Geology and Hydrology: Time Scale, Sedimentary & Metamorphic Rocks, Weathering, Stream Dynamics, and Groundwater

Geologic time scale

Cambrian → Ordovician → Silurian → Devonian → Carboniferous (Mississippian & Pennsylvanian) → Permian → Triassic → Jurassic → Cretaceous → Paleogene → Neogene → Quaternary

Grain size order

clay → silt → sand → gravel

Sedimentary rock types

shale (clay), siltstone (silt), sandstone (sand), conglomerate/breccia (gravel)

Effect of grain size

Grain size affects other things - what it tells you, etc.

Energy of the depositional environment

Energy refers to the strength of water or wind where sediments are deposited—high energy carries large grains (rivers, beaches); low energy deposits fine grains (lakes, deep ocean).

Causes of metamorphism

Heat, pressure, and chemically active fluids alter existing rock to form metamorphic rock.

Kinds of metamorphic rocks

Foliated (slate, schist, gneiss) and non-foliated (marble, quartzite).

Kinds of weathering

Mechanical (frost wedging, abrasion), chemical (oxidation, hydrolysis), and biological (roots, organisms).

Landforms associated with weathering

Caves, sinkholes, karst topography, tors, and exfoliation domes.

Kinds of sedimentary rock

Clastic, chemical, and organic sedimentary rocks.

Grain size relation to clastic sedimentary rock

Clay → shale, silt → siltstone, sand → sandstone, gravel → conglomerate/breccia.

Angularity

Angularity measures how sharp or rounded grains are; more rounded = longer transport, more angular = closer to source.

Kinds of unconformity

Disconformity (parallel layers with erosion gap), angular unconformity (tilted layers under flat ones), nonconformity (sedimentary over igneous/metamorphic).

How fossils form

Formed when organisms are rapidly buried and preserved through mineral replacement, molds, or casts.

How coal forms

Plant material in swamps → peat → lignite → bituminous coal → anthracite (with increasing heat and pressure).

Hydrologic cycle

Evaporation → condensation → precipitation → infiltration → runoff → transpiration → back to oceans/atmosphere.

Drainage patterns

Dendritic (uniform rock), radial (volcano or dome), rectangular (faulted rock), trellis (folded or layered rocks).

Stream discharge

What is stream discharge?

Smaller grains

Indicate low-energy environments and longer transport; larger grains indicate high-energy environments and shorter transport distance.

Discharge

The volume of water flowing past a point in a stream per unit time (discharge = width × depth × velocity)

Meandering Stream

A stream with a single sinuous channel and low sediment load.

Braided Stream

A stream with multiple channels, high sediment load, and variable flow.

Meanders

Bends in a stream that form from erosion on the outer banks (cut banks) and deposition on inner banks (point bars) causing bends to grow over time.

Features of Meandering Stream

Cut bank, point bar, oxbow lake, meander scar, floodplain.

Delta

A delta forms where a river enters standing water (lake or ocean) and deposits sediment as flow velocity decreases.

Flash Floods

Short-term, local floods caused by intense rain.

Regional Floods

Long-lasting, widespread floods from prolonged rainfall or snowmelt.

Groundwater

Water in pore spaces beneath Earth's surface; about 1% of all Earth's water is groundwater.

Porosity

Percentage of pore space in a material.

Permeability

Ability for fluids to pass through a material; both porosity and permeability affect water storage and movement.

Water Table

The upper boundary of the saturated zone where groundwater fully fills pore spaces.

Grain Size in Porosity and Permeability

Fine grains = high porosity but low permeability; coarse grains = higher permeability and faster flow.

Artesian Well

A well that taps a confined aquifer where water rises under its own pressure without pumping.

Aquifer

A permeable rock or sediment layer that stores and transmits groundwater.

Cone of Depression

A cone-shaped drop in groundwater level created by pumping that lowers the local water table around a well.

Non-renewable Groundwater

Deep or ancient groundwater that recharges very slowly, taking thousands of years to replenish once removed.

Dynamic Subsurface Water Environment

Groundwater moves, dissolves minerals, and interacts with rock layers, shaping caves and aquifers over time.