Glacial ice from the last major advance covered the state of Connecticut and reached its glacial maximum on Long Island ∼21,000 years ago. As glacial ice melted and retreated northward, meltwater streams deposited sediments, like gravel, sand, silt and clay, in low-lying areas. Many periglacial lakes formed in central Connecticut as meltwater accumulated into valleys that were dammed by ice or glacial sediments. The Cromwell delta was deposited into glacial Lake Middletown. Previous studies have identified seven types of morphosequences, which are sedimentary facies that were deposited contemporaneously. The Cromwell delta is an ice-marginal deltaic morphosequence, with proximal deposits laid atop stagnant glacial ice and distal deposits built up as free fronts in open waters of glacial Lake Middletown. Proximal deposits experienced collapse as stagnant ice blocks melted. Thus, each ice-marginal deltaic morphosequence within the Cromwell delta includes two sections bounded by an east-west-trending topographic high delineating a previous ice-margin position: north of this boundary are collapsed deltaic deposits dipping northward; south are non-collapsed deltaic deposits dipping southward. Ground penetrating radar was used at River Highlands State Park to map sections of the Cromwell delta. The purpose of the study is threefold: (1) to demonstrate the capabilities of ground penetrating radar for identifying deltaic structures and locating previous ice-margin positions; (2) to provide insight into the collapsed delta formation by examining the areal extent and geometry of collapsed structures; (3) to show how ground penetrating radar can be used in an exploratory manner, with limited access to direct subsurface data, by combining ground penetrating radar with shallow auger samples and results from previous studies in areas near River Highlands State Park, the Cromwell delta and other contemporaneous deltas. Results show that ground penetrating radar can be used to map deltaic morphosequences and ice-marginal positions to provide a more detailed understanding of the Cromwell delta history at River Highlands State Park.

中文翻译：

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康涅狄格州中部用探地雷达绘制的塌陷和非塌陷冰缘冰川三角洲形态序列结构

上一次重大进展的冰川冰覆盖了康涅狄格州，并在大约 21,000 年前在长岛达到了冰期最大值。随着冰川融化并向北退缩，融水流在低洼地区沉积了砾石、沙子、淤泥和粘土等沉积物。许多冰缘湖在康涅狄格州中部形成，因为融水积聚到被冰或冰川沉积物堵塞的山谷中。克伦威尔三角洲沉积在米德尔敦冰川湖中。以前的研究已经确定了七种类型的形态序列，它们是同时沉积的沉积相。克伦威尔三角洲是一个冰边缘三角洲地貌层序，近端沉积物位于停滞的冰川冰之上，远端沉积物在米德尔敦冰川湖的开阔水域形成自由锋。随着停滞的冰块融化，近端的沉积物经历了坍塌。因此，克伦威尔三角洲内的每个冰缘三角洲形态序列都包括两个以东西向地形高地为界的部分，该地势高点描绘了先前的冰缘位置：该边界以北是向北倾斜的坍塌三角洲沉积物；南部是未坍塌的三角洲沉积物向南倾斜。River Highlands 州立公园使用探地雷达绘制克伦威尔三角洲的部分地图。这项研究的目的有三个：（1）展示探地雷达识别三角洲结构和定位先前冰缘位置的能力；(2) 通过检查倒塌结构的面积范围和几何形状，深入了解倒塌三角洲的形成；(3) 通过将探地雷达与浅层螺旋钻样品和先前在克伦威尔三角洲河高地州立公园附近地区的研究结果相结合，展示探地雷达如何以探索性方式使用，但对直接地下数据的访问有限和其他同时期的三角洲。结果表明，探地雷达可用于绘制三角洲形态序列和冰缘位置，以更详细地了解高地河州立公园的克伦威尔三角洲历史。