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…