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 Formation (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) calcareous 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