Pachmarhi Fm
Type Locality and Naming
Satpura Basin: Named after Pachmarhi Plateau, Hosangabad district, Madhya Pradesh by Medlicott (1873) as Pachmarhi Sandstone, it was given the status of formation and referred as the Pachmarhi Formation by Raja Rao (1982). [Original Publication: Medlicott, H. B., 1873. Notes on the Satpura Coal Basin. Mem. Geol. Surv. Ind., 10(2), 133-188; Raja Rao, C. S., 1982: Coalfield of India-2. Coal resources of Tamil Nadu, Andhra Pradesh, Orissa and Maharashtra, Geol. Surv. Ind., Bull., Ser. A, No. 45, 9-40.]
[Figure 1: a) Map of India showing Gondwana basins of the peninsular India with the red rectangle marking the Satpura Basin (after Bandyopadhyay, 1999); b) Geological map of the Satpura Gondwana Basin with the red rectangle showing the Upper Gondwana formations (after Ghosh et al., 2012) (after Sengupta et al., 2016)]
Lithology and Thickness
Coarse-grained sandstone. It consists of numerous vertically stacked, cross-stratified, thick beds of coarse, white sandstone, separated from one another by layers of white quartz. The sandstone is hard, massive, thickly bedded, medium- to coarse-grained with yellowish to dark brown color. Angular chips of feldspar are quite common in coarse layers. Cross-bedding is universal. At some places, pedogenically altered red mudstones occur in between sandstone bodies. Its average thickness is about 750 m (ranging from 150-900 m) (Sastry et al, 1977; Peter, 2009). It occupies high hill ranges and weathers into vertical scarps of great height (Casshyap and Khan, 2000).
Relationships and Distribution
Lower contact
The lower contact with Bijori Fm is unconformable and marked by a change in lithology and uneven contact west of Pachmarhi (Crookshank, 1936, Tewari, 1995).
Upper contact
The upper contact with Denwa Fm clay is gradational and conformable.
Regional extent
Satpura Basin: Excellent sections are exposed west, southwest and south of the Gopad River, between Sukhdongar and Alimod, in upper Denwa river, and about 1.5 km northwest of Binora.
GeoJSON
Fossils
A few poorly preserved branchlets and a rachis of fern are recorded near Dorri (Crookshank, 1936). Sastry et al. (1977) mentions fossil estheriids finds from this formation by S. Chandra. A thin concretion of white siltstone, within the cross-bedded sandstone of Pachmarhi Formation at the base of Dhupgarh Hill, contains multiple taxa of fossil conchostraca, mostly of Vertexiidae family (Ghosh, ). A few fragmentary weathered amphibian skull bones have been collected from the Panchmarhi Formation by Bandyopadhyay and Sengupta (1999).
Age
Depositional setting
The Pachmarhi Formation were deposited in braided river environment (Tewari, 1995; Maulik et al., 2000) with predominantly warm, subhumid climate with semi-arid intervals.
Additional Information
References
Casshyap, S. M., and Khan, A., 2000. Tectono- sedimentary of the Gondwana Satpura basin of Central India: evidence of pre-trap doming, rifting and palaeoslope reversal. J. Afr. Earth Sci. 31, 65-76. Crookshank, H. 1936. The geology of the northern slopes of the Satpuras between Morand and Sher Rivers. Mem. Geol. Surv. Ind. 66 (2). Maulik, P. K., Chakraborty, C., Ghosh, P. and Rudra, D. 2000. Meso- and macro-Scale architecture of a Triassic fluvial succession: Denwa Formation, Satpura Gondwana Basin, Madhya Pradesh. Jour. Geol. Soc. India, 56, 489–504. Medlicott, H. B., 1873. Notes on the Satpura Coal Basin. Mem. Geol. Surv. Ind., 10(2), 133-188. Peter, 2009 Raja Rao, C. S., 1982: Coalfield of India-2. Coal resources of Tamil Nadu, Andhra Pradesh, Orissa and Maharashtra, Geol. Surv. Ind., Bull., Ser. A, No. 45, 9-40. Sastry et al, 1977 Tewari, C. (1995). Tectono-sedimentary evolution of Bijori (Late Permian) and Pachmarhi (Early Triassic) Formations of Satpura Gondwana basin, central India. Indian Jour . Petrol. Geol., 4, 75-86.