Print this pageBiostratigraphy and Paleoenvironmental Interpretation Along Eastern Margin in Gamij Area of Cambay Basin, Gujarat, India
The Eastern margin area of Cambay Basin is the thrust area for exploration in Ahmedabad block. Recent hydrocarbon discoveries in horst blocks of Gamij field has upgraded the prospectivity of the area and also added impetus to exploration activities. New pools and hydrocarbon finds have opened up the area for Paleocene-Eocene prospects. Integrated laboratory studies were carried out to precisely delineate the biostratigraphic and litho-stratigraphic boundaries between Deccan Trap basement, overlying volcanoclastic sediments of Olpad and Cambay formations and reconstruct the paleoecology of the area.
The Olpad sediments of Paleocene age is the first sedimentary unit deposited over Deccan basalt and comprises two major lithofacies:conglomeratic trapwacke and silty trapwacke.The conglomeratic trapwacke was deposited in both middle and distal part of a fan in coastal to brackish environment.The silty trapwacke is more clayey and deposited in distal fan as levee to flood plain deposits under coastal,tidal and brackish conditions and has poor reservoir characteristics. The top of Cambay Formation is mainly sideritic in nature.It is reddish brown,ooidal shale which marks an unconformity surface between Cambay Formation and over- lying Kalol Formation.
The palynological assemblages of a variety of spores, pollen and dinoflagellate cysts in Olpad and Cambay and lower part of Kalol formations, precisely mark the age boundaries between Early Paleocene/Eocene and Early Eocene/Middle Eocene. The stratigraphic ranges of various marker taxa enabled the dating and correlation of the sediments in the area. Two palynozones corresponding to the Olpad Formation of Paleocene age and Cambay Formation of Early Eocene age have been demarcated in the subsurface. The top of Paleocene and Early Eocene is marked by first downhole appearance of the index marker taxa Rhombipollis geniculatus and Pellicieroipollis langenheimii respectively.
The palynofloral assemblage indicates a subtidal to inner shelf environment during the deposition of Olpad Formation and overlying Cambay Formation respectively. The microfaunal assemblages comprising of N. burdigalensis and Baculogypsinoides, Operculina sp. and Cibicides sp. in Cambay Formation suggest a shallow bathymetry. The integrated studies have helped in reconstructing a paleoecology of the area and facilitated in locating suitable reservoir and cap rock facies for further hydrocarbon exploration.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil