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Australia: The Land Where Time Began |
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The Jehol Biota – Early Cretaceous Wang & Zhou have compared the formation of the site
of the Jehol Biota, the “Mesozoic Pompeii”, to the situation at the time
of the Pompeii disaster when the town of Pompeii was buried beneath
volcanic ash and the people and animals were buried where they fell.
The development of the Jehol Biota occurred over a
relatively short time, geologically speaking, rapidly spreading into a
large area of East Asia, and it was one of the largest terrestrial
vertebrate radiations of the Cretaceous. The fossils of the Jehol Biota
are exquisitely preserved, revealing many evolutionary events of
terrestrial life. The discovery in the western part of Liaoning
Province in the late 1980s and 1990s of birds and feathered dinosaurs
attracted worldwide attention of palaeontologists. In this region there
are several dozen localities where major discoveries of birds and
dinosaurs have been made, mostly by people from the Institute of
Vertebrate Palaeontology and Palaeoanthropology (IVPP) and the Nanjing
Institute of Geology and Palaeontology (NIGP), Chinese Academy of
Sciences. Important discoveries have also been made in the neighbouring
area of Hebei Province and southeastern Inner Mongolia (Nei Mongol
Autonomous Region) that are similar to those from Liaoning. About half a
dozen large-scale excavations have been launched by IVPP field crews
since 1997 in Beipiao, Chaoyang, Fuxin in Liaoning, Fengning in Hebei
and Ningcheng in Inner Mongolia, collecting hundreds of significant
specimens that included fish, amphibians, turtles, aquatic reptiles,
lizards, pterosaurs, dinosaurs, birds and mammals. The climate of the area was warm with plenty of
water in most seasons in the area of the Jehol Biota. Animals and plants
thrived and differentiated in this ideal climate, with lakes being
widespread. Wang & Zhou suggest that some of the water bodies were
probably wide and deep, plants flourishing around the margins of the
lakes. At this time there were frequent volcanic eruptions, and most of
the vertebrates recovered had been preserved in lake deposits in water
that is believed to have been rather deep. Volcanic activity increased throughout the Late
Cretaceous in the area of the Jehol Biota, with at least 3 major
eruptions occurring during the Yixian Formation deposition that were
responsible for the 4 lake deposit-volcanic eruption cycles. Basalts and
Andesites are the major components of the volcanic rocks in the Yixian
Formation, the lake deposits in this formation being mainly formed in
the intervals between the major intermediate-basic eruptions, though
occasionally there were volcanic eruptions that were small-sized and of
intermediate-acid type. At the time the Jiufotang Formation was
deposited volcanic activity was less frequent and relatively weak. The development and evolution of the Jehol Biota
were subjected to an impact of the volcanic eruptions that was
long-lasting. Large volumes of poisonous gases were produced and put in
the atmosphere by the intermediate-acid eruptions which had the
potential to cause the deterioration of the entire ecological system,
such as occurred at the time of the deposition of several layers that
were highly fossiliferous in the Sihetun locality that were preserved
exquisitely indicating major mass mortality events of birds and
feathered dinosaurs. Greyish black lacustrine shale and mudstone are the
main rocks containing the vertebrate fossils, and these are frequently
found covered by a layer of volcanic ash (tuff). Almost all the fossils
preserved are articulated; and birds and dinosaurs often have feathers
visible, with skins and soft tissues often in the form of imprints or
impressions with organic traces. Some of the dinosaur specimens were
uncovered with eggs, Gastroliths and stomach contents, the remains being
identifiable as plant seeds, and the skeletons of lizards and mammals.
Wang & Zhou suggest it is most likely the volcanic eruptions resulted in
environmental changes and it was these that caused the mass mortality of
birds and other vertebrates. It is also suggested that after floating on
the surface of the lakes for a short time the bodies of the dead rapidly
descended into the water where they were buried in deep water, the
deposition process being speeded up by the abundant volcanic ash, the
result being that the dead bodies were rapidly completely preserved, as
occurred in the Pompeii eruption. Among the better known fossil localities of the
Jehol Biota are Sihetun and Lujiatun in Beipiao; Fanzhangzi and Shanzui
(Dawangzhangzi) in Lingyuan; Wanfotang, Hejiaxin, Wujiatun and
Xierhuqiao in Yixian, Jinzhou; Shangheshou, Dapingfang, Lianhe and
Dongdadao in Chaoyang, western Liaoning Province; Schaakou Senjitu in
Fengning, northern Hebei Province; and Daohugou and Xitaizi in
Ningcheng, southeastern Inner Mongolia. Knowledge of the Jehol Biota has been increased
greatly after more than 50 years of research, especially after
the unusual discoveries of the last 10 years, when compared with the
earlier knowledge represented by the
Eosestheria-Ephemeropsis-Lycoptera
(E.E.L. Fauna, as has traditionally been defined). New insights have
been gained on the origin of birds and their flight by recent
discoveries of fossil vertebrates in western Liaoning, and the origin of
feathers, the early radiation of birds, mammals and angiosperms, as well
as furthering understanding of the continental ecosystem of the Early
Cretaceous. The rock layers need to be studied systematically
to determine where the fossils are and the geological age of the rocks
they are embedded in, and these rocks have been studied for many years
before the recent discovery of feathered dinosaurs and birds. An
American geologist, Amadeus W. Grabau was the first to propose the
“Jehol Series” and the “Jehol Fauna” in the 1920s. The Jehol Group which
was introduced into the literature in 1962 by Prof. Zhi-wei Gu. The
Jehol Group is a set of rocks from the Late Mesozoic that consists of
volcanic and lacustrine deposits, interlaced with each other, that are
rich in tuffaceous materials. The Yixian Formation and the Jiufotang
Formation that overlies it comprise the Jehol Group. Northern Hebei Province, western Liaoning Province
and Inner Mongolia in northeast China are the main areas in which the
Jehol Group is distributed. In northeastern Asia the deposits formed in
a series of northeast faulting basins during the late Mesozoic. The
Fuxin-Yixian Basin, Jinlingsi-Yangshan Basin, Beipiao-Chaoyang Basin,
Jianchang-Kazuo Basin, Lingyuan-Sanshijiazi Basin, Pingzhuang-Ningcheng
Basin, and Chifeng-Yuanbaoshan Basin are some of the main basins. In the
western rim of the Pacific vigorous plate collisions led to the
intensive tectonic activities in the eastern margin of the European
continent that occurred at that time. The depositional history in
different basins were complicated by frequent volcanic eruptions and
tectonic activities have increased the difficulty of correlating the
deposits in these basins. The Yixian Formation, Jiufotang Formation, Shahai
Formation, chronologically from earliest to most recent, comprise the
traditional Jehol Group. The lithographic characteristics and fossil
assemblages of the Shahai and Fuxin Formation have been shown by recent
studies to differ greatly from those of the Yixian and Jiufotang
Formations. The Yixian Formation is mostly comprised of basalts and
andesites with interbedded lacustrine sediments composed of tuffaceous
sandstones, grey shales, grey-black shales, mudstones and tuffs. Within
the Yixian Formation 4 beds containing fossils have been recognised. The
Jiufotang Formation is mostly comprised of lacustrine sediments –
greyish, grey-yellow, and grey-black sandstones, siltstones, shales and
mudstones, with intercalated tuffs. Coal deposits and clastics,
occasionally with volcanic contents, are the components of the Shahai
and Fuxin Formations. The Yixian and Jiufotang Formations are the only
formations in which the typical Jehol elements, such as
Eosestheria-Ephemeropsis-Lycoptera
assemblage, as well as the feathered dinosaurs, early birds, together
with some other vertebrates that are distinctive are found. A major
biological radiation event that occurred in the Early Cretaceous is
represented by their appearance in the Yixian Formation, or possibly
slightly earlier deposits, most of which continued through until the
Jiufotang, the result being that a complete history of the Jehol Biota
is recorded in the Yixian and Jiufotang Formations. At present the Jehol
Group is generally accepted as comprising only these 2 formations. There are 5 fossil-bearing beds, or “members”, of
different ages and with distinctive vertebrate assemblages that have
recently been recognised. From the bottom up they are Lujiatun Bed of
the lower Yixian Formation (Jeholosaurus-Repenomamus
assemblage), Jianshangou Bed of the lower Yixian Formation (Lycoptera
sinensis-Confusiornis avian fauna assemblages), Dawangzhangzi Bed, middle
Yixian Formation (Lycoptera
davidi-Hyphalosaurus assemblage), Jingangshan Bed, the upper
Yixian Formation (Lycoptera muroii-Manchurochelys
manchoukuoensis assemblage), and the Boluochi Bed, Jiufotang
Formation (Jinanichthys-Cathayornis
avian fauna assemblage). According to Wang et
al. most of the fossil localities of the Jehol Group can be referred
to 1 of these 5 beds. Jehol Biota
Extension into Southern China – chronological evidence In this paper the authors report that strata that
may correlate with those of localities in which the classic Jehol Biota
have been discovered are also known over much of central and eastern
China, and also in Korea, Japan, Mongolia and Siberia. Based on known
fossil assemblages it has been hypothesised previously that the Jehol
Biota expanded progressively from the classic Jehol area, the younger
representatives covering a progressively increasing geographic range.
The youngest layers containing the Jehol Biota have been interpreted as
being in the East Anhui Province, South China. They present 40Ar/39Ar
dates of a rhyolite sample, that are considered to be robust, of 129 ±
0.2 Ma, from the lower Longwanshan Formation, and for 2 volcanic samples
from the upper Honghuaqiao Formation, of 127.1 ± 1.3 Ma and 128.9 ± 0.9
Ma from outcrops of the Jehol fossils in East Anhui. The authors2
say it is indicated by their results that the fossils in these
formations are time equivalent with fossils of the second phase from the
lower Yixian Formation in western Liaoning, NE China, and the deposition
of these beds is 6 Ma older, at least, than earlier estimates. It is
therefore suggested by their results that there should be a
re-evaluation of the Jehol radiation and migration hypothesis.
1.
Wang, X-l & Zhou, Z-h, in Chang, Mee-mann
(ed.), 2008, The Jehol Fossils: The Emergence of Feathered Dinosaurs,
Beaked Birds, and Flowering Plants, Academic Press
2.
Chang, S.-C., et al. (2012).
"Chronological evidence for extension of the Jehol Biota into Southern
China." Palaeogeography, Palaeoclimatology, Palaeoecology
344–345(0): 1-5.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |