Publications

The Rajamandala Formation is well exposed in Padalarang area, near Bandung, and is the objective of a collaborative study between ITB, Rice University, ExxonMobil and BPMigas. The collaborative work focuses on the biostratigraphy, the interpretation of the depositional facies and geometries, and the relationship to tectonism. Detailed preliminary work presented here is focused in two areas, Cikamuning and Gn. Guha. Cikamuning is a well exposed carbonate outcrop ridge located near the Tagogapu train station that represents a shelf-to-basin transition. Gn. Guha is a large quarry with excellent 3D exposures of the uppermost Rajamandala Limestone. Both Cikamuning and Gn. Guha outcrops are capped by mixed carbonate-siliciclastic facies. Based on field and thin sections observations, 5 environments of deposition have been identified: platform top, reef margin, foreslope, carbonate turbidite apron, and mixed carbonate-siliciclastic deep-water breccia. The reef margin, foreslope and carbonate turbidite apron are well exposed at Cikamuning. The reef margin is composed of coralalgal boundstone and skeletal grainstones, whereas floatstone, rudstone and occasional boundstone. Depositional dip on the foreslope deposits is between 10 and 230 to the NE. The carbonate turbidite apron is characterized by normally-graded, thin bedded grainstones to packstones (turbidites) and thick bedded breccias, grainstones and siltstones. The stratigraphic relationships at Cikamuning indicate that margin and foreslope deposits form a depositional continuum reflecting a shallow-water prograding carbonate platform. The deep-water carbonate turbidite apron rests unconformably on the prograding carbonate platform with an onlapping geometry. The turbidite deposits fill the lows created by the underlying unconformity and foreslope paleotopography. Based on both large benthic and planktonic foraminifera, the prograding carbonate platform was deposited during the early part of the Chattian (Stages Te1 and Te2-3) and the turbidite apron during middle-late Chattian (Te2-3 and Te4). The platform top facies exposed in Gn. Guha consist of alternating red-algal boundstone and grainstone, which are interpreted to represent an open shelf environment. The lowermost deposits of the Gn. Guha section are interpreted as Te 2-3. The majority of the Gn. Guha section is, however, Te4 in age with the uppermost section section clearly late Te4. The mixed carbonate-siliciclastic deepwater breccias that overlie both areas consist of three main lithologies: carbonate breccia (with rare matrix) with carbonate, quartz and sandstone clasts (only seen near Gn. Guha), carbonate breccia, andclaystone. The mixed carbonate-siliciclastic deepwaterbreccia is late Chattian (Te4) to earlyAquitanian (Te5) in age.The biostratigraphic correlation between the twoareas suggests that during the Early Chattian ashallow water platform occurred in both areas, inCikamuning the platform prograded to the NE. During middle Chattian time the platform margin at Cikamuning was partially truncated and later covered by deep-water turbidites. In contrast, shallow-water open marine conditions prevailed at Gn. Guha during the Middle Chattian suggesting backstepping. Possible, after exposure of parts of the platform, the entirety of the area was covered by deep-water deposits by the end of the Chattian as evidenced by the deposition of claystone with breccias resulting from the erosion of nearby limestones throughout the area. The uniqueness of this event is further emphasized by the presence of sandstone and quartz clasts in the breccias in the southern outcrops suggesting the erosion of an unidentified land. The studied outcrops presented here provide insight into the evolution and demise of Oligocene carbonate platforms in tectonically active areas and high amplitude sea level changes.