COLLABORATIVE RESEARCH: Organic Carbon Burial, Anoxia, and Ecological-Evolutionary Events in the Appalachian Basin During the Middle and Late Devonian (Givetian-Famennian)

9725803 Brett地球历史上海相富碳相（ORF）的广泛而幕式沉积已被公认为地质科学中的一个重要问题。水柱分层和随后的缺氧通常被认为是解释古代ORF沉积的有利假说，但近年来出现了其他假说，强调生物地球化学和沉积学耦合过程的重要性（例如，高生产力，地层冷凝），甚至表明水柱缺氧可能不像以前认为的那样普遍。然而，无论是作为有机碳埋藏的原因还是结果，缺氧都被认为是显生宙进化变化和灭绝的潜在驱动力。例如，它最近被认为是导致阿巴拉契亚盆地志留纪和泥盆纪底栖动物群中断的翻覆事件的可能原因。这些底栖动物被称为生态-进化亚单位，群落水平上的时间变化模式被称为协调停滞，已迅速成为进化古生态学研究的前沿，很少有研究将动物群变化分析与同期环境变化的独立评估结合起来，也没有研究关注氧化还原动力学的作用。有机质埋藏事件与缺氧之间的时空关系是什么？氧气消耗与群落、盆地或生态系统内的进化变化有何关系？本研究计划对阿巴拉契亚盆地中-晚泥盆世（埃菲尔世晚期至法门世早期）的ORF沉积起源假设进行重新评估，并利用收集到的数据研究动物群停滞和翻转的原因。从岩心样品中生成的地球化学分析的初步数据集（图3，表2）说明了为什么以前关于阿巴拉契亚盆地ORF起源的假设需要更新。该数据集为有关OFR沉积和协调停滞的工作假设的发展提供了基础，并为选择研究中使用的最佳古环境参数提供了试验。这个为期两年的项目将集中于纽约中西部的两个岩心，对它们进行沉积学和技术趋势分析，并取样进行地球化学分析。将收集三种对氧化还原动力学敏感的地球化学数据（碳同位素；C、Fe、S和P的丰度；以及微量金属的浓度），并将结果与阿巴拉契亚盆地内外已发表和未发表的大型动物趋势数据汇编进行比较。对氧化还原敏感代用物和动物群的统计协方差进行检验，将使氧气消耗控制动物群更替的基本假设得到证实或驳斥。还将考虑其他机制，例如与相对海平面变化有关的物种-区域效应。近年来，人们越来越认识到海洋环流和生物地球化学变化对过去全球变化的重要性。研究结果将为理解陆表前陆盆地演化过程中的有机碳聚集过程，以及岩石记录中碳循环、氧化还原历史与生态演化事件之间的关系提供重要依据。

9725803 Brett The widespread but episodic deposition of organic carbon-rich facies (ORF) in marine basins during Earth history has been recognized as an important problem in the geological sciences. Water column stratification and consequent anoxia has commonly been the favored hypothesis to account for ancient ORF deposition, but in recent years alternate hypotheses have emerged that highlight the importance of coupled biogeochemical and sedimentological processes (e.g., high productivity, stratigraphic condensation), and even suggest that water column anoxia may not have been as prevalent as once thought. Yet oxygen deficiency, whether as a cause or consequence of organic carbon burial, has been postulated as a potential driving force for evolutionary change and extinction during the Phanerozoic. For example, it was recently implicated as a possible cause of overturn events punctuating distinct Silurian and Devonian benthic faunas of the Appalachian basin. These benthic faunas are termed ecological-evolutionary subunits, the pattern of punctuational change at the community level is called coordinated stasis has rapidly become a forefront of research in evolutionary paleoecology, very few studies have integrated analyses of faunal changes with independent assessments of coeval environmental change, and none have focused on the role of redox dynamics. What are the spatial and temporal relationships between organic matter burial events and oxygen deficiency? How does oxygen depletion relate to evolutionary change within a community, a basin, or an ecosystem? This proposal outlines a plan to re-evaluate hypotheses for the origin of ORF deposits in the Middle to Late Devonian Appalachian basin (late Eifelian through early Famennian), and to use the data collected for this purpose to investigate the causes of faunal stasis and overturn. A preliminary data set of geochemical analyses from core samples has been generated (Fig.3, Table 2) that illustrates why previous hypotheses for the o rigin of ORF in the Appalachian basin need to be updated. This data set has provided a foundation for the development of working hypotheses relating OFR deposition and coordinated stasis, as well as a trial for selection of the best paleoenvironmental parameters to employ in the study. The two year project will focus on two cores from west central New York that will be analyzed for sedimentologic and ichnologic trends and sampled for geochemical analyses. Three types of geochemical data sensitive to redox dynamics will be collected (carbon isotopes; abundance of C, Fe, S, and P; and concentration of trace metals), and the results will be compared to a compilation of published and unpublished data on macrofaunal trends within and around the Appalachian basin. Tests for the statistical covariance of redox sensitive proxies and faunas will allow the fundamental hypothesis, that oxygen depletion controls faunal turnover, to be confirmed or refuted. Alternate mechanisms, such as species-area effects related to relative sea level changes, will also be considered. In recent years the importance of changes in ocean circulation and biogeochemistry to past global change have been increasingly recognized. The results of this study will provide a major contribution to the understanding of organic carbon accumulation processes in the evolution of epicontinental foreland basins, and of the relationship between carbon cycling, redox history, and ecological-evolutionary events in the rock record.