--> Abstract: Diagenesis of the Oligocene-Early Miocene Panjgur Formation, Paleocene Ispikan Formation and Wakai Exotic Blocks in the Makran Accretionary Belt, Southwest Pakistan, by Jeffry D. Grigsby, Akhtar M. Kassi, and Abdul S. Khan; #90078 (2008)

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Diagenesis of the Oligocene-Early Miocene Panjgur Formation, Paleocene Ispikan Formation and Wakai Exotic Blocks in the Makran Accretionary Belt, Southwest Pakistan

Jeffry D. Grigsby1, Akhtar M. Kassi2, and Abdul S. Khan3
1Geology, Ball State University, Muncie, IN
2Geology, University of Balochistan, Quetta, Pakistan
3Centre of Excellence in Mineralogy, University of Balochistan, Quetta, Pakistan

The Oligocene-Early Miocene Panjgur Formation is exposed in the Makran accretionary wedge in southwest Pakistan. Isolated exotic blocks of older age, the Ispikan Formation and Wakai exotic blocks, also outcrop in the area. Petrographic and geochemical study indicate that the Panjgur and Ispikan detritus was transported from the Himalaya-Karakorum-Hindukush orogen southward and deposited as a deep marine turbidite complex in the northeast-southwest aligned Katawaz remnant ocean and east-west aligned Makran trench. The Bela-Muslimbagh ophiolites, associated mélanges to the east, and the Chaghai-Raskoh volcanic arc to the west contributed mafic to ultramafic detritus to the Panjgur and Ispikan sediments.

Sandstones of the Wakai exotic blocks, rich in mafic volcanic fragments and associated with sheared mafic volcanic rocks, purple colored shale, chert, marble, and pelagic limestone, suggest obduction of oceanic crust of the Gulf of Oman. The tectonics of these sandstones has led to a complex diagenetic history. Cements include ferroan>nonferroan calcite, ankerite, dolomite and chlorite>illite with carbonate cements dominant in the Panjgur and Ispikan Formations, and chlorite dominant in the Wakai exotic blocks. Physical compaction precedes cementation in the Panjgur and Ispikan Formations. Early nonferroan calcite inhibits physical compaction in the Wakai exotic blocks. Secondary porosity developed during dissolution of nonferroan calcite, feldspars and rock fragments and was later destroyed by precipitation of chlorite, ferroan calcite, ankerite, and dolomite. Chlorite predates ferroan calcite, and both show signs of a second stage of dissolution with chlorite filling secondary pores in a nonchlorite-like I-beam morphology. Ankerite and dolomite form late and replace earlier stages of calcite, framework grains, and fill secondary pores.

 

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas