Sedimentation process in Kuala Gigieng Coast, Aceh Besar based on magnetic and gravity surveys

The study of the sedimentation process in coastal can be used to investigate historical settlements and paleo disaster in the area. We have conducted magnetic and gravity survey to model the sedimentation process in Kuala Gigieng area, Aceh Besar, one of the important harbors during the Aceh Sultanate in 16th. The magnetic and gravity methods are able to map structures based on magnetic susceptibility and density distribution below the surface, respectively. The total magnetic field data were measured by the magnetic method, while the gravity method measured gravitational acceleration data. The data were acquired in an area of 1858 x 725 m2 with stations spacing between 70 -100 meters in grid. The standard magnetic and gravity correction was applied to the data, so that the total magnetic field anomaly and Bouguer anomaly are obtained which reflect the conditions the subsurface. The anomaly map obtained shows the pattern of maximum and minimum values, which the patterns were the same as the topography of the measurement area. To get a clearer sediment model, gravity data has been carried out 2D forward modeling with cross sections cutting from coast to land. The 2D model illustrates the existence of 3 layers in the measurement area, sequentially consisting of alluvial and clay, sandstone, and tuff sandstone sediments. The alluvial deposits in the first layer form a repetitive pattern from the land side to the coast; the pattern was formed by coastal activity. The sequence of sediment layers shows the age of the sediment, with the oldest layers formed far from the coast and the youngest layers formed near the coast.