出磺坑背斜沉積與熱史研究;A depositional and thermal history study of Chuhuangkeng anticline

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Title:	出磺坑背斜沉積與熱史研究;A depositional and thermal history study of Chuhuangkeng anticline
Authors:	李沅銘;Li, Yuan-Ming
Contributors:	應用地質研究所
Keywords:	出磺坑背斜;沉積環境;岩象分析;X光繞射;鏡煤素反射率;核飛跡定年;熱歷史;Chuhuangkeng anticline;Depositional environment;Petrography;X-ray diffraction;Vitrinite reflectance;Fission track dating;thermal history
Date:	2017-11-22
Issue Date:	2018-01-16 11:15:08 (UTC+8)
Publisher:	國立中央大學
Abstract:	新生代中新世晚期開始的造山運動在臺灣西部形成前陸盆地，而區域性的快速抬升構造活動進一步形成出磺坑背斜。由於具有適當的構造封閉條件與有機質成熟度達到油窗，部分儲集層依然保有良好之油氣潛能。本研究目的為藉由評估此區域之沉積與熱史了解前陸盆地演化為背斜之過程，並且進一步提供油氣生成與移棲之沉積過程和年代資料。樣本採自出磺坑背斜出露地層與探採鑽井井下地層，實驗方法結合薄片岩象分析、X光繞射(XRD)、鏡煤素反射率與核飛跡定年分析。岩象分析與XRD結果指出出磺坑背斜地層礦物組成主要為石英(49-89%)，部分為岩屑(9-48%)及長石(0-4%)並且從上新世至更新世之間開始接收造山帶材料(變質岩岩屑)。結合岩象分析之沉積古氣候條件、XRD結果之黏土礦物組成以及伊萊石化學風化指數，結果指出此區域中新世時期高嶺石的增加，指示為濱面帶沉積並且古氣候環境條件相對濕潤，以化學風化作用為主，而整個地層層序經歷多次之沉積循環。伊萊石結晶度趨勢不明顯，無法看出造山材料的進入，僅能用來區分地層。井下樣本鏡煤素反射率(0.71-1.69%)與深度呈正相關，代表樣本最大受熱溫度主控因素為深埋作用，計算之古地溫梯度範圍為40°C/km ~ 24°C/km，推估出磺坑背斜構造抬升與剝蝕作用約2.5公里。鋯石核飛跡定年顆粒集合年代約為103.7 Ma，沉積物來源與中國東南方之早白堊紀末－晚白堊紀初時期之火山活動(120-80 Ma)相關，而結合鏡煤素反射率與磷灰石核飛跡分析資料，形成出磺坑背斜之構造抬昇與地表剝蝕作用從4 Ma開始直到現在，切穿出磺坑背斜中心處的後龍溪流域發育則早於卓蘭層之沉積年代。;Chuhuangkeng anticline which located at NW Taiwan had been a major oil and gas producing field in the past. Rapid uplift caused by local tectonic activity thus formed the Chuhuangkeng anticline in the foreland basin. Because of its favorable tectonic trapping and organic maturation had reached oil window, the reservoir rocks still possess good HC potential. The purpose of this study is to understand the evolution of foreland basin, it is crucial to evaluate the depositional and thermal history of sedimentary basin and further knowing the generation and migration of oil and gas. Sequences of outcrop and borehole samples were collected in this study.　Various analytical methods including XRD, petrographic thin section, vitrinite reflectance, and fission track analysis were combined to examine depositional and thermal history of the foreland basin which evolved to anticline. The results of petrographic and XRD analysis indicate that mineral composition in Chuhuangkeng anticline sequence is mostly quartz (49-89%), some lithic fragments (9-48%) and feldspar (0-4%). It had experienced series of cyclothems and started receiving orogenic sediments during Plio-Pleistocene. However, illite crystallinity has an unclear trend in Chuhuangkeng anticline sequence duo to the complicate evolution environment of foreland basin. Furthermore, organic maturation exhibits linear correlation with depth in boreholes (Ro=0.71~1.45%), which indicates that burial was the main controlling factor of thermal history. The calculated paleogeothermal gradient ranges from 40°C/km to 24°C/km, and the converted thickness of tectonic rift and exhumation is about 2.5 km. Moreover, pooled age of zircon fission track (PL-CL) is about 103.7 Ma, the origin of sediments is related to volcanic activity during lower Cretaceous to upper Cretaceous (120-80 Ma) in southeastern China. Integration of data from vitrinite reflectance and apatite fission track analysis indicates tectonic uplift process started from 4 Ma until now. Finally, the development of Houlong river should be earlier than the deposition of Cholan Formation, across central part of Chuhuangkeng anticline.
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