The editorial board of the journal Geosciences announces the publication of a special issue on the topic of terrestrial impacts and impact structures and would welcome submissions of research articles, review articles, and short communications alike.
on the EPSC 2022 Meeting abstract paper of Juan Antonio Sánchez Garrido, Jens Olof Ormö, Carl Alwmark, Sanna Alwmark, Gabriel Zachen, Robert Lilljequist, and Sebastián Tomás Sánchez Gómez : A probable impact structure in Betic Cordillera, Almeria, SE Spain.
and its relation to the Azuara impact event comprising the Azuara impact structure and the Rubielos de la Cérida impact basin (Spain)
by Kord Ernstson1 and Ferran M. Claudin2
Abstract.- 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.
1 University of Würzburg, 97074 Würzburg (Germany); firstname.lastname@example.org; 2 Associate Geological Museum Barcelona (Spain); email@example.com
Keywords: Azuara impact event, Azuara impact structure, Rubielos de la Cérida impact basin, Spain, Almería impact, manipulation of science
At the recently concluded EPSC 2022 meeting in Granada, authors Juan Antonio Sánchez Garrido, Jens Olof Ormö, Carl Alwmark, Sanna Alwmark, Gabriel Zachen, and Sebastián Tomás Sánchez Gómez (University of Almería, Centro Astrobiología, Madrid, Lund University (Sweden), and University of Copenhagen) and Eurogeologist Robert Lilljequist had an abstract contribution entitled “A probable impact structure in Betic Cordillera, Almeria, SE Spain.”
The “probable impact” of the paper is based on a polymict breccia clast and three quartz grains with weak PDF but without any confirmation of cristallographic orientation, and with no further shock metamorphism. After 15-20 years of their research, no word on regional geology, no geophysics, no shatter cones, no impact melt, no impact glasses, no ejecta deposits, no drilling on the presumed impact basement.
We do not want to question the possible evidence of an impact in Almería. What we characterize as dirty science is the fact that immediately after the meeting a large number of media are writing in unison about the FIRST impact structure in Spain:
— First probable impact crater discovered in Spain (phys.org).
— Researchers believe they have discovered the first impact crater in Spain in Almería (time.news).
–First Probable Impact Crater Discovered in Spain (europlanet society.
–First probable impact crater discovered in Spain (Alphagalileo).
— Researchers believe they have discovered the first impact crater in Spain in Almería (Chicago Today).
— First Probable Impact Crater Discovered in Spain (Toptek News).
— Discovered the first possible impact crater by meteorite in Spain (spainsnews) — Discovered the first probable impact crater in Spain (daily-how)
… and many others.
This mass of reports about the FIRST Spanish impact structure has probably been initiated by the media by a press release of the authors of the abstract, and this is exactly what we call dirty science that these authors talk against better knowledge and rather infamously about the FIRST impact structure in Spain. We stand by the word “infamously”, which we will justify in detail below.
2 The current state of research of the established Azuara multiple impact event with the Azuara impact structure and the Rubielos de la Cérida impact basin in the provinces of Zaragoza and Teruel (Spain)
Since the first publication about the impact origin of the Azuara impact in 1985 in Earth and Planetary Science Letters followed by a dozen of diploma and doctoral theses, and the publications in 2001 and 2002 on the meanwhile established Azuara and Rubielos de la Cérida twin impacts, a host of impact-typical proofs have been published having made this Spanish impact to one of the most prominent impact events worldwide. The importance is underlined by the very easy access (frequently simply by car) to a hundred of outcrops or more, where the impact can be experienced up close, and spectacular samples can be obtained effortlessly – in contrast, for example, to the Chicxulub impact, where comparably significant samples are only tangible via kilometer-deep drillings. We list the scientifically most important findings:
— a roughly 40 km-diameter Azuara impact structure with roundish morphological signature
— a roughly 80 km x 40 km-size Rubielos de la Cérida multiple impact basin with impressive elongated basin morphology and a significant central uplift chain
— geophysical, gravity and geomagnetic, signature
In both structures:
— in part brilliantly exposed impact “tectonics” of impressive folds and faults, also documenting the everywhere occurring indication of tensile impact shock rarefaction signature
— a host of impact monomictic and polymictic impact breccias everywhere frequently showing multiple breccia generations typical of impact
— extended suevite breccias
— well-known and unusal impact melt rocks and glasses
— a host of monomictic and polymictic breccia dikes forming dike generations and extended breccia dike systems not known in this impressive concentration from other impacts worldwide
— a host of impact megabreccias (the large Pelarda Fm. ejecta deposit – Azuara; the large Puerto Mínguez ejecta deposit – Rubielos de Cerida; the prominent megabreccias of Barrachina, Belchite/Almonacid de la Cuba and Herrera)
— abundantly exposed accretionary lapillistones
— shatter cones
— strong shock metamorphism: shock melt, diaplectic glass from quartz and feldspar; planar deformation features PDFs in quartz and feldspar, multiple sets of planar fractures PFs in quartz, multiple sets in strongly kinked quartz and mica, multiple sets of microtwinning in calcite
Proofs for all these impact-realated features are published and are easily accessed on clicking the vast of Internet contributions listed below.
3 Lists of early and recent publications on the Spanish impact structures
… and several dozens, maybe more than 100, of WIKIPEDIA URLs for Google “azuara impact” and Rubielos de la Cérida impact” and “Spain impact structures”.
3.2 WEBSITES. pertinent
33 publications about the Spanish impact structures Azuara and Rubielos de la Cerida addressed in Researchgate
2 Research Projects on the Spanish Azuara and Rubielos de la Cérida impacts
22 publications about the Spanish impact structures Azuara and Rubielos de la Cerida addressed in Researchgate
2 Research Projects on the Spanish Azuara and Rubielos de la Cérida impacts
3.4 Recent publications (2012-2022) of Ernstson and Claudin on the Spanish impact event, the Azuara impact structure and the Rubielos de la Cérida impact basin.
3.5 A few early publications
Ernstson, K., Schüssler, U., Claudin, F., Ernstson, T., 2003: An Impact Crater Chain in Northern Spain. – Meteorite, 9, 35-39.
Claudin, F. and Ernstson, K. (2003): Geologia planetaria y Geologia regional: el debate sobre un impacto múltiple en aragón. Enseñanza de las ciencias de la Tierra, vol 11, nº 3, pp 202-212.
Schüssler, U., Hradil, K., Ernstson, K.2002: Impact-related melting of sedimentary target rocks of the Rubielos de la Cérida structure in Spain. Berichte der Deutschen Mineralogischen Gesellschaft, Beiheft 1 zum European Journal of Mineralogy, Vol. 14, S. 149.
Ernstson, K., Claudin, F., Schüssler, U., Hradil, K., 2002: The mid-Tertiary Azuara and Rubielos de la Cérida paired imapct structures (Spain). Treb. Mus. Geol. Barcelona, 11, 5-65.
Ernstson, K., Rampino, M.R. & Hiltl, M.: Cratered of cobbles in Triassic Buntsandstein conglomerates in NE Spain: Shock deformation of in-situ deposits in the vicinity of large impacts. Geology, v. 29, no.1, 11-14, 2001
Hradil, K., Schüssler, U., and Ernstson, K.: Silicate, phosphate and carbonate melts as indicators for an impact-related high-temperature influence on sedimentary rocks of the Rubielos de la Cérida structure, Spain. Abstracts, 6th ESF IMPACT workshop, Impact Markers in the Stratigraphic record, pp. 49-50, 2001.
Ernstson, K., Rampino, M.R., and Hiltl, M.: Shock-induced spallation in Triassic Buntsandstein conglomerates (Spain): an impact marker in the vicinity of large impacts. Abstracts, 6th ESF IMPACT workshop, Impact Markers in the Stratigraphic record, pp. 25-26, 2001.
Ernstson, K., Claudin, F., Schüssler, U., Anguita, F, and Ernstson, T.: Impact melt rocks, shock metamorphism, and structural features in the Rubielos de la Cérida structure, Spain: evidence of a companion to the Azuara impact structure. Abstracts, 6th ESF IMPACT workshop, Impact Markers in the Stratigraphic record, pp. 23-24, 2001.
Ernstson, K., Rampino, M.R., Anguita, F., Hiltl, M., and Siegert, I.: Shock deformation of autochthonous conglomerates near the Azuara impact structure, Spain: Geological Society of America Abstracts with Program, v. 31, p. A-122., 1999.
Ernstson, K. & Claudin, F.: Pelarda Formation (Eastern Iberian Cains, NE Spain): Ejecta of the Azuara impact structure. – N.Jb.Geol.Paläont.Mh., 1990, 581-599, 1990.
Müller, H. & Ernstson, K.: Curved joint sets: Indication of impact-induced fracturing. – In: Mechanics of Jointed and Faulted Rock, H.P.Rossmanith, ed., 257-263, Balkema, Rotterdam 1990.
Ernstson, K.: Looking for Geological Catastrophes: The Azuara Impact Case. – In: Extinción y registro fósil (Extinction and the fossil record, E. Molina, ed.), Cuadernos Interdisciplinares No. 5, 31-57, SIUZ, 1994.
Ernstson, K. & Fiebag, J.: The Azuara impact structure (Spain): new insights from geophysical and geological investigations. – Int. J. Earth Sci., 81/2, 403-427, 1992.
Ernstson, K., Feld, H. & Fiebag, J.: Impact hypothesis for the Azuara structure (Spain) strengthened. – Meteoritical Society Meeting, Newcastle upon Tyne, 1987. – Meteoritics, 22, 373, 1987.
Ernstson, K., Hamman, W., Fiebag, J. & Graup, G.: Evidence of an impact origin for the Azuara structure (Spain). – Earth Planet. Sci. Let., 74, 361-370, 1985.
The discovery and scientific treatment of the Spanish impact structures has a long history of about 40 years. In 1981, the first field work began in the province of Zaragoza near the village of Azuara, which, together with initial mineralogical studies at the University of Würzburg, resulted in the first publication in Earth and Planetary Science Letters in 1985. As evidence for the impact was considered already at that time the unmistakable finding of PDFs in quartz, for which the spectrum with the typical crystallographic directions of the shock metamorphism from breccias (Fig. 1) of the also already morphologically addressed Azuara structure. Two years later in 1987, Azuara was already listed as a proven impact structure in the book of Richard A.F. Grieve TERRESTRIAl IMPACT STRUCTURES “Annual Review of Earth and Planetary Sciences” and subsequently included in the Canadian Impact Database under the direction of R.A.F. Grieve as a proven impact. R.A.F. Grieve will be mentioned also later. Further articles on the Azuara impact followed in international journals. This remained generally accepted knowledge in the impact community. Until 1996.
In an abstract article of the LPSC Langenhorst & Deutsch (1996) claim [The Azuara and Rubielos structures, Spain: Twin impact craters or Alpine thrust systems? TEM investigations on deformed quartz disprove shock origin (abstract). Lunar and Planetary Science, v. XXVII: 725-726] that there is no evidence of shock in the Azuara impact structure. They base this claim solely on the TEM analysis of a sample given to them by one of the present authors (K.E.). However, this sample did not come from the Azuara structure at all, but was taken far outside the structure. Furthermore, Langenhorst & Deutsch had not taken note at all of the exact description (given to them by K.E.) of the sample, which shows basal deformation lamellae, but not at all planar deformation features (PDF). Although K.E. had insistently pointed out the elementary mistake to the authors, Langenhorst & Deutsch did not withdraw the contribution, which would have been possible. The two authors were then accused of scientific dishonesty.
Fig. 1. PDF diagram from the first publication 1985 on the Azuara impact proving impact shock deformation.
The consequences continue to this day. This abstract was promptly the trigger of the manifold unpleasant campaigns especially by geologists of the University of Zaragoza and the Spanish Geological Survey, who vehemently denied an existence of the impact structures. This was understandable especially against the background that practically all these geologists had made and published their thick doctoral theses exactly in the impact areas, without recognizing such significant eye-catching geological impact findings. Such controversies are known from the whole impact research.
A new phase of the fight against the huge Spanish impact event started around the year 2000. An article by Ernstson, K., Claudin, F., Schüssler, U., Hradil, K.: “The mid-Tertiary Azuara and Rubielos de la Cérida paired impact structures (Spain)”, submitted to the journal Earth and Planetary Science Letters, was rejected by the peer reviewers C. Koeberl and R.A.F. Grieve, by Koeberl with partly absurd falsifications of the text statements. In an adapted 60 pages version, this article was then published in 2002 in the series of the Geological Museum of Barcelona (see above), without this work ever being cited by the Spanish opposing authors.
At the 2001 meeting of the 6th ESF IMPACT workshop in Granada, Impact Markers in the Stratigraphic Record, four poster papers by different authors (cited above) on the Azuara and Rubielos de la Cérida impacts were presented. At a subsequent associated discussion, Dr. Therriault of the Canadian Geological Service had presented her written analysis, initiated by Prof. Anguita (Madrid) and Dr. Rampino (New York), on 31 pages, of a large number of shocked quartz grains from Azuara impact breccias with all the strictly known features of PDFs: Therriault, A. (2000): Report on Azuara, Spain, PDFs, 31 p. In the session she oddly enough presented the PDFs as uncertain, apparently on instruction “from above”. Her fantastically good work can still be consulted today.
At that time there was the next cut. The Canadian Impact Database from the Survey moved to the University of New Brunswick under the new leadership of John Spray. And suddenly the Azuara structure had disappeared from the database and has not been reinstalled in it to this day, not to mention the magnificent multiple Rubielos de la Cérida impact basin, which has also never before been included in the Earth Impact database despite overwhelming published impact evidence. We estimate that in this database over 90% of the impact structures considered proven there do not have this extent of impact evidence of geology, geochemistry, mineralogy-petrography, geophysics and schock metamorphism as is the case for the great Spanish impact event. Characteristic of John Spray’s odd understanding of science: In a written inquiry Ferran Claudin asked him why the Azuara structure formerly established as a proven impact had been eliminated and disqualified from the data base and why also Rubielos de la Cérida despite overwhelming impact evidence has not been recorded. Moreover, Ferran offered to send him reprints of all published articles on the impacts. John Spray wrote back that Ferran were free to do it but that he, John Spray, would not read the articles.
According to the Database Website, major contributions to the development of earlier versions of this database have been made by Richard Grieve and James Whitehead. This is a circumstance that leaves us perplexed that Richard Grieve, who was the first important impact researcher to qualify the Azuara impact as confirmed and proven and absolutely worthy for the Canadian database until 2001 (rightly so), tolerates to this day, despite his closeness to the database, that both Azuara and Rubielos de Cérida are swept under the table by a small clique from the so-called impact community as impact-wise very questionable and not confirmed, still after 40 years of research.
And this is exactly the point with which we want to close the discussion and return to Almería. Because on this concealment of the Spanish Azuara and Rubielos de la Cérída impacts in the Earth impact database until today, in the entire newer Spanisch geological literature including newest text books, the Azuara impact event is nowhere quoted, also not with any counterarguments. And again and again reviewers of impact journal articles demand from the authors that references to the Spanish impacts are taken out with the reason that the Earth Impact Datenbase does not recognize them. Against this background, the Almería authors have of course a carte blanche to publish their assumed crater as the first one in Spain.
The first conclusion is not directly about science, but about the media and their reporters who trumpet questionable “messages” without the slightest researche. Apart from the Internet articles listed at the beginning, the inglorious article by Lydia Lawson in techupdate should be mentioned in particular. Although on the one hand she meritoriously deals critically to skeptically with the message about the Almería structure, on the other hand she refers in a single sentence to the discussion about the Azuara impact in 1997 (i.e. 25 (!) years ago) and to the fact that an impact formation is excluded today. This is clearly pretty bad science journalism. We probably hope in vain that the authors of the Web papers mentioned here will present things correctly and apologize to their readers for the dubious “snap judgments”.
Second: Around the early 2000’s, when Azuara and Rubielos de la Cérida had long been treated as print and extensively on the Internet, a strong desire to do their geological fieldwork for their master’s and doctoral exam papers arose among many students of geology at Spanish universities who were, of course, already well informed via the Internet about the exciting and forward-looking research being done there. We have been told by the University of Madrid that students who expressed this wish were told in no uncertain terms: If you ever want to make a career in geology, just don’t do your exam papers in these structures.
We fear that this has not changed to this day; we have not become aware of any such work, although there are still a vast number of geologically-mineralogically highly attractive topics awaiting further work. We wonder if this deplorable behavior within the “impact community” (we will refrain from naming well-known persons and names) makes those responsibles aware that they are not only causing and have caused immeasurable damage to impact research in general, but also are preventing young people eager to produce new significant research results in an exciting field from doing so. Irresponsible that is.
Click the ePoster – Galery: Meteoritical Society Meeting Glasgow 2022 – See details by enlarging the PDF.
Anonymous reviewers from the LPI have rejected the following two abstracts submitted to the 13th Planetary Crater Consortium 2022 Meeting:
A Probable Holocene Meteorite Crater Strewn Field in Lower Franconia (Germany): Evidence from Digital Terrain Models and Geophysical Surveys (GPR, Electrical Imaging, Geomagnetics)” by J. Poßekel, G. Schulz-Hertlein, T. Ernstson & K. Ernstson
Click to enlarge.
Pingos and Mardels: High- Resolution Digital Terrain Models Suggest Meteorite Impact Craters in Addition to Permafrost, Sinkhole and Dead-Ice Formation Models” by K. Ernstson & J. Poßekel
Click to enlarge.
The reader of these reasons may make his/her own thoughts.
Those who read the justifications will have to conclude that the LPI reviewers have obviously not yet arrived in the 21st century and are not (or do not want to be) familiar with the latest impact literature.
Contributions to the Saarland (Saarlouis/Nalbach), Steinheim, Singra-Jiloca, Czech and Salt Lake impacts: (peer-reviewed abstracts and iPoster Gallery)
THE PROPOSED METEORITE IMPACT EVENT IN THE CZECH REPUBLIC: EVIDENCE STRENGTHENED BY INVESTIGATIONS WITH THE DIGITAL TERRAIN MODEL J. Poßekel, M. Molnár, and K. Ernstson
SHATTER CONES IN LITERMONT QUARTZITES: SAARLOUIS/NALBACH (SAARLAND, GERMANY) METEORITE IMPACT EVENT STRENGTHENED. U. Siegel, J. Rommelfangen, W. Müller, S. Michelbacher and K. Ernstson
TRANSPRESSION AND TRANSTENSION IMPACT CRATERING FEATURES: THE STEINHEIM, SAARLOUIS (BOTH GERMANY) AND SINGRA-JILOCA (SPAIN) CASES. K. Ernstson and F. Claudin
Secondary cratering on Earth: The Wyoming impact crater field: More than three question marks. – Comment on the Kenkmann et al. article (GSA Bulletin).
Kord Ernstson, Hans-Peter Matheisl, Jens Poßekel and Michael A. Rappenglück
A short version has been accepted as an abstract paper (for poster presentation) for the 85th Annual Meeting of the Meteoritical Society 2022 in Glasgow, Scotland (6079.pdf, LPI Contrib. No. 2695):
Abstract, table of contents and the full article follow here directly for reading.
Abstract. – Secondary craters in impacts on moon, planets and their moons are a well known phenomenon, which has been investigated many times. In the article commented by us here, the authors report on a crater strewn field in the American state of Wyoming, which is interpreted as a field of secondary craters of a so far unknown larger primary impact structure and as a first on Earth. We compare the Wyoming crater strewn field with the Chiemgau impact crater strewn field in SE Germany and find that both have nearly identical characteristics of virtually all relevant features, in terms of geometries and petrography. We conclude that the alleged Wyoming secondary crater field is a fiction and the craters attributable to a primary impact. The alleged evidence is very poor to easily refuted. A primary crater does not exist to this day. The negative free-air gravity anomaly referred to, but not even shown, is invalid for this purpose. The Bouguer gravity map shows no indication of a possible large impact structure. Also unsuitable is the use of asymmetries with elongations of assumed secondary craters with a very questionable corridor intersection for the ejecta. Of 31 craters surveyed as proven, 15 are circular (eccentricity 1) and more than half (19) have an eccentricity ≤1.2. Circular and elongated craters are intermixed. The evaluated crater axes may just as well originate in a multiple primary impact. Elongated craters may also result from doublets of overlapping craters that are no longer fresh, as described by the authors themselves. In their paper, the authors do not show a Digital Terrain Model with contour lines for any of the surveyed craters, but only aerial photos blurred by vegetation. A verification of the crater measurements with the deduced eccentricities and strike directions is impossible. Not a single topographic profile over even a single crater in the strewn field is shown, either from DTM data or from an optical leveling, which could have been accomplished in an instant given the relatively small craters. Grave is the misconception that such a large crater field of 90 km length with four separate clusters is not possible according to 20 years old model calculations. A primary impact with multiple projectiles could perhaps be conceivable under rare circumstances, which are described by the authors as not relevant. The alleged impossibility of such a large primary strewn field with referring to the known small impact fields of Morasko, Odessa, Wabar, Henbury, Sikhote Alin, Kaalijärv, and Macha is contradicted by the three larger impact strewn fields of Campo del Cielo, Bajada del Diablo (very likely), and Chiemgau, which are best described in the literature but are not mentioned by Kenkmann et al. with a single word. The comparison of the Wyoming strewn field with the Chiemgau impact crater strewn field of about the same size here in the commentary article proves the scientifically clearly much greater significance of the Chiemgau impact, which must be considered as currently the largest and most significant Holocene impact despite the rejection and ignoring in some parts of the so-called impact community.
GSA Bulletin Kenkmann et al. article. (Kenkmann, T., Müller, L., Fraser, A., Cook, D., Sundell, K., and Rae, A.S.P)
Article Editors: Rob Strachan, W.U. Reimold
Key Words: secondary impact cratering, Wyoming, Chiemgau impact, impact crater strewn fields, Bajada del Diablo, Campo del Cielo
At this year’s LPSC, there have been two iPoster contributions to the Steinheim Ìmpaktkrater. It is about the alleged time difference between the impacts of Ries and Steinheim Basin (articles Buchner et al. 2020). In the LPSC article the authors Schmedemann and Hiesinger show that depending on plausible assumptions of the statistics the probability of a non-simultaneous impact is in the per mille range. A separate impact is therefore described as extremely unlikely.
The second LPSC contribution takes up in this context once more the topic of the small pseudo impact of the Steinheim Basin, which is used in the so-called “impact community” against actually better knowledge further everywhere in the impact literature with consistently wrong results.
Lacquer print from the wall of a quarry in Dřenice near Cheb in West Bohemia (Czech Republic). It is a river sediment, probably of Pliocene age. The rusty part is discolored by limonite and goethite. Rarely moldavites occur in it. The black part is discolored by psilomelane. 56 cm x 56 cm.
Impact feature: thermal shock in quartz
Using shock effects in quartz as an impact indicator has a long tradition. They are created in the first phase of impact cratering (contact and compression phase) and produce well known PDFs, PFs and diaplectic glasses in various minerals. The fact that thermal shock has so far been virtually ignored in impact research is due to the fact that the effects mentioned above precede thermal shock during pressure release. However, if extreme shock pressures lead to melting and vaporization of the rocks (> roughly 50 GPa), violent thermal shock can occur when slightly or not at all shocked material is immersed in melt and/or vapor. In anticipation of a publication, some photomicrographs of isolated quartz grains from meteorite impact sites are shown here, which have obviously experienced such a short thermal shock and reveal quite unusual micro-fracturing patterns.
Photomicrographs (crossed polarizers): Isolated quartz grains (size about 1 mm) “floating” in a fine grained matrix. In many of the grains this micro-fracturing is more or less sharply limited to a concentric rim zone encasing a largely untouched core with a few sub-planar fractures in some cases. Chrudim impact, Czech Republic.
Quartz grains from the same impact site showing irregular micro-fracturing that merges into sets of planar fractures (PF) after the rhombohedron.
Saarland impact: Quartz grains in impact melt nearly pulverized by extreme micro-fracturing.
Sanchez, M.A. ; Gil, A. y Simón, J.L. (2017): Las rocas de falla del cabalgamiento de Daroca (sector central de la Cordillera Ibérica): Interpretación reológica y cinemática. Geogaceta, 61: 75-78. (http://www.sociedadgeologica.es/archivos/geogacetas/geo61/geo61_19p75_78.pdf)
Casas-Sainz, A.M., Gil-Imaz, A., Simón, J.L., Izquierdo Llavall, Aldega, E.L., Román-Berdiel, T., Osácar, M.C., Pueyo-Anchuela, O., Ansón, M., García-Lasanta, C., Corrado, S., Invernizzi, C., Caricchi, C. (2018): Strain indicators and magnetic fabric in intraplate fault zones: Case study of Daroca thrust, Iberian Chain, Spain. Tectonophysics, 730: 29-47 (10.1016/j.tecto.2018.02.013) (https://zaguan.unizar.es/record/78325/files/texto_completo.pdf
Gutierrez, F, Carbonela, D., Sevil, J., Moreno, D., Linares, R, Comas, X., Zarroca, M., Roqué,C., McCalpin, J.P. (2020): Neotectonics and late Holocene paleoseismic evidence in the Plio-Quaternary Daroca Half-graben, Iberian Chain, NE Spain. Implications for fault sorce characterization. Journal of Structural Geology, 131: 1-17 (https://doi.org/10.1016/j.jsg.2019.103933)
by Ferran Claudin & Kord Ernstson (March 2020)
The town of Daroca in the Spanish Province of Zaragoza hides a peculiar geologic scenario – an enigma for geologists from time out of mind. Being enthroned above the town the geologic stratigraphy shows with a very sharp cut Cambrian dolomite (Ribota dolomite) over Tertiary young sediments (Fig. A). Older layers over younger ones are not uncommon in geology, and overthrust and thrust faulting are related processes. But Daroca is different. The Cambrian plate is kilometer-sized and fragmented into larger blocks, and a Tertiary 180° overtrust can reasonably be excluded. Early geologists confronted with the situation in sheer desperation thought of a preexisting Cambrian autochthonous plate and a vast undercutting by the Tertiary. Today this explanation is left out of consideration and simple thrust faulting is being favored. But the case is all but simple. There is no root zone and not any relief from where the giant plate could have started to override the Tertiary around Daroca. Nevertheless, the thrust kinematics are developed further by geologists (e.g., Capote et al. 2002), and tens of kilometers long faults are drawn within models of syn-tectonic sedimentation (Casas et al. 2000; Fig. 3).
Fig. A. The prominent Daroca exposure.
In 2012 we published an extended article (Claudin and Ernstson 2012) under the title “Azuara impact structure: The Daroca thrust geologic enigma – solved? A Ries impact structure analog“.. which proposes a new and in our opinion reasonable model of formation and a physically plausible solution of the enigma. To cut the story short, the Daroca thrust originated in the meanwhile generally established Azuara impact event, when according to the spall plate model of Melosh (1989) the Daroca Ribota dolomite plate started from the developing excavation crater and the near-surface interference zone with extreme velocity (Fig. B), supported by enormous volumes of rock melt, water and gases (water vapor and carbon dioxide from the shocked target) as a kind of hovercraft. This is no speculation but has much earlier been discussed for the so-called role-and-glide mode in the excavation process of the Ries impact crater (Germany). In our paper on the Daroca thrust we write about the affinity of both events and point to Ries giant megablocks having been excavated and transported over enormous distances.
In the case of the Daroca thrust this impressive way of transport can so nicely and conclusively be observed on the geological general map 1 : 200 000, sheet Daroca, which we show in simplified manner below (Fig. B) and in a copy of the geological map in Fig. 11 of the Spanish complete version).
Fig. B. The impact cratering model for the Daroca thrust – no intraplate fault zone (see text).
We do not know with certainty whether the authors of the three papers have read our paper and whether they have understood the herein presented simple explanation, but strangely enough since the publication of our paper on the Daroca thrust with the close relation to the Azuara impact structure, practically “overnight” a series of publications has appeared to demonstrate that the Daroca thrust has a normal tectonic fault origin, after not any geologist from Spain or elsewhere had paid attention to the enigma for decades (apart from the Casas et al. (2000) and Capote et al. (2002) papers, only seeing a tectonic fault despite all non-tectonic field evidence).
Of course, science thrives on controversy on certain topics and especially on new discoveries and models, but one principle is that the different views should be on a scientific level and that both views should be carefully discussed and balanced.
In all three papers we miss the observance of this basic scientific constitution. Not a single word is used to mention the Daroca article and the Azuara impact structure in general, and not a single one of the abundant publications on one of the most spectacular geological scenarios in Spain is found in their works. Today the Internet is a common medium and broadly used to get information about serious scientific publications (ResearchGate e.g.), and on preparing their papers a few clicks by the authors of the three papers had of course opened a host of literature about the Azuara impact event and the Daroca thrust.
In principle our Comment article could therefore end here. But we do not want to make the same omission ignoring the papers under discussion here. In the main part of our Comment paper following below, F. Claudin has compiled an exhaustive analysis of the three Daroca “tectonic” papers confronting their in many respects rather questionable claims with standard geologic literature and with the impressive meteorite impact-related features, once more described here point by point with a host of figures that do not exist for the authors.
Exemplarily, one point of importance is addressed already here, the Casas-Sainz et. al. paper about magnetic fabric from AMS (anisotropy of magnetic susceptibility) and strain indicators. From the text we learn that magnetic AMS analyses were performed at 6 sites, but only a single one (no.16) is located in Daroca at the thrust exposure (their Fig. 2A). Since the site is navigated at fractures of a second, we have to proceed from a spot analysis (their Table. 1), and the rock for 12 specimen measurements is described as a fault microbreccia (their Table 3). The rest of the 5 AMS sites is located roughly 1 km southeast of Daroca (their Fig. 2A).
We imagine: For the Daroca thrust as described in very detail in our paper (Claudin & Ernstson 2012), a spot few meters sized at best served for an AMS analysis of a microbreccia (we assume of Ribota dolomite) for which it is obviously not known when it acquired the brecciation and a resulting AMS texture.
Considering now the Daroca thrust impact model of an enormously dislocated spall plate, which Casas-Sainz et al. completely ignore, what will a point AMS tell us about old in situ tectonics and intraplate fault zones? Nothing. The Daroca plate may have transported magnetic textures from its original place more than 10 km to the east, intense brecciation and other deformation (which can be seen in Daroca outcrops) in the excavation, ejection, transport and emplacement processes should have produced a completely new texture, not to forget possible strong temperature overprint in the impact cratering process.
The same holds true for the five other sites of AMS analyses. Since the aim and outcome of the paper is basically the AMS of the thrust zone, more than a little methodological insight into the authors’ working cannot be recognized. The paper of Gutierrez et al. (2020) does not differ in any way in this respect. Their ground penetrating radar (GPR) and resistivity measurements at Daroca are good to look at, but for the topic under discussion they are absolutely meaningless. The idea arises that the visual impression of scientific evidence for the so-called Daroca Half-graben is to be created by the pure application of a few geophysical measurements on a very small area.