a. The age of a fossil organism or of a particular geologic event or
feature referred to the geologic time scale and expressed in terms either
of time units (absolute age) or of comparison with the immediate
surroundings (relative age); an age datable by geologic methods.
AGI
b. The term is also used to emphasize the long-past periods of time in
geologic history, as distinct from present-day or historic times.
See also:age
Pertaining to or related to geology. The choice between this term and
geologic is optional, and may be made according to the sound of a spoken
phrase or sentence. Geological is generally preferred in the names of
surveys and societies, and in English and Canadian usage. Syn:geologic
AGI
An interface that indicates a particular position in a stratigraphic
sequence. In practice it is commonly a very thin bed.
An area throughout which geological history has been essentially the same
or one that is characterized by particular structural or physiographic
features.
See:geologic section
a. A systematic investigation of an area determining the distribution,
structure, composition, history, and interrelations of rock units. Its
purpose may be either purely scientific or economic with special attention
to the distribution, reserves, and potential recovery of mineral
resources. Syn:geologic survey
b. An organization engaged in making surveys; e.g., a state survey or the
U.S. Geological Survey.
See:geochronology
a. A composite diagram that shows in a single column the subdivisions of
part or all of geologic time or the sequence of stratigraphic units of a
given locality or region (the oldest at the bottom and the youngest at the
top, with dips adjusted to the horizontal) so arranged as to indicate
their relations to the subdivisions of geologic time and their relative
positions to each other. See also:columnar section
b. The vertical or chronologic arrangement or sequence of rock units
portrayed in a geologic column. See also:geologic section
Drilling done primarily to obtain information from which the geology of
the formations penetrated can be determined. Long
See:formation
A written and/or graphic record of the geologic data obtained from
drillhole core and/or cuttings. In noncore drilling, the cuttings are
separated at depth intervals of about 1 m or 2 m and examined. In core
drilling, the core is kept in sequence and examined. The essential
description of core includes lithology, alteration, mineralization, and
structural discontinuities. CF:geotechnical log
A map on which is recorded geologic information, such as the distribution,
nature, and age relationships of rock units (surficial deposits may or may
not be mapped separately), and the occurrence of structural features
(folds, faults, joints), mineral deposits, and fossil localities. It may
indicate geologic structure by means of formational outcrop patterns, by
conventional symbols giving the direction and amount of dip at certain
points, or by structure-contour lines. AGI
Substance that promotes mineral concentration and crystallization during
solidification of rock-forming material, particularly in pegmatite dikes.
Syn:ore-forming fluid; mineralizer. Bennett
Any sequence of rock units found in a given region either at the surface
or below it (as in a drilled well or mine shaft); a local geologic column.
Syn:geological section; stratigraphic section.
See also:geologic column
See:geothermometer
The period of time dealt with by historical geology, or the time extending
from the end of the formative period of the Earth as a separate planetary
body to the beginning of written or human history; the part of the Earth's
history that is represented by and recorded in the succession of rocks.
The term implies extremely long duration of remoteness in the past,
although no precise limits can be set. AGI
An arbitrary chronologic arrangement or sequence of geologic events, used
as a measure of the relative or absolute duration or age of any part of
geologic time, and usually presented in the form of a chart showing the
names of the various rock-stratigraphic, time-stratigraphic, or
geologic-time units, as currently understood; e.g., the geologic time
scales published by Harland et al. (1982), Odin (1982), Palmer (1983), and
Salvador (1985). Syn:time scale
The time unit corresponding with a time-stratigraphic unit; e.g., period,
epoch, or age. See also:geochronologic unit
One who is trained in and works in any of the geological sciences.
AGI