Laki Fm
Type Locality and Naming
Holotype section: Mari Nai, located southwest of Bara Nai. Author: F. Noetling, 1903. Reference section: None.
Lithology and Thickness
It is comprised mostly of hard, white, massive or nodular limestone. The formation consists mainly of cream colored to grey limestone that forms the cores of large anticlines in southern KrP; marl, calcareous shale, sandstone, and lateritic clay may become significant constituents of the formation locally and towards its base. The formation's chronostratigraphic equivalent, the Sui Main Limestone Fm has been discussed in detail, above.
Two basal members have been formalized by the SCP. A section exposed about 5 km SSW of Meting is designated as the type section of the above two members:
Sohnari Member: It consists of varicolored lateritic clay and shale with locally developed beds of yellow arenaceous pockets of limestone or ochre and lignite seams. Lenticular beds of variegated, ferruginous sandstone and white calcareous sandstone are common in the member. The member represents the basal part of Laki Fm and directly overlies the Ranikot Gr (Group).
Chat Member: It consists mainly of creamy white nodular limestone in the lower part and interbedded shale and limestone with subordinate sandstone in the upper part. The limestone is thin bedded and arenaceous where as the sandstone is commonly ferruginous. The shale is grey, greenish yellow weathering dark rusty brown, ferruginous and gypsiferous.
Thickness: 209-500 m. At the type locality, the formation is 240 m thick, and same at Bara Nai. It is 600 m at Tatti section in Kirthar fold belt, but absent in Marri-Bugti Hills. In the offshore, it seems to be increasing in thickness, but generally Ghazij shales and Laki limestone thickness is combined in offshore well reports. In the wells drilled to the east of Sulaiman and Kirthar provinces in PP and Badin area, respectively, the formation has been encountered, and ranges in thickness from 400-500 m.
Relationships and Distribution
Lower contact
Unconformably underlain by Lakhra Fm = upper Ranikot Gr.
Upper contact
Conformably overlain by Kirthar Fm in most places, but in Laki Range the Nari Fm and Manchar Fm (Oligocene) unconformably overlie the Laki Fm.
Regional extent
The formation is extensively developed and exposed in the KrP, particularly in southern Kirthar fold belt and the Laki Range. It forms a 45 km long prominent scarp along the western flank of the Laki Range, where its thickness varies from 200 to 300 m. In the subsurface, it has been encountered in wells drilled in Badin area and the Punjab Platform. In central Pakistan its chronostratigraphic equivalent, the Sui Main Limestone Fm, is a prolific reservoir of gas (Siddiqui, 2004).
GeoJSON
Fossils
Foraminifers: Assilina granulosa, A. pustulosa, Lockhartia hunti var. pustulosa, Flosculina globosa, Opertorbitolites douvillei, Fasciolites oblonga, Linderina brugesi, Dictyoconoides vredenburgi. Molluscs: Gisortia murchisoni, Velates perversus, Blagraveia sidensis . Echinoids: Amblypygus subrotundus, Echinolampas nummulitica . These fossils indicate an Early Eocene age.
Age
Depositional setting
Additional Information