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AAPG Bulletin


AAPG Bulletin, V. 86, No. 7 (July 2002), P. 1285-1303.

Copyright ©2002. The American Association of Petroleum Geologists. All rights reserved.

Massive recrystallization of low-Mg calcite at high temperatures in hydrocarbon source rocks: Implications for organic acids as factors in diagenesis

Ezat Heydari,1 William J. Wade2

1Department of Physics, Atmospheric, and General Science, Jackson State University, P.O. Box 17660, Jackson, Mississippi, 39217; email: [email protected]
2Location Sample Service International, 34 Highbush Court, The Woodlands, Texas, 77381; email: [email protected]


Ezat Heydari finished his undergraduate studies in geology at the University of Tehran in Iran. His graduate education in geology includes a Master's degree from the Pennsylvanian State University and a Ph.D. from Louisiana State University (LSU). He has worked as a research scientist at LSU and at the Mississippi Office of Geology. He is currently an assistant professor at Jackson State University. Heydari has conducted research on the sedimentology and diagenesis of Mesozoic formations of the northern United States Gulf Coast and Permian and Triassic strata of Iran. His interests revolve around the depositional environment, diagenesis, and geochemistry of carbonate rocks to solve issues related to fluid-rock interactions and to the Earth's history.

William Wade earned B.A. and M.S. degrees in geology from Vanderbilt University and his Ph.D. from Louisiana State University. He has worked for the Tennessee Division of Geology and Champlin Petroleum Company; more recently he formed and manages Applied Tomographics Inc. and Location Sample Service International, providers of analytical services to the oil industry.


This article was supported by the Mississippi Office of Geology and Jackson State University. Michael B. E. Bograd, David Dockery, and Jack Moody reviewed the manuscript and provided constructive criticism. Critical comments by AAPG reviewers John D. Humphrey, Neil Hurley, and Clyde H. Moore significantly improved the manuscript. Editorial assistance by Paula Sillman, John Shelton, and Ken Wolgemuth is appreciated.


We document massive recrystallization of low-Mg calcite lime mudstone source rocks at moderately high temperatures in the Smackover Formation of Mississippi. This process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons, secondary porosity generation in reservoirs, and global environmental change. This interpretation is based on contrasting the following petrographic and bulk-rock geochemical characteristics of organic-poor vs. organic-rich lime mudstones:

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