--> ABSTRACT: Metamorphism, High Temperature Diagenesis, and Enhanced Hydrocarbon Maturation by Igneous Intrusion in the Smackover Formation, Northeastern Louisiana, by E. Heydari, G. Byerly, and D. Henry; #90941 (1997).
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ABSTRACT: Metamorphism, High Temperature Diagenesis, and Enhanced Hydrocarbon Previous HitMaturationNext Hit by Igneous Intrusion in the Smackover Formation, Northeastern Louisiana


The lower member of the Smackover Formation has been considered an important hydrocarbon source rock in the northern Gulf of Mexico. Numerous igneous dikes intruded the lower member in Monroe Uplift, northeastern Louisiana during the Late Cretaceous time. Intense heating from igneous intrusions resulted in enhanced Previous HitmaturationTop, early destruction of liquid hydrocarbons, generation of significant amounts of hydrocarbon gases, and high temperature water/rock/hydrocarbon diagenetic and metamorphic interactions.

One of the dikes was encountered at a depth of 2.1 km in Morehouse Parish. The dike is 10 m thick and exhibits holocrystalline but porphyritic texture. It is composed of complexly zoned phenocrysts and microphenocrysts of titanaugite, analcime, sphene, and apatite. Microprobe analyses of titanaugite and bulk rock trace element analyses suggest compositions typical of those found in highly undersaturated, moderately magnesian igneous rocks. Na2O content of the dike decreases while its K2O composition increases toward the margin of the intrusion, suggesting significant exchange with the country rocks.

The intrusion caused contact metamorphic effects to 6 m above and 4 m below the dike. This asymmetric contact aureole is observed in textures, mineral assemblage, and delta180 and delta13C compositions. Within one meter of the dike, contact metamorphic assemblages include calcite (cc) + feldspar + albite + diopside + grossular + apophyllite, and pyrite (py). Farther from the dike, poikiloblastic cc locally includes sprays of pectolite + py in a fine grained matrix of cc + quartz +/- dolomite. Calcite delta18O composition at the dike contact is -13 (o/oo PDB) and decreases logarithmically to -4 for unmetamorphosed rock. Calcite delta13C composition is -3 at the contact and increases to +4 for the sedimentary carbonates. Farther from the dike, the reaction of anhydrite with hydrocarbon gases in grainstone reservoirs resulted in generation of H2S and CO2.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana