Genetic Type and Sedimentary Geological Significance of Cretaceous Glauconite in Oriente Basin,Ecuador

Yang Xiaofa; Xie Yinfu; Zhang Zhiwei; Ma Zhongzhen; Guo Chunen; Zhou Yubing; Wang Dandan; Liu Yaming; Zhao Yongbin

doi:10.3799/dqkx.2016.501

Abstract：Glauconitic sandstones in Napo UT Member of Cretaceous developed widely in the Oriente Basin,Ecuador.Petro-graphic,mineralogical,geochemical,and spatial and temporal investigations of glauconite can reveal its composition,maturi-ty,formation and genetic types,which,together with geological constraints,can better the understanding of the significance of sedimentary geology.Using the microscopy,X-ray diffraction (XRD),electron probe microanalyzer (EPMA)and Qemscan, petrography,mineral composition and major elements were analyzed systematically.Glauconite in UT Member shows dark green and curved rosette-like nanostructure and has high K2 O content (8 wt%),indicating it evolved to highly evolved and formed at low sedimentation rate in marine environment.Chemical composition and spatial and temporal attributes of glauconite reveal its characteristics of intrasequential (parautochthonous)glaucony,and indicate as well that it has undergone transport of storm surges and/or tidal currents processes.All evidences,including upward increasement of glauconite content,maturity variation,and similarity of morphology and chemical composition between samples from the outcrop and within the basin,indi-cate characteristics of parautochthonous glaucony.Upward increasement of glauconite content also suggests that the parautoch-thonous glauconite formed in the outer shelf shifted landward,indicating the relative sea-level rise during the marine trans-gressive setting.Widespread distribution of contemporaneous/para-contemporaneous glauconites usually represents the epeiric sea environment with stable tectonic setting.