Collaborative research: Pleistocene Hydrogeology of the Atlantic Continental Shelf, New England

合作研究：新英格兰大西洋大陆架更新世水文地质学

• 批准号: 0337182
• 负责人: Denis Cohen-corticchiato
• 金额: $ 9.18万
• 依托单位: Iowa State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-02-01 至 2007-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0337182&HistoricalAwards=false
• 关键词: Collaborative; research; Pleistocene; Hydrogeology; Atlantic

0337182CohenIn many coastal settings around the world the distribution of freshwater within continental shelf sediments is not in equilibrium with modern sea level conditions. One of the most extreme examples of this can be found in New England where groundwater within a shallow Miocene sand about 150 km offshore Long Island, New York is remarkably fresh ( ~ 3000 mg/l salinity). Closer to the mainland, a 512m borehole on Nantucket Island, Massachusetts, contains freshwater ( 2000 mg/l salinity) in all permeable units. Thick confining units within this well have a parabolic salinity profile consistent with ongoing vertical diffusion. Analytical calculations suggest that diffusion began within the confining units as recently as 21ka. Heads within the Cretaceous section beneath Nantucket Island are overpressured by about 4 m above the local water table. We propose to use mathematical modeling and environmental isotope analysis to determine whether flushing of coastal plain sediments offshore New England was caused by: (1) meteoric recharge during Pleistocene sea-level low-stands; (2) sub- ice-sheet recharge during the last glacial maximum; (3) recharge from proglacial lakes; (4) clay dehydration reactions; (5) vertical infiltration of freshwater associated with local flow cells that may have developed on the continental shelf during sea level low stands. A second goal of this research is to determine whether the observed excess heads on Nantucket Island can be explained by solely by Pleistocene sediment loading or whether more exotic mechanisms such as clay dewatering reactions must be invoked. We will construct a three-dimensional, variable-density groundwater flow, heat, and solute mass transport model for the Atlantic continental shelf between Maine and New Jersey. The code will be run on the Indiana University SP Supercomputer. Direct simulation of isotope transport and groundwater residence times will be compared to environmental isotopic data (C-13, C-14, O-18, H-2) collected from wells tapping confined aquifers on the continental shelf. In order to constrain the isotopic composition of pro-glacial lake recharge, we will drill one well to extract pore fluids from lacustrine sediments 230 feet below land surface on Nantucket Island. Pleistocene ice sheet, climatic, and sea-level reconstructions will be used to constrain temporal variations in hydrologic, chemical, and isotopic boundary and initial conditions. Flexural adjustments of land surface topography during Wisconsin glaciations will be made to account for the effects of ice sheet loading on relative sea level.

0337182 COHENIN世界各地许多沿海环境在大陆架子沉积物中的分布在现代海平面状况不足。最极端的例子之一可以在新英格兰找到，在新英格兰，纽约近海长岛约150公里的地下水中的地下水非常新鲜（〜3000 mg/l盐度）。靠近大陆，马萨诸塞州南特基特岛（Nantucket Island）的512亿个钻孔，所有可渗透单元中均包含淡水（2000 mg/l盐度）。该井中厚的限制单元具有与持续的垂直扩散一致的抛物线盐度剖面。分析计算表明，最近的扩散始于21KA。宁片岛下白垩统区域内的头部被当地地下水位上方约4 m所压制。 我们建议使用数学建模和环境同位素分析来确定新英格兰沿海沿海沉积物的冲洗是否是由以下方式引起的：（1）在更新世海平面的低台上的陨石充电； （2）在最后一次冰川最大值期间的冰盖补给； （3）从冰期湖中充电； （4）粘土脱水反应； （5）与局部流动细胞相关的垂直浸润，这些淡水与局部流动细胞相关，这些流动细胞可能在海平面低的林木架上可能在大陆架子上发展。这项研究的第二个目标是确定仅通过更新世的沉积物加载，是否可以通过使用更大的外来机制（例如粘土脱水反应）来确定nantucket岛上观察到的过量头部。我们将在缅因州和新泽西之间建造一个三维，可变密度的地下水流量，热量和溶质质量传输模型。该代码将在印第安纳大学SP超级计算机上运行。将同位素传输和地下水停留时间的直接模拟与环境同位素数据（C-13，C-14，O-18，H-2）进行比较，这些数据是从大陆架上的井中挖掘的密闭含水层收集的。为了限制亲冰湖充电的同位素组成，我们将钻一个井以从nantucket岛陆地表面以下230英尺的湖泊沉积物中提取孔隙液。更新世冰盖，气候和海平面重建将用于限制水文，化学和同位素边界和初始条件的时间变化。 威斯康星州冰川期间土地表面形貌的弯曲调整将考虑冰盖装载对相对海平面的影响。