natural Gas-- Reserves
Geology
& Exploration
58 GEOSCIENCES
580100 -- Geology & Hydrology-- (-1989)
APPALACHIA
APPALACHIAN MOUNTAINS
DEVONIAN PERIOD
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
GEOLOGY
MOUNTAINS
NATURAL GAS DEPOSITS
NORTH AMERICA
PALEOZOIC ERA
PETROLOGY
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SILT
STRATIGRAPHY
USA