Facies, sequence stratigraphy and depositional environment of the Lower Cretaceous Giumal Formation in Spiti (Tethyan Himalaya, India)

The Lower Cretaceous marine deposits of the Himachal Himalaya are assigned to the Giumal Formation and best exposed in Spiti Valley (Northern India). To date, three sections near the villages of Chikkim, Domal and Gete are studied concerning its general lithological character and age. However, only the biostratigraphically constrained section near Chikkim exposes a complete succession of approximately 300 m in thickness with both lithostratigraphic boundaries preserved. Thus, it is representative for the entire Spiti area. Although some few lithological details on the siliciclastic sequence of the Giumal Formation are known, a comprehensive study of the regional sedimentary development is missing. A detailed microfacies study is performed for the entire sequence of Lower Cretaceous outer neritic to slope environments of Spiti. The specific sedimentary character of the unit results in discrimination of eleven microfacies types. Furthermore, twenty-three sedimentary sequences are identified which correspond with four major regressive/transgressive cycles. Reconstruction of a relative sea-level curve clearly indicates 10 major and minor sea-level drops which correlate well with eustatically induced megacycles between the latest Tithonian to the late Albian. The depositional environment of the Giumal Formation in Spiti is discussed in view of 16 coeval sedimentary sequences framing the Indian Craton during the Late Jurassic and Cretaceous time slice.