The Punta del Este Terrane, located in southeastern Brazil and eastern Uruguay, is a tectonostratigraphic terrane recognized in the Dom Feliciano Belt, the southern segment of Mantiqueira Province ...(Brasiliano Orogen). The northern sector of the terrane, called here by the Jaguarão Domain, is constituted by Arroio Telho, Arroio Grande, Matarazzo metamorphic complexes, and the Arroio Pedrado Gneisses. The first is composed of low to medium-grade metasedimentary rocks. Metasiliciclastic schists and marbles constitute the second, with serpentinites, magnesian schists, amphibolites, and metagabbros. The Matarazzo Complex comprises pure and siliceous dolomitic marble, metadolerite, and metagabbro. Arroio Pedrado unit comprises granodioritic to monzogranitic augen-gneisses. The rocks of the complexes were poly-deformed and intruded by high-K calc-alkaline peraluminous and metaluminous granitoids. The Pedro Osório, Arroio Grande, and Cerro Amaro dextral shear zones delimited the domain to the north. To the south and east, the units of the Jaguarão Domain were covered by coastal plain sediments. In gravimetric maps, the domain shows a high-density relief in contrast with the rocks of the granite belt (Pelotas Batholith). U-Pb zircon data from garnet-muscovite granites present crystallization ages of 587-568 Ma, which point to a widespread Ediacaran magmatism in the northern Punta del Este Terrane. U-Pb zircon provenance data of the metasedimentary sequences indicate main Meso- to Paleoproterozoic contribution, with subordinate Tonian to Cryogenian age populations. The geochronological results of the supracrustal rocks indicate a sedimentary deposition in an extensional setting, in which posterior deformation and metamorphism/magmatism compatible with a syn-orogenic setting in the context of the Dom Feliciano Belt framework.
The assessment of groundwater quality in shallow aquifers is of high societal relevance given that large populations depend directly on these water resources. The purpose of this study was to ...establish links between groundwater quality, groundwater residence times, and regional geology in the St. Lawrence Lowlands fractured bedrock aquifer. The study focuses on a 4500 km2 watershed located in the St. Lawrence Lowlands of the province of Quebec in eastern Canada. A total of 150 wells were sampled for major, minor, and trace ions. Tritium (3H) and its daughter element, 3He, as well as radiocarbon activity (A14C) were measured in a subset of wells to estimate groundwater residence times. Results show that groundwater evolves from a Ca–HCO3 water type in recharge zones (i.e., the Appalachian piedmont) to a Na–HCO3 water type downgradient, toward the St. Lawrence River. Locally, barium (Ba), fluoride (F), iron (Fe), and manganese (Mn) concentrations reach 90, 2, 18, and 5.9 mg/L respectively, all exceeding their respective Canadian drinking water limits of 1, 1.5, 0.3, and 0.05 mg/L. Release of these elements into groundwater is mainly controlled by the groundwater redox state and pH conditions, as well as by the geology and the duration of rock–water interactions. This evolution is accompanied by increasing 3H/3He ages, from 4.78 ± 0.44 years upgradient to more than 60 years downgradient. Discrepancies between calculated 3H/3He and 14C water ages (the latter ranging from 280 ± 56 to 17,050 ± 3410 years) suggest mixing between modern water and paleo-groundwater infiltrated through subglacial recharge when the Laurentide Ice Sheet covered the study area, and during the following deglaciation period. A linear relationship between 3H activity and corrected 14C versus Mg/Ca and Ba support a direct link between water residence time and the chemical evolution of these waters. The Ba, F, Fe, and Mn concentrations in groundwater originate from Paleozoic rocks from both the St. Lawrence Platform and the Appalachian Mountains. These elements have been brought to the surface by rising hydrothermal fluids along regional faults, and trapped in sediment during their deposition and diagenesis due to reactions with highly sulfurous and organic matter-rich water. Large-scale flow of meltwater during subglacial recharge and during the subsequent retreat of the Laurentide Ice Sheet might have contributed to the leaching of these deposits and their enrichment in the present aquifers. This study brings a new and original understanding of the St. Lawrence Lowlands groundwater system within the context of its geological evolution.
•Water chemistry, tritium, 14C and noble gases were measured in the study area.•Ba, F, Fe and Mn were exceeding Canadian standards for drinking supply.•Groundwater residence times were measured using 3H/3He and 14C methods.•The presence of several water masses has an impact on ions presence in water.•Ion overruns are linked to the geology and processes releasing them in water.
Satellite remote sensing imagery is especially useful for geological investigations in Antarctica because of its remoteness and extreme environmental conditions that constrain direct geological ...survey. The highest percentage of exposed rocks and soils in Antarctica occurs in Northern Victoria Land (NVL). Exposed Rocks in NVL were part of the paleo-Pacific margin of East Gondwana during the Paleozoic time. This investigation provides a satellite-based remote sensing approach for regional geological mapping in the NVL, Antarctica. Landsat-8 and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) datasets were used to extract lithological-structural and mineralogical information. Several spectral-band ratio indices were developed using Landsat-8 and ASTER bands and proposed for Antarctic environments to map spectral signatures of snow/ice, iron oxide/hydroxide minerals, Al-OH-bearing and Fe, Mg-OH and CO3 mineral zones, and quartz-rich felsic and mafic-to-ultramafic lithological units. The spectral-band ratio indices were tested and implemented to Level 1 terrain-corrected (L1T) products of Landsat-8 and ASTER datasets covering the NVL. The surface distribution of the mineral assemblages was mapped using the spectral-band ratio indices and verified by geological expeditions and laboratory analysis. Resultant image maps derived from spectral-band ratio indices that developed in this study are fairly accurate and correspond well with existing geological maps of the NVL. The spectral-band ratio indices developed in this study are especially useful for geological investigations in inaccessible locations and poorly exposed lithological units in Antarctica environments.
Over the last 25 years the Italian national geological mapping program of the Italian Geological Survey (CARG Project, italian: Progetto Carta Geologica) at 1:50,000 scale has led to significant ...improvements in the geological knowledge for the Island of Sardinia (Italy). As a result, about one half of the island now is covered by new geological maps with 1:10,000-1:25,000 accuracy and geological maps at the 1:50,000 scale whose explanatory notes are available electronically. At the beginning of the CARG Project a geological map for Sardinia Island at 1:200,000 scale was published Carmignani, L. (1996). Carta Geologica della Sardegna (1:200.000). Servizio Geologico Nazionale, Regione Autonoma della Sardegna, summarizing all the geological information available at that time, and a book with explanatory notes for the map was later published Carmignani, L., Oggiano, G., Barca, S., Conti, P., Salvadori, I., Eltrudis, ... Pasci, S. (2001). Geologia della Sardegna: Note Illustrative della Carta Geologica della Sardegna in scala 1:200.000, Memorie Descrittive della Carta Geologica d'Italia (Vol. 60). Roma: Servizio Geologico d'Italia, 283 pp. The enclosed Geological map of Sardinia at 1:250,000 scale incorporates all maps of the CARG Project, unpublished author studies and recently published maps and represents the most updated synthesis of an area characterised by a complex geological evolution that, with few exceptions, can be considered continuous during the last 540 Ma. The main events that influenced the geology of the island are the Variscan orogen that deeply involved the passive margin of North Gondwana and then the complex episodes that occurred in the present-day Mediterranean area after the accretion of Pangea up to the opening of the Tyrrhenian basin.
A comparison is made between an existing stratigraphic model and new data in the same area of southeast Sundaland; the composite tectonic plate that underlies much of SE Asia. A previous view that ...the Neogene eustatic stratal signature was detectable is refuted with new well data. A new interpretation of stratigraphy and regional geology is made through an evidence-based, inductive approach. Care is taken in assessing the precision and accuracy of observational inputs, similar to confidence ranges declared by other sciences, especially in determining geological age and facies.
At a low resolution the new interpretation appears to match the expected rift phase which gradually faded to basinal sag, then mild compression in Miocene times. However it also identifies distinct episodes of sedimentation, separated by times of rapid change in the basin morphology. These times of change correlate over a wide area, and appear to be the primary controls on sedimentation. Their highly variable geographic intensity identities them as having been produced by tectonic movements.
The previous model-based and deductive interpretation of the area can be summarised as being introspective, with the focus being on the idealised, technical model rather than a wider reality. The evidence-based, inductive approach is outward looking as it is built on, and seeks verification through, cross-checking data types. It is also predictive and potentially falsifiable, that is, it has a stronger emphasis on science rather than technique. For example, a sudden reduction in rates of sedimentation coinciding with the Eocene to Oligocene boundary predicts the sudden appearance and growth of sediment traps (new basins) in a proximal location, and the variable polarity of vertical movement through the Oligocene and up to the Oligo-Miocene boundary predicts non-epeirogenic type tectonic movement. Both these hypotheses can be tested and augmented.
This review argues that a change from model-based and deductive approaches to an inductive method, as well as more qualified descriptions of data reliability, is necessary to develop a better understanding of tectonically active and complex regions. The currently popular method of having a stratigraphic summary based on a poorly described relative sea-level curve and an un-evaluated rift to sag basin genesis is neither rigorously deductive nor properly inductive, and has little scientific (predictive) value. A new tectono-stratigraphic method is needed to improve our understanding of both stratigraphy and the Cenozoic tectonic processes that developed SE Asia.
•Well and seismic data is used to identify the natural sequences of sedimentation.•New data suggest tectonic controls and not eustasy are dominant.•An evidence-based approach is argued to be better than a model-based method.•Tectonically active basins require a new workflow to understand their development.
Catchments, generally understood as the drainage areas of low‐order streams, are often regarded as closed hydrologic entities; that is, precipitation (P) minus evapotranspiration (ET) over a ...catchment equates stream outflow (Q
r). Here, we review evidence that catchments can be leaky due to groundwater outflow or inflow across topographic divides, based on catchment mass balance across a continent and several site‐based studies across the globe. It appears that a catchment is more likely to be leaky with the combination of the following factors: small catchment size, positioned at either the high or low end of a steep regional topographic and climatic gradient, underlain by deep permeable substrates that extend beyond the study catchment, and in drier climate or dry seasons and droughts. Catchment leakage has hydrological, geochemical, and ecological implications. Thus, catchments are best framed as semiclosed hydrologic units perched on top of a larger, regional hydrogeological system with no real boundaries regarding the movement of water and solutes.
This article is categorized under:
Science of Water > Hydrological Processes
Water and Life > Nature of Freshwater Ecosystems
Catchments are leaky units perched on a larger, regional hydrogeological system.
We investigated soil organic carbon dynamics at three freshwater coastal sites in the Laurentian Great Lakes using a simple carbon budget box model. Long-term carbon budgets (1939–2018) were ...developed using aerial photography and then compared to short-term carbon export (2018–2019) developed using drone data. This study puts forth a refined coastal carbon budget model that advances previous model iterations by: (1) examining spatial variability in carbon budgets, (2) including a temporally dynamic carbon inventory term, and (3) updating the erosional term. Half of the initial carbon stock of the combined sites was lost in the 80-year study period, which is severely imbalanced with the age of those coastal habitats (400–2000 cal years BP). Major periods of carbon loss corresponded to periods of elevated water level. Short-term loss of carbon during 2018–2019 corresponded to northeasterly extreme wave events during a period of above-average water level.
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•A coastal carbon budget model was refined to account for spatiotemporal heterogeneity•Half the soil organic carbon stored at the study sites was exported in 80 years•Carbon loss occurs during decadal periods of water level rise•High wave events and/or elevated water level cause carbon loss
Regional Geology; Soil Science; Erosion; Environmental Management
The diverse geological and geophysical data sets compiled, interrogated and interpreted for the largely undercover southern Thomson Orogen region reveal a Paleozoic terrane dominated by deformed ...metasedimentary rocks intruded by S- and I-type granites. An interpretive basement geology map and synthesis of geochronological constraints allow definition of several stratigraphic packages. The oldest and most widespread comprises upper Cambrian to Lower Ordovician metasedimentary rocks deposited during the vast extensional Larapinta Event with maximum depositional ages of ca 520 to ca 496 Ma. These units correlate with elements of the northern Thomson Orogen, Warburton Basin and Amadeus Basin. The degree of deformation and metamorphism of these rocks varies across the region. A second major package includes Lower to Middle Devonian volcanic and sedimentary units, some of which correlate with components of the Lachlan Orogen. The region also includes a Middle to Upper Ordovician package of metasedimentary rocks and a Devonian or younger package of intermediate volcaniclastic rocks of restricted extent. Intrusive units range from diatremes and relatively small layered mafic bodies to batholithic-scale suites of granite and granodiorite. S-type and I-type intrusions are both present, and ages range from Ordovician to Triassic, but late Silurian intrusions are the most abundant. Two broad belts of intrusions are recognised. In the east, the Scalby Belt comprises relatively young (Upper Devonian) intrusions, while in the west, the Ella Belt is dominated by intrusions of late Silurian age within a curvilinear, broadly east-west trend. The stratigraphic distributions, characteristics and constraints defined by this interpretive basement mapping provide a basic framework for ongoing research and mineral exploration.
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