Karakteristik Evolusi Sistem Karbonat Formasi Wonosari di Daerah Giritontro, Wonogiri, Jawa Tengah, Indonesia
DOI:
https://doi.org/10.29303/goescienceed.v7i4.3329Keywords:
Limestone, Wonosari Formation, Karst, Depositional Environment, Stratigraphy.Abstract
The Wonosari Formation is one of the major Miocene carbonate units developed in the Southern Mountains Zone of Java and records changes in depositional conditions during the evolution of the carbonate system. However, the relationship between changes in lithofacies, age, paleobathymetry, and hydrodynamic conditions of the Wonosari Formation in the Giritontro area has not been comprehensively documented. This study aims to identify the lithofacies characteristics, age, paleobathymetry, and depositional environment of the Wonosari Formation in Giritontro, Wonogiri, and its surroundings. The study was conducted through geological mapping over an area of 25 km² at a scale of 1:25,000, covering 171 observation points, along with petrographic, micropaleontological, and calcimetric analyses of representative samples. The study area consists of packstone and wackestone limestone units. The packstone unit is predominantly grain-supported and, based on planktonic foraminifera, is interpreted as N12–N13 in age, while the benthic foraminiferal assemblage indicates an outer neritic environment with an estimated paleobathymetry of approximately 100–200 m. The wackestone unit is characterized by a mud-supported texture, is interpreted as N14–N15 in age, and was deposited in a middle neritic zone with an estimated paleobathymetry of approximately 20–100 m. Calcimetric analysis indicates CaCO₃ contents of 97.2% at LP 106 and 95.6% at LP 77. Stratigraphic relationships and paleobathymetric data indicate a relative shallowing trend from the outer neritic to the middle neritic zone. Variations in packstone–wackestone lithofacies, along with the occurrence of ripple marks and bioturbation, indicate fluctuations in hydrodynamic conditions during sedimentation. The results show that the development of the Wonosari Formation carbonate system in the Giritontro area was associated with changes in paleobathymetry and hydrodynamic conditions during the Miocene.
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