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Abstract paper: IMPACT HYPOTHESIS FOR THE KAŞ BAY STRUCTURE (TURKEY/GREECE) STRENGTHENED

Authors:
IMPACT HYPOTHESIS FOR THE KAŞ BAY STRUCTURE (TURKEY/GREECE) STRENGTHENED.
A..Ure1, R. Westaway2, D.R. Bridgland3, T. Demir4, K. Ernstson5, 1School of Environmental, Earth and Ecosystem
Science, The Open University, UK; alijoure@hotmail.com. 2School of Engineering, University of Glasgow, UK;
robert.westaway@gla.ac.uk. 3Department of Geography, Durham University, UK; d.r.bridgland@dur.ac.uk. 4Faculty
of Letters, Geography Department, Akdeniz University, Antalya, Turkey; tuncerdemir@akdeniz.edu.tr. 5Faculty of
Philosophy 1, University of Würzburg, Germany; kernstson@ernstson.de
Introduction: Since the publication of Ure et al.
[1], field studies and laboratory analyses have further
strengthened the hypothesis for the Kaş impact struc-
ture. Kaş is a small town on the Mediterranean coast of
the Teke Peninsula in southern Turkey: 36.1999° N,
29.6396° E (Fig. 1). The local bedrock is Cretaceous
marine limestone, and the proposed impact structure
shows many features with extreme similarity to The
Rubielos de la Cérida impact structure in Spain [2].
Based on stratigraphical evidence, uplift and subsid-
ence rates, an age from the Pleistocene epoch is proba-
ble.
Fig. 1: Google Earth view of Kaş Bay and its sur-
roundings. Yellow lines delineate suggested extrapola-
tion of concentric structures on the Turkish mainland
to the sea implying a diameter of the structure of at
least 10 km. Circle denotes the group of small islands
interpreted as the central peak of this inferred impact
structure.
Method: Extended field studies focused on further
impact event characteristics. The geology was exam-
ined for signs of shock metamorphism and impact re-
lated rock deformation along with possible melt or
decarbonization. Complementing earlier field cam-
paigns [1] rock samples were collected for analysis
including thin section preparation, X-ray fluorescence
(XRF) and magnetic susceptibility.
Results: Geomorphology As is clearly observed in
the field, the concentric structures to the east of Kaş
bay (Fig.1) are stepped in a uniform pattern and are
therefore assumed to be marginal collapse zones from
the impact cratering modification stage [3] (Fig. 2a).
The same geomorphological structure to the north-
west of Kaş bay is seen in the cross section marked A-
A (Fig. 2b,c)[4].
Fig. 2: (a) Diagrammatic view from ‘The development
of a complex impact structure’ [3], showing the final
structure. (b) Simplified geological map of the Teke
Peninsula [4]. (c) Cross section through A-A showing
marginal collapse towards the bay on the north-west of
Kaş Bay.
Impact breccias Increased amounts of polymict and
monomict breccias, along with breccia dikes, a promi-
nent feature in impact structures [5], megabreccias, and
breccia-in-breccia [6] were found to encircle the area
interpreted as the central peak (Fig. 3a). Peculiar brec-
cias containing coherent fractured clasts with pre-
served fitting (Fig. 3b&c) indicate movement under
confining pressure conditions [6].
Decarbonization/carbonate melt In contrast to sili-
cate rocks, carbonate rocks do not quench to form
glass. Under impact high PT conditions, limestone can
melt or decarbonize with subsequent, in part immedi-
ate, recrystallization. Like in other impact structures
1455.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)
with a partial carbonate target (e.g. Azuara/Rubielos de
la Cérida, Spain [2], Haughton Dome, Canada [7])
such relics of carbonate melt/decarbonization are
abundant in the investigated area. On Kastellorizo a
white porous carbonate rock was observed in contact
with a scour plane of a polymict breccia interpreted as
a variety of pseudotachylite (Fig. 4a ) [2]. Limestone
clasts from the central peak show a vesicular and
skeletal texture as probable relics of decarbonization
and/or carbonate melt (Fig. 4 b, c). In many outcrops in
the study area white powder agglomerations also sug-
gest decarbonized limestone/dolostone (Fig. 4 d).
Fig. 4: Relics of recrystallized decarbonized lime-
stone/carbonate melt are abundant in the study area
(see text).
Fig. 5. Multiple sets of densely grouped microtwin-
ning and kink banding (kb) in calcite. Fig. 6. Accre-
tionary lapilli in limestone breccia. Photomicrographs
Petrographic thin section analyses As is well
known carbonate minerals are not so susceptible to
typical shock deformation. We observe abundant oc-
currences of multiple sets of microtwinning in calcite
frequently in combination with kink banding (Fig. 5).
Regularly the size of the twins is of the order of 1 µm
(Fig. 5) which points to high-pressure deformation
similar to the development of shock-produced PDF in
quartz (eg., [8, 9]. Spallation as indicative of dynamic
shock deformation is observed on a microscopic level.
Accrecionary lapilli usually associated with volcanic
eruptions but also occurring in meteorite impacts add
to geologicical conspicuousness (Fig. 6).
Magnetic suscebtibility analyses Breccias were
tested for magnetic susceptibility and revealed rela-
tively strong readings (up to 430x10-5 SI) for the car-
bonate matrix in comparison to the embedded lime-
stone clasts. Enhanced magnetic susceptibilities in
silicate impact breccias are common, but they have
also been measured in purely carbonate impactites [7].
XRF analyses Apart from the enhanced magnetic
susceptibility an interesting level of nickel in the brec-
cia matrix was established by XRF [10]. Control sam-
ples from outside the ejecta area will indicate if the
XRF and magnetic susceptibility data are significant.
Conclusion: Commonly, shock metamorphism or
geochemical signature is considered diagnostic of me-
teorite impact, and silicate minerals are in particular
susceptible to typical shock effects. Because of the
purely carbonate target stratigraphy, probable shock
deformation in minerals in the Kaş structure, is as yet
restricted to the abundant and widespread occurrence
of microstructures in calcite, like multiple sets of mi-
cro-twins and planar deformation features. Apart from
this stringent attribute the pertinent impact geological
field evidence and the laboratory results discussed
above strengthen the hypothesis for Kaş bay as a prob-
able large impact structure.
Acknowledgements: We thank Paul Forrester and
Alex Hilton for assisting in fieldwork and sampling,
and, from Durham University, Neil Tunstall for image
analysis, XRF and magnetic susceptibility analyses.
References: [1] Ure, A. et al. (2017) LPSC XLVIII,
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1455.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)
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din, F. Impact Structures http://www.impactstructures.com/impact-rocks-impactites/the-impactbreccia-page/polymictic-polygenetic-polylithologicbreccia/, accessed 12/03/17. [7] Osinski, G.R. et al. (2005) Meteoritics Planet. Sci., 40, 1759-1776. [8]
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