fan radius—gcep.host.ualr.edu/archives/2002/2002orientation/wilkinson.pdf · – handheld...
TRANSCRIPT
Fan radius—
• river profile is critical to fanradius, especially—– profile slope
– profile altitude (incision/aggradation regime)
Fig. 12
Fig. 12
Fig. 12
Fig. 1
Fig. 1
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
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
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
• even small riverscan generate fansas large ascoastal deltas ofmajor rivers
Nile R. delta
Okavango R. fan
Fig. 2
Fan size—
Andean forelandN Argentina
western Paraguay
• Foreland basin overfilling produces large fan radii
Parag
uay R
AndesMts
Fig. 11
Fan radius—
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
Fan radius—
• river profile is critical to fanradius, especially—– profile slope
– profile altitude (incision/aggradation regime)
Fig. 12
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
Fish speciation andRiver switching on large fans—
Green parent populationspeciates into—• red,• black• yellowdaughter species thatreenter the regionaldrainage
Lakes andriver switching
• Green parent populationspeciates, after river switch,into Reds
• After a second switch, theoriginal river has GreenAND Red populations
Inhospitable trunk river andriver switching
Greens’ river issuddenly invaded byRedsfrom the neighboring basin
Neighboring basins andriver switching Okavango fan
NW Botswana
Large fans (“inlanddeltas”) are—
• Far larger than expected
• Widespread—unexpec-tedly so
• Cover enormous areas ofsome continents
Conclusions—
Andes MtsChaco plains—N ArgentinaW Paraguay
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
Thus, large fans are also models for —
– Paleogeographies, crucial to variousdisciplines, including historicalgeology and modeling hydrocarbonenvironments
– Speciation of aquatic organisms
Okavango R. fan
Conclusions—