A gravity study of the triassic valley in southern Connecticut

美合衆國 Connecticut의 Triassic 紀盆地에 대하여 重力探査方法에 依한 地下地質構造 및 堆積過程을 규명하였다. 總測點數 約 800點에 대한 重力測定値을 Bouguer 方法에 依한 Bouguer 重力異常圖을 作成하였으며 七個重力斷面圖을 選定하여 地下地質構造에 대한 定量的 解析을 加하였다. 殘留重力異常値(Residual gravity anomaly)를 計算하기 위하여 (1) “Grid-residual” 방법과 (2) “Profile smoothing” 방법을 적용하였던바 本地域의 地質構造를 파악하기 위해서는 “Profile smoothing” 방법이 적합함이 증명되었다. 地質的 證據와 殘留重力 異常値의 定量的 解析으로부터 다음과 같은 結論을 얻을 수 있다. (1) Triassic 盆地의 最探深는 地質學的으로 推定된 것과는 달리 盆地의 中央部에 位置한다. (2) Triassic 盆地는 連續的 階斷式 斷層에 依하여 形成되었다. (3) 堆積岩層에 挾在되어있는 玄武岩層과 玄武岩質岩脈의 根源이라고 추정되는 高密度의 岩體가 Chesire 地域과 Gaillard 地域 地下에 賦存한다. (4) Triassic 盆地의 盤底는 地質的 推算과는 달리 盆地의 中央部가 東部境界斷層部(Eastern Border Fault)下部보다 약 7,000 feet 깊은 것으로 判斷된다. (5) 堆積岩層의 東頃은 本盆地에 堆積이 完了된 후 盆地의 西境部(Western Border)에 융기의 軸이 있었기 때문이다. (6) Triassic 盆地의 地殼厚(“Moho”까지의 깊이)는 약 14 mile이며 東部및西部高地帶(Eastern and Western Highlands)는 각각 20 mile 및 19 mile이다.

The structure and geologic history of the Triassic basin in southern Connecticut have been interpreted by using gravimetric data. A gravity survey of 800 gravity stations was made by the U.S Geological Survey in the southern Connecticut area. The resulting data were reduced by the Bouguer method and then plotted contoured along with the generalized geology. Residual gravity maps were prepared by different methods to obtain the most plausible agreement with the known geology of the area. Seven gravity profiles across the basin are presented to show the distribution of the Triassic deposits that could produce the measured anomalies. It is concluded that the basin was formed by successive step faulting in the late Triassic period and that the sediments accumulated progressively in this basin. The deepest portion of the basin is located in the middle of the present Triassic belt and reaches a depth of about 2 miles below the surface. The data also appear to indicate the possible source areas for the basalt which at present forms the lava flows, sills, and dikes exposed in the Cheshire and Gaillard regions. The information concerning the tectonic history of the Connecticut Triassic Valley aids considerably in establishing the geologic history of the Appalachians in late Triassic time.