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ISCS
Working Groups
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Working Groups
and Task Group of the International
Subcommission
on Cambrian Stratigraphy
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The Cambrian Subcommission has devised and
approved a plan for subdividing the Cambrian
System into four series and 10 stages. This
four-fold division of the Cambrian supersedes
all previous three-part ("Lower", "Middle" and
"Upper" Cambrian) and two-part ("Lower" and
"Upper" Cambrian) subdivisions that had been
used in the past and which had varying
meanings in different parts of the world. The
two lower series will embrace two stages each,
and the upper two series will embrace three
stages each. Through June 2013, two series
(Terreneuvian and Furongian) and five stages
(Fortunian, Drumian, Guzhangian, Paibian and
Jiangshanian) had been ratified with GSSPs. In
addition, an ASSP has been ratified for the
Jiangshanian Stage. During 2018, the
Miaolingian (previously Stage 3) and the
Wuliuan (Series 5) have been added.
Remaining stages and series to be
defined by GSSPs are Stage 2 through 4 (and
Series 2), and Stage 10. Until GSSPs for
these stages and series are ratified, their
boundary positions are considered provisional.
The Cambrian Subcommission has
formed a Working Group to examine issues
concerning the definition of the Fortunian Stage
base. The base of the stage, which is
conterminant with the bases of the
Terreneuvian Series, Cambrian System,
Paleozoic Erathem and Phanerozoic Eonothem,
was ratified in 1992.
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Working
Group on the Terreneuvian Series and Fortunian
Stage
Chaired by
Maoyan Zhu (China)
A Working Group has been assembled to investigate
the definition of the base of the Fortunian Stage,
which is conterminant with the bases of the
Terreneuvian Series, Cambrian System, Paleozoic
Erathem and Phanerozoic Eonothem. The GSSP for the
base of the Fortunian Stage and conterminant
boundaries was ratified in 1992, and will remain
the standard unless modification of the definition
is recommended by the Working Group, and then
approved by the International Subcommission on
Cambrian Stratigraphy, the International
Commission on Stratigraphy and the International
Union of Geological Sciences.
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Working
Group on the Stage 2 GSSP
Chaired by
Michael Steiner (Germany)
The base of the second stage of the Cambrian has
not yet been defined, and a criterion for defining
the boundary has not yet been determined. Several
fossils have been suggested as criteria for
determining the boundary level. Among them, the
First Appearance Datum (FAD) levels of two widely
distributed microfossils, have emerged as leading
candidates. They are the micromollusk
(rostroconch) Watsonella
crosbyi and the mollusk Aldanella
attleborensis.
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Working
Group on the Stage 3 GSSP
Chaired by
Xingliang Zhang (China)
The base of Cambrian Stage 3, which is also the
base of Cambrian Series 2, has not been defined.
This boundary is expected to be marked by a
significant and widely recognizable event that
will divide the lower half of the Cambrian
subequally into a subtrilobitic series and a
trilobite-dominated series. The FAD of trilobites,
with its historic aspects, is a possibility for
the boundary position. However, precise
correlation of a horizon marked solely by the FAD
of trilobites will be difficult because trilobites
appear in strata at slightly different times in
different regions. It is more likely that the FAD
of a Small Shell Fossil (SSF) will be selected as
the primary marker of the boundary.
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Working
Group on the Stage 4 GSSP
Chaired by James
B. Jago (Australia)
The base of provisional Stage 4 has not been
formally defined. One level, the base of the
interval bearing the eodiscoid trilobites Hebediscus, Calodiscus, Serrodiscus,
and Triangulaspis,
referred to as the HCST band has been suggested as
a potential stage marker. Another possibility for
the base of Stage 4 is a level coinciding with the
FAD of a single trilobite species. Possibilities
include a species of Olenellus (s.l.), Redlichia
(s.l.), Judomia
or Bergeroniellus.
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Working
Group on the Stage 10 GSSP
Chaired by Per
Ahlberg (Sweden)
The base of Cambrian Stage 10, the uppermost stage
of the Furongian Series and the Cambrian System,
is undefined. The Cambrian Subcommission favours
marking the base at or close to the FAD of the
cosmopolitan agnostoid Lotagnostus americanus. L. americanus
co-occurs with the polymerid trilobite Hedinaspis in
certain regions, and the FAD of Hedinaspis
can be used as a proxy marker for the level of L. americanus
where L.
americanus is absent. Two conodont
species, Eoconodontus
notchpeakensis and Cordylodus andresi,
also have been suggested as possible markers for
the base of the uppermost Cambrian stage.
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Web
Page Task Group
Chaired by
Malgorzata Moczydlowska-Vidal (Sweden)
Webmaster is
Michael Streng (Sweden)
The Web Page Task Group facilitates web-based
communication about progress toward definition of
chronostratigraphic boundary positions within the
Cambrian System.
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