Sequence stratigraphy, depositional and diagenetic environments of the late Cambrian glauconite bearing oolitic limestones in the Kelan Section, Shanxi, China.

The current study presents results on depositional and diagenetic environments of the glauconite-bearing oolitic carbonates of the upper part of the basal third-order depositional sequence (DS6) of the Cambrian Fengshan Formation at Kelan in the North China Platform. The Fengshan Formation comprises calcareous mudstone and shale of shelf environment followed by calcareous mudstone, micritic limestone of deep ramp to oolitic limestones of shallow ramp environments. The glauconite-bearing oolitic carbonates are restricted in the upper part of the sequence which was deposited during the forced regressive event. Petrographic study revealed that the sediments comprised of both carbonate and non-carbonate framework constituents. These constituents are mostly comprised of rounded to elliptical, radial-concentric ooids, dolomitized ooids, bioclasts (trilobites, brachiopod, and echinoderms), glauconitic pellets with fibro-radiating rims, and pyrite crystals. The radial-concentric structure of ooids suggests high-energy shallow water deposition conditions. Also, the presence of glauconite along with oolitic grainstone in the restricted upper portion of the Fengshan Formation provides credible evidence of its deposition under high-energy conditions during relative sea-level fall. It is therefore inferred that the glauconite was precipitated on or in close proximity to the Cambrian calcite seafloor during the forced regressive event prior to calcite cementation. [ABSTRACT FROM AUTHOR]