KARAKTERISTIK DAN PROSES PENGENDAPAN SEDIMEN DASAR LAUT DI PERAIRAN GOSONG BUNGA, KUALANAMU KAB. SERDANG BEDAGEI, PROV. SUMATERA UTARA

Abstract

Daerah penelitian terletak di perairan Gosong Bunga, lepas pantai Kualanamu dengan kedalaman antara 10 – 20 meter dan di bagian tengah hanya 2 - 3 meter pada saat air laut surut. Hasil analisis besar butir di daerah penelitian diperoleh beberapa jenis satuan tekstur sedimen dasar laut, yaitu: pasir lanauan, pasir, pasir lumpuran sedikit krikilan, lumpur pasiran, lanau pasiran, krikil pasiran, lumpur pasiran sedikit krikilan dan pasir sedikit krikilan. Berdasarkan hubungan antara besar butir dan persentase jumlah/frekuensi butiran; pengendapan sedimen dipengaruhi oleh arus sungai dan arus pantai dengan pola pergerakan butiran adalah saltasi, rolling (gulungan) dan sliding (dorongan) serta suspensi, dan secara umum membentuk pola saltasi.
Sedangkan hasil analisis kimia pada beberapa contoh sedimen terpilih menunjukkan kandungan kuarsa (SiO2) berkisar antara 66,33 - 74,21% dan kandungan rata-rata sebesar 69,88%. Analisis fotomikro memperlihatkan komposisi utama adalah butiran kuarsa hampir 85%, mineral berat (magnetit, ilmenit, hematit dan limonit) 10% dan cangkang foram dalam keadaan utuh 5%. Hasil interpretasi rekaman seismik menujukkan ketebalan sedimen Kuarter di daerah penelitian antara 7 – 15 meter, di bagian tengah mencapai 20 meter.

Kata kunci: sedimen dasar laut, proses pengendapan, pola pergerakan, lepas pantai Kualanamu


The survey area is located on the Gosong Bunga waters, offshore of Kualanamu coast with waters depth between 10 – 20 meters, and part of central area only 2 – 3 meters depth on low sea level. Grain size analysis result from the survey area is several types of seafloor sediment textures silty sand, sand, slightly gravelly muddy sand, sandy mud, sandy silt, sandy gravel, slightly gravelly sandy mud and slightly gravelly sand. Based on relation between size, and cumulative and frequency percent of grains; depositional process of sediment influenced by river and coastal current with movement pattern are saltation, rolling, sliding and suspension, and generally to form a saltation pattern.
While, result of chemical analysis on some the samples indicates that the quartz content (SiO2) content are between 66,73 – 74,21%, and the average content is 69,88%. Microphoto analysis indicates that the main content are quartz approximately 85%, 10% heavy minerals (magnetite, ilmenite, hematite and limonite) and good condition foram shell 5%. Seismic interpretation shows that the thickness of Quaternary sediments are about 7 to 15 meters except in the centre of the study area which is 20 meters.

Keywords: seafloor sediment, depositional process, movement pattern, offshore of Kualanamu