Understanding Geology Through Maps

Graham Borradaile

• Publisher: Elsevier
• Year: 2014
• Print ISBN: 9780128008669
• eBook ISBN: 9780128010938
• Topic: Technology & Engineering
• Subtopic: Geology & Earth Sciences
• Index: Technology & Engineering

Understanding Geology through Maps guides young professional geologists and students alike in understanding and interpreting the world's dynamic and varying geological landscapes through the liberal use of visual aids including figures, maps, and diagrams.This highly visual reference introduces the skills of interpreting a geological map and relating it to the morphology of the most important types of geological structure. Thoroughly revised, and with more international examples, it is ideal for use by students with a minimum of tutorial supervision.Maps of geological structures provide all of the realism of a survey map without the huge amount of data often present, so readers can develop or hone their skills without becoming overwhelmed or confused. In particular, emphasis is placed throughout on developing the skill of three-dimensional visualization so important to geologists.- Authored by a master geologist with more than 40 years of experience in research and instruction- Features more than 130 figures, diagrams, and illustrations—many in full color—to highlight major themes and aid in the retention of key concepts- Leads to a broad understanding of Earth's geology through the use of real and theoretical map- Exercises conclude each chapter, making it an ideal tool for self-guided and quick study

Chapter 1

Geological Maps and Some Basic Terminology

Abstract

Characteristics of layered rocks are explained including their correlation from one location to another. Uniformitarianism and the use of a stratigraphic column are introduced. Metamorphic, igneous, and plutonic rock relations are less easily interpreted from maps.

Keywords

Clastic sedimentary rocks; Correlation; Faunal succession; Igneous rocks; Lithology; Mapping; Metamorphic rocks; Plutonic rocks; Sedimentary rocks; Stratigraphic correlation; Superficial deposits; Superposition; Uniformitarianism; Volcaniclastic sedimentary rocks

Chapter Outline

Uniformitarianism (and Its Limitations) 4

Stratigraphic Correlation 6

What is Meant by “Mapping” 6

Initial Terminology for Lithology 9

Sedimentary Rocks 10

Clastic Sedimentary Rocks 10

Volcaniclastic Sedimentary Rocks 10

Superficial Deposits (Sediments as Opposed to Sedimentary Rock) 11

Some Glacial Sediments and Features 11

Some Special Glacial Landform Feature Recorded on Maps 11

Some Nonglacial Sediments 11

Map Representation of Superficial Deposits 12

Igneous rocks 12

Metamorphic rocks 13

Plutonic Rocks 13

William Smith (1736–1839) created the first geological map in southern England (see Simon Winchester’s book, 2001 listed in the Foreword). He expanded it through his lifetime’s work to be a geological map of England and Wales which is little different from the map we know today (Figure 1.1 shows the modern geological map of the United Kingdom). His initial map focused on a small area around Bath (Figure 1.2). First appearing and acknowledged in 1799, and published in 1802, the original geological map provided a revolutionary breakthrough in that it provided a way of showing map distribution of rock types from which one could deduce their relative age (≈chronostratigraphic sequence) and three-dimensional configuration at depth from visual inspection of the surface map alone. The father of the geological map, Smith, grew up in a rural environment in Oxfordshire but was exposed to geology at an early age through an interest in the locally abundant fossils. Parenthetically, a wealthy nephew John Phillips became the first Professor of Paleontology and Geology at Oxford and in later life assisted his uncle from discrediting attacks by formally educated intellectuals. Most of the population denied the antiquity of fossils due to religious reasons or they attributed their presence to the effects of the biblical flood. However, William Smith, like other better educated and more fortunate natural philosophers, grew to suspect the great ages required for the accumulation of thick sequences of sediment (later to be lithified to become sedimentary rock). Despite the controversy about their origin, Smith was the first person to recognize that specific fossils characterized each stratigraphic horizon. A further quantum step in knowledge was made when he realized that the fossil content could then be used to correlate comparable sequences of rocks between different locations (Figure 1.3). The details for central and southern England differ little from Smith’s final compilation, which was published in 1815. With the benefit of recent geochronological work, the absolute ages of the geological periods have been established (Figure 1.4).

Smith introduced the term stratigraphical and stratigraphy about 1795. The worldwide stratigraphic column as we now know it is shown in Figure 1.4. One of the few pieces of memory work in studying this book is to become familiar with the sequence of names and their approximate geochronological ages. Stratum (plural strata) derives from the Latin for street, since the well-known Roman Roads of Britain (and elsewhere in Europe) have survived two millennia due to their well designed layered structure, from the foundation of gravel, through a sand layer, to cobbles at the top. Bed and bedding are more-or-less English synonyms for stratum and stratification, although strictly speaking “bed” would describe a sedimentary rock, whereas stratification also encompasses sequentially layered igneous rocks such as lavas and even layered magmatic rock.

Bedding plane is subtly and importantly different. It refers to the discrete horizon of no thickness, a stratum-parallel boundary that separates two different beds, e.g., between a bed of sandstone and a bed of limestone. A bedding plane represents some unknown interval of nondeposition that may have endured for seconds or thousands of years. James Hutton (1726–1797) recognized the importance of a very special class of bedding surface, the unconformity. Hutton, quite unlike Smith, was a formally educated scholar and a medical doctor and a Professor at the University of Edinburgh at the acme the intellectual interval known as the period of Scottish Enlightenment. Hutton observed tilted strata, eroded, and subsequently overlain by lithified sedimentary rock. His classic observation was at Siccar Point, Berwickshire, a couple of day’s horse ride south of Edinburgh (see later, Figure 8.1). He could not avoid the conclusion that an immense but unknown time interval was required for the lithification of the lowest sediment, its emergence above sea level, its tilting, its erosion, its submergence and the deposition and lithification of an overlying series of strata. (For this example, we now know the time interval exceeds 70 million years.)

FIGURE 1.1 Geological map of Scotland, England, and Wales. England and Wales were the first countries to be mapped in this way.

FIGURE 1.2 The small circular area around Bath was the first area ever mapped geologically by William Smith (1788). Its location is shown in SW England together with a cross-section.

Pragmatically, coal miners in Somerset, SW England (like miners elsewhere in Europe) had already recognized that within a specific region, certain strata always occur in the same order in a given coalfield (Figure 1.2) and they may be correlated from one area to another (Figure 1.3). Moreover, in Somerset, miners knew that certain fossils characterized certain strata. This ordering was not unique to one mine but occurred throughout an extensive coalfield. Smith first comprehended the combined scientific significance of these facts and their practical value. Although he had no formal education beyond grammar school, Smith was a keen observer and had a natural instinct for the scientific metho...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Foreword
• Acknowledgments
• Chapter 1. Geological Maps and Some Basic Terminology
• Chapter 2. Relative Ages
• Chapter 3. Absolute Ages
• Chapter 4. Age Relationships from Map View
• Chapter 5. Layered (Stratified) Rocks and Topography
• Chapter 6. Strata and Plane-Dipping Features
• Chapter 7. Dips, Thicknesses Structure Contours and Maps
• Chapter 8. Unconformities
• Chapter 9. Faults
• Chapter 10. Folds
• Appendix 1
• Appendix 2. Final Project Possible after Completion of Studying This Book
• Index