Césari, S. N., and Colombi, C. E. 2013. A new Late Triassic phytogeographical scenario in westernmost Gondwana. Nature Communications 4, Article number: 1889 doi:10.1038/ncomms2917
Abstract - Floral provincialism within the Southern Hemisphere during the Late
Triassic (230 Ma) is characterized by the Ipswich and Onslow provinces, recognized originally in eastern Gondwana. However, new palynological assemblages from the Ischigualasto Formation, northwestern Argentina (231–225 Ma), change the phytogeographic interpretation for the Carnian–Norian in the westernmost Gondwana,
which was previously considered part of the southern floral Ipswich province. Here we show the presence of diagnostic Euramerican species within assemblages dominated by Gondwanan taxa that allows us to refer the palynofloras to the Onslow province. Our new data extend the Onslow floral belt, previously recognized from the western edge of Tethys to Timor, to the western margin of South America. This has implications for palaeophytogeography, palaeoclimate reconstructions and the palaeoecology of a Triassic ecosystem, which has yielded significant vertebrate remains and is regarded important in the early evolution of groups such as the Dinosauria.
Showing posts with label palynology. Show all posts
Showing posts with label palynology. Show all posts
Vegetation History and Climate Change Across the Tr/J Boundary
Bonis, N. R., and W. M. Kürschner. 2012. Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary. Paleobiology 38:240-264. doi: http://dx.doi.org/10.1666/09071.1
Abstract - High-resolution palynological data sets
from shallow marine Triassic-Jurassic (Tr/J) boundary beds of two principal
sections in Europe (Hochalplgraben in Austria and St. Audrie's Bay in the
United Kingdom) were analyzed to reconstruct changes in vegetation,
biodiversity, and climate. In Hochalplgraben, a hardwood gymnosperm forest with
conifers and seed ferns is replaced by vegetation with dominant ferns, club
mosses and liverworts, which concurs with an increased diversification of spore
types during the latest Rhaetian. Multivariate statistical analysis reveals a
trend to warmer and wetter conditions across the Tr/J boundary in
Hochalplgraben. The vegetation changes in St. Audrie's Bay are markedly
different. Here, a mixed gymnosperm forest is replaced by monotonous vegetation
consisting mainly of Cheirolepidiaceae (80–100%). This change is caused by a
transition to a warmer and more arid climate. The observed diversity decrease
in St. Audrie's Bay affirms this interpretation. Although both sections show major
vegetation changes, neither of them demonstrates a distinctive floral mass
extinction. A compilation of Tr/J boundary sections across the world
demonstrates the presence of Cheirolepidiaceae-dominated forests in the
Pangaean interior and increases in abundance of spore-producing plants adjacent
to the Tethys Ocean. We propose that the non-uniform vegetation changes
reflected in the Tr/J palynological records are the result of environmental
changes caused by Central Atlantic Magmatic Province volcanism. The increase in
greenhouse gases caused a warmer climate and an enhanced thermal contrast
between the continent and the seas. Consequently, the monsoon system got
stronger and induced a drier continental interior and more intensive rainfall
near the margins of the Tethys Ocean.
...and one more from the End-Triassic Event.
Mander, L., Kuerschner, W. M., and J. C. McElwain. 2010. An explanation for conflicting records of Triassic–Jurassic plant diversity. PNAS Early Edition, www.pnas.org/cgi/doi/10.1073/pnas.1004207107. Suppl.files at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1004207107/-/DCSupplemental.
Abstract - Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic–Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10–12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene– Eocene Thermal Maximum.
Abstract - Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic–Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10–12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene– Eocene Thermal Maximum.
No Single Unambiguous Global End-Triassic Spore Spike
Bonis, N. R., Ruhl, M., and W. M. Kuerschner. 2010. Milankovitch-scale palynological turnover across the Triassic–Jurassic transition at St. Audrie’s Bay, SW UK. Journal of the Geological Society, London 167:877–888. doi: 10.1144/0016-76492009-141.
Abstract - A high-resolution palynological study of the Triassic–Jurassic boundary in the St. Audrie’s Bay section revealed a palynofloral transition interval with four pronounced spore peaks in the Lilstock Formation. Regular cyclic increases in palynomorph concentrations can be linked with periods of increased runoff, and correspond to the orbital eccentricity cycle. Spore peaks can be related to precession-induced variations in monsoon strength. An implication is that the initial carbon isotope excursion lasted for at least 20 ka. Emergence during deposition of the Cotham Member had an influence on one of the peaks, which is dominated by spore-producing pioneer plants (e.g. horsetails and liverworts). There is no compelling evidence of a global end-Triassic spore spike that, by analogy with the K–T boundary fern spike, could be related to a catastrophic mass extinction event. Climate change is a more plausible mechanism to explain the increased amount of spores.
Abstract - A high-resolution palynological study of the Triassic–Jurassic boundary in the St. Audrie’s Bay section revealed a palynofloral transition interval with four pronounced spore peaks in the Lilstock Formation. Regular cyclic increases in palynomorph concentrations can be linked with periods of increased runoff, and correspond to the orbital eccentricity cycle. Spore peaks can be related to precession-induced variations in monsoon strength. An implication is that the initial carbon isotope excursion lasted for at least 20 ka. Emergence during deposition of the Cotham Member had an influence on one of the peaks, which is dominated by spore-producing pioneer plants (e.g. horsetails and liverworts). There is no compelling evidence of a global end-Triassic spore spike that, by analogy with the K–T boundary fern spike, could be related to a catastrophic mass extinction event. Climate change is a more plausible mechanism to explain the increased amount of spores.
The Permian-Triassic Global Extinction Was Possibly Not Global
Hochuli, P. A., Os Vigran, J., Hermann, E., and H. Bucher. 2010. Multiple climatic changes around the Permian-Triassic boundary event revealed by an expanded palynological record from mid-Norway. Geological Society of America Bulletin 122:884-896. doi: 10.1130/B26551.1
Abstract - Here, we present the palynological record from two shallow core holes(6611/09-U-01 and -02) from the Trøndelag Platform offshore mid-Norway consisting of 750 m of Upper Permian and Lower Triassic sediments. The relatively homogeneous assemblages recovered from the Upper Permian deposits are dominated by gymnosperm pollen, mainly pteridosperms. At the base of the Griesbachian, numerous spore species appear in the record, leading to an increased diversity. The change at this boundary is also marked by the massive reduction of one group of pteridosperm pollen (Vittatina). Together with other typical Permianelements (e.g., Lueckisporites virkkiae), this group is rare but consistently present in the lower part of the Griesbachian, and it gradually disappears in its upper part. The distribution of other groups such as taeniate and non-taeniate bisaccate gymnosperm pollen (pterido sperms and conifers) shows no significant change across the boundary, whereas spores and other gymnosperm pollen increase in diversity and abundance. These changes coincide with the formational change between the Schuchert Dal Formation (Upper Permian) and the Wordie Creek Formation (Griesbachian) equivalents. Late Permian and Griesbachian palynomorph assemblages display different patterns. The former show a homogeneous composition of low diversity, whereas the latter reflect diverse and variably composed floras. The data suggest that the arid phase of the Late Permian was followed by a humid phase at the base of the Griesbachian. In the Griesbachian section, a succession of six distinct palynological assemblages (phase II–VII) can be inferred. Comparable changes have been described from East Greenland. The variations in the palynological record are interpreted to reflect changing ecological conditions (e.g., changing humidity). Comparable variations in the distribution of δ13C isotope values reported from various sections from Greenland and China, showing stable values during the Late Permian and highly variable values during the Griesbachian, suggest common causes for the observed fluctuations. Multiphase volcanic activity of the Siberian traps seems to be the most likely candidate to have caused the variations in the δ13C isotope as well as in the palynological record. In contrast to the common claim that marine and terrestrial biota both suffered a mass extinction related to the Permian- Triassic boundary event, the studied material from the Norwegian midlatitudinal sites shows no evidence for destruction of plant ecosystems. The presence of diverse microfloras of Griesbachian age supports the idea that the climate in this area allowed most plants to survive the Permian-Triassic boundary event.
Abstract - Here, we present the palynological record from two shallow core holes(6611/09-U-01 and -02) from the Trøndelag Platform offshore mid-Norway consisting of 750 m of Upper Permian and Lower Triassic sediments. The relatively homogeneous assemblages recovered from the Upper Permian deposits are dominated by gymnosperm pollen, mainly pteridosperms. At the base of the Griesbachian, numerous spore species appear in the record, leading to an increased diversity. The change at this boundary is also marked by the massive reduction of one group of pteridosperm pollen (Vittatina). Together with other typical Permianelements (e.g., Lueckisporites virkkiae), this group is rare but consistently present in the lower part of the Griesbachian, and it gradually disappears in its upper part. The distribution of other groups such as taeniate and non-taeniate bisaccate gymnosperm pollen (pterido sperms and conifers) shows no significant change across the boundary, whereas spores and other gymnosperm pollen increase in diversity and abundance. These changes coincide with the formational change between the Schuchert Dal Formation (Upper Permian) and the Wordie Creek Formation (Griesbachian) equivalents. Late Permian and Griesbachian palynomorph assemblages display different patterns. The former show a homogeneous composition of low diversity, whereas the latter reflect diverse and variably composed floras. The data suggest that the arid phase of the Late Permian was followed by a humid phase at the base of the Griesbachian. In the Griesbachian section, a succession of six distinct palynological assemblages (phase II–VII) can be inferred. Comparable changes have been described from East Greenland. The variations in the palynological record are interpreted to reflect changing ecological conditions (e.g., changing humidity). Comparable variations in the distribution of δ13C isotope values reported from various sections from Greenland and China, showing stable values during the Late Permian and highly variable values during the Griesbachian, suggest common causes for the observed fluctuations. Multiphase volcanic activity of the Siberian traps seems to be the most likely candidate to have caused the variations in the δ13C isotope as well as in the palynological record. In contrast to the common claim that marine and terrestrial biota both suffered a mass extinction related to the Permian- Triassic boundary event, the studied material from the Norwegian midlatitudinal sites shows no evidence for destruction of plant ecosystems. The presence of diverse microfloras of Griesbachian age supports the idea that the climate in this area allowed most plants to survive the Permian-Triassic boundary event.
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