Shock metamorphism in the Rubielos de la Cérida impact basin (Eocene-Oligocene Azuara multiple impact event, Spain) – reappraisal and photomicrograph image gallery

Abstract

Abstract. - We present a new compilation of previously abundantly studied and published shock effects in minerals and rocks of the Middle Tertiary Rubielos de la Cérida Impact Basin in northeastern Spain. Typologically, we organize by: shock melt - accretionary lapilli - diaplectic glass - planar deformation features (PDF) - deformation lamellae in quartz - isotropic twins in feldspar - kink banding in mica and quartz - micro-twinning in calcite - shock spallation. Included are the newly associated Jiloca-Singra impact in the so-called Jiloca graben and the Torrecilla ring structure, which immediately adjoins the Rubielos de la Cérida basin to the northeast. The compilation and presentation also opposes once more the still existing fundamental rejection of an impact genesis of the Azuara impact event by leading impact researchers of the so-called impact community and by regional geologists from the University of Zaragoza.

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Shock! metamorphism! in! the! Rubielos! de! la! Cérida! impact! basin!
(Eocene-Oligocene! Azuara! multiple! impact! event,! Spain)! -!
reappraisal!and!photomicrograph!image!gallery!
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by#Kord#Ernstson1#and#Ferran#Claudin2#(April#2021)#
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Abstract.!-!We present a new compilation of previously abundantly studied and
published shock effects in minerals and rocks of the Middle Tertiary Rubielos
de la Cérida Impact Basin in northeastern Spain. Typologically, we organize by:
shock melt - accretionary lapilli - diaplectic glass - planar deformation features
(PDF) - deformation lamellae in quartz - isotropic twins in feldspar - kink
banding in mica and quartz - micro-twinning in calcite - shock spallation.
Included are the newly associated Jiloca-Singra impact in the so-called Jiloca
graben and the Torrecilla ring structure, which immediately adjoins the Rubielos
de la Cérida basin to the northeast. The compilation and presentation also
opposes once more the still existing fundamental rejection of an impact genesis
of the Azuara impact event by leading impact researchers of the so-called impact
community and by regional geologists from the University of Zaragoza.
________________________________________________________________
1 University of Würzburg, 97074 Würzburg (Germany); kernstson@ernstson.de;
2 Associate Geological Museum Barcelona (Spain); fclaudin@xtec.cat
1#Introduction#
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Rubielos de la Cérida (Fig. 1 -3) is still hushed up by the so-called impact
community of a few researchers (e.g. French and Koeberl 2010, Reimold et al.
2014, Spray, written communication, Schmieder and Kring 2020) despite the
extensive documentation of all impact-relevant finds and findings (a compilation
see e.g. here: Ernstson and Claudin 2021). In these past 20 years, a lot of new

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findings and insights have accumulated, and some of them may have been
forgotten in the confusion of various publications and internet sites. As
particularly significant for the proof of an impact genesis, mineral and rock
changes of a shock metamorphism are still considered rightly, which occur
extremely richly with the Azuara impact event and above all in the Rubielos de
la Cérida impact basin.
Fig. 1. Location map for the Azuara and Rubielos de la Cérida impacts.
Fig. 2. Map for general orientation in the multiple impact field of the Azuara
impact structure and the Rubielos de la Cérida impact basin. CAL. =
Calamocha, CAM = Caminre-al, CAR = Cariñna, MUN = Muniesa; A-23 =
Autovía Mudéjar.

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Fig. 3. Digital map 1 : 250,000 of the Azuara multiple im-pact event, which
produced a crater chain of about 120 km length.
From a review of previous scattered published and unpublished findings, we
have assembled here a typologically organized gallery of shock effects, which
has three objectives: It should be a kind of teaching material for all those
geologists, but also mineralogists, who have had difficulties with impact and its
phenomena, especially in view of the fact that the presented shock effects are all
in sedimentary rocks and partly very unusual and largely unknown formations.
Furthermore, all amateur impact researchers are addressed, from whom very
valuable contributions to impact research are made again and again.
As a second reason we attempt to make the mentioned impact researchers (and
those who uncritically let themselves be "infected" by it) to end their absurd,

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science killing insistence on the silence and the rejection of the Azuara/Rubielos
de la Cérida impact.
A third aspect focuses on Spanish geologist in particular from the Zaragoza
university, who completely ignore impact genesis and effects in a significant
part of the Tertiary Iberian System, almost maliciously conceal the extensive
literature on the Spanish impacts of Azuara and Rubielos de la Cérida against all
scientific rules, and still steadfastly adhere to their old, long-disproved models.
Only recently, as in an article on the Jiloca graben (Ernstson and Claudin 2020),
we have shown geologically irrefutably that the entire ideas of the Spanish
geologists dealing with the region completely miss the geological reality. They
are basing their ideas and models on erroneous mapping and seeing the proven
big impact as non-existent. This includes the recent work of Simón et al. (2021)
on the Daroca thrusting, which has recently become a remarkable recurrent
focus of Zaragoza geologists, after we provided undoubted evidence of the
Azuara impact process in the formation of the prominent Daroca thrusting a few
years ago (Claudin and Ernstson 2012, 2020 a, b), relegating all other Zaragoza
regional geological explanations and models to the realm of fable.
Fig. 4. Digital Terrain Model of the Rubielos de la Cérida impact basin and
locations where shock metamorphism has so fas been established.

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2 The compilation of shock metamorphism (Fig. 4) in the Rubielos
de la Cérida impact basin.
In the following gallery of SEM and optical images, as well as of the vast
majority of photomicrographs, we organize them into typologically related
complexes, each with brief captions and, where applicable, links to more
detailed characterization.
A note should already stand here in relation to the Shock Melt complex. Impact
melt and impact glass are not only produced by the extreme temperatures during
shock pressure release but can also be the result of frictional heat during the
partly gigantic movements under extreme pressure and at high speed in the
impact phases of excavation and ejection as well as modification. If no
cogenetic accompanying shock effects are detectable, an exact address must
remain open, provided that the geological finding situation does not speak for
one or the other.
Without doubt a very special shock effect in the Azuara impact event and also
widespread in the Rubielos de la Cérida impact basin are accretionary lapilli,
mostly in suevites of the basal breccia, but in many cases also as pure
lapillistones. In the absence of volcanism, from which accretionary lapilli are
otherwise known to geologists, these very special and typical formations are
now also described from a number of impact structures, where they can logically
form in the massive explosion cloud.
An at least theoretical restriction is to be made with the shock effect of bent
mica. Kink bands in mica can also develop under extreme tectonic pressures of a
regional metamorphism. However, if crossing sets of kink bands with extreme
kink band frequency are observed, as is regularly the case in the Spanish
impacts, tectonic stress can reasonably be excluded and a true shock effect
diagnosed, in particular if kink banding of mica occurs in otherwise shocked
rocks. Similar considerations apply to kink banding in quartz, which occurs here
in sometimes spectacular form.
A very special form of shock effects, which has not been recognized as such by
impact research at all, are abundant open spallation fissures in quartz grains, for
whose open wide tensile cracks, purely physically, no other interpretation
possibility remains than that of a shock spallation (Ernstson 2014).
3 Conclusion
The conclusion is anticipated here before the extensive compilation of virtually
all known strong and moderate shock effects in meteoritic impacts follows. This
evidence is not found in a few hand pieces, but widely scattered over a vast area

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of about 80 km x 40 km. The operators of the Canadian Earth Impact Database
under the leadership of John Spray, for which the multiple Azuara impact event
with the Azuara impact structure and the Rubielos de la Cérida impact basin still
does not exist at all, are reminded that the published impact findings of geology,
geophysics, petrography, mineralogy, and geochemistry at Azuara and Rubielos
de la Cérida exceed in richness and significance, with extremely good terrain
accessibility, the vast majority (perhaps more than 90%) of all impact structures
listed as established in the database. In its singularity as a multiple impact with
Azuara and the stringed Rubielos de la Cérida crater chain there is no equal on
Earth. This is a scientific absurdity for impact research when a few leading
people in the "impact community" articulate their personal aversions in this way.
That this obviously has not remained without effect is shown especially by the
behavior of Spanish geologists, in particular the regional geologists of the
University of Zaragoza, who can refer to this non-existence in the Canadian
database and who stick to their long since thoroughly disproved textbook
graben-basin models of the Iberian System and publish it as they have done for
20 years and more and up to the present day (e.g., Simón et al. 2021). One can
only advise them: Closing their eyes does not eliminate the great Spanish
impact.
References
Claudin, F. and Ernstson, K. (2020a) El cabalgamiento de Daroca (Cordillera
Ibérica, España) y la estructura de impacto de Azuara - la controversia continúa.!
URL
Claudin, F. and Ernstson, K. (2020b) Daroca thrust (Iberian Chain, Spain) and
the Azuara impact structure - the controversy continues. URL
Claudin, F and Ernstson, K. (2012) Azuara and Ries impact structures: The
Daroca thrust geologic enigma – solved? URL
Ernstson, K. and Claudin, F. (2021) Comment on: ” Schmieder, M. and Kring,
D. A. (2020) Earth’s Impact Events Through Geologic Time: A List of
Recommended Ages for Terrestrial Impact Structures and Deposits. –
Astrobiology, 20, 91-141.” - URL.
Ernstson, K. and Claudin, F. (2021) When modeling ignores observations: The
Jiloca graben (NE Spain) and the Rubielos de la Cérida impact basin. - URL
French, B.M. & Koeberl, C.: The convincing identification of terrestrial
meteorite impact structures: What works, what doesn’t, and why. – Earth-
Science Reviews, 98, 123-170, 2010.

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Reimold, W.U., Ferrière, L., Deutsch, A., and Koeberl, C. (2014): Impact
controversies: Impact recognition criteria and related issues. – Meteoritics &
Planetary Science, 49, 723-731.
Schmieder, M. and Kring, D. A. (2020) Earth’s Impact Events Through
Geologic Time: Martin A List of Recommended Ages for Terrestrial Impact
Structures and Deposits. – Astrobiology, 20, 91-141.
Simón, J.L., Casas-Sainz, A.M., Gil-Imazes, A. (2021) ReferencControversial
epiglyptic thrust sheets: The case of the Daroca Thrust (Iberian Chain, Spain). -
J. Structural Geology, 145 (2021) 104298.
APPENDIX: GALLERY
Shock!melt!
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Silicate(melt
Patches! of! silicate! melt! in! Lower! Tertiary! claystones.! Barrachina!
megabreccia.!
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Ribbon!of!silicate!melt!in!the!Barrachina!megabreccia.!-!Spanish!geologists,!
confronted!with! the! for!them! completely! unexpected!melt! rock! composed!
of! 90%! glass! with! clay-shale! chemism! in! this! stratification,! did! not! know!
how! to! help! themselves! other! than! to! declare! it! as! volcanic! ash,! without!
explaining!where!this!"ash"!should!have!come!from!at!this!place.!
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Silicate shock melt rock, >90% pure glass from melted shale; Barrachina
megabreccia. Optical microscope; field width 15 mm.

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SEM images taken from the impact glass above (shock-melted shale);
Barrachina megabreccia. Scale bar to the right 10 µm.
The silicate melt rock under the
SEM. 1 µm scale bar. SEM Images: ZEISS.

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Melt glass, PPL and XX. Suevite from the Barrachina megabreccia.

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Shock-produced or pseudotachylite(?) glass coating a sandstone in the southern
uplift chain near Caudé.
The glass in close-up.

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The glass-bearing sandstone cut perpendicularly to the glass crust (in the upper
part). The field is 16 cm wide.
Photomicrograph (the field is 240 µm wide) of the glass-bearing
sandstone; three sets of planar features in a quartz grain.

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Carbonate-phosphate melt
Clast of carbonate-phosphate melt rock (white) in the Barrachina megabreccia.
Coin diameter 23 mm.
Carbonate-phosphate melt: surface of a break.

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Carbonate-phosphate melt in close-up: Calcite amoebic bodies (darker) in a
matrix of phosphate glass (white). The field is 30 mm wide.
Carbonate-phosphate melt rock: Photomicrograph (crossed polarizers) of
amoebae-like calcite bodies within a matrix of phosphate glass (dark). Note that
the size of the individual calcite crystals increases towards the centers of the
bodies. Also note that the peripheral calcite obviously has grown perpendicular
to the rim because of the orientation. In part, especially along the borders to the
calcite bodies, the phosphate glass has recrystallized to form apatite (elongated,
sometimes flaser-like minerals tangentially orientated to the calcite bodies). The
field is 6 mm wide.

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Sulfate melt rock
Clast of sulfate melt rock in the Barrachina megabreccia. Coin for scale.
The sulfate melt rock in close up. Note the quartzite clasts in the low-density,
highly porous CaSO4 matrix.

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The sulfate melt rock under the SEM. Note the vesicular texture.
Carbonate melt rocks
Carbonate melt rock dike cutting through Jurassic limestone.

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Carbonate melt rock from the Corbalán limestone quarry, southern impact basin.
Close-up below.
The low-density, highly porous material shows a distinct vesicular
texture (the field is 7 mm wide).
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White! relics! of! carbonate! melt! coating! a! disintegrated,! decarbonized!
vesicular! limestone.! Megabreccia! between! Escorihuela! and! El!
Pobo/Corbalán;!southeastern!rim!of!the!impact!basin.!
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SEM!image! of!the! relics! of!carbonate! melt;!basin!rim! between!Escorihuela!
and!El!Pobo.!Note!the!vesicular!felted!texture.!
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SEM!image! of! the!relics!of! carbonate!melt,!formerly! probably! Muschelkalk!
limestone.!Note!the!dendritic!crystallites!(field!width!25!µm).!
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Relics!of!carbonate!melt.!Torrecilla!ring!structure.!
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Accretionary lapilli
System of dikes composed of accretionary lapilli in a light-colored matrix is
cutting through the basal suevite breccia near Fuentes Calientes, eastern basin
region.
Close-up of the lapilli-bearing dike penetrating the basal breccia near Fuentes
Calientes. Note that many lapilli have the typical onion skin structure around a
stony core.

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Large parts of the basal breccia outcropping near Escriche in the southern part of
the impact basin are composed of a lapillistone matrix with only few sharp-
edged rock fragments, probably Muschelkalk limestone. Note that the sample
shown here has the character of a matrix-within-matrix texture. Also note the
matrix dike in the right part penetrating the afore formed matrix giving evidence
of a very peculiar lithification.
Close-up of the lapilli breccia exposed near Escriche. The field is 18 mm wide.

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Accretionary lapilli in the matrix of the basal suevite breccia from near
Corbatón, east of the Rubielos de la Cérida central uplift. Field width 3 cm.
Accretionary lapilli from the Corbatón basal breccia in thin section.
Photomicrograph, xx polarizers, field width 6.5 mm. The lapilli are basically
carbonate with some accessory silicate material (e.g., quartz fragments in the
large lapillo).

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More accretionary lapilli from the Corbatón basal suevite breccia.

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Muschelkalk breccia-within-breccia in lapillistone matrix (accretionary lapilli)
near Olalla.
Close-up of the lapillistone matrix

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For comparison: lapillistone from a volcanic diatreme. Sawed and polished
sample of accretionary lapilli in the Avon kimberlitic diatremes, Missouri, USA.
Field width 3.5 cm. Note the remarkable similarity of volcanic and impact
accretionary lapilli rock texture not allowing to make a prompt distinction.
Diaplectic glass
Diaplectic glass in quartz grain, XX, field of view 560 µm. Torrecilla ring.!!

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Close-up: Multiple sets of diaplectic glass lamellae.
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Diaplectic! feldspar! (the! long! grain).! Impact! melt! rock,! Barrachina!
megabreccia,! XX!and! PPL.! Note!the! preservation! of! the! grain! boundaries!
and!the!fractures!typically!different!from!melted!minerals.!
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Diaplectic!glass!and!PDF!in!feldspar.!Barrachina!megabreccia.!XX.!
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Shocked!feldspar!with!isotropic!(diaplectic)!twin!lamellae!and!faint!PDF,!XX.!
Sandstone,!Buntsandstein!central!uplift!in!the!10!km-diameter!Jiloca-Singra!
impact!crater!in!the!Jiloca!"graben".!!
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Shocked! feldspar! with! isotropic! (diaplectic)! twin! lamellae,! XX.! Cretaceous!
sandstone;!Torrecilla!ring.!
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Planar!deformation!features!(PDF)!
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Multiple!sets!of!PDF!in!quartz!merging!into!diaplectic!glass.!Torrecilla!ring.!
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Planar! deformation! features! (PDF)! in! quartz;! shocked! Cretaceous!
sandstone;!Torrecilla!ring!near!Portalrubio!
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Multiple! sets! of! planar! deformation! features!(PDF)!in! quartz;! shocked!
sandstone!clast,!Corbatón.!
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Multiple! sets! of! planar! deformation! features!(PDF)!in! quartz;! shocked!
sandstone!clast,!Corbatón.!
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Crossing!sets!of!PDF!in!quartz.!Cretaceous!sandstone,!Portalrubio.!
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Kinked deformation lamellae in quartz and associated PDF. Cretaceous
sandstone near Portalrubio.
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PDFs!in!quartz;!basal!suevite!breccia!near!Celadas.!
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PDFs!in!quartz;!Buntsandstein!sandstone,!southern!basin!near!Caudé.!
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PDFs!in!quartz;!basal!suevite!breccia,!northeastern!basin!rim.!
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Kink!banding!-!Kink!bands!
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Mica(
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Multiple! sets! (four! at! least)! of! kink! bands! in! muscovite.!Buntsandstein!
sandstone!central!uplift,!Jiloca-Singra!crater!in!the!Jiloca!"graben".!
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Two! sets! of! crossing! kink! bands! in! muscovite.!Cretacous! sandstone,!
Torrecilla!ring.!
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Quartz(
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Deformation!lamellae!(N!-!S)!and!closely!spaced!kink!banding!(NW!-!SE).!
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Multiple!sets!of!distinct!kink!banding!in!quartz.!
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Plastically!deformed!kink!bands!in!quartz!and!faint!PDF.!
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Multiple!sets!of!kink!banding!in!quartz!and!crossing!planar!features.!
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Shock-produced( deformation( lamellae,( planar( features(and( kink( banding( in(
quartz( -( the( four( images( above;(photomicrographs,( crossed( polarizers.(
Shocked( sandstones( and( quartzites,( northwestern( basin( rim.( Width( of( the(
fields(is(between(200(and(500(µm.(
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Kink!banding!and!crossing!planar!features!in!quartz,!Cretaceous!sandstone,!
Torrecilla!ring.!Field!width!350!µm.!
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Microtwinning!calcite!
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Multiple! sets! of! micro-twins,!field! width! 480! µm.! Polymictic! breccia!
Torrecilla!ring.!Twin!size!down!to!1!µm.!

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Multiple!sets!of!planar!deformation!features!(micro-twins)!in!calcite!from!a!
polymictic! breccia,! Torrecilla! ring.! The! twin! spacing! and! width! is! about! 1!
µm.!Crossed!polarizers.!
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Shock!spallation!
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Shocked sandstone with subparallel open spallation fractures in quartz grains.
The shock front moved from WSW to ENE, or vice versa. Photomicrograph,
crossed polarizers, field width ca. 2.5 mm. Buntsandstein central uplift, Jiloca-
Singra crater in the Jiloca "graben".
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More shocked quartz grains in a sandstone from the central uplift.
Sample with distinct subparallel open spallation fractures. Field width
ca. 800 µm.
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Open! shock! spallation! fractures! in! quartz,! XX,! Cretaceous! sandstone!
Portalrubio.!!
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Spallation:!A! spall!is! completely!(2-D)! detached! from!a! quarzite!grain!in! a!
shocked! Buntsandstein! conglomerate,! and! more! open! tensile! spallation!
fractures! are! cutting! through! the! clasts.! The! image! shows! pure! tension!
without! contact! between! the! neighboring! grains! (in! 2-D).! The! matrix! is!
opaque! from! iron-hydroxide.! Field! width! 9! mm.!Central-uplift! chain! near!
Caudé.!