Pub Date : 2018-09-01DOI: 10.5604/17313708.1148657
D. Pană, T. Poulton, L. Heaman
Abstract The Jurassic system of the Western Canada Sedimentary Basin records the transition in its tectonic setting from a “passive” back-arc platformal basin to a foreland basin at the western margin of ancient North America. We report new U-Pb zircon ages from bentonite layers and from probable volcanic ash components of clastic detritus in other strata of the Fernie Formation, which encompasses most of the Jurassic in the western portions of the basin and which is now deformed in the Rocky Mountain fold-and-thrust belt. The bentonite ages come from the lower Nordegg Member (Pliensbachian) and an equivalent ash layer in the Lower Fernie phosphatic shale. Detrital zircon spectra from the Bathonian Gryphaea Bed silty limestone and the zircon ages from the mainly Oxfordian Green Beds glauconitic sandstone also are likely indicative of contemporaneous ash-falls. In addition, we review previously published U-Pb bentonite ages from the Fernie Formation and comment on the Jurassic time scale as represented on the International Chronostratigraphic Chart. We have compiled an updated local stratigraphic correlation chart against a time scale that incorporates ages for some of the Middle and Upper Jurassic stage boundaries, from the literature, that differ from those on the current standard charts. The presence of multiple volcanic ashes throughout the Jurassic system in the Western Canada Sedimentary Basin supports tectonostratigraphic models with relatively nearby western magmatic activity. The southeastern Omineca crystalline belt and Quesnellia terrane contain magmatic rocks with ages that could account for all of the Fernie ashes, and are closest to the depositional basin, but source terranes farther afield cannot be ruled out.
摘要加拿大西部沉积盆地侏罗系记录了其构造环境从“被动”弧后平台盆地向古代北美西缘前陆盆地的转变。我们报告了新的U-Pb锆石年龄，这些锆石来自膨润土层和Fernie组其他地层中碎屑碎屑碎屑的可能火山灰成分，该组包括盆地西部的大部分侏罗纪，现在在落基山脉褶皱和逆冲带中变形。膨润土年龄来自下Nordegg段（Pliensbachian）和下Fernie磷质页岩中的等效灰层。Bathonian Gryphaea层粉质石灰岩的碎屑锆石光谱和主要是Oxfordian Green Beds海绿石砂岩的锆石年龄也可能表明了同时代的火山灰降落。此外，我们还回顾了先前发表的Fernie组U-Pb膨润土年龄，并对国际年代地层图上的侏罗纪时间尺度进行了评论。我们根据时间尺度编制了一份更新的当地地层对比图，其中包含了文献中侏罗纪中期和上侏罗纪阶段边界的一些年龄，这些年龄与当前标准图上的年龄不同。加拿大西部沉积盆地侏罗纪系统中存在多个火山灰，这支持了具有相对邻近西部岩浆活动的构造介形图模型。东南部的Omineca结晶带和Quesnellia地体含有岩浆岩，其年龄可以解释Fernie火山灰的全部原因，并且最接近沉积盆地，但不能排除更远的来源地体。
{"title":"U-Pb zircon ages of volcanic ashes integrated with ammonite biostratigraphy, Fernie Formation (Jurassic), Western Canada, with implications for Cordilleran-Foreland basin connections and comments on the Jurassic time scale","authors":"D. Pană, T. Poulton, L. Heaman","doi":"10.5604/17313708.1148657","DOIUrl":"https://doi.org/10.5604/17313708.1148657","url":null,"abstract":"Abstract The Jurassic system of the Western Canada Sedimentary Basin records the transition in its tectonic setting from a “passive” back-arc platformal basin to a foreland basin at the western margin of ancient North America. We report new U-Pb zircon ages from bentonite layers and from probable volcanic ash components of clastic detritus in other strata of the Fernie Formation, which encompasses most of the Jurassic in the western portions of the basin and which is now deformed in the Rocky Mountain fold-and-thrust belt. The bentonite ages come from the lower Nordegg Member (Pliensbachian) and an equivalent ash layer in the Lower Fernie phosphatic shale. Detrital zircon spectra from the Bathonian Gryphaea Bed silty limestone and the zircon ages from the mainly Oxfordian Green Beds glauconitic sandstone also are likely indicative of contemporaneous ash-falls. In addition, we review previously published U-Pb bentonite ages from the Fernie Formation and comment on the Jurassic time scale as represented on the International Chronostratigraphic Chart. We have compiled an updated local stratigraphic correlation chart against a time scale that incorporates ages for some of the Middle and Upper Jurassic stage boundaries, from the literature, that differ from those on the current standard charts. The presence of multiple volcanic ashes throughout the Jurassic system in the Western Canada Sedimentary Basin supports tectonostratigraphic models with relatively nearby western magmatic activity. The southeastern Omineca crystalline belt and Quesnellia terrane contain magmatic rocks with ages that could account for all of the Fernie ashes, and are closest to the depositional basin, but source terranes farther afield cannot be ruled out.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"66 1","pages":"595-622"},"PeriodicalIF":0.0,"publicationDate":"2018-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49533415","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 : 2018-06-01DOI: 10.1306/13391705M1023583
J. M. Wood, H. Sanei, O. Haeri-Ardakani, M. Curtis, Takashi Akai
Abstract Although shale gas systems constitute a new target for commercial hydrocarbon production, only a little attention has been paid to the evolution of these unconventional systems with increasing thermal maturation. This study reports the characterization of samples of the Lower Toarcian (Lower Jurassic) Posidonia Shale from northern Germany at varying levels of thermal maturity (0.5–1.45%Ro [vitrinite reflectance]). Observations were made using an original combination of focused ion beam–scanning electron microscopy (FIB-SEM) and transmission electron microscopy (TEM). We document the formation of microfracture-filling bitumen in close association with kerogen residues with increasing maturity. Porosity evolves from mostly submicrometric interparticle pores in immature samples to intramineral and intraorganic pores (irregular-shape pores of about 1 to 200 nm occurring within the macromolecular structure of pyrobitumen masses) in overmature (gas mature) samples. This intraorganic nanoporosity has most likely come about by the exsolution of gaseous hydrocarbon and been hydrocarbon wet during the thermal maturation processes. The mineralogical assemblage of the investigated samples strongly evolves with increasing thermal maturity. The formation of most of the mineral phases within the oil and gas mature samples is interpreted as resulting from the percolation of sulfate-rich evaporite-derived brines at temperatures of about 140 to 180°C. Although FIB-SEM and TEM images are small compared to field size, the present study emphasizes the need for nanoscale imaging to better constrain hydrocarbon generation processes in gas shale systems.
{"title":"Organic petrography and scanning electron microscopy imaging of a thermal maturity series from the Montney tight-gas and hydrocarbon liquids fairway","authors":"J. M. Wood, H. Sanei, O. Haeri-Ardakani, M. Curtis, Takashi Akai","doi":"10.1306/13391705M1023583","DOIUrl":"https://doi.org/10.1306/13391705M1023583","url":null,"abstract":"Abstract Although shale gas systems constitute a new target for commercial hydrocarbon production, only a little attention has been paid to the evolution of these unconventional systems with increasing thermal maturation. This study reports the characterization of samples of the Lower Toarcian (Lower Jurassic) Posidonia Shale from northern Germany at varying levels of thermal maturity (0.5–1.45%Ro [vitrinite reflectance]). Observations were made using an original combination of focused ion beam–scanning electron microscopy (FIB-SEM) and transmission electron microscopy (TEM). We document the formation of microfracture-filling bitumen in close association with kerogen residues with increasing maturity. Porosity evolves from mostly submicrometric interparticle pores in immature samples to intramineral and intraorganic pores (irregular-shape pores of about 1 to 200 nm occurring within the macromolecular structure of pyrobitumen masses) in overmature (gas mature) samples. This intraorganic nanoporosity has most likely come about by the exsolution of gaseous hydrocarbon and been hydrocarbon wet during the thermal maturation processes. The mineralogical assemblage of the investigated samples strongly evolves with increasing thermal maturity. The formation of most of the mineral phases within the oil and gas mature samples is interpreted as resulting from the percolation of sulfate-rich evaporite-derived brines at temperatures of about 140 to 180°C. Although FIB-SEM and TEM images are small compared to field size, the present study emphasizes the need for nanoscale imaging to better constrain hydrocarbon generation processes in gas shale systems.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"66 1","pages":"53-66"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43054998","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 : 2018-06-01DOI: 10.1016/J.MARPETGEO.2015.10.005
X. Cui, B. Nassichuk
{"title":"Permeability of the Montney Formation in the Western Canada Sedimentary Basin: insights from different laboratory measurements","authors":"X. Cui, B. Nassichuk","doi":"10.1016/J.MARPETGEO.2015.10.005","DOIUrl":"https://doi.org/10.1016/J.MARPETGEO.2015.10.005","url":null,"abstract":"","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"66 1","pages":"394-424"},"PeriodicalIF":0.0,"publicationDate":"2018-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/J.MARPETGEO.2015.10.005","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45870022","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 : 2017-06-01DOI: 10.2113/GSCPGBULL.65.2.279
F. Ferri, M. McMechan, O. Ardakani, H. Sanei
Abstract In Liard Basin of northern British Columbia, syn-depositional motion on the Bovie structure resulted in greater thicknesses of Cretaceous sediments. The Early Cretaceous Garbutt Formation was deposited during the initiation of a major marine transgression. Organic-rich shales and siltstones in its lower part record maximum flooding and have been informally termed the Radioactive Zone (RZ). The Garbutt Formation is dominated by shales and siltstones and is here subdivided into three informal units; the lower Garbutt Formation (LGF), the succeeding RZ and the upper Garbutt Formation (UGF). The combined thickness of the Radioactive Zone and lower Garbutt Formation is 40 to over 120 m thick and can be at greater than 2000 m depth in Liard Basin. The lower Garbutt Formation is not recognized east of the Bovie structure and the RZ is considerably thinner or absent locally, suggesting this area remained high relative to Liard Basin. Total organic carbon and Rock-Eval data suggest that the RZ is a good to very good source rock and that the LGF is also a good source rock. Organic matter is dominantly Type II kerogen, although more terrestrial Type III input becomes prevalent in western parts of the basin. Thermal maturity inferred from Tmax, in addition to hydrogen index levels, indicate that these rocks are in the oil window in northern Liard Basin and in the wet gas window within central Liard Basin. Porosities average 8% and matrix compositions average 39 wt.% quartz, 4 wt.% feldspar and calcite and 53 wt.% clays (illite/mica, kaolinite and chlorite). The properties of the RZ and LGF indicate that a potential liquids-rich shale gas play may occur within central Liard Basin.
{"title":"The Garbutt Formation of Liard Basin, British Columbia: a potential liquids-rich play","authors":"F. Ferri, M. McMechan, O. Ardakani, H. Sanei","doi":"10.2113/GSCPGBULL.65.2.279","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.65.2.279","url":null,"abstract":"Abstract In Liard Basin of northern British Columbia, syn-depositional motion on the Bovie structure resulted in greater thicknesses of Cretaceous sediments. The Early Cretaceous Garbutt Formation was deposited during the initiation of a major marine transgression. Organic-rich shales and siltstones in its lower part record maximum flooding and have been informally termed the Radioactive Zone (RZ). The Garbutt Formation is dominated by shales and siltstones and is here subdivided into three informal units; the lower Garbutt Formation (LGF), the succeeding RZ and the upper Garbutt Formation (UGF). The combined thickness of the Radioactive Zone and lower Garbutt Formation is 40 to over 120 m thick and can be at greater than 2000 m depth in Liard Basin. The lower Garbutt Formation is not recognized east of the Bovie structure and the RZ is considerably thinner or absent locally, suggesting this area remained high relative to Liard Basin. Total organic carbon and Rock-Eval data suggest that the RZ is a good to very good source rock and that the LGF is also a good source rock. Organic matter is dominantly Type II kerogen, although more terrestrial Type III input becomes prevalent in western parts of the basin. Thermal maturity inferred from Tmax, in addition to hydrogen index levels, indicate that these rocks are in the oil window in northern Liard Basin and in the wet gas window within central Liard Basin. Porosities average 8% and matrix compositions average 39 wt.% quartz, 4 wt.% feldspar and calcite and 53 wt.% clays (illite/mica, kaolinite and chlorite). The properties of the RZ and LGF indicate that a potential liquids-rich shale gas play may occur within central Liard Basin.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"65 1","pages":"279-306"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.65.2.279","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44243412","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 : 2017-06-01DOI: 10.2113/GSCPGBULL.65.2.262
A. Shchepetkina, M. Speta, M. Gingras, B. Rivard, S. Pemberton, David Keighley
Abstract The paleoenvironments represented by the middle McMurray Formation have been actively debated within the last few decades. Highly detailed core studies have investigated the ichnology of the middle McMurray to gain insight on the paleodepositional conditions of these sediments. However, oil saturation makes diagnostic sedimentary and biogenic features difficult to see in core surfaces. Following on earlier published research, shortwave infrared (SWIR) hyperspectral imagery is collected, analyzed and compared to a previously studied McMurray Formation core. The method is tested on one well to be applied to the future studies. SWIR imagery significantly enhances the visibility of physical and biological sedimentary structures, especially within coarse-grained, bitumen-saturated intervals. The new observations provide support for interpretations derived from the direct study of the core and, in some cases, provide new observations that refine the core interpretation. Specifically, based on additional trace-fossil observations, lithosome L1 (high- and low-angle cross-stratified sandstone) is interpreted to represent bioturbation consistent with the middle estuary rather than the inner estuary. Deposition of lithosomes L2a (sandstone-dominated IHS) and L2b (equally interbedded sandstone and mudstone IHS) likely occurred in the middle estuary instead of inner to middle estuary. Interpretation of depositional locale is not changed for L2c, whereas L2d (mudstone-dominated burrowed IHS) is now interpreted to be deposited in the middle estuary instead of the previously suggested inner-middle estuary.
{"title":"Hyperspectral imaging as an aid for facies analysis in massive-appearing sediments: a case study from the middle McMurray Formation","authors":"A. Shchepetkina, M. Speta, M. Gingras, B. Rivard, S. Pemberton, David Keighley","doi":"10.2113/GSCPGBULL.65.2.262","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.65.2.262","url":null,"abstract":"Abstract The paleoenvironments represented by the middle McMurray Formation have been actively debated within the last few decades. Highly detailed core studies have investigated the ichnology of the middle McMurray to gain insight on the paleodepositional conditions of these sediments. However, oil saturation makes diagnostic sedimentary and biogenic features difficult to see in core surfaces. Following on earlier published research, shortwave infrared (SWIR) hyperspectral imagery is collected, analyzed and compared to a previously studied McMurray Formation core. The method is tested on one well to be applied to the future studies. SWIR imagery significantly enhances the visibility of physical and biological sedimentary structures, especially within coarse-grained, bitumen-saturated intervals. The new observations provide support for interpretations derived from the direct study of the core and, in some cases, provide new observations that refine the core interpretation. Specifically, based on additional trace-fossil observations, lithosome L1 (high- and low-angle cross-stratified sandstone) is interpreted to represent bioturbation consistent with the middle estuary rather than the inner estuary. Deposition of lithosomes L2a (sandstone-dominated IHS) and L2b (equally interbedded sandstone and mudstone IHS) likely occurred in the middle estuary instead of inner to middle estuary. Interpretation of depositional locale is not changed for L2c, whereas L2d (mudstone-dominated burrowed IHS) is now interpreted to be deposited in the middle estuary instead of the previously suggested inner-middle estuary.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"65 1","pages":"262-278"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.65.2.262","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44131429","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 : 2017-06-01DOI: 10.2113/GSCPGBULL.65.2.307
A. Hedinger
Abstract The term “Sukunka Formation” is proposed for a 113 to 169 metre thick mixed siliciclastic and carbonate unit lying between the Middle Devonian Stone and Dunedin Formations in the Rocky Mountain Front Ranges of northeastern British Columbia. The unit is best developed near the headwaters of the Sukunka River, where it outcrops along a series of closely spaced imbricate thrusts. In the type area, it can be divided into three (informal) members: lower, middle and upper. The lower member overlies the Stone Formation unconformably and consists of inter-bedded orthoquartzite, dolostone and sandy dolostone. It is overlain by the middle member that consists predominantly of brick red weathering siltstones interbedded with minor amounts of dolostone. These ‘red beds’ are readily recognizable in the field and can be used elsewhere in the area to identify thrust imbricates. The upper member consists of a series of thick to massive bedded, well cross-bedded and resistant weathering clean quartzose sandstones which gradationally overlie the middle member. The top of the formation is also disconformable. It is transgressed and overlain by the basal calcareous shales and limes of the Dd-1 member of the Dunedin Formation. However, lag deposits from the Sukunka Formation occur within the basal calcareous shales and limes of the Dd-1 member. This condition is thought to reflect progressive transgression of higher stratigraphic levels of the Sukunka Formation to the east by the rising waters that led to accumulation of the Dunedin Formation. Diagnostic fossils have not been recognized in the Sukunka Formation. Presently, it is dated as early Middle Devonian based solely on stratigraphic position. In the subsurface, in the same stratigraphic position between the Stone and Dunedin formations, unnamed argillaceous, sandy and silty carbonates have also been identified. These, further to the east, may be equivalent to the unnamed detrital unit of the Chinchaga Formation.
{"title":"GEOLOGICAL NOTE Sukunka Formation: a new Middle Devonian lithostratigraphic unit, northeastern British Columbia, Canada","authors":"A. Hedinger","doi":"10.2113/GSCPGBULL.65.2.307","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.65.2.307","url":null,"abstract":"Abstract The term “Sukunka Formation” is proposed for a 113 to 169 metre thick mixed siliciclastic and carbonate unit lying between the Middle Devonian Stone and Dunedin Formations in the Rocky Mountain Front Ranges of northeastern British Columbia. The unit is best developed near the headwaters of the Sukunka River, where it outcrops along a series of closely spaced imbricate thrusts. In the type area, it can be divided into three (informal) members: lower, middle and upper. The lower member overlies the Stone Formation unconformably and consists of inter-bedded orthoquartzite, dolostone and sandy dolostone. It is overlain by the middle member that consists predominantly of brick red weathering siltstones interbedded with minor amounts of dolostone. These ‘red beds’ are readily recognizable in the field and can be used elsewhere in the area to identify thrust imbricates. The upper member consists of a series of thick to massive bedded, well cross-bedded and resistant weathering clean quartzose sandstones which gradationally overlie the middle member. The top of the formation is also disconformable. It is transgressed and overlain by the basal calcareous shales and limes of the Dd-1 member of the Dunedin Formation. However, lag deposits from the Sukunka Formation occur within the basal calcareous shales and limes of the Dd-1 member. This condition is thought to reflect progressive transgression of higher stratigraphic levels of the Sukunka Formation to the east by the rising waters that led to accumulation of the Dunedin Formation. Diagnostic fossils have not been recognized in the Sukunka Formation. Presently, it is dated as early Middle Devonian based solely on stratigraphic position. In the subsurface, in the same stratigraphic position between the Stone and Dunedin formations, unnamed argillaceous, sandy and silty carbonates have also been identified. These, further to the east, may be equivalent to the unnamed detrital unit of the Chinchaga Formation.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"65 1","pages":"307-326"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.65.2.307","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44823236","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 : 2017-06-01DOI: 10.2113/GSCPGBULL.65.2.235
J. Adam, I. Al-Aasm
Abstract Carbonate rocks of the Pekisko Formation make up an important reservoir in west-central Alberta, especially in fields along the Pekisko subcrop edge. They represent a transgressive-regressive carbonate platform sequence comprised of upward shallowing facies, which subsequently underwent extreme erosion leading to the development of karst topography. As a result, diagenetic alteration, mainly through dolomitization and karstification, has affected reservoir characterization for most of the carbonate facies. Several generations of calcite cementation and dolomite are the result of complex diagenetic changes. Calcite cements include isopachous fibrous, equant drusy mosaic, pendant/meniscus, blocky spar, syntaxial, fibrous, and bladed. These cements formed during early and late diagenetic events; pre- syn- and post exposure in shallow and deeper burial realms. There are five types of dolomite identified in the Pekisko Formation, based on petrographic and geochemical analyses: 1) pervasive, fine to coarse crystalline, subhedral to anhedral replacive dolomite;2) void-filling, coarse crystalline, euhedral dolomite cement;3) selective, fine to coarse crystalline, euhedral to anhedral dolomite; 4) dissolution seam-associated, fine crystalline, euhedral dolomite; and 5) saddle dolomite. Dolomite types 1), 3) and 4) are interpreted to have formed early in the diagenetic history and subsequently recrystallized, whereas void-filling, coarse crystalline, euhedral dolomite and saddle dolomite formed later in deeper burial setting. Petrographic evidence for recrystallization of dolomite types, excluding void-filling and saddle dolomite, includes: etching, displayed mainly on euhedral crystals; dissolved cores on many crystals of varying shapes; non-planar crystal boundaries, exclusively in pervasive dolomites; and coarsening crystal size, evident in both pervasive and selective dolomite types. Geochemical evidence, such as pronounced negative shift in oxygen isotopes (by up to 8‰ VPDB) and enrichment of radiogenic Sr isotopes further support this interpretation. There is a definite negative trend whereby wells closest to the subcrop edge have the most negative isotopic values and those farthest away show the least depletion. This trend in δ18O isotope values points to recrystallization of the earlier formed dolomites.
{"title":"Petrologic and geochemical attributes of calcite cementation, dolomitization and dolomite recrystallization: an example from the Mississippian Pekisko Formation, west-central Alberta","authors":"J. Adam, I. Al-Aasm","doi":"10.2113/GSCPGBULL.65.2.235","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.65.2.235","url":null,"abstract":"Abstract Carbonate rocks of the Pekisko Formation make up an important reservoir in west-central Alberta, especially in fields along the Pekisko subcrop edge. They represent a transgressive-regressive carbonate platform sequence comprised of upward shallowing facies, which subsequently underwent extreme erosion leading to the development of karst topography. As a result, diagenetic alteration, mainly through dolomitization and karstification, has affected reservoir characterization for most of the carbonate facies. Several generations of calcite cementation and dolomite are the result of complex diagenetic changes. Calcite cements include isopachous fibrous, equant drusy mosaic, pendant/meniscus, blocky spar, syntaxial, fibrous, and bladed. These cements formed during early and late diagenetic events; pre- syn- and post exposure in shallow and deeper burial realms. There are five types of dolomite identified in the Pekisko Formation, based on petrographic and geochemical analyses: 1) pervasive, fine to coarse crystalline, subhedral to anhedral replacive dolomite;2) void-filling, coarse crystalline, euhedral dolomite cement;3) selective, fine to coarse crystalline, euhedral to anhedral dolomite; 4) dissolution seam-associated, fine crystalline, euhedral dolomite; and 5) saddle dolomite. Dolomite types 1), 3) and 4) are interpreted to have formed early in the diagenetic history and subsequently recrystallized, whereas void-filling, coarse crystalline, euhedral dolomite and saddle dolomite formed later in deeper burial setting. Petrographic evidence for recrystallization of dolomite types, excluding void-filling and saddle dolomite, includes: etching, displayed mainly on euhedral crystals; dissolved cores on many crystals of varying shapes; non-planar crystal boundaries, exclusively in pervasive dolomites; and coarsening crystal size, evident in both pervasive and selective dolomite types. Geochemical evidence, such as pronounced negative shift in oxygen isotopes (by up to 8‰ VPDB) and enrichment of radiogenic Sr isotopes further support this interpretation. There is a definite negative trend whereby wells closest to the subcrop edge have the most negative isotopic values and those farthest away show the least depletion. This trend in δ18O isotope values points to recrystallization of the earlier formed dolomites.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"65 1","pages":"235-261"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.65.2.235","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47071547","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 : 2017-06-01DOI: 10.2113/GSCPGBULL.65.2.327
Timothy P. Bata, J. Parnell, N. Samaila, J. Still
Abstract Seventeen thin sections of Cretaceous oil sands from the Neuquen Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Western Canadian Sedimentary Basin (Canada), Junggar Basin (China), Lower Saxony Basin (Germany), Kangerlussuaq Basin (Greenland), Arabian Basin (Kuwait), Chad Basin (Nigeria), Dahomey Basin (Nigeria), Western Moray Firth Basin (UK), Wessex Basin (UK) and Utah (USA) were examined using the scanning electron microscope (SEM) to improve our understanding on how oil emplacement impairs the progress of diagenesis. Our results show that diagenetic processes affecting sandstones prior to oil emplacement include burial/compaction, silica/calcite cementation, calcite replacement of detrital grains/cements as well as the development of silica overgrowth. Most diagenetic processes were inferred to cease upon oil emplacement into the pores of the sandstones, however, diagenetic processes such as the alteration of detrital grains/cements and precipitation of authigenic minerals/metallic compounds were observed to occur after oil emplacement into the pores of the sandstones. Oil was emplaced in some of the studied Cretaceous oil sands at a relatively early stage when the sandstones were not compacted or cemented. Such Cretaceous oil sands were observed to have had anomalously high porosities of above 38% prior to oil emplacement. The only cement observed in these oil sands are the viscous heavy oils (bitumens) associated with them. Upon extraction of these heavy oils, the oil sands collapse into unconsolidated sands. Occurrence of these bitumen supported Cretaceous sands implies availability of migrating oils while some of the Cretaceous sands were depositing in various basins. Oil emplacement occurred in some of the studied Cretaceous oil sands after the sandstones had undergone some diagenetic processes which did not destroy all their pore spaces. Such Cretaceous oil sands were observed to have had moderate to high porosities of 10%–30% prior to oil emplacement, with some of these sandstones showing evidence of silica overgrowth. Emplacement of oil into the pores of such sandstones is believed to have stopped further development of the silica overgrowth that would have led to the total loss of porosity in these Cretaceous reservoir sands. In some of the studied Cretaceous oil sands, oil emplacement occurred when the sands had experienced a long history of diagenetic events leading to almost total loss of porosity. Common diagenetic features observed in such Cretaceous oil sands include sutured quartz grain-grain contacts and quartz overgrowth.
{"title":"Impact of oil emplacement on diagenesis in Cretaceous oil sands","authors":"Timothy P. Bata, J. Parnell, N. Samaila, J. Still","doi":"10.2113/GSCPGBULL.65.2.327","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.65.2.327","url":null,"abstract":"Abstract Seventeen thin sections of Cretaceous oil sands from the Neuquen Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Western Canadian Sedimentary Basin (Canada), Junggar Basin (China), Lower Saxony Basin (Germany), Kangerlussuaq Basin (Greenland), Arabian Basin (Kuwait), Chad Basin (Nigeria), Dahomey Basin (Nigeria), Western Moray Firth Basin (UK), Wessex Basin (UK) and Utah (USA) were examined using the scanning electron microscope (SEM) to improve our understanding on how oil emplacement impairs the progress of diagenesis. Our results show that diagenetic processes affecting sandstones prior to oil emplacement include burial/compaction, silica/calcite cementation, calcite replacement of detrital grains/cements as well as the development of silica overgrowth. Most diagenetic processes were inferred to cease upon oil emplacement into the pores of the sandstones, however, diagenetic processes such as the alteration of detrital grains/cements and precipitation of authigenic minerals/metallic compounds were observed to occur after oil emplacement into the pores of the sandstones. Oil was emplaced in some of the studied Cretaceous oil sands at a relatively early stage when the sandstones were not compacted or cemented. Such Cretaceous oil sands were observed to have had anomalously high porosities of above 38% prior to oil emplacement. The only cement observed in these oil sands are the viscous heavy oils (bitumens) associated with them. Upon extraction of these heavy oils, the oil sands collapse into unconsolidated sands. Occurrence of these bitumen supported Cretaceous sands implies availability of migrating oils while some of the Cretaceous sands were depositing in various basins. Oil emplacement occurred in some of the studied Cretaceous oil sands after the sandstones had undergone some diagenetic processes which did not destroy all their pore spaces. Such Cretaceous oil sands were observed to have had moderate to high porosities of 10%–30% prior to oil emplacement, with some of these sandstones showing evidence of silica overgrowth. Emplacement of oil into the pores of such sandstones is believed to have stopped further development of the silica overgrowth that would have led to the total loss of porosity in these Cretaceous reservoir sands. In some of the studied Cretaceous oil sands, oil emplacement occurred when the sands had experienced a long history of diagenetic events leading to almost total loss of porosity. Common diagenetic features observed in such Cretaceous oil sands include sutured quartz grain-grain contacts and quartz overgrowth.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"65 1","pages":"327-342"},"PeriodicalIF":0.0,"publicationDate":"2017-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.65.2.327","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43776809","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 : 2017-03-01DOI: 10.2113/GSCPGBULL.65.1.64
G. Hoffman
Abstract The name “Steepbank Formation” is proposed for a paleokarst diamictite deposit that is present along the margins of the Middle Devonian Prairie Evaporite Formation in the Western Canada and Williston sedimentary basins, including the eastern portion of the Athabasca Oil Sands region. This poorly lithified diamictite forms a mappable unit that is distinct in both age and lithology from all contiguous formations. The Steepbank consists of clasts of dolostone, limestone, and siltstone up to the size of boulders with a matrix of silty to sandy calcareous mudstone. The material shows little or no evidence of bedding or sorting. Most clasts are angular and their orientation is commonly random. The diamictite formed in response to the dissolution of thick (up to 300 m) sequences of halite, anhydrite, and gypsum in the Prairie Evaporite Formation and the subsequent failure and collapse of interbedded and overlying insoluble strata. The top contact occurs where the intact strata of an overlying formation can be identified and is commonly gradational. The basal contact with the underlying Keg River Formation is sharp. Both contacts are unconformable. Evaporite dissolution and diamicton deposition likely began in late Middle Devonian time, moving down dip toward the west, and are continuing today near the Athabasca River.
{"title":"The Steepbank Formation: a paleokarst diamictite deposit in the Athabasca Oil Sands region of northeastern Alberta, Canada","authors":"G. Hoffman","doi":"10.2113/GSCPGBULL.65.1.64","DOIUrl":"https://doi.org/10.2113/GSCPGBULL.65.1.64","url":null,"abstract":"Abstract The name “Steepbank Formation” is proposed for a paleokarst diamictite deposit that is present along the margins of the Middle Devonian Prairie Evaporite Formation in the Western Canada and Williston sedimentary basins, including the eastern portion of the Athabasca Oil Sands region. This poorly lithified diamictite forms a mappable unit that is distinct in both age and lithology from all contiguous formations. The Steepbank consists of clasts of dolostone, limestone, and siltstone up to the size of boulders with a matrix of silty to sandy calcareous mudstone. The material shows little or no evidence of bedding or sorting. Most clasts are angular and their orientation is commonly random. The diamictite formed in response to the dissolution of thick (up to 300 m) sequences of halite, anhydrite, and gypsum in the Prairie Evaporite Formation and the subsequent failure and collapse of interbedded and overlying insoluble strata. The top contact occurs where the intact strata of an overlying formation can be identified and is commonly gradational. The basal contact with the underlying Keg River Formation is sharp. Both contacts are unconformable. Evaporite dissolution and diamicton deposition likely began in late Middle Devonian time, moving down dip toward the west, and are continuing today near the Athabasca River.","PeriodicalId":56325,"journal":{"name":"Bullentin of Canadian Petroleum Geology","volume":"65 1","pages":"64-86"},"PeriodicalIF":0.0,"publicationDate":"2017-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.2113/GSCPGBULL.65.1.64","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41384216","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 : 2017-03-01DOI: 10.2113/GSCPGBULL.65.1.87
T. Hauck, J. T. Peterson, B. Hathway, M. Grobe, K. MacCormack
Abstract The distribution and extent of Paleozoic strata within an area encompassing 874 townships in northeast Alberta have been updated based on detailed regional-scale lithostratigraphic mapping and modelling. Precambrian basement paleotopography strongly influenced the distribution of Keg River Formation carbonate buildups and interbuildup basins, which in turn largely controlled the depositional patterns in the overlying Prairie Evaporite Formation. Keg River paleotopography controlled the type of evaporites that were deposited, particularly at the Whitkow Member level of the Prairie Evaporite Formation. Keg River paleotopography continued to have an effect on the overlying sedimentary succession including the Cretaceous strata in areas where evaporites in the Prairie Evaporite Formation were removed by intrastratal dissolution. East of the regional Prairie Evaporite halite dissolution scarp, enhanced structuring of the sub-Cretaceous unconformity occurs by the draping of Waterways strata over Keg River paleotopography, especially along the Athabasca Arch. Structural mapping and modelling of the Prairie Evaporite Formation, and isopach mapping of halite and anhydrite therein using modern well control, provide the basis for an updated version of the location and extent of the Prairie Evaporite halite dissolution scarp. A new regionally correlatable marker bed, the Conklin, is introduced within the Prairie Evaporite Formation. Detailed correlation of this marker bed, along with previously established member and marker bed stratigraphy from the Prairie Evaporite Formation, reveals a well-defined pattern of evaporite karst within the halite dissolution scarp, and provides evidence for the top-down removal of halite throughout the study area. A regional Devonian subcrop model, together with a paleogeographic reconstruction of the sub-Cretaceous unconformity, highlight the control that karst processes in the Prairie Evaporite Formation and resulting Devonian structure have had on accommodation space and depositional patterns in the overlying lowermost formations within the Mannville Group.
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