Fluid flow processes at basin scale

S u b s u r face fluid flow plays a significant role in many geologic processes and is increasingly being studied in the scale of sedimentary basins and geologic time perspective. Many economic resources such as petroleum and mineral deposits are products of basin scale fluid flow operating over large periods of time. Such ancient flow systems can be studied through analysis of diagenetic alterations and fluid inclusions to constrain physical and chemical conditions of fluids and rocks during their paleohy d r og e o l ogic evolution. Basin simulation models are useful to complement the paleohy d r og e o l ogic record preserved in the rocks and to derive conceptual models on hydraulic basin evolution and generation of economic resources. Different types of fluid flow regimes may evo l ve during basin evolution. The most important with respect to flow rates and capacity for transport of solutes and thermal energy is gr avitational fluid flow driven by the topographic configuration of a basin. Such flow systems require the basin to be elevated above sea level. Consolidational fluid flow is the principal fluid migration process in basins below sea level, caused by loading of compressible rocks. Flow rates of such systems are several orders of magnitude below topogr a p hy driven flow. Howeve r, consolidation may create significant fluid ove rpressure. Episodic dewatering of ove rpressured compart m e n t s m ay cause sudden fluid release with elevated flow velocities and may cause a transient local thermal and chemical disequilibrium betwe e n fluid and rock. This paper gives an ove rv i ew on subsurface fluid flow processes at basin scale and presents examples related to the Pe n e d è s basin in the central Catalan continental margin including the offshore Barcelona half-graben and the compressive South-Pyrenean basin.

Approach to the Lower Pliocene marine-continental correlation from southern Spain. The micrommamal site of Alhaurín el Grande-1 (Málaga Basin, Betic Cordillera, Spain)

A new micromammal site at Alhaurín el Grande (Málaga, southern Spain) located above early Pliocene marine deposits allows an approach to the marine-continental correlation for this age. The early Pliocene marine filling throughout the Málaga Basin is developed in three transgressive-regressive sequences (Pl-1, Pl-2, and Pl-3 units) bounded by discontinuities. At the top of the intermediate sequence Pl-2, peaty sediments have yielded fossils of Rodentia, Lagomorpha, Insectivora, and Crocodylia. The presence of Cricetus barrieri Mein & Michaux, 1970 in combination with murids, both of primitive morphology, such as Apodemus gudrunae Van de Weerd, 1976, and more advanced forms (i.e. Occitanomys brailloni Michaux, 1969 and Stephanomys donnezani cordii Ruiz Bustos, 1986), points to an early Ruscinian age (MN 14 biozone). Based on the planktonic foraminifers, the biostratigraphic data indicate that marine sediments just below the micromammal beds belong to the MPl-2 biozone of the early Zanclean. Available paleomagnetic data from the marine sediments show that the micromammal bed must be located between the normal geomagnetic subchron C3n3n (4.89-4.80 Ma) and the subchron C3n2n (4.63-4.49 Ma), limiting the age of this site to the late part of the early Zanclean.

Upper Eocene-Lowermost Miocene charophyte succession in the Ebro Basin (Spain). Contribution to the charophyte biozonation in Western Europe

A charophyte succession has been established in nineteen sections and eight isolated outcrops from the Ebro Basin, ranging from the Priabonian ro the Aquitanian. Most assemblages were recovered fmm continuous sections and their abundance and diversity allow to define a new zonal scheme for the Upper Eocene-Lower Miocene of Europe. The new zonation includes nine subdivisions, based on the distribution of thirty-two species and directly correlated with the mammal standard levels. Changes in diversity, occurring mainly in the Middle and Upper Oligocene, have been related to climatíc variations. A new species, Chara sp. A. is also described and figured.

Architectural characterization of a delta-front reservoir analogue combining ground penetrating radar and electrical resistivity tomography: Roda Sandstone (Lower Eocene, Graus-Tremp basin, Spain)

Three-dimensional reconstruction of reservoir analogues can be improved combining data from different geophysical methods. Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT) data are valuable tools, since they provide subsurface information from internal architecture and facies distribution of sedimentary rock bodies, enabling the upgrading of depositional models and heterogeneity reconstruction. The Lower Eocene Roda Sandstone is a well-known deltaic complex widely studied as a reservoir analogue that displays a series of sandstone wedges with a general NE to SW progradational trend. To provide a better understanding of internal heterogeneity of a 10m-thick progradational delta-front sandstone unit, 3D GPR data were acquired. In addition, common midpoints (CMP) to measure the sandstone subsoil velocity, test profiles with different frequency antennas (25, 50 and 100MHz) and topographic data for subsequent correction in the geophysical data were also obtained. Three ERT profiles were also acquired to further constrain GPR analysis. These geophysical results illustrate the geometry of reservoir analogue heterogeneities both depositional and diagenetic in nature, improving and complementing previous outcrop-derived data. GPR interpretation using radar stratigraphy principles and attributes analysis provided: 1)tridimensional geometry of major stratigraphic surfaces that define four units in the GPR Prism, 2) image the internal architecture of the units and their statistical study of azimuth and dips, useful for a quick determination of paleocurrent directions. These results were used to define the depositional architecture of the progradational sandbody that shows an arrangement in very-high-frequency sequences characterized by clockwise paleocurrent variations and decrease of the sedimentary flow, similar to those observed at a greater scale in the same system. This high-frequency sequential arrangement has been attributed to the autocyclic dynamics of a supply-dominated delta- front where fluvial and tidal currents are in competition. The resistivity models enhanced the viewing of reservoir quality associated with cement distribution caused by depositional and early diagenetic processes related to the development of transgressive and regressive systems tracts in igh-frequency sequences.

Quaternary Glacial Geology of Alta Ribagorqa Basin (Central Southern Pyrenees)

This paper is an abstract of the doctoral thesis presented by the autor at the University of Barcelona on September 1983. It constitutes a regional study about the Quatemary Glacial Geology in the Ribagorca high valleys. It is the first work in relation to the geomorphology, sedimentology and stratigraphy of the glacial and related deposits in this zone of the Pyrenees. Several formations of quatemary deposits have been studied in detail (mainly in Llauset Valley and in Tall area); and the local quatemary stratigraphy is established and finally a correlation with some previously studied areas in the Pyrenees is attemped.

Preliminary integrated magnetostratigraphic and biostratigraphic correlation in the Miocene Lorca Basin (Murcia, SE Spain).

The Lorca basin is one of the Neogene basins OS South Eastern Spain. The infilling Tortonian-Messinian deposits are mainly composed OS marls and reach up to 1,200 m in thickness. A biostratigraphic survey OS these deposits, assisted by the determination OS the magnetic polarity reversal pattern Sor most OS these deposits (900 m), has enabled the Tortonian-Messinian chronostratigraphy to be precised. The close sampling space for biostratigraphic determination has enabled the accurate location OS Sour main biostratigraphic events than can be correlated with charactenstic events of the Mediterranean biostratigraphic Zones. In addition, the location OS the TortonianNessinian boundary has been accurately placed at some 150 m below the main gypsurn unit outcropping in the basin. The integrated bio-magnetostratigraphic data fiom the studied section allows a tentative interpretation OS the identified magnetozones. Thus, a correlation to the Geomagnetic Polarity Time Scale is presented for more than 900 m of pre-evaporite Miocene stratigraphic succession fiom the Lorca basin. Moreover, about 15' OS anticlockwise rotation has been detected. Its significance is evaluated in the basin geodynamic framework.

Tectonic-palaeoenvironmental forcing of clay-mineral assemblages in nonmarine settings: the Oligocene-Miocene As Pontes Basin (Spain)

Two small, alluvial-lacustrine subbasins developed during the early restraining overstep stages of the Oligocene-Miocene As Pontes strike-slip Basin (NW Spain). Later, the basin evolved into a restraining bend stage and an alluvial-swamp-dominated depositional framework developed. The palaeobiological record demonstrates that the Oligocene-Miocene palaeoclimate in NW Spain was subtropical, warm and humid to subhumid.

An interactive web-GIS tool for risk analysis: a case study in the Fella River basin, Italy

This paper presents a prototype of an interactive web-GIS tool for risk analysis of natural hazards, in particular for floods and landslides, based on open-source geospatial software and technologies. The aim of the presented tool is to assist the experts (risk managers) in analysing the impacts and consequences of a certain hazard event in a considered region, providing an essential input to the decision-making process in the selection of risk management strategies by responsible authorities and decision makers. This tool is based on the Boundless (OpenGeo Suite) framework and its client-side environment for prototype development, and it is one of the main modules of a web-based collaborative decision support platform in risk management. Within this platform, the users can import necessary maps and information to analyse areas at risk. Based on provided information and parameters, loss scenarios (amount of damages and number of fatalities) of a hazard event are generated on the fly and visualized interactively within the web-GIS interface of the platform. The annualized risk is calculated based on the combination of resultant loss scenarios with different return periods of the hazard event. The application of this developed prototype is demonstrated using a regional data set from one of the case study sites, Fella River of northeastern Italy, of the Marie Curie ITN CHANGES project.

Factors affecting Hg (II) adsorption in soils from the Rio Negro basin (Amazon)

Mercury (II) adsorption studies in top soils (top 10 cm) from the Rio Negro basin show this process depends strongly on some selected parameters of the aqueous phase in contact with the soils. Maximum adsorption occurred in the pH range 3.0-5.0 (>90%). Dissolved organic matter shows an inhibitory effect on the availability of Hg (II) to be adsorbed by the soils, whereas a higher chloride content of the solution resulted in a lower adsorption of Hg (II) at pH 5.0. Soils with higher organic matter content were less affected by changes in the salinity. An increase in the initial Hg (II) concentration increased the amount of Hg (II) adsorbed by the soil and decreased the time needed to reach equilibrium. A Freundlich isotherm provided a good model for Hg (II) adsorption in the two types of soil studied. The kinetics of Hg (II) adsorption on Amazonian soils showed to be very fast and followed pseudo-second order kinetics. An environmental implication of these results is discussed under the real scenario present in the Negro River basin, where acidic waters are in contact with a soil naturally rich in mercury.

The age of the"Grande Coupure" mammal turnover: New constraints from the Eocene Oligocene record of the Eastern Ebro Basin (NE Spain.)

The Grande Coupure represents a major terrestrial faunal turnover recorded in Eurasia associated with the overall climate shift at the Eocene-Oligocene transition. During this event, a large number of European Eocene endemic mammals became extinct and new Asian immigrants appeared. The absolute age of the Grande Coupure, however, has remained controversial for decades. The Late Eocene-Oligocene continental record of the Eastern Ebro Basin (NE Spain) constitutes a unique opportunity to build a robust magnetostratigraphy- based chronostratigraphy which can contribute with independent age constraints for this important turnover. This study presents new magnetostratigraphic data of a 495-m-thick section (Moià-Santpedor) that ranges from 36.1 Ma to 33.3 Ma. The integration of the new results with previous litho- bio- and magnetostratigraphic records of the Ebro Basin yields accurate ages for the immediately pre- and post-Grand Coupure mammal fossil assemblages found in the study area, bracketing the Grande Coupure to an age embracing the Eocene-Oligocene transition, with a maximum allowable lag of 0.5 Myr with respect to this boundary. The shift to drier conditions that accompanied the global cooling at the Eocene-Oligocene transition probably determined the sedimentary trends in the Eastern Ebro Basin. The occurrence and expansion of an amalgamated-channel sandstone unit is interpreted as the forced response of the fluvial fan system to the transient retraction of the central-basin lake systems. The new results from the Ebro Basin allow us to revisit correlations for the controversial Eocene-Oligocene record of the Hampshire Basin (Isle of Wight, UK), and their implications for the calibration of the Mammal Palaeogene reference levels MP18 to MP21.

20 Myr of eccentricity paced lacustrine cycles in the Cenozoic Ebro Basin

Long-period orbital forcing is a crucial component of the major global climate shifts during the Cenozoic as revealed in marine pelagic records. A complementary regional perspective of climate change can be assessed from internally drained lake basins, which are directly affected by insolation and precipitation balance. The Ebro Basin in northeastern Iberia embraces a 20 Myr long continuous sedimentary record where recurrent expansions and retractions of the central lacustrine system suggest periodic shifts of water balance due to orbital oscillations. In order to test climatic (orbital) forcing a key-piece of the basin, the Los Monegros lacustrine system, has been analyzed in detail. The cyclostratigraphic analysis points to orbital eccentricity as pacemaker of short to long-term lacustrine sequences, and reveals a correlation of maxima of the 100-kyr, 400-kyr and 2.4-Myr eccentricity cycles with periods of lake expansion. A magnetostratigraphy-based chronostratigraphy of the complete continental record allows further assessing long-period orbital forcing at basin scale, a view that challenges alternate scenarios where the stratigraphic architecture in foreland systems is preferably associated to tectonic processes. We conclude that while the location of lacustrine depocenters reacted to the long-term tectonic-driven accommodation changes, shorter wavelenght oscillations of lake environments, still million-year scale, claims for a dominance of orbital forcing. We suggest a decoupling between (tectonic) supply-driven clastic sequences fed from basin margins and (climatic) base level-driven lacustrine sequences in active settings with medium to large sediment transfer systems.

Organochlorine pesticides in Piracicaba river basin (São Paulo/Brazil): a survey of sediment, bivalve and fish

The main objective of this paper was to evaluate the level of occurrence of the organochlorine compounds in samples of sediments, bivalves and two fish species collected in the Piracicaba River basin (São Paulo, Brazil). The isomers alpha and gamma of HCH and Heptachlor were most frequently detected in samples of sediments and specimens of bivalve and fish. Therefore, although the levels of these compounds found were not critically high, they are still found in the environment. This fact suggests that they are still being used, despite the fact that the use of these compounds was outlawed more than twenty years ago.