Quantitative analysis of depositional systems using numerical models can provide insights into the interaction of sedimentological and diagenetic processes, difficult to interpret from observation of the geological products alone. Numerical models can highlight the interactions between controlling parameters, and generate best estimate simulations of case studies from the geological record. Different data sources (e.g., outcrop data, uniformitarian constraints, paleogeography) need to be considered in the process of defining the parameters required to produce models that honour individual case studies. We present a best-estimate forward model of a high-relief Triassic carbonate platform (Southern Alps, Italy) generated using CARB3D+, a 3D process-based forward modelling package able to simulate sedimentary facies, geometries and early diagenesis of isolated carbonate platforms. The parameters used for the presented forward model have been deduced by the study of architectural, sedimentological and diagenetic features of the platform, and by data from modern and ancient analogues. Sensitivity analysis is used to tune values of the parameters within ranges defined from field, laboratory and uniformitarian constraints. Critical evaluation of the model allowed 1) verification of the validity of the used parameters; 2) evaluation of the interaction between controlling parameters; 3) development of a numerical model that can be used for quantitative elaborations. Furthermore, the process of generating the numerical model required a detailed interpretation of field and laboratory data, crucial to define the required input parameters. Modelling the studied carbonate platform also enabled evaluation of the effects of the interaction between productivity, environmental energy and creation of accommodation space, promoting the understanding of their role on the architecture of carbonate systems. Forward modelling also allows the integration of data from conventional data sets with data from present-day observations and seismic geometries, promoting a transition from a qualitative to a semi-quantitative/quantitative sedimentological approach. Forward models can further be used to parameterise petrophysical properties of complex geobodies, with potential application for the management of georesources.

Whilst sophisticated multiphase fluid flow models are routinely employed to understand behaviour of oil and gas reservoirs, high-resolution data describing the three-dimensional (3D) distribution of rock characteristics is rarely available to populate models. We present a new approach to developing a quantitative understanding of the effect of individual controls on the distribution of petrophysical properties and their impact on fluid flow. This involves simulating flow through high-detail permeability architectures generated by forward modelling of the coupled depositional–diagenetic evolution of isolated platforms using CARB3D+. This workflow is exemplified by an investigation of interactions between subsidence and climate, and their expression in spatial variations in reservoir quality in an isolated carbonate platform of similar size and subsidence history to the Triassic Latemar Platform. Dissolutional lowering during subaerial exposure controls platform-top graininess via platform top hydrodynamics during the subsequent transgression. Dissolved carbonate is reprecipitated as cements by percolating meteoric waters. However, associated subsurface meteoric dissolution generates significant secondary porosity under a more humid climate. Slower subsidence enhances diagenetic overprinting during repeated exposure events. Single-phase streamline simulations show how early diagenesis develops more permeable fairways within the finer-grained condensed units that can act as thief zones for flow from the grainier but less diagenetically altered cyclic units.

Identifying flows into, out of, and across boreholes is important for characterizing aquifers, determining the depth at which water enters boreholes, and determining the locations and rates of outflow. This study demonstrates how Single Borehole Dilution Tests (SBDTs) carried out under natural head conditions provide a simple and cheap method of identifying vertical flow within boreholes and determining the location of in-flowing, out-flowing, and cross-flowing fractures. Computer simulations were used to investigate the patterns in tracer profiles that arise from different combinations of flows. Field tracer tests were carried out using emplacements of a saline tracer throughout the saturated length of boreholes and also point emplacements at specific horizons. Results demonstrated that SBDTs can be used to identify flowing fractures at the top and bottom of sections of vertical flow, where there is a change in vertical flow rate within a borehole, and also where there are consistent decreases in tracer concentration at a particular depth. The technique enables identification of fractures that might be undetected by temperature and electrical conductance logging, and is a simple field test that can be carried out without pumping the borehole.

Abstract Conch Bar Cave, Middle Caicos, comprises a series of large phreatic chambers open to the surface along the southern margin of an eolianite ridge. From these, phreatic passages run towards and terminate abruptly in the interior of the ridge, continuing in most cases only as centimeter-sized tubes. The simplest passages are elliptical tubes with relatively horizontal floors and ceilings punctuated by domes. Most passage sections are more complex, with remnants of former roof and floor levels. Some of these are bedding-concordant and lithologically controlled. But overall, there are strong modes present in the passage ceiling-elevation data, which suggest that the ceilings indicate past positions of the formative mixing zone or water table. The highest level present in the cave is more than 17 m above present sea level, and suggests either that there has been uplift of the platform or that past sea levels have been above this elevation. The eastern parts of the cave show submergence, while the western parts are dry. This suggests that there may have been tilting of the platform to the east toward the direction of the open-platform margin. Despite the size (>3 km surveyed passages) and antiquity of the cave (U-series age >195 ka obtained for a speleothem at sea level), its preservation potential in the geological record is low. The cave has been intercepted by surface lowering and back-wasting of the ridge, and the low mechanical strength of poorly cemented carbonates limits roof stability. Such caves may therefore be only rarely preserved as paleokarst cavities, more commonly being represented by residual cliffed embayments and breccia bodies, if at all. Under ice house conditions with frequent sea level changes, it is unlikely that any clear association between past sea-level still-stands and cave or enhanced porosity zones could be established from the rock record.

Autoregressive modelling is used to investigate the internal structure of long-term (1935–1999) records of nitrate concentration for five karst springs in the Mendip Hills. There is a significant short term (1–2 months) positive autocorrelation at three of the five springs due to the availability of sufficient nitrate within the soil store to maintain concentrations in winter recharge for several months. The absence of short term (1–2 months) positive autocorrelation in the other two springs is due to the marked contrast in land use between the limestone and swallet parts of the catchment, rapid concentrated recharge from the latter causing short term switching in the dominant water source at the spring and thus fluctuating nitrate concentrations. Significant negative autocorrelation is evident at lags varying from 4 to 7 months through to 14–22 months for individual springs, with positive autocorrelation at 19–20 months at one site. This variable timing is explained by moderation of the exhaustion effect in the soil by groundwater storage, which gives longer residence times in large catchments and those with a dominance of diffuse flow. The lags derived from autoregressive modelling may therefore provide an indication of average groundwater residence times. Significant differences in the structure of the autocorrelation function for successive 10-year periods are evident at Cheddar Spring, and are explained by the effect the ploughing up of grasslands during the Second World War and increased fertiliser usage on available nitrogen in the soil store. This effect is moderated by the influence of summer temperatures on rates of mineralization, and of both summer and winter rainfall on the timing and magnitude of nitrate leaching. The pattern of nitrate leaching also appears to have been perturbed by the 1976 drought.

Kent's Cavern has long been known as potentially among the oldest Palaeolithic sites in the country, with the basal Breccia deposit containing a sparse Lower Palaeolithic industry. The sediment consists of a chaotic clayey conglomerate emplaced as a series of debris flows, which entered the cave via blocked entrances at its southwest end. The Breccia contains a fauna dominated by the bear Ursus deningeri, with lion Felis leo and the voles Arvicola cantiana and Microtus oeconomus, establishing a late Cromerian age for the deposit. The artefacts comprise an industry of crudely manufactured handaxes and flakes, and show damage suggesting that they were brought into the cave by the debris flows, and may thus predate the sediment and fauna. We demonstrate an age of >340ka for the Breccia using two independant dating methods, consistent with existing models of the age of the British Middle Pleistocene sequence.

We have investigated the signal response characteristics of a commonly used (ETP) secondary electron multiplier (SEM) using a ThermoFinnigan Neptune multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) over a range of applied beam intensities from 10 to 5 x 10(5) counts per second (cps). Sample switching while maintaining the same tuning parameters allows a "static" SEM-Faraday cup assessment of nonlinearity by MC-ICPMS, rather than a peak-switching approach as recently reported using thermal ionisation mass spectrometry (TIMS) [S. Richter, S.A. Goldberg, P.B. Mason, A.J. Traina, J.B. Schwieters, Int. J. Mass Spectrom. 206 (2001) 105]. For two SEMs of the same type (ETP) we find a count rate nonlinearity of 0.3 and 1.1% per decade of ion beam intensity variation for intensities of less than about 3 x 104 and 105 cps, respectively. Above a nominal threshold of 3 x 104 and 105 Cps there is a more pronounced nonlinearity effect with an additional 0.4 and 1.6% per decade. A previous TIMS study on the same type of multiplier [S. Richter, S.A. Goldberg, P.B. Mason, AT Traina, J.B. Schwieters, Int. J. Mass Spectrom. 206 (2001) 105] found evidence of nonlinearity at the higher intensity range only. Although the SEM we have most rigorously tested may display an anomalously high degree of nonlinearity, we suggest that the form of behaviour is general and must be well-calibrated prior to routine high precision sample analysis.Additional tests show that after a high intensity beam was measured on the SEM of the MC-ICPMS system, the SEM yield is elevated for at least 15-20 s, which can be envisaged as a memory effect related to the intensity of previously measured signals. Therefore, it is impossible to see the nonlinearity effect at low count rates using a peak jumping routine on the ICPMS because of intervening high intensity beams (e.g., U-235 and U-238) applied to the SEM. This "memory" effect has important implications for MC-ICPMS measurement protocols that use multi-static or peak jump routines. (c) 2005 Elsevier B.V. All rights reserved.

Density-driven seawater circulation may occur in carbonate platforms due to geothermal heating and/or reflux of water of elevated salinity. In geothermal circulation lateral contrasts in temperature between seawater and platform groundwaters warmed by the geothermal heat flux result in upward convective flow, with colder seawater drawn into the platform at depth. With reflux circulation, platform-top waters concentrated by evaporation flow downward, displacing less dense underlying groundwaters. We have used a variable density groundwater flow model to examine the pattern, magnitude and interaction of these two different circulation mechanisms, for mesosaline platform-top waters (50 parts per thousand) and brines concentrated up to saturation with respect to gypsum (150 parts per thousand) and halite (246 parts per thousand). Geothermal circulation, most active around the platform margin, becomes restricted and eventually shut-off by reflux of brines from the platform interior towards the margin. The persistence of geothermal circulation is dependent on the rate of brine reflux, which is proportional to the concentration of platform-top brines and also critically dependent on the magnitude and distribution of permeability. Low permeability evaporites can severely restrict reflux whereas high permeability units in hydraulic continuity enhance brine transport. Reduction in permeability with depth and anisotropy of permeability (kv < < kh) focuses flow laterally in the shallow subsurface (<1 km), resulting in a horizontally elongated brine plume. Aquifer porosity and dispersivity are relatively minor controls on reflux. Platform brines can entrain surficial seawater when brine generating conditions cease but the platform-top remains submerged, a variant of reflux we term "latent reflux". Brines concentrated up to gypsum saturation have relatively long residence times of at least 100 times the duration of the reflux event. They thus represent a long-term control on post-reflux groundwater circulation, and consequently on the rates and spatial patterns of shallow burial diagenesis, such as dolomitization.

Several geomorphic features and palaeobiotic remains in now semi‐arid northeastern Brazil indicate major palaeoenvironmental changes during past periods of increased rainfall. 230Th mass spectrometric ages of speleothems and travertines have allowed the determination of the timing and duration of wetter than present conditions. The data demonstrate that wet events have occurred throughout much of the Pleistocene, present dry conditions having been established at the end of the Younger Dryas. A markedly different fauna comprising megafaunal elements not adapted to the present low arboreal scrubland caatinga vegetation existed in the area. Palaeobotanical remains embedded in travertine indicate forested vegetation at these wetter intervals, suggesting that the caatinga was then replaced or mixed with a semi‐deciduous forest. Due to the abundance of travertine sites containing fossil botanical remains in northeastern Brazil, it is believed that forest expansion occurred over large areas of the now semi‐arid zone, showing that the long hypothesised forested links between biodiversity‐rich Amazon and Atlantic rainforests may indeed have existed during these moister phases. Copyright © 2004 John Wiley & Sons, Ltd.

Earth Surface Processes and LandformsVolume 28, Issue 7 p. 803-804 Book Review Tracers and modelling in hyydrogeology edited by A. Dassargues, International Association of Hydrological Sciences Publication 262, IAHS Press, Wallingford, Oxfordshire, 2000. No. of pages: 571. ISBN 1 901502 21 X P. L. Smart, School of Geographical Sciences, University of BristolSearch for more papers by this author P. L. Smart, School of Geographical Sciences, University of BristolSearch for more papers by this author First published: 22 July 2003 https://doi.org/10.1002/esp.461AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume28, Issue7July 2003Pages 803-804 RelatedInformation

Very extensive cave systems are developed in Precambrian Una Group carbonates in the Campo Formoso area, eastern Brazil. In contrast, the area is largely devoid of significant surface karst landforms, as would be expected given its semi-arid climate. The caves in the area display many morphological features characteristic of deep-seated hypogenic caves, such as lack of relationship with the surface, ramiform/network pattern, abrupt variations of passage cross-sections and absence of fluvial sediments, but do not show evidence of vertical passages marking the ascending path of acidic water nor present extensive gypsum or acid clay mineral deposits. Hydrochemical analyses of present-day ground water indicate that oxidation of bedrock sulphide is an active process, and sulphuric acid may be the main agent driving carbonate dissolution in the area. A shallow mode of speleogenesis is thus proposed, in which sulphuric acid produced through the oxidation of sulphide beds within the carbonates controls cave initiation and development. Moreover, the geological situation of the area in an ancient stable passive margin precludes the possibility of deep-seated sources of acidity.Under dry climate, due to the absence of recharge, solutional landforms will be largely subdued in the surface. Hypogenic processes, if present, are likely to predominate, producing a landscape characterized by a marked disparity in the comparative degree of development between surface and underground landforms. Rates of karst landform development have traditionally been analysed through a climatic perspective, runoff being the main controlling factor in promoting karst development. This view needs to be reassessed in the light of the growing awareness of the importance of climate-independent processes related to hypogenic sources of acidity. Copyright (C) 2003 John Wiley Sons, Ltd.

Active reflux may occur during periods of platform-top brine generation, but the role and fate of these brines after reflux events are uncertain. We have used a numerical flow model to investigate and quantify the response of reflux brines to changes in platform-top salinity. Simulations suggest that reflux brines, originally concentrated to gypsum saturation (150parts per thousand), have a relatively long platform residence time, on the order of 100 times the duration of the reflux event. When brine-generating conditions cease, brines win continue to sink through the platform, entraining seawater, a variant of reflux circulation we term latent reflux. Mesosaline brines intercepted by drilling of carbonate margins by the Ocean Drilling Program may have originated from Pleistocene reflux event(s) on the adjacent platform top and be currently moving by latent reflux. Latent-reflux circulation could deliver a significant quantity of dissolved reactants to platform carbonates, including Mg for dolomitization.