ABSTRACT The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian 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.
Geological Society of America Abstracts with Programs,, Mar 20, 2008
The Thaynes Formation is known by both professionals and amateurs for its densely concentrated am... more The Thaynes Formation is known by both professionals and amateurs for its densely concentrated ammonoid beds. Indeed, the best locality in the Confusion Range seems to be inexhaustible, despite the sporadic but dedicated efforts of collectors over at least the past several decades. Here's my co-author, Kevin Bylund, doing a grid study of a Thaynes ammonoid bed about 12 years ago.
As interest in the end Permian mass extinction event and the Triassic recovery has grown in recen... 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...
ABSTRACT This work focuses on well-exposed Lower Triassic sedimentary rocks in the area of Torrey... 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.
ABSTRACT A reduction in body size (Lilliput effect) has been repeatedly proposed for many marine ... 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.
... White Mere is a 25 ha, relatively deep (16.5 m max.) lake lying to the south of the ... It ha... more ... White Mere is a 25 ha, relatively deep (16.5 m max.) lake lying to the south of the ... It has no surface inflows or outflows and its water level remains relative-ly constant. ... water and a retention time estimated, from net catchment precipita-tion and volume data, at between 2.5 and 5 ...
Following the Permian-Triassic (PT) mass extinction event, a long-lasting eclipse of metazoan ree... more Following the Permian-Triassic (PT) mass extinction event, a long-lasting eclipse of metazoan reefs and their replacement by an anachronistic proliferation of various microbial deposits have been traditionally perceived as a hallmark of the Early Triassic (~5 m.y.). Here, we document new occurrences of large Early Triassic bioaccumulations and buildups from western USA. They are formed by various sponges and cementing bivalves associated with abundant and diversified dwellers (foraminifera, gastropods, bivalves, ammonoids, ostracods, bryozoans, brachiopods, echinoderms). These new occurrences of metazoan bioconstructions as soon as ~1.5 m.y. after the PT crisis stand in contrast with the currently-favored models of a delayed recovery for benthic communities and metazoan bioconstructions. It also restricts the predominance of microbial reefs and disaster forms to much shorter episodes at the very beginning of the Early Triassic.
The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian... more 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 are commonly assumed to be associated with numerous perturbations (productivity changes, acidifica-tion, 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 relationships 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 microbialite associations are controlled primarily 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.
ABSTRACT The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian 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.
Geological Society of America Abstracts with Programs,, Mar 20, 2008
The Thaynes Formation is known by both professionals and amateurs for its densely concentrated am... more The Thaynes Formation is known by both professionals and amateurs for its densely concentrated ammonoid beds. Indeed, the best locality in the Confusion Range seems to be inexhaustible, despite the sporadic but dedicated efforts of collectors over at least the past several decades. Here's my co-author, Kevin Bylund, doing a grid study of a Thaynes ammonoid bed about 12 years ago.
As interest in the end Permian mass extinction event and the Triassic recovery has grown in recen... 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...
ABSTRACT This work focuses on well-exposed Lower Triassic sedimentary rocks in the area of Torrey... 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.
ABSTRACT A reduction in body size (Lilliput effect) has been repeatedly proposed for many marine ... 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.
... White Mere is a 25 ha, relatively deep (16.5 m max.) lake lying to the south of the ... It ha... more ... White Mere is a 25 ha, relatively deep (16.5 m max.) lake lying to the south of the ... It has no surface inflows or outflows and its water level remains relative-ly constant. ... water and a retention time estimated, from net catchment precipita-tion and volume data, at between 2.5 and 5 ...
Following the Permian-Triassic (PT) mass extinction event, a long-lasting eclipse of metazoan ree... more Following the Permian-Triassic (PT) mass extinction event, a long-lasting eclipse of metazoan reefs and their replacement by an anachronistic proliferation of various microbial deposits have been traditionally perceived as a hallmark of the Early Triassic (~5 m.y.). Here, we document new occurrences of large Early Triassic bioaccumulations and buildups from western USA. They are formed by various sponges and cementing bivalves associated with abundant and diversified dwellers (foraminifera, gastropods, bivalves, ammonoids, ostracods, bryozoans, brachiopods, echinoderms). These new occurrences of metazoan bioconstructions as soon as ~1.5 m.y. after the PT crisis stand in contrast with the currently-favored models of a delayed recovery for benthic communities and metazoan bioconstructions. It also restricts the predominance of microbial reefs and disaster forms to much shorter episodes at the very beginning of the Early Triassic.
The Lower Triassic Mineral Mountains area (Utah, USA) preserves diversified Smithian and Spathian... more 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 are commonly assumed to be associated with numerous perturbations (productivity changes, acidifica-tion, 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 relationships 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 microbialite associations are controlled primarily 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.
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