Fan radius—gcep.host.ualr.edu/Archives/2002/2002Orientation/Wilkinson.pdf · – handheld...
Transcript of Fan radius—gcep.host.ualr.edu/Archives/2002/2002Orientation/Wilkinson.pdf · – handheld...
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Fan radius—
• river profile is critical to fanradius, especially—– profile slope
– profile altitude (incision/aggradation regime)
Fig. 12
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Fig. 12
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Fig. 12
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Fig. 1
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Fig. 1
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Global Geomorphic Survey ofGlobal Geomorphic Survey ofLarge Modern Non-coastal FansLarge Modern Non-coastal Fans
(“inland deltas”)(“inland deltas”)
M. JUSTIN WILKINSONM. JUSTIN WILKINSON
Lockheed Martin Space Operations, NASA Johnson Space Center, Houston, Texas, USA
Fig. 1
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Rationales for examininglarge terrestrial fans—
Large modern fans—– have not been studied
systematically– several claimed to be possibly
the “largest” or “one of thelargest” on the planet
• all exclude the largestidentified in this study
• one radius arbitrarilyassigned as >100 km
– are seen as merely as largeend-members of the alluvialfan continuum
– are analogs for features in therock record
Data sources—– handheld photographs from
Shuttle, Mir and InternationalSpace Station taken over mostparts of the Earth 55°N - 55°S
– 1: 1,000,000 ONC charts
STS73-749-91Himalayas, Tibetan Plateau, Gangeticplain—Kosi and Tista large fans
Fig. 3
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Characteristics—
• Kosi River avulsions—
– cover entire surface of fan
– average rate ~19 yr betweenswitching events
– slowest rate encountered is> 30,000 yr between switchingevents
Kosi R. avulsions
Fig. 5
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• even small riverscan generate fansas large ascoastal deltas ofmajor rivers
Nile R. delta
Okavango R. fan
Fig. 2
Fan size—
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Andean forelandN Argentina
western Paraguay
• Foreland basin overfilling produces large fan radii
Parag
uay R
AndesMts
Fig. 11
Fan radius—
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Andes MtsChaco plains—N ArgentinaW Paraguay
Foreland basin—nested patternof large fans
100 km 100 km
100 km
Fig. 14
Andes Mts
—contiguous large fans cover an area of >750,000 in the Andean foreland
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Fan radius—
• river profile is critical to fanradius, especially—– profile slope
– profile altitude (incision/aggradation regime)
Fig. 12
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fromRippon 1996
Basin paleogeography—
interpreted from detailed mining data(Westphalian A & B British Isles)
– divergent drainage
– on a scale of hundreds of km
Fig. 17
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Fish speciation andRiver switching on large fans—
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Green parent populationspeciates into—• red,• black• yellowdaughter species thatreenter the regionaldrainage
Lakes andriver switching
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• Green parent populationspeciates, after river switch,into Reds
• After a second switch, theoriginal river has GreenAND Red populations
Inhospitable trunk river andriver switching
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Greens’ river issuddenly invaded byRedsfrom the neighboring basin
Neighboring basins andriver switching Okavango fan
NW Botswana
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Large fans (“inlanddeltas”) are—
• Far larger than expected
• Widespread—unexpec-tedly so
• Cover enormous areas ofsome continents
Conclusions—
Andes MtsChaco plains—N ArgentinaW Paraguay
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Large fans (“inlanddeltas”) are—
• Far larger than expected
• Widespread—unexpec-tedly so
• Cover enormous areas ofsome continents
Conclusions—
Large fans may be the—• dominant• mesoscale• depositional landform on continents
Andes MtsChaco plains—N ArgentinaW Paraguay
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Thus, large fans are also models for —
– Paleogeographies, crucial to variousdisciplines, including historicalgeology and modeling hydrocarbonenvironments
– Speciation of aquatic organisms
Okavango R. fan
Conclusions—