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

9806235渔业尽管进行了广泛的研究，但关于中白垩纪温室地球表海中有机碳积累原因的理论仍然存在争议。开发一个综合模型需要了解水团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纬向温度梯度减少，因此与今天有很大不同。温室时代表层海环流有两个基本的潜在驱动机制：1)由风向和风力主导的环流（如Erickson和Slingerland, 1990； Glancy等，1993）；2)当水在经向海道中移动时，由盐度和温度变化共同引起的密度对比主导的环流（Hay, 1988,1989; Hay et al., 1993）。尽管最近在西部内海密度和风力驱动环流的数值模拟方面取得了重大进展（Jewel， 1993年和Slingerland等人，1996年），但文献中现有的地质数据不足以严格检验这些模型。在可能的情况下，从特定物种的浮游生物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剖面（Fisher和Arthur， 1994年）。不幸的是，在许多西部内陆地层中，有孔虫经历了部分成岩作用，地球化学分析没有意义。因此，需要一个不同的相对密度代理。研究者提出，对西部内陆盆地选定地点浮游有孔虫孔隙度的重点分析将为解决海水相对密度的空间差异提供证据，这是了解海道环流本质所必需的。通过扫描电镜照片测量的浮游有孔虫孔隙度将被用作密度代理。BÚ（1968）、Frerichs et al.（1972）和BÚ et al.（1973）得出结论，现代有孔虫的孔隙度测试可以作为水温的指标（他们将其解释为密度指标）。Frerichs和Ely（1978）将这一假设应用于美国西部内陆白垩纪有孔虫样本。正如该假说所预测的那样，他们发现现代有孔虫的孔隙度测试可以作为水温的指标（他们将其解释为密度指标）。Frerichs和Ely（1978）将这一假设应用于美国西部内陆白垩纪有孔虫样本。正如假设所预测的那样，他们发现测试孔隙度向低纬度方向增加。研究者的研究计划补助金支持了Frerichs和Ely（1978）的结论，显示了向温暖的南纬地区增加孔隙度的趋势。WIS一些沿海地区附近的淡水也可能对孔隙度产生额外影响。将绘制相对水密度（孔隙度）的地理分布。海水密度的差异反映在海面的地形上；较轻的水形成小山，较稠密的水形成海面上较低的区域。海洋表面的地形差异导致水往下坡流动。海道地形将被用来重建密度驱动环流。调查人员将对已经收集到的材料进行抽样，并收集更多的地点。通过关注明确的地层间隔，并对盆地的广泛纬度样带进行采样，可以从孔隙度数据中合理估计相对水质量密度和海洋动力学。该项目的主要目标是：1)确定水体的相对密度（通过检查浮游有孔虫孔隙度）；2)确定从Boreal（加拿大）到Tethyan（德克萨斯州）源区的水质量密度的纬度变化（通过检查沿盆地N-S样带的孔隙度变化），并绘制通过海道的密度梯度图；3)确定确定的和地质上有重要意义的时期（代表大约1米的地层剖面）的水质量密度的时间稳定性和动态。（在西内海格林霍恩海旋回期间跨越了一个离散的海侵期）

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)