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The current state of knowledge about shatter cones: Introduction to the special issue

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  • Institut de Recherche pour le Développement & Institut Fondamental d'Afrique Noire Ch. Anta Diop

Abstract and Figures

Shatter cones are a fracture phenomenon that is exclusively associated with shock metamorphism and has also been produced in the laboratory in several shock experiments. The occurrence of shatter cones is the only accepted meso- to macroscopic recognition criterion for impact structures. Shatter cones exhibit a number of geometric characteristics (orientation, apical angles, striation angles, sizes) that can be best described as varied, from case to case. Possible links between geometric properties with impact or crater parameters have remained controversial and the lack of understanding of the mechanism of formation of shatter cones does not offer a physical framework to discuss or understand them. A database of shatter cone occurrences has been produced for this introduction paper to the special issue of Meteoritics and Planetary Science on shatter cones. Distribution of shatter cones with respect to crater size and lithology suggests that shatter cones do not occur in impact craters less than a few kilometers in diameter, with a few, currently questionable exceptions. All pertinent hypotheses of formation are presented and discussed. Several may be discarded in light of the most recent observations. The branching fracture mechanism and the interference models proposed, respectively, by Sagy et al. (2002) and Baratoux and Melosh (2003) require further evaluation. New observations, experiments, or theoretical considerations presented in this special issue promise an important step forward, based on a renewed effort to resolve the enigmatic origin of these important features.
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The current state of knowledge about shatter cones: Introduction to the special issue
David BARATOUX
1,2*
and Wolf Uwe REIMOLD
3,4
1
G!
eosciences Environnement Toulouse, University of Toulouse, CNRS, IRD, Toulouse 31 400, France
2
Institut Fondamental d’Afrique Noire, Univesity Cheikh Anta Diop, Dakar, Senegal
3
Museum f
ur Naturkunde Leibniz Institute for Evolution and Biodiversity Research, Invalidenstrasse 43, 10115 Berlin,
Germany
4
Humboldt Universit
at zu Berlin, Unter den Linden 6, 10099 Berlin, Germany
*
Corresponding author. E-mail: david.baratoux@get.obs-mip.fr
(Received 10 August 2015; revision accepted 16 May 2016)
Abstract–Shatter cones are a fracture phenomenon that is exclusively associated with shock
metamorphism and has also been produced in the laboratory in several shock experiments.
The occurrence of shatter cones is the only accepted meso- to macroscopic recognition
criterion for impact structures. Shatter cones exhibit a number of geometric characteristics
(orientation, apical angles, striation angles, sizes) that can be best described as varied, from
case to case. Possible links between geometric properties with impact or crater parameters
have remained controversial and the lack of understanding of the mechanism of formation
of shatter cones does not offer a physical framework to discuss or understand them. A
database of shatter cone occurrences has been produced for this introduction paper to the
special issue of Meteoritics and Planetary Science on shatter cones. Distribution of shatter
cones with respect to crater size and lithology suggests that shatter cones do not occur in
impact craters less than a few kilometers in diameter, with a few, currently questionable
exceptions. All pertinent hypotheses of formation are presented and discussed. Several may
be discarded in light of the most recent observations. The branching fracture mechanism
and the interference models proposed, respectively, by Sagy et al. (2002) and Baratoux and
Melosh (2003) require further evaluation. New observations, experiments, or theoretical
considerations presented in this special issue promise an important step forward, based on a
renewed effort to resolve the enigmatic origin of these important features.
INTRODUCTION
Shatter cones (originally: Strahlenkegel; Branco and
Fraas 1905) are the only distinct meso- to macroscopic
recognition criterion for impact structures (e.g., Dietz
1960; Melosh 1989; French and Koeberl 2010; Reimold
and Koeberl 2014). Despite them having been known
for 110 yr, the processes related to their genesis are still
largely obscure. With this special issue dedicated to this
impact shock-related fracturing phenomenon we hope
to provide a series of publications that represents an
overview of the state-of-the-art knowledge about shatter
cones and that may initiate a renewed effort to resolve
the enigmatic origin of these features.
Observations, descriptions, and analyses of shatter
cone occurrences are historically closely related to the
awareness that some enigmatic crustal disturbances that
were originally interpreted as loci of cryptovolcanic
explosions are actually impact structures resulting from
the high-velocity collision of asteroids or comets with
the surface of the Earth (e.g., Branco and Fraas 1905;
Shrock and Malott 1933; Bucher 1933; Dietz 1968).
Note that the term “impact structure” is applied here
for all impact-derived geological structures, irrespective
of whether a crater structure is in evidence or not (due
to erosion or cover with postimpact sediment). Where a
distinct “impact crater” is in evidence, this termin
principlemay be applied though. At the beginning of
the 20th century, impact structures were identified only
from the association of a crater with meteoritic
fragments, such as in the case of Meteor Crater at Coon
Butte, Arizona (Barringer 1905; this impact crater is
Meteoritics & Planetary Science 1–46 (2016)
doi: 10.1111/maps.12678
1©The Meteoritical Society, 2016.
also known as Barringer Crater), considered to be the
first confirmed terrestrial impact structure.
The first descriptions of shatter cones were provided
by Branco and Fraas (1905) from the Steinheim Basin,
southern Germany (Figs. 1a and 1c). The English
terminology derives from the German word
“Strahlenkegel” (radiation or striation cone). The
peculiar conical fractures and deformation observed at
Steinheim (Fig. 1b) were initially interpreted as the
result of hidden or buried explosive volcanic activity
(i.e., a cryptovolcanic explosion) in the absence of any
exposure of volcanic rocks in the immediate vicinity of
the structure. The original description by Branco and
Fraas (1905) is first recounted here in German and then
followed by our translation into English:
Sodann zeigt sich im Innern des Kessels an den
Weis-Jura-Kalken eine ganz eigenthumliche
Erscheinung, die unseres Wissens noch nicht
beschrieben zu sein scheint. Wie die beiden
Abbildungen 7 und 8 zeigen, handelt es sich um durch
Pressung hervorgerufene strahlen- oder b
undelf
ormige
Absonderungen in dem Kalkstein, welche man am
besten mit jenen problematischen, als Cancellofycus,
Taonurus u. dergl. beschriebenen Algen vergleichen
kann.
Die einzelnen B
undel erreichen L
angen von 0.30 m,
vereinigen sich oben zu einer Spitze, w
ahrend die
Strahlen nach unten divergiren und in einer genau
begrenzten ausgefranzten Linie endigen. Zuweilen
divergiren auch zwei B
undel nach entgegengesetzten
Seiten, so das das Ganze eine sanduhrf
ormige Gestalt
annimmt. Die Oberfl
ache ist gew
olbt, so das die
Spitze einen Kegel bildet, der sich leicht aus dem
Gestein herausspalten l
at; doch ist der Kegel an der
Spitze nicht vollst
andig geschlossen, sondern endet
entweder mit halbkreisf
ormigem Abschnitte, oder aber
l
ast sich eine gewisse Aufrollung der
Absonderungsfl
ache beobachten. Gegenseitige
Durchschneidungen der B
undel sind sehr h
aufig, auch
scheinen zuweilen mehrere parallele Lagen auf
einander zu liegen.
Die Oberfl
ache besteht wie beim Nagelkalk, an
welchen auch sonst die Erscheinung am n
achsten
anzureihen ist, aus feinen dichtgedr
angten Spitzen,
welche alle in demselben Sinne wie die B
undel selbst
orientirt sind. Soweit sich beobachten lies, stehen die
B
undel in steilem Winkel gegen die Schichtfl
ache.
Vielfach finden sich in der Gries-Breccia vollst
andig
zerpreste derartige Strahlenkalke. Das weist darauf
hin, das die Bildung dieser eigenthumlichen
Strahlenkalke schon vor der Zertr
ummerung des
Materiales abgeschlossen sein mus. Jedenfalls kann
es sich nur um eine eigenartige Druckerscheinung
handeln, wie wir sie bisher im doch so viel
ausgedehnteren Riesgebiete nicht beobachtet hatten.”
Translation (the authors):
Then in the interior of the [Steinheim] basin on the
Weiss-Jura limestone there is a strange appearance
that to our knowledge does not seem to have been
reported. As figures 7 and 8 show, it is a strahlen-
[striation-] or sheaf-like formation in the limestone
caused by constriction, which one can best compare to
the problematic algae known as Cancellofyrus,
Taunurus, or similar.
The individual sheaves attain lengths of 0.30 m,
congregate to a tip, while the striations diverge
towards the bottom and end in a well-defined, irregular
line. Sometimes two sheaves diverge to opposite
directions, so that the configuration takes on an
hourglass shape. The surface is curved, so that the tip
forms a cone that can be readily separated from the
rock; however, the cone is not complete at the tip, but
terminated in a semi-annular section, or one observes a
kind of rolling of the discharge area. Mutual
intersections of sheaves are quite abundant, and
sometimes several parallel layers seem to lie on top of
each other.
The surface comprises, as is observed in Nagelkalk to
which this appearance has closest resemblance, fine,
densely spaced tips, which are oriented in the same
sense as the sheaves. As far as one can observe, the
sheaves form a tight angle against the bedding.
Frequently one finds completely crushed Strahlenkalke
in the Gries-Breccia. This indicates that the formation
of these strange Strahlenkalke must have been
completed before the destruction of this material.
Obviously this must be a type of unique pressure
formation, as we did not observe it to date in the much
more extended Ries region.
In subsequent decades, shatter cones were observed
in association with disturbed strata in the Kentland area
(Indiana, USA) Bucher 1933; Shrock and Malott 1933).
A link with Steinheim was made, and the disturbances
in the Ordovician rocks of the Kentland area were also
considered the result of cryptovolcanic activity (Bucher
1933; Shrock and Malott 1933).
Contemporaneous with these observations, Boon
and Albritton (1936) were the first to realize that rocks
subject to impact of a large extraterrestrial projectile
may experience pressures exceeding that at the center of
2 D. Baratoux and W. U. Reimold
Fig. 1. Shatter cones of the Steinheim impact structure. a) Aerial view of the Steinheim basin and town of Steinheim am Albuch,
showing the eroded rim and central uplift (source: Google Earth). b) Example of shatter cones in limestone from the Steinheim
structure; image reproduced from Branco and Fraas (1905). c) Historical sketch map of the Steinheim basin area by Branco and
Fraas (1905). Weiss Jura corresponds to the upper Jurassic, and Brauner Jura corresponds to the middle Jurassic.
Shatter conesCurrent knowledge 3
the Earth. Unfortunately this important observation
was published in a rather obscure journal and did not
gain wide recognition. From physical principles, they
compared the impact event with a violent explosion and
predicted the formation of a crater form and of ejecta, a
central uplift (as a result of elastic rebound), and the
fragmentation of the extraterrestrial projectiles. They
interpreted shatter cones as the result of such a violent
explosion phenomenon. They, furthermore, proposed
that six cryptovolcanic structures in the USA listed by
Bucher (1933)Decaturville (Missouri), Jeptha Knob
(Kentucky), Kentland (Indiana), Serpent Mound
(Ohio), Upheaval Dome (Utah), and Wells Creek
(Tennessee)had been formed by impacts of
extraterrestrial projectiles and argued that many more
impact structures would be discovered, considering the
evidence for more frequent falls of large extraterrestrial
rock fragments in the geological past.
Another decisive step was then taken by Dietz
(1947), who observed a common upward orientation of
apices of shatter cones at Kentland. He interpreted this
as evidence for an explosion that occurred above the
beds rather than below them and used this finding to
propose that shatter cones were the result of
hypervelocity impacts of meteorites. Following this,
Dietz promoted the idea that shatter cones are
exclusively associated with impact structures and could,
therefore, be used as a macroscopic diagnostic feature for
their recognition (Dietz 1960). Increasing support for the
impact hypothesis by Dietz was received after the
discovery of the high-pressure silica polymorph coesite in
the Ries crater by Shoemaker and Chao (1961).
However, shatter cones had not yet been reported from
the larger of the two German impact structures in the
early 1960s, and the debate surrounding the origin of the
so-called cryptovolcanic structures was not yet settled by
that time. Bucher (1963) used the apparent nonrandom
occurrence of known cryptovolcanic structures against
the meteoritic impact hypothesis and continued to refute
the use of shatter cones as diagnostic deformation caused
by impact-generated shock waves. The lack of shatter
cones at Barringer Crater was also referenced as a
possible explanation for the still persisting skepticism
about the shatter cone–impact link (Johnson and Talbot
1964).
The first published map of shatter cone occurrences
by Dietz and McHone (1984) demonstrated a near-
systematic association of this deformation phenomenon
with putative or known impact structures, whereas
shatter cones had never been observed in any tectonic
or volcanic context. In addition, Dietz (1960) had
reported that shatter cones were observed in rocks
affected by atomic explosion tests. Shatter cones were
also produced in explosion experiments (Bunch and
Quaide 1968; Milton 1977; Roddy and Davis 1977) and
in laboratory impact (shock) experiments (Shoemaker
et al. 1961; Schneider and Wagner 1976; Kenkmann
et al. 2012; Wilk and Kenkmann 2015a, 2015b, 2016).
The intensities of the shock waves associated with the
explosion experiments (26 GPa) are comparable with
estimated shock levels in zones of shatter cone
occurrences in natural impact structures (from 2 to
30 GPa, e.g., Gibson and Reimold 2008). Exact shock
pressure levels achieved in the impact experiments could
not be properly estimated but tiny shatter cones
produced with impact velocities of 7 km s
!1
and peak
shock pressures up to 70 GPa have been reported
(Kenkmann et al. 2012; Wilk and Kenkmann 2015a,
2015b, 2016). These studies have established that shatter
cones can be formed by shock waves propagating from
impact loci.
Several attempts have been made to assess the
genetic processes leading to the formation of shatter
cones. Johnson and Talbot (1964) were the first to
explore a possible mechanism of formation from rock
mechanics and shock wave theory. Since then, four
further different hypotheses have been proposed (Gash
1971; Sagy et al. 2002; Baratoux and Melosh 2003;
Dawson 2009) that will be discussed in detail in the
Genetic Hypotheses section below. None of these ideas
has been definitively accepted by a large majority of the
impact research community knowing that none of these
models is able to account for all the observations.
Detailed field studies such as those by Nicolaysen and
Reimold (1999) and Wieland et al. (2006) have provided
interesting new findings such as the widely observed link
between subparallel, often curviplanar joint sets (termed
multiply striated joint sets, MSJS) of different
orientations and shatter cones of mostly polygonal
geometries, but they did not result in significant
elucidation of the genesis of shatter cones.
Despite the proposed mechanisms of formation not
having been capable of offering a unique and convincing
explanation for the different geometric properties of
these objects, shatter cones are now widely accepted as
the only shock-deformation feature diagnostic of large-
bolide impact, which can be seen with the naked eye.
Also, as shatter cones occur widely in rocks subjected to
relatively low shock pressures, they occur relatively
frequently, sometimes quite widespread, and they have
been preserved in deeply eroded impact structures (e.g.,
Gibson and Reimold 2008).
It is also of note that again and again reports of
shatter cones are submitted, and actually published,
where nonimpact=related deformation phenomena
have been mistaken for impact-induced shatter cones.
Part of this review is a discussion of such features and
their comparison with bona fide shatter cones.
4 D. Baratoux and W. U. Reimold
Shatter cones occur in supracrustal and/or
crystalline basement rocks of impact structures, but
also as clasts in ejecta outside of an impact structure
(e.g., Gostin et al. [1986] for the Acraman impact
structure; Masaitis [1999] for the Kara impact
structure) or within impact breccia of the crater fill, as
illustrated in the case of the pseudotachlitic breccias at
the Sudbury impact structure (Thompson and Spray
1994), limestone fragments at the Steinheim basin
(Buchner and Schmieder 2010), and recent reports of
shatter cones in the polymict breccia from the Vista
Alegre structure of Brazil (e.g., Cr!
osta et al. 2010;
Pittarello et al. 2015), or from drill cores of the
El’gygytgyn impact structure, Siberia (Raschke et al.
2013) and Siljan (Reimold et al. 2015). They have been
variably described from crater rim settings and from
central uplifts, although the association with central
uplifts is more common. Recently, shatter cones have
even been described from meteorites (McHone et al.
2012; Ferri#
ere et al. 2013), pertaining to impact events
on their parent bodies. The search for shatter cones
will remain a major aspect in future field exploration
toward the recognition and/or confirmation of new
impact structures. Unfortunately, the lack of
understanding of their formation still precludes the
possible use of their geometric properties to determine
shock levels or other impact parameters.
SHATTER CONE DEFINITION
Definition
Shatter cones are represented by a range of curved
to curvilinear fractures decorated with more or less
divergent striations (Figs. 2af). Striations radiate from
an apex of a conical feature or from a narrow (a few
millimeters to a few centimeters wide) apical area. The
striation geometry is distinct: ridges and valleys
generally have smooth surfaces and are well rounded
(e.g., Nicolaysen and Reimold 1999). They do not show
the sharp edges associated with striations on
slickensides, another fracture phenomenon that is also
recognized by distinct transverse steps that can be used
as kinematic indicators (see also the Slickenside section
and compare with Fig. 7). The apical areas are
sometimes crudely roundish, but have in recent years
also been frequently observed to be distinctly
polygonal, that is, delimited by fractures (e.g., Hasch
et al. 2016). Shatter cones may be coated locally with
thin layers of melt (Gibson and Spray 1998; Nicolaysen
and Reimold 1999; and references to earlier work
therein), an observation that was recently also reported
from shatter cones in basalts of several impact
structures in Brazil: the Varge~
ao Dome (Cr!
osta et al.
2012; Yokoyama et al. 2015) and the Vista Alegre
structure (Pittarello et al. 2015). There may be shock
deformation in shatter cone-bearing rocks, as already
noted by Carter (1965, 1968) in thin sections of shatter
cones from Vredefort. Shock deformation in shatter
cone-bearing rocks has been since reported by
Hargraves and White (1996) and Ferri#
ere and Osinski
(2010), and is also the topic of contributions by Hasch
et al. (2016) and Zaag et al. (2016).
It should also be noted that, except in the case of
ejecta fragments, shatter cones do often not appear as
isolated occurrences but instead occur in clusters (e.g.,
Hasch et al. 2016). Shatter coning may be pervasive at
the scale of an outcrop (e.g., Figs. 2c, 2d, and 2f).
However, there are cases where only rare shatter cones
have been observed, for example, in deeply eroded
impact structures or in small ones.
As already noted by Manton (1965) and then
emphasized by Nicolaysen and Reimold (1999), shatter
cones occur quite frequently in association with intense
subplanar to curviplanar jointing, which was referred by
the latter authors as multiply striated joint sets (MSJS)
(see also Wieland et al. 2006). These joints are
invariably striated on the joint plane, and they are
spaced at several millimeters to a centimeter apart. The
term “multiply (or multipli by some authors)” refers to
the occurrence of multiple subparallel fractures
belonging to a given set, as well as to the observation of
such sets of multiple orientations occurring in a given
rock volume. As Hasch et al. (2016) point out and
others have referred to in recent years in the literature,
such joints of different orientations may combine to
polygonal (Fig. 3) and even apparent near-circular
arrangements.
A wide range of conical angles has been measured
in a large number of studies, ranging from >70°(Milton
1977) to 130°(Wieland et al. 2006), or as observed by
one of us (WUR) in Huronian sandstone of the South
Range of the Sudbury Structure where obvious near-
basal cuts through shatter cones yielded angles of
around 120°.
However, the recognition of shatter cones in the
field is not always easy, and questionable shatter cones
have been sometimes reported and qualified as poorly
developed shatter cones, pseudoshatter cones, or
ambiguous shatter cones (e.g., Krinov 1971; Becq-
Giraudon et al. 1992; Paillou et al. 2004, 2006; Fazio
et al. 2014; Newsom et al. 2015). Complete (360 degree)
cones are rare, and from some structures only rare cone
segments have been described. Where poorly developed
features have been reported, this corresponds to the
lack of complete cones, occurrence of subplanar
surfaces, barely discernable striations, or near-parallel
striations, or striations partially removed by weathering
Shatter conesCurrent knowledge 5
Fig. 2. Six examples of shatter cones. a) Near-complete shatter cone in dolomite from the Haughton Dome impact structure,
Canada. b) Near-complete shatter cone in sandstone from the Jebel Waqf as Suwwan structure in Jordan. c) Shatter cones in
Maraisburg quartzite, Schoemansdrif, western collar of the Vredefort Dome, South Africa. d) Shatter cones in the Booysens
shale of the northwest sector of the Vredefort Dome, South Africa. e) Shatter cones in Jurassic marly limestone from the
Agoudal site in the High Atlas domain of Morocco (cf. El Kerni et al. 2014). f) Shatter cones in sandstone from Gosses Bluff,
Australia.
6 D. Baratoux and W. U. Reimold
processes. Weathering overprint may not help either.
Confirmation of the validity of such field observations
or confirmation of the presence of shatter cones from
photographs may then be impossible in such cases,
especially if the accompanying descriptions are also
substandard.
Other geological processes may actually produce
curved or curviplanar surfaces, decorated with striations
or not, that can to some extent resemble shatter cones,
especially to nonexperts. A detailed comparison between
shatter cones and other phenomena was published by
Lugli et al. (2005). Gibson and Spray (1997) provided
three basic criteria whether a structure should be
considered a shatter cone or not
"The suspected feature must be a conical, or a part
conical fracture surface.
"Ridge and groove striations diverging from an apex
or central striae must be present.
"The structure must be pervasive and not surficial
(striations must develop not only on a single plane
or surface, but must occur in the three directions of
space).
However, bona fide shatter cones develop
sometimes as near-planar surfaces that are striated but
with very low angles between near-parallel striations.
This was already observed by Manton (1965) and also
elaborated by Nicolaysen and Reimold (1999).
Thus, for nonexperts, confusion with simple
fractures, plumose fractures, blast fractures, percussion
marks, striated fault surfaces (linear marks on
slickensides), ventifacts, cone-in-cone structures, or
crenulation cleavage is possibleand has occasionally
entered the literature, and a refinement of the shatter
cone recognition criteria, taking into account all
available information, is necessary to allow
identification of shatter cones that do not present the
well-developed characteristics listed by Gibson and
Spray (1997).
A chart for the discrimination of shatter cones
from other fracture phenomena is given in Fig. 4. The
chart is based on seven properties which should be
systematically described in addition to the presentation
of pictures: distribution of striated surfaces, lithology,
shape of striated surfaces, amplitudes of striations,
orientation of striated surfaces, tracks of striations, and
morphology of striations. The chart may also be used
as a guide for written descriptions. According to this
chart, observations of striated surfaces can be
considered as an undisputable evidence for shatter
cones, provided that the following properties are
reported: rounded and diverging striations appearing on
curved and spaced fracture surfaces of variable
orientations distributed within the volume of rock. The
observation of surfaces that partially meet these criteria
cannot be taken as evidence for shatter cones.
However, the observations of some of the listed
properties (e.g., a planar surface with divergent
rounded striations) should prompt the geologist to
search for further, undisputable evidence for shatter
cones. In addition to this chart, we discuss below the
characteristics of other shatter cone-unrelated
phenomena and indicate additional criteria that may be
used for discrimination. All criteria may be applied
during fieldwork, but additional observations with the
microscope or the electron microscope may, in some
cases, offer useful additional support of the initial
interpretation (e.g., for slickensides, crenulation
cleavage, or cone-in-cone structures).
COMPARISON WITH OTHER GEOLOGICAL
PHENOMENA
Simple Joints
Tensional or shear fractures are generally planar,
but may be occasionally curved, or present a succession
of linear segments with different orientations, due to
various factors including pre-existing voids, lithological
heterogeneities, or weaknesses that affect the
propagation of a crack, or due to deformation
overprint. The absence of striations on the surface is
sufficient to discard such a fracture as purely a
resemblance to shatter coningand one that does not
constitute evidence for an impact origin.
Plumose Fracture and Fringe Cracks
Fractures exhibit sometimes a planar striated
surface known as plumose fractures (or feather-like
fractures) (Fig. 5; Bankwitz 1965). They are also
described as “hackle” or “herring-bone” structures, or
“rib” or “augen” marks (Syme-Gash 1971). Plumose
structures are thought to develop in response to local
variations of the stress field (Syme-Gash 1971) and
result from an advancing fracture front in closely
spaced planes of weakness in an anisotropic material
(Ernstson and Schinker 1986). They can be used as
indicators of direction and sense of fracture propagation
(Woodworth 1896; Simon et al. 2006). The sizes of such
developments may vary from a few centimeters to a few
meters, but giant plumose markings (several tens of
meters in size) have also been reported in sandstones
(Bahat 1980). Plumose structures form planar surfaces.
The relief of striations associated with plumose fractures
is generally limited in comparison with the striations
associated with shatter cones, although this has been
never accurately quantified.
Shatter conesCurrent knowledge 7
8 D. Baratoux and W. U. Reimold
Ventifacts
Ventifacts are features produced by the erosive
action of wind-driven sand or ice crystals on the surface
of rocks. They can be found in all types of rocks but
usually develop in arid regions with little or no
vegetation to interfere with particle transport. The
different sides of boulders exposed to the action of
saltating grains may be polished, or may exhibit pitted,
etched, or grooved surfaces. Sharp edges develop
between the different sides that were exposed to wind
blowing with shifting directions. The progressive
abrasion of the rock surface can produce curved
surfaces of various shapes. Conical surfaces with
apparent apices pointing parallel to the direction of the
prevailing wind may form and represent a source of
confusion with shatter cones (Fig. 6). In addition, finely
laminated and/or foliated rocks, when abraded
obliquely to the sedimentary or tectonic phenomenon,
can exacerbate the false impression of shatter coning.
However, shatter cones may be easily distinguished
from ventifacts, as the latter appear only on the surface
exposed to wind, whereas the striated and curved
surfaces of shatter cones occur throughout the volume
of rock. Careful attention should be given to the
possibility of presence of ventifacts in dry/desert areas
known for intense aeolian erosionwhen considering
the option of shatter cone presence.
Striated Fault Surfaces
Slickensides, defined as polished fault surfaces, may
contain linear markings or striations (also known as
slickenlines) that indicate the slip direction along the
slickenside (Passchier and Trouw 2005). A slickenside is
caused by frictional movement along the two sides of a
fault. This surface is planar and may be covered by
slickenfibers (fibrous grains parallel to the later
movement along the fault), or present indentations
(teeth) that are classified as stylolites when teeth are
normal to the surface or as stickolites when teeth are
oblique to the surface. The occurrence of steps on
slickensides, developed transverse to the extension of
striae, can be used to determine the sense of movement
across the fault (Fig. 7). Contrary to the smooth and
rounded ridges and valleys on shatter cone surfaces,
slickenside striations have a distinctly angular
morphology (sharp edges, steps, teeth). The absence of
curvature of the fracture and the presence of generally
strictly parallel and stepped striations distinguish these
surfaces from shatter cones, which show divergent
striations. However, slickensides can sometimes form
curved sets on fault planes, for example, when fault
breccia components start to rotate upon displacement
within the shear zone. The striations appear on distinct
planes in the volume of the rock (not only on the
exposed surface), and show preferential orientations
controlled by the stress tensor (fault plane), which also
help to distinguish them from shatter cone surfaces.
Crenulation Cleavage
Crenulation cleavage occurs exclusively in
metamorphic rocks, when an early foliation (S1) is
overprinted by a later one (S2), whereby the second
phase of deformation occurs at some angle from the
earlier one (Passchier and Trouw 2005). Folding of the
earlier foliation by the later one creates a crenulation
that is observed in planes parallel to the original
foliation (Fig. 8). Microfold axes define planes that are
perpendicular to the first principal stress of the second
phase of deformation. Therefore, striations are
pervasive, but parallel to each other and in a single
direction. The morphology of crenulation cleavage is
variable, depending on the degree of overprinting by the
later phase with respect to the earlier one. Confusion
with shatter cones in metamorphic rocks is possible,
and caution should be paid when very low angles
between striations are reported. Examination of thin
sections under the microscope may be required to reveal
the true nature of such cleavage. As a matter of
principle, neither lineations (including all types of
intersection lineations) nor foliations are associated with
shatter cone surfaces.
Fig. 3. ab) Two examples of well exposed shatter cones at Jylh
anniemi, a prominent shatter cone exposure on a peninsula in
the central area of the deeply eroded Keurusselk
a impact structure, Finland (see also Hasch et al. 2016). The apex is cut off in
both examples, which gives an excellent view of the shatter cone as well as apical area. Note that the shapes are polygonal rather
than roundish, in both cases (as emphasized by black lines). Each segment can be correlated with anat the outcrop scale
important joint system. cf) Four images of shatter cones, also from Jylh
anniemi (Keurusselk
a) but smaller than the prime
examples shown in Figs. 3a and 3b. c) Two cup-shaped shatter cones, each between 10 and 20 cm long. Their apices are oriented
in opposite directions. The apex at the left is cut off by a joint plane, demonstrating that this “inverted cone” is also polygonal
in geometry. d) Several shatter cones that are all oriented along prominent joint planes. The area shown is ca. 60 cm wide. e)
Shatter cones oriented upward and exhibiting shapes that can be readily associated with several mutually interfering joint
systems. The area shown is ca. 30 cm wide. Glacial striations can be seen on the subhorizontal outcrop surface. f) A shatter
coned rock of ca 20 cm width. The shatter cone apex is cut off by a subhorizontal fracture, which illuminates that the shatter
cone not only has an angular shape, but that the “rampart” in the foreground is actually formed against a joint plane as well (all
images courtesy of Maximilian Hasch, Museum f
ur Naturkunde Berlin; see also Hasch et al. 2016).
Shatter conesCurrent knowledge 9
Fig. 4. Chart for the discrimination of shatter cones from other, possibly similar appearing geological features. The expression “spaced fracturing occurring in the
volume of rock” is used to refer to the observations of striated surfaces that do not occur only on exposed surfaces (as in the case of ventifacts) but occur in the
volume of rock as multiple surfaces separated by unfractured rock. Shatter cones have been sometimes qualified with the term “pervasive at the outcrop scale,” as
spaces separating individual shatter cones are usually small (typically of the order of 1 to several mm). The term “amplitude of striations” refers to amplitude of
the topography between ridges and valleys. In some cases (small samples, poorly developed shatter cones, shatter cones in coarse-grained rocks, etc.) it is nearly
impossible to reach a definitive conclusion, and these cases are indicated as “probable shatter cones.” Such observations should not be used for impact recognition,
but should prompt a search for better samples providing definitive evidence for shatter cones.
10 D. Baratoux and W. U. Reimold
Cone-in-Cone Features
Cone-in-cone structures occur exclusively in
sedimentary rocks. They were discussed and compared
against shatter cones in detail by Lugli et al. (2005).
They mostly occur in calcareous marly limestone and
shale and are generally composed of fibrous carbonate
and films of argillaceous material (Fig. 9). The rare
siliceous cone-in-cone structures known are considered a
result of replacement of calcite by silica. The cones are
developed perpendicular to the bedding plane and point
downward in nondeformed sediments. The mechanism
Fig. 5. a) Detail of plumose fractures in limestone, Glacier National Park (detail of a photograph by Michael C. Rygel, via
Wikipedia Commons). b) Shatter cone striations and plumose fracture striations can occur in the same outcrop, as illustrated in
the case of the Booysens shale locality northwest of Venterskroon in the collar of the Vredefort Dome, South Africa. Both
images were processed with
!
Photoshop to visually enhance the striations associated with the plumose fractures.
Shatter conesCurrent knowledge 11
of formation is still unclear but the following criteria
have been given (Lugli et al. 2005) to discriminate
between cone-in-cone structures and shatter cones in
sedimentary rocks. (1) Shatter cone striations have a
roundish shape, whereas cone-in-cone striae are step-
like; (2) shatter cones never show scaled surfaces; (3)
broken cone-in-cone structures invariably produce one
surface with striated cone features, but its opposite side
would display scaled cone cups, whereas the opposed
sides of shatter cones display the typical striations; (4)
shatter cones do not telescope out of the bedding plane,
as cone-in-cone structures may do; and (5) at the thin
section scale, the internal structure of cone-in-cone
features is well preserved, even after complete
silicification of the primary carbonate.
Percussion Marks
Percussion marks or percussion features (also
referred in sedimentology literature as “impact
features”) are curved to circular fractures due to low-
velocity rock-rock impacts (Lugli et al. 2005).
Percussion marks can show crude and sometimes
intricate striations that in the field may show close
resemblance to shatter cones (Reimold and Minnitt
1996). These authors showed an example that had been
Fig. 6. Examples of ventifact occurrences. a) Wind-abraded rocks from the Dyngj
okull area, central Iceland (see also Baratoux
et al. 2011). b) Wind-abraded andesite, Altiplano, Northern Argentina. c) Wind abrasion features from the Gilf Kebir Plateau
(Photo courtesy M. Di Martino, Osservatorio Astrofisico di Torino). Such features were erroneously considered shatter cones
(Paillou et al. 2004, 2006) suggesting to Paillou et al. (2004) the existence of a large field of impact craters. The putative
discovery was invalidated later by Orti et al. (2008). d) Mastcam image from the Rover Curiosity (Mars Science Laboratory,
image 0044ML0001990000102057E01, Sol 44) of rounded rocks that were proposed as the first ever observed shatter cones on
Mars (Newsom et al. 2015). Contrast and details of the image have been enhanced and reveal a smooth surface texture. The
similar appearance and shape of the other rocks in this image suggest that the observed blocks were affected by wind abrasion,
and that these images cannot be considered as the first observation of shatter cones at a Martian impact crater.
12 D. Baratoux and W. U. Reimold
weathered out to some extent and actually very closely
resembles a 3-D shatter conebut with an atypically
broad apical area (Fig. 10). Percussion marks are,
however, limited to the surface of block-impacted rock
and of specimens derived from it (Gibson and Spray
1997).
Blast Fractures
Blast fractures are fractures induced by blasting
with explosives and may be noted in quarries, along
roads, or at tunnel walls. They are true fracture
surfaces, but never display a conical fracture surface
Fig. 7. Two examples of slickensides. a) Slickensides in metapelite, near Støren (Norway). Photo courtesy U. Raschke, Museum
f
ur Naturkunde Berlin. b) Slickensides from the Upper Rhine Graben. Photo courtesy O. Vanderheaghe, University of Toulouse.
Shatter conesCurrent knowledge 13
(Gibson and Spray 1997). They show radial fractures
(Fig. 11) that are characterized by an angular geometry,
but they do not show surface striations. Usually the
macroscopically visible subplanar fractures radiate from
the explosion point. They are oriented perpendicular to
the drill hole, into which the explosive was placed (a
trace of such a drill hole is still evident as a near-
circular fracture in the innermost part of the feature
shown in Fig. 11). Generally, it is easy to obtain
corroborating evidence for a former blasting operation.
Fig. 8. Crenulation cleavage. a) Sketch of successive phases of deformation leading to the formation of a crenulation cleavage.
b) Example of crenulation cleavage from the Tarkwaian-type sediments (~2110 Ma) of the Hounde greenstone belt, Burkina
Faso. Photo courtesy L. Baratoux, IRD, G!
eosciences Environnement Toulouse.
14 D. Baratoux and W. U. Reimold
OCCURRENCES AND DISTRIBUTION OF
SHATTER CONES
On Earth
Since the first published map of global distribution
of shatter cones (Dietz and McHone 1984), many more
impact structures have been discoveredfrequently
through initial reports of shatter cone presenceand
others have been revisited in more detail. Here, we
present results of a new survey of the literature, more
than three decades after a first map was published
(Dietz and McHone 1984). For each impact structure,
the absence or presence of shatter cones was noted with
the respective lithological association(s) (Table 1).
Buried impact structures are flagged, as findings of
shatter cones are rarely possible in these cases. Drill
cores are sometimes available (or conditions leading to
Fig. 9. a) Cone-in-cone structures from Devonian-Silurian shale south of Erfoud (Morocco). Note the different surface
structures (fibrous growth of carbonate in the front and ripple-shaped structures on the upper side). Specimen ca. 6 cm wide. b)
Cone-in-cone structure from Devonian-Silurian shale south of Erfoud (Morocco) occurring in-situ in Devonian-Silurian shale.
Note how the specimen is divided by open fractures into aggregates of densely packed fibers. Knife for scale 9 cm long.
Shatter conesCurrent knowledge 15
partial exposure), but rarely provide good shatter cone
samples.
To date, 188 impact structures are listed in the
Earth Impact Database (last visited on 3 February
2016). The Saqqar impact structure that was discovered
this year (Kenkmann et al. 2015) has not been entered
into the database yet. Among 189 known impact
structures in total, 133 are exposed; of these 77 impact
structures are unambiguously associated with shatter
cones (which is actually less than the preliminary
estimation of Ferri#
ere and Osinski 2010). Ambiguous
observations of shatter cones have been reported for 8
additional impact structures (Kamil, Tabun-Khara-Obo,
Shunak, Matt Wilson, Bigach, Flaxman, Upheaval
Dome, and El’gygytgyn). Shatter cones have also been
reported from the Agoudal (Morocco) site, for which
there is no other evidence for the presence of an impact
structure (Chennaoui-Aoudjehane et al. 2016) and at
Bernhardzell (Switzerland) where they are considered to
occur in distal ejecta from the Ries crater. A map of the
global distribution of impact structures and shatter cone
occurrences is given in Fig. 12. A few dubious cases
were identified from a systematic examination of
published shatter cone images. These include the
Sikhote Alin meteorite impact craters (Russia, Krinov
1971), the Kamil impact crater (Egypt, Fazio et al.
2014), the Aorounga impact structure (Chad; Koeberl
et al. 2005), and the El’gygytgyn impact structure
(Raschke et al. 2013).
The picture reported in Krinov (1971) lacks the
principal shatter cone characteristics such as divergent
striations, and would be more compatible with foliated
sediment. The field photograph from the Aorounga
structure by Koeberl et al. (2005) corresponds to
ventifacts (lack of striations), whereas the description
cautiously mentioned “fracturing phenomenon
resembling shatter cones.” For the Kamil structure, a
close-up view of divergent striations on a fraction of the
sample surface and evidence of a thin Si-rich glass
coating on the fracture surface were provided. However,
the finding of a single, poorly developed shatter cone in
ejecta from the Kamil crater (Fazio et al. 2014) is
problematic, and more observations are needed to
confirm that shatter cones may be observed for such a
small crater (see also discussion in Chennaoui-
Aoudjehane et al. 2016), even acknowledging the fact
that tiny shatter cones were experimentally generated in
sandstone shock experiments (Kenkmann et al. 2012;
Wilk and Kenkmann 2015a, 2015b, 2016). Definitive
identification of shatter cones at the El’gygytgyn impact
structure remains challenging given the sediment cover
on the central part of the crater and the small size of
the samples recovered from drill core.
The proportion of impact structures associated with
shatter cones as a function of diameter (for the exposed
impact structures only) is illustrated in Fig. 13. Shatter
cones are reported for 100% of exposed impact
structures larger than 32 km, but this number
Fig. 10. Percussion mark from a site at the eastern circumference of the Bushveld Complex (South Africa). The cone-shaped
deformation structure with radially outward diverging striations was formed underneath a fossil water-fall, when a large boulder
fell down onto the lower ground surface. See Reimold and Minnitt (1996) for detail. The mark is, at base, 9 cm wide.
16 D. Baratoux and W. U. Reimold
progressively drops to ~20% of the confirmed structures
in the 12 km range. Below 1 km, a dubious shatter
cone has been only reported for 45-m-diameter Kamil
(Fazio et al. 2014). The smallest impact crater allegedly
associated with shatter cones, besides Kamil, is Tabun-
Khara-Obo (TKO), a 1.3 km crater in Mongolia
(Raikhlin et al. 1993; Masaitis 1999). No shatter cones
were reported from similar-sized Barringer Crater
formed in sandstone and from Tswaing, also of
comparable size, formed in coarse-grained granite. No
pictures have been provided in the TKO literature, but
shatter cones are said to be common in the schist, and a
sketch presents two outcrops along the rim of the crater
where shatter cones had been observed (Masaitis 1999).
Several explanations may be offered for the lack of
shatter cones at small craters. On an airless body, there
should be no lower limit for the formation of shatter
cones in an impact event. However, the volume of target
rocks that experiences shock pressures high enough to
produce shatter cones must scale with the volume of
the crater. This is illustrated, for instance, in the case
of the explosion experiments where beautiful examples
of shatter cones were formed close to the explosion
center only (Roddy and Davis 1977). In the case of
Earth, the deceleration induced by the atmospheric
drag reduces the impact velocity of small objects. This
effect, considered to be responsible for the paucity of
melt for kilometer-sized or sub-kilometer impact stru-
ctures such as Meteor Crater (Melosh and Collins 2005),
may also limit the formation of shatter cones in the
smallest impact structures, even acknowledging the fact
that shock pressures typical for shatter cone formation
may be locally attained at the impact point for velocit-
ies as low as a few km s
!1
(see, for instance, estimations
by Fazio et al. [2014] for the Kamil impact structure
using the planar impact approximation, or numeri-
cal simulations for the shatter cones of Agoudal by
Lorenz et al. 2015). The small volume of shatter cones
Fig. 11. A typical blast hole generated during the mid-20th century quarrying operation at Otavi, northeast of the town of Parys
in the outer core of Archean basement of the Vredefort Dome. Photo courtesy M. Hoffmann (University Potsdam and Museum
f
ur Naturkunde Berlin).
Shatter conesCurrent knowledge 17
Table 1. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Acraman 90 !32 1 135 27 Australia
(South Australia)
~590 Yes Dacite Yes No 1986 X Williams (1986, 1994;
Williams et al. (1986))
Amelia Creek 20 !20 55 134 50 Australia (Northern
Territory)
6001640 Yes Quartzite Yes No 2003 X MacDonald and
Mitchell (2003);
MacDonald et al.
(2005)
Ames 16 36 15 !98 12 USA (Oklahoma) 470 #30 No No Yes
Amguid 0.450 26 5 4 23 Algeria <0.1 No Yes No Reimold and Koeberl
(2014)
Aorounga 16 19 6 19 15 Chad <345 No Yes No Koeberl et al. (2005);
Becq-Giraudon
et al. (1992)
Aouelloul 0.390 20 15 !12 41 Mauritania 3.0 #0.3 No Yes No Reimold and Koeberl
(2014)
Araguainha 40 !16 47 !52 59 Brazil 254.7 #2.5 Yes Sandstone Yes No 2012 X Tohver et al. (2012)
Avak 12 71 15 !156 38 USA (Alaska) 395 No No Yes Therriault and Grantz
(1995)
B.P. 2.00 25 19 24 20 Libya <120 No Yes No Reimold and Koeberl
(2014)
Barringer 1.19 35 2 !111 1 USA (Arizona) 0.049 #0.003 No Yes Yes
Beaverhead 60 44 36 !113 0 USA (Montana) ~600 Yes Sandstone Yes No 1990 X Hargraves et al. (1990)
Beyenchime-
Salaatin
8.0 71 0 121 40 Russia 40 #20 Yes Carbonate Yes No 1976 Masaitis (1976, 1999);
Masaitis et al. (1980)
Bigach 8.0 48 34 82 1 Kazakhstan 5 #3 Amb. Basalt, Andesite Yes Yes 1986 Masaitis (1999); Kiselev
and Korotuschenko
(1986)
Boltysh 24 48 45 32 10 Ukraine 65.17 #0.64 Yes Granite No No 1976 Masaitis (1976, 1999);
Masaitis et al. (1980);
Bosumtwi 11 6 30 !1 25 Ghana 1.07 No No Yes Reimold and Koeberl
(2014)
Boxhole 0.170 !22 37 135 12 Australia
(Northern
Territory)
0.0054 #0.0015 No Yes No
Brent 3.80 46 5 !78 29 Canada (Ontario) >453 No No Yes
Calvin 8.5 41 50 !85 57 USA (Michigan) 450 #10 No No Yes Masaitis (1999)
Campo del
Cielo
0.050 !27 38 61 42 Argentina <0.004 No Yes Yes
Carancas 0.014 !16 40 !69 3 Peru 0.000007 No Yes No
Carswell 39 58 27 !109 30 Canada
(Saskatchewan)
115 #10 Yes Gneiss Yes Yes 2004 Duhamel et al. (2004)
Charlevoix 54 47 32 !70 18 Canada (Quebec) 342 #15 Yes Gneiss, Sandstone,
Limestone,
Quartzite
Yes Yes 1968 X Robertson (1968, 1975b)
Roy and Rondot (1970;
Roy (1978), Lemieux
et al. (2000)
Chesapeake
Bay
40 37 17 !76 1 USA (Virginia) 35.3 #0.1 No No Yes Bartosova et al. (2009)
(petrography of drill
cores)
18 D. Baratoux and W. U. Reimold
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Chicxulub 150 21 20 !89 30 Mexico (Yucatan) 64.98 #0.05 No No Yes
Chiyli 5.5 49 10 57 41 Kazakhstan 46 #7 No Yes Yes
Chukcha 6.0 75 42 97 48 Russia <70 No Yes Yes Vishnevsky (1995) (no
traces of shatter
cones are present)
Clearwater
East
26 56 5 !74 7 Canada (Quebec) 460470 No Yes Yes
Clearwater
West
36 56 13 !74 30 Canada (Quebec) 290 #20 Yes Gneiss Yes Yes 1964 X Dence (1964)
Cloud Creek 7.0 43 7 !106 45 USA
(Wyoming)
190 #30 No No Yes Stone and Therriault
(2003)
Colonia 3.60 !23 52 !46 43 Brazil 536 No Yes Yes Riccomini et al. (2011)
Connolly
Basin
9.0 !23 32 124 45 Australia (Western
Australia)
<60 No Yes No Haines (2005);
Shoemaker and
Shoemaker (1988)
Couture 8.0 60 8 !75 20 Canada (Quebec) 430 #25 No Yes No Dence (1964) (shatter
cones were not
reported)
Crawford 8.5 !34 43 139 2 Australia (South
Australia)
>35 No Yes No
Crooked
Creek
7.0 37 50 !91 23 USA (Missouri) 320 #80 Yes Dolomite Yes No 1980 Dietz and Lambert
(1980)
Dalgaranga 0.024 !27 38 117 17 Australia (Western
Australia)
~0.27 No Yes No
Decaturville 6.0 37 54 !92 43 USA (Missouri) <300 Yes Dolomite Yes Yes 1979 X Evans et al. (2008);
Offield and Pohn
(1979)
Deep Bay 13 56 24 !102 59 Canada
(Saskatchewan)
99 #4 No No Yes
Dellen 19 61 48 16 48 Sweden 89.0 #2.7 No Yes No
Des Plaines 8.0 42 3 !87 52 USA (Illinois) <280 Yes Dolomite No Yes 1986 McHone et al.
(1986, 1987)
Dhala 11 25 18 78 8 India >1700, <2100 No Yes Yes Pati et al. (2008)
Dobele 4.5 56 35 23 15 Latvia 290 #35 Yes Carbonate,
Sulfate
Yes Yes 1999 Masaitis (1999);
Abels et al. (2002)
Eagle Butte 10 49 42 !110 30 Canada (Alberta) <65 Yes Limestone No Yes 1985 X Ezeji-Okoye (1985);
Hanova et al. (2005)
El’gygytgyn 18 67 30 172 5 Russia 3.5 #0.5 Amb. Crystalline Yes Yes 2013 X Raschke et al. (2013)
Elbow 8.0 50 59 !106 43 Canada
(Saskatchewan)
395 #25 No No Yes
Flaxman 10 !34 37 139 4 Australia
(South Australia)
>35 Amb. Breccia Yes No 1999 Haines et al. (1999)
Flynn Creek 3.80 36 17 !85 40 USA (Tennessee) 360 #20 Yes Dolomite Yes Yes 1979 X Evenik et al. (2004);
Roddy (1979)
Shatter conesCurrent knowledge 19
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Foelsche 6.0 16 40 136 47 Australia (Northern
Territory)
>545 No Yes No Haines (2005) (shatter
cones were not
reported in this partly
buried impact
structure)
Gardnos 5.0 60 39 9 0 Norway 500 #10 No Yes No Dons and Naterstad
(1992)
Glasford 4.0 40 36 !89 47 USA (Illinois) <430 Yes Breccia Yes Yes 1986 McHone et al. (1986,
1987); Dietz and
McHone (1991)
Glikson 19 !23 59 121 34 Australia (Western
Australia)
<508 No Yes No Haines (2005)
Glover Bluff 8.0 43 58 !89 32 USA (Wisconsin) <500 Yes Dolomite Yes Yes 1983 X Read (1983)
Goat Paddock 5.1 !18 20 126 40 Australia (Western
Australia)
<50 Yes Sed. rock Yes Yes 1980 Harms et al. (1980);
Shoemaker and
Shoemaker (1988)
Gosses Bluff 22 !23 49 132 19 Australia (Northern
Territory)
142.5 #0.8 Yes Sandstone Yes Yes 1967 X Haines (2005); Dietz
(1967)
Gow 5.0 56 27 !104 29 Canada
(Saskatchewan)
<250 No Yes No Osinski et al. (2012)
Goyder 3.00 !13 28 135 2 Australia (Northern
Territory)
<1400 Yes Sandstone Yes No 1996 X Haines (1996)
Granby 3.00 58 25 14 56 Sweden ~470 No No Yes
Gusev 3.00 48 26 40 32 Russia 49.0 #0.2 No No Yes Masaitis (1999)
Gweni-Fada 14 17 25 21 45 Chad <345 No Yes No Koeberl et al. (2005)
Haughton 23 75 22 !89 41 Canada (Nunavut) 39 Yes Sandstone,
Limestone
Yes No 1975 X Robertson (1975a);
Robertson and Grieve
(1975); Osinski (2007)
Haviland 0.015 37 35 !99 10 USA (Kansas) <0.001 No Yes No
Henbury 0.157 !24 34 133 8 Australia (Northern
Territory)
0.0042 #0.0019 No Yes No
Holleford 2.35 44 28 !76 38 Canada (Ontario) 550 #100 No No Yes
Hummeln 1.20 57 22 16 15 Sweden ~470 No Yes No Alwmark et al. (2015)
Ile Rouleau 4.0 50 41 !73 53 Canada (Quebec) <300 Yes Dolomite Yes No 1976 Caty et al. (1976)
Ilumets
a 0.080 57 58 27 25 Estonia ~0.0066 No Yes Yes
Ilyinets 8.5 49 7 29 6 Ukraine 378 #5 Yes Granite No Yes 1980 Masaitis et al. (1980);
Masaitis (1999)
Iso-Naakkima 3.00 62 11 27 9 Finland >1000 No No Yes
J
anisj
arvi 14 61 58 30 55 Russia 700 #5 Yes Siltstone Yes No 1976 X Maisaitis (1976);
Masaitis et al. (1980)
Jebel Waqf
as Suwwan
5.5 31 3 36 48 Jordan 5637 Yes Sandstone,
Limestone
Yes No 2008 X Salameh et al.
(2006, 2008)
Kaalij
arv 0.110 58 24 22 40 Estonia 0.004 #0.001 No Yes No
Kalkkop 0.640 !32 43 24 26 South Africa 0.250 #0.050 No Yes Yes Reimold and Koeberl
(2014)
20 D. Baratoux and W. U. Reimold
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Kaluga 15 54 30 36 12 Russia 380 #5 No No Yes Masaitis et al. (1980);
Masaitis (1999)
(shatter cones were
not reported)
Kamensk 25 48 21 40 30 Russia 49.0 #0.2 Yes Sandstone,
Limestone
No Yes 1976 X Masaitis (1976);
Masaitis et al. (1980)
Kamil 0.045 22 1 26 5 Egypt <0.005
a
Amb. Sandstone Yes No 2014 X Fazio et al. (2014
(
a
age from Folco
et al. 2011)
Kara 65 69 6 64 9 Russia 70.3 #2.2 Yes Sandstone No Yes 1980 X Dietz and McHone
(1991); Masaitis et al.
(1980); Masaitis (1999)
Kara-Kul 52 39 1 73 27 Tajikistan <5 Yes Schist Yes No 1993 Gurov et al. (1993);
Gurov and Gurova
(1993)
K
ardla 4.0 59 1 22 46 Estonia ~455 No Yes Yes Masaitis (1999)
Karikkoselk
a 1.50 62 13 25 15 Finland ~230 Yes Granite Yes No Lehtinen and Pesonen
(1996)
Karla 10 54 55 48 2 Russia 5 #1 Yes Limestone Yes Yes 1999 X Masaitis (1999)
Kelly West 10 !19 56 133 57 Australia (Northern
Territory)
>550 Yes Sandstone No No 1973 Tonkin (1973);
Shoemaker and
Shoemaker (1996)
Kentland 13 40 45 !87 24 USA (Indiana) <97 Yes Limestone Yes Yes 1947 X Dietz (1947)
Keurusselk
a 30 62 8 24 36 Finland <1800 Yes Schist, Granite,
Gneiss,
Granodiorite,
Metavolcanic
Yes No 2007 X Hietala and Moilanen
(2007); Ferri#
ere and
Osinski (2010)
Kgagodi 3.50 !22 29 27 35 Botswana <180 No Yes Yes Reimold and Koeberl
(2014)
Kursk 6.0 51 42 36 0 Russia 250 #80 No No Yes Masaitis (1999) (Shatter
cones were not
reported)
La Moinerie 8.0 57 26 !66 37 Canada (Quebec) 400 #50 No Yes No Robertson and Grieve
(1975)
Lappaj
arvi 23 63 12 23 42 Finland 76.20 #0.29 Yes Granite, Gneiss Yes Yes 1976 Lehtinen (1976)
Lawn Hill 18 !18 40 138 39 Australia
(Queensland)
>515 Yes Quartzite Yes No 1987 X Stewart and Mitchell
(1987); Shoemaker
and Shoemaker (1996);
Salisbury et al. (2008)
Liverpool 1.60 !12 24 134 3 Australia (Northern
Territory)
150 #70 No Yes No Haines (2005); Guppy
et al. (1971)
Lockne 7.5 63 0 14 49 Sweden ~458 No Yes Yes Therriault and
Lindstr
om (1995)
Logancha 20 65 31 95 56 Russia 40 #20 Yes Siltstone,
Claystone,
Dolomite
No No 1983 X Fel’dman et al. (1983);
Vishnevsky (1986);
Masaitis et al. (1980);
Masaitis (1999)
Shatter conesCurrent knowledge 21
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Logoisk 15 54 12 27 48 Belarus 42.3 #1.1 Yes Gneiss, Dolomite No Yes 1980 Masaitis et al. (1980)
Lonar 1.83 19 58 76 31 India 0.052 #0.006 Yes Basalt Yes Yes 1973 Fredriksson et al. (1973);
Masaitis et al. (1980)
Luizi 17 !10 10 28 0 Democratic Republic
of Congo
<573 Yes Sandstone Yes No 2011 X Reimold and Koeberl
(2014); Ferri#
ere
et al. (2011)
Lumparn 9.0 60 9 20 6 Finland ~1000 Yes Granite No Yes 1993 Svensson (1993)
Macha 0.300 60 6 117 35 Russia <0.007 No Yes No
M
$
alingen 1.00 62 55 14 33 Sweden ~458 No Yes Yes
Manicouagan 85 51 23 !68 42 Canada (Quebec) 214 #1 Yes Gneiss Yes Yes 2014 Dressler (1990);
Thompson (2014)
Manson 35 42 35 !94 33 USA (Iowa) 74.1 #0.1 No No Yes Koeberl and Anderson
(1996)
Maple Creek 6.0 49 48 !109 6 Canada
(Saskatchewan)
<75 No No Yes Grieve et al. (1988)
(shatter cones were
not reported)
Marquez 13 31 17 !96 18 USA (Texas) 58 #2 Yes Sed. Rock No Yes 1994 Wong et al. (1994)
Matt Wilson 7.5 !15 30 131 11 Australia (Northern
Territory)
1402 #440 Amb. Yes No 2005 Haines (2005);
Kenkmann and
Poelchau (2009)
Middlesboro 6.0 36 37 !83 44 USA (Kentucky) <300 Yes Siltstone Yes Yes 1966 Dietz (1966a)
Mien 9.0 56 25 14 52 Sweden 121.0 #2.3 No Yes Yes
Mishina Gora 2.50 58 43 28 3 Russia 300 #50 Yes Schist, Gneiss Yes Yes 1976 X Masaitis (1976,1999);
Masaitis et al. (1980)
Mistastin 28 55 53 !63 18 Canada (Labrador,
Newfoundland)
36.4 #4 Yes Anorthosite Yes No 1968 Currie (1968)
Mizarai 5.0 54 1 23 54 Lithuania 500 #20 Yes Gneiss,
Metagabbro,
Granite
Yes Yes 1980 X Masaitis et al. (1980);
Masaitis (1999)
Mjølnir 40 73 48 29 40 Norway 142.0 #2.6 No No Yes
Montagnais 45 42 53 !64 13 Canada
(Nova Scotia)
50.50 #0.76 No No Yes
Monturaqui 0.460 !23 56 !68 17 Chile <1 No Yes No
Morasko 0.100 52 29 16 54 Poland <0.01 No Yes No
Morokweng 70 !26 28 23 32 South Africa 145.0 #0.8 No No Yes Reimold and Koeberl
(2014)
Mount
Toondina
4.0 !22 57 135 22 Australia (South
Australia)
<110 No Yes Yes Shoemaker and
Shoemaker (1988)
Neugrund 8.0 59 20 23 40 Estonia ~535 No No No
New Quebec 3.44 61 17 !73 40 Canada (Quebec) 1.4 #0.1 No Yes No
Newporte 3.20 48 58 !101 58 USA
(North Dakota)
<500 No No Yes Koeberl and Anderson
(1996)
Nicholson 13 62 40 !102 41 Canada (Northwest
Territories)
<400 No No No
Oasis 18 24 35 24 24 Libya <120 No Yes No Reimold and Koeberl
(2014)
22 D. Baratoux and W. U. Reimold
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Obolon’ 20 49 35 32 55 Ukraine 169 #7 Yes Breccia Yes Yes 1977 Val’ter et al. (1977);
Masaitis (1999)
Odessa 0.168 31 45 !102 29 USA (Texas) <0.0635 No Yes Yes Koeberl and Anderson
(1996)
Ouarkziz 3.50 29 0 !7 33 Algeria <70 No Yes No Reimold and Koeberl
(2014)
Paasselk
a 10 62 2 29 5 Finland <1800 No Yes Yes Pesonen et al. (1999)
(shatter cones were
not reported)
Piccaninny 7.0 !17 32 128 25 Australia (Western
Australia)
<360 No Yes No Shoemaker and
Shoemaker (1988)
Pilot 6.0 60 17 !111 1 Canada (Northwest
Territories)
445 #2 No Yes No
Popigai 90 71 39 111 11 Russia 35.7 #0.2 Yes Gneiss, Sandtone,
Metagreywacke,
Gabbro
Yes Yes 1972 Masaitis et al.
(1972, 1980)
Presqu’ile 24 49 43 !74 48 Canada (Quebec) <500 Yes Basalt,
Rhyodacite
Yes No 1990 X Higgins and Tait (1990)
Puchezh-
Katunki
40 56 58 43 43 Russia 167 #3 Yes Carbonate,
Argillites
No Yes 1999 X Masaitis (1999);
Masaitis and Pevzner
(1999)
Ragozinka 9.0 58 44 61 48 Russia 46 #3 Yes Sedimentary rock No Yes 1999 Masaitis (1999)
Red Wing 9.0 47 36 !103 33 USA
(North Dakota)
200 #25 Yes Breccia No Yes 1975 Brenan et al. (1975);
Koeberl et al. (1996)
Riachao Ring 4.5 !7 43 !46 39 Brazil <200 No Yes No Romano and Cr!
osta
(2004)
Ries 24 48 53 10 37 Germany 15.1 #0.1 Yes Limestone Yes Yes 2006 X Hofmann and Gnos
(2006)
Rio Cuarto 4.5 !32 52 !64 14 Argentina <0.1 No Yes No
Ritland 2.70 59 14 6 26 Norway 520 #20 Yes Calcite Yes No 2012 Kalleson et al. (2012)
Rochechouart 23 45 50 0 56 France 201 #2 Yes Schist, Granite Yes No 1971 X Kraut and French (1971);
Sapers et al. (2014)
Rock Elm 6.0 44 43 !92 14 USA (Wisconsin) <505 No Yes No French and Cordua
(1999)
Roter Kamm 2.50 !27 46 16 18 Namibia 3.7 #0.3 No Yes No Reimold and Koeberl
(2014) (shatter cones
were not reported)
Rotmistrovka 2.70 49 0 32 0 Ukraine 120 #10 No No No Masaitis et al. (1980);
Masaitis (1999)
S
a
aksj
arvi 6.0 61 24 22 24 Finland ~560 No Yes Yes Kinnunen and Lindqvist
(1998)
Saarij
arvi 1.50 65 17 28 23 Finland >600 No No Yes Pesonen (1998)
Saint Martin 40 51 47 !98 32 Canada (Manitoba) 220 #32 No No Yes
Santa Fe 6.0 35 45 !105 56 USA
(New Mexico)
<1200 Yes Granitoid,
Metasediment
No No 2008 Fackelman et al. (2008)
Santa Marta 10 !10 10 !45 15 Brazil 66100 Yes Sandstone,
Quartzite
No No 2014 X De Oliveira et al. (2014)
Shatter conesCurrent knowledge 23
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Saqqar 34 29 35 38 42 Saudi Arabia 70410
a
No No Yes Kenkmann et al. (2015);
Neville et al. (2014)
(
a
age from Kenkmann
et al. 2015)
Serpent
Mound
8.0 39 2 !83 24 USA (Ohio) <320 Yes Breccia Yes Yes Carlton et al. (1998)
Serra da
Cangalha
12 !85 !46 52 Brazil <300 Yes Sandstone Yes Yes 2011 X Kenkmann et al. (2011);
Vasconcelos et al. (2013)
Shoemaker 30 !25 52 120 53 Australia (Western
Australia)
1630 #5 Yes Granite Yes No 1980 X Haines (2005); Bunting
et al. (1980)
Shunak 2.80 47 12 72 42 Kazakhstan 45 #10 Amb. Yes Yes 1978 X Fel’dman and Granovksy
(1978); Masaitis et al.
(1980)
Sierra Madera 13 30 36 !102 55 USA (Texas) <100 Yes Dolomite, Calcite,
Siltstone,
Sandstone,
Chert
Yes Yes 1968 X Howard and Offield
(1968); Wilshire et al.
(1972); Adachi and
Kletetschka (2008)
Sikhote Alin 0.020 46 7 134 40 Russia 0.000067 No Yes No Pashkovskii (1977),
Alexander Basilevsky
(personal
communcation)
Siljan 52 61 2 14 52 Sweden 376.8 #1.7 Yes Granite,
Sedimentary rock
Yes Yes 2011 Holm et al. (2011)
Slate Islands 30 48 40 !87 0 Canada (Ontario) ~450 Yes Basalt, Diorite,
Rhyolite
Yes No 1978 X Officer and Neville
(1991); Stesky and
Halls (1979); Sage
(1978)
Sobolev 0.053 46 18 137 52 Russia <0.001 No Yes Yes
S
oderfj
arden 6.6 63 2 21 35 Finland ~600 No No Yes
Spider 13 !16 44 126 5 Australia (Western
Australia)
>570 Yes Quartzite Yes No 1996 X Shoemaker and
Shoemaker (1996);
Haines (2005)
Steen River 25 59 30 !117 38 Canada (Alberta) 91 #7 No No Yes
Steinheim 3.80 48 41 10 4 Germany 15 #1 Yes Sandstone,
Claystone
Yes Yes 1905 X Branco and Fraas
(1905); Schmieder
and Buchner (2010a,
2010b); Buchner and
Schmieder (2010)
Strangways 25 !15 12 133 35 Australia (Northern
Territory)
646 #42 Yes Sandstone Yes No 1971 Shoemaker and
Shoemaker (1988);
Guppy et al. (1971)
Suavj
arvi 16 63 7 33 23 Russia ~2400 No No No
Sudbury 130 46 36 !88 11 Canada (Ontario) 1850 #3 Yes Quartzite,
Sandstone
Yes Yes 1964 X Dietz (1964); Dressler
et al. (1984); Ferri#
ere
and Osinski (2013)
Suvasvesi N 4.0 62 42 28 10 Finland <1000 No Yes Yes Pesonen et al. (1996)
24 D. Baratoux and W. U. Reimold
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Suvasvesi S 3.80 62 42 28 10 Finland ~250 Yes Gneiss,
Granodiorite
Yes Yes 2002 X Lehtinen et al. (2002)
Tabun-
Khara-Obo
1.30 44 7 109 39 Mongolia 150 #20 Amb. Schist Yes No 1999 Masaitis (1999)
Talemzane 1.75 39 19 4 2 Algeria <3 No Yes Yes Reimold and Koeberl
(2014)
Tenoumer 1.90 22 55 !10 24 Mauritania 0.0214 #0.0097 No Yes No Reimold and Koeberl
(2014)
Ternovka 11 48 8 33 31 Ukraine 280 #10 Yes Syenite No Yes 1999 X Masaitis (1999)
Tin Bider 6.0 27 36 5 7 Algeria <70 No Yes No Reimold and Koeberl
(2014)
Tookoonooka 55 !27 7 142 50 Australia
(Queensland)
128 #5 No No Yes Haines (2005)
Tswaing 1.13 !25 24 28 5 South Africa 0.220 #0.052 No Yes Yes Reimold and Koeberl
(2014)
Tunnunik 25 72 28 !113 58 Canada
(Victoria Island)
>130, <450 Yes Limestone Yes No 2013 Dewing et al. (2013)
Tv
aren 2.00 58 46 17 25 Sweden ~455 No No Yes
Upheaval Dome 10 38 26 !109 54 USA (Utah) <170 Amb. Sandstone,
Siltstone
Yes Yes 1999 Kriens et al. (1999)
Varge~
ao Dome 12 !26 50 !52 7 Brazil 123 #1.4 Yes Basalt Yes Yes 2012 X Cr!
osta et al. (2012)
Veevers 0.080 !22 58 125 22 Australia (Western
Australia)
<1 No Yes No
Vepriai 8.0 55 5 24 35 Lithunia >160 #10 Yes No Yes 1980 Masaitis et al. (1980)
Viewfield 2.50 49 35 !103 4 Canada
(Saskatchewan)
190 #20 No No Yes
Vista Alegre 9.5 !25 57 !52 41 Brazil <65 Yes Basalt Yes No 2010 X Cr!
osta et al. (2010)
Vredefort 160 !27 0 27 30 South Africa 2023 #4 Yes Shale,
Metasediment,
Granite
Yes Yes 1927 X Nel (1927), Hargraves
(1961); Manton (1965);
Nicolaysen and Reimold
(1999); Wieland
et al. (2006)
Wabar 0.116 21 30 50 28 Saudi Arabia 0.00014 No Yes Yes Gnos et al. (2013)
Wanapitei 7.5 46 45 !80 45 Canada (Ontario) 37.2 #1.2 No No No
Wells Creek 12 36 23 !87 40 USA (Tennessee) 200 #100 Yes Sedimentary Rock Yes Yes 2012 X Ford et al. (2012)
West Hawk 2.44 49 46 !95 11 Canada (Manitoba) 351 #20 No No Yes
Wetumpka 6.5 32 31 !86 10 USA (Alabama) 81.0 #1.5 No Yes Yes Neathery (1976)
Whitecourt 0.036 54 0 !115 36 Canada (Alberta) <0.0011 No Yes No Kofman et al. (2010)
Wolfe Creek 0.875 !19 10 127 48 Austalia (Western
Australia)
<0.3 No Yes No
Woodleigh 40 !26 3 114 39 Australia (Western
Australia)
364 #8 No No Yes Reimold et al. (2003)
Xiuyan 1.80 40 21 123 27 China >0.05 No Yes Yes Chen et al. (2010)
Yarrabubba 30 !27 10 118 50 Australia
(Western Australia)
~2000 Yes Crystalline Yes No 2003 X MacDonald et al. (2003)
Zapadnaya 3.20 49 44 29 0 Ukraine 165 #5 No No Yes Masaitis (1999)
Zeleny Gai 3.50 48 4 32 45 Ukraine 80 #20 Yes Granite No Yes 1999 Masaitis (1999)
Shatter conesCurrent knowledge 25
Table 1. Continued. Database of shatter cone occurrences at terrestrial impact structures.
Crater name
(sorted by
diameter)
Diameter
(km)
a
Latitude Longitude
Country (state)
Age #error
(Myr)
Shatter
cones
Shatter cone
lithologies Exposed Drilled
First
mention Pict. References°°
Zhamanshin 14 58 24 60 58 Kazakhstan 0.9 #0.1 Yes Volcanosediment,
Limestone
Yes Yes 1980 X Florenskiy and
Dabizha (1980)
Shatter cone occurrences lacking association with other evidence for an impact structure (or association not definitively proven)
Agoudal nd 31 59.2 !5 31.0 Morocco Yes Limestone —— X Lorenz et al. (2015);
Chennaoui-Aoudjehane
et al. (2016)
Bernhardzell nd 47 28.3 9 20.2 Switzerland Yes Limestone —— Hofmann and Gnos
(2006) (probably distal
ejecta from Ries crater)
Craters with occurrences of shatter cones are written in bold font. Ambiguous reports of shatter cones are noted in bold italics font. References corresponding the impact structures
with no shatter cone are cited when detailed field observations were reported, or when lack of shatter cone was explicitly mentioned.
a
Impact crater diameters and ages are taken from the impact crater database (http://www.passc.net/EarthImpactDatabase)The reader is referred to this database for the references
associated with these values.
26 D. Baratoux and W. U. Reimold
formed under these conditions will occur only at shallow
layers, and they may be rapidly affected by erosion and
erased.
Shatter cones are found in a wide range of
lithologies. It has been generally thought that they
occur more frequently and are better developed in fine-
grained rocks than in coarse-grained rocks. It can be
stated that the finer grained the host lithology is, the
more intricately the striations are developed and the
shatter cone itself will be displayed. The lesser findings
of shatter cones in coarse-grained rocks could simply
reflect that they are more difficult to detect due to their
cruder appearance. However, as demonstrated by Hasch
et al. (2016) and Zaag et al. (2016), the Keurusselk
a
impact structure in Finland was formed in medium-
grained to even pegmatoidal granitoid basement and is
a notable exception to this rule. Keurusselk
a is
characterized by an abundance of well-developed shatter
cones in relatively coarse-grained granitoids.
Furthermore, WUR reports that in recent years
excellent shatter cones have been observed at a number
of sites in the medium-grained granitic lithologies of the
outer core of the Vredefort central uplift (the Vredefort
Dome; e.g., Fig. 14).
A survey of shatter cone relation to lithology
(Table 2) reveals that shatter cones are known most
commonly from sedimentary rocks (quartzite,
sandstone, and calcareous sediments), whereas they
Fig. 12. Global distribution of impact structures and shatter cones. Each impact structure is represented by a colored circle. Its
size relates to the structure’s diameter and its color represents the age of the impact event. Impact structures associated with
shatter cones are represented by filled circles (white circles indicate ambiguous reports of shatter cones). Non exposed impact
structures are noted with a cross. Exposed structures lacking evidence for shatter cones are represented with an open circle. The
unknown size of a possibly eroded impact structure, or remnant thereof, associated with findings of shatter cones at Agoudal
(Morocco) and the shatter cones observed at Bernhardzell are noted with a diamond.
Shatter conesCurrent knowledge 27
occur also rather frequently in gneiss, granite, and other
granitoids. These associations most likely reflect the fact
that known impacts have generally affected the near-
surface sedimentary supracrustal strata of the
continental crust, whereas larger impact structures
frequently occur in cratonic terranes dominated by, and
extending into, granitic or gneissic units.
There is ample evidence that in well-bedded
sedimentary strata shatter cone sizes are at least
codetermined by the spacing between bedding planes.
Where it is at the centimeter level, shatter cones will
also not exceed such a length, and where it is distinct at
the decimeter-scale, larger cones will be observed. Even
larger cones at the several decimeter to meter size have
been observed by one of us (WUR) in the collar of the
Vredefort Dome and in the central uplift of the
Araguainha impact structure in Brasil. Larger (~2 m)
shatter cones appear to be found in massive
homogeneous rocks at the outcrop scale at Santa Fe,
but these rock types often show common meso- to
microscale grain-size variations and textural
heterogeneities (Fackelman et al. 2008).
Association of shatter cones with mafic rocks is
naturally restricted by the areal proportion of the
continental Large Igneous Provinces dominated by
basaltic lava flows. Shatter cones in fine-grained basalts
have been described from the Presqu’^
ıle structure
(Higgins and Tait 1990). In recent years, shatter cones
have also been described from the Varge~
ao and Vista
Alegre impact structures formed in mafic volcanic
terranes (Cr!
osta et al. 2010; Pittarello et al. 2015;
Yokoyama et al. 2015) and from gabbro at the Sudbury
impact structure (Ferri#
ere and Osinski 2010). And the
felsic volcanics of the El’gygytgyn impact structure of
Siberia, as exposed in an ICDP sponsored drill core
D1c into the inner part of the impact structure, would
be another notable exceptionif confirmed (Raschke
et al. 2013).
Extraterrestrial Shatter Cones
Because impact cratering is a universal geological
process, shatter cones may be expected to occur on all
solid bodies in our solar system, including asteroids,
terrestrial planets, and their satellites. No reports of
shatter cones have been made for lunar samples to
date. However, shatter cones in meteorites were first
indicated by Dietz (1966b), although he presented some
ambiguous striations. Since then, shatter cones in
meteorites have been reported by McHone et al. (2012),
soon followed by a second observation (Ferri#
ere et al.
2013). Both these findings have pertained to ordinary
chondrites. It must be expected that the number of
meteorite samples where shatter cones are recognized
will increase, as other microscopic evidence of shock
metamorphism is common for these objects.
Martian rovers and landers have provided
thousands of images of ejecta or material that may have
been affected by shock waves, but no shatter cones have
been reported at this stage. Curved fractures in float
materials with barely visible striations, and striated
surfaces displaying parallel striations, have been
Fig. 13. Percentage of exposed impact structures associated with shatter cones as a function of diameter.
28 D. Baratoux and W. U. Reimold
reported at Gale crater and presented as “possible
poorly developed” shatter cones (Newsom et al. 2015).
The claim is associated with close-up views of two
samples, but lack sufficient description and data
supplementing the images, especially as image resolution
is not good enough to determine whether striations are
actually present. At least one of these two surfaces
appears typical of ventifacts.
ASSOCIATIONS WITH JOINTS
Many shatter cones do not have circular or near-
circular apical areas but instead show distinctly
polygonal margins of such surfaces (Fig. 3).
Furthermore, the opposite, terminating cone sides
frequently do not display a circular or rounded outline
either. Rather, there too, linear or near-linear segments,
at angles between a few degrees and as much as 20
degrees, can be distinguished (see also Hasch et al.
2016). Nicolaysen and Reimold (1999) inferred from
detailed outcrop studies in the western and northern
parts of the inner collar of the Vredefort Dome, the
central uplift of the Vredefort impact structure, that
there is a closemaybe inherentrelationship between
shatter cones and multiple, differently oriented but
intersecting sets of numerous near-parallel, curviplanar
to near-planar joints (and microjoints, as thin section
studies have shown). Spacing of such joints can be as
large as 1 cm but generally are macroscopically
recognized at 15 mm. Nicolaysen and Reimold (1999)
thought that the so-called “S-fractures” discussed by
Albat and Mayer (1989) represented two conjugate sets
of what they termed multiply striated joint sets (MSJS).
At a particular location Nicolaysen and Reimold (1999)
identified not less than 12 such joint sets, each of a
different orientation. They also noted in thin sections
cut across such joint sets that there was a shear
component involved, which had led to various
displacements at the grain scale (up to several 100 lm)
along such joints. And they observed small pockets of
melt, notably at intersections of such joints. All this
attests to shearing and frictional heating at a local scale
being involved in MSJSand by implication, shatter
cone formation. Further possible evidence for melt
along microfractures is presented by Hasch et al. (2016)
for a shatter cone from Keurusselk
a Finland. These
occurrences of melt may relate, by extension, to shatter
cone formation.
Since these early observations, MSJS have been
observed at many impact structures where shatter cones
Fig. 14. Excellent shatter cone development of ca. 30 cm width in medium-grained Archean granite-gneiss from farm
Kopjeskraal, northwestern outer limit of the core of crystalline basement in the Vredefort Dome of South Africa.
Shatter conesCurrent knowledge 29
also occur. A notable examplealready referenced by
Nicolaysen and Reimold (1999)is the Huronian
sandstone of the South Range of the Sudbury impact
structure, where extensive developments of such
curviplanar joint sets occur intimately associated with
shatter cones (Fig. 15a). Wieland et al. (2006) show a
prime example of jointing and shatter coning occurring
together at the half centimeter to several centimeter
scale (again in a sandstone from of the western collar of
the Vredefort Dome; we here include another
photograph of this sample in Fig. 15b).
ASSOCIATION OF SHOCK-DEFORMATION
FEATURES, GLASS/MELT WITH SHATTER
CONES
Rocks or minerals that experienced shock
metamorphism can show distinct deformation or
transformation effects such as planar deformation
features (PDF), mosaicism, and formation of diaplectic
glass, the creation of high-pressure polymorphs, and
feather features (FF) that in all likelihood also
constitute shock-metamorphic evidence as they have
never been described as a result of other geological
processes (see Poelchau and Kenkmann 2011). Detailed
discussions of the latter effects and their relation to
shatter cone formation are given in Fackelman et al.
(2008) and Zaag et al. (2016). These latter effects are,
however, not restricted to shatter cones. As already
stated, shatter cones are exclusively generated as a result
of hypervelocity impact under natural conditions. A
shatter cone itself can, therefore, be regarded as a
shock-deformation effect.
Macroscopically, a separation between the convex
and concave parts of shatter cones may not be
discerned. Such fractures may be filled with secondary
deposits (such as oxides of Fe or Mn), which may also
make them readily recognizable in outcrop. On the
microscopic scale shatter cones can show both
separation and displacement of the order of up to a few
hundreds of micrometers. The occurrence of glass or
melt on and in shatter cones can be obscured by their
replacement by alteration products, as fractures are
preferential pathways for postimpact aqueous solutions
(see, e.g., Hasch et al. 2016).
Shatter cone surfaces, especially the grooves, can be
coated with melt splats, smears, fibers, and spherules
(e.g., Gay 1976; Gay et al. 1978; Gibson and Spray
1998; Nicolaysen and Reimold 1999; Pittarello et al.
2015). Most authors explain the occurrences of melt due
to severe heating caused by frictional movement. The
steps and striae on shatter cone surfaces can show
characteristic melt or glass occurrences. These
occurrences are also observed in microscopic melt
pockets at intersections of microfaults along major,
pervasive joints termed MSJSrelated to the shatter
cone phenomenon by Nicolaysen and Reimold (1999).
Nicolaysen and Reimold (1999) reported minute
displacements on MSJS and consequently referred to
shearing and associated friction melting. Kenkmann
et al. (2012) and Wilk and Kenkmann (2015a, 2015b,
2016) found, during microstructural SEM investigations
of shatter cone surfaces, highly vesicular melt films
alternating with smooth polished surfaces on shatter
cones in sandstone. Similar observations have
previously been reported by Gibson and Spray (1998)
and Nicolaysen and Reimold (1999). According to Wilk
and Kenkmann (2015a, 2015b, 2016) the surface shows
shear offsets; vesicular melt is predominantly located
where release step occur on the surface. Kenkmann
et al. (2012) pointed out that the shatter cones
developed in sandstone whose porosity was previously
crushed out. Thus, shatter cones had formed after the
compressive stress had been high enough to crush the
porosity. According to Gay (1976), the occurrence of
spherules is an indicator of rapid melting and fusion on
the surface of shatter cones during their formation.
According to Gibson and Spray (1998), the formation
Table 2. Association of shatter cones with lithology.
Number of occurrences Proportion
a
Sedimentary rocks 59 50.0%
Carbonate sediments 22 22.0%
Claystone 3 2.5%
Siltstone 4 3.4%
Sandstone 18 15.2%
Shale 1 0.8%
Sulfates 1 0.8%
Chert 1 0.84%
Other/undetermined 5 4.2%
Metamorphic rocks 26 22.0%
Gneiss 9 9.3%
Quartzite 5 5.1%
Schist 3 3.4%
Other/undetermined 5 4.2%
Igneous rocks 29 24.6%
Volcanic mafic 5 4.2%
Volcanic felsic 3 2.5%
Plutonic mafic 1 0.8%
Plutonic felsic 15 12.7%
Plutonic intermediate 1 0.8%
Volcanic intermediate 1 0.8%
Anorthosite 1 0.8%
Other/undetermined 2 1.7%
Fragments in breccias 4 3.4%
a
Proportions are based on occurrence (excluding ambiguous
observations) at each crater and not on volume of rock affected or
abundance of shatter cones observed. At any given impact structure,
shatter cones may occur in one or more rock type(s).
30 D. Baratoux and W. U. Reimold
of spherules on shatter cone surfaces is due to melting
and possible vaporization as a result of a combination
of friction and shock. However, further observations
are required to determine beyond doubt that shock
deformation is enhanced at or near a shatter cone
surface, in comparison to the shock level observed
further away from the shatter cone surface (see also
Hasch et al. [2016] and Zaag et al. [2016]).
Fig. 15. Examples of multiply striated joint sets (MSJS). a) Huronian sandstone from the South Range of the Sudbury impact
structure. Dense sets of mostly curviplanar joints are recognizable, most of which follow prominent orientations (some of them
highlighted by white lines). This deformation style corresponds to the MSJS deformation first described by Nicolaysen and
Reimold (1999) from the Vredefort Dome. Lighter for scale ca 7 cm long. b) MSJS in sandstone at the Vredefort impact
structureseveral closely spaced sets of fractures of different orientations on a quartzite boulder found on the Schurwedraai
alkali-granite complex in the northwestern part of the collar of the Vredefort Dome (Wieland et al. 2006; photo courtesy R.L.
Gibson, University of Witswatersrand, Johannesburg). The pen for scale is ~10 cm long.
Shatter conesCurrent knowledge 31
Spherules tend to develop preferentially on shatter
cone surfaces in argillaceous lithologies, and Nicolaysen
and Reimold (1999) reported melt on shatter cones in
quartzite and in alkali granite, but they are considered to
be rarely associated with this latter type of rock (Gay
1976). Hasch et al. (2016) also found evidence for likely
melt formation on shatter cone surfaces in granitic gneiss
from the Keurusselk
a impact structure (Finland). They
report such melt having intruded into fractures extending
into the rock below shatter cone surfaces. Pittarello et al.
(2011, 2015) found, in places, a homogeneous melt film of
50 lm thickness coating parts of the surface of shatter
cones in fine-grained basalt from the Vista Alegre impact
structure (Brazil). Dendritic microlites of 45lm size
were observed within the melt and an amorphous phase
that has remained to be further investigated was observed
in the melt coating (Pittarello et al. 2015). In the absence
of evidence for friction, the melt was thought to be
associated with shock heating in this case.
HYPOTHESES FOR THE GENESIS OF SHATTER
CONES
The genetic hypotheses for shatter cone
development are based on theoretical considerations
about the behavior of shock waves in solids and
fracture mechanics. Before getting into the details of
each hypothesis, key aspects of shock wave propagation
in geological materials with respect to the genesis of
shatter cones are recalled here. For a complete
description, the reader is referred to Melosh (1989). In
the case of an ideal point-source representation of the
impact into a homogeneous medium, a strong shock
wave propagates from the impact center, and its
intensity decays with distance from the origin at a
power greater than 2, as inelastic processes dissipate
energy. Initially, the velocity of the wave is greater than
that of the speed of sound in the material concerned.
When intensity approaches the Hugoniot Elastic Limit,
Fig. 16. Evolution of the radial (a) and hoop stresses (b) corresponding to the propagation of a shock wave and its elastic
precursor from a point source in a solid homogeneous medium. Stresses are represented as function of distance from the source
at three different times. The elastic precursor separates from the plastic wave when the radial stress approaches the Hugoniot
Elastic Limit. Gray arrows represent wave velocities (c
e
for sound speed, c
p
for the velocity of the plastic wave, c
p
<c
e
and c
s
for
the velocity of the shock wave, and c
s
>c). Compressive stresses are represented as positive values, extensive stresses are
negative. Upper right insert represents the hoop and radial stresses at the wave front (1), as well as behind the wave front (2)
when the hoop stress becomes extensive.
32 D. Baratoux and W. U. Reimold
the shock wave decomposes into a plastic wave
propagating at a velocity less than the speed of sound,
and an elastic precursor. Further away from the impact
center, the shock intensity declines into the elastic
regime. The principal stresses are compressive during
the rise of pressure, whereas the hoop stress (normal
stresses perpendicular to the direction of propagation)
becomes extensive behind the shock front. A
representation of the stress patterns inspired from
numerical simulations of shock propagation into a
homogeneous medium after Baratoux and Melosh
(2003) is given in Fig. 16.
Our understanding of the structure of the shock
pulse in natural heterogeneous materials is, however,
limited. Data from nuclear explosions indicate that the
rise times of stress waves (at low pressure) in rocks are
up to 300 ms (Melosh 2003), but would be less than
1 ms at formation pressures of shatter cones as expected
from the increase of bulk modulus with pressure
(Baratoux and Melosh 2003). Observations of the
distribution of microscopic high-pressure phases or
shock-deformation effects have revealed that shock
intensity is extremely heterogeneous at the grain scale
(e.g., Gibson and Reimold 2005; Kowitz et al. 2013).
The structure of a shock wave in rocks may, therefore,
be extremely complex, with internal fluctuations of
intensity and multiple rises of pressure as a result of
nonideal point sources, reflection, refraction, and
scattering at grain boundaries, or at other microscopic
and macroscopic defectsat any kind of heterogeneity
or discontinuity in the medium (e.g., preshock
microfractures/joints, porosity, mineral inclusions, etc).
In the following, the hypotheses for the genesis of
shatter cones are examined.
The Johnson and Talbot (1964) Hypothesis
Johnson and Talbot (1964) considered the effect of
a scattered elastic wave generated by an inclusion of
different density and/or compressibility from that of the
surrounding rock. They developed analytical equations
to calculate the stress tensor resulting from the
superposition of the stress behind the elastic precursor
and that of a scattered wave. As radial stresses are
greater than hoop stresses, it was shown that the
resulting radial stress in a conical region, with the
inclusion at its apex, exceeds the Hugoniot Elastic Limit
(Fig. 17). Outside of this region, the superposition of
the scattered and elastic precursor waves reduces the
differences between radial and hoop stress, and the
stress remains below the Hugoniot Elastic Limit. It is
then predicted that plastic deformation of the conical
region induces a permanent deformation, whereas the
elastic region may return to its initial state. The two
regions should then separate to form a cone. The
authors assumed that the separation between the elastic
and plastic regions occurs during unloading of the
material before the arrival of the shock wave.
The Gash (1971) Hypothesis
Gash (1971) proposed that shatter cones are tensile
fractures, whose conical geometry is the consequence of
the superposition of the shock wave radiating from a
point source beneath the surface and reflected tensile
waves from the free surface (Fig. 18). Arguments were
deduced from the propagation of elastic waves and
considered to remain valid for plastic or shock waves at
higher pressures. The principal stresses and contours
represented in Fig. 18 were calculated by Gash (1971)
from radial stresses of the shock and reflected waves,
whereas hoop stresses were neglected. According to this
idea, shatter cone surfaces would develop along the
conical trajectories of r
1
(principal compressive stress), as
controlled by the interaction of the shock wave with
reflected tensile waves. In this scenario, shatter cones
should develop directly beneath the impact point, and
apex angles should be near 90°, but lower values may be
obtained by increasing the depth of the source. Shatter
cones should be also exclusively oriented in the vertical
direction.
Formation of shatter cones at various locations
requires the existence of multiple source points, but
interferences between the different waves should then
limit their formation. Interestingly, Gash (1971) briefly
explored the stresses resulting from the interaction of an
Fig. 17. Formation of a shatter cone according to Johnson
and Talbot (1964). The elastic stress tensor for the elastic
precursor (blue square at the bottom left) combines with the
stress associated with the scattered wave (green squares). The
superposition of the two waves generates stresses above the
Hugoniot Elastic Limit within a conical region (plastic region).
The apical angle of the cone depends on the density and
compressibility contrasts between the inclusion and the
surrounding rock.
Shatter conesCurrent knowledge 33
elastic wave and a scattered wave due to local presence of
an inclusion, following the earlier suggestion of Johnson
and Talbot (1964). Ignoring the aspect associated with
plastic yielding developed in Johnson and Talbot (1964),
he focused on interferences between the main wave and
the reflected wave at the inclusion, and demonstrated
that conical fractures may also develop along r
1
trajectories for a main tensile pulse, but not a
compressive one. He finally excluded this scenario for
two reasons: incident elastic tensile waves are not limited
to impact contexts (but shatter cones are), and apical
angles predicted by this idea would be lower than 90°
which was considered inconsistent with observations.
The Sagy et al. (2002) Hypothesis
The hypothesis of Sagy et al. (2002, 2004) has its
origin in the long-standing question regarding the
mechanism for the formation of nontrivial fracture
surfaces. Indeed, analytic treatment assumes that a crack
will travel along a straight trajectory (Freund 1990),
whereas the fracture surface formed by a crack is known to
become increasingly rougher as crack velocity increases
(Sharon and Fineberg 1996). Sagy et al. (2002, 2004)
focused first on the multilevel (and possibly fractal) three-
dimensional networks of shatter cone surfaces. They
suggested that the shape and network of fractures
resembles the structure of branched networks of
experimental dynamic fractures (Sharon et al. 1995; Sagy
et al. 2001) that propagate at velocities approaching the
theoretical limiting velocity for tensile fractures (Rayleigh
Speed, noted V
R
). An interpretative sketch of a shatter
cone from the Haughton structure (Canada) summarizes
the proposed mechanism of formation of shatter cones
(Fig. 19). Branching fractures are curved and the distance
of the branch from the main crack as a function of
distance along the direction of propagation appears to
follow an empirical power-law. A theoretical interpretation
of the observed functional form of the shape of branching
fractures has, however, not yet been proposed.
The second aspect of the work of Sagy et al. (2002,
2004) concerns the systematic association of shatter
Fig. 18. Formation of shatter cones beneath the impact point according to Gash (1971). The red filled circle represents the
source of the shock wave beneath the surface (distance to the surface is exaggerated for clarity). Red solid and dotted lines
represent the shock front and ray paths of the shock wave, respectively. Green solid and dotted lines represent respectively the
front of the reflected wave at the free surface and ray paths of the reflected waves. Blue lines represent the trajectories of r
1
(most compressive principal stress) and dotted gray lines represent the contour of the intensity of r
3
(tensile stress) decreasing
away from the source region. Fractures along the conical trajectories of r
1
are proposed to correspond to shatter cone surfaces.
Trajectories and contours were drawn from Gash (1971).
34 D. Baratoux and W. U. Reimold
cone surfaces with diverging (or V-shape) striations.
Here again, experimental results on rapid fractures
offered a possible explanation for striations. Sharon
et al. (2001) and Fineberg et al. (2003) observed a new
type of elastic waves, termed front waves (FW), which
are excited when a rapidly moving fracture front
encounters material heterogeneities. The front waves
create a pair of tracks on the fracture surface emanating
from the inhomogeneity (Sharon et al. 2001, 2002;
Fineberg et al. 2003). The angle between the pair of
striations is related to the main crack velocity (V)
through the following equation:
cosða=2Þ¼V=VFW;(1)
where V
FW
is the front wave velocity that is independent
of the intensity of the tensile wave and equal or slightly
less than the Rayleigh speed (>0.96 V
R
). As the crack
velocity depends on the intensity of the tensile wave, the
striation angle is thought to reflect the local intensity of
the shock wave. Sagy et al. (2002) proceeded to illustrate
this process with data from Vredefort. However, Wieland
et al. (2006) refuted, using a broader database, their
conclusion that the V angle decreased with distance from
the center of the impact structure.
The Baratoux and Melosh (2003) Hypothesis
The role of material heterogeneities was also
examined by Baratoux and Melosh (2003). The
hypothesis is based on the constructive interference of
the main shock wave with a scattered wave that creates
alocalizedexcessoftensilestress(Fig.20).Aninclusion
in a homogeneous rock is expected to generate a
scattered wave. Extensive stresses perpendicular to the
direction of propagation of the scattered wave (hoop
Fig. 19. Shatter cone surface (a specimen formed in dolomite from the Haughton Dome impact structure, from the collection of
W.U. Reimold, donated by B.O. Dressler, Vancouver Island, Canada) interpreted as branching fractures, decorated by so-called
V-striations, formed as front waves propagating from material heterogeneities. The blue circle marks a possible branching point
on a hypothetical main fracture plane, from which the curved shatter cone surface would have developed. Red lines mark
possible V-striations decorating the shatter cone surface, and red question-mark tags indicate the position of putative (not
observed) heterogeneities at the apex of V-striations.
Shatter conesCurrent knowledge 35
stresses) are produced if the inclusion has lower density
of lower bulk modulus than the surrounding rock. The
combination of this stress with the hoop stress of the
main shock wave that becomes extensive behind the
front creates an excess of tensile stress along a curved
surface. When such a stress exceeds the resistance of the
material in tension, the phenomenon of interference
localizes the rupture along a curved surface resembling
that of a shatter cone.
As nonlinear effects arise when stresses are above
the Hugoniot Elastic Limit and ruptures are expected,
this idea was tested by numerical simulations. A two-
dimensional version of the numerical hydrocode SALE
(Simplified Arbitrary Lagrangian Eulerian; Amsden
et al. 1980) was enhanced with the Grady-Kipp-Melosh
fragmentation model (Grady and Kipp 1980; Melosh
and Ryan 1992) to study fracturing associated with the
propagation of a shock wave emanating from a point
source and its interaction with an inclusion having
variable density and elastic properties. Calculations
were done in axisymmetric geometry. The numerical
model successfully reproduced a curved or curviplanar
surface of a fracture for a range of pressures between 3
and 6 GPa (damage becomes more pervasive above this
value) and for a bulk modulus ratio between the rock
and the inclusion greater than, or equal to, 5. However,
it was shown that the shatter cones form only if the
width of the shock pulse is similar to the dimension of
the inclusion, which corresponds to the necessary
condition to generate a scattered wave.
The Dawson (2009) Hypothesis
This hypothesis was proposed during the 9th
International Conference on the Mechanical and
Physical Behavior of Materials and has never been
formally published. According to Dawson (2009),
shatter cones are adiabatic shear bands that are
triggered by material heterogeneities. An adiabatic shear
band is a nearly planar region of significant shearing as
typically observed in metals and alloys experiencing
intense dynamic loading (Wright 2002), as in the case of
ballistic impact. Such shear bands are caused by
thermal softening due to shear strain-induced heating.
Numerical simulations were applied to a cube of 1 m
3
,
into which a flaw was placed. Shear banding was
simulated by assuming that localization of deformation
occurs until a threshold value of plastic strain is
exceeded. Plastic strain is distributed evenly throughout
the material below this threshold value. The numerical
simulation showed the formation of a conical zone of
intense shearing that develops from the inclusion. It was
then argued that intense shearing was compatible with
the presence of melt observed occasionally on some
shatter cone surfaces.
The Phenomenological Model by Kenkmann et al. (2016)
Kenkmann et al. (2016) argued that spoon-like
branching (Sagy et al. 2002) is a form of asymmetric
branching that is not consistent with observations.
Asymmetric branching implies that only a minor
fraction of fracture energy would go into the
asymmetrically branched fracture. In this case, the
branched crack does not further propagate and cannot
branch itself, in contradiction with the occurrence of the
horse-tail structure. Kenkmann et al. (2016) proposed a
phenomenological model in which cascades of
bifurcations explain the horse-tailing effect. According
to them multiple symmetric crack branching is the
Fig. 20. Formation of shatter cones according to Baratoux and Melosh (2003). The shock pulse emerges from a point source
(not represented) and the front wave is spherical. The black circle represents an inclusion. The front of the scattered wave and
the contour for a negative value of the hoop stress (extensive) of the main wave are represented with dotted white lines. Rupture
is expected to occur at the intersection of these lines.
36 D. Baratoux and W. U. Reimold
result of rapid fracture propagation that may approach
the Raleigh wave speed. They interpret diverging
striations as the intersection lineations delimiting each
subcone.
Synthesis and Discussion
It is interesting to note that authors of successive
hypotheses for shatter cone formation expended little
effort to demonstrate that previous work was not valid
before moving forward to their newly proposed
hypothesis. When a new model is advocated, it is stated
that previous hypotheses cannot explain all the
properties of shatter cones. Here, we show first that
some hypotheses have intrinsic issues, physical
inconsistencies, or contradictions regarding actual
observations.
Johnson and Talbot (1964) indicated that
separation between the plastic and elastic regions occurs
during unloading and before the arrival of the plastic
wave. However, there is no such unloading before the
arrival of the plastic wave and the principal stress r
1
behind the elastic precursor remains close to the
Hugoniot Elastic Limit. This structure of the elastic
precursor and plastic wave was illustrated in Baratoux
and Melosh (2003) and was also properly described in
the work of Dawson (2009). Without such an unloading
phase, the deformed material would be engulfed into
the plastic wave without having any possibility for the
elastic region to return to its initial state and separate
from the plastic region. In addition, this hypothesis
requires that shatter cones form exclusively when the
shock wave has decomposed into a plastic wave and an
elastic precursor. This implies a strong constraint on the
pressure domain of formation or range of distance from
the point of impact. According to this hypothesis,
shatter cones should be found only in the plastic
domain where the longitudinal stress is above the
Hugoniot Elastic Limit and where the plastic wave
velocity (c
p
) remains below that of the elastic wave (c
e
).
The shock (or plastic) wave velocity is given
experimentally by a linear relationship:
cp=s¼CþSu (2)
where uis the particle velocity. Using the second
equation of Hugoniot, the pressure of the shock (or
plastic wave) is given by:
P¼qcpðcp!CÞ
S(3)
The plastic wave would merge with the elastic
precursor when the speed of the elastic longitudinal
wave (elastic precursor) in the rock is equal to that of
the plastic wave. With typical values for crustal
crystalline rocks of S ~1, q~3000, c
p
~5000 m s
!1
and C ~4000 m s
!1
, the elastic precursor should not be
observed above ~15 GPa (Melosh 1989). The occurrence
of shatter cones in the central peaks of several impact
structures and their association with PDFs provide
evidence for pressures exceeding 10 GPa and up to
30 GPa (e.g., Dietz 1968; French and Koeberl 2010;
Milton 1977; Dressler 1990; Hasch et al. 2016; Zaag
et al. 2016) and suggests that shatter cones might form
in the absence of an elastic precursor.
A major issue with the hypothesis of Gash (1971) is
the prediction that shatter cones would form essentially
beneath the impact point and would point exclusively
upward, whereas shatter cones are observed in large
impact structures at great distances from the center of
the impact structure and exhibit various orientations.
The proposed scenario would not allow easily the
formation of shatter cones of different shapes and sizes,
which also contradicts observation. It should be noted
also that calculations were done in the elastic regime
and were assumed to be valid for strong plastic/shock
wave, whereas hoop stresses were also been
systematically neglected.
Dawson (2009) argued that shear banding and
associated extreme heating would offer an explanation
for the occurrence of melt on shatter cone surfaces.
However, melt may be also produced at the tip of
tensile fractures and is not a unique feature of this
hypothesis. Also, it is likely that these melts are the
result of frictional melting on shatter cone fractures,
considering thatadmittedly smalldisplacements have
been observed repeatedly on associated fractures (e.g.,
Nicolaysen and Reimold 1999; Hasch et al. 2016).
Moreover, material with adiabatic shear bands usually
retains full continuity from one side to the other,
whereas shatter cone surfaces are fractures. The
numerical simulation of Dawson (2009) shows a region
of intense shearing, but this is not necessarily associated
with a fracture.
Baratoux and Melosh (2003) and Sagy et al. (2002,
2004) require the presence of heterogeneities to form
shatter cones. All types of rock contain abundant
heterogeneities at various scales (porosity, microscopic
defects, grain boundaries, fractures, joints). However, it
is not clear which types of heterogeneities may play a
role in triggering shatter cone formation, and why other
heterogeneities may not be the locus of shatter cone
development. The two models implicitly assume that the
width of the shock pulse has dimensions comparable to
some of the heterogeneities in the rock, which is
conceivable according to nuclear test experiments
(Melosh 2003). Baratoux and Melosh (2003) offer an
Shatter conesCurrent knowledge 37
explanation for the curved to curviplanar shapes of
shatter cones, but do not directly address the formation
of V-striations. According to Baratoux and Melosh
(2003), shatter cone sizes and apical angles would be
controlled by the decay time of the shock wave and by
the contrast between elastic properties and densities
within the rock. These predictions have not been tested
against observations, due to the lack of appropriate
data.
Sagy et al. (2002, 2004) offered an explanation for
both the shapes of shatter cones and the striations.
Using the relationship between the intensity of the
tensile wave and the striation angle, Sagy et al. (2002,
2004) concluded that the V angle decreased with
distance of observations from the center of an impact
structure (in their case, the central uplift of the
Vredefort impact structure, the Vredefort Dome), and
they supported this notion with some field
measurements. Wieland et al. (2006), however,
investigated this further and did not find support for
this alleged relationship. It remains possible that large
fluctuation of the shock intensity at the outcrop scale
explains the scatter of angles of V-striations, but the
principal observation supporting the formation of
striations by front waves has been dismissed.
Furthermore, it should be noted that the proposed
scenario is based on resemblance to results of
laboratory experiments showing either tracks of front
waves, or branching fractures, but none of these
experiments reproduced a curved surface of fractures
decorated by striations that would be directly
comparable to shatter cones produced in an impact
context. Understanding of these experiments is also the
subject of ongoing research, and, for instance, the
curved shape of a branching fracture cannot be
predicted based on theoretical grounds, and has been
described as a “spoon-like” shape. In the absence of
quantitative prediction, this aspect of the model is
difficult to assess. The formation of well-developed
conical features (e.g., 510% of shatter cones are
complete cones at the Haughton impact structure
according to Osinski and Spray [2006], but much less,
or even extremely rare, in other structures) is not easily
explained by the branching fracture mechanism.
Wieland et al. (2006) proposed that a combination
of the ideas proposed by Sagy et al. (2002) and
Baratoux and Melosh (2003) may be able to explain the
observations, whereas Sagy et al. (2004) also envisaged
that interferences between the main shock wave and
scattered waves may be a trigger for the branching
initiation.
Kenkmann et al. (2016) propose a
phenomenological model, which results from the
examination of the hierarchical arrangement of
subcone ridges on a main shatter cone surface. The
observation central to this idea is “that each ridge
branches after some distance into two symmetrically
equivalent sub-cone ridges.” This model does not
require the existence of front waves or the presence of
heterogeneities. These ideas need to be factored into the
reflection about shatter cone formation, but the
following difficulties require further examination (a) the
hypothesis that the horse-tail structure results from a
cascade of bifurcation is difficult to apply to shatter
cones which show a clear break in the fractal behavior
and not a continuous hierarchical behavior of subcone
ridges, (b) it seems difficult to explain the formation of
a complete cone (360°) in this framework. It should be
also noted that a phenomenological model, which does
not derive from first principles, is intrinsically limited in
the sense that it is difficult to build on these ideas to
infer physical parameters of the impact or shock from
shatter cone observations. Despite these remarks, it is
interesting to note that this study questions the role of
front waves in explaining the striations, and highlights
the importance of the hierarchical organization of
shatter cone surfaces, which need to be further
examined from all available 3-D data.
ASSESSMENT OF SPECIAL ISSUE
CONTRIBUTIONS AND OUTLOOK
Following this introduction, which has reviewed
both the occurrence of shatter cones in the world, and
the current hypotheses for their genesis, the following
six contributions of the special issue present new
observations of natural and experimental shatter cones.
New observations, descriptions, and analyses of shatter
cones and of their relationships with pre-existing
structures or other microscopic shock-deformation
effects are presented for samples from 14 sites including
Agoudal (Morocco), Charlevoix (Canada), Gosses Bluff
(Australia), Haughton, Jebel Waqf as Suwwan (Jordan),
Keurusselk
a (Finland), Marquez (USA), Rochechouart
(France), Serra da Cangalha (Brazil), Siljan (Sweden),
Steinheim (Germany), Varge~
ao (Brazil), Vista Alegre
(Brazil), and Vredefort (South Africa).
A first notable aspect of the special issue is the
recent development of analytical techniques and
innovative applications of existing techniques to
characterize the structure of these objects, their 3-
dimensional geometry, or the internal distributions of
fractures. Such new developments include the
application of the nondestructive microcomputer
tomography technique to visualize the interior fracture
pattern of a sample (Zaag et al. 2016), whereas white-
light interferometry, laser scanning, and image analysis
are used in the laboratory or in the field to create
38 D. Baratoux and W. U. Reimold
digital shape models of the surfaces of shatter cones and
allow the morphometric analysis of the macroscopic
shapes or of the surface striations (Baratoux et al. 2016;
Kenkmann et al. 2016; Wilk and Kenkmann 2016).
Morphometric observations of natural or
experimental shatter cones (Baratoux et al. 2016;
Kenkmann et al. 2016; Wilk and Kenkmann 2016),
observations of vesicular films in experimentally
produced shatter cones (Wilk and Kenkmann 2016) and
relationships between shatter cones and pre-existing
joints (Hasch et al. 2016) are systemically confronted
with the predictions of the various hypotheses of
formation, whereas Kenkmann et al. (2016) has
elaborated and examined the value of a
phenomenological model to reconstruct the geometry of a
shatter cone, and in particular of the horse-tailing effect.
These discussions generally examine the role of pre-
existing heterogeneities in the rocks and the timing of
formation. Although these data are certainly promising
to elucidate the mechanism of formation, they also
illustrate the fact that more theoretical development, as
well as experimental and numerical simulations are still
required to evaluate further the hypotheses of formation.
The special issue also offers a contribution focusing
on the enigmatic finding of shatter cones overlapping
with a meteorite strewn field at the site of Agoudal,
Morocco (Chennaoui-Aoudjehane 2016). This article
presents a new map of the distribution of shatter cones
and of the meteorite strewn field and concludes that the
circa 105,000 yr old fall coincidentally hit on an ancient
eroded impacted terrain, in contrast to the interpretation
of Lorenz et al. (2015) who argued for a genetic
relationship between the meteorite fall and the
occurrence of shatter cones.
Acknowledgments—DB is supported by the Institut de
Recherche pour le Developpement (France) during his
visit at the Institut Fondamental d’Afrique Noire,
Universit!
e Cheikh Anta Diop, Dakar, Senegal. WUR’s
research is supported by the German Science
Foundation (Deutsche Forschungsgemeinschaft) and the
Museum f
ur Naturkunde Berlin. Jay Melosh and
Ludovic Ferri#
ere are acknowledged for their
constructive reviews and for their careful examination
of the database of shatter cone occurrences published in
this manuscript. We thank Kai W
unnemann for his
comments on the discussion of the Johnson and
Talbot’s hypothesis. Carl Awlmark (Lund University,
Sweden), Alexander Basilevsky (Vernadsky Institute,
Moscow, Russia), Williams Exbrayat (University of
Toulouse, France), Boris Ivanov (Russian Academy of
Sciences, Moscow), Hanna Krejzlikova (University
Charles of Prague, Czeech Republic), Camille Moulis
(University of Toulouse, France), and Sergey A.
Vishnevsky (Institute of Geology and Mineralogy,
Novosibirsk, Russia) are acknowledged for their
precious help for access to some of the bibliographic
references cited in this article.
We also thank Carl Alwmark (Lund University,
Sweden), Marc Biren (Arizona State University, USA),
Alvaro Cr!
osta (University of Campinas, Brazil), Bertrand
Devouard (CEREGE, France), Ludovic Ferri#
ere
(Natural History Museum, Vienna), Roger Gibson
(University of the Witwatersrand, South Africa), Thomas
Kenkmann (University of Freiburg), Lutz Hecht
(Museum f
ur Naturkunde), Stefan Hergarten (Albert-
Ludwigs-Universit
at Freiburg, Germany), Dmitry
Koroteev (Schlumberger, Inc.), Cristiano Lana
(Universidade Federal de Ouro Preto, Brazil), Jay
Melosh (Purdue University, USA), Lidia Pittarello (Vrije
Universiteit Brussel), Martin Schmieder (Lunar and
Planetary Institute, USA), and Birger Schmitz (Lund
University, Sweden) for their formal reviews of the
articles of the special issue “Shatter ConesNature and
Genesis.” Associate Editor Michael Poelchau dealt with
several of these manuscripts in cases where both Guest
editors of this Special Issue were compromised. The
database of shatter cones is made available at the
following website: http://shattercones.obs-mip.fr/
database/.
Editorial Handling—Dr. Michael Poelchau
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46 D. Baratoux and W. U. Reimold
... Shatter cones are the only macroscopic evidence of shock deformation that can be used to confirm an impact event from field observations (Dietz 1960;French 1998;French and Koeberl 2010;Ferrière and Osinski 2013). The cones consist of an apex from which striations radiate out to form a conical shape (Baratoux and Reimold 2016), and are predicted to form at pressures of 5-30 GPa based on natural occurrences and experiments (e.g., French 1998; Gibson and Reimold 2005;Wilk and Kenkmann 2016). They can form in almost any target rocks but are best developed in fine-grained rocks such as limestone and sandstone (e.g., Baratoux and Reimold 2016). ...
... The cones consist of an apex from which striations radiate out to form a conical shape (Baratoux and Reimold 2016), and are predicted to form at pressures of 5-30 GPa based on natural occurrences and experiments (e.g., French 1998; Gibson and Reimold 2005;Wilk and Kenkmann 2016). They can form in almost any target rocks but are best developed in fine-grained rocks such as limestone and sandstone (e.g., Baratoux and Reimold 2016). Identification of shatter cones in the field can be difficult in coarse-grained rocks, such as granite, which can form poor cones, and they can also look similar to other geological features that are not a product of impact (Baratoux and Reimold 2016). ...
... They can form in almost any target rocks but are best developed in fine-grained rocks such as limestone and sandstone (e.g., Baratoux and Reimold 2016). Identification of shatter cones in the field can be difficult in coarse-grained rocks, such as granite, which can form poor cones, and they can also look similar to other geological features that are not a product of impact (Baratoux and Reimold 2016). Shatter cones range in size from millimeter to several meters in length, and are commonly observed in target rocks from the central uplift of an impact structure (French 1998). ...