The ichnogenus Teredolites and the Teredolites Ichnofacies is an accepted proxy for marine influe... more The ichnogenus Teredolites and the Teredolites Ichnofacies is an accepted proxy for marine influence in paralic to open marine depositional environments. Actualistic approaches and the process-ichnologic framework allow independent analysis of both quantitative and semiquantitative data to interpret the physicochemical conditions when Teredolites are present. Measurements collected in modern environments and Jurassic–Eocene successions produce a spatially and temporally robust dataset of 14,137 borings from 17 tracemaking genera. Life history strategies of extant tracemakers are reflected in Mesozoic borings, which allow reconstruction of paleosalinity. Trends extrapolated indicate four ecotones in modern paralic to nearshore settings, which can be identified into the Late Cretaceous. These zones display variation in boring metrics (length [L], width [W], L:W ratio, size diversity index), densities, and relative composition of Teredolites. Zone 1 represents upper estuary to tidally ...
Abstract Conditions for deposition of tidally influenced facies are most commonly associated with... more Abstract Conditions for deposition of tidally influenced facies are most commonly associated with transgression; however, tidal influence can also be observed in regressive deposits. Herein we present a regional study that correlates the Loyd and Sego sandstones across the Uinta–Piceance basins, an area rich in both outcrop and subsurface data. Variable energy conditions in these tidally modified deltas result in a complex arrangement of facies and environments, making it difficult to correlate sequence stratigraphic surfaces. We highlight the controls, including tectonics, eustasy, and sediment supply, on depositional environments and sand distribution in these regressive tidally modified deposits. Five environments of deposition (EOD) were identified from a combination of vertical and lateral facies trends and stratal geometries found in outcrops and core. EODs were assigned unique well-log signatures and identified, correlated, and mapped in subsurface logs and outcrop from the Uinta to the Piceance Basin. From a proximal to distal position along shorelines these EODs are: 1) coastal-plain channels and floodplains, 2) tidally influenced valley fills, 3) tidally modified deltas, 4) delta front, and 5) open marine. The regional distribution and stacking of these environments were used to identify ten flooding surfaces and map nine genetic sequences: two in the Loyd Sandstone, four in the lower Sego Sandstone, and three in the upper Sego Sandstone. The interplay of sediment supply, sea-level fluctuations, and active tectonics contribute to the distribution of environments of deposition and sequence stacking patterns. This study is the first to identify the Loyd Sandstone in outcrops along the Rangely Anticline. During deposition of the Loyd Sandstone, sediment supply from up-dip fluvial systems was high. The Loyd Sandstone is interpreted as being deposited in river-flood-dominated but tidally modified deltas that exhibit a generally lobate geometry. In contrast, the lower Sego Sandstone comprises tidally influenced deltas and valley fills, and forms regionally extensive shore-parallel sandstone belts. An increase in tidal energy prevalent in the lower Sego Sandstone is attributed to a combination of high sediment supply, slow relative base-level rise, and active faulting over the Laramide-age Douglas Creek Arch. This process formed complex coastline geometries, which likely amplified tides. The upper Sego Sandstone is interpreted to comprise aggradationally stacked sequences composed of tide- and wave-modified deltas. During the deposition of the upper Sego, sediment supply and accommodation were balanced, causing deltaic depocenters to remain stationary over time. Decreased tectonic activity in the upper Sego diminished the influence of tides on sedimentation. This study correlates the Loyd and Sego from the Uinta to the Piceance basins and sheds light on the applicability of this interval for use as analogs for tidally influenced systems in regressive sequences.
Abstract Turnabout Ridge, a remote outcrop belt in the Beardmore Glacier Region of the Central Tr... more Abstract Turnabout Ridge, a remote outcrop belt in the Beardmore Glacier Region of the Central Transantarctic Mountains, comprises subglacial–glaciomarine deposits of the Pagoda Formation (Fm) overlain by a postglacial deltaic succession of the Mackellar–Fairchild formations (fms). Four depositional environments were identified in the Mackellar–Fairchild fms: 1) prodelta to distal-delta-front deposits that record the initial filling of a newly formed intracratonic basin; 2) an interval dominated by subaqueous terminal distributary channels and levees that signal the advancement of a delta into the region; 3) mouth bars and associated subaqueous terminal distributaries representing the proximal delta front; and 4) an overlying sand-dominated braidplain. A companion ichnologic study identified 30 ichnogenera in the Mackellar Fm that combine to form six ichnocoenoses. Twelve traces are known only from marine settings, 18 are found across marine, brackish, and freshwater systems, and none are known solely from freshwater systems. The ichnology refines paleoenvironmental and paleosalinity interpretations for the Mackellar Fm, and indicates a predominantly brackish water paleoenvironment. Subaqueous terminal distributary channels record the highest energies, suspended sediment concentrations, and sediment loads, and are the conduits that delivered sediment to the delta front and prodelta. Abundant traction deposits (hyperpycnites) displaying only minor wave or tide modification suggest that the delta is best classified as river-flood dominated. The succession exhibits similarities to the Panther Tongue and Ferron Notom deltas of the Cretaceous Western Interior Seaway, USA, and a Late Ordovician proglacial delta from the Murzuq Basin in Libya. The combined ichnologic and sedimentologic evidence suggests that sediment-laden glacial outburst floods produced freshets that recurrently prepped a shallow-marine basin, reducing salinities and allowing for abundant channelization and hyperpycnite deposition along the delta front. Turnabout Ridge likely occupied a proximal and axial position relative to an Antarctic freshwater- and sedimentation-stressed, river-dominated marine deltaic system along the shoreline of an epeiric seaway during the Early Permian.
The ichnogenus Teredolites and the Teredolites Ichnofacies is an accepted proxy for marine influe... more The ichnogenus Teredolites and the Teredolites Ichnofacies is an accepted proxy for marine influence in paralic to open marine depositional environments. Actualistic approaches and the process-ichnologic framework allow independent analysis of both quantitative and semiquantitative data to interpret the physicochemical conditions when Teredolites are present. Measurements collected in modern environments and Jurassic–Eocene successions produce a spatially and temporally robust dataset of 14,137 borings from 17 tracemaking genera. Life history strategies of extant tracemakers are reflected in Mesozoic borings, which allow reconstruction of paleosalinity. Trends extrapolated indicate four ecotones in modern paralic to nearshore settings, which can be identified into the Late Cretaceous. These zones display variation in boring metrics (length [L], width [W], L:W ratio, size diversity index), densities, and relative composition of Teredolites. Zone 1 represents upper estuary to tidally ...
Abstract Conditions for deposition of tidally influenced facies are most commonly associated with... more Abstract Conditions for deposition of tidally influenced facies are most commonly associated with transgression; however, tidal influence can also be observed in regressive deposits. Herein we present a regional study that correlates the Loyd and Sego sandstones across the Uinta–Piceance basins, an area rich in both outcrop and subsurface data. Variable energy conditions in these tidally modified deltas result in a complex arrangement of facies and environments, making it difficult to correlate sequence stratigraphic surfaces. We highlight the controls, including tectonics, eustasy, and sediment supply, on depositional environments and sand distribution in these regressive tidally modified deposits. Five environments of deposition (EOD) were identified from a combination of vertical and lateral facies trends and stratal geometries found in outcrops and core. EODs were assigned unique well-log signatures and identified, correlated, and mapped in subsurface logs and outcrop from the Uinta to the Piceance Basin. From a proximal to distal position along shorelines these EODs are: 1) coastal-plain channels and floodplains, 2) tidally influenced valley fills, 3) tidally modified deltas, 4) delta front, and 5) open marine. The regional distribution and stacking of these environments were used to identify ten flooding surfaces and map nine genetic sequences: two in the Loyd Sandstone, four in the lower Sego Sandstone, and three in the upper Sego Sandstone. The interplay of sediment supply, sea-level fluctuations, and active tectonics contribute to the distribution of environments of deposition and sequence stacking patterns. This study is the first to identify the Loyd Sandstone in outcrops along the Rangely Anticline. During deposition of the Loyd Sandstone, sediment supply from up-dip fluvial systems was high. The Loyd Sandstone is interpreted as being deposited in river-flood-dominated but tidally modified deltas that exhibit a generally lobate geometry. In contrast, the lower Sego Sandstone comprises tidally influenced deltas and valley fills, and forms regionally extensive shore-parallel sandstone belts. An increase in tidal energy prevalent in the lower Sego Sandstone is attributed to a combination of high sediment supply, slow relative base-level rise, and active faulting over the Laramide-age Douglas Creek Arch. This process formed complex coastline geometries, which likely amplified tides. The upper Sego Sandstone is interpreted to comprise aggradationally stacked sequences composed of tide- and wave-modified deltas. During the deposition of the upper Sego, sediment supply and accommodation were balanced, causing deltaic depocenters to remain stationary over time. Decreased tectonic activity in the upper Sego diminished the influence of tides on sedimentation. This study correlates the Loyd and Sego from the Uinta to the Piceance basins and sheds light on the applicability of this interval for use as analogs for tidally influenced systems in regressive sequences.
Abstract Turnabout Ridge, a remote outcrop belt in the Beardmore Glacier Region of the Central Tr... more Abstract Turnabout Ridge, a remote outcrop belt in the Beardmore Glacier Region of the Central Transantarctic Mountains, comprises subglacial–glaciomarine deposits of the Pagoda Formation (Fm) overlain by a postglacial deltaic succession of the Mackellar–Fairchild formations (fms). Four depositional environments were identified in the Mackellar–Fairchild fms: 1) prodelta to distal-delta-front deposits that record the initial filling of a newly formed intracratonic basin; 2) an interval dominated by subaqueous terminal distributary channels and levees that signal the advancement of a delta into the region; 3) mouth bars and associated subaqueous terminal distributaries representing the proximal delta front; and 4) an overlying sand-dominated braidplain. A companion ichnologic study identified 30 ichnogenera in the Mackellar Fm that combine to form six ichnocoenoses. Twelve traces are known only from marine settings, 18 are found across marine, brackish, and freshwater systems, and none are known solely from freshwater systems. The ichnology refines paleoenvironmental and paleosalinity interpretations for the Mackellar Fm, and indicates a predominantly brackish water paleoenvironment. Subaqueous terminal distributary channels record the highest energies, suspended sediment concentrations, and sediment loads, and are the conduits that delivered sediment to the delta front and prodelta. Abundant traction deposits (hyperpycnites) displaying only minor wave or tide modification suggest that the delta is best classified as river-flood dominated. The succession exhibits similarities to the Panther Tongue and Ferron Notom deltas of the Cretaceous Western Interior Seaway, USA, and a Late Ordovician proglacial delta from the Murzuq Basin in Libya. The combined ichnologic and sedimentologic evidence suggests that sediment-laden glacial outburst floods produced freshets that recurrently prepped a shallow-marine basin, reducing salinities and allowing for abundant channelization and hyperpycnite deposition along the delta front. Turnabout Ridge likely occupied a proximal and axial position relative to an Antarctic freshwater- and sedimentation-stressed, river-dominated marine deltaic system along the shoreline of an epeiric seaway during the Early Permian.
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