Download blank geological history table to complete.
Geological history concerns the events that have formed or affected the rocks of an area, arranged in a time-sequence. The standard approach is usually to “Write an account of the geological history of area X”. This often forms an important part of geological reports or background information in theses and papers. We will arrange the information in the form of a summary table. The table will comprise information about:
the relative age of each event, arranged in rows, with youngest at the top,
the type of each event, arranged in columns according to type (depositional, erosional, intrusive, metamorphic, deformation or movement and economic) and
the main characteristics of the events (e.g., the type of unconformity or intrusion, the tightness and direction if folds), entered in the relevant cell in the table
The sequence in the geological history table will be youngest at the top to oldest at the bottom, similar to the arrangement of strata (sedimentary and extrusive volcanic layers that are deposited on the earth’s surface) in a stratigraphical column.
The time sequence will be based on superposition and cross-cutting deduced from contact relations between rock bodies and from relations between structures shown on a map or in outcrop.
Approach deduction of geological history in the following order:
Relief: briefly look for alluvium near drainage lines and hill capping units between drainage lines.
Stratigraphical succession: group conformable units and determine their relative age using younging criteria and strike-dip information of dipping layers.
Unconformities: define these based on angular relationships or non-conformable relationships with the next older event in your history table.
Intrusives: determine the relative timing of intrusive igneous activity (dykes and plutons).
Deformation: uplift, tilts, faults, folds.
Metamorphism: contact or regional.
Economic Mineralisation: always associated with another event on the table (same row).