The fluvial-tidal transition(FTT)is a complex depositional zone,where fluvial flow is modified by tides as rivers approach a receiving marine basin.Variations in the relative importance of tidal versus fluvial process...The fluvial-tidal transition(FTT)is a complex depositional zone,where fluvial flow is modified by tides as rivers approach a receiving marine basin.Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars.The FTT generally consists of three broad zones:(1)a freshwater-tidal zone;(2)a tidally influenced freshwater to brackish-water transition:and(3)a zone of relatively sustained brackish-water conditions with stronger tides.A very common type of deposit through the fluvial-tidal transition,especially on the margins of migrating channels,is inclined heterolithic stratification(IHS).At present,a detailed account of changes in the character of IHS across the FIT of a paleo-channel system has not been reported,although a number of modern examples have been documented.To fill this gap,we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley("A"Valley)in the Lower Cretaceous McMurray Formation of Alberta.Canada.We compare the data to trends defined along the FTT in the present-day Fraser River in British Columbia.Canada to interpret paleo-depositional position in the ancient fluvial-tidal channels.Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area(SA).Mean thickness increases to 11 cm in the central study area(CA),and decreases again to 4.4 cm in the northern study area(NA).The proportion of mudstone is 31%in SA,44%in CA,and 27%in NA.Thicknessweighted mean bioturbation intensity in sands varied from 0.29 in SA and CA.to 0.28 in NA.On the other hand,thickness-weighted mean bioturbation intensity(Bl)in mudstone increases from 1.46 in SA.to 1.77 in CA.and is 1.94 in NA.The ichnological diversity also increased from south to north.Sedimentological results show sinilar trends to those of the Fraser River,enabling the identification of a freshwater to brackish-water transition zone with tidal influence.The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends,indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions.Together,these data suggest that a broad FTT existed in the"A"Valley,with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow,and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximun zone.The FIT zone appears to have extended for several hundred kilometers fron south to north.Based on the sedimentological and ichnological data,as well as estimations of lateral accretion rates,we refute the colmonly applied Mississippi River depositional analogue for McMurray Formation channels.Rather,we show that while not a perfect fit,the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS.Future work on the McMurray system should focus on characterizing tide-dominatecl deltaic and estuarine systems,such as the Ganges-Brahmaputra,and on forward-modeling the evolution of tide-dominated and tideinfluenced river systems.展开更多
Dealing with scarcity events is nowadays gaining relevance in electricity market studies, as traditionally predictable generation and consumption patterns are fading. Policymakers and system planners use therefore ade...Dealing with scarcity events is nowadays gaining relevance in electricity market studies, as traditionally predictable generation and consumption patterns are fading. Policymakers and system planners use therefore adequacy studies to a) understand if the current market design will attract sufficient generation capacity to meet electricity demand in the future and b) to comprehend what drives system inadequacy or resource scarcity when future scenarios lack adequate capacity. This work addressed the latter and showcases a first in-its-kind rulebased methodology that filters scarcity events from a large set of electricity market simulations. In this proof-of-concept, a rule-mining algorithm is applied to outputs from ENTSO-E’s Pan-European electricity market model, which is run for 700 model scenarios, each covering 8760 time steps. The developed methodology shows how to unveil potential reasons behind scarcity events in an automated, interpretable, and scalable manner.展开更多
The United States needs a comprehensive policy and market-based solutions to address the challenges and demands of energy provision in President Barack Obama’s State of the Union address in January 2009, he called fo...The United States needs a comprehensive policy and market-based solutions to address the challenges and demands of energy provision in President Barack Obama’s State of the Union address in January 2009, he called for the building of "a new generation of safe, clean nuclear power plants." This was followed by his high- profile speech in Prague in April 2009,展开更多
基金The Natural Sciences and Engineering Research Council of Canada and Carbon Management Canada funded the rock record portion of this study
文摘The fluvial-tidal transition(FTT)is a complex depositional zone,where fluvial flow is modified by tides as rivers approach a receiving marine basin.Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars.The FTT generally consists of three broad zones:(1)a freshwater-tidal zone;(2)a tidally influenced freshwater to brackish-water transition:and(3)a zone of relatively sustained brackish-water conditions with stronger tides.A very common type of deposit through the fluvial-tidal transition,especially on the margins of migrating channels,is inclined heterolithic stratification(IHS).At present,a detailed account of changes in the character of IHS across the FIT of a paleo-channel system has not been reported,although a number of modern examples have been documented.To fill this gap,we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley("A"Valley)in the Lower Cretaceous McMurray Formation of Alberta.Canada.We compare the data to trends defined along the FTT in the present-day Fraser River in British Columbia.Canada to interpret paleo-depositional position in the ancient fluvial-tidal channels.Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area(SA).Mean thickness increases to 11 cm in the central study area(CA),and decreases again to 4.4 cm in the northern study area(NA).The proportion of mudstone is 31%in SA,44%in CA,and 27%in NA.Thicknessweighted mean bioturbation intensity in sands varied from 0.29 in SA and CA.to 0.28 in NA.On the other hand,thickness-weighted mean bioturbation intensity(Bl)in mudstone increases from 1.46 in SA.to 1.77 in CA.and is 1.94 in NA.The ichnological diversity also increased from south to north.Sedimentological results show sinilar trends to those of the Fraser River,enabling the identification of a freshwater to brackish-water transition zone with tidal influence.The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends,indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions.Together,these data suggest that a broad FTT existed in the"A"Valley,with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow,and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximun zone.The FIT zone appears to have extended for several hundred kilometers fron south to north.Based on the sedimentological and ichnological data,as well as estimations of lateral accretion rates,we refute the colmonly applied Mississippi River depositional analogue for McMurray Formation channels.Rather,we show that while not a perfect fit,the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS.Future work on the McMurray system should focus on characterizing tide-dominatecl deltaic and estuarine systems,such as the Ganges-Brahmaputra,and on forward-modeling the evolution of tide-dominated and tideinfluenced river systems.
文摘Dealing with scarcity events is nowadays gaining relevance in electricity market studies, as traditionally predictable generation and consumption patterns are fading. Policymakers and system planners use therefore adequacy studies to a) understand if the current market design will attract sufficient generation capacity to meet electricity demand in the future and b) to comprehend what drives system inadequacy or resource scarcity when future scenarios lack adequate capacity. This work addressed the latter and showcases a first in-its-kind rulebased methodology that filters scarcity events from a large set of electricity market simulations. In this proof-of-concept, a rule-mining algorithm is applied to outputs from ENTSO-E’s Pan-European electricity market model, which is run for 700 model scenarios, each covering 8760 time steps. The developed methodology shows how to unveil potential reasons behind scarcity events in an automated, interpretable, and scalable manner.
文摘The United States needs a comprehensive policy and market-based solutions to address the challenges and demands of energy provision in President Barack Obama’s State of the Union address in January 2009, he called for the building of "a new generation of safe, clean nuclear power plants." This was followed by his high- profile speech in Prague in April 2009,