Quaternary Sedimentary Deposits Research Articles

Setorização do subsistema sul da lagoa da Conceição, Santa Catarina

The aim of this work is to propose a regionalization of southern Conceicao Lagoon subsystem, located at the Santa Catarina Island - SC, based on its grain size, compositional and physiographic characteristics. The subsystem is part of a chocked lagoon, being connected to the remaining lagunar body by a narrow 3.5 m deep channel on its northern portion. It is surrounded by granitic rocks at west and by quaternary sedimentary deposits at east, north and south. Sediment samples were sampled at 16 regularly distributed points and were processed to determinate biodetritic carbonate, organic carbon content and conventional grain size parameters. Continuous surfaces of the variables were obtained through kriging interpolation. A bathymetric map resulted from the interpolation of 2.464 depth points digitalized from charts at the scale of 1:2.000 m. Individual sectors were identified based on data integration and spatial analysis of sedimentologic and bathymetric parameters. The integration of the variables through cluster analysis yielded the regionalization of the subsystem, were three depositional environments were defined: a predominantly sandy, a sand-muddy and a muddy environment. Besides these three, a fourth transitional environment situated between the banks and deeper areas was recognized. The muddy environment was subdivided in three distinct sub environments: deep muddy, sheltered muddy and organic muddy. Their limits were set through the analysis of the spatial behavior of sediment descriptors and bathymetry. From the results it is possible to conclude that the spatial and cluster analysis of morpho-sedimentological descriptors was efficient on the regionalization of the environment in study, even considering the small number of sediment samples.

Late Quaternary deformation and slip rates in the northern San Andreas fault zone at Olema Valley, Marin County, California

Quaternary sedimentary deposits along the structural depression of the San Andreas fault (SAF) zone north of San Francisco in Marin County provide an excellent record of rates and styles of neotectonic deformation in a location near where the greatest amount of horizontal offset was measured after the great 1906 San Francisco earthquake. A high-resolution gravity survey in the Olema Valley was used to determine the depth to bedrock and the thickness of sediment fill along and across the SAF valley. In the gravity profile across the SAF zone, Quaternary deposits are offset across the 1906 fault trace and truncated by the Western and Eastern Boundary faults, whose youthful activity was previously unknown. The gravity profile parallel to the fault valley shows a basement surface that slopes northward toward an area of present-day subsidence near the head of Tomales Bay. Surface and subsurface investigations of the late Pleistocene Olema Creek Formation (Qoc) indicate that this area of subsidence was located further south during deposition of the Qoc and that it has migrated northward since then. Localized subsidence has been replaced by localized contraction that has produced folding and uplift of the Qoc. This apparent alternation between transtension and transpression may be the result of a northward-diverging fault geometry of fault strands that includes the valley-bounding faults as well as the 1906 SAF trace. The Vedanta marsh is a smaller example of localized subsidence in the fault zone, between the 1906 SAF trace and the Western Boundary fault. Analyses of Holocene marsh sediments in cores and a paleoseismic trench indicate thickening, and probably tilting, toward the 1906 trace, consistent with coseismic deformation observed at the site following the 1906 earthquake. New age data and offset sedimentary and geomorphic features were used to calculate four late Quaternary slip rate estimates for the SAF at this latitude. Luminescence dates of 112–186 ka for the middle part of the Olema Creek Formation (Qoc), the oldest Quaternary deposit in this part of the valley, suggest a late Pleistocene slip rate of 17–35 mm/year, which replaces the unit to a position adjacent to its sediment source area. A younger alluvial fan deposit (Qqf; basal age ∼30 ka) is exposed in a quarry along the medial ridge of the fault valley. This fan deposit has been truncated on its western side by dextral SAF movement, and west-side-down vertical movement that has created the Vedanta marsh. Paleocurrent measurements, clast compositions, sediment facies distributions, and soil characteristics show that the Bear Valley Creek drainage, now located northwest of the site, supplied sediment to the fan, which is now being eroded. Restoration of the drainage to its previous location provides an estimated slip rate of 25 mm/year. Furthermore, the Bear Valley Creek drainage probably created a water gap located north of the Qqf deposit during the last glacial maximum ∼18 ka. The amount of offset between the drainage and the water gap yields an average slip rate of 21–30 mm/year. Finally, displacement of a 1000-year-old debris lobe approximately 20 m from its hillside hollow along the medial ridge indicates a minimum late Holocene slip rate of 21–25 mm/year. Similarity of the late Pleistocene rates to the Holocene slip rate, and to previous rates obtained in paleoseismic trenches in the area, indicates that the rates may not have changed over the past 30 ka, and perhaps the past 200–400 ka. Stratigraphic and structural observations also indicate that valley-bounding faults were active in the late Pleistocene and suggest the need for further study to evaluate their continued seismic potential.

Estrutura dos depósitos sedimentares quaternários da bacia hidrográfica do rio Santana, Miguel Pereira, Estado do Rio de Janeiro

The present work deals with stratigraphy, sedimentology and geomorphology of Quaternary sedimentary deposits of Santana river hydrographic basin. through facies and arquitectural elements descriptions. Based on five arquitectural elements characterized by ten lithofacies the following structural and depositional evolutions were scheduled: 1) formation of thick soil horizons over the basement; 2) deposition of several alluvial fans on the soils (lithofacies Gm and Fm, element E); 3) above an unconformity we can recognize a fluvial system, characterized by a non well drainage floodplain. This floodplain is overlaid by high-sinuosity channels (lithofacies Sp and St, element C) genetically related to other floodplain (lithofacies Fl and Fsc, element A) where the interfigering with crevasse splay deposits (lithofacies Sh, Sl, and Sp, element B) is ususal; 4) an erosional phase suceed by a new depositional phase characterized by low-sinuosity channels (lithofacies Gp, Gt, Sp, St, and Sh, element D). Nowadays anthropogenic action produces a new erosional phase. The geomorphological features recognized were scheduled: 1) the present floodplain 1.5m above the river bed; 2) the low terrace ( named T2) 5m above the river bed and its deposits is related to element D; 3) the high terrace ( named T1) 11m above the river bed and its deposits is related to elements A, B, C and E.

NEOTECTÔNICA DA REGIÃO DO ALTO ESTRUTURAL DE QUELUZ (SP-RJ, BRASIL)

The region of the Paraiba do Sul River Valley between the cities of Cruzeiro (Sao Paulo) and Itatiaia (Rio de Janeiro), in Southeastern Brazil, comprises the eastern and western terminations, respectively, of the Cenozoic Taubate and Resende rift basins, as well as the Precambrian terranes of the Queluz Structural High separating these basins, and includes much evidence of recurrent or resurgent tectonic movements that have been active until recent times. The morphostructural analysis of this region, combined with the characterization of the Quaternary sedimentary deposits and brittle tectonic structures, has permitted the recognition of three phases of neotectonic movements. The oldest movements were related to a NW-SE compressive stress field, during the Pleistocene, associated with an E-W right-lateral transcurrent binary. The structures related to this phase affected colluvium and stone-line deposits, which are often overthrust by blocks of basement rocks along faults trending NE to ENE. Probably in the beginning of the Holocene the stress regime changed to an E-W (WNW-ESE) extension, responsible for the generation of N-S-trending grabens with syntectonic sedimentary filling. Finally, a new change in the stress field is recorded by conspicuous and widespread families of shear joints, systematically orientated ENE and WNW, that affect colluvium, colluvium-alluvium and alluvium deposits. The accute bissectrix of the families of joints indicate an E-W direction of compression. The reliability of the neotectonic data presented in this study and the proposed neotectonic model are particularly significant due to important human activities in the region, including such major engineering projects as a radioactive fuel factory, a hydroelectric power station and reservoir as well as a nuclear power plant.

Quaternary sedimentary deposits on the Cameroon shelf: Characterization of facies and late quaternary shorelines

Abstract Several high-resolution (SPARKER) seismic-reflection surveys, associated with 450 dredgings and 75 Kullenberg core samplings, allowed the definition of the main Quaternary sedimentary bodies of the Cameroon shelf. The distribution of the Holocene mantle is very uneven: its thickness reaches 40 m at the northern end of the shelf where there are sandy stratified deposits in the lower part and a High System Tract in the upper part. These deposits cross obliquely offshore and towards the south where the Holocene is either absent or localized as backfill in low-level ravines. This distribution is controlled by the Sanaga flow deflected northwards by the predominantly SW swell and by the Niger River flow driven southwards by the Guinean current. The sensu lato Pleistocene mantle is substantial in the north where fluvio-deltaic sands issued from the Nigerian complex. Southward coarse sands from the Sanaga-Nyong complex accumulate in progradient structures. In the southern part of the plateau, the Cenozoic-Mesozoic and Pre-Cambrian substratum at the outcrop is indented by extensive unevenness defining asedimentary shoals and Pleistocene-silted depressions. These depressions present paralic littoral successions towards the coast and circa-littoral to littoral successions seawards. As a result of the last eustatic movements, the roof of these successions has been planed off and has been more and less intensely modified. In some cases it is possible to date the last oscillations of the shoreline, using 14 C.

Tectonic setting of the Portland-Vancouver area, Oregon and Washington: Constraints from low-altitude aeromagnetic data

Seismic activity in the Portland-Vancouver metropolitan area may be associated with various mapped faults that locally offset volcanic basement of Eocene age and younger. This volcanic basement is concealed in most places by young deposits, vegetation, and urban development. The U.S. Geological Survey conducted an aeromagnetic survey in September 1992 to investigate the extent of these mapped faults and possibly to help identify other seismic and volcanic hazards in the area. The survey was flown approximately 240 m above terrain, along flight lines spaced 460 m apart, and over an area about 50 × 50 km. These magnetic data indicate a pronounced northwest-striking magnetic lineation east of the Willamette River in downtown Portland associated with a fault concealed beneath Quaternary sedimentary deposits and previously inferred from shallow well data. The magnetic lineation confirms the existence of the fault and suggests that it has had a prolonged history: (1) Although well data indicate <200 m of vertical offset of underlying volcanic basement, models based on the aeromagnetic data from downtown Portland suggest reverse faulting with up to 1 km of offset deeper in the section. (2) The magnetic lineation associated with this fault extends southeast to the Clackamas River drainage, a distance of 50 km and considerably beyond the mapped extent of the fault. A northwest-striking magnetic anomaly located southwest of the Tualatin Mountains corresponds closely with another mapped fault and with mixed reverse and strike-slip faulting during a seismic swarm (M ≤ 3) in 1991. We believe these and other anomalies in the aeromagnetic data reflect the Portland Hills fault zone, believed to be the southwestern boundary of a structural basin now occupied by Portland and Vancouver. The postulated northeastern boundary of the basin, the Frontal fault zone, is also evident, although less well represented in the aeromagnetic data. Aeromagnetic anomalies, geologic mapping, and earthquake focal-plane solutions demonstrate a complex deformational history in the Portland-Vancouver area since middle Miocene time that includes elements of compression, extension, and dextral slip. These complexities reflect Portland-Vancouver's unique position within a north-south transition in tectonic styles along the Cascadia margin, from compressional in the north to extensional in the south.

The application of geophysical methods to the geological mapping of Quaternary sediments

Abstract The geological mapping of Quaternary sedimentary deposits is usually hindered by the lack of exposure and by the rapid lateral and vertical variations in the lithologies. With the continuing development of new techniques, geophysical methods offer practical means of complementing conventional mapping in these conditions. The methods available are suitable for application to problems ranging from regional mapping to detailed site investigation. The application of the appropriate method can produce solutions to these problems and reduce expenditure on drilling and trenching, the main alternative means of sub-surface investigation. In this paper, the use of geophysical methods in the geological mapping of Quaternary sediments is reviewed and illustrated by a number of case histories from eastern England.

Etude stratigraphique et hydrogeologique de l'extremite meridionale de la Hamada du Guir

Abstract The Miocene and lower Pliocene sandstone and overlying limestone, and the upper Pliocene and Quaternary sedimentary rocks and detrital deposits of the southern portion of the Hamada du Guir (Algeria) rest upon the eroded surface of deformed Paleozoic basement rocks. Significant amounts of ground water in the upper Tertiary sandstones are indicated by four wells in the area west and northwest of Beni-Abbes. Solution pockets and channels, travertine, and other vestiges of ground water are widespread in Quaternary deposits.