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10. Kaolinite Cement and Its Formation Mechanism in the Reservoir Sandstones from the Panyu Low-uplift, Pearl River Mouth Basin

Author

Li Wei, DU Guichao, Wang Qi, Lv Chengfu, Chen Guojun, Zhang Gongcheng, and Li Chao

Subjects
Provenance, Computer Networks and Communications, Computer science, Geochemistry, engineering.material, Feldspar, Diagenesis, chemistry.chemical_compound, chemistry, visual_art, Illite, engineering, Meteoric water, visual_art.visual_art_medium, Kaolinite, Clay minerals, Chlorite, Software
Abstract

Based on porosity and permeability measurements, mercury porosimetry measurements, thin section analyses, SEM observations, X-ray diffraction (XRD) analysis and granulometric analyses, diagenetic features of reservoir sandstones taken from the Panyu low-uplift of the Pear River Mouth Basin were examined. This study shows that kaolinite cement is one of the most important diagenetic features of reservoir sandstones. The kaolinite cements began to develop early in eo-diagenesis and continued to B stage of middle diagenesis and its precipitation was controlled by multiple factors. In early stage of eo-diagenesis, its formation was mainly controlled by infiltration of meteoric water and provenance. Abundant Al3+ and Si2+ were supplied during infiltration of meteoric water and provided advantageous conditions for precipitation of early kaolinite in eo-diagenesis. With the burial depth increasing, diagenetic temperature increased and smectite tended to be transformed into kaolinite. It’s one of the most important factors that affect the formation of kaolinite in eo-diagenesis. From late in B stage of eo-diagenesis to A stage of middle diagenesis, diagenetic environment has been changed from weak acid-weak alkaline environment to acid-strong acid environment. In acid conditions, feldspar grains were strongly dissolved and caused widely precipitation of kaolinite cements, with characteristics of co-exists of kaolinite and quartz overgrowth. In A to B stage of middle diagenesis, the reservoir sandstones of the studied area have a deeper burial depth and diagenetic environment of weak aicd-weak alkine. In this stage, kaolinite was gradually transformed into chlorite and illite cements. This study shows that the temperature that kaolinite begins to transformed into chlorite is approximately 120°C-140°C. Kaolinite illitization widely accurred in alkaline and weak alkaline conditions with high K+ irons in pore waters, especially when diagenetic temperature is over 120°C (burial depth over 3800m). In deeply buried sandstones, kaolinite chloritization and kaolinite illitization are main reasons that kaolinite the content of cements decrease and gradually dispeared.

Published
2012

14. Petrography and geochemistry of Oligocene to Lower Miocene sandstones in the Baiyun Sag, Pearl River Mouth Basin, South China Sea: Provenance, source area weathering, and tectonic setting.

Author

Ma, Ming, Chen, Guojun, Li, Chao, Zhang, Gongcheng, Lv, Chengfu, Xue, Lianhua, Shen, Huailei, Zhao, Zhao, and Tyrrell, Shane

Subjects
PETROLOGY, GEOCHEMISTRY, OLIGOCENE paleontology, CHEMICAL weathering
Abstract

There is a controversy regarding the source area and weathering intensity of Oligocene to Lower Miocene sediments in the Baiyun Sag of the Pearl River Mouth Basin. Detrital modes, geochemistry, heavy mineral data, and detrital zircon U–Pb ages were analysed to understand the provenance, source area weathering, and tectonic setting of Oligocene to Lower Miocene sandstones in the Baiyun Sag. Petrographic data reveal that the sandstones were derived from a recycled orogen. With increasing transport distance, sediment maturity increased correspondingly. The Oligocene to Lower Miocene sandstones in the Baiyun Sag have low compositional maturity and have experienced low to moderate weathering. The sediments of the Zhuhai Formation have experienced relatively strong weathering intensity compared with those of the Enping and lower Zhujiang formations. Due to low degree of illitization and differences in the geochemical compositions of the sediments, the continental island arc data from different boreholes in the Baiyun Sag are more irregularly distributed in the A‐CN‐K plot. The modal composition (e.g., quartz, feldspar, and lithic fragments) and geochemical indices (Al2O3/TiO2 ratio; Al2O3‐TiO2 diagram; discriminant F1‐F2 diagram; Eu/Eu*, La/Sc, La/Co, Th/Sc, and Th/Co ratios; Hf‐La/Th and La/Sc‐Co/Th diagrams; and rare earth element patterns) indicate that the sediments in the Baiyun Sag are mainly derived from felsic source rocks. Although the uplift around the Baiyun Sag includes multistage magmatism and basic rocks, it has little influence on the sediment in the depression, and no sediments were transported by the Han River to the Baiyun Sag. Geochemical data and detrital zircon U–Pb ages suggest that the Pearl River was formed in the Early Oligocene and became the main source for the sediments in this area. The river carried felsic material from the South China Coast forming a large delta on the northern slope of the Baiyun Sag. The ratios of Eu/Eu*, La/Sc, La/Co, Th/Sc and Th/Co, and heavy mineral data indicate that the sediments transported by the Pearl River to the Baiyun Sag were changed from the arc‐dominated coastal zone to the interior of the South China Block during the Late Oligocene to Early Miocene and even reached the south‐eastern margin of the Tibetan Plateau (West Yunnan Plateau). The La‐Th‐Sc and Th‐Sc‐Zr/10 diagrams suggest that the provenance of these sandstones is evolved continental island arc or an active continental margin setting. [ABSTRACT FROM AUTHOR]

Published
2019
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