Water Quality Issues in India: Geological, Historical and Modern Perspectives
NEW PERSPECTIVES ON THE TAPHONOMY AND GEOLOGICAL …
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Lotosaurus Quarry NW Hunan NEW PERSPECTIVES ON THE TAPHONOMY AND GEOLOGICAL CONTEXT OF LOTOSAURUS ADENTUS (ARCHOSAURIA:POPOSAUROIDEA): RE-EXAMINATION OF THE TYPE LOCALITY FROM THE MIDDLE TRIASSIC BADONG FORMATION, HUNAN, CHINA Cedric J. Hagen 1 , Eric M. Roberts 2 , Jun Liu 3 , Corwin Sullivan 3,4 , Yanyin Wang 3 , Xing Xu 3,4 1 Department of Geology, Macalester College, Saint Paul, MN 55105, USA; 2 Department of Earth and Oceans, James Cook University, Townsville, QLD 4811, Australia; 3 Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; 4 Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China 0 1 2 3 4 5 6 7 8 9 14 13 12 11 10 9 8 7 6 5 4.75 4.5 4.25 4 3.75 3.5 3.25 3 2.75 2.5 2.25 2 1.75 1.5 1.25 1 0.75 0.5 0.25 0 -0.25 -0.5 -0.75 -1 Percentage (%) Phi Figure 7. (Above) Rose diagrams showing pale- ocurrent data taken from ~700 elements in situ (mean vector is 78.1° – 258.1°). The rose on the left was constructed traditionally using Stereonet and the rose on the right was constructed using moving averages. ABSTRACT The Lotosaurus Quarry, traditionally dated to the Anisian, is unique in that it is a dense bonebed from which tens to hundreds of individual bones and partially articulated skeletons of Lotosaurus adentus have been collected since its discovery in 1970. Lotosaurus adentus is a highly unusual sail-backed, edentulous poposauroid pseudosuchian archosaur known primarily from a single locality in Sangzhi County, Hunan Province, south China. Members of our team returned to the Lotosaurus Quarry in 2012 in order to excavate an expansive new region of the bonebed in a search for other Middle Triassic vertebrates. Due to their work over 600 new Lotosaurus bones were exposed and left in situ. Local authorities consequently built a protective structure over the site to facilitate future research and geotourism. Our team mapped the distribution of the exposed fossils and investigated the taphonomy of this important locality in early 2015. Few details were recorded during the original excavations but we have found that the bonebed is a monospecific assemblage, characterised by pervasive disarticulation, a lack of apparent damage from predators and scavengers, and a preferential orientation of elements. Detailed sedimentological analyses of the locality and other exposures of the Middle Triassic Badong Formation were conducted. We also utilized U-Pb detrital zircon geochronology to better constrain the age of the locality and formation, and to help reconstruct sedimentary provenance patterns and paleogeography. Our results indicate that the locality formed in a fluvial-floodplain depocenter with sediment derived from numerous sources, rather than in a tidal flat setting as previously suggested. The presence of a population of younger than anticipated detrital zircons from the bonebed unit indicates that Lotosaurus is likely to be Ladinian in age, rather than Anisian as previously reported. Lotosaurus lies among, or just outside, a grouping of derived poposauroids known from the Upper Triassic of North and South America, making this result more congruent with the phylogenetic projections. Maximum Depositional Age 236.3 +/- 8.0 Ma Maximum Depositional Age 250.8 +/- 3.3 Ma 12 m 13 m 14 m 15 m 16 m 17 m 18 m 19 m 20 m 21 m 22 m 23 m 24 m 25 m 26 m 27 m 28 m 29 m 30 m 31 m 32 m 33 m 34 m 35 m 36 m 37 m 38 m 11 m 10 m 9 m 8 m 7 m 6 m 5 m 4 m 3 m 2 m 1 m 0 m ms ss cs * DZ SAMPLE 16-1-15-3 Lotosaurus Bonebed Figure 2. Magnetostratigraphy of the Badong Formation from Huang and Opdyke (2000). Lotosaurus section shown in Green. See Fig 4. for a more detailed stratigraphic section. A BADONG FORMATION • The Badong Formation exposure at the Lotosaurus locality is ~37m thick , and correlates to the top of member 2 in the Sangzhi area. • Member 2 has traditionally been interpretted as Middle Triassic (Anisian) based of regional biostratigraphy, but minimal previous geologic investigation of the fm near the quarry has been conducted (Liu, 1995; Fig. 1, 2). • These units were interpreted to be from tidal flat environments by Liu (1995), but our study indicates a more continental setting for study area dominated by fluvial-floodplain deposition in a semi-arid setting. 1 m 2 Figure 5. (Above) Lotosaurus adentus bonebed digitized via Adobe Illustrator. Bone elements are color-coded according to criteria described by Getty et. al (2010). Lotosaurus Bonebed Map Hubei Hunan CHINA Lotosaurus bonebed locality Cretaceous Permian Upper Triassic Jurassic Middle Triassic Lower Triassic Silurian Devonian-Carboniferous Ordovician Cambrian Sangzhi A B C Figure 1. Lotosaurus bone bed locality map in Hunan Province, China. A. Map of China; B. Google earth image of northern Hunan Province showing locality of bonebed & other sampling sites in the region; C. Ge- ologic Map of northern Hunan. Arrows show location of sites from B. Figure 3. Photographs of the Lotosaurus bonebed. A. 15 x 15 m exposed bonebed shown in fenced area; B-C. Excavated bonebed with exposed Lotosaurus bones. D-E. Geology of fluvial/floodplain strata of Unit 2 of the Badong Formation at the site. B C E D 0 0.1 0.2 0.3 0.4 0.5 1 59 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101 105 109 113 117 121 125 129 133 137 141 145 149 153 157 161 165 169 181 193 197 201 205 209 213 217 221 225 229 233 237 241 245 249 253 257 261 265 269 273 277 281 285 289 293 297 301 305 309 313 317 321 325 329 333 337 341 n = 698 vector mean: 78.1° - 258.1° Figure 6. (Right) Laser grain size analyses were run for bonebed adentus bonebed. Results indicate a bimodal sediment distribution dominated by fine-sand to silt. Lotosaurus samples to better understand the genesis of the Our data suggest that Lotosaurus adentus is likely to be Ladinian in age, rather than Anisian as previously reported. Our results indicate that this locality formed in a fluvial-floodplain depocenter with sediment derived from numerous sources, rather than in a tidal flat setting as previously suggested. SUMMARY OF RESULTS ACKNOWLEDGEMENTS •Thanks to the National Natural Science Foundation of China for their support of this project under grants 41472017 and 41120124002. •Support for this work was provided by Macalester College through the Beltmann Summer Research Fund. •Thanks to the entire Gravelmonkeys research group (James Cook University), Dr. Ray Rogers (Macalester College) and Dr. Andrew Elstad-Havales (Macalester College) for advice. DZ GEOCHRONOLOGY • The maximum depositional age we find for sample 17-1-15-1A is 252.2 ± 5.9 MA, whereas the maximum depositional age we find for sample 16-1-15-3 is 236.3 ± 8.0 MA (Figure 8). • Our data suggest that Lotosaurus adentus may be slightly younger than previously thought. • Provenance analysis of the sediments suggest that sediment was primarily derived from local sources in the South China Block and do not provide any direct evidence to suggest connectivity between the North and South China Blocks by this time, suggest- ing that Lotosaurus evolved on the South China Block. TAPHONOMY OF BONEBED • This bonebed is a large, monospecific assemblage which shows little to no damage from predators and scavengers, thorough disarticulation, and preferential orientation (Zhang, 1975) (Figure 5). • We believe that the bones primarily accumulated due to the flow conditions in an ancient river. • Fractal analyses will be used to analyze the overall bone distribution. We hope that this work demonstrates that these fractal analyses may be a useful tool in similar, future studies. We will also employ clay mineral analyses in an attempt to address paleoclimate questions. Figure 8. U-Pb detrital zircon frequency distribution plots with histograms shown for samples from the Mid-Triassic Badong Fm and overlying Late Triassic unit. This work suggests a maximum depositional age for the Loto- saurus bonebed of 236.3+/-8.0 Ma. Figure 4. (Left) Stratigraphic section of the Lotosaurus adentus bonebed locality showing the changes in sedimentology between units. The locality is part of Member 2 of the Badong Formation and is characterised by a semi-arid, fluvial and floodplain succession. The bonebed location and detrital zircon sample site are both shown. REFERENCES • Zhang Fa-kui, 1975. A new theocodont lotosaurus from Middle Triassic of Hunan. Vertebrate PalAsiatica Vol. 13, No. 3. • Huang, K., and Opdyke, N.D., 2000. Magnetostratigraphic investigations of the Middle Triassic Badong Formation in South China. Geophysical Journal Interna- tional 142, 74-82. • Liu, S., 1995. Triassic continental strata and conchostracan faunas in China. Albertiana 16.
Transcript of NEW PERSPECTIVES ON THE TAPHONOMY AND GEOLOGICAL …
Lotosaurus Quarry
NW Hunan
NEW PERSPECTIVES ON THE TAPHONOMY AND GEOLOGICAL CONTEXT OF LOTOSAURUS ADENTUS (ARCHOSAURIA:POPOSAUROIDEA): RE-EXAMINATION OF THE TYPE LOCALITY FROM THE MIDDLE TRIASSIC BADONG FORMATION, HUNAN, CHINA
Cedric J. Hagen1, Eric M. Roberts2, Jun Liu3, Corwin Sullivan3,4, Yanyin Wang3, Xing Xu3,4
1Department of Geology, Macalester College, Saint Paul, MN 55105, USA; 2Department of Earth and Oceans, James Cook University, Townsville, QLD 4811, Australia;3Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China; 4Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, China
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Figure 7. (Above) Rose diagrams showing pale-ocurrent data taken from ~700 elements in situ (mean vector is 78.1° – 258.1°). The rose on the left was constructed traditionally using Stereonet and the rose on the right was constructed using moving averages.
ABSTRACTThe Lotosaurus Quarry, traditionally dated to the Anisian, is unique in that it is a dense bonebed from which tens to hundreds of individual bones and partially articulated skeletons of Lotosaurus adentus have been collected since its discovery in 1970. Lotosaurus adentus is a highly unusual sail-backed, edentulous poposauroid pseudosuchian archosaur known primarily from a single locality in Sangzhi County, Hunan Province, south China. Members of our team returned to the Lotosaurus Quarry in 2012 in order to excavate an expansive new region of the bonebed in a search for other Middle Triassic vertebrates. Due to their work over 600 new Lotosaurus bones were exposed and left in situ. Local authorities consequently built a protective structure over the site to facilitate future research and geotourism. Our team mapped the distribution of the exposed fossils and investigated the taphonomy of this important locality in early 2015. Few details were recorded during the original excavations but we have found that the bonebed is a monospecific assemblage, characterised by pervasive disarticulation, a lack of apparent damage from predators and scavengers, and a preferential orientation of elements. Detailed sedimentological analyses of the locality and other exposures of the Middle Triassic Badong Formation were conducted. We also utilized U-Pb detrital zircon geochronology to better constrain the age of the locality and formation, and to help reconstruct sedimentary provenance patterns and paleogeography. Our results indicate that the locality formed in a fluvial-floodplain depocenter with sediment derived from numerous sources, rather than in a tidal flat setting as previously suggested. The presence of a population of younger than anticipated detrital zircons from the bonebed unit indicates that Lotosaurus is likely to be Ladinian in age, rather than Anisian as previously reported. Lotosaurus lies among, or just outside, a grouping of derived poposauroids known from the Upper Triassic of North and South America, making this result more congruent with the phylogenetic projections.
Maximum Depositional Age236.3 +/- 8.0 Ma
Maximum Depositional Age250.8 +/- 3.3 Ma
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* DZ SAMPLE 16-1-15-3
Lotosaurus Bonebed
Figure 2. Magnetostratigraphy of the Badong Formation from Huang and Opdyke (2000). Lotosaurus section shown in Green. See Fig 4. for a more detailed stratigraphic section.
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BADONG FORMATION• The Badong Formation exposure at the Lotosaurus locality is ~37m thick , and correlates to the top of member 2 in the Sangzhi area.
• Member 2 has traditionally been interpretted as MiddleTriassic (Anisian) based of regional biostratigraphy, but minimal previous geologic investigation of the fm near thequarry has been conducted (Liu, 1995; Fig. 1, 2).
• These units were interpreted to be from tidal flat environments by Liu (1995), but our study indicates amore continental setting for study area dominatedby fluvial-floodplain deposition in a semi-arid setting.
1 m2
Figure 5. (Above) Lotosaurus adentus bonebed digitized via Adobe Illustrator. Bone elements are color-coded according to criteria described by Getty et. al (2010).
Lotosaurus Bonebed Map
Hubei
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CHINA
Lotosaurus bonebed locality
Cretaceous
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Figure 1. Lotosaurus bone bed locality map in Hunan Province, China. A. Map of China; B. Google earth image of northern Hunan Province showing locality of bonebed & other sampling sites in the region; C. Ge-ologic Map of northern Hunan. Arrows show location of sites from B.
Figure 3. Photographs of the Lotosaurus bonebed. A. 15 x 15 m exposed bonebed shown in fenced area; B-C. Excavated bonebed with exposed Lotosaurus bones. D-E. Geology of fluvial/floodplain strataof Unit 2 of the Badong Formation at the site.
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n = 698vector mean: 78.1° - 258.1°
Figure 6. (Right) Laser grain size analyses were run for bonebed
adentus bonebed. Results indicate a bimodal sediment distribution dominated by fine-sand to silt.
Lotosaurussamples to better understand the genesis of the
Our data suggest that Lotosaurus adentus is likely to be Ladinian in age, rather than Anisian as previously reported.
Our results indicate that this locality formed in a fluvial-floodplain depocenter with sediment derived from numerous sources, rather than in a tidal flat setting as previously suggested.
SUMMARY OF RESULTS
ACKNOWLEDGEMENTS•Thanks to the National Natural Science Foundation of China for their support of this projectunder grants 41472017 and 41120124002.
•Support for this work was provided by Macalester College through the Beltmann Summer Research Fund.
•Thanks to the entire Gravelmonkeys research group (James Cook University), Dr. Ray Rogers (Macalester College) and Dr. Andrew Elstad-Havales (Macalester College) for advice.
DZ GEOCHRONOLOGY• The maximum depositional age we find for sample 17-1-15-1A is 252.2 ± 5.9 MA, whereas the maximum depositional age we find for sample 16-1-15-3 is 236.3 ± 8.0 MA (Figure 8).
• Our data suggest that Lotosaurus adentus may be slightly younger than previously thought.• Provenance analysis of the sediments suggest that sediment was primarily derived from local sources in the South China Block and do not provide any direct evidence to suggest connectivity between the North and South China Blocks by this time, suggest-ing that Lotosaurus evolved on the South China Block.
TAPHONOMY OF BONEBED• This bonebed is a large, monospecific assemblage which shows little to no damage from predators and scavengers, thorough disarticulation, and preferential orientation (Zhang, 1975) (Figure 5).
• We believe that the bones primarily accumulated due to the flow conditions in an ancient river.
• Fractal analyses will be used to analyze the overall bone distribution. We hope that this work demonstrates that these fractal analyses may be a useful tool in similar, future studies. We will also employ clay mineral analyses in an attempt to address paleoclimate questions.
Figure 8. U-Pb detrital zircon frequency distribution plots with histograms shown for samples from the Mid-Triassic Badong Fm and overlying Late Triassic unit. This work suggests a maximum depositional age for the Loto-saurus bonebed of 236.3+/-8.0 Ma.
Figure 4. (Left) Stratigraphic section of the Lotosaurus adentus bonebed locality showing the changes in sedimentology between units. The locality is part of Member 2 of the Badong Formation and is characterised by a semi-arid, fluvial and floodplain succession. The bonebed location and detrital zircon sample site are both shown.
REFERENCES• Zhang Fa-kui, 1975. A new theocodont lotosaurus from Middle Triassic of Hunan. Vertebrate PalAsiatica Vol. 13, No. 3.
• Huang, K., and Opdyke, N.D., 2000. Magnetostratigraphic investigations of the Middle Triassic Badong Formation in South China. Geophysical Journal Interna-tional 142, 74-82.
• Liu, S., 1995. Triassic continental strata and conchostracan faunas in China. Albertiana 16.
