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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 68 (1984)

Issue: 4. (April)

First Page: 524

Last Page: 524

Title: Depositional and Diagenetic History of Bodcaw Sand, Cotton Valley Group (Upper Jurassic), Longwood Field, Caddo Parish, Louisiana: ABSTRACT

Author(s): Billy Joe Russell, Jr.


Bodcaw Sand contains fine-grained sandstones and siltstones deposited within a barrier-bar-complex. Based on vertical changes in sedimentary structures, texture, and mineralogical composition, upper-, middle-, and lower-shoreface lithofacies in the Bodcaw Sand can be identified. Cross-stratification and low-angle laminations, rarely disrupted by biogenic structures, characterize the fine-grained upper-shoreface sandstones. Middle-shoreface sandstones have undergone extensive reworking by biotic and abiotic factors. Few primary sedimentary structures and early generation trace fossils are preserved in middle-shoreface sandstones. Lower-shoreface siltstones and very fine-grained sandstones contain lenticular and wavy bedding, much of which is disrupted by bioturbation.

Bodcaw Sand has low porosity and permeability. Vertical and lateral variation in porosity and permeability are related to depositional textures and diagenetic fabric of Cotton Valley sediments. Bodcaw Sand has experience a complicated diagenetic history. Compaction, cementation, replacement, and dissolution modified primary rock properties following deposition of barrier-bar sediments. Cementation plays an important role in modification of reservoir properties. Important authigenic minerals identified in Bodcaw Sand include silicates, carbonates, and phyllosilicates. Based upon textural relationships between allogenic grains, authigenic constituents, and pore characteristics, a relative succession of diagenetic events can be interpreted. Two major diagenetic sequences occurred within odcaw Sand. Diagenetic events within one sequence included cementation by silica, phyllosilicates, and calcite, as well as, dissolution and replacement reactions. The other sequences primarily involved diagenetic reactions of calcite precipitation, dissolution, and replacement.

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