The Upper Bhuban Member in the Sitakund anticline, Chittagong, Southeastern Bangladesh is constituted by the light gray, light yellow and greenish gray sandstone and siltstone with dark gray, bluish black and black finely laminated silty shale to shale. The lithofacies of massive sandstone(Sm), turbidite sandstone (ST), flat bedded sandstone-siltstone (Sh), ripple cross laminated sandstone-siltstone (Sr), laminated sandstone-siltstone (Sl), lenticular laminated sandstone-siltstone-shale (Sll), wavy laminated silty shale to shale (Fw), laminated shale (Fl) with sub-facies black shale (Flbk) and blue shale (Flb) and mudstone (Fm) have been delineated in this member. Based on genetic aspects the facies are grouped into (1) turbidity generated - and (2) deep marine basin plain facies association. The medium to fine grained facies Sm and ST with or without Sh, Sr, Sl Sll Fw and Fm facies constitutes the turbidity generated facie association. The deep marine basin plain facies association is characterized by the monotonous hemi-pelagic bluish black shale (subfacies Flb) and pelagic black shale (subfacies Flbk) with rare to scare silty stringers of facies Sh, Sr, Sl, Sll and Fw. The facies Sm is turbidity channel in the inner part of medial fan and the complete ST sequence indicates channelized forms, while incomplete ones have been identified as channel or interchannel deposits in medial to distal fan. The facies Flb and Flbk denote deep marine environments above and below the carbonate compensation depth, where the lithofacies facies Sh, Sr, Sl, Sll and Fw were deposited as distal turbidites. The facies sequence of medial to distal fan and deep marine basin plain were repeated and randomly juxtaposed one upon other due to instability of basin probably by faulting along Dauki and adjoining area accompanied by sea level change. The paleoflow pattern indicates that the dominant source of detrius was the Shillong plateau along with minor contribution from the Himalayas and Arakan Yoma Folded Belt. Keywords: Turbidites; Upper Bhuban Member; Sitakund anticline; SE Bangladesh. DOI: 10.3329/jles.v2i2.7491 J. Life Earth Sci., Vol. 2(2) 1-16, 2007

Mineralogical analysis of Moheskhali beach sands revealed the presence of high amount of ilmenite. About 50% of these ilmenites are unaltered which are characterized by the presence of exsolution of ilmenite with hematite, ilmenite with magnetite, and ilmenite with rutile. Others (50%) are unexsolved where 30-50% grains partially or fully altered. These altered and unaltered phases of ilmenite are confirmed by X-Ray diffraction study. Ilmenite-hematite exsolution comprising 70-80% of the total exsolution. The widely banded exsolved phases were formed by continuous exsolution mechanism while the second generation thinner bands were formed discontinuously. Seriate texture dominates (about 75%) over emulsion, granular, quadrangular, sub graphic, veined and special types. Optical study suggests that the alteration of ilmenite is seen to proceed along grain boundaries and/or fractures resulting in an amorphous to microcrystalline mass resembling leucoxene. The chemical composition of the alteration products of ilmenite frequently fluctuates within definite ranges (pseudoilmenite and pseudorutile ranges) of a nonstoichiometric composition and thus deviates from their ideal composition. Key words: Ilmenite; Rutile; Opaque; Exsolution; Alteration. DOI: 10.3329/bjsir.v45i1.5173 Bangladesh J. Sci. Ind. Res. 45(1), 17-26, 2010

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