Dimensions, texture- distribution, and geochemical heterogeneities of fracture– related dolomite geobodies hosted in Ediacaran limestones, northern Oman

Veerle Vandeginste, Cedric John, John Cosgrove, Christina Manning

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Predicting spatial distribution, dimension, and geometry of diage-netic geobodies, as well as heterogeneities within these bodies, is challenging in subsurface applications, and can impact the results of reservoir modeling. In this outcrop–based study, we generated a data set of the dimensions of fracture–related dolomite geobod-ies hosted in Ediacaran (Khufai Formation) limestones of the Oman Mountains that are up to several hundreds of meters long and a few tens of meters wide. The dolomite formed under burial conditions by fluids that interacted with siliciclastic layers, as demonstrated by the enriched Fe (up to 4.4%) and Mn (up to 0.8%) contents and 87 Sr∕ 86 Sr (∼0.710) signatures. Dolomitization probably occurred during the Hercynian Orogeny (or pre-Permian) because dolomitization predates some folding and pre-Permian rocks have seen intense deformation related to the Carboniferous Hercynian Orogeny. Moreover, dolomitization occurred between the onset and termination of bedding-parallel stylolitization and thus most likely before deep burial related to the Alpine Orogeny. Hence, dolomitization most likely occurred before deep burial related to the Alpine Orogeny and during or following the intense deformation related to the Carboniferous Hercynian Orogeny had affected pre–Permian rocks. The clumped–isotope signature yields a temperature of approximately 260°C (500°F), interpreted as the apparent equilibrium tempera-ture obtained during uplift after deepest burial during the Late Cretaceous. Lateral transects across the dolomite bodies show that
zebra dolomite textures are common throughout the body and that
vugs are more common at the rim than the center of the bodies.
Moreover, a weak geochemical trend exists with more depleted
18O, Fe, and Mn concentrations in the core than at the rim of the
dolomite bodies. These results show that minor heterogeneities
exist within the dolomite bodies investigated. These data contrast
with previous studies, in which more significant variation is
reported in width of the dolomitization halo and texture for larger
dolomite bodies that formed in host rocks more permeable than
the examples from the Oman Mountains.
Original languageEnglish
JournalAAPG Bulletin
Issue number9
Publication statusPublished - 1 Sept 2014

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