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Previously Unrecognized Large Impact Basins on
Mars and the Moon: Implications for the
Late Heavy Bombardment in
the Inner Solar System
Herbert V FreyGoddard Space Flight Center
Workshop on
Early Solar System Impact Bombardment
Lunar and Planetary Institute19-20 November 2008
TWO MAJOR POINTS
We have likely significantly underestimated (at least) the large diameter impact inventory of both Mars and the Moon (and therefore of the Earth),
and therefore underestimated the likely effects of a Late Heavy Bombardment everywhere
Ages of large impact basins on Mars support a Nice-like Late Heavy Bombardment / Terminal Planetary Cataclysm throughout the inner solar system
OUTLINE
Evidence for previously unrecognized large impact basins on Mars and the Moon
Ages of large impact basins on Mars
implications for Mars
implications for the inner solar system LHB
Mounting evidence for still more large impact basins
Future efforts / Caveats, Qualms and Questions
MORE THAN MEETS THE EYE
Evidence for previously unrecognized large impact basins on Mars and the Moon
Cassini
MOLA shaded relief
Stretched MOLA topography
“MOLA Hole”
Cassini
MOLA data revealed a very large number of probable impact basins on Mars that were not previously known from imagery ? ?
UNRECOGNIZED IMPACT BASINS ON MARS
Quasi-Circular Depressions (QCDs) > 50km in the martian lowlands
From Frey et al., GRL 29, No. 10, 10.10291.2001GL013832, 2002
100 KM
N (D>50 km) = 644 (~90 visible)
If the not-visible-on-images QCDs areburied impact basins, then
the bulk of the population is “not visible”
the lowland crust is much older than
we previously thought
Mapping QCDs from MOLA data alone will never find all the buried basins
All crater retention ages based only on visible + buried QCDs alone are minimum ages, because
there are likely many basins are so completely buried they lack topographic expression in MOLA data
Cassini “MOLA Hole”
“visible” “buried” unrecognizable in MOLA data
alone
But more deeply buried basins might have a signature in crustal thickness (from topography AND gravity)
CRUSTAL THICKNESS DATA (Neumann et al.)
Circular Thin Areas (CTAs) may be additional buried impact basins
Many do correspond to visible or buried Quasi - Circular Depressions (QCDs)
[but many do not]
Ratio of non-QCD CTAs (possible new basins) to QCDs is greatest in areas of greatest burial (Lowlands, Tharsis)
Cumulative frequency curves for the combined QCDs + CTAs (not related to QCDs) are similar to those for QCDs
From Edgar and Frey (2008), Geophys. Res. Lett. 35, L02201, doi:10.1029/2007GL031466
CUMULATIVE FREQUENCY CURVESFor visible QCDs, Visible + Buried QCDs, and
Visible + Buried QCDs + non-QCD CTAS
ba
HIGHLANDS LOWLANDS
N(300)N(300)
“AGING” OF THE MARTIAN CRUST
How N(300) crater retention ages have changed as more buried basins were counted using topography and crustal thickness data
N(300) Crater Retention Ages AREA Vis Vis + Topo Vis + Topo + CT Highlands 0.27 1.98 ( 7.3x) 3.18 ( 1.6x) [11.8x] Lowlands 0.04 0.87 (21.8x) 3.19 ( 3.7x) [79.8x]
(Based on Edgar and Frey, 2008, GRL 35, L02201, doi:1029/2007GL031466)
Cumulative large diameter cratering on the martian highlands ~ 12 times greater (at least) than originally thought
It is likely we have seriously underestimatedthe early (LHB) cratering on Mars
It’s really important to count both visible and buried craters
Highlands, Lowlands have same N(300) Crater Retention Age!
If there is a very large population of impact basins on Mars which we did not recognize before we had the MOLA topography……
…..is there also a population of unrecognized impact basins on the Moon that might be revealed by lunar topography (e.g, ULCN2005)?
GH
O
M-RA
SEARCHING ULCN2005 FOR LUNAR BASINSLeft: Default color for ULCN topography. Blue = low. A-D Below: Progressive stretches of ULCN (top row) with 400 m contours (bottom row). C Below: QCDs > 300 km, solid where identified by Wilhelms, dashed where newly identified in ULCN topography. Upper right: profile (from C) through Grimaldi and unnamed basin.
H = Hertzsprung, A = Apollo, O = Orientale, G = Grimaldi, M-R = Mendel-Rydberg
GrimaldiUnnamed
260 km 370 km
A B C D
LUNAR BASINS FOUND IN ULCN2005(bottom line result #1)
The ULCN2005 topography confirms the centers and diameters of many of the basins listed by Wilhelms (1987), but
10 have centers and/or diameters different from those suggested by the topography.
10 on his list are not obvious topographic basins.
LUNAR BASINS FOUND IN ULCN2005(bottom line result #2)
Wilhelms (1987) lists 45 basins > 300 km diameter, described as “distinct”, “probable”, “possible” and “doubtful” basins (at least 10 of which do not have basin topography)
We find at least 92 circular topographic basinsover the same size range.
D
D
DP
(C)
K
F-S
K
F-S
(B)
Stretched lunar topography with 400 m contours
White Circles: Basins listed by Wilhelms: Freundlich-Sharanov (F-S, 600 km) and Korolev (K, 440 km)
Black circles: Basins identified in lunar topography, dashed where new.D = definite, P = Probable
Many basins were not “seen” by photogeologists
170W, 10N 170W, 10N
Korolev Unnamed
478 km 519 km
A’
A
A A’
4.1 km
3.2 km
Topographic Profile through Korolev, N of Korolev
The unnamed basin north of Korolev is about as large, not quite as deep
Stretched lunar topography with 300 m contours
White Circles: Basins listed by Wilhelms: Birkhoff (Bi, 330 km), Coulomb-Sartan (CS, 530 km) and Lorentz (Lo, 360 km)
Black circles: Basins identified in lunar topography, dashed where new. D = definite, P = Probable
Many basins were not “seen” by photogeologists
CS
Bi
Lo
CS
Bi
Lo
D
D
D
PP
125W, 45N 125W, 45N
120W 0W 240W
120W 0W 240W
Wilhelms Basins (White) Compared with Basins from Topography (Black) (newly identified basins shown dashed)
More newly identified basins on the far side and at high latitudes
CUMULATIVE FREQUENCY CURVES FOR LARGE LUNAR BASINS
Wilhelms’ list
Frey’s List
(from ULCN)
Histogram of basin diameters (100 km bins, 200 to 3200 km)
Generally expect an exponential increase with decreasing
diameter
At D <500 kmWilhelms basins fall
off the -2 curve(observational loss)
Except for Procellarum, Wilhelms (all) and Frey curves are similar from1000 down to ~ 500 km
Both follow a -2 powerlaw distribution atD = 500 - 800 km
N(300)
VISIBLE NOT TOTAL
Basins > 100 km diameter in SPA identified in ULCN
“Total” = “Visible” + “Not Visible”
visible = obvious on imagesnot = not obvious on images
Total Crater Retention Age (CRA)[e.g., N(100) or N(300)] ~ 1.8 times greater than the Visible CRA
Total = Visible, Not Visible, combined
PRELIMNARY
WHAT DOES THIS MEAN?
There is a significant and likely large population of previously unrecognized large impact basins (and likely smaller craters) on the Moon
We have likely under-estimated the total cratering and therefore the early cratering rate on the Moon
WHY IS THIS IMPORTANT?
Because the lunar cratering rate is the basisfor estimating absolute ages on
all other planetary bodies
The (Large Diameter) Late Heavy Bombardment on Mars
Crater Retention and “Absolute” Ages of the largest impact basins on Mars
0, 300W 0, 180W
S POLE
0, 60W
N POLE
Ac
Cr
UtNP
IAAz
He
SW
DaSi
Ag
So
He
So
Ag
Cr
Ac
NT
Sc
Is
Ar
IA
Am
Ut
NT
Ut
SEAm
Si
Ze
Hm
SW Da
NT
6 new basins identified in crustal thickness data:Amazonis (Az), inside Amazonis (IA), North Tharsis (NT),
Sirenum (Si), Solis (So), and SE Elysium (SE)
Az
HOW OLD ARE THE LARGEST
BASINS ON MARS?
(There are ~20 with a diameter > 1000 km)
From Frey, 2008, GRL 35, L13103, doi:10.1029/2008GL033515
N(300) AGES FOR LARGE BASINSFrom counting smaller basins on the rim and interior
(both QCDs and non-QCD CTAs > 300 km)
65% of the basins (13 of 20, including 4 of the 5 largest) have an N(300) CRA in the range 2.5-5.0
Highland Basins
Lowland Basins
Tharsis Basins
Age distribution is peaked!
From Frey (2008) GRL 35, L13103, doi: 10.1029/2008GL033515
Crustal Thickness
Converting N(300) CRAs to Hartmann-Neukum Model Ages
15/20 (75%) including the 5 largest (D>2500 km) may have formed in only a 100 million year interval.
18/20 (90%) may have formed in a 200 million year interval.
Highland Basins
Lowland Basins
Tharsis Basins
Crater Retention
Age distribution is peaked!
Highland Basins
Lowland Basins
Tharsis Basins
Absolute Age distribution is very peaked!
H-N
Was the large diameter martian LHB like a “Terminal Lunar Cataclysm”
If so,there were
very important implications for Mars and for the rest of the inner
solar system
A “Terminal Martian
Cataclysm”?
Utopia3300 km
Hellas2100 km
Isidis1350 km
Mars-sized object(Moon-maker)
~6700 km, Crater ?
Chixulub (Dinosaur-Killer)10-16 km, Crater~180 km
Mars~6700
Unnamed~300 km
Imbrium1200 km
Moon
LHB Life Busters
Large enough to sterilize the planet!
~1/2
THERE’S EVEN MORE BAD NEWS
The short formation time for most of the largest martian impact basins includes the time when Mars switched from a core magnetic dynamo to no-dynamo state*
The dynamo may have shut off in < 50 MY*this work done in collaboration with Rob Lillis
Lillis et al. (2008) GRL 35, L14203, doi: 10.1029/GL2008034338
Highland Basins
Lowland Basins
Tharsis Basins
BASIN MAGNETIZATION VS AGE
The dynamo may have shut off in < 50 (<20?) MYduring the peak in large basin formation!!!This work done in collaboration with Rob Lillis, UC BerkeleySee: Lillis et al. (2008) GRL 35, L14203, doi: 10.1029/GL2008034338
Dynamo gone
between N(300) = 2.7-3.8 X
Dynamo
No DynamoX
COINCIDENCE? or CAUSE?
Is the demise of the dynamo in the youngest quarter of the large basin impact interval just a coincidence?
OR
Could formation of 4 of the 5 largest basins (all > 2500 km in diameter) in a relatively short time (< 60 MY?) have actually contributed to the loss of the main magnetic field?
“Too good a coincidence to be one.”
(The possibility of “cause” deserves serious consideration)
COINCIDENCE? or CAUSE?
Recent Results Relevant to Death of the Dynamo:
Kuang et al. (2008, GRL 35, L14205, doi: 10.1029/GL2008034183) show that a relatively small perturbation (e.g., a 1-2% change in core-mantle boundary heat flow) could kill off the dynamo relatively suddenly if it was already subcritical.
Roberts (unpublished results) calculates that the thermal effects of the largest of these impacts (D>2000 km) can produce a 10% or more change in the heat flow across the core-mantle boundary.
Disappearance of the global magnetic field on Marsduring the period of large basin formation
may be more than a coincidence
The period of LHB on Mars was likely catastrophic for several reasons
An intense period of large impact formation had enormous environmental consequences
sterilization of the surface, loss of atmosphere
The global magnetic field disappearedatmosphere no longer protected from solar wind erosion
X
What does the large diameter impact spike on Mars imply for the LHB
in the rest of the inner solar system?
If this is part of an inner solar system-wide
event?
A “Terminal Martian
Cataclysm”?
Is this part of aninner solar system-wide event?
The interval for peak formation of martian basins is ~ consistent with the Nice model Impact spike (at the Moon) would last
~150-200 MY
But the H-N model “absolute” age is wrong: The Late Heavy Bombardment (on the
Moon) peaked at ~3.9 BYA
If this is part of an inner solar system-wide event It may be possible to tie the lunar & martian chronologies
together at ~3.9 BYA
A “Terminal Martian
Cataclysm”?
TWO IMPORTANT QUESTIONS ABOUT THE LARGE MARS BASINS AND THEIR AGES
If not, then the LHB likely was a short
duration “spike”
Were there really no
very large basins before these?
Should this peak be at 3.9
BYA?
?
Present area of large martian basins (even allowing for rings larger than the “diameter” of the basin)
leaves a lot of Mars “uncovered”
Area of 20 largest basins ~ 43% surface area of Mars(based on diameter of basins)
With overlap, ~35 % of Mars is “occupied” by large basins
COULD EVEN OLDER BASINS SURVIVE ON MARS?
30N,120W 30S,0W 30S,240W
If large impacts erase the record out to 1.5D (above) or 2.0D (below), less of Mars is available to record earlier ages. At 3D almost no area remains.
30S,0W
1.5D
30S,240W
1.5D
30N,120W
1.5D
30S,240W
2.0D
30N,120W
2.0D
30S,0W
2.0D
It seems likely that some fraction of the surface area of Mars might be available to retain impacts older than the oldest basin we currently date
And there is now a new crustal thickness model (MarsCrust3, Neumann et al., 2008) that should (and does!) reveal even more subtle CTAs
30S,240W
1.5D
30S,240W
1.5D
1.5D mask
30N,120W 30S,240W
30S,0W
New large CTAs > 500 km diameter
Based on a very preliminary study ofthe new MarsCrust3
crustal thickness model
Some of these lie outside the likely effects of the
very large basins...
…and therefore could be older than the basins
already dated.
Very, Very Preliminary!!!
VERY, VERY PRELIMINARY RESULTS
Not all of the candidates will survive further studySome are probably NOT additional large impact basins
But some may be additional large impact basins, andSome of these are > 1000 km diameterSome lie in possibly older terrain, and
have the potential to predate the dated basins
It may be possible to determine if there are basins older than those in the narrow interval
Can show very preliminary results for 4 cases
N(300) CRATER RETENTION AGES (CRAs) and DERIVED HARTMANN-NEUKUM MODEL “ABSOLUTE” AGES
PREVIOUSLY PROPOSED LARGE BASINS (Frey, 2008)
PREVIOUSLY PROPOSED LARGE BASINS (Frey, 2008)
NEW CANDIDATE BASINS from MarsCrust3 (Neumann et al., 2008)
VERY, VERY PRELIMINARY (and INCOMPLETE)
N(300) CRATER RETENTION AGES (CRAs) and DERIVED HARTMANN-NEUKUM MODEL “ABSOLUTE” AGES
BACK TO THE MOON
Crustal thickness data has revealed a number of new large impact basins on Mars
What about lunar crustal thickness data?
0 N, 120W
0 N, 0W
0 N, 240W
Blue = Thin crustRed = Thick crust
Contour Interval = 4 km
Circular Thin Areasrevealed in
LunarCrustal
ThicknessModels
from
Wieczorick et al.(2006)
Most visible basins (solid circles) and those identified in ULCN topography (dashed circles)
have fairly obvious signatures in crustal
thickness data
EVIDENCE FOR MORE LARGE LUNAR BASINS?
15N, 205W
CrustalThickness
Most visible basins (solid circles) and those identified in ULCN topography (dashed circles)
have fairly obvious signatures in crustal
thickness data
EVIDENCE FOR MORE LARGE LUNAR BASINS?
But there are many CTAs – possible
impact basins - not previously identified in the topography
alone15N, 205W
CrustalThickness
DISTRIBUTION OF LUNAR BASIN DIAMETERSShown at same horizontal and vertical scale
100 km Bins (Min = 200, Max = 3400 km)
Frey CTAs
(crustal thickness)
Frey QCDs
(topography)
Wilhelms
(photogeology)
QCDs + CTAs
(topography & crustal thickness)
Generally expect a roughly exponential increase in the
number of basins with decreasing diameter
Preliminary!!~55 new
CUMULATIVE FREQUENCY CURVES FOR LARGE LUNAR BASINS
The QCD+CTA curve follows a -2 powerlaw
from 600 to 300 km diameter (as does the
QCD curve alone)
GLOBAL LUNARN(300) CRAs are
Wilhelms = 1.2
QCDs = 2.5
QCDs + CTAs = 3.9
The cumulative large diameter crateringis at least 3x that
previously thought
FUTURE WORK
Mars: Determine CRAs for previously recognized, newly found large basins and intra-basin areas using the new crustal thickness data (MarsCrust3)
Any basins significantly older than those in the peak?Are intra-basin areas significantly older than basins?Can we date the age of the Borealis Basin?
Moon: Determine large diameter CRAs for larger impact basins using ULCN data (down to 100 km?)
Do the CRAs cluster and if so, how tightly?Can we determine the spread in (absolute?) ages
between SPA and Orientale?
CAVEATS, QUALMS and QUESTIONSThe CRAs for the large martian basins are assumed to be formation ages.
Maybe they represent global resurfacing ages?
Perhaps large impact basin formation at Mars (and the Moon) “wipes out” prior history and we cannot look back beyond the last stages of the LHB
So we cannot really tell if it is a short duration impact “spike” as suggested by the Nice model.
If the Borealis Basin is real, when it occurred is really important for understanding the LHB history on Mars
“Well before” or “just before” the large basin “spike”?
RECAP: TWO MAJOR POINTSWe have significantly underestimated (at least) the large diameter impact inventory of both Mars [by at least 12x in the highlands] and the Moon [by at least 3x globally] (and therefore of the Earth),
and therefore underestimated the likely effects of a Late Heavy Bombardment everywhere
(Current) Crater Retention and Model Absolute Ages of large impact basins on Mars support a Nice-like Late Heavy Bombardment / “Terminal Planetary Cataclysm” throughout the inner solar system. But….
there are more CRAs to be determined, on known and newly found basins, using the MarsCrust3 CTAs
Thank you!
Back- up Slides
CRATER RETENTION AGE vs BASIN DIAMETER
Isidis has no superimposed basins > 300 km diameter not because it is small, but
because it is young
Isidis1354 km
Sirenum1056 km
Crustal thickness
Crustal thickness
A “relative-to-absolute” age converter
BLACK BOXAGE CONVERTER
Tanaka’s counts for major stratigraphic boundaries were first averaged, then extrapolated to N(300) with a -2 power law, and plotted against averaged Hartman-Neukum “absolute ages” for the same boundaries. The nearly linear relation was fitted and extrapolated to “pre-Noachian” time.
Using the Hartmann-Neukum Model Chronology
Will newly identified CTAs fill in the “deficit” of large martian basins between 500 and 1000 km diameter?
The global cumulative frequency curve fits a -2 power law at both the large and small diameter ends,
but appears to have a “deficit” at the middle (~ 500 – 2000 km) diameters
Combined Cumulative Frequency Curves for the Highlands, Lowlands and Tharsis
N(300) CRAs(Crater Retention Ages)
Highlands: 3.18Lowlands: 3.19
Tharsis: 2.06
The cumulative frequency curves for the Highlands
and the Lowlands are essentially identical
over the range300<D<1000 km
Combined Population = Visible and buried QCDs
+ non-QCD CTAs
Edgar & Frey, 2008
(GRL 35, L02201, doi:1029/2007GL031466)
N(300)
From Edgar and Frey (2008), Geophys. Res. Lett. 35, L02201, doi:10.1029/2007GL031466
TOPOGRAPHIC CHARACTER OF LUNAR BASINS(28 Described by Wilhelms as “Distinct Basins”)
TABLE 1. ULCN CHARACTER OF LUNAR BASINS IDENTIFIED BY WILHELMS (1987)TYPE NAME LAT WEST DIAM TOPOGRAPHIC CHARACTER
LONG (km)DISTINCT South Pole-Aitken -56.0 180.0 2500 Strong basin signatureDISTINCT Imbrium 33.0 18.0 1160 Strong basin signatureDISTINCT Crisium 17.5 301.5 1060 Strong basin signatureDISTINCT Orientale -20.0 95.0 930 Strong basin signatureDISTINCT Australe* -51.5 265.5 880 NO TOPOGRAPHIC BASI NDISTINCT Nectaris -16.0 326.0 860 Strong basin signatureDISTINCT Smythii -2.0 273.0 840 Strong basin signature but smallerDISTINCT Humorum -24.0 39.5 820 Strong basin signatureDISTINCT Keeler-Heaviside* -10.0 198.0 780 Much smaller, offset DISTINCT Serenitatis 27.0 341.0 740 Strong basin signatureDISTINCT Mendel-Rydberg -50.0 94.0 630 offset from DEWDISTINCT Humboldtianum 61.0 276.0 600 strong basin signature but largerDISTINCT Freundlich-Sharonov* 18.5 185.0 600 Strong basin signature, inner ringsDISTINCT Hertzsprung 1.5 128.5 570 Strong basin signatureDISTINCT Ingenii -34.0 197.0 560 Strong basin signatureDISTINCT Coulomb-Sarton 52.0 123.0 530 Strong basin signatureDISTINCT Apollo -36.0 151.0 505 Strong basin signatureDISTINCT Moscoviense 25.0 213.0 445 Strong basin signatureDISTINCT Korolev -4.5 157.0 440 Strong basin signatureDISTINCT Grimaldi -5.0 68.0 430 Strong basin signature but smallerDISTINCT Lorentz 34.0 97.0 360 Strong basin signatureDISTINCT Poincare -57.5 198.0 340 Strong basin signatureDISTINCT Mendeleev 6.0 219.0 330 Strong basin signatureDISTINCT Birkhoff 59.0 147.0 330 Strong basin signatureDISTINCT Schiller-Zucchius -56.0 44.5 325 main is larger than DEWDISTINCT Planck -57.5 224.5 325 Strong basin signature but offsetDISTINCT Schrodinger -75.0 226.0 320 Strong basin signatureDISTINCT Bailly -67.0 68.0 300 Strong basin signature
10 on Wilhelms’ list are not obvious topographic basins!Australe (“distinct”), Tranquilitatis (“probable”) and
8 others (6 “possible”, 2 “doubtful”)
TABLE 1. ULCN CHARACTER OF LUNAR BASINS IDENTIFIED BY WILHELMS (1987)TYPE NAME LAT WEST DIAM TOPOGRAPHIC CHARACTER
LONG (km)
PROBABLE Fecunditatis -4.0 308.0 990 Strong basin signature but offsetPROBABLE Tranquillitatis 7.0 320.0 800 NO TOPOGRAPHIC BASINPROBABLE Mutus-Vlacq -51.5 339.0 690 offset from DEW, largerPROBABLE Nubium -21.0 15.0 690 offset from DEWPROBABLE Lomonsov-Fleming 19.0 255.0 620 slightly offset, smallerPROBABLE Balmer-Kapteyn -15.5 291.0 550 Strong basin signature but offset
possible Procellarum 26.0 15.0 3200 NO TOPOGRAPHIC BASINpossible Tsiolkovskiy-Stark -15.0 232.0 700 Much smaller, offsetpossible Grissom-White -44.0 161.0 600 NO TOPOGRAPHIC BASINpossible Insularum 9.0 18.0 600 NO TOPOGRAPHIC BASINpossible Marginis 20.0 276.0 580 NO TOPOGRAPHIC BASINpossible Flamsteed-Billy -7.5 45.0 570 NO TOPOGRAPHIC BASINpossible Amundsen-Gaswindt -81.0 240.0 355 Strong basin signaturepossible Sikorsky-Rittenhouse -68.5 249.0 310 Moderate basin signaturepossible Pingre-Hausen -56.0 82.0 300 NO TOPOGRAPHIC BASIN
doubtful Al-Khwarismi-King 1.0 248.0 590 NO TOPOGRAPHIC BASINdoubtful Werner-Airy -24.0 348.0 500 NO TOPOGRAPHIC BASIN
TOPOGRAPHIC CHARACTER OF LUNAR BASINS(17 Described by Wilhelms as “Probable, Possible or Doubtful”)
Maximum Scalar Magnetization Within .5R of Basin Center and CRA
0
5
10
15
20
25
30
35
40
45
50
0 1 2 3 4
N(20,10000)
Ma
xim
um
Sc
ala
r M
ag
ne
tiza
tio
n W
ith
in
.5R
of
Ba
sin
Ce
nte
r (n
T)
Visible Basins (Maria)
Visible Basins (Highlands)
QCDs (Highlands)
Nectrais
Nectaris (Highlands only)
QCDs (Maria)
Bodine (2008)(unpublished work)
CRA N(20,10000) = cumulative number > 20 km diameter / 10,000 sq km(visible craters only: most mare basins likely older)
Maximum Scalar Magnetization within 0.5R of Basin CenterVersus Crater Retention Age (CRA)
CRATER RETENTION AGES FOR KNOWN & NEW BASINS
PRELIMINARY!
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