TY  - BOOK
AU  - Ohnmar Soe Yin
TI  - Triassic Ammonite Faunas Of Shan State, Myanmar
PY  - 2010///
CY  - Yangon
PB  - Department Of Geology, University Of Yangon
KW  - Ammonoidea--Fossil
KW  - Geology
KW  - Triasis
KW  - Shan State
N1  - ABSTRACT

The present doctoral thesis deals with taxonomy, biostratigraphy and paleobiogeography of Triassic ammonite faunas reported from the western part of the Shan Plateau. Two ammonite faunas, one from the Kondeik Limestone of Kalaw-Aungban area and the other from the Plateau Limestone of Lungyaw-Indawgaing area, are studied and analyzed in detail.

The present work made it possible to discriminate a total of nine ammonite taxa from the Kondeik Limestone exposed at a small hill located at about one-and-a-half miles northeast of Zegon village, Kalaw Township. They are, namely, Balatonites cf. balatonicus, ? Judicarites sp., Ptychites cf. cochleatus, Meekoceras sp., Ceratites sp., Danubites cf. dritarashtra, Flexoptychites cf. mahendra, Paraceratites cf. thuillieri, Paraceratites sp. indet.

On the other hand, the present work could also recovered a total of seventeen ammonite taxa from a cephalopodal limestone of the Plateau limestone exposed on the west of Indawgaing village, Ywa-ngan Township. They are, namely, Paraceratites cf. thuillieri, Paraceratites cf. himalayanus, Paraceratites sp. indet., Ceratites sp., Meekoceras spp., Beyrichites srikanta, Flexoptychites cf. mahendra, Ptychites cf. cochleatus, Ptychites cf. rugifer, Danubites cf. dritarashtra, Frechites cf. tuberculatus, Bulogites cf. mojsvori, Noetlingites sp., Pseudohollandites cf. onustus, ?Gymnotoceras sp., ? Paracrochordiceras sp. and Proptychites sp.

On the basis of stratigraphic distribution of ammonites in the Kondesk measured section, three ammonite biozones, namely from lower to upper, Balatonites balatonicus zone, Ptychites cf. cochleatus zone and Paraceratites cf. thuillieri zone, are proposed for the ammonite fauna of the western margin of the Shan Plateau. On the other hand, the ammonite fauna of Indawgaing area is designated only as an assemblage, namely, Ptychites cf. cochleatus-Paraceratites cf. thuillieri assemblage because all the ammonite taxa are found assembled in a single limestone bed. This assemblage is considered to be equivalent to the Paraceratites cf. thuillieri zone.

Both the Kondeik and Indawgaing ammonite faunas and biozones are compared and correlated with those of the areas from Tethyan and Mid-continent regions. From this correlation and comparison, it is revealed that both the Kondeik and Indawgaing faunas are Middle Triassic in age (mainly Anisian).

Triassic ammonite faunas of Kondeik area and Indawgaing area can also be considered as a single fauna representing the Middle Triassic fauna of the Shan Plateau. Faunal comparison of the present work reveals that the early Middle Triassic (early Anisian) fauna of the Shan Plateau is characterized by the presence of Meekoceras spp. that have not been reported in other provinces. In the middle Anisian, the Shan Plateau fauna contains two Tethyan genera, Bulogites and Beyrichites, of which Bulogites is of the Western and Central Tethys affinities, but Beyrichites the Eastern Tethys affinity. In the late Anisian, generic diversity of the Shan Plateau fauna is greater than those of the early and middle Anisian. In this time, the Shan Plateau fauna is characterized by the genera Frechites, Ceratites, Ptychites, Flexoptychites and Pseudohollandites and much more closely similar to the Central and Eastern Tethys affinities. In brief, although paleobiogeographic affinity of the ammonite fauna of Shan Plateau cannot be defined clearly in early Anisian, it can be regarded as a Tethyan affinity in the middle Anisian and then exhibits greater similarities to the Central and Eastern Tethys affinities in the late Anisian. In addition, the Ladinian of the Shan Plateau fauna is characterized by Protrachyceras resembling the Central Tethys affinities.

The present ammonite fauna affinities imply that the Shan Plateau as part of the Shan-Thai block would have been in a position between the Indochina block in the north and Lahsa (Himalaya) and West Burma block in the far south under prevailing tropical to subtropical climatic condition during the Middle Triassic period.

A total of 19 known species and two undifferentiated ones assignable to 16 genera can be discriminated in the present work. These taxa are herein systematically described with relevant illustrations; Includes References and Appendices; CONTENTS

ABSTRACT

ACKNOWLEDGEMENTS

CONTENTS

LIST OF FIGURES

LIST OF TABLES

I INTRODUCTION

1.1 General Statements

1.2 Location of the Study Areas

1.3 Purpose of the Present Investigation

1.4 Previous Works

1.5 Regional Geologic Setting

1.6 Materials and Methods of Study

2.1 General Statement

II LITHOSTRATIGRAPHIC FRAMEWORK

2.2 Stratigraphy of the Ammonite-bearing Units in Kondeik Area

2.2.1 Thigaungdaung Limestone

2.2.2 Kondeik Limestone

2.3 Stratigraphy of the Ammonite-bearing Units in Indawgaing Area

2.3.1 Plateau Limestone Group

2.3.1.1 Dolomitic Limestone Unit

2.3.1.2 Cherty Limestone Unit

2.3.1.3 Reefal Limestone Unit

III AMMONITE BIOSTRATIGRAPHY

3.1 Distribution of Shan Plateau Triassic Ammonite Fauna

3.2 Biostratigraphy of the Kondeik Ammonite Fauna

3.2.1 Balatonites balatonicus zone

3.2.2 Ptychites cf. cochleatus zone

3.2.3 Paraceratites cf. thuillieri zone

3.3 Biostratigraphy of the Indawgaing Ammonite Fauna

3.4 Faunal Comparison with Previous Works

3.4.1 Kondeik Fauna

3.4.2 Indawgaing fauna

3.5 Synthesis of Middle Triassic Ammonite Biozones of the Shan Plateau

3.6 Biostratigraphic Correlation

3.6.1 Zonal Correlation with Eastern Tethys Areas

3.6.2 Zonal Correlation with Central Tethys Areas

3.6.3 Zonal Correlation with Southwest China

3.6.4 Zonal Correlation with Western Tethys Area.

3.6.5 Zonal Correlation with Midcontinent Areas

IV PALEOBIOGEOGRAPHY OF AMMONITES

4.1 General Statement

4.2 Faunal Affinity and Paleobiogeography of the Kondeik Fauna

4.3 Faunal Affinity and Paleobiogeography of the Indawgaing Fauna

4.4 Paleogeographic Consideration

V SYSTEMATIC PALAEONTOLOGY OF AMMONITES

VI SUMMARY AND CONCLUSION

VII REFERENCES

PLATES (1-20); Ohnmar Soe Yin; Triassic Ammonite Faunas Of Shan State, Myanmar
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