Fan radius—gcep.host.ualr.edu/Archives/2002/2002Orientation/Wilkinson.pdf · – handheld...

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—