Clay Mineralogical Study of the Tertiary Malubog Formation, Cebu Province, Philippines

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The Early Miocene Malubog Formation (MbF) is one of the most widespread Tertiary formations in Central Cebu, Philippines. The formation consists of mudstone, shale and occasional beds of conglomerate, limestone and coal. It exhibits poor bedding and shows rapid lithologic changes vertically and horizontally. The formation is subdivided into several members which are all essentially coal measures and limestones. Mineralogical study of the Malubog Formation focused on the gently dipping strata of the argillaceous-arenaceous sedimentary rocks with generally minimal coal seam interbeds. Analytical testworks, involving x-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX), performed on the <2 μm size fraction indicate that multi-phase phyllosilicates of smectite, kaolinite, illite, mica, chlorite and mixed-layer varieties constitute essentially the argillaceous- arenaceous sedimentary rocks. These clays blend into several mineral assemblages that are almost all smectite-dominated. Most combinations include three or four clay species with varying peculiarities. Accessory non-phyllosilicates minerals are finely crystalline silica polymorphs (quartz, cristobalite, tridymite), feldspar, calcite, zeolite and jarosite (some alunite). Although the mineralogical components in many assemblages may appear the same, they reflect quite differences in characteristics and diversity of the sedimentary horizons. Most of these clays and mineral assemblages seem to convey diagenetic style of sedimentary petrogenesis, few relate to pedogenesis, and some exhibit efffects of hydrothermal alteration. The regime of diagenetic alterations infers to have progressed in alkaline marine environment, stimulated by low to moderate thermodynamic conditions at shallow to moderate burial depth. In the pedogenetic environment, chemical weathering suggests moderate conversion condition without reaching monosiallitization. Clays and mineral assemblages in hydrothermally altered ground reveal acid-sulfate to intermediate types.
鹿児島大学の論文
2003-12-30

Clay Mineralogical Study of the Tertiary Malubog Formation, Cebu Province, Philippines

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