The mid-Tertiary Azuara and Rubielos de la Cérida paired imapct structures (Spain). (original) (raw)
Related papers
Impact-related melting of sedimentary target rocks of the Rubielos de la Cérida structure in Spain
Berichte der …, 2002
The Rubielos de la Cérida impact structure forms a companion crater to the Late Eocene-Oligocene Azuara impact structure. Both are located more or less at the margin of the Iberian chains and the Ebro basin south of Zaragoza. Within the Rubielos structure, silicate melt rocks, carbonate-phosphate melts with small-scaled immiscibility features, very fine mixtures of silicate melt and carbonate forming clasts in suevite, as well as glassy particles of amorphous carbon were found. These melt rocks clearly reflect the chemical composition of various parts of the thick sedimentary pile in the target area and show the shockinduced high-temperature influence on these rocks.
Evidence of an impact origin for the Azuara structure (Spain)
Earth and Planetary Science Letters, 1985
Some 50 km south of Zaragoza (northeast Spain) there is a tectonically peculiar area, which is suspected to be a large impact site. It has a morphologically conspicuous ring structure with a diameter of roughly 30 km and consists mainly of Mesozoic sediments emerging from the Ebro Tertiary Basin, and partly of Palaeozoic rocks from the Iberian System. The strata of the ring, in general, dip to the center and are highly folded and faulted. Intense and unusual deformation is indicated by abundant mixed and monomict breccias. A single poorly exposed outcrop of a mixed breccia with sedimentary fragments exhibits shock-metamorphic effects. Within quartz grains, systems of crystallographically oriented microscopic planar features and planar fractures can be observed, as well as kink bands in micas within the breccia matrix. The age of the impact is estimated to be between Lower Cretaceous and Miocene.
Sedimentary record of impact events in Spain
A review of the evidence of meteorite-impact events in the sedimentary record of Spain reveals that the only proven impact-related bed is the clay layer at the Cretaceous-Tertiary boundary (at Zumaya and Sopelana in the Bay of Biscay region, and at Caravaca, Agost, and Alamedilla in the Betic Cordilleras). Other deposits previously proposed as impact related can now be rejected, or are dubious and still debated. These include the Pelarda Formation, alleged to represent proximal ejecta from the Azuara structure; the Paleocene-Eocene boundary near Zumaya (western Pyrenees) and Alamedilla (Betic Cordillera); and the Arroyofrío Oolite Bed, which has been alleged as distal ejecta of an unknown Callovian-Oxfordian impact event. The scarcity of evidence for meteorite-impact events in the sedimentary record is possibly due to a lack of detailed studies. We propose several sedimentary units that could potentially be related to impact events, and where future research should focus.
2019
The Pelarda Formation (Fm.), located in the Iberian System in northeast Spain, is a sedimentary deposit with an extension of roughly 12 km x 2.5 km and an estimated thickness of no more than 400 m. The formation was first recognized as a peculiar unit in the early seventies and underwent interpretations like a fluvial or an alluvial fan deposit having a postulated age between Paleogene and Quaternary. Since the early nineties the Pelarda Formation has been considered an impact ejecta deposit originating from the large ca. 40 km-diameter Azuara impact structure and meanwhile being among the largest and most prominent terrestrial impact ejecta occurrences, which however is questioned by regional geologists still defending the fluvial and alluvial fan models. Roughly speaking, the Pelarda Fm. is a grossly unsorted, matrix-supported diamictite with grain sizes between silt fraction and metersized clasts and a big intercalated megablock. Strong clast deformations and abundant shock metam...
http://www.impact-structures.com, 2019
The Pelarda Formation (Fm.), located in the Iberian System in northeast Spain, is a sedimentary deposit with an extension of roughly 12 km x 2.5 km and an estimated thickness of no more than 400 m. The formation was first recognized as a peculiar unit in the early seventies and underwent interpretations like a fluvial or an alluvial fan deposit having a postulated age between Paleogene and Quaternary. Since the early nineties the Pelarda Formation has been considered an impact ejecta deposit originating from the large ca. 40 km-diameter Azuara impact structure and meanwhile being among the largest and most prominent terrestrial impact ejecta occurrences, which however is questioned by regional geologists still defending the fluvial and alluvial fan models. Roughly speaking, the Pelarda Fm. is a grossly unsorted, matrix-supported diamictite with grain sizes between silt fraction and meter-sized clasts and a big intercalated megablock. Strong clast deformations and abundant shock metamorphic effects like planar deformation features (PDF) are observed throughout the Pelarda F. deposit compatible with its impact ejecta origin. Aligned bigger clasts and smaller intercalated bands of sandstones, siltstones and clayey material indicate some local stratification obviously adjusted to flow processes within the impact ejecta curtain. This suggests that gravitational flows predominated in a transport by water in both liquid and gas states. Transport and deposition as a kind of pyroclastic surge are discussed. A sketch sequence describes the emplacement process of the Pelarda Fm. as 2 part of the Azuara crater formation and the integration in the general frame of pre-impact geology and some post-impact layering.
Geology, 2002
Quartzite cobbles in Lower Triassic Buntsandstein conglomerates from northeastern Spain display unusual millimeter-to centimeter-sized circular craters, commonly having central mounds and surrounded by radial fractures. The conglomerates are also marked by intense fracturing down to microscopic scale. These features have traditionally been attributed to tectonic compression and pressure dissolution at cobble contacts. Sections through the cratered cobbles reveal pervasive internal fracturing, segments detached along concave spall fractures, and zones marked by quartz grains with planar deformation features. Comparison with results of impact experiments on artificial conglomerates suggests that these features were produced by internal accelerations, grain collisions, and spallation related to shock-wave propagation through inhomogeneous deposits. The proximity of the outcrops to the Azuara and proposed Rubielos de la Cérida impact structures suggests that shock deformation of conglomerates can provide an easily recognizable regional impact signature.
Abstracts, 6th ESF IMPACT workshop, Impact Markers in the Stratigraphic record, pp. 15-16, 2001, 2001
The Puerto Mínguez ( ) was first described as the location of an "enigmatic" deposit of Paleozoic quartzite clasts [1]. By road construction meanwhile continuously exposed over 5 km length, the deposit is now considered part of an enormous impact ejecta blanket around the Azuara and Rubielos de la Cérida twin impact structures 3].
ERNSTSON CLAUDIN IMPACT STRUCTURES – METEORITE CRATERS Research on impact geology, geophysics, petrology, and impact cratering, 2022
In an abstract paper presented at the EPSC 2022 Granada (Europlanet Sociey) the authors above from Spain, Sweden and Denmark report about research on what they called the first impact structure in Spain. Numerous media reports about this “first impact structure in Spain” immediately after the meeting suggest that this formulation was directly put into the world by the authors in a press release and that they thereby commit a bad falsification by not mentioning the worldwide prominent gigantic Azuara impact event with the 40 km-diameter Azuara impact structure and the Rubielos de la Cérida impact basin measuring approx. 80 km x 40 km, which has been established for more than 20 years, and, hence, declaring it as non-existent. We report here on key stages of the study of these really first Spanish impact structures since 1985, comment this massive expression of scientific dishonesty, and bring for all less informed and the media-believing people a compilation of the innumerable extremely easily in the Internet accessible contributions in English, Spanish and German, which leads the statement of the alleged first impact structure in Spain ad absurdum.