ASBOG FG PG flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Moho

The Mohorovičić discontinuity is the boundary between Earth's crust and mantle, marked by an abrupt increase in seismic P-wave velocity to about 8 km/s.

Principle of superposition

In an undisturbed sequence of sedimentary rock layers, the oldest layer lies at the bottom and each overlying layer is progressively younger.

Angular unconformity

An erosion surface where tilted or folded strata are truncated and overlain by younger, nearly horizontal layers, indicating deformation followed by erosion and renewed deposition.

Airy isostasy

Model in which topographic loads are supported by variations in crustal thickness, so mountain belts possess deep, low-density roots floating in the denser mantle.

Bowen's reaction series

The ordered sequence in which silicate minerals crystallize from cooling magma, from olivine and calcium plagioclase at high temperature to quartz and potassium feldspar at low temperature.

Mohs hardness scale

A relative scratch-hardness scale from talc (1) to diamond (10); calcite is 3, a fingernail about 2.5, and quartz 7.

Metamorphic facies

A set of mineral assemblages that form under a defined range of pressure and temperature, such as greenschist, amphibolite, blueschist, granulite, and eclogite.

Compatible element

An element with a high partition coefficient that preferentially enters solid minerals rather than melt, so it concentrates in early-formed crystals and is depleted in evolved magma.

Walther's law

The principle that a conformable vertical succession of facies reflects the lateral migration of adjacent depositional environments through time.

Dunham classification

A carbonate classification based on depositional texture: mudstone, wackestone, packstone, grainstone, and boundstone, reflecting mud content and whether grains support the framework.

Graded bedding

A sedimentary structure in which grain size decreases upward within a single bed, typically deposited by a waning current such as a turbidity flow.

Index fossil

A fossil species with a wide geographic range and a short stratigraphic duration, used to correlate and date rock units between regions.

Normal fault

A dip-slip fault in which the hanging wall moves down relative to the footwall, formed by crustal extension and typically dipping about 60 degrees.

Anderson's fault theory

Fault type depends on which principal stress is vertical: normal faults with vertical sigma-1, thrust faults with vertical sigma-3, and strike-slip faults with both horizontal.

Anticline

A fold in which strata arch upward so that the oldest rocks occur in the core, with limbs dipping away from the axial trace.

Thrust fault

A low-angle reverse fault where the hanging wall moves up and over the footwall, accommodating crustal shortening and common in fold-and-thrust belts.

Strahler stream order

A hierarchical numbering of streams in which headwater channels are order 1, and order increases only where two channels of equal order join.

Slope factor of safety

The ratio of shear strength, or resisting forces, to shear stress, or driving forces, along a potential failure surface; values below 1 indicate failure.

Dendritic drainage pattern

A branching, tree-like drainage network developed on relatively uniform, gently dipping terrain where rock resistance and structure exert little channel control.

U-shaped valley

A broad, steep-walled valley with a rounded floor carved by glacial erosion, contrasting with the V-shape typical of fluvial valleys.

Darcy's law

Groundwater discharge equals the product of hydraulic conductivity, cross-sectional area, and hydraulic gradient, written Q = -K A (dh/dL) and valid for laminar flow.

Storativity

The volume of water released from storage per unit surface area of aquifer per unit decline in hydraulic head; equal to specific yield in unconfined aquifers.

Cone of depression

The downward-curved potentiometric surface surrounding a pumping well, caused by drawdown, that expands outward with continued pumping.

Ghyben-Herzberg relation

In coastal aquifers, the freshwater lens extends about 40 times deeper below sea level than the water table stands above sea level, given the density contrast.

Plasticity index

The range of water content between the liquid limit and plastic limit, calculated as PI = LL - PL, indicating a soil's plasticity and clay content.

Effective stress

The intergranular stress carried by the soil skeleton, equal to total stress minus pore water pressure, which controls soil strength and consolidation behavior.

Liquefaction

Loss of shear strength in saturated loose sandy soil when seismic shaking raises pore pressure until effective stress approaches zero, producing flow-like behavior.

Rock quality designation

The percentage of drilled core recovery consisting of intact pieces 10 cm or longer, used together with joint data to rate rock mass quality.

Porphyry deposit

A large, low-grade copper-molybdenum-gold deposit associated with felsic porphyritic intrusions and stockwork veinlets above a magmatic-hydrothermal system.

Oil window

The temperature interval of roughly 60 to 120 degrees Celsius in which kerogen in source rock matures into liquid petroleum before cracking to gas.

Coal rank

The degree of coalification from peat through lignite, subbituminous, bituminous, and anthracite, reflecting increasing carbon content, heat, and pressure.

Reserve versus resource

A resource is a concentration of material that may be economically extracted; a reserve is the portion demonstrated to be profitable under current conditions.