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Sedimentary Basins(Part One)
What are Sedimentary Basins?
Holes in the ground where sediment accumulates
Global distribution: Sub-aerial and submarine
Why are Basins Interesting?
Hydrocarbons:
Oil, Gas, Coal
Ores & Minerals
Liquid hydrocarbon production will peak in
~10 years at 30 Billion Barrels per annum,
declining to ~5 Billion Barrels per annum
by the end of the 21st Century
Some estimates…
Keeping up Supply: Polar Exploration?
Keeping up Supply: Deep Water Exploration?
Technologies:
Seismic Reflection Imaging
Deep Water drilling/production
Finding: Direct hydrocarbon Indicators
Extracting: Mopping up the dregs
1973 Year 2003
BP Forties Field:Monthly Average
Oil Production Rate
1988 and 1995 3D seismic surveys
Keeping up Supply: Importance of Technology
Peak Oil: Supply Peaks & Declines Smoothly?
Technology buffers decline?
Why does Sediment Accumulate Here?
Accommodation Space
Sea-Level Change
Tectonic Uplift / Subsidence
Basins form through Tectonic Subsidence
Thickest sediment accumulations are 15 to 20 km
Tend to form in enclosed basins supplied by major rivers
World’s Thickest Sediment Accumulations
Sedimentary basins around
Ireland
Probing Sedimentary Basins
• Surface sampling and mapping
• Topography and bathymetry
• Boreholes (<5 km)
• Seismic experiments (2D, 3D, 4D)
• Earthquake analysisUndeformed basins are subsurface
Very little of a typical underformed basin is accessible by surface sampling / mapping
12 km
Ninian Fault Block, North Seavertical exageration x3 to x4
Seismic Reflection Imaging
Seismic Reflection Imaging Technology
Borehole Records
1. Thicknesses2. Ages3. Sediment Composition
Reconstruct sediment acccumulation history
Hence reconstruct tectonic subsidence history
Stratigraphic Growth
Timing of source maturation:Cumulative Stratigraphy Plot
Sediment Loading Correction
Tectonic Subsidence Curves
Basin Classification: Process
‘Basin Analysis’, Allen & Allen, Chapter 1
Basin Classification: This Course
• Extensional basins (60-70%)
• Flexural or foreland basins (10-20%)
• Basins associated with subduction zones
• Other basin types…