Sequence Stratigraphy (eBook)

Dominic Emery, Keith Myers (Herausgeber)

eBook Download: EPUB

2013
John Wiley & Sons (Verlag)
978-1-118-68504-4 (ISBN)

Infos

The innovation and refinement of the techniques and concepts of sequence stratigraphy has been one of the most exciting and profound developments in geology over the past thirty years. Seismic stratigraphy has now become one of the standard tools of the geoscientist, and there is a pressing need for an introductory text on sequence stratigraphy. This new book sets out to define and explain the concepts, principles and applications of this remarkably influential approach to the study of sedimentary strata. The authors take a rigorous objective stance in evaluating the techniques and interpretation of sequence stratigraphy - basing the text on an internal training course developed by British Petroleum (BP).

• A new text on this increasingly important field
• A practical guide based on the experience of practising sequence stratigraphers
• Based on a highly successful BP training course

Autor

Dominic Emery and Keith Myers are the authors of Sequence Stratigraphy, published by Wiley.

Inhalt

List of Contributors.

Preface.

1 Historical Perspective.

2 Concepts and Principles of Sequence Stratigraphy.

3 Seismic Stratigraphy.

4 Outcrop and Well Data.

5 Chronostratigraphic Charts.

6 Biostratigraphy.

7 Fluvial Systems.

8 Paralic Successions.

9 Deep-marine Clastic Systems.

10 Carbonate Systems.

11 Organic-rich Facies and Hydrocarbon Source Rocks.

12 Computer Modelling of Basin Fill.

References.

Index.

Textauszug

CHAPTER TWO

Concepts and Principles of Sequence Stratigraphy

2.1 Introduction

2.1.1 Basin forming processes

2.1.2 Basin-margin concepts

2.2 Relative sea-level, tectonics and eustasy

2.2.1 Definitions of sea-level

2.2.2 Accommodation

2.2.3 Accommodation through time

2.2.4 Orders of cyclicity and global correlation

2.3 Sediment supply

2.3.1 Principles of clastic sediment supply

2.3.2 Filling of accommodation

2.3.3 Basin architecture

2.4 Sequences and systems tracts

2.4.1 Sequences and sequence boundaries

2.4.2 Systems tract definition

2.4.3 Lowstand systems tract

2.4.4 Transgressive systems tract

2.4.5 Highstand systems tract

2.4.6 Type 2 sequence boundary and the shelf-margin systems tract

2.4.7 Lowstand systems tracts on a ramp margin

2.4.8 Controls on systems tract boundaries

2.4.9 Other possible systems tracts within a relative sea-level cycle

2.4.10 Composite (second and third order) sequences and systems tracts

2.4.11 Genetic stratigraphic sequences

2.5 High-resolution sequence stratigraphy and parasequences

2.5.1 Introduction

2.5.2 Parasequences and their continental equivalents

2.5.3 Parasequence sets

2.5.4 Parasequence thickness trends

2.5.5 Sequence boundaries

2.5.6 Maximum flooding surfaces

2.5.7 Ravinement surfaces

2.5.8 Problems and pitfalls of high-resolution sequence stratigraphy

2.1 Introduction

The stratigraphic signatures and stratal patterns in the sedimentary rock record are a result of the interaction of tectonics, eustasy and climate. Tectonics and eustasy control the amount of space available for sediment to accumulate (accommodation), and tectonics, eustasy and climate interact to control sediment supply and how much of the accommodation is filled. Autocyclic sedimentary processes control the detailed facies architecture as accommodation is filled. The purpose of this chapter is to introduce the principles that govern the creation, filling and destruction of accommodation. It then shows how these principles are used to divide the rock record into sequences and ‘systems tracts’, which describe the distribution of rocks in space and time.

The chapter uses siliciclastic systems to introduce the concepts and principles of sequence stratigraphy. Carbonate systems differ from clastic systems in their ability to produce sediment ‘in situ’, and they respond in a different manner to accommodation changes. Carbonates are therefore discussed separately in Chapter 10.

2.1.1 Basin forming processes

Tectonism represents the primary control on the creation and destruction of accommodation. Without tectonic subsidence there is no sedimentary basin. It also influences the rate of sediment supply to basins. Tectonic subsidence results from two principle mechanisms, either extension or flexural loading of the lithosphere. Figure 2.1 illustrates theoretical tectonic subsidence rates in extensional, foreland and strike-slip basins. These curves in effect govern how much sediment can accumulate in the basin, modified by the effects of sediment loading, compaction and eustasy.

Extensional basins form in a variety of plate tectonic settings, but are most common on constructive plate margins. In extensional basins, tectonic subsidence rates vary systematically through time, with an initial period of very rapid subsidence caused by isostatic adjustment to lithosphere stretching, followed by a gradual (60–100 million years) and decreasing thermal subsidence phase as the asthenosphere cools. This systematic change in tectonic subsidence rate has a strong influence on the geometry of the basin-fill, such that it may be possible to divide the stratigraphy into pre-, post- and syn-rift phases (these phases have been termed megasequences; Hubbard, 1988). In the simple syn-rift megasequence model the sediments are deposited in the active fault-controlled depocentres of the evolving rift and can show roll-over and growth into the active faults. Differential subsidence across the extensional faults may exert a strong control on facies distributions. In the post-rift megasequence, any remaining rift-related topography is gradually buried beneath sediments that fill the subsiding basin and onlap the basin margin, creating the typical ‘steers head’ geometry (McKenzie, 1978). The syn-rift and post-rift megasequences in a marine rift will contain sequences in which development is controlled by higher frequency changes in relative sea-level.

Fig. 2.1 Tectonic subsidence histories in rift, foreland and strike-slip basins

Foreland basins develop in response to loading of the lithosphere below thrust belts. The lithosphere bends in response to loading as the thrust sheets are emplaced, and creates a depression that is accentuated towards the load. The sedimentary fill to this foreland basin has a characteristic wedge shape, thickening towards the thrust front and forming a foreland basin megasequence. The width of the basin is proportional to the rigidity of the underlying lithosphere, and the depth is proportional to the size of the load. Foreland basins formed adjacent to growing mountain belts are characterized by large, and initially rapidly increasing, rates of sediment supply. Cessation of thrusting and continued erosion of the mountain belt leads to an eventual decrease in load, and many foreland basins become uplifted.

Strike-slip basins do not have a characteristic subsidence pattern, although in general, rates of subsidence (and uplift) are extremely rapid.

Tectonic subsidence curves provide a fundamental control on sediment accommodation, upon which higher frequency controls, such as eustasy, fault movement and diapirism, are superimposed. Figure 2.2 shows calculated tectonic subsidence curves for two real basins. In the Llanos Basin, Colombia, sediment supply has exceeded tectonic subsidence. The basin has remained full to base level, with excess sediment bypassed northwards to the sea. The subsidence curve shows slow subsidence through the late Cretaceous and early Tertiary, linked to thermal subsidence in a back-arc basin setting. Two distinct increases in subsidence rate occur in the mid –late Eocene and mid-Miocene, corresponding to two phases of mountain building in the Andes.

In the South Viking Graben example (Fig. 2.2), typical of a number of ritts, sedimentation has not always kept pace with true tectonic subsidence. This led to periods in the Cretaceous where water depths increased and sediment starvation occurred. In the Tertiary, uplift of the Scottish mainland and adjacent North Sea Basin resulted in increased sediment input to the basin (Milton et al., 1990), which locally filled to base level. The remainder of the basin subsequently filled with sediment, resulting in the present-day shallow sea. Separation of the syn-rift and post-rift in this basin is difficult, because the transition occurred during a period of sediment starvation (Milton, 1993).

During periods of rapid basin subsidence, sequence boundaries generated by higher frequency eustatic sea-level falls will be obscured. In times of slow tectonic subsidence or basin uplift, sequence boundaries will be enhanced.

2.1.2 Basin-margin concepts

Many of the concepts and principles of sequence stratigraphy are based on the observation from seismic data that prograding basin-margin systems often have a consistent depositional geometry (Fig. 2.3). Topset is a term used to describe the proximal portion of the basin-margin profile characterized by low gradients (< 0.1°). Topsets effectively appear flat on seismic data and generally contain alluvial, deltaic and shallow-marine depositional systems.

Fig. 2.2 Calculated tectonic subsidence histories for two sedimentary basins (reproduced by permission of BP Exploration Ltd)

The shoreline can be located at any point within the topset. It can coincide with the offlap break or may occur hundreds of kilometres landward. The proximal termination of the topset is usually termed the point of coastal onlap, referring to the up-dip limit of coastal-plain or paralic facies. Clinoform is used to describe the more steeply dipping portion of the basin-margin profile (commonly > 1°) developed basinward of the topset. Clinoforms generally contain deeper water depositional systems characteristic of the slope. The slope of the clinoform generally can be resolved on seismic data. Bottomset is a term sometimes used to describe the portion of the basin-margin profile at the base of the clinoform characterized by low gradients and containing deep-water depositional systems.

Fig. 2.3 Typical profile of a prograding basin-margin unit, comprising topsets...

Produkt-Details

• Erscheint lt. Verlag: 3.7.2013
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Technik
• Schlagworte: American • association • controversial disciplines • Driven • Dust • earth • earth sciences • Fill • Forward • Geologists • Geowissenschaften • Landmark • largely • liveliest • Memoir • Petroleum • Publication • Science • Sciences • sedimentary • Sedimentologie u. Stratigraphie • Sedimentology & Stratigraphy • Sequence • Stratigraphy • traditional subject • Work
• ISBN-10: 1-118-68504-0 / 1118685040
• ISBN-13: 978-1-118-68504-4 / 9781118685044