Rakhi Gaj Fm
Type Locality and Naming
Holotype section: Rakhi Nallah, Sulaiman Range. Author: F.E. Eames, 1952. Reference section: None.
Lithology and Thickness
Sandy claystone. It consists dominantly of dark greenish grey and light olive grey shale with subordinate amounts of sandstone and some bands of limestone. It is interbedded with thin bands of siltstone, and some bands of sandstone at the base, which weathers to moderate yellowish orange. At the type locality, the shale is bioturbated and contains calcareous, carbonaceous and ferruginous concretions. In the middle part of the formation, the sandstone is grayish red and medium to coarse grained, which becomes conglomeratic with common grayish red, quartzose and oolitic hematite pebbles. The lower part of the formation (140 m at the type section) has now been formalized as Girdu Member (Gorge Beds of Eames,
1952).
Girdu Member (Author: S. M. Hussain): The member mainly comprises cross-bedded, glauconitic, pyritic, micaceous with quartzose, red brown conglomeratic sandstone; shale, limestone and siltstone are in minor amounts. The limestone is medium grey in color and is bioclastic.
Thickness: 170-340 m. In the type section the formation is 340 m thick (inclusive of 140 m thick Girdu Member), and 170 m on the eastern flank of Zindapir anticline, farther north.
Relationships and Distribution
Lower contact
Conformably underlain by Khadro Fm
Upper contact
Conformably overlain by Dungan Fm [But see Note under Additional Information]
Regional extent
The formation is primarily restricted to the eastern Sulaiman Range and the eastern part of Marri-Bugti Hills.
GeoJSON
Fossils
The formation is fossiliferous, but age-diagnostic fossils are rare.
Age
Depositional setting
A decreasing clastic content is observed towards the top of Rakhi Gaj Fm, which is probably the result of deposition in a transgressive sea that eventually submerged the Rakhi Gaj delta, this at places gave rise to transitional nature of the upper contact, and the restricted development of limestone above it; as in Rakhi Nallah section i.e. Zindapir Limestone, 'lower part' of Eames (1952), which he identified to be of Paleocene age.
Additional Information
Regional extent:
The formation is primarily restricted to the eastern Sulaiman Range and the eastern part of Marri-Bugti Hills.
GeoJSON:
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Fossils:
The formation is fossiliferous, but age-diagnostic fossils are rare.
Age:
Paleocene (on stratigraphic position).
Age span:
Beginning stage: Thanetian
Fraction up in beginning stage: 0.0
Beginning date (Ma):
Ending stage: Thanetian
Fraction up in ending stage: 1.0
Ending date (Ma):
Depositional setting:
A decreasing clastic content is observed towards the top of Rakhi Gaj Fm, which is probably the result of deposition in a transgressive sea that eventually submerged the Rakhi Gaj delta, this at places gave rise to transitional nature of the upper contact, and the restricted development of limestone above it; as in Rakhi Nallah section i.e. Zindapir Limestone, 'lower part' of Eames (1952), which he identified to be of Paleocene age.
Depositional-pattern:
Additional Information
Note: In literature Rakhi Gaj Formation is reported to be conformably overlain by Dungan Fm, but a section where it could be seen is not mentioned. At Rakhi Nallah Eames (1952) recognized Zindapir Limestone Fm the 'lower part' (~40m) which he identified to be of Paleocene age, but it is restricted only to Rakhi Nallah; this seems to be the only place where a Paleocene limestone is overlying Rakhi Gaj Formation. However, based on a regional picture, the author feels that the Rakhi Gaj Formation is most probably a chronostratigraphic equivalent of Dungan Fm (limestone). In areas of pinch-outs a limestone tongue may be overlying the Rakhi Gaj shales which may have been inadvertently interpreted to represent an upper conformable contact e.g. Khalgari Nallah in south and area between Tangi Sar/Drug Lahar and the Moghal Kot sections toward north of Rakhi Nallah (Siddiqui, 2004).