High-Resolution Seismic Reflection Surveys at the Manson Crater, Iowa

爱荷华州曼森陨石坑的高分辨率地震反射调查

• 批准号: 9211602
• 负责人: Ross Black
• 金额: --
• 依托单位: University of Kansas Main Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1992
• 资助国家: 美国
• 起止时间: 1992-07-15 至 1995-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9211602&HistoricalAwards=false
• 关键词: Resolution; Seismic; Reflection; Surveys; Manson

The major objective of this project is to delineate the shallow (upper 300 m) subsurface structural configuration within the Manson Impact Structure (MIS), Iowa, using state-of-the-art high resolution seismic imaging techniques. The MIS is a bollide impact feature 65.7 Ma in age, and is an important candidate for a source of the Cretaceous/Tertiary-boundary iridium anomaly. The feature may thus have played a central role in one of the best documented examples of mass extinction due to global change in geological history. A detailed knowledge of the structure, stratigraphy, and petrology of the MIS is needed as basic data for the construction of a model of the impact dynamics. However, the exact geometry within the structure is poorly known due to a 30-90 m thick Pleistocene till cover. Seismic reflection lines will provide a direct image of the structure and gross stratigraphy of the impact feature, and will constrain stratigraphic and petrological interpretations inferred from drilling transects, at least in the vicinity beneath the seismic lines. The major seismic line is along an east-west radius of the crater, from the central peak structure to the undisturbed stratigraphic section outside the crater. In addition to delineating the general structure of the central uplift, moat and ring graben, specific objectives include locating the presence (or absence) of faults, defining the depth and extent of the peak pit, and resolving the internal geometry of the impact breccia and melt zones at the edge of the central uplift. This study will provide fundamental geologic knowledge to contribute to an understanding of the global change in the biosphere that may have occurred, at least in part, as a direct result of the bollide impact at Manson. The seismic data will greatly enhance the interpretation of all data sets acquired as a result of the Manson drilling program, and will constrain the shallow subsurface structure and stratigraphy, allowing more accurate models of impact dynamics to be constructed. The seismic reflection data will help to identify targets for future drilling and for subsequent detailed surface geophysical studies such as electromagnetic, magnetic, and microgravity surveys by others.

该项目的主要目标是利用最先进的高分辨率地震成像技术，圈定爱荷华州曼森撞击构造(Manson Impact Structure)内的浅层(300米以上)地下构造形态。其年龄为65.7 Ma，是白垩纪/第三系界线Ir异常的重要候选者。因此，这一特征可能在地质史上由于全球变化而导致的大规模灭绝的最好记录之一中发挥了核心作用。需要详细了解管理信息系统的结构、地层学和岩石学，作为建立撞击动力学模型的基础数据。然而，由于更新世直到盖层厚度为30-90米，该结构内的确切几何形状鲜为人知。地震反射线将提供影响特征的结构和总体地层学的直接图像，并将约束从钻井横断面推断的地层学和岩石学解释，至少在地震线下的附近。主要地震线沿着火山口东西半径，从中央山峰结构到火山口外未受干扰的地层剖面。除了描绘中央隆起、护城河和环状地块的总体结构外，具体目标还包括定位断层的存在(或不存在)、确定峰坑的深度和范围，以及解决中央隆起边缘的冲击角砾岩和熔融带的内部几何问题。这项研究将提供基本的地质学知识，以帮助理解生物圈中可能发生的全球变化，这种变化至少部分是由于曼森的闪电撞击直接造成的。地震数据将极大地增强对曼森钻井计划所获得的所有数据集的解释，并将约束浅层地下结构和地层，从而能够建立更准确的撞击动力学模型。地震反射数据将有助于为未来的钻探和随后的详细地表地球物理研究识别目标，例如其他人进行的电磁、磁力和微重力调查。