| 摘要: | 過去對石油系統的研究顯示，碳酸鹽岩為重要的生油岩及儲集層，為探究海相生油岩中重要的前身-生物礁環境之沈積特性，本研究以台灣西北海域之碳酸鹽沈積環境—觀新藻礁為研究區域，區分沈積環境之空間差異，以針對現生淺層沈積物進行樣本分析，依沈積環境特徵、材料性質、來源及生油潛能探討有機質沈積機制。本研究選擇遠濱及近濱兩個相距100 m的採樣點，採集沈積深度相異樣本（表層-5 cm、5-15 cm、15-30 cm、30-40 cm），採樣同時測量現地水質資料，兩站點水質條件相近，近濱水質具有較低的溶氧與較高的鹽度，水質受潮水控制，而總有機碳分析（TOC）及Rock-Eval熱裂分析，顯示TOC低於0.5%；S1、S2分別小於0.5 mg HC/g rock 及2.5 mg HC/g rock，樣本皆為低成熟度、低有機質豐度；遠濱樣本有機質豐度隨深度增加且樣本間展現差異性較大，根據生物指標（Biomarker）分析結果，研究區域為富氧沈積環境，有機質保存條件較差，且少數樣本受陸源訊號主導，其來源可能為石油污染或高成熟度陸域有機質，及少數新鮮陸源有機質，X光繞射分析（XRD）中全岩分析及黏土礦物分析在兩個採樣點皆表現隨深度增加的石英訊號，以及相似的黏土礦物組成，以伊萊石為主要成分，根據伊萊石結晶度及風化指數結果顯示，黏土礦物來源區為受化學風化且母岩變質度低之環境，而受陸域訊號影響嚴重的樣本結晶度高於其餘樣本，來自變質度較高之黏土礦物母岩。本研究之樣本屬於早成岩環境，因此雖來自相同沈積環境，但樣本分析結果差異明顯，且碳酸鹽類礦物含量低，顯示藻礁填充沈積物主要構成礦物材料來源為外來，有機質以海相為主，有不穩定的外來有機質供給，雖有機質保存條件不佳，現地有機質仍隨沈積深度累積而增加。;Carbonate has significant contribution in world oil and gas production. In order to explore the process and mechanisms of organic matter during burial and preservation processes in present carbonates sedimentary setting, the Guanxin algal reef, which is an intertidal zone enriched with algal organic matters in NW Taiwan, is selected as the study area. In this study, there are two sampling sites: Off shore and near shore. Samples were collected from different depths（0-5 cm, 5-15 cm, 15-30 cm and 30-40 cm）for both sampling sites. Seawater quality were examined by using a water analyzer while collecting samples. The water qualities are controlled by sea tide, whereas two sampling sites present similar results. As for Rock-Eval Pyrolysis and total organic carbon（TOC）contents, all samples show TOC, S1 and S2 below 0.5%, 0.5 mg HC/g rock, and 2.5 mg HC/g rock, respectively. Hydrocarbon potential is low due to low organic carbon content and low maturity. Off shore samples exhibit higher organic carbon content and vertical variation, organic carbon is also enriched with depth. Biomarker analysis indicate an oxic environment of all samples, leading to the poor preservation of organic matter. Meanwhile, strong terrigenous inputs were found in some samples, which might be coming from oil pollution or other highly matured terrigenous material. X-Ray Diffraction（XRD）of clay mineral and whole rock show the domination of illite, which indicate marine signal and high intensity of silicate mineral. The sources are believed coming from low metamorphic clay mineral and further influenced by chemical weathering. The variation among all samples and low carbonates content can be attributed to the incomplete diagenesis. Finally, most of the minerals belong to allochthonous material, with inconsistent input and preservation of autochthonous organic carbon. |
