Subsurface diagenetic evolution and porosity evaluation of Middle-Upper Devonian Kee Scarp reef, Norman Wells, Northwest Territories, Canada.

The Middle-Upper Devonian Kee Scarp Formation at Norman Wells consists of a carbonate platform and an overlying reefal buildup. Episodic increases in the rate of sea-level rise produced multiple cycles of reef growth, with a backstepping character. Reservoir porosity of these reefs is mostly represented by micropores of various types developed during diagenesis by the action of aggrading neomorphism and dissolution. The microporosity was developed as intercrystalline microvoids within the present low-magnesium calcite (LMC) stromatoporoid, algal and matrix components. SEM studies show that microporosity development responded to neomorphism at various rates. Reef margins, grain shoals and lower, middle and upper foreslope facies have the highest and best developed microporosity compared to lagoon, reef flat and tidal flat facies. The micropores in Kee Scarp limestone can be classified into four categories based on their shapes: (1) stepwise rhombic, about 1$\mu$m to 2$\mu$m in diameter; mainly developed in stromatoporoids; (2) intercrystalline rhombic, about 1$\mu$m in diameter; mainly in algal aggregates; (3) microvugs, 4$\mu$m to 10 $\mu$m in diameter; mainly in algal aggregates; (4) microchannels, 12$\mu$m length and 0.5$\mu$m width; in algal aggregates and stromatoporoids. (Abstract shortened by UMI.)Dept. of Geology and Geological Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1992 .A958. Source: Masters Abstracts International, Volume: 31-04, page: 1695. Thesis (M.Sc.)--University of Windsor (Canada), 1992

Rare Earth Elements of modern shelf and deep-water articulated brachiopods: evaluation of seawater masses

Modern Rhynchonellids and Tcrcbratulids, obtained from water depths below the neritic zone (>500m) at 23 stations in the Caribbean Sea, North Atlantic, South Pacific and Southern Oceans, were investigated for their rare earth clement (REE) contents (Fig. I, Table I). The ΣREE of shelf (500-I 000 m) or deep-water (> I 000 m) brachiopod populations do not vary significantly between oceans/seas irrespective of water mass origins or influences by major currents

Dolomitization of the Lower Ordovician Aguathuna Formation carbonates, Port au Port Peninsula, western Newfoundland, Canada: implications for a hydrocarbon reservoir

The Lower Ordovician Aguathuna Formation (∼100 m thick) is formed of shallow-marine carbonates, which constitute the uppermost part of the St. George Group of western Newfoundland. Sedimentation was paused by a major subaerial exposure (St. George Unconformity), which likely developed a significant pore system in the underlying carbonates by meteoric dissolution. The sequence has been affected by multiphase dolomitization that caused complex changes in the rock porosity. The Aguathuna dolomites are classified into three main generations ranging in crystal size between ∼4 µm and 2 mm. The occurrence of fabric-retentive dolomicrites implies that dolomitization likely started during the early stages of diagenesis. Although dolomitization is pervasive in the upper part of the formation and significantly occludes the pores, some intervals in the lower part have higher porosity. The development of lower permeable layers overlain by an impermeable (seal) cap suggests a possible potential diagenetic trap. Unlike sabkha deposits, the Aguathuna carbonates do not have evaporite interlayers. Furthermore, the low Sr contents (∼96 ppm) and the δ18O values of earlier dolomites (–3.3‰ to –6.9‰ VPDB (Vienna Pee Dee Belemnite)) are also difficult to reconcile with a brine origin. The Sr/Ca molar ratios (0.0067–0.0009), calculated for the earliest dolomitizing fluid, suggest a modified seawater origin, likely mixed sea and meteoric waters. The least radiogenic 87Sr/86Sr values of the earliest dolomite are consistent with those of early Ordovician seawater, which supports an early-stage diagenesis. Petrography, geochemistry, and fluid inclusions of the late dolomites suggest precipitation at higher temperatures (∼73–95 °C) in deeper burial environments from hydrothermal solutions

As sucessões carbonáticas neoproterozóicas do Cráton do São Francisco e os depósitos de fosfato: correlações e fosfogênese

Neoproterozoic Carbonate Sequences of the São Francisco Craton and the Phosphate Deposits: Correlation and Phosphogenesis. The neoproterozoic carbonate successions of the São Francisco craton are formed by thick carbonate and siliciclastic strata accumulated in epicontinental seaways, and on passive margins. At least two transgressive-regressive sea level cycles have been recognized during the evolution of the carbonate mega-sequences. These successions, represented by the Vazante, Bambuí, and Una Groups, lie above basal glacio-marine diamictites of probable Sturtian age, and an upper glacio-marine diamictite, was observed in upper units of the Vazante Group. The broad similarities of lithofacies, as well as the presence of phosphate and sulfide (Zn,Pb) deposits restricted to narrow stratigraphic intervals, suggest that the Vazante, Bambuí and Una Groups may be correlative. The Sr isotope data from well preserved carbonates and carbonate fluorapatite from each of these successions, ranging from 0.70763 to 0.70794, support the general correlation and are indicative of seawater composition around 650 Ma, although the lower 87Sr/86Sr values of 0.70614 at the Vazante carbonates may suggest that this unit is older than the Bambuí and Una carbonate rocks. Carbon isotope data of carbonate fluorapatite reveal sharp negative excursions between -3.47 and -12.25‰ VPDB in the cratonic area, and between -1.3 and -9.61‰ VPDB in the carbonate fluorapatite hosted by the passive margin Vazante carbonates, suggesting that primary P concentration was accumulated in strong anoxic environments in both geotectonic settings. Carbonate hosting the phosphate deposits in these units are moderately enriched in 13C, ranging from positive δ13C values of +2.0 and +9.6‰ VPDB in the different sections. Primary phosphate accumulations occur above glaciogenic successions. We suggest that these concentrations may be due to high organic productivity after glacial events

Coupling of surface temperatures and atmospheric CO_2 concentrations during the Palaeozoic era

Atmospheric carbon dioxide concentrations seem to have been several times modern levels during much of the Palaeozoic era (543–248 million years ago), but decreased during the Carboniferous period to concentrations similar to that of today. Given that carbon dioxide is a greenhouse gas, it has been proposed that surface temperatures were significantly higher during the earlier portions of the Palaeozoic era. A reconstruction of tropical sea surface temperatures based on the δ^(18)O of carbonate fossils indicates, however, that the magnitude of temperature variability throughout this period was small, suggesting that global climate may be independent of variations in atmospheric carbon dioxide concentration. Here we present estimates of sea surface temperatures that were obtained from fossil brachiopod and mollusc shells using the 'carbonate clumped isotope' method—an approach that, unlike the δ^(18)O method, does not require independent estimates of the isotopic composition of the Palaeozoic ocean. Our results indicate that tropical sea surface temperatures were significantly higher than today during the Early Silurian period (443–423 Myr ago), when carbon dioxide concentrations are thought to have been relatively high, and were broadly similar to today during the Late Carboniferous period (314–300 Myr ago), when carbon dioxide concentrations are thought to have been similar to the present-day value. Our results are consistent with the proposal that increased atmospheric carbon dioxide concentrations drive or amplify increased global temperatures

Redox conditions across the Cambrian–Ordovician boundary: Elemental and isotopic signatures retained in the GSSP carbonates

The final publication is available at Elsevier via https://doi.org/10.1016/j.palaeo.2015.09.014 © 2015. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/Lime mudstone samples (rhythmites) were collected at high resolution from outcrops of the Cambrian–Ordovician GSSP boundary section at Green Point (western Newfoundland, Canada). The sequence (~45 mthick) consists of slope carbonates with alternating shale and siltstone interbeds, and it spans the boundary located between the Martin Point and Broom Point members of the Green Point Formation (Cow Head Group). Samples were extracted frommicritic rhythmites by microdrilling and subsequently screened using petrographic and geochemical criteria to evaluate their degree of preservation. Although the δ13Corg profile (−29.7 to−25.6‰ VPDB) shows insignificant variations, the TOC values (0.1 to 4.1%) exhibit a generally upward decreasing trend. A negative δ13Ccarb excursion, reflecting a sealevel rise, marks a geochemical anomaly that correlates with an increase in the N contents (0 to 2.9%) of organic matter and the δ15Norg values (−0.6 to +6.0‰), which suggests a change to more reducing oceanic conditions. The U contents vary from 0.1 to 3.0 ppm and the δ238U values (−0.97 to −0.18‰) generally decrease with the negative δ13Ccarb excursion. The U isotopic variations suggest a widespread increase in reducing conditions associated with sealevel rise during this interval. The investigated sedimentary rocks were slope carbonateswhere dysoxic conditions likely dominated throughout the entire section. Therefore, the changes in the TOC, N, δ15Norg, and δ238U profiles across the boundary are not as sharp as would be expected by a local change from oxic shallow-water to dysoxic/anoxic deep-water settings.Petroleum Exploration Enhancement Program (PEEP) NSERC Discovery Grant || (RGPIN-435930) Carlsberg Foundation || (2013_01_0664

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

High-resolution isotope stratigraphy of the Lower Ordovician St. George Group of western Newfoundland, Canada: implications for global correlation

The Lower Ordovician St. George Group of western Newfoundland consists mainly of shallow-marine-platform carbonates (*500 m thick). It is formed, from bottom to top, of the Watts Bight, Boat Harbour, Catoche, and Aguathuna formations. The top boundary of the group is marked by the regional St. George Unconformity. Outcrops and a few cores from western Newfoundland were sampled at high resolution and the extracted micritic materials were investigated for their petrographic and geochemical criteria to evaluate their degree of preservation. The d13C and d18O values of wellpreserved micrite microsamples range from –4.2% to 0% (VPDB) and from –11.3% to –2.9% (VPDB), respectively. The d13Ccarb profile of the St. George Group carbonates reveals several negative shifts, which vary between *2% and 3% and are generally associated with unconformities disconformities or thin shale interbeds, thus reflecting the effect of or link with significant sea-level changes. The St. George Unconformity is associated with a negative d13Ccarb shift (*2%) on the profile and correlated with major lowstand (around the end of Arenig) on the local sea-level reconstruction and also on those from the Baltic region and central Australia, thus suggesting that the St. George Group Unconformity might have likely had an eustatic component that contributed to the development–enhancement of the paleomargin. Other similar d13Ccarb shifts have been recorded on the St. George profile, but it is hard to evaluate their global extension due to the low resolution of the documented global Lower Ordovician (Tremadoc – middle Arenig) d13Ccarb profile

Dolomitization of the lower St. George Group on the Northern Peninsula in western Newfoundland: implications for lateral distribution of porosity

The Watts Bight Formation constitutes the lowermost part of the St. George Group in western Newfoundland. On the Northern Peninsula, it consists of Tremadocian (lower Ordovician) shallow marine platform carbonates (approximately 50 m thick). Dolomitization is extensive throughout the formation except for its topmost part. Petrographic examinations suggest that the succession was affected by at least three successive phases of dolomitization, which influenced secondary porosity. These phases have crystal-size ranges of approximately 4 to 50 μm (earliest sub- to euhedral dolomite D1), 50 to 200 μm (eu- to subhedral D2), and 300 μm to 3mm (anhedral saddle dolomite D3), respectively. They occur as replacement and/or pore-filling cements and exhibit dull (D1 and D3) to zoned (D2) luminescence under the cold cathodoluminoscope. The D2 phase is the dominant dolomite while the other two phases are rare. Microthermometric measurements of the primary two-phase fluid inclusions in D2 (homogenization temperatures up to 157o C and salinity estimates up to 24.3 eq. wt% NaCl) suggest that it formed under relatively deep burial conditions. This is supported by the petrographic character (eu- to subhedral relatively big crystals) and geochemical composition (depleted δ18O mean value of –8.7±1.2‰ VPDB and low Sr contents of 68±30ppm) of the D2 phase. Thin-section examination suggests that porosity is dominantly intercrystalline and associated with the D2 phase. Visual estimates suggest that porosity varies from <1% in most of the formation to approximately 10% in two horizons, each approximately 2m thick, at approximately 10 m and 20 m from formation base. Correlations with the equivalent Watts Bight Formation section in the Isthmus Bay (300 km to South) reveal porous intervals at comparable stratigraphic levels. Also the geochemical results and microthermometric measurements suggest that D2 in the Northern Peninsula section was formed from hotter fluids under relatively more reducing conditions relative to their Isthmus Bay counterparts. The porous zones seem to be associated with fluctuations in sea-level marked by negative shifts in the δ13C profile

Source of diagenetic fluids from fluid-inclusion gas ratios

Alteration of marine carbonates, such as those from the Mesoproterozoic and Lower Ordovician, during burial history is carried out by diagenetic fluids that could potentially have different sources. During precipitation diagenetic minerals may trap tiny amounts of those solutions in fluid inclusions, thus providing fossil archives and aliquots that offer valuable record about the origin of fluids. The analysis of various fluid-inclusion gases (e.g., CH4, CO2, N2, He and Ar) may provide reliable information which allows the discrimination among different fluid sources. Generally speaking, the meteoric cements should have N2/Ar ratio around 38 (the value for air-saturated water). However, the gases in inclusions of the current study, trapped by diagenetic carbonates (cements), from independent depositional basins of different ages (Mesoproterozoic, Early Ordovician, and Modern) and locations (Canada, USA, Brazil and Java Sea), have N2/Ar ratios (~92) which match non-magmatic (modified marine or meteoric) fluids. Also, the Ar/He ratios (~3) in the studied fluid inclusions are significantly lower than those of calc-alkaline magmatic fluids (≥20), thus excluding magmatic fluids as a potential source. On the other hand, some N2/Ar and Ar/He ratios of the studied samples approach values reported for basinal fluids from the Hansonburg MVT deposit in New Mexico (68 and 1, respectively), suggesting that both meteoric/mixed marine–meteoric (evolved meteoric) and basinal fluids may be involved during carbonate diagenesis