Book contents
- Frontmatter
- Contents
- Acknowledgments
- Figure credits
- PART 1 Introduction
- PART 2 Production of sediment at the Earth's surface
- 3 Weathering of rocks, production of terrigenous sediment, and soils
- 4 Biogenic and chemogenic sediment production
- PART 3 Fundamentals of fluid flow, sediment transport, erosion, and deposition
- PART 4 Environments of erosion and deposition
- PART 5 Sediment into rock: diagenesis
- PART 6 Long-term, large-scale processes: mountains and sedimentary basins
- References
- Appendix: Methods of study of Earth surface processes, landforms, and sediments
- Index
- Plate section
4 - Biogenic and chemogenic sediment production
from PART 2 - Production of sediment at the Earth's surface
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Acknowledgments
- Figure credits
- PART 1 Introduction
- PART 2 Production of sediment at the Earth's surface
- 3 Weathering of rocks, production of terrigenous sediment, and soils
- 4 Biogenic and chemogenic sediment production
- PART 3 Fundamentals of fluid flow, sediment transport, erosion, and deposition
- PART 4 Environments of erosion and deposition
- PART 5 Sediment into rock: diagenesis
- PART 6 Long-term, large-scale processes: mountains and sedimentary basins
- References
- Appendix: Methods of study of Earth surface processes, landforms, and sediments
- Index
- Plate section
Summary
Introduction
Ancient biogenic (actually biochemogenic) and chemogenic sedimentary rocks include (1) limestones and dolostones (collectively referred to as carbonates); (2) cherts and related siliceous deposits; (3) saline deposits (commonly referred to as evaporites); (4) iron-rich sedimentary rocks; and (5) phosphorites (Pettijohn, 1975). Modern analogs help guide the interpretation of these ancient sediments. However, modern sediments generally differ from their ancient counterparts in terms of scale, details of mineralogy, and details of depositional environment and processes. Such differences stem from two sources. First, chemogenic and biogenic sedimentary rocks are very susceptible to changes in chemical composition and mineralogy during diagenesis (Chapter 19). Second, there have been changes in the compositions of the lithosphere, atmosphere, hydrosphere, and biosphere through geological time, for example (1) the outpourings of flood basalts in the Permian and Cretaceous, (2) the rise in concentration of oxygen in the Paleoproterozoic atmosphere, (3) variations in the amount of CO2 in the atmosphere, (4) variation in the major-ion composition of seawater, and (5) the origin and evolution of shell-building organisms (see Chapter 2). Biogenic and chemogenic sediments are governed by these changes in the various spheres through geological time and are, in fact, the most important sources of information about these changes.
Two important features of modern chemogenic and biogenic sediments are that (1) they originate as either biochemical precipitates or physico-chemical precipitates in the depositional environment where they accumulate, and (2) the majority of the grains are subjected to physical transport and deposition, although some of the grains remain at the precipitation site.
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- Earth Surface Processes, Landforms and Sediment Deposits , pp. 85 - 118Publisher: Cambridge University PressPrint publication year: 2008