Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020

Poster presentations and abstracts

TP4

Impact processes shaped the solar system and modify planetary surfaces until today. This session aims at understanding planetary impact processes at all scales in terms of shock metamorphism, dynamical aspects, geochemical consequences, environmental effects and biotic response, and cratering chronology. Naturally, advancing our understanding of impact phenomena requires a multidisciplinary approach, which includes (but it is not limited to) observations of craters, strewn field or airbursts, numerical modelling, laboratory experiments, geologic and structural mapping, remote sensing, petrographic analysis of impact products, and isotopic and elemental geochemistry analysis.

We welcome presentations across this broad range of study and particularly encourage work that bridges the gap between the investigative methods employed in studying planetary impact processes at all scales.

Convener: Robert Luther | Co-conveners: Natalia Artemieva, Christopher Hamann, Isabel Herreros, Elena Martellato, Jens Ormö, Francisco Javier Rodriguez Tovar

Session assets

Session summary

Chairperson: Robert Luther, Elena Martellato, Jens Ormo, Christopher Hamann, Francisco Javier Rodríguez Tovar, Isabel Herreros
EPSC2020-65
Francisco Javier Rodriguez Tovar, Christopher M. Lowery, Timothy J. Bralower, Sean P.S. Gulick, and Heather L. Jones

The Cretaceous-Paleogene (K-Pg) mass extinction, 66.0 Ma (Renne et al., 2013), was one of the most important events in the Phanerozoic, severely altering the evolutionary and ecological history of biotas (Schulte et al., 2010). This extinction was caused by paleoenvironmental changes associated with the impact of an asteroid (Alvarez et al., 1980) on the Yucatán carbonate-evaporite platform in the southern Gulf of Mexico, which formed the Chicxulub impact crater (Hildebrand et al., 1991). Prolonged impact winter resulting in global darkness and cessation of photosynthesis, and acid rain have been considered as major killing mechanisms on land and in the oceans. Major animal groups disappeared across the boundary (e.g., the nonavian dinosaurs, marine and flying reptiles, ammonites, and rudists), and other groups suffered severe species level (but not total) extinction, including planktic foraminifera, and calcareous nannofossils. Other groups, including many deep sea benthic organisms, did not experience extinctions but did undergo observable changes in abundance, diversity and composition (Schulte et al., 2010). Thus, the end-Cretaceous impact event had a major importance in the evolution of life in the Earth from the Paleogene.
To evaluate the significance of the asteroid impact in the K-Pg mass extinction it is important to study the impact crater itself. On this challenge, in April and May 2016, a joint expedition of the International Ocean Discovery Program and the International Continental Scientific Drilling Program Expedition 364 drilled into the Chicxulub peak ring and recovered ~130 m of impact deposits which provide a record of the recovery of life in a sterile zone. Analysis of trace fossils reveals the effect of impact-driven paleoenvironmental changes on the macrobenthic community, a group comparatively poorly known. Trace fossils, as records of macrobenthic tracemakers, are closely related to paleoenvironmental conditions; ichnological research is being increasingly used as a tool to study the “Big Five” mass extinctions, with special attention to the K-Pg impact mass extinction event (Lavandeira et al., 2016).
Ichnological data, integrated with planktic foraminifera and calcareous nannoplankton datasets, revealed that life reappeared in the basin just years after the impact. Clear, discrete trace fossils, including Planolites and Chondrites, are registered in the sediments deposited just immediately after the event (Lowery et al., 2018). Thus, proximity to the impact did not delay recovery and that there was therefore no impact-related environmental control on recovery (Lowery et al., 2018). To follow up on this study, ichnological research has been conducted to investigate the initial diversification, evolution, restructuring, and stabilization of the macrobenthic community following the impact event (Rodríguez-Tovar et al., 2020). After the initial recovery a first phase of diversification is recognized, extended to ~45 k.y. after the K-Pg impact event, characterized by the increase in the abundance and size of the trace fossils and the development of an initial community with Planolites, Chondrites, and Palaeophycus, as well as a shallow indeterminate infauna. Subsequently, a phase of stabilization is registered in the infaunal community, with changes only in relative abundance between ichnotaxa, until ~640–700 k.y. into the Paleocene. At this time, following the prolonged phase of stabilization, a second phase of diversification is observed, characterized by the appearance of well-developed Zoophycos. This diversification marks the beginning of the highest diversity, abundance, and size of traces, with a community of Zoophycos, Chondrites, Planolites, and Palaeophycus representing the establishment of a well-developed tiered assemblage within ~700 k.y. This community is maintained during the phase of consolidation/dominance, through at least ~1.25 m.y. after the K-Pg boundary. 
These data support the fast progression of recovery in the macrobenthic tracemaker community in the impact area, with a total reestablishment ~700 k.y. after the impact event. This is rapid in comparison with other mass extinction events, as that occurred at the end-Permian, which took millions of years (Twitchett, 2006). Such rapid recovery demonstrates the ephemeral nature of environmental change at the K-Pg boundary compared to earlier mass extinctions driven by fundamentally slower mechanisms. 

Hildebrand, A.R., Penfield, G.T., Kring, D.A., Pilkington, M., Camargo, A.Z., Jacobsen, S.B., and Boynton, W.V., 1991, Chicxulub Crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico: Geology, v. 19, 867–871.
Lowery, C.M., Bralower, T.J., Owens, J.D., Rodríguez-Tovar, F.J., Jones, H., Smit, J., Whalen, M.T., Claeys, P., Farley, K., Gulick, S.P.S., Morgan, J.V., Green, S., Chenot, E., Christeson, G.L., Cockell, C.S., Coolen, M.J.L., Ferrière, L., Gebhardt, C., Goto, K., Kring, D.A., Lofi, J., Ocampo-Torres, R., Perez-Cruz, L., Pickersgill, A.E., Poelchau, M.H., Rae, A.S.P., Rasmussen, C.,  Rebolledo-Vieyra, M., Riller, U., Sato, H., Tikoo, S.M., Tomioka, N., Urrutia-Fucugauchi, J., Vellekoop, J., Wittmann, A., Xiao, L., Yamaguchi, K.E., and Zylberman, W., 2018, Rapid recovery of life at ground zero of the end Cretaceous mass extinction: Nature, v. 558, 288–291.
Renne, P.R., Deino, A.L., Hilgen, F.J., Kuiper, K.F., Mark, D.F., Mitchell, W.S., Morgan, L.E., Mundil, R., and Smit, J., 2013, Time scales of critical events around the Cretaceous-Paleogene boundary: Science, v. 339, p. 684–687.
Rodríguez-Tovar, F.J., Lowery, C.M., Bralower, T.J., Gulick, S.P.S., Jones, H.L., 2020.Rapid macrobenthic diversification and stabilization after the end-Cretaceous mass extinction event: Geology (in press). 
Schulte, P., Alegret, L., Arenillas, I., Arz, J.A., Barton, P.J., Bown, P.R., Bralower, T.J., Christeson, G.L., Claeys, P., Cockell, C.S., Collins, G.S., Deutsch, A., Goldin, T.J., Goto, K., Grajales-Nishimura, J.M., Grieve, R.A.F., Gulick, S.P.S., Johnson, K.R., Kiessling, W., Koeberl, C., Kring, D.A., MacLeod, K.G., Matsui, T., Melosh, J., Montanari, A., Morgan, J.V., Neal, C.R., Nichols, D.J., Norris, R.D., Pierazzo, E., Ravizza, G., Rebolledo-Vieyra, M., Reimold, W.U., Robin, E., Salge, T., Speijer, R.P., Sweet, A.R., Urrutia-Fucugauchi, J., Vajda, V., Whalen, M.T., and Willumsen, P.S., 2010, The Chicxulub asteroid impact and mass extinction at the Cretaceous-Paleogene boundary: Science, v. 327, p. 1214–1218.
Twitchett, R.J., 2006, The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 232, p. 190–213.

How to cite: Rodriguez Tovar, F. J., Lowery, C. M., Bralower, T. J., Gulick, S. P. S., and Jones, H. L.: The end-Cretaceous mass extinction event at the impact area: A rapid macrobenthic diversification and stabilization, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-65, https://doi.org/10.5194/epsc2020-65, 2020.

EPSC2020-843ECP
Elodie Gloesener, Orkun Temel, Özgür Karatekin, Sarah Joiret, and Véronique Dehant

The series of methane detection and non-detection in the atmosphere of Mars over the last two decades has raised numerous questions about methane generation and destruction mechanisms, which still remain unexplained.  It has been suggested that Martian methane could have a biological origin and be generated by organisms living in the subsurface where conditions are more hospitable [1]. Methane could also be produced through several abiologic processes, including Fischer-Tropsch Type (FTT) reactions where H2 reacts with CO2 in the presence of a metal catalyst [2]. The H2 necessary for the FTT reactions can be produced by several processes and notably by serpentinization [3]. Many of the proposed generation mechanisms for methane would take place hundreds of meters to several kilometers deep in the crust of Mars. Once produced, methane can migrate upwards and be either directly released at the surface or trapped in subsurface reservoirs, such as clathrate hydrates, where it could accumulate over long time before being episodically liberated during destabilizing events. These phenomena leading to surface degassing imply a change in temperature/pressure conditions of the methane reservoirs and are multiple: faulting and landslide generated by seismicity, impact, climatic changes...

In this study, we investigate the capacity of small-sized (a few tens to a few hundred meters diameter) impact craters to thermally penetrate the Martian ground and release methane through the dissociation of subsurface clathrate reservoirs. The impacts of small meteorite are more frequent on present-day Mars and could represent a likely process that would sporadically destabilize shallow gas reservoirs, inducing the degassing of methane in the atmosphere of the planet. We use a one-dimensional finite difference thermal model of the subsurface to calculate the depth of stable methane clathrate hydrates. The impact-induced heat, calculated using the Murnaghan equation of state, is then added to geothermal temperatures to obtain the post-impact temperature distributions similarly to [4]. We apply our model to different case studies in order to constrain the impactor radius, velocity and impact angle required to destabilize a subsurface clathrate layer that would discharge methane amounts corresponding to the observations.

Acknowledgements

This work was supported by the Fonds de la Recherche Scientifique - FNRS and by the Research Foundation Flanders (FWO) under Grant n° EOS-30442502.

References

[1] Atreya, S. K. et al., Planet. Space Sci. 55, 358-369, 2007.

[2] Oehler, D. Z. and Etiope, G., Astrobiology 17, 1233-1264, 2017.

[3] Oze, C. and Sharma, M., Geophys. Res. Lett. 32, 2005.

[4] Schwenzer, S. P. et al., Earth Planet. Sci. Lett. 335-336, 9-17, 2012.

How to cite: Gloesener, E., Temel, O., Karatekin, Ö., Joiret, S., and Dehant, V.: Destabilization of methane clathrate hydrate by meteorite impacts on present-day Mars, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-843, https://doi.org/10.5194/epsc2020-843, 2020.

EPSC2020-783
Thomas Ruedas, Kai Wünnemann, John Lee Grenfell, and Heike Rauer

We constructed a system of parameterized representations of impact-related processes such as crater formation, atmospheric erosion, and impact melt production in order to model how impactors of different types and a large range of sizes could affect CO2-H2O atmospheres and interiors of terrestrial planets similar to Mars, Venus, or the early Earth. Impactor-induced mass fluxes leading to e.g. atmospheric escape, delivery and outgassing are calculated assuming CO2-H2O atmospheres in order to assess under which conditions atmospheres and interiors could be depleted or enriched by processes related to impacts and associated melting or weathering.

By combining parameterized models of single impacts with statistical information about the impactor flux such as the size-frequency distribution of impactors and the cratering chronology, one can deduce evolutionary paths of the volatile contents of the atmosphere and, within limits, of the interior.

We consider rocky S-type and icy-rocky C-type asteroids as well as comets, covering a range of impactor-target density contrasts from about 1/6 to about 4/5 and a range of (absolute) impact velocities from a little less than 10 to almost 65 km/s. Impactor size ranges from 1 m to half the planetary radius. Atmospheric surface pressures cover almost five orders of magnitude, ranging from a few millibars (~modern Mars) up to 95 bar (~modern Venus). Mostly CO2-dominated atmospheric compositions representative for modern-day Mars and Venus were assumed; other gases were not included.

With regard to atmospheric effects, there is a fundamental distinction to be made between blast-producing and crater-forming impacts; the boundary that separates these two regimes is mostly defined by the deceleration of the impactor and its resistance to breakup under the ram pressure during its traversal of the atmosphere. The direct effects of the former leave the interior essentially unaffected and interact only with the atmosphere. We use the formalism by Svetsov (2007) to assess the bulk mass transfer and balance resulting from mechanical erosion of the atmosphere and the disintegration of the impactor and estimate the balance for the individual volatiles from estimates of the impactor composition. In crater-forming impacts, there are additional effects that need to be included. Ejecta can contribute to the mechanical erosion of the atmosphere (e.g., Shuvalov et al., 2014) and also produce layers of porous material with a large, reactive surface that can absorb CO2 from the atmosphere by weathering in the long-term aftermath of an impact. Moreover, they produce craters which facilitate the interior-atmosphere mass exchange.

A key process in this context is the production of impact melt, which can serve as a vehicle for volatiles between the atmosphere and the interior by either releasing or dissolving CO2 and water, depending mostly on the pressure conditions at the interface; generally outgassing is expected to be more common, but still the two volatiles may behave quite differently. Consistent with previous studies we find that CO2 is expelled from the melt much more easily than H2O and could therefore enter the atmosphere under all the conditions considered, whereas water may be retained in the melt at high atmospheric pressures.

References

  • Shuvalov, V. V. et al. (2016): Determination of the height of the “meteoric explosion”. Sol. Syst. Res. 50(1), 1-12, doi: 10.1134/S0038094616010056
  • Svetsov, V. V. (2007): Atmospheric erosion and replenishment induced by impacts of cosmic bodies upon the Earth and Mars. Sol. Syst. Res. 41(1), 28-41, doi: 10.1134/S0038094607010030

How to cite: Ruedas, T., Wünnemann, K., Grenfell, J. L., and Rauer, H.: Impact-atmosphere-interior interactions in terrestrial planets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-783, https://doi.org/10.5194/epsc2020-783, 2020.

EPSC2020-764ECP
Lukas Manske, Ana-Catalina Plesa, Thomas Ruedas, and Kai Wuennemann

We revisit the long-standing problem of melt generation in impacts on terrestrial planets. Traditionally, estimates of melt volumes are derived by semi-analytical models and parameterized results from hydrocode simulations that account for melt generation due to the impact-induced shock (e.g., Bjorkman and Holsapple 1987, Pierazzo at al. 1997). These so-called scaling laws take the form of a power law that connects the melt volume with impactor diameter and velocity as well as the densities of impactor and target and the internal energy of melting, which are assumed constant. While this is a valid assumption for small impacts, which encounter an essentially homogeneous target, it becomes problematic if impact-related length scales such as the depth of penetration or the size of the shocked volume approach the length scales on which the properties of the target change substantially (e.g., Miljković et al., 2013; Potter et al., 2015). On even larger scales, decompression melting can contribute significantly to melt production if the change of target properties with increasing depth is substantial (e.g., the target temperature approaches the solidus [Manske et al., in revision.]). The contribution of plastic work to melt production should also be taken into account in impact scenarios with impactor speeds lower than 15 km/s (Kurosawa and Genda 2018,  Melosh and Ivanov 2018).


We revisit this problem with a set of generic models of terrestrial planets in which we consider the interdependencies between certain properties of the target planet, impact parameters, and the characteristics of impact melt production. We calculate the radial thermal structure of the target planet by employing parameterized thermal evolution models that account for partial melting of the mantle and crustal growth (Tosi et al., 2017, Grott et al., 2011) and consider the heat transport in both stagnant lid and plate tectonics regimes. This leads to a heterogeneous structure of the target that we evaluate at different times and use as initial condition for the fully dynamical model of the impact itself, which is calculated with iSALE (e.g., Collins et al. 2004, Wünnemann et al. 2006). To accurately calculate impact-induced melt volumes, we developed a Lagrangian tracer-based method that accounts for the generation of impact-induced melt by shock-heating as well as decompression and plastic work due to material deformation and displacement in the course of crater formation. By these means we explore the dependence of melt production on impactor size and velocity as well as target temperature, which in turn depends on the temporal evolution of the mantle's Rayleigh number and hence on its depth and gravity. The latter in turn is a function of the mass of the target planet, which also influences the impact velocity and thus the depth of penetration of the impactor. While the models are derived for generic planets ranging in size from Moon-sized objects to super-Earths, they are also applied to planets of our Solar System, in particular Mars.

 

The ultimate goal is to find a comprehensive representation of these complex interdependencies. Furthermore, we aim to narrow down parameter ranges where scaling laws represent melt production satisfactorily and indicate in which scenarios target heterogeneities or melting due to decompression or plastic work affects the overall melt production significantly.

References:

Bjorkman, M. D.; Holsapple, K. A. (1987): Velocity scaling impact melt volume. Int. J. Impact Engng. 5(1-4), 155-163, doi: 10.1016/0734-743X(87)90035-2

Pierazzo, E. et al. (1997): A reevaluation of impact melt production. Icarus 127(2), 408-423, doi: 10.1006/icar.1997.5713

Miljković, K. et al. (2013). Asymmetric distribution of lunar impact basins caused by variations in target properties. Science, 342(6159), 724-726.

Potter, R. W. K. et al. (2015): Scaling of basin-sized impacts and the influence of target temperature. In: Large Meteorite Impacts and Planetary Evolution V, ed. by Osinski, G. R. and Kring, D. A., vol. 518 in Special Papers, Geological Society of America, pp. 99-113, doi: 10.1130/2015.2518(06)

Tosi, N. et al. (2017): The habitability of a stagnant-lid Earth. Astronomy & Astrophysics, 605, A71.

Grott, M. et al. (2011): Volcanic outgassing of CO2 and H2O on Mars. Earth and Planetary Science Letters, 308(3-4), 391-400.

Wünnemann, K. et al. (2006): A strain-based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets. Icarus, 180(2), 514-527.

Kurosawa, K., & Genda, H. (2018): Effects of friction and plastic deformation in shock‐comminuted damaged rocks on impact heating. Geophysical Research Letters, 45(2), 620-626.

Melosh, H. J., & Ivanov, B. A. (2018): Slow impacts on strong targets bring on the heat. Geophysical Research Letters, 45(6), 2597-2599.

How to cite: Manske, L., Plesa, A.-C., Ruedas, T., and Wuennemann, K.: The influence of interior structure and thermal state on impact melt generation in terrestrial planets
, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-764, https://doi.org/10.5194/epsc2020-764, 2020.

EPSC2020-1120ECP
Jakob Wilk and Gerwin Wulf
Introduction:
The Ries crater is a 26 km sized complex impact structure of Miocene origin (14.34+-0.08 Ma) [1, 2]. The impact event itself was caused by an oblique impact of a 1.5 km diameter stony meteorite exceeding an impact velocity of 15 km s-1 [3] The impact occurred in a two-layered target of crystalline rocks (mainly granites, gneisses and amphibolites) overlain by ~650 m thick, partly water-saturated, sedimentary cover of Tertiary, Jurassic and Permian shale, sand- and limestones [4]. The ejecta material builds up a continuous polymict lithic breccia, called Bunte breccia, with unshocked to weakly shocked sedimentary target clasts, reworked surficial sediments, and minor amounts of crystalline basement fragments [5], overlain by patches of shocked and partly melted crystalline basement material, called suevite [6, 7]. This succession of Bunte breccia and suevite is typically presented as an undulating contact, strikingly exposed for instance in the Aumühle quarry near the NE crater rim of the Ries (Fig.1).
 
 
Different formation models have been proposed for the emplacement of the Bunte breccia. One possible mechanism includes rampart formation similar to the formation of Martian rampart craters [8-12], which typically show a characteristic thickening (rampart) and thinning (moat) of the inner and outer ejecta deposits and radially oriented grooves and ridges (“striations”) [14, 15]. We hypothesize: groves and ridges present in the Ries ejecta can be traced in the scale of the Aumühle quarry by the undulating contact of Bunte breccia and suevite radially extending into a striation-like subsurface morphology.
 
Methods: 
For characterizing the lateral extend of the undulated contact plane between Bunte breccia and suevite, we carried out a geophysical survey in 2019 for the surrounding area of the Aumühle quarry. In addition, we conducted a photogrammetric drone mapping for the entire quarry and its surrounding.
For the geophysical survey, in total 34 GPR profiles were collected (Fig.2) with a bi-static, common-offset, sled mounted, and unshielded 200 MHz antenna equipped with a pulseEKKO Pro transmitter and a pulseEKKO receiver unit (Sensors & Software). The antennas were oriented perpendicular broadside, with an antenna separation of 0.5 m. Traces along the GPR-profiles were recorded with a spacing of 0.2 m, triggered by an odometer wheel attached to the rear of the sled.