Oxic-dysoxic Tidal Flat Carbonates from Sadara, Pachham Island, Kachchh

Sadara limestones in Goradonagar Formation of Pachham Island are dominantly intramicritic and contain bioclast, pellet, peloid, ooid; with nodular anhydrite. They exhibit intraformational chert breccia at the base, early diagenetic dolomite and predominant lime flake pebbles of intrabasinal origin in the middle, with development of algal laminated structures and desiccation cracks in the upper part; representing subtidal-intertidal-supratidal mudflat environment. Higher content of insoluble residue (av. 11.56%) and presence of illite, kaolinite, anhydrite, gypsum; indicate restricted circulation in coastal sabkha-like intertidal-supratidal zones. They exhibit higher CaO, low SiO2, Fe2O3, Al2O3, TiO2, K2O and P2O5. Trace element composition of these sediments reveals higher Na, lower Mn, Ni, Cu, Co, Pb, U, Th, Sr contents, V/Cr and Ni/Co ratios. These signatures, together with seawater like REE pattern with low ∑REE + Y content, LREE depletion, positive La, Eu and negative Gd, Y, Ce anomalies, (Nd/Yb) SN and Y/Ho in these limestones; substantiates shallow marine oxic-dysoxic nature with an insignificant terrigenous contribution. The δ13C (av. −1.06‰), δ18O (av. −5.06‰), Z values (av. > 120) support the shallow marine nature of these limestones.