dynamics of sediment routing systems in tectonically-active mountain ranges or

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Dynamics of sediment routing systems in tectonically- active mountain ranges OR Control of margin dynamics by sediments, part 4: erosion and transport Alex Densmore Department of Geography & Institute of Hazard, Risk and

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Dynamics of sediment routing systems in tectonically-active mountain ranges OR Control of margin dynamics by sediments, part 4: erosion and transport Alex Densmore Department of Geography & Institute of Hazard, Risk and Resilience Durham University. - PowerPoint PPT Presentation

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Page 1: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Dynamics of sediment routing systems in tectonically-active mountain rangesOR

Control of margin dynamics by sediments, part 4: erosion and transport

Alex DensmoreDepartment of Geography & Institute of Hazard, Risk and ResilienceDurham University

Page 2: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Sanjeev discussed sedimentary basins as bathtubs that evolve and fill over geological time scales, and (importantly) preserve a record of the detritus from margin evolution

The taps in this case are the sediment routing systems which (1) liberate sediment from bedrock and (2) feed it into the developing basin

What role do those systems play?

“…the Steering Committee envisions a successor program that will investigate the coupled geodynamic, surficial, and climatic processes that build and modify continental margins over a wide range of timescales (from s to My).”

Page 3: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Gawthorpe et al. Basin Research (1994)

Densmore et al. JGR-Solid Earth (2003)

Why we should care:

1) We’ve talked about the fault framework setting the entry points for sediment, but we need a sediment source as well, and that source is intimately linked to the deformation field

Page 4: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Why we should care:

2) Good theoretical reasons to expect that erosion and mass transfer can affect tectonic deformation rates and patterns along active convergent margins

Not so much work done in extensional settings – see Dorsey et al. white paper

Willett et al. Geology (2006)

Page 5: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Two key concepts have shaped our understanding of sediment delivery in tectonically active areas:

1) The growth of fault arrays

2) Coupled sediment routing systems

Lost River Range and Borah Peak, Idaho

Page 6: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Gupta and Scholz JSG (2000)

Schlische et al. Geology (1996)

Faults grow by a combination of lateral tip propagation and linkage of existing segments, preserving a roughly linear displacement-length relationship

Page 7: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

This systematic pattern invites a space-for-time substitution that gives us a powerful framework in which to interpret spatial variations in topography, erosion and sediment flux

Foster et al. Geomorph. (2008)

Page 8: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Evolution of topography

In many fault-bounded ranges, relief is decoupled from fault displacement and slip rate, due to

1) Strength-limited hillslopes and efficient surface processes (e.g. landsliding) and/or

2) Glacial erosion

This sets up challenges for the tectonic ‘fidelity’ of landscapes (= none?) and for paleo-topographic reconstruction from sediment records (= possible?)

uniform relief

Densmore et al. JGR-Solid Earth (2004)

Page 9: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Koppes & Montgomery Nature Geosci. (2009)

This should not be surprising – we know that both rivers and glaciers are capable of eroding at rates that equal or exceed even rapid rock uplift rates (>1-10 mm/y)...

Page 10: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Koppes & Montgomery Nature Geosci. (2009)

...and that these high rates can be sustained over geological time scales

We now have a wide range of tools at our disposal to measure these rates (at scales from 100 to 108 y)

Page 11: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Stock et al. Lithosphere (2009)

In detail, however, the relationships between rates of rock uplift and erosion remain a challenge to unpick

Much depends on the time scale over which they are measured; short-term rates are perturbed by non-steady erosion processes and by (long) EQ recurrence intervals

So what actually sets the rates that we measure?

Page 12: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

The second major conceptual advance is to examine source-to-sink relationships in small, tractable systems that can be easily characterized over a range of temporal scales – such as catchments and their associated fans

Key question: how sensitive are these systems to changes in tectonic or climatic boundary conditions, and over what time scales?

Dolomite Canyon, California

The answer to this determines their utility as a recorder of those changes (sedimentology, but also geometry, geomorphology...)

Page 13: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

We have moved from prescriptive sediment routing models in which sediment flux qs is set arbitrarily (LEFT), to those in which the catchment and fan interact (RIGHT):• fan sets base level for catchment, modulating erosion and

sed supply• sediment plus subsidence rate sets base level and filling

pattern, etc.

Marr et al. Basin Research (2000) Allen & Densmore Basin Research (2000)

Page 14: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

These models typically suggest long (105 to 106 y) system-scale response times to perturbations in tectonic forcing. The landscape is thus perpetually ‘catching up’ to tectonic inputs

Raises a set of questions:1) How and where can we look for the signal of individual events if response times are so long?

2) What are the implications for building stratigraphy (Mohrig, Gupta talks)?

Carretier & Lucazeau Basin Research (2005)

Page 15: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Where do we go from here?1. How can we better read the record? Grain size of sedimentary deposits is a promising potential ‘fingerprint’ of past tectonic subsidence rates and sediment discharge (e.g. Fedele & Paola, 2007), if we can decipher it

Duller et al. JGR-Earth Surf. (2010)

Page 16: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Bell et al. Basin Research (2009)Where do we go from here?

2a. What does the tectonic driver look like? Can we get the 3d tectonic defm field through the life span of an orogen? This absolutely requires the stratigraphic record (and a wide range of settings...)

Page 17: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

2b. Can we move beyond single fault blocks to consider sediment pathways when many faults and sources are involved?

(we’d better try!)

Where do we go from here?

Page 18: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

3. Can we apply our MARGINS-type joined-up thinking to a better characterization of hazards, given that they are focused in many of the geographical locations of interest to MARGINS research

Where do we go from here?

Non-seismic fatal landslides 2006-2008Dave Petley

(Intl Landslide Centre/Durham University)

Page 19: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

http://www.eeri.org/site/images/lfe/china_20080512_zwang.ppt

The co-occurrence of major geological hazards (especially the earthquake-landslide-tsunami trinity) remains a major challenge, both for

1) our physical understanding of long-term mountain building and sediment transfer (e.g., what was the net mass in the Sichuan earthquake?), and

2) disaster resilience and response

This need not involve compromise: we must understand the magnitude-frequency distribution BOTH for sediment routing and for hazard, and hazard research will move (is moving) toward longer time scales to deal with the data gap

Page 20: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

• ~50 MtC yr-1 eroded from mountain islands to oceans

• Compare to terrestrial biosphere re-growth after Last Glacial Maxium: ~ 50-100 MtC yr-1

• Silicate weathering atm CO2 consumption: ~110 MtC yr-1

Oblique view of Taiwan(LANDSAT 7 - NASA Worldwind)

4. What about the carbon cycle? Marginal rivers are a potentially(?) large (~50 MtC yr-1? Recall Lou Derry’s ‘error bars’) source of carbon to the oceans; compare with• Terrestrial biosphere re-growth after LGM: ~ 50-100 MtC yr-1

• Silicate weathering atmos CO2 consumption: ~110 MtC yr-1

Where do we go from here?

(Ittekkot, 1988; Meybeck, 1993; Gaillardet et al. 1999; Schlünz & Schneider, 2000; Broecker et al. 2001)

Page 21: Dynamics of sediment routing systems in tectonically-active mountain ranges OR
Page 22: Dynamics of sediment routing systems in tectonically-active mountain ranges OR

Western Southern Alps New Zealand

1 km

Hilton et al. Nature Geosci. (2008)

Very large floods dominate POC erosion and export

Do earthquakes ‘liberate’ carbon from bedrock and vegetation and deliver it to the river network via landsliding... and if so, do the big events matter more?