Sedimentology: Weathering, Transport, and Sedimentary Structures

Vocabulary practice flashcards covering sedimentary rock classifications, weathering mechanisms, clay mineral genesis, transport dynamics, and diagnostic sedimentary structures based on the lecture course.

Sedimentary Basin

A low-lying depressional region of the Earth's crust in which large quantities of sediment accumulate; basins can be continental or marine and vary widely in size.

Sediments

Unconsolidated accumulations of solid particles deposited by water, wind, or ice that originate from the breakdown of pre-existing continental rocks or from the activity of living organisms.

Sedimentary Rock

A rock formed either through the consolidation and lithification of loose sediments during diagenesis or via the direct chemical precipitation of ions from solution.

Rudites

Coarse-grained clastic sedimentary rocks or sediments characterized by a grain size greater than $2\,\text{mm}$.

Arenites

Medium-grained clastic sediments or sedimentary rocks with grain diameters ranging between $0.0625\,\text{mm}$ and $2\,\text{mm}$.

Lutites

Fine-grained sedimentary rocks or particles possessing a grain diameter smaller than $0.0625\,\text{mm}$.

Sedimentary Rock Textural Components

The structural elements that compose a clastic rock: grains (framework particles), matrix (fine interstitial material), cement (mineral precipitates binding grains), and porosity (open void spaces).

Evaporites

Chemical sedimentary rocks formed by the precipitation of soluble salts from aqueous solutions undergoing progressive solar evaporation.

Weathering (Altération)

The in situ physical disintegration and chemical decomposition of minerals and rocks near the lithosphere-atmosphere boundary by atmospheric agents, surface waters, groundwater, or hydrothermal fluids.

Haloclasty

A mechanical weathering mechanism caused by the crystallization and growth of salt crystals inside rock pores and fractures, frequently initiating honeycomb-like tafoni cavities.

Cryoclasty (Gélifraction)

A physical weathering process in which repeated freeze-thaw cycles of water within cracks and fissures fracture and shatter solid rock.

Hydrolysates (Precipitating Cations)

Cations with an intermediate ionic potential ($3 < Z/R < 10$) that bond with $OH^-$ to form insoluble hydroxides, such as $Fe(OH)_3$ and $Al(OH)_3$.

Hydrolysis

A chemical weathering reaction in which $H^+$ ions replace mineral cations in silicates, resulting either in complete breakdown into dissolved silica and hydroxides (total hydrolysis) or conversion into clay minerals (partial hydrolysis).

Granitic Arenite (Arène granitique)

A loose, gravelly sand produced in place by the chemical hydrolysis and physical disaggregation of minerals in a granite body.

Granitic Chaos (Chaos granitique)

An accumulation of rounded residual granite boulders (corestones) left in place after the surrounding weathered grus/arenite has been washed away, guided by joint systems.

Bisiallitisation

A weathering regime typical of temperate climates characterized by the formation of 2:1 (TOT) clay minerals (such as illite and smectite), involving the loss of approximately $60\%$ of silica and $67\%$ of exchangeable cations.

Monosiallitisation

A strong weathering regime characteristic of warm, humid, well-drained tropical climates that produces 1:1 (TO) clays like kaolinite, with a loss of over $66\%$ of silica and $100\%$ of exchangeable cations.

Allitisation

An intense, ultimate weathering regime occurring under hot, wet equatorial climates that strips away all silica and exchangeable cations, leaving behind residual aluminum hydroxides such as gibbsite.

Bauxite

An aluminum-rich residual sedimentary ore formed primarily in lateritic weathering horizons under tropical-to-equatorial climates through the extreme leaching of silica and soluble cations.

Hjulström Diagram

A hydrodynamic graph plotting critical current velocity against grain diameter to define the boundary thresholds for particle erosion, transport, and sedimentation in water.

Bedload (Charge de fond)

Coarse sediment grains transported along or immediately adjacent to the sediment bed via traction processes: rolling, sliding, and saltation.

Creep (Reptation)

The slow, continuous downhill movement of surficial soil and weathered mantle under gravity, evidenced on slopes by curved tree trunks and displaced retaining walls.

Pre-sedimentary Structures

Sedimentary relief features developed on the top of an underlying bed (commonly via erosive currents) and preserved as positive casts on the basal surface of the overlying bed.

Flute Cast

An elongated, scoop-shaped erosional scour mark preserved on the sole of a sedimentary bed, exhibiting a steep, bulbous upstream nose that tapers out in the downstream direction.

Crescent Mark

A horseshoe-shaped scour depression carved into mud or sand by horseshoe vortices wrapping around an upstream obstacle resting on the sediment floor.

Groove Mark (Cannelure)

A straight, continuous, linear furrow carved into a mud substrate by an object dragging, sliding, or rolling in a unidirectional current, preserved as a positive ridge on the base of the overlying sand layer.

Current Ripples vs. Oscillation Ripples

Current ripples are asymmetric bedforms with a gentle stoss and steep lee side produced by unidirectional flows; oscillation ripples are symmetric bedforms generated by bidirectional wave action.

Flaser Bedding

A mixed heterolithic bedding style dominated by sand ripples, where thin mud or clay drapes are preserved exclusively within the ripple troughs.

Lenticular Bedding

A heterolithic bedding structure where fine mud dominates and contains isolated, discontinuous lenses of sand ripples.

Bioturbation

The biological churning, disruption, and reworking of unconsolidated sediment by the active movement, burrowing, or rooting of organisms.

Desiccation Cracks (Mudcracks)

Polygonal fracture patterns formed when muddy, clay-rich sediment dries out, contracts, and dehydrates upon subaerial exposure.

Slump

A syn- or post-depositional gravity-driven deformation involving coherent shearing, sliding, and contorted internal folding of semi-consolidated sediment masses down a paleoslope.

Seismites

Sedimentary layers showing soft-sediment deformation, liquefaction, and fluidized disruption triggered by seismic shaking from earthquake activity.

Load Casts (Figures de charge)

Bulbous, irregular downward protrusions of a dense sand bed sinking gravitationally into an underlying, hydroplastic, water-rich mud layer.