ASBOG FG PG cheat sheet

Earth's layered structure: felsic continental crust (~35 km), mafic oceanic crust (~7 km), mantle to 2900 km depth, liquid outer core, and solid inner core.

Major seismic discontinuities: Moho (crust–mantle), Gutenberg (mantle–core at ~2900 km), and Lehmann (inner-core boundary).

Relative dating principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions, and faunal succession.

Unconformity types: angular (truncated tilted beds), disconformity (erosion surface between parallel beds), and nonconformity (sedimentary rocks over igneous or metamorphic basement).

Airy isostasy supports topography by variations in crustal thickness (mountains have deep roots); Pratt isostasy supports it by lateral density contrasts at a constant compensation depth.

Geologic time hierarchy: eon, era, period, epoch; Phanerozoic eras are Paleozoic, Mesozoic, and Cenozoic.

Plate boundaries: divergent (new crust, normal faults), convergent (subduction or collision, thrusts), and transform (strike-slip).

Radiometric dating depends on closure temperature; U-Pb in zircon is the most robust method for old rocks, while 14C is limited to about 50 ka.

Seafloor magnetic anomalies record geomagnetic field reversals and provide the primary evidence for seafloor-spreading rates.

Bowen's reaction series: olivine → pyroxene → amphibole → biotite (discontinuous branch) and Ca-plagioclase → Na-plagioclase (continuous branch); quartz and K-feldspar crystallize last.

Silicate structural classes: nesosilicate (olivine), sorosilicate, cyclosilicate, single-chain inosilicate (pyroxene), double-chain inosilicate (amphibole), phyllosilicate (mica, clay), and tectosilicate (quartz, feldspar).

Mohs hardness: 1 talc, 2 gypsum, 3 calcite, 4 fluorite, 5 apatite, 6 orthoclase, 7 quartz, 8 topaz, 9 corundum, 10 diamond.

Igneous classification by SiO2: felsic >63%, intermediate 52–63%, mafic 45–52%, ultramafic <45%; plutonic versus volcanic texture reflects cooling rate.

Metamorphic facies series: low P/T gives greenschist–amphibolite–granulite; high P/T gives blueschist–eclogite; index minerals include chlorite, biotite, garnet, staurolite, kyanite, and sillimanite.

Goldschmidt element classes: lithophile, siderophile, chalcophile, atmophile; compatible elements (Ni, Cr) enter early solids, incompatible elements (Rb, Ba, U, Th, Nb) concentrate in melts.

Radioactive decay: N = N0 e^(−λt) with λ = ln2 / half-life; isochron methods use multiple isotopic ratios to solve for age and initial ratio simultaneously.

Gibbs phase rule F = C − P + 2; eutectic and peritectic relations plus fractional crystallization control melt paths and enrich residual liquids in silica and incompatible elements.

Wentworth scale: clay <1/256 mm, silt 1/256–1/16 mm, sand 1/16–2 mm, and gravel (granule, pebble, cobble, boulder) >2 mm.

Textural maturity increases with better sorting, greater roundness, and removal of clay matrix; quartz arenite is the most mature sandstone.

Dunham carbonate classification: mudstone, wackestone, packstone, grainstone, and boundstone; Folk classification uses allochem type and orthochem matrix.

Diagnostic sedimentary structures: cross-bedding (flow direction), graded bedding (waning currents), ripples, mudcracks (subaerial exposure), and bioturbation.

Walther's law: conformable vertical facies successions record laterally adjacent environments; fining-upward successions commonly record transgression.

Sequence stratigraphic systems tracts: lowstand, transgressive, highstand, and falling stage, bounded by sequence boundaries and maximum flooding surfaces.

Index fossils: trilobites (Paleozoic), ammonites (Mesozoic), graptolites (Ordovician–Silurian), conodonts, and planktonic foraminifera and nannofossils (Cretaceous–Cenozoic).

Stratigraphic codes recognize lithostratigraphic, biostratigraphic, chronostratigraphic, and magnetostratigraphic units, each governed by separate naming rules.

Orientation conventions: strike is the compass trend of a horizontal line on a plane; dip is the steepest inclination perpendicular to strike; apparent dip is always less than or equal to true dip.

Fold elements: limb, hinge line, axial surface, plunge, and vergence; anticlines contain the oldest rocks in the core, synclines the youngest.

Anderson's theory: normal faults form with vertical σ1, thrust faults with vertical σ3, and strike-slip faults with σ1 and σ3 horizontal and σ2 vertical.

Hanging wall moves down in normal faults (extension) and up in reverse faults (shortening); thrusts are reverse faults dipping less than about 45°.

Mohr–Coulomb failure: τ = c + σn tan φ; Byerlee's law gives friction coefficients of roughly 0.6–0.85 for most rocks at depth.

Shear-sense indicators include S-C fabrics, rotated porphyroclasts, asymmetric folds, and sigmoidal vein arrays; all indicators in one outcrop must agree.

Thrust-belt geometry: ramp-flat staircase trajectories, fault-bend and fault-propagation folds, duplexes, and hinterland-dipping versus foreland-dipping panels.

Strain is described by stretch and shear: pure shear (flattening) versus simple shear (rotation), with finite strain ellipsoid axes X ≥ Y ≥ Z.

Weathering: hydrolysis of feldspars to clays, oxidation of iron-bearing minerals, and carbonate dissolution; physical processes include freeze-thaw, salt wedging, and unloading exfoliation.

Mass wasting classes: fall, topple, slide (rotational or translational), flow (debris flow, earthflow), and creep; triggers include water, seismic shaking, and toe undercutting.

Drainage patterns: dendritic (uniform substrate), trellis (folded strata), radial (domes and volcanoes), rectangular (jointed rock), and deranged (glaciated terrain).

Strahler ordering: order 1 at headwaters; order increases only where two channels of equal order join; drainage density equals channel length divided by basin area.

Graded streams have concave-up longitudinal profiles controlled by base level; knickpoints mark disequilibrium and migrate upstream.

Glacial landforms: erosional features include cirques, arêtes, horns, U-shaped valleys, and roches moutonnées; depositional features include till, moraines, drumlins, eskers, and outwash.

Eolian features: barchan dunes (limited sand, unidirectional wind), transverse ridges, longitudinal seifs, and star dunes; loess is wind-blown silt.

Karst features include sinkholes, caves, disappearing streams, and large springs formed by carbonate dissolution along joints; karst aquifers transmit water rapidly with little filtration.

Soil profile horizons: O (organic), A (topsoil), E (eluviation), B (accumulation), C (weathered parent material), and R (bedrock).

Darcy's law: Q = −K A (dh/dL); specific discharge q = Q/A = −K i, valid for laminar flow; transmissivity T = K b.

Porosity distinctions: total versus effective porosity; specific yield is drainable porosity and specific retention is water held against gravity; confined storativity ranges roughly 1e-5 to 1e-3.

Hydraulic head h = z + P/(ρg); groundwater flows from high to low head; the potentiometric surface represents confined-aquifer head and the water table represents unconfined head.

Aquifer tests: Theis solution uses the exponential integral; Cooper–Jacob straight-line applies when u < 0.01; leaky aquifers follow Hantush type curves.

Pumping produces a cone of depression; well interference reduces yield; specific capacity Q/s is a practical index of transmissivity.

Groundwater budget: recharge = discharge + change in storage; baseflow sustains streams between storms and is estimated from hydrograph separation.

Contaminant transport: advection velocity v = q/n_e, mechanical dispersion and diffusion, sorption with retardation factor R = 1 + (ρb/n) Kd, and first-order decay.

Ghyben–Herzberg relation: freshwater-saltwater interface depth below sea level is about 40 times the water-table elevation above sea level; overpumping causes saltwater intrusion.

Atterberg limits: liquid limit, plastic limit, and shrinkage limit; plasticity index PI = LL − PL; liquidity index = (w − PL)/PI.

Effective stress σ' = σ − u controls strength and consolidation; Terzaghi 1-D consolidation theory gives settlement; OCR = preconsolidation stress / current effective stress.

Mohr–Coulomb strength: τ = c' + σ' tan φ'; drained and undrained (φ = 0, cu) parameters must match the drainage conditions expected in the field.

Slope stability factor of safety FS = resisting shear strength / driving shear stress; for an infinite slope FS = [c' + (γ − mγw) z cos²β tan φ'] / (γ z sinβ cosβ).

Rock mass classification: RQD (percentage of core in intact pieces >10 cm), RMR (RQD, UCS, spacing, joint condition, water), and Q-system (RQD/Jn × Jr/Ja × Jw/SRF).

Landslide triggers include rainfall infiltration, rapid drawdown, seismic shaking, toe erosion, and loading; warning signs include tension cracks, bulging, and tilting trees.

Earthquake size: moment magnitude Mw = (2/3) log10 M0 − 6.07 with M0 in N·m; Modified Mercalli intensity describes observed shaking effects.

Liquefaction susceptibility is highest in loose, saturated, well-sorted sands and silts with a shallow water table and strong shaking; mitigation includes densification and drainage.

Magmatic ore deposits: layered mafic intrusions (Cr, PGE), magmatic sulfide Ni-Cu, carbonatites (REE, Nb), and kimberlites (diamond).

Hydrothermal deposit types: porphyry Cu-Mo-Au, epithermal Au-Ag, volcanogenic massive sulfide Cu-Zn, SEDEX Pb-Zn, Mississippi Valley-type Zn-Pb, skarn W-Cu, and orogenic Au.

Ore deposition mechanisms: cooling, boiling, fluid mixing, pH change, and wall-rock reaction; boiling is especially effective for gold precipitation.

Sedimentary and surficial deposits: banded iron formation, phosphorite, evaporites (potash, gypsum, halite), placer gold and heavy minerals, and roll-front uranium.

Coal rank series: peat → lignite → subbituminous → bituminous → anthracite, tracking increases in vitrinite reflectance, carbon content, and calorific value.

Petroleum system elements: source rock (kerogen types I–IV), maturation (oil window roughly 60–120 °C), migration, reservoir with porosity and permeability, seal, and trap.

Trap types: structural (anticline, fault block) and stratigraphic (pinch-out, reef, unconformity); API gravity classifies light (<35°) and heavy (>20°) oils.

Resource classification: resources include undiscovered and subeconomic material; reserves are discovered, economically recoverable under current prices and technology and are defined by a cut-off grade.