XI Congreso Geológico de España, 2-6 de julio 2024, Ávila.-- 3 pages, 1 figure | [EN] Based on an integration of chronostratigraphical, sedimentological, and compositional analysis we define three stratigraphic models for the Alboran contourites formed by the light intermediate (LMW) and dense deep Mediterranean (DMW) bottom currents, during the last glacial period to the Holocene. The contourite terrace model (I) is characterized by coarse-grained sediment sequences. It is an archive of the interplay between the high-energy Atlantic Water-LWM interface and glacioeustasy from the Younger Dryas (YD) to the Holocene. The contourite drift models (II) comprise coarse-grained sediment sequences formed by a relatively fast LMW and also, fine-grained sediment sequences formed by a relatively weak DMW, except for the Heinrich Stadials HS3 to HS1 and YD when coarse-grained sequences were deposited. These models represent archives of rapid ocean-climate coupled fluctuations since 29 kyr. Finally, the contourite/turbidite mixed model (III) comprising a fine and coarse-grained sediment sequences, represents another archive of DMW and glacioeustasy interplay from the end of the late Pleistocene to Holocene. These three contourite stratigraphic models allows us to decode for the first time the relative variability of the LMW versus DMW flow regimes, which records differences and similarities. The distinct impact of LMW and DMW on sedimentation may offer new insights into their different palaeoceanographic responses to rapid climatic oscillations | [ES] El análisis cronológico, sedimentológico y composicional de testigos de sedimento en el NO del mar de Alborán permite definir tres modelos estratigráficos formados por las corrientes de fondo de las masas de agua mediterráneas intermedia (LMW) y profunda (DMW), para el último período glacial hasta el Holoceno. El modelo de terraza de contornítica (I) presenta secuencias de grano grueso y es un archivo de los procesos oceanográficos de alta energía que acontecen en la interfase entre la masa de agua del Atlántico y la LWM desde el Dryas Reciente (YD) hasta el Holoceno. Los modelos de crestas contorníticos (II) comprenden secuencias de grano grueso formadas una LMW rápida y secuencias de grano fino formadas por una DMW débil, excepto para los estadiales de Heinrich estadiales HS3 a HS1 y YD. Estos modelos estratigráficos contorníticos representan archivos de fluctuaciones rápidas de la interacción océano-clima desde hace 29.000 años. El modelo mixto contornita/turbidita (III) comprende secuencias de grano fino y grueso formados por cambios de dinámica en la DMW durante el cambio glacioeustático, desde finales del Pleistoceno tardío. Estos tres modelos estratigráficos contorníticos permiten decodificar por primera vez la variabilidad relativa de los regímenes de flujo de LMW versus DMW | The contribution is dedicated to memory of our colleague and friend Mª Pilar Mata. Research was funded by FAUCES (CTM2015-65461-C2-1-R) and CONTOURIBER (CTM 2008-06399-C04) projects. ICM-CSIC scientists thank for the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S)

Los niveles piezométricos medidos en el acuífero del Valle Querétaro de los últimos 40 años registran descensos de más de 100 m, con un promedio de 120 m. La Pérez Villareal variación espacial de las condiciones de descenso evidencia la existencia de un sistema acuífero determinado por la estratigrafía del subsuelo, donde las fallas y fracturas pueden actuar como barreras o canales de flujo. Estudios previos han reportado que el acuífero del Valle de Querétaro es multicapa, profundo, con interacciones de secuencias granulares y fracturadas. Para este trabajo 60 muestras de agua de 38 sitios del acuífero fueron caracterizadas. Las propiedades físico-químicas fueron medidas en campo y los aniones cationes y algunos elementos traza se cuantificaron en el laboratorio. En ocho pozos de monitoreo se muestreo agua subterránea en dos profundidades y durante tres periodos de tiempo. Los resultados de iones mayores (diagramas de Piper y Stiff) indican que la mayoría de las aguas son bicarbonatadas-sódico-potásicas, lo que es indicativo de aportes de aguas profundas. Los sólidos disueltos y la conductividad eléctrica de las muestras evidencian que existía un sistema de flujo somero y libre que fluía hacia el centro del Valle de Querétaro hace más de 50 años, coincidiendo con estudios anteriores de evolución piezométrica del acuífero en el hecho de que se está extrayendo agua de reservorios más profundos. La actividad hidrotermal y los patrones en la caracterización química del agua subterránea en zonas aledañas a discontinuidades geológicas indican que las fallas y fracturas determinan el flujo. El diagrama de Piper, junto con el análisis de clusters e índices de correlación, permitieron establecer una relación entre la estratigrafía y la composición química del agua subterránea. Al caracterizar agua subterránea de un mismo sitio en tres periodos diferentes se detectaron ciertos cambios en su composición química. La información aportada en este estudio demuestra que en acuíferos complejos, los registros piezométricos no son suficientes para determinar los sistemas de flujo de agua subterránea. La implementación de un monitoreo de las características químicos y físicas del acuífero dentro del marco geológico específico de la zona de estudio ha probado ser adecuado para el entendimiento de los sistemas de flujo en ambiente complejos. | The piezometric levels measured in the aquifer of the Valley of Querétaro for the last 40 years record decrease of more than 100 m, with an average of 120 m. The spatial variation of the declining conditions evidence the existence of an aquifer system determined by the subsurface stratigraphy, where faults and fractures can act as barriers or channels flow. Previous studies have reported that the aquifer of the Valley of Querétaro is multi-layer, deep, with granular and fractured intercalated sequences. In this kind of aquifers the piezometric measurements are not enought to determine groundwater flow directions. For this work 60 water samples of 38 aquifers sites were characterized. The physicochemical parameters were measured in field and the anions, cations and some trace elements were quantified in the laboratory. In eight minitoring wells groundwater was sampled in two different depths, and during three time periods. The results of major ions (Piper diagrams and Stiff) indicate that most waters are bicarbonate-sodium-potassium, which is indicative of contributions from deep water. The dissolved solids and electrical conductivity of the samples evidence that there was a shallow and free flow system flowing towards the center of Valley of Querétaro more than 50 years ago, consistenting with previous piezometric evolution studies in the fact that groundwater is currently being extracted from deeper reservoirs. Hydrothermal activity and chemical patterns of groundwater in areas surrounding geologic discontinuities suggest that faults and fractures determine the groundwater flow. The Piper diagram, along with the of clusters, and correlation index allowed to establish a relationship between the stratigraphy and chemical composition of ground water. With the characterization of groundwater from the same site in three different periods some changes were detected in their chemical composition. Information brought in this study demonstrate that in complex, the piezometric record is not enough to determine groundwater flow systems. Implementation of a monitoring of the analysis chemical and physical characteristics of the aquifer with the specific geological setting has proven suitable to understanding flow system mechanism in complex environments.

Variations in the sedimentary organic matter were documented throughout the Agua de la Mula Member (late Hauterivian) of the Agrio Formation, at a combined section in the type area of the Agrio Formation; the base at Agrio del Medio and the middle to top at Bajada del Agrio. A main organic-rich interval was identified in the basal Agua de la Mula Member, dominated by marine-derived Amorphous Organic Matter (AOM), coinciding with the highest Total Organic Carbon (TOC) content, between 1.4 and 3.8 wt.%, suggesting dysoxic conditions. The rest of the Member is predominantly characterized by terrestrially-derived organic matter, mainly phytoclasts, with low TOC values, around 1% or lower, indicating predominantly oxic depositional settings. By integrating stacking pattern and shell beds analysis, four depositional sequences SQ1–SQ4 were recognized. The organic-rich, finely laminated bituminous black shales of the Spitidiscus riccardii zone constitute a mayor and rapid inundation defining a Transgressive System tract (TST), related to a third order asymmetrical mesosequence dominated by a thick High System Tract (HST). It represents the most widespread and important flooding episode within the Neuquén Basin during the late Hauterivian. Inside sequences of higher frequency (SQ1, SQ2, SQ3, SQ4) of probably fourth order were recognized and analysed including several ammonids zones (Spitidiscus riccardii, Crioceratites schlagintweiti, C. diamantensis and Paraspiticeras groeberi). With the exception of the oxygen-controlled, basinal and outer ramp settings indicated for the TST1, which is equivalent to the TST of a lower order sequence, and the lower TST2, respectively, the prevalence of well oxygenated, inner to middle ramp depositional environments, is suggested for the rest of the sedimentary succession and emphasized in HST of SQ2, SQ3 and SQ4. Thus, a shallowing-upward trend with improved oxygenation is recorded through the Agua de la Mula Member, reflected by decreasing TOC, AOM content and preservation state of the organic matter. Based on the whole rock fluorescence analysis of the two selected organic-rich intervals from the Spitidiscus riccardii and the lowermost Crioceratites diamantensis zones, the presence of hydrocarbons suggests a very early in situ generation.

A FEFLOW three-dimensional (3D) groundwater model is developed to enhance the understanding of groundwater processes in the complex alluvial stratigraphy of Maules Creek Catchment (New South Wales, Australia). The aquifer vertical heterogeneity is replicated by indexing 204 lithological logs into units of high or low hydraulic conductivity, and by developing a 3D geological conceptual model with a vertical resolution based on the average lithological unit thickness for the region. The model mesh is populated with the indexed geology using nearest neighbour gridding. The calibrated model is successful in simulating the observed flow dynamics and in quantifying the important water-budget components. This indicates that the lateral groundwater flow from the mountainous region is the main inflow component of the system. Under natural conditions, the Namoi River acts as a sink of water, but groundwater abstraction increasingly removes a large amount of water each year causing dewatering of the system. The pumping condition affects the river–aquifer interaction by reversing the flow, from gaining to losing river conditions during the simulation period. The procedure is relevant for the development of groundwater models of heterogeneous systems in order to improve the understanding of the interplay between aquifer architecture and groundwater processes.

Based on the regional hydrogeology and the stratigraphy beneath the Los Alamos National Laboratory (LANL) site, New Mexico (USA), a site-scale groundwater model has been built with more than 20 stratified hydrofacies. A stepwise inverse method was developed to estimate permeabilities for these hydrofacies by coupling observation data from different sources and at various spatial scales including single-well test, multiple-well pumping test and regional aquifer monitoring data. Statistical analyses of outcrop permeability measurements and single-well test results were used to define the prior distributions of the parameters. These distributions were used to define the parameter initial values and the lower and upper bounds for inverse modeling. A number of inverse modeling steps were performed including the use of drawdown data from the pump tests at two wells (PM-2 and PM-4) separately, and a joint inversion coupling PM-2 and PM-4 pump test data and head data from regional aquifer monitoring. Parameter sensitivity coefficients for different data sets were computed to analyze if the model parameters can be estimated accurately with the data provided at different steps. The joint inversion offers a reasonable fit to all data sets. The uncertainty of estimated parameters for the hydrofacies is addressed with the parameter confidence intervals.

Offshore hydrogeology has been much less studied compared to onshore hydrogeology. The marine Quaternary system in Hong Kong (China) consists of interlayers of aquitards and aquifers and was part of the Pearl River Delta when the sea level was low before the Holocene. Core samples from six offshore boreholes were collected to measure the chloride concentration in the system by adding deionized water. A method was proposed to convert the sediment chloride into that of the original pore water. A one-dimensional sedimentation-transport model was developed to simulate the historical conservative transport of the reconstructed pore-water chloride. The model integrates present knowledge of stratigraphy and the historical evolution of the geological system. The chloride concentration profiles show that the chloride decreases from an average of 13,800 mg/L in the first marine unit to an average of 5,620 mg/L in the first aquifer. At the bottom of one borehole, the concentration is only 1,420 mg/L. The numerical model shows that the vertical chloride distribution is due to diffusion-controlled downward migration of seawater. The second marine unit obstructs the downward migration, indicating its low permeability and good aquitard integrity. The relatively fresh or brackish water in deep aquifers protected by the aquitard has the potential to be used as drinking water following some treatment, or at least as raw water with much cheaper desalinization compared with using seawater. The methodology and findings in this study are instructional for other coastal areas with similar geology and history in the South China Sea.

Groundwater total dissolved solids (TDS) distribution was mapped with a three-dimensional (3D) model, and it was found that TDS variability is largely controlled by stratigraphy and geologic structure. General TDS patterns in the San Joaquin Valley of California (USA) are attributed to predominantly connate water composition and large-scale recharge from the adjacent Sierra Nevada. However, in smaller areas, stratigraphy and faulting play an important role in controlling TDS. Here, the relationship of stratigraphy and structure to TDS concentration was examined at Poso Creek Oil Field, Kern County, California. The TDS model was constructed using produced water TDS samples and borehole geophysics. The model was used to predict TDS concentration at discrete locations in 3D space and used a Gaussian process to interpolate TDS over a volume. In the overlying aquifer, TDS is typically <1,000 mg/L and increases with depth to ~1,200–3,500 mg/L in the hydrocarbon zone below the Macoma claystone—a regionally extensive, fine-grained unit—and reaches ~7,000 mg/L in isolated places. The Macoma claystone creates a vertical TDS gradient in the west where it is thickest, but control decreases to the east where it pinches out and allows freshwater recharge. Previously mapped normal faults were found to exhibit inconsistent control on TDS. In one case, high-density faulting appears to prevent recharge from flushing higher-TDS connate water. Elsewhere, the high-throw segments of a normal fault exhibit variable behavior, in places blocking lower-TDS recharge and in other cases allowing flushing. Importantly, faults apparently have differential control on oil and groundwater.

Hydrogeological models of mountain regions present the opportunity to understand the role of geological factors on groundwater resources. The effects of sedimentary facies and fracture distribution on groundwater flow and resource exploitation are studied in the ancient fan delta of Sant Llorenç de Munt (central Catalonia, Spain) by integrating geological field observations (using sequence stratigraphy methods) and hydrogeological data (pumping tests, hydrochemistry and environmental isotopes). A comprehensive analysis of data portrays the massif as a single unit, constituted by different compartments determined by specific layers and sets of fractures. Two distinct flow systems—local and regional—are identified based on pumping test analysis as well as hydrochemical and isotopic data. Drawdown curves derived from pumping tests indicate that the behavior of the saturated layers, whose main porosity is given by the fracture network, corresponds to a confined aquifer. Pumping tests also reflect a double porosity within the system and the occurrence of impervious boundaries that support a compartmentalized model for the whole aquifer system. Hydrochemical data and associated spatial evolution show the result of water–rock interaction along the flow lines. Concentration of magnesium, derived from dolomite dissolution, is a tracer of the flow-path along distinct stratigraphic units. Water stable isotopes indicate that evaporation (near a 5% loss) occurs in a thick unsaturated zone within the massif before infiltration reaches the water table. The hydrogeological analysis of this outcropping system provides a methodology for the conceptualization of groundwater flow in similar buried systems where logging and hydrogeological information are scarce.

Nitrate is found in groundwater due to natural and anthropic processes. Nitrate content in groundwater is associated with factors such as human activities, soil type, climate, geology and chemistry of groundwater. Some of these factors (climate and geology) coincide with those that determine the type of groundwater flow system (local, intermediate or regional) present in an area which, in turn, is influenced by climate, stratigraphy, and type of subsoil and surface rocks; therefore, it is expected that the concentration of nitrate is related to the type of groundwater flow. The relationship between the concentration of nitrate in groundwater samples and the type of flow was analyzed in an aquifer system located in the Trans-Mexican Volcanic Arc, within the Michoacán-Guanajuato volcanic complex. The system is composed of two hydrogeological units, one volcanic and the other sedimentary, with the presence of geological faults, in a context where there is agricultural activity and deficient domestic wastewater management. To improve understanding of the overall aquifer system, 34 groundwater samples (28 wells, 6 springs) were analyzed. The results indicate that each flow system presents characteristic patterns of nitrate concentration and groundwater chemical composition. A high nitrate concentration was found in local and local-intermediate flow systems. Nitrate concentration decreased from local to intermediate and regional flows. The nitrate concentration decreased depending on groundwater flow direction, so it is possible to use nitrate as a parameter to differentiate groundwater flow systems.