Revised lithostratigraphic classification of the Cambrian Kunzam La Formation and its biostratigraphic correlations from Zanskar to Spiti, Tethyan Himalaya

Abstract

In the northwest Himalayas, the Cambrian sequences forming part of the Tethyan Himalayan Zone are well preserved in the Zanskar and Spiti regions. In the present work, we critically examine the geologic, stratigraphic and biostratigraphic aspects of the Cambrian Kunzam La Formation exposed in the Zanskar (i.e., in the Niri-Tsarap Chu and Kurgiakh valleys) and Spiti regions (i.e., in Chandra, Parahio, Pin and Sumna valleys sections). Although the Kunzam La Formation is extensively developed, none of the sections from Zanskar to the Spiti regions preserves its complete succession. The present work reveals the presence of a fault in each studied section, which has eliminated different stratigraphic portions of the Kunzam La Formation. Therefore, based on overall lithologic characteristics, biostratigraphic parameters and local preservation state, this formation is re-classified into three formal members: the Chandra, Parahio and Purni. We also present lithostratigraphic and biostratigraphic correlations of the Kunzam La Formation from the Zanskar to Spiti regions, which validate our lithostratigraphic division.