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Geochemical Characterization of Exposed Black Shale Sediments of Matamuhari Anticline, Bangladesh

Ashraf Ali Seddique
Department of Environmental Science and Engineering, Jatiya Kabi Kazi Nazrul Islam University, Mymensingh, Bangladesh

Nazmul Islam
Department of Petroleum and Mining Engineering, Jessore University of Science and Technology, Jessore, Bangladesh

Shree Bipulendu Basak
Department of Environmental Science and Engineering, Jatiya Kabi Kazi Nazrul Islam University, Mymensingh, Bangladesh

Muhammad Badruzzaman
3Department of Biochemistry and Molecular Biology, Bangabandhu Sheikh Mujibur Rahman Agricultural University, Gazipur, Bangladesh

Abdul Batin
Bangladesh Petroleum Exploration and Production Company Ltd., Dhaka, Bangladesh

Abstract/ Executive Summary:

Matamuhari anticline is one of the largest anticline situated at Bandarban district of Bangladesh which is 60 km long and 20 km wide in the part of Bangladesh. Like other part of Bangladesh, the whole sequence of exposed rocks of Matamuhari anticline is composed with Neogene sedimentary rocks of shale, sandstone, siltstone, silty shale, tabular and spheroidal calcareous concretions. Seven outcrop black shale samples were collected during February 2013 from the different parts of the anticline namely Boro Bari Jhiri, Ochir Jhiri and Tak Chara area were mineralogically and geochemically examined in order to better understand the depositional environment in the studied area. The major and trace elements were analyzed using XRF spectrometry. Two distinct lithofacies assemblages, mud and silty-clay are found in the collected sediments. The shales are predominated by quartz, kaolinite, chlorite, mica (muscovite and biotite), feldspar (both K-feldspar and plagioclase), and in addition to a variable ratio of vermiculite. Lithologial characteristics and geochemical data demonstrated that sediments are enriched with TOC contents ranging from 0.39 to 0.67 wt.% and shows distinctive correlation to concentration of TOC and particle size distribution. These shales are characterized by a low Mg and K as well as high Al and Fe contents. Studies also show that the values of MgO/Al₂O₃ and K₂O/Al₂O₃ ratio ranges from 0.15 to 0.17 and 0.18 to 0.20 respectively. The relationship of log MgO/Al₂O₃ and log K₂O/Al₂O₃ values reveals that all of the studied samples fell within the marine environment. Ni/Co ratio of the studied shale samples ranges from 2.84 to 3.88 (average 3.36). These low values of Ni/Co ratio suggest that the sediments were deposited under oxic conditions. However, the above observations suggest that the sediments of Matamuhari anticline area were deposited in a shallow marine environment under oxic conditions.

Keywords: Matamuhari Anticline, Black Shale, Environment, Total Organic Carbon

Location: Lama, Alikadam and Naikhangchari Upazilla of Bandarban at South-Eastern part of Bangladesh

Start Date: 00-00-2013

End Date: 00-00-2013

Program Area: Risk Management in Agriculture

Commodity: Physico-Chemical, Sediment

Objectives:

(i). to draw a general picture of geochemical characteristics of exposed black shale sediments, and

(ii). to better understand the depositional environment in the area studied.

Methodology:

The study was conducted in Lama, Alikadam and Naikhangchari Upazilla of Bandarban at South-Eastern part of Bangladesh. The studied area encompasses mostly Neogene Hills of Matamuhari anticline. The study area lies between 21⁰34' N to 21⁰45' N latitude and 92⁰04' E to 92⁰19' E longitude. The area is bounded by Matamuhari River to the north and east, Cox’s Bazar to the west and Rakhaing of Myanmar to the south. The accessibility of the area is trouble- free in the northern part of the structure, but very tough in the southern part. The study area is in tropical climatic region and receives heavy rainfalls during monsoon. The extent of rainfalls take place during the monsoon that prevails month of June to September. The maximum average temperature is about 32⁰C which prevails in the month between April and May weather the minimum average temperature is 13⁰C which prevails in the month of December. The intense rainfall is the main cause of developing abundant growth of vegetation in the study area. The entire hilly area is covered with dense mixed forest with a variety of trees and wide number of bamboos, shrubs and herbs. With the help of satellite image, the sampling location was selected and seven outcrop black shale samples were collected during Feb. 2013 from the different parts of the anticline such as Boro Bari Jhiri (TCB-01, BBJ-01), Ochir Jhiri (OJ-02, OJ-03) and Tak Chara (TC-01, TC-02, TC-03) area to the depth of 26cm below the surface to avoid weathered outcrop. Undisturbed sediment cores were collected from the Bokabil formation shale of Surma group by penetration of a 3.5cm diameter split-barrel sampler (Raymond sampler) by a private drilling company (Eastern Geotechnical, Dhaka). Samples were immediately vacuum packed in O2-impermeable film bags (Escal film, Mitsubishi Gas Chemical Co., Japan) with deoxidizer. Later these sample were kept in the laboratory of Jessore University of Science and Technology freezer (-18°C) unit analysis. Prior to analysis, about 50 g of undisturbed sediment core was immediately transferred from the freezer (-18⁰ C) to a vacuum drying oven (Advantec, VO-320) in order to avoid oxidation of the reduced compounds, and freeze dried. The dried samples were ground gently by hand with an agate mortar and pestle, and used for the analyses outlined. Grain size distribution was determined by laser diffraction and scattering spectroscopy (SALD-3000S, Shimadzu) after dispersion of the samples in sodium hexametaphosphate solution. The reproducibility of the results for the duplicate samples was within ± 5 % at maximum. Bulk mineralogy of the sediments was identified by X-ray powder diffraction (XRD) using a Rigaku Geigerflex instrument (RAD-IA system) with Ni filtered Cu Ka radiation (30 kV, 10 mA), operating in step scan mode, over an angular range of 20 to 650 2θ with 0.020 2θ steps and a 2s count time on 200 mg unoriented side-packed powder mounts. Approximate relative abundance ratios of major minerals were estimated from the relative intensities of the most intense and specific peak of each mineral from an XRD chart. The major chemical composition of bulk sediments was determined by X-ray fluorescence (XRF) photometry (VXQ-160S, Shimadzu) using glass bead samples, which were prepared by fusion of sediment samples with lithium borate (1:3 ratio). The analytical errors for major elements were within ± 3 %. Total Organic Carbon of bulk sediment samples was measured by dry combustion according to a method described by using an elemental analyzer (FLASH EA1112 series, IRMS) after HCl digestion. Analytical precision for duplicate samples was within ± 5 %.

Source of Information: International Journal of Environmental Protection and Policy, 2019; 7(3): 86-92 ISSN: 2330-7528 (Print); ISSN: 2330-7536 (Online)

Article Link (Online Journal): http://www.sciencepublishinggroup.com/j/ijepp

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Two distinct lithofacies assemblages, i.e. clayey-silt and silty-clay are found in the collected Bokabil black shales sediments. Lithologial characteristics and geochemical data demonstrated that the sediments are enriched with TOC contents ranging from 0.39 to 0.67 wt.% and show distinctive correlation to concentration of TOC and particle size distribution. The mineralogical composition of the studied sediments is predominated quartz, kaolinite, chlorite, mica (muscovite and biotite), feldspar (both K-feldspar and plagioclase), and in addition to a variable ratio of vermiculite and illite. These shales are characterized by a low Mg and K as well as high Al and Fe contents indicating that they were formed through intensive weathering of intermediate and mafic igneous rocks. Mineralogical and geochemical studies (organic and inorganic) indicate the deposition of these shales under a shallow marine environment with some terrestrial input. The studied shales have poor to fair organic richness. They indicate the capability to produce gas and fair oil source.

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