Chapter 3: Map and Cross-Section Interpretation

angular unconformity

An unconformity between two groups of rocks that are dipping at different angles. The older rocks below are often dipping more steeply than the rocks above.

disconformity

A type of paraconformity in which the rocks above and below are essentially parallel but the unconformity surface is not parallel to the bedding.

eon

Four subdivisions of time on Earth: Three eons - Hadean, Archean, and Proterozoic - cover almost half the time on Earth; the four eon - Phanerozoic - incorporates the Paleozoic, Mesozoi, snd Cenozoic eras

epoch

Subdivision of the Tertiary and Quaternary periods

era

subdivision of the Phanerozoic: Paleozoic, Mesozoic, and Cenozoic

Ga

Abbrviation for Giga-annum; one billion years

GIS

Geographic Information System, A computer system that stores, organizes, analyzes, and displays geographic data.

GPS

Global positioning system, a radio navigation system that allows land, sea, and airborne users to determine their exact location, velocity, and time 24 hours a day, in all weather conditions, anywhere in the world

Ka

Abbreviation for Kilo-annum; one thousand years

key beds

A well-defined, easily identified strata that is distinctive enough to be useful in correlation in mapping

Ma

Abbreviation for Kilo-annum; one million years

magnetic declination

The angle between true North and magnetic North

nonconformity

An unconformity formed by older igneous rocks in the contact with younger sediments, indicating a missing time after the igneous intrusion

paraconformity

An unconformity in which the beds are parallel above and below the break

period

Subdivisions of the three eras: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian in the Paleozoic, Triassic, Jurassic, and Cretaceous in the Mesozoic, and Tertiary and Quaternary in the Cenozoic.

rule of V's

The outcrop pattern of a formation as it crosses a valley forms a V shape (as viewed on a map). The V points in the direction that the formation underlies the valley.

State Plane Coodinate System

A two dimensional coodinate system developed by the National Geodetric Survey for use in the states and counties

Township and Range

A surveyed unit of the Public Land Survey System that forms a 6 mile by 6 mile square and is divided into 36 sections. Townships are measured in rows north and south of a Baseline and Ranges are measured in columns and east and west of a Principal Meridian

unconformity

A ap in the geologic record; an interruption in the depositional sequence that implies uplift and erosion have removed part of the geologic record or non-deposition has occurred