Indonesia Conference Directory

The research area is located in Lubuk Tarok Village, Sijunjung Regency, West Sumatra and is geologically part of the Ombilin Basin. Previous researchers examined Sawahtambang Formation as part of Ombilin Basin stratigraphy on a regional basis. The purpose of this study is to characterize sediment deposition, interpret and model the depositional environment. The method carried out in this study is the making of outcrop stratigraphic profiles with detailed observations of lithofacies and architectural elements in eight observation locations divided in two north-south oriented segments. The observation location is positioned in a geological cross section to find out the stratigraphic position of the unconformity with the Sangkarewang Formation below it. Interpretation of the lithofacies and architectural elements characteristics are carried out to know the process and its depositional environment. The final stage is making comparative modeling, refers to Nichols (2009) to show the vertical and lateral relation of lithofacies. Both segments in the west and east of the research area showed similarities in types of litofacies, there are Scourfills (Ss), Sandy through crossbeds (St), Sandy planar crossbeds (Sp) and Sandy horizontal (Sh). Ss is sandstones that fill the scour surface. St is found in the channel migration part. Sp is found above the channel migration, and Sh is fine deposits at the top of the runoff flow deposits. The architectural element shows repetitions and combination of channel and sandy bedform sedimentary geometry. Litofasies changes show how the the deposition process changed by the cause of channels that intersect each other. The deposit formed by this channel activity is called multistorey channels which are interpreted as the result of braided river environmental deposits with paleocurrent direction to the west. The characteristics of the Sawahtambang Formation which has very thick sandstones are significant value for the study of reservoirs in Ombilin Basin.