Integrated lithofacies, microfacies and sequence stratigraphic framework of the Takche Formation (Ordovician- Early Silurian), Pin Valley, Spiti Himalaya, India

An integrated litho-microfacies and sequence stratigraphic analysis of the Takche Forma-tion (Ordovician-Silurian) has been carried out in the Pin Valley, Spiti region. Ten lithofacies were identified in the Takche Formation, i.e. (i) siltstone-sandstone facies, (ii) sandy limestone facies A, (iii) sandy limestone facies B, (iv) sandy limestone facies C, (v) sandy limestone facies D, (vi) calcar-eous shale-siltstone facies, (vii) fossiliferous limestone facies, (viii) nodular/ribbon mudstone facies, (ix) bedded sandstone facies and (x) silicified sandstone-siltstone facies. The rocks of the Takche Formation belong to nine distinct microfacies characteristic for a shallow marine carbonate ramp deposited under highly fluctuating energetic condition. The sequence stratigraphic analysis of the Takche Formation in the Pin Valley revealed the presence of three sequences (S1-S3), two maximum flooding surfaces (MFSs) and five upward shoaling cycles indicating transgressive and regressive events. The three disconformity surfaces (U1-U3) resulted from submarine erosion or rapid fall in relative sea-levels.