Meteorite impact craters as hotspots for mineral resources and energy fuels:A global review

The ever-increasing recovery rate of natural resources from terrestrial impact craters over the last fewdecades across the globe offers new avenues for further exploration of mineral and hydrocarbon resources in such settings.As of today,60 of the 208 terrestrial craters have been identified to host diverseresources such as hydrocarbons,metals and construction materials.The potential of craters as plausibleresource contributors to the energy sector is therefore,worthy of consideration,as 42(70%)of the 60craters host energy resources such as oil,gas,coal,uranium,mercury,critical and major minerals as wellas hydropower resources.Among others,19 craters are of well-developed hydrocarbon reserves.Mineraldeposits associated with craters are also classified similar to other mineral resources such as progenetic,syngenetic and epigenetic sources.Of these,the progenetic and syngenetic mineralization are confinedto the early and late excavation stage of impact crater evolution,respectively,whereas epigenetic deposits are formed during and after the modification stage of crater formation.Thus,progenetic andsyngenetic mineral deposits(like Fe,Ni,Pb,Zn and Cu)associated with craters are formed as a directresult of the impact event,whereas epigenetic deposits(e.g.hydrocarbon)are hosted by the impactstructure and result from post-impact processes.In the progenetic and syngenetic deposits,the shockwave induced fracturing and melting aid the formation of deposits,whereas in the epigenetic deposits,the highly fractured lithostratigraphic units of higher porosity and permeability,like the centralelevated area(CEA)or the rim,act as traps.In this review,we provide a holistic view of the mineral andenergy resources associated with impact craters,and use some of the remote sensing techniques toidentify the mineral deposits as supplemented by a schematic model of the types of deposits formedduring cratering process.

Enigmatic Glass-Like Carbon from the Alpine Foreland, Southeast Germany: A Natural Carbonization Process

Unusual carbonaceous matter, termed here chiemite, composed of more than 90% C from the Alpine Foreland at Lake Chiemsee in Bavaria, southeastern Germany has been investigated using optical and atomic force microscopy, X-ray fluorescence spectroscopy, scanning and transmission electron microscopy, high-resolution Raman spectroscopy, X-ray diffraction and differential thermal analysis, as well as by δ13 C and 14 C radiocarbon isotopic data analysis. In the pumice-like fragments, poorly ordered carbon matter co-exists with high-ordering monocrystalline α-carbyne, and contains submicrometersized inclusions of complex composition. Diamond and carbyne add to the peculiar mix of matter. The required very high temperatures and pressures for carbyne formation point to a shock event probably from the recently proposed Holocene Chiemgau meteorite impact. The carbon material is suggested to have largely formed from heavily shocked coal, vegetation like wood, and peat from the impact target area. The carbonization/coalification high PT process may be attributed to a strong shock that instantaneously caused the complete evaporation and loss of volatile matter and water, which nevertheless preserved the original cellular structure seen fossilized in many fragments. Relatively fresh wood encapsulated in the purported strongly shocked matter point to quenched carbon melt components possibly important for the discussion of survival of organic matter in meteorite impacts, implying an astrobiological relationship.

The seismite problem

During a period of 82 years （1931-2013）, 39 genetic terms were introduced for various deposits. Of the 39 terms, only ten are meaningful in understandin8 the true depositional origin （e.9., turbidites）, the remaining 29 are just jargons （e.g., seismites, tsunamites, etc.）. The genetic term ＂seismites＂, introduced by Seitacher （1969） for recognizing pa[aeoearthquakes in the sedimentary record, is a misnomer. The term was introduced in haste, based on an examination of a single exposure of the Miocene Monterey Formation （10 m） in California, without a rigorous scientific analysis. The fundamental problem is that earthquake is a triggering mechanism, not a depositional process. Type of triggers cannot be recognized in the ancient sedimentary record because evidence for triggers is not preserved by nature. Soft-sediment deformation structures （SSDS）, commonly used as the criteria for interpreting seismites, are a product of liquefaction. However, liquefaction can be induced by any one of 21 triggers, which include earthquakes, meteorite impacts, tsunamis, sediment loading, among others. Brecciated ciasts, typically associated with earthquake-induced deposits in the Dead Sea Basin, are also common depositional products of debris flows （i.e., synsedimentary product unrelated to earthquakes）. Also, various types of SSDS, such as duplex-like structures and ctastic injections, can be explained by synsedimentary processes unrelated to earthquakes. Case studies of sandstone petroleum res- ervoirs worldwide, which include Gulf of Mexico, North Sea, Norwegian Sea, Nigeria, Equatorial Guinea, Gabon, and Bay of Bengal, reveal that there is compelling empirical evidence for sediment loading being the primary cause of SSDS. The Krishna-Godavari Basin, located on the eastern continental margin of India, is ideal for sediment failures by multiple triggering mechanisms where overpressure and liquefaction have ted to multi-origin SSDS. Because tsunamis and meteorite impacts are important phenomena in developing extensive deposits, lateral extent of SSDS cannot be used as a unique distinguishing attribute of earthquakes. For these reasons, the genetic term ＂seismites＂, which has no redeemable scientific value, is obsolete.

The fallacy of interpreting SSDS with different types of breccias as seismites amid the multifarious origins of earthquakes:Implications

At present, there are no criteria to distinguish soft-sediment deformation structures （SSDS） formed by earthquakes from SSDS formed by the other 20 triggering mechanisms （see a companion paper in Vol 5, No. 4 of this journal by Shanmugam, 2016）. Even if one betieves that earthquakes are the true triggering mechanism of SSDS in a given case, the story is stiff incomptete. This is because earthquakes （seismic shocks） are induced by a variety of causes： 1） glbaltectonics and associated faults （i.e., midocean ridges, trenches, and transform fautts）; 2） meteorite-impact events; 3） volcanic eruptions; 4） post-gtacialuplift; 5） tsunami impact; 6 cyclonic impact; 7） landslides （mass-transport deposits）; 8） tidal activity; 9） sea-tevet rise; 10） erosion; and 11） fluid pumping. These different causes are important for devetoping SSDS. Breccias are an important group of SSDS. Although there are many types of breccias classified on the basis of their origin, five types are discussed here （fault, volcanic, meteorite impact, sedimentary-depositionaL, sedimentary-collapse）. Atthough different breccia types may resemble each other, distinguishing one type （e.g., meteorite breccias） from the other types （e.g., fault, volcanic, and sedimentary breccias） has important imptications. 1） Meteorite breccias are characterized by shock features （e.g., planar deformation features in mineral grains, planar fractures, high-pressure polymorphs, shock melts, etc.）, whereas sedimentary- depositional breccias （e.g., debrites） do not. 2） Meteorite breccias imply a confined sediment distribution in the vicinity of craters, whereas sedimentary-depositional breccias imply an unconfined sediment distribution, variable sediment transport, and variable sediment provenance. 3） Meteorite, volcanic, and fault breccias are invariabty subjected to diagenesis and hydrothermat mineratization with attered reservoir quality, whereas sedimentary-depositional breccias exhibit primary （unaltered） reservoir quality. And finalty, 4） sedimentary-collapse breccias are associated with economic mineralization （e.g., uranium ore）, whereas sedimentary-depositional breccias are associated with petroleum reservoirs. Based on this important group of SSDS with breccias, the current practice of interpreting all SSDS as ＂seismites＂ is inappropriate. Ending this practice is necessary for enhancing conceptuat clarity and for advancing this research domain.

Structural analysis of rubble-pile asteroids applied to collisional evolution

Solar system small bodies come in a wide variety of shapes and sizes,which are achieved following very individual evolutional paths through billions of years.Nevertheless,some common mechanisms can still be found during these processes,e.g.,rubble-pile asteroids tend towards fluid equilibrium as they are reshaped by external disturbances.This paper focuses on the reshaping process of rubble-pile asteroids driven by meteorite impacts.A mesoscale cluster of solid spheres is employed as the principal model for a rubble-pile asteroid,for which little is actually known about their interior structure.We take this simple model as a rough guide to the qualitative aspects of the reshaping processes,and it can reveal,to some degree,the inner workings of rubble-pile asteroids.In our study,numerous possible equilibrium configurations are obtained via Monte Carlo simulation,and the structural stability of these configurations is determined via eigen analysis of the geometric constructions.The eigen decomposition reveals a connection between the cluster’s reactions and the types of external disturbance.Numerical simulations are performed to verify the analytical results.The gravitational N-body code pkdgrav is used to mimic the responses of the cluster under intermittent non-dispersive impacts.We statistically confirm that the stability index I S,the total gravitational potential P G,and the volume of inertia ellipsoid V E show consistent tendency of variation.A common regime is found in which the clusters tend towards crystallization under intermittent impacts,i.e.,only the configurations with high structural stability survive under the external disturbances.The results suggest the trivial non-disruptive impacts might play an important role in the rearrangement of the constituent blocks,which may strengthen these rubble piles and help to build a robust structure under impacts of similar magnitude.The final part of this study consists of systematic simulations over two parameters,the projectile momentum and the rotational speed of the cluster.The results show a critical value exists for the projectile momentum,as predicted by theory,below which all clusters become responseless to external disturbances;and the rotation proves to be significant for it exhibits an“enhancing”effect on loose-packed clusters,which coincides with the observation that several fast-spinning asteroids have low bulk densities.