Detecting the b asement and the fault s under Ilan plain , northeastern Taiwan, using seismic reflection method
Speaker: An-Ho Huang
Abstract
Study on mineral contents in sandstone-mudstone succession is the essential method to better understand diagenesis process. In this talk, I first review the general procedure for identifications of clay minerals using X-ray diffraction method. Then a case study from Canada is presented. This case study shows the mineralogical consequences of subaerial weathering and early diagenesis in Cretaceous flucial sediments. The samples were collected from a RR-97-23 borehole in the central Elmsvale Basin, southeastern Canada, which penetrated through the full predominantly muddy Chaswood Formation. The succession of samples is from depth spanning 51 -192 m and 176 samples of representative lithologies were taken. Mineralogy is determined by X-ray diffraction, electron microscope analysis and scanning electron microscopy. The cored rocks can be divided into five facies associations: light gray mudstone, dark gray mudstone, silty mudstone and muddy sandstone, sorted sandstone and conglomerate, and paleosols. Light gray mudstone facies are mostly resulted from early diagenesis of the dark gray mudstone faces due to the input of meteoric water. The dark gray mudstone facies associations were accumulated in swamps. Sandstones are mostly quartz arenites, including minor amounts of minerals of feldspar, chlorite, biotite and muscovite. Principle minerals in mudstones are illite/muscovite, kaolinite, vermiculite and quartz. Illite and muscovite are detrital in origin. Variations in their abundance show that they were altered to kaolinite of the light gray mudstone facies association. Kaolinite is an early cement, it forms mainly as small grains around quartz mineral, or forms as well-crystallized, pore-filling booklets that were probably synchronous with the formation of the light gray mudstone. Later illite and barite cement indicate sources of abundant potassium and Barium from formation water. In paleosols, rutile, hematite, and goethite formed by oxidation of iron-titanium oxides. Findings of this study are applicable to other mid-latitude Cretaceous weathering and early diagenetic environments.
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