Volume 49 Number 3

Beach ridge evolution in response to the Holocene sea-level change from Surat Thani, Thai-Malay Peninsula

Sinenard Polwichai^a, Sumet Phantuwongraj^b, Montri Choowong^b,*

 
ABSTRACT:     Sets of beach ridge plains and sand spit at Laem Pho, Chaiya coast of Surat Thani, the Thai-Malay peninsula, the Gulf of Thailand show their evolution in response to a long-term sea-level change from the middle Holocene to the present. The most landward set of beach ridges defines the paleo-shoreline located at 4.5 km far inland with an elevation up to 4 m of ancient sea level above the present mean sea level. Interestingly, the orientation of beach ridges reflects that they were mainly formed by longshore current in southeast direction likely similar to beach ridges in the other coastal sectors of the western part of the Gulf. The major composition of beach ridge included quartz, whereas minor composition was feldspar. Roundness and sphericity of beach ridge sediments showed sub-rounded and sub-angular. Physical properties of beach sediment and the preservation of feldspar in beach sediment suggest the main source from granite exposure near this coastal plain. Major sediment pathway was possibly supplied from the Phum Rieng canal. Optically stimulated luminescence dating revealed the formation of beach ridge plain here starting from 7,171?460 years BP. The sand spit has been formed at 440 years BP. These ages responded to the formation of beach ridge after sea level had reached the highstand in the middle Holocene.

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* Corresponding author, E-mail: montri.c@chula.ac.th

Received 19 Aug 2022, Accepted 26 Jan 2023