Paleoenvironmental reconstruction of a Late Quaternary lagoon system in southern Brazil (Jaguaruna region,Santa Catarina state) based on multi‐proxy analysis

This paper provides a paleoenvironmental reconstruction of a Late Quaternary lagoon system in the Jaguaruna region of Santa Catarina state, southern Brazil. Integrated results of bulk sedimentary organic matter characterization (δ¹³C, δ¹⁵N and C/N), microfossil (pollen and diatom) and grain‐size analysis from three shallow cores (～2.5 m depth) allowed us to propose an evolving paleogeographic scenario in this coastal region for the last ca. 5500 cal a BP. The lagoonal system in this area was more extensive during the mid‐Holocene than today, with a gradual and continuous lagoon–sea disconnection until the present. We add to the debate regarding relative sea‐level (RSL) variations for the Brazilian coast during the Holocene and discuss the importance of sedimentary dynamics for interpreting changes in coastal ecosystems. The multi‐proxy analysis suggests that changes in coastal ecosystems could be directly related to local sedimentary processes, which are not necessarily linked to RSL fluctuations and/or to climatic variations. Copyright © 2011 John Wiley & Sons, Ltd.     

Apatite fission track dating of fluorite ore veins from Santa Catarina state,Brazil: a complex hydrothermal evolution

The fluorite of Santa Catarina that occurs in veins cutting Precambrian granitic rocks of coastal Brazil has been difficult to date by Rb/Sr, K/Ar and Sm/Nd methods. New fission track dating of apatite in granites next to the veins yields ages of 144–76 Ma, which are related to the opening of the South Atlantic Ocean. Four groups of fission track ages were identified: the ca 145 Ma group is a hydrothermal event that preceded fluorite mineralization; the second group of ages, 131–107 Ma, records the first hydrothermal mineralizing event; the third group, 98–93 Ma, represents the second hydrothermal mineralizing event; and the fourth group, 89–76 Ma, dates the last hydrothermal mineralizing event. As shown by previous studies, the temperatures of these events varied from 170° to 70°C, but the last hydrothermal event occurred during a gradual cooling. The smaller lengths of the confined fission tracks from the fourth event support this interpretation. These results are based on sixteen carefully selected samples from four veins ranging from 1 to 4 m in thickness. The ages of these samples were established using the standard methods of fission track dating. Our study clearly demonstrates the value of apatite fission track dating for deposits whose mineralization occurred over a long time span at a wide range of temperatures.     

Late-Pleistocene and mid-Holocene environmental changes in highland valley head areas of Santa Catarina state, Southern Brazil

Low resolution of the continental sedimentary record is a common source of skepticism about the application of geomorphology and sedimentology to Quaternary studies. In spite of this, when supported by independent proxy data, geomorphology and sedimentology may favor palaeo-hydrologic interpretation. This paper associates geomorphologic, stratigraphic, sedimentologic, isotopic, palynologic and geochronologic data. The research was conducted in valley head sites in southern Brazilian highlands, under mild subtropical climate. The results point to environmental changes, the ages of which coincide to Marine Isotopic Stages (MIS) 5b, 3, 2 and 1. Although late-Pleistocene temperatures and precipitation were lower than those of today, the study valley heads seem to have sustained locally wetter environments, which fed shallow soil–water saturated zones. These saturated zones are believed to have expanded during transitions between stadial and interstadial states, contributing to hillslope erosion and sedimentation regardless of the sign of the climatic change. The interior organization of holocenic slope-wash deposits suggests that the mid-Holocene climate was drier than today’s and was under the influence of seasonally contrasting precipitation regimes. The predominance of overland flow-related sedimentary records suggests that an excess of precipitation over evaporation influenced local palaeo-hydrology. This palaeo-hydrologic condition seems to have been recurrent and also explains the alternating periods of pedogenesis and sedimentation.     

The use of vein fluorite as probe for paleofluid REE and Sr-Nd isotope geochemistry: The Santa Catarina Fluorite District, Southern Brazil

Fluorite can be used as a probe for the source of Sr and REE, as well as for the Sr and Nd isotope systematics of mineralizing solutions, allowing characterization of the composition, oxidation state and sources of the fluids. The ⁸⁷Sr / ⁸⁶Sr ratios in vein fluorite from the Santa Catarina Fluorite District, southern Brazil, are low (0.720 to 0.745) relative to those of the majority of host granites at the time of mineralization (90 Ma), but are similar to those of less abundant and less evolved Sr- and Ca-rich granites and plagioclases of the heterogeneous Pedras Grandes granite association. Major contributions of Sr from the unradiogenic Parana Basin rocks (⁸⁷Sr / ⁸⁶Sr_{90 Ma} = 0.705 to 0.718) are unlikely, considering the radiogenic character of the lower ⁸⁷Sr / ⁸⁶Sr end-member in fluorite mixing lines. Estimated fluorite fluid partition coefficients (K_d^Sr-Ca = 0.019 and D^Sr ≈ 600) indicate a Sr / Ca ratio in the fluorite-forming solution of 0.012, and Sr contents of 0.05 to 0.25 ppm, which are similar to those of present-day granitic geothermal waters. Initial Nd isotopic compositions of the vein fluorites (0.5120 to 0.512) are similar to those of the Pedras Grandes granites. The ¹⁴³Nd / ¹⁴⁴Nd_{90 Ma} of the evolved granites of the Tabuleiro granite association, their accessory fluorites and the Parana Basin rocks are considerably more radiogenic (0.5120 to 0.5127) and these are thus considered to be unlikely sources of the fluids. The REE patterns of vein fluorites, normalized to upper continental crust, show a range of LREE-depleted patterns, with highly variable positive and negative Eu anomalies. The host Pedras Grandes granites show flat to slightly depleted UCC normalized LREE patterns with strong negative Eu anomalies. Depletion of the LREE in fluorites resulted from the mobility of HREE fluoride complexes during fluid migration. A REE fractionation model based on ionic potential ratios indicates that Eu³⁺ was stable during fluid migration and fluorite precipitation. The coexistence of pyrite and Eu³⁺ in the mineralizing fluids is consistent with low pH and oxygen fugacities near the hematite-magnetite buffer.     

Geophysical exploration of Guajará, a prehistoric earth mound in Brazil

An interdisciplinary team studied Guajará, a prehistoric artificial mound in the Brazilian Amazon. The geophysical surveys and excavations were interactive;this interaction furnished more information than either geophysics or excavation alone could have provided. While seven different geophysical methods were applied, the magnetic survey reported here was particularly valuable. A detailed interpretation of this survey quantified the magnetic material in the mound, and this furnished an initial estimate of the number of cooking hearths in the mound. Ten test excavations were concentrated at magnetic anomalies. These excavations located cooking hearths and burial urns. A reevaluation of the magnetic survey was then done in order to refine the estimate of the number of hearths in the mound; this yielded an estimate of 2200 hearths. This allowed the population of the site to be approximated at 78–156 people. The geophysical survey and excavations also identified possible locations for subsequent broad‐area excavations. © 2003 Wiley Periodicals, Inc.     

Origin of high fluoride contents in groundwater of the Santa Maria Formation, Guarany Aquifer System, southern Brazil

Fluoride anomalies （up to 11 mg/L） have been detected in the porous confined Santa Maria Aquifer （Guarany Aquifer System） in the central region of Rio Grande do Sul State, southern Brazil, leading to endemic fluorosis. Two hypotheses are investigated concerning the fluoride origin： contamination by long-term phosphate-fertilizer application due to extensive tobacco plantation or lithogeochemical affiliation from regional rocks. The results are discussed based on statistical and geochemical modeling and stable isotope data of water, nitrate and sulfate. Field monitoring of phreatic and confined aquifer during two years and laboratory leaching and retention experiments were performed. Regional statistical analysis （factorial and cluster analysis） on the basis of 350 wells discriminates four different hydrochemical groups in the confined aquifer, considering magnesium, calcium bicarbonate, sodium chlorinate and sodium bicarbonate as specific parameters. The last two groups reach higher fluoride contents and represent deeper aquifer levels where geochemical modeling shows carbonates （calcite and dolomite） are of super-saturation. The laboratory experiments confirmed that local soils with high CTC and aluminum contents （Udults） represent an efficient geochemical barrier, preserving the aquifer from fluoride contamination and supporting remediation strategies for fluoride removal. δ^18O and δD groundwater data and the local meteoric water line （LMWL） indicate that local precipitation is the main groundwater recharge source in the area.     

Morphosedimentary analysis of the Limoeiro Stream (center-northern Minas Gerais State,Brazil): clues to the eastward tilting of southern Espinhaco range sites

The morphosedimentary evolution of a sector of the southern Espinhaco range (northern Minas Gerais State, Brazil) and its regional neotectonic setting are presented herein. The studied site is a stream at base level flowing along the western border of the range. Its identification was accomplished by using remote sensing techniques including the analysis of 3D slope models generated with shuttle radar topography mission images. The main geomorphological features of the identified site were surveyed in a 1:500 scale. In addition, seven stratigraphic logs are described. A regional geologic compilation and facies diagrams were used as a basis for the integration of the geomorphological and stratigraphic data, which produced some conclusions about the recent tectonic reactivations at the eastern border of Sao Francisco Craton. The results point to a local eastward tilting of the Espinhaco range. This fact is in accordance with previous findings in neighboring areas and results in the asymmetric evolution of the fluvial valley, as well as the regional relief.     

Using correlation and multivariate statistical analysis to identify hydrogeochemical processes affecting the major ion chemistry of waters: a case study in Laoheba phosphorite mine in Sichuan,China

Prior to mining, the water in and around the mine is rarely influenced by human activities, and hydrogeochemical processes are the major factors influencing and controlling water chemistry. To identify these natural hydrogeochemical processes in Laoheba phosphorite mine (Sichuan Province, China), correlation and multivariate statistical techniques were used. Results show that water quality in the area is generally good before the Laoheba phosphorite mine goes into construction and production. The cluster analysis classified water samples into 4 clusters (C1–C4). Samples from C1 and C2 are of HCO₃?Ca·Mg and HCO₃?Ca type, while those from C3 and C4 are of HCO₃?Ca·Mg type. Most parameters except Cl^? and pH show an increasing trend in the order of C1 to C4. Three principal components were extracted, and PC1 represents the ion exchange and the weathering of calcite, dolomite, and silicate minerals. PC2 and PC3 indicate the process of water recharge from upstream waters and the process of evaporation, respectively. The hydrochemistry of waters in the area is a result of multiple factors, and natural mineral weathering and ion exchange are the most important ones.     

Burying processes carried out by a mobile transversal dunefield, Paracuru County, State of Ceará, Brazil

The migration of dunes and the consequent burying of the city of Paracuru by a transversal dunefield with perpendicular ridges oriented to the dominant windstream have been investigated. Overlapping aerial photographs taken during different flights have been used as a reference. Two sediment transportation directions were identified: the first is fed by the prevailing easterly winds; the second corresponds to the secondary southeasterly winds. With the maintenance of current wind conditions and pluvial precipitation, dunes will bury part of Paracuru town in approximately 120 years. Within this context, the geological evolution model that was applied proved to be satisfactory for the comprehension of sediment transportation mechanisms along the transversal dunes. Considering the prognosis in relation to Paracuru and its urban growth towards the dunefield, it is necessary to continue to study aeolian dynamics, aiming to develop support for the elaboration of future projects directed towards environmental management of the area.     

The Santa Rita gold deposit in the Proterozoic Paranoá Group, Goiás, Brazil: An example of fluid mixing during ore deposition

The Santa Rita gold deposit (Central Goiás, Brazil) is hosted by Middle to Upper Proterozoic carbonate-pelite sequences of the Paranoá Group that have been metamorphosed in the greenschist facies. The ore is contained in pyrite-bearing quartz-carbonate veins. The mineralization is structurally controlled by WNW-ESE high-angle faults and fractures resulting from the reactivation of older NE-SW lineaments. Pyrite is the sole sulphide and it shows growth zones enriched in Co, Ni and As (up to 4 wt%). Hydrothermal alteration zones are enriched in Co, Ni and As and are characterized by diffuse albitization, carbonatization, silicification and pyritization.A fluid inclusion study on quartz from pyrite-bearing quartz-carbonate veins led to the identification of two fluids: (1) a highly saline CO₂---N₂-rich aqueous fluid with halite and ± sylvite daughter minerals, and (2) a CO₂---N₂ rich aqueous fluid with moderate salinity. The two fluid types occur in the same quartz domain and display great variation in the degree of filling and notable dispersion of the microthermometric data. On heating, all the inclusions decrepitate between 200° and 300°C. Raman spectrometry detected high concentrations of N₂ in the gas phase, with a molar ratio between 1 and 19 and a small proportion of CH₄ (up to 2 mole %).The simultaneous entrapment of compositionally variable fluids in the system H₂O---CO₂---N₂---NaCl---KCl allow us to propose a mechanism of heterogeneous trapping. The entrapment may result from the mixing of a high-salinity fluid (H₂O---NaCl---KCl system) with a carbonic fluid (H₂O---CO₂---N₂ system) produced by the devolatilization process of carbonate and phyllitic host rocks. Considering the absence of spatially and temporally related igneous activity and the low P-T regional metamorphism in the Paranoá Group, the brines are inferred to result from leaching of evaporites occurring in the lower part of the Paranoá lithostratigraphic column.Gold was probably initially transported as an AuCl₂-complex (T>300°C, low pH, moderate ƒ_O2-pyrite field stability). As temperature decreased below 290°C, the “switch-over” process would lead to the predominance of Au(HS)₂⁻ in the fluid. Pyrite precipitated in this temperature interval. The oscillatory zoning of the As---Co---Ni-bearing pyrites indicates episodic fluctuation of the fluid composition. Such changes in fluid composition are favoured by a mechanism of fluid mixing by intermittent supplies in the hydrothermal system. The proposed mechanism of heterogeneous trapping of two separate fluids in the system H₂O---CO₂---N₂---NaCl---KCl and the resulting changes in the physicochemical conditions caused by the fluid mixing appears as a conspicuous process for the Santa Rita hydrothermal fluid evolution.A model based on the existence of a Proterozoic geothermal system involving the regional thermal gradient is proposed.     

Carbonate deposition in a fluvial tufa system: processes and products (Corvino Valley – southern Italy)

In a multi‐scale approach to the study of the organic and mineral components in an active barrage‐type tufa system of southern Italy, neo‐formed deposits, in both natural depositional sites and on inorganic substrates placed in the stream for this study, were observed and compared through one year of monitoring. Dams and lobes representing the basic morpho‐facies of the deposits are composed of two depositional facies: vacuolar tufa (a mixture of phytoclastic and framestone tufa) and stromatolitic tufa (phytoherm boundstone tufa). Three petrographic components comprise both facies: micrite and microsparite, often forming peloidal to aphanitc, laminar and dendrolitic fabrics, and sparite, which occurs as isolated to coalescent fan‐shaped crystals forming botryoids or continuous crusts. All fabrics occurring in all depositional facies are organized into layers with a more or less well‐developed cyclicity, which has its best expression in stromatolitic lamination. The precipitation of all types of calcite (with Mg 1·0 to 3·2 mole % and Sr 0·5 to 0·8 mole %) takes place more or less constantly during all seasons, in spite of the low saturation state of the water (the saturation index range is 0·75 to 0·89) within the active depositional zone; the latter extends for a few hundred microns through the external surface of the deposit. The active depositional zone has a particular micro‐morphology composed of porous micro‐columns (50 to 150 μm in size), separated by interstitial channels. Mineral precipitation occurs upon both external surfaces and within internal cavities of the micro‐columns, while further point sites of precipitation occur suspended within the masses of cyanobacterial tufts. Sub‐spherical mineral units, ‘nano‐spheres’ (10 to 20 nm in diameter) are the basic biotic neo‐precipitate; they commonly form by replacing non‐living degrading organic matter and at point sites along the external surface of living cyanobacterial sheaths. Nano‐spheres agglutinate to form first rod‐shaped aggregates (100 to 200 nm) which then evolve into triads of fibres or polyhedral structures. Successively, both triads and polyhedral solids coalesce to form larger calcite crystals (mainly tetrahedrons tens of microns in size) that represent the fundamental bricks for the construction of the micro‐columns in the active depositional zone. Precipitation is attributed to the presence of a widespread biofilm that occurs in the active depositional zone; this is composed of a heterogeneous community comprising epilithic and endolithic filamentous cyanobacteria, green algae, unicellular prokaryotes, actinobacteria and fungi, with a variable amount of extracellular polymeric substances. No precipitation takes place where the biofilm is absent, indicating that the biological activities of the biofilm are crucial, with its living organisms and non‐living organic matter. Basic aggregates of neo‐precipitates do not form in association with any one particular type of organic matter substrate, but appear to be related to the seasonal temperature variation: polyhedral micro‐crystals mainly precipitate in the colder season, short triads in the intermediate seasons, and long triads in the warmest conditions. These three basic crystal aggregates have a petrographic counterpart, respectively, in the spar, microspar and micrite.     

Using a modern analogue to interpret depositional position in ancient fluvial-tidal channels: Example from the McMurray Formation,Canada

The fluvial–tidal transition (FTT) is a complex depositional zone, where fluvial flow is modified by tides as rivers approach a receiving marine basin. Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars. The FTT generally consists of three broad zones: (1) a freshwater-tidal zone; (2) a tidally influenced freshwater to brackish-water transition; and (3) a zone of relatively sustained brackish-water conditions with stronger tides. A very common type of deposit through the fluvial–tidal transition, especially on the margins of migrating channels, is inclined heterolithic stratification (IHS). At present, a detailed account of changes in the character of IHS across the FTT of a paleo-channel system has not been reported, although a number of modern examples have been documented. To fill this gap, we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley (“A” Valley) in the Lower Cretaceous McMurray Formation of Alberta, Canada. We compare the data to trends defined along the FTT in the present-day Fraser River in British Columbia, Canada to interpret paleo-depositional position in the ancient fluvial–tidal channels.Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area (SA). Mean thickness increases to 11 cm in the central study area (CA), and decreases again to 4.4 cm in the northern study area (NA). The proportion of mudstone is 31% in SA, 44% in CA, and 27% in NA. Thickness-weighted mean bioturbation intensity in sands varied from 0.29 in SA and CA, to 0.28 in NA. On the other hand, thickness-weighted mean bioturbation intensity (BI) in mudstone increases from 1.46 in SA, to 1.77 in CA, and is 1.94 in NA. The ichnological diversity also increased from south to north.Sedimentological results show similar trends to those of the Fraser River, enabling the identification of a freshwater to brackish-water transition zone with tidal influence. The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends, indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions. Together, these data suggest that a broad FTT existed in the “A” Valley, with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow, and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximum zone. The FTT zone appears to have extended for several hundred kilometers from south to north.Based on the sedimentological and ichnological data, as well as estimations of lateral accretion rates, we refute the commonly applied Mississippi River depositional analogue for McMurray Formation channels. Rather, we show that while not a perfect fit, the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS. Future work on the McMurray system should focus on characterizing tide-dominated deltaic and estuarine systems, such as the Ganges-Brahmaputra, and on forward-modeling the evolution of tide-dominated and tide-influenced river systems.     

Mineralogical and microfabric characteristics of magnetite in the Wuyang Precambrian BIFs,southern North China Craton: Implications for genesis and depositional processes of the associated BIFs

Precambrian Banded Iron Formations (BIFs) are widely distributed in the North China Craton (NCC). Among them, the Wuyang BIFs located in the southern margin of NCC occur in the Late Archaean Tieshanmiao Formation and can be subdivided in two different sub-types: (i) quartz–magnetite BIFs (QMB), consisting of magnetite, fine-microcrystalline quartz and minor calcite and (ii) pyroxene–magnetite BIFs (PMB), composed of pyroxene, fine-microcrystalline quartz and subordinate feldspars. Both sub-types display apparent discrepancies in terms of petrography and mineral composition.As shown in Electron BackScattered Diffraction (EBSD) images and micrographs, magnetite grains from the QMB range in size from tens up to hundreds of μm, whereas magnetite crystals from the PMB can be up to a few tens of μm across. The X-ray diffraction (XRD) structural data indicate that magnetite from both BIF sub-types is equiaxed (cubic) and was generated by sedimentary metamorphic processes. The cell parameters of magnetite in the QMB are a = b = c = 8.396 Å and Z = 8, which deviate slightly from these of magnetite in the PMB: a = b = c = 8.394 Å and Z = 8. The analytical results of Raman spectroscopy analysis revealed micro-structural signatures of both magnetite (Raman shifts near 552 cm⁻¹ and 673 cm⁻¹) and hematite (Raman shifts near 227 cm⁻¹, 295 cm⁻¹ and 413 cm⁻¹). In magnetite from both QMB and PMB, the crystallinity degree is similar for magnetite micro-structures but varies significantly for hematite micro-structures. Oxygen fugacity (fO₂) conditions fluctuated during the recrystallization of magnetite in the QMB, whereas no evident variation of fO₂ occurred during the formation of magnetite in the PMB. Analytical results of laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) show that the Si, Al and Mg abundances are higher in magnetite from the QMB, whereas the Ti and Mn contents are more elevated in magnetite from the PMB. Magnetite composition also denotes that both BIF sub-types are sedimentary-metamorphic origin, whereas the deposition of PMB was also affected by volcanic activities. Overall data indicate that the differences in the depositional environment of each BIF sub-type are due to the involvement of volcanic eruption processes in the genesis of the PMB. Thus, this paper indicated that the QMB was deposited by chemical deposition at the long-term interval of volcanic eruptions, and the PMB were the product of chemical deposition affected by the volcanic eruption.     

Structural characterization of deep-water deposits in a foreland basin, Silla Syncline (Chilean Patagonia), with applications to depositional processes

Based on our detailed structural characterization, we examine possible relationships between thrust faults and strike-slip faults and thrust-cored folds and depositional units in the Silla Syncline, a 4 km wide fold composed of fine-grained mudstone, coarse sandstone and conglomerate deposits of the Cerro Toro Formation in the Magallanes foreland basin, Chilean Patagonia. The syncline is bounded on its western flank by an asymmetric anticline and on its eastern flank by a broad zone of thrust faults and associated folds, which are oriented sub-parallel to the syncline axis. Deposition of the coarse-grained units of the Silla Syncline appears to have taken place in this structurally defined trough controlled primarily by thrust fault related growth structures flanking the syncline.The syncline and surrounding area have also been deformed by two sets of strike-slip faults, one right-lateral and one left-lateral. The strike-slip and thrust faulting operated contemporaneously for much of their active periods, although it appears that thrust faulting, confined within the fine-grained units, initiated slightly earlier than strike-slip faulting. In addition, younger igneous intrusions at high angle to bedding generally localize along the strike-slip faults. The cross-cutting relationships among the intrusions, strike-slip faults, and flexural slip faults show that all these structures were active during the same period, which extends beyond mid-Miocene.These conclusions support the premise that structures in deep-water sediments are important for understanding not only the deformation of a foreland basin, but also its depositional architecture.     

From river to shelf,anatomy of a high‐frequency depositional sequence: The Late Pleistocene to Holocene Tiber depositional sequence

The Late Pleistocene/Holocene Tiber delta succession represents the most recent and one of the best preserved, high‐frequency/low‐rank depositional sequences developed along the Latium continental margin of the Italian peninsula. Several previous studies have established a robust data set from which it has been possible to describe the stratigraphic architecture of the entire Tiber depositional sequence from the landward to seaward sectors and over a distance of 60 km. The Tiber depositional sequence shows many characteristics found in other Late Pleistocene to Holocene deltaic and coastal successions of the Mediterranean area. The stratigraphic architecture of the Tiber depositional sequence is controlled mainly by glacioeustasy, although factors such as tectonic uplift, volcanism and subsidence, exert an influence at a local scale. The resulting depositional model allowed discussion of some important points such as: (1) the genesis of the Tiber mixed bedrock‐alluvial valley, extending from the coastal plain to the innermost portion of the shelf, recording (i) multiple episodes of incision during relative sea‐level fall, and (ii) a downstream increase of depth and width of the valley during the base‐level fall and the subsequent base‐level rise; (2) the different physical expression of the Tiber depositional sequence boundary from landward to seaward, and its diachronous and composite character; (3) the maximum depth reached by the Tiber early lowstand delta at the end of the sea‐level fall is estimated at ca 90 m below the present sea‐level and not at 120 m as suggested by previous works; (4) the backward position of the Tiber late lowstand delta relative to the deposit of early lowstand; (5) the change of the channel pattern and of the stacking pattern of fluvial deposits within the Lowstand Systems Tract, Transgressive Systems Tract and Highstand Systems Tract. All of these features indicate that the Late Pleistocene/Holocene Tiber delta succession, even if deposited in a short period of time from a geological point of view, represents the result of the close interaction among many autogenic and allogenic factors. However, global eustatic variations and sediment supply under the control of climatic changes can be considered the main factors responsible for the stratigraphic architecture of this sedimentary succession, which has been heavily modified by human activity only in the last 3000 years.     

Stratigraphic architecture and anthropic impacts on subsoil to assess the intrinsic potential vulnerability of groundwater: the northeastern Campania Plain case study, southern Italy

This study attempts to assess the aquifer vulnerability in the northeastern sector of the Campania Plain (southern Italy). The area is a highly populated region with anthropic impacts caused by rapid urban growth, quarrying, agricultural and industrial activities and uncontrolled waste storage. The main geologic feature of this plain is the alternation of alluvial/transitional and volcaniclastic deposits of Late Pleistocene–Holocene age. The study was performed integrating different sets of geologic and environmental data to restore the stratigraphic architecture and to assess anthropic impacts on subsoil. The reconstruction of stratigraphic subsurface architecture was based on remarkable geodatabase, concerning well log stratigraphies. Specific insights have been delineated on the volcaniclastic lithofacies heteropies across the entire area of study to highlight the differences in lithification degree and permeability. The contribution of pedogenesis on the reconstruction of the stratigraphic setting was also considered for the relative implications on groundwater quality concerns, as paleosols are usually regarded as aquitards. All of this information has been managed into a GIS project to produce a detailed 3D geological reconstruction, integrated with hydrogeological information to provide a model of the aquifer under study, highlighting sites of greater vulnerability to pollution. The anthropic impacts on subsoil were assessed by evaluating land-uses and overlaying the ANHI (Agricultural Nitrate Hazard Index) Map. The integration of the above datasets has allowed to check the reliability of the previsional empirical model with respect to the hydrostratigraphic model based on a thorough stratigraphic model and to verify the real potential of contamination.     

The Maesan fan delta, Miocene Pohang Basin, SE Korea: architecture and depositional processes of a high-gradient fan-delta-fed slope system

The Maesan fan-delta-fed slope system in the Miocene Pohang Basin occurs between two Gilbert-type fan deltas. Detailed analysis of sedimentary facies and bed geometry reveals that the sequence is represented by 13 sedimentary facies. These facies can be organized into three facies associations, representing distinct depositional environments: alluvial fan (facies association I), steep-faced slope (facies association II), and basin plain (facies association III). Subaerial debris flows and dense, inertia-dominated currents were transformed into subaqueous sediment gravity flows in steep-faced slope environments. Further downslope, these flows were channelized and formed lobate conglomerate and sandstone bodies at the terminal edge of the channels (or chutes). Interchannel and interlobe areas were dominated by homogeneous mudstone and muddy sandstone, deposited by suspension settling of fine-grained materials. Part of the steep-faced slope deposits experienced large-scale slides and slumps. The chutes/channels, lobes and splays on the steep-faced slope of the Maesan system are similar to those in modern subaqueous coarse-grained fan-delta systems.     

Evolution of Pleistocene travertine depositional system from terraced slope to fissure-ridge in a mixed travertine-alluvial succession (Jebel El Mida,Gafsa, southern Tunisia)

The Quaternary stratigraphic record of Jebel El Mida, composed of continental deposits, is a useful example of concomitant travertines and alluvial deposition in an extensional setting. Travertine deposition occurred in a faulted Pleistocene alluvial fan giving rise to seven (recognised) facies interfingering with five other alluvial ones. The travertine depositional events indicate a tectonically driven evolution from terraced slope (facies group FC1–FC6) to a travertine fissure ridge-type depositing phase (facies group of FC1–FC7). Interfingering between travertine and alluvial facies indicates the co-existence of adjacent and time-equivalent depositional environments. The travertine deposition resulted from deep origin hydrothermal fluids channelled along damaged rocks volumes associated to a regional fault system, named as the Gafsa Fault (GF). The travertine–terrigenous succession in Jebel El Mida highlights the major role played by the GF in controlling: (i) the hydrothermal fluid flow, still active as also indicated by the numerous thermal springs aligned along the fault zone; (ii) paleoflow directions, discharge locations, volume, rate and fluctuations of the water supply. The paleoclimatic correlation with adjacent localities reveals that, at that time, humid episodes could have contributed to the recharge of the hydrothermal system and to the deposition of alluvial sediments.     

A Natural Gamma Spectrometry approach to derive clay mineral composition and depositional environment of a reservoir facies in Ramnad sub-basin,Cauvery basin,southern India

The Ramnad sub-basin is one of the most explored for hydrocarbons in Cauvery basin. A number of exploratory wells have been drilled to delineate hydrocarbon bearing horizons. Nannilam Formation of Santonian–Campanian age hosts considerable thickness of reservoir facies. The reservoir facies is mainly clastics such as sandstone and siltstone with lot of clay content. In addition to normal logs, the NGS (Natural Gamma Ray Spectrometry) logs are widely employed to estimate sediment composition and broad depositional environment of reservoir facies. The present study employs and analyses NGS logs of four well sections from Kanjirangudi area of Ramnad sub-basin to determine the clay mineral composition and depositional environment of Nannilam Formation. Thorium (Th), potassium (K) and uranium (U) concentrations and their interrelationships reveal that montmorillonite, illite and kaolinite are the dominant clay minerals. The clay mineral composition suggests that the sediments of the Nannilam Formation were derived from a provenance of acid igneous rocks during warm, humid and tropical conditions. Also, the ratios of Th/K indicate a deep open marine condition under which the sediments of the Nannilam Formation were deposited. These results would aid a better understanding and characterization of reservoir facies in the sub-basin.     

利用两种指纹因子判别小流域泥沙来源

为精确识别黄土高原丘陵沟壑区典型小流域泥沙来源,分析了流域内“源-汇”地区土壤的理化性质及生物标志物（正构烷烃）作为潜在指纹识别因子,并建立了复合指纹模型。结果显示:单独的土壤理化指纹及正构烷烃均不能有效识别泥沙来源;土壤理化指纹和正构烷烃分别在林地、农地及沟道的辨别上显示出其局限性。多元化的复合指纹（碳优势指数CPI、Ca、TP、C₂₀、C₂₉、Fe）则能辨别90.5%的泥沙来源。模型结果显示沟道是该流域泥沙的主要来源,占60.8%,其次为农地占20.7%,林地占11.3%,草地占7.2%。研究表明,结合生物标志物的复合指纹法能更精确地反映泥沙来源,适用于各泥沙源头的地质条件差异较小的流域,对黄土高原小流域水土流失治理具有指导意义。