Facies Architecture and Sedimentary Structures in the drill cores of Uranium Bearing Sediments of Banganapalle Formation of Palnad Sub-basin, Guntur District, Andhra Pradesh

Abstract

The Banganapalle Formation, the lowest member of the Neoproterozoic Kurnool Group of rocks, resting over the basement granites, has been identified as the host rock for uranium in Koppunuru area in the western part of Palnad sub-basin. The uppermost arenite facies of the Banganapalle Formation is exposed on surface and shows only few bedform indicators like ripple marks, planer laminations etc. Down-hole lithological examinations on course of core drilling in Koppunuru and adjoining areas identified five recognizable lithofacies of Banganapalle Formation, viz. basal conglomerate unit, quartzite-shale intercalated facies, and two quartz arenite facies separated by a grey shale dominated argillaceous facies.
 The polymictic conglomerate, with unsorted grit to pebble size clasts of granite, shale, quartzite, vein quartz and dolerite indicate short distance transportation and derivation from nearby granitoids traversed by quartz reef/dolerite dykes. Cyclic repetitions of arenaceous and argillaceous sediments in Banganapalle lithocolumn above the basal conglomerates point to alternate rhythmic marine transgression and regression regimes. These units can also be discriminated based on their sedimentary texture, bedforms and several soft-sedimentary penecontemporaneous deformational structures (PCD) like load structure, convolute bedding/laminations, and slump structures such as micro-slips, gravity faults and folds. These syn-sedimentary structures clearly indicate perturbation and submergence of the basin contemporaneous to deposition. Cross-beds suggests change in current direction/intensity while bi-directional symmetrical ripples in outcrops of upper arenite facies suggests that the Banganapalle sediments are derived from the basement granitoids exposed to the north as well as upper Cuddapah sediments to its west. Overall, the sedimentary structures, textural and composition variation of the lithounits suggest deposition of these sediments in marginal marine, inter- to supra-tidal flat environment. The porous and permeable nature of the quartz arenite and the basal conglomerates and the presence of available reductants in the form of sulphides and carbonaceous matter make them the best suited loci for fluid movement and precipitation of uranium.

Geochemical characterization of shale deposits around Afikpo area, southeastern Nigeria

“…According to Deconinck et al (2005) and Dera et al, (2009), clay minerals study is considered to be a powerful tool for the interpretation of weathering conditions and paleoclimate in the source area while Da-Peng et al (2012) documented that trace and rare earth element geochemical study of ne-grained sediments, in most cases are assumed to give a clue to the average composition for the upper continental crust (UCC) more than any other sedimentary rock, because, they preserve the signature of the precursors and diagenetic history (Mondal et al, 2012;Madhavaraju et.al., 2016). Some authors, although not limited to Cullers, 2000Cullers, , 2002Gupta et al, 2012;Raza et al, 2012; Armstrong-Altrin, 2009; Fatima and Khan, 2012; Madhavaraju, 2015; Ramachandran et al, 2016 have demonstrated that geochemical compositions of clastic sediments are helpful in understanding the source-area weathering conditions and provenance. Although, chemical weathering, modi cation in redox conditions and post-depositional diagenesis can rework the main chemical composition of the shale (Nesbitt et al, 1996;Armstrong-Altrin et al, 2015;Madhavaraju, 2015).…”