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TARGETS. A..Ure1, R. Westaway2, D.R. Bridgland3, F. Claudin4, K. Ernstson5, 1School of Environmental, Earth
and Ecosystem Science, The Open University, UK; 2School of Engineering, University of
Glasgow, UK; 3Department of Geography, Durham University, UK; 4Llinars del Vallès. Barcelona-08450, Spain; 5Faculty of Philosophy 1,
University of Würzburg, Germany;
Introduction: After initial promising signs of a
new large impact structure at the Turkish-Greek border
(Fig. 1) [1] and a subsequent further verification [2],
the Kaş structure began to crystallize in many ways as
a faithful copy of the large Spanish Rubielos de la
Cérida impact structure (Figs. 1, 2), and the extensive
geological impact inventory of Rubielos de la Cérida
became a helpful guideline in the terrain exploration of
the new Kaş structure. What is special about this is that
both structures are laid out in a purely sedimentary
target, which is also largely formed in carbonate facies.
While the products of meteorite impacts into dense,
mostly crystalline and mixed targets are relatively well
understood and macroscopic and microscopic defor-
mations of these target rocks are the norm, the re-
sponse of volatile-rich sedimentary rocks, in particular
carbonate rocks, to impact, remains debated. Here we
report on a selection of amazingly remarkable similari-
ties in both impact structures as instructive illustrative
material for impact terrain studies, especially as they
are terrain with predominantly excellent field condi-
tions and mostly easily accessible outcrops in pleasant
Fig. 1. The Kaş and Rubielos de la Cérida impacts in
Spain and Turkey/Greece. - Location map for the Kaş
structure at the Greek/Turkish boundary (green), the
suggested extrapolation of the structure to the sea (yel-
low) and a distinct central uplift in the form of a peak
ring (red; see Fig. 2). Google Earth. Fig. 2. The Azuara
and Rubielos de la Cérida impacts in the digital map of
Spain 1: 250,000 (courtesy M. Cabedo). Central uplifts
(peak ring, Kaş, and chain, Rubielos de la Cérida).
The Kaş impact structure: Ure et al. [1, 2] have
for the first time suggested a possible Kaş Bay impact
structure based on preliminary geologic field evidence.
New field studies and laboratory analyses further
strengthen the impact hypothesis. With a diameter of
about 10 km and a central uplift (Figs. 1, 2) Kaş Bay is
classified as a complex impact structure. The local
bedrock is Cretaceous neritic limestone. Based on
stratigraphical evidence, uplift and subsidence rates, an
age from the Pleistocene epoch is probable.
The Rubielos de la Cérida impact structure is
an elongated impact basin with a central-uplift chain as
part of the Mid-Tertiary Azuara multiple impact event
(Fig. 2) [3, 4, and references therein]. The target is
sedimentary with about 10 km thickness. Clear impact
evidence, which is still doubted by some Spanish re-
gional geologists, is given by geological and geophysi-
cal evidence like ubiquitous monomictic and polymic-
tic breccias, large systems of monomictic and polymic-
tic breccia dikes, enormous and extended megabrecci-
as, shatter cones, extended impact ejecta, gravity and
geo-magnetic anomalies, strong shock metamorphism
like shock melt, planar deformation features (PDFs)
and diaplectic glass in various minerals [3, 4].
Comparison: Although the impact basin of Rubie-
los de la Cérida is much more extensive than the Kaş
basin and offers much more exploration possibilities, it
is amazing how similar the effects of the impact are by
and large. This applies to comparable structural condi-
tions, rock types and deformations right down to the
micro range, and it has not been difficult to compare
findings of the most varied but impact-typical kind
with each other, which is done below in a selection. In
fact, comparable scenarios in the field and in the hand
sample are much more extensive, which, however,
forces a strong restriction here. It should first be noted
that in the illustrations the letters K and R indicate the
respective assignment to the two impact structures.
Megabreccias and scour planes: In general mega-
breccias are characterized by great extension and by
large-sized components (megablocks), occur at best
with gigantic landslides and otherwise are typical for
larger impact structures. It is not surprising that with
large impacts the enormous mass movements often
lead to connections of megabreccias and impressive
sliding surfaces, partly with mirror polish. Examples
are shown in Figs. 3, 4.
Polymictic breccias and breccia dikes: Dike
breccias are a prominent feature in impact structures
frequently allowing detailed reconstruction of the cra-
tering process [5]. Fig. 5 compiles a few examples of
very characteristic polymictic dikes. In fact, the varia-
bility of the breccia dikes in the two structures is con-
1196.pdf50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)
siderably greater and counts entire systems of dikes
that can occur as generations of intersecting dikes.
Especially the Rubielos de la Cérida structure is known
for its enormous wealth of different breccia dikes [4].
Fig. 3. Megabreccias. Fig. 4. Scour planes.
Fig. 5. Breccia dikes (dike breccias).
In impact stuctures monomictic and polymictic
breccas in general characteristically originate in the
rapidly proceeding stages of cratering - excavation,
ejection, modification, landing of ejecta and their high-
ly energetic mixing with the local target material. This
is the reason for the formation of breccias-within-
breccias right up to multiple breccia generations nor-
mally not observed in geological processes (Fig. 6).
Decarbonization/carbonate melt rock: In contrast
to silicate rocks, carbonate rocks do not quench to
form glass. Under impact high PT conditions, lime-
stone can melt or decarbonize with subsequent, in part
immediate, recrystallization. Like in other impact
structures with a partial carbonate target (e.g. Haugh-
ton Dome, Canada [6]) such relics of carbonate
melt/decarbonization are abundant in the investigated
Kaş and Rubielos de la Cérida areas (Fig. 7).
Fig. 6. Polymictic breccias Fig. 7. Decarbonization
and breccia generations. and carbonate melt rocks.
Fig. 8. Photomicrographs, crossed polarizers.
Petrographic thin section analyses: Unlike in the
Rubielos de la Cérida structure, where the entire shock
inventory of silicate rocks is abundantly represented
[3,4], corresponding observations in the Kaş structure
are inevitably limited to carbonate rocks. There we see,
completely parallel to corresponding deformations in
the Spanish structure abundant occurrences of multiple
sets of microtwinning in calcite frequently in combina-
tion with kink banding (Fig. 8). Regularly the size of
the twins is of the order of 1 µm which points to high-
pressure deformation similar to the development of
shock-produced PDF in quartz. Accrecionary lapilli
usually associated with volcanic eruptions but also
occurring in meteorite impacts add to geologicical con-
spicuousness (Fig. 8) and has nearly identical counter-
parts in the Rubielos de la Cérida structure (Fig. 8).
Conclusion: Very large impact structures in purely
sedimentary, in particular predominantly carbonate
targets, are rare and have not been much investigated
to date. The comparison of two such big structures
with an overabundant inventory of impact-typical for-
mations, deformations and petrographic evidence,
clearly shows that a considerable neglect of impact
research can be observed here. Even in recent publica-
tions, e.g. in a review "of impact melt and breccia
dikes in terrestrial impact structures" [7], sedimentary
targets are mentioned only casually in a single sen-
tence about lithic breccia dikes, apparently forgetting
that such an inventory exists to a much greater extent
and variability as exemplified here.
Acknowledgement: We thank Kenneth Harvey for
assisting in fieldwork.
References: [1] Ure, A. et al. (2017) LPSC XLVIII,
Abstract #1144. [2] Ure, A. et al. (2018) LPSC XLIX,
Abstract #1455.[3] Ernstson, K., et al. (2002). Treballs
del Museu de Geologia de Barcelona, 11, 5-65. [4]
Ernstson, K. and Claudin, F. http://www.impact- 14/12/18. [5] Lambert, P.
(1981). In: R.B. Merrill, R.B. and Schultz P.H.
(eds.), Lunar Planet. Sci. Proc. 12A, 59-78. [6]
Osinski, G.R. et al. (2005) Meteoritics Planet. Sci., 40,
1759-1776. [7] Pilles, A. et al. (2018) LPSC XLIX,
Abstract #1994.
1196.pdf50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132)
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.
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