Articulated thecae of the holocystitid diploporitan echinodermHolocystites scutellatusfrom the mi... more Articulated thecae of the holocystitid diploporitan echinodermHolocystites scutellatusfrom the middle Silurian (Wenlock: Sheinwoodian) Massie Formation of southeastern Indiana, USA, are encrusted by distinctive structures belonging to another echinoderm. A dendritic attachment structure consisting of multiple slender, branching radices, attributable to the camerate crinoidEucalyptocrinites, is present on one side of each of the diploporitan thecae. However, the development of radices is remarkably asymmetrical, with all radices—including one more than 25 mm in length—being present exclusively on one side of the attachment structure. This reflects initial settlement by the encrusting crinoids near the oral or marginal regions rather than the central portion of the diploporitan thecae, which were on their sides; this essentially prohibited further outward growth of radices toward the oral area or edges, but allowed radices oriented in the opposite direction to extend over nearly the e...
New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the c... more New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the chronostratigraphic resolution of the nearly 2 km thick Ordovician section below Anticosti Island. A total of 1414 horizons, spaced at 1.0–1.5 m intervals, were sampled from the New Associated Consolidated Paper (NACP) drill core and analyzed for major and trace elemental composition by portable X-ray fluorescence analyzer (pXRF). Select micrite and calcareous shale powders were then analyzed for δ13Ccarb (number of samples, N = 364) and 87Sr/86Sr (N = 25). Our results indicate a Floian to early Darriwilian (F3–Dw1) age for the Romaine Formation, a middle Darriwilian to Sandbian (Dw2–Sa1) age for the Mingan Formation, a lower to mid-Katian (Ka1–Ka2) age for the Macasty Formation, an upper Katian (Ka3) age for the lower Vauréal Formation, an uppermost Katian (Ka4) age for the upper Vauréal, and a Hirnantian (H1) age for the Ellis Bay Formation. This integrated chemostratigraphic and biostr...
This is an XLSX file with three sheets. The first contains the specimen numbers (field numbers on... more This is an XLSX file with three sheets. The first contains the specimen numbers (field numbers only, as the specimens have not been accessioned), measurements, and regeneration status for all eucladid anal sac spines used in this study; the second contains the same for eucladid calyx spines, and the third for spines of Gennaeocrinus goldringae.
The Upper Silurian Salina Group of eastern North America is well known for its thick evaporite su... more The Upper Silurian Salina Group of eastern North America is well known for its thick evaporite successions and hydrocarbon resources. These strata have been assigned to numerous chronostratigraphic schemes within Ohio and Michigan and are currently identified by varying subsurface and outcrop nomenclatural schemes. These chronostratigraphic challenges have persisted for over 50 yr and dramatically inhibit the correlation of events recorded in the Silurian section of eastern North America with the global record of Silurian biogeochemical events. To help resolve the chronostratigraphic correlation of these units, we provide new high-resolution δ13Ccarb chemostratigraphic analyses of a core located in central Ohio for strata assigned to the Greenfield and Tymochtee Formations and integrate existing biostratigraphic, chemostratigraphic, and subsurface geophysical data in western, southern, and eastern Ohio. The new data presented here, integrated for the first time with basinwide subsur...
Recent studies of eurypterid paleoecology suggest that formation of eurypterid Lagerstätten in th... more Recent studies of eurypterid paleoecology suggest that formation of eurypterid Lagerstätten in the mid-Paleozoic of Laurentia was controlled by the presence of an ecological–taphonomic window that recurred predictably in nearshore, marginal environments during transgressions. We tested this hypothesis by performing a high-resolution taxonomic, environmental, and stratigraphic survey and quantitative analysis of all Silurian–Lower Devonian eurypterid-bearing intervals in the Appalachian basin, the most prolific region for eurypterid remains in the world. Canonical correspondence analysis of sedimentological and faunal associations revealed a strong lithologic gradient between groupings of eurypterid genera and associated taxa across the basin, and a significant association of eurypterids with microbialites (thrombolites, stromatolites) and evaporitic structures. Field observations confirmed that, stratigraphically, eurypterids in the basin frequently occur above the microbialite structures and beneath evaporites and other indicators of increased salinity or subaerial exposure. Following interpretation of these features within a sequence stratigraphic framework, we present a preservational model in which (1) eurypterids inhabited nearshore settings following freshening conditions concomitant with minor transgressions, (2) their remains were subsequently buried by storms or microbialite sediment baffling, and (3) subsequent long-term preservation of tissues was facilitated by regression and cyclical shallowing-up successions that promoted hypersalinity and anoxia. In the central and southern region of the basin, where microbial structures and evidence for hypersalinity are less common, a similar pattern of cyclical shallowing-upward deposition within eurypterid-bearing units holds. Thus, eurypterid preservation appears to reflect a combination of ecological preferences and abiotic conditions that promoted inhabitation and eventual preservation within the same setting. This study provides the first quantitative support for a sea level–based control on preservation of eurypterids and adds to the growing body of evidence that suggests that analysis of exceptional preservation in the fossil record benefits from interpretation within a sequence stratigraphic framework
Articulated thecae of the holocystitid diploporitan echinodermHolocystites scutellatusfrom the mi... more Articulated thecae of the holocystitid diploporitan echinodermHolocystites scutellatusfrom the middle Silurian (Wenlock: Sheinwoodian) Massie Formation of southeastern Indiana, USA, are encrusted by distinctive structures belonging to another echinoderm. A dendritic attachment structure consisting of multiple slender, branching radices, attributable to the camerate crinoidEucalyptocrinites, is present on one side of each of the diploporitan thecae. However, the development of radices is remarkably asymmetrical, with all radices—including one more than 25 mm in length—being present exclusively on one side of the attachment structure. This reflects initial settlement by the encrusting crinoids near the oral or marginal regions rather than the central portion of the diploporitan thecae, which were on their sides; this essentially prohibited further outward growth of radices toward the oral area or edges, but allowed radices oriented in the opposite direction to extend over nearly the e...
New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the c... more New high-resolution chemostratigraphy, in combination with updated biostratigraphy, refines the chronostratigraphic resolution of the nearly 2 km thick Ordovician section below Anticosti Island. A total of 1414 horizons, spaced at 1.0–1.5 m intervals, were sampled from the New Associated Consolidated Paper (NACP) drill core and analyzed for major and trace elemental composition by portable X-ray fluorescence analyzer (pXRF). Select micrite and calcareous shale powders were then analyzed for δ13Ccarb (number of samples, N = 364) and 87Sr/86Sr (N = 25). Our results indicate a Floian to early Darriwilian (F3–Dw1) age for the Romaine Formation, a middle Darriwilian to Sandbian (Dw2–Sa1) age for the Mingan Formation, a lower to mid-Katian (Ka1–Ka2) age for the Macasty Formation, an upper Katian (Ka3) age for the lower Vauréal Formation, an uppermost Katian (Ka4) age for the upper Vauréal, and a Hirnantian (H1) age for the Ellis Bay Formation. This integrated chemostratigraphic and biostr...
This is an XLSX file with three sheets. The first contains the specimen numbers (field numbers on... more This is an XLSX file with three sheets. The first contains the specimen numbers (field numbers only, as the specimens have not been accessioned), measurements, and regeneration status for all eucladid anal sac spines used in this study; the second contains the same for eucladid calyx spines, and the third for spines of Gennaeocrinus goldringae.
The Upper Silurian Salina Group of eastern North America is well known for its thick evaporite su... more The Upper Silurian Salina Group of eastern North America is well known for its thick evaporite successions and hydrocarbon resources. These strata have been assigned to numerous chronostratigraphic schemes within Ohio and Michigan and are currently identified by varying subsurface and outcrop nomenclatural schemes. These chronostratigraphic challenges have persisted for over 50 yr and dramatically inhibit the correlation of events recorded in the Silurian section of eastern North America with the global record of Silurian biogeochemical events. To help resolve the chronostratigraphic correlation of these units, we provide new high-resolution δ13Ccarb chemostratigraphic analyses of a core located in central Ohio for strata assigned to the Greenfield and Tymochtee Formations and integrate existing biostratigraphic, chemostratigraphic, and subsurface geophysical data in western, southern, and eastern Ohio. The new data presented here, integrated for the first time with basinwide subsur...
Recent studies of eurypterid paleoecology suggest that formation of eurypterid Lagerstätten in th... more Recent studies of eurypterid paleoecology suggest that formation of eurypterid Lagerstätten in the mid-Paleozoic of Laurentia was controlled by the presence of an ecological–taphonomic window that recurred predictably in nearshore, marginal environments during transgressions. We tested this hypothesis by performing a high-resolution taxonomic, environmental, and stratigraphic survey and quantitative analysis of all Silurian–Lower Devonian eurypterid-bearing intervals in the Appalachian basin, the most prolific region for eurypterid remains in the world. Canonical correspondence analysis of sedimentological and faunal associations revealed a strong lithologic gradient between groupings of eurypterid genera and associated taxa across the basin, and a significant association of eurypterids with microbialites (thrombolites, stromatolites) and evaporitic structures. Field observations confirmed that, stratigraphically, eurypterids in the basin frequently occur above the microbialite structures and beneath evaporites and other indicators of increased salinity or subaerial exposure. Following interpretation of these features within a sequence stratigraphic framework, we present a preservational model in which (1) eurypterids inhabited nearshore settings following freshening conditions concomitant with minor transgressions, (2) their remains were subsequently buried by storms or microbialite sediment baffling, and (3) subsequent long-term preservation of tissues was facilitated by regression and cyclical shallowing-up successions that promoted hypersalinity and anoxia. In the central and southern region of the basin, where microbial structures and evidence for hypersalinity are less common, a similar pattern of cyclical shallowing-upward deposition within eurypterid-bearing units holds. Thus, eurypterid preservation appears to reflect a combination of ecological preferences and abiotic conditions that promoted inhabitation and eventual preservation within the same setting. This study provides the first quantitative support for a sea level–based control on preservation of eurypterids and adds to the growing body of evidence that suggests that analysis of exceptional preservation in the fossil record benefits from interpretation within a sequence stratigraphic framework
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