RUI: THE CHENGJIANG SCIENTIFIC DRILLING PROJECT AND AN INTEGRATED MODEL FOR UNDERSTANDING BURGESS SHALE-TYPE DEPOSITS

瑞：澄江科学钻探项目和理解布尔吉斯页岩型沉积的综合模型波莫纳学院地质系罗伯特·R·盖恩斯EAR-1046233 ABSTRACT寒武纪布尔吉斯页岩型(BST)沉积保存了软体生物，对我们理解后生动物的初始辐射和早期演化至关重要；然而，这些沉积与控制化石记录典型操作的约束条件有很大偏离。自1909年沃尔科特·S发现伯吉斯页岩以来，这个问题一直没有得到解释。本研究将高分辨率厘米到微米尺度的分析与现代地球化学方法相结合，以云南澄江矿床中国南部为例，对神秘的伯吉斯页岩型化石矿床的成因进行了综合模型检验。在这个项目中，将沿着近-远断面提取总共4个钻芯，用于微观分析导致余鞍山页岩澄江生物群异常石化的古环境和地质微生物过程。澄江在我们对动物生活史的理解中占有特殊的地位，它是九个主要寒武纪BST沉积物中最古老的，也是迄今描述的最多样化的寒武纪生物群。利用余鞍山页岩的动态和地理分布的地层，该项目将检验一个新的假设，即只有在满足一套特定的古环境标准时，才能在离散的地点保存特殊的化石。来自8个主要BST沉积的数据表明，BST间隔发生在冲刷远端边缘的特定物理沉积窗口，那里没有重新加工，但粘土大小的颗粒沉积是事件驱动的和快速的。在这种有利的物理环境中，假设底栖生物环境的化学作用是下一个控制因素，只有在缺氧的底栖生物条件下才会发生异常的石化。最终，早期埋藏环境和早期显生界海水的化学被认为决定了哪些微生物反应是有利的，以及每一种微生物反应的进展程度。特殊的保存被认为是显著抑制正常微生物过程的因素的组合所致；这一假设很容易用ä34S系统进行验证。这项工作将应用新开发的跨学科方法，在统一的背景下研究澄江矿床的古环境、保存和地质微生物学，并重建保存特殊化石的生态环境。因此，这项工作将在各种尺度上进行，包括地层尺度的地层学分析、以实验室为基础的微观地层学分析(毫米-厘米尺度)、扫描电子显微镜调查以及与微地层学框架相联系的广泛的地球化学分析。

RUI: THE CHENGJIANG SCIENTIFIC DRILLING PROJECT AND AN INTEGRATED MODEL FOR UNDERSTANDING BURGESS SHALE-TYPE DEPOSITSRobert R. Gaines, Geology Department, Pomona CollegeEAR-1046233ABSTRACTCambrian Burgess Shale-type (BST) deposits preserve soft-bodied organisms and are central to our understanding of the initial radiation and early evolution of the Metazoa; however, these deposits represent significant deviations from the constraints that govern the typical operation of the fossil record. This problem has remained unexplained since Walcott?s discovery of the Burgess Shale in 1909. By combining high resolution centimeter to micron-scale analyses with modern geochemical approaches, this study will test an integrative model for the origin of enigmatic Burgess Shale-type fossil deposits using the Chengjiang deposit of Yunnan Province, South China. In this project a total of 4 drill cores will be extracted along a proximal-distal transect for micro-scale analysis of the paleoenvironments and geomicrobiological processes that led to exceptional fossilization of the Chengjiang Biota of the Yu?anshan Shale. The Chengjiang occupies a special position in our understanding of the history of animal life as the oldest of nine principal Cambrian BST deposits and the most diverse Cambrian biota yet described. Using the dynamic and geographically widespread strata of the Yu?anshan Shale, this project will test a new hypothesis that conservation of exceptional fossils occurred at discrete loci only when a specific set of paleoenvironmental criteria was satisfied. Data from 8 of the principal BST deposits indicate that BST intervals occur in a specific physical depositional window at the distal margin of scour, where re-working was absent, yet deposition of clay-sized particles was event-driven and rapid. Within this favorable physical environment, it is hypothesized that the chemistry of the benthic environment exerted the next control, with exceptional fossilization occurring only under anoxic benthic conditions. Ultimately, the chemistry of the early burial environment and of early Phanerozoic seawater are proposed to have determined what microbial reactions were favored and the extent to which each could progress. Exceptional preservation is suggested to have resulted from a combination of factors that significantly inhibited normal microbial processes; a hypothesis readily tested using the ä34S system. This work will apply newly-developed, interdisciplinary methods to examine the paleoenvironments, preservation and geomicrobiology of the Chengjiang deposit in a unified context, and to reconstruct the ecological environments in which exceptional fossils were conserved. Accordingly, this work will be conducted at a variety of scales, including formation-scale stratigraphic analyses, lab-based microstratigraphic analyses (mm-cm scale), SEM investigations, and extensive geochemical analyses tied into a microstratigraphic framework.