terminal distributary channels and mouth-bar sedimentation...
TRANSCRIPT
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
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
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.