The Tectonized Indus Suture Zone, Ladakh, and NW Himalaya, India: A Promising Area for Future Exploration

摘要

The Indus Suture Zone is a major crustal lineament between Himalayan range and Tibet. This important tectonic belt is a site of Cretaceous subduction zone along which a large portion of pre- Tertiary Tethyan ocean crust was consumed. The per-Tertiary Tethys Ocean has had an important influence on the accumulation and distribution of petroleum in the world. In view of these observations together with occurrence of major oil fields with subduction zone an attempt has been made to evaluate the prospect of petroleum generation from argillaceous sediments of the Indus Suture Zone. Based on lithological characters and vertical and lateral continuity of the formations various lithostratigraphic units have been identified .The present study is mainly concerned with the sediments of the Lamayuru Formation (Cretaceous-Jurassic), Nindum Formation (Cretaceous) and Indus Formation (Early Cretaceous- Early Eocene). Various geochemical and geooptical techniques were used for characterization and evaluation of source rocks for petroleum by determining the amount of organic matter, the type and nature of organic matter and thermal maturation of organic matter found in the argillaceous sediments of various formations of Indus Suture Zone. The mean value of total organic carbon (TOC) is highest in the Indus Formation, followed by Lamayuru Formation and Nindum Formation, indicating thereby these sediments have sufficient organic matter to generate petroleum. The nature and type of organic matter have been determined using analysis of extractable organic matter , gas chromatographic analysis of saturates (C15+), optical examination of kerogen and stable carbon isotopic analysis. Based on these studies, it has been found that organic matter of various formations is mainly land-derived type III kerogen with some amount of oil prone type II kerogen. Vitrinite reflectance study of selected samples reveals that mean reflectance value varies from 0.6 to 1.7% in the Indus Formation, from 1.44 to 1.51% in the Nindum Formation and from 1.34 to 1.44% in the Lamayuru Formation. These values indicate that organic matter in these formations have undergone sufficient thermal maturation to generate petroleum hydrocarbons, mainly gas. These observations are further supported by the gas chromatographic analysis of C15+, componental analysis of extractable organic matter (EOM) and stable carbon isotopic analysis. Thick pile of sediments exhibiting alternation of sandstone with shale, their large lateral continuity and good combination of source and reservoir has made the area attractive for petroleum exploration.