Geochemisity, weathering characterics, and mineralogy of the residual soils developed from Notopuro Tuff, Western Part of Sragen, Central Java, Indonesia

Abstract

The Notopuro Formation tuff in western part of Sragen Regency, Central Java, a region of economic importance and agricultural productivity, has been subject to limited geochemical, weathering, and mineralogical research, along with its residual soil. Understanding these characteristics is vital for safe construction and land use, given their influence on soil properties like cation exchange capacity, plasticity, water retention, and nutrient dynamics, which also indicate agricultural potential and geotechnical challenges. This study aims to fill this knowledge gap by comprehensively analyzing the geochemistry, weathering, and mineralogy of the Notopuro Tuff and its residual soils. Advanced techniques such as SEM, thin section petrography, and XRD will be employed. The tuff originates from a basaltic andesite magma with low-K, calcic, and magnesian affinity, exhibiting metaluminous alumina saturation. Its composition is primarily lithic fragments (50%) and volcanic glass (39%). Observed weathering involves Al₂O₃ and Fe₂O₃ enrichment, with the latter being more pronounced. SiO₂ stability suggests kaolinitization, not lateritization or bauxitization. Weathered tuff crystal minerals include microcline and quartz, with notable cristobalite and magnetite, and generally low crystallinity.