COLLABORATIVE RESEARCH: Distinguishing Regional Tectonic, Global Eustatic, and Isotopic Events in Chesterian Rocks of East-Central Idaho and Southwestern Montana

近年来的地层学和同位素研究揭示了石炭纪冰川作用的复杂性，并强调需要进一步研究冈瓦纳冰川作用的时间和方式，以及它与海平面波动、大陆风化速率变化、古海洋学和气候条件的联系。一些同位素代用资料表明，中石炭纪（白垩纪）甚至可能是一个全球变暖和冰川期之间的冰川消退时期。我们假设，海平面的变化，大陆风化模式，海洋和古气候条件，将伴随着重大变化的冰盖动态与主阶段的冰川或潜在的incrementdeglaciation在密西西比晚期的开始应记录在地层学和同位素组成的Chelsean地层。我们进一步假设，上述两种情况中的每一种都将赋予Chelsean沉积物一套独特的地层和地球化学特征，这些特征可以用来对冈瓦纳冰川作用的假设演化路径进行定量约束。为了验证这些假设，我们建议进行一个综合的、高分辨率的旋回和层序地层学，对来自爱达荷州中东部和蒙大拿州西南部的白垩纪碳酸盐和硅质碎屑的同位素研究集中于在泛海拉萨的这一部分发展白垩纪期间环境变化的记录。为了最大限度地提高拟议的层序地层框架中年代地层对比的分辨率，将从研究区的近端和远端环境对Chelman宏化石和微体化石生物地层进行详细的区域重新评估。我们将对Chelan岩石进行等级层序地层学分析，以破译其沉积历史，并确定潮缘和潮下准层序的性质和分布，主要层序边界不整合面和局部和区域尺度的准层序边界。这将有助于评价准层序和表面与微妙的构造运动或记录海平面升降波动的关系。古生物学分析将提供重要的定性和定量限制的相对海平面上升和/或下降的数量记录在每个准层序或序列。我们建议在最近导出的石炭纪稳定同位素和放射性同位素曲线的基础上，（d13 C，d18 O和d34 S）和放射成因（87 Sr/86 Sr）同位素记录的贡献应该是独一无二的：（1）精炼现有同位素曲线的一部分，（2）定义耦合的d13 Ccarb和d13 Corg记录，（2）对Antler前陆盆地的O和C同位素垂直梯度重建潜力进行了测试。受约束的沉积，我们将能够评估相对速率和相位（即，铅滞后）的关系，地层和同位素代用记录，这方面已在以前的盆地内研究中受到损害。这种方法应允许长期构造事件从更高频率的海平面变化事件在这个盆地的分化，从而提供了相当深入的了解构造强迫的作用，对地层和同位素特征的Chelsean地层。反过来，这应该提供深入了解的作用，构造强迫控制盆地住宿，区域海洋条件和流通。此外，我们预计，这项研究应定量限制的频谱Chalanan期间发生的环境变化，在这一部分的泛地中海，包括全球古海洋和古气候扰动。最后，这项研究的结果应该提供洞察力的性质之间的任何机械的联系euclidean，物理和化学的海洋条件和古气候，从而最终有助于约束冈瓦纳冰川的启动时间和模式。

ABSTRACTRecent stratigraphic and isotopic studies reveal a more complex nature to Carboniferousglaciation than previously considered, and highlight a need for further study of the timing and mode of initiation of Gondwanan glaciation, and its mechanistic link to eustatic fluctuations, changes in continental weathering rates, and paleoceanographic and climatic conditions.Furthermore, some isotopic proxy data suggest that the mid-Carboniferous (Chesterian) may even have been a time of global warming and deglaciation between glacial episodes. We hypothesize that the changes in sea level, continental weathering patterns, and oceanographic and paleoclimatic conditions that would have accompanied the significant change in ice-sheet dynamics associated with either onset of main-stage glaciation or potentially intermittentdeglaciation during the Late Mississippian should be recorded in the stratigraphy and isotopic compositions of Chesterian strata. We further hypothesize that each of the two aforementioned scenarios would have imparted, on Chesterian deposits, a unique set of stratigraphic andgeochemical signatures that can be used to place quantitative constraints on the hypothesized evolutionary paths of Gondwanan glaciation.In order to test these hypotheses, we propose to carry out an integrated, high-resolution cycle- and sequence-stratigraphic, and isotopic study of Chesterian carbonates and siliciclastics from east-central Idaho and southwestern Montana focused on developing a record of environmental change during the Chesterian in this portion of Panthalassa. A detailed regional reassessment of the Chesterian macrofossil and microfossil biostratigraphy will be made from proximal and distal settings of the study area in order to maximize the resolution of chronostratigraphic correlation in the proposed sequence stratigraphic framework. We will carry out a hierarchical sequence stratigraphic analysis of the Chesterian rocks in order to decipher their depositional history, and to determine the nature and distribution of peritidal and subtidal parasequences, major sequence-bounding unconformities and parasequence boundaries at a local- and regional-scale. This will allow for evaluation of how the parasequences and surfaces relate to subtle tectonic movements or record eustatic fluctuations. Paleontologic analysis will provide important qualitative and quantitative constraints on the amount of relative sea level rise and/or fall recorded in each parasequence or sequence. We propose to build on the recently derived set of stable and radiogenic isotope curves for the Carboniferous by developing a set of integrated stable (d13C, d18O, and d34S) and radiogenic (87Sr/86Sr) isotope records for the Chesterian that should contribute uniquely by: (1) refining a portion of the existing isotope curves, (2) defining a coupled d13Ccarb and d13Corg record, and (2) testing the potential for reconstructing O and C isotope vertical gradients for the Antler foreland basin.By developing a series of high-resolution proxies from the same set of chronostratigraphically well-constrained deposits, we will be able to evaluate the relative rates and phase (i.e., lead-lag) relationships of the stratigraphic and isotopic proxy records, an aspect that has been variably compromised in previous intrabasinal studies. This approach should allow for differentiation of long-term tectonic events from higher frequency eustatic events in this basin, and thus provide considerable insight into the role of tectonic forcing on the stratigraphic and isotopic character of the Chesterian strata. In turn this should provide insight into the role of tectonic forcing in controlling basin accommodation, and regional oceanographic conditions and circulation. Moreover, we anticipate that this study should quantitatively constrain the spectrum of environmental changes that occurred during the Chesterian in this portion of Panthalassa, including global paleoceanographic and paleoclimatic perturbations. Lastly, the results of this study should provide insight into the nature of any mechanistic links between eustasy, physical and chemical oceanographic conditions and paleoclimate, thus ultimately contributing towards constraining the timing and mode of initiation of Gondwanan glaciation.