STUDY OF PETROGENESIS AND TECTONOGENESIS OF SANDSTONE BULUKUNING FORMATION IN THE SCALY CLAY MATRIX OF BANJARNEGARA AREA, CENTRAL JAVA

• Main Author: PUSWANTO, EKO
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/45294
• Institution: Institut Teknologi Bandung

Sedimentary rock units in the research area, with a whole moderately deformed and slightly-metamorphosed sedimentary rocks are exposed in the Bulukuning area, Purwanegara district, Banjarnegara regency, Central Java. Previously, these sedimentary rock units have been mapped as pre-Eocene sedimentary sequence, partly of Early Cretaceous – Paleocene Melange Complex. Previous research reported that these sandstone unit as greywacke partly of Luk Ulo Melange Complex. Recent research proposed these sedimentary sequence as a metasedimentary rocks of Bulukuning Formation that younger than the Luk Ulo Melange Complex. In this research, characteristic of these sedimentary rocks units were analyzed in detail, especially the presence of sandstone within the scaly clay matrix. This research also related to the sandstone provenance and age of the sedimentary sequence, to give information about deformation mechanism within the scaly clay matrix. The sandstone unit was found in the middle part of the research area, between claystone unit continuously spread from the Kali Sat in the west to the Kali Lebak Menak in the eastern part of the research area. The presence of sandstone in these rock units are associated with several conditions; intercalation between sandstone and claystone; intercalated within claystone; embedded in the scaly clay matrix. Sedimentary rock units in the research area are moderately deformed, in some part are folded and faulted. Boudin structure formed in the bedding of sandstone and claystone, showed a lenses with rounded at the end of the portion. Boudin structure also found in the incompetent clay matrix. Clay matrix showed scaly and oriented in the form of cleavage. The sandstone units in the research area are sublitharenite and lithic-subarkose type, showed diagenesis and slightly metamorphosed. The internal deformation of the sandstone related to the fault that control the forming of the boudin structure. Following the simple shear concept, that occurred under a temperature of approximately 205.916 – 223.014oC (± 30°). Based on the characteristics and the nannofosil ages indicates that the sedimentary rock units in the research area is not part of Luk Ulo Melange Complex. A few nannofosil: Ponthosphaera pulchra, Ponthosphaera versa, Discoaster asymmetricus were found in the sediment, suggesting the Middle Eocene age. iv Sandstone provenance analysis in the research area showed the tectonic setting of source rock related to recycled orogeny, especially from tectonic collision orogen. This happened because of collision between East Java Microcontinent and Sundaland in the Early Eocene – Early Oligosen, than caused the Karangsambung accretion complex uplifted and finally deposited in foreland basin.