Quaternary Basin Research Articles

Nature and age of Late Quaternary basin fill deposits in the Basin of Persepolis/Southern Iran

Late Quaternary basin fill deposits exposed in the north-western part of the plain of Marvdasht were investigated in order to elucidate the nature of near-surface basin fill deposits as well as the timing of sediment aggradation, soil formation and incision of Kor River. Besides sedimentological and paleopedological analysis, a chronological frame was set up by infrared stimulated luminescence (IRSL) and radiocarbon dating. The near-surface basin fill consists of silty to clayey fluvial and aeolian deposits documenting gradual horizontal and vertical changes of low velocity fluvial and limnic sedimentation on the one hand and subaerial deposition on the other hand. The accumulation of the sediments decreased during a phase of soil formation possibly between 27 and 22 ka. This phase is represented by a strongly developed brown paleosol which developed under a climate similar to today, while contemporaneously formed grey paleosols indicate topographically wet conditions in backswamp paleo-environments. Between about 21 and 7 ka, high rates of sediment deposition occurred and the upper sediments of the plain accumulated, probably under drier and cooler climatic conditions than today. From about 16 to 10 ka, a gradually dessicating lake covered parts of the plain. At the same time, several weakly developed brown and grey paleosols were formed indicating comparatively stable paleo-environments with strongly reduced sediment accumulation and/or topographically moist paleo-environments in the alluvial plain. The formation of the strongly developed modern soils started after a change to moister climatic conditions during the early to mid Holocene, most likely between 7 and 4 ka. Increased river incision has started at about 10 ka and was likely retarded at about 4 ka owing to mid Holocene tectonic uplift in the lower parts of the basin.

Active nappe with a high slip rate: Seismic and gravity profiling across the southern part of the Itoigawa-Shizuoka Tectonic Line, central Japan

Nappe structures at different scales have been reported from many orogenic belts in the world, but almost all the examples are old, inactive structures. Under conditions of low erosion rate and/or high tectonic strain rate, active nappes are expected to grow with time. We report in this paper an example of active nappe from central Japan. The Itoigawa-Shizuoka Tectonic Line (ISTL) in central Japan is a fault zone with a very high slip rate in Pliocene–Quaternary time. We carried out seismic reflection, refraction and gravity surveys along a 30-km line across the Shimotsuburai-Ichinose Fault (SIF), a main active strand of ISTL west of the Kofu Basin. Seismic and gravity data indicate that the fault is a west-dipping, low-angle (~ 15°) thrust, which separates horizontally-layered basin-fill sediments (total thickness ~ 1.5 km) on the east from highly deformed Miocene and older rocks on the west. On the hanging wall side of the fault, the seismic line is located in a deeply incised valley. We precisely determined the surface projection of the fault in this valley by analyzing closely spaced gravity data, and found that the fault emerges 1.35 ± 0.10 km west of the mountain front. This indicates that the frontmost 1.35 km of the hanging wall lies horizontally over Pliocene–Quaternary basin fill, forming an active nappe. Fault-bend folding is associated with the nappe formation. A fluvial terrace, which is tephrochronologically dated at 50–60 ka, is involved in this deformation. The amount of slip during the past 50–60 kyr is estimated from tectonic landforms, yielding an average slip rate as high as 7.5–11 mm/yr. It is likely that the front of the nappe on SIF is nearly at a dynamic equilibrium between erosive and tectonic forces, because the present-day width (~ 1.35 km) of the nappe in the valley is only a fraction of the total amount of thrust-front advance. A comparison is made with the Miocene Main Central Thrust (MCT) in the central Himalaya, which evolved under climatic conditions similar to those in central Japan but at a slip rate twice as high as that on the ISTL. The High Himalayan nappe front, after the MCT became inactive, has been retreating due to head-ward erosion by small tributaries of Ganges; cooling ages of crystalline klippen in the Lesser Himalaya give an estimate of the retreating rate (~ 10 mm/yr). This value is about a half of the present-day convergence rate (~ 20 mm/yr) between India and Tibet. It is therefore likely that, in Early to Middle Miocene time when the MCT was active, the High Himalayan nappe had been growing laterally at a rate as high as 10 mm/yr.

Barite-forming environments along a rifted continental margin, Southern California Borderland

The Southern California Continental Borderland (SCCB) is part of the broad San Andreas transform-fault plate boundary that consists of a series of fault-bounded, petroleum-generating basins. The SCCB has high heat flow and geothermal gradients produced by thinned continental crust and Neogene volcanism. Barite deposits in the SCCB occur along faults. Barite samples from two sea-cliff sites and four offshore sites in the SCCB were analyzed for mineralogy, chemical (54 elements) and isotopic (S, Sr) compositions, and petrography. Barite from Palos Verdes (PV) Peninsula sea-cliff outcrops is hosted by the Miocene Monterey Formation and underlying basalt; carbonate rocks from those outcrops were analyzed for C, O, and Sr isotopes and the basalt for S isotopes. Cold-seep barite from Monterey Bay, California was analyzed for comparison. SCCB offshore samples occur at water depths from about 500 to 1800 m. Those barites vary significantly in texture and occurrence, from friable, highly porous actively growing seafloor mounds to dense, brecciated, vein barite. This latter type of barite contrasts with cold-seep barite in being much more coarse grained, forms thick veins in places, and completely replaced rock clasts in breccia. The barite samples range from 94 to 99 wt% BaSO4, with low trace-element contents, except for high Sr, Zr, Br, U, and Hg concentrations compared to their crustal abundances. δ34S for SCCB offshore barites range from 21.6‰ to 67.4‰, and for PV barite from 62‰ to 70‰. Pyrite from PV sea-cliff basalt and sedimentary rocks that host the barites averages 7.8‰ and 2.2‰, respectively. Two offshore barite samples have δ34S values (21.6‰, 22.1‰) close to that of modern seawater sulfate, whereas all other samples are enriched to strongly enriched in 34S. 87Sr/86Sr ratios for the barites vary over a narrow range of 0.70830–0.70856 and are much lower than that of modern seawater and also lower than the middle Miocene seawater ratio, the time of deposition of the host rocks for the PV samples. This indicates that the mineralizing fluids were not unaltered seawater. We develop a model in which the barites precipitated both below the sediment–water interface and at the seafloor from low-temperature fluids that circulated along faults. The isotopic, chemical, and textural data indicate that the barites formed by several processes. Mesozoic and Cenozoic basement rocks (crystalline and overlying sedimentary rocks), Quaternary basin fill, turbidite fans, and seawater provided various elements for the barites in different environments. The fluids had a deep-seated source and were hydrothermal in the deeper parts of the system for all the barite types, including the seafloor cold-seep deposit, based on Sr isotopes and regional geothermal gradients. These deep-seated fluids mixed with other fluids as they ascended, including seawater at and near the seafloor. The high δ34S values may have resulted from extreme Rayleigh fractionation during bacterially mediated (semi)closed-system sulfate reduction, probably driven by the flux of methane- and hydrocarbon-bearing fluids through basement rocks and basin sediments. Early diagenetic dolomite and pyrite in the host Monterey Formation in the PV Headland also formed in a zone of sulfate reduction, but within sediment buried only centimeters to a few meters and with a predominantly seawater source for the sulfur. Dolomite occurring with vein barite in the PV Headland formed at temperatures in the range of 40–90 °C. The cold-seep barites have δ34S values near that of modern seawater, although still somewhat fractionated. The barites that precipitated below the sediment–water interface have higher δ34S values, suggesting that the fluids were relatively reduced with molar dissolved barium in excess of dissolved sulfate. Those samples were exposed at the seafloor by uplift along faults and are composed predominantly of massive, brecciated, and vein barite.

Late Quaternary basin evolution of the Gulf of Corinth: Sequence stratigraphy, sedimentation, fault–slip and subsidence rates

The Gulf of Corinth is a graben, which has undergone extension during the Late Quaternary. The subsidence rate is rapid in the currently marine part whereas uplift now affects a large part of the initially subsiding area in the North Peloponnese. In this paper, we document the rates of subsidence/uplift and extension based on new subsurface data, including seismic data and long piston coring in the deepest part of the Gulf. Continuous seismic profiling data (air gun) have shown that four (at least) major oblique prograding sequences can be traced below the northern margin of the central Gulf of Corinth. These sequences have been developed successively during low sea level stands, suggesting continuous and gradual subsidence of the northern margin by 300 m during the Late Quaternary (last 250 ka). Subsidence rates of 0.7–1.0 m kyr − 1 were calculated from the relative depth of successive topset to foreset transitions. The differential total vertical displacement between the northern and the southern margins of the Corinth graben is estimated at about 2.0–2.3 m kyr − 1 . Sequence stratigraphic interpretation of seismic profiles from the basin suggests that the upper sediments (0.6 s twtt thick) in the depocenter were accumulated during the last 250 ka at a mean rate of 2.2–2.4 m kyr − 1 . Long piston coring in the central Gulf of Corinth basin enabled the recovery of lacustrine sediments, buried beneath 12–13.5 m of Holocene marine sediments. The lacustrine sequence consists of varve-like muddy layers interbedded with silty and fine sand turbidites. AMS dating determined the age of the marine–lacustrine interface (reflector Z) at about 13 ka BP. Maximum sedimentation rates of 2.4–2.9 m kyr − 1 were calculated for the Holocene marine and the last glacial, lacustrine sequences, thus verifying the respective rates obtained by the sequence stratigraphic interpretation. Recent accumulation rates obtained by the 210Pb-radiometric method on short sediment box cores coincide with the above sedimentation rates. Vertical fault slip rates were measured by using fault offsets of correlated reflector Z. The maximum subsidence rate of the depocenter (3.6 m kyr − 1 ) exceeds the maximum sedimentation rate by 1.8 m kyr − 1 , which, consequently, corresponds to the rate of deepening of the basin's floor. The above rates indicate that the 2.2 km maximum sediment thickness as well as the 870 m maximum depth of the basin may have formed during the last 1 Ma, assuming uniform mean sedimentation rate throughout the evolution of the basin.

Neotectonics of the SW Marmara region, NW Anatolia, Turkey

This study reports on the geometric and structural characteristics of the North Anatolian Fault Zone in the southwest Marmara region. The geometric and kinematic features of the faults in the region are described, based on field observations. In addition, the Neogene and Quaternary basin fill which occupies large areas in the region has been determined, and the tectonic regimes controlling these basins are explained. The neotectonic regime is also explained considering different deformation phases affecting the region. The N–S extension and E–W strike-slip have affected the region possibly since the latest Pliocene–Quaternary. Field observations show that these extensional tectonics around the south Marmara region are related to right strike-slip on the E–W North Anatolian fault zone and the N–S Aegean extensional system. The faults in this zone trend approximately E–W in the eastern part of the region and NE–SW towards the west of the region, indicating that they accommodate rotation in addition to differential movement between adjacent blocks.

FACIES ANALYSIS, STRATIGRAPHY AND PALAEONTOLOGY (MOLLUSCS AND VERTEBRATES) IN THE UPPER PLIOCENE SANDY FLOOD-BASIN DEPOSITS OF THE UPPER VALDARNO BASIN (NORTHERN APENNINES)

The Upper Valdarno Basin, one of the most investigated Neogene–Quaternary basins of the Northern Apennines, developed during three main phases, as testified by the occurrence of three unconformity-bounded stratigraphic units (UBSUs) in the basin infill. Despite numerous studies having been carried out, biochronological, paleoecological and stratigraphical issues in the lower portion of the Montevarchi Synthem (second phase) have yet to be understood. Sandy deposits (Montecarlo Sand and Silt Unit), stratigraphically located in this portion of the Montevarchi Synthem, are the focus of this multidisciplinary study. These deposits conformably overlie sandy fluvio-eolian sediments and are, in turn, capped by fluvio-palustrine deposits through a progressive unconformity. Facies analysis suggest a sandy flood-basin environment for these deposits, characterised by variations in water discharge and flood event energy. Mollusc and fish remains, pointing to quiet or slow-moving shallow waters, have been affected by transport processes before final burial in overbank areas. Fish remains of the primary marine family Mugilids highlight a connection between the basin and the sea that was previously only supposed. Small mammal remains, referred to the rodent Mimomys polonicus , are coherent with a water-rich environment. Cyclic variations in shell content and sedimentological characteristics testify to the occurrence of short-term climatic oscillations during this warming phase. This study fits with paleomagnetic and radiometric datings and mammal biochronology, in indicating that the Montecarlo Sand and Silt Unit belongs to a time interval preceding the Reunion paleomagnetic event. The depositional evolution of the Montecarlo Unit was driven by climatic change from arid to humid conditions, related to a global increase in temperature that occurred between 2.4 and 2.2 Ma.

Active faulting in the western Pyrénées (France): Paleoseismic evidence for late Holocene ruptures

We have identified a 50-km-long active fault scarp, called herewith the Lourdes Fault, between the city of Lourdes and Arette village in the French Pyrénées. This region was affected by large and moderate earthquakes in 1660 (Io = VIII–IX, MSK 64,), in 1750 (Io = VIII, MSK 64) and in 1967 ( M d = 5.3, Io = VIII, MSK 64). Most earthquakes in this area are shallow and the few available focal mechanism solutions do not indicate a consistent pattern of active deformation. Field investigations in active tectonics indicate an East–West trending and up to 50-m-high fault scarp, in average, made of 3 contiguous linear fault sub-segments. To the north, the fault controls Quaternary basins and shows uplifted and tilted alluvial terraces. Deviated and abandoned stream channels of the southern block are likely due to the successive uplift of the northern block of the fault. Paleoseismic investigations coupled with geomorphic studies, georadar prospecting and trenching along the fault scarp illustrate the cumulative fault movements during the late Holocene. Trenches exhibit shear contacts with flexural slip faulting and thrust ruptures showing deformed alluvial units in buried channels. 14C dating of alluvial and colluvial units indicates a consistent age bracket from two different trenches and shows that the most recent fault movements occurred between 4221 BC and 2918 BC. Fault parameters and paleoseismic results imply that the Lourdes Fault and related sub-segments may produce a M W 6.5 to 7.1 earthquake. Fault parameters imply that the Lourdes Fault segment corresponds to a major seismic source in the western Pyrénées that may generate earthquakes possibly larger than the 1660 historical event.

Paleosols derived from loess and loess-like sediments in the Basin of Persepolis, Southern Iran

In the Basin of Persepolis, late Quaternary basin fills consist of loess, loess-like sediments and fine- or coarse-textured alluvium. The loess and its derivatives are divided by various paleosols, which consist of well-developed fBw(t)-horizons, weakly developed fBwC- and fBwgC-horizons, as well as fAh-horizons. Strongly developed fBtk-horizons occur in stony alluvial fan deposits or superimpose residual loams of carbonate bedrock mixed with loess. The different types of paleosols result from various degrees of soil development as evidenced by micromorphological features such as the birefringence fabrics, and less clearly by pedochemical properties. Based on the stratigraphy and different degrees of soil development, various phases of soil formation and sediment deposition can be distinguished. Infrared optically stimulated luminescence (IRSL), thermoluminescence (TL) and radiocarbon dating methods are consistent with the stratigraphy and yielded, except for one sample, age estimates of less than about 30 ka. The strongly developed fBw(t) and fBtk horizons reflect soil-forming periods prior to the Last Glacial Maximum (LGM) and probably during Marine Isotope Stage 5 (MIS 5), with climatic conditions comparable to the present-day. The upper loess deposits likely formed under considerably cooler and drier climatic conditions during the LGM. However, poor bleaching of sediments prior to final deposition, as indicated by greater TL than IRSL dates, suggest fluvial reworking of these loesses. The weakly developed fAh, fBwC, and fBwgC horizons may indicate interstadial periods of MIS 3 and short phases of climate amelioration during the early Holocene. The formation of the modern soil probably did not start before 7–9 ka.

Connecting seismically active normal faults with Quaternary geological structures in a complex extensional environment: The Colfiorito 1997 case history (northern Apennines, Italy)

The northern Apennines of Italy are characterized by a complex Tertiary tectonic history, where superposed compressional and extensional deformation occurred. In such regions, characterized by low active extensional strain rate, the coseismic surface ruptures are rare and often a matter of much debate resulting in a difficult connection between “geological” faults (i.e., faults which can be mapped at the surface) and “seismological” faults (i.e., faults which actually generate earthquakes). The availability of detailed geological mapping and high‐resolution seismological data for the Colfiorito area, struck in 1997 by a sequence of six 5 <Mw≤ 6 normal faulting earthquakes, allow us to compare and verify the existence of geometric and kinematic correspondence between the mapped geological Quaternary faults and the activated structures. In map view, the earthquakes distribution reflects the fault pattern mapped at the surface, the length of activated and mapped faults is quite similar (7–10 km), the coseismic subsided region imaged by interferometric synthetic aperture radar data, is located in the hanging wall of the mapped normal faults that bound the Quaternary basins. In section view, there is a geometric connection between mapped normal faults and the aftershock alignments used to image fault geometry at depth. Comparison of striated fault planes and aftershock focal mechanism solutions show a strong kinematic consistency. This study points out that the Quaternary tectonosedimentary evolution and the present‐day geological and geomorphologic setting of the Colfiorito area can be interpreted as the result of repeated, extensional earthquakes, similar to the 1997 events, occurring on NW‐SE trending normal faults. Our data also show that the main shocks of the Colfiorito sequence nucleated close to the intersections between the normal faults and the preexisting compressional/transpressional structures, which in 1997 acted as lateral barriers to rupture propagation and consequently constrained the fault size.

Segmentation and interaction of normal faults within the Colfiorito fault system (central Italy)

Abstract Fault segments belonging to a fault population can link and interact, eventually forming a single larger fault, and thus affecting the estimation of the maximum expected earthquake. We present throw distribution data along the Quaternary normal faults of the Colfiorito fault system (central Italy), which consists of four main fault segments and where a seismic sequence occurred in 1997–1998. Throw values along the two central overlapping, en-échelon segments (8.5–9.5 km long) were measured on a good stratigraphic marker, by constructing a set of closely spaced geological cross-sections, perpendicular to the fault strike. As these faults are commonly retained active and border Quaternary basins, we compare morphological and geological throws in order to verify the faults neotectonic activity. Geological and morphological throw distributions show good correlation, testifying that recent faulting affected the topographic surface and suggesting that the observed offset completely accumulated during the Quaternary. The throw distribution along the fault segments is asymmetric and reaches maximum values (500–550 m) within the zone of fault overlap, suggesting mechanical interaction between the studied faults. Maximum length-throw correlation suggests that the studied faults grew according to a linear scaling relationship.

Active tectonics and Quaternary basin formation along the Vienna Basin Transform fault

The Vienna Basin Transform fault is an active fault system extending over a distance of some 300 km from the Eastern Alps through the Vienna Basin into the West Carpathians. Active sinistral movement is indicated by moderate seismic activity in a NE-striking zone paralleling the fault, focal plane solutions and recent stress measurements. By analogy to the Miocene kinematics we propose that the sinistral strike-slip fault terminates in the Carpathians where horizontal offset is transformed into thin-skinned thrust-type deformation. Hypocenter depths mostly well above 12 km are in line with the inferred thin-skinned style of deformation with active faults restricted to the overthrust Alpine–Carpathian units. Mapping of active fault segments in the Vienna Basin using subcrop data, thickness maps of Quaternary deposits, seismological data, and geomorphological features seen in the digital elevation model shows that virtually all active faults are reactivated Miocene structures. In the southern part of the basin active faulting defines a small-scale pull-apart structure with an actively subsiding Quaternary basin, which is filled with up to 140 m fluvial gravel, sand and paleosoils. For this basin Quaternary sinistral displacement was quantified by adopting a geometrical model for thin-skinned extensional strike-slip duplexes. Accordingly, 1.5–2 km sinistral slip accumulated during deposition of the basin fill in the last 400 ky corresponding to a slip rate of 1.6–2.5 mm/y. Results are in good agreement with published GPS data indicating 2 mm slip per year. A second group of Quaternary basins is related to listric normal faulting, rollover and crestal collapse of the reactivated normal faults at the NW basin margin. Rollover also resulted in tilting and dissecting Late Pleistocene river terraces of the Danube.

Geological database for liquefaction hazard analysis in the Kathmandu valley, Nepal

The Quaternary basin fill of the Kathmandu valley contains discontinuous and heterogeneous layers of lacustrine and fluvial sediments. The available stratigraphic information derived mainly from 185 boreholes ranging in depth from 35 to 575 m was used to study the layer model of the Kathmandu basin. For this purpose, the entire basin till was grouped into three representative layers containing mainly fluvial deposits, lacustrine deposits, and the overlying fluvial and anthropogenic materials. The information from borehole logs was incorporated into the three layers, and a digital elevation model of their depth of contacts was generated. The model was compared with the bedrock depth to obtain the thickness of each layer. A liquefaction susceptibility map of the Kathmandu valley was generated using the above information of the representative layers as well as 328 shallow (<30 m) boreholes.

3-D mapping of segmented active faults in the southern Vienna Basin

In this paper we present novel data on the location and kinematics of seismically active fault segments of the Vienna Basin Transfer Fault System in the southern Vienna Basin. Spatial mapping of active faults and kinematical analyses are based on commercial 3-D reflection seismic data, geomorphological features such as tilted Quaternary river terraces and fault scarps, the geometry of subsided Quaternary basins, and published geodetic data. Accordingly, active faulting in the southern Vienna Basin occurs partly by reactivation of the Miocene fault system related to the formation of the Vienna pull-apart basin between c. 17 and 8 Ma. Two domains of Quaternary and active faults can be distinguished with, (1) predominantly strike-slip and (2) mainly normal faulting. (1) A seismically active NE-striking sinistral strike-slip fault zone with large negative flower structures is mapped at the south-eastern margin of the basin. Subsidence within the reflection seismically imaged flower structure is documented by up to 1000 m of throw since Pannonian times and the accumulation of up to 150 m thick Quaternary gravels. At the surface the fault zone is characterized by en-echelon faults with some prominent scarps. (2) Major E-dipping normal faults branch off from the transfer strike-slip fault system. The normal faults extend into the central and western part of the basin as well as into the urban area of Vienna. Close to Vienna, the normal offset along such a normal fault is at minimum 300 m since Pannonian times. Surface expressions of active normal faulting are tilted Quaternary terraces of the Danube river and tilted ancient land surfaces in the hanging wall of the normal faults. The mapped active normal faults are kinematically linked by a common detachment horizon, which is in contact with the seismically active strike-slip zone along the south-eastern border of the basin. Northeast of the Vienna Basin the seismically active zone continues as a straight line indicating a rather linear transfer fault zone than a pull-apart step over geometry.

Structural controls on hydrothermal flow in a segmented rift system, Taupo Volcanic Zone, New Zealand

AbstractVigorous hydrothermal convection transfers 10 times the average continental heat flow through the central Taupo Volcanic Zone (TVZ), a region of active extension (approximately 8 mm year−1) and productive rhyolitic volcanism. Over 20 high‐temperature (>250°C) geothermal fields occur within Quaternary pyroclastic basins, with convective circulation to depths of 7–8 km presumably extending through basement rocks. Parallel‐striking normal faults, fractures and dikes dissect the convective regime, interacting with fluids to either enhance or restrict flow according to the relative permeability of structure and host rock. In the basement, high bulk permeability is maintained by focussed flow through faults and associated fractures well oriented for reactivation in the prevailing stress field. In contrast, distributed flow through fault‐bounded compartments prevails within Quaternary basins, masking any signal of deeper structural control. Exceptions occur where more competent rocks are exposed at the surface. As in narrow magmatic rifts elsewhere, the extensional fabric is partitioned into discrete rift segments linked along strike by accommodation zones. Eighty per cent of TVZ geothermal fields correlate spatially with rift architecture, with 60% located in accommodation zones. We suggest that segmented rift fabrics generate bulk permeability anisotropy that is to some extent predictable, with rift segments characterized by enhanced axial flow, and accommodation zones characterized by locally enhanced vertical permeability that is tectonically maintained. This provides a plausible explanation for the common occurrence of geothermal fields within accommodation zones and their notable absence within densely faulted rift segments. Maintenance of structural permeability in zones of active hydrothermal precipitation necessarily requires repeated brittle failure. Geothermal plumes therefore exploit tectonically maintained permeability within accommodation zones, with rift segments functioning mostly as drawdown regions. The influence of rift architecture on flow paths has important implications for geothermal extraction and epithermal mineral exploration within the TVZ and other structurally segmented hydrothermal systems, both active and extinct.

The Gubbio normal fault (Central Italy): geometry, displacement distribution and tectonic evolution

Normal faults within orogenic belts can be pre-, syn- or post-orogenic features. We studied the Gubbio normal fault (central Italy), which is an example of a pre-orogenic fault reactivated in a post-orogenic stage. The Gubbio Fault is a 22-km-long fault bordering a Quaternary basin and part of an active faults system in the Umbria–Marche region (Central Italy). The interpretation of a set of seismic profiles enables us to reconstruct the fault geometry in detail and to measure displacement and throw distributions along the fault strike. Seismic data indicate that the Gubbio Fault represents an example of multiple reactivation: at least a portion of the fault was active in the Miocene and only a part of the total displacement was achieved in the Quaternary. The reconstruction of the fault geometry at depth shows that the fault is characterised by listric geometry. The fault is also characterised by a bend along strike and structure contours show that this geometry is maintained at depth. As the fault is commonly addressed as presently active, the maximum fault dimensions are correlated to the maximum expected earthquake, and the presence of the fault bend is discussed as a possible barrier to seismic ruptures propagation.

Collapse in a Quaternary shelf basin off East Cape, New Zealand: Evidence for passage of a subducted seamount inboard of the Ruatoria giant avalanche

The Ruatoria margin indentation and its associated giant avalanche off East Cape, New Zealand, have been inferred to result from margin instability following oblique subduction of a large seamount. The earlier studies hypothesise that a diachronous seamount‐wake trough formed the northern part of the indentation, and collapse between the oblique trough and an oversteepened margin front formed the southern indentation and giant avalanche. If correct, then the impacting seamount must now be landward of the indentation. New seismic profiles, supported by multibeam bathymetry and core samples, from landward of the Ruatoria Indentation, provide support for the passage of a large seamount deep beneath the continental shelf. The continental margin around the head of the indentation is underlain by Quaternary basins that are inferred to result from transpression associated with oblique plate convergence. One basin underlies the shelf landward of the indentation, its seaward edge having collapsed into the indentation. There, faults and a graben with gravitational collapse structures that are transverse to the northeast‐southwest regional trends may be evidence of passage of a seamount. A tentative sequence stratigraphy, based on Quaternary unconformities and shelf‐edge prograding units, suggests that the main phase of collapse occurred on the outer shelf before the penultimate, major, glacial sea‐level lowering c. 155–135 000 yr ago. Depths to the post‐last‐glacial erosion surface indicate that the basin is subsiding rapidly at >4 m/ka. If a significant part of the subsidence relates to wake collapse behind a subducting seamount, then the seamount must now underlie the adjacent land. Onshore, doming hills, with coastal terraces indicating uplift of 2.6 m/ka, suggest that the seamount is now c. 10 km west of East Cape.

3D geologic framework models for regional hydrogeology and land-use management: a case study from a Quaternary basin of southwestern Quebec, Canada

During a regional hydrogeologic survey in the St. Lawrence Lowlands, Canada, a computer-based 3D Geologic Framework Model (GFM) was constructed to obtain a consistent representation of this typical Quaternary glaciated basin over a 1,400 km2 area. Such a detailed stratigraphic reconstruction was needed because the Quaternary sediments control the recharge to the underlying regional fractured rock aquifer and also because buried granular aquifers are partly connected to the regional system. The objectives of this geomodeling effort are 1) to improve understanding of subsurface conditions above the regional aquifer and; 2) to provide a common stratigraphic framework for hydrogeologic applications. The method draws on knowledge-driven discrete modeling using gOcad, as well as standardization and quality control procedures to maximize the use of a multisource database. The resulting model represents the bedrock topography and the complex stratigraphic architecture of overlying sediments. The regional till aquitard, the marine clay aquiclude and the buried granular aquifers have been modeled with unprecedented details thus providing a well-constrained 3D hydrostratigraphic framework. The recharge zones of the rock aquifer represent about 35% of the study area. Buried granular aquifers are directly connected to the regional aquifer system over about 10% of the area. The model allows several applications such as assessing aquifer vulnerability and areal groundwater recharge rates; improving the GFM inter-operability with groundwater modeling systems would be the next logical step.

Contribution to the study of Greek thermal springs: hydrogeological and hydrochemical characteristics and origin of thermal waters

A large number of chemical analyses of Greek thermal waters were evaluated in order to investigate spring water origin, water–rock interaction mechanisms, and estimate the thermal potential of the geothermal areas. Four water types were distinguished from geochemical diagrams. The relatively fresher waters include samples of Ca–HCO3 and Mg–HCO3 type waters originating from the schistose Rhodope Massif and the Quaternary basin of Aridea, respectively. Samples of the Na–HCO3 water type are typical of springs located in the post-orogenic basins of northern Greece. These hot, deep-rising Na–HCO3 waters circulate in a CO2-rich environment that favours the solubility of alkaline ions such as Na from siliceous rocks. Most of the samples belong to the Na–Cl water type and originate from Greek islands and coastal springs. These are characterized by the mixing of deep thermal solutions with seawater and fresh water. The presence of CO2 in thermal and mineral springs is due to the metamorphism of buried marine carbonate horizons while H2S is due to both local pyrite oxidation and the reduction of sulphates. The use of geothermometers suggested that the investigated geothermal areas have low enthalpy fluids at depth, while higher temperatures are likely present in Milos, Lesvos, Nisyros islands and Xanthi Basin.

The Gubbio fault: can different methods give pictures of the same object?

Different investigation techniques (field geology and structural analysis, geomorphology, seismic reflection profiles and seismological data) have been used to develop images of the Gubbio fault, giving us the opportunity to compare different approaches and evaluate points of consensus and controversy in fault analysis and characterization. From our integrated analysis we define a well-focussed image of the geometry and kinematics of the Gubbio fault and the related Quaternary basin, while the seismogenic role of the fault is still ambiguous.

Late quaternary seismic sequences and sedimentation along the coast off Taishan, Guangdong, as revealed by high resolution seismic data

Seismic stratigraphic analysis of 150 km of high-resolution seismic profiles (GEOPULSE and 3.5 kHz) obtained along the muddy coast off Taishan, Guangdong provided valuable information on the offshore Quaternary stratigraphy, tectonics, sedimentary evolution, and environmental and engineering geology of this area. The following late Quaternary stratigraphic sequences were mapped. (1) Pleistocene alluvial sitty sand and shallow marine clay; (2) coarse fluvial channel sand; (3) nearshore and bay clayey sediments. The incision of fluvial channels occurred in two stages: during the Late Pleistocene and at the beginning of the Holocene. The Pleistocene fluvial channels have been filled by coarse sand overlain by more than 10 m of late Pleistocene clay and 20–30 m of Holocene clay. The coastal area is dissected by two major fault systems: the first group strikes ENE-WSW and controls the evolution of the adjacent Quaternary basin, while the second one trends NNE-SSW. These fault systems must be taken into account in any coastal engineering considerations. In addition, both granitic and metamorphic basements were recognized.