Formation of the large impact crater field in Wyoming, USA: secondary cratering or asteroid breakup?

美国怀俄明州大型撞击坑场的形成：二次撞击坑还是小行星破碎？

• 批准号: 470678063
• 负责人: Professor Dr. Thomas Kenkmann
• 金额: --
• 依托单位: Lehrstuhl Allgemeine Geologie
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/470678063?language=en
• 关键词: Formation; large; impact; crater; field

In 2018, a large number of small impact craters, 10-120 m in diameter, was discovered in Wyoming. Shock effects were detected in many of these craters. The size of this so-called Douglas impact crater strewn field is 12.8 x 6.9 km. All craters occur stratiform in the uppermost layer of the Permo-Carboniferous Casper Formation and have a uniform age of about 280 Myr. Preliminary work now shows that additional craters are located outside the reported crater field in the same stratigraphic horizon, further increasing the size of the crater field. The size and age of the crater field are extremely unusual. The objective of this proposal is to survey the entire extent of the Wyoming impact crater field, characterize the craters, and interpret the origin of the crater field. Two basic hypotheses will be tested: Scenario 1 - The Wyoming crater field was caused by fragmentation of one or more asteroids as they entered the atmosphere.Scenario 2 - The craters of the Wyoming crater field represent secondary craters formed by ejection of large blocks from around a large, as yet unknown, primary crater. If this hypothesis proves true, the immediate question is the size and location of the causative primary impact crater. Scenario 1 can be verified by evidence of traces of the meteoritic projectile, parallel impact trajectories, and by a distribution of craters in the form of a strewn field ellipse. Scenario 2, on the other hand, can be characterized by the absence of traces of meteoritic projectile material, radial impact trajectories, and a large-scale distribution of secondary craters. The location of the primary crater would be determined by intersecting the reconstructed trajectories.To assess the size of the crater field, remote sensing methods will be used to examine the stratigraphic horizon of the Casper Formation in southeastern Wyoming for additional crater structures. Detected craters will be characterized morphometrically, structurally, and petrographically, with crater ellipticity and asymmetry of ejecta distribution providing information on impact trajectory. The detection of shock effects plays a central role. Equally important is the geochemical identification of potential projectile traces using isotopic signatures and siderophile elements. The favored formation scenario will be quantitatively analyzed by numerical methods. Simulation of meteoroid fragmentation (Scenario 1) is performed by the "Pancake" and "Separated Fragments" models. In the case of secondary crater formation (Scenario 2), numerical simulation using iSALE will first determine the impact energy and velocity of the secondary craters, then model the ballistic path taking into account the atmosphere, and finally model the primary crater itself. The backward modeling is validated by forward modeling of the entire impact process. Environmental disturbances such as heat radiation from the ejecta plume or the atmospheric shock wave will be also simulated.

2018年，怀俄明州发现了大量直径10-120 m的小型撞击坑。在许多陨石坑中都检测到了冲击效应。这个所谓的道格拉斯撞击坑散布场的大小为 12.8 x 6.9 公里。所有陨石坑均呈层状，位于二叠纪-石炭纪 Casper 地层的最上层，其统一年龄约为 280 Myr。现在的初步工作表明，额外的陨石坑位于同一地层层位中报告的陨石坑场之外，进一步增加了陨石坑场的规模。陨石坑场的大小和年龄都极其不寻常。该提案的目的是调查怀俄明州撞击坑场的整个范围，描述陨石坑的特征，并解释陨石坑场的起源。将测试两个基本假设： 场景 1 - 怀俄明州陨石坑场是由一颗或多颗小行星进入大气层时破碎造成的。场景 2 - 怀俄明州陨石坑场的陨石坑代表由周围大块物质喷射而形成的次级陨石坑一个巨大的、至今未知的主陨石坑。如果这个假设被证明是正确的，那么直接的问题就是造成主要撞击坑的大小和位置。场景 1 可以通过陨石射弹痕迹、平行撞击轨迹以及散布场椭圆形式的陨石坑分布来验证。另一方面，情景 2 的特点是没有陨石射弹物质的痕迹、径向撞击轨迹以及大规模分布的次级陨石坑。主陨石坑的位置将通过与重建轨迹相交来确定。为了评估陨石坑区域的大小，将使用遥感方法检查怀俄明州东南部卡斯珀组的地层层位，以寻找其他陨石坑结构。检测到的陨石坑将从形态、结构和岩石学上进行表征，陨石坑椭圆度和喷射物分布的不对称性提供了撞击轨迹的信息。冲击效应的检测起着核心作用。同样重要的是使用同位素特征和亲铁元素对潜在射弹痕迹进行地球化学鉴定。有利的形成方案将通过数值方法进行定量分析。流星体碎片的模拟（场景 1）是通过“煎饼”和“分离碎片”模型进行的。对于次要弹坑形成的情况（场景 2），使用 iSALE 进行数值模拟将首先确定次要弹坑的撞击能量和速度，然后对考虑大气的弹道路径进行建模，最后对主弹坑本身进行建模。通过整个影响过程的正向建模来验证反向建模。还将模拟喷射物羽流的热辐射或大气冲击波等环境扰动。