Genus <i>Porpoceras</i> Buckman, 1911 TYPE SPECIES. — <i>Ammonites</i> <i>vortex</i> Simpson, 1855 by monotypy.
Early Triassic (Griesbachian to Spathian) ostracod faunas are here first discovered and described form the Guangxi Province, South China. Thirty-seven species belonging to fourteen genera are recognized. Seven species are new: Bairdia... more
Early Triassic (Griesbachian to Spathian) ostracod faunas are here first discovered and described form the Guangxi Province, South China. Thirty-seven species belonging to fourteen genera are recognized. Seven species are new: Bairdia fengshanensis n.sp., Bairdia wailiensis n.sp., Liuzhinia guangxiensis n.sp., Ptychobairdia luciaae n.sp., Ptychobairdia aldaae n.sp., Paracypris jinyaensis n.sp. and Paracypris gaetanii n.sp. The Griesbachian assemblage from the basal microbial limestone is well diversified and does not suggest any abnormal palaeoenvironmental conditions in terms of salinity, temperature or oxygen content. Particularly, the ostracods are typical of well oxygenated water and do not reflect any anoxia. Dienerian and Smithian ostracods are evidenced for the first time and the assemblages suggest less favourable palaeoenviromental conditions. Diversity and abundance of ostracod assemblages recovered from the Spathian on. The main taxonomic turnover among ostracod assemblag...
Research Interests:
1 Palaontologisches Institut der Universitat Zurich, Karl Schmid-Strasse 4, 8006 Zurich, Switzerland, email: galfetti@pim.uzh.ch, hugo.FR.bucher@pim.uzh.ch, bruehwiler@pim.uzh.ch, goudemand@pim.uzh.ch, peter.hochuli@erdw.ethz.ch; 2... more
1 Palaontologisches Institut der Universitat Zurich, Karl Schmid-Strasse 4, 8006 Zurich, Switzerland, email: galfetti@pim.uzh.ch, hugo.FR.bucher@pim.uzh.ch, bruehwiler@pim.uzh.ch, goudemand@pim.uzh.ch, peter.hochuli@erdw.ethz.ch; 2 Department of Mineralogy, University of Geneva, rue des Maraichers 13, CH-1205 Geneva, Switzerland, email: maria.ovtcharova@terre.unige.ch, urs.schaltegger@terre.unige.ch; 3 UMR 5125 PEPS CNRS, Universite Lyon I, Campus de la Doua, 69622 Villeurbanne Cedex, France, email: arnaud.brayard@univ-lyon1.fr, Fabrice.Cordey@univ-lyon1.fr; 4 Department of Earth Science, ETH, Sonneggstrasse 5, 8006 Zurich, Switzerland, email: helmut.weissert@erdw.ethz.ch; 5 Guangxi Bureau of Geology and Mineral Resources, Jiangzheng Road 1, 530023 Nanning, China
Research Interests:
The end-Permian mass extinction is the biggest known crisis in life history and wiped out more than 90% of all marine species. In its aftermath, the Early Triassic was a time of profound instabilities in the sedimentary, geochemical and... more
The end-Permian mass extinction is the biggest known crisis in life history and wiped out more than 90% of all marine species. In its aftermath, the Early Triassic was a time of profound instabilities in the sedimentary, geochemical and climatic evolution. Full recovery of many marine, essentially benthic clades as well as pre-crisis level of marine ecosystem complexity was not reached until the Middle Triassic (e.g. reefal communities). On the contrary, at least some faunal groups such as ammonoids and conodonts recovered much faster than other marine clades. However, the evolution of Early Triassic ammonoids was not a smooth, nor a gradual process. It was characterized by the following main features: (i) a very low diversity in the Griesbachian (early Induan), (ii) a moderate diversity increase in the Dienerian (late Induan), (iii) an explosive radiation in the early Smithian (early Olenekian), (iv) a late Smithian extinction event followed by (v) a second explosive radiation in t...
Research Interests:
Abstract The late Smithian extinction represents a major event within the Early Triassic. This event generally corresponds to a succession of two, possibly three successively less diverse, cosmopolitan ammonoid assemblages, which when... more
Abstract The late Smithian extinction represents a major event within the Early Triassic. This event generally corresponds to a succession of two, possibly three successively less diverse, cosmopolitan ammonoid assemblages, which when present, provide a robust biostratigraphic framework and precise correlations at different spatial scales. In the western USA basin, known occurrences of latest Smithian taxa are rare and until now, have only been documented from northeastern Nevada. Based on these restricted basinal occurrences, a regional zone representing the latest Smithian was postulated but not corroborated, as representative taxa had not yet been reported from outside Nevada. Here we document two new ammonoid assemblages from distant localities in northern Utah, overlying the late Smithian Anasibirites beds and characterized by the unambiguous co-occurrence of Xenoceltites subevolutus and Pseudosageceras augustum. The existence of a latest Smithian zone in the western USA basin is therefore validated, facilitating the identification of the Smithian/Spathian boundary and intra-basin correlation. This zone also correlates with the latest Smithian zone recognized from southern Tethyan basins. Additionally, these new data support other observed occurrences of Xenoceltites subevolutus throughout most of the late Smithian.
Research Interests:
The mass extinction characterizing the Permian/Triassic boundary (PTB; ~ 252 Ma) corresponds to a major faunal shift between the Palaeozoic and the Modern evolutionary fauna. The temporal, spatial, environmental, and ecological dynamics... more
The mass extinction characterizing the Permian/Triassic boundary (PTB; ~ 252 Ma) corresponds to a major faunal shift between the Palaeozoic and the Modern evolutionary fauna. The temporal, spatial, environmental, and ecological dynamics of the associated biotic recovery remain highly debated, partly due to the scarce, or poorly-known, Early Triassic fossil record. Recently, an exceptionally complex ecosystem dated from immediately after the Smithian/Spathian boundary (~ 3 myr after the PTB) was reported: the Paris Biota (Idaho, USA). However, the spatiotemporal representativeness of this unique assemblage remained questionable as it was hitherto only reported from a single site. Here we describe three new exceptionally diverse assemblages of the same age as the Paris Biota, and a fourth younger one. They are located in Idaho and Nevada, and are taxonomic subsets of the Paris Biota. We show that the latter covered a region-wide area and persisted at least partially throughout the Spa...
Research Interests:
Research Interests:
Background Many pathologies that modify the shell geometry and ornamentation of ammonoids are known from the fossil record. Since they may reflect the developmental response of the organism to a perturbation (usually a sublethal injury),... more
Background Many pathologies that modify the shell geometry and ornamentation of ammonoids are known from the fossil record. Since they may reflect the developmental response of the organism to a perturbation (usually a sublethal injury), their study is essential for exploring the developmental mechanisms of these extinct animals. Ammonoid pathologies are also useful to assess the value of some morphological characters used in taxonomy, as well as to improve phylogenetic reconstructions and evolutionary scenarios. Results We report on the discovery of an enigmatic pathological middle Toarcian (Lower Jurassic) ammonoid specimen from southern France, characterized by a pronounced left-right asymmetry in both ornamentation and suture lines. For each side independently, the taxonomic interpretations of ornamentation and suture lines are congruent, suggesting a Hildoceras semipolitum species assignment for the left side and a Brodieia primaria species assignment for the right side. The fo...
Research Interests:
Research Interests:
Research Interests:
Abstract Intensive sampling of three earliest Spathian sites represented by the Lower Shale unit and coeval beds within the Bear Lake vicinity and neighboring areas, southeastern Idaho, yielded several new ammonoid and nautiloid... more
Abstract Intensive sampling of three earliest Spathian sites represented by the Lower Shale unit and coeval beds within the Bear Lake vicinity and neighboring areas, southeastern Idaho, yielded several new ammonoid and nautiloid assemblages. These new occurrences overall indicate that the lower boundary of the Tirolites beds, classically used as a regional marker for the base of the early Spathian, and therefore the regional Smithian/Spathian boundary, must be shifted downward into the Lower Shale unit and coeval beds. Regarding ammonoids, one new genus (Caribouceras) and two new species (Caribouceras slugense and Albanites americanus) are described. In addition, the regional temporal distribution of Bajarunia, Tirolites, Columbites, and Coscaites is refined, based on a fourth sampled site containing a newly reported occurrence of the early Spathian Columbites fauna in coeval beds of the Middle Shale unit. As a complement to ammonoids, changes observed in nautiloid dominance are also shown to facilitate correlation with high-latitude basins such as Siberia during this short time interval, and they also highlight the major successive environmental fluctuations that took place during the late Smithian–early Spathian transition.
Research Interests:
Protomonaxonid sponges are a major group of Cambrian and Ordovician fossils in exceptionally preserved (especially Burgess Shale-type) faunas, but are rare thereafter. Rare examples of apparent surviving lineages are known from the late... more
Protomonaxonid sponges are a major group of Cambrian and Ordovician fossils in exceptionally preserved (especially Burgess Shale-type) faunas, but are rare thereafter. Rare examples of apparent surviving lineages are known from the late Palaeozoic and Mesozoic, but by this time more derived groups of sponges have generally displaced them in at least shallow-water (shelf depth) ecosystems. The early Spathian (Early Triassic) Paris Biota includes abundant material of a new leptomitid protomonaxonid, Pseudoleptomitus advenus Botting nov. gen., nov. sp., distinguished by having an unbundled longitudinal skeleton and very weak transverse component. This is the first post-Ordovician leptomitid known, and indicates long-term survival of the group in unknown environments. Its occurrence near storm wave base is similar to the preferred environment of earlier examples of the family, suggesting either ecological rarity or taphonomic reasons for their 200-million-year absence from later Palaeozoic rocks.
Research Interests:
Research Interests:
Research Interests:
Bed-by-bed sampling of the lower portion of the Daye Formation at Gujiao, Guizhou Province, South China, yielded new Griesbachian–Dienerian (Induan, Early Triassic) ammonoid faunas showing a new regional Induan ammonoid succession. This... more
Bed-by-bed sampling of the lower portion of the Daye Formation at Gujiao, Guizhou Province, South China, yielded new Griesbachian–Dienerian (Induan, Early Triassic) ammonoid faunas showing a new regional Induan ammonoid succession. This biostratigraphic scheme includes in chronological order the late Griesbachian Ophiceras medium and Jieshaniceras guizhouense beds, and the middle Dienerian Ambites radiatus bed. The latter is recognized for the first time as a separate biozone in South China. Eight genera and 13 species are identified, including one new species, Mullericeras gujiaoense n. sp. The new data show that a relatively high level of ammonoid taxonomic richness occurred rather rapidly after the Permian/Triassic mass extinction in the late Griesbachian, echoing similar observations in other basins, such as in the Northern Indian Margin.UUID: http://zoobank.org/a24a3387-f3dd-4da4-a134-84372352a63d
Research Interests:
Research Interests:
Research Interests:
We present the first quantitative palaeobiogeographical analysis in terms of distribution and abundance of Early Triassic ammonoids from the western USA basin during the Smithian, c. 1 myr after the Permian–Triassic boundary mass... more
We present the first quantitative palaeobiogeographical analysis in terms of distribution and abundance of Early Triassic ammonoids from the western USA basin during the Smithian, c. 1 myr after the Permian–Triassic boundary mass extinction. The faunal dataset consists of a taxonomically homogenized compilation of spatial and temporal occurrences and abundances from 27 sections distributed within the western USA basin. Two complementary multivariate techniques were applied to identify the main biogeographical structuring recorded in the analysed presence/absence data: additive cluster analysis using the neighbor‐joining algorithm (NJ) and non‐metric multidimensional scaling (NMDS). Regarding abundance data, a taxonomic diversity (sensu evenness) analysis was coupled with graphical comparisons of relative abundances of selected taxa. The identified relationships indicate that middle Smithian ammonoids of the western USA basin were geographically organized in terms of both distribution and abundance, with the biogeographical distinction of a southern and a northern cluster. This N–S structuring in the distribution and abundance of middle Smithian ammonoids is notably paralleled by the relative amount of siliciclastics, which suggests that clastic load of the water column was a major controlling factor. In marked contrast with the middle Smithian, the studied late Smithian ammonoid assemblages do not show any significant differences, whatever the depositional environment. This abrupt biogeographical homogenization, independent from intrabasinal facies heterogeneity, indicates a switch from regional to global drivers, associated with the well‐known late Smithian global extinction and remarkable cosmopolitan ammonoid distributions during that time.
Research Interests:
Sediments deposited from the Permian–Triassic boundary (~252 Ma) until the end-Smithian (Early Triassic; c. 250.7 Ma) in the Sonoma Foreland Basin show marked thickness variations between its southern (up to c. 250 m thick) and northern... more
Sediments deposited from the Permian–Triassic boundary (~252 Ma) until the end-Smithian (Early Triassic; c. 250.7 Ma) in the Sonoma Foreland Basin show marked thickness variations between its southern (up to c. 250 m thick) and northern (up to c. 550 m thick) parts. This basin formed as a flexural response to the emplacement of the Golconda Allochthon during the Sonoma orogeny. Using a high-resolution backstripping approach, a numerical model and sediment thickness to obtain a quantitative subsidence analysis, we discuss the controlling factor(s) responsible for spatial variations in thickness. We show that sedimentary overload is not sufficient to explain the significant discrepancy observed in the sedimentary record of the basin. We argue that the inherited rheological properties of the basement terranes and spatial heterogeneity of the allochthon are of paramount importance in controlling the subsidence and thickness spatial distribution across the Sonoma Foreland Basin.
Research Interests:
A new marine fossil assemblage from the Early Triassic shows unexpected phyletic diversity and functional complexity.
Research Interests:
Research Interests:
Research Interests:
Research Interests:
The Great Salt Lake, Utah, USA is a shallow, hypersaline, intracontinental lake hosting extensive microbial deposits. At a large spatial scale, the distribution of these deposits is driven by environmental and geodynamical factors (i.e.... more
The Great Salt Lake, Utah, USA is a shallow, hypersaline, intracontinental lake hosting extensive microbial deposits. At a large spatial scale, the distribution of these deposits is driven by environmental and geodynamical factors (i.e. water-level fluctuations and a fault-related framework). A detailed mapping of the Buffalo Point area, in the north-western part of Antelope Island, indicates the presence of an anomalous concentration of microbial deposits dated ca. 5.8 ka BP and distributed along a lobe-shaped geometry. This uncommon microbial deposit geometry results from an extensive colonization of a conglomerate substrate exhibiting an accumulation of m-sized rounded Cambrian quartzite boulders. We suggest that this conglomerate substrate provides a stable nucleation point that promotes the development and preservation of the lobe-shaped microbial deposits. Microbial deposits may also have protected the conglomerate substrate from erosional processes and thereby increased the preservation potential of the lobe-shaped structure. Based on the characteristics of the conglomerate (e.g. grain size, texture) and its location (i.e. 200 m beyond the average shoreline), this lobe-shaped structure likely results from subaqueous debris or a hyperconcentrated density flow that transports sedimentary material from the Buffalo Point slopes downward to the shore. We estimate the age of the conglomerate deposition to be between 21 and 12 ka BP. The initiation of the flow may have been triggered by various mechanisms, but the existence of a major active normal fault in the vicinity of these deposits suggests that an earthquake could have destabilized the accumulated sediments and resulted in conglomerate emplacement. The catastrophic 15 ka BP Bonneville Flood, which led to a drop in the lake level (approximately 110 m), may also provide an explanation for the initiation of the flow.
Research Interests:
La crise permo-triasique a decime plus de 90% des especes marines vivant a cette epoque. La recuperation biotique consecutive etait jusqu’alors consideree comme extremement lente. Dans ce contexte, les ammonoides du Trias inferieur... more
La crise permo-triasique a decime plus de 90% des especes marines vivant a cette epoque. La recuperation biotique consecutive etait jusqu’alors consideree comme extremement lente. Dans ce contexte, les ammonoides du Trias inferieur constituent un ensemble phylogenetiquement bien contraint particulierement approprie a l’etude de l’impact des conditions climatiques et oceaniques sur les dynamiques macroecologiques post-crises. Afin d’apprehender l’impact de ces parametres, nous avons elabore un modele de simulation 2D ou les temperatures et les courants forcent la dispersion geographique d’un ensemble phylogenetique genere aleatoirement. Le registre fossile indique que les ammonoides sont parmi les organismes marins les plus rapides a se rediversifier. Le debut du Trias inferieur est marque par un gradient latitudinal de diversite tres faible. Ce gradient s’accentue progressivement correspondant au developpement d’un fort gradient latitudinal de temperatures au cours du Trias inferieur
Research Interests:
Active, carbonate-mineralizing microbial mats flourish in a tropical, highly evaporative, marine-fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary... more
Active, carbonate-mineralizing microbial mats flourish in a tropical, highly evaporative, marine-fed lagoonal network to the south of Cayo Coco Island (Cuba). Hypersaline conditions support the development of a complex sedimentary microbial ecosystem with diverse morphologies, a variable intensity of mineralization and a potential for preservation. In this study, the role of intrinsic (i.e. microbial) and extrinsic (i.e. physicochemical) controls on microbial mat development, mineralization and preservation was investigated. The network consists of lagoons, forming in the interdune depressions of a Pleistocene aeolian substratum; they developed due to a progressive increase in sea-level since the Holocene. The hydrological budget in the Cayo Coco lagoonal network changes from west to east, increasing the salinity. This change progressively excludes grazers and increases the saturation index of carbonate minerals, favouring the development and mineralization of microbial mats in the easternmost lagoons. Detailed mapping of the easternmost lagoon shows four zones with different flooding regimes. The microbial activity in the mats was recorded using light–dark shifts in conjunction with microelectrode O2 and HS− profiles. High rates of O2 production and consumption, in addition to substantial amounts of exopolymeric substances, are indicative of a potentially strong intrinsic control on mineralization. Seasonal, climate-driven water fluctuations are key for mat development, mineralization, morphology and distribution. Microbial mats show no mineralization in the permanently submersed zone, and moderate mineralization in zones with alternating immersion and exposure. It is suggested that mineralization is also driven by water-level fluctuations and evaporation. Mineralized mats are laminated and consist of alternating trapping and binding of grains and microbially induced magnesium calcite and dolomite precipitation. The macrofabrics of the mats evolve from early colonizing Flat mats to complex Cerebroid or Terrace structures. The macrofabrics are influenced by the hydrodynamic regime: wind-driven waves inducing relief terraces in windward areas and flat morphologies on the leeward side of the lagoon. Other external drivers include: (i) storm events that either promote (for example, by bioclasts covering) or prevent (for example, by causing erosion) microbial mat preservation; and (ii) subsurface degassing, through mangrove roots and desiccation cracks covered by Flat mats (i.e. forming Hemispheroids and Cerebroidal structures). These findings provide in-depth insights into understanding fossil microbialite morphologies that formed in lagoonal settings.
Research Interests: Geology and Sedimentology
The Triassic is a turning point in the evolutionary history of ammonoids, characterized by the flourishing Ceratitida and the appearance of the first heteromorphs. Following the end-Permian mass extinction, ammonoids were among the first... more
The Triassic is a turning point in the evolutionary history of ammonoids, characterized by the flourishing Ceratitida and the appearance of the first heteromorphs. Following the end-Permian mass extinction, ammonoids were among the first groups to rediversify by producing many new taxa. Already in the late nineteenth century, the still currently recognized Triassic stages and substages were introduced. The historical development of Triassic ammonoid biostratigraphy is a good example of worldwide cooperation between many geographically-diverse research groups, which initially began in Germany and the European Alps. This cooperation was then extended to North America, Transcaucasia, North Indian Margin, South China, and Russia. A renewed interest in Triassic ammonoid biozonation has occurred during the last few decades, leading to the recognition of tens of ammonoid zones spanning about 50.9 Myr (leading to an average duration for ammonoid biochronozones of about 0.74 Myr), whose correlation and definition are herein synthesized.
Research Interests:
As interest in the end Permian mass extinction event and the Triassic recovery has grown in recent decades, greater attention has necessarily been focussed on the time framework for this important interval. Intensive sampling of the lower... more
As interest in the end Permian mass extinction event and the Triassic recovery has grown in recent decades, greater attention has necessarily been focussed on the time framework for this important interval. Intensive sampling of the lower portion of the Thaynes and Moenkopi Groups (Lower Triassic) in central and southern Utah (USA), has lead to the recognition of a new key regional Smithian ammonoid succession. The new biostratigraphic zonation is comprised of twelve subdivisions, resulting in a sequence with much higher resolution than the long-recognized Meekoceras gracilitatis and Anasibirites kingianus Zones, that can be correlated not only with other western USA sites, but also with major localities worldwide. Middle and late Smithian faunas contain many taxa with wide geographic distributions allowing long-distance correlation with faunal successions from other regions such as British Columbia, the Canadian Arctic, South China, Spiti and Oman. Combined with Dienerian data from...
Research Interests:
ABSTRACT After the end-Permian mass extinction, ammonoids experienced an explosive recovery followed by episodes of radiation and extinction. These events were associated with sudden biogeographic changes often closely related to major... more
ABSTRACT After the end-Permian mass extinction, ammonoids experienced an explosive recovery followed by episodes of radiation and extinction. These events were associated with sudden biogeographic changes often closely related to major climatic and oceanographic changes. Previous biogeographic studies of Triassic ammonoids have rarely focused on a specific time-interval and were rarely based on quantitative methods. Thus, we will first review biogeographical methods and the biogeographical signals known from Triassic ammonoids. Secondly, we will focus on quantitative approaches that improve our knowledge of ammonoid biogeographical structuring and dynamics during the Triassic, and we will discuss controlling factors such as Sea Surface Temperature and oceanic circulation. We show that a biogeographical latitudinal structuring of faunas persisted along the eastern Panthalassa during the Ladinian, as a marked differentiation between Tethys and Panthalassic realms. Biogeographical configurations of the Carnian, Norian and Rhaetian appear more homogeneous, although a weak latitudinal structuring may have continued up to the late Carnian.
ABSTRACT A reduction in body size (Lilliput effect) has been repeatedly proposed for many marine organisms in the aftermath of the Permian-Triassic (PT) mass extinction. Specifically-reduced maximum sizes of benthic marine invertebrates... more
ABSTRACT A reduction in body size (Lilliput effect) has been repeatedly proposed for many marine organisms in the aftermath of the Permian-Triassic (PT) mass extinction. Specifically-reduced maximum sizes of benthic marine invertebrates have been proposed for the entire Early Triassic. This concept was originally based on observations on Early Triassic gastropods from the western USA basin and the Dolomites (N Italy) and it stimulated subsequent studies on other taxonomic groups. However, only a few studies have tested the validity of the Lilliput effect in gastropods to determine whether the paucity of large-sized gastropods is a genuine signal or the result of a poor fossil record and insufficient sampling. In combination with a review of the literature, we document numerous new, abundant, large-sized gastropods from Griesbachian outcrops of Greenland and from the Smithian-early Spathian interval in the southwestern USA. We show that large-sized (“Gulliver”) gastropods (i) were present soon after the PT mass extinction, (ii) occurred in various basins, sedimentary facies and environmental contexts (from shallow to deeper settings), and (iii) belong to diverse higher-rank taxa. Focusing on the western USA basin, we investigate areas from which microgastropod shell-beds were previously presented as being typical. However, we show that Gulliver gastropods do occur in the very same areas. Insufficient sampling effort is probably the main reason for the rarity of reports of large Early Triassic gastropods, which is supported by preliminary rarefaction-based simulations. Finally, it appears that the recently documented middle to late Smithian climate shifts and the severe end-Smithian extinction of nekto-pelagic faunas did not reduce maximum shell sizes of gastropods.
Research Interests:
ABSTRACT This work focuses on well-exposed Lower Triassic sedimentary rocks in the area of Torrey (south-central Utah, USA). The studied Smithian deposits record a large-scale third order sea-level cycle, which permits a detailed... more
ABSTRACT This work focuses on well-exposed Lower Triassic sedimentary rocks in the area of Torrey (south-central Utah, USA). The studied Smithian deposits record a large-scale third order sea-level cycle, which permits a detailed reconstruction of the evolution of depositional settings. During the middle Smithian, peritidal microbial limestones associated with a rather low-diversity benthic fauna were deposited seaward of the tidal flat siliciclastic red beds. Associated with siliceous sponges, microbial limestones formed small m-scale patch reefs. During the late middle to late Smithian interval, the sedimentary system is characterized by tidal flat dolostones of an interior platform, ooid-bioclastic deposits of a tide-dominated shoal complex, and mid-shelf bioclastic limestones. Microbial deposits, corresponding to sparse stromatolites formed in the interior platform, are contemporaneous with a well-diversified marine fauna living in a seaward shoal complex and mid-shelf area. The nature and distribution of these Smithian microbial deposits are not related to any particular deleterious environmental condition, highlighting that observed patterns of biotic recovery after the end-Permian mass extinction were directly influenced by depositional settings. Facies evolution and stratal stacking patterns allow us to identify large, medium and small-scale, as well as elementary depositional sequences. Large and medium-scale sequences are consistent with sea-level changes, whereas small-scale and elementary sequences are better explained by autocyclic processes.
Research Interests:
ABSTRACT Intensive sampling of the lower portion of the Thaynes and Moenkopi Groups (Lower Triassic) at separate localities within the Confusion Range, Pahvant Range, Mineral Mountains, Star Range, Kanarraville, Cedar City, Torrey and San... more
ABSTRACT Intensive sampling of the lower portion of the Thaynes and Moenkopi Groups (Lower Triassic) at separate localities within the Confusion Range, Pahvant Range, Mineral Mountains, Star Range, Kanarraville, Cedar City, Torrey and San Rafael Swell areas (mainly central and southern Utah, USA) leads to the recognition of a new key regional Smithian ammonoid succession. The new biostratigraphical sequence, which is more precise than the long-recognized Meekoceras gracilitatis and Anasibirites kingianus Zones, comprises twelve subdivisions, thus resulting in a sequence with much higher resolution that can be correlated not only with other western USA sites, but also with major worldwide localities as well. Middle and late Smithian faunas contain many taxa with wide geographic distribution, thus enabling long-distance correlation with faunal successions from other regions (e.g., British Columbia, Canadian Arctic, South China, Spiti and Oman). New assemblages from the lowermost beds are the least diversified and poorest preserved; they represent the earliest early/middle Smithian ammonoid faunas reported from the western North American basin. They highlight (a) the sudden Smithian advancement of the marine transgression within this epicontinental sea, (b) that this event is diachronous, and (c) that the paleotopography of the basin most likely was highly irregular. The newly obtained ammonoid succession also allows us to date and follow the transgression from the northern and central part of the basin to the southwesternmost and southeasternmost parts, which were reached during the late Smithian (Anasibirites kingianus beds). In addition, we briefly discuss the now-limited previous regional biozonation in the light of these new results. One new genus (Minersvillites) and nine new species (Kashmirites utahensis, Kashmirites confusionensis, Kashmirites stepheni, ?Xiaoqiaoceras americanum, Minersvillites farai, Inyoites beaverensis, Meekoceras olivieri, Meekoceras millardense, Vercherites undulatus) are also described.
Research Interests:
One of the major issues of macroecology and macroevolution concerns the spatiotemporal fluctuations of biodiversity. Although distinct, those research fields treat two dimensions of biological evolution that are functionally related. The... more
One of the major issues of macroecology and macroevolution concerns the spatiotemporal fluctuations of biodiversity. Although distinct, those research fields treat two dimensions of biological evolution that are functionally related. The fossil record permits their unification by analyzing simultaneously the spatial organization of biodiversity and its temporal evolution. Here we address the following question: how - and to what extent - does phylogeny and morphology influence the macroecological properties of taxa? Our study consists of an integrated approach that quantifies the relationships among the spatial distribution, phylogeny and morphological disparity of early Pliensbachian ammonoids. We analyzed a comprehensive dataset that consists of 104 localities with known palaeocoordinates from the western Tethys and adjacent areas, 214 fully revised ammonoid species, their morphology and phylogenetical relationships. This database covers the early Pliensbachian (Early Jurassic), a...
ABSTRACT The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral-microbialites and various benthic and pelagic organisms. Ecological and... more
ABSTRACT The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian reefs and bioaccumulations that contain fenestral-microbialites and various benthic and pelagic organisms. Ecological and environmental changes during the Early Triassic commonly are assumed to be associated with numerous perturbations (productivity changes, acidification, redox changes, hypercapnia, eustatism and temperature changes) post-dating the Permian–Triassic mass extinction. New data acquired in the Mineral Mountains sediments provide evidence to decipher the relations between depositional environments and the growth and distribution of microbial structures. These data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the Smithian–early Spathian. The studied section records a large-scale depositional sequence during the Dienerian(?)–Spathian interval. During the transgression, depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral–microbial limestones, shallow subtidal marine sponge–microbial reefs to deep subtidal mud-dominated limestones. Storm-induced deposits, microbialite–sponge reefs and shallow subtidal deposits indicate the regression. Three microbialite associations occur in ascending order: (i) a red beds microbialite association deposited in low-energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure; (ii) a Smithian microbialite association formed in moderate to high-energy, tidal conditions where microbialites include stromatolites and associated carbonate grains (oncoids, ooids and peloids); and (iii) a Spathian microbialite association developed in low-energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes. Data indicate that the morphologies of the three microbialites associations are primarily controlled by accommodation, hydrodynamics, bathymetry and grain supply. This study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions. Due to the presence of numerous metazoans associated with microbialites throughout the Smithian increase in accommodation and Spathian decrease in accommodation, the commonly assumed anachronistic character of the Early Triassic microbialites and the traditional view of prolonged deleterious conditions during the Early Triassic time interval is questioned.
Research Interests:
Research Interests:
Research Interests:
Recovery from the devastating Permian–Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch 1, 2. The post-crisis interval was characterized by... more
Recovery from the devastating Permian–Triassic mass extinction about 252 million years ago is usually assumed to have spanned the entire 5 million years of the Early Triassic epoch 1, 2. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity 3. During this interval, metazoan-dominated reefs are thought to have been replaced by microbial deposits that are ...
Research Interests:
The end-Permian mass extinction removed more than 80% of marine genera. Ammonoid cephalopods were among the organisms most affected by this crisis. The analysis of a global diversity data set of ammonoid genera covering about 106 million... more
The end-Permian mass extinction removed more than 80% of marine genera. Ammonoid cephalopods were among the organisms most affected by this crisis. The analysis of a global diversity data set of ammonoid genera covering about 106 million years centered on the Permian-Triassic boundary (PTB) shows that Triassic ammonoids actually reached levels of diversity higher than in the Permian less than 2 million years after the PTB. The data favor a hierarchical rather than logistic model of diversification coupled with a niche incumbency hypothesis. This explosive and nondelayed diversification contrasts with the slow and delayed character of the Triassic biotic recovery as currently illustrated for other, mainly benthic groups such as bivalves and gastropods.
Research Interests:
As interest in the end Permian mass extinction event and the Triassic recovery has grown in recent decades, greater attention has necessarily been focussed on the time framework for this important interval. Intensive sampling of the... more
As interest in the end Permian mass extinction event and the Triassic recovery has grown in recent decades, greater attention has necessarily been focussed on the time framework for this important interval. Intensive sampling of the lower portion of the Thaynes and Moenkopi Groups (Lower Triassic) in central and southern Utah (USA), has lead to the recognition of a new key regional Smithian ammonoid succession. The new biostratigraphic zonation is comprised of twelve subdivisions, resulting in a sequence with much higher resolution than the long-recognized Meekoceras gracilitatis and Anasibirites kingianus Zones, that can be correlated not only with other western USA sites, but also with major localities worldwide. Middle and late Smithian faunas contain many taxa with wide geographic distributions allowing long-distance correlation with faunal successions from other regions such as British Columbia, the Canadian Arctic, South China, Spiti and Oman. Combined with Dienerian data from Nevada, and Spathian data from Nevada, Idaho, California, and Utah, a refined biostratigraphic scheme for the Lower Triassic of the Western USA can be achieved.