Basin Analysis

Principles and Application to Petroleum Play Assessment

Philip A. Allen, John R. Allen

• Publisher: Wiley-Blackwell
• Year: 2013
• ISBN:
  9781118450307
• Edition: 3
• Topic: Physical Sciences
• Subtopic: Geology & Earth Sciences

Basin Analysis is an advanced undergraduate and postgraduate text aimed at understanding sedimentary basins as geodynamic entities. The rationale of the book is that knowledge of the basic principles of the thermo-mechanical behaviour of the lithosphere, the dynamics of the mantle, and the functioning of sediment routing systems provides a sound background for studying sedimentary basins, and is a pre-requisite for the exploitation of resources contained in their sedimentary rocks. The third edition incorporates new developments in the burgeoning field of basin analysis while retaining the successful structure and overall philosophy of the first two editions.

The text is divided into 4 parts that establish the geodynamical environment for sedimentary basins and the physical state of the lithosphere, followed by a coverage of the mechanics of basin formation, an integrated analysis of the controls on the basin-fill and its burial and thermal history, and concludes with an application of basin analysis principles in petroleum play assessment, including a discussion of unconventional hydrocarbon plays. The text is richly supplemented by Appendices providing mathematical derivations of a wide range of processes affecting the formation of basins and their sedimentary fills. Many of these Appendices include practical exercises that give the reader hands-on experience of quantitative solutions to important basin analysis processes.

Now in full colour and a larger format, this third edition is a comprehensive update and expansion of the previous editions, and represents a rigorous yet accessible guide to problem solving in this most integrative of geoscientific disciplines.

Additional resources for this book can be found at: www.wiley.com/go/allen/basinanalysis.

PART 1

The Foundations of Sedimentary Basins

CHAPTER ONE

Basins in Their Geodynamic Environment

Summary

Sedimentary basins are regions of prolonged subsidence of the Earth’s surface. The driving mechanisms of subsidence are related to processes originating within the relatively rigid, cooled thermal boundary layer of the Earth known as the lithosphere and from the flow of the mantle beneath. The lithosphere is composed of a number of plates that are in motion with respect to each other. Sedimentary basins therefore exist in a background environment of plate motion and mantle flow.

The Earth’s interior is composed of a number of compositional and rheological zones. The main compositional zones are between crust, mantle and core, the crust containing relatively low-density rocks overlain by a discontinuous sedimentary cover. The mechanical and rheological divisions do not necessarily match the compositional zones. A fundamental rheological boundary is between the lithosphere and the underlying asthenosphere. The lithosphere is sufficiently rigid to comprise a number of relatively coherent plates. Its base is marked by a characteristic isotherm (c.1600 K) and is commonly termed the thermal lithosphere, which encloses a mechanical lithosphere. The upper portion of the thermal lithosphere is able to store elastic stresses over long time scales and is referred to as the elastic lithosphere. The continental lithosphere has a strength profile with depth that reflects its composition, temperature and water content. A weak, ductile zone exists in the lower crust below a brittle–ductile transition, but the strength of the underlying lithospheric mantle is uncertain. The oceanic lithosphere lacks this low-strength layer, its strength increasing with depth to the brittle–ductile transition in the upper mantle.

The relative motion of plates produces deformation, magmatism and seismicity concentrated along oceanic plate boundaries. Continental lithosphere is more complex, exhibiting seismicity and deformation far from plate boundaries, and with a heat flow and geotherm that is strongly influenced by radiogenic self-heating. Plate boundary forces and elevation contrasts strongly influence the state of stress of lithospheric plates.

Sedimentary basins have been classified principally in terms of the type of lithospheric substratum (i.e. continental, oceanic, transitional), their position with respect to the plate boundary (intracontinental, plate margin) and type of plate motion nearest to the basin (divergent, convergent, transform). The formative mechanisms of sedimentary basins fall into a small number of categories, although all mechanisms may operate during the evolution of a basin:

• Isostatic consequences of changes in crustal/lithospheric thickness, such as caused mechanically by lithospheric stretching, or purely thermally, as in the cooling of previously upwelled asthenosphere in regions of lithospheric stretching.
• Loading (and unloading) of the lithosphere causes a deflection or flexural deformation and therefore subsidence (and uplift), as in foreland basins.
• Viscous flow of the mantle causes non-permanent subsidence/uplift known as dynamic topography, which can most easily be recognised in the domal uplifts of the ocean floor at volcanic hotspots.

From the point of view of lithospheric processes there are two major groups of basins: (i) basins due to lithospheric stretching and subsequent cooling, belonging to the rift–drift suite; and (ii) basins formed primarily by flexure of continental and oceanic lithosphere.

1.1 Introduction and Rationale

Maps of the global or plate-scale distribution of sediment thickness reveal strong variations (Fig. 1.1). It can be seen at both the global scale (Fig. 1.1) and the plate or continental scale (Fig. 1.2) that much of the area of the continental interiors is devoid of any sedimentary cover, with Precambrian crystalline rocks exposed at the surface. Elsewhere, the greatest sedimentary thicknesses are found in particular geological settings such as at extensional continental margins and fringing the world’s great collisional mountain belts. These regions of large sedimentary thickness have undergone extensive and prolonged subsidence (Bally & Snelson 1980). The complexities of geological history have resulted in a patchwork of currently subsiding active basins and their ancient counterparts. Sedimentary basins, ancient and modern, are the primary archive of information on the evolution of the Earth over billions of years.

Fig. 1.1 (a) Global sediment thickness, from Laske & Masters (1997) based on the digital database of Gabi Laske at the University of San Diego, California (http://mahi.ucsd.edu/Gabi). (b) A higher-resolution map of the total sediment thickness in the ocean, from Divins (2003).

Fig. 1.2 (a) Sediment thicknesses, Australia. Note that the greatest sediment thicknesses are in continental margin basins superimposed on Paleozoic basement rocks. In addition, there are high sediment thicknesses in the continental interior related to structural inversion of intracontinental mountain belts (e.g. Petermann and Alice Springs orogenies) bordering the Officer and Georgina basins. This tectonic activity compartmentalised large cratonic basins. Note also that large areas of old cratons have no sedimentary cover. (b) Outlines of ancient and modern sedimentary basins shown according to basement age. Note that the bulk of the basement ages are Precambrian (green). Younger basement rocks underlie basins of the continental margins (e.g. NW Shelf, Ceduna Basin in south), and the terranes east of the Tasman Line. Both (a) and (b) fromFrOG Tech Pty Ltd. (2005).

The location of sedimentary basins and their driving mechanisms are intimately associated with the motion of discrete, relatively rigid slabs, which together represent the cooled thermal boundary layer of the Earth. The outer shell of the Earth comprises a relatively small number of these thin, relatively rigid plates, which are in a state of motion with respect to each other. Such motions set up plate boundary forces that may be transferred considerable distances into the interior of the plates, so that sedimentary basins exist in a background environment of stress set up by plate motion.

The lithospheric plates are the surface manifestation of a slow thermal convection in the mantle, and are subject to differential thermal stresses along their bases. The mantle and lithosphere therefore do not operate as independent systems. We see spectacular evidence for the interaction of mantle processes and the lithosphere in the volcanic and topographic expression above mantle flow structures, some of which may have risen from the core–mantle boundary. We also discern, though less spectacularly, the effects on mantle flow caused by the subduction of cold slabs of oceanic crust at ocean–continent boundaries.

Deep Earth processes involving the thermomechanical behaviour of the lithosphere and the flow of the underlying mantle are coupled to Earth surface processes of erosion, sediment and solute transport and deposition in sedimentary basins. This coupling between ‘deep’ and ‘surface’ is the fundamental basis for the practice of broad, integrative thinking in basin analysis, and underpins the understanding of sedimentary basins as geodynamical entities. It is also the framework for the study of petroleum systems in sedimentary basins (Fig. 1.3). The connectedness between deep and surface geodynamics is emphasised throughout this text, and the fruits of an improved understanding derived by studying such connections are illustrated in the application to the exploration of hydrocarbons in Chapters 11 and 12.

Fig. 1.3 The basis for integration in basin analysis is the coupling between deep and surface geodynamics, the effects of which cascade through the various aspects of basin analysis to the application to petroleum systems.

Two key, dovetailed concepts therefore underlie this necessity of integration in basin analysis:

1. The dynamics of the solid Earth results in tectonic processes at various scales that control the generation of space in which sediment may accumulate for long periods of time. Tectonic processes determine the bulk strain and strain rate at which the basin and its structures form, and also control thermal history, magmatism a...