台灣卵礫石層的地質背景

Geological Background of the Gravel Formations of Taiwan

鄧屬予(Louis S. Teng)

《地工技術》 55期 (1996/06) Pp. 5-24

https://doi.org/10.30140/SG.199606.0001

摘要

台灣的卵礫石層主要分布在中央山脈的四周，由於中央山脈山高坡陡，岩盤常在經歷輕微的風化後，就崩解成岩塊而隨著山崩下滑，並順著土石流、洪流和濁流搬向河川的下游，堆積在河谷、沖積扇、氾擺平原、海灘，乃至於深海中，形成各種型態的礫石。當礫石被後續的沈積層覆蓋，逐漸地深埋於地下後，就會被壓密固結成礫岩。在造山運動的影響下，地表的常會被抬升成河階和台地的蓋層，而深埋於地下的礫岩，也會被摺曲成傾斜的地層，出露在山脈中。卵礫石層的時空分佈主要是由造山運動來主宰。在新生代早期，台灣是中國大陸邊緣海的一角，沈積物主要來自福建地區。由於福建從中生代晚期以來，一直是個丘陵地，沈積物以砂泥為主，碟石很少，因此台灣新生代早期的地層以砂頁岩為主，礫岩只以細礫薄層出現。但到了上新世以後，蓬萊造山運動逐漸進入高峰期，中央山脈快速隆起，釋出了大量的岩礫，堆積在山脈邊緣的盆地裡，因而累積成厚層的上新統和第四系卵礫石層。

關鍵字

礫石 ； 礫岩 ； 沈積 ； 台灣

並列摘要

Gravel formations are mainly distributed in the areas surrounding the Central Range of Taiwan. Owing to the high altitude and steep slope, the rock strata of the Central Range often crumble to blocky debris after slight weathering and slide down slope with mass movements. The rock fragments are transported downstream by debris flows, floods and turbidity currents and deposited in the river valleys, alluvial fans, floodplains, beaches, and eventually deep seas. After deposition, gravels may be buried to depth, compacted and consolidated to become conglomerates. If subjected to orogenic influence, the gravel beds may be uplifted as terrace and tableland deposits, or folded as tilted conglomerates.The temporal-spatial distribution of gravel formation s in Taiwan is mainly controlled by orogeny. In early Tertiary time, Taiwan was part of the China continental margin which was covered by sediments derived from Fujian. Since the late Mesozoic time, Fujian has been a hilly terrain which produced mainly sands and muds, and few pebbles. Hence the early Cenozoic strata of Taiwan are dominated by sandstones and shales with only a few thin-bedded conglomerates. After the Pliocene, the Penglai orogeny gradually reached its climax and the Central Range uplifted rapidly. A huge amount of rock fragments were derived from the Central Range and deposited in the surrounding basins to form the thick piles of Pliocene-Quaternary gravel formations.

並列關鍵字

gravel ； conglomerate ； sedimentation ； Taiwan