Regional Geology and Tectonics: Principles of Geologic Analysis

Volume 1: Principles of Geologic Analysis

Nicola Scarselli, Jürgen Adam, Domenico Chiarella

• Publisher: Elsevier
• Year: 2020
• Edition: 2
• eBook ISBN:
  9780444641359
• Topic: Technology & Engineering
• Subtopic: Geology & Earth Sciences
• Index: Technology & Engineering

Regional Geology and Tectonics: Principles of Geologic Analysis, 2nd edition is the first in a three-volume series covering Phanerozoic regional geology and tectonics. The new edition provides updates to the first edition's detailed overview of geologic processes, and includes new sections on plate tectonics, petroleum systems, and new methods of geological analysis. This book provides both professionals and students with the basic principles necessary to grasp the conceptual approaches to hydrocarbon exploration in a wide variety of geological settings globally. - Discusses in detail the principles of regional geological analysis and the main geological and geophysical tools - Captures and identifies the tectonics of the world in detail, through a series of unique geographic maps, allowing quick access to exact tectonic locations - Serves as the ideal introductory overview and complementary reference to the core concepts of regional geology and tectonics offered in volumes 2 and 3 in the series

Chapter 1

Regional geology and tectonics of sedimentary basins

Ian James Stewart, Integrated Petroleum Exploration Ltd., Uplands, Pond Road, Woking, Surrey, United Kingdom

Abstract

The most important question every geoscientist should continually ask is ‘why’? Why do I see what I see? Too often it is accepted, for example, that a sedimentary basin ‘is there’, and geoscientists continue to work on surfaces and units within its boundaries, without ever questioning ‘why do I have this hole in the ground’? Everything is where it is for a reason, and fundamental questions are rarely answered with a parochial approach such as that which is governed by a small acreage or data position in a much larger sedimentary basin. Regional understanding is essential in providing the necessary insights for basin analysis and inevitably requires study beyond the limits of the basin itself. Regional Geology provides this bridge from a crustal to a prospect scale, encompassing not just the basin but its hinterland, its crustal structure, and its inheritance from earlier geological events.

Keywords

Regional geology; tectonics; sedimentary basin; geochronology; inheritance

The most important question every geoscientist should continually ask is ‘why’? Why do I see what I see? Too often it is accepted, for example, that a sedimentary basin ‘is there’, and geoscientists continue to work on surfaces and units within its boundaries, without ever questioning ‘why do I have this hole in the ground’? Why is it here? What governed its geometry and stratigraphic architecture? What controlled the sediment entry points? What dictates the thermal structure? In resource evaluation and field development, the focus is commonly further narrowed, with management only requesting a map on a ‘Green Horizon’ picked on seismic data in a workstation environment covering only a small segment of the total basin area; insights from the broader regional and mega-regional geological understanding are lost.

In simple terms, the majority of sedimentary basins develop through contraction and lithospheric loading or crustal extension and subsequent thermal subsidence; both these processes include and can be dominated by oblique- or strike-slip tectonics. Their geometry and internal architecture are commonly strongly influenced by more regional structural fabrics inherited from the broader geological past.

The only way we can answer the key questions of ‘why?’, is to build an understanding of the basin’s regional geology. The regional geological understanding forms the bridge from the basin to its province, plate and often multiplate-scale context. D.G. Roberts, in his teaching of geology, would always assert the ‘Principle of Least Geological Astonishment’ to basin-scale interpretation: the geological equivalent of Occam’s Razor. The more special geological pleading an interpretation requires, the less likely it is to be correct. We can add another guiding principle: ‘The Principle of Non-Randomness’. Everything is where it is for a reason, and our role in basin interpretation is to understand ‘why’? Regional understanding of the basin’s location and its relationship to the tectonic history of its exposed margins and hinterland is essential. Integrated with the knowledge of far-field tectonic effects on a plate scale, or a palaeo-plate scale commonly provides the most powerful insights in moving towards a valid and viable basin solution.

While regional geology began through observations in the field (for a historical review, see Roberts and Bally, 2012), it has been supplemented in recent years by an ever-improving crustal-scale understanding through deep seismic reflection and refraction data, global magnetic and gravity datasets, seismic wave tomography and locally magnetotelluric profiling. The advent of digital elevation modelling and GIS technology allows accurate interpretation of the deeper processes within the mantle and their long-wavelength influence on the dynamic surface topography of the earth (e.g. Flament et al., 2013; Rubey et al., 2017). Mantle plumes are now imaged by tomography below the upper/lower mantle interface (French and Romanowicz, 2015), although their sole contribution to large igneous provinces (LIPs) is still a matter of debate. The important aspects of the regional crustal geometry to the basin-centric geoscientist include the terrane construct, and the thickness of the component crustal layers and the likely heat flow consequences for thermal modelling of the shallower sediment pile. Regional-scale thermo-chronological studies utilizing apatite fission track analysis (AFTA) are now widespread and frequently provide the timing of sediment maturity within the basin as well as changes in basin-margin elevation via structural inversion or thermal processes. Coupled with the broader structural geology and provenance studies, sequence stratigraphy can clarify sediment entry points into the basin.

To the exploration geoscientist at the basin-scale, however, probably the most significant image is that of a deep seismic reflection profile, illustrating a well-defined Moho and a layered crust, with their often relatively insignificant sedimentary basin carried above it at a crustal scale. In the last 20 years, industry has sponsored and supported numerous commercial deep reflection surveys across most of the world’s continental margins. The academic community (often oil company–sponsored) had previously demonstrated their value in the 1970s and 1980s with the COCORP, BIRPS, LITHOPROBE, BABEL and ECORS datasets. These surveys focused on elucidating crustal structure, largely over collisional orogens in the northern hemisphere. A thorough review of the early phases of this (still on-going) era of academic-led research and its conclusions is given in Snyder and Hobbs (1999).

One of the most profound observations of the original BIRPS programme was the confirmation of frequent reactivation of originally contractional crustal-scale faults, a view long-held by many field geologists. Their detachment in a seismically reflective lower crust or upper mantle, with a shallow near-surface half-graben in their hanging-wall, gave rise to the ‘typical BIRP’ (Matthews and Cheadle, 1986). This observed reactivation of crustal fault zones as extensional structures controlling subsequent basin formation (e.g. Klemperer and Hobbs, 1991), is now widespread. Crustal-scale faults have been frequently shown to be re-used in later contraction during basin inversion as a consequence of tectonic events further afield. Cycles of successive extension and contraction on these faults are common during the geological evolution of a basin.

Modern long-record commercial seismic data have increasingly been focused over the ‘new geography’ of increasingly deeper water, as the petroleum industry moves outboard to the limits of exploration and development technology. The revelations from these data on the nature of the thinning of continental crust towards the ocean-continent transition (OCT) and the differential and often depth-dependent behaviour of both upper and lower crust during extension has revolutionized the understanding of passive margins. Coupled with deep-sea drilling programmes, the nature of the OCT has been demonstrated to include exhumed lower crust and locally the mantle beneath low-angle extensional surfaces in largely nonmagmatic margins. Over magma-rich margins, which dominate the majority of continent-ocean transitions, long-record reflection seismic has spectacularly imaged seaward-dipping reflections or SDRs (from largely nonmarine lava flows that approach the base of the seaward tapering ductile crust), magmatic underplating and extensive dyke and sill emplacement associated with interpreted plume-driven activity or adiabatic decompression (Franke et al., 2007; Paton et al., 2017; Quirk et al., 2014).

Field geology and observations at a regional scale remain essential to sedimentary basin understanding, as well as informing directly on the crustal processes interpreted from the broader geophysical approaches. Regional geological interpretations have been enhanced in recent years by advances in geochronology, particularly in situ Zircon and Baddeleyite U–Pb geochronology, which allows precise dating of both igneous and metamorphic crystallization events (Schoene et al., 2013). In detrital grains, it permits the provenance and maximum depositional age of clastic strata to be determined (Gehrels, 2012). The chronology established from the 35 or so Archaean cratonic nuclei (Bleeker, 2003) and the presence of rifted and collisional margins around their borders reveals a long history of largely lateral crustal accretion since at least Late Archaean times. Each accretionary event leaves an indelible imprint in the lithospheric ‘memory’. The palaeomagnetic and chronological record preserved in extension-related LIPs and their plumbing systems documented as dyke swarms and sills provides LIP ‘barcodes’ (Ernst et al., 2013) for pre-Gondwanan early continents and their progressively accreted margins. This allows not only the correlation in time and space of previous continent and supercontinent configurations, their growth and dispersal, but also the demonstration of the longevity of tectonic processes evident in well-documented younger Phanerozoic terranes of lateral accretion, contraction and subsequent relaxation.

Archaean cratonic areas and their progressively accreted Proterozoic margins have been extensively studied by academia and the extractive industries, and few areas are better known than southern Africa. Here, the rock record documents multiple cycles of crustal accretion and dispersal over 3 Ga. In a book focused on Phanerozoic sedimentary basins, the study of Proterozoic tectonic cycles may seem somewhat academic and irrelevant. It is not. The structural template observed in outcrop is a profound reminder of the antiquity of upper crustal inhomogeneity that needs to be studied to understand subsequent basin development.

The Zimbabwe and Kaapvaal cratons of southern Africa each consist of numerous Archaean terranes, partitioned by greenstone belts. They are separated by the Limpopo Belt (Fig. 1.1A), a remnant of a Neo-Archaean collisional orogen between them that had stabilized by 2.6 Ga. It is probably one of the most-studied mobile belts in the world. The contractional deformation extended into both craton margins and reactivated the Murchison–Thabazimbi zone that delimits an earlier Meso-Archaean suture between the northern Pietersburg terrane and the southern Kaapvaal craton (Fig. 1.1B). Dyke swarms of 2.57 Ga (Great Dyke) and c.2.4 Ga (Sebanga swarm) are prominent in the Zimbabwe craton but not on the northern margin of the Kaapvaal, and the 2.06 Ga Bushveld-Molopo Farms complexes are not replicated in the Zimbabwe block. This has been interpreted by Söderlund et al. (2010) to indicate that the two cratons were not in their current configuration by these times. Apparent re-amalgamation and extensive reworking and metamorphic overprinting occurred in the Palaeoproterozoic Magondi orogen at c.2.0 Ga (Eglington et al., 2009 and references therein), although by 1.92-Ga voluminous dyke swarms, sills and basalt flows record at least one phase of extension between the two blocks during deposition of the syn-rift Soutspanburg/Palapye Groups and the marginally older Waterberg Group (Dorland et al., 2006) which carries extensive 1.87-Ga sills (Fig. 1.1B). Massive sill complexes of comparable age (Söderlund ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Foreword
• Introduction
• Chapter 1. Regional geology and tectonics of sedimentary basins
• Chapter 2. The Earth: core, mantle and crust
• Chapter 3. Age of the oceans
• Chapter 4. Plate boundaries and driving mechanisms
• Chapter 5. Plate kinematic reconstructions
• Chapter 6. Resolving geological enigmas using plate tectonic reconstructions and mantle flow models
• Chapter 7. Tectonostratigraphic Megasequences and Chronostratigraphy
• Chapter 8. Fault classification, fault growth and displacement
• Chapter 9. Thrust systems and contractional tectonics
• Chapter 10. Inverted fault systems and inversion tectonic settings
• Chapter 11. Salt- and shale-detached gravity-driven failure of continental margins
• Chapter 12. Carbonate systems
• Chapter 13. Lake systems and their economic importance
• Chapter 14. Clastic shorelines and deltas
• Chapter 15. Tidal straits: basic criteria for recognizing ancient systems from the rock record
• Chapter 16. Submarine landslides – architecture, controlling factors and environments. A summary
• Chapter 17. Turbidites and turbidity currents
• Chapter 18. Controls on reservoir distribution, architecture and stratigraphic trapping in slope settings
• Chapter 19. Geological methods
• Chapter 20. Regional tectonics and basin formation: the role of potential field studies – an application to the Mesozoic West and Central African Rift System
• Chapter 21. Wide-angle refraction and reflection
• Chapter 22. An introduction to seismic reflection data: acquisition, processing and interpretation
• Chapter 23. Sequence stratigraphy
• Chapter 24. Concepts of conventional petroleum systems
• Chapter 25. The accumulation of organic—matter–rich rocks within an earth system’s framework: The integrated roles of plate tectonics, atmosphere, ocean, and biota through the Phanerozoic
• Chapter 26. Modelling fluid flow and petroleum systems in sedimentary basins
• Global Maps
• Chapter 27. Tectonic and basin maps of the world
• Index