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We report on the Azuara impact structure and its Rubielos de la Cérida compa- nion crater, which establish the largest terrestrial doublet impact structure presently known. Both structures have diameters of roughly 35 - 40 km and they have been formed in a purely sedimentary target. From stratigraphic considerations and palaeontologic dating, an Upper Eocene or Oligocene age is very probable Geological mapping has established abundant geologic impact evidence in the form of monomictic and polymictic breccias and breccia dikes, megabreccias, dislocated megablocks, remarkable structural features, extensive impact ejecta and impact sig- natures even in distant autochthonous deposits. The most striking impact evidence for both structures is given by strong shock metamorphism, including melt and dia- plectic glass, planar deformation features (PDFs), different kinds of impact melt rocks (from former silicate melt, carbonate melt, carbonate-phosphate melt) and suevite breccias. Glassy amorphous carbon particles in a solid C-O compound may be related with fullerenes and may originate from a quenched melt of extremely shocked coal or from extremely shocked limestones. It is assumed that the impact had considerable influence on the Mid-Tertiary regional geology of the Iberian System, and we suggest that respective geologic models which have so far not con- sidered this peculiar and far-reaching event, need considerable revision.
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... Sometimes, limestone clasts show a ghost texture (Fig. 5A); only the clast rim is preserved and the clasts are frequently replaced by white, microcrystalline/colloidal material. High temperature decarbonisation, formation of carbonate melts, and subsequent recrystallisation are the probable causes (Ernstson and Fiebag, 1992;Ernstson et al., 2002) of this texture. This breccia contains amorphous meteorite fragments,~4-5 cm in size, that are chemically and texturally closely tied with the breccia (Fig. 5B). ...
... Furthermore, breccia dikes are distinctive features in impact structures (Ernstson et al., 2002;Oskierski, 1987, 1988). Breccia dikes are generally suggested to be largely formed during the penetrating stage by injection of brecciated material into the walls and the floor of the expanding excavation cavity (Melosh, 1989). ...
... A few limestone fragments that constitute the breccias contain centimetric fragments of the meteorite, which are surrounded by a whitish rim (Fig. 7A), possibly corresponding to a contact metamorphic aureole. In other words, the whitish rims of the meteorite portions in contact with the limestone are probably the beginning of the decarbonisation process caused by the impact thermal effect (Ernstson et al., 2002). Moreover, a centimetric meteorite found NE of the crater is surrounded by a melted rim (Fig. 7B). ...
Article
Geological studies and tomographic profiles of a locality nearby the Agoudal village (Morocco) showed the presence of a single impact crater, 500–600 m diameter, largely hidden by a limestone block, 220 m long and 40 m deep. The site was interpreted as a landslide that followed the fall of a cosmic body. The Agoudal impact crater was not affected by intense erosion. The lack of an evident impact structure, as well as the sporadic distribution of impactites and their limited occurrence, can be explained by a complex geological framework and by recent tectonics. The latter is the result of the sliding of limestone block, which hides almost two-thirds of the crater's depression, and the oblique fall of the meteoroid on sloping ground. In addition, some impact breccia dikes sharply cut the host rock in the Agoudal impact structure. They do not show any genetic relationship with tectonics or hydrothermal activity, nor are they related to any karst or calcrete formations. Altogether, the overlapping of the meteorite strewn field (11 km long and 3 km wide) with the area of occurrence of shatter cones and impact breccias, together with the presence of meteorite fragments (shrapnel) ejected from the crater, the presence of shatter cones contaminated by products of iron meteorites and the presence of impact breccias that contain meteorite fragments of the same chemical composition of the Agoudal meteorite indicate that the fall of this meteorite can be responsible for the formation of the impact structure.
... Nevertheless, the thrust kinematics are developed futher by geologists (e.g., Capote et al. 2002), and tens of kilometers long faults are drawn within models of syn(gin)-tectonic sedimentation Fig. 3). Different from earlier workers on the Daroca geology we took a somwhat closer look at the facies and the structural setting of the involved Cambrian and Tertiary units, and here we present a model that relates the Daroca geology with the near Azuara impact structure (Ernstson et a. 1985(Ernstson et a. , 1987(Ernstson et a. , 2002Ernstson and Fiebag 1992;Ernstson and Claudin 1990;Claudin and Ernstson 2003;Ernstson 1991Ernstson , 1994 and that is able to explain many features so far not having been taken into consideration by geologists. ...
... Shatter cones are rare in the Azuara structure because they require shock pressures for their formation that are best given in the center of an impact crater and more or less limited to the crater area. The interior of the Azuara structure is filled by post-impact young sediments, and therefore shatter cones have so far been found only in the rim region (Ernstson et al. 2002). Since the impact shock pressure rapidly decreases with distance a shatter cone formation about 10 km distant from the crater rim in an autochthonous Olalla block seems to be rather unlikely. ...
... Hence, their opposition is fed on theoretical models, on textbook knowledge, on simple assertions and sometimes even on falsification which we have lengthily addressed elsewhere [4]. For these geologists, the carefully analyzed impact melt rocks and impact glasses (Hradil et al. 2001) are volcanic ash, the polymictic, in part strongly shocked impact breccias and impact breccia dikes (Ernstson et al. 2002) are soil formation and karst features, the established shock effects like planar deformation features (PDFs) (A. Therriault, written report, Ernstson et al. 2002) and diaplectic quartz and feldspar glass (Ernstson et al. 2002) are tectonically produced, the Pelarda Fm. and Puerto Mínguez impressive impact ejecta deposits (Ernstson and Claudin 1990, Ernstson et al. 2002 are Quaternary alluvial fans (see Figs. 20,25) and Tertiary conglomerates, the young Tertiary fill in the middle of the Azuara impact structure is said to be undisturbed Devonian (J. ...
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A nappe-like thrust of Cambrian over Tertiary, the Daroca thrust, in northeast Spain has puzzled gelogists since longtime. Because of a lacking root zone and a lacking relief it didn't match a reasonable geologic pattern. In the younger regional geologic literature the thrust is nevertheless incorporated in Alpine regional tectonics. An obviously first closer investigation of the involved Cambrian and Tertiary units, their facies and structural setting leads to a model that relates the Daroca thrust to the nearby roughly 40 km-diameter Azuara impact structure. The thrust is part of the excavation stage of impact cratering which may have affected both the Cambrian plate and the diamictic Tertiary below. The model is strongly substantiated by comparison with the Ries impact structure where similar thrusts and related features occur. The Daroca thrust is one more example reflecting the work of the regional geologists who pretend the giant Azuara impact event with the formation of the Azuara impact structure and the adjacent about 70 km Rubielos de la Cérida elongated impact basin never happened. Hence, all their regional geologic models still developed which completely ignore the impact and its radical influence on the Tertiary regional geology are without any scientific relevance.
... Spherical shapes (Fig. 3), degraded Raman bands (Fig. S6 in the ESM), occurrence in cracks together with carbonatite and silicate glass (Fig. 7a), and deformations by neoformed plagioclase in palisade bands (Fig. 5e) indicate that the phosphate globules are solidified liquids rather than resorbed mineral grains. The compositionally identical phosphate domains in the globular calcite and segregated phosphate globules in the melilitic glass suggest separation of a Ca-phosphate liquid from P-rich carbonatite similar to those described from metasomatised mantle xenoliths (Rosenbaum et al. 1997;Zhang et al. 2007), alkaline rocks and carbonatites (Naumov et al. 1988;Panina and Motorina 2008), impact structures (Ernstson et al. 2002), an alvikite dyke (Sommerauer and Katz-Lehnert 1985), limburgite (Shao et al. 2000), and highly fractionated peraluminous granitic pegmatite (Thomas et al. 1999). Phosphate-carbonate-silicate immiscibility was also reported from the Mushugai Khuduk alkaline igneous complex of Mongolia, where cogenetic silicate-salt and phosphatecarbonate melt inclusions occur in apatite from theralite associated with carbonatites (Andreeva et al. 1999). ...
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A plagioclase megacryst containing composite crystal-glass inclusions was ejected in a Pliocene basaltic diatreme in the Carpathian back-arc basin (Pannonian Basin). The megacryst grew from phonolitic melt, relics of which are preserved in the crystal-glass inclusions. Most of the pristine melt has undergone substantial compositional resetting by interaction with several batches of a low-viscosity carbonated, P-rich melilitite melt, which infiltrated and largely replaced the original inclusion content. The melilitite melt also caused partial resorption of the host megacryst and crystallisation of new calcic plagioclase forming stringers and palisades. A P-rich calcic carbonatite melt exsolved from the melilitite and later crystallised to aragonite at ~ 800 °C and 1.9 GPa. The phosphate melt fraction exsolved from the carbonatite and solidified as CO 3 ²⁻ -rich A-B type apatite. At a very late evolutionary stage, K- and Si-rich fluids caused potassic and silicic alteration of the solidified melilitite glass along cracks and interfaces between calcic carbonate globules and glass at temperatures below 680 °C. The oxygen isotope composition of the plagioclase megacryst (6.2 ‰ V-SMOW; Vienna Standard Mean Ocean Water) and the ⁸⁷ Sr/ ⁸⁶ Sr isotope ratio of carbonates in the inclusions (0.7034) are consistent with a mantle-derived melt. ⁸⁷ Sr/ ⁸⁶ Sr isotope ratios (0.7047–0.7051) in interstitial carbonates from associated syenite and carbonatite xenoliths indicate a metasomatised mantle source contaminated with radiogenic crustal material or altered marine carbonate. The O-isotope ratios in the carbonates, 22.7 ± 0.6 ‰ V-SMOW in calcite and 23.6 ± 0.7 ‰ V-SMOW in aragonite, are also consistent with a sedimentary precursor. Contrasting δ ¹³ C values in the calcite, -12.7 ± 0.5 ‰ V-PDB (Vienna PeeDee Belemnite), and the aragonite (-4.6 ± 0.5 ‰ V-PDB) indicate low-temperature modification of calcite assisted by $$\delta$$ δ ¹³ C-depleted CO 2 and preservation of primary magmatic $$\delta$$ δ ¹³ C values in aragonite. The microstructural and geochemical evidence points towards heterogeneous silicate-carbonate melt fractions generated during the metasomatism and partial melting of a supra-subduction mantle wedge.
... These so called spallation features are the typical result of dynamic shock deformation well known from observed conglomerates near large impact structures [17,18]. ...
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The Triffa plain is located in the north-eastern part of Morocco. It’s considered as sedimentary basin of a Quaternary age containing a wide variety of breccias that we consider as impactites. Thereby, we have found monomict breccia and polygenic breccia. The presence of glassy clasts allows us to determine the suevite that contains many indices of shock metamorphism. The effect of the shock is observed in quartz grains that show fractures and planar deformation, the mosaicism texture and ballen-quartz. The pebble breccia shows deformations of shock such as spallation fractures and striation. However, we suggest that the sediments in the Triffa depression are mainly impact breccias.
... Bereits seit vielen Jahren wird versucht, die Strukturen von Azuara und Rubielos de la Cérida in Spanien als Impaktstrukturen zu erklären (vgl. Ernstson et al. 2002vs. Cortés et al. 2002und Diaz Martinez et al. 2002, ebenso das "Astroblem" von Ševětín in Tschechien (Vrána 1987), die Struktur von Guarda in Portugal (Monteiro 1991;vgl. ...
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Europe has a rich heritage of meteorite impact structures of varied size, ranging from some metres to several tens of kilometres, and geologic age, from the Proterozoic to the Quaternary. The Ries-Steinheim event in Southern Germany is considered a prime example of a double impact system and has produced two of the best-preserved complex impact structures worldwide. This summary briefly reviews the proven impact structures in Germany, France, Eastern Europe including the Baltic countries, Finland, Sweden and Norway, as well as impact ejecta deposits in Scotland and elsewhere, and presents the recent developments in European impact crater research.
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We use Schmieder and Kring's article to show how science still works within the so-called "impact community" and how scienti c data are manipulated and "rubber-stamped" by reviewers (here, e.g., C. Koeberl and G. Osinski). We accuse the authors of continuing to list the Azuara and Rubielos de la Cérida impact structures and one of the world's most prominent ejecta occurrences of the Pelarda Fm. in Spain 1 2 as non-existent in the compilation. The same applies to the spectacular Chiemgau impact in Germany, which has been proven by all impact criteria for several years. For the authors' dating list, we propose that the multiple impact of Azuara is included together with the crater chain of the Rubielos de la Cérida impact basin as a dated candidate for the third, so far undated impact markers in the Massignano outcrop in Italy.
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The Iberian System in NE Spain is characterized by a distinctive graben/basin system (Calatayud, Jiloca, Alfambra/Teruel), among others, which has received much attention and discussion in earlier and very recent geological literature. A completely different approach to the formation of this graben/basin system is provided by the impact crater chain of the Rubielos de la Cérida impact basin as part of the important Middle Tertiary Azuara impact event, which has been published for about 20 years. Although the Rubielos de la Cérida impact basin is characterized by all the geological, mineralogical and petrographical impact findings recognized in international impact research, it has completely been hushed up in the Spanish geological literature to this day. The article presented here uses the example of the Jiloca graben to show the absolute incompatibility of the previous geological concepts with the impact structures that can be observed in the Jiloca graben without much effort. Digital terrain modeling and aerial photography together with structural and stratigraphic alien geology define a new lateral Singra-Jiloca complex impact structure with central uplift and an inner ring, which is positioned exactly in the middle of the Jiloca graben. Unusual topographic structures at the rim and in the area of the inner ring are interpreted as strike-slip transpression and transtension. Geological literature that still sticks to the old ideas and develops new models and concepts for the graben/basin structures, but ignores the huge meteorite impact and does not even enter into a discussion, must at best cause incomprehension.
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Visit the full web article via http://www.impact-structures.com/impact-educational/meteorite-impact-spallation-from-mega-to-micro-scale/ ******* Abstract.- Spallation, a well-known process in fracture mechanics, plays a major role in meteorite impact events and is evident on all scales from megascopic spall plates and with larger structural features, over mesoscopic dynamic deformations in particular of conglomeratic target deposits, down to microscopic shock spallation in mineral grains. Here I report on experimental spallation, on various geological implications of impact spallation and on mineralogical spallation evidence, with a special focus on the Spanish Azuara and Rubielos de la Cérida impact structures and the Ries impact crater in Germany.
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We use and variegate the title of this article published in Earth-Science Reviews to show how science may (mal)function, how scientific results are manipulated, and how a few exposed impact researchers (the authors of the Earth-Science Reviews article included) are counteracting exactly the ideas presented in that article.
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The "round rocks" of the Weaubleau-Osceola impact structure have phenomenological counterparts in the Spanish Azuara/Rubielos de la Cérida impact structures where they occur within voluminous heavily brecciated rock units. Related nodular bodies within large monomictic movement breccias are observed also in the Ries impact structure. A process similar to the formation of monomictic impact breccias with rounded clasts as part of a mortar texture is suggested. A relation to the Weaubleau-Osceola "round rocks" may exist but not necessarily.
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The Earth is the most endogenically active of the terrestrial planets and, thus, has retained the poorest sample of impacts that have occurred throughout geological time. The current known sample consists of approximately 160 impact structures or crater fields. Approximately 30% of known impact structures are buried and were initially detected as geophysical anomalies and subsequently drilled to provide geologic samples. The recognition of terrestrial impact structures may, or may not, come from the discovery of an anomalous quasi-circular topographic, geologic or geophysical feature. In the geologically active terrestrial environment, anomalous quasi-circular features, however, do not automatically equate with an impact origin. Specific samples must be acquired and the occurrence of shock metamorphism, or, in the case of small craters, meteoritic fragments, must be demonstrated before an impact origin can be confirmed. Shock metamorphism is defined by a progressive destruction of the original rock and mineral structure with increasing shock pressure. Peak shockl pressures and temperatures produced by an impact event may reach several hundreds of gigaPascals and several thousand degrees Kelvin, which are far outside the range of endogenic metamorphism. In addition, the application of shock-wave pressures is both sudden and brief. Shock metamorphic effects result from high strain rates, well above the rates of normal tectonic processes. The well-characterized and documented shock effects in quartz are unequivocal indicators and are the most frequently used indicator for terrestrial impacjt structures and lithologies.