The present research work deals with the lithofacies analysis along with the sequence stratigraphy of the Dupi Tila Formation, Lalmai Hills, Comilla to infer the depositional environment and paleogeography. The Dupi Tila Formation consists of alternation of yellow to light brown medium to fine grained sandstones and siltstone, grayish black to bluish gray shale to siltyshale and mudstone with local conglomerate. Different sedimentary facies are genetically grouped into coarse grained facies association (FAC), tide dominated facies association (FAT), heterolithic facies association (FAHL) and shallow marine facies association (FASM). The study of sequence stratigraphy indicates a lowstand systems tract for the basal part, a transgressive systems tract for the middle to lower horizon of upper part and highstand systems tract for the uppermost part. The whole Dupi Tila Formation is a Type-I sequence, as the upper boundary with the Modhupur Clay Formation is erosive and unconformable and lower contact with the underlying Girujan Clay Formation is also erosive and unconformable, though not exposed here. The study of the facies, facies relationship, facies association, paleocurrent analysis and sequence stratigraphy indicates that the depositional environment was extended from shallow marine shore face to intertidal flat through estuarine to tidal channel except the basal part, where deposition was confined to the piedmont alluvial set up of alluvial fan to braid plain. At the latest time, the area was inundated by sea when black shale and black mudstone with Sll facies and glauconite were deposited. Tripura-Sylhet Hills in the east to northeast and Shillong Massif in the north acted as sources of sediment derivation.

The Lalmai hilly area, Comilla, lying between the latitudes 2320' N to 2330' N and longitudes 9105' E to 9110' E (Figure 1), covers an area of about 33 sq. km. Bangladesh is mostly covered by Recent Alluvium but Tertiary sediments are exposed in the north, east and south eastern part of Sylhet district and in the folded flank of Chittagong and Chittagong Hill Tracts. The Tertiary Dupi Tila Formation, Modhupur Clay Formation and Alluvium of Quaternary age form the Lalmai Hills of Comilla district. The hilly area is the cornerstone of this research work. Notable places of the study area are Rupbhanmura, Salmanpur, South Salmanpur, Lalmai College, Bara Dharampur and Chandimura. The sedimentological study of the Dupi Tila rocks was made with a view to study the lithofacies analysis along with the sequence stratigraphy and construction of depositional model during the deposition of the Formation. Dupi Tila is the main aquifer of the Bengal Basin. Various authors have worked on the Dupi Tila Formation in different parts of the Bengal Basin, but very few studies have been made in the Dupi Tila Formation of Lalmai Hills, Comilla. Bakr (1977) made a study on the Modhupur Clay of Pleistocene Epoch at the Lalmai Hills and at the base of the Tripura Hills. Mohammod Hasan from VUB, Brussels, made an extensive work on the Lalmai area, entitled, “Stratigraphical and Sedimentological studies on Quaternary deposits of the Lalmai Hills”. But sedimentological work in association with sequence stratigraphy of the Dupi Tila Formation on Lalmai Hills is rare. So, the present study is aimed at.

Earth Sciences Journal, Palaeoenvironmental Studies, Rajapuram and Somanapally Sandstones, Palaeocurrent Analysis, Crossbedding, Proterozoic Rocks, Godavari Valley, Pakhal Sandstones, Polycrystalline Grains, Precambrian Sediments, Bimodal System.