Lower to Middle Triassic ostracods from the Tulong section, south Tibet, are described here for t... more Lower to Middle Triassic ostracods from the Tulong section, south Tibet, are described here for the first time. Samples from the first two stages of the Early Triassic (Griesbachian and Dienerian) are barren of ostracods; the following stage (Smithian) revealed low diversity ostracod faunas; a substantial diversification in taxa began at the base of the fourth stage (Spathian) and developed into the first stage of the Middle Triassic (Anisian). Furthermore, exploration of additional feeding modes is developed in the Spathian and Anisian, with notable occurrence of filter-feeding taxa. High abundance of filter-feeding ostracods in Spathian and lower Anisian units indicates that benthic habitats became oligotrophic. These habitats typically harbored ostracod faunas of Mesozoic affinities, suggesting that the evolutionary turnover of ostracods was fostered by the declining input of nutrients from the Spathian on. Marked faunal similarities with other Tethyan areas, mainly the northern part of Tethys, are observed during Spathian and Anisian times.► In this study we examine ostracod (Crustacea) faunas from Early and early Middle Triassic of Tulong section, Tibet. ► We examine palaeoenvironmental significance of these assemblages. ► We consider biodiversity indices in relation to feeding modes of ostracods. ► We give new insights into recovery mode in the aftermath of the end-Permian extinction.
Changes of community structure in response to competition usually take place on timescales that a... more Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end-Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10–100 ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and heterogeneity. In the absence of both environmental and taxonomic changes, we attribute this pattern to the long-term effects of interspecific competition, which acted at an unusually slow pace because the number of competing species and potential immigrants was dramatically reduced by the end-Permian mass extinction. We suggest that these non-actualistic conditions led to decreased rates of niche differentiation and hence to the delayed rediversification of benthos that characterizes the aftermath of the greatest Phanerozoic mass extinction event. A hyperbolic diversification model is proposed, which accounts for the positive relationship between the intensity of interspecific competition and the rate of niche differentiation and resolves the conundrum of delayed rediversification at a time when niche space was largely vacated.
The Lower Triassic sedimentary and carbonate/organic carbon isotope records from the Tulong area ... more The Lower Triassic sedimentary and carbonate/organic carbon isotope records from the Tulong area (South Tibet) are documented in their integrality for the first time. New age control is provided by ammonoid and conodont biostratigraphy. The basal Triassic series consists of Griesbachian dolomitic limestones, similar to the Kathwai Member in the Salt Range (Pakistan) and to the Otoceras Beds in Spiti (India). The overlying thin-bedded limestones of Dienerian age strongly resemble the Lower Ceratite Limestone of the Salt Range. They are followed by a thick series of dark green, silty shales of Dienerian–early Smithian age without fauna that strikingly resemble the Ceratite Marls of the Salt Range. This interval is overlain by thin-bedded, light grey fossil-rich limestones of middle to late Smithian age, resembling the Upper Ceratite Limestone of the Salt Range. These are followed by a shale interval of early Spathian age that has no direct counterpart in other Tethyan sections. Carbonate production resumes during the late early and middle Spathian with the deposition of red, bioclastic nodular limestone (“Ammonitico Rosso” type facies). Apart from its colour this facies is similar to the one of the Niti Limestone in Spiti and of the Spathian nodular limestone in Guangxi (South China). As in other Tethyan localities such as Spiti, the early–middle Anisian part of the Tulong section is strongly condensed and is characterized by grey, thin-bedded limestones with phosphatized ammonoids.As for many other Tethyan localities the carbon isotope record from Tulong is characterized by a late Griesbachian–Dienerian positive δ13Ccarb excursion (2‰), and a very prominent positive excursion (5‰) at the Smithian–Spathian boundary, thus confirming the well-documented perturbations of the global carbon cycle following the Permian–Triassic mass extinction event.
New ichnological data from the Lower Triassic Werfen Formation (Dolomites, Italy) revealed an une... more New ichnological data from the Lower Triassic Werfen Formation (Dolomites, Italy) revealed an unexpectedly diverse and complex ichnofauna in mixed siliclastic–carbonate shelf sediments of the western tropical Tethys shortly after the end-Permian mass extinction event. Common elements are Thalassinoides, Palaeophycus and Planolites. Other associated ichnogenera include Spongeliomorpha, Rhizocorallium, Lockeia, Catenichnus, Helminthopsis, and Taenidium. One structure is tentatively determined as Curvolithus. Biostratigraphic data (conodonts and bivalves) of the trace fossil interval (lower Seis/Siusi Member) suggest a late Griesbachian age, less than 1 Ma after the end-Permian mass extinction event. Similarly diverse ichnofossil communities from this time interval have recently been described from the Boreal Realm, but this is the first record of a diverse Griesbachian ichnoassemblage from the tropics, indicating that the early recovery of trace fossil producers was not latitudinally restricted, as previously proposed. Accordingly, relatively advanced recovery stages were reached on a global scale much earlier than the Spathian as is commonly acknowledged. The early and interregional peak in ichnofaunal recovery implies subsequent ecological setbacks in post-Griesbachian times that explain the overall delay of benthic recovery until the Spathian. Rather than persistent catastrophic conditions during the Griesbachian, a global and synchronous succession of crises and relaxation phases after the Griesbachian is proposed as an explanatory model for the recovery pattern of benthic ecosystems.
A new sampling of Early Triassic (Griesbachian) conodonts is obtained from the microbialite overl... more A new sampling of Early Triassic (Griesbachian) conodonts is obtained from the microbialite overlying the latest Permian peri-reefal shallow water limestone in Wuzhuan section (Nanpanjiang Basin, Guangxi, South China). High resolution sam-pling in the lower twelve meters of the Luolou Formation provides rather diversified conodont faunas and allows const-ructing a well resolved conodont distribution for this crucial earliest Triassic interval. In the Wuzhuan section, the nine meters thick microbialite is bracketed by two calcarenite beds and contains several fossiliferous lenses. The co-occurrence of typical Permian foraminifera such as Paraglobivalvulina mira (Reitlinger) and Dagmarita chanakchiensis (Reitlinger) in the calcarenite underlying the microbialite indicates a late Permian age. Our preliminary results indicate the presence of one residual maximal horizon (RMH) based on conodont faunas in the microbialite and of a second one in the overlying calca-renite. The lowest RMH o...
Benthic organisms are known to have recovered much slower after the end-Permian mass extinction e... more Benthic organisms are known to have recovered much slower after the end-Permian mass extinction event than ammonoids, but hitherto the poor age-control of most Early Triassic benthic faunas prevented detailed comparisons. A new dataset that includes occurrences of bivalve and ...
Ongoing work in California, S-China, Tibet, Pakistan and Oman has led to a refined biochronologic... more Ongoing work in California, S-China, Tibet, Pakistan and Oman has led to a refined biochronologic subdivision of the late Early Triassic and allows reconstructing a high resolution diversity time series, partly constrained by new U-Pb ages from S-China [1-2].
Lower to Middle Triassic ostracods from the Tulong section, south Tibet, are described here for t... more Lower to Middle Triassic ostracods from the Tulong section, south Tibet, are described here for the first time. Samples from the first two stages of the Early Triassic (Griesbachian and Dienerian) are barren of ostracods; the following stage (Smithian) revealed low diversity ostracod faunas; a substantial diversification in taxa began at the base of the fourth stage (Spathian) and developed into the first stage of the Middle Triassic (Anisian). Furthermore, exploration of additional feeding modes is developed in the Spathian and Anisian, with notable occurrence of filter-feeding taxa. High abundance of filter-feeding ostracods in Spathian and lower Anisian units indicates that benthic habitats became oligotrophic. These habitats typically harbored ostracod faunas of Mesozoic affinities, suggesting that the evolutionary turnover of ostracods was fostered by the declining input of nutrients from the Spathian on. Marked faunal similarities with other Tethyan areas, mainly the northern part of Tethys, are observed during Spathian and Anisian times.► In this study we examine ostracod (Crustacea) faunas from Early and early Middle Triassic of Tulong section, Tibet. ► We examine palaeoenvironmental significance of these assemblages. ► We consider biodiversity indices in relation to feeding modes of ostracods. ► We give new insights into recovery mode in the aftermath of the end-Permian extinction.
Changes of community structure in response to competition usually take place on timescales that a... more Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end-Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10–100 ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and heterogeneity. In the absence of both environmental and taxonomic changes, we attribute this pattern to the long-term effects of interspecific competition, which acted at an unusually slow pace because the number of competing species and potential immigrants was dramatically reduced by the end-Permian mass extinction. We suggest that these non-actualistic conditions led to decreased rates of niche differentiation and hence to the delayed rediversification of benthos that characterizes the aftermath of the greatest Phanerozoic mass extinction event. A hyperbolic diversification model is proposed, which accounts for the positive relationship between the intensity of interspecific competition and the rate of niche differentiation and resolves the conundrum of delayed rediversification at a time when niche space was largely vacated.
The Lower Triassic sedimentary and carbonate/organic carbon isotope records from the Tulong area ... more The Lower Triassic sedimentary and carbonate/organic carbon isotope records from the Tulong area (South Tibet) are documented in their integrality for the first time. New age control is provided by ammonoid and conodont biostratigraphy. The basal Triassic series consists of Griesbachian dolomitic limestones, similar to the Kathwai Member in the Salt Range (Pakistan) and to the Otoceras Beds in Spiti (India). The overlying thin-bedded limestones of Dienerian age strongly resemble the Lower Ceratite Limestone of the Salt Range. They are followed by a thick series of dark green, silty shales of Dienerian–early Smithian age without fauna that strikingly resemble the Ceratite Marls of the Salt Range. This interval is overlain by thin-bedded, light grey fossil-rich limestones of middle to late Smithian age, resembling the Upper Ceratite Limestone of the Salt Range. These are followed by a shale interval of early Spathian age that has no direct counterpart in other Tethyan sections. Carbonate production resumes during the late early and middle Spathian with the deposition of red, bioclastic nodular limestone (“Ammonitico Rosso” type facies). Apart from its colour this facies is similar to the one of the Niti Limestone in Spiti and of the Spathian nodular limestone in Guangxi (South China). As in other Tethyan localities such as Spiti, the early–middle Anisian part of the Tulong section is strongly condensed and is characterized by grey, thin-bedded limestones with phosphatized ammonoids.As for many other Tethyan localities the carbon isotope record from Tulong is characterized by a late Griesbachian–Dienerian positive δ13Ccarb excursion (2‰), and a very prominent positive excursion (5‰) at the Smithian–Spathian boundary, thus confirming the well-documented perturbations of the global carbon cycle following the Permian–Triassic mass extinction event.
New ichnological data from the Lower Triassic Werfen Formation (Dolomites, Italy) revealed an une... more New ichnological data from the Lower Triassic Werfen Formation (Dolomites, Italy) revealed an unexpectedly diverse and complex ichnofauna in mixed siliclastic–carbonate shelf sediments of the western tropical Tethys shortly after the end-Permian mass extinction event. Common elements are Thalassinoides, Palaeophycus and Planolites. Other associated ichnogenera include Spongeliomorpha, Rhizocorallium, Lockeia, Catenichnus, Helminthopsis, and Taenidium. One structure is tentatively determined as Curvolithus. Biostratigraphic data (conodonts and bivalves) of the trace fossil interval (lower Seis/Siusi Member) suggest a late Griesbachian age, less than 1 Ma after the end-Permian mass extinction event. Similarly diverse ichnofossil communities from this time interval have recently been described from the Boreal Realm, but this is the first record of a diverse Griesbachian ichnoassemblage from the tropics, indicating that the early recovery of trace fossil producers was not latitudinally restricted, as previously proposed. Accordingly, relatively advanced recovery stages were reached on a global scale much earlier than the Spathian as is commonly acknowledged. The early and interregional peak in ichnofaunal recovery implies subsequent ecological setbacks in post-Griesbachian times that explain the overall delay of benthic recovery until the Spathian. Rather than persistent catastrophic conditions during the Griesbachian, a global and synchronous succession of crises and relaxation phases after the Griesbachian is proposed as an explanatory model for the recovery pattern of benthic ecosystems.
A new sampling of Early Triassic (Griesbachian) conodonts is obtained from the microbialite overl... more A new sampling of Early Triassic (Griesbachian) conodonts is obtained from the microbialite overlying the latest Permian peri-reefal shallow water limestone in Wuzhuan section (Nanpanjiang Basin, Guangxi, South China). High resolution sam-pling in the lower twelve meters of the Luolou Formation provides rather diversified conodont faunas and allows const-ructing a well resolved conodont distribution for this crucial earliest Triassic interval. In the Wuzhuan section, the nine meters thick microbialite is bracketed by two calcarenite beds and contains several fossiliferous lenses. The co-occurrence of typical Permian foraminifera such as Paraglobivalvulina mira (Reitlinger) and Dagmarita chanakchiensis (Reitlinger) in the calcarenite underlying the microbialite indicates a late Permian age. Our preliminary results indicate the presence of one residual maximal horizon (RMH) based on conodont faunas in the microbialite and of a second one in the overlying calca-renite. The lowest RMH o...
Benthic organisms are known to have recovered much slower after the end-Permian mass extinction e... more Benthic organisms are known to have recovered much slower after the end-Permian mass extinction event than ammonoids, but hitherto the poor age-control of most Early Triassic benthic faunas prevented detailed comparisons. A new dataset that includes occurrences of bivalve and ...
Ongoing work in California, S-China, Tibet, Pakistan and Oman has led to a refined biochronologic... more Ongoing work in California, S-China, Tibet, Pakistan and Oman has led to a refined biochronologic subdivision of the late Early Triassic and allows reconstructing a high resolution diversity time series, partly constrained by new U-Pb ages from S-China [1-2].
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