CAMBRIAN TRILOBITES AND STRATIGRAPHIC CORRELATIONS WITHIN TETHYAN HIMALAYA

The ages of Early Paleozoic sedimentary rocks of central and southeastern Tethyan Himalaya are poorly constrained. This has hindered understanding of stratigraphic relationships along the northern margin of the Indian subcontinent, from Pakistan to Bhutan. New collections have enabled refined biostratigraphic correlations within the Tethyan Himalaya and clarify the relationships between the Kashmir, Zanskar, and Spiti. Within Zanskar and Spiti lower and middle Middle Cambrian trilobites were recovered from relatively thin limestones atop relatively thick clastic cycles of likely deltaic origin. The prominent Karsha Dolomite is overlain by shelfal clastics containing trilobites of late middle Cambrian age. Tethyan Cambrian rocks are overlain by an angular unconformity and a prominent conglomerate in the Zanskar to Kumaon sector of the Himalaya. Within this sector the unconformity apparently cut deeper into the Cambrian succession to the east. This unconformity is not currently recorded in the Nepali or Bhutanese Himalaya. In the Annapurna Range of Nepal, metasedimentary rocks stratigraphically below Middle Ordovician limestones and above the South Tibetan Fault System are reported to contain trilobite fragments and bear lithological similarities to the Zanskar-Spiti succession. Correlations between the Phe/Kunzum La Formation and the Sanctuary Formation, the Karsha Dolomite and the Annapurna/Larjung Limestone, the Kargiakh and the lower portion of the Pi Formation provide a reasonable working hypothesis, but remain to be tested by biostratigraphic work in Nepal and Tibet. Similar metasedimentary rocks and a metaconglomerate are located below the South Tibetan Fault System in the Everest region within the uppermost strata of the Greater Himalaya.