Layered by water: Impact excavation processes on terrestrial analogues for Mars.

Comparative planetological studies show that the excavation of rock debris during impact processes and their distribution (ejecta) around impact craters are strongly influenced by rheology and volatile content of the affected crust [1]. The formation of so-called Double-layered ejecta (DLE) craters on mars specifically is linked to the presence of water-ice in the Martian subsurface (see review by [2]). Although morphological features, in particular the ejecta blankets, have largely been destroyed for most of the terrestrial impact structures (e.g., [3]), recent studies have shown that at least Lonar crater in India [4], Ries crater in Germany [5] and Bosumtwi crater in Ghana [6, 7] possess ejecta ramparts, similar to martian DLE impact craters.

We test this hypothesis of DLE-like craters on earth by examining ejecta features, such as radial grooves, of Ries and Lonar crater. For this study, we combine geophysical (GPR and ERT), analysis of micro-fracture networks and photogrammetric (drone photogrammetry) techniques in key locations of the Ries and Lonar crater.

As a result of from processed DEMs an apparent thickening of the ejecta deposits are observable in distal parts of the Ries and Lonar craters, similar to rampart structures of martian impact craters [5, 7]. Geophysical measurements suggest the presence of lateral striations in the morphometric contact of the Ries crater ejecta layers. We intend to construct an area-wide reconstruction of the ejecta boundary layer also for Lonar. The formation of martian-like DLE craters on earth could help to substantiate analogoues to constrain boundary conditions for DLE craters on other planets, specifically in aformentioned volatile content of the affected crust.

 

Literature: [1] Osinski et al. 2011 Earth and Planetary Science Letters 310, 167–181. [2] Weiss and Head 2018 Meteoritics & Planet. Science 53, 741-777. [3] Hergarten and Kenkmann 2015 Earth and Planetary Science Letters 425, 187–192. [4] Maloof et al. 2009 Geological Society of America Bulletin 122:109–126. [5] Sturm et al. 2013 Geology, 41, 531-534. [6] Baratoux et al. 2019 Meteoritics & Planetary Science 54, 2541–2556. [7] Wulf et al. 2019 Earth and Planetary Science Letters 506, 209–220.