GEOLOGI DAERAH SEKARBANYU, KECAMATAN SUMBERMANJING, KABUPATEN MALANG, JAWA TIMUR

Abstract

This research was conducted in Sekarbanyu Village, Sumbermanjing District, Malang Regency, East Java, with the aim of analyzing the geological conditions and reconstructing the geological history of the area. The analysis includes studies of geomorphology, petrography, geological structures, micropaleontology, and biostratigraphy. The research methodology consists of preparation, geological field mapping, laboratory analysis, data interpretation, and report writing. The study area is divided into four geomorphological units: Pyroclastic Hill Unit, Karst Hill Unit, Faulted Hill Unit, and Remnant Volcanic Hill Unit. From a stratigraphic perspective, the area comprises four rock units, namely: Andesite Lava Unit (Late Oligocene–Early Miocene), Pyroclastic Breccia Unit (Middle Miocene), Sandstone Unit (Middle Miocene), and Limestone Unit (Late Miocene–Early Pliocene). The geological structures developed in this area consist of two northwest–southeast–trending thrust faults: the Srimulyo Right Thrust Slip Fault and the Sumbersuko Right Thrust Slip Fault, as well as a north–south–trending strike-slip fault: the Sekarbanyu Reverse Left Slip Fault. The geological history began in the Late Oligocene–Early Miocene with magma intrusion reaching the surface, forming a volcanic edifice and producing the Andesite Lava Unit. During the Middle Miocene, the Pyroclastic Breccia Unit was deposited, interpreted as originating from a different volcanic source, followed by extensional tectonic inversion that created a basin filled with the Sandstone Unit. Environmental changes in the Late Miocene led to the dominance of Limestone Unit deposition. Subsequently, in the Late Miocene–Pliocene, compression occurred, uplifting and affecting the positions of the Sandstone and Limestone Units, and tectonic processes have continued to the present, marked by the formation of faults that control the geological conditions of the study area.