Terminal distributary channels and mouth-bar sedimentation ...ijolite.geology.uiuc.edu/08SprgClass/geo415-515/Terminal... · Terminal distributary channels and mouth-bar sedimentation

Terminal distributary channels and mouth-bar sedimentation in

deltaic sediments

Team River DominationElizabeth Luber, Meghan Ori, Amanda Raddatz,

Lindsay Rathnow, Kelly Voigt

Importance of Deltas

• Reconstruction of paleoenvironments

• Oil and gas exploration

– Sandy deposits serve as excellent reservoir rocks

• Drinking water

– Many deltas reach below the water table

– Paleo-channels good for large-scale pumping

Introduction• Terminal Distributary

Channels (TDCs) can reveal information about depositional processes

• River-, Wave-, and Tide-dominated deltas display unique sedimentation patterns

• Observations of modern processes provide insight into processes that formed ancient deltas

• Processes can be confused due to deformation

• Prograde into basins with low tides and low wave energy

• Many terminal distributary channels, coeval

• Usually lobate in shape• Channels split and change

position within short periods of time (<100 yrs)

• Mouth bars move laterally through time

• Thin stratigraphic deposits• Shallow channels

High-Constructive Deltas

www.wikipedia.com

Modern example- Volga Delta

• flows into Caspian Sea

• 800 terminal distributary channels

• Sea level fall around 1800-1980 resulted in delta progradation

http://earthasart.gsfc.nasa.gov/

High-Destructive Delta• Long time (100s to 1,000s years)

– Distributary channel splitting

– Lobe switching

• Types of deltas– Tide-dominated

• 10-20 terminal distributairy channels

• 1-10s km between terminal distributary channels

– Wave-dominated

• 1-2 terminal distributairy channels

• How it happens– Steep slopes

– Compaction of sediments

Elongate Type Delta

• Thicker deposits than lobate delta

• Stacked sediment types

Case Study- Lena Delta, Siberia

• Lobate? Evidence:

– Many bifurcations

– Shallow TDCs

• BUT Elongate in shape…

• Explanation:

Tectonic activity caused subsidence steeper slope increased discharge more bifurcations

http://ipy.nasa.gov

Bringing it Home

How the Tullig Measures Up

Conclusions

• Deltas are important indicators of paleoclimates, they provide us with drinking water, and they can be good reservoirs for oil and gas.

• River-, wave-, and tidal-dominated deltas all produce significantly different patterns of TDCs.

• Modern delta characteristics can tell us about ancient formations.

• In Ireland, the Tullig, Kilkee, and Doonlicky Cyclothems represent high-constructive deltaic environments with some wave influences.

References

Coleman,, J.M., and Wright, L.D., 1971, Analysis of major river systems and their deltas, procedures and rationale, with two examples:

Louisiana State Univer., Coastal Studies Inst. Tech. Rept. 95, 125 p.

Olariu, C. and Bhattachraya, J.P. 2006. Terminal distributary channels and delta front architecture of river-dominated delta systems, Journal of Sedimentary Research, 76, 212-233.

Pulham, A. J. 1989. Controls on internal structure and architecture of sandstone bodies within Upper Carboniferous fluvial-dominated deltas, County Clare, western Ireland, in Whateley, M.K.G., and Pickering, K.T., eds., Deltas: Sites and traps for fossil fuels: Geologic Society of London Special Publication 41, p. 179-203.

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