Pub Date : 2019-12-01DOI: 10.35767/GSCPGBULL.67.4.215
D. Garner
{"title":"Closing the Gap III: Advances in Applied Geomodeling for Hydrocarbon Reservoirs","authors":"D. Garner","doi":"10.35767/GSCPGBULL.67.4.215","DOIUrl":"https://doi.org/10.35767/GSCPGBULL.67.4.215","url":null,"abstract":"","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"67 1","pages":"215-216"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47594790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.35767/GSCPGBULL.67.4.231
S. Hudson, Scott R. Meek, Blake J. Steeves, Austin Bertoch, Chelsea A. Jolley, A. Trevino, Jason Klimek
Abstract The practice of building analog models and training images from outcrop exposures is an important tool in better predicting subsurface facies distribution in the petroleum industry. As with subsurface data, however, incomplete information and data bias can lead to inaccurate characterization of outcrop geology at multiple scales. Cretaceous fluvial strata of Wyoming offers excellent exposure of two systems — the sand-rich and highly amalgamated Trail Member of the Ericson Sandstone and the sand-poor, isolated channels of the Dry Hollow Member of the Frontier Formation. For each system, multiple outcrops were characterized through the traditional means of stratigraphic column measurement, as well as through photogrammetric survey acquisition and interpretation. We saw in both studies that, despite an effort to measure sections that were representative of the entire outcrop, measured sections consistently overestimated the reservoir proportions. Ten measured sections within the Trail Member show a Net-to-Gross (NTG) ranging from 50–80% sandstone, with an average of 72%. A more complete spatial characterization of the entire outcrop through photogrammetric interpretation suggests a much lower NTG of 53%. Similarly, for the Dry Hollow Member fluvial strata, measured sections show NTG ranges of 8–50% with an average of 37% sandstone, while the photogrammetric model shows a NTG of only 16%. These differences are significant and lead to very different reservoir models. Further, the assumption is commonly made that the outcrop, if well characterized, is representative of the formation at a larger scale. Models of the Dry Hollow Member at Cumberland Gap show that this is a tenuous assumption and can lead to models that are not representative of the system. Outcrops of the Dry Hollow are sparse and often discontinuous, and extrapolation of calculated facies proportions between two well-exposed outcrops at Cumberland Gap led to significant placement of sands between the outcrops, where the lack of exposure leads to a lack of control data in the model. This resulted in increased reservoir connectivity that is not representative of the system, and shows that even on a sub-kilometer scale, the extrapolation of detailed, quantitative facies proportions can be inappropriate, and if done blindly can lead to an inaccurate characterization of the system. Through detailed characterization of the Trail and Dry Hollow fluvial systems, it is shown that building quantitative geomodels from outcrop exposures, even using modern techniques such as photogrammetric analysis, can be subject to significant bias and mischaracterization at multiple scales and for multiple reasons if care is not taken.
{"title":"Characterization of complex fluvial architecture through outcrop studies – dealing with intrinsic data bias at multiple scales in the pursuit of a representative geomodel","authors":"S. Hudson, Scott R. Meek, Blake J. Steeves, Austin Bertoch, Chelsea A. Jolley, A. Trevino, Jason Klimek","doi":"10.35767/GSCPGBULL.67.4.231","DOIUrl":"https://doi.org/10.35767/GSCPGBULL.67.4.231","url":null,"abstract":"Abstract The practice of building analog models and training images from outcrop exposures is an important tool in better predicting subsurface facies distribution in the petroleum industry. As with subsurface data, however, incomplete information and data bias can lead to inaccurate characterization of outcrop geology at multiple scales. Cretaceous fluvial strata of Wyoming offers excellent exposure of two systems — the sand-rich and highly amalgamated Trail Member of the Ericson Sandstone and the sand-poor, isolated channels of the Dry Hollow Member of the Frontier Formation. For each system, multiple outcrops were characterized through the traditional means of stratigraphic column measurement, as well as through photogrammetric survey acquisition and interpretation. We saw in both studies that, despite an effort to measure sections that were representative of the entire outcrop, measured sections consistently overestimated the reservoir proportions. Ten measured sections within the Trail Member show a Net-to-Gross (NTG) ranging from 50–80% sandstone, with an average of 72%. A more complete spatial characterization of the entire outcrop through photogrammetric interpretation suggests a much lower NTG of 53%. Similarly, for the Dry Hollow Member fluvial strata, measured sections show NTG ranges of 8–50% with an average of 37% sandstone, while the photogrammetric model shows a NTG of only 16%. These differences are significant and lead to very different reservoir models. Further, the assumption is commonly made that the outcrop, if well characterized, is representative of the formation at a larger scale. Models of the Dry Hollow Member at Cumberland Gap show that this is a tenuous assumption and can lead to models that are not representative of the system. Outcrops of the Dry Hollow are sparse and often discontinuous, and extrapolation of calculated facies proportions between two well-exposed outcrops at Cumberland Gap led to significant placement of sands between the outcrops, where the lack of exposure leads to a lack of control data in the model. This resulted in increased reservoir connectivity that is not representative of the system, and shows that even on a sub-kilometer scale, the extrapolation of detailed, quantitative facies proportions can be inappropriate, and if done blindly can lead to an inaccurate characterization of the system. Through detailed characterization of the Trail and Dry Hollow fluvial systems, it is shown that building quantitative geomodels from outcrop exposures, even using modern techniques such as photogrammetric analysis, can be subject to significant bias and mischaracterization at multiple scales and for multiple reasons if care is not taken.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"67 1","pages":"231-254"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.35767/GSCPGBULL.67.4.231","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45874965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.35767/GSCPGBULL.67.4.283
O. Babak, J. Gallop
{"title":"Uncovering potential of seismic for reservoir characterization in Canadian oil sands","authors":"O. Babak, J. Gallop","doi":"10.35767/GSCPGBULL.67.4.283","DOIUrl":"https://doi.org/10.35767/GSCPGBULL.67.4.283","url":null,"abstract":"","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"67 1","pages":"283-291"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.35767/GSCPGBULL.67.4.283","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43263086","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.35767/GSCPGBULL.67.4.217
I. Aarnes, H. Vegt, R. Hauge, B. Fjellvoll, K. Nordahl
{"title":"Utilizing sedimentary process-based models as training images for multipoint facies simulations","authors":"I. Aarnes, H. Vegt, R. Hauge, B. Fjellvoll, K. Nordahl","doi":"10.35767/GSCPGBULL.67.4.217","DOIUrl":"https://doi.org/10.35767/GSCPGBULL.67.4.217","url":null,"abstract":"","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"67 1","pages":"217-230"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.35767/GSCPGBULL.67.4.217","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49624790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-01DOI: 10.35767/gscpgbull.67.3.141
S. Agar, W. Li, R. Goteti, Dawn Jobe, Shuo Zhang
A Bayesian Belief Network (BN) has been developed to predict fractures in the subsurface during the early stages of oil and gas exploration. The probability of fractures provides a first-order proxy for spatial variations in fracture intensity at a regional scale. Nodes in the BN, representing geologic variables, were linked in a directed acyclic graph to capture key parameters influencing fracture generation over geologic time. The states of the nodes were defined by expert judgment and conditioned by available datasets. Using regional maps with public data from the Horn River Basin in British Columbia, Canada, predictions for spatial variations in the probability of fractures were generated for the Devonian Muskwa shale. The resulting BN analysis was linked to map-based predictions via a geographic information system. The automated process captures human reasoning and improves this through conditional probability calculations for a complex array of geologic influences. A comparison between inferred high fracture intensities and the locations of wells with high production rates suggests a close correspondence. While several factors could account for variations in production rates from the Muskwa shale, higher fracture densities are a likely influence. The process of constructing and cross-validating the BN supports a consistent approach to predict fracture intensities early in exploration and to prioritize data needed to improve the prediction. As such, BNs provide a mechanism to support alignment within exploration groups. As exploration proceeds, the BN can be used to rapidly update predictions. While the BN does not currently represent time-dependent processes and cannot be applied without adjustment to other regions, it offers a fast and flexible approach for fracture prediction in situations characterized by sparse data.
{"title":"Bayesian artificial intelligence for geologic prediction: Fracture case study, Horn River Basin","authors":"S. Agar, W. Li, R. Goteti, Dawn Jobe, Shuo Zhang","doi":"10.35767/gscpgbull.67.3.141","DOIUrl":"https://doi.org/10.35767/gscpgbull.67.3.141","url":null,"abstract":"\u0000 A Bayesian Belief Network (BN) has been developed to predict fractures in the subsurface during the early stages of oil and gas exploration. The probability of fractures provides a first-order proxy for spatial variations in fracture intensity at a regional scale. Nodes in the BN, representing geologic variables, were linked in a directed acyclic graph to capture key parameters influencing fracture generation over geologic time. The states of the nodes were defined by expert judgment and conditioned by available datasets. Using regional maps with public data from the Horn River Basin in British Columbia, Canada, predictions for spatial variations in the probability of fractures were generated for the Devonian Muskwa shale. The resulting BN analysis was linked to map-based predictions via a geographic information system. The automated process captures human reasoning and improves this through conditional probability calculations for a complex array of geologic influences. A comparison between inferred high fracture intensities and the locations of wells with high production rates suggests a close correspondence. While several factors could account for variations in production rates from the Muskwa shale, higher fracture densities are a likely influence. The process of constructing and cross-validating the BN supports a consistent approach to predict fracture intensities early in exploration and to prioritize data needed to improve the prediction. As such, BNs provide a mechanism to support alignment within exploration groups. As exploration proceeds, the BN can be used to rapidly update predictions. While the BN does not currently represent time-dependent processes and cannot be applied without adjustment to other regions, it offers a fast and flexible approach for fracture prediction in situations characterized by sparse data.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49018729","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-09-01DOI: 10.35767/gscpgbull.67.3.185
N. Bingham-Koslowski, M. Miller, T. McCartney, J. Carey
Paleozoic rocks occur in seven wells in the Hopedale Basin, offshore Labrador (Hopedale E-33, South Hopedale L-39, Tyrk P-100, Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87), where they represent erosional remnants primarily associated with Cretaceous syn-rift half grabens. Previous palynological studies have reported a range of ages for the Paleozoic in these wells, including Ordovician, Devonian, Carboniferous, and undifferentiated Paleozoic. Palynological analyses in the present study confirm that recovery is limited, primarily due to the predominance of lithologies that hinder palynomorph preservation, specifically dolostones. Palynomorphs (predominantly acritarchs and chitinozoans) have been analyzed from new and archived samples from the seven wells and have, for the first time, produced consistent age determinations for the Paleozoic strata in all wells: palynomorph assemblages considered in place indicate a Middle to Late Ordovician age. Thermal maturity was determined from Ordovician acritarchs and leiospheres observed in the Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87 wells, with thermal alteration indices (TAI) ranging from approximately 5+ to 6+ (dry gas). Carboniferous miospores are present from Paleozoic strata in the southern Hopedale Basin wells, where their TAI values range from 3+ to 4. These miospores are interpreted as contaminants introduced into the samples via cavings or as drilling mud contamination. The data presented here provides new biostratigraphic constraints for the Paleozoic of the Hopedale Basin (Middle to Late Ordovician), facilitates the correlation of the Paleozoic intervals in these wells, and enables the consideration of Labrador margin Lower Paleozoic strata in regional studies as well as in paleogeographic and paleoenvironmental reconstructions.
{"title":"Revised biostratigraphic and thermal alteration interpretations for the Paleozoic of the Hopedale Basin, offshore Labrador, Canada","authors":"N. Bingham-Koslowski, M. Miller, T. McCartney, J. Carey","doi":"10.35767/gscpgbull.67.3.185","DOIUrl":"https://doi.org/10.35767/gscpgbull.67.3.185","url":null,"abstract":"\u0000 Paleozoic rocks occur in seven wells in the Hopedale Basin, offshore Labrador (Hopedale E-33, South Hopedale L-39, Tyrk P-100, Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87), where they represent erosional remnants primarily associated with Cretaceous syn-rift half grabens. Previous palynological studies have reported a range of ages for the Paleozoic in these wells, including Ordovician, Devonian, Carboniferous, and undifferentiated Paleozoic. Palynological analyses in the present study confirm that recovery is limited, primarily due to the predominance of lithologies that hinder palynomorph preservation, specifically dolostones. Palynomorphs (predominantly acritarchs and chitinozoans) have been analyzed from new and archived samples from the seven wells and have, for the first time, produced consistent age determinations for the Paleozoic strata in all wells: palynomorph assemblages considered in place indicate a Middle to Late Ordovician age. Thermal maturity was determined from Ordovician acritarchs and leiospheres observed in the Gudrid H-55, Roberval K-92, Indian Harbour M-52, and Freydis B-87 wells, with thermal alteration indices (TAI) ranging from approximately 5+ to 6+ (dry gas). Carboniferous miospores are present from Paleozoic strata in the southern Hopedale Basin wells, where their TAI values range from 3+ to 4. These miospores are interpreted as contaminants introduced into the samples via cavings or as drilling mud contamination. The data presented here provides new biostratigraphic constraints for the Paleozoic of the Hopedale Basin (Middle to Late Ordovician), facilitates the correlation of the Paleozoic intervals in these wells, and enables the consideration of Labrador margin Lower Paleozoic strata in regional studies as well as in paleogeographic and paleoenvironmental reconstructions.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46335297","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-01DOI: 10.35767/gscpgbull.67.2.117
Simone Booker, S. Hubbard, C. Rommens, J. Zonneveld
The Upper Triassic (Carnian) Charlie Lake Formation in northeastern British Columbia, Canada is a heterolithic mixed siliciclastic-carbonate succession of dolomite dolomitic siltstone, well-sorted sandstone, bioclastic sandstone, and anhydrite. This succession is unusual in that it records the only significant non-marine interval in the Triassic of the Western Canadian Sedimentary Basin. In the Kobes-Altares-Blueberry area, moderately abundant core are available through the middle members of the Charlie Lake Formation. All available core were analyzed in order to interpret the depositional setting of constituent members and identify reservoir quality lithofacies and horizons. The middle Charlie Lake Formation in the Kobes-Altares-Blueberry area was deposited in an arid coastal setting. Sixteen lithofacies were identified and placed in three lithofacies assemblages and the latter characterize three depositional settings: coastal salina/playa, aeolian dune, and proximal marine ramps. The coastal salina/playa lithofacies assemblage is heterolithic, and is dominated by dolomitic and anhydritic facies. Depositional subenvironments include intertidal flat, ephemeral lagoon, shore proximal ephemeral lake, sabkha and supratidal paleosol. Potential reservoir lithofacies in this assemblage includes peloidal to stromatolitic dolomitic siltstone deposited in lagoonal and intertidal flat settings. The aeolian dune lithofacies assemblage preserves the movement of small, shore-proximal dunes and associated interdune successions. Well-sorted, fine-grained sandstone beds comprise the best reservoir lithofacies in this assemblage. The proximal marine ramp facies assemblage records several marine transgressions that punctuate the dominantly nonmarine/marginal marine Charlie Lake Formation. Bioclastic packstone, bioclastic sandstone and peloidal dolomitic siltstone to sandstone beds, all exhibit good porosity and are potential hydrocarbon reservoir units within this lithofacies assemblage.
{"title":"Facies associations and depositional environments of a mixed siliciclastic-carbonate marginal marine succession: The Lower Carnian (Upper Triassic) middle Charlie Lake Formation, Kobes-Blueberry area, British Columbia, Canada","authors":"Simone Booker, S. Hubbard, C. Rommens, J. Zonneveld","doi":"10.35767/gscpgbull.67.2.117","DOIUrl":"https://doi.org/10.35767/gscpgbull.67.2.117","url":null,"abstract":"\u0000 The Upper Triassic (Carnian) Charlie Lake Formation in northeastern British Columbia, Canada is a heterolithic mixed siliciclastic-carbonate succession of dolomite dolomitic siltstone, well-sorted sandstone, bioclastic sandstone, and anhydrite. This succession is unusual in that it records the only significant non-marine interval in the Triassic of the Western Canadian Sedimentary Basin. In the Kobes-Altares-Blueberry area, moderately abundant core are available through the middle members of the Charlie Lake Formation. All available core were analyzed in order to interpret the depositional setting of constituent members and identify reservoir quality lithofacies and horizons.\u0000 The middle Charlie Lake Formation in the Kobes-Altares-Blueberry area was deposited in an arid coastal setting. Sixteen lithofacies were identified and placed in three lithofacies assemblages and the latter characterize three depositional settings: coastal salina/playa, aeolian dune, and proximal marine ramps. The coastal salina/playa lithofacies assemblage is heterolithic, and is dominated by dolomitic and anhydritic facies. Depositional subenvironments include intertidal flat, ephemeral lagoon, shore proximal ephemeral lake, sabkha and supratidal paleosol. Potential reservoir lithofacies in this assemblage includes peloidal to stromatolitic dolomitic siltstone deposited in lagoonal and intertidal flat settings. The aeolian dune lithofacies assemblage preserves the movement of small, shore-proximal dunes and associated interdune successions. Well-sorted, fine-grained sandstone beds comprise the best reservoir lithofacies in this assemblage. The proximal marine ramp facies assemblage records several marine transgressions that punctuate the dominantly nonmarine/marginal marine Charlie Lake Formation. Bioclastic packstone, bioclastic sandstone and peloidal dolomitic siltstone to sandstone beds, all exhibit good porosity and are potential hydrocarbon reservoir units within this lithofacies assemblage.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45480614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-01DOI: 10.35767/gscpgbull.67.2.71
A. Plint, Michael A. Kreitner
The great Late Cenomanian transgression of the Greenhorn Sea is recorded in western Alberta and adjacacent British Columbia by shallow-marine deposits of the lower Kaskapau Formation that blanket underlying deltaic deposits of the Dunvegan Formation. Overlying the basal ‘A-X unit’ of the Kaskapau are the allostratigraphically-defined Doe Creek and Pouce Coupe units, each of which forms a SW-thickening wedge up to about 100 m thick. The Doe Creek and Pouce Coupe units comprise, respectively, 10 and 8 allomembers, each defined by a marine flooding surface. Doe Creek facies are organized in upward-shoaling successions less than about 10 m thick. Shallow-water marginal-marine facies prevail in the west and north, with transgressive mudstones overlain by thin, sharp-based shoreface sandstones that, in places, contain roots and dinosaur tracks. In some instances, marine mudstone grades directly upward into a rooted, muddy paleosol. Mapped regionally, these facies define a broad, shallow, SE-facing embayment approximately 200 x 200 km. Trace and molluscan fossils suggest that salinity was below normal marine level, and benthic fauna were, at times, stressed by high turbidity and sedimentation rate. The central part of the embayment is dominated by offshore mudstone that encloses isolated, sharp-based lenticular bodies of clean sandstone up to 9 m thick. Sandstones are ovoid to elongate in plan view, and commonly extend many tens of km N-S or NE-SW. These sandstones are interpreted as top-truncated lowstand delta and strandplain deposits that became isolated on the outer ramp following marine transgression. The sharp base of most shoreface sandstones implies that deposition took place during relative sea-level fall. All Doe Creek allomembers thicken into the foredeep, with the tectonically-flexed surface inclined to the SW. Palaeogeographic maps show, however, that lowstand shorelines were oriented approximately NE-SW, and that the depositional surface sloped to the SE. This geometric relationship implies that, despite tectonic subsidence increasing to the SW, the rate of sediment supply and efficiency of redistribution were able to maintain a wave-graded surface sloping to the SE. Because shorelines migrated across, rather than up and down tectonic dip, allomembers are interpreted to have been controlled primarily by high-rate, high-frequency eustatic cycles, rather than by tectonic movements. The Pouce Coupe unit represents a complete reversal of basin paleogeography relative to the Doe Creek. Pouce Coupe shoreface sandstones are stacked in a linear belt just west of 120°W and grade westward into offshore muddy facies that thicken to the WSW. The entire unit is truncated eastward by the K1 unconformity and is absent over most of Alberta. It is postulated that the Proterozoic Kiskatinaw domain acted as a crustal weak zone, forming a hinge that defined the eastern margin of the Pouce Coupe flexural depocentre.
{"title":"High-frequency sequences, paleogeography, and syn-depositional tectonism on a shallow clastic ramp: Doe Creek and Pouce Coupe members of the Late Cenomanian Kaskapau Formation, Western Canada Foreland Basin","authors":"A. Plint, Michael A. Kreitner","doi":"10.35767/gscpgbull.67.2.71","DOIUrl":"https://doi.org/10.35767/gscpgbull.67.2.71","url":null,"abstract":"\u0000 The great Late Cenomanian transgression of the Greenhorn Sea is recorded in western Alberta and adjacacent British Columbia by shallow-marine deposits of the lower Kaskapau Formation that blanket underlying deltaic deposits of the Dunvegan Formation. Overlying the basal ‘A-X unit’ of the Kaskapau are the allostratigraphically-defined Doe Creek and Pouce Coupe units, each of which forms a SW-thickening wedge up to about 100 m thick. The Doe Creek and Pouce Coupe units comprise, respectively, 10 and 8 allomembers, each defined by a marine flooding surface. Doe Creek facies are organized in upward-shoaling successions less than about 10 m thick. Shallow-water marginal-marine facies prevail in the west and north, with transgressive mudstones overlain by thin, sharp-based shoreface sandstones that, in places, contain roots and dinosaur tracks. In some instances, marine mudstone grades directly upward into a rooted, muddy paleosol. Mapped regionally, these facies define a broad, shallow, SE-facing embayment approximately 200 x 200 km. Trace and molluscan fossils suggest that salinity was below normal marine level, and benthic fauna were, at times, stressed by high turbidity and sedimentation rate. The central part of the embayment is dominated by offshore mudstone that encloses isolated, sharp-based lenticular bodies of clean sandstone up to 9 m thick. Sandstones are ovoid to elongate in plan view, and commonly extend many tens of km N-S or NE-SW. These sandstones are interpreted as top-truncated lowstand delta and strandplain deposits that became isolated on the outer ramp following marine transgression. The sharp base of most shoreface sandstones implies that deposition took place during relative sea-level fall. All Doe Creek allomembers thicken into the foredeep, with the tectonically-flexed surface inclined to the SW. Palaeogeographic maps show, however, that lowstand shorelines were oriented approximately NE-SW, and that the depositional surface sloped to the SE. This geometric relationship implies that, despite tectonic subsidence increasing to the SW, the rate of sediment supply and efficiency of redistribution were able to maintain a wave-graded surface sloping to the SE. Because shorelines migrated across, rather than up and down tectonic dip, allomembers are interpreted to have been controlled primarily by high-rate, high-frequency eustatic cycles, rather than by tectonic movements. The Pouce Coupe unit represents a complete reversal of basin paleogeography relative to the Doe Creek. Pouce Coupe shoreface sandstones are stacked in a linear belt just west of 120°W and grade westward into offshore muddy facies that thicken to the WSW. The entire unit is truncated eastward by the K1 unconformity and is absent over most of Alberta. It is postulated that the Proterozoic Kiskatinaw domain acted as a crustal weak zone, forming a hinge that defined the eastern margin of the Pouce Coupe flexural depocentre.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48281864","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-03-01DOI: 10.35767/gscpgbull.67.1.47
D. Petty
Recently, most researchers have argued for a deep-water origin for black shale in the Bakken Formation of the Williston basin based on sedimentology, paleontology and geochemistry characteristics that place black, laminated, sparsely fossiliferous, radiolarian, pyritic shale as the seaward lithology in an assemblage that originally transitioned landward into shallow-water facies. The shallow-water interpretation advocated in this paper is based on stratigraphic characteristics that include the absence of strata that represent a landward equivalent to the shale, gradual landward shale pinchouts, the restriction of Bakken strata to basinal areas, the Bakken onlap depositional style, and placement of a major maximum flooding surface near the base of the overlying Lodgepole. Black mud deposition in the Bakken is interpreted to have occurred in a low-relief, semi-enclosed, epeiric-lagoon environment with typical water depths of 0–30 m. It is theorized that a high-rainfall climate caused salinity stratification that produced bottom-water anoxia, which preserved organic material. Perhumid climate conditions (year-round rainfall) fostered thick soils and dense vegetation that limited sediment release and induced mud-dominated, sand-poor deposition. During middle Bakken deposition, an arid to semi-arid climate eliminated the bottom-water anoxic conditions and caused carbonate-siliciclastic deposition. The abrupt vertical transitions from black shale (lower Bakken), to carbonate-siliciclastic lithologies (middle Bakken), to black shale (upper Bakken) were caused by paleoclimate change.
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Pub Date : 2019-03-01DOI: 10.35767/gscpgbull.67.1.1
A. Plint
The late Cenomanian Kaskapau Formation records transgression of the Greenhorn Sea over deltaic strata of the Dunvegan Formation. However, stratigraphic and paleogeographic details of the initial stages of this profound reorganization of basin geography have not previously been determined. The basal Kaskapau strata above the Dunvegan Formation are assigned to the informal allostratigraphic ‘A-X unit’. Subsurface and outcrop correlation shows that five regionally-mappable allomembers, bounded by marine flooding surfaces, can be mapped within the A-X unit which, as a whole, forms a wedge that thickens south-westward from <5 to 60 m over approximately 300 km. Within each allomember, three main depositional environments can be distinguished. Sandy heterolithic facies in the north and west form few-metre scale, upward-shoaling successions that contain abundant brackish-water molluscs and are capped by paleosols and dinosaur-trampled surfaces. These rocks represent river-dominated deltas that prograded into a low-energy embayment, about 200 x 200 km, and open to the SE. The central part of the embayment accumulated mud-dominated heterolithic successions with a restricted fauna of lingulid brachiopods and inoceramids, suggestive of turbid, low-energy and reduced salinity conditions. The muddy facies enclose isolated units of well-sorted fine- to very fine-grained sandstone that form NE-SW elongate bodies up to 170 km long, 50 km wide and 11 m thick. Each sandstone body is interpreted to represent the shoreface of one or more strandplains and/or wave-dominated deltas that developed across the mouth of the embayment at sea-level lowstand. Isopach mapping shows that the A-X unit, as a whole, forms a prismatic wedge, thickest adjacent to the fold and thrust belt in the SW. This geometry indicates that accommodation was created by spatially uniform flexural subsidence in response to a linear tectonic load striking NW-SE. Isopach maps of individual allomembers, however, show that subsidence took place in a more complex pattern, with localized depocentres of approximately 100 km radius that suggest brief periods of subsidence before being superseded by a new depocentre along-strike. This pattern may reflect temporally and spatially discontinuous deformation in the adjacent orogenic wedge. During each relative sea-level cycle, the shoreline oscillated by about 150–200 km in a NW-SE direction. Shoreline movement was perpendicular to the direction that would be expected (i.e. SW-NE), if flexural subsidence had been the dominant control on relative sea-level change. This geometric relationship suggests that allomembers were generated by high-frequency, high rate eustatic changes that were superimposed on a lower rate of flexural subsidence. Isopach maps spanning Dunvegan allomembers C, A+B, and the Kaskapau A-X unit show a near 90° anticlockwise rotation of isopleths. This abrupt re-orientation of the axis of flexure marks a new phase of subsidence linked to the
晚Cenomanian Kaskapau组记录了Greenhorn海在Dunvegan组三角洲地层上的海侵。然而，盆地地理深度重组初期的地层和古地理细节此前尚未确定。Dunvegan组上方的基底Kaskapau地层被划分为非正式的异地层“A-X单元”。地下和露头对比表明，在A-X单元内可以绘制出五个以海洋泛滥面为界的区域可绘制的异构体，作为一个整体，A-X单元形成了一个楔形，在大约300km的范围内从<5到60m向西南增厚。在每个异构体内，可以区分三种主要的沉积环境。北部和西部的砂质异石器时代形成了几米规模的向上变浅序列，其中包含丰富的微咸水软体动物，并被古土壤和恐龙践踏的表面覆盖。这些岩石代表以河流为主的三角洲，这些三角洲前进成一个低能量的海湾，约200 x 200公里，并向东南方向开放。海湾的中心部分堆积了以泥浆为主的异石器时代序列，其中有局限的林古利腕足类和无神经酰胺动物群，这表明存在浑浊、低能量和盐度降低的条件。泥相包含分选良好的细粒至极细粒砂岩的孤立单元，这些砂岩形成长170公里、宽50公里、厚11米的NE-SW细长体。每个砂岩体都被解释为代表一个或多个搁浅平原和/或波浪主导三角洲的海岸面，这些三角洲在海平面低水位的海湾河口发育。等厚图显示，A-X单元作为一个整体，形成了一个棱柱楔，在西南部褶皱和逆冲带附近最厚。这种几何形状表明，容纳是由空间均匀的弯曲沉降产生的，以响应NW-SE方向的线性构造载荷。然而，单个同种成员的等厚图显示，沉降以更复杂的模式发生，局部沉积中心半径约100公里，表明在被沿走向的新沉积中心取代之前有短暂的沉降期。这种模式可能反映了相邻造山楔在时间和空间上的不连续变形。在每个相对海平面周期中，海岸线沿NW-SE方向振荡约150–200公里。如果弯曲沉降是相对海平面变化的主要控制因素，海岸线的运动垂直于预期的方向（即SW-NE）。这种几何关系表明，同种成员是由高频、高速率的海平面变化叠加在较低的弯曲沉降率上产生的。Dunvegan同种成员C、A+B和Kaskapau A-X单元的等厚线图显示等厚线逆时针旋转近90°。弯曲轴的突然重新定向标志着一个新的沉降阶段，该阶段与NE向逆冲的开始有关，该逆冲是由穿过落基山脉北部海沟断层约束弯曲的右旋转压驱动的。这种新的应力状态反过来又与北美板块和法拉隆板块之间会聚方向的变化有关。
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