Reconstruction of Holocene Sea Level Change and Paleocoastline for the Eastern Coastal Margin of Bangladesh Using Micropaleontological Evidences (original) (raw)
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Journal of Earth System Science, 2016
Temporal changes in benthic foraminiferal morpho-groups were suggested as an effective proxy to reconstruct past monsoon intensity from the Arabian Sea. Here, in order to test the applicability of temporal variation in morpho-groups to reconstruct past monsoon intensity from the Bay of Bengal, we have documented recent benthic foraminiferal distribution from the continental shelf region of the northwestern Bay of Bengal. Based on the external morphology, benthic foraminifera were categorized into rounded symmetrical (RSBF) and angular asymmetrical benthic foraminifera (AABF). Additionally, a few other dominant groups were also identified based on test composition (agglutinated, calcareous) and abundance (Asterorotalids and Nonions). The relative abundance of each group was compared with the ambient physico-chemical conditions, including dissolved oxygen, organic matter, salinity and temperature. We report that the RSBF are abundant in comparatively warm and well oxygenated waters of low salinity, suggesting a preference for high energy environment, whereas AABF dominate relatively cold, hypersaline deeper waters with low dissolved oxygen, indicating a low energy environment. The agglutinated foraminifera, Asterorotalids and Nonions dominate shallow water, low salinity regions, whereas the calcareous benthic foraminiferal abundance increases away from the riverine influx regions. Food availability, as estimated from organic carbon abundance in sediments, has comparatively less influence on faunal distribution in the northwestern Bay of Bengal, as compared to dissolved oxygen, temperature and salinity. We conclude that the factors associated with freshwater influx affect the distribution of benthic foraminiferal morpho-groups in the northwestern Bay of Bengal and thus it can be used to reconstruct past monsoon intensity from the Bay of Bengal.
Journal of Climate Change, 2015
Sedimentological, palynological data indicate that mangrove community developed under transgressive condition in and around Maheskhali and Kutubdia Island areas during Mid Holocene time (7000 to 5500 years BP) leading to the locally wide spread deposition of organic-rich sediments. During Holocene time global rise and fall of eustatic sea level played an important role not only on the depositional environment but in creating a geomorphic feature on the island. Recurrent occurence of freshwater and mangrove pollen in Maheskhali and Kutubdia Island area indicate that these areas have undergone cyclic marine and non-marine influence. Since the Last Glacial Maximum (about 20,000 years ago), sea level has risen by over 120 m at locations far from present and former ice sheets, as a result of loss of mass from these ice sheets. There was a rapid rise between 15,000 and 6,000 years ago at an average rate of 10 mm/yr. Based on geological data, global average sea level may have risen at an average rate of about 0.5 mm/yr over the last 6000 years and at an average rate of 0.1 to 0.2 mm/yr over the last 3000 years. Vertical land movements are still occurring today as a result of these large transfers of mass from the ice sheets to the ocean. During the last 6000 years, global average sea level variations on timescales of a few hundred years and longer are likely to have been less than 0.3 to 0.5 m. First transgression was noticed around 6000-5500 cal BP and then a subsequent regression of the bay had been observed from around 5500 cal BP. This was again followed by another small scale transgression episode occurred around 2500-2000 cal BP. So the palynomorph assemblages from the Holocene sediment sample indicate that Maheskhali and Kutubdia Island and its surrounding area was an intertidal environment occupied by mangrove community.
Indian journal of marine sciences, 2007
An attempt has been made to reconstruct sea-level variations along the central east coast of India during the late Pleistocene and early Holocene. A total of 39 surface sediment samples collected from water depth range of 27 -2,777 m were studied for foraminiferal content. The samples within the depth range of 36-110 m showed presence of relict foraminiferal tests along with recent foraminifers. The relict foraminiferal assemblage of Amphistegina, Operculina, Calcarina and Alveolinella in the selected surface samples is characteristic of coral reef environment and has been inferred as evidence for past low sea levels. Based on extrapolation of previously published radiocarbon dates from the region, we propose a pliable sea level curve for the period between ~9,000 to ~14,000 years BP.
Coastal and sea-level changes during the Holocene in Bangladesh
Quaternary International, 1999
The aim of the study is to reconstruct the Holocene sea-level history along a section of the coast of Bangladesh. Detailed litho-, bio- and chronostratigraphic techniques have been applied to unveil the nature of sedimentary sequences in association with the events of the Holocene marine transgressions and regressions. Samples were collected from Panigati near Khulna. The study provides evidence of five periods of marine transgression, each followed by a regression, during the Holocene. Each minerogenic sediment layer indicates a marine episode and the sediments were deposited under intertidal to estuarine conditions. Each peat layer is in situ and indicates a regression of the sea. It is difficult to separate the regional eustatic components contributing to these relative sea-level movements, although processes operating locally and regionally are clearly evident. A sea-level curve together with possible error ranges, has been proposed for this part of Bangladesh. Since the early to mid-Holocene, an average relative sea-level rise of 1.07 mm/yr has been estimated.
The Dhaka University Journal of Earth and Environmental Sciences, 2021
The present research is concerned with the investigations of the paleoenvironment of the benthic foraminifera and their diversity in St. Martin’s Island, Bangladesh. About 300 specimens of foraminifera were collected from three sampling sites of the island. Among them 44 species, 39 genera and 25 families were identified which were mostly benthic in origin. Astrorhiza, Elphidium, Cyclammina, Cibicides, and Eponoide were the most abundant genera all over the island based on their relative abundance and frequency of occurrence. Among the three sections, Uttar Para can be designated as Astrorhiza- Elphidium assemblage zone, Maddhya Para as Astrorhiza- Elphidium assemblage zone and Dakkhin para as Astrorhiza-Cibicides assemblage zone. The relative abundance chart of foraminifera and its correlation with the Saraswati and Srinivasan (2016) model diagram indicates that the paleoenvironment signature of the island belongs to the inner shelf to the middle shelf region. The plot of shell-typ...
Journal of the Asiatic Society of Bangladesh, Science
The contemporary intertidal foraminifera and estuarine environment information were collected from the four sites adjoining the deltaic mangrove environment in the Sundarbans. The marsh zones of the south-western coastal region of Bangladesh were examined for modern benthic foraminifera and to expound on the relationship of the foraminiferal assemblages with the environment. Due to high inaccessibility and remoteness, the taxonomic study of foraminifera and its depositional environment remains largely overlooked in the Sundarbans of Bangladesh. This study includes a detailed survey of depositional environment of these fluvio-deltaic to shallow marine sediments. The seventeen species belonging to fourteen genera representing nine families were recorded from surficial sediment of supratidal, intertidal, and dune environment of Kotka, Jamtala, Kochikhali, and Dimer char area. In the present study, these foraminiferal assemblages are characterized calcareous and agglutinated foraminifer...
Foraminiferal biodiversity and Holocene evolution of the Phetchaburi coastal area (Thailand Gulf)
Marine Micropaleontology, 2006
Twenty three surface sediments were collected in May 2002, in the Phetchaburi coastal area (Thailand Gulf) starting from the outer margin of the vegetated zone, to a depth of about 20 m, covering an area of about 800 km 2 . One core was taken in the northeastern area of the Mae Khlong delta plain to investigate the recent paleoenvironmental evolution of this zone, thirteen core levels were collected for micropaleontological (foraminifers) investigation. This highly populated area is characterized by the inflow of the Mae Khlong, the second major river in Thailand, and the Khlong Ban Labun River. Empty tests pertaining to the thanathocoenosis are dominant and, as for the few living specimens, are most frequently represented by Ammonia spp. The collected species are typically of brackish-water settings. Foraminiferal diversity is rather low and increases from the northern part to the central-southern part of the studied area, where taxa typical of the Indo-Pacific realm (such as Miliolids and Schackoinella globosa) are more abundant than the cosmopolitan species such as Ammonia tepida and Gaudryina exilis. The geographic distribution of the four foraminiferal assemblages, defined on the basis of the cluster analysis, indicates that the northern sector is affected by severe environmental conditions. Since this area is affected by the Mae Khlong River input, the salinity fluctuation is probably a controlling factor on the foraminifers distribution. Ammonia tepida, A. inflata, Murrayinella murrayi and Miliolinella sp.1 are the most opportunistic species, able to tolerate wide environmental variability. As regards to the Holocene data, the study carried out on the core located on the Mae Khlong delta plain, indicates that the tidal flat paleoenvironment has been subject to different fresh-water influence, with a general prograding trend.
Paleoceanography, 1995
We have studied the sediment geochemistry and benthic foraminiferal fauna in a 'piston core from the northwest Arabian Sea (covering the last 150,000 years), and compared the results with the stable isotopic record from both benthic (Uvigerina peregrina) and planktonic (Globigerinoides sacculifer) foraminifera. The 6 •80 record of the planktonic foraminiferal species shows excursions towards heavier 6 •80 values when compared to the benthic record and the SPECMAP stack, particularly in stage 3, between approximately 30 and 45-50 kyr. We call this the "stage 3 event." Species diversity and relative abundance data on benthic foraminifera reveal that some species, e.g. Cibicidoides wuellerstorfi, Oridorsalis umbonatus, ?ullenia bulloides, ?yrgo spp., and the uvigerinids increased in relative abundance during glacial stages 2 and 4 and during the stage 3 event, whereas other (e.g., Astrononion novozealandicum, Cibicidoides bradyi, Eggerella bradyi, Gyroidina altiformis, Hoeglundina elegans, oeullenia subcarinata, and $igmoilina edwardsii) decreased. Using correspondence analysis we determined that approximately 50 % of the total sample variation may be accounted for by three first factors which all are interpreted as primarily related to surface water productivity and the quality of the organic matter that reaches the seafloor. The relative abundance of some species appears to vary on a precessional cycle, perhaps responding to monsoon-driven upwelling and associated increased food supply, whilst the abundances of other species are related to the 100 kyr ice volume cycle, and may be responding to changes in intermediate and deep water chemistry. Geochemical paleoproductivity tracers, such as the Ba content of the sediment, have a very similar distribution to specific foraminiferal factors in both time and frequency domains. Certain planktonic foraminifera, (e.g., Globigerina bulloides), also display obvious maxima in the stage 3 event. The stage 3 event occurs at a time of reduced rate of amplitude change in both solar radiation and monsoon pressure index. We conclude, that there was a period 15 to 20 kyr duration during stage 3 with cooler-than-normal surface waters, enhanced productivity and rapid settling of biogenic matter.
Data in Brief, 2019
The data presented herein were collected from the Straits of Malacca, along the west coast of Peninsular Malaysia. A 3.9 m core sample was retrieved from the Straits of Malacca in 2001. This core was continuously sub-sampled at 5-cm intervals between selected core depths of 220 cm and 380 cm. The 32 sub-samples obtained were analysed to understand the species composition of benthic Foraminifera in them and the changes in lithology during the Holocene. The data available in this article include the raw counts of different species of Foraminifera and the weight percentages of sediment of different grain sizes and organic matter at different depth. In addition, the estimated ages of the sediment samples are also provided. The chronostratigraphic framework of the core was based on radiocarbon-14 Accelerator Mass Spectrometry (AMS) dates estimated from three selected sediment intervals. The results of carbon dating were calibrated to calendar years (cal BC/AD) and calibrated radiocarbon years (cal BP). Calibration was done using the INTCAL program with a Delta R value of À19 ± 70.
Reconstruction of Holocene Paleoenvironment and Evidence of Sea-level Changes in the Bengal Lowland
Chigaku Zasshi (Jounal of Geography), 2009
This paper provides a detailed description of sedimentary facies including pollen and diatom analyses, and 14 C ages obtained from a hand-excavated outcrop in the central part of the Bengal Lowland. Based on this examination, seven sedimentary facies were recognized in relation to relative sea-level (RSL) changes since the mid Holocene. With the help of a standard reference datum, the required Mean Sea Level (MSL) has been calculated at the surface of the outcrop. The top of the outcrop was about 1.9 m above MSL and the base is 4.1 m below the MSL. The lowermost bioturbated sand flat facies, 3.75 m below the present MSL, contains mangrove pollen and represents an intertidal coastal-plain and estuarine-channel deposits that were dominated by tidal current. A 14 C age of 7570⊖ 7430 cal BP was obtained for this unit. The evidence supports a transgressive mode in the Bay of Bengal during the middle-Holocene epoch. A subsequent regression interval was found in a salt marsh facies before 6670⊖6410 cal BP. The salt marsh facies has a sharp contact with an underlying (lower) mud flat facies, shaped by downcutting of the upper bed, indicating a regression. In response to this regression, the environment changed gradually from a mud flat to a salt marsh. The salt-marsh deposits contain abundant mangrove pollens and marine-and brackish-water diatoms, providing support for inflow of shallow-marine water into a supratidal, brackish-water mangal environment. The bioturbated mud flat facies indicates that the succession was dominated by tidal current, and the relative sea-level started to rise again after a small rebound. Hence, the transgressive conditions prevailed during the deposition of this mud flat facies in an intertidal coastal-plain environment. The underlying bluish-black medium-bedded peat layer contains grass pollen. This indicates that after the mid-Holocene the environment around the site changed gradually from mangrove to freshwater swamp vegetation, in response to regression of the bay between 4080⊖4030 cal BP. The above evidence suggests that the central part of the Bengal Lowland represented as an intertidal to supratidal coastal-plain estuarine environment that experienced with mid-Holocene relative sea-level changes between 7570⊖7430 and 4080⊖4030 cal BP.