Impact Processes Revealed by Distal Impact Ejecta

Distal impact ejecta layers preserved in the Earth`s stratigraphy hold information about the ejecta`s journey from meteorite impact to sedimentation on the ground. This is especially important for distal ejecta deposits, such as the multiple Archean spherule layers found in South Africa and Australia, which are not associated with known impact structures. However, we do not yet fully understand what these enigmatic layers, which have been reworked by waves and altered by diagenetic processes, tell us about the size and location of these ancient impacts. By compiling data about spherule layers both from previous studies and from new analyses, we hope to gain a greater understanding of these spherule layers and the impact and post-impact processes that form them. We propose to conduct a detailed microstratigraphic study of the Archean spherule layers from a number of localities. The goal is to extract the primary sedimentology and stratigraphy of the layers, including spherule size and size sorting, layer thickness, and other characteristics. We can then numerically model the deposition of these spherule layers through the Earth`s atmosphere to extract information such as the spherule flux to the upper atmosphere as a function of time. This can be compared to ballistic models of spherule transport from the impact site to extract information from the impact event itself such as impact size. Additional microstratigraphic and modeling work on younger spherule layers with known host craters, such as the Eocene spherule beds, permit calibration of our calculations. Detailed analysis of the spherule layers will assist in the future identification of ejecta layers in the stratigraphic record and thus increased understanding of the Earth`s cratering record. In addition to the mechanical style and timescale of spherule deposition, numerical modeling of interactions between falling ejecta and the atmosphere will aid in understanding the fate of the huge amount of energy deposited in the atmosphere by hypervelocity ejecta and the potential environmental effects of large meteorite impacts. Through the combined effort of detailed microstratigraphic analysis and numerical modeling of the Archean spherule layers and comparisons with other spherule deposits, we will gain a broader understanding of impact spherule sedimentation on Earth.