| 摘要: | 台灣的新生代地層可依不同地體構造時期區分為同張裂期、後張裂(被動大陸邊緣)期以及前陸盆地期層序，並以張裂不整合、分離不整合、前陸基底不整合三個部整合面區分(Lin et al., 2003)。後分離時期之地層以北港基盤高區為界，分為南、北兩套地層命名，北部的地層向南一路延伸至苗栗一帶，但至中、南投地區，卻又以另外一套地層名稱命名。黃等人 (2012, 2013)指出，在南投中寮鄉之地層粗坑層中發現分離不整合，不整合上下之地層應給予不同名稱，故粗坑層之名稱應不再使用。依照火成岩鈾鉛定年資料及不整合之上的生物地層，不整合以上之地層應屬於和五指山層同時期之地層序列。
此研究利用層序地層，將南投縣中寮鄉之沉積序列對比至台灣海峽及地面之井測資料，以重建層序堆疊歷史。研究的地層名稱包含：平林凝灰岩、五指山層(上部)、木山層、大寮層、石門層(在此研究分作石底層及北寮層)以及樟湖坑頁岩(打鹿頁岩)，時間從晚始新世至早中新世，為台灣地體構造時期之同張裂及後分離時期。
綜合露頭岩相分析及整理Lin et al. (2003)井測資料解釋，我們整理出五種沉積環境，火山周圍淺海、潟湖河口灣、波浪主導、潮汐影響海岸，以及遠濱大陸棚等四種在露頭皆可以看到，而陸上河道系統則只有在井測資料可以見到。
層序對比結果顯示，同張裂至後分離時期的地層共有11套。11套層序在前期 (層序1至4)有東、西兩個沉積中心，沉積物來源從兩側匯來，但是之後的層序 (5至11)則可以看出沉積物由西側向東側漸漸變薄，沉積物應由中國大陸搬運而來。由露頭和井測之解釋資料，區域之沉積古環境得以建立，也可建立沉積環境於時間上的演化。由沉積環境的比較可以發現，中寮鄉之露頭，和北部地層隨時間的變化有高度的相關。
;The Cenozoic sequences of Taiwan had been studied by many geologists, and recent publish, which gave a new strata division and correlated some of the successions to northern ones, used biostratigraphy and U-Pb dating of pyroclastic deposits. The oldest cropped out stratum in central Taiwan is used to be called Tsukeng Formation, and is now been renamed as Pinglin Tuff and Wuchishan Formation (Huang et al., 2012, 2013). 11 well logs data had been used for helping strata correlation. 14 samples from filed investigate are depositional environments assistants.
The name of the scrutinized oldest stratum is Pinglin Tuff, and other strata in survey included Wuchishan Formation, Shihszeku Formation, Tanliaoti Shale, Shihmen Formation and Changhukeng Shale. Glauconites were found in Wuchishan Formation and Peliao Formation, especially Peliao Formation. The mineral is a wonderful environments indicator stands for warm, shallow water with low depositional rate. Calcite cements often found in transgressive sands.
Sequence stratigraphy and depositional facies analysis had been used for this study, which can built up a time related depositional model and the environmental description. The environmental interpretation result implies that the outcrops remain deposits of four environments, there are: shallow marine volcano apron, Lagoon-wave dominated estuary, Wave-dominated, tidal-influenced coasts and offshore continental shelf, and interpretation of well logs gets addition one is fluvial system. 11 sequences were divided out from outcrops and wells deposits, the sequences are well correlated, and give the perfect result of strata correlation: Tanliaoti Shale to Taliao Formation, Shihmen Formation is equivalence to Shihti and Peiliao Formation, and Changhukeng Shale to Talu Shale.
The northern three well log data were used to be belong to another river system. The field survey area is the closest spot to depositional basin among all check points. The east west profile shows that sequence accumulation at two depocenter in sequence 1 to 4, which deposits thickness doesn’t show regularity, but in the later deposit stages, sediments show stable thinning from source to sink.
The study concluded that: The field survey area shows high relativity to the northern depositional system, that’s makes the field area to be a perfect correlated successions. |
