Sediments and sedimentary rocks (Chapter 5 and lectures 05a, 05b, and 05c)

What are sediments?

Sediments are loose particles of rock, minerals, or organic material that are produced by weathering and erosion and can be transported and deposited.

What are sedimentary rocks?

Sedimentary rocks form when sediments or other materials accumulate and become solid rock, or when minerals precipitate from water or organic material accumulates.

What is weathering?

Weathering is the physical breakdown and chemical alteration of rock at or near Earth's surface.

What is physical weathering?

Physical weathering breaks rock into smaller pieces without changing its chemical composition.

What are examples of physical weathering?

Examples include frost wedging, abrasion, root wedging, salt crystal growth, and unloading or exfoliation.

What is frost wedging?

Frost wedging occurs when water enters cracks in rock, freezes and expands, and forces the cracks to widen.

What is abrasion?

Abrasion is physical weathering caused when rocks or sediment scrape, grind, or collide with other rocks, wearing them down.

What is root wedging?

Root wedging occurs when plant roots grow into cracks in rocks and expand, forcing the cracks wider.

What is chemical weathering?

Chemical weathering changes the chemical composition of minerals in a rock through chemical reactions.

What are important processes of chemical weathering?

Important processes include dissolution, oxidation, and hydrolysis.

What is dissolution?

Dissolution occurs when minerals dissolve in water or acidic water. It is especially important for soluble minerals such as calcite.

What is oxidation?

Oxidation occurs when oxygen reacts with minerals, especially iron-bearing minerals, producing oxides similar to rust.

What is hydrolysis?

Hydrolysis occurs when minerals chemically react with water and are transformed into new minerals, such as clay minerals.

What conditions generally increase chemical weathering?

Warm and wet conditions generally increase the rate of chemical weathering because water and higher temperatures promote chemical reactions.

What is differential weathering?

Differential weathering occurs when different rocks or minerals weather at different rates because some are more resistant to weathering than others.

How does weathering attack a block of rock?

Weathering attacks exposed surfaces and enters cracks and joints. Corners and edges can weather faster because they have more exposed surface area relative to their volume.

How does surface area affect weathering?

Greater exposed surface area generally causes faster weathering because more rock is available to interact with water, air, and other weathering agents.

What is soil?

Soil is a mixture of weathered mineral material, organic matter, water, air, and living organisms that develops at Earth's surface.

How does soil form?

Soil develops as parent material is weathered and mixed with organic matter while water, organisms, climate, topography, and time alter and redistribute its components.

What is a soil horizon?

A soil horizon is a distinct layer of soil with characteristic physical and chemical properties.

What is a soil profile?

A soil profile is a vertical section through the soil that shows its different horizons from the surface downward.

What is the O horizon?

The O horizon is the upper organic layer containing leaves, decomposing plant material, and other organic matter.

What is the A horizon?

The A horizon is topsoil, containing mineral material mixed with organic matter and substantial biological activity.

What is the E horizon?

The E horizon is a zone of leaching where clay, iron, aluminum, or other materials have been removed by downward-moving water.

What is the B horizon?

The B horizon is subsoil and commonly contains materials such as clay, iron, and aluminum that have accumulated from layers above.

What is the C horizon?

The C horizon consists mainly of partially weathered parent material beneath the more developed soil horizons.

What is the R layer?

The R layer is relatively unweathered bedrock beneath the soil.

What are the major factors of soil formation?

The major soil-forming factors are parent material, climate, organisms, topography or relief, and time.

How does climate affect soil formation?

Temperature and precipitation control weathering rates, biological activity, and movement of materials through soil.

How does parent material affect soil?

The original rock or sediment provides much of the mineral material from which soil develops and influences its composition.

How do organisms affect soil formation?

Plants, animals, microorganisms, and other organisms add organic matter, mix soil, and contribute to physical and chemical weathering.

How does topography affect soil formation?

Slope and landscape position influence drainage, erosion, sediment accumulation, and soil thickness.

How does time affect soil formation?

Soils generally become more developed and differentiated into horizons as weathering and other soil-forming processes operate over longer periods.

How are soils classified?

Soils are classified using characteristics such as their horizons, composition, texture, color, structure, and other physical and chemical properties.

What is Florida's official state soil?

Myakka fine sand is Florida's official state soil.

What are the major categories of sedimentary rocks?

The major categories are clastic, biochemical, chemical, and organic sedimentary rocks.

What are clastic sedimentary rocks?

Clastic sedimentary rocks form from fragments of preexisting rocks and minerals that are weathered, transported, deposited, and lithified.

How do clastic sedimentary rocks form?

Preexisting rocks are weathered into sediment, the sediment is eroded and transported, deposited, and then lithified into solid sedimentary rock.

What characteristics are used to describe clastic sediments?

Important characteristics include grain size, sorting, rounding, and composition.

What is sorting in sediment?

Sorting describes how similar the sediment grains are in size. Well-sorted sediment contains grains of similar size, while poorly sorted sediment contains a wide range of grain sizes.

What is rounding in sediment?

Rounding describes how smooth or angular sediment grains are. Longer transport commonly causes grains to become more rounded through abrasion.

What is lithification?

Lithification is the process that converts loose sediment into solid sedimentary rock, mainly through compaction and cementation.

What is compaction?

Compaction occurs when the weight of overlying sediment presses grains closer together and reduces pore space.

What is cementation?

Cementation occurs when dissolved minerals precipitate from groundwater in pore spaces and bind sediment grains together.

What clastic rock forms from gravel-sized sediment?

Conglomerate or breccia forms from gravel-sized sediment. Conglomerate contains rounded gravel-sized clasts, while breccia contains angular gravel-sized clasts.

What is the difference between conglomerate and breccia?

Conglomerate contains rounded gravel-sized fragments, while breccia contains angular gravel-sized fragments.

What clastic sedimentary rock forms from sand-sized sediment?

Sandstone forms from lithified sand-sized sediment.

What clastic sedimentary rock forms from silt-sized sediment?

Siltstone forms from lithified silt-sized sediment.

What clastic sedimentary rock commonly forms from clay-sized or very fine mud sediment?

Shale is a common fine-grained sedimentary rock formed from compacted clay and mud and typically splits into thin layers.

What happens to sediment grain size as transporting energy decreases?

Larger and heavier grains are deposited first, while smaller grains can remain suspended and be transported farther.

What are biochemical sedimentary rocks?

Biochemical sedimentary rocks form from materials produced or accumulated by living organisms, such as shells and skeletal fragments.

What is biochemical limestone?

Biochemical limestone forms largely from calcium carbonate shells, skeletons, or other remains of organisms.

What is coquina?

Coquina is a biochemical limestone composed mainly of loosely cemented, visible shell fragments.

What is chalk?

Chalk is a fine-grained biochemical limestone formed largely from microscopic calcium carbonate remains of marine organisms.

What is chert?

Chert is a hard, silica-rich sedimentary rock that can form from accumulated microscopic silica-rich skeletal material or by chemical processes.

What are chemical sedimentary rocks?

Chemical sedimentary rocks form when dissolved minerals precipitate directly from water.

What are evaporites?

Evaporites are chemical sedimentary rocks that form when water evaporates and dissolved minerals precipitate.

How does rock salt form?

Rock salt forms when saline water evaporates and the mineral halite precipitates and accumulates.

How does rock gypsum form?

Rock gypsum forms when evaporation causes dissolved gypsum minerals to precipitate and accumulate.

What are organic sedimentary rocks?

Organic sedimentary rocks form primarily from accumulated organic material, especially plant remains.

How does coal form?

Coal forms from accumulated plant material that is buried, compacted, and altered over time.

What is a sedimentary depositional environment?

A depositional environment is a location and set of physical conditions where sediment accumulates.

What are the three broad groups of depositional environments?

Depositional environments can broadly be classified as continental, transitional or shoreline, and marine environments.

What are examples of continental depositional environments?

Examples include rivers, lakes, deserts, glaciers, and alluvial fans.

What are examples of transitional depositional environments?

Examples include beaches, deltas, tidal flats, lagoons, and other environments near the boundary between land and sea.

What are examples of marine depositional environments?

Examples include shallow continental shelves, reefs, continental slopes, and deep-ocean environments.

How can geologists recognize an ancient depositional environment?

Geologists use rock type, grain size, sorting, fossils, sedimentary structures, and relationships between rock layers to interpret the environment in which sediment was deposited.

What does coarse sediment generally indicate about depositional energy?

Coarse sediment generally indicates a relatively high-energy environment capable of transporting larger particles.

What does fine sediment generally indicate about depositional energy?

Fine sediment commonly accumulates in lower-energy environments where small particles can settle from suspension.

What are sedimentary structures?

Sedimentary structures are features produced during or shortly after sediment deposition that provide clues about past environmental conditions.

What is a sedimentary bed?

A bed is an individual layer of sediment or sedimentary rock separated from layers above and below by bedding surfaces.

What are ripple marks?

Ripple marks are small ridges formed on sediment surfaces by moving water or wind.

What can ripple marks tell geologists?

Ripple marks can provide information about the movement of water or wind and the depositional environment.

What are mud cracks?

Mud cracks form when wet, muddy sediment dries, shrinks, and cracks.

What do mud cracks indicate about a past environment?

Mud cracks indicate that sediment was periodically wet and then exposed to air long enough to dry.

What are cross-beds?

Cross-beds are inclined layers within a larger sedimentary bed produced by migrating ripples, dunes, or other sediment forms.

What can cross-bedding tell geologists?

Cross-bedding can indicate the direction of past water or wind movement and can provide clues about the depositional environment.

What is graded bedding?

Graded bedding is a sedimentary layer in which grain size changes vertically, commonly from coarse grains at the bottom to finer grains at the top.

Why does normal graded bedding become finer upward?

As the transporting flow loses energy, the largest and heaviest grains settle first, followed by progressively smaller grains.

What is a turbidity current?

A turbidity current is a dense, sediment-rich underwater flow that moves downslope under gravity.

What is a turbidite?

A turbidite is a sedimentary deposit produced by a turbidity current and commonly displays graded bedding.

How do turbidites form?

A sediment-rich underwater flow moves downslope and loses energy. Coarser particles settle first, followed by progressively finer particles, producing graded deposits.

What is a sedimentary basin?

A sedimentary basin is a region where the crust subsides or provides long-term accommodation space, allowing thick sequences of sediment to accumulate.

Where can sedimentary basins form?

Sedimentary basins can develop in several tectonic settings, including areas of crustal stretching, along continental margins, and near mountain belts.

What is a marine transgression?

A marine transgression occurs when relative sea level rises and the shoreline moves landward, causing marine environments to spread over areas that were previously closer to shore or on land.

What is a marine regression?

A marine regression occurs when relative sea level falls and the shoreline moves seaward, exposing areas that were previously underwater.

What happens to the shoreline during a transgression?

The shoreline moves landward as relative sea level rises.

What happens to the shoreline during a regression?

The shoreline moves seaward as relative sea level falls.

Has sea level always been the same during Florida's geologic history?

No. Sea level has risen and fallen repeatedly, causing large portions of Florida to be submerged at some times and exposed at others.

What type of rock forms much of Florida's bedrock?

Limestone forms much of Florida's bedrock.

Why is limestone common in Florida's bedrock?

Much of Florida was submerged beneath warm, shallow seas where calcium carbonate from marine organisms and chemical or biochemical processes accumulated and eventually became limestone.

Where did much of Florida's surface sand come from?

Much of Florida's surface quartz sand was transported from rocks eroded farther north, especially from the Appalachian region, and was redistributed by rivers, currents, waves, and changing shorelines.

What is the easiest way to remember transgression versus regression?

Transgression = sea advances onto land and the shoreline moves landward. Regression = sea retreats and the shoreline moves seaward.

What is the basic sequence for forming a clastic sedimentary rock?

Weathering → erosion and transport → deposition → burial → compaction and cementation → sedimentary rock.