全國中小學科展

翻開東北角那一頁---和美一帶漸新統貝類化石排列方式和古水流關係之探討

科展類別

臺灣國際科展

屆次

2004年

科別

地球與太空科學

學校名稱

臺北市立第一女子高級中學

指導老師

金若蘭、陳文山

作者

劉怡偉

關鍵字

貝類化石

摘要或動機

This study tries to reveal how the velocity of flow influents the orientations and scattering patterns of the two-valve shells (we use Pecten in this study) during depositing processes by comparing the laboratory studies with the field observations. We learn from the laboratory experiments that the shells deposit at random directions when they are too crowded and are oriented to a certain direction when they are more scattered. We also find out that the shell fossils whose dorsal sides towards downstream with upward concaves are most likely to move. On the contrary, the shells whose dorsal sides towards upstream with downward concave are the most reluctant to move Examinations of the outcrop of the bedding of Pecten fossils, which are located near Long Dong, the northeastern tip of Taiwan, show that a lot of the shells settled along a certain direction and most of their concaves are upward. However, some of the shells with obvious orientation have downward concaves, which implies the depositional environments were under high current velocity. And the numbers of the shells whose dorsal sides are oriented to Northern East are about equal to those whose dorsal sides are oriented to Southern West. This result coincides with the results of the laboratory study. However, the experimental results can apply to the field analysis under certain assumptions.本研究就影響貝殼排列的水速作試驗,尋找水流和貝殼排列的關係,並和地層中實際的貝類化石做比較,藉以回推古老沉積環境。結果發現大量貝殼集中的情況下,貝殼間彼此的影響力會大於單純的水流沖擊;當貝殼較分散時,可以看出貝殼的頭部皆會一致朝向水流的來向作排列。而最適合移動的型態是凹口向上且頭部不朝水流來向的貝殼,而最穩定的型態是頭部朝水流來向的凹口向下貝殼。觀察實際地層,貝類化石大致上也有方向性的排列且正反面貝殼都有,可以推得當時沉積的水流大,故有足夠的動能讓貝殼重新排列。但由於試驗環境定和自然環境有所差異,仍有限制存在。

翻開東北角那一頁---和美一帶漸新統貝類化石排列方式和古水流關係之探討

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