Page 39 - 雕鐫海之角

蕈狀岩 交錯層

Mushroom rock Cross-bedding

蕈狀岩又稱為蕈岩、擎柱石、蘑菇石。因為 This formation is characterized by their 砂岩中經常發現呈弧形的斜面，這些互相平
岩塊上下岩性的不同，上層含有較多的碳酸鈣， mushroom-like shape, with relatively thin stems topped 行的斜面與上下的層面呈斜交，這種紋理稱為交
by larger rocks. The cap of the mushroom rocks are
質地較硬，抵抗風化侵蝕作用較強，下層相對較 錯層。在野外推測古沉積環境的水流方向時，交
rich in Calcium Carbonate (CaCO3) and are therefore
弱，形成上粗下細，酷似蕈狀而得名。 錯層是最佳判斷水流方向的工具，其斜面傾斜方
relatively more resistant to weathering than the
stem. Through time, the stem becomes narrower and 向表示水流的流動方向。鼻頭角的交錯層在同一
narrower because of differential erosion. 個剖面上出現許多層面，顯示本區海水面是不穩

定的狀態。

Cross-bedding structures are formed in bedforms
such as ripples and dunes by the motion of sediment
due to the flowing fluid. Sediment grains bounce up the
windward/upstream side of a ripple, and then tumble
down the lee side.
Cross-bedding is an indicator of past climate and
drainage patterns. Sand dunes preserve the prevalent
wind directions, and the pattern of ripples indicate the
flow directions of the rivers.

地質圖書 Geopark at Northeast and Yilan Coast National Scenic Area