Clay Mineralogy of the Middle Miocene Paghumayan Formation, Vallehermoso, Negros Oriental, Philippines

概要

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Clay minerals of stratified tuff and mudrocks of the Middle Miocene Paghumayan Formation in Vallehermoso, Negros Oriental, Philippines were examined. The results showed homogeneity of clay mineralogy in the sedimentary sequence with single-phase smectite as the dominant phyllosilicate present and with little association of kaolinite. Feldspar, zeolite, cristobalite, quartz and calcite are typical non-sheeted accessories that yield to some mineral assemblages along with smectite. The signature mineral assemblage is smectite-feldspar-zeolite-silica. The smectite is of the dioctahedral montmorillonite type, the feldspar is plagioclase and the zeolite is of the clinoptilolite or heulandite species. Between the silica polymorphs, cristobalite is more prevalent than quartz in most of the assemblages. One sample is detected to contain almost entirely of crystalline calcite with smectite which authenticate the presence of calcareous horizon or several horizons intercalated with the tuff and mud beds. The minerals and mineral assemblages formation is strongly implicit of halmyrolysis in continuum with early diagenesis in a closed system submarine environ and envisaged to have been induced favorably by calcic-silicic-alkalic, moderate pH, and low-temperature-pressure conditions of shallow burial sedimentation.
鹿児島大学の論文
2002-12-30