Carbonate rocks in northern of West Jiwo Hills Bayat: The indication of thrust belt development in southern Central Java

Abstract

Bayat, Klaten, Central Java, is one of three locations in Java with complete types of rocks exposed at the earth’s surface. All those rocks are scattered over a short distance in Bayat, revealing past processes of rock deformation (folding, fracturing, and faulting) and present-day processes of rock weathering and erosion. In this study, we present how clastic carbonate rock of the Oyo Formation at northern Jiwo Hills could be separated about ±15 km northern from its platforms as an indication of thrust fault growth. This study uses aerial photography for photogrammetry (drones) combined with structural geology and microfossil analyses (to know the exact formation) from the outcrop observation. Recent studies have certified that drones are one reliable observation tool in various aspects with better resolution, especially in structural geology studies. Aerial photogrammetry is very well done to see the exact condition of a wide area combined with high resolution on an outcrop scale. The result shows that the carbonate rocks are from Oyo Formation (N9–N11) with the Middle Neritic bathymetric zone. The structural geology phenomenon kinematically indicates the impact of the transpressional movement called flower structure. Based on subsurface interpretation, the authors hypothesize this area was the product of an imbrication thrust stack uplifted basement as the result of the thrust fault rather than horst or paleo-basement high.