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Detrital Record Orogenesis (Ask yourself: (What is the nature of sed…
Detrital Record Orogenesis
Detrital sed premise
Use sediment record to infer:
When exhumation began
Exhumation rate ∆
How much ∆ & when
Infer info about early uplift / erosion / exhumation of mtns
= Erosive product/sed removed from mtn belt
Detrital sed record allows
Reconstruction early phase uplift & erosion
Discern source history
(palaeodrainage reconstructions)
Detrital record limitation
Composition & preservation of sediment record
Influences accuracy of dating
Sediment biases can limit accuracy
Suitability
sed record
for dating
= f (
Preservation
sediment biases = hindrance
loss via transport / abrasion
Composition
Dating techniques often have mineral-specific application
Minerals
& nuclides
Ne-23
Found in
quartz
He-3
Found in olivine (stime garnet)
Ar
Found in
limestone
Transport
Factors influencing what components reach basin:
Preferential erosion
Alteration
Density selectivity
Ask yourself:
What is the nature of sed eroding ?
What happens to sed when transported ?
How much of it is lost / never sees basin ?
How much reaches the basin ?
Detrital record = only part of the story (what's preserved)
Detrital record
Prehistory
Provenance of material shed from mountain
Exhumation
Mvmt of material to surface via tectonic & climatic processes
Variable temporal
& spatial scales
In-situ vs detrital
Detrital techniques
Petrography
Geochemistry
Thermochronology
Petrography
(cheapest)
A.
Thin section
Analyse tectonic setting of formation
Gives first order info
Recycled from orogenic system?
Came off continent?
Source = magmatic arc?
by looking @ qts vs fsp vs lithics
B.
Density separation
Heavy, index metamorphic minerals
Tells us what eroded to form that sediment
If absent - infer source area
not
metamorphic terrane
Accurate flux estimates:
Require msmts of:
Suspended sed load
Bedload
Floodplain deposits
only seasonally active
flooding - extend Q across plains
Q ↓ ∴ deposits disconnected from river