0-9
A
- Active Folding
- Folding of layers by layer parallel shortening controlled by contrasts in viscosity between layers (buckling)
- Antiform
- Fold in which limbs dip down away from the hinge zone
- Antithetic fault
- An Antithetic fault fault is a fault dipping in the opposite direction to an adjacent master fault or dominating fault set
- Aspect ratio
- Long dimensions divided by short dimensions of an ellipse or rectangle.
- Asperity
- Irregularity along a fracture zone
- Attenuation
- The gradual loss of intensity as a wave propagates through a medium. A seismic wave loses energy as it propagates through the earth.
- Axial plane cleavage
- Cleavage that is subparallel to the axial surface of a fold. The cleavage must have formed during the process of folding. Also called axial planar cleavage.
B
- Back-thrust
- Thrust displacing the hanging wall towards the hinterland. Opposite to the general thrusting direction.
- Backstripping
- Isostatic basin restoration where focus is on the subsidence history of a basin by excessively removing sedimentary sequences and balancing
- Backward modelling
- Starting with the present state and modelling (restoring) back to the pre-deformational stage.
- Blind fault
- Fault that terminates without reaching another fault or the surface. Traditionally used in thrust fault terminology.
- Boudinage
- The process leading to the formation of boudins.
- Box fold
- Fold with two axial planes and two hinge zones that formed simultaneously. Reminiscent of a (bottomless) box in cross-section.
- Breccia
- Cohesive or Non-cohesive fault rocks consisting of randomly oriented fragments resulting from brittle fracturing. Breccia fragments must constitute more than 30% of the rock.
- Brittle deformation
- Deformation by means of brittle deformation mechanisms (fracturing, friction sliding, cataclastic flow).
- Buckle folds
- Folds that form by buckling. They show a certain regularity with regard to wavelength and amplitude as a function of layer thickness and the viscosity contrast between layer(s) and the matrix.
- Buckling
- A folding mechanism that occurs when layers that are more competent than the matrix are compressed parallel to the layering. As stress increases the layer becomes unstable and buckles through the amplification of minute irregularities along the layer interfaces.
- Byerlee’s law
- Relation between critical shear stress on a fracture and the related normal stress across it. The normal stress reflects the depth in the crust, hence this law models critical shear through the frictional upper crust.
C
- Cataclastic flow
- Flow of rock during deformation by means of cataclasis, but at a scale that makes the deformation continuous and distributed over a zone.
- Chevron fold
- Fold with angular hinge and where the axial surface forms more or less perpendicular to sigma 1.
- Chocolate tablet Boudinage
- Boudinage in two directions (in the XY-plane), forming more or less square or rectangular boudins in three dimensions.
- Cleavage refraction
- A change in cleavage orientation across an interface between layers of contrasting competence.
- Coaxial deformation
- Lines along ISA do not rotate during the deformation, Wk = 0. The principal strain axes (X,Y and Z) remain stationary throughout the deformation history.
- Compaction cleavage
- Cleavage formed by lithostatic compaction of sediments into sedimentary rocks. Best developed in mud rocks.
- Competency
- A relative expression that compares the mechanical strength or resistance to flow of a layer or object to that of its adjacent layers or matrix. Competent objects are more resistance to flow than their matrix.
- Compressive strength
- The amount of compression that a rock can withstand before fracturing, usually many times its tensile strength. ( eight times according to Griffith)
- Couette flow
- Simple shear-type flow caused by translation of the overburden relative to the substrate.
- Crenulation cleavage
- Cleavage formed by micro folding at low metamorphic conditions of phyllosilicate-rich and well-foliated rocks.
- Cryoturbation
- Cryoturbation is the mixing of soils by free and thawing process of ground ice. It is mostly found in the Gelisols
- Cylindrical fold
- fold with straight hinge line, so that an imaginary cylinder can be fitted to the hinge zone.
D
- Decollement
- Large scale detachment, fault or shear zone that is located along a weak layer in the crust or in a stratigraphic sequence. The term is used in both extensional and contractional settings.
- Deformation bands (1)
- Millimeter-thick zones of strain localization formed by grain reorganization and/or grain cursing. Shear bands with some compaction across the band from the most common type.
- Deformation bands (2)
- Microscopic zones in a mineral grain with similar optical orientation (extinction), forming between dislocation walls.
- Deformation twins
- The result of mechanical twinning. Deformation twins are common in calcite crystals.
- Deviatoric stress
- The difference between the total stress and the mean stress. Closely related to tectonic stress.
- Dextral
- Right lateral, moving right relative to a point of reference.
- Diapir
- A body, usually of salt, magma or water-saturated mud or sand that gravitationally moves upward and intrudes the overburden.
- Diffusion
- The movement of vacancies in an atomic lattice. Volume diffusion occurs within the lattice while grain boundary diffusion (the diameter of the Mohr circle).
- Dilation band
- Deformation band where displacement is dilation (volume increase) without shear. Dilation bands show an increase in porosity and are relatively uncommon as compared to other types of deformation bands.
- Dip Isogones
- Theoretical lines connecting points of equal dip on the upper and lower boundaries of a folded layer oriented in an upright position (vertical bisecting surface).
- Dipmeter log
- Well log showing dip and azimuth of planar features based on interpretations of resistivity measurements along the wellbore. Measurements are done by running a dipmeter tool through the wellbore, and the planar features represent bedding, deformation bands or fractures.
- Disharmonic folding
- Folds in multilayered rocks that change shape and wavelength along the axial trace.
- Dislocation creep
- Strain accumulation through the movement of dislocations through the crystal, where mechanisms called climb and cross-slip are used to bypass obstacles in the lattice.
- Dislocation glide
- The self-healing (and caterpillar-style) process by which edge dislocations move.
- Dislocation walls
- Concentration of dislocations forming walls within a crystal. Dislocation walls mark the boundary between deformation bands and subgrains.
- Displacement vector
- Vector connecting the positions of a material point (sand grain) before and after deforamtion.
- Domainal cleavage
- Cleavage composed of domains of different minerals, usually micaceous M-domain and quartzo-feldspathic QF-domains. When individual domains are visible in hand sample, the domainal cleavage is a spaced cleavage.
- Dome
- Bowl-shaped geometry with layers dipping in every direction form a summit.
- Doubly Plunging fold
- Fold plunging in two directions because of curved hinge line.
- Drag fold
- Zone of folding on one or both sides of a fault or salt structure. The folding must be related to the fault deformation and /or growth. Originally a genetic term implying that the folding is controlled by frictional resistance along a fault. Now used as a purely descriptive term.
- Ductile deformation
- Continuous deformation at the scale or observation, resulting form any deformation mechanism (brittle/ plastic). Some geologists restrict the term to crystal-plastic deformation.
- Duplex
- Tectonic unit consisting of a series of horses that are arranged in a piggy-back fashion between a sole and a roof thrust. Also used for similar structures in extensional and strike slip settings (extensional and strike-slip duplex).
E
- Epicontinental sea
- A large shallow sea that usually projects inland into a continent.
- Equilibrium Line Altitude
- Equilibrium Line Altitude is the area or zone where Snow accumulation and ablation is equals over the period of the year
F
G
H
I
J
K
- Khondalite
- Khondalite series refers to the rock of gray and red colored foliated garnet-sillimanite schist containig quartz, feldspar and graphite. Khondalites are regarded as the product of ‘dry metamorphism’. The P-T condition of khondalite series are similar to those of the charnokites
L
M
- Mesophytes
- Mesophytes are terrestrial plants which are adapted to neither particularly dry nor particularly wet environments.
N
O
P
- Paralic environment
- These are the marginal environment between the terrestrial and marine.
- Perennial
- Accumulation or flow all over the year
- Photochemical Smog
- Photochemical smog is a type of smog produced when Ultraviolet light coming from the sun reacts with nitrogen oxides and volatile organic compounds in the atmosphere creating brown haze above cities.
- Planation Surface
- Planation surface is a large scale surface that is flat or near flat with possible exception of some residual hills
- Pro-arc foreland basin
- It is formed in the orogenic belt and on the subsiding plate
- Pseudo-Karst
- Glacial caves are sometimes called as pseudo-karst as they also formed below the exposed surface and have streams within. the only difference is that glacial caves are formed by melting rather than dissolution as in the case of Limestone Karst.
Q
R
- Retro-arc foreland basin
- The basin formed close to the orogen but opposite to the subducting plate or on the overriding plate
- Rifting
- A response to upwelling of the asthenosphere, which generates tensile stresses that leads to normal faulting and stretching in the lithosphere
S
- Solum
- Solum is consists of the surface and subsoil layers that have undergone the same soil forming conditions. The base of the solum is the untethered parent material.
- Squall line
- Squall is a Quasi Linear Convective System (QLCS). Squall line is a convective system and a line of thunderstorms forming along or ahead of cold front.
T
U
V
W
X
Y
Z