Depositional Environment of Phosphorites of the Sonrai Basin, Lalitpur District, Uttar Pradesh, India

Abstract

Phosphates are regarded as one of the most important fertilizer minerals used by man. In Sonrai basin of Lalitpur the phosphorites are found to occur as lenticular and detached bodies throughout the Formation of the "ijawar Group. Individual bodies range from a few meters to about km in length, and width varies from thin bands to about meter with P O concentration ranging from to %. The Paleoproterozoic "ijawar Group are overlain by the "rchaean "undelkhand "asement Complex and underlain by Vindhyan Supergroup. The occurrence of phosphorites is confined to the Sonrai Formation which consists of massive to brecciated phosphorite within the lower reddish shales, with at least three bands identified. Megascopic study reveals that the brecciated phosphorite is reddish brown in color and fine to medium grained with angular fragments of chert and quartz embedded in a groundmass of iron oxides and secondary silica intercalated with minor veins of chert and iron oxides. The phosphorite horizon in the Lalitpur area is associated with pink to white brecciated massive quartzite, shale, dolomite and limestone of the basal unit. The concentration trends of certain major oxides indicate that the phosphorites are more enriched in CaO, P O and SiO than "l O , Fe O , TiO , Na O and K O. The concentration trends of trace elements reveal that the phosphorites are moderately enriched in Co, Zn, Zr, Pb, U than in Sc, "a, V, Cr, Ni, , Rb, Sr, Y and Th. The dispersion patter, correlation coefficient and mutual relationship of significant major oxides represented by plotted diagrams, indicate that SiO , CaO, MgO are antipathetically related with P O . The relationship suggests a gradual replacement among these oxides during diagenesis. High values of P O and CaO in the phosphorites indicate more concentration of apatite constituent. The difference in geochemical behavior of CaO and MgO may be due to ionic substitution of Ca + by MgO + in the apatite crystal lattice during alkaline environment of the basin. The strong negative relationship between P O with Fe O in phosphorites may be due to leaching and/mild weathering of iron from the ores and reprecipitation along with P O in the pore spaces, cavities/voids, veins, etc in highly oxidizing marine environment of the basin. The minimum evidence of organic matter, absence of sulphide minerals and lower concentration of V, Ni, and

Magmatic underplating associated with Proterozoic basin formation: insights from gravity study over the southern margin of the Bundelkhand Craton, India

“…3) also suggests the presence of a high-density body with a large extent in the areas covered by the Proterozoic sedimentary basins. With the upward-continued regional-residual gravity anomaly maps and computed 2D forward models, it can be said that the highs observed are due to the volcanogenic sequences of Kurrat volcanics (Dar and Khan, 2016;Rawat et al, 2018) within the Bijawar Group of rocks along with the thick highdensity underplating emplaced in the lower crust just above the Moho. The underplating appears to be thickest under the central regions of the profiles, lying along the contact between the Bundelkhand Craton and the sedimentary basin sequences, as seen from the forward models of the two profiles (Figs.…”

Magmatic underplating associated with Proterozoic basin formation: insights from gravity study over the southern margin of Bundelkhand craton, India

“…The central high observed in the Bouguer 360 anomaly utilizing the global grid data also suggests the presence of a high-density body with a large extent in the areas covered by the Proterozoic sedimentary basins. With the computed 2D forward models, it can be sufficiently said that the highs observed is due to the volcanogenic sequences of Kurrat volcanics (Dar and Khan, 2016;Rawat et al, 2018) within the Bijawar group of rocks along with the thick high-density underplating emplaced in the lower crust just above the Moho.…”

Geochemistry and paleoenvironment of the phosphorites from the Ameki Formation, Niger delta, Nigeria

“…The prime genetic process in the formation of diagenetic phosphorites however, is believed to be the replacement of carbonate by phosphate (Ames, 1959;Simpson, 1964). Depositional environments of ancient phosphorites and phosphatic sediments have been reconstructed using geochemical proxies (e.g., Galfati et al, 2010;Dumoulin et al, 2011;Khan et al, 2012;Dar and Khan, 2016;Garnit et al, 2017). The Eocene Ameki Formation has been described asa clastic unit of about 1,550 m thick (Arua, 1982).…”

“…ONUIGBO, EVANGELINE NJIDEKA, OKORO, ANTHONY UWAOMA A geochemical proxies (e.g., Galfati et al, 2010;Dumoulin et al, 2011;Khan et al, 2012;Dar and Khan, 2016; The Eocene Ameki Formation has been described asa , 1982). Nwajide (2013) gave the maximum thickness of between 1,200 and 1,500 m for the formation.…”