t – metric tonnes.
t/d – tonnes per day.
t/y – tonnes per year.
Tableland – Large elevated region with a relatively low relief surface.
Tailings Storage Facility – Confined area, natural or man-made, that is suitable for depositing the material that remains after the treatment of ore.
Talus – Deposit of large angular fragments of physically weathered bedrock that is usually at the base of a cliff or steep slope.
Talus Slope – In geology it defines a pile of rocks that accumulates at the base of a cliff, chute, or slope.
Taphonomy – Study of what happens to a fossil from the time of deposition to the time that the fossil is discovered.
Tar Sand – Sandstone containing the densest asphaltic components of petroleum which is the end-product of evaporation of volatile components or of some thickening process.
Target – Object at which a survey sighting is aimed.
Tectonics – Study of the movements and deformation of the crust on a large scale including epeirogeny, metamorphism, folding, faulting, and plate movements.
Tectosilicate – Mineral with a three-dimensional framework of silicate tetrahedra. The most common form of minerals in the earth’s crust which include quartz and feldspar.
Temperature Log – Log of the temperature of the fluids in the borehole A differential temperature log records the rate of change in temperature with depth and is sensitive to very small changes.
Tephra – Rock fragments and particles ejected by a volcanic eruption.
Terminal Moraine – Sinuous ridge of unsorted glacial till deposited by a glacier at the location of its farthest advance.
Terrace – Level surface part of the way up a slope and often made by waves or a flowing stream.
Terrain Conductivity – Geophysical method in which EM methods measure directly the average electrical conductivity of the ground. Operates at low induction number.
Terrain-Corrected Gravity – Value obtained after latitude correction, elevation correction, the Eötvös correction, and terrain correction have been applied to gravity data. Sometimes called Bouguer Gravity or Complete Bouguer Anomaly.
Terrain Correction – Correction to gravity data required because the surroundings are not all at the same elevation as the meter. Relief in the immediate vicinity of the station may require special terrain surveying, whereas corrections for more remote relief often are made from a topographic map using a terrain-correction template or zone chart. Alternatively, a correction to seismic data because of the effect of topographic loading on velocity. Also a correction to magnetic or electrical data because of terrain effects.
Terrane – Term used to refer to a piece of the earth’s crust that is usually smaller than a continent but larger than an island.
Terrestrial Planet – Planet similar in size and composition to the earth; especially Mars, Venus, and Mercury.
Terrestrial Sediment – Deposit of sediment that accumulated above sea level in lakes, alluvial fans, floodplains, moraines, and so on, regardless of its present elevation.
Tertiary – Informal sub-era from 65.5 to 2.58 or 1.8 million years ago, depending on how the Quaternary is defined. The Tertiary overlaps with the Neogene Period and is divided into five epochs: the 1) Paleocene, 2) Eocene, 3) Oligocene, 4) Miocene, and 5) Pliocene epochs.
Texture – Rock characteristics of grain or crystal size, size variability, rounding or angularity, and preferred orientation.
Thalweg – Sinuous imaginary line following the deepest part of a stream.
Thermal Conductivity – Measure of a rock’s capacity for heat conduction.
Thermal Expansion – Property of increasing in volume as a result of an increase in internal temperature.
Thermal Neutron – Neutron that is in equilibrium with the surrounding medium such that it will not change energy (average 0.025 eV) until it is captured.
Thermonuclear Reaction – Reaction in which atomic nuclei fuse into new elements with a large release of heat; especially a reaction that is self-sustaining.
Thermokarst – Land surface in Arctic areas characterized by very irregular surfaces of marshy hollows and small mounds formed when ice-rich permafrost thaws.
Thermoremanent Magnetization – Permanent magnetization acquired by igneous rocks in the presence of the earth’s magnetic field as they cool below the Currie point.
Thrust and Nappe Surfaces – Physical arrangement of rock units that results from structurally emplacing older rock over younger rock, usually during orogenic activity
Thrust Fault – Dip-slip fault in which the upper block above the fault plane moves up and over the lower block so that older strata are placed over younger.
Tidal Current – Horizontal displacement of ocean water under the gravitational influence of sun and moon causing the water level to rise relative to the coast at high tide and decrease in level at low tide.
Tidal Flat – Broad, flat region of muddy or sandy sediment covered and uncovered in each tidal cycle.
Till – Unsorted combination of all sizes of sedimentary particles of all sizes, from clay to boulders, mixed together as well as unstratified loose material deposited by a glacier.
Tillite – Rock formed by consolidation of glacial till.
Time Constant – Time in seconds required for an analog system to record 63 percent of the change that actually occurred from one signal level to another.
Time Domain – In geophysics refers to measurements analyzed according to their behavior in time. The usual alternative is frequency domain measurements.
Time Domain Electromagnetics – TDEM methods represent an alternative approach to detecting weak secondary magnetic fields. This works by simply switching the primary field off and observing the decay of the secondary magnetic fields. This method is often referred to as transient electromagnetic exploration (TEM) or time-domain electromagnetic (TDEM) exploration. Measurements are made in the off-times between pulses, usually after the primary field has stopped changing. Principal advantages of transient methods over continuous-wave methods are that the primary field is not present during the measurement of the secondary field and that measurements of the secondary field as a function of time are equivalent to continuous-wave measurements over a wide frequency range.
Time Domain Reflectometry – TDR utilizes a device which measures electrical characteristics of wideband transmission systems. Commonly used to measure soil moisture content.
Tomography – Method for determining the distribution of physical properties within the earth by inverting the results of a large number of measurements made in three dimensions such as seismic, radar, resistivity, or EM, between different source and receiver locations.
Topographic Map – Contour map or drawing of prominent landforms indicated by conventionalized symbols.
Topography – Shape of the earth’s surface above and below sea level acknowledging the set of landforms in a region and the distribution of elevations. It includes the mountains, hills, creeks, and other bumps and lumps on a particular sector of the earth.
Topset Bed – Horizontal sedimentary bed formed at the top of a delta and overlying the foreset beds.
Total Magnetic Intensity – Often referred to as TMI or total magnetic field strength in geophysics, it is a measure of the magnitude of the earth’s magnetic field at a given location.
Tourmaline – Silicate mineral that contains boron and usually occurs as long, black, three-sided, striated crystals. Tourmaline is common in granite pegmatite veins and some metamorphic rocks.
Trace Element – Element that appears in minerals in a concentration of less than 1 percent (often less than 0.001 percent).
Trace Fossil – Evidence left by organisms such as burrows, imprints, coprolites, or footprints.
Tracer Log – Log made for the purpose of measuring fluid movement in a well by means of following a tracer injected into the well bore. These tracers can be radioactive or chemical.
Track – In the petroleum industry this is a term used for the areas in the American Petroleum Institute log grid that are standard for most large well-logging companies; track 1 is to the left of the depth column, and tracks 2 and 3 are to the right of the depth column, but are not separated.
Transducer – Device that converts an input signal to an output signal of a different form. It can be a transmitter or receiver in a logging probe.
Transform Fault – Strike-slip fault connecting the ends of an offset in a mid-ocean ridge. Some pairs of plates slide past each other along transform faults.
Transgression – Rise in sea level relative to the land which causes areas to be submerged and marine deposition to begin in that region.
Transient – Geophysics term referring to occurring when the system is still changing with time; i.e., a steady state has not been attained. Most groundwater flow systems are transient, not steady state.
Transient Electromagnetics – TEM is an electromagnetic surveying method in which the waveform of the transmitted signal is a pulse, step function, ramp or other form which can be considered to be non-periodic and in which measurements are made after the primary field has stopped changing (Shariff, 1973). Generally used as a sounding method for differentiating electrically contrasting geologic media. Also referred to as Time Domain Electromagnetics (TDEM).
Transition Element – Any element belonging to one of three series of elements with atomic numbers between 21 and 30, 39 and 48, and 57 and 80. They are characterized by multiple valences, colored compounds, and the ability to form stable complex ions.
Transpiration – Removal of water from the ground into plants which is then to be evaporated into the atmosphere by them.
Transverse Dune – Dune that has its axis transverse to the prevailing winds or to a current.
Trap – Oil and gas industry term for a sedimentary or tectonic structure that impedes the upward movement of oil and gas and allows it to collect beneath the barrier.
Travel-Time Curve – Curve on a graph of travel time versus distance for the arrival of seismic waves from distant events. Each type of seismic wave has its own curve.
Travertine – Terrestrial deposit of limestone formed in caves and around hot springs where cooling, carbonate-saturated groundwater is exposed to the air.
Trellis Drainage – System of streams in which tributaries tend to lie in parallel valleys formed in steeply dipping beds in folded belts.
Trench – Long and narrow deep trough in the sea floor..
Trenching in Mineral Exploration – Process used to investigate outcrop, soil, and geochemical anomalies by the excavation of narrow trenches across anomalous zones of mineralization to observe geological structures and to allow sampling.
Triassic – Period from 251 to 200 mya divided into three epochs: The Early Triassic Epoch has two Ages: the 1) Induan and 2) Olenekian ages. The Middle Triassic Epoch has two Ages: the 1) Anisian and 2) Ladinian ages. The Late Triassic Epoch has three Ages: the 1) Carnian, 2) Norian, and 3) Rhaetian ages.
Trilobite – Extinct marine animal found as fossil remains that is distantly related to crabs and lobsters.
Triple Junction – Point that is common to three of the earth’s plates and which must also be the meeting place of three boundary features such as divergence zones, convergence zones, or transform faults.
Tsunami – Large destructive wave caused by sea-floor movements during an earthquake.
Tuff – Consolidated rock composed of pyroclastic fragments and fine ash. If particles are melted slightly together from their own heat then it is referred to as a welded tuff.
Turbidite – Sedimentary deposit of a turbidity flow typically showing graded bedding and sedimentary structures on the undersides of the sandstones.
Turbidity Current – Mass of mixed water and sediment that flows downhill along the bottom of an ocean or lake because it is denser than the surrounding water. It may reach high speeds and erode their surroundings rapidly.
Turbulent Flow – High-velocity flow in which streamlines are not straight but instead are curled into small tight eddies.
Twinned Holes – Drill holes that are placed in close proximity to each other with the objective of verifying results of the first of the two holes drilled.