Abstract: Development of Porosity in Carbonate Rocks of Evaporitic Basins, Alternative Mode of Formation

B. C. Schreiber, D. J. J. Kinsman, R. D. Nurmi

The development of high porosities in carbonate deposits associated with evaporitic sediments is believed to have developed during periods of drawdown within a formative basin and consequent subaerial exposure. One alternative suggestion for the high porosities in such carbonate deposits may be that migrating pore waters, released during burial and dewatering of the associated sulfate deposits and salts, leach the carbonates. A second alternative is based on observation of massive replacement developed in comparatively modern deposits of upper Miocene patch-reef carbonate rocks (Messinian, Sicily). We suggest that the observed high porosities may be generated by very early replacement of carbonates by sulfates without the necessity of subaerial exposure and the developmen of vadose features. Comparable replacement of carbonates by salt has been observed in the Upper Silurian (Salina Formation, Michigan basin). In this case autochthonous algal stromatolites and oolitic carbonate rocks are replaced by halite without clear-cut evidence of subaerial exposure. In both instances (Miocene and Silurian) the simple removal of the highly soluble sulfate and halite in the subsurface would leave carbonate rocks of very high porosities. Evaporitic drawdown may relate to the replacement process by providing the hydraulic gradient required for the massive pore-water migration which leads to the carbonate replacement.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA