El Niño Patterns and Sediment Flux to the Deep Sea

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Influence of millennial-‐scale El Niño pa4erns on sediment delivery from land to the deep sea

Insights from the Holocene Santa Monica Basin, CA

Brian Romans Virginia Tech Geosciences

NASA

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•  Marine sediment ‘sinks’ (basins that accumulate sediment at the terminal end of the system) can end up preserved in the long-term geologic record

•  In deep time (>106 yr), the source of

sediment (eroding uplands) are inherently not preserved – that mass is transferred

•  Relative to partially preserved ancient

systems, Quaternary sedimentary systems can be investigated in their entirety

Using Quaternary ‘experiments’ to better understand deep time

Sedimentary System Analysis at ‘Time Zero’

•  production and transport of sediment in net-erosional source areas

•  transfer of mass to net-depositional sinks (sedimentary basins)

•  spatial configuration of sediment routing on full display

•  emphasis on quantifying rates of erosion, transfer, and storage (101-103 yr) SOURCE

TRANSFER ZONE / SINK

TERMINAL SINK

Examination of these systems permits robust investigation of forcings: climatic fluctuation, sea-level changes, oceanographic conditions, tectonics (activity/geometry), etc.

diagram from Romans & Graham (in prep)

Sedimentary System Analysis in Deep Time

As We Scroll Back Through Geologic Time …

•  source area modified; removed completely as mass is transferred

•  sinks in transfer zone might be preserved in long-lived systems; terminal sinks only segment remaining (if anything) when tectonic regime changes

•  temporal resolution diminishes (degree of time-averaging increases)

•  direct to inferential

Chronostratigraphic (Paleogeographic) Surface


As We Scroll Back Through Geologic Time …

In some cases, this is all that is left of an ancient S2S system

Chronostratigraphic (Paleogeographic) Surface

•  source area modified; removed completely as mass is transferred

•  sinks in transfer zone might be preserved in long-lived systems; terminal sinks only segment remaining (if anything) when tectonic regime changes

•  temporal resolution diminishes (degree of time-averaging increases)

•  direct to inferential

Sedimentary System Analysis in Deep Time


Thin- and medium-bedded turbidites interbedded with siltstone, Paleocene German Rancho Fm., northern California coast (photo taken by Brian Romans)

I’m a geologist … I want to know what controls these patterns

Meter-scale turbidite beds in the Upper Cretaceous Tres Pasos Formation, southern Chile (photo taken by Brian Romans)


Controls on stratigraphic patterns are divided into two general categories: Allogenic

Autogenic

Meter-scale turbidite beds in the Upper Cretaceous Tres Pasos Formation, southern Chile


Controls on stratigraphic patterns are divided into two general categories: Allogenic

Autogenic

Forcings external to the sedimentary system (e.g., sea

level, tectonic movement, climate)

Processes and dynamics internal to the sedimentary system (e.g., channel/lobe

avulsion, bar growth, progradation)

Meter-scale turbidite beds in the Upper Cretaceous Tres Pasos Formation, southern Chile


Controls on stratigraphic patterns are divided into two general categories: Allogenic vs. Autogenic?

One way to approach this problem is to carefully investigate ‘modern’ systems where the controls are much better constrained

Why study sediment-routing systems in the California Borderland?

§  basins are small à data coverage of an individual system is good

§  relatively sand-rich submarine fan systems adjacent to nearby and uplifting sediment sources

§  External forcings such as climatic fluctuations, sea level, and tectonism is well constrained

NOAA

Sediment Transfer Across Continental Margins

Los Angeles

Santa Barbara

Ventura

basemap made with GeoMapApp; annotations by authors

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California Borderland Sediment-Dispersal System



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A single watershed feeds multiple sinks and one sink receives material from multiple watersheds



The Santa Barbara littoral cell moves coarse-grained sediment laterally across the margin



Routing of Coarse-Grained Sediment (sand + gravel)

Santa Clara River

Calleguas Creek

Hueneme Canyon

Vast majority of post-Last Glacial Maximum sand delivered to coast ends up in Santa Monica Basin



Santa Monica Basin and Hueneme submarine fan

Hueneme canyon and fan is dominant feature since post-glacial transgression

SMB is a closed basin - no bypass to other Borderland basins

fan divisions from Normark et al. (1998)

Santa Monica Basin and Hueneme submarine fan

fan divisions from Normark et al. (1998)

ODP Site 1015 – radiocarbon-dated core

•  Interval of interest is from sea floor to ~12 m deep; interbedded sandy turbidites and mud deposition

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Romans et al. (2009); GSA Bulletin



•  Eleven radiocarbon dates going back to ~7,000 years ago

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•  Eleven radiocarbon dates going back to ~7,000 years ago

•  Tied to seismic-reflection data à five stratigraphic intervals mapped

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Mapping basinal sediment distribution


Mapping basinal sediment distribution

area of sediment volume calculations


Volumes and rates of basinal sedimentation

Over the past 7,000 years, the average sediment accumulation rate in Santa Monica Basin = 3.74 million tons/year


Historical Santa Clara River sediment flux

Measured sediment flux at modern river mouth averages

3.10 million tons/year

Warrick & Farnsworth (2009)

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Historical Santa Clara River sediment flux

Measured sediment flux at modern river mouth averages

3.10 million tons/year


So, that’s an average over several millennia …what about the variability of flux at shorter time scales?

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Using the basin plain record to assess variability in flux

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5 Changes in thicknesses among the five stratigraphic intervals measured in the basin plain are proportional to changes among their volumes


Using the basin plain record to assess variability in flux

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5 Changes in thicknesses among the five stratigraphic intervals measured in the basin plain are proportional to changes among their volumes

In this case, the basin plain is an adequate representation of sedimentation in Santa Monica Basin as a whole for this time period.


Timing and magnitude of turbidity-current events


Timing and magnitude of turbidity-current events

What’s controlling the observed increase in sand delivery to the basin plain?


Climate influence on sediment delivery to the deep sea

Moy et al. (2002)



Barron et al. (2003)

Moy et al. (2002)


Relationship to Holocene seismicity

paleoseismologic compilation shows increased seismic activity of LA region faults ~1-3 ka

Dolan et al. (2007)


Relationship to record in adjacent Santa Barbara Basin

event beds in ODP 893 (interpreted to be result of Santa Clara River floods)

Santa Monica Basin

Santa Barbara Basin

Santa Clara River

Rack & Merrill (1995)


Relationship to record in adjacent Santa Barbara Basin

event beds in ODP 893 (interpreted to be result of Santa Clara River floods)

Santa Monica Basin

Santa Barbara Basin

Santa Clara River

history of beach accretion and erosion along Santa Barbara coast

Sand eroded from Santa Barbara beaches very likely made its way into Santa Monica Basin via turbidity currents

Rack & Merrill (1995)

Masters (2006)


head of Hueneme submarine canyon

avulsion of river mouth ~2-3 ka

Hitchcock et al., 2000

Linking River History to Changes in Basinal Deposition

How does the change from direct feed (river mouth directly into canyon head) to indirect feed (littoral cell to canyon head) impact basinal sedimentation?

Shift in river recorded in basin plain stratigraphy?

direct river input

littoral cell input


Interacting controls on delivery of sediment to the basin

•  The timing and distribution of large turbidity currents are investigated.




•  Increase in magnitude and frequency of ENSO cycles à increased sediment flux to deep sea.





•  Shift in sediment routing from direct river-input to indirect littoral-input.





•  Shift in sediment routing from direct river-input to indirect littoral-input.

•  Increased earthquake activity may have been important trigger for large turbidity currents.


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•  From a geological perspective, Quaternary sedimentary system analysis allows us to test our conceptual models of how basins fill with sediment

•  These models inform/constrain

numerical models of system evolution that are important for:

•  predicting how sedimentary systems will respond to environmental change

•  understanding transfer of other

materials from land to sea (pollutants, terrestrial carbon, etc.)

•  predicting distribution/heterogeneity of

subsurface fluid reservoirs (hydrocarbon extraction, CO2 injection, etc.)

Using Quaternary ‘experiments’ to better understand deep time

The research summarized in this talk was published in the journal Geological Society of America Bulletin in 2009

More details about this study

Link: http://gsabulletin.gsapubs.org/content/121/9-10/1394.abstract PDF: https://sites.google.com/site/romansbrian/2009Romansetal-SantaMonicaBasinHoloceneflux.pdf?attredirects=0

El Niño Patterns and Sediment Flux to the Deep Sea

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