RPG: Millennial-Scale Paleoclimatic Cycles Expressed in Paleozoic Basinal Marine Sequences

本研究旨在研究四个不同的古生代盆地海相层序中韵律性互层灰岩-泥灰岩耦合的成因和周期性。在每个层序中，灰岩-泥灰岩对的特征是均匀层状、层状石灰岩和泥灰岩的分米级交替；泥灰岩层中保存良好的钙质化石表明夹层是原生沉积(而不是成岩成因)。将对石灰岩-泥灰岩夹层进行光谱分析，以确定层理对是否有规律的旋回性，旋回的持续时间将根据为每个单独层序计算的沉积速率范围来确定。提交了一份规划拨款，以研究拟议层序之一-犹他州西部中寒武纪(惠勒和马尔朱姆组)中有节奏地层状石灰岩-泥灰岩对的沉积学起源和周期性。试点项目的重点是开发准确和省时的采样技术，以生成互层石灰岩和泥灰岩相的时间序列。在以前的研究中，由盐酸不溶性残留物的变化产生的时间序列被证明是一种准确的方法，但它非常耗费实验室时间。因此，另外三种耗时较少的方法将在中寒武世对联上进行测试，以确定哪种技术(S)最能反映沉积物的韵律性质。具体的规划赠款活动将包括描述和解释盆地相的沉积学和地层学特征，评估石灰岩-泥灰岩组合的横向连续性，对暴露最好的剖面取样，以了解盐酸不溶残留物、磁性和岩层厚度变化的变化。将不同时间序列的光谱分析结果进行比较，以确定哪种时间序列采样技术(S)适合于互层灰岩-泥灰岩相。千年尺度古气候波动的原因尚不清楚，但已将其归因于太阳活动的变化或气候对进动(约20000年)轨道强迫的非线性响应。如果能够表征这种持续振荡的周期，它们就有可能发展高分辨率的年代地层学，其分辨率高于米兰科维奇周期，可用于校准绝对基准面之间的时间长度、沉积速率、生物演化速率以及发生地磁逆转的时间间隔。

The proposed research is to investigate the origin and periodicity of rhythmically interbedded limestone-marl couplets in four separate Paleozoic basinal marine sequences. In each of the sequences, the limestone-marl couplets are characterized by decimeter-scale alternations of even-bedded, laminated limestone and marls; well-preserved calcareous fossils in marl layers indicates a primary depositional(versus diagenetic origin) to the interbeds. Spectral analysis of the limestone-marl interbeds will be conducted to determine whether there is a regularly cyclicity to the bedding couplets, and the duration of the cycles will be determined from a range of sedimentation rates calculated for each individual sequence. A planning grant is submitted to study the sedimentologic origin and periodicity pf rhythmically bedded limestone-marl couplets in one of the proposed sequences; the Middle Cambrian of western Utah (Wheeler and Marjum Formations). The emphasis of the pilot project is to develop accurate and time-efficient sampling techniques for generating time series in interbedded limestone and marl facies. In previous studies, time series generated from variations in HCI-insoluble residues has proven to be an accurate method, however it is very laboratory-time intensive. Consequently, three other less-time consuming methods will be tested on the Middle Cambrian couplets determine which technique (s) best reflects the rhythmic nature of the deposits. Specific planning grant activities will include describing and interpreting the sedimentologic and stratigraphic characteristics of the basinal facies, evaluating the lateral continuity of limestone-marl couplets, sampling the best-exposed section for variations in HCI-insoluble residues, magnetic properties, and bed- thickness variations. Results from spectral analysis of the different time series will be compared to determine which time series sampling technique(s) are appropriate for interbedded limestone-marl facies. The cause of millennial-scale paleoclimatic fluctuations is not well understood, however they have been attributed to changes in solar activity or due to the nonlinear response of the climate to precessional (~20,000 yr) orbital forcing. If the periods of such persistent oscillations can be characterized, they offer the potential for developing high-resolution chronostratigraphy, with a greater resolution than Milankovitch cycles, that can be used to calibrate the length of time between absolute datums, variations in sedimentation rates, biologic evolution rates, and the time intervals over which geomagnetic reversals occur.