Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been ... more Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been severely limited because of the very low intensity of visible luminescent emissions, which required long photographic exposure times, and because of the difficulty in obtaining quantitative data from CL observations. The solution to this problem is to fit the microscope with a high-sensitivity digital colour video camera linked to a computer with image enhancement and image analysis software. The new technique described in this paper:
Mississippian reservoirs in the Williston Basin characteristically exhibit a high degree of verti... more Mississippian reservoirs in the Williston Basin characteristically exhibit a high degree of vertical and lateral heterogeneity, which largely results from rapid lateral facies changes as well as a complex history of diagenetic processes. In the Alida Beds of southeastern Saskatchewan, a succession of 22 different diagenetic events has been identified based on petrographic and fluid-inclusion work. The diagenetic events can be subdivided into four distinct stages of diagenesis that include: early diagenesis, initial burial diagenesis, diagenesis related to the Mississippian unconformity, and diagenesis during reburial of Mississippian strata under Mesozoic and Cenozoic sediments.
The Mississippian Alida Beds of southeastern Saskatchewan contain a number of prolific oil and ga... more The Mississippian Alida Beds of southeastern Saskatchewan contain a number of prolific oil and gas pools and have produced significant amounts of hydrocarbons over several decades. The unit represents a variety of shallowwater carbonate lithologies interlayered with thin sandy beds. Core examination, well-log analysis, and thin-section petrography of the Alida Beds have been carried out to characterize the sedimentology, delineate facies, and describe the spatial distribution of the unit. Six main lithofacies identified in this study include: crinoidal mudstone/wackestone (and its dolomitized equivalent); echinoderm packstone/grainstone; oolitic packstone/grainstone; peloidal packstone/grainstone; a dolomitic sandstone locally interlayered with the carbonate facies; and a dense anhydrite-dolomite 'caprock' that cross-cuts all other facies. Depositional environments range from subtidal inner shelf to shelf edge and foreslope. Angular caprock clasts within the overlying 'red beds' indicate that the caprock formed before deposition of the Jura-Triassic Lower Watrous Formation.
... Data from the Upper-Middle Devonian Swan Hills Formation in the Rosevear field and Nisku Form... more ... Data from the Upper-Middle Devonian Swan Hills Formation in the Rosevear field and Nisku Formation reefs were also included. ... Analyses5960 EW Mount joy et al. ~ _ Pine PointPresq~l. ~ ~~ .I~'/ ~ III 0 150 + +-+, X .,MieNe_+ Rosevear .~ ~ / 11 ~ II.. ...
ABSTRACT The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the N... more ABSTRACT The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years. Because of the dolomite-hosted reservoirs in the Feixianguan Formation, these dolomites and their formation mechanisms have been a research focus for sedimentary geologists and petroleum geologists. Based on the homogenization temperatures of fluid inclusions, oxygen isotopic composition and their calculated temperatures, and the burial and thermal history of the typical well, it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation, Northeastern Sichuan Basin. Only a minority of dolomites are formed by high-temperature dolomitizing fluids. The ending depth interval of low-temperature dolomitizing fluids was about 1000–2500 m, of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic. The main depth interval of high-temperature dolomitizing fluids was about 3200–4500 m, of which the correspondingly main timing interval was approximately early-middle Middle Jurassic. The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation, Northeastern Sichuan Basin.
There is considerable debate regarding the origin of dolomitization patterns within the Yeoman Fo... more There is considerable debate regarding the origin of dolomitization patterns within the Yeoman Formation. Particular attention has been given to regional dolomitization models and, more recently, to micro-environmental models. However, there is a paucity of studies which focus on the organic matter in these rocks. Analyses of the organic matter can contribute to a better understanding of the paleodepositional environments, the timing of the second generation of burrows, and, perhaps, of the dolomitization patterns within Yeoman strata. Three biozones are recognized based upon the analyses of organic matter content. Biozone 1 is characterized by low organic content and low TOC values; it is associated with dolostones. Biozone 2 contains moderate organic content and has intermediate TOC values. Biozone 2 is generally associated with calcareous dolostones to dolostones. Biozone 3 is typified by high organic content and high TOC values. This biozone is associated with carbonates ranging...
The Middle Devonian Winnipegosis carbonate unit in south-central Saskatchewan is partially to com... more The Middle Devonian Winnipegosis carbonate unit in south-central Saskatchewan is partially to completely dolomitized. Two major types of replacive dolomite are distinguished. Microcrystalline to finely crystalline dolomite (type 1) displays nonplanar-a to planar-s textures, mimetically replaces the precursor limestone, accounts for about four-fifths of dolomite phases volumetrically, and mainly occurs in the Winnipegosis mounds and the Lower Winnipegosis Member directly underlying the mounds. Medium crystalline dolomite (type 2) shows planar-s to planar-e textures, commonly occurs in the Lower Winnipegosis and Brightholme members, and decreases upward in abundance. The 87 Sr/ 86 Sr ratios of type 1 dolomite (0AE70795 to 0AE70807) fall within the estimated Sr-isotopic range for Middle Devonian marine carbonates. Stratigraphic, petrographic and geochemical data constrain the formation of type 1 dolomite to hypersaline sea water in a near-surface environment, after marine cementation and sub-aerial diagenesis and prior to precipitation of the Middle Devonian Leofnard salts. Movement of dolomitizing fluids could be driven by density differences and elevation head. The shift to lower d 18 O values of type 1 dolomite [)7AE4 to )5AE1& Vienna Pee Dee Belemnite (VPDB)] is interpreted as the result of recrystallization at elevated temperatures during burial. Type 2 dolomite has higher 87 Sr/ 86 Sr ratios (0AE70809-0AE70928), suggesting that the dolomite probably formed from basinal fluids with an increased richness in the radiogenic Sr isotope. In type 2 dolomite, Sr 2+ concentrations are lower, and Fe 2+ and Mn 2+ concentrations are higher, compared with the associated limestone and type 1 dolomite. Type 2 dolomite is interpreted as having been formed from upward-migrating basinal fluids during latest Devonian and Carboniferous period.
Two types of 'pseudobreccia', one with grey and the other with brown mottle fabrics, occur in sho... more Two types of 'pseudobreccia', one with grey and the other with brown mottle fabrics, occur in shoaling-upward cycles of the Urswick Limestone Formation of Asbian (Late Dinantian, Carboniferous) age in the southern Lake District, UK. The grey mottle pseudobreccia occurs in cycle-base packstones and developed after backfilling and abandonment of Thalassinoides burrow systems. Burrow infills consist of a fine to coarse crystalline microspar that has dull brown to moderate orange colours under cathodoluminescence. Mottling formed when an early diagenetic 'aerobic decay clock' operating on buried organic material was stopped, and sediment entered the sulphate reduction zone. This probably occurred during progradation of grainstone shoal facies, after which there was initial exposure to meteoric water. Microspar calcites then formed rapidly as a result of aragonite stabilization. The precipitation of the main meteoric cements and aragonite bioclast dissolution post-date this stabilisation event. The brown mottle pseudobreccia fabrics are intimately associated with rhizocretions and calcrete, which developed beneath palaeokarstic surfaces capping cycle-top grainstones and post-date all depositional fabrics, although they may also follow primary depositional heterogeneities such as burrows. They consist of coarse, inclusion-rich, microspar calcites that are always very dull to non-luminescent under cathodoluminescence, sometimes with some thin bright zones. These are interpreted as capillary rise and pedogenic calcrete precipitates. The d 18 O values ()5& to )8&, PDB) and the d 13 C values (+2& to )3&, PDB) of the 'pseudobreccias' are lower than the estimated d 18 O values ()3& to )1& PDB) and d 13 C values of (+2& to +4& PDB) of normal marine calcite precipitated from Late Dinantian sea water, reflecting the influence of meteoric waters and the input of organic carbon.
Dolomitized calcrete is a widespread diagenetic feature in the uppermost portions of the Middle D... more Dolomitized calcrete is a widespread diagenetic feature in the uppermost portions of the Middle Devonian Winnipegosis mud mounds in the subsurface of south -central Saskatchewan. Individual calcrete profiles are composed of 2 to 5 horizons, including (in descending order) laminar crust, massive, pisolitic, breccia, chalky and transitional horizons. The calcrete profiles are interpreted to be pedogenic in origin, formed by diagenetic alteration of the host carbonate deposits during subaerial exposure of the mud mounds. This interpretation is based on the occurrence of an orderly set of well-differentiated horizons, disconformities, vadose pisoids, micritic stringers, circumgranular cracks, linkage coatings, and gradational contacts between the calcrete and underlying host carbonate rocks. Lack of root-related structures, such as rhizoconcretion and alveolar -septal fabric in the Winnipegosis calcrete, suggests a limited influence of macrophytes on the formation of calcrete. The occurrence of up to three discrete pedogenic calcrete profiles in a single Winnipegosis calcrete succession indicates the mounds underwent three periods of subaerial exposure that resulted from drops of water level in the Elk Point Basin of Saskatchewan during Middle Devonian time. D
With a reserve of ∼ 200 Mt ore grading 6.08% Zn and 1.29% Pb (i.e., a metal reserve of ∼ 15 Mt) h... more With a reserve of ∼ 200 Mt ore grading 6.08% Zn and 1.29% Pb (i.e., a metal reserve of ∼ 15 Mt) hosted in Cretaceous and Tertiary terrestrial rocks, the Jinding deposit is the largest Zn-Pb deposit in China, and also the youngest sediment-hosted super giant Zn-Pb deposit in the world. The deposit mainly occurs in the Jinding dome structure as tabular orebodies within brecciabearing sandstones of the Palaeocene Yunlong Formation (autochthonous) and in the overlying sandstones of the Early Cretaceous Jingxing Formation (allochthonous). The deposit is not stratiform and no exhalative sedimentary rocks have been observed. The occurrence of the orebodies, presence of hangingwall alteration, and replacement and open-space filling textures all indicate an epigenetic origin. Formation of the Jinding Zn-Pb deposit is related to a period of major continental crust movement during the collision of the Indian and Eurasian Plates. The westward thrusts and dome structure were successively developed in the Palaeocene sedimentary rocks in the ore district, and Zn-Pb mineralisation appears to have taken place in the early stage of the doming processes.
One hundred and two articulate brachiopods and twenty-one marine cements from Ordovician strata w... more One hundred and two articulate brachiopods and twenty-one marine cements from Ordovician strata were analyzed for oxygen and carbon isotopes. These, together with 200 previously published analyses of Ordovician brachiopods (mostly of Upper Ordovician age), define a general trend of increasing 6'*0 values with decreasing age, from a minimum of -10.5% in the earliest Ordovician to a maximum of -1.5% at the Ordovician/Silurian boundary. The 6 "C values show a general positive correlation with 6180 and increase from -2.5% in the earliest Ordovician to as high as +7% at the Ordovician/Silurian boundary. The magnitudes of Ordovician excursions for both 6 I80 and d 13C are similar to those reported previously for the entire Phanerozoic.
One hundred and fifty-six 87 Sr/ 86 Sr ratios were measured from Ordovician and Silurian brachiop... more One hundred and fifty-six 87 Sr/ 86 Sr ratios were measured from Ordovician and Silurian brachiopod shells, marine calcite cements, and conodonts in order to establish the secular strontium isotope curve for the coeval seawater. Preservation of the brachiopod shell material has been evaluated by petrographic and geochemical criteria and only the well preserved internal secondary layer of the shells has been utilized for strontium isotope measurements. The results document a gradual decrease in 87 Sr/ 86 Sr, from 0.7091 to 0.7087, from Tremadoc to Llandeilo, a sharp decline to 0.7078 during the late Llandeilo-early Caradoc; little change during Caradoc and the Ashgil; and a steady rise to 0.7087 through the Silurian. These long-term (10 7 yr) variations, with magnitudes in the range of 10 Ϫ3 , are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering.
Carbonate rocks of the Middle Devonian Ratner Formation in southern Saskatchewan vary from undolo... more Carbonate rocks of the Middle Devonian Ratner Formation in southern Saskatchewan vary from undolomitized, to partly dolomitized, to completely dolomitized. Two major types of medium and coarsely crystalline dolomite are differentiated in the formation: medium crystalline, planar-e to planar-s (ME) dolomite, and medium to coarsely crystalline, nonplanar-a (CA) dolomite. ME dolomite, which commonly occurs in the lower and middle parts
The Middle Devonian Ratner Formation in south-central Saskatchewan consists of laminated carbonat... more The Middle Devonian Ratner Formation in south-central Saskatchewan consists of laminated carbonate and interlaminated to interbedded carbonate and anhydrite, and the Ratner carbonate is preserved as limestone in many cored intervals. Medium to very coarsely crystalline (MVC) limestone (up to 4 m in thickness) is dominantly present in the uppermost part or the upper cycle of the Ratner Formation directly overlain by the Whitkow anhydrite. Generally, both abundance and size of the MVC calcite crystals decrease downward away from contact between the Ratner carbonate and the Whitkow anhydrite. The average 87 Sr/ 86 Sr ratio of the MVC calcite is 0.7078, comparable to that of Middle Devonian seawater. The Ratner MVC limestone is interpreted to result from neomorphism of the precursor microcrystalline lime mudstone in burial environments, and neomorphic fluids might have consisted of gypsumdehydration water mixing with minor various ratios of formation waters, based on petrographic observation, O-and Srisotopic data, and stratigraphic evidence. This research provides a case study in which the neomorphism of limestone is related to gypsum-dehydration water.
Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been ... more Diagenetic studies of sedimentary rocks using cold cathodoluminescence (CL) microscopy have been severely limited because of the very low intensity of visible luminescent emissions, which required long photographic exposure times, and because of the difficulty in obtaining quantitative data from CL observations. The solution to this problem is to fit the microscope with a high-sensitivity digital colour video camera linked to a computer with image enhancement and image analysis software. The new technique described in this paper:
Mississippian reservoirs in the Williston Basin characteristically exhibit a high degree of verti... more Mississippian reservoirs in the Williston Basin characteristically exhibit a high degree of vertical and lateral heterogeneity, which largely results from rapid lateral facies changes as well as a complex history of diagenetic processes. In the Alida Beds of southeastern Saskatchewan, a succession of 22 different diagenetic events has been identified based on petrographic and fluid-inclusion work. The diagenetic events can be subdivided into four distinct stages of diagenesis that include: early diagenesis, initial burial diagenesis, diagenesis related to the Mississippian unconformity, and diagenesis during reburial of Mississippian strata under Mesozoic and Cenozoic sediments.
The Mississippian Alida Beds of southeastern Saskatchewan contain a number of prolific oil and ga... more The Mississippian Alida Beds of southeastern Saskatchewan contain a number of prolific oil and gas pools and have produced significant amounts of hydrocarbons over several decades. The unit represents a variety of shallowwater carbonate lithologies interlayered with thin sandy beds. Core examination, well-log analysis, and thin-section petrography of the Alida Beds have been carried out to characterize the sedimentology, delineate facies, and describe the spatial distribution of the unit. Six main lithofacies identified in this study include: crinoidal mudstone/wackestone (and its dolomitized equivalent); echinoderm packstone/grainstone; oolitic packstone/grainstone; peloidal packstone/grainstone; a dolomitic sandstone locally interlayered with the carbonate facies; and a dense anhydrite-dolomite 'caprock' that cross-cuts all other facies. Depositional environments range from subtidal inner shelf to shelf edge and foreslope. Angular caprock clasts within the overlying 'red beds' indicate that the caprock formed before deposition of the Jura-Triassic Lower Watrous Formation.
... Data from the Upper-Middle Devonian Swan Hills Formation in the Rosevear field and Nisku Form... more ... Data from the Upper-Middle Devonian Swan Hills Formation in the Rosevear field and Nisku Formation reefs were also included. ... Analyses5960 EW Mount joy et al. ~ _ Pine PointPresq~l. ~ ~~ .I~'/ ~ III 0 150 + +-+, X .,MieNe_+ Rosevear .~ ~ / 11 ~ II.. ...
ABSTRACT The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the N... more ABSTRACT The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years. Because of the dolomite-hosted reservoirs in the Feixianguan Formation, these dolomites and their formation mechanisms have been a research focus for sedimentary geologists and petroleum geologists. Based on the homogenization temperatures of fluid inclusions, oxygen isotopic composition and their calculated temperatures, and the burial and thermal history of the typical well, it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation, Northeastern Sichuan Basin. Only a minority of dolomites are formed by high-temperature dolomitizing fluids. The ending depth interval of low-temperature dolomitizing fluids was about 1000–2500 m, of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic. The main depth interval of high-temperature dolomitizing fluids was about 3200–4500 m, of which the correspondingly main timing interval was approximately early-middle Middle Jurassic. The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation, Northeastern Sichuan Basin.
There is considerable debate regarding the origin of dolomitization patterns within the Yeoman Fo... more There is considerable debate regarding the origin of dolomitization patterns within the Yeoman Formation. Particular attention has been given to regional dolomitization models and, more recently, to micro-environmental models. However, there is a paucity of studies which focus on the organic matter in these rocks. Analyses of the organic matter can contribute to a better understanding of the paleodepositional environments, the timing of the second generation of burrows, and, perhaps, of the dolomitization patterns within Yeoman strata. Three biozones are recognized based upon the analyses of organic matter content. Biozone 1 is characterized by low organic content and low TOC values; it is associated with dolostones. Biozone 2 contains moderate organic content and has intermediate TOC values. Biozone 2 is generally associated with calcareous dolostones to dolostones. Biozone 3 is typified by high organic content and high TOC values. This biozone is associated with carbonates ranging...
The Middle Devonian Winnipegosis carbonate unit in south-central Saskatchewan is partially to com... more The Middle Devonian Winnipegosis carbonate unit in south-central Saskatchewan is partially to completely dolomitized. Two major types of replacive dolomite are distinguished. Microcrystalline to finely crystalline dolomite (type 1) displays nonplanar-a to planar-s textures, mimetically replaces the precursor limestone, accounts for about four-fifths of dolomite phases volumetrically, and mainly occurs in the Winnipegosis mounds and the Lower Winnipegosis Member directly underlying the mounds. Medium crystalline dolomite (type 2) shows planar-s to planar-e textures, commonly occurs in the Lower Winnipegosis and Brightholme members, and decreases upward in abundance. The 87 Sr/ 86 Sr ratios of type 1 dolomite (0AE70795 to 0AE70807) fall within the estimated Sr-isotopic range for Middle Devonian marine carbonates. Stratigraphic, petrographic and geochemical data constrain the formation of type 1 dolomite to hypersaline sea water in a near-surface environment, after marine cementation and sub-aerial diagenesis and prior to precipitation of the Middle Devonian Leofnard salts. Movement of dolomitizing fluids could be driven by density differences and elevation head. The shift to lower d 18 O values of type 1 dolomite [)7AE4 to )5AE1& Vienna Pee Dee Belemnite (VPDB)] is interpreted as the result of recrystallization at elevated temperatures during burial. Type 2 dolomite has higher 87 Sr/ 86 Sr ratios (0AE70809-0AE70928), suggesting that the dolomite probably formed from basinal fluids with an increased richness in the radiogenic Sr isotope. In type 2 dolomite, Sr 2+ concentrations are lower, and Fe 2+ and Mn 2+ concentrations are higher, compared with the associated limestone and type 1 dolomite. Type 2 dolomite is interpreted as having been formed from upward-migrating basinal fluids during latest Devonian and Carboniferous period.
Two types of 'pseudobreccia', one with grey and the other with brown mottle fabrics, occur in sho... more Two types of 'pseudobreccia', one with grey and the other with brown mottle fabrics, occur in shoaling-upward cycles of the Urswick Limestone Formation of Asbian (Late Dinantian, Carboniferous) age in the southern Lake District, UK. The grey mottle pseudobreccia occurs in cycle-base packstones and developed after backfilling and abandonment of Thalassinoides burrow systems. Burrow infills consist of a fine to coarse crystalline microspar that has dull brown to moderate orange colours under cathodoluminescence. Mottling formed when an early diagenetic 'aerobic decay clock' operating on buried organic material was stopped, and sediment entered the sulphate reduction zone. This probably occurred during progradation of grainstone shoal facies, after which there was initial exposure to meteoric water. Microspar calcites then formed rapidly as a result of aragonite stabilization. The precipitation of the main meteoric cements and aragonite bioclast dissolution post-date this stabilisation event. The brown mottle pseudobreccia fabrics are intimately associated with rhizocretions and calcrete, which developed beneath palaeokarstic surfaces capping cycle-top grainstones and post-date all depositional fabrics, although they may also follow primary depositional heterogeneities such as burrows. They consist of coarse, inclusion-rich, microspar calcites that are always very dull to non-luminescent under cathodoluminescence, sometimes with some thin bright zones. These are interpreted as capillary rise and pedogenic calcrete precipitates. The d 18 O values ()5& to )8&, PDB) and the d 13 C values (+2& to )3&, PDB) of the 'pseudobreccias' are lower than the estimated d 18 O values ()3& to )1& PDB) and d 13 C values of (+2& to +4& PDB) of normal marine calcite precipitated from Late Dinantian sea water, reflecting the influence of meteoric waters and the input of organic carbon.
Dolomitized calcrete is a widespread diagenetic feature in the uppermost portions of the Middle D... more Dolomitized calcrete is a widespread diagenetic feature in the uppermost portions of the Middle Devonian Winnipegosis mud mounds in the subsurface of south -central Saskatchewan. Individual calcrete profiles are composed of 2 to 5 horizons, including (in descending order) laminar crust, massive, pisolitic, breccia, chalky and transitional horizons. The calcrete profiles are interpreted to be pedogenic in origin, formed by diagenetic alteration of the host carbonate deposits during subaerial exposure of the mud mounds. This interpretation is based on the occurrence of an orderly set of well-differentiated horizons, disconformities, vadose pisoids, micritic stringers, circumgranular cracks, linkage coatings, and gradational contacts between the calcrete and underlying host carbonate rocks. Lack of root-related structures, such as rhizoconcretion and alveolar -septal fabric in the Winnipegosis calcrete, suggests a limited influence of macrophytes on the formation of calcrete. The occurrence of up to three discrete pedogenic calcrete profiles in a single Winnipegosis calcrete succession indicates the mounds underwent three periods of subaerial exposure that resulted from drops of water level in the Elk Point Basin of Saskatchewan during Middle Devonian time. D
With a reserve of ∼ 200 Mt ore grading 6.08% Zn and 1.29% Pb (i.e., a metal reserve of ∼ 15 Mt) h... more With a reserve of ∼ 200 Mt ore grading 6.08% Zn and 1.29% Pb (i.e., a metal reserve of ∼ 15 Mt) hosted in Cretaceous and Tertiary terrestrial rocks, the Jinding deposit is the largest Zn-Pb deposit in China, and also the youngest sediment-hosted super giant Zn-Pb deposit in the world. The deposit mainly occurs in the Jinding dome structure as tabular orebodies within brecciabearing sandstones of the Palaeocene Yunlong Formation (autochthonous) and in the overlying sandstones of the Early Cretaceous Jingxing Formation (allochthonous). The deposit is not stratiform and no exhalative sedimentary rocks have been observed. The occurrence of the orebodies, presence of hangingwall alteration, and replacement and open-space filling textures all indicate an epigenetic origin. Formation of the Jinding Zn-Pb deposit is related to a period of major continental crust movement during the collision of the Indian and Eurasian Plates. The westward thrusts and dome structure were successively developed in the Palaeocene sedimentary rocks in the ore district, and Zn-Pb mineralisation appears to have taken place in the early stage of the doming processes.
One hundred and two articulate brachiopods and twenty-one marine cements from Ordovician strata w... more One hundred and two articulate brachiopods and twenty-one marine cements from Ordovician strata were analyzed for oxygen and carbon isotopes. These, together with 200 previously published analyses of Ordovician brachiopods (mostly of Upper Ordovician age), define a general trend of increasing 6'*0 values with decreasing age, from a minimum of -10.5% in the earliest Ordovician to a maximum of -1.5% at the Ordovician/Silurian boundary. The 6 "C values show a general positive correlation with 6180 and increase from -2.5% in the earliest Ordovician to as high as +7% at the Ordovician/Silurian boundary. The magnitudes of Ordovician excursions for both 6 I80 and d 13C are similar to those reported previously for the entire Phanerozoic.
One hundred and fifty-six 87 Sr/ 86 Sr ratios were measured from Ordovician and Silurian brachiop... more One hundred and fifty-six 87 Sr/ 86 Sr ratios were measured from Ordovician and Silurian brachiopod shells, marine calcite cements, and conodonts in order to establish the secular strontium isotope curve for the coeval seawater. Preservation of the brachiopod shell material has been evaluated by petrographic and geochemical criteria and only the well preserved internal secondary layer of the shells has been utilized for strontium isotope measurements. The results document a gradual decrease in 87 Sr/ 86 Sr, from 0.7091 to 0.7087, from Tremadoc to Llandeilo, a sharp decline to 0.7078 during the late Llandeilo-early Caradoc; little change during Caradoc and the Ashgil; and a steady rise to 0.7087 through the Silurian. These long-term (10 7 yr) variations, with magnitudes in the range of 10 Ϫ3 , are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering.
Carbonate rocks of the Middle Devonian Ratner Formation in southern Saskatchewan vary from undolo... more Carbonate rocks of the Middle Devonian Ratner Formation in southern Saskatchewan vary from undolomitized, to partly dolomitized, to completely dolomitized. Two major types of medium and coarsely crystalline dolomite are differentiated in the formation: medium crystalline, planar-e to planar-s (ME) dolomite, and medium to coarsely crystalline, nonplanar-a (CA) dolomite. ME dolomite, which commonly occurs in the lower and middle parts
The Middle Devonian Ratner Formation in south-central Saskatchewan consists of laminated carbonat... more The Middle Devonian Ratner Formation in south-central Saskatchewan consists of laminated carbonate and interlaminated to interbedded carbonate and anhydrite, and the Ratner carbonate is preserved as limestone in many cored intervals. Medium to very coarsely crystalline (MVC) limestone (up to 4 m in thickness) is dominantly present in the uppermost part or the upper cycle of the Ratner Formation directly overlain by the Whitkow anhydrite. Generally, both abundance and size of the MVC calcite crystals decrease downward away from contact between the Ratner carbonate and the Whitkow anhydrite. The average 87 Sr/ 86 Sr ratio of the MVC calcite is 0.7078, comparable to that of Middle Devonian seawater. The Ratner MVC limestone is interpreted to result from neomorphism of the precursor microcrystalline lime mudstone in burial environments, and neomorphic fluids might have consisted of gypsumdehydration water mixing with minor various ratios of formation waters, based on petrographic observation, O-and Srisotopic data, and stratigraphic evidence. This research provides a case study in which the neomorphism of limestone is related to gypsum-dehydration water.
Uploads
Papers by Hairuo Qing