Identifikasi dan Karakterisasi Endapan Tsunami Berdasarkan Studi Sedimentologi dan Paleontologi di Desa Air Pinang dan Desa Sambai, Pulau Simeulue, Provinsi Aceh

Abstract

Simeulue Island, Aceh Province is one of the areas that affected by the tsunami due to the Sumatra-Andaman earthquake. A lot of research about tsunami sediments around Aceh and Simeulue Island has been conducted, but there are only few in the eastern Simeulue. In 2017, the geological coastal chapter team of the 'Widya Nusantara Expedition' LIPI did the research and took samples including SIM 5A in Air Pinang Village and SIM 5C in Sambay Village. The study aims to determine the characteristic of tsunami deposits by sedimentological and paleontological data. The research continue with laboratory analysis which are granulometric analysis, X ray Fluorescence (XRF), Loss of Ignition (LoI) and diatom abundance. Based on granulometry analysis, the candidate of SIM 5A has a grain size is bimodal - unimodal pattern, very coarse silt – coarse silt, poorly sorted - very poorly sorted. While SIM 5C has fine sand - very coarse silt, distribution patterns are unimodal, bimodal and trimodal. LoI analysis shows average value of carbonate material 26,26% with organic material value 15,37% while SIM 5C has average value of carbonate material 13,42% and organic material value 6,55%. The candidate of both samples has the dominant chemical composition of Zr, Fe, K, Sr, Rb, Ca, Ti. Paleontological analysis of tsunami deposit has diatom species with three different salinity environments: air tawar, air payau and marine. In conclusion, all of the results show that tsunami candidates are proven to be tsunami deposit. Differents of characteristic deposits influenced by factors such as micro- topography and post-deposition process.

Pulau Simeulue, Provinsi Aceh merupakan salah satu daerah yang mengalami dampak tsunami akibat gempa Sumatra-Andaman. Penelitian mengenai endapan tsunami di sekitar Aceh dan Pulau Simeulue sudah banyak dilakukan, namun masih sedikit pada daerah Simeulue bagian timur. Pada tahun 2017 Tim Geologi coastal chapter 'Ekspedisi Widya Nusantara' LIPI melakukan penelitian dan pengambilan sampel diantaranya SIM 5A pada Desa Air Pinang dan SIM 5C pada Desa Sambay. Penelitian ini bertujuan untuk mengetahui karateristik endapan tsunami secara sedimentologi dan paleontologi. Pada kedua sampel tersebut masing-masing ditemukan satu kandidat endapan tsunami. Penelitian dilanjutkan dengan analisis laboratorium berupa analisis granulometri, X-Ray Fluorescence (XRF), Loss of Ignition (LOI) dan kelimpahan diatom. Analisis granulometri menunjukkan kandidat endapan tsunami SIM 5A memiliki distribusi ukuran butir pola bimodal – unimodal dengan ukuran lanau sangat kasar – lanau kasar, sortasi jelek – sangat jelek, sedangkan SIM 5C memiliki ukuran butir pasir halus – lanau sangat kasar, distribusi ukuran butir pola unimodal, bimodal dan trimodal. Analisis LOI memberikan nilai rata-rata material karbonat 26,26% dengan rata-rata material organik 15,37% sedangkan SIM 5C memiliki nilai rata-rata material karbonat 13,42% dan rata-rata material organik 6,55%. Endapan kandidat tsunami kedua sampel tersebut memiliki komposisi kimia dominan berupa Zr, Fe, K, Sr, Rb, Ca, Ti. Analisis paleontologi pada endapan tsunami memiliki spesies diatom dengan tiga lingkungan salinitas berbeda yaitu tawar, payau, asin. Keseluruhan hasil analisis menunjukkan bahwa kandidat endapan tsunami terbukti endapan tsunami. Perbedaan karakteristik dapat dipengaruhi oleh beberapa faktor seperti mikrotopografi dan proses pasca pengendapan.