Although the calcimicrobial reefs of the basinal Little Dal Group (<1080 Ma; >780 Ma) are well-de... more Although the calcimicrobial reefs of the basinal Little Dal Group (<1080 Ma; >780 Ma) are well-described, little is known about related shallow-water facies to the southeast. Study of these platformal carbonates shows that they represent inner, mid-and shallow outer ramp zones of a homoclinal, storm-influenced ramp. Seven depositional sequences are recognized and correlated with reef-bearing strata in the Little Dal basin and in the Shaler Supergroup of Victoria Island.
Page 1. Neoproterozoic reef microstructures from the Little Dal Group, northwestern Canada Elizab... more Page 1. Neoproterozoic reef microstructures from the Little Dal Group, northwestern Canada Elizabeth С Turner Guy M. Narbonne Noel P. James Department of Geological Sciences, Queen's University, Kingston, Ontario K7L ...
Latest Neoproterozoic to earliest Cambrian strata in north-western Canada provide an example of a... more Latest Neoproterozoic to earliest Cambrian strata in north-western Canada provide an example of a pre-vegetation braid-delta depositional system. Depositional environments represented in the succession include braided fluvial and braid-delta distributary channels, aeolian dune fields and interdistributary lagoons/bays, as well as mouth bar, beach to shoreface, and prodelta to distal shelf settings. Three formations have been investigated: the Ingta Formation formed in wave-dominated nearshore to offshore shelf environments with little or no apparent deltaic influence, whereas the overlying Backbone Ranges and Vampire formations contain an extensive record of braid-delta deposits ranging from braidplain to distal prodelta facies. On the braid-plain, river channels reached widths of up to several kilometres. Such channels terminated seaward in braid deltas that showed soke shoreline protuberance and were characterized by fluvial-dominated mouth-bar deposition with lesser wave influence; wave-dominated deltaic successions are rare in the succession. Interdeltaic areas were characterized by wave-dominated prograding shorelines. Interdistributary lagoons probably formed primarily in abandoned distributary channels. Deltafront/prodelta deposits are silt-rich and contain abundant soft-sediment deformation, including slumps. The deposits in these formations illustrate the significantly different nature of sedimentation prior to the advent of land plants. This is illustrated in the dominance of braided fluvial deposition and of silt-rich offshore facies that may have resulted from enhanced aeolian transport of loess. The non-actualistic effects of limited bioturbation and extensive microbial binding apparently exerted relatively little control on the distribution of facies. However, the absence of extensive bioturbation is manifest in pristine preservation of primary sedimentary structures, while the hypothesized latest Proterozoic-earliest Cambrian decline in microbial binding may be reflected in the upward increase in the abundance of sole marks in the succession.
A superbly exposed stromatolite reef complex occurs in the Victor Bay Formation near Strathcona R... more A superbly exposed stromatolite reef complex occurs in the Victor Bay Formation near Strathcona River on northern Baffin Island. Individual reefs are up to 130 m thick and nearly 1 km in length, and their development was clearly related to their position in the facies spectrum and to sea-level dynamics. In the first sea-level cycle, metre-scale reefs grew amongst mid-ramp calcarenites and outer-ramp shales during slow sea-level rise; a 25-m-thick oblate reef tract, separating mid-ramp and outer-ramp facies, formed during the highstand. The greatest period of reef growth was during the second sea-level cycle. Pinnacle reefs nucleated on the karsted upper surface of the oblate reef tract and aggraded rapidly in response to rising sea-level, producing structures with more than 75 m of depositional relief. A gradual symmetrical succession of stromatolite growth forms, from stratiform to cylindrical columns to conical columns and then back through cylindrical columns to stratiform, is mirrored by evidence in offreef deposits for deepening to a maximum flooding surface and then shallowing. The tops of these high-standing reefs were karsted during the following regression, while dolomite 'cryptodomes' grew as sheets on their submerged flanks and as progradational tongues extending basinward of the reefs. Continued sea-level fall resulted in subaerial exposure of the entire reef complex and the extensive formation of surface and subsurface karst.
Ca isotopic compositions of Marinoan post-glacial carbonate successions in Brazil and NW Canada w... more Ca isotopic compositions of Marinoan post-glacial carbonate successions in Brazil and NW Canada were measured. Both basal dolostones display ␦ 44/40 Ca values between 1 and 0.7‰, overlying limestones show a negative Ca isotope excursion to values around 0.1‰, and ␦ 44/40 Ca values rapidly increase up-section to near 2.0‰. In the Brazilian successions, those high ␦ 44/40 Ca values rapidly decrease and stabilize to values between 0.6 and 0.9‰. These Ca isotope secular variation trends are unlike those of Sturtian post-glacial carbonate successions, but similar to those of Marinoan post-glacial carbonate successions in Namibia, suggesting that the perturbation of the marine Ca cycle was global. This recommends Ca isotope stratigraphy as a tool to correlate Neoproterozoic post-glacial carbonate successions worldwide.
Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproterozoic; 565-575 ... more Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproterozoic; 565-575 Ma) represent the oldest known animal communities. In contrast to most Phanerozoic fossil assemblages, in which postmortem transportation, bioturbation, and the accumulation of hardparts obscure community relationships, all fossils in the Mistaken Point assemblages were sessile, soft-bodied organisms that show no evidence of mobility in life or transportation after death. Mistaken Point assemblages are spectacularly preserved on large bedding planes as in situ census populations of hundreds to thousands of fossils, recording the living soft-bodied benthic community at the moment it was smothered by volcanic ash. This unique preservation style allows ecological tests routinely conducted in modern communities (e.g., species richness, abundance, ''biomass,'' diversity, and evenness, as well as statistical tests of nearest-neighbor interactions) to be applied to the fossil communities. Observed patterns of community variability are consistent with the theory that Mistaken Point fossil surfaces are ''snapshots'' recording different stages of ecological succession, progressing from communities of low-level feeders (e.g., pectinates and spindles) to frond-dominated communities with complex tiering and spatial structure. The presence of diverse slope communities at Mistaken Point suggests that the deep sea was colonized rapidly during the evolution of complex organisms. Species richness, abundance, and diversity values, as well as levels of intraspecific interaction, all fall within the typical range observed in modern slope communities. These structural similarities imply that ecological processes present in Ediacaran communities at Mistaken Point were strikingly similar to the processes that operate in modern deepsea animal communities.
Bioturbation long has been 'blamed' for eliminating late Proterozoic-style sedimentary structures... more Bioturbation long has been 'blamed' for eliminating late Proterozoic-style sedimentary structures and fabrics. While the presence of diverse and complex burrows in lowermost Cambrian strata is indisputable, analysis of Precambrian-Cambrian successions in southeast Newfoundland demonstrate that this burrowing style did not produce typical Phanerozoic-style ichnofabrics. Three hundred meters of the siltstone/sandstone facies of member 2 of the Chapel Island Formation were examined in the area of the Precambrian-Cambrian boundary stratotype. Gyrolithes, Planolites, and Skolithos occur as sand infills ubiquitously throughout siltstone beds, most commonly without direct contact with an overlying sandstone bed, as if ''floating'' in the siltstone. In contrast, Treptichnus pedum occurs as sand infills adhering onto the base of thin sandstone beds that have different grain size and texture than the burrow infills. Both of these burrow types represent a style of preservation in which the burrows are unattached to an overlying bed of the casting sediment. These styles of preservation occur frequently in the Treptichnus pedum Zone and continue into the Rusophycus avalonensis Zone in spite of an increase in trace fossil diversity. The sandstone beds are bioturbated only very rarely. The resultant fabric produced by floating and, in particular, adhering burrows in these shallow marine deposits appears to be characteristic of many Lower Cambrian rocks. Silt layers appear to have been firm enough to have supported open burrows, likely as a result of a negligible mixed layer. This line of reasoning would predict that preservation of this type would be uncommon in younger strata deposited in open marine settings.
Abstract Ediacaran fronds at Spaniard&amp;amp;amp;#x27;s Bay on the Avalon Peninsula of Newfo... more Abstract Ediacaran fronds at Spaniard&amp;amp;amp;#x27;s Bay on the Avalon Peninsula of Newfoundland exhibit exquisite, three-dimensional preservation with morphological features less than 0.05 mm in width visible on the best preserved specimens. Most of the nearly 100 specimens are juvenile rangeomorphs, an extinct Ediacaran clade that numerically dominated the early evolution of complex multicellular life. Spaniard&amp;amp;amp;#x27;s Bay rangeomorphs are characterized by cm-scale architectural elements exhibiting self-similar branching over several fractal ...
Three-dimensionally phosphatized, spherical fossils, interpreted as metazoan eggs and embryos on ... more Three-dimensionally phosphatized, spherical fossils, interpreted as metazoan eggs and embryos on the basis of taphonomic features and cleavage patterns, are reported for the first time from the Cambrian of North America. These microfossils occur with a phosphatized biota of skeletonized fossils, including specimens indicative of the earliest Cambrian Anabarites-Protohertzina Zone in the Wernecke Mountains of eastern Yukon Territory, northwestern Canada. They range in size from 0.25 mm to more than 1.0 mm in diameter and can be referred to two genera, Olivooides Archaeooides Qian, 1977. The North American discovery extends the biogeographic range of earliest Cambrian eggs and embryos from coeval successions in China and Siberia, suggesting a wide geographic distribution of these taxa, and emphasizes the crucial role of local environmental and taphonomic conditions in preserving this phosphatic window into the record of early animal evolution. In addition to previously reported taxa, the phosphatized biota also include indeterminate spheroids, fused clusters of Protohertzina siciformis Missarzhevsky, 1973, the enigmatic rodlike fossil Zhejiangorhabdion comptum Yue and Zhao, 1993, phosphatized fossils, including Paradoxiconus typicalis Qian et al., 2001, protoconularid Carinachites sp., and phosphatic tubes assigned to Hyolithellus cf. H. isiticus Missarzhevsky, 1969, cf. Pseudorthotheca sp., and ?Rugatotheca sp.
The Neoproterozoic Ediacara biota at Mistaken Point contains the oldest diverse Ediacaran assembl... more The Neoproterozoic Ediacara biota at Mistaken Point contains the oldest diverse Ediacaran assemblages and is one of the few known deepwater localities, yet the biota is dominated by endemic forms, nearly all of which remain undescribed. Thectardis avalonensis new genus and species, one of these endemic forms, is a cm-scale triangular fossil with a raised rim and a featureless-tofaintly-segmented central depression. More than 200 specimens occur on two bedding plane surfaces: the 565 Ma E surface and the 575 Ma Pigeon Cove surface, nearly 2,000 m lower in the succession. Morphological and taphonomic data suggest that the organism was an elongate cone that may have lived as a suspension-feeding ''mat sticker'' with its pointed base inserted into the microbially bound sediment. If true, Thectardis n. gen. would be the tallest-known mat sticker, reaching a maximum height of over 15 cm. Specimens display little ontogenetic change in length:width ratio, suggesting that Thectardis grew uniformly by incremental addition of material to its distal end. Morphological differences between specimens at two well-separated stratigraphic levels may have resulted from evolutionary or ecophenotypic variation.
Charniodiscus is a leaf-shaped Ediacaran (terminal Neoproterozoic) fossil with a worldwide distri... more Charniodiscus is a leaf-shaped Ediacaran (terminal Neoproterozoic) fossil with a worldwide distribution, but the scarcity of complete specimens has previously hindered evaluation of its taxonomy and ecology. The presence of hundreds of complete (fronds with stem and disc attached) Charniodiscus specimens from the Avalon Zone of Newfoundland has allowed for detailed morphometric analysis of Charniodiscus specimens and permits determination of characteristics which vary with growth (e.g., stem length, frond width, and disc diameter) versus those that reflect taxonomic differences (e.g., number of primary segments, presence of a distal spine, shape ratios). This has led to the recognition of three species of Charniodiscus in the Mistaken Point biota, including numerous specimens of two new taxa, C. procerus n. sp. and C. spinosus n. sp., and rare specimens of the Australian species C. arboreus. C. procerus n. sp. and C. spinosus n. sp. represent similar, yet ecologically distinct forms of upper-level filter feeders with diverging feeding strategies in order to reduce the competition for resources. Ratio plots and principal components analyses (PCAs) confirm the existence of five (possibly six) morphologically distinct species of Charniodiscus worldwide.
Epifaunal tiering, the subdivision of vertical space within a community, is a fundamental attribu... more Epifaunal tiering, the subdivision of vertical space within a community, is a fundamental attribute of Phanerozoic suspension-feeding communities. This paper documents tiering, including the presence of meter-tall organisms, in Neoproterozoic Ediacaran communities. Ediacaran tiering was studied from three exceptionally preserved deep-water communities at Mistaken Point, Newfoundland, which contain in situ census populations of hundreds to thousands of organisms. Tiering consists of overlapping populations of dominant organisms and is characterized by gradational, rather than abrupt, tier boundaries. At least three tiers are apparent: a lower level 0-8 cm above the seafloor, an intermediate level between 8-22 cm above the seafloor, and an upper level that extends as high as 120 cm. Tier boundaries are relatively consistent between communities, but the constituent organisms in each level are variable, suggesting that some Ediacaran taxa could fill different tiers interchangeably. Development of a tiered epifaunal structure is consistent with suspension feeding or absorbing dissolved nutrients directly from seawater. Despite the common occurrence of tall organisms, all communities share a similar population structure in which biomass is concentrated in the basal 10 cm above the seafloor. Comparison with shallow-water Ediacaran localities suggests that the observed tiering structure is typical of Ediacaran communities. Ediacaran tierers also show the fundamental subdivision between organisms and/or colonies that fed along their entire length and those that developed a specialized feeding apparatus, implying that the features of Phanerozoic tiered skeletal ecosystems were first initiated in soft-bodied communities in the late Neoproterozoic. Figure 1. Occurrence of complexly tiered Ediacaran communities at Mistaken Point, Newfoundland. A: Location map (Avalon terrane is shaded). B: Composite stratigraphic section, showing position of Lower Mistaken Point (LMP), D, and E fossil surfaces and ash dated as 565 ؎ 3 Ma.
... The Twitya-Keele transition records mixed siliciclastic-carbonate deposition on a storm-domin... more ... The Twitya-Keele transition records mixed siliciclastic-carbonate deposition on a storm-dominated shelf whose water depths, on the basis of physical sedimentary structures, were ... 1 p. 9-12. AbstractFree; Figures OnlyFree to you; » Full TextFree to you; Full Text (PDF)Free to you. ...
... 2 South Australian Museum, Division of Natural Science, North Terrace, Adelaide, South Austra... more ... 2 South Australian Museum, Division of Natural Science, North Terrace, Adelaide, South Australia 5000, Australia. Next Section. ... Abstract/FREE Full Text. ↵ Kirschvinck, JL, 1992, Late Proterozoic, low-latitude global glaciation: The snowball Earth, in Schopf, JW, and Klein, C., eds ...
The range of Treptichnus pedum, the index trace fossil for the Treptichnus pedum Zone, extends so... more The range of Treptichnus pedum, the index trace fossil for the Treptichnus pedum Zone, extends some 4 m below the Global Standard Stratotype-section and Point for the base of the Cambrian Period at Fortune Head on the Burin Peninsula in southeastern Newfoundland. The identification of zigzag traces of Treptichnus isp., even further below the GSSP than T. pedum in the Fortune Head section, and in other terminal Proterozoic successions around the globe, supports the concept of a gradational onset of three-dimensional burrowing across the Proterozoic-Cambrian boundary. Although T. pedum remains a reasonable indicator for the base of the Cambrian Period, greater precision in the stratotype section can be achieved by a detailed re-evaluation of the stratigraphic ranges and the morphological variation of ichnotaxa included in the T. pedum Zone.
Although the calcimicrobial reefs of the basinal Little Dal Group (<1080 Ma; >780 Ma) are well-de... more Although the calcimicrobial reefs of the basinal Little Dal Group (<1080 Ma; >780 Ma) are well-described, little is known about related shallow-water facies to the southeast. Study of these platformal carbonates shows that they represent inner, mid-and shallow outer ramp zones of a homoclinal, storm-influenced ramp. Seven depositional sequences are recognized and correlated with reef-bearing strata in the Little Dal basin and in the Shaler Supergroup of Victoria Island.
Page 1. Neoproterozoic reef microstructures from the Little Dal Group, northwestern Canada Elizab... more Page 1. Neoproterozoic reef microstructures from the Little Dal Group, northwestern Canada Elizabeth С Turner Guy M. Narbonne Noel P. James Department of Geological Sciences, Queen's University, Kingston, Ontario K7L ...
Latest Neoproterozoic to earliest Cambrian strata in north-western Canada provide an example of a... more Latest Neoproterozoic to earliest Cambrian strata in north-western Canada provide an example of a pre-vegetation braid-delta depositional system. Depositional environments represented in the succession include braided fluvial and braid-delta distributary channels, aeolian dune fields and interdistributary lagoons/bays, as well as mouth bar, beach to shoreface, and prodelta to distal shelf settings. Three formations have been investigated: the Ingta Formation formed in wave-dominated nearshore to offshore shelf environments with little or no apparent deltaic influence, whereas the overlying Backbone Ranges and Vampire formations contain an extensive record of braid-delta deposits ranging from braidplain to distal prodelta facies. On the braid-plain, river channels reached widths of up to several kilometres. Such channels terminated seaward in braid deltas that showed soke shoreline protuberance and were characterized by fluvial-dominated mouth-bar deposition with lesser wave influence; wave-dominated deltaic successions are rare in the succession. Interdeltaic areas were characterized by wave-dominated prograding shorelines. Interdistributary lagoons probably formed primarily in abandoned distributary channels. Deltafront/prodelta deposits are silt-rich and contain abundant soft-sediment deformation, including slumps. The deposits in these formations illustrate the significantly different nature of sedimentation prior to the advent of land plants. This is illustrated in the dominance of braided fluvial deposition and of silt-rich offshore facies that may have resulted from enhanced aeolian transport of loess. The non-actualistic effects of limited bioturbation and extensive microbial binding apparently exerted relatively little control on the distribution of facies. However, the absence of extensive bioturbation is manifest in pristine preservation of primary sedimentary structures, while the hypothesized latest Proterozoic-earliest Cambrian decline in microbial binding may be reflected in the upward increase in the abundance of sole marks in the succession.
A superbly exposed stromatolite reef complex occurs in the Victor Bay Formation near Strathcona R... more A superbly exposed stromatolite reef complex occurs in the Victor Bay Formation near Strathcona River on northern Baffin Island. Individual reefs are up to 130 m thick and nearly 1 km in length, and their development was clearly related to their position in the facies spectrum and to sea-level dynamics. In the first sea-level cycle, metre-scale reefs grew amongst mid-ramp calcarenites and outer-ramp shales during slow sea-level rise; a 25-m-thick oblate reef tract, separating mid-ramp and outer-ramp facies, formed during the highstand. The greatest period of reef growth was during the second sea-level cycle. Pinnacle reefs nucleated on the karsted upper surface of the oblate reef tract and aggraded rapidly in response to rising sea-level, producing structures with more than 75 m of depositional relief. A gradual symmetrical succession of stromatolite growth forms, from stratiform to cylindrical columns to conical columns and then back through cylindrical columns to stratiform, is mirrored by evidence in offreef deposits for deepening to a maximum flooding surface and then shallowing. The tops of these high-standing reefs were karsted during the following regression, while dolomite 'cryptodomes' grew as sheets on their submerged flanks and as progradational tongues extending basinward of the reefs. Continued sea-level fall resulted in subaerial exposure of the entire reef complex and the extensive formation of surface and subsurface karst.
Ca isotopic compositions of Marinoan post-glacial carbonate successions in Brazil and NW Canada w... more Ca isotopic compositions of Marinoan post-glacial carbonate successions in Brazil and NW Canada were measured. Both basal dolostones display ␦ 44/40 Ca values between 1 and 0.7‰, overlying limestones show a negative Ca isotope excursion to values around 0.1‰, and ␦ 44/40 Ca values rapidly increase up-section to near 2.0‰. In the Brazilian successions, those high ␦ 44/40 Ca values rapidly decrease and stabilize to values between 0.6 and 0.9‰. These Ca isotope secular variation trends are unlike those of Sturtian post-glacial carbonate successions, but similar to those of Marinoan post-glacial carbonate successions in Namibia, suggesting that the perturbation of the marine Ca cycle was global. This recommends Ca isotope stratigraphy as a tool to correlate Neoproterozoic post-glacial carbonate successions worldwide.
Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproterozoic; 565-575 ... more Ediacaran fossils at Mistaken Point, southeastern Newfoundland (terminal Neoproterozoic; 565-575 Ma) represent the oldest known animal communities. In contrast to most Phanerozoic fossil assemblages, in which postmortem transportation, bioturbation, and the accumulation of hardparts obscure community relationships, all fossils in the Mistaken Point assemblages were sessile, soft-bodied organisms that show no evidence of mobility in life or transportation after death. Mistaken Point assemblages are spectacularly preserved on large bedding planes as in situ census populations of hundreds to thousands of fossils, recording the living soft-bodied benthic community at the moment it was smothered by volcanic ash. This unique preservation style allows ecological tests routinely conducted in modern communities (e.g., species richness, abundance, ''biomass,'' diversity, and evenness, as well as statistical tests of nearest-neighbor interactions) to be applied to the fossil communities. Observed patterns of community variability are consistent with the theory that Mistaken Point fossil surfaces are ''snapshots'' recording different stages of ecological succession, progressing from communities of low-level feeders (e.g., pectinates and spindles) to frond-dominated communities with complex tiering and spatial structure. The presence of diverse slope communities at Mistaken Point suggests that the deep sea was colonized rapidly during the evolution of complex organisms. Species richness, abundance, and diversity values, as well as levels of intraspecific interaction, all fall within the typical range observed in modern slope communities. These structural similarities imply that ecological processes present in Ediacaran communities at Mistaken Point were strikingly similar to the processes that operate in modern deepsea animal communities.
Bioturbation long has been 'blamed' for eliminating late Proterozoic-style sedimentary structures... more Bioturbation long has been 'blamed' for eliminating late Proterozoic-style sedimentary structures and fabrics. While the presence of diverse and complex burrows in lowermost Cambrian strata is indisputable, analysis of Precambrian-Cambrian successions in southeast Newfoundland demonstrate that this burrowing style did not produce typical Phanerozoic-style ichnofabrics. Three hundred meters of the siltstone/sandstone facies of member 2 of the Chapel Island Formation were examined in the area of the Precambrian-Cambrian boundary stratotype. Gyrolithes, Planolites, and Skolithos occur as sand infills ubiquitously throughout siltstone beds, most commonly without direct contact with an overlying sandstone bed, as if ''floating'' in the siltstone. In contrast, Treptichnus pedum occurs as sand infills adhering onto the base of thin sandstone beds that have different grain size and texture than the burrow infills. Both of these burrow types represent a style of preservation in which the burrows are unattached to an overlying bed of the casting sediment. These styles of preservation occur frequently in the Treptichnus pedum Zone and continue into the Rusophycus avalonensis Zone in spite of an increase in trace fossil diversity. The sandstone beds are bioturbated only very rarely. The resultant fabric produced by floating and, in particular, adhering burrows in these shallow marine deposits appears to be characteristic of many Lower Cambrian rocks. Silt layers appear to have been firm enough to have supported open burrows, likely as a result of a negligible mixed layer. This line of reasoning would predict that preservation of this type would be uncommon in younger strata deposited in open marine settings.
Abstract Ediacaran fronds at Spaniard&amp;amp;amp;#x27;s Bay on the Avalon Peninsula of Newfo... more Abstract Ediacaran fronds at Spaniard&amp;amp;amp;#x27;s Bay on the Avalon Peninsula of Newfoundland exhibit exquisite, three-dimensional preservation with morphological features less than 0.05 mm in width visible on the best preserved specimens. Most of the nearly 100 specimens are juvenile rangeomorphs, an extinct Ediacaran clade that numerically dominated the early evolution of complex multicellular life. Spaniard&amp;amp;amp;#x27;s Bay rangeomorphs are characterized by cm-scale architectural elements exhibiting self-similar branching over several fractal ...
Three-dimensionally phosphatized, spherical fossils, interpreted as metazoan eggs and embryos on ... more Three-dimensionally phosphatized, spherical fossils, interpreted as metazoan eggs and embryos on the basis of taphonomic features and cleavage patterns, are reported for the first time from the Cambrian of North America. These microfossils occur with a phosphatized biota of skeletonized fossils, including specimens indicative of the earliest Cambrian Anabarites-Protohertzina Zone in the Wernecke Mountains of eastern Yukon Territory, northwestern Canada. They range in size from 0.25 mm to more than 1.0 mm in diameter and can be referred to two genera, Olivooides Archaeooides Qian, 1977. The North American discovery extends the biogeographic range of earliest Cambrian eggs and embryos from coeval successions in China and Siberia, suggesting a wide geographic distribution of these taxa, and emphasizes the crucial role of local environmental and taphonomic conditions in preserving this phosphatic window into the record of early animal evolution. In addition to previously reported taxa, the phosphatized biota also include indeterminate spheroids, fused clusters of Protohertzina siciformis Missarzhevsky, 1973, the enigmatic rodlike fossil Zhejiangorhabdion comptum Yue and Zhao, 1993, phosphatized fossils, including Paradoxiconus typicalis Qian et al., 2001, protoconularid Carinachites sp., and phosphatic tubes assigned to Hyolithellus cf. H. isiticus Missarzhevsky, 1969, cf. Pseudorthotheca sp., and ?Rugatotheca sp.
The Neoproterozoic Ediacara biota at Mistaken Point contains the oldest diverse Ediacaran assembl... more The Neoproterozoic Ediacara biota at Mistaken Point contains the oldest diverse Ediacaran assemblages and is one of the few known deepwater localities, yet the biota is dominated by endemic forms, nearly all of which remain undescribed. Thectardis avalonensis new genus and species, one of these endemic forms, is a cm-scale triangular fossil with a raised rim and a featureless-tofaintly-segmented central depression. More than 200 specimens occur on two bedding plane surfaces: the 565 Ma E surface and the 575 Ma Pigeon Cove surface, nearly 2,000 m lower in the succession. Morphological and taphonomic data suggest that the organism was an elongate cone that may have lived as a suspension-feeding ''mat sticker'' with its pointed base inserted into the microbially bound sediment. If true, Thectardis n. gen. would be the tallest-known mat sticker, reaching a maximum height of over 15 cm. Specimens display little ontogenetic change in length:width ratio, suggesting that Thectardis grew uniformly by incremental addition of material to its distal end. Morphological differences between specimens at two well-separated stratigraphic levels may have resulted from evolutionary or ecophenotypic variation.
Charniodiscus is a leaf-shaped Ediacaran (terminal Neoproterozoic) fossil with a worldwide distri... more Charniodiscus is a leaf-shaped Ediacaran (terminal Neoproterozoic) fossil with a worldwide distribution, but the scarcity of complete specimens has previously hindered evaluation of its taxonomy and ecology. The presence of hundreds of complete (fronds with stem and disc attached) Charniodiscus specimens from the Avalon Zone of Newfoundland has allowed for detailed morphometric analysis of Charniodiscus specimens and permits determination of characteristics which vary with growth (e.g., stem length, frond width, and disc diameter) versus those that reflect taxonomic differences (e.g., number of primary segments, presence of a distal spine, shape ratios). This has led to the recognition of three species of Charniodiscus in the Mistaken Point biota, including numerous specimens of two new taxa, C. procerus n. sp. and C. spinosus n. sp., and rare specimens of the Australian species C. arboreus. C. procerus n. sp. and C. spinosus n. sp. represent similar, yet ecologically distinct forms of upper-level filter feeders with diverging feeding strategies in order to reduce the competition for resources. Ratio plots and principal components analyses (PCAs) confirm the existence of five (possibly six) morphologically distinct species of Charniodiscus worldwide.
Epifaunal tiering, the subdivision of vertical space within a community, is a fundamental attribu... more Epifaunal tiering, the subdivision of vertical space within a community, is a fundamental attribute of Phanerozoic suspension-feeding communities. This paper documents tiering, including the presence of meter-tall organisms, in Neoproterozoic Ediacaran communities. Ediacaran tiering was studied from three exceptionally preserved deep-water communities at Mistaken Point, Newfoundland, which contain in situ census populations of hundreds to thousands of organisms. Tiering consists of overlapping populations of dominant organisms and is characterized by gradational, rather than abrupt, tier boundaries. At least three tiers are apparent: a lower level 0-8 cm above the seafloor, an intermediate level between 8-22 cm above the seafloor, and an upper level that extends as high as 120 cm. Tier boundaries are relatively consistent between communities, but the constituent organisms in each level are variable, suggesting that some Ediacaran taxa could fill different tiers interchangeably. Development of a tiered epifaunal structure is consistent with suspension feeding or absorbing dissolved nutrients directly from seawater. Despite the common occurrence of tall organisms, all communities share a similar population structure in which biomass is concentrated in the basal 10 cm above the seafloor. Comparison with shallow-water Ediacaran localities suggests that the observed tiering structure is typical of Ediacaran communities. Ediacaran tierers also show the fundamental subdivision between organisms and/or colonies that fed along their entire length and those that developed a specialized feeding apparatus, implying that the features of Phanerozoic tiered skeletal ecosystems were first initiated in soft-bodied communities in the late Neoproterozoic. Figure 1. Occurrence of complexly tiered Ediacaran communities at Mistaken Point, Newfoundland. A: Location map (Avalon terrane is shaded). B: Composite stratigraphic section, showing position of Lower Mistaken Point (LMP), D, and E fossil surfaces and ash dated as 565 ؎ 3 Ma.
... The Twitya-Keele transition records mixed siliciclastic-carbonate deposition on a storm-domin... more ... The Twitya-Keele transition records mixed siliciclastic-carbonate deposition on a storm-dominated shelf whose water depths, on the basis of physical sedimentary structures, were ... 1 p. 9-12. AbstractFree; Figures OnlyFree to you; » Full TextFree to you; Full Text (PDF)Free to you. ...
... 2 South Australian Museum, Division of Natural Science, North Terrace, Adelaide, South Austra... more ... 2 South Australian Museum, Division of Natural Science, North Terrace, Adelaide, South Australia 5000, Australia. Next Section. ... Abstract/FREE Full Text. ↵ Kirschvinck, JL, 1992, Late Proterozoic, low-latitude global glaciation: The snowball Earth, in Schopf, JW, and Klein, C., eds ...
The range of Treptichnus pedum, the index trace fossil for the Treptichnus pedum Zone, extends so... more The range of Treptichnus pedum, the index trace fossil for the Treptichnus pedum Zone, extends some 4 m below the Global Standard Stratotype-section and Point for the base of the Cambrian Period at Fortune Head on the Burin Peninsula in southeastern Newfoundland. The identification of zigzag traces of Treptichnus isp., even further below the GSSP than T. pedum in the Fortune Head section, and in other terminal Proterozoic successions around the globe, supports the concept of a gradational onset of three-dimensional burrowing across the Proterozoic-Cambrian boundary. Although T. pedum remains a reasonable indicator for the base of the Cambrian Period, greater precision in the stratotype section can be achieved by a detailed re-evaluation of the stratigraphic ranges and the morphological variation of ichnotaxa included in the T. pedum Zone.
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Papers by Guy Narbonne