The Yangtze Platform (or Southwest China Platform)
is represented by Cambrian outcrops in the Chinese Guizhou, Hubei, Sichuan,
Yunnan, Guangxi, southern Shaanxi, Anhui and Jiangsu provinces. Cambrian
deposits in this area predominantly consists of carbonates which were formed
on a huge platform that was continuously sloping towards the present-day
southeast and created distinct facies belts in this direction.
The outer Jiangnan belt in the southeast is characterized
by lithofacies of dark grey or black silty and shaly sediments in association
with dark limestones. It apparently continues into South Korea. However,
along the western margin, the Cambrian is composed of detrital rocks, such
as sandstones and shales, deposited in an inner detrital belt landward
to the carbonate platform.
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The Proterozoic (Sinian)-Cambrian boundary
on the Yangtze Platform: a carbonate succession with numerous unconformities.
Copyright (c) G. Geyer, 1997
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Earliest Cambrian calcareous deposits are well known
for their Small
Shelly Fossil faunas, such as the Meishucun Formation, but commonly include
major hiati. The middle part of the Lower Cambrian is dominated by sandstones
and shales in an inner carbonate belt and by coarser clastics in the inner detrital
belt, whereas latest Early Cambrian sediments are usually limestones and dolostones.
The Middle and Upper Cambrian sequences, if present, are variably developed
but generally dominated by calcareous deposits.
Naraoia longicaudata, a soft-bodied trilobite.
Specimen with largely exfoliated thorax exposing preserved appendages.
The biofacies clearly portrays the paleogeographic and
bathymetric situation and is characterized by benthic or nektobenthic trilobite
assemblages. Many genera of redlichioid and ptychoparioid trilobites lived in
this area, especially in the inner detrital belt. Of particular interest is
the Chengjiang
fauna from the middle Early Cambrian Qiongzhusi stage of Yunnan, one of the
most important fossil
archives.
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The Chengjiang fossil lagerstätte:
Major outcrop in the Qiongzhusi Formation
near Chengjiang, Yunnan Province
Copyright (c) E. Landing, 1997
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Korea
by Duck Keun Choi, Seoul
Cambro-Ordovician sedimentary rocks in Korea, the so-called Choson Supergroup,
are mainly exposed in the central-eastern part of the Korean Peninsula. The
sediments consist predominantly of carbonates with lesser amounts of sandstones
and shales. The supergroup has been differentiated into the Taebaek, Yongwol,
Yongtan, Pyongchang, and Mungyong groups based on distinct lithologic successions
and geographic distribution. The Taebaek, Yongwol, and Mungyong groups are fossiliferous,
whereas no trilobites have been reported from the Yongtan and Pyongchang groups.
The Cambrian trilobite faunas of the Taebaek Group have been known to belong
to the Hwangho Faunal Province indicating shallow inner shelf, whereas those
of the Yongwol Group belong to the Jiangnan Fauna representing deeper-water
slope to basinal environment. The Ordovician faunal similarity between the two
areas suggests a progressive shallowing in the Yongwol area, while shallow marine
setting was maintaining in the Taebaek area. These Ordovician trilobite faunas
of Korea provide a biogeographic connection to North China. The later early
Paleozoic sedimentary basin in Korea was a continental margin-type depression
which was presumably connected through contiguous shallow waters to the North
China block.
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The lower part of the Machari Formation (Middle to Upper Cambrian) seen
in this photo is strongly deformed. It yields the trilobites Glyptagnostus
reticulatus and Olenus asiaticus indicative of a lowermost
Upper Cambrian age at this level.
Copyright (c) D. K. Choi, 1999
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The milky white to light brown, coarse-grained quartz arenites
represent the Lower Cambrian Changsan Formation,
the lowermost formation of the Taebaek Group.
Further
reading