In this chapter we provide a survey of the most common clastic and carbonate environments and talk about their geometry, occurrence, typical lithologies and structures, and provide numerous pictures of each. Given the scale of these features, the kind of facies analysis needed to determine depositional environments is best learned in the field or by looking at drill core.
Learning Objectives
Describe the most common lithologies, sedimentary structures, and fossils in major clastic and carbonate depositional environments.
Explain what processes are important in these environments.
Chapter thumbnail shows a cast of a standing lycopsid in floodplain deposits of the Pennsylvanian Joggins Formation, Nova Scotia (Michael C. Rygel via Wikimedia Commons; CC BY-SA 4.0).
Alluvial fans form where river systems spill from confined channels into open, unconfined areas; they are composed of a mixture of debris flow deposits and stream flow deposits. Fluvial channel bodies are typically composed of sand and gravel and have erosional bases. Floodplain deposits are finer grained and show evidence of terrestrial deposition and/or subaerial exposure. Avulsion and aggradation rates influence the architecture of fluvial and floodplain deposits.
Deserts form in arid environments where water is limited and wind is the primary mechanism for sediment transport. Desert deposits are characterized by thick sets of cross-bedded sandstones and a combination of evaporites, mud, gravel, and fluvial deposits in interdune areas.
Marginal marine environments form at the intersection of land and sea, where terrestrial and marine processes converge. In regions with a moderate supply of clastic sediment, these environments are shaped by the balance between waves, rivers, and tides which results in the development of beaches, deltas, and tidal flats, respectively.
Pericontinental seas mark the transition from the continents to the open oceans. Environments include the shelf (dominated by storm waves and tides on its landward side and suspension deposition on its seaward side), the relatively steep continental slope (dominated by suspension deposition, slumping, and turbidite generation), the continental rise (dominated by turbidite deposition), and the abyssal plain (dominated by suspension deposition of mud, calcareous oozes, and siliceous oozes).
Carbonate environments are most common in areas with warm, shallow marine water that is far removed from sources of clastic sediment. Distinctive carbonate facies can be used to recognize a spectrum of environments that include peritidal areas, lagoons, shoals, reefs, ramps, slopes, and deep marine settings.
Glacial environments do not form a single, coherent depositional system but instead interact with and overprint existing systems such as fluvial, lacustrine, and eolian environments. While glacially-overprinted environments closely resemble warmer-climate versions of those same environments, diagnosis of glacial influence depends on recognizing the diagnostic features described in this section.
