Dolomite cement eogenetic

The mass transfer problem may be resolved if eogenetic pore fluids were transmitted locally across the GGF in response to fault-related changes in pore pressure and near-surface hydrology (e.g. Knipe, 1993). The cemented fractures at Ballycastle show clear evidence for elevated pore fluid pressures and hydraulic fracturing, and the pulsed nature of dolomite cementation implies a tectonic drive. Kerr (1987) commented on the likelihood that the GGF was active in the Late Carboniferous/ Permian. Argillaceous coastal plain sediments asso-... 

Lateral variations in the eogenetic association may be related to changes in sedimentary conditions or to the starting mineral composition. The development of nitrates was probably controlled in part by sedimentary rhythms. In the border zones of the Triassic Basin of the Sahara where the source of supply (Hoggar Massif) was probably closer by, calcretes were formed and the deposits were cemented by calcite with a heterogeneous structure. In the case of farther removed source areas and a more stable sedimentation the sandstones are characterized by a poikilitic nodular dolomite cement. Variations in the composition of the sandstone cements between calcite and dolomite may be explained by the ionic composition of the solutions in the... 

Sediments were also extensively cemented by near-surface and pre-compactional eogenetic siderite (8 0 = -16.9%o to -8.1%o), calcite (5 0 = -10.2%o to -4.8%o) and dolomite (5 0 = -4.3%o to -1.5%o). The anomalously low5 0 values of siderite are attributed to microbial oxygen isotopic fractionation, as it would otherwise indicate unreasonably high precipitation temperatures (up to 120°C). The eogenetic caleites and dolomites precipitated from such meteoric waters at temperatures of 10-30°C. 

---