Accumulation of Meter-Scale Carbonate Parasequences

米级碳酸盐准层序的堆积

• 批准号: 9405551
• 负责人: Bruce Wilkinson
• 金额: $ 13.62万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-07-15 至 1998-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9405551&HistoricalAwards=false
• 关键词: Accumulation; Meter; Scale; Carbonate; Parasequences

9405551 Wilkinson The nature and genesis of shallow marine cyclic carbonate units has been a subject of alluring interest for over several decades, with origins variably attributed to the central importance of high-frequency sealevel change, to periodic but intrabasinal variation in subtidal carbonate production, and even to stochastic episodes of random carbonate deposition. Numerical simulations incorporating a wide variety of allocyclic, autocyclic, and aperiodic scenarios can all be tuned to yield reasonable scenarios of repeated upward-shoaling peritidal carbonate accumulation. Moreover, no single paradigm of intrabasinal versus extrabasinal or haphazard versus periodic accumulation has proven to be a superior predictor of the composition and distribution of cyclic limestone deposits in epicratonic settings. Recent analysis of stratigraphic data on cyclic peritidal carbonates over a wide geographic and geologic range indicates that measured thickness frequencies are strongly skewed and that the actual distribution of cycle thickness is perhaps exponential. We wish to explore the nature of thickness structures among peritidal lithofacies and lithofacies associations in order to evaluate this postulate, and believe that important progress in developing an understanding of cycle generation will be gained from careful investigation of facies arrangements and thicknesses. Funds are therefore requested to: 1) determine differences between minimum carbonate production rates and maximum carbonate accumulation rates in several subtidal coquinoid parasequences; 2) carry out detailed examination of several shallow-water carbonate sequences to quantitatively determine if statistically-important asymmetrically- stacked lithofacies associations are present, and 3) analyze measured and synthetic facies associations in order to determine if frequency distributions of cycle thicknesses delineate patterns anticipated from periodic or random deposition. In the first instance, comparison of data on carbonate generation versus accumulation will not only allow for assessment of early Phanerozoic stratigraphic completeness at a kiloyear scale of resolution, but will also provide the first tangible basis for evaluating the usefulness of Holocene rate data in ancient platform settings. In the second case, presence or absence of numerically significant facies associations will provide a quantitative assessment of the importance of upward-shoaling motifs in several classic examples of carbonate cyclicity. This will be one of the first extensive attempts to quantitatively discern and document the presence (or absence) of repetitive upward-shoaling facies associations among shallow marine carbonates, and plainly is (and should be) a requisite step in investigations of any supposedly cyclic sequence. In the third case, the nature of cycle thickness distributions bears directly on questions of depositional periodicity. Should data on natural cycles result in differentiation of some modal thickness class, such a distribution would largely be in agreement with presumed repetitive and periodic carbonate accumulation. Presence of exponential thickness distributions, on the other hand, is not as yet easily rationalized when assuming periodic accumulation, but is in agreement with anticipated trends if cycle formation reflects a random probability of deposition during uniform subsidence.

9405551威尔金森 几十年来，浅海循环碳酸盐岩单元的性质和成因一直是一个诱人的兴趣主题，其成因被认为是高频率海平面变化的核心重要性，潮下碳酸盐岩生产的周期性但盆内变化，甚至是随机的随机碳酸盐岩沉积。 将各种各样的allocyclic，autocyclic，和非周期性的情况下的数值模拟都可以调整，以产生合理的情况下，反复向上变浅的潮缘碳酸盐岩堆积。 此外，没有一个单一的范例，盆内与盆外或偶然与定期积累已被证明是一个上级预测的组成和分布的循环石灰岩矿床在epicratonic设置。 最近对广泛的地理和地质范围内的旋回潮缘碳酸盐岩地层数据的分析表明，测得的厚度频率是强烈偏斜的，旋回厚度的实际分布可能是指数分布。 我们希望探讨的厚度结构之间的围潮岩相和岩相组合的性质，以评估这一假设，并认为，重要的进展，在发展的理解周期生成将获得仔细调查的相安排和厚度。 因此，要求提供资金，以便：（1）确定几个潮下带coquinoid准层序的最低碳酸盐生产率和最高碳酸盐积累率之间的差异; 2）对几个浅水碳酸盐岩层序进行详细检查，以定量确定是否存在重要的非对称叠加岩相组合，以及3）分析测量的和合成的相关联，以便确定周期厚度的频率分布是否描绘了从周期性或随机沉积中预期的模式。 在第一种情况下，碳酸盐生成与积累的数据的比较，不仅允许在一个千年尺度的分辨率的早古生代地层完整性的评估，但也将提供第一个有形的基础，评估古平台设置的全新世速率数据的有用性。 在第二种情况下，存在或不存在的数值显着的相协会将提供一个定量评估的重要性，向上变浅图案在几个经典的例子碳酸盐岩旋回。 这将是定量识别和记录浅海碳酸盐岩中存在（或不存在）重复的向上变浅相关联的第一次广泛尝试之一，显然是（也应该是）调查任何假定的循环层序的必要步骤。 在第三种情况下，旋回厚度分布的性质直接关系到沉积的周期性问题。 如果自然循环数据导致某些模态厚度等级的差异，则这种分布将在很大程度上与假定的重复性和周期性碳酸盐堆积一致。 另一方面，指数厚度分布的存在，在假设周期性积累时，尚不容易合理化，但如果周期形成反映了均匀沉降期间沉积的随机概率，则与预期趋势一致。