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When modeling ignores observations: The Jiloca graben (NE Spain) and the Rubielos de la Cérida impact basin

Authors:

Abstract and Figures

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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When!modeling!ignores!observations:!The!Jiloca!graben!(NE!
Spain)!and!the!Rubielos!de!la!Cérida!impact!basin!!
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by!Kord!Ernstson1!and!Ferran!Claudin2!
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June!2020!
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Abstract.!-!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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Key+words:!meteorite!impact,!Azuara!impact!event,!Alfambra-Teruel!graben,!Calatayud!basin,!
strike-slip!transgression,!transtension,!Singra-Jiloca!impact!
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1 University of Würzburg, 97074 Würzburg (Germany), ernstson@ernstson.de
2 Associate Geological Museum Barcelona (Spain); fclaudin@xtec.cat
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1!Introduction!
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According!to!current!geological!characterization,!the!Jiloca!Graben!in!northeastern!Spain!
is!part!of!an!important!intramontane!graben-basin!system!together!with!the!Calatayud!
Basin/Graben!and!the!Alfambra-Teruel!Basin/Graben!(Fig.!1),!both!terms!being!used!
synonymously!in!the!literature.!The!origin!of!the!remarkable!topographic!depression!is!
controversial,!and!tectonic!subsidence!(Rubio!and!Simón!2007)!and!erosive!deepening!
are!mainly!attributed!to!either!Tertiary!erosion!pediplains!or!karst!subrosion,!whereby!
combined!formation!processes!are!also!discussed!(Casas-Sainz!and!Cortés-Gracia!2002)!
Gracia!et!al.!2003).!!
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In!the!literature!(e.g.,!Sanz!de!Galdeano!et!al.!2019,!!Gutiérrez!et!al.!2012)!,!the!Jiloca!
graben!is!described!as!having!originated!in!the!Neogene!and!Quaternary,!being!limited!
by!normal!faults!(the!Menera!and!Palomera!faults)!with!measurable!several!hundred!
meters!throws,!cutting!pre-existent!NW-SE!striking!folds.!The!sedimentary!fill!consists!
of!at!least!80!m!thick!Neogene!and!Quaternary.!!
The!contradictory!interpretations!of!the!genesis!of!the!Jiloca!graben!also!find!expression!
in!the!fact!that!the!structure!is!called!both!a!graben!and!sometimes!a!half-graben!(Fig.!
5.9.!in![Sanz!de!Galdeano!et!al.!2019]).!!
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In!the!aforementioned!articles!and!even!in!the!most!recent!literature,!there!is!no!
mention!of!an!approximately!20-year-old!alternative!hypothesis!on!the!formation!of!the!
Jiloca!graben!in!the!context!of!discussions!and!publications!on!the!large!multiple!Azuara!
impact!with!the!formation!of!the!Azuara!impact!structure!and!an!associated!Rubielos!de!
la!Cérida!impact!basin!(Ernstson!et!al.!2001,!2002,!!2003,!Claudin!et!al.!2001,!2003,!
Schüssler!et!al.!2002,!Hradil!et!al.!2001,!Ernstson!and!Claudin,!http://www.impact-
structures.com/impact-spain/the-rubielos-de-la-cerida-impact-basin,!no!year).!This!is!
accompanied!by!the!observation!that!the!Azuara!impact!structure!published!since!1985!
(Ernstson!et!al.!1985,!1987,!2002,!Müller!and!Ernstson!1990,!Ernstson!and!Claudin!
1990,!Ernstson!1994,!Ernstson!and!Fiebag!1992!,!Claudin!and!Ernstson!(2012),!Ernstson!
and!Claudin!http://www.impact-structures.com/impact-spain/the-azuara-impact-
structure,!no!year)!is!not!mentioned!at!all!in!the!discussion!of!the!other!basin!structures!
mentioned!(Calatayud!and!Alfambra-Teruel),!even!in!the!latest!geological!literature!(e.g.!
Sanchez!et!al.!2017,!Casas-Sainz!et!al!2018,!Gutiérrez!et!al.!2012,!2020,!Simón!et!al.!
2019,!Sanz!de!Galdeano!et!al.!2019!).!!
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In!view!of!this!fact!in!the!newer!and!most!recent!Spanish!geological!literature,!we!feel!
compelled!to!contrast!the!conventional!ideas!about!the!intramontane!basins!mentioned!
at!the!beginning!with!the!extensive!geological,!mineralogical!and!petrographical!findings!
from!the!Rubielos!de!la!Cérida!impact!basin!with!the!result!that!the!formation!
hypotheses!discussed!so!far!can!be!geologically!coherently!replaced!by!the!formation!of!
the!region!in!a!massive!impact!event.!We!start!here!with!a!first!article!focusing!on!the!
Jiloca!graben,!which!will!be!followed!by!further!articles!on!the!geological!structure!and!
the!extensive!impact!finds!and!features!of!the!entire!Rubielos!de!la!Cérida!impact!basin,!
which!is!not!known!on!earth!as!its!equal.!
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Fig.1.!Standard!graben/basin!configuration!on!the!Digital!Terrain!Modell!(DTM!source!M.!Cabedo).!
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Fig.!2.!The!Azuara!multiple!impact!event!produced!the!more!circular!Azuara!impact!structure!
together!with!the!elongated!Rubielos!de!la!Cérida!impact!basin.!
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2!The!Rubielos!de!la!Cérida!impact!basin!
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Originally,!the!Rubielos!de!la!Cérida!basin!was!defined!by!an!approximately!circular!
uplift!of!Mesozoic!rocks!(Fig.!2,!3),!surrounded!by!a!semi-circular!to!elliptical!depression!
of!Quaternary!and!post-impact!Neogene!deposits!(Fig.!4;!simplified!and!modified!from!
the!geological!maps!1:!200.000;!ITGE,!1991;!IGME,!1986).!This!circular!uplift!with!rocks!
of!the!Muschelkalk!Fm.!in!the!very!center!at!the!village!of!Rubielos!de!la!Cérida!and!!
tectonically!very!surprising!in!the!region,!was,!after!abundant!impact!findings!with!clear!
shock!metamorphism!and!structural!abnormalities!(Fig.!4),!quickly!recognized!as!a!
companion!to!the!then!already!established!Azuara!impact!structure!(Ernstson!et!al!
(2002).!Continuing!geological!investigations!soon!showed!that!from!the!central!uplift!
there!was!an!unmistakable!extension!of!the!structure!towards!Teruel,!which!continued!
to!provide!ample!impact!findings!(Abb.!4)!and!led!to!the!definition!of!a!Rubielos!de!la!
rida!impact!basin!(Ernstson!et!al.!2003).!
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Fig.!3.!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!=!Caminreal,!CAR!=!Cariñna,!MUN!=!
Muniesa;!A-23!=!Autovía!Mudéjar.!
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Fig.!4.!Simplified!geologic!map!of!the!Rubielos!de!la!Cérida!impact!basin!and!major!occurrences!of!
impact!features.!1!=!Paleozoic,!Mesozoic!and!Lower!Tertiary,!2!=!Upper!Tertiary!and!Quaternary,!3!
=!Pelarda!Formation!ejecta,!4!=!Muschelkalk,!5!=!Keuper,!6!=!Rhaethian!and!Liassic,!7!=!Dogger,!8!=!
Malmian,!9!=!Cretaceous,!10!=!drainage!pattern.!A!=!basal!suevite!breccia,!B!=!breccia!dikes,!C!=!
megabreccias!and!monomictic!movement!breccias,!D!=!shock!metamorphism,!E!=!shatter!cones,!F!
=!impact!melt!rocks,!suevites!(Barrachina!type)!and!suevite-like!breccias,!G!=!impact!glass!
(pseudotachylite?).!Also!shown!a!WSW-ENE!section!of!the!central!uplift.!
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It!soon!became!clear!during!the!mapping!of!the!geology!in!the!basin!that,!apart!from!the!
Palomera!steeply!raised!block!(Figs.!5,!6),!we!were!dealing!with!extreme!structural!
compression!along!and!within!the!Central!uplift!chain!(Figs.!7-9),!which!goes!against!all!
assumptions!of!direct!contact!graben!structures!postulated!west!(Jiloca)!and!east!
(Alfambra/Teruel),!but!would!provide!a!very!strong!argument!for!impact!cratering!
processing!(Fig.!10).!
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!!Fig.!5.!Location!of!the!exposures!in!Figs.!6-8.!
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Fig.!6.!Part!of!the!central!uplift!chain!(Sierra!Palomera)!emerging!from!the!Quaternary!of!the!
impact!basin!(continuation!of!the!Rubielos!de!la!Cérida!central!uplift!to!the!south;!see!Fig.!2).!
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Fig.!7.!Megabreccia!near!Bueña.!Intense!criss-cross!layering!of!Jurassic!limestones!in!the!central!
uplift!chain!indicates!extreme!compression.!
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Fig.!8.!!Folding!and!megabrecciation!of!Jurassic!limestones!in!the!central-uplift!chain!(between!
Bueña!and!Caminreal).!Note!that!only!some!“ghost”!layering!has!survived!the!intense!brecciation.!
As!in!Fig.!7!an!extreme!compression!is!indicated.!
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Fig.!9.!The!image!shows!part!of!an!extended!megabreccia!deposit!in!the!southern!central!uplift!
near!Caudé.!Within!a!chaotic!accumulation!of!limestone!blocks!and!fragments,!a!large!surface!
displaying!prominent!striae!and!polish!occurs!(hammer!length!40!cm).!Any!relation!to!tectonic!
structures!is!clearly!missing.!It!is!assumed!that!the!peculiar!deformations!formed!in!the!highly!
compressive!process!of!the!central!uplift!development!(modification!stage!of!impact!cratering).!
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Fig.!10.!Simple!models!of!graben!tectonics!and!impact!cratering.!
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3!The!Mesozoic!uplift!in!the!middle!of!the!Jiloca!graben!
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In!the!course!of!the!field!work!in!the!Rubielos!de!la!Cérida!impact!basin,!the!special!
stratigraphic!constellation!with!the!Buntsandstein!hill!northeast!of!Singra!in!the!middle!
of!the!plain!of!the!Neogene-Tertiary!Jiloca!Graben!(Fig.!11)!understandably!attracted!
attention.!As!a!silicate!lithostratigraphic!unit,!it!was!an!invitation!to!look!for!shock-
metamorphic!rocks,!which!led!quite!quickly!to!success!(Fig.!4).!The!accompanying!
investigations!on!the!stratigraphic!outcrop!of!the!Singra!hill!provided!extensive!further!
impact-specific!evidence!in!the!form!of!the!suevite!basal!breccia,!dike!breccias!and!
monomictic!movement!breccias,!so!that!the!whole!complex!together!with!the!adjacent!
rising!arch!of!Rhaetian!and!Liassic!rocks!were!classified!as!impact-related.!!
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Since!this!situation!does!not!even!exist!in!the!latest!geological!literature,!the!basic!
discrepancy!between!conventional!and!impact-related!interpretation!is!shown!below,!
followed!by!a!structural!model,!which!also!includes!the!morphological!situation!with!the!
Digital!Terrain!Model!(DTM).!
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Fig.!11.!Map!section!of!the!Jiloca!graben!in!the!Digital!Terrain!Model.!The!rectangle!spans!the!
generalized!geologic!map!of!the!Mesozoic!structure!(arrow)!in!the!middle!of!the!Jiloca!graben!(Fig.!
11).!
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Fig.!12.!Geological!sketch!of!the!Mesozoic!uplift!in!the!middle!of!the!graben.!!Legend!of!the!
stratigraphic!units!in!Fig.!12.!Copied!from!the!maps!1!:!200!000,!sheets!Daroca!and!Teruel,!and!the!
maps!1!:!50!000,!sheets!Monreal!del!Campo!(IGME!1983)!and!Santa!Eulalia!(IGME!1959).!Because!of!
its!exotic!stratigraphic!position,!the!Upper!Malmian!(Kimmeridgian)!block!(C)!must!be!considered!
as!a!dislocated!megablock!or!assigned!to!downward!"elevator"!tectonics!over!enormous!drop.!The!
layer!dip!has!been!copied!from!the!1!:!50!000!maps.!
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Fig.!13.!Geological!profile!(see!Fig.!12)!of!the!uplift.!The!sketched!dip!of!the!units!refers!to!Fig.!12.!
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As!can!be!seen!in!Fig.!11,!the!unusual!topographical!situation!of!the!structure!can!
already!be!seen!in!the!DTM,!which!will!also!be!discussed!later.!Fig.!12!shows!a!highly!
simplified!geological!map!for!the!rectangle!with!a!restriction!to!an!indexing!of!the!
Mesozoic!units.!For!the!white!profile!line!Fig.!13!shows!a!corresponding!section!with!the!
corresponding!legend.!In!principle!the!structural!situation!is!roughly!half!of!the!circular!
central!uplift!of!Rubielos!de!la!Cérida!(Fig.!4).!!The!impossibility!of!a!Jiloca!graben!in!its!
previous!interpretation!in!this!area!cannot!be!better!characterized!than!by!this!
stratigraphically!and!structurally!completely!alien!situation.!!
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The!position!of!this!structure!within!the!formation!of!the!entire!impact!basin!can!only!be!
conjectured.!The!most!plausible!explanation!is!the!formation!of!a!smaller!side!crater!in!
the!chain!of!adjacent!central!craters,!with!an!inner!ring!and!its!own!central!uplift.!The!
diameter!may!be!estimated!to!roughly!10!km!(see!5).!
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4!Transpression!and!transtension!in!complex!impact!structures!
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Transpression!and!transtension!are!strike-slip!deformations!that!deviate!from!simple!
shear,!when!!a!component!of!shortening!or!extension!orthogonal!to!the!deformation!
zone!occurs.!These!three-dimensional!non-coaxial!strains!develop!principally!in!
response!to!obliquely!convergent!or!divergent!relative!motions.!For!complex!impact!
structures,!Kenkmann!and!Dalwigk!(2000)!have!shown!that!such!deformations!can!be!a!
new!and!noteworthy!feature!that!arises!in!the!modification!phase!of!impact!cratering!
during!converging!and!diverging!gravitational!collapse!movements.!
Very!simple!models!of!these!strike-slip!deformations!have!been!sketched!in!Fig.!14,!
which!should!serve!to!classify!the!very!unusual!morphological!conditions!in!the!Singra!
area!(Fig.!15).!
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Fig.!14.!Simple!models!of!strike-slip!transpression!and!transtension!structures!in!complex!impact!
craters.!
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A!look!at!the!DTM!in!Fig.!15!suggests!that!the!postulated!side!crater!with!the!uplift!and!a!
partially!formed!inner!ring!could!be!the!result!of!exactly!this!strike-slip!deformation.!It!
is!important!to!understand!that!these!structures!have!not!been!noticed!in!previous!
mapping,!where!only!a!more!or!less!elongated!Rhaetian-Liassic!stripe!with!partial!
anticlinal!character!was!registered.!Only!with!the!DGM!this!quite!unusual!pattern!of!
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almost!equally!spaced!narrow!morphological!bars!is!recognized,!where!the!individual!
bars!also!show!a!certain!elongation!orthogonal!to!the!postulated!inner!ring.!
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Fig.!15.!Interpretation!of!unusual!topographic!features!in!the!middle!of!the!Jiloca!graben!as!impact-
related!transpression!and!transtension!structures.!!
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5!The!Singra-Jiloca!crater!!
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With!the!topographical!and!geological!features!discussed!above!and!in!view!of!the!
impact-related!observations!in!the!Singra!uplift!and!on!the!neighboring!Buntsandstein!
hill!(Fig.!4),!a!remarkable!lateral!extension!of!the!central!uplift!chain!right!through!the!
middle!of!the!Jiloca!graben,!as!it!has!always!been!interpreted!so!far,!becomes!evident.!
Apart!from!the!geologically!fundamentally!alien!stratigraphic!elevations!in!the!middle!of!
the!graben,!this!insight!is!made!possible!above!all!by!the!high-resolution!DTM!(Fig.!15)!
and!aerial!imagery!(Google!Earth,!Fig.!16)!,!which!clearly!show!impact-related!features.!!
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Fig.!16.!Aerial!photograph!(Google!Earth)!in!which!the!special!topographic!position!of!the!Singra-
Jiloca!structure!with!postulated!transpression!and!transtension!is!also!clearly!visible.!For!the!
white!lines!marked!in!the!small!image!inset,!Fig.!17!shows!the!profiles!of!the!terrain!elevations!
taken!from!the!Google!map.!
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The!topographical!peculiarities!should!not!be!overstressed!here,!especially!since!the!
geological!maps!give!practically!no!better!stratigraphic!itemization!of!a!transpression!at!
the!crater!rim,!but!the!conspicuous!correspondence!of!the!peculiar!structures!exactly!in!
this!area!(Figs.!16,!17)!strongly!supports!the!reality!of!this!Singra-Jiloca!complex!impact!
structure!as!a!lateral!companion!to!the!main!impact!chain!extending!between!the!
Rubielos!de!la!Cérida!uplift!and!Teruel.!
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Fig.!17.!The!terrain!forms!along!the!profiles!in!Fig.!16!interpreted!as!transpression!and!
transtension!support!this!point!of!view,!whereby!almost!periodically!occurring!ridges!of!a!
transpression!and!troughs!of!a!transtension!appear!to!be!formed.!Source!Google!Earth.!
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For!the!time!being,!questions!remain!unanswered!regarding!the!extension!of!the!Singra-
Jiloca!structure!in!the!form!of!the!inner!ring!to!the!north!(Figs.!15,!16)!and!a!certain!
topographic!west-east!asymmetry!at!the!edge!of!the!Sierra!Palomera!(Figs.!16).!From!
the!point!of!view!of!a!complex!impact!cratering,!the!formation!of!the!central!mountain!
chain!with!primary!compression!and!subsequent!partial!collapse!and!laterally!strong!
pressure!to!the!outside!-!here!especially!in!the!area!of!the!Palomera!uplift!-!cannot!have!
remained!without!influence!on!the!more!or!less!simultaneous!formation!of!the!Singra-
Jiloca!structure,!and!a!consequently!formed!asymmetry!is!not!necessarily!surprising.!A!
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Fig.!18.!!A!diametrical!elevation!profile!through!the!structure!across!the!Jiloca!graben!provides!an!
appropriate!interpretation!and!at!the!same!time!once!again!highlights!the!contrast!between!the!
traditional!geological!approach!on!the!one!hand!and!the!coherent!results!of!impact!research!on!the!
other.!
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6!Discussion!and!conclusions!
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The!starting!point!for!this!article!was!described!at!the!beginning!and!refers!to!the!fact!
that!the!great!multiple!impact!that!the!Azuara!impact!structure!and!the!associated!
Rubielos!de!la!Cérida!impact!basin!does!not!occur!in!the!newer!and!most!recent!Spanish!
geological!literature,!and!even!these!terms!do!not!appear!in!the!indexes!of!textbooks!on!
Spanish!geology.!We!have!taken!this!as!an!opportunity!to!show!by!means!of!an!example!
how!ignoring!the!extensively!published!impact!material!on!the!impacts!means!that!old!
and!long!outdated!views!on!the!Tertiary!geology!of!the!Iberian!system!are!being!
perpetuated,!and!also!very!special!aspects!of!tectonics!and!geophysical,!e.g.!
seismological,!conditions!are!necessarily!misleading.!!
!
The!structure!of!the!Jiloca!Graben!taken!here!as!an!example!is!symptomatic!for!this!
conflict,!which!in!the!conventional!view!works!with!model!conceptions!(here:!tectonic!
graben!lowering!or!erosion!with!subrosion!and!karst)!of!a!whole!graben/basin!system,!
but!ignores!simple!geological!observations.!We!have!already!made!similar!experience!in!
connection!with!the!ejecta!of!the!Azuara!impact!structure!(Pelarda!Formation)!and!the!
remarkable!impact!thrust!of!Daroca!(Claudin!and!Ernstson!2019,!2020,!and!references!
therein).!
!
With!regard!to!the!Jiloca!graben,!we!would!like!to!concede!that!this!striking!depression,!
in!a!relatively!cursory!view!and!discussion,!has!certainly!offered!itself!as!a!graben!
formation,!and!even!with!regard!to!the!impact,!the!Jiloca!graben!and!the!
Alfambra/Teruel!graben!belong!to!graben-like!depressions!between!Rubielos!de!la!
Cérida's!central!uplift!and!the!basin!rim.!That!the!discrepancy!between!tectonic!graben!
subsidence!and!impact!interpretation!due!to!the!enormous!stratigraphic!uplift!at!Singra!
and!the!enormous!subsidence!of!the!Kimmeridgian!block!directly!next!to!it,!and!all!that!
in!the!middle!of!the!Jiloca!graben,!should!have!given!food!for!thought.!This!should!be!put!
aside!here,!as!should!the!published!impact!shock-metamorphic!effects!throughout!the!
entire!impact!basin.!
!
The!new!view!of!an!independent!lateral!crater!with!a!central!uplift!and!inner!ring!with!a!
diameter!of!perhaps!10!km,!which!is!now!located!exactly!in!the!middle!of!the!formerly!
interpreted!Jiloca!graben,!results!mainly!from!the!use!of!the!DTM!digital!terrain!model!
and!the!so!very!informative!historical!aerial!photographs!of!Google!Earth,!which!have!
been!changing!over!30!years.!Both!strongly!reinforce!the!interpretation!as!a!new!impact!
structure!belonging!to!the!multiple!Azuara!impact!event!and!should!not!allow!the!
tectonic!or!subrosion-affected!Jiloca!graben!to!continue!to!exist!geologically.!This!should!
also!apply!without!restriction!to!the!Alfambra/Teruel!graben!as!part!of!the!Rubielos!de!
la!Cérida!impact!basin!and!all!related!geotectonic!work!and!processing!in!the!region!
(e.g.,!Anchuela!et!al.!2016,!Arlegui!2006,!Casas-Sainz!&!Cortés-Gracia!2002,!Casas-Sainz!
et!al.!2018,!Casas!et!al.!2000,!Ezquerro!et!al.!2019,!2020,!Gutiérrez!et!al!2012,!2020,!Sanz!
de!Galdeano!et!al!2019,!Simón!et!al!2005,!2012,!2017).!
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17!
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Article
Full-text available
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.
Article
Full-text available
Abstract The northern part of the eastern margin of the extensional Neogene Teruel Basin (central-eastern Spain) consists of a non-linear, zigzag fault zone made of alternating ca. 2 km long, NNW-SSE trending segments and shorter NNE-SSW ones. Good outcrop conditions made possible a comprehensive integrated stratigraphic and structural study, especially focused on coarse clastic sediments deposited along the basin margin. Well-exposed stratal relationships with boundary faults, allowed the analysis of tectonic influence on sedimentation. Synsedimentary deformation includes growth faulting, rollover anticlines, and monoclines and associated onlap stratal terminations, angular unconformities, and other complex growth strata geometries. One of them is the onlap-over-rollover bed arrangement described here for the first time, which reveals the competition between tectonic subsidence and sedimentary supply. Both, the structural inheritance (dense Mesozoic fracture grid) and the dominant, nearly ‘multidirectional’ (σ1 vertical, σ2 ≈ σ3), Pliocene extensional regime with σ3 close to E-W, are considered to have controlled the margin structure and evolution. Tectono-stratigraphic evolution includes: (i) reactivation of inherited NNW-SSE faults and development of W-SW-directed small alluvial fans (SAF) while NNE-SSW segments acted as gentle relay ramp zones; (ii) progressive activation of NNE-SSW faults and development of NW-directed very small alluvial fans (VSAF); during stages i and ii sediments were trapped close to the margin, avoiding widespread progradation; (iii) linking of NNW-SSE and NNE-SSW structural segments, overall basin sinking and widespread alluvial progradation; (iv) fault activity attenuation and alluvial retrogradation. The particular structure and kinematic evolution of this margin controlled alluvial system patterns. Size of alluvial fans, directly set up at the border faults, was conditioned by the narrowness of the margin, small catchment areas, and proximity between faults, which prevented the development of large alluvial fans. The size of the relay zones, only a few hundred meters wide, acted in the same way, avoiding them to act as large sediment transfer areas and large alluvial fans to be established. These features make the Teruel Basin margin different to widely described extensional margins models.
Article
Full-text available
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 part of the Azuara crater formation and the integration in the general frame of pre-impact geology and some post-impact layering.
Research
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Results of geologic field work in the Spanish Rubielos de la Cérida impact basin - www.impact-structures.com
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Full-text available
Among the conspicuous extensional structures that accommodate the onshore deformation of the Valencia Trough at the central-eastern Iberian Chain, a number of large faults show evidence of activity during Pleistocene times. At the eastern boundary of the Jiloca graben, the Concud fault has moved since mid Pliocene times at an average rate of 0.07-0.08 mm/y, while rates from 0.08 to 0.33 mm/y have been calculated using distinct stratigraphic markers of Middle to Late Pleistocene age. A total of nine paleoseisms associated to this fault have been identified between 74.5 and 15 ka BP, with interseismic periods ranging from 4 to 11 ka, estimated coseismic displacements from 0.6 to 2.7 m, and potential magnitudes close to 6.8. The other master faults of the Jiloca graben (Calamocha and Sierra Palomera faults) have also evidence of Pliocene to Late Pleistocene displacement, with average slip rates of 0.06 and 0.11-0.15 mm/y, respectively. At the eastern boundary of the Teruel graben, the Sierra del Pobo fault has been active since Late Miocene times, at slip rates of 0.06-0.11 mm/y. Quaternary activity its better constrained for the Teruel fault, which offsets two fluvial terraces, with an estimated slip rate of 0.12 mm/y since 76 ka BP. A widespread, NNE-SSW trending fault system extends over the easternmost Iberian Chain (Maestrat sector), with abundant proofs of activity during Early to Middle Pleistocene s.l. times. Nevertheless, such proofs are mainly geomorphologic, while dated stratigraphic markers allowing precise assessment of slip rates are absent.
Conference Paper
Full-text available
Structural investigations in the Azuara impact structure in north-east Spain have exhibited an unusual joint pattern, which is unfamiliar to structural geologists. 10-15 km distant from the center of the structure Jurassic limestones show curved joint sets in the meter range, which cut the rocks into bars of approximately rhomboidal cross- section. Models of listric faulting as well as sedimentational and diagenetic processes fail to explain the observed features, which rather point to dynamic formation. It is assumed that the curved joint surfaces have resulted from impact-induced dynamic stress modulation of running fractures during the excavation flow. Probably, curved joint sets belong to the regular structural inventory of impact structures.
Article
The NNW-SSE trending Teruel Basin rift is the largest Late Miocene-Quaternary extensional intracontinental structure located within the central-eastern Iberian Chain (Spain). The structural and morphotectonic study carried out in the central-northern part of this half graben basin (north of Teruel city) has allowed us to analyse rift segmentation, deformation partitioning and rift evolution. Results are based on vertical displacement calculations (fault throw and bending) of the main border and intrabasin fault zones. We use two geomorfological-stratigraphical markers, the Intramiocene Erosion Surface (IES; 11.2 Ma) and the Fundamental Erosion Surface (FES; 3.5 Ma). While the first marker reveals rift initiation under an E-W extension, the late marker records vertical displacements associated to a second, Late Pliocene–Quaternary rifting stage characterized by a nearly multidirectional extension regime with prevailing ENE-WSW trending ó3. Despite the along-axis rift segmentation into three structural domains (northern, central and southern) and the distribution of deformation among border and intrabasin faults in the central and southern domains, a consistent average slip rate (post-IES) of 0.09 mm/a has been calculated on distinct transects across the basin, suggesting a homogeneous crustal-scale extension process in the region. The results also reveal that slip rates during the Late Pliocene-Quaternary (0.12–0.16 mm/a) are higher than the Late Miocene-Early Pliocene (0.05–0.07 mm/a). Slip rate increase is caused by (i) a westward propagation of deformation from the Valencia Through, and (ii) a change in the regional stress field, both enhanced by crustal doming affecting central-eastern Iberia, as well as progressive fault linkage. Throw vs. distance graphs suggest that the main faults are in a transient stage towards coalescence, less advanced within the southern domain. Regional Late Pliocene-Quaternary uplift, concomitant with increasing slip rates in the Teruel Basin rift, has caused the basin to rise, so that synrift sedimentation only took place in rapidly subsiding residual basins until the region became exorheic and the basin was incised by the present-day fluvial network.
Article
Abstract The official seismic hazard models in Spain used in the seismic building codes do not incorporate Quaternary faults, largely due to insufficient data for their proper characterization. There is an obvious need to conduct investigations in most of the recognised Quaternary faults to unambiguously demonstrate their Quaternary tectonic activity and assess their seismogenic potential. This work illustrates the integration of cartographic, tectonic, geomorphological, paleoseismological and geophysical methods for the characterization of the slow-moving extensional Daroca Fault, related to the negative inversion of the Alpine Daroca Thrust, Iberian Chain, NE Spain. Cartographic data indicate that the 27 km long Daroca Fault and the 17 km long Calamocha Fault, separated by a stepover 1.9 km wide, can be considered as segments of the same structure that might rupture jointly and generate Mw7 earthquakes. A long-term slip rate of 0.06–0.02 mm/yr has been estimated for the 27 km long Daroca Fault using an ESR-dated (Electro Spin Resonance) offset pediment. The work discusses why this slip rate is significantly lower than those estimated in nearby normal faults using OSL ages (Optically Stimulated Luminiscence), but comparable with those derived from offset early Pliocene limestones. A trench excavated across the Daroca Fault exposed evidence of the MRE (most recent event) on the fault, with bracketing ages of 2354–1544 cal yr BP (404 BC – 386 AD). This event likely caused the destruction and abandonment of Roman cities in the vicinity of the fault. Several explanations are proposed for the anomalously low vertical displacement of this surface faulting event recorded in the central sector of a 27 km long fault segment: multi-strand rupture, full-segment rupture, partial segment rupture, spillover rupture, and secondary sympathetic rupture.
Article
Anisotropy of magnetic susceptibility (AMS) has been applied to the study of shallow fault zones, although interpretation of the results requires establishing clear relationships between petrofabric and magnetic features, magnetic behaviour of fault rocks, and an extensive knowledge of P-T conditions. In this work, we demonstrate that magnetic methods can be applied to the study of heterogeneous fault zones, provided that a series of requisites are met. A major fault zone within the Iberian plate (Daroca thrust), showing transpressional movements during Cenozoic time was chosen for this purpose, because of the exceptional outcrops of fault gouge and microbreccia and its relevance within the context of the northeastern Iberian Plate. Magnetic fabrics were analysed and the results were compared with foliation and S-C structures measured within the fault zone. Clay mineral assemblages suggest maximum burial depths shallower than 2 km (<60–70 °C) for fault rocks in the footwall of the Daroca thrust. The orientation of the AMS axes is consistent with mesostructural strain indicators: kmin parallels the mean pole to S, or it is intermediate between S and C poles; kmax is oriented at a high angle (nearly orthogonal in overall) to the transport direction, which can be explained from both deformational and mineralogical controls. Both magnetic fabrics and kinematic indicators are consistent with a reverse movement for most of the fault zone.
Article
The relationship of independence, interaction or linkage between two neighbouring intraplate active extensional faults, the Teruel and Concud faults, are investigated from structural and paleoseismological data, and the results are discussed to improve seismic hazard assessment for the region. This paper provides the structural and paleoseismological characterization of the almost unknown Teruel Fault from detailed mapping and trench analysis, and discusses its kinematic and dynamic relationships with the Concud Fault. Four individual events occurred between 76.0 ka and 9.2 ka BP have been recorded at two branches of the Teruel Fault. Unfortunately, these only represent a small fraction of its overall activity during such time lapse, and their time constraints do not allow correlating them with those at the Concud Fault. The Teruel and Concud faults are independent structures from the geometric and kinematic point of view, as evinced by their distinct (i) transport directions (N275°E and N220°E, respectively), and (ii) average coseismic displacements (0.5 m and 1.9 m, respectively). These displacements are consistent with their respective lengths (9.0 km and 14.2 km) and significantly smaller than those expected for a hypothetically joint Concud-Teruel, 23 km-long fault. However, their displacement gradients close to the relay zone indicate that both faults undergo dynamic interaction, thus suggesting a transient stage from independence to linkage. We hypothesize that slip on both structures occurred, at the scale of the seismic cycle, in a broadly alternating manner, which induced strain partitioning between them and allowed accommodating bulk biaxial extension in the region. Such deformation pattern would have increased the earthquake frequency with respect to the scenario of a hypothetically linked Concud-Teruel Fault, but diminished the potential seismic magnitude.
The Pelarda Formation is an isolated continuous deposit which is up to 200 m thick and extends over an area of about 12 X 2.5 km2. It was originally described as a Tertiary fluvial boulder conglomerate. From the occurrence of striated and plastically deformed boulders and pebbles which partly show moderate shock effects, we conclude that the Pelarda Formation is the remnant of an originally extended ejecta blanket around the large Azuara impact structure. This interpretation is substantiated by statistical analyses of the striae azimuth and the normals to locally developed bedding planes. The admixture of lo- cal substrate with the Pelarda Formation indicates secondary cratering as a consequence of ballistic transport and ballistic sedimentation of the primary ejecta. — Models of palaeogeography and morphogenesis based on the fluvial-deposit interpretation must be re-examined.