General paleo environmental interpretations with ostracod tool

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Adopted taxonomic classification (Fossil Ostracods)

(Moore, 1961; Hou & Chen, 1962; LSP, 1981; Hao & Mao, 1993; Holmes & Chivas, 2002; Liebau, 2005; ∗) Since 1961, many researchers have been contributing to perfect the classification (the milestones of ostradological development in early times summarized here in Tab. 2-1-5-A). It seems as if impossible to form a stable framework. Liebau (2005) proposed the preliminary revised classification of ostracoda. But the common result has not been made officially. In my work, I still followed mainly the Treatise classification (Moore, 1961) (Tab. 2-1-5-B) but distil the later achievements by other ostracodologists for some new taxa. At the same time, integrated with the study on living ostracoda, I agree with getting to the unified routine in taxa, e.g. “oidea” is adopted as the uniform postfix for Superfamily here (Holmes & Chivas, 2002, p.8).

Dongpan Section (DP)

84 samples were collected from the Bed 2 to Bed 12 of the Dongpan Section (Fig.1-B). 41 samples from mudstones, siliceous mudtones, muddy siliceous rocks and bedded siliceous rocks yielded more than 1,600 ostracods (remarks: some samples were combined or added to samples in Yuan et al. (2007)). In general, ostracods were abundantly yielded and diverse in some samples but majority of them were in very poor preservation. 28 genera and 50 species with 2 new species Bairdia dongpanensis Yuan & Crasquin-Soleau, 2007 and Spinomicrocheilinella anterocompressa Yuan & Crasquin-Soleau, 2007 distributed in 26 samples (mainly below the Bed 6) were recognized (Fig.3-1-A). There are still many undetermined specimens excluded in this work.

Liuqiao Section (LQ)

38 samples were collected along the Liuqiao Section (Fig.1-B) and processed. About 480 ostracods were yielded from 20 samples of siliceous mudstones and muddy siliceous rocks. The ostracod fauna has not so high abundance as in the Dongpan Section, but has rather high diversity. 21 genera and 39 species (1 new genus Denticupachydomella n.gen. and 1 new species Denticupachydomella spinosa n.sp. are proposed) have been recognized (Fig.3-1-B).

Shaiwa Section (SW)

The Shaiwa section (Fig.1-B) was sampled according to each sub-bed, 87 samples collected in total. Only 16 samples from siliceous mudstones yielded few ostracods (about 250 individuals) in very poorly preservation. 14 genera and 37 species (1 new species Pseudobythocypris guiqianensis n.sp. is proposed) were identified (Fig.3-1-C). Some of them are still in open nomenclature due to the poor.

Chaohu Section (CH)

25 samples and 12 samples were collected respectively from the siliceous mudstones and mudstones (marl) along the Chaohu section (Fig.1-B). The samples were extracted with two different methods according to the lithology (details see §3.2 Methodology). However, there was still not any microfossil found from the samples of mudstone. All the 420 specimens were yielded from 15 samples of siliceous mudstone. This ostracod fauna is very poor in diversity (5 genera and 14 species as shown in Fig.3-1-D). Remarks: In the figures above, the numbers in the third row/column correspond to the bed numbers.
The arrows indicate the positions of the studied samples. The numbers labeled in the ostracod distribution are sample numbers.

General features and correlation with previous studies

The discovered material is exceptional because this is the first time that ostracods are extracted and identified from Latest Permian deep facies. In general, the discovered ostracod faunas are relatively diverse although many samples did not yield any species (especially in the Shaiwa Section). Some samples of siliceous mudstone and muddy siliceous rock yielded relatively high diversity of ostracods, As the diversity, some samples yielded abundant specimens such as the sample 03DP 3-14, 278 individuals picked. In contrary, some samples are barren. Generally, in the relatively abundant horizons, the diversity is relatively higher. However, the diversity and abundance are not strictly corresponding.
In most of case, the species are represented by very few specimens (one or two). The ostracod faunas are dominated by small, thin-shelled individuals with length between 0.2mm-0.5mm, except most of Kirkbyoidea and some ornamented Bairdioidea which are larger than 0.6mm (<1.1mm). As mentioned above, many individuals are very poorly preserved. The faunas are mainly represented by single valves (e.g. in the Dongpan Section, only 139 carapaces vs. >1 500 valves), some of which are incomplete and thus indeterminate for identifying. One possible reason for the poor preservation is that the shells are so thin that they could not endure the complex process of sedimentation and laboratory extraction. However, the delicate ornamentations were still very well preserved in some specimens (e.g. very fragile spine and delicate striae presented in Bythocytheridae).
This indicates that the faunas have not been transported. For the delicate specimens living a crawler life, the soft substrate may be needed. However, if the substrate was soft, there should be many complete 2008/5 PhD dissertation of University of Pierre Marie Curie & China University of Geosciences (Wuhan) 95 carapace well preserved. But in fact, the discovered faunas are dominated by single valves. Thus the delicate specimens could be swimmer as proposed by Becker & Bless (1990, p.423). The substrate might be hard with very low sedimentation rate so that the delicate ornamentation can be preserved.
In the taxonomic view, the ostracod faunas are composed of three orders (Palaeocopida, Podocopida and Myodocopida). The species number and percentage for each order in studied sections are list in the table below (Tab.3-2-A). The Palaeocopids had been considered as the index Paleozoic ostracods, until recently they were reported from the lowermost Triassic strata of Australia, Pakistan, South China, Hungary and Turkey and considered as the survivors in the earliest Triassic (Jones, 1970; Sohn, 1970; Zheng, 1976; Wang, 1978; Kozur, 1985a; Hao, 1992a; Crasquin-Soleau et al., 2004a, 2004b, 2007; Crasquin-Soleau & Kershaw, 2005). However, the generally low percentage of the palaeocopids indicates the clear decline of this order in the latest Permian. In the studied sections, the fauna in the Liuqiao Section has the highest percentage of Palaeocopids. This may imply that the Liuqiao Section was not only underlied the Dongpan Section but the earliest sedimented among the studied sections. If so, the percentage of Palaeocopida may be considered as an index for stratigraphic comparison during the Latest Permian. The higher the percentage of Palaeocopida is, the earlier the strata were deposited. The heavily shelled and strongly ornamented Bairdiidae (e.g. the genera Mirabairdia, Abrobairdia, Lobobairdia, Petasobairdia), which are the important Mesozoic representatives or affinities, are found here in the latest Permian strata. This type of Bairdiidae has been also reported from the Late Permian of other localities in South China and Turkey (Chen & Shi, 1982; Shi & Chen, 1987; Crasquin-Soleau et al., 2004a, b). This indicates that the first new comers in the earliest Triassic have begun to appeare in the studied sections. The studied horizons should belong to the mixed interval during the Permian-Triassic transition.

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General paleo environmental interpretations with ostracod tool

The interpretation of paleoenvironment related to the family/superfamily has been undertaken by many pioneering researchers (e.g. Gründel, 1961; Blumenstengal, 1965; Peterson & Kaesler, 1980;
Lethiers, 1982; Crasquin, 1984; Casier, 1987, 2004; Melnyk & Maddocks, 1988; Wang, 1988b; Kozur, 1991b; Casier et al., 2003, 2005; Crasquin-Soleau et al., 2006). The paleoenvironmental interpretation on the families and superfamilies here are based on studies by these authors. Yuan Aihua: Latest Permian Deep-Water Ostracod (Crustacea) Fauna from South China 2008/5 100 The Youngiellidae are the indicator of onshore conditions (the environment see Fig.4-1)∗. The Kirkbyidae are representatives of the inner platform. The Amphissitidae, Scrobiculidae, and Kellettinidae were the typical neritic ostracods. The Paraparchitidae were marine inhabitants and showed tolerance to some extreme environments such as with the abnormal salinity, but were absent beyond the outer shelf. The Bairdioidea exclusively represent neritic and shallow to deep open-marine environment with normal salinity. The heavily shelled and strongly ornamented bairdioids usually live in the shallow environment with high energy, whereas the elongated, thin-shelled or delicately spinose baridioids are found in the deeper environments (e.g. the acuminate Acratia). The heavily spined Bythocytheridae, Tricorninidae, Berounellidae and Rectonariidae are known as the paleopsychrospheric elements which indicate a deep (bathyal or abyssal), calm and cold environment (detail introduction see below 4.2). The Cavellinidae are eurybathic. The large cavellinids were common in the nearshore environments with high terrigenous influx, whereas the smaller ones lived further offshore. The Healdioidea appear to prefer the relatively nearshore, muddy environments below the wavebase, but the healdiid species with strong spines are considered as the paleopsychrospheric elements. The Entomozoidea live a pelagic/nektobenthic life in open-marine, but not necessary deep, environments. According to the fundamentals above, the proportion of the families/superfamilies found in this work can be grouped as below in the table (Tab.4-1-A) (at specific level).

Table of contents :

Chapter 1 Regional Geology and Stratigraphic Correlation
§1.1 Description of sections
1.1.1 Dongpan Section (DP) & Liuqiao Section (LQ)
1.1.2 Shaiwa Section (SW)
1.1.3 Chaohu Section (CH)
§1.2 Stratigraphic correlation
1.2.1 Permian-Triassic Boundary
1.2.2 Section Correlation
Chapter 2 Taxonomy of Ostracoda
§2.1 Generality on ostracods
2.1.1 Soft parts of living ostracods
2.1.2 Reproduction and ontogeny
2.1.3 Shell morphology
2.1.4 Principles for orientation and measurement
2.1.5 Adopted taxonomic classification (Fossil Ostracods)
§2.2 Methodology
2.2.1 Sampling
2.2.2 Extracting
2.2.3 Picking, scanning and identifying
§2.3 Systematic descriptions
Chapter 3 General features and distribution of ostracod faunas
§3.1 Ostracod distribution in studied sections
3.1.1 Dongpan Section (DP)
3.1.2 Liuqiao Section (LQ)
3.1.3 Shaiwa Section (SW)
3.1.4 Chaohu Section (CH)
§3.2 General features and correlation with previous studies
Chapter 4 Paleoecological analysis
§4.1 General paleo environmental interpretations with ostracod tool
§4.2 Paleobathymetric variation
4.2.1 Introduction of concept
4.2.2 Adopted model
4.2.3 Paleobathymetric evaluation on ostracod faunas
4.2.4 Integration with other data
§4.3 Oxygen level reconstruction
4.3.1 Oxygen level reconstruction by other data
4.3.2 Generality on ostracod alimentation mode
4.3.3 Oxygen level reconstruction on ostracods
4.3.4 Discussion
Chapter 5 Was there an « Extinction Event » in Deep Water Ostracod Faunas?
§5.1 Review on ostracod extinction during Permian-Triassic events
§5.2 “Extinction event” in the studied ostracod faunas
5.2.1 Discussion on several hotspots related to the extinction event
5.2.2 Concrete discussion on Dongpan and Liuqiao faunas
5.2.3 Comparison and Discussion
Chapter 6 Conclusions and Perspectives
§6.1 Conclusions
§6.2 Perspectives


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