The term “First Appearance Datum” (FAD) is commonly used by geologists and paleontologists to designate the initial occurrence of a species in the geologic record. When determining the FAD, scientists identify the oldest known fossil of a particular species discovered to date.

Here are some key points about FADs:

Definition: The FAD marks the first appearance of a species in the rock layers.
Significance: FADs are essential for defining segments in the geologic time scale.
Global Boundary Stratotype Section and Point (GSSP): A specific FAD can be used to establish a GSSP, which serves as a reference point for defining geologic boundaries.

to fossilized remains that have been moved from their original location. Here are some interesting examples:

Chucarosaurus diripienda:
About 90 million years ago, this ginormous long-necked dinosaur roamed what is now Patagonia, Argentina. Measuring nearly 100 feet (30 meters) long, it was a titanosaur, the largest of the long-necked dinosaurs.
The fossils of Chucarosaurus were so heavy that they caused a traffic accident during transport to Buenos Aires for study.
Remarkably, the bones were unscathed and even managed to break the asphalt of the road!
Its scientific name reflects this adventure: Chucarosaurus diripienda—where “Chucaro” means “hard and indomitable animal” in Quechua, and “diripienda” means “scrambled” in Latin1.
Climate Change and Transport:
The transport sector, which still relies on burning fossil fuels, contributes significantly to energy-related emissions.
With 95% of the world’s transport energy coming from fossil fuels, this sector produces a quarter of all energy-related emissions.
Extreme weather events due to climate change can disrupt transportation and infrastructure.
Investing in climate-resilient transport infrastructure is crucial to mitigate these effects2.
Adapting Ports in Asia-Pacific:
Upgrading transport infrastructure for climate resilience is essential.
A study estimated that adapting 53 ports in the Asia-Pacific region could cost between $31 to $49 billion.
However, the World Bank suggests that the overall net benefits of investing in resilient infrastructure could amount to $4.2 trillion over the lifetime of new infrastructure2.

A dispersion of one immiscible liquid into another through the use of a chemical that reduces the interfacial tension between the two liquids to achieve stability.

Two emulsion types are used as muds:

oil-in-water (or direct) emulsion, known as an "emulsion mud"
water-in-oil (or invert) emulsion, known as an "invert-emulsion mud."
The former is classified as a water-base mud and the latter as an oil-base mud.

A type of damage in which there is a combination of two or more immiscible fluids, including gas, that will not separate into individual components. Emulsions can form when fluid filtrates or injected fluids and reservoir fluids (for example oil or brine) mix, or when the pH of the producing fluid changes, such as after an acidizing treatment. Acidizing might change the pH from 6 or 7 to less than 4. Emulsions are normally found in gravel packs and perforations, or inside the formation. Most emulsions break easily when the source of the mixing energy is removed.

However, some natural and artificial stabilizing agents, such as surfactants and small particle solids, keep fluids emulsified. Natural surfactants, created by bacteria or during the oil generation process, can be found in many waters and crude oils, while artificial surfactants are part of many drilling, completion, or stimulation fluids. Among the most common solids that stabilize emulsions are iron sulfide, paraffin, sand, silt, clay, asphalt, scale, and corrosion products. Emulsions are typically treated using mutual solvents.

A worldwide grid system of rectangular map coordinates that uses metric (SI) units. A location is specified on the basis of its location within one of 60 zones worldwide of 6° of longitude and 8° of latitude each that are subdivided into subzones that are 100,000 m [330,000 ft] on each side. Locations consist of a series of numbers and letters that can be accurate to within an area of one square meter. The headquarters of the Geological Society of America are at 13TDQ8743172 (Merrill, 1986). Information about the UTM grid, including grid ticks on quadrangle maps, can be found on most maps produced by the US Geological Survey. Latitude and longitude coordinates, or geographic coordinates, are another means of locating a point at the Earth's surface, but the accuracy, computer compatibility, and uniqueness of UTM have resulted in its finding acceptance within the scientific community.

A partial differential equation describing the variation in space and time of a physical quantity that is governed by diffusion. The diffusion equation provides a good mathematical model for the variation of temperature through conduction of heat and the propagation of electromagnetic waves in a highly conducting medium. The diffusion equation is a parabolic partial differential equation whose characteristic form relates the first partial derivative of a field with respect to time to its second partial derivatives with respect to spatial coordinates. It is closely related to the wave equation.
∇2E = j ω μ σ E,where
E = electrical field
ω = angular frequency
μ = magnetic permeability
σ = electrical conductivity
∇ = vector differential operator.

Vint = [(t2 VRMS22 − t1 VRMS12) / (t2 − t1)]1/2,

where
Vint = interval velocity
t1 = traveltime to the first reflector
t2 = traveltime to the second reflector
VRMS1 = root-mean-square velocity to the first reflector
VRMS2 = root-mean-square velocity to the second reflector.

ε ≡ ½ [(C11 − C33) / C33] = ½ [(VP⊥2 − VP∥2) / VP∥2]

P-wave parameter (ε) for a medium in which the elastic properties exhibit vertical transverse isotropy, where C11 is the horizontal P-wave modulus (perpendicular to the symmetry axis), C33 is the vertical P-wave modulus (parallel to the symmetry axis), VP⊥ is the horizontal P-wave velocity and VP∥ is the vertical P-wave velocity.

η = (ε − δ) / (1 + 2δ)

Anellipticity of P-wave phase slowness for a medium in which the elastic properties exhibit vertical transverse isotropy. Eta (η) is the anellipticity and ε and δ are the P-wave anisotropy parameters. When ε and δ are equal, η = 0 and the P-wave phase slowness is an ellipse. When ε = δ = 0, the P-wave phase slowness is isotropic.

Relation of group velocity to phase velocity. As a wave travels through a medium, its energy moves at the group velocity (vg) and its individual phases, or components, move at their phase velocity (vp). The wave changes shape with distance as each frequency (f), or wavelength (λ), component moves at its separate phase velocity through the phenomenon of dispersion. Relative to the group velocity, each component moves with faster or slower phase velocity, depending on how phase velocity changes with wavelength or frequency.

amplitude variation with offset
bright or dim spot(s) in amplitude as a result of variations in lithology and pore fluids, sometimes occurring in groups of stacked reservoirs
change or reversal in polarity because of velocity changes, also called phasing
conformity with local structures
diffractions that emanate from fluid contacts
flat spot that represents a fluid (gas-oil or gas-water) contact, which can also show the downdip limit of the reservoir in some cases
gas chimneys above leaking reservoirs
shadow zones below the accumulation
velocity push-down because of lower velocities of hydrocarbons than rocks
difference in response between reflected pressure and shear energy.
Hydrocarbon indicators are most common in relatively young, unconsolidated siliciclastic sediments with large impedance contrasts across lithologic boundaries, such as those in the Gulf of Mexico and offshore western Africa. An ongoing issue in exploration for hydrocarbon indicators is the difficulty in distinguishing between gas accumulations and water with a low degree of gas saturation ("fizz water").

the main magnetic field.
the crustal field.
external disturbance field.
local magnetic interference.
The significance of these contributions to direction, strength and stability of the magnetic field varies with geographic region and with magnetic survey direction.

(1.) ∇·D = ρ

(2.) ∇×H = J + (∂D/∂t)

(3.) ∇·B = 0

(4.) ∇×E = −(∂B/∂t),

where
D = electric displacement
ρ = electric charge density
H = magnetic field strength
J = electric current density
B = magnetic flux density
E = electric field strength.

Equation (1) is equivalent to Coulomb's law, the inverse square attraction of static electric charges. Equation (2) is Ampere's law relating magnetic fields and currents, which was extended by Maxwell to include induction of a magnetic field by a time-varying electric displacement. Equation (3) is Coulomb's law for magnetic flux, expressing the absence of isolated magnetic charges. Equation (4) is Faraday's law of induction, relating an electric field to a time-varying magnetic flux. Maxwell's equations are the starting point for all calculations involving surface or borehole EM methods.

μ = τ / γ = (ΔF/A) / (ΔL/L),

where
μ = Shear modulus
τ = Shear stress = ΔF/A
ΔF = Increment of shear force
A = Area acted on by the shear force
γ = Shear strain = ΔL/L
ΔL = Increment of transverse displacement parallel to A
L = Original length.

V/I = R.

vp = vg + λ (∂vp/∂λ) = vg − f (∂vp/∂f)

Relation of phase velocity to group velocity. As a wave travels through a medium, its energy moves at the group velocity (vg) and its individual phases, or components, move at their phase velocity (vp). The wave changes shape with distance as each frequency (f), or wavelength (λ), component moves at its separate phase velocity through the phenomenon of dispersion. Relative to the group velocity, each component moves with faster or slower phase velocity, depending on how phase velocity changes with wavelength or frequency.

σ = ½ (VP2 − 2VS2) / (VP2 − VS2)

Note that if VS = 0, then Poisson's ratio equals 0.5, indicating either a fluid, because shear waves do not pass through fluids, or a material that maintains constant volume regardless of stress, also known as an ideal incompressible material. Poisson's ratio for carbonate rocks is ~0.3, for sandstones ~0.2, and greater than 0.3 for shale. The Poisson's ratio of coal is ~0.4.

δs = (2/σμω)1/2 = (2/σ)(ε/μ)1/2,

where
δs = skin depth
σ = electrical conductivity
ω = 2πf = angular frequency in radians/s
f = frequency in Hz
μ = μrμ0 = magnetic permeability
μr = relative magnetic permeability of the conductor
μ0 = relative magnetic permeability of free space = 4π × 10−7 newton per ampere squared (N/A2)
ε = εrε0 = dielectric permittivity
εr = relative dielectric permittivity of the material
ε0 = dielectric permittivity of free space = 8.854 × 10−12 farads per meter (F/m).

Z = VI/2.8 fmax,
where Z = tuning thickness of a bed, equal to 1/4 of the wavelength
VI = interval velocity of the target
fmax = maximum frequency in the seismic section.
The equation assumes that the interfering wavelets are identical in frequency content and are zero-phase and is useful when planning a survey to determine the maximum frequency needed to resolve a given thickness. Spatial and temporal sampling requirements can then be established for the survey.

E = (F/A) / (ΔL/L),

where
E = Young's modulus
F = longitudinal force
A = area
F/A = longitudinal stress
ΔL = change in length
L = original length
ΔL/L = longitudinal strain.