Water's Properties in Sedimentary Rock Formation

• Sedimentary rock creation involves weathering, erosion, and lithification, with water as a key element.

Unique Properties of Water

• Water is essential for creating minerals in chemical sedimentary rocks and for weathering/erosion, producing grains for detrital sedimentary rocks.
• Water molecules consist of two hydrogen atoms covalently bonded to one oxygen atom at an angle of approximately 105 degrees.
• Polarity enables water molecules to adhere to other substances (adhesion).
• Water molecules are attracted to themselves (cohesion), forming droplets and causing surface tension.
• Liquid water is denser than solid water, a rare property due to hydrogen bonds formed by water's polarity.
• The density of water changes with temperature, being densest at 4°C, causing ice to float and preventing oceans from freezing solid from the bottom.
• Water remains liquid over a wide temperature range (0°C-100°C / 32°F-212°F) due to hydrogen bonding, allowing it to absorb high energy levels, which is crucial for life on Earth.
• Water is a universal solvent, dissolving more substances than any other naturally occurring liquid by prying ions using polarity and hydrogen bonds.

Weathering and Erosion

• Bedrock transforms into sediment through weathering.
• Mechanical weathering includes pressure expansion, frost wedging, root wedging, and salt expansion.
• Chemical weathering includes carbonic acid and hydrolysis, dissolution, and oxidation.
• Erosion is a mechanical process involving water, wind, gravity, or ice, transporting sediment from weathering sites.
• Erosion resistance affects the formation of geological features like cliffs and hoodoos.

Mechanical Weathering

• Mechanical weathering breaks bedrock into smaller pieces through pressure, temperature, freezing/thawing cycles, plant/animal activity, and salt evaporation.
• Pressure expansion occurs when bedrock surfaces due to uplift and erosion, causing temperature and pressure drops and leading to cracking, sheeting, exfoliation, and spheroidal weathering.
• Frost wedging involves water entering cracks, expanding upon freezing, and prying rocks apart through repeated cycles.
• Root wedging occurs when plant roots grow into cracks, splitting rocks apart, and can lead to fossilized roots (rhizoliths).
• Salt expansion happens in high evaporation or marine areas where salts precipitate and expand in rock cracks which causes tafoni (series of holes in a rock), cracks, and weaknesses that promote weathering.

Chemical Weathering

• Chemical weathering dominates in warm, humid environments, chemically degrading minerals into water-soluble ions for transport.
• Chemical and mechanical weathering work together via surface-area-to-volume ratio to increase reaction rates, as mechanical weathering exposes more surface area for chemical weathering.
• Carbonic acid (H2CO3) forms from carbon dioxide dissolving in water which causes hydrolysis and dissolution.
• Hydrolysis occurs when water molecules ionize and replace mineral cations or when carbonic acid reacts with minerals like feldspars to form clay minerals.
• Dissolution is when hydrolysis dissolves minerals like salt and calcite, leaving ions in solution and is increased with acidity, biological agents, and moisture content.
• The Goldich Dissolution Series shows the rate of chemical weathering related to crystallization order in Bowen’s Reaction Series, with high-temperature minerals weathering faster.
• Karst topography, featuring sinkholes and caves, results from dissolution weathering in carbonate bedrock.
• Oxidation, forms rust when iron atoms in minerals bond with oxygen, producing minerals like hematite, goethite, and limonite which can permeate rock or act as coatings.

Erosion

• Erosion transports sediment from weathering sites via water, gravity, wind, or ice.
• Erosion resistance shapes geological features like the Grand Canyon and hoodoos.

Soil

• Soil is a mix of air, water, minerals, and organic matter at the biosphere-geosphere transition, made through weathering and organism activity.
• Soil contains humus, a source of bioavailable nitrogen converted by nitrogen-fixing bacteria.
• Soil productivity depends on water and nutrient content.
• Soil characteristics are affected by factors like mineralogy of parent material, topography, weathering, climate, and inhabiting organisms.
• Well-formed soils have horizons, or distinct layers, forming a soil profile with assigned letters to designate layers.
• O Horizon: A top layer of organic material in the process of decaying.
• A Horizon: Topsoil layer, consisting of humus mixed with mineral sediment.
• E Horizon: A leached layer.
• B Horizon: Subsoil layer, consisting of sediment mixed with humus removed from upper layers.
• C Horizon: Substratum layer.
• R Horizon: Unweathered, parent bedrock layer.
• The USDA classifies soil types into soil orders, which include xoxisols, ardisol, andisols and alfisols.
• Soil color indicates conditions: black soils are anoxic, red soils are oxygen-rich, and green soils are oxygen-poor.
• The Dust Bowl disaster in the 1930s resulted from poor farming practices, leading to the ruin of soil profile and erosion and impacted the midwestern United States.

Sedimentary Rocks

• Clastic sedimentary rocks are made from pieces of weathered bedrock, and chemical sedimentary rocks precipitate from water saturated with dissolved minerals.

Lithification and Diagenesis

• Lithification turns loose sediment into rock through deposition, compaction, and cementation.
• Diagenesis is a low-temperature metamorphism that chemically alters sediments, for example aragonite converting to calcite.

Detrital Sedimentary Rocks (Clastic)

• Detrital rocks consist of weathered bedrock and are classified by grain size on the Wentworth scale.
• Grain sizes range from clay to boulders, with sand between 2 mm and 0.0625 mm.
• Sorting describes the range of grain sizes and rounding refers to the removal of angular corners during transport.
• Composition of rocks is influenced by source rock, hydrology, and mineral components, like quartz, feldspar, and lithic fragments.
• Provenance, determined by mineral composition, fossils, and textural features, identifies the sediment source and geologic history.
• Clastic rocks are classified by sediment grain size, groundmass, and clast shape (e.g. conglomerates, breccias, sandstone, mudstone, shale, siltstone, claystone).

Chemical, Biochemical, and Organic

• Chemical sedimentary rocks precipitate from dissolved minerals.
• Biochemical and organic sediments come from organic material.
• Inorganic chemical sedimentary rocks precipitate from ions in solution.
• Biochemical sedimentary rocks need living organisms.
• Organic sedimentary rocks come from organic remains.

Inorganic Chemical

• Inorganic chemical sedimentary rocks are formed when minerals precipitate out of an aqueous solution and form evaporites like gypsum and halite.
• The deposition order of evaporites is opposite to their solubility order, meaning less soluble minerals precipitate out sooner.
• Calcium carbonate precipitates tufa in porous calcite masses.
• Cave deposits like stalactites and stalagmites are travertine.
• Common in early Earth history, banded iron formation deposits are iron-rich and silica-rich.
• Chert precipitates as silica from groundwater, forming geyserite or sinter, and includes varieties like jasper, flint, onyx, and agate.
• Oolites are limestone forms created when calcite precipitates around a nucleus, forming ooids.

Biochemical

• Biochemical sedimentary rocks are created by living organisms.
• Limestone is made of calcite (CaCO3) and sometimes dolomite (CaMg(CO3)2).
• Various forms of limestone include fossiliferous limestone, coquina, chalk, and micrite.
• Biogenetic chert forms from microscopic organic shells like radiolarians and diatoms.

Organic

• Organic sedimentary rocks, associated with sedimentary strata, form from organic material through burial, compaction, and diagenesis.

Classification of Chemical Sedimentary Rocks

• Chemical sedimentary rocks are classified based on mineral composition.
• Rock salt consists of halite, and limestone (calcite) has complex classifications.

Sedimentary Structures

• Sedimentary structures are textures or arrangements of sediments that are used to interpret rock formation processes and environments.

Bedding Planes

• Bedding planes separate layers or strata, indicating changes in sediment deposition conditions, and each layer is called a bed or stratum.
• Varves are bedding planes created by repetitive cycles in laminae and beds.

Graded Bedding

• Graded bedding is a sequence of coarse- or fine-grained sediment layers.
• The Bouma sequence is graded bedding in turbidite, formed by offshore sediment gravity flows.

Flow Regime and Bedforms

• Bedforms are sedimentary structures created by fluid systems and sandy sediment.
• The flow regime is divided into upper and lower regimes.
• Plane beds are flat, parallel layers forming in lower flow regimes, with upper-flow-regime beds showing parting lineations.
• Ripples are ridges or undulations created as sediment grains pile up, with shapes determined by flow type.
• Dunes are large versions of ripples, resulting in trough cross beds or planar cross beds.
• Herringbone cross bedding is developed in tidal locations with strong in-and-out flows.
• Hummocky cross stratification beds are formed due to hurricane-strength winds and have a 3D-architecture.
• Antidunes form in fast-flowing upper flow regimes and are rarely preserved.

Bioturbation

• Bioturbation results from organisms burrowing, which disrupts bedding layers.

Mudcracks

• Mudcracks occur in clay-rich sediment that dries out, making them useful for determining depositional environments.

Sole Marks

• Sole marks are small features that are typically found in river deposits, on the base of a bed.
• Flute casts or scour marks are grooves carved by fluid flow and sediment loads.
• Groove casts are grooves made by larger clasts or debris.
• Tool marks are depressions from objects carried in the fluid.
• Load casts are indentations made by coarse sediment intruding into finer sediment.

Raindrop Impressions

• Raindrop impressions are pits or bumps in soft sediment.

Imbrication

• Imbrication consists of large clasts stacked in the direction of fluid flow.

Geopetal Structures

• Geopetal structures identify the original up direction in sedimentary rock layers by using mudcracks, sole marks, raindrop impressions.

Depositional Environments

• Depositional environment analysis helps determine how a sedimentary rock was formed.

Marine

• Marine depositional environments are submerged which depend on the depth of water.

Abyssal

• Abyssal sedimentary rocks form on the abyssal plain.
• Abyssal sediment includes calcareous oozes, siliceous oozes, and pelagic clay.
• Submarine fans and turbidite deposits transport sediment

Continental Slope

• Continental slope deposits include contourites, formed by deep-water ocean currents.

Lower Shoreface

• The fine sediments typically found in the lower shoreface are not subject to deposition every day.

Upper Shoreface

• The well-sorted, sediment in the upper shoreface are sediments within the zone of normal wave action.

Transitional coastline environments

• The sequence stratigraphy used to study these environments looks and examines depositional changes.
• Fluctuations in sea levels in these environments result from the daily tides, as well as climate changes and plate tectonics.
• A steady rise in sea level relative to the shoreline is called transgression, where regression is the opposite.
• Common components in transitional coastline environments are littoral zones, tidal flats, reefs, lagoons, and deltas.

Littoral

• The beach consists of homogeneous, well-sorted sand grains made mostly of quartz.
• Sediment is moved around via multiple processes.

Tidal Flats

• Tidal flats have large areas of fine-grained sediment.
• Multi-directional ripple marks and mudcracks are commonly seen.
• Tidal water focuses flow through a narrow tidal inlet.

Reefs

• A reef is any topographically-elevated feature on the continental shelf, located oceanward of and separate from the beach.
• Reefs can natural buildups of sand or rock.
• Reefs that are underwater, on the top of a seamount are called coral-ring atolls.

Lagoon

• Fine-grained sediment are commonly found in lagoons that are caused by a geographic features from the flow of water.
• Evaporation around lagoons can cause salt flats

Deltas

• Found where rivers enter lakes or oceans.
• Shapes of deltas: river-dominated deltas, wave-dominated deltas, and tide-dominated deltas.

Terrestrial

• Diversity stems from water availability and state, and arid conditions

Fluvial

• They generally come in two main varieties: meandering or braided.

Alluvial

• Alluvial deposits are common in arid places with little soil development.
• A sedimentary deposit is the alluvial fan.

Lacustrine

• Lake systems
• Lake bottom deposits tend to be fine grained.

Paludal

• Lots of organic matter in wetlands
• Tidal, deltaic, lacustrine, and/or fluvial deposition may be associated with Paludal environments

Aeolian

• Small, dusty sediments from glaciers
• Aeolian systems can form dunes.

Glacial

• Glacial sedimentation consists of poorly-sorted sediment deposits
• Glacial systems create fluvial, deltaic, lacustrine, pluvial, alluvial, and/or aeolian, individualized depositional environments

Facies

• Geologists classify sedimentary rock by its depositional characteristics.
• Geologists analyze sedimentary rock facies for the deposition environment, as well as geological events.
• Biological facies consist of remnants or evidence of living organisms.
• Fossil assemblages greatly enhance of Earth’s ancient history by illustrating the correlation between stratigraphic sequence and geologic time scale.