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Summary Sedimentology and Stratigraphy chapter 19
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Samenvatting Sedimentology and Stratigraphy Gary Nichols Chapter 19: stratigraphy: concepts and lithostratigraphy
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19 Stratigraphy: Concepts and lithostratigraphy“Our observations about rock need to be set in the context of a time framework if we are to use them
to understand Earth processes and history. That framework is provided by stratigraphy, and is one of
the oldest disciplines of the geological sciences. Stratigraphy is primarily concerned with the following
issues: the recognition of distinct bodies of rock and their spatial relationship with each other; the
definition of lithostratigraphic units and the correlation of the lithostratigraphic units with each
other; the correlation of rock units with a chronostratigraphic standard, which is a formal time-
framework to which all of Earth geology can be related. Lithostratigraphy forms the basis for making
geological maps and by correlating lithostratigraphic units it is possible to reconstruct the changing
palaeogeography of an area through time.”
19.1 Geological time
The passage of time since the formation of the Earth is divided into geochronological units they may
be referred to by years or by name.
Before Present: 1950.
Dates:
o Ma = millions of years BP
o Ka = thousands of years BP
o Ga = thousands of millions of years BP
Intervals:
o m. yr.
19.1.1 Geological time units
Geochronology: “houdt zich bezig met het bepalen van de opeenvolging van gebeurtenissen
in de tijd tijdens de geologische geschiedenis en de onderverdeling van die geologische tijd”
Chronostratigraphy: “Het onderdeel van stratigrafie dat zich bezighoudt met de (relatieve)
ouderdom van lagen en hun onderlinge tijdsrelaties”
o Beschrijving en ordening van lagen in termen van (relatieve) tijd.
Geochronometrie: “tak van de geochronologie die zich bezighoudt met het kwantitatief
meten van geologische tijd”
Chronostratigraphy: eenheid vertegenwoordigd alle gesteentes die gevormd zijn tijdens een
bepaalde tijdsperiode (bv. Jura Systeem)
o Divided into lower, middle and upper
Geochronologische: eenheid verwijst naar die tijdsperiode zelf (bv Chattian Age van de
Oligocene Epoch); het is dus geen stratigrafische eenheid.
o Divided into early, middle and late
There is a hierarchical set of terms for geochronological units that has an exact parallel in
geostratigraphical units. This distinction is not made by all geologists.
, Terms of the geochronological units, with the equivalent chronostratigrapic units:
Eons:
Longest periods of the history of the Earth. 3 Eons:
Archaean Eon up to 2.5 Ga Archaean + Proterozoic = Precambrium
Proterozoic Eon from 2.5 Ga to 542 Ma
Phanerozoic Eon from 542 Ma to the
present
Eras:
3 divisions in the Phanerozoic:
Paleozoic era up to 251 Ma
Mesozoic era from 251 Ma to 65.5 Ma
Cenozoic era from 65.5 Ma to the present
Periods/Systems
Basic unit of geological time. Era divided into multiple periods. System is used for the rocks deposited
in this time.
Epochs/Series
Epochs: major divisions of periods; some have names others get early-, mid-, late-.
Series: chronostratigraphic equivalent, with lower-, middle- and late-.
Ages/Stages
Ages: smallest commonly used division.
Stage: chronostratigraphic equivalent.
Chrons: short periods of time that are sometimes determined from palaeomagnetic information, but
these units do not have widespread usage outside magnetostratigraphy.
Geochronologie Chronostratigrafie
Eon Eonothem
Era Erathem
Period System
Epoch Series
Age Stage
Chron Chronozone
19.1.2 Stratgraphic charts
Published geological time scales are constructed by combining: biostratigraphy, magnetostratigraphy
and data from radiometric dating to determine the chronostratigraphy of rock units throughout the
Phanerozoic.
Sedimentary rocks are not called by there age, because this is not definitive, but are called by their
name, based on certain fossils or other characteristics. (19.2)
19.1.3 Golden spikes
Cambrian not defined as the interval of time, because those numbers are currently thoughts to be
the times, but will likely be revised.
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