Abstract

Evaluation of the hydrocarbon potential of a sedimentary basin must take into consideration its tectonic evolution, which is a prime factor in the migration and accumulation of hydrocarbon. Tectonic control is imposed on the development of sedimentary basins preserving the resultant signatures. Since the structural framework of a sedimentary basin is inherently a part of, and consequently the result of the regional tectonic control, the study of the tectonic signatures assumes considerable importance for basin analysis. Sedimentary basin analysis, to a large extent depends on the physical examination of exposed rock section within the basin. It is axiomatic that the geologist aims for as full an understanding as possible of what he observes. The development of shear zones bears significant importance in establishing the petroleum system of a sedimentary basin. The effects of shearing are in general manifested in form of change in grain size, development of micro fractures, development of foliation, rearrangement of mineral distribution and shape (framework collapse) under geometrical weakening, permeability enhancement (dialatancy) etc. The associated structures observed in the field due to shearing include fault planes, shear fractures (at variety of scales), microfracturing, granulation, foliations (mica alignment), mylonites, slickensides, polished surfaces, grooves, striations, boudins, veins, stylolites etc. Manifestation of shearing needs to be observed in the field thoroughly before establishing tectonic history of a basin. The direction of movement on shear zones is important for reconstruction of the tectonic history of an area and the sense of displacement is of prime importance, which can be dextral or sinistral, normal or reverse. There are a large number of useful criteria for deduction of the sense of shear on a microscopic and macroscopic scale. Hence identification of the shear sense indicators in the field and collection of structural data from the shear zone manifestations holds immense importance for interpretation