Paleontology, Sedimentology, and Isotopic Geochemistry of the Middle Proterozoic Bangemall Group, Western Australia

在过去的一个世纪里，大多数古生物学研究都集中在过去5.5亿年沉积的沉积岩上。然而，现在很清楚的是，这些引人注目的动植物记录只记录了地球生命史的最近15%。早期（动物出现之前）的生物记录写在微生物的化石中，也写在沉积岩中微生物活动的化学痕迹中。晚元古代（9 - 5.5亿年）的岩石包含了丰富的化石记录，包括各种浮游藻类和海藻，以及多种细菌。化石表明这是一个快速进化变化的时期。化学和地质资料进一步表明，晚元古代地球以气候、构造、大气化学和重要生物元素循环的重大变化为特征。相比之下，早元古代（2500-18亿年）的岩石反映了一个非常不同的世界——在这个世界里，只有细菌生物群在不受晚元古代气候和生物地球化学变化影响的环境中茁壮成长。要清楚地认识早元古代地球向晚元古代行星过渡的关键，必须在于中元古代（18 - 9亿年）沉积的岩石。将对西澳大利亚邦格马尔群（Bangemall Group）的14 -13亿年进行仔细的实地和实验室研究，这组岩石特别适合获得这一时期生物和环境变化的关键信息。将对这些岩石的厚度、组成和特征进行实地测量；这样就可以确定岩石的年龄和环境关系。在这个基质中收集的样品将被检查它们的微化石含量，岩石结构和蚀变历史，以及地球化学（特别是某些岩石中含有的碳和锶同位素的比率）。结果将是一个多学科的数据集，将提供对中元古代生物学和环境的重要见解。这些数据对于了解生命的早期进化以及生物和地球表面环境如何随着时间的推移相互影响以产生现代世界的努力非常重要。虽然这一研究是基础性的，但在元古界的油气勘探中具有重要的应用价值。化石和地球化学标志分布的记录将提高我们对比元古代岩石的能力，这是地质找矿的重要第一步。更好地了解地球的环境历史，还将有助于限制元古代沉积岩中丰富的层控矿床的勘探模式。

For the past century, most paleontological research has concentrated on sedimentary rocks deposited over the past 550 million years. It is now clear, however, that this conspicuous record of animals and plants documents only the latest 15% of the history of life on Earth. The earlier (pre-animal) biological record is written in the fossils of microorganisms, as well as in the chemical traces of microbial activity contained in sedimentary rocks. Rocks of Late Proterozoic age (900-550 million years) contain a rich fossil record that includes diverse planktonic algae and seaweeds, as well as bacteria of many kinds. The fossils indicate that this was a period of rapid evolutionary change. Chemical and geological data further suggest that the Late Proterozoic Earth was characterized by major changes in climate, tectonics, atmospheric chemistry, and the cycling of biologically important elements. In contrast, rocks of Early Proterozoic age (2500-1800 million years) reflect a very different world -- one in which an exclusively bacterial biota thrived in environments unaffected by the kinds of climatic and biogeochemical variability seen in the Late Proterozoic era. The key to understanding the transition from the Early Proterozoic Earth to the Late Proterozoic planet clearly must lie in rocks deposited during Middle Proterozoic times (1800- 900 million years). Careful field and laboratory studies will be conducted of the 1400-1300 million year of Bangemall Group, Western Australia -- a suite of rocks especially well suited to yield critical information on biological and environmental change during this period. Field measurements of the thickness, composition, and characteristic features of these rocks will be made; this will permit determination of the age and environmental relationships of the rocks. Samples collected within this matrix will be examined for their microfossil content, rock fabric and alteration history, and geochemistry (especially the ratios of the isotopes of carbon and strontium contained in certain of these rocks). The result will be a multidisciplinary data set that will provide critical insights into Middle Proterozoic biology and environments. Such data are of great importance in efforts to understand life's early evolution and how biology and Earth surface environments have influenced each other through time to produce the modern world. Although this research is basic in nature, it has important applications to mineral and petroleum exploration in Proterozoic rocks. Documentation of fossil and geochemical marker distributions will improve our ability to correlate Proterozoic rocks, the important first step in geological prospecting. A better understanding of Earth's environmental history will additionally serve to constrain patterns of exploration for the rich deposits of stratabound ores locked in Proterozoic sedimentary rocks.