A New Approach for Evaluating Controls on Depositional Sequence Architecture

近十年来，层序地层学的概念已被应用于碳酸盐岩相的研究。然而，在很大程度上，我们对控制碳酸盐沉积序列位置和几何形状的变量的理解是不够的，因为能够分离这些变量的研究很少。本研究的目的是通过使用量化的相对海平面历史、高分辨率的年代地层相关性和选择允许隔离不同变量的地点的独特组合，评估海平面波动、区域海平面波动、构造作用、基底古斜坡、背风与迎风位置、硅屑输入和自生控制等变量的影响。我们之所以选择上中新世，是因为地中海地区上中新世碳酸盐层序的特殊暴露。比较不同地区定量相对海平面曲线显示的相对海平面波动的形状和幅度，结合野外资料和辐射测年、生物地层学和磁地层学的高分辨率年龄控制，可以提供确定局部、区域和全球控制对沉积层序发育的影响所需的详细数据。为了达到总体目标，建议的项目分为四个阶段。第一阶段已经完成。它的目的是对相对海平面历史、年代地层学进行定量记录，并对一个地方的层序地层学进行详细的了解。它开发了一种量化相对海平面历史（钉定点）的新方法，该方法基于对海平面或略低于海平面的沉积相的识别，以及对古斜坡上海相岩石的地面暴露证据的追踪。它也产生了一个高分辨率的年代地层校准与放射性日期。该项目的一期工程的成功完成已经表明，基底古斜坡的重要性与普遍接受的层序地层学模型存在重大偏差，并表明系统域方法预测的体系结构不适用。本提案要求为第二和第三阶段提供经费。二期将在同一构造块的不同地点开发与一期相同的信息。这些信息包括地质填图、岩石学、钉点曲线构造、磁地层学、生物地层学和放射性测年。区域间沉积序列的时间相关性可以分析基底古坡度、背风与迎风位置、硅屑输入和自生控制等局部变量，而相对海平面变量由于位于同一构造块上，应保持相对恒定。第三阶段涉及与其他研究人员合作，这些研究人员正在研究地中海不同构造块上的区域，以在这些地点开发类似的定量相对海平面历史、年代地层学和层序地层学。这种比较将有助于分析构造对相对海平面历史和层序地层学的影响，这些单元经历了相同的整体地中海海平面历史。第四阶段是研究的最后阶段。它将为地中海以外的地点发展类似的定量相对海平面历史、年代静止学和层序地层学，以区分地中海当地海平面的影响和海平面上升的影响。本研究的目的是了解控制碳酸盐岩沉积层序位置和结构的变量。因此，该产品将定量了解沉积层序几何形状、位置和相分布是如何受到以下因素的控制：(1)古斜坡的局部变量、自生控制、硅屑输入和向风位置；(2)构造对可容纳空间和地中海海平面的区域控制变量；(3)全球海平面。一旦了解了这些变量的沉积学影响，就可以更好地了解地质记录，并且可以改进预测模型，以帮助石油和天然气生产。

Franseen 9527004 For the past decade, concepts of sequence stratigraphy have been applied to studies of carbonate facies. However, in large part, our understanding of the variable that control the location and geometry carbonate depositional sequences are inadequate because of the few studies that are able to isolate these variables. The objectives of this study are to evaluate the effect of variables such as eustatic sea level fluctuation, regional sea level fluctuation, tectonism, substrate paleoslope, leeward versus windward location, siliciclastic input and autogenic controls, by using a unique combination of quantified relative sea level histories, high resolution chronostratigraphic correlations, and selection of localities which allow isolation of different variables. We have selected the Upper Miocene because of exceptional exposures of Upper Miocene carbonate sequences from Mediterranean region. The comparison of shapes and magnitudes of relative sea level fluctuations shown on quantitative relative sea level curves from different areas, combined with field data and high resolution age control from radiometric dating, biostratigraphy and magnetostratigraphy, can provide the detailed data necessary to determine the effects of local, regional and global controls on depositional sequence development. To arrive at the overall goal the proposed project is divided into four phases. Phase I is complete. It was designed to develop a quantitative record of the relative sea level history, chronostratigraphy, and to develop a detailed understanding of the sequence stratigraphy for one locality. It has developed a new method for quantification of relative sea level history (pinning points) based on identification of facies deposited at or just below sea level and on tracing evidence of subaerial exposure on marine rocks down paleoslope. It has also produced a high resolution chronostratigraphy calibrated with radiometric dates. The successful completion of Phase I of this project h as already illustrated significant deviations from commonly accepted sequence stratigraphic models by showing the importance of substrate paleoslope and illustrating that the architecture predicted by the systems tract approach is not applicable. Funding is requested for Phase II and Phase III in this proposal. Phase II will develop the same information as in Phase I in separate localities on the same tectonic block. This information includes geologic mapping, petrography, construction of pinning point curve, magnetostratigraphy, biostratigraphy, and radiometric dating. Time correlation of depositional sequences between the areas will allow the analysis of local variables such as substrate paleoslope, leeward versus windward location, siliciclastic input and autogenic controls while the variable of relative sea level should be held relatively constant because of the location on the same tectonic block. Phase III involves working with other researchers who are studying areas on separate tectonic blocks of the Mediterranean to develop similar quantitative relative sea level histories, chronostratigraphy and sequence stratigraphy in those locations. This comparison will allow analyses of the tectonic effects on relative sea level history and sequence stratigraphy in unites that have experienced the same overall Mediterranean sea level history. Phase IV is the final phase of the study. It will develop similar quantitative relative sea level histories, chronostatigraphy and sequence stratigraphy for sites outside of the Mediterranean to separate local Mediterranean sea level effects from eustatic effects. The purpose of this research is to develop an understanding of the variables that control the location and architecture of carbonate depositional sequences. Thus, the product will be a quantitative understanding of how depositional sequence geometry, location, and facies distribution is controlled by: (1) local variables of paleoslope, autogenic controls, siliciclastic input, and seaw ard versus windward location; (2) regional variables of tectonic controls on accommodation space and Mediterranean sea level, and (3) global sea level. Once the sedimentologic effect of these variables are understood , a better general understanding of the geologic record may be gained, and predictive models may be refined to the point of aiding oil and gas production.