Claudin, F. and Ernstson, K. (2004): Comment on
TRIASSIC CRATERED COBBLES: SHOCK EFFECTS OR TECTONIC PRESSURE? by M.G. Shapman, M.A. Evans, and J.F. McHone
In the article written by M.G.Shapman, M.A. Evans, and J.F.McHone, the suggested shock deformation of three Triassic conglomeratic deposits as contrasting with traditional models (pressure dissolution, tectonic/overburden stress) is discussed. As we never investigated the Upper Triassic Shinarump and the Upper Triassic Quaco Fm. conglomeratic deposits, we are not able to comment on the critical discussion of the deformed cobbles.
This is different for the Buntsandstein conglomerates surrounding the Azuara and Rubielos de la Cérida doublet impact structure in northern Spain. We made a detailed field study of the deposits and performed a petrographic analysis with a host of sections and thin sections of the deformed cobbles. Thermomicrometrical analyses of fluid inclusions were added. Moreover, we made shock experiments on artifical conglomerates. The results have been published (Ernstson et al. 2001a, b; download: http://pubs.giss.nasa.gov/docs/2001/2001_Ernstson_etal.pdf), and, moreover, the whole complex is lengthily and in detail discussed in the web on http://www.impact-structures.com/impact-spain/shock-deformation-in-triassic-buntsandstein-conglomerates-spain/. From these investigations, a deformation process other than by impact shock can practically be excluded.
Unfortunately, Shapman et al. do not refer to these basic conclusions but prefer to refer to critics of the Spanish impacts and of the shock-deformation model for the Buntsandstein conglomerates. This is used to support their critical view of the impact origin for the Shinarump and Quaco Fm. deformations – different from what we consider to be sound and honest scientific argumentation. In the following, we exemplify our point of view.
1. Shapman et al. refer to percussion marks, radial fractures and halos to be observed on the cobbles of the three deposits, but they do not mention the basic deformation of the Spanish quartzite cobbles: deformation by spallation. Spallation, well known from fracture mechanics, results from dynamic deformation by shock pulses. Details can be read and seen in the Geology article (Ernstson et al. 2001; download:http://pubs.giss.nasa.gov/docs/2001/2001_Ernstson_etal.pdf ) and on http://www.impact-structures.com/spain/shocked.htm . Did Shapman et al. forget to mention spallation because it is incompatible with tectonic deformation and pressure dissolution?
2. Shapman et al. refer to the Discussion paper by H. Stel, H.Rondeel and J.Smit in the Geology Forum (Stel et al. 2002). In this paper, Stel et al. doubt that the deformed Buntsandstein cobbles are generally related with the Azuara/Rubielos de la Cérida impact. Thus, Shapman et al. are practising bad scientific style while referring to the Discussion paper but completely ignoring the respective Reply paper (Ernstson & Hiltl 2002). In the Reply paper, Ernstson and Hiltl discuss the arguments presented by Stel et al. and they prove them wrong point by point. Some of the arguments presented by Stel et al. are considered to even support the impact evidence.
3. Evidently, Shapman et al. are knowing the papers on the Azuara and Rubielos de la Cérida impact structures by hearsay only. Different from their reference, the Rubielos de la Cérida impact structure has never been mentioned in the Ernstson et al. (1985) EPSL paper. Different from their age statement, Azuara and Rubielos de la Cérida have never been suggested to be Late Tertiary impact structures. In all published papers, an Upper Eocene or Oligocene age is proposed.
4. Shapman et al. refer to several efforts in the past to bring discredit on the Spanish impact structures, despite the clear impact evidence strong shock metamorphism included.
In the first place, we mention Spanish geologists from the Zaragoza university and the Madrid Center of Astrobiology. They have been working in the impact region and published quite a few models for the Tertiary regional geology but did not recognize the omnipresent impact evidence. So, we can comprehend that they try to defend their models. This resulted in the submission of a paper to Meteoritics and Planetary Science – MAPS – (Cortés et al. 2002) referred to also by Shapman et al. The mystery why this paper of such a quality was accepted and printed by MAPS is unsolved until today. This holds true also for the paper by Diaz-Martínez et al. (2002). Both papers and the enigmatic attendant circumstances of their publication are addressed here:
and in more detail here:
In the Montanary & Koeberl (2000) paper referred to by Shapman et al., Azuara – after 15 years existence as an established impact structure – surprisingly has «disappeared». As far as we know, the authors Montanary and Koeberl never put their foot on Azuara terrain, they never had Azuara impact rocks in hand, and they never made any thin-section inspection of Azuara shock metamorphism. Enigmatic and mysterious …. There is of course the story about the Langenhorst & Deutsch (1995) paper on the TEM analysis of an Azuara sample from outside the impact structure. From this single analysis, Langenhorst and Deutsch – in a study of scientific acumen and efficiency without precedent – concluded that there is no shock in the Azuara structure ignoring all previously published papers on shock effects in polymictic breccias from within the Azuara structure. They also refused to withdraw the paper although having been informed about their mistake. This was the reason why Langenhorst and Deutsch were reproached with scientific dishonesty. The complete story may be read here:
We may speculate that the elimination of the Azuara impact structure also from the Earth Impact Database, again referred to by Shapman et al., has its roots in this controversy. Azuara was eliminated from the list in 2003 after the Database had changed from R.A.F.Grieve to J.Whitehead and J.Spray. Having been aware of the elimination, Ferran Claudin wrote a letter to John Spray asking about the reason for the deletion despite the clear and established impact evidence. He especially pointed to the thorough PDF analysis performed by Dr. Ann Therriault clearly proving strong shock in Azuara polymictic breccias and impact ejecta. John Spray kindly answered that they would re-consider Azuara as soon as possible, but he gave no answer to the «why?». In the next months, Ferran Claudin sent two more e-mails to John Spray reminding him of the Azuara structure. The answers were always the same: They plan to re-consider the evidence, but John Spray didn’t have an answer to the «Why was Azuara eliminated?» – until today. When Ferran Claudin offered to send reprints of the papers published on the Spanish impacts, John Spray answered that Ferran Claudin could send him the papers but he would not read them. So much about John Spray and the Earth Impact Database at the New Brunswick university.
Summarizing, Shapman et al. should well consider whether the mysteriously disappered Spanish impacts are able to support their questioning an impact origin for the deformations of the Triassic conglomerates.