Diagenesis and geochemistry of the Aptian dolomite (cretaceous) in the Razzak Oil Field, western Desert, Egypt

Abstract

Petrographic study of selected thin sections from the Aptian dolomites in the Razzak Oil Field, Egypt reveals three dolomite textures. These textures have been classified based on crystal size, shape, uniformity, and trace element distribution. These textures are as follows: I) finely crystalline, planar-e dolomite, 2) medium to coarsely crystalline, non-planar dolomite, and 3) very coarsely crystalline, non-planar dolomite (saddle dolomite). Stable isotope analyses indicates that the Aptian dolomites formed in a marine environment and were later subjected to several diagenetic modifications that affected the original sediments. The finely crystalline, planar-e dolomite is penecontemporaneous in origin with 8 18 0 that ranges from -7.51 to -8.14%0VPDB and 8 lJ e that ranges from +0.39 to -1.27%0 VPDB. The medium to coarsely crystalline, non-planar dolomite is a replacement type with a meteoric origin. In this non-planar dolomite, the 1) 18 0 ranges from -7.99 to -8.82%0 VPDB and the o l3e ranges from -0.58 to -1.35%0VPDB. The void-filling (saddle dolomite) is the product of chemical compaction and is associated with the thermal sulfate reduction event. This saddle dolomite has 8 18 0 that ranges from -7.89 to -8.76%0 VPDB and 8 1lC that ranges from + 1.41to +2.42%0 VPDB. The diagenetic parasequence ofthe Aptian Dolomite is recorded by: I) deposition of the original sediments (lime mud); 2) dolomitization; 3) silicification, 4) pyritization, and 5) precipitation of saddle dolomites (pore-filling dolomite).

Temporal evolution, petrography and composition of dolostones in the Upper Devonian Plavinas Regional Stage, southern Estonia and northern Latvia

“…during their burial history (Warren 2000;Rifai et al 2006;Machel & Buschkuehle 2008). Large, replacive dolostone bodies are post-depositional and formed during some degree of burial, which includes effects of sedimentary loading, tectonic compression and pressure solution (Coniglio et al 2003 The bulk chemical composition of 63 rock samples was determined by XRF spectrometry on the Bruker S-4 spectrometer.…”

Cretaceous (Hauterivian–Cenomanian) palaeoceanographic conditions in southeastern Tethys (Matruh Basin, Egypt): Implications for the Cretaceous climate of northeastern Gondwana

“…The Alamein Dolomite is secondary in origin. It was originally formed from accumulation of lime mud in a low energy, relatively shallow neritic environment that was later subjected to various diagenetic processes (e.g., dolomitization, silcification, and pyritization; Abou Khadrah et al, 1978;Rifai, et al, 2006).…”

“…Dolomitization has probably biased the palynofacies extracted from the dolostone samples, and caused diminishing in the abundance of the dinocysts among other terrestrial and marine palynomorphs (Traverse, 2007;Rifai, et al, 2006, and particles/g) is confined to the shale horizons of the lowermost and uppermost parts of the sequence yielding PF-1B, indicating these fragile, oxidation-prone tissues were deposited in slightly more distal, lower energy marine settings, but still nearshore, possibly prodelta, during brief low stands (e.g., Tyson, 1995). The ternary plot of the palynomorph contents of samples yielding PF-1B indicates a shift in deposition from distal deltaic to deeper (shallow marine) conditions and a return to the more nearshore setting through time (Fig.…”