Survei graviti di Ulu Melaka, Pulau Langkawi, Kedah

702001-100703-501-B
Author : Abdul Rahim Samsudln, Umar Hamzah & Lim Cheng Han
Publication : Bulletin of the Geological Society of Malaysia
Page : 315-318
Volume Number : 45
DOI : https://doi.org/10.7186/bgsm45200248

Bulletin of the Geological Society of Malaysia, Volume 45, May 2002, pp. 315 - 318

 

Survei graviti di Ulu Melaka, Pulau Langkawi, Kedah

(A gravity survey at Ulu Melaka, Langkawi Island)

Abdul Rahim Samsudin, Umar Hamzah & Lim Cheng Han

Program Geologi, Pusat Pengajian Sains Sekitaran & Sumber Alam, Fakulti Sains & Teknologi, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia

 

Abstrak: Satu struktur cincin yang dipercayai merupakan kesan hentaman meteorik telah dikesan di bahagian barat daya Pulau Langkawi melalui kajian imej satelit. Kajian lanjut keatas linemen berdasarkan gambarfoto udara juga menunjukkan kehadiran fitur yang berbentuk membulat. Sampel batuan yang diambil daripada kawasan tersebut menunjukkan kehadiran butiran kuarza yang telah mengalami kejutan akibat daripada impak yang kuat dipercayai oleh hentaman meteorik. Struktur cincin tersebut berada dalam batuan metasedimen yang terdiri daripada syis dan kuartzit. Cincin tersebut dan juga kawasan disekitar telah ditutupi oleh endapan lempung aluvium. Survei graviti telah dijalankan di sepanjang beberapa rentasan memotong struktur membulat tersebut dalam rangka untuk menyiasat morfologi subpermukaan disekitar cincin yang dipercayai dibentuk oleh hentaman meteorik. Pengukuran graviti dilakukan disebanyak 100 stesen menggunakan alat La Coste Romberg pada sela 200-500 meter di antara stesen-stesen. Anomali graviti baki di sepanjang garis rentasan ditafsir untuk memperolehi model geologi subpermukaan 2-D kawah meteorik. Rentasan pada arah timur-barat struktur cincin menunjukkan struktur subpermukaan yang menyerupai lembangan dengan kedalaman aluvium di pusat pengendapan setebal 104 meter dan garispusat disekitar 2.0 kilometer. Satu lagi lembangan telah dijumpai pada jarak 0.5 kilometer disebelah barat lembangan tersebut pada rentasan yang sama. Lembangan kedua ini mempunyai kedalaman maksimum 47 meter dan garispusat sepanjang 2.5 kilometer. Lembangan ini telah dipenuhi dengan alluvium Kuaterner. Rentasan lain yang dibuat pada arah timur laut-barat daya struktur cincin juga menunjukkan kehadiran struktur lembangan dengan kedalaman aluvium maksimum di sekitar 107 meter dan garispusat 1.8 kilometer. Struktur-struktur lembangan ini adalah bukti tambahan untuk menguatkan lagi bahawa kawasan kajian ini telah mengalami hentaman meteorik.

 

Abstract: A ring structure considered as a remnant of a meteoric impact has been spotted in a satellite image of the southwestern part of Langkawi Island, Malaysia. A follow up lineament study of the area based on aerial photograph also indicates similar circular structure. Rock samples taken from the area show the presence of shocked quartz grains which is interpreted to have been developed by meteoric impact. The ring structure is formed by the metasediment formation consisting of schist and quartzite rocks. The whole area within the ring structure is mainly covered by recent alluvial clay deposit. Gravity surveys were carried out along several traverses across the rounded structure in order to investigate the subsurface features of the possible meteoric crater. Gravity measurements were made at 100 stations using La Coste Romberg at an interval of about 200-500 metres between each station. The residual gravity anomalies along the traverses were interpreted for possible 2-D subsurface geological models of the meteorite crater. The east-west traverse direction crossing the ring structure shows basin-like subsurface structures with depth of alluvium depocentre approximately about 104 metres and diametre of about 2 kilometres. Another basin is found about 0.5 kilometre towards the west along the same traverse. The deepest part of the basin is about 47 metres and the diametre length is about 2.5 kilometres. These basins are covered with Quaternary alluvium. Another traverse along the NE-SW direction across the ring also shows the presence of a basin structure with maximum alluvium depth of 107 metres and diametre length of 1.8 kilometres. These basin structures further strengthened the evidents that the study area has previously suffered meteoric impacts.

https://doi.org/10.7186/bgsm45200248