Earth's Impact Events Through Geologic Time: A List of Recommended Ages for Terrestrial Impact Structures and Deposits

Abstract

This paper presents a current (as of September 2019) list of recommended ages for proven terrestrial impact structures (n=200) and deposits (n=46) sourced from the primary literature. High-precision impact ages can be used to (1) reconstruct and quantify the impact flux in the inner Solar System and, in particular, the Earth-Moon system, thereby placing constraints on the delivery of extraterrestrial mass accreted on Earth through geologic time; (2) utilize impact ejecta as event markers in the stratigraphic record and to refine bio- and magnetostratigraphy; (3) test models and hypotheses of synchronous double or multiple impact events in the terrestrial record; (4) assess the potential link between large impacts, mass extinctions, and diversification events in the biosphere; and (5) constrain the duration of melt sheet crystallization in large impact basins and the lifetime of hydrothermal systems in cooling impact craters, which may have served as habitats for microbial life on the early Earth and, possibly, Mars.

Full text

Earth’s Impact Events Through Geologic Time:
A List of Recommended Ages for Terrestrial Impact
Structures and Deposits
Martin Schmieder
1,2
and David A. Kring
1,2
Abstract
This article presents a current (as of September 2019) list of recommended ages for proven terrestrial impact
structures (n=200) and deposits (n=46) sourced from the primary literature. High-precision impact ages can be
used to (1) reconstruct and quantify the impact flux in the inner Solar System and, in particular, the Earth–Moon
system, thereby placing constraints on the delivery of extraterrestrial mass accreted on Earth through geologic
time; (2) utilize impact ejecta as event markers in the stratigraphic record and to refine bio- and magneto-
stratigraphy; (3) test models and hypotheses of synchronous double or multiple impact events in the terrestrial
record; (4) assess the potential link between large impacts, mass extinctions, and diversification events in the
biosphere; and (5) constrain the duration of melt sheet crystallization in large impact basins and the lifetime
of hydrothermal systems in cooling impact craters, which may have served as habitats for microbial life on the
early Earth and, possibly, Mars. Key Words: Impact craters—Ejecta—Ages—Geochronology—Terrestrial—
Cratering record. Astrobiology 20, 91–141.
1. Introduction
Impact cratering is a fundamental process in the Solar
System, shaping asteroids, planets, and their satellites
(e.g., Baldwin, 1971; Shoemaker, 1983; Melosh, 1989;
Ryder, 1990; French, 1998, 2004; Canup and Asphaug, 2001;
Kring and Cohen, 2002; Osinski and Pierazzo, 2012). Unlike
the Moon, whose surface has been modified by numerous
large and small impacts for more than 4 billion years (Ga,
Gyr) (e.g., Sto
¨ffler et al., 2006), the Earth has retained a
limited impact cratering record due to tectonic recycling of
the crust, erosion, and the burial of impact craters underneath
layers of sediment and lava (e.g., Grieve, 1987, 2001a,
2001b) (Fig. 1).
Before *3.7 Ga before present, when most of the large
lunar impact basins were created, impact rates in the Earth–
Moon system were much higher than they are today (e.g.,
Turner et al., 1973; Tera et al., 1974; Ryder, 1990; Kring and
Cohen, 2002; Grieve et al., 2006; Johnson and Melosh, 2012;
Bottke and Norman, 2017). However, no traces of those
Hadean (>4.0 Ga) and Eoarchean (4.0–3.6 Ga) impacts on the
early Earth are currently known in the geologic record (e.g.,
Koeberl, 2006). Only 200 proven impact structures (counting
fields of small impact craters produced during the same event
as one) and 46 individual horizons of proximal and distal
impact ejecta (again, counting layers with the same age at
different localities as one) have thus far been recognized on
our planet (Fig. 2). Those impact structures and deposits span
a time from more than *3.4 Ga, represented by Paleoarchean
impact spherule layers in South Africa and Western Australia
produced by large impacts (e.g., Glass and Simonson, 2012,
2013), to roughly 6 years ago when the Chelyabinsk airburst
in Russia (February 15, 2013) shattered windows and its
main stony meteorite mass produced an *7 m-wide circular
impact penetration hole in frozen Lake Chebarkul (e.g.,
Borovic
ˇka et al., 2013; Popova et al., 2013).
The smallest geologic features on Earth’s surface produced
by impact, usually only a few meters wide and commonly
associated with surviving meteorite fragments, are (fields of)
penetration funnels, pits, and small craters that form at rel-
atively low, atmosphere-decelerated (ballistic) impact ve-
locities (e.g., Melosh, 1989; Beauford, 2015). Some of the
impact structures listed in this article belong to that type of
low-energy impact feature (e.g., the crater-like pits produced
1
Lunar and Planetary Institute—USRA, Houston, Texas.
2
NASA Solar System Exploration Research Virtual Institute (SSERVI).
Martin Schmieder and David A. Kring, 2020; Published by Mary Ann Liebert, Inc. This Open Access article is distributed under the
terms of the Creative Commons License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly credited.
ASTROBIOLOGY
Volume 20, Number 1, 2020
Mary Ann Liebert, Inc.
DOI: 10.1089/ast.2019.2085
91

during the fall of the Imilac pallasite in Chile, or the tem-
porary Chalyabinsk ice-penetration hole, which we chose to
include in the present listing). Hypervelocity impacts of lar-
ger meteoroids, at much higher incoming velocities, produce
craters that show different morphologies with increasing size
(e.g., Melosh, 1989; French, 1998). A textbook example of a
well-preserved simple, bowl-shaped impact crater associated
with its ejecta blanket is the *1.2 km-diameter Meteor
Crater (a.k.a. Barringer Meteorite Crater) in Arizona (Shoe-
maker, 1960; Kring, 2017b) (Fig. 1). Earth’s impact craters
larger than *2 to 4km in diameter are of complex mor-
phology and structure, such as the *3.8 km-diameter
Steinheim Basin in Germany characterized by a pronounced
central peak (uplift) and the *25 km-diameter No
¨rdlinger
Ries with an *10 km-wide inner ring of uplifted target rock
and a well-preserved blanket of proximal impact ejecta sur-
rounding the crater (e.g., Sto
¨ffler et al., 2002, 2013; Kring,
2005; Schmieder and Buchner, 2013). The 180 km-diameter
Chicxulub crater on the Yucata
´n Peninsula in Mexico is a
peak-ring basin similar in morphology and structure to the
Schro
¨dinger Basin on the Moon (Kring, 1995; Kring et al.,
2016, 2017a; Morgan et al., 2016). The deeply eroded Vre-
defort impact structure in South Africa, probably
*250 to 300 km in original diameter, may represent the
remnants of a terrestrial multiring basin (e.g., Melosh, 1989;
Spudis, 1993; Therriault et al., 1997; French, 1998).
FIG. 1. Degradation of terrestrial impact craters over time, exemplified by a number of simple, bowl-shaped impact
craters that are most easily erased from the terrestrial impact cratering record. The same principle applies to complex impact
craters on Earth larger than *2 to 4 km in diameter (not shown here). (A) The *1.2 km-diameter and roughly 50 kyr-old
Meteor Crater (aka Barringer Meteorite Crater) in Arizona is one of the best-preserved simple impact craters on Earth (e.g.,
Shoemaker, 1960; Kring, 2017b). Its ejecta blanket forms a hummocky terrain surrounding the crater. Note the pronounced
topography of the crater indicated by low-angle sunlight coming from the WSW. ISS spacecraft image ISS-038-E-67508.
(B) The 1.13 km-diameter and *220 kyr-old Tswaing impact crater in South Africa (e.g., Brandt and Reimold, 1995), with
its crater bowl seen from the uplifted crater rim. After more than 2000 centuries of erosion, its topographic features have
been smoothed out considerably compared with Meteor Crater. Photo taken during 2008 field expedition. (C) The *1.3 km-
diameter Tavan Khar Ovoo (aka Tabun Khara Obo) impact crater in Mongolia ( Masaitis, 1999; Schmieder et al., 2013).
The crater rim is less pronounced than those at Meteor Crater and Tswaing, and the crater bowl is filled with a thick pile of
postimpact sediments, mainly lake sediments and alluvium. The age of the crater is somewhat uncertain but likely on the
order of a few Myr. Photo taken during 2011 field expedition. (D) Satellite image of the *3.4 km-diameter and *1.1 Myr-
old New Que
´bec (Pingualuit) impact crater in Canada (e.g., Grieve et al., 1991; Marvin and Kring, 1992; Grieve, 2006),
with parts of its elevated crater rim preserved despite Pleistocene glacial overprint. The crater is filled with a modern-day
lake. (E) The *2.5 km-diameter and *4 to 5 Myr-old Roter Kamm impact crater in Namibia (e.g., Grant et al., 1997;
Miller, 2010). After a few million years of surface exposure, the crater has been modified by notable degradation and
postimpact sediment infill. (F) Satellite view of the Tavan Khar Ovoo crater shown in (C), characterized by a level of
erosion similar to that of the New Que
´bec crater and the Roter Kamm crater. (G) Satellite image of the 3.8 km-diameter and
*453 Ma Brent crater in Canada, filled with postimpact sediments and today partly occupied by lakes. After several
hundred Myr, this crater (dashed circle) is vaguely recognizable by its morphology, and most of the impact crater geology is
known from drillings (Grieve, 1978, 2006). (H) Satellite image of the recently discovered *2.6 km-diameter Summanen
impact structure in Finland of uncertain age (Plado et al., 2018). After perhaps hundreds of millions of years of exposure,
the crater (dashed circle) has been significantly overprinted by erosion, sedimentary infill, and glaciation and is today
concealed by a lake. The discovery and characterization of such old, ‘‘invisible’’ small impact structures usually requires
detailed geologic mapping and field work, as well as drilling. Scale bars are 1 km.
92 SCHMIEDER AND KRING

To assess the temporal distribution of impact events and
calculate impact rates as an expression of the impact flux
through time, different geochronologic techniques have
been developed and applied. These include, first, crater
counting and the calculation of isochrons based on the cra-
ter size–frequency distribution for the Moon, Mars, and
other planetary bodies characterized by a crater production
record (e.g., Hartmann and Neukum, 2001; this technique is
not applicable to the geologically active Earth); second,
stratigraphic age constraints (e.g., Koeberl et al., 2001;
Lindstro
¨met al., 2005; Schmieder and Buchner, 2008);
third, isotopic age determinations using the U–Pb, Ar–Ar
(K–Ar), Rb–Sr, and (U–Th)/He geo-/thermochronometers
and/or the
14
C method with impact lithologies sampled in
natural outcrop or drillings on Earth, in meteorites, or sam-
ples returned from space missions (e.g., Tera et al., 1974;
Bottomley et al., 1990; Deutsch and Scha
¨rer, 1994; Jourdan
et al., 2009, 2012); and, finally, methods other than those
mentioned above. We here predominantly focus on the stra-
tigraphic and isotopic methods. Due to improvements in
U–Pb (e.g., chemical abrasion thermal ionization mass spec-
trometry [CA-TIMS]) (Schoene, 2014; Kenny et al., 2019a),
secondary ion mass spectrometry (SIMS) (Kenny et al.,
2019b), and
40
Ar–
39
Ar geochronologic instrumentation and
methods (e.g., Renne et al., 2010, 2011, 2013; Sprain et al.,
2015; Schmieder et al., 2018a), the most precisely con-
strained ‘‘impact ages’’ today come with uncertainties on
the thousands-of-years (ka, kyr) level.
This article provides a current (as of September 2019)
summary of predominantly stratigraphic and isotopic re-
commended ages for proven impact structures and deposits
on Earth. Structures and deposits of likely but, to some
degree, uncertain impact origin (e.g., numerous oblong de-
pressions near Rio Cuarto in Argentina; Schultz and Lianza,
FIG. 2. Map of impact structures (n=200) and deposits (n=46) on Earth (including prominent impact holes, funnels, and
pits) and their best-estimate ages. For poorly constrained ages, the stratigraphic maximum age was chosen. Only a few
representative ejecta localities are shown (e.g., Thailand for the Australasian tektite strewn field) because some distal ejecta
deposits, such as the end-Cretaceous Chicxulub ejecta (plotted at Beloc, Haiti; yellow-green symbols) or the Popigai-
derived Upper Eocene clinopyroxene spherules (plotted near Hawaii), have a global or semiglobal distribution. Some
prominent terrestrial impact structures are labeled as follows: Ac, Acraman; Ar, Araguainha; B, Bosumtwi; Bo, Boltysh; C,
Chicxulub; CB, Chesapeake; CW, West and East Clearwater Lake; E, El¢gygytgyn; H, Haughton; K, Kara; KK, Kara-Kul;
L, Lappaja
¨rvi; M, Manicouagan; Mo, Morokweng; N, No
¨rdlinger Ries; P, Popigai; PK, Puchezh-Katunki; R, Rochechouart;
S, Sudbury; Si, Siljan; V, Vredefort; W, Woodleigh; Y, Yarrabubba; Z, Zhamanshin. The gray star symbol marks the site of
the June 30, 1908, Tunguska (Tu) explosion that downed trees in a vast area but left no impact structure on the ground.
Compare Table 1 with ages for impact structures and Table 2 with ages for impact deposits.
EARTH’S IMPACT EVENTS THROUGH TIME 93

1992; cf. Cione et al., 2002; Reimold et al., 2018; Cro
´sta
et al., 2019c; the recently reported Hiawatha ‘‘impact cra-
ter’’ in Greenland; Kjær et al., 2018; and enigmatic glass
deposits such as the Edeowie glass found in South Australia;
Haines et al., 2001; glasses found near Dakhleh, Egypt;
Osinski et al., 2008; and the Pica glass found in the Atacama
Desert of Chile; Roperch et al., 2017) are, therefore, not
included. Likewise, the 1908 Tunguska airburst event in
Russia, which seemingly did not produce any geologic
feature other than uprooted trees, is not listed here (e.g.,
Kulik, 1940; Krinov, 1960). The present article does not
intend to be the latest reference pertaining to the formation
of simple and complex impact craters, their impact ejecta,
and the physical aspects of the cratering process (e.g., Me-
losh, 1989; Melosh and Ivanov, 1999; Osinski et al., 2011,
2012; Kenkmann et al., 2012), the petrology of impactites
(rocks produced or modified by impact) (e.g., French, 1998;
Sto
¨ffler and Grieve, 2007; Grieve and Therriault, 2012), or
the verification of impact structures through the identifica-
tion of macro- and microscopic shock-metamorphic features
(e.g., shatter cones and shocked quartz and zircon grains)
(French, 1998; French and Koeberl, 2010; Ferrie
`re and
Osinski, 2012). For details about the more specific geologic
features of terrestrial impact structures, we refer the reader
to a number of review articles that summarize the impact
cratering record of each continent on Earth, such as the
works of Grieve (2006) for Canada in North America,
Reimold et al. (2018) and Cro
´sta et al. (2019b) for South
America, Schmieder and Buchner (2013) for Europe,
Reimold and Koeberl (2014) and Chabou (2019) for Africa
and the Arab World, respectively, Masaitis (1999) and
Reimold et al. (2008) for Russia and Asia, and Haines
(2005) for Australia. [Somewhat surprisingly, there is cur-
rently no up-to-date review of the impact cratering record
of the United States, and Walter H. Bucher’s (1936) early
work on the country’s ‘‘cryptoexplosion structures’’ proba-
bly remains the most recent systematic review of its kind;
however, many impact structures in the United States were
included in the more general listings of Freeberg (1969),
Classen (1977), and Grolier (1985), and a website project
maintained by Beauford (2019) provides basic information
and the relevant literature for almost all impact structures
and crater fields recognized in the country.] Nor does this
relatively short summary provide an in-depth explanation
and discussion of the isotopic methods commonly used to
determine impact ages, such as the U–Pb and Ar–Ar geo-
chronometers. In this context, we recommend the compre-
hensive summaries on the U–Pb technique by, for example,
Corfu (2013) and Schoene (2014), and on the Ar–Ar (and
K–Ar) method by McDougall and Harrison (1999) and
Kelley (2002). Previous U–Pb, Ar–Ar, and Rb–Sr geo-
chronologic work on several terrestrial impact structures
includes that of Bottomley et al. (1990) and Deutsch and
Scha
¨rer (1994), from which much was learned regarding
how different geochronometers behave with different types
of impact crater materials analyzed. This summary builds
upon that previous work, including critical evaluations of
Earth’s impact crater ages that ensued ( Jourdan et al., 2009,
2012; Jourdan, 2012). It should serve as a robust geochro-
nologic database and a backbone for ongoing and future
studies that make use of Earth’s impact crater ages for, for
example, statistical calculations and cratering flux models
(e.g., Mazrouei et al., 2019). Such studies have, in part,
relied on a flawed representation of the terrestrial impact
cratering record with partly inaccurate ages as input param-
eters (e.g., Telecka and Matyjasek, 2011; and the recently
published Encyclopedic Atlas of Terrestrial Impact Craters
of Flamini et al., 2019 that lists numerous inaccurate impact
ages), inevitably compromising the validity and significance
of their conclusions (see also discussions in Miljkovic
´et al.,
2013, 2014; Schmieder et al., 2014c; Rampino and Caldeira,
2015; Meier and Holm-Alwmark, 2017). Finally, this work
presents a referenced source for current best-estimate ages
that can be listed in online impact databases, such as the
Earth Impact Database (hosted at the University of New
Brunswick, Fredericton, Canada), which has recently been
complemented by the database Impact Earth maintained by
Osinski and Grieve (2019).
2. Data and Methods
Stratigraphic, isotopic, and additional age constraints are
predominantly sourced from the primary literature, high-
lighting the work that led to the establishment of the (cur-
rently) preferred age for any particular impact event. Some
ages are taken from summary articles (e.g., Grieve, 2006).
Impact ages are grouped into three main categories: (1)
stratigraphic age constraints; (2) isotopic ages, including
U–Pb, Ar–Ar, K–Ar, Rb–Sr, (U–Th)/He, and
14
C ages
(while considering ages obtained using the high-temperature
U–Pb and Ar–Ar geochronometers are usually preferred);
and (3) age constraints other than the ones mentioned above.
2.1. Stratigraphic ages
The determination of relative stratigraphic ages, by su-
perposition, can be applied to all impact structures on Earth
and elsewhere, where the age of the host rock is to some
degree constrained. Every impact structure has a target rock
that the impacting body penetrated and, through simple
geologic cross-cutting relationships, the youngest rock units
affected by the impact provide a maximum (oldest possible)
age for the impact. In turn, the oldest undisturbed rocks that
fill the crater after its formation, commonly crater lake sed-
iments in continental paleosettings, constrain the minimum
(youngest possible) impact age. Some terrestrial impact cra-
ter ages are only very imprecisely constrained by the age
of the impacted target rock as a maximum age (e.g., the
<1800 million years [Ma, Myr] I
ˆle Rouleau impact struc-
ture, Que
´bec, Canada) (Grieve, 2006). Sometimes, the stra-
tigraphic age for an impact can only be bracketed within
several hundred million years, as in the case of the 12 km-
diameter Wells Creek impact structure in Tennessee (e.g.,
Wilson, 1953; Ford et al., 2012; Ford, 2015, and references
therein). The crater must be younger than Mississippian
(*323 Ma) and older than Late Cretaceous (*100 Ma) (see
Cohen et al., 2013, for current stratigraphic age values),
suggesting a ‘‘best-estimate’’ age of *211 –111 Ma and a
relative error on the age of >100% (the commonly published
age is 200 –100 Ma) (e.g., Grieve, 2001a). However, other
stratigraphically constrained impact ages are remarkably
precise, such as that of the *14 km-wide marine Lockne
crater in Ordovician rocks of Central Sweden. There, the im-
pact age is precisely constrained to be 455 Ma plus and
minus a few hundred thousand years, because both the
94 SCHMIEDER AND KRING

youngest preimpact and oldest postimpact sediments lie in
the late Sandbian (early Caradocian) lower Lagenochitina
dalbyensis chitinozoan microfossil zone studied in great
detail (Grahn et al., 1996; Grahn, 1997; Ormo
¨et al., 2014).
The stratigraphic method equally applies to impact ejecta
layers.
2.2. Isotopic ages
Both the Wells Creek and Lockne impact craters described
above have no or little recognized impact melt, respectively,
that could potentially be used as material for radioisotopic
analysis. However, a relatively large number of terrestrial im-
pact structures have preserved impact melt-bearing rocks (e.g.,
Dence, 1971; von Engelhardt, 1984; Dressler and Reimold,
2001; Sto
¨ffler and Grieve, 2007; Osinski et al., 2018), such as
the up to *2.5 km-thick, differentiated crystalline melt sheet
(the Sudbury Igneous Complex) overlain by *1.5 km of melt-
bearingimpact breccia (the Onaping Formation)at the *200 to
250 km-diameter Sudbury Basin in Ontario, Canada (e.g.,
Grieve, 2006; Davis, 2008; Rousell and Brown, 2009; Grieve
et al., 2010); the up to *1.2 km-thick melt sheet at the
100 km-diameter Manicouagan impact structure in Que
´bec,
Canada (e.g., Floran et al., 1978; Grieve, 2006; Spray et al.,
2010) (Fig. 3A); and the up to *250 m-thick melt-bearing
impact breccia (suevite) of the 25 km-diameter No
¨rdlinger
Ries crater in Germany (e.g., von Engelhardt et al., 1995; von
Engelhardt, 1997; Sto
¨ffler et al., 2013) (Fig. 3B). The Ries
impact also produced green glassy tektites (moldavites)
(Fig. 3C), distal melt ejecta found *200 to 500 km northeast
of the crater (e.g., Sto
¨ffler et al., 2002; Trnka and Houzar,
2002). Because of the (partial to complete) resetting of
geochronometers, for example, the U–Pb and K–Ar system,
during high-temperature melting and degassing (diffusion)
events such as major impacts (e.g., Jourdan et al., 2012),
impact melt lithologies are in most cases suitable for geo-
chronologic analysis using a variety of radioisotopic geo-
chronometers.
2.2.1. U–Pb ages. One method used to determine im-
pact ages is the uranium–lead (U–Pb) and coupled lead–lead
(Pb–Pb) geochronometer (e.g., Nier, 1939; Wetherill, 1956,
1963; Tera and Wasserburg, 1972, 1974; and see Corfu,
2013 and Schoene, 2014 for reviews of its historical de-
velopment and application). The U–Pb geochronometer is
today used with several different technical setups. These in-
clude laser ablation inductively coupled plasma mass
FIG. 3. Impact crater materials commonly used for geochronologic analysis and two exemplary results. (A) Approxi-
mately 100 m-tall cliff of the impact melt sheet at the Manicouagan impact structure, Que
´bec, Canada (Baie Memory
Entrance Island, photo taken by M. Schmieder in summer 2006). This type of impact melt rock is suitable for whole-rock
Ar–Ar analysis and usually contains minerals (e.g., zircon) that can be analyzed using the U–Pb method. (B) Suevite, a
polymict impact breccia with dark, elongated fla
¨dle of impact glass from the Ries crater, Germany (Katzenstein Castle near
Dischingen, Baden-Wu
¨rttemberg). Impact glass is commonly used as sample material for Ar–Ar geochronology. (C) A
green, glassy Ries tektite (moldavite) found in Besednice, Czech Republic. (D) Concordia (Wetherill) diagram showing
U–Pb geochronologic results for zircon in impact melt rock from the Rochechouart impact structure in France (unpublished
data). (E) Shocked zircon grain with LA-ICP-MS laser ablation pit created during U–Pb analysis in impact melt rock from
the Charlevoix impact structure, Que
´bec, Canada (backscattered electron image) (Schmieder et al., 2019). (F) Argon–argon
age diagram showing a well-defined plateau age, including relevant statistics for a Ries tektite sample similar to the one
shown in (C) (from Schmieder et al., 2018a). LA-ICP-MS, laser ablation inductively coupled plasma mass spectrometry.
EARTH’S IMPACT EVENTS THROUGH TIME 95

spectrometry (LA-ICP-MS), SIMS (SIMS and nanoSIMS),
sensitive high-resolution ion microprobe (SHRIMP) analysis,
and thermal ionization mass spectrometry after chemically
abrading the mineral sample for better results (CA-TIMS).
The latter, again, comes in different variations (isotope di-
lution, ID-TIMS; and total evaporation, TE-TIMS) (e.g.,
Davis, 2008). Each of these techniques has its advantage and
disadvantage. While LA-ICP-MS and SIMS/SHRIMP are
routinely and rapidly applied to thin-section or grain mount
samples that can preserve the textural context of the sample,
producing moderately precise U–Pb and Pb–Pb ages, CA-
TIMS completely dissolves the mineral sample but produces
much more precise ages with errors commonly in the range
of a few thousands to tens of thousands of years (e.g.,
Schoene, 2014; Schaltegger et al., 2015). The U-bearing
minerals most commonly used for the U–Pb geochronologic
analysis of impact materials are either intensely shocked or
melt-grown zircon crystals (Fig. 3D, E) (e.g., Davis, 2008;
Crow et al., 2017; Kenny et al., 2019a, 2019b), baddeleyite
(Krogh et al., 1984; Corfu and Lightfoot, 1996), monazite
(e.g., Tohver et al., 2012; Erickson et al., 2017, 2019a,
2019b), and to a lesser degree titanite (Ames et al., 1998)
and apatite, although recent results for terrestrial impact
craters suggest the latter is a promising target mineral for
future studies (McGregor et al., 2018, 2019). Uranium–lead
results are typically visualized in a concordia diagram
(Wetherill or Tera-Wasserburg plot) alongside their internal
statistics (mean square weighted deviation [MSWD] and
probability pas a measure of statistical fit) and can be
corrected for a nonradiogenic (‘‘common’’) lead component.
Zircon crystals from the less severely shocked, unmelted
portion of the target rock of an impact structure commonly
tend to yield older dates on or near concordia (the curve
along which U–Pb ages from different U decay series are
equal), reflecting the crystallization and/or metamorphic
age(s) of the host rock (e.g., Scha
¨rer and Deutsch, 1990;
Wielicki et al., 2012; Schmieder et al., 2015b). In contrast,
intensely shocked and recrystallized zircon grains (so-called
granular zircon, locally with mm-sized baddeleyite domains
as a thermal decomposition product of zircon) (Wittmann
et al., 2006; Timms et al., 2017) are chronometrically reset
and commonly yield younger concordia ages, potentially
reflecting the impact (Fig. 3D) (e.g., Hodych and Dunning,
1992; Krogh et al., 1993; Wielicki et al., 2012; Kenny et al.,
2019b). If the isotopic system is affected by variable loss of
Pb, a discordant array of dates may define a lower intercept
with concordia from which the age of the impact can be
derived (e.g., Kamo et al., 1996; Ma
¨ntta
¨ri and Koivisto,
2001). However, episodic and/or modern postimpact Pb loss
can cause significant disturbance of the U–Th–Pb system,
and some zircon U–Pb ages obtained for impact events (e.g.,
the Ediacaran Acraman impact in South Australia) and their
geologic significance are not straightforward to interpret
(Schmieder et al., 2015b). A special type of zircon is
typically U- and Th-rich metamict (internally radiation-
damaged, pseudoamorphous) zircon (e.g., Pidgeon et al.,
1966; Meldrum et al., 1998; Nasdala et al., 2001), which is
more susceptible to U–Pb-chronometric resetting during
impact events (and other thermometamorphic processes)
than nonmetamict zircon (e.g., Schwarz et al., 2016a and
unpublished data; Stockli et al., 2018; McGregor et al.,
2019; Schmieder et al., 2019). The use of metamict (do-
mains in) shocked zircon grains in impact geochronology,
therefore, warrants additional future research.
Uranium–lead and Pb–Pb ages of 3470 –2 Ma for zircon
crystals extracted from the Paleoarchean S1 impact spherule
layer in the Onverwacht Group of the Barberton Greenstone
Belt in South Africa and the Warrawoona Group of the
Pilbara Block in Western Australia define the oldest impact
ages on Earth (Byerly et al., 2002); a number of additional
younger Archean and Proterozoic spherule layers occur in
those regions and elsewhere (e.g., Glass and Simonson,
2012). Earth’s oldest partially preserved impact structure
is the roughly 50 km-diameter Yarrabubba impact structure
in Western Australia, with a Pb–Pb age for shock-
recrystallized monazite of 2229 –5 Ma (Erickson et al.,
2019a, 2019b). Shocked zircon crystals in melt rock from
the *250 to 300 km-diameter Vredefort impact structure,
the largest one and also among the three oldest on Earth,
yielded a U–Pb age of 2023 –4 Ma (Kamo et al., 1996).
Zircon grains crystallized from Sudbury’s impact melt sheet
produced a U–Pb age of 1850 –1 Ma (Krogh et al., 1984).
In a recent study, intensely shock-metamorphosed zircon
grains recrystallized into microgranular aggregates yielded a
precise concordia age of 77.85 –0.78 Ma for the 23-km
Lappaja
¨rvi impact crater in Finland (Kenny et al., 2019b).
This result for Lappaja
¨rvi has wider biological and astro-
biological implications with respect to the role particularly
of medium-sized (approximately 20–30 km-diameter) im-
pact craters as habitats for microbial life on the early Earth
(e.g., Kring, 2000, 2003; Osinski, 2003, 2011; Osinski et al.,
2001; Cockell et al., 2003; Cockell, 2006) and, possibly,
Mars (e.g., Newsom, 1980; Rathbun and Squyres, 2002;
Abramov and Kring, 2005; Rummel et al., 2014; Osinski
et al., 2017) (see also discussion in Section 4).
2.2.2. Ar–Ar ages. Another technique prominently used
in impact geochronology is the
40
Ar/
39
Ar (henceforth sim-
ply Ar–Ar) method pioneered by Wa
¨nke and Ko
¨nig (1959)
and Merrihue and Turner (1966), an improved variation of
the classical K–Ar technique. McDougall and Harrison
(1999) and Kelley (2002) provide useful and comprehensive
reviews. After sample selection, processing, and meticulous
handpicking of virtually fresh and clast-poor sample splits
(typically particles of impact melt rock, ideally separated
into the melt groundmass and clast portion therein; impact
glass; or feldspar £500 mm in particle size) (e.g., Schmieder
and Jourdan, 2013a; Swindle et al., 2014), the potassium-
bearing rock or mineral sample, together with standard
minerals, is first irradiated by fast neutrons to produce
39
Ar
from
39
K as a proxy for K in the sample; the argon isotope
ratios in the aliquots are then measured in a mass spec-
trometer (i.e., thereby eliminating the need to determine a
less precise ratio of absolute K and Ar concentrations from
separate sample splits) and ages can be calculated by using
the latest K decay constants and standard mineral ages
(Renne et al., 2010, 2011). The Ar–Ar method is today most
commonly applied by using the total fusion of a sample with
a laser (e.g., Kelley and Spray, 1997) or, alternatively, the
stepwise heating of a sample using a resistance furnace
or laser (e.g., Bottomley et al., 1990; Swisher et al., 1992;
Jourdan, 2012; Schmieder et al., 2018a). Generally, the step-
heating method produces a more comprehensive set of data
than the total-fusion method and allows for a more robust
96 SCHMIEDER AND KRING

statistical assessment of resulting ages (e.g., Jourdan et al.,
2008, 2011; Schmieder and Jourdan, 2013a).
Argon–argon results for impact structures can be dis-
turbed by the effects of sample alteration causing the dif-
fusive loss of radiogenic
40
Ar* and younger apparent ages
(e.g., Schmieder et al., 2014a), and also the incorporation of
inherited
40
Ar* with inclusions of incompletely degassed
older target rock material and/or excess argon from Ar-
bearing fluids interacting with the sample, both causing
older apparent ages (inherited and excess argon are sum-
marized under the term ‘‘extraneous argon’’) (e.g., Kelley,
2002). Such effects can be identified, quantified, and cor-
rected for using the isochron approach (e.g., Roddick, 1978;
Kuiper, 2002; Jourdan et al., 2008, 2011; Jourdan, 2012;
Schmieder et al., 2015a). Statistically robust Ar–Ar results
ideally form a ‘‘plateau’’ in the age spectrum (Fig. 3F), a
sequence of individual degassing steps with increasing tem-
perature that all overlap within a narrow error limit and
include most (ideally at least 70%) of the
39
Ar extracted
from the sample (e.g., Jourdan, 2012). They are, moreover,
characterized by their internal statistics expressed through
MSWD and pvalues for plateau sections and isochrons (and
are typically reported with 2serrors; that is, at the *95%
confidence level, as is done in this work unless otherwise
stated). Precise Ar–Ar ages have been obtained for a number
of impacts on Earth, such as 66.052 –0.031 Ma for glassy
microtektites from the 180 km-diameter Chicxulub crater
linked to the end-Cretaceous mass extinction (Renne et al.,
2018). High-precision Ar–Ar results for the Chicxulub mi-
crotektites at the K/T boundary (more recently also known
as the K/Pg boundary) were recently used to calibrate the
timing and duration of the contemporaneous reverse mag-
netic chron C29r (Sprain, 2017; Sprain et al., 2018). Simi-
larly, Ries tektites (Fig. 3C) yielded a precise Ar–Ar age of
14.808 –0.038 Ma (Schmieder et al., 2018a) that can also
be used to (re-)calibrate the paleomagnetic and orbitally
tuned astronomical timescale (Schmieder et al., 2018b). An
increasingly robust intercalibration between the U–Pb and
Ar–Ar geochronometers (e.g., Villeneuve et al., 2000;
Ramezani et al., 2005; Renne et al., 2010, 2011) provides
growing confidence that ages obtained when using both
techniques are not only precise (i.e., with a small error) but
also accurate (i.e., close to the ‘‘true’’ age) and can be di-
rectly compared and correlated.
As the K decay constants and ages for standard (monitor)
minerals in
40
Ar/
39
Ar geochronology have been continu-
ously refined (e.g., Steiger and Ja
¨ger, 1977; Renne et al.,
2010, 2011), modern Ar–Ar ages are today directly com-
parable with U–Pb ages (e.g., Renne et al., 2013, 2018;
Sprain et al., 2015, 2018; Clyde et al., 2016). This, however,
also means that ‘‘legacy’’ Ar–Ar ages published in the older
literature are, in many cases, inaccurate and require re-
calculation (e.g., Jourdan et al., 2012; Schwarz et al.,
2015; Mercer and Hodges, 2016; Schmieder et al., 2018a).
Table 1 contains the most current Ar–Ar ages that were
(re-)calculated, where possible, using the revised K decay
constants and monitor ages of Renne et al. (2010, 2011). For
example, the original melt rock age of 64.98 –0.05 Ma (1s)
for the Chicxulub impact crater, Mexico, published by
Swisher et al. (1992) using the K decay constants of Steiger
and Ja
¨ger (1977) and the Fish Canyon sanidine (FCs) stan-
dard with a then-reported age of 27.84 Ma, becomes 66.05 –
0.18 Ma (2s) after the recalculation of individual step ages,
plateau sections and ages, and weighted mean (average)
ages (n=3 plateau ages; MSWD =0.18; p=0.84) obtained
from those results using Isoplot 4.15 (Ludwig, 2008) and the
ArAR tool of Mercer and Hodges (2016). This recalculated
age is within uncertainty indistinguishable from the more
recent U–Pb age of 66.021 –0.081 Ma for zircon crystals in
ash layers around the K/T boundary in the Denver Basin
(Clyde et al., 2016). It is also equivalent to Ar–Ar results of
66.038 –0.049 Ma for glassy microtektites found at the K/T
boundary in Beloc, Haiti (Renne et al., 2013; Sprain et al.,
2015), an age of 66.051 –0.031 Ma for similar microtektites
at a K/T section exposed on Gorgonilla Island off the coast
of Colombia (Renne et al., 2018), and an age of 66.052 –
0.043 Ma for tephra in the ‘‘Iridium Z coal’’ layer *1cm
above the iridium anomaly of the K/T boundary interval
(Renne et al., 2013; Sprain et al., 2018). The *24 km-
diameter Boltysh impact structure in Ukraine, another end-
Cretaceous impact structure (Kelley and Gurov, 2002), has
a recalculated age of 65.80 –0.67 Ma that is, within
a somewhat larger error envelope, identical to the age of
the Chicxulub impact ( Jourdan, 2012). However, from the
identification of distal Chicxulub ejecta in the basal lake
sediments of the Boltysh crater, we know that this impact
predates Chicxulub by a few thousand years ( Jolley et al.,
2010).
Likewise, through recalculation, the age of the *35 km-
diameter Manson impact structure, Iowa (decades ago still a
contender for the K/T boundary impact site), also sees a
notable shift from 74.1 –0.1 Ma (Izett et al., 1998) to an
older recommended age of 75.9 –0.1 Ma (Table 1). The
*100 km-diameter Popigai impact structure in Russia, with
a previously recommended Ar–Ar age of 35.7 –0.2 Ma
(Bottomley et al., 1997) has, after a reinterpretation of the
original Ar–Ar results, a more conservative recalculated age
of 36.63 –0.92 Ma, which accounts for the spread of *1
Myr between four plateau ages, not all of which over-
lap (n=4 plateau ages; MSWD =7.6; p=0.000) (see also
Jourdan et al., 2009). From this recalculation, a time gap of
at least *0.5 Myr (and up to *3 Myr) seems to occur
between Popigai and the somewhat younger (34.86 –0.32
Ma) *40 to 45 km-diameter Chesapeake impact structure
(a.k.a. Chesapeake Bay; final collapsed diameter *85 km)
on the East coast of the United States (Assis Fernandes
et al., 2019). This asteroid ‘‘one-two punch’’ is in agreement
with the occurrence of two relatively closely spaced, but
separate, distal ejecta layers in the Upper Eocene (Glass
et al., 1985; Koeberl, 2009) (Table 2), known as the older
clinopyroxene layer geochemically linked to the Popigai
impact (Whitehead et al., 2000) and the younger North
American (micro-)tektites linked to the Chesapeake impact
(Deutsch and Koeberl, 2006).
In a few cases, recalculation of the original Ar–Ar results
was omitted due to potentially unreliable standard ages used
in the original geochronologic analysis. This, for example,
applied to ages obtained using the B4M muscovite standard,
which was commonly used in geochronology laboratories in
the 1980s (e.g., for the Haughton impact structure, Canada)
( Jessberger, 1988) and later (for the Ilyinets impact structure,
Ukraine) (Pesonen et al., 2004). The B4M standard was re-
cently shown to be quite heterogeneous in composition and
age between finer- and corser-grained domains of the
EARTH’S IMPACT EVENTS THROUGH TIME 97

Table 1. List of Proven Terrestrial Impact Structures, Select Age Constraints, and Recommended Impact Ages Sorted by Age
No
Impact
structure Country Latitude Longitude
Diameter
(km)
Type of
target rock
a
Type of
impactor
b
Stratigraphic
age
constraints
Radioisotopic
age
constraints
Other age
constraints
Recommended
age (Ma)
Recommended
age
reference
c
Pre-
recalculation
age (Ma)
1 Chelyabinsk
d
Russia 458¢N6018¢E 0.007 Ice LL-chondrite Recent Fall February 15, 2013,
main mass left 8 m-
wide temporary hole
in frozen Lake
Chebarkul
0.000006 Borovic
ˇka et al.
(2013)
2 Carancas Peru 1640¢S6902¢W 0.0135 Sedimentary H-chondrite Recent Fall September 15,
2007
0.000012 Tancredi et al.
(2009)
3 Sterlitamak
e
Russia 5340¢N5559¢E 0.0094 Sedimentary
(soil, loam)
IIIAB iron Recent Fall May 17, 1990 0.000029 Petaev (1992)
4 Sikhote Alin
(Field)
f
Russia 4609¢N 13439¢E 0.027 Crystalline IIAB iron Recent Fall February12, 1947 0.000072 Krinov (1971)
5 Imilac
e
Chile 2412¢S6848¢W 0.015 Crystalline
(volcanic,
soil)
Pallasite Recent Found 1822 AD; fall
produced *15 m-
wide impact pit,
*4 m deep
>0.0002 Buchwald (1973);
Bevan (2006)
6 Sobolev
e
Russia 4617¢N 13754¢E 0.053 Sedimentary Iron? Recent Trees in crater 0.00030–
0.00025
Yarmolyuk (1951);
Khryanina (1981)
7 Wabar
(Field)
f
Saudi Arabia 2130¢N5028¢E 0.116 Sedimentary
(sand)
IIIAB iron Historical? Luminescence dating,
historical
*0.0003 Basurah (2003);
Prescott et al.
(2004)
8 Whitecourt Canada 5400¢N 11536¢W 0.036 Sedimentary IIIAB iron
14
C (charcoal) <0.0011 Herd et al. (2008)
9 Dalgaranga Australia 2745¢S 11705¢E 0.021 Crystalline Mesosiderite Quaternary Preservation of
morphology
<0.003? Shoemaker and
Shoemaker (1988)
10 Kamil Egypt 2201¢N2605¢E 0.045 Sedimentary Iron (ataxite) Thermoluminescence
dating
£0.004 Sighinolfi et al.
(2015)
11 Kaali
(Kaalija
¨rv)
(Field)
f
Estonia 5822¢N2240¢E 0.11 Sedimentary IAB iron
14
C (charcoal) *0.00324 Losiak et al. (2016)
12 Vaca Muerta
(Field)
e
Chile 2545¢S7030¢W 0.007 Crystalline
(volcanic)
Mesosiderite Quaternary?
14
C Fall produces field of
pits, largest is
*7.16 m in
diameter and 1.35 m
deep
*0.0035 Pedersen et al.
(1992)
13 Campo del
Cielo
(Field)
f
Argentina 2738¢S6142¢W 0.115 Sedimentary IAB iron Quaternary
14
C (charcoal) *0.004 Roman
˜a and Cassidy
(1973)
14 Veevers Australia 2258¢S 12522¢E 0.08 Sedimentary IIAB iron Preservation of ejecta
blanket
*0.004? Shoemaker and
Shoemaker
(1988); Haines
(2005);
Shoemaker et al.
(2005)
15 Morasko
(Field)
f
Poland 5229¢N2724¢E 0.1 Sedimentary IAB iron Quaternary Luminescence dating *0.005 Stankowski et al.
(2007)
16 Ilumetsa
(Field)
Estonia 5757¢N1654¢E 0.08 Sedimentary Unknown Quaternary
14
C (charcoal) *0.007 Raukas et al. (2001);
Losiak et al.
(2017); A. Losiak
(2019), personal
communication
17 Macha
(Field)
f
Russia 6005¢N 11739¢E 0.3 Sedimentary Iron
14
C (charcoal) 0.007315 –
0.00008
Gurov et al. (1987);
Gurov and Gurova
(1998)
18 Haviland
e
United States 3735¢N9910¢W 0.015 Sedimentary Pallasite
(Brenham)
Cosmogenic nuclides
(
14
C)
0.020 –0.002 Honda et al. (2002)
19 Boxhole Australia 2237¢S 13512¢E 0.185 Crystalline IIIAB iron
10
Be/
26
Al exposure age 0.030 –0.005 Shoemaker et al.
(1990)
20 Henbury
(Field)
f
Australia 2435¢S 13309¢E 0.157 Sedimentary IIIAB iron Cosmogenic nuclides
(
14
C)
0.042 –0.019 Kohman and Goel
(1963)
21 Amguid Algeria 2605¢N423¢E 0.45 Sedimentary Lower Devonian
target rocks
Freshness of crater
morphology
£0.1? Lambert et al.
(1980)
22 Hickman Australia 2302¢S 11941¢E 0.26 Mixed (banded
iron formation,
rhyolite)
Iron? Paleoproterozoic
(Boolgeeda Iron
Fm.) or younger
Plumbing of local
drainage system
£0.1? Glikson et al.
(2008); Haines
(2014)
23 Barringer
(Meteor
Crater)
United States 3502¢N 11101¢W 1.186 Sedimentary IAB iron Early Triassic to
Quaternary
36
Cl surface exposure;
10
Be,
26
Al exposure
*0.056?;
0.0611 –0.0048
Sutton (1985);
Marrero et al.
(2010); Kring
(2017b) and
references therein;
Barrows et al.
(2019)
24 Odessa
(field)
f
United States 3145¢N 10229¢W 0.168 Sedimentary IAB iron Optically stimulated
luminescence
0.0635 –0.0045 Holliday et al.
(2005)
(continued)
98

Table 1. (Continued)
No
Impact
structure Country Latitude Longitude
Diameter
(km)
Type of
target rock
a
Type of
impactor
b
Stratigraphic
age
constraints
Radioisotopic
age
constraints
Other age
constraints
Recommended
age (Ma)
Recommended
age
reference
c
Pre-
recalculation
age (Ma)
25 Wolfe Creek
(Kandimalal)
Australia 1918¢S 12746¢E 0.875 Sedimentary IIIAB iron Optically stimulated
luminescence,
10
Be,
26
Al exposure
0.120 –0.009 Shoemaker et al.
(1990, 2005);
Barrows et al.
(2019)
26 Tswaing (Pretoria
Saltpan)
South Africa 2524¢S2805¢E 1.13 Crystalline Chondrite Glass fission track 0.220 –0.104 Storzer et al. (1999);
Jourdan et al.
(2007)
27 Kalkkop South Africa 3243¢S2426¢E 0.64 Sedimentary Chondrite? U–Th series dating of
limestone
0.25 –0.05 Reimold et al.
(1998)
28 Lonar India 1959¢N7631¢E 1.83 Crystalline (basalt) Carbonaceous
chondrite?
Ar–Ar (impact melt
rock)
0.576 –0.047 Jourdan et al.
(2011),
recalculated
0.570 –0.047
29 Monturaqui Chile 2356¢S6817¢W 0.46 Crystalline (granite,
volcanics)
IAB? iron (U–Th)/He (zircon and
apatite from
impactite)
0.663 –0.09 Ukstins Peate et al.
(2010)
30 Pantasma Nicaragua 1312¢N8557¢W 14 Crystalline
(volcanic)
Ar-Ar (impact glass) 0.815–0.011 Rochette et al.
(2019)
31 Zhamanshin Kazakhstan 4824¢N6058¢E 14 Mixed Carbonaceous
chondrite
Ar-Ar (impact glass) 0.91 –0.14 Deino et al. (1990),
recalculated
0.87 –0.13
(range)
32 Bosumtwi Ghana 632¢N125¢W 10.5 Crystalline Chondrite? Iron? Ar-Ar (Ivory Coast
tektites)
1.13 –0.10 Jourdan (2012) after
Koeberl et al.
(1997b)
33 New Que
´bec
(Pingualuit)
Canada 6117¢N7340¢W 3.44 Crystalline Chondrite (L?) Ar–Ar (impact melt
rock)
1.4 –0.1 Grieve et al. (1991)
34 Talemzane
(Maa
ˆdna)
Algeria 3319¢N402¢E 1.75 Sedimentary Eocene or younger Preservation of crater
morphology
£3? Lambert et al.
(1980); Reimold
and Koeberl
(2014)
35 Tenoumer Mauritania 2255¢N1024¢W 1.9 Crystalline Ar-Ar (impact melt
rock)
1.57 –0.14 Schultze et al.
(2016)
36 Aouelloul Mauritania 2015¢N1241¢W 0.36 Sedimentary Iron K-Ar (impact glass) 3.1 –0.3 Fudali and Cressy
(1976)
37 El’gygytgyn Russia 6730¢N 17205¢E 18 Crystalline
(volcanic)
Achondrite? Ar-Ar (impact melt
rock)
3.65 –0.08 Layer (2000) 3.58 –0.04
38 Roter Kamm Namibia S2746¢1618¢E 2.5 Mixed Ar-Ar (impact melt
rock)
3.8 –0.3; *4 to 5 Koeberl et al.
(1993); Hecht
et al. (2008)
3.7 –0.3
39 Bigach Kazakhstan 4830¢N8200¢E 7 Mixed Miocene or younger 5 –3 Masaitis (1999)
40 Karla Russia 5454¢N4800¢E 12 Sedimentary Miocene to Pliocene 5 –1 Masaitis (1999)
41 Xiuyan China 4021¢N 12327¢E 1.8 Crystalline Proterozoic to
Quaternary
14
C (charcoal) 5–0.05? Chen et al. (2011);
Liu et al. (2013)
42 Shunak Kazakhstan 4712¢N7242¢E 2.8 Crystalline
(volcanic)
Middle/Late
Devonian to
Miocene
Crater morphology 12–5 Masaitis et al.
(1980); Masaitis
(1999)
43 No
¨rdlinger
Ries (Ries
crater)
Germany 4853¢N1037¢E 24 Mixed No contamination?
(achondrite?)
Middle Miocene Ar-Ar (moldavite
tektites)
14.808 –0.038 Schmieder et al.
(2018a, 2018b)
44 Steinheimer
Becken
(Steinheim
Basin)
Germany 4840¢N1004¢E 3.8 Sedimentary Pallasite? Miocene crater lake
sediments
Presumably
synchronous with
Ries impact
14.808 –0.038? Sto
¨ffler et al. (2002);
Schmieder et al.
(2018a, 2018b)
45 Haughton Canada 7522¢N8941¢W 24 Mixed No contamination Ar-Ar (impactites) 23.4 –1.0 Jessberger (1988);
Young et al.
(2013)
23.4 –1.0
46 Jebel Waqf as
Suwwan
Jordan 3103¢N3648¢E 6 Sedimentary Middle Eocene or
younger
<48 Salameh et al.
(2008)
47 Karakul (Kara-Kul) Tajikistan 3901¢N7327¢E 52 Crystalline Tectonic history <60 Gurov et al. (1993);
Baratoux et al.
(2012)
48 Logoisk Belarus 5412¢N2748¢E 17 Mixed Ar-Ar (impact glass) 30.0–0.5 Jourdan et al. (2012)
after Sherlock
et al. (2009)
49 Beyenchime-Salaatin Russia 7150¢N 12330¢E 8 Sedimentary Cenozoic?
(preservation of
crater)
33 –33 Masaitis (1999)
50 Eagle Butte Canada 4942¢N 11035¢W 10 Sedimentary Late Cretaceous or
younger
<65 Grieve (2006)
51 Gusev Russia N 4821¢E4014¢3 Sedimentary Younger than Late
Cretaceous
<66 Movshovic et al.
(1991)
52 Chesapeake
(Chesapeake Bay)
United States 3715¢N7605¢W*40 to 45 Sedimentary Chondrite (L?) Ar-Ar (tektites and
impact melt rock)
34.86 –0.32 Assis Fernandes
et al. (2019)
53 Chukcha (Chykcha) Russia 7542¢N9748¢E 6 Mixed Cretaceous or
younger
<70 Vishnevsky (1995)
54 Maple Creek Canada 4948¢N 10906¢W 6 Sedimentary Maastrichtian or
younger
<72 Grieve (2006)
(continued)
99

Table 1. (Continued)
No
Impact
structure Country Latitude Longitude
Diameter
(km)
Type of
target rock
a
Type of
impactor
b
Stratigraphic
age
constraints
Radioisotopic
age
constraints
Other age
constraints
Recommended
age (Ma)
Recommended
age
reference
c
Pre-
recalculation
age (Ma)
55 Popigai Russia 7130¢N 11100¢E 100 Mixed Chondrite (H or L?) Ar-Ar (impact melt
rock)
36.63 –0.92 Bottomley et al.
(1997),
recalculated,
mean of 4 plateau
ages
35.7 –0.2
56 Wanapitei Canada 4645¢N8045¢W 7.5 Crystalline Chondrite (L or
LL?)
Ar-Ar (impact melt
rock)
37.7 –1.2 Grieve (2006) after
Bottomley et al.
(1979),
recalculated
37.2 –1.2
57 Mistastin Canada 5553¢N6318¢W 28 Crystalline No contamination?
Achondrite? Iron?
U–Pb (CA-TIMS, melt
rock zircon)
37.83 –0.05 Sylvester et al.
(2013)
58 Connolly Basin Australia 2332¢S 12445¢E 9 Sedimentary Paleogene *66 to 23 Shoemaker and
Shoemaker (1986)
59 Logancha Russia 6530¢N9548¢E 20 Mixed Paleogene *66 to 23 Masaitis (1999)
60 Tin Bider (Tademaı
¨t) Algeria 2736¢N507¢E 6 Sedimentary Coniacian or
younger
£90 Lambert et al.
(1981)
61 Chiyli (Shyili) Kazakhstan 4910¢N5751¢E 5.5 Sedimentary Early to Middle
Eocene
*56 to 41 Vishnevsky (2007)
62 Santa Marta Brazil 1010¢S4514¢W 10 Sedimentary Late Cretaceous
(Posse Fm.) to
Neogene
(Chapada
˜o Fm.)
<100 Oliveira et al.
(2017); Cro
´sta
et al. (2019b)
63 Kamensk Russia 4820¢N4015¢E 25 Sedimentary Ar-Ar (impact glass) 50.37 –0.40 Jourdan et al. (2012)
after Izett et al.
(1994)
64 Montagnais Canada 4253¢N6413¢W 45 Sedimentary (shelf) Ar-Ar (impact melt
rock)
51.1 –1.6 Bottomley and York
(1988),
recalculated
50.5 –1.6
65 Goat Paddock Australia 1820¢S 12640¢E 5.1 Sedimentary Early Eocene
(palynology)
*56 to 48 Milton and
Macdonald (2005)
66 Ragozinka Russia 5818¢N6200¢E 9 Mixed Thanetian, Early
Eocene (Serov
Suite)
*59 to 56 Vishnevsky (1999)
67 Sierra Madera United States 3036¢N 10255¢W 13 Sedimentary Albian (Georgetown
Fm.) or younger
<113 Wilshire et al.
(1972)
68 Marquez United States 3117¢N9618¢W 13 Sedimentary Around Paleocene/
Eocene transition
Apatite fission track 58.3 –3.1 Sharpton and Gibson
(1990); McHone
and Sorkhabi
(1994)
69 BP structure Libya 2519¢N2420¢E 2 Sedimentary Early Cretaceous or
younger (Nubian
Sandstone)
£120 Koeberl et al.
(2005b)
70 Oasis Libya 2435¢N2424¢E 18 Sedimentary Early Cretaceous or
younger (Nubian
Sandstone)
£120 Koeberl et al.
(2005b)
71 Mount Toondina Australia 2757¢S 13522¢E 4 Sedimentary Aptian to Albian,
Early Cretaceous,
or younger
(Bulldog Shale)
<125 Plescia et al. (1994)
72 Chicxulub Mexico 2120¢N8930¢W 180 Mixed Carbonaceous
chondrite?
K/T (K/Pg)
boundary
Ar-Ar (impact melt
rock and glassy
microtektites)
66.052 –0.043 Swisher et al.
(1992),
recalculated
Renne et al.
(2013, 2018);
Sprain et al.
(2015, 2018);
Clyde et al.
(2016)
73 Boltysh Ukraine 4845¢N3210¢E 24 Crystalline Chondrite? Slightly older than
Chicxulub (distal
K/T ejecta in post-
impact sediments)
Ar-Ar (impact melt
rock)
65.80 –0.67 Kelley and Gurov
(2002),
recalculated
Jourdan (2012)
74 Cerro do Jarau Brazil 3012¢S5632¢W 13.5 Mixed Early Cretaceous
(Serra Geral Fm.)
or younger
£135 Cro
´sta et al. (2019a)
75 Kara Russia 6905¢N6418¢E 65 Mixed Chondrite? Ar-Ar (impact melt
rock)
70.7 –2.2 Trieloff et al.
(1998),
recalculated
70.3 –2.2
76 Manson United States 4235¢N9431¢W 35 Mixed Chondrite Ar-Ar (sanidine in melt
breccia)
75.9 –0.1 Izett et al. (1998),
recalculated
74.1 –0.1
77 Lappaja
¨rvi Finland 6309¢N2342¢E 23 Mixed H-chondrite U-Pb (zircon in impact
melt rock)
77.85 –0.78 Schmieder and
Jourdan (2013a);
Kenny et al.
(2019b)
(continued)
100

Table 1. (Continued)
No
Impact
structure Country Latitude Longitude
Diameter
(km)
Type of
target rock
a
Type of
impactor
b
Stratigraphic
age
constraints
Radioisotopic
age
constraints
Other age
constraints
Recommended
age (Ma)
Recommended
age
reference
c
Pre-
recalculation
age (Ma)
78 Zeleny Gai Ukraine 4842¢N3254¢E 3.5 Crystalline Archean to
Paleogene
80 –20? Masaitis (1999)
79 Wetumpka United States 3231¢N8611¢W 6.5 Mixed Chondrite? Close to Santonian/
Campanian
boundary
(U–Th)/He (apatite and
zircon)
*83.5 King et al. (2007);
Wartho et al.
(2012)
80 Suvasvesi North Finland 6239¢N2810¢E 3.5 Crystalline Ar-Ar (impact melt
rock)
*85 Schwarz et al.
(2016a);
Schmieder et al.
(2016b)
81 Yallalie Australia 3028¢S 11547¢E 15 Sedimentary Coniacian, Late
Cretaceous
89.8–83.6 Ma Cox et al. (2019)
82 Agoudal Morocco 3159¢N531¢W 1–3 Sedimentary Middle Jurassic or
younger
£174 Chennaoui
Aoudjehane et al.
(2016)
83 Kgagodi Botswana 2229¢S2735¢E 3.5 Crystalline Early Jurassic
(Karoo dolerite)
to Paleogene
£180 Brandt et al. (2002)
84 Avak United States 7115¢N 15636¢W 12 Sedimentary Turonian, Late
Cretaceous
(palynology)
94–90 Banet and Fenton
(2008)
85 Upheaval Dome United States 3826¢N 10954¢W 10 Sedimentary Early Jurassic
(Toarcian) or
younger
<183 Kriens et al. (1999)
86 Deep Bay Canada 5624¢N 10259¢W 13 Crystalline Late Albian to Early
Cenomanian
(palynology)
102–95 Grieve (2006)
87 Rotmistrovka Ukraine 4900¢N3200¢E 2.7 Crystalline Early Cretaceous to
Turonian
*145 to 94 Masaitis (1999)
88 Vista Alegre Brazil 2557¢S5241¢W 9.5 Mixed Early Cretaceous
(*134 Ma Serra
Geral Fm.) or
younger
Ar-Ar (minimum age) *111 to 134 Cro
´sta et al. (2019b)
89 Mien Sweden 5625¢N1452¢E 9 Crystalline Stone? Ar–Ar (impact melt
rock)
122.4 –2.3 Bottomley et al.
(1990),
recalculated
121.0 –2.3
90 Vargea
˜o Brazil 2650¢S5207¢W 12 Early Cretaceous
(*134 Ma Serra
Geral Fm.) or
younger
U-Pb (zircon in impact
melt breccia)
123.0 –1.4 Ne
´de
´lec et al. (2013)
91 Serra da Cangalha Brazil 805¢S4652¢W 12 Sedimentary Late Permian or
younger
£250 Kenkmann et al.
(2011)
92 Tookoonooka Australia 2700¢S 14300¢E 55 Sedimentary Barre
ˆmian/Aptian
boundary
125 –1; *121.8 to
123.8?
Bron and Gostin
(2012); Olierook
et al. (2019)
93 Dellen Sweden 6155¢N1639¢E 19 Crystalline Stone? Ar-Ar (impact melt
rock)
140.82 –0.51 Mark et al. (2014)
94 Mjølnir Norway 7348¢N2940¢E 20–40 Sedimentary (sea
floor)
Early Berriasian
(Volgian/
Ryazanian
boundary)
*143.0 –2 Smelror et al. (2001)
95 Morokweng South Africa 2628¢S2332¢E 70 Crystalline LL-chondrite U-Pb (CA-ID-TIMS,
melt-grown zircon)
146.06 –0.16 Hart et al. (1997);
Koeberl et al.
(1997a); Kenny
et al. (2019a)
96 Des Plaines United States 4203¢N8752¢W 8 Sedimentary Post-Pennsylvanian <299 Emrich and
Bergstrom (1962)
97 Kentland United States 4045¢N8724¢W 13 Sedimentary Younger than
Mississippian,
older than
Pleistocene
*300 to 1 Weber et al. (2005)
98 Middlesboro United States 3637¢N8344¢W 6 Sedimentary Younger than
Pennsylvanian
<299 Englund and Roen
(1963)
99 Riacha
˜o Brazil 743¢S4639¢W 4.5 Sedimentary Early Permian
(Pedra do Fogo
Fm.) or younger
<299 Maziviero et al.
(2013); Cro
´sta
et al. (2019b)
(continued)
101

Table 1. (Continued)
No
Impact
structure Country Latitude Longitude
Diameter
(km)
Type of
target rock
a
Type of
impactor
b
Stratigraphic
age
constraints
Radioisotopic
age
constraints
Other age
constraints
Recommended
age (Ma)
Recommended
age
reference
c
Pre-
recalculation
age (Ma)
100 Tavan Khar Ovoo
(Tabun-Khara-Obo)
Mongolia 4406¢N 10936¢E 1.3 Crystalline Late Triassic to Late
Cretaceous
Maximum age based
on morphologic
expression; likely a
few Myr old
150 –20? Masaitis (1999)
101 Vepriaj Lithuania 5506¢N2436¢E 8 Sedimentary Middle Devonian to
Late Jurassic,
likely Middle
Jurassic
160 –5? Masaitis et al.
(1980); Masaitis
(1999)
102 Decaturville United States 3754¢N9243¢W 6 Mixed Younger than
Pennsylvanian
<323 Offield and Pohn
(1977)
103 Zapadnaya
(Bilylivka)
Ukraine 4944¢N2900¢E 3.2 Crystalline K-Ar (impact melt
rock)
165 –6? Masaitis (1999);
Gurov et al.
(2002)
104 Obolon’ Ukraine 4930¢N3255¢E 20 Sedimentary Iron? Early Triassic to
Middle Jurassic
(Bathonian)
K-Ar (impact melt
rock)
169 –7? Gurov et al. (2009)
105 Mishina Gora Russia 5840¢N2800¢E 2.5 Mixed Latest Devonian or
younger
<360 Masaitis (1999)
106 Serpent Mound United States 3902¢N8324¢W 8 Sedimentary Tournaisian, Early
Mississippian
(Cuyahoga Fm.)
or younger
<359 Bucher (1936);
Reidel and
Koucky (1981)
107 Viewfield Canada 4935¢N 10304¢W 2.5 Sedimentary Younger than
Mississippian,
likely older than
Triassic-Jurassic
190 –20 Grieve (2006)
108 Sa
˜o Miguel
do Tapuio
Brazil 538¢S4123¢W 20 Sedimentary Late Devonian or
younger (Cabec¸as
Fm.)
<382 Cro
´sta et al. (2019a,
2019b)
109 Aorounga Chad 1906¢N1915¢E 16 Sedimentary Late Devonian (?) or
younger
£383 Koeberl et al.
(2005a)
110 Gweni-Fada Chad 1725¢N2145¢E 22 Sedimentary Late Devonian (?) or
younger
£383 Koeberl et al.
(2005a)
111 Piccaninny Australia 1732¢S 12825¢E 7 Sedimentary Frasnian (Late
Devonian) or
younger
<383 Shoemaker and
Shoemaker
(1985); Haines
(2005)
112 Puchezh-Katunki Russia 5706¢N4335¢E 80 Mixed Early Triassic to
Middle Jurassic
Ar-Ar (impact melt
rock)
196–192 Holm-Alwmark
et al. (2019)
113 Gow Lake Canada 5627¢N 10429¢W 5 Crystalline Iron? Ar-Ar (impact melt
rock)
196.8 –9.9 Pickersgill et al.
(2019b); A.
Pickersgill (2019),
personal
communication
114 Cloud Creek United States 4307¢N 10645¢W 7 Sedimentary Late Triassic
(Norian?) to
Middle Jurassic
(Bathonian?)
*227 to 166 Stone and Therriault
(2003)
115 Ouarkziz Algeria 2900¢N733¢W 3.5 Sedimentary Visean,
Carboniferous to
Paleogene
345–65 Reimold and
Koeberl (2014)
116 Rochechouart France 4550¢N056¢E 23–40 Crystalline Chondrite? Iron?
Stony-iron?
Ar-Ar (impact melt
rock)
206.92 –0.32 Schmieder et al.
(2010b); Cohen
et al. (2017)
117 Red Wing Creek United States 4736¢N 10333¢W 9 Sedimentary Permo-Triassic
(Spearfish Fm.) to
Bathonian,
Middle Jurassic
(Piper Fm.)
*250 to 167 Brenan et al. (1975);
Koeberl et al.
(1996)
118 Wells Creek United States 3623¢N8740¢W 12 Sedimentary Post-Mississippian,
older than Late
Cretaceous
*323 to 100 Ford (2015)
119 Manicouagan Canada 5123¢N6842¢W 100 Mixed No contamination?
Chondrite?
Achondrite?
U-Pb (ID-TIMS, melt-
grown zircon)
215.56 –0.05 Hodych and
Dunning (1992);
Ramezani et al.
(2005)
120 Lake Saint Martin Canada 5147¢N9832¢W 40 Mixed No contamination Devonian to Middle
Jurassic
Ar-Ar (impact-melted
feldspar and melt
rock)
227.8 –0.9 Schmieder et al.
(2014a)
121 Lumparn Finland 6008¢20¢¢N2007¢30¢¢E 9 Mixed Middle Ordovician
(Caradocian) or
younger
£458 Merrill (1980);
Abels (2003)
(continued)
102

Table 1. (Continued)
No
Impact
structure Country Latitude Longitude
Diameter
(km)
Type of
target rock
a
Type of
impactor
b
Stratigraphic
age
constraints
Radioisotopic
age
constraints
Other age
constraints
Recommended
age (Ma)
Recommended
age
reference
c
Pre-
recalculation
age (Ma)
122 Paasselka
¨Finland 6212¢N2923¢E 10 Mixed Younger than
Mesoproterozoic
Ar-Ar (recrystallized
feldspar glass and
impact melt breccia)
231.0 –2.2 Schmieder et al.
(2010c); Schwarz
et al. (2015)
123 Saqqar Saudi Arabia 2935¢N3842¢E 34 Sedimentary Early Devonian
( Jauf Fm.) to Late
Cretaceous
70–410 Neville et al. (2014);
Kenkmann et al.
(2015)
124 Glover Bluff United States 4358¢N8932’W 8 Sedimentary Early Ordovician or
younger
<485 Read (1983)
125 Karikkoselka
¨Finland 6213¢N2514¢E 1.5 Crystalline *9 Ma (U–Th)/
He zircon age
Older paleomagnetic
age
*260 to 230?;
*9?
Pesonen et al. (1999;
Schmieder et al.
(2010a)
126 Steen River Canada 5931¢N 11737¢W 25 Mixed Younger than Late
Devonian, older
than Mid-Albian
U-Pb (SIMS, zircon in
impact melt rock)
*383 to 108;
132 –1.3?
MacLagan (2018);
MacLagan et al.
(2018)
127 Araguainha Brazil 1646¢S5259¢W 40 Mixed Late Permian to
Early Triassic
U-Pb (SHRIMP, LA-
ICP-MS, SIMS,
monazite and
zircon), Ar-Ar (var.
lithologies)
254.7 –2.5?;
259 –5?;
251.5 –2.9?
Tohver et al. (2012);
Erickson et al.
(2017); Hauser
et al. (2019)
128 Glikson Australia 2359¢S 12134¢E 19 Sedimentary Paleozoic <508 –5 Macdonald et al.
(2005)
129 Kursk Russia 5140¢N3600¢E 6 Sedimentary Early Carboniferous
to Middle Jurassic
359–163 Masaitis (1999)
130 Gosses Bluff
(Tnorala)
Australia 2350¢S 13219¢E 22 Sedimentary Late Devonian or
younger
Ar-Ar minimum age
(impact melt rock)
*383 to 165 Schmieder, Tohver
and Jourdan
(unpublished
data); Haines
(2005)
131 Douglas (Sheep
Mountain)
(Field)
Wyoming, United
States
4240¢N 10528¢W 0.15 Sedimentary Early Permian
(Uppermost
Casper Fm.)
*280 Kastning and
Huntoon (1996);
Kenkmann et al.
(2018)
132 Ternovka (Terny) Ukraine 4801¢N E3305¢16–19 Mixed Chondrite? K-Ar (feldspar and
mica)
280 –10 Val’ter et al. (1981)
133 West Clearwater
Lake
Canada 5613¢N7430¢W 36 Mixed No contamination Ar-Ar (impact melt
rock)
286.2 –2.6 Bottomley et al.
(1990); Schmieder
et al. (2015a)
134 Luizi Democratic
Republic of
Congo
1010¢S2755¢E 17 Sedimentary Late Neoproterozoic
or younger
£573 Master et al. (2001);
Ferrie
`re et al.
(2011)
135 Elbow Canada 5059¢N 10643¢W 8 Sedimentary Middle Devonian to
pre-Jurassic
393–201 Grieve (2006)
136 Saarija
¨rvi Finland 6517¢N2825¢E 1.5 Crystalline Ediacaran to Early
Cambrian or
younger
<600–520 O
¨hman (2007)
137 Dobele Latvia 5635¢N2