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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 67 (1983)

Issue: 3. (March)

First Page: 466

Last Page: 467

Title: Deep-To-Shallow Carbonate Ramp Transition in Viola Limestone (Ordovician), Southwest Arbuckle Mountains, Oklahoma: ABSTRACT

Author(s): Patrick K. Galvin

Article Type: Meeting abstract


The Viola Limestone (Middle and Upper Ordovician) of the

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southwest Arbuckle Mountains was deposited on a carbonate ramp within the southern Oklahoma Aulacogen. Depositional environments include (1) anaerobic, deep-ramp setting represented by microfacies RL, CH, CGL, and A, (2) dysaerobic, mid-ramp setting represented by microfacies B, and (3) aerobic, shallow-ramp setting represented by microfacies C and D.

Deposition in the deep- and mid-ramp environments was dominated by bottom-hugging currents produced by off-platform flow of denser waters. These currents moved down a broad slope that was locally incised by gullies. Deposits of the broad slope, microfacies A and B, originated from a line-source and are found throughout much of southern Oklahoma. Primary sedimentary structures include millimeter-size laminations, starved ripples, and concave-up and inclined erosional surfaces. Shelly benthic fauna are rare in A and B; trace fossils are common only in B. Deposits associated with the line-source gully, microfacies RL, CH, and CGL, are laterally confined; they have been observed only in the southwest Arbuckle Mountains. Primary sedimentary structures present in RL include wavy and ripple- ross laminae. Microfacies CH, contained within RL and interpreted as a submarine channel deposit, is present only at one locality. Primary sedimentary structures present in CH include an erosional base and several internal erosional surfaces, lateral accretionary sets, and imbricated, locally derived intraclasts.

Deposition in the aerobic, shallow-ramp setting (microfacies C and D) was dominated by storm processes and intervening periods of bioturbation. An increase in both size and abundance of pelmatazoan fragments is the characteristic feature of these microfacies.

High total organic carbon (TOC) values have been reported for the lower Viola. TOC values of 1% have been reported from microfacies A, and TOC values of 5% have been reported from microfacies RL. These high values suggest that A and RL may act as hydrocarbon source rocks. Recognition of these microfacies in the subsurface will contribute to our knowledge of the Viola Limestone as an exploration target.

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