Phreatic Research Articles

Fondo actual de nitrato como metodología en la relación agua superficial – subterránea aplicado en el sudeste Bonaerense, Argentina

La contaminación con nitrato en agua superficial y subterránea es un problema mundial vinculado especialmente con la intensa actividad agrícola. Las concentraciones elevadas afectan la calidad de las aguas y resulta ser un indicador importante de la influencia del hombre. En un acuífero libre de una cuenca de llanura en el sudeste bonaerense en Argentina se midieron 4-235 mg/L en octubre 2013 y 5,7-250 mg/L en julio 2014. Respecto a los tenores en el agua superficial se midieron concentraciones de 7–79,6 mg/L durante octubre 2013-julio 2014 y 1–120 mg/L de julio 2014 a abril 2015. Se calcularon los valores de Fondo Actual del acuífero mediante un análisis estadístico y se los comparó para monitorear sus variaciones. En cuanto al agua superficial, se calcularon sus variaciones de Fondo Actual en los dos periodos para cotejarlos con el acuífero. A partir de los resultados se propone una nueva metodología para analizar la vinculación agua superficial-subterránea.

New species and records of phreatic snails (Caenogastropoda: Cochliopidae) from the Holocene of Coahuila, Mexico

New species and records of phreatic snails (Caenogastropoda: Cochliopidae) from the Holocene of Coahuila, Mexico

Propuesta Metodológica para el Análisis de la Licuefacción de Suelos Asociada a Sismos Destrucutivos. Pre-Andes Centrales, Argentina (31º 30’ S y 68º 25’ O)

En este trabajo se evalua la susceptibilidad a la ocurrencia de procesos de licuefaccion de suelos asociados a sismos destructivos en el area ubicada al norte del rio San Juan. Los terremotos de 1894, 1944, 1952 y 1977 provocaron licuefaccion en el centro oeste de Argentina y particularmente en numerosos sitios de la provincia San Juan, resultando la zona norte del valle de Tulum, una de las mas afectadas. Los registros historicos de procesos de licuefaccion de suelos (PLS) ocurridos durante los terremotos mencionados, evidencian grietas, volcanes de arena, crateres y asentamientos diferenciales, los que ocasionaron importantes danos a las viviendas y al sector agro industrial de la region. En este estudio se efectuo un analisis de los factores principales que influyen en su ocurrencia, como tambien los efectos de la licuefaccion. Se evaluaron y ponderaron los factores condicionantes tales como origen y granulometria del deposito, edad de los depositos, profundidad del nivel freatico y registros historicos entre otros. Del analisis de los factores resulto un mapa asociado a una tabla evaluativa. La influencia de los factores en la evaluacion de la susceptibilidad se realizo mediante un proceso iterativo de superposicion de mapas. Una vez conseguida la combinacion optima se obtuvo un mapa final de susceptibilidad a la licuefaccion. La zonificacion lograda se relaciono a un indice de susceptibilidad (IS), catalogado cualitativamente como Muy Alto, Alto, Moderado y Bajo. Los resultados obtenidos permiten concluir que el sector medio del abanico aluvial del rio San Juan, donde se concentran los centros urbanos y la mayor actividad agropecuaria, es el sitio donde se exponen las condiciones de Muy Alta susceptibilidad, mientras que las de Alta susceptibilidad ocupan algunas zonas del sector medio-distal del abanico y las de Moderada a Baja se circunscriben al sector proximal del abanico.

EVIDENCE FOR LADINIAN (MIDDLE TRIASSIC) PLATFORM PROGRADATION IN THE GYULAKESZI AREA, TAPOLCA BASIN, WESTERN HUNGARY: MICROFACIES ANALYSIS AND BIOSTRATIGRAPHY

A shallowing-upward carbonate sequence was studied from the outcrop at Gyulakeszi, Tapolca Basin (western Hungary), and it is interpreted as a Middle Triassic ( Curionii or younger) platform progradation. Two lithostratigraphic units are distinguished. Microfacies analysis and micropaleontological investigation conducted on the red nodular, cherty limestone (Vaszoly and Buchenstein formations) suggest that the lower unit was deposited during the Reitzi and the Secedensis ammonoid zones. The overlying white platform limestone (upper unit) is typical of a prograding platform and includes gravity-driven deposits at the base followed by periplatform facies deposited in shallow marine warm waters around the fair-weather wave base. The section at Gyulakeszi was unaffected by fabric-destructive dolomitization, which is uncharacteristic of similar platform facies in the Balaton Highland. Isopachous and radiaxial fibrous calcite cement found in the grainstone and boundstone facies are indicative of early lithification and diagenesis in the marine phreatic zone. “Evinospongiae”-type cement is described for the first time from the Balaton Highland and it is similar to the outer platform cements published previously from the Alps (Italy and Austria). The progradation could have advanced over the pelagic limestones as early as the Curionii zone, which is an undocumented event in the Veszprem Plateau. Similar event, however, is well known from the Western Dolomites, where aggradation was followed by intense progradation during the Gredleri and Archelaus ammonoid zones. The length of this progradation event at Gyulakeszi, however, is ambiguous since proven Ladinian (Longobardian) rocks are not exposed in the study area and were not penetrated by boreholes in the Tapolca Basin.

Hydrogeophysical delineation of groundwater prospect zones at Odigbo, Southwestern Nigeria

Data from dc resistivity depth sounding and hydrogeologic measurements from Odigbo, Nigeria, were incorporated to delineate the groundwater prospect zones in the area. The area is underlain by the basement complex rocks of southwestern Nigeria, and characterised by biotite-gneiss and quartzite lithologies. The hydrogeologic data acquisition involved determination of depths (of wells) and static water levels which enabled determination of thickness of vadose and phreatic zones in 45 existing wells. The dc resistivity measurements involved Schlumberger depth soundings in 61 locations. The interpretation of the sounding data enabled the delineation of geoelectric sequence across the area. Depth to water table (groundwater head) ranges from 2.3 to 9.6 m while the thickness of the phreatic zone, an approximation of water column thickness, varies from 0.1 to 3.0 m, with the thickness in the range of 2.1 to 3 m constituting about 9%, and occurring in the central segment of the study area. The regolith overlying the basement rock constitutes the main water-bearing layer, since the resistivity parameters of the bedrock across the area do not suggest significant fractures or faults. The northwest – southeast and north – south trend of the aquifer unit within the regolith, with resistivity below 210 Ω-m, and constituting about 62% of the area, are considered the groundwater prospect zones. Based on aquifer thickness parameters, the groundwater prospect zones have been classified into low ( 40 m) respectively. 46% falls within the medium/high groundwater prospect rating while 54% falls within the low rating. The maps derived from the above are considered reliable prospect guides for groundwater developers in the area. Key words: Groundwater, unconsolidated regolith, phreatic zone, resistivity sounding, geoelectric layers.

Modified Aver'yanov's phreatic evaporation equations under crop growing

Modified Aver'yanov's phreatic evaporation equations under crop growing

CAPILARITY AND SOLUTE TRANSPORT IN SWELLING AND SHRINKING SOILS

The Aranca Low Plain (SW of Romania), with accumulative relief, a slow dip and an obvious subsidence, is covered with fluvio-lacustrine deposits with various grain sizes, from gravels to smectite clays. The phreatic waters are mineralized and sodium ions reach into the colloidal complex, destroying soil structure. The rise of water in the soil from a free water surface has been termed capillarity rise. The maximum height to which water may rise through capillarity varies between 1.5 and 4 m in Fluvisols and Vertisols. Capillarity rise of soil water takes place above the ground water level and is due to matric suction. The complex geometry of soil pare space creates numerous combinations of interfaces, capillaries and wedges in which water is retained. In addition, water is absorbed on to solid surfaces, with considerable force at close distances. Solutes can interact strongly with soil surfaces and their transport can be slowed in a process known as retardation. In Fluvisols, like in Chernozems and Phaeozems, soluble salts are concentrated in the first 50 cm of the soil profile, while in Vertisols most soluble salts are concentrated at the bottom of the profile. The water potential in a Vertisol is the sum of gravitational potential, capillarity potential and overburden potential. The overburden potential is related to civil engineers effective stress. The phenomenon of capillarity is thus dependent on solid and liquid interfacial properties such as surface tension, contact, angle and solid surface roughness and geometry. These phenomena, partial attributed to capillarity, determine retention and movement of water and solutes through soils.

Natural vulnerability evaluation of the the río Laja basin phreatic aquifer, central-southern Chile.

Se evaluo la vulnerabilidad natural del acuifero freatico de la cuenca hidrografica del rio Laja, mediante la determinacion de la resistencia hidraulica vertical, empleando la metodologia de 'Aquifer Vulnerability Index' (AVI), que permite determinar la velocidad de infiltracion de los contaminantes al pasar el flujo del agua por los distintos horizontes de suelos. El analisis de las tendencias de comportamiento de los contenidos de nitratos, fosfatos, cloruros, sulfatos y solidos totales disueltos, en el agua subterranea permiten establecer una correlacion entre AVI y la fuente-contaminacion acuifera en las areas de diferentes usos del suelo. El comportamiento de los diferentes solutos en el agua subterranea es semejante, con una tendencia de incremento desde la Precordillera Andina hacia la cordillera de la Costa. Las concentraciones mayores se presentan en el contacto de la depresion Central con la cordillera de la Costa, donde el riesgo de contaminacion, segun AVI es moderadamente alto a muy alto. Esto indica que los suelos arenosos de textura media-fina, con escaso contenidos de material arcilloso proporcionan un bajo grado de proteccion para el acuifero, puesto que tienen menores reservas de materia organica y sulfuro disponible para sorcion de fosfatos y denitrificacion; ademas, los niveles freaticos altos, reducen la capacidad de atenuacion propia de dichos suelos y facilitan el transporte de los contaminantes de origen agricola hacia las aguas subterraneas. Por el contrario, los contaminantes agricolas estan menos concentrados en el agua subterranea relacionada con los suelos arenosos de textura gruesa y media, con mayor contenido de material arcilloso, donde la capacidad para atenuar contaminantes esta relacionada con los mayores contenidos de sulfuro disponible y materia organica sorbible/labil, asi como por la mayor profundidad del nivel del agua subterranea.

Calcretes e registros de paleossolos em depósitos continentais neocretáceos

The results presented are based on regional research of calcrete and palaeossols records in the Eastern part of the Bauru Basin, in Sao Paulo State and Triângulo Mineiro region. This basin was filled by Upper Cretaceous siliciclastic sandy sequence, in semi-arid climate on the edges, desert in the center. The most significant calcretes occurrences belong to the the Marilia Formation (Bauru Group), whichon a regional scale, are represented by two extreme types, related to the depositional context. The Ponte Alta type was formed in marginal alluvial fan deposits, the Echapora type in inner aeolian sandy deposits, of wide sand sheets and smooth depressions with temporary rivers and lakes. Three genetic contexts are proposed for the Marilia Formation calcretes: pedogenetic peripheral (Pp), pedogenetic interior (Pi) and phreatic (F). In the first two contexts the edaphic vadose and palustrine processes prevailed, as well as soil profiles poorly developed. It was noticed in them a big frequency of the beta microstructure association. They occur in the Triângulo Mineiro (MG), regions of Monte Alto, Agudos and Bauru (SP). In the phreatic context there was intense development of micritic and spar textures, which probably destroyed the original features of the beta association, generated in contexts Pp and Pi. The superimposed phreatic processes determined the predominance of the alpha microstructure association. They were probably more intense and of the last and/or the most important event in the internal calcrete formation of the basin,in Echapora type profiles. They occur in the regions of Echapora and Marilia (SP). The dendritic configuration of the long and narrow plateaux, sustained by calcified sandstones of the Marilia Formation indicates processes of landscape elaboration through the relief invertion .

Threatened Fishes of the World: Silvinichthys bortayro (Fernandez and de Pinna, 2005) (Trichomycteridae)

Fil: Fernandez, Luis Alfredo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina. Fundacion Miguel Lillo; Argentina

Perfiles paleokarsticos en el techo de la unidad intermedia del mioceno de la cuenca de Madrid

En el techo de la Unidad Intermedia del Mioceno de la Cuenca de Madrid se ha desarrollado un paleokarst temprano, somero y de forma tabular que muestra un marcado control litologico y del dispositivo de facies deposicionales en su genesis. Integrando criterios geomorfologicos, petrograficos y geoquimicos se ha establecido una zonacion hidrogeologica en los perfiles paleokarsticos estudiados, diferenciandose: (i) una zona vadosa caracterizada por la existencia de cavidades alargadas en la vertical tapizadas discontinuamente por espeleotemas y otros cementos vadosos; (ii) una franja de oscilacion del nivel freatico de unos 3-7 metros de espesor, caracterizado por el desarrollo extensivo de cuerpos brechoides estratiformes, la yuxtaposicion de cementos vadosos y freaticos y los contenidos mas bajos en Fe y Mn en el material encajante, y (iii) una zona freatica caracterizada por un aumento en los valores de 813C y el predominio de la cementacion freatica. La correlacion de los perfiles paleokarticos revela una paleogeografia para el techo de la Unidad Intermedia con un paisaje topograficamente descendente de norte a sur en la cuenca para el Vallesiense. [ABSTRACT] An intra-Vallesian (Upper Miocene) paleokarst developed at the top of the Intermediate Miocene Unit in the continental Madrid basin is recognized. This paleokarst is a early shallow, tabular-shaped karst that shows a marked control by the depositional facies pattem and lithologies. By integrating morphological, petrological and geochemical data, three hydrogeological or environmental zones have been established throughout the paleokarstic profiles: (i) a vadose zone, characterized by vertically elongated caves and discontinuous speleothems and vadose cements (ii) a 3-7 m thick water table fringe, characterized by the wide development of stratiform breccia bodies, the superimposition of both vadose and phreatic features, and the lowest Fe and Mn contents in host-rock carbonates; and (iii) a phreatic zone characterized by an increase of 813C values and the predominance of phreatic cementation. The paleogeographic reconstruction for the intra-Vallesian paleokarst using paleokarstic profiles reveals relative topographic highs to the north and topographic lows to the south drawing the paleokarst landscape.

The first occurrence of a neritopsine gastropod from a phreatic community

The first occurrence of a neritopsine gastropod from a phreatic community

16th August 1997 phreatic explosion of Akita-Yakeyama volcano, northeast Japan

1997年8月16日午前11時頃, 秋田焼山(標高1366m)山頂の北東500mの空沼(からぬま)付近で水蒸気爆発が発生し, 同時に継続時間約1時間の火山性微動が観測された. 噴火の起こった地点は1949年の火口群の位置にほぼ相当する(第1図; 津屋, 1954). ここでは, 噴火の二日後の18日に撮影した写真を中心に水蒸気爆発噴出物およびその火口について紹介する. 現時点で見つかった地質学的証拠から8月16日の噴火の過程を再現すると次のようになる: 1) 新火口b1あるいはb2から泥が吹き出し, 空沼火口に「泥流」となって流れ込み, 2) 次に新火口aから火山灰, 噴石が噴出, 3) 最後に新火口b2から少量の泥が噴出し. それ以前の堆積物を同心円状におおった. なお, 今回の噴火の総噴出量は1万m3以下と推定される.

The Abenaki Formation, Nova Scotia Shelf, Canada -- A Depositional and Diagenetic Model for a Mesozoic Carbonate Platform

ABSTRACT Seismic data and well control released to the end of 1976 permit preliminary modelling of the 900 to 1200 m (3000 to 4000 ft) thick Abenaki Formation of Middle Jurassic to earliest Cretaceous age. The lowest member (Scatarie), which overlies the deepening-upward Mohican Formation clastic rocks, shows a cyclicity of oolitic, then oncolitic to muddy limestones, and culminates in the neritic middle shale member (Misaine). These regionally developed cycles are interpreted as transgressive pulses resulting from initial rise of the North Atlantic mid-oceanic ridge system. The thick upper limestone member (Baccaro) was deposited along the paleocontinental-shelf-edge and adjacent to the early Sable Island delta. A neritic 'moat' zone separates the nearshore sandy basement ridge zone from the shallow-water Baccaro platform. Oolitic-bar, mud-shoal, shelf-edge stromatoporoid-coral-algal reef and possible channel depositional environments were recognized. Both oolite beds and lagoonal loferite cyclothems occur in correlative, mainly terrigenous sediments of the Orpheus basin. Interpreted eustatic sea-level changes affected both deposition and diagenesis. During lowered sea levels paleo-highs, whether reefal, salt- or basement-cored, may have been subjected to freshwater diagenesis in a humid, subtropical climate. The only significant dolomitization appears to have occurred in freshwater-marine phreatic mixing zones beneath subaerially exposed reefs. Porosity is associated with the dolomite when present and with limestones altered in the overlying freshwater and vadose paleo-environments. Most of the Abenaki has little porosity and shows mainly submarine and deep subsurface diagenesis. Stromatactis with multiple fibrous calcite druse occurs in pelleted mudstones interbedded with minor, algal?-coated, skeletal grainstones beneath the shelf-edge reefal beds and may represent thin mud mounds with flanking platform sands. The shallow-water Baccaro carbonates were finally buried by coarser MicMac or Missisauga Formation siliciclastics near the Sable Island delta or drowned by Verrill Canyon Formation shale and locally by a deeper-water, slightly phosphatized, sponge reefal limestone and shale, the uppermost member (Artimon).

Phreatic Floor Slot in Model Cave, Nevada

Phreatic Floor Slot in Model Cave, Nevada