Quaternary Lacustrine Research Articles

Geo-Engineering Properties and Swelling Potential of Quaternary Lacustrine Clays in North of Burdur, Turkey

In areas surrounding the city of Burdur, Turkey, where water contents are high, no swelling–shrinkage-dependent deformations are visible because the active zone depth is adjacent to the surface. There are some deformations in areas with low water levels, especially those with low-rise construction. Thus, in some areas around Lake Burdur, increased swelling–shrinkage-dependent deformation is inevitable owing to a steadily decreasing water level of the lake. However, development around Lake Burdur, such as an organized industrial area, a civilian airport, and a military airport currently under construction, exacerbates the problem. Therefore, we examined swelling potentials of lacustrine clay in the active zone within a selected area around lake. Lacustrine soils in the selected area were studied using a hand auger, with a total of 379 samples at 50 points, through depths of 1–3 m. Clayey levels in the research area were separated into three different clay–clayey levels and were analyzed by X-ray diffraction and scanning electron microscope. Results showed that clay minerals at all levels averaged 39–52 % and that most were smectite group clays. Microstructures were plate-like and were aligned face to face. It was also determined that swelling potentials of all examined clayey levels were high to low, with change between 0.22 and 2.59 % and swelling pressures between 2.9 and 71 kPa. Because the water level was close to the surface, so was the active zone; therefore, deformation was noticeable. Swelling–shrinkage-dependent deformations are inevitable in the future with decreasing lake water level.

Seismogenic structures in Quaternary lacustrine deposits of Lake Van (eastern Turkey)

Abstract Soft-sediment deformation structures formed by liquefaction and/or fluidisation of unconsolidated sediments due to seismic shocks are frequent in the Quaternary sandy, silty and clayey deposits of Lake Van. They are present in both marginal and deep lacustrine facies. Their morphology and interpreted genesis imply that they should be considered as fluid-escape structures (dish and pillar structures, flame structures and sand volcanoes), contorted structures (simple and complex convolutions and ball-and-pillow structures) and other structures (disturbed layers and slump structures). The most recently formed structures are related to the October 23rd, 2011 Van-Tabanli (M 7.2) earthquake. The existence of seismites at various stratigraphic levels in the lacustrine deposits is indicative of tectonic activity that frequently triggered earthquakes with magnitudes of 5 or more, affecting the Lake Van Basin.

Mobilization of arsenic and other naturally occurring contaminants in groundwater of the Main Ethiopian Rift aquifers

This study investigates the mechanisms of arsenic (As) and other naturally occurring contaminants (F−, U, V, B, and Mo) mobilization from Quaternary sedimentary aquifers of the Main Ethiopian Rift (MER) and their enrichment in the local groundwater. The study is based on systematic measurements of major and trace elements as well as stable oxygen and hydrogen isotopes in groundwater, coupled with geochemical and mineralogical analyses of the aquifer rocks. The Rift Valley aquifer is composed of rhyolitic volcanics and Quaternary lacustrine sediments. X-ray fluorescence (XRF) results revealed that MER rhyolites (ash, tuff, pumice and ignimbrite) and sediments contain on average 72 wt. % and 65 wt. % SiO2, respectively. Petrographic studies of the rhyolites indicate predominance of volcanic glass, sanidine, pyroxene, Fe-oxides and plagioclase. The As content in the lacustrine sediments (mean = 6.6 mg/kg) was higher than that of the rhyolites (mean: 2.5 mg/kg). The lacustrine aquifers of the Ziway-Shala basin in the northern part of MER were identified as high As risk zones, where mean As concentration in groundwater was 22.4 ± 33.5 (range of 0.60–190 μg/L) and 54% of samples had As above the WHO drinking water guideline value of 10 μg/L. Field As speciation measurements showed that most of the groundwater samples contain predominantly (∼80%) arsenate-As(V) over arsenite-As(III) species. The As speciation together with field data of redox potential (mean Eh = +73 ± 65 mV) and dissolved-O2 (6.6 ± 2.2 mg/L) suggest that the aquifer is predominantly oxidative. Water-rock interactions, including the dissolution of volcanic glass produces groundwater with near-neutral to alkaline pH (range 6.9–8.9), predominance of Na–HCO3 ions, and high concentration of SiO2 (mean: 85.8 ± 11.3 mg/L). The groundwater data show high positive correlation of As with Na, HCO3¯, U, B, V, and Mo (R2 > 0.5; p < 0.001). Chemical modeling of the groundwater indicates that Fe-oxides and oxyhydroxides minerals were saturated in the groundwater, suggesting that the As reactivity is controlled by adsorption/desorption processes with these minerals. The data show that As and other oxyanion-forming elements such as U, B, Mo, and V had typically higher concentrations at pH > ∼8, reflecting the pH-dependence of their mobilization. Based on the geochemical and stable isotope variations we have established a conceptual model for the occurrence of naturally occurring contaminants in MER groundwater: 1) regional groundwater recharge from the Highland, along the Rift margins, followed by lateral flow and water–rock interactions with the aquifer rocks resulted in a gradual increase of the salinity and naturally occurring contaminants towards the center of the valley; and (2) local δ18O-rich lake water recharge into adjacent shallow aquifers, followed by additional mobilization of As and other oxyanion-forming elements from the aquifer rocks. We posit that the combined physical-chemical conditions of the aquifers such as oxidizing state, Na–HCO3 composition, and pH>∼8 lead to enhanced mobilization of oxyanion-forming elements from Fe-oxides and consequently contamination of local groundwater. These geochemical conditions characterize groundwater resources along the Eastern African Rift and thus constitute a potential threat to the quality of groundwater in larger areas of Eastern Africa.

Reconstruction of environmental changes based on MSCL- and XRF-measurements of Quaternary lacustrine sediments from Banyoles Lake, Northern Spain

Reconstruction of environmental changes based on MSCL- and XRF-measurements of Quaternary lacustrine sediments from Banyoles Lake, Northern Spain

OSL and radiocarbon dating on late Quaternary lacustrine sediments from Tengger Desert in China and its implication for palaeolake highstands

Based on the detailed meteorological data in the Tengger Desert, this paper aims to clarify the characteristics of windblown sand and to show the dynamical environment in the Tengger desert. Results of data analysis indicate that both the wind direction and the sand-drift intensity exhibit obvious spatial and temporal variations. The prevailing wind directions for the desert are NW and SE, depending on the regional landform and season. The mean annual wind speed in the hinterland of the desert is greater than its periphery. The mean annual drift potential (DP) is 358.72 VU in Shapotou region on the southern margin of the desert, indicating the intermediate wind environment of the desert.

Sources and transport routes of fine detritus material to the Late Quaternary Dead Sea basin

The sources and routes of transport of fine detritus material (FDM) to the lakes filling the late Quaternary Dead Sea basin were studied by petrographic, mineralogical, grain size, chemical and Sr–Nd isotope analyses on sediments of the late Quaternary lacustrine formations, including river flood material, dust, and loess from the lake watershed. The lacustrine formations comprise two sedimentary facies: one that consists of alternating laminae of primary aragonite and silty-detritus material (aad facies), and another that consists mainly of laminated detritus particles and generally lacks aragonite (ld facies). The aad facies characterizes the glacial intervals (e.g. MIS2 and 4) when lake levels were high, while the ld facies characterizes interglacials (e.g. MIS1, 5) and warmer glacial intervals (e.g. MIS3), when lake levels were low. The detritus of both aad and ld facies show similar mineralogy: mainly quartz and calcite grains with minor feldspars and clays, but distinct grain-sizes (8–10 μm and 50–60 μm, respectively), and distinct 87Sr/86Sr and εNd (0.711–0.712 and ∼−7 to −8, versus 0.709–0.710 and ∼−5, respectively). The aad and ld FDM comprise desert dust of mixed granitic – basaltic composition that was blown from the Sahara desert and from the Nile delta to the northern Negev desert (e.g. the loess deposits) and the Judean Mountains bordering the Dead Sea basin, mainly during glacial intervals along with enhanced Mediterranean rain fronts. The aad FDM reflects an enhanced transport of Saharan granitic dust to the vicinity of the lake mainly during glacials. The ld FDM was recycled from the loess surface cover of the Negev desert mainly during interglacials and warm glacial intervals.

Long chain alkenones preserved in Miocene lake sediments

Over the last few decades, the occurrence of long chain alkenones (LCAs) in Quaternary lacustrine settings has been reported, the distributions being remarkably different from those of open ocean settings. We report here the occurrence of LCAs with modern lake-type composition from Middle Miocene sedimentary strata in the Dahonggou Section, Qaidam Basin, northern Tibetan Plateau. This is the first report of LCAs with preserved lake compositions in pre-Quaternary lacustrine sediments. The discovery implies that the producers of modern lacustrine LCAs could originate from similar lake species living at least as far back as the Miocene epoch. It also sheds new light on the potential of “alkenones” as palaeotemperature indicators in lacustrine systems back to at least 10.5Ma.

Quaternary Lacustrine Deposition and Geological Environment Variations of Doqen Co-Gala Co Basin in Tibet

To verify the lacustrine deposition and geological environment in Gala Co of Tibet in Quaternary Period,the authors carried out studies in this aspect by using remote sensing technologies such as DEM,ETM and ASTER interpretation images,The results show that severe deformation of lake deposition in southern Tibet during Middle Pleistocene epoch was caused by differential uplift of Gonghe movement,and angular unconformity proved the existence of this movement.It is held that the drastic drying of Gala Co was caused by its running dry after the adjacent Mabu Co had become a new dividing range in the basin as a consequence of global warming.The dryness of Gala Co has caused desertification in the region and worsened the regional natural environment.

Geometry and faults tectonic activity of the Okavango Rift Zone, Botswana: Evidence from magnetotelluric and electrical resistivity tomography imaging

We used Magnetotelluric (MT) and Electrical Resistivity Tomography (ERT) to investigate the geometry and nature of faults activity of the Okavango Rift Zone (ORZ) in Botswana, an incipient rift at the southern tip of the Southwestern Branch of the East African Rift System. The ORZ forms a subtle topographic depression filled with Quaternary lacustrine and fluvio-deltaic sediments and is bounded by NE-trending normal faults that are more prominent in the southeastern portion of the rift basin. An MT model from a regional (∼140km) NW–SE trending MT transect shows that much of the rift basin is underlain by a broad asymmetrical low resistivity anomaly that slopes gently (∼1°) from NW to SE reaching a depth of ∼300m. This anomaly suggests that faults in the southeastern part of the rift form a NW-dipping border fault zone and that the lacustrine and fluvio-deltaic sediments contain brackish to saline water filling the broad half-graben structure. Furthermore, MT and ERT models from detailed (4–13kmlong) MT transects and resistivity profiles show that one border fault (Thamalakane) and two within-basin faults (Lecha and Tsau) in the southeastern part of the ORZ are characterized by a localized high conductivity anomaly while another border fault (Kunyere) lacks such an anomaly. These localized anomalies are attributed to channelized fresh surface water and saline groundwater percolating through these faults forming “fault zone conductors” and suggest actively displacing faults. The lack of a “fault zone conductor” in the Kunyere fault is interpreted as indicating diminishing displacement on this fault, and that strain was transferred to the Thamalakane fault further to the east. The fluids provide lubricant for the ORZ faults, hence preventing infrequent large magnitude earthquakes, but favoring frequent micro-seismicity.

Cosmogenic nuclide and uranium-series dating of old, high shorelines in the western Great Basin, USA

Research Article| March 01, 2011 Cosmogenic nuclide and uranium-series dating of old, high shorelines in the western Great Basin, USA Gabrielle Kurth; Gabrielle Kurth * 1Department of Earth and Environmental Science, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801, USA *Current address: O'Reilly, Talbot & Okun Associates, Inc., 293 Bridge Street, Springfield, Massachusetts 01375, USA. Search for other works by this author on: GSW Google Scholar Fred M. Phillips; Fred M. Phillips † 1Department of Earth and Environmental Science, New Mexico Tech, 801 Leroy Place, Socorro, New Mexico 87801, USA †E-mail: phillips@nmt.edu Search for other works by this author on: GSW Google Scholar Marith C. Reheis; Marith C. Reheis 2U.S. Geological Survey, MS 980, Box 25046, Denver Federal Center, Denver, Colorado 80225-0046, USA Search for other works by this author on: GSW Google Scholar Joanna L. Redwine; Joanna L. Redwine 3Desert Research Institute, 2215 Raggio Parkway, Reno, Nevada 89512, USA Search for other works by this author on: GSW Google Scholar James B. Paces James B. Paces 2U.S. Geological Survey, MS 980, Box 25046, Denver Federal Center, Denver, Colorado 80225-0046, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2011) 123 (3-4): 744–768. https://doi.org/10.1130/B30010.1 Article history received: 14 Jan 2009 rev-recd: 04 Feb 2010 accepted: 09 Feb 2010 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Gabrielle Kurth, Fred M. Phillips, Marith C. Reheis, Joanna L. Redwine, James B. Paces; Cosmogenic nuclide and uranium-series dating of old, high shorelines in the western Great Basin, USA. GSA Bulletin 2011;; 123 (3-4): 744–768. doi: https://doi.org/10.1130/B30010.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Closed-basin pluvial lakes are sensitive recorders of effective moisture, and they provide a terrestrial signal of climate change that can be compared to marine and ice records of glacial-interglacial cycles. Although the most recent deep-lake cycle in the western Great Basin (at ca. 16 ka) has been studied intensively, comparatively little is known about the longer-term Quaternary lacustrine history of the region. Lacustrine features higher than those of the most recent highstand have been discovered in many locations throughout the western Great Basin. Qualitative geomorphic and soil studies of shoreline sequences above the latest Pleistocene level suggest that their ages increase as a function of increasing altitude.The results of cosmogenic nuclide dating using chlorine-36 depth profiles from three sites in Nevada (Walker Lake, Columbus Salt Marsh, and Newark Valley), combined with uranium-series and radiocarbon ages, corroborate the geomorphic and soil evidence. The 36Cl results are consistent with available 14C ages and together indicate that the most recent highstands of all three lakes occurred ca. 20–15 ka, late in marine isotope stage (MIS) 2, as shown by previous ages. The 36Cl ages indicate that older lakes in all three basins reached highstands between 100 and 50 ka, and most likely during MIS 4. Shorelines of this age are at about the same or higher altitudes as the younger, MIS 2 shorelines in those basins. The 36Cl results combined with uranium-series ages and one tephra correlation obtained on shorelines higher in altitude than those of MIS 4 and 2 lakes suggest that there were also major lake highstands in the western Great Basin at ca. 100–200 ka, likely corresponding with MIS 6, and during at least two older periods. From these results, we conclude that the preserved shorelines show an apparent decrease in maximum levels with time, suggesting long-term drying of the region since the early middle Pleistocene. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structural architecture of the Colima Volcanic Complex

The Colima Volcanic Complex (CVC) is currently the most active Mexican volcano and is located in the western sector of the Trans–Mexican Volcanic Belt, inside the active Colima Rift, a regional N‐S‐striking extensional structure. The Colima Rift is filled by a ∼1 km‐thick sequence of quaternary lacustrine sediments, alluvium, and colluvium, mostly underling the about 3000‐m‐thick volcanic pile of the CVC. In this work we present the results of a detailed morphostructural and field study of Quaternary faults and fractures in the CVC and the surrounding area, including the regional structures of the Colima Rift. We also present a geometrical modeling of the faults inside the volcano and a numerical model of the gravity‐induced stress and strain fields of the CVC. The study attempts to characterize the geometry, kinematics, and dynamics of the deformation features of the CVC and relate it with the volcano structure, the geology of the substratum, and the geodynamic setting of the region. Our model considers that the observed deformation of the CVC and the surroundings results from the interplay between the active N‐S‐trending regional extensional tectonics and the southward spreading of the volcano over its basement forming an E‐W‐oriented volcanotectonic graben. The interaction between regional tectonics and previously unrecognized volcanic spreading can control magma migration and flank instability, in an area where eruptions and sector failures represent a potential high risk for more than 500,000 people.

Quaternary transpression and lacustrine sedimentation in the San Lorenzo area (Sant'Arcangelo Basin, Italy)

Quaternary lacustrine sedimentation of the San Lorenzo Succession represents one of the more recent steps in the evolution of the northern part of the Sant'Arcangelo Basin. The latter is a large Pliocene to Pleistocene wedge-top depozone of the southern Apennines foreland-basin system that developed close to the front of the thrust belt in southern Italy. The lower to middle Pleistocene lacustrine deposits are composed of siltstone and claystone interbedded with sandstone, carbonate and volcaniclastic beds, arranged in fining-upward sequences. The overall stratigraphical, sedimentological, and structural data collected demonstrate that the San Lorenzo lacustrine deposits formed when the northern sector of the Sant'Arcangelo Basin was undergoing tectonic deformation. In particular, new data reveal the presence of strike-slip syndepositional faults. These faults belong to positive flower-type structures, which developed in a left-lateral transpressive tectonic regime characterized by a E–W horizontal component of shear stress. The lacustrine deposits recorded the activity of these faults showing growth structures represented mainly by gentle synclines, as well as other minor folds. The tectonic activity of the main faults formed an endorheic area with at least two different depocentres accumulating lacustrine successions.

Estimation of the tectonic slip-rate from Quaternary lacustrine facies within the intraplate Albacete province (SE of Spain)

The Quaternary lacustrine basin of Cordovilla (CB) represents one of the most active tectonic areas of the Prebetic Zone (Albacete, SE of Spain). The Quaternary sedimentary deposits of this basin are mainly endoreic lacustrine carbonate and alluvial deposits, developed in a semi-arid climate (Pleistocene-present). The basin is a NW–SE-elongated graben bounded by a major right-lateral oblique-fault, the Pozohondo Fault. This fault trends NW–SE, with an approximate trace of 55 km, and is composed of various segments which are identified by fault scarps. In order to establish the slip-rate of the most active segment of the Pozohondo Fault, called the Cordovilla segment, we carried out a detailed study of the affected Quaternary lacustrine deposits. We found that the lacustrine facies could be related to episodic moderate paleoearthquakes. The slip-rate is calculated to be 0.05 and 0.09 mm/yr, using radiometric dating for the vertical offsets of the lacustrine facies. A trenching study at the northern part of the Cordovilla segment revealed two events caused by paleoearthquakes, with the most recent expressed as an oblique-fault off-setting a poorly-developed soil. The magnitude of the last event was greater than 6, using various empirical relationships for the fault displacement and the surface-length rupture. We estimate episodic activity across the Cordovilla segment, to be characterized by moderate-sized paleoearthquakes (M6), which is in agreement with the tectonic context of an intraplate zone of the Iberian plate.

Mapping the thickness of sediments in the Ljubljana Moor basin (Slovenia) using microtremors

The Ljubljana Moor basin is characterized by moderate bedrock topography and thicknesses of Quaternary lacustrine and fluvial sediments ranging from 0 to 200 m. More than 65 boreholes which reached the bedrock were drilled in the area, but their distribution in the basin is very uneven and some data from the boreholes uncertain. There are also no data on S-velocity distribution within the basin, but seismic refraction measurements pointed out a rather uniform increase of P-velocity with depth, great impedance contrast with the bedrock and relatively small lateral velocity variations. The microtremor horizontal-to-vertical spectral ratio (HVSR) method was therefore applied as a complementary tool to seismic refraction survey to map the thickness of sediments. First, microtremors were measured at the locations of boreholes which reached the bedrock and the resonance frequencies determined. The inverse power relationship between the resonance frequency and the thickness of sediments was then determined from 53 data pairs. The quality of the correlation is moderate due to possible heterogeneities in sediments and possible 3D effects in some minor areas, but the obtained parameters correspond well to the values obtained in six other European basins. Secondly, a 16 km-long discontinuous seismic refraction profile was measured across the whole basin, leaving uncovered some larger segments where active seismic measurements were not possible. Microtremors were then measured at 64 locations along the same profile, using 250 m point spacing, without leaving any gaps. The frequency–thickness relationship was used to invert resonance frequencies to depths. These were first validated using the results of the seismic refraction survey, which showed good agreement, and finally used for interpolation in the segments of missing refraction data to obtain a continuous depth profile of the bedrock. The study has shown that the microtremor method can be used as a complementary tool for mapping the thickness of unconsolidated sediments also in areas characterized by moderate bedrock topography. As the input data are always to some extent uncertain, it is important to have a sufficiently large number of borehole data to establish a frequency–thickness relationship, as well as some additional independent geophysical information for its validation.

A CLAY MINERALOGY OF IRELAND

This paper concisely reviews the occurrence and type of clay minerals in Ireland. Working back through time, the occurrences include: soils; Quaternary glacial, lacustrine and alluvial sedi ments; residual deposits formed during Tertiary and earlier weathering; Tertiary clays; fillings within karstic depressions; the matrix of the Triassic Sherwood Sandstone; shales, fire-clays and bentonites of Devonian and Carboniferous age; and Lower Palaeozoic shales, metabentonites and altered basalts.

Space geodetic imaging of rapid ground subsidence in Mexico City

Since the late 1950s, several areas of Mexico City have undergone accelerated ground subsidence and have developed associated fracturing and faulting. New interferometric synthetic aperture radar (InSAR) and global positioning system (GPS) data indicate that rates of current land subsidence in Mexico City exceed 350 mm/yr. These rates are close to historical maximum levels of the mid-twentieth century, when mitigation efforts were fi rst undertaken to reduce damage to urban infrastructure. The locus of maximum subsidence has shifted from its historical location in the old city center to the east. Correlation of our InSAR results with seismically mapped stratigraphic units suggests that subsidence is primarily controlled by compaction of Quaternary lacustrine clays and silts. We also evaluate spatial gradients in subsidence and suggest that this, rather than subsidence magnitude, is the key factor in risk assessment. Subsidence represents a major geologic risk for Mexico City and imposes serious constraints to any further urban development.

Pedostratigraphy of Terra Rossa and Quaternary geological evolution of a lacustrine limestone plateau in central Italy

AbstractPedostratigraphic levels (PLs) are typical assemblages of soil‐genetic horizons, formed by materials having the same degree of weathering. The pedostratigraphic approach can be very useful to comprehend the formation of the Quaternary soil cover, the environmental evolution of a territory, and to estimate the age of paleosols. A pedostratigraphic study of a Terra Rossa was carried out to understand the soil–parent material origin and to estimate the time of the beginning of pedogenesis.Besides soil and geomorphological survey, the Terra Rossa was analyzed for Fe forms, geochemistry, clay mineralogy, micromorphology, and with scanning electron microscope. Optical dating was applied to obtain age estimates for the deposition of the parent material of soil formation. The insoluble residue of limestone was obtained and analyzed for geochemistry and clay mineralogy.The bedrock is constituted by Quaternary lacustrine limestone, showing pronounced karst landforms. The soil profile is situated in a little dissolution doline and was divided into three PLs: PL1 (0–110 cm) is constituted by cambic and ochric horizons, formed during Holocene in a mixture of colluvial soil sediments and fresh limestone, with aeolian components; PL2 (110–290 cm) includes two argic horizons, which began to form during Late‐Middle Pleistocene in colluvial soil sediments, with few aeolian additions; PL3 (290–330 cm) is constituted by a red argic horizon, with nitic properties, which developed from the insoluble residue of the limestone. The age of PL3 was calculated through a mass balance and an estimation of the limestone‐dissolution rate during the Quaternary, which led to an approximate age of Middle Pleistocene, between 250 and 500 ky BP. The time of the beginning of pedogenesis on limestone can be used as a reference for the tectonic uplifting of the area and emersion of the plateau.

Sismoestratigrafia de alta resolução no lago Juparanã, Linhares (ES - Brasil) como base para estudos sobre a sedimentação e tectônica quartenária

O estudo sismoestratigrafico de alta resolucao do lago Juparana, o maior do sistema de lagos do baixo vale do rio Doce (Espirito Santo, Sudeste do Brasil), foi realizado, fornecendo informacoes para discutir sobre a origem e evolucao deste sistema de lagos ao longo do Quaternario. Duas sismossequencias foram identificadas. A sismossequencia mais antiga e caracterizada pelo padrao transparente de reflexao (reflection free ), tendo sido associada a depositos aluviais holocenicos. A sismossequencia mais recente e caracterizada por um padrao paralelo de reflexoes sismicas e foi associada a fase lacustre instalada apos a barragem do antigo ''vale Juparana''. O mapa de isopacas da sismossequencia mais nova documenta uma distribuicao irregular dos depositos lacustres em tres depocentros distintos, com limites relativamente abruptos, sugerindo um possivel controle neotectonico na evolucao do lago.

The Lago Cardiel Basin, Argentina (49°S): Origin and evolution revealed by high-resolution multichannel seismic reflection studies

A multichannel, high-resolution seismic reflection survey was conducted with an airgun source in the closed lake system of Lago Cardiel, Argentina (49°S). As part of an ongoing study of interhemispheric correlations in climate change, it was intended to determine the maximum age and depth of the lake sediments and better understand the origin and evolution of the lake basin. In agreement with previous single-channel, 3.5-kHz surveys, six major seismic sequences throughout the lake’s subsurface were mapped. The stronger seismic source of this study allows the deepest sequence (Sequence VI) to be interpreted as folded Cretaceous marls with a highly eroded surface. Further examination of this sequence reveals various stratigraphic signatures and mechanisms of the generally east–west orientation of tectonic compression. The nature and continuity of Sequence VI do not indicate a volcanic or impact-related origin of the lake. The original basin has a maximal depression of 154 ms (∼114 m) deep beneath the modern lake surface and is overlain by an alluvial fan (Sequence V) of likely Pleistocene age in the western portion and late Quaternary lacustrine sediments (Sequences I–IV) everywhere else. The data confirm that southern Patagonia was dominated by extremely contrasting climatic conditions during the Quaternary.

Deformation features within an active normal fault zone in carbonate rocks: The Gubbio fault (Central Apennines, Italy)

The Gubbio fault is an active normal fault defined by an important morphological scarp and normal fault focal mechanism solutions. This fault truncates the inherited Miocene Gubbio anticline and juxtaposes Mesozoic limestones in the footwall against Quaternary lacustrine deposits in the hanging wall. The offset is more than 2000 m of geological throw accumulated during a poly-phased history, as suggested by previous works, and has generated a complex zone of carbonate-rich fault-related structures. We report the results of a multidisciplinary study that integrates detailed outcrop and petrographic analysis of two well-exposed areas along the Gubbio fault zone, geochemical analysis (fluid inclusions, stable isotopes, and trace elements) of calcite-sealed fault-related structures and fault rocks, and biostratigraphic controls. Our aims are: (i) the characterization of the deformation features and their spatial–temporal relationships, and (ii) the determination of the P/ T conditions and the fluid behaviour during deformation to achieve a better understanding of fluid–rock interaction in fault zones. We show that few of the observed structures can be attributed to an inherited shortening phase while the most abundant structures and fault rocks are related to extensional tectonics. The outcropping extensional patterns formed at depths less than 2.5–3 km, in a confined fluid system isolated from meteoric water, and the fault structures are the response to a small amount of cumulated displacement, 12–19% of the total geological throw.