A Reinterpretation of the Baturetno Formation: Stratigraphic Study of the Baturetno Basin, Wonogiri, Central Java

DOI:10.17014/ijog.2.3.125-137This paper focuses on the Quaternary Baturetno Formation. An earlier research concluded that the black clay of the Baturetno Formation formed as a ‘palaeolake' deposit. The ‘palaeolake' was interpreted to form due to the shifting course of the Bengawan Solo Purba River in relation to Pliocene tectonic tilting in the southern Java. The stratigraphy of the Baturetno Formation was observed in the western part of the Baturetno Basin, and based on marker beds, the Baturetno Formation was classified into three units: (1) Gravel unit (GR) in the upper part, (2) clay unit (CU) in the middle part, and (3) sand-gravel unit (SG) in the lower part. There are floating gravel fragments of andesite, claystone, coral, and limestone with diameters of up to 10 cm in the clay unit. The particle size of sediment reflects the environment, but the lake deposition occurs under very quiet conditions. The occurrence of these fragments within the clay cannot be explained if the clay was deposited within a lake environment. The occurrence of floating fragments in the black clay of Baturetno Formation can best be explained through mudflow process. The cohesive strength of the mudflow is responsible for the ability of large fragments to float within the mud matrix. In general, the Baturetno Formation is inferred to be an alluvial fan deposit. The presence of sand, gravel, and mud are characteristics of alluvial fan deposits

Sedimentological and Micropaleontological Characteristics of the Black Clay Deposit of the Baturetno Formation, Wonogiri, Central Java

DOI:10.17014/ijog.3.3.163-171A previous research on black clay of the Baturetno Formation identified that this clay was a palaeolake deposit. In this study, the black clay deposit was characterized by using sedimentological and micropaleontological approaches to reveal its origin. The black clay of the Baturetno Formation has a low organic matter (mostly less than 8%) and almost no pollen content. These characteristics are not representative of a lake deposit. This black clay was suggested a mud flow deposit. This conclusion is supported by the occurrence of dispersed rock fragments in the clay deposit. In addition, the previous research has identified that the formation of a palaeolake was related to the Late Pliocene tilting in South Java. The carbon dating indicates that the deposition of this clay has no relationship to the Late Pliocene tilting in South Java as the age of this clay was determined to be much younger (around 7000 BP; early Holocene)

Depositional Environment of the Batuasih Formation on the Basis of Foraminifera Content: a Case Study in Sukabumi Region, West Java Province, Indonesia

DOI: 10.17014/ijog.v7i2.139The research was carried out on the sediments of the Batuasih Formation cropping out at Batuasih Village, Cibatu River, Padaarang Sukabumi. Data obtained from field observation, as well as foraminifera and sedimentology analyses conducted in the laboratory, were used to interpret its depositional environment. The investigation was focused on planktonic and benthic foraminiferal assemblages for depositional environment interpretation that might not be used by previous researchers. The Batuasih Formation is composed of black shaly claystone, where the lower part is rich in clay ball, and limestone intercalations in the upper part of the formation. In Cibatu Section, no clay balls is recognized in the lower part, but intercalations of limestone still occur. However, a contrast difference is found in Padaarang section, where green claystone interbeds with fine-grained sandstone. The Batuasih Formation conformably overlies the Walat Formation containing conglomerate. Foraminifera fossil found in the Batuasih Formation consists of bad preserved black benthic and planktonic foraminifera, more abundant towards the lower part of formation. Based on foraminifera assemblage comprising genus Uvigerina, Cibicides, Elphidium, Operculina, Bulimina, Bolivina, Eponides, and Neoconorbina, supported by sedimentology data, the Batuasih Formation was deposited in a shallow to deep marine environtment, during Early Oligocene (P19) time. Upwards to be the Rajamandala Formation, the depositional environment tends to be shallower gradually