Linking early diagenesis and sedimentary facies to sequence stratigraphy on a prograding oolitic wedge: The Bathonian of western France (Aquitaine Basin) |
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| Institution: | 1. Department of Earth Sciences, Laurentian University, Sudbury, ON P3E 2C6, Canada;2. Department of Geological Science, University of Manitoba, 240 Wallace Bldg, 125 Dysart Rd, Winnipeg, MB R3T 2N2, Canada;3. Department of Earth Sciences, Alexander Murray Building, 300 Prince Philip Drive, Memorial University of Newfoundland, St. John''s, NL A1B 3X5, Canada;1. Center of Advanced Study in Geology, Banaras Hindu University, Varanasi 221005, India;2. Department of Earth and Planetary Sciences, University of Allahabad, Allahabad 211002, India;3. National Centre for Antarctic and Ocean Research, Vasco-da-Gama 403804, Goa, India;4. CSIR-National Institute of Oceanography, Dona Paula 403004, Goa, India |
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| Abstract: | To improve the understanding of the distribution of reservoir properties along carbonate platform margins, the connection between facies, sequence stratigraphy, and early diagenesis of discontinuities along the Bathonian prograding oolitic wedge of the northeastern Aquitaine platform was investigated. Eight facies are distributed along a 50 km-outcropping transect in (1) toe-of-slope, (2) infralittoral prograding oolitic wedge, (3) platform margin (shoal), (4) open marine platform interior, (5) foreshore, and (6) terrestrial settings. The transition from shallow platform to toe-of-slope facies is marked in the field by clinoforms hundred of meters long. Carbonate production was confined to the shallow platform but carbonates were exported basinward toward the breakpoint where they cascaded down a 20–25° slope. Ooid to intraclast grainstones to rudstones pass into alternating marl-limestone deposits at an estimated paleodepth of 40–75 m. Three sea-level falls of about 10 m caused the formation of discontinuities corresponding to sequence boundaries. Along these discontinuities, erosional marine hardgrounds formed in a high-hydrodynamic environment at a water depth of less than 10 m, displaying isopachous fibrous cements and meniscus-type cements. The cements pass landward into meniscus and microstalactitic forms along the same discontinuities, which are characteristic of subaerial exposure. During the deposition of transgressive systems tracts, carbonate accumulation remained located mostly on the shallow platform. Energy level increased and carbonates were exported during the deposition of highstand systems tracts forming the infralittoral prograding oolitic wedge. During the deposition of lowstand systems tracts, carbonate production fell to near zero and intraclast strata, derived from the erosion of hardgrounds on the shallow platform, prograded basinward. Early diagenetic cements are related exclusively to discontinuities that are not found within the prograding wedge because of the continuous high sedimentation rate under lower hydrodynamic conditions. This absence of early cementation within the infralittoral prograding oolitic wedge was conducive to porosity conservation, making such features good targets for carbonate reservoir exploration. This study proposes a novel sequence stratigraphy model for oolitic platform wedges, including facies and early diagenesis features. |
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| Keywords: | Infralittoral prograding oolitic wedge Carbonate platform Depositional model Early diagenesis Facies Sequence stratigraphy Jurassic |
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