Geology and Stratigraphy of Dinosaur Eggs and Eggshell-Bearing Infra- and Intertrappean Beds of Peninsular India

Abstract

The dinosaur-egg-rich Lameta Formation is widely distributed over 10,000 km and varies in thickness from 3 to 12 m and is well exposed in five inland basins: (1) Jabalpur; (2) Dhar and Jhabua Districts; (3) Salbardi-Belkhar, Betul district, Madhya Pradesh; (4) Kheda–Panchmahal district, Gujarat; and (5) Pisdura, Nand–Dongargaon, Chandrapur District in Maharashtra. The Lameta Formation represents the relict of an ancient soil cover formed on several old shield basements such as Archaeans, Aravalli metasediments, Godhra Granites, Bijawar metamorphics, Vindhyans, Gondwanas and Bagh Beds, ranging in age from Precambrian to Lower Cretaceous, in peninsular India along the Narbada River region. In the Jabalpur area, three sections, namely Chui Hill, Bara Simla Hill (including Pat Baba Mandir) and Lameta Ghat, were selected for dinosaur egg and eggshell studies. The Lameta Formation has been divided into five lithounits: (1) Green Sandstone, (2) Lower Limestone, (3) Mottled Nodular Bed, (4) Upper Limestone and (5) Upper Sandstone. Thickness of the Lameta Formation varies from 3 to 5 m in the Dhar-Jhabua area. Six lithostratigraphic sections (Bagh Caves, Padalya, Dholiya, Padiyal, Kadwal, Walpur and Kulwat) were selected for dinosaur eggshell morphotaxonomic studies. Stratigraphically, the oldest lithounit is represented by the Bijawar metamorphics of Archean age as a basement, which is overlain by the marine Bagh Beds such as the Nimar Sandstone, Nodular Limestone and Coralline Limestone. In the Kheda-Panchmahal area, six Lameta sections (Rahioli, Dhuvediya, Khempur, Balasinor, Paori, Dholidhanti/Wanawao) were studied for dinosaur eggshell oospecies diversity. The basement rocks are Aravalli metasediments and Godhra granitoids, which are unconformably overlain by the 3–5 m thick, dinosaur-nest-rich Lameta Formation. The uppermost part of the Lameta Formation is characterized by cherty limestone. Abundant ornithoid eggshells have been recorded from 2-m-thick third and fourth intertrappean levels of the Anjar area in Gujarat. In Pisdura, Nand–Dongargaon area, the thickness of the dinosaur-eggshell-rich Lameta Formation varies from 1to 11 m. The Lameta Formation rests unconformably on rocks of Precambrian age and the Gondwana Super Group. In all of the 22 investigated stratigraphic sections, the Lameta Formation is overlain by the Deccan traps. The dinosaur-egg-bearing pedogenic calcrete is characterized by features such as shrinkage cracks, rhizoconcretionary structures and nodular, prismatic, brecciated and autobrecciated structures. The petrographic study of these calcretes identifies fabrics with a high percentage of skeleton grains, micritic and spar rims, glaebules, voids, vugs, crystallaria and chalcedony spherulites that can be chiefly ascribed to pedogenic calcretization.