Khaskheli Basalt Fm
Type Locality and Naming
Holotype section: Bara Nai, northern Laki Range. Author: N.K. Siddiqui, 1987 (proposed, as in Shah, 2009). Reference section: None.
Lithology and Thickness
Basalt. These lava flows occur at the base of Khadro Formation and were originally included in the same formation. In the outcrops in Laki Range they have a small vertical extent, and are interbedded with mudstone and claystone. However, the wells drilled to the east of the Kirthar fold belt and those drilled in the Badin area encountered much larger thickness of basalts with lesser sedimentary influx within, and overlain by Khadro Fm. In view of their subsurface lateral extent to the east and much increased thickness, they are being proposed as a formation. In the type locality, these basalt flows are dark green to black in color with abundant basic glass filling the vesicles and amygdules. The formation is generally interbedded with mudstone and claystone. Top and base of the unit exhibit weathering effect showing reddish to brownish grey colors, which have been caused by abundant pyroxene, olivine and chlorite that fill the cavities. Unlike the Deccan Traps Fm, which are generally free from olivine, the Khaskheli basalt as encountered in wells both onshore and offshore contains abundant olivine (Kadri and Khan, 1972).
Thickness: 27-177 m. At the type locality it is 27 m. In old wells combined thickness of Khadro and volcanics have been reported which have resulted in erroneously large thickness of basalt in literature and for that matter Khadro Fm, particularly for offshore. The basalt thickness from south to north in offshore well Dabbo Creek-1 is 177 m, in Dasori-1 it is 77 m, while at Paniro-1 the basalt is only 26 m thick.
Relationships and Distribution
Lower contact
Unconformably underlain by different Cretaceous rocks.
Upper contact
Unconformably overlain by Khadro Fm and other Paleocene rocks.
Regional extent
It has limited exposures where ever it outcrops in the Laki Range (Bara Nai, Karkh and Jakker) to the west, however, it thickens towards east in the subsurface and has been encountered in oil wells as east as 69 degrees longitude, and from offshore (Lat. 24 degrees) to onshore (Lat. 26 degrees) in the Badin area. From west to east, it is underlain by successively older formations of Cretaceous age. In the type section it is underlain by Pab Sandstone while at Paniro well it is underlain by U. Goru shale, farther about 10 km east of Paniro well, at Digh-1 and beyond at Marvi-1 this basalt is not present. On seismic evidence it overlies Lower Goru shale farther east. The lava flows have been encountered in most of the wells drilled east of Indus River, particularly in the Badin area, and in the offshore.
GeoJSON
Fossils
The interbedded sand layers contain Danian fossils.
Age
Depositional setting
The basalt is interbedded with sandstone and mudstone beds, which represent quiescent period between volcanic eruptions. The basalt marks the K/T Boundary.
Additional Information