POWRE: Topographic Mapping of The Greenhorn Seaway Based on Planktonic Foraminiferal Porosity

POWRE：基于浮游有孔虫孔隙度的新手海道地形图

• 批准号: 9806235
• 负责人: Cynthia Fisher
• 金额: $ 7.59万
• 依托单位: West Chester University of Pennsylvania
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-09-15 至 2002-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9806235&HistoricalAwards=false
• 关键词: POWRE; Topographic; Mapping; Greenhorn; Seaway

9806235FisherDespite extensive research, theories of the cause of organic carbon accumulation in epeiric seas of the mid-Cretaceous greenhouse Earth remain controversial. Development of a comprehensive model requires understanding of water mass circulation and its effects on phytoplankton productivity and sedimentation. Latitudinal temperature gradients that today play a critical role in ocean circulation were reduced and therefore significantly different from today. There are two basic, underlying driving mechanisms for circulation in the epeiric seas of Greenhouse times: 1) circulation dominated by wind direction and strength (e.g. Erickson and Slingerland, 1990; Glancy et al., 1993); and 2) circulation dominated by density contrasts resulting from a combination of salinity and temperature alterations as water moves through the meridional seaways (Hay, 1988, 1989; Hay et al., 1993). Although recently there have been significant advances in efforts to numerically model density and wind-driven circulation in the Western Interior Sea (Jewel, 1993 and Slingerland et al., 1996), geologic data available in the literature is insufficient to critically test these models. Where available, stable Oxygen and Carbon isotopes taken from species specific planktonic and benthic foraminifers can be used to reconstruct the vertical relative density profile of the water column (Fisher and Arthur, 1994). Unfortunately, in many Western Interior strata the foraminifers have undergone partial diagenesis and geochemical analysis is not meaningful. Thus, a different relative density proxy is required. The investigator proposes that a focused analysis of the porosity of planktonic foraminifera from selected sites in the Western Interior Basin will provide evidence to resolve spatial differences in relative density of seawater needed to understand the nature of seaway circulation.Planktonic foraminiferal porosity, measured on SEM photographs, will be used as a density proxy. BÚ (1968), Frerichs et al. (1972), and BÚ et al. (1973) have concluded that test porosity in modern foraminifera can be used as an indicator of water temperature (which they interpreted as a density indicator). Frerichs and Ely (1978) applied this hypothesis to foraminifera sampled from the Cretaceous Western Interior of the United States. As predicted by the hypothesis, they found that test porosity in modern foraminifera can be used as an indicator of water temperature (which they interpreted as a density indicator). Frerichs and Ely (1978) applied this hypothesis to foraminifera sampled from the Cretaceous Western Interior of the United States. As predicted by the hypothesis, they found that test porosity increased toward lower latitudes. The investigator's Research Planning Grant supported the conclusions of Frerichs and Ely (1978), showing a trend of increasing porosity toward the warmer, southern latitudes. There may also be an additional influence on porosity from freshwater near some coastal areas of the WIS.The geographic distribution of relative water density (porosity) will be mapped. Water density differences are reflected in the topography of the sea surface; lighter water forms hills and more dense water forms low areas on the sea surface. Topographic differences in the ocean surface cause water to flow downhill. Seaway topography will be used to reconstruct the density driven circulation.The investigator will subsample already collected material and collect additional sites. By focusing on well-defined stratigraphic intervals, and sampling a broad latitudinal transect of the basin, reasonable estimates of relative water mass density and oceanographic dynamics for the Western Interior Sea can be interpreted from the porosity data. The main objectives of the project are to: 1) determine the relative density of water masses (by examining planktonic foraminifera porosity); 2) determine the latitudinal variations in water mass density from Boreal (Canada) to Tethyan (Texas) source areas (by examining variations in porosity from sites along a N-S transect of the basin), and map the density gradients through the seaway; 3) determine the temporal stability and dynamics of water mass density for well defined and geologically significant time periods (stratigraphic sections representing about 1m.y., spanning a discrete transgressive episode during the Greenhorn marine cycle of the Western Interior Sea)

9806235费希尔尽管进行了广泛的研究，但关于白垩纪中期温室地球的陆表海中有机碳积累原因的理论仍然存在争议。 发展一个全面的模式需要了解水体循环及其对浮游植物生产力和沉积的影响。 今天在海洋环流中起关键作用的垂直温度梯度减少了，因此与今天有很大不同。 温室效应时期陆表海环流有两种基本的、潜在的驱动机制：1）由风向和风力主导的环流（例如，Erickson和Slingerland，1990年; Glancy等人，（1993年）;和2）当水通过大西洋航道时，由盐度和温度变化引起的密度对比主导的环流（Hay，1988，1989; Hay等人，1993年）。 虽然最近在数值模拟西部内海的密度和风驱动环流方面取得了重大进展（Jewel，1993年和Slingerland等人，1996年），地质资料在文献中是不够的，以严格测试这些模型。 在可能的情况下，从特定物种的浮游有孔虫和底栖有孔虫中提取的稳定氧和碳同位素可用于重建水柱的垂直相对密度分布（Fisher和亚瑟，1994年）。 不幸的是，在许多西部内陆地层中，有孔虫已经经历了部分成岩作用，地球化学分析没有意义。 因此，需要不同的相对密度代理。 研究人员建议，从西部内陆盆地选定的地点的浮游有孔虫的孔隙度的集中分析将提供证据，以解决空间差异的海水相对密度需要了解海道circulation.Planktonic有孔虫的孔隙度，扫描电镜照片上测量的性质，将被用作密度代理。 Bennett（1968）、Frerichs等人（1972）和Bennett等人（1973）得出结论，现代有孔虫的测试孔隙度可用作水温的指标（他们将其解释为密度指标）。 Frerichs和伊利（1978年）将这一假说应用于美国白垩纪西部内陆的有孔虫样本。 正如假设所预测的那样，他们发现现代有孔虫的测试孔隙度可以用作水温的指标（他们将其解释为密度指标）。 Frerichs和伊利（1978年）将这一假说应用于美国白垩纪西部内陆的有孔虫样本。 正如该假设所预测的那样，他们发现测试孔隙度随着纬度的降低而增加。 研究者的研究计划资助支持了Frerichs和伊利（1978）的结论，表明孔隙度向更温暖的南半球纬度增加的趋势。 在WIS的一些沿海地区附近，淡水也可能对孔隙度产生额外的影响。将绘制相对水密度（孔隙度）的地理分布图。 水密度的差异反映在海面的地形上;较轻的水形成山丘，较密集的水形成海面上的低洼地区。 海洋表面的地形差异导致水向山下流动。 航道地形将被用来重建密度驱动的循环。调查人员将对已经收集的材料进行二次取样，并收集更多的地点。 通过重点明确的地层间隔，并采样广泛的纬度断面的盆地，相对水质量密度和海洋动力学的西部内海的合理估计可以解释从孔隙度数据。 该项目的主要目标是：1）确定水团的相对密度（通过检查浮游有孔虫孔隙度）; 2）确定从北方（加拿大）到特提斯（得克萨斯州）源区的水团密度的纬度变化（通过检查沿着盆地的南北向断面各地点的孔隙度变化），并绘制通过海道的密度梯度图; 3）确定在明确定义的和地质上重要的时间段内水质量密度的时间稳定性和动态（地层剖面代表约100万年，在西部内海的Greenhorn海洋旋回期间跨越一个离散的海侵事件）