Sains Malaysiana 31: 23-31 (2002)                                                                                                                Sains Bumi /

Earth Science

Holocene Seas at Pulau Pinang and

Pulau Langkawi: New Dates

Tosido Nakamura

Dating and Materials Research Center

Nagoya University, Nagoya 464, Japan Shoji Fujii

Fuji Laboratory for Environmental Geology

8-20, Imaizumi-Seibu,Toyamashi, Japan 939-8282

Hong Djin Tjia

Petronas Research & Scientific Services

Lots 3288 & 3289

Off Jalan Ayer Itam (Bangi) Kajang, Malaysia

ABSTRACT

The radiocarbon ages of four groups of fossil subsea bivalve accumulations and four elevated fossil oyster clusters from the vicinity of Pulau Pinang and from Pulau Langkawi were determined at the Dating and Materials Center of Nagoya University, Japan. The subsea samples indicated that the Pinang Channel remained under water during 1500-1900y B.P. [0 B(efore) P(resent) refers to year 1950] and around 450y B.P. In the northern Strait of Melaka, sea level declined regional from + 2.5 m aMSL at 4600y B.P. to + 1.25 m aMSL at 1400y B.P. The eight new data is consistent with the established Late Quaternary - Holocene sea level curve of Peninsular Malaysia. In the Langkawi islands several good shoreline indicators (corals and rock-clinging oysters) between 6500 and 9500y B.P. show early Holocene seas that were 20 to 40 metres above the established sea-level curve. The cause of these anomalous positions is still problematic. Drastic geoidal change or rebound of the land surface following impacts by two recent (6500-5000y B.P.) extraterrestrial objects offer the more plausible explanations.

ABSTRAK

Usia radiokarbon empat kumpulan moluska dwikatup yang terkandung dalam lempung bawah laut dan empat gugusan fosil tiram daripada Pulau Pinang dan Pulau Langkawi telah dianalisis di Dating and Materials Center, Universiti Nagoya, Jepun. Usia sampel bawah laut menyatakan bahawa Terusan Pinang sentiasa bersekitaran laut antara 1500 dan 1900th B.P. [0 B(efore) P(resent) adalah tahun 1950] dan juga sekitar 450th B.P. Di hujung utara Selat Melaka, iaitu di Pulau Pinang dan Pulau Langkawi, aras laut telah menurun secara rantau dari +2.5 m di atas aras laut min (aPLM) ke + 1.25 m aPLM dalam jangkamasa 4600th B.P. ke 1400th B.P. Kesemua lapan maklumat terbaharu ini tidak menyimpang daripada garis lengkung aras laut penghujung Holosen yang telah dikenalpasti di Semenanjung Malaysia. Bagaimanapun, di Kepulauan Langkawi didapati sejumlah penunjuk aras laut kuno yang unggul (karang dan tiram) berusia antara 6500th dan 9500th B.P. menunjukkan kedudukan aras laut setinggi 20 hingga 40 meter di atas garis lengkung tersebut. Sebab musababnya masih berupa tanda tanya. Mungkinkah kedudukan anomali itu disebabkan pertukaran geoid, ataukah akibat pantulan menegak daripada mukabumi setelah mengalami kejatuhan dua objek luar angkasa sekitar 6500 - 5000th B.P.?

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