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Stable Carbon and Oxygen Isotopic Composition of Mio-pliocene Bivalve Shells and Calcareous Sediments in Nhila Anticline, Southeast Bengal Basin, Bangladesh

H. M. Zakir Hossain*
Department of Petroleum and Mining Engineering, Jessore University of Science and Technology, Jessore-7408, Bangladesh

Md. Sultan-Ul-Islam
Department of Geology and Mining, University of Rajshahi, Rajshahi-6205, Bangladesh

John S. Armstrong-Altrin
Instituto de Ciencias del Mar y Limnología, Unidad de Geología Marina y Ambiental, Universidad Nacional Autónoma de México, Circuito Exterior s/n, 04510, Mexico DF, Mexico

Alcides N. Sial
Nucleo de Estudos Geoquímicos e Laboratooac

Sabbir Ahamed
Department of Petroleum and Mining Engineering, Jessore University of Science and Technology, Jessore-7408, Bangladesh

Md. Nahid Nowsher
Department of Petroleum and Mining Engineering, Jessore University of Science and Technology, Jessore-7408, Bangladesh

Md. Abdullah-Al-Kawsar
Department of Geology and Mining, University of Rajshahi, Rajshahi-6205, Bangladesh

Abstract/ Executive Summary:

Stable carbon (δ13C) and oxygen (δ18O) isotopes of bivalve shells and calcareous sediments of the Mio-Pliocene Nhila Anticline, southeast Bengal Basin, Bangladesh have been investigated to obtain information on paleoclimate and paleoenvironment conditions during deposition. The δ13CPDB, δ18OPDB and δ18OSMOW values in bivalve shell range from -2.81‰ to -1.56‰, -3.57‰ to -2.39‰ and 27.18‰ to 28.40‰ in bivalve shells and -13.90‰ to -1.75‰, -4.71‰ to -2.13‰ and 26.01‰ to 28.66‰ in calcareous sediments, respectively. The δ13CPDB values in bivalve shells are comparable to that of calcareous sediments (~ -1.75‰) in the upper section, but δ13CPDB values in calcareous sediments are more negative excursion towards lower section (up to -13.90‰). These results signify that salinity gradients could modified the isotope values and/or strong influence of freshwater conditions. The variable δ18OPDB values in both bivalve shell and calcareous sediment suggesting diagenetic alteration of carbonates and water temperature effects. The more negative δ18OPDB values imply humid paleoclimatic conditions during the Mio-Pliocene sedimentation. Therefore, the δ18OPDB values of the Mio-Pliocene sediments of Nhila Anticline are probably controlled by paleotemperature leading to intensification of high rainfall.

Keywords: Stable isotopes; Bivalve shells; Calcareous sediments; Bengal Basin; Bangladesh

Location:

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Land development productivity

Objectives:

The objective of this study is to evaluate paleoclimate and paleoenvironment proxies using stable carbon (δ13C) and oxygen (δ18O) isotopes of bivalve shells and calcareous sediments of the Nhila Anticline, southeast Bengal Basin, Bangladesh.

Methodology:

A total of 10 samples (3 bivalve shells and 7 calcareous sediments) were collected from the upper Boka Bil and Tipam Sandstone Formations in Mio-Pliocene Nhila Anticline, southeast Bengal Basin, Bangladesh. Stable isotope analyses were performed at the Stable Isotope Laboratory (LABISE) of the Federal University of Pernambuco, Brazil. Detailed sample preparation and analytical techniques are illustrated in Armstrong-Altrin et al. (2011), but are also summarized below. CO₂was removed from powdered carbonates in a high vacuum line after reaction with H3PO4 at 25°C, and cryogenically cleaned based on the technique explained by Craig (1957). The SMOW (Standard Mean Ocean Water) conversion values to PDB (Peedee Belemnite) standard were carried out using the following equation δ18Ocalcite (SMOW) = 1.03086 δ18Ocalcite (PDB) + 30.86 (Friedmnan and O’ Neil, 1997).

Source of Information: J. Life Earth Sci., Vol. 8: 113-117, 2013 ISSN 1990-4827

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Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Stable carbon (δ13C) and oxygen (δ18O) isotope compositions of bivalve shell and calcareous sediment from Mio-Pliocene Nhila Anticline, southeast Bengal Basin were used to evaluate paleoclimate and paleoenvironment conditions. The δ13CPDB values (- 2.81‰ to -1.56‰) in the bivalve shells show little negative excursion, and the more negative and wide variation of δ13CPDB values of calcareous sediment samples (up to -13.90‰) are also most probably influenced by plant root respiration of variable plant community photosynthesis paths during pedogenic processes in sediment. The δ18OPDB values in the bivalve shell and calcareous sedimentary rock samples range from -2.39‰ to -3.57‰ and -4.71‰ to -2.13‰, respectively. The variable δ18OPDB values of the Nhila Anticline indicate diagenetic modification of carbonates, and negative δ18OPDB values suggest humid climate during the Mio-Pliocene time. Thus, the δ18OPDB values in the region are largely controlled by paleotemperature as well as strong rainfall.

Knowledge Management: Journal