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Simon Schneider - One of the best experts on this subject based on the ideXlab platform.
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Autochthonous to parautochthonous bivalve concentrations within transgressive marginal marine strata of the Upper Jurassic of Portugal
Palaeobiodiversity and Palaeoenvironments, 2009Co-Authors: Franz Theodor Fürsich, Winfried Werner, Simon SchneiderAbstract:Bivalve concentrations are a conspicuous feature of the Upper Jurassic Rock succession of the central Lusitanian Basin. In order to illustrate the mode of their formation and their palaeoecological and sequence stratigraphic significance, we describe and interpret in detail 27 assemblages of bivalves based on their taphonomic and ecological features. Bivalve concentrations are particularly widespread in marginally marine, salinity-controlled environments and less common in open shelf settings. Only the Eomiodon and Myophorella concentrations are dominated by a shallow infaunal bivalve; all other concentrations are composed mainly of epi- or endobyssate [ Isognomon ( Rostroperna ), I . ( Isognomon ), Pteria , Alaperna , Juranomia ] and cementing taxa ( Praeexogyra , Actinostreon ). Most of the concentrations are mono- to paucispecific, except for the highly diverse Alaperna polita–Pteria credneriana concentrations, which occur in nearshore shelf environments. Lack of sorting, a high percentage of articulated shells, and shells preserved in growth position are evidence that, with few exceptions, the concentrations are autochthonous. Main factors leading to their formation are, apart from a gregarious life habit, a high productivity and a reduced rate of sedimentation. Autogenic and allogenic successional stages can be recognized on the basis of their spatial separation. The time involved in the formation of the concentrations is generally in the order of 10^2–10^3 years. Due to the lack of compositional changes within concentrations, time-averaging played no or only a minor role, except in the Alaperna polita–Pteria credneriana concentrations. In sequence stratigraphic terms, most of the concentrations are the product of the maximum flooding zone, but in some cases they constitute the transgressive systems tract. Invariably, they are useful tools for defining depositional sequences. Several of the concentrations described here are not restricted to the Lusitanian Basin but also occur elsewhere in the epicontinental seas bordering the northern margin of the Neotethys.
Franz Theodor Fürsich - One of the best experts on this subject based on the ideXlab platform.
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Autochthonous to parautochthonous bivalve concentrations within transgressive marginal marine strata of the Upper Jurassic of Portugal
Palaeobiodiversity and Palaeoenvironments, 2009Co-Authors: Franz Theodor Fürsich, Winfried Werner, Simon SchneiderAbstract:Bivalve concentrations are a conspicuous feature of the Upper Jurassic Rock succession of the central Lusitanian Basin. In order to illustrate the mode of their formation and their palaeoecological and sequence stratigraphic significance, we describe and interpret in detail 27 assemblages of bivalves based on their taphonomic and ecological features. Bivalve concentrations are particularly widespread in marginally marine, salinity-controlled environments and less common in open shelf settings. Only the Eomiodon and Myophorella concentrations are dominated by a shallow infaunal bivalve; all other concentrations are composed mainly of epi- or endobyssate [ Isognomon ( Rostroperna ), I . ( Isognomon ), Pteria , Alaperna , Juranomia ] and cementing taxa ( Praeexogyra , Actinostreon ). Most of the concentrations are mono- to paucispecific, except for the highly diverse Alaperna polita–Pteria credneriana concentrations, which occur in nearshore shelf environments. Lack of sorting, a high percentage of articulated shells, and shells preserved in growth position are evidence that, with few exceptions, the concentrations are autochthonous. Main factors leading to their formation are, apart from a gregarious life habit, a high productivity and a reduced rate of sedimentation. Autogenic and allogenic successional stages can be recognized on the basis of their spatial separation. The time involved in the formation of the concentrations is generally in the order of 10^2–10^3 years. Due to the lack of compositional changes within concentrations, time-averaging played no or only a minor role, except in the Alaperna polita–Pteria credneriana concentrations. In sequence stratigraphic terms, most of the concentrations are the product of the maximum flooding zone, but in some cases they constitute the transgressive systems tract. Invariably, they are useful tools for defining depositional sequences. Several of the concentrations described here are not restricted to the Lusitanian Basin but also occur elsewhere in the epicontinental seas bordering the northern margin of the Neotethys.
Gonzalo Pardo - One of the best experts on this subject based on the ideXlab platform.
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Current tufa sedimentation in a high discharge river: A comparison with other synchronous tufa records in the Iberian Range (Spain)
Sedimentary Geology, 2015Co-Authors: Concha Arenas, Luis F. Auqué, C. Osácar, Carlos Sancho, María Victoria Lozano, Marta Vázquez-urbez, Gonzalo PardoAbstract:Abstract The results from sedimentological, isotopic and hydrochemical analyses of current tufa sedimentation conducted in a high-discharge river (Ebron River, northeastern Spain; 1.49 m 3 /s) through six-month monitoring over 3.5 years are discussed in terms of the factors that control local carbonate deposition through space and time, and compared with results from other synchronous tufa records in the same climatic domain. The findings allow for discerning the influence of the riverbed slope, hydrochemistry, discharge and groundwater inputs on tufa attributes and assess the significance of tufa as archives of certain climatic events on a regional scale. In the Ebron River, the dominant upstream karstic springs from a Jurassic-Rock aquifer determined the river's HCO 3 –Ca composition. Two river stretches were differentiated according to localised increments in both pCO 2 , resulting from additional groundwater inputs, and SO 4 content, influenced by evaporite-bearing units. The variations in tufa's thickness through space were strongly controlled by CO 2 -rich springs and local slope variations. The monitored sites represent four primary subenvironments with distinct sedimentary facies, whose attributes suggest that 1) the tufa deposition rates in each fluvial subenvironment are mainly controlled by the CO 2 -outgassing intensity linked to local flow conditions and the biological substrate type, and 2) stromatolites represent the thickest and most complete record. The six-month variations in tufa thickness and calculated calcite mass in the Ebron River were controlled by temperature-dependent physico-chemical and biological parameters, coupled with high-discharge events that provoked tufa erosion. The smaller deposition of the Ebron River compared to two other synchronous tufa records in the Iberian Range is linked to 1) the absence of long areas of increased slope, 2) the occurrence of significant CO 2 -rich groundwater springs in the middle reach, and 3) the higher discharge and water depth. Certain high-discharge events were recorded as lower deposition rates concurrent in the three rivers. Moreover, anomalous water temperatures calculated from the calcite δ 18 O in the three rivers for a coincident time span support a regional anomaly in the precipitation δ 18 O. Thus, the evolution of the short-term tufa deposition rates and calcite δ 18 O composition through time can detect regional climate and hydrology changes and therefore can be robust criteria for correlation in the geological record.
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Current tufa sedimentation in a changing-slope valley: The River Añamaza (Iberian Range, NE Spain)
Sedimentary Geology, 2014Co-Authors: Luis F. Auqué, Concha Arenas, C. Osácar, Carlos Sancho, Gonzalo Pardo, Marta Vázquez-urbezAbstract:Abstract A three-year study of modern carbonate sedimentation was conducted through analysis of sedimentological and hydrochemical parameters measured every six months at 10 sites along a high-slope river in northeastern Spain (River Anamaza). Three stretches of the river were characterised. The dominant water inputs from the upstream karstic springs, primarily from the Jurassic Rock aquifer, determined the SO4–HCO3–Ca composition of the river water. From this area, decreasing trends in alkalinity, calcium and total dissolved inorganic carbon occurred downstream in both the warm and cool periods as a result of calcite precipitation. Tufa thickness variations were consistent with such hydrochemical evolution. Deposition rates increased downstream, primarily where the gradient is steeper (middle stretch), and subsequently decreased at the downstream gently sloped stretch. Therefore, the slope along the river and the distance from the main upstream springs conditioned the spatial distribution of tufa deposits by determining the chemical characteristics of the water. The monitored sites represent four primary fluvial subenvironments with distinct sedimentary facies. The highest carbonate deposition rates were measured in fast-flow conditions (stromatolites, facies A). Deposits with calcite-coated algae and mosses (facies C) formed in cascades and small jumps with very fast-flowing water exhibited lower deposition rates and typical erosion. Lower rates corresponded to slow flow conditions in which thin stromatolite crusts and/or filamentous and calcareous algae and tufa fragments (facies B) accumulated. In slow-flowing water areas near springs (upstream stretch) calcite was absent, linked to the higher pCO2 of water; microbial films and aquatic flora composed the biofacies (facies D) in such subenvironment. Therefore, tufa deposition rates in each fluvial subenvironment were controlled by the amount of CO2 outgassing linked to local flow conditions, the biological substrate type and the chemical attributes of the water along each stretch. A six-month pattern of deposition rates, best marked in the steeper stretch, was recorded from thickness measurements (spring + summer periods = 4.30 mm; autumn + winter periods = 1.22 mm). Parallel variations were recorded using PWP (Plummer, Wigley, Parkhurst) and calcite mass balance calculations. Multivariate statistical analyses (HCA and PCA) clearly separated hydrochemical and sedimentological attributes in samples from warm and cool periods. Exceptions to this pattern were related to changes in the water discharge; high discharge events caused the dilution of the chemical composition and erosion of the tufa deposits. Therefore, temperature-dependent factors (i.e., physico-chemical and biological processes) coupled with discharge changes controlled the seasonal variations in deposition rates. The stable-isotope composition of calcite and river water also reflected the discharge effects. However, the seasonal variation signature of temperature was preserved in the δ18O of sediment.
Marta Vázquez-urbez - One of the best experts on this subject based on the ideXlab platform.
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Current tufa sedimentation in a high discharge river: A comparison with other synchronous tufa records in the Iberian Range (Spain)
Sedimentary Geology, 2015Co-Authors: Concha Arenas, Luis F. Auqué, C. Osácar, Carlos Sancho, María Victoria Lozano, Marta Vázquez-urbez, Gonzalo PardoAbstract:Abstract The results from sedimentological, isotopic and hydrochemical analyses of current tufa sedimentation conducted in a high-discharge river (Ebron River, northeastern Spain; 1.49 m 3 /s) through six-month monitoring over 3.5 years are discussed in terms of the factors that control local carbonate deposition through space and time, and compared with results from other synchronous tufa records in the same climatic domain. The findings allow for discerning the influence of the riverbed slope, hydrochemistry, discharge and groundwater inputs on tufa attributes and assess the significance of tufa as archives of certain climatic events on a regional scale. In the Ebron River, the dominant upstream karstic springs from a Jurassic-Rock aquifer determined the river's HCO 3 –Ca composition. Two river stretches were differentiated according to localised increments in both pCO 2 , resulting from additional groundwater inputs, and SO 4 content, influenced by evaporite-bearing units. The variations in tufa's thickness through space were strongly controlled by CO 2 -rich springs and local slope variations. The monitored sites represent four primary subenvironments with distinct sedimentary facies, whose attributes suggest that 1) the tufa deposition rates in each fluvial subenvironment are mainly controlled by the CO 2 -outgassing intensity linked to local flow conditions and the biological substrate type, and 2) stromatolites represent the thickest and most complete record. The six-month variations in tufa thickness and calculated calcite mass in the Ebron River were controlled by temperature-dependent physico-chemical and biological parameters, coupled with high-discharge events that provoked tufa erosion. The smaller deposition of the Ebron River compared to two other synchronous tufa records in the Iberian Range is linked to 1) the absence of long areas of increased slope, 2) the occurrence of significant CO 2 -rich groundwater springs in the middle reach, and 3) the higher discharge and water depth. Certain high-discharge events were recorded as lower deposition rates concurrent in the three rivers. Moreover, anomalous water temperatures calculated from the calcite δ 18 O in the three rivers for a coincident time span support a regional anomaly in the precipitation δ 18 O. Thus, the evolution of the short-term tufa deposition rates and calcite δ 18 O composition through time can detect regional climate and hydrology changes and therefore can be robust criteria for correlation in the geological record.
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Current tufa sedimentation in a changing-slope valley: The River Añamaza (Iberian Range, NE Spain)
Sedimentary Geology, 2014Co-Authors: Luis F. Auqué, Concha Arenas, C. Osácar, Carlos Sancho, Gonzalo Pardo, Marta Vázquez-urbezAbstract:Abstract A three-year study of modern carbonate sedimentation was conducted through analysis of sedimentological and hydrochemical parameters measured every six months at 10 sites along a high-slope river in northeastern Spain (River Anamaza). Three stretches of the river were characterised. The dominant water inputs from the upstream karstic springs, primarily from the Jurassic Rock aquifer, determined the SO4–HCO3–Ca composition of the river water. From this area, decreasing trends in alkalinity, calcium and total dissolved inorganic carbon occurred downstream in both the warm and cool periods as a result of calcite precipitation. Tufa thickness variations were consistent with such hydrochemical evolution. Deposition rates increased downstream, primarily where the gradient is steeper (middle stretch), and subsequently decreased at the downstream gently sloped stretch. Therefore, the slope along the river and the distance from the main upstream springs conditioned the spatial distribution of tufa deposits by determining the chemical characteristics of the water. The monitored sites represent four primary fluvial subenvironments with distinct sedimentary facies. The highest carbonate deposition rates were measured in fast-flow conditions (stromatolites, facies A). Deposits with calcite-coated algae and mosses (facies C) formed in cascades and small jumps with very fast-flowing water exhibited lower deposition rates and typical erosion. Lower rates corresponded to slow flow conditions in which thin stromatolite crusts and/or filamentous and calcareous algae and tufa fragments (facies B) accumulated. In slow-flowing water areas near springs (upstream stretch) calcite was absent, linked to the higher pCO2 of water; microbial films and aquatic flora composed the biofacies (facies D) in such subenvironment. Therefore, tufa deposition rates in each fluvial subenvironment were controlled by the amount of CO2 outgassing linked to local flow conditions, the biological substrate type and the chemical attributes of the water along each stretch. A six-month pattern of deposition rates, best marked in the steeper stretch, was recorded from thickness measurements (spring + summer periods = 4.30 mm; autumn + winter periods = 1.22 mm). Parallel variations were recorded using PWP (Plummer, Wigley, Parkhurst) and calcite mass balance calculations. Multivariate statistical analyses (HCA and PCA) clearly separated hydrochemical and sedimentological attributes in samples from warm and cool periods. Exceptions to this pattern were related to changes in the water discharge; high discharge events caused the dilution of the chemical composition and erosion of the tufa deposits. Therefore, temperature-dependent factors (i.e., physico-chemical and biological processes) coupled with discharge changes controlled the seasonal variations in deposition rates. The stable-isotope composition of calcite and river water also reflected the discharge effects. However, the seasonal variation signature of temperature was preserved in the δ18O of sediment.
Concha Arenas - One of the best experts on this subject based on the ideXlab platform.
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Current tufa sedimentation in a high discharge river: A comparison with other synchronous tufa records in the Iberian Range (Spain)
Sedimentary Geology, 2015Co-Authors: Concha Arenas, Luis F. Auqué, C. Osácar, Carlos Sancho, María Victoria Lozano, Marta Vázquez-urbez, Gonzalo PardoAbstract:Abstract The results from sedimentological, isotopic and hydrochemical analyses of current tufa sedimentation conducted in a high-discharge river (Ebron River, northeastern Spain; 1.49 m 3 /s) through six-month monitoring over 3.5 years are discussed in terms of the factors that control local carbonate deposition through space and time, and compared with results from other synchronous tufa records in the same climatic domain. The findings allow for discerning the influence of the riverbed slope, hydrochemistry, discharge and groundwater inputs on tufa attributes and assess the significance of tufa as archives of certain climatic events on a regional scale. In the Ebron River, the dominant upstream karstic springs from a Jurassic-Rock aquifer determined the river's HCO 3 –Ca composition. Two river stretches were differentiated according to localised increments in both pCO 2 , resulting from additional groundwater inputs, and SO 4 content, influenced by evaporite-bearing units. The variations in tufa's thickness through space were strongly controlled by CO 2 -rich springs and local slope variations. The monitored sites represent four primary subenvironments with distinct sedimentary facies, whose attributes suggest that 1) the tufa deposition rates in each fluvial subenvironment are mainly controlled by the CO 2 -outgassing intensity linked to local flow conditions and the biological substrate type, and 2) stromatolites represent the thickest and most complete record. The six-month variations in tufa thickness and calculated calcite mass in the Ebron River were controlled by temperature-dependent physico-chemical and biological parameters, coupled with high-discharge events that provoked tufa erosion. The smaller deposition of the Ebron River compared to two other synchronous tufa records in the Iberian Range is linked to 1) the absence of long areas of increased slope, 2) the occurrence of significant CO 2 -rich groundwater springs in the middle reach, and 3) the higher discharge and water depth. Certain high-discharge events were recorded as lower deposition rates concurrent in the three rivers. Moreover, anomalous water temperatures calculated from the calcite δ 18 O in the three rivers for a coincident time span support a regional anomaly in the precipitation δ 18 O. Thus, the evolution of the short-term tufa deposition rates and calcite δ 18 O composition through time can detect regional climate and hydrology changes and therefore can be robust criteria for correlation in the geological record.
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Current tufa sedimentation in a changing-slope valley: The River Añamaza (Iberian Range, NE Spain)
Sedimentary Geology, 2014Co-Authors: Luis F. Auqué, Concha Arenas, C. Osácar, Carlos Sancho, Gonzalo Pardo, Marta Vázquez-urbezAbstract:Abstract A three-year study of modern carbonate sedimentation was conducted through analysis of sedimentological and hydrochemical parameters measured every six months at 10 sites along a high-slope river in northeastern Spain (River Anamaza). Three stretches of the river were characterised. The dominant water inputs from the upstream karstic springs, primarily from the Jurassic Rock aquifer, determined the SO4–HCO3–Ca composition of the river water. From this area, decreasing trends in alkalinity, calcium and total dissolved inorganic carbon occurred downstream in both the warm and cool periods as a result of calcite precipitation. Tufa thickness variations were consistent with such hydrochemical evolution. Deposition rates increased downstream, primarily where the gradient is steeper (middle stretch), and subsequently decreased at the downstream gently sloped stretch. Therefore, the slope along the river and the distance from the main upstream springs conditioned the spatial distribution of tufa deposits by determining the chemical characteristics of the water. The monitored sites represent four primary fluvial subenvironments with distinct sedimentary facies. The highest carbonate deposition rates were measured in fast-flow conditions (stromatolites, facies A). Deposits with calcite-coated algae and mosses (facies C) formed in cascades and small jumps with very fast-flowing water exhibited lower deposition rates and typical erosion. Lower rates corresponded to slow flow conditions in which thin stromatolite crusts and/or filamentous and calcareous algae and tufa fragments (facies B) accumulated. In slow-flowing water areas near springs (upstream stretch) calcite was absent, linked to the higher pCO2 of water; microbial films and aquatic flora composed the biofacies (facies D) in such subenvironment. Therefore, tufa deposition rates in each fluvial subenvironment were controlled by the amount of CO2 outgassing linked to local flow conditions, the biological substrate type and the chemical attributes of the water along each stretch. A six-month pattern of deposition rates, best marked in the steeper stretch, was recorded from thickness measurements (spring + summer periods = 4.30 mm; autumn + winter periods = 1.22 mm). Parallel variations were recorded using PWP (Plummer, Wigley, Parkhurst) and calcite mass balance calculations. Multivariate statistical analyses (HCA and PCA) clearly separated hydrochemical and sedimentological attributes in samples from warm and cool periods. Exceptions to this pattern were related to changes in the water discharge; high discharge events caused the dilution of the chemical composition and erosion of the tufa deposits. Therefore, temperature-dependent factors (i.e., physico-chemical and biological processes) coupled with discharge changes controlled the seasonal variations in deposition rates. The stable-isotope composition of calcite and river water also reflected the discharge effects. However, the seasonal variation signature of temperature was preserved in the δ18O of sediment.
