Using the Benthic Foraminifera as an Indicator of Holocene Sea Level Rise from Eastern Coastal Margin of Bangladesh

Abstract

The study examined the utility of intertidal foraminifera to assess the Holocene sea-level rise using benthic foraminiferal (>63 µm) assemblages both qualitatively and quantitatively from 20 closely spaced (around 1 km) locations. These sampling points were divided into four regions mainly Teknaf, Bordel, Inani and Himchori region. These surficial sediment samples were collected across the supratidal, intertidal (low tide and high tide) and dune environment along the shelf region. A total of 250 species belonging to 50 genera and 40 families were recorded. The Teknaf zone is noticed by Nonion-Elphidium assemblage which shows Intertidal to Marsh zone of environment of deposition. The Bordel area is demarcated as Nonion-Elphidium assemblage which shows also Intertidal to Marshy environment of deposition. The Inanizone is demarcated as DiscorbisEponides; Epistomina-Operculina; and Cibicides assemblage respectively which shows Supratidal environment of deposition. The Himchori is demarcated by Anomalina-Elphidiella assemblage which shows Intertidal zone of environment of deposition. It interprets that the environment was suitable for benthic forams and a shift of coast line towards land, during the transgression phase. This study confirms that from bottom to middle of the shore a calcareous foraminifera bio-facies characterizes Bay or Lagoonal environment with marine influence. An agglutinated bio-facies from the middle to top represents brackish lagoon with less marine influence. In the shoreline the period of high-frequency sea-level oscillations can be confirmed by the bottom calcareous bio-facies followed by the top agglutinated one.