The record of large-scale cratering on Earth is scant, and the only currently 'proven' 100-km-class impact structure known to have formed within the Cenozoic is Popigai, located in the Siberian Arctic at 71.5 deg N, 111 deg E. Popigai is clearly a multiringed impact basin formed within the crystalline shield rocks (Anabar) and platform sediments of the Siberian taiga, and estimates of the volume of preserved impact melt typically exceed 1700 cu km, which is within a factor of 2-3 of what would be predicted using scaling relationships. We present the preliminary results of an analysis of the present-day topography of the Popigai structure, together with refined absolute age estimates, in order to reconstruct the pre-erosional morphology of the basin, as well as to quantify the erosion or sediment infill rates in the Popigai region

Deino, A. L.

Garvin, J. B.

English

NASA Technical Reports Server

11
0138
NEW PERSPECTIVES ON THE POPIGAI IMPACT
STRUCTURE. J. B. Ganw1 and A. L. Deino1,'NASA/Goddard,
Geodynamics, Code 921. Greenbelt, MD 20771. USA,
zGeochronology Center of the Institute of Human Origins, 2453
Ridge Road, Berkeley CA 94709. USA.
The record of large-scale cratcring on Earth is scant, and the only
currently "proven" 100-km-class impact structure known to have
formed within the Cenozoic is Popigai, located in die Siberian
Arctic at 71.5°N, 111 °E (Masaitis et al.. 1975). Popigai is clearly a
mul tiringed impact basin formed within the crystalline shield rocks
(Anabar) and platform sediments of the Siberian taiga, and esti-
mates of the volume of preserved impact melt (i.e., Masaitis and
Mashchak. 1986) typically exceed 1700 km3, which is within a
factor of 2-3of what would be predicted using scaling relationships
(Melosh, 1989; Grieve and Pesonen, 1992). In this report, we
present the preliminary results of an analysis of the present-day
LPl Contribution No. 790 27
topography of the Popigai structure, together with refined absolute
age estimates, in order to reconstruct the prc-erosional morphology
of the basin, as well as to quantify the erosion or sediment infill rates
in the Popigai region.
We have assembled an -90 -m -resolution digital elevation model
(DEM) data for the Popigai region (see Fig. 1 for cross sections
derived from the 2-D DEM), and are in the process of attempting to
reconcile absolute age discrepancies that have resulted from "As/
"Ar radiomctric analyses of glass samples provided to U.S. and
Canadian investigators over the past five years by Russian impact
crater specialists such as V. Masaitis (VSEGEI/St. Petersburg). In
1991 (tccLPSCXXII, pp. 297-298), we reported on "Ar/^Ar laser
step-heating ages of glass fragments removed from suevite (melt
breccia) from the interior cavity of Popigai (provided by V. Masaitis),
and obtained ages in the -70-60-Ma range. We now have prelimi-
nary results from the ^ Ar/" Ar step-heating of six additional glass
samples from suevite and allogenic breccia from Popigai (again
TABLE 1. Volumetri c maty lit of cratcn.
Crater Name
Henbury
Wolf Creek
Dmrwin
Bamnger
Go«lP«ddock
Bofumtwi
Zhvnanihin
Got ic. Bluff
Popigmi*
Diameter
(km)
0.20
0.94
1.00
1.20
5.00
1050
14.40
22.00
100.00
Age
(Ma)
0.0040
0.1000
0.7300
0.0490
55.0000
1.3000
0.8700
142.0000
34.0000
Model
Interior
Volume
(km1)
4.00E-04
4.20E-02
5.10E-02
8.90E-02
4.13E+00
2.28E+01
4.71E+01
1.25E+02
4.06E+03
Volume
of Excavation
(km3)
2.40E-04
2.50E-02
3.00E-02
5.20E-02
7.30E+00
4.91E+01
1.08E+02
3.18E+02
1.51E+04
Model
Melt
Volume
(km1)
3.00E-08
6.00E-04
7.00E-04
1.30E-03
1.67E-01
2.08E+00
6.07E+00
257B+01
4.42E+03
Observed
Interior
Volume
(km1)
7
7
7
0.105
7
16.100
20.100
7
1300.000
Max Depth
to Melting
(km1)
0.011
0.065
0.070
0.086
0.431
1.000
1.400
2.300
12.700
Model
Kinetic
Energy
(Megatone)
l.OOE-02
1.90E+00
2.40E+00
4.50E+00
5.78E402
7.20E+03
2.10E+04
8.90E+04
1J3E+07
•Age discrepancy: other »ge i» 66 M» (K/T)
Popigai : Volume
Popigoi.,,
d: 015km Vi : 728.39km*
0: :08.20Vm Vefc: 2874.60km'
Popigai.^
d: 0.26km Vi : 1270.14km'
D: 102.66km Vek: 4226.21km*
d: 013km Vi : 48061km'
0: 99.20km Vet: 298378km'
250
Fig. 1.
https://ntrs.nasa.gov/search.jsp?R=19930000950 2020-03-17T10:06:15+00:00Z
28 7992 Sudbury Conference
provided courtesy of V. Mastitis). Data analysis is still underway,
but it is evident that none of the new samples are as well-behaved
in age release patterns as was the original sample, due most likely
to alteration and the presence of old target-rock mineral inclusions.
Predominant ages in these spectra are commonly between -60 and
40 Ma, but portions of the gas release in the -40-30 range are also
observed. We draw no conclusions as to the age of the Popigai
impact event from these data at this early stage. Planned chemical,
hydrogen, and oxygen isotopic analyses may help us son out die
effect alteration has had on the Ar age systematics. It is curious to
note that independent results of ^ Ar/^Ar laser step-heating of other
samples conducted by Bouomley, Grieve, and York (R. Grieve,
personal communication, 1992) indicate well-behaved release pat-
terns that suggest an age in the vicinity of -34 Ma (Eocene -
Oligocene boundary). At this point, our impression is that a
combination of analyses of pristine melt glasses and unaltered
mineral phases is recommended in order to resolve the age disparity
that apparently exists with respect to the absolute age of the Popigai
impact
Using the high-resolution topography data illustrated in Fig. 1,
we can attempt to reconstruct the initial crater geometry by means
of standard dimensional scaling relationships, such as those sum-
marized in Mclosh (1989) and by Grieve and Pesonen (1992).
Table 1 highlights some of the parameter values derived for Popigai
in comparison with a small set of representative smaller terrestrial
features. The maximum degree of original relief at the crater (floor
to rim crest) is between 520 and 960 m (depending on the model
chosen), while the present-day dynamicrangcof relief is 260-408 m.
This suggests that between 260 and 552 m of relief has been lost due
to slumping, erosion, and other processes (interior cavity sediment
infill). If we adopt typical erosion models for high-latitude shield
terrains (see Garvin and Schnetzler, this volume), we find that up to
0.0052 mm/yr could be eroded at Popigai, which translates into
-176 m over a 34-Ma lifetime, or 350 m over a 66-Mi lifetime.
Clearly, a refined absolute age for the structure is needed to refine
these erosion estimates; however, the suggestion is mat Popigai has
experienced up to a factor of 5 more erosional infill than the much
smaller equatorial shield crater Bosumtwi. (We acknowledge die
cooperation of V. Masaitis at the VSEGEI in St. Petersburg for
providing us with Popigai glass samples on several occasions).iron:
TABLE 1. Obwrved and model parameters for the ZIP and the BIC as
derived from analysis of topography and scaling rel»tkm»hip«.
Parameter in BoSOMwi Rrf.
THE ZH AM ANSHIN IMPACT FEATURE: A NEW CLASS
Of COMPLEX CRATER? J. B. Garvin1 and C. C. Schnetzler1.
'NASA/GSFC, Geodynamics Branch. Code 921. Greenbelt MD
20771. USA. 'Department of Geography. University of Maryland,
College Park MD 20742, USA.
The record of 10-km-scaJe impact events of Quaternary age
includes only two "proven" impact structures: die Zhamanshin
Impact Feature (ZIP) and the Bosumtwi Impact Crater (BIC). What
makes these impact landforms interesting from die standpoint of
recent Earth history is their almost total lack of morphologic
similarity, in spiteof similar absolute ages and dimensions. The BIC
resembles pristine complex craters on die Moon to first order (i.e.,
"U"-shaped topographic cross section with preserved rim), while
the ZIF displays vniuallynoT^ of the typical morphologic elements
of a 13- to 14-km -diameter complex crater. Indeed, this apparent
lack of a cnuerlike surficial topographic expression initially led
Soviet geologists [1] to conclude that die structure was only 5.5 to
Age(Ma=10>yr)
Apparent diam. Da (km)
Apparent depth da (km)
Observed aspect da/Da
Obs. HL Rim Ejecta hej (m)
Obs. VoL Cavity Vcav (km')
Obs. Vcav/SAcav (km)
Obs. VoL Ejecta Vej (knP)
Obs. Tej = Vej/SAej (km)
A V lost = Vcav-Vej (km>)
Tejloa = AV losl/SAej (m)
EJER = Tejlost/Age <mm/yr)
Model VoL UL Vi (km>)
Model VoL Excav. Vex (km')
Model mk. depth di (km)
Model Aspect di/Da
Model Vi/SAi (km)
Model hej* (m)
her = hej*-hej(m)
ER1 M = her/Age (mm/yr)
A Z = di-d* (km)
A Vol. = IVi-V«vl (kirP)
Ter = A VoUSA (km)
CER = A V/SA/Age (mm/y r)
AZ/Age(mm/yr)
Erosion Model for Target
Kin Erosion Model
Erosion (mm/y r) @ AZ in m
Erosion (m) for Crmler Age
Max. VoL Eroded (knP)
0.87
14.4
0.182
0.013
30.3
20.1 (max)
0.018
16.7
0.041
3.4
8.3
0.0095
47.1
107.9
0.436
0.030
0.289
360.0
329.7
038
0.254
27.0
0.166
0.19
0.29
K AZ**
1.05E-4
0.019
16.5
2.7
1.3
10.5
0.300
0.030
83.0
16.05
0.201
11.6
0.049
4.45
18.6
0.014
22.8
48.2
0.384
0.037
0.263
263 JO
180.0
0.14
0.084
6.75
0.078
0.060
0.065
KAZ™«
4.2SE-7
0.00016
0.21
0.018
P.U]
Meas.
Comp.
"
•
M
M
M
•
"*
«
•
"
•
M
[31
[31
Comp,
M
m
6 km in diameter and at least 45 Ma in age [ 1,10]. However, more
recent drilling and geophysical observations at die Z3F have indi-
cated that its pre-erosional diameter is at least 13.5 km. and that its
age is most probably 0.87 Ma [23.7.9.15]. Why die present topo-
graphic expression of a 13.5-km complex impact crater less than 1
m.y. old most closely resembles heavily degraded Mesozoic shield
craters such as Lappajarvi is a question of considerable debate
[6,7.9-11J. Hypotheses for die lack of a clearly defined craterlike
form at die ZIP include a highly oblique impact, a low-strength
"cometary" projectile, weak or water-saturated target materials, and
anomalous erosion patterns [ 1.2,6,7.9]. The problem remains unre-
solved because typical erosion rates within die arid sedimentary
platform environment [3] of central Kizrirhrtm in which die £IF is
located are typically low (see Table 1); it would require at least a
factor of 10 greater erosion at die ZIP in order to degrade die near-
rim ejecta typical of a 13.5-km complex crater by hundreds of
meters in only 0.87 Ma, and to partially infill an inner cavity with
27 km1 (an equivalent uniform thickness of infill of 166 m). Our
analysis of die degree of erosion and infill at die ZIF calls for rales
in die 0.19 to 0.38 mm/yr range over die lifetime of die landform,
which are a factor of 10 to 20 in excess of typical rales for die
Kazakhstan semidcscrt [3]. If we apply similar erosional models to
die BIC. which is located in an equatorial crystalline shield region


New perspectives on the Popigai impact structure

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