Classification of gastropoda and bivalvia fossils from the Khao Sam Roi Yod National park, Prachulap Khiri Khan, Thailand

Abstract

The purposes of this study are to classify Gastropoda and Bivalvia fossils from the Khao Sam Roi Yod National Park, Prachuap Khiri Khan Province, Thailand and to correlate paleoenvironment of molluscan fossils. The specimens of molluscan fossils were collected from 5 localities: Wat Ban Khao Daeng, Khao Rap. Wat Thung Noi School, Ban Don Makham and Ban Nong Tao Pun Lang. The distance from the recent coastline to these areas is about 1.5, 1.8, 4.2 and 4.3 km respectively, More than 75 species belongings to 55 genera and 35 familiar of marine molluscan fossils and recent mollusca can be classified. The dominant molluscan fossils are Cerithidea (Cerithideopsilla) cingulata, Natica tigrina, Nassarius pullus, Placamen chloroticum and Marcia hianine. The analysis and correlation between the dominant molluscan fossils and recent mollusca show the similarity in their shapes and sizes. Thus, the living environment of recent molluscan can be used to interpret the paleoenvironment of the study area. It can be assumed the environment in the past was intertidal or mangrove, except Wat. Ban Khao Daeng area which is recent coastline. The results from C14 dating of molluscan fossils are shown as follows; the age molluscan fossils from Khao Rap is 1520+250 BP, the ones from Wat Thung Noi School is 2200+270 BP in age and molluscan fossils from Ban Don Makham is 7360+420 BP. They are during Holocene epoch. Furthermore, sea notch found in adjacent area which caused by the marine erosion, as well as the evidence and analysis of marine molluscan fossils can be concluded that one of the study areas at Ban Don Makham which is around 4 km from recent coastline used to be affected by the transgression and the intertidal or mangrove environment occurred in 7360+420 BP. After that the regression had been occurred until reaching the mean sea level at the present coastline.