Composition of neogene shales from the Surma Group, Bengal Basin, Bangladesh: Implications for provenance and tectonic setting

The geochemical composition of the Neogene shales from the Surma Group in the Bengal Basin, Bangladesh encountered in petroleum exploration wells were analyzed by lithium metaborate/tetraborate fusion inductively Coupled Plasma (ICP) and Inductively Coupled Plasma Mass spectrometry (ICP-MS). Geochemically, the mean major element composition of the Neogene shales is similar to that of the average shale with the exception of the CaO content, which is lower here. The low CaO content (1.37, wt %), could be due to lower carbonate content. The Neogene shales are enriched with V, Cr Co, Ni in compared to UC (Upper Crust. The REE content (186-228) is higher than those of UC and NASC but is in agreement with those of PAAS. The Eu/Eu (∼0.58). (La/Lu)cn (∼0.43), La/Sc (∼2.64), Th/Sc (∼1.06), La/Co(∼2.71 Th/Co (∼.08), and Cr/Th (∼5.59) ratios as well as Chondrite-normalized REE patterns with flat HREE. LREE enrichment, and negative Eu anomaly indicate the derivation of the Neogene Surma Group shales from felsic rock sources. The geochemical characteristics suggest the active continental margin setting for the Neogene Surma Group shales and preserve the signatures of recycled provenance field that have undergone significant weathering at the source areas.