Fades Associations and Sedimentary Petrological Characteristics of Lameta Sequences of the Dongargaon Area, Central India

The Lameta Formation of the Dongargaon area is associated with the locally occurring basal Deccan lava flows. These sequences have been studied for their facies associations, petrographic, and diagenetic attributes in four localities: (1) Dongargaon hill, (2) Dongargaon nala, (3) Dhamni/Pavna and (4) Bijoli/Sagra. Four facies associations -(a) lacustrine- A, (b) lacustrine-B, (c) overbank with minor sheetwash deposits and (d) minor channels have been recognized by previous workers as well as in this study. An upsection shallowing trend is inferred.

Petrographic studies resulted in the identification of two types of sandstones in the minor channel facies - one composed largely of calcrete grains and the other composed of quartzose grains. Diagenetic structures and fabrics of significance include septarian concretions and radiaxial fibrous calcite; and pedodiagenetic structures include mainly calcrete nodules and rhizocretions. The septarian concretions show a bimineralic character with a dolomicrite groundmass and a coarse crystalline spar filling up the cracks. Stable isotope composition of the calcrete nodules suggests a possibledual origin i.e., phreatic-pedogenic. Marl, calcareous siltstone and ostracods of the lacustrine facies range in values from -2.9%o to ~6.4%o for 8^I3C and -2.7%o to -5.9%o for 5^!80, and suggest marked fluctuations in the lake's hydrological regime.

Facies analysis, petrographic studies and stable isotope compositional data of selected carbonate facies and fabrics suggests that the Lameta Formation of the Dongargaon area is dominated by overbank and shallow lake environments. This contrasts with the dominance of palustrine and pond facies described previously from the Lameta Formation of the type locality of Jabalpur in Central India.