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，在怀俄明州发现了大量直径10-120米的小型撞击坑。在许多这些陨石坑中发现了冲击效应。这个所谓的道格拉斯撞击坑散布区的大小为12.8 x 6.9公里。所有陨石坑都呈层状出现在石炭纪-二叠纪卡斯珀组的最上层，统一的年龄约为2.8亿年。目前的初步工作表明，在报告的陨石坑区之外，在同一地层层位上还有其他陨石坑，进一步增加了陨石坑区的规模。陨石坑的大小和年龄都非常不寻常。本提案的目的是调查整个范围的怀俄明州撞击坑领域，陨石坑的特点，并解释陨石坑领域的起源。两个基本假设将被测试：情景1 -怀俄明州陨石坑场是由一个或多个小行星进入大气层时的碎片造成的。情景2 -怀俄明州陨石坑场的陨石坑是由一个大的，至今未知的，主要的陨石坑周围的大块喷射形成的次级陨石坑。如果这一假设被证明是正确的，那么最直接的问题就是造成这一现象的主要撞击坑的大小和位置。情况1可以通过陨石射弹的痕迹、平行的撞击轨迹和以散布场椭圆形式分布的陨石坑来证实。另一方面，设想2的特点是没有陨石抛射物的痕迹、放射状撞击轨迹和大规模分布的次级撞击坑。原始撞击坑的位置将通过与重建的轨迹相交来确定。为了评估撞击坑区域的大小，将使用遥感方法来检查怀俄明州东南部卡斯珀组的地层层位，以寻找其他撞击坑结构。探测到的陨石坑将从形态、结构和岩相学上加以表征，陨石坑的椭圆度和喷出物分布的不对称性将提供关于撞击轨迹的信息。冲击效应的检测起着核心作用。同样重要的是利用同位素标记和亲铁元素对潜在抛射物痕迹进行地球化学鉴定。将通过数值方法定量分析有利地层情况。流星体碎裂模拟（设想1）是用“煎饼”和“分离碎片”模型进行的。在二次弹坑形成的情况下（情景2），使用iSALE进行的数值模拟将首先确定二次弹坑的撞击能量和速度，然后在考虑大气层的情况下模拟弹道路径，最后模拟一次弹坑本身。通过对整个碰撞过程的正演模拟，验证了后向建模的正确性。还将模拟环境扰动，如喷出物羽流或大气冲击波的热辐射。