An electrostratigraphic cross-section across the central Po plain : bearings on subsurface geology and hydrostratigraphy

A 72-km-long N\u2013S cross-section was surveyed with direct current resistivity soundings through the Quaternary clastic infill of the Apennine foredeep in the Po plain of Lombardy (Northern Italy). The aims are (1) to test the potential of DC resistivity methods at the regional scale; (2) to draw the electrostratigraphic picture of the basin fill, down to the pre-Quaternary substratum; (3) to refine and test the methodology and concepts of hierarchic electrostratigraphy at the basin scale; (4) to contribute to characterize the regional hydrostratigraphy of a relevant hydrogeological basin. 163 resistivity-versus-depth profiles with a maximum investigation depth of 450 m were obtained from vertical electrical soundings. To draw the electrostratigraphic cross-section, the polarity of the resistivity contrast across resistivity interfaces (i.e. resistive over conductive layers or vice versa) was considered and the discontinuities were correlated according to the persisting pattern from north to south. Doing so, the hierarchic assemblage of four major electrostratigraphic boundaries and the five intervening groups of electrostratigraphic units (EsUs) was established. The resulting picture was compared to the available subsurface reconstructions from the literature, using the 1-D borehole data only to check the geophysical image at some random sample sites. The results show that the electrostratigraphic picture captures the geological and hydrostratigraphic complexity of the subsurface of the basin comparing well with the available direct subsurface geological and hydrostratigraphic reconstructions. At the regional scale of the cross-section, two hierarchic orders of EsUs and correlative boundaries could be drawn (first-order groups and second-order individual EsUs), while the lowermost third-order rank, the electrolayer, is recognized at the single-VES sites only

A new perspective to model subsurface stratigraphy in alluvial hydrogeological basins, introducing geological hierarchy and relative chronology

This paper presents a novel perspective for modelling alluvial stratigraphy. It integrates the spatial geological information, geological maps and well-log descriptions, with the rules describing the hierarchy and relative chronology of the geological entities. As geological modelling tools are moving fast forward, the urgent need for expert geological input, codified as modelling rules, persists. Concerning subsurface alluvial architectures, the concepts of \u201cstratigraphic hierarchy\u201d and \u201crelative chronology\u201d provide the most relevant rules which permit to link the modelling procedure to the geo-history of a region. The paper shows how to formalize this knowledge into modelling rules. This is illustrated and implemented in a Python\u2122 module named HIEGEO which is applied on a 2-D cross-section from the Po Basin (N-Italy). The stratigraphic correlation yields 2-D pictures of the hierarchic stratigraphy and relative chronology of the units. The input are: an attribute table of stratigraphic boundaries expressing their hierarchy and chronology; contact points where these boundaries cross the control logs. Since the aim of HIEGEO is to illustrate the principle of the method but not to replace existing 3-D geological modelling tools, it implements a linear interpolation algorithm which creates joins between contact points. It plots linear joins framing polygons based on their hierarchy, at any user\u2019s desired detail. HIEGEO highlights potential inconsistencies of the input dataset, helping to re-evaluate the geological interpretation. The proposed workflow allows to: i) translate geological knowledge into modelling rules; ii) compute stratigraphic models constrained by the hierarchy of stratigraphic entities and the relative chronology of geological events; iii) represent internal geometries of the stratigraphic units, accounting for their composite nature; iv) reduce uncertainty in modelling alluvial architectures. It represents a starting point for multi-scale applications and could be easily integrated into 3-D modelling packages, to couple the hierarchical concept proposed here with existing advanced interpolation methods

LE RELAZIONI TRA LE ARENARIE DI SARNICO (CONIACIANO) E LE UNITA' CENOMANIANO-TURONIANE NELL'AREA DI CAPRIOLO - CORNO PENDITA (BS) (BACINO LOMBARDO, ALPI MERIDIONALI)

The Cenomanian-Coniacian units of the Capriolo - Corno Pendita area belong to the eastern margin of the Lombardy Basin. The Coniacian turbidite sandstone lithosome (Arenarie di Sarnico) unconformably overlies the Cenomanian-Turonian units. The unconformity should be due to slumping and sliding during Late Turonian time. The Arenarie di Sarnico seal the geometries related to the Cenomanian - Turonian synsedimentary tectonic. Evidences for this activity are provided by slumpings and chaotic beds (Early-Late Cenomanian) and by unconformities predating the submarine erosion phase

Geology of the San Colombano hill, a Quaternary isolated tectonic relief in the Po Plain of Lombardy (Italy)

The 1:10,000 geological map of the San Colombano hill covers 60 km 2 in the Po Plain, south of Milan. The new and the historical surface geological data-sets are managed by a GeoDB aiming to contribute to re-interpret the Quaternary evolution at the Po Plain-Northern Apennine border. On the hill, the Calabrian shallow marine San Colombano Fm. unconformably overlies the truncated deeper-marine Miocene formations, up-thrusted by the external fronts of the Apennine Emilian Arc during Mio-Pliocene. Late Pleistocene alluvial units rest in unconformity above the marine succession both on the uplifted hilltop and on the surrounding plain. Fault-related offset of Late Pleistocene units, stratigraphic and morpho- structural evidences (facets, relic surfaces and drainage patterns), document the Quaternary tectonic history. Early to Middle Pleistocene ongoing thrust-folding at the northernmost buried reaches of the Emilian Arc was followed by Latest Pleistocene-Holocene transtension, possibly relating to the NNE striking Pavia-Casteggio lateral ramp

A hierarchical multiple-point statistics simulation procedure for the 3D reconstruction of alluvial sediments

A correct representation of the heterogeneity of porous formations and of their preferential flow paths is crucial for a reliable modelization of the contaminant transport processes. Several geostatistical tools have been developed to tackle this challenge. Many of these tools are often applied in a multi-scale framework, where the geostatistical simulation is applied fist trying to reproduce the big scale features of the sedimentary formations, and finally to reproduce their small scale features. However, many of the developed multi-scale and hierarchical techniques have a quite complex work-flow and rely on diverse simulation methods. Here a simplified hierarchical simulation procedure is proposed, where only multiple-point statistics (MPS) is used to simulate the target heterogeneities at different scales. The simulation procedure is organized in a tree-like frame, where MPS is applied at each simulation branch using a simplified binary training image and the corresponding available conditioning data. At each simulation branch, the MPS simulation is performed in a sub- domain defined by one of the two facies codes simulated at the parent branch. The proposed procedure is tested in the three-dimensional (3D) reconstruction of two model blocks of alluvial sediments, using the available two-dimensional (2D) outcrop information as training images. It is compared against a non hierarchical MPS simulation procedure in terms of connectivity indicators and breakthrough curves obtained from 3D particle tracking numerical experiments. All the aforementioned tests are performed considering 100 equiprobable realizations for each simulation technique. This allows to make statistically reliable comparisons, and to extract statistical distributions of the transport parameters by fitting analytical curves to the results of the particle tracking experiments. These statistical distributions are used to perform one-dimensional transport experiments on spatial scales ten times bigger than the block scale using the Kolmogorov-Dmitriev approach in a Monte Carlo framework

Aquifer architecture of the Quaternary alluvial succession of the southern lambro basin (Lombardy-Italy)

Aquifer stratigraphy of the sector of the Pleistocene - Holocene alluvial plain of Lombardy, run by the Lambro valley system south of Milan, has been reconstructed on the basis of geological mapping at 1:10.000 and subsurface interpretation and correlation of more than 150 among water wells, boreholes and deep excavations. The Middle (?) - Late Pleistocene sedimentary evolution of this sector includes four major progradation cycles of alluvial depositional systems that migrated from the alpine northern side towards the axial palaeo-Po depositional system. These cycles were governed by Pleistocene glacial cycles, in combination with ramp-folding of the San Colombano - Salerano apenninic anticlines and minor uplift of the alpine side. Every major cycle is soled by an erosion surface, and is shaped by minor fining upward sequences. Both major and minor sequences record at first the advance of coarse-grained units (distal braided alluvial fan or sandy braid plain) which fringe-out south-eastwards into meandering fluvial systems, and are replaced upwards by alluvial plain fines, which close the sequences. Physical stratigraphy and geomorphology, analysis of facies associations, characterisation of gravel composition, radiocarbon dating on 4 peat and plant relic samples and findings of transported artefacts allowed the correlation of the four cycles with the regional evolution. The Post Glacial meandering depositional systems of the deeply entrenched Lambro valley system (Unit 4, Holocene; Unit 5, historical), are cut into the braided stream to meandering depositional systems that developed during L.G.M. times, at present outside the Lambro valley (Unit 3, Late Pleistocene). These represent the uppermost aquifer unit, i.e. the phreatic - non saturated zone. The underlying Unit 2 (Late Pleistocene) can be correlated with the Besnate Allogroup, and therefore developed during the corresponding glaciations. It is formed by three stacked sequences, controlled by glacial cycles, which are deeply scoured into the lowermost succession that could be studied (Unit 1 Middle ? - Late Pleistocene ?). It represents the most important and permeable intermediate aquifer unit, that is only partly confined by the flood-plain fines of the uppermost sub-unit 2C

Validation of Hurst statistics : a predictive tool to discriminate turbiditic sub-environments in a confined basin

Turbidite sequences within confined basins constitute important hydrocarbon reservoirs worldwide; for this reason the discrimination of sedimentary sub-environments based on an objective statistical method is of interest for pure and applied science. We investigated the potential use of the Hurst test (Chen & Hiscott 1999) as a statistical tool to discriminate sub-environments within geologically complex turbiditic units that fill a confined basin with well exposed facies transitions and onlaps, at the scale of several stacked reservoirs (Cengio and Bric la Croce - Castelnuovo Turbidite Systems in the Tertiary Piedmont Basin, Oligocene, Northern Italy). In vertical stratigraphic sections, the Hurst test determines the degree of clustering of low and high values of sedimentological variables like bed-thickness, grain-size and sand/mud ratio that are dependent on sub-environments of deposition. We applied the Hurst test to depocentral and marginal sub-areas across the basin (parallel and perpendicular to the main palaeo-current direction), documenting a different clustering of thick and thin beds, and of high and low values of the sand/mud ratio, in the depocentre-distal sector with respect to the onlap areas. A new field (onlap sub-environment) could thus be added to the Chen & Hiscott (1999) classification diagram of turbidite settings based on the Hurst index. The Hurst phenomenon i.e. clustering of high and low values of the selected variables, was also able to distinguish between proximal and distal (depocentral) lobe settings, and to recognize the fingerprint of the different depositional lobes (fully confined aggrading, prograding, backstepping). The map of turbidite sub-environments obtained by interpolation of the Hurst index is quite comparable to the field-observed facies map, providing impressive robust validation of the Hurst statistics. This method seems to represent a very promising predictive tool for subsurface studies of turbiditic oil fields based on core and log analyses