geology 101 test 3

What is an unconformity?

An erosional boundary representing missing time between depositional events.

What is a nonconformity?

Boundary between igneous/metamorphic rocks and sedimentary cover rocks (includes the Great Unconformity).

What is a disconformity?

Boundary between parallel sedimentary layers where time is missing; hard to recognize.

What is an angular unconformity?

Boundary where older sedimentary layers are tilted at an angle beneath younger flat layers.

What is a facies?

A genetically linked sequence of sedimentary beds tied to a specific depositional environment.

Exam 3 review

What characteristics define a facies?

Sediment type, grain size/shape, structures, fossils, other context.

What features would you expect in a sandy desert sandstone?

Quartz-rich, well-rounded, well-sorted fine sand; crossbeds; ripples; few fossils; evaporites.

What is a diamictite?

Glacial till rock with angular clasts in fine mud (glacial flour)

Key characteristics of alluvial fan deposits?

Poorly sorted sediments, mixed grain sizes, semi-angular, close to source, small channels.

What dominates braided river deposits?

Coarse, well-sorted pebbles and cobbles; imbricated clasts; high energy

What defines anastomosing rivers?

Multiple channels, medium-high flow, coarse bars, cross-bedding, sole marks.

What sediments form in meandering rivers?

Fine sediments, point-bars, cut-banks; oxbow lakes from abandoned channels.

What forms in playa environments?

Evaporites like rock salt and gypsum

What is loess?

Wind-blown silt/clay, typically derived from glacial flour

What do desert dunes produce?

Large crossbeds and ripples in fine quartz sand

What characterizes delta deposits?

Fine silts/clays, channels, crossbeds, organic-rich dark muds.

What dominates beach deposits?

Well-rounded, mature quartz sand; high-energy ripples; marine shells

What rocks are common in shallow marine settings?

Fossiliferous limestone, coquina, ooids

What forms at reef platforms?

Coral reef structures, CaCO3 deposition, fossiliferous limestone.

What is siliceous ooze and what does it form?

SiO₂ skeletons of microscopic organisms; becomes chert.

What is carbonaceous ooze?

CaCO₃ skeletons of micro-organisms; becomes chalk/limestone.

What are turbidites?

Underwater sediment avalanches forming Bouma sequences

What is transgression?

Sea level rise; beach → shallow marine → deep marine.

What is regression?

Sea level fall; deep marine → shallow marine → beach.

How do oceanic and continental crust differ?

Oceanic = mafic, 7–10 km; Continental = felsic, 35–40 km.

What layer allows plates to move?

The asthenosphere (partially melted, plastic).

What generates Earth’s magnetic field?

The liquid outer core and solid inner core

What drives plate motion?

Mantle convection dragging plates.

Name evidence for plate tectonics.

Continental fit, past glaciations, climate belts, fossils, stratigraphic correlation.

What forms at divergent boundaries?

Rift zones; new crust at mid-ocean ridges.

What happens when two oceanic plates converge?

Older plate subducts; island arcs form

What forms at continent-ocean convergence?

Subduction and volcanic arcs

What forms in continent-continent convergence?

Mountains (orogeny), no subduction

What is a transform boundary?

Plates sliding past each other; example: San Andreas Fault.

How do hotspots form island chains?

Plate moves over stationary hotspot; each island marks plate movement direction (e.g., Hawaii).