416 s EXAM 1

Mechanical compaction

The loss of porosity by rearrangement due to overburden pressure

Overburden pressure

The vertical pressure or stress caused by the combined weight of overlying rock and sediment

Lithification

Processes through which loose sediment becomes solid rock through formation of cement

siliciclastic sediments

Sediment that forms from weathering/ erosion of older rocks composed of silicate minerals.

Chemical sediments

Sediment that forms by direct inorganic (chemical) precipitation of minerals in the depositional basin

biogenic sediments

Sediment that precipitate or form through a biogenic agent ( i.e. Life including bacteria) typically within the depositional basin.

Clastic

Refers to any deposit composed of grains that were transported by a fluid. Clastic deposits can incorporate siliciclastic, chemical, and/or biogenic sediments.

Textural maturity

Rough proxy for the intensity/duration of transport that sediment underwent prior to deposition. (More mature: little to no clay, well sorted, rounded, high energy)

Porosity

Total amount of inter-granular space in the deposit

Permeability

How fluid moves through the deposit

Weathering

Process that breaks down rocks both chemically and physically. (The first Step in sediment production)

Erosion

Initial movement of weathered material (sediment). Primary agent is gravity but commonly together with a fluid (water or air).

Where does physical weathering dominate?

Arid, cold environments; sites as significant relief

Chemical weathering

Alteration of original rock/sedimet composition. Including mineralogy and chemistry

Principle agent of chemical weathering

Water (catalyst for ion exchange)

Chemical weathering is dependent on…

Grain size, climate, type/amount of vegetation, original rock composition

Quartz makes up _% of earths crust

20

Feldspar makes up _% of earth's crust

60

3 common styles of chemical reactions associated with chemical weathering of rocks and minerals

Dissolution, hydrolysis, oxidation/reduction

Dissolution

Formation of carbonic acid (lower pH typically increases dissolution)

Hydrolysis

Parent mineral reacts with water and causes exchange of ions, leaving behind a new/modified secondary (clay) mineral.

Simplest way to classify siliciclastic deposits

Grain size

Larger grains = _ energy

Higher energy ( harder to transport large grains )

Pore space

Empty or void space between grains

Framework grains

The main grains defining the deposit/rock are the framework grains

Matrix

Smatter clastic grains deposited with framework grains; common in poorly sorted sediment

Cement

Secondary minerals precipitated between framework grains after deposition (during diagnosis)

Conglomerate / breccia

Sedimentary rock/deposit with >30% gravel. Conglomerate is rounded grains and breccia is angular grains

Composition of Earth'S crust

Granite: 60% feldspar, 20-25% Quartz, 10% mica

Lithic grains

Grains of another rock. Can be sedimentary rock fragments, metamorphic rock fragments, volcanic rock fragments.

Sediment transport

Movement of sediment grains that can occur in a range of systems

Fluids

Substance that has no shear strength

Gas

Fluid that has a loose configuration of molecules

Liquid

Fluid that has a tighter configuration of molecules and can form a free surface

Laminar flow

A fluid movement regime where a liquid or gas flows in smooth, parallel layers with no mixing between them.

Turbulent flow

Fluid motion where liquids or gases move in chaotic, unpredictable patterns with rapid variation in pressure and velocity.

Inertial forces

Related to scale and velocity of the fluid; promote turbulence

Viscous forces

Related to fluid viscosity; suppress turbulence

Traction transport

Moving gran is in (nearly) constant contact with the bed. Can occur by rolling, sliding, or creeping

Saltation

Grains move in hopping motion in intermittent contact with the bed.

Bedload

Sediment moves at or near the bed. Grain velocity < fluid velocity

Suspended load

Sediment moves above the bed, in the main flow. Grain velocity ~ fluid velocity

Lower plane bed

Occurs mostly at low transport stages and typically with low sediment supply rates; results in a bed topography that has an approximately planar surface with grain transport as a mixture of rolling and saltation

Sedimentary structure

Any observable feature left behind in the sedimentary rock record resulting from the arrangement of particles into patterns or the geometry/patterns associated with surfaces of erosion

Stratification

Organization of the grain framework

What creates stratification

Spatial segregation & size segregation

Subcritical

only a portion of the bed form lee face will be preserved in the cross strata due to the climb angle being less than the stoss slope.

Supercritical

The full bed form will be preserved if the climb angle is greater than the stoss slope.

Bedforms ( dunes +- ripples)

Smaller with height limited to a fraction of the flow depth. Generated by variation in vertical structure of flow velocity

Barforms

Larger and height can grow to approximately the water surface ( made up of bedforms )