Sequence Stratigraphy of the Neogene and Quaternary Siliciclastics in the Offshore Indus Basin of Pakistan

Abstract

  The siliciclastic dominated sequences interpreted within the Neogene (Miocene-Pliocene) and Quaternary (Pleistocene-Recent) in the Offshore Indus Basin of Pakistan indicated conventional interpretation of unconformity bound depositional sequences. These sequences were preserved as a result of combined effect-of the relative sea level fluctuation and tectonism. The post Paleogene siliciclastic sequences in the postrift Tertiary mega-sequence reveal prominent incisions in most of the Neogene and Quaternary sequences. The Paleogene carbonate dominated mega-unit is separated from the overlying Neogene. siliciclastic dominated mega-unit by an unconformity produced as a result of high amplitude lowstand of sea level, associated with Early Miocene tectonism in this region. Another high amplitude lowstand of sea level produced an erosional unconformity between the Neogene and Quaternary mega-units. The basal sequence of the Neogene megaunit comprising Early-Middle Miocene Gaj Formation has been the target for hydrocarbon exploration in past due to existence of reservoir quality rocks. This sequence has been divided into its systems tracts/units and time thickness maps have been produced for each unit. The rest of sequences above the Early-Middle Miocene in the Neogene and Quaternary mega-units are not important for hydrocarbon exploration in the basin. However high quality incision produced in these sequences, make them important for interpretation of younger sequences with erosional unconformities. This also gives good knowledge of interpretation about the incised valleys, channels and levees in the siliciclastic sequences of the Neogene and Quaternary mega-units in the Offshore Indus Basin of Pakistan.
Key words: Siliciclastic Sequence Stratigraphy, Incisions,Offshore Indus Basin.