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The graptolite strata of the Ordovician in the hongyi
area of Jiangxi were first discovered by Zhang Qianshen and others(1964).
Subsequently, the Early Ordovician graptolite strata were report by Xiao
Chengxie and others(1975) from Niupiwan-Niupilong at Guobu of Chongyi.
From August to November, 1978, Xiao Chengxie, Xia Tianliang, Wang Zhaoyun
and Zhou Chonggui made a detailed survey and mapping of the Ordovician
Zhangmuqu section at Guobu and Baishi'ao section at Sishun, with a systematic
collection of graptolites; in 1982, Xiao Chengxie, Chen Hongye and Xie
Wenwei make a further investigation into the Baishi'ao section at Geobu,
Baishi'ao at Sishun, etc., making observation on the Ordovician section
and supplementary collection of graptolites. Later, the writers selected
the better-preserved graptolite specimens from those collected in abundance
by Xiao Chengxie and others over the past years, with a systematic description
of the graptolites from the Ningkuoan of Early Ordovician Assigned to
45 genera, 7 subgenera, 168 species and subspecies, including 3 new species.
The Ningkuoan graptolites in the Chongyi area had been reported for several
times(Yang et al., 1983; Li, 198; Xiao et al., 1985 erected two new subgenera,
namely Oncograptus (Proncograptus) and Cardiograptus (Procardiograptus),
and some new species. Some of the above-mentioned graptolites are revised
in the book.
As a whole, the Early Ordovician strata in Chongyi area belongs to the
graptolitic facies with rich graptolies, especially those of the Ningkuoan,
Whick are more abundant, with more genera and species forming a complete
graptolite sequence, and may be divided into 10 graptolite zones, providing
valuable material for the precise correlation of the Ningkuoan graptolite
zones with those of the same time in the world. On the other hand, the
discovery of Isograptus together with its allied genera is of most essential
significance to the exploration into some curcial problems such as the
evolution, classification of graptolites. Statistics of the diversity
of the graptolite fauna indicates that the high diversity just conincides
with the major development stage of Isograptus and its allied genera,
while the fauna with a lower diversity appeared in the replacement stage
of the replacement stage of the faunas, in which the Anisograpti fauna,
for example, was replaced by the Dichograpti fauna. Statistical data on
changes of the graptolite fauna indicate that the fauna with a greater
change appeared in Xinchang and Ningkuo stages and the Ningkuo and Hulo
stages respectively; the latter is also the boundary between Lower and
Middle Ordovician boundary between Llanvirnian and Llandelian, which represents
the most distinct boundary in the development stage of organisms. In addition,
this book also makes a detailed statistical analysis on the ningkuoan
graptolite fauna in different places of the cirum-Pacific region, with
their genera and species tabulated in a list for correlation. The common
presence of many identical and some comparable in this and other place
shows the close relationship among them. It also has been found thast
in this region the Ningkuoan graptolite fauna is the most abundant among
those of the circum-Pacific region. Moreover, this graptolite fauna can
be taken as a typical representative of the Ningkuoan graptolites of the
Pacific fauna. |
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