Sedimentary Basins Part One What are Sedimentary Basins

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

Some estimates… 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 21 st Century

Keeping up Supply: Polar Exploration?

Keeping up Supply: Deep Water Exploration?

Keeping up Supply: Importance of Technology 1988 and 1995 3 D seismic surveys BP Forties Field: Monthly Average Oil Production Rate 1973 Technologies: Seismic Reflection Imaging Deep Water drilling/production Finding: Direct hydrocarbon Indicators Extracting: Mopping up the dregs Year 2003

Peak Oil: Supply Peaks & Declines Smoothly? Technology buffers decline?

Why does Sediment Accumulate Here?

Basins form through Tectonic Subsidence Accommodation Space Sea-Level Change Tectonic Uplift / Subsidence

World’s Thickest Sediment Accumulations Thickest sediment accumulations are 15 to 20 km Tend to form in enclosed basins supplied by major rivers

Sedimentary basins around Ireland

Probing Sedimentary Basins • Surface sampling and mapping • Topography and bathymetry • Boreholes (<5 km) • Seismic experiments (2 D, 3 D, 4 D) • Earthquake analysis Undeformed basins are subsurface

Very little of a typical underformed basin is accessible by surface sampling / mapping

Seismic Reflection Imaging Ninian Fault Block, North Sea vertical exageration x 3 to x 4 12 km

Seismic Reflection Imaging Technology

Borehole Records 1. Thicknesses 2. Ages 3. 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…