Woodford Shale (Upper Devonian-Lower Mississippian) and associated phosphate nodules

Conference · Thu Feb 01 04:00:00 EST 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6891768

Siy, S ^[1]

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1. Bridge Oil (U.S.A.) Inc., Dallas, TX (USA)

A deep-water marine environment is inferred for the Woodford Shale formation (Upper Devonian-Lower Mississippian) in the Arbuckle and Ouachita mountains of southern Oklahoma. Black shales and associated phosphate nodules were deposited peripherally to the carbonate shelf adjacent to the North American craton. Analysis indicates that shales and interbedded cherts lack siliciclastic detritus and shallow-water fauna, and that they have an abundance of siliceous organisms. Depletion of Ce in the Woodford Shale relative to average shale compositions suggests the influence of deep oceanic water. Carbon isotope compositions of shales, cherts, and phosphates for {delta}{sup 13}C range from {minus}27.5 to {minus}30.2 {per thousand}. These values are comparable to Devonian-Mississippian values reported for distal marine sediments that get successively lighter farther from shore. In-situ phosphate nodules occurring in the top of the formation are early diagenetic features that formed in the upper few centimeters of organic-rich sediment in a poorly oxygenated subaqueous environment. A hierarchy of apatite morphologies in nodules indicates stages of diagenesis. Structureless collophane probably is representative of primary marine apatite. Higher order apatite phases successively include globular collophane, botryoidal apatite, and apatite crystallites. The latter commonly is associated with silicified nodules. Silicification of phosphate nodules represents the most advanced stage of diagenesis prior to sediment lithification, and it implies that silica diagenesis within the Woodford occurred after nodules formed. Preserved radiolarians and sponge spicules observed in nodules also indicate that apatite precipitated before biogenic silica dissolved.

• OSTI ID: 6891768
• Report Number(s): CONF-9003145--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (USA) Journal Volume: 74:2
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
BITUMINOUS MATERIALS
BLACK SHALES
CARBON 13
CARBON ISOTOPES
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CARBONIFEROUS PERIOD
CHATTANOOGA FORMATION
DEPOSITION
DEVONIAN PERIOD
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MINERAL RESOURCES
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NUCLEI
OIL SHALES
OKLAHOMA
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PETROLEUM DEPOSITS
PHOSPHATE ROCKS
RESOURCES
ROCKS
SEDIMENTARY ROCKS
SOURCE ROCKS
STABLE ISOTOPES
USA