--> Abstract: Bedded Cherts in the Early Ordovician Arbuckle Group of Southwestern Oklahoma, by D. A. Ragland and R. N. Donovan; #91004 (1991)

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Bedded Cherts in the Early Ordovician Arbuckle Group of Southwestern Oklahoma

RAGLAND, DEBORAH A., Consulting Geologist, Ponca City, OK, and R. N. DONOVAN, Texas Christian University, Forth Worth, TX

Bedded cherts are a rarely occurring but environmentally significant facies in the Early Ordovician Arbuckle Group. Two such units have been identified: one in the Cool Creek Formation and one in the Kindblade Formation. In each, microcrystalline calcite and dolomite alternate in thin laminae with microcrystalline silica in units up to 25 cm in thickness. The areal extent of the bedded cherts encompasses more than 130 sq km.

It is hypothesized that the interlaminated cherts and micrites were deposited in very shallow marine conditions. A relatively small part of the Oklahoma Aulacogen was cut off from open ocean circulation, resulting in an isolated lagoon. The chert/micrite couplets may represent seasonal deposits in the lagoon. During seasonal flooding, slightly deeper water resulted in algal growth with accompanying precipitation of carbonates and solution of detrital quartz sand. During the dry season, the dissolved silica precipitated, resulting in thin layers of microcrystalline chart. Some carbonate layers contain small pseudomorphs after what may have been gypsum and anhydrite crystals and nodules, indicating that salinities increased enough to permit formation of evaporites. At least ten couplets occur in the thickest units, suggesting that the lagoon existed for ten wet-dry seasons.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)