Quaternary Sedimentary Deposits Research Articles

Facies of Quaternary Sediments In Bunga Village, North Luwuk District, Banggai Regency, Central Sulawesi

Abstract The distribution of Quaternary sedimentary rock deposits in Indonesia is quite extensive, and one of them is in the Quaternary coral reef units, which are evenly distributed along the eastern arm of Sulawesi. The research was conducted in Bunga Village, North Luwuk District, Banggai Regency, Central Sulawesi Province. This research was motivated by the lack of geological data, so the topic of developed facies became an interesting topic to be researched. Data was collected from a cliff at the coordinates 0053′57,57.1″N-122054′43′6″E. Stratigraphic measurements aim to determine the facies, depositional environment, and sedimentation mechanisms developed in the study area. The research was conducted using the method of field data collection and laboratory analysis. Collecting field data was carried out with measured stratigraphic with a 1:100 scale and taking several rock samples. Laboratory analysis was carried out in paleontological and petrographic analysis, which was carried out to determine the composition of the constituent rock and fossil identification, especially foraminifera in thin sections of rock that were selected. Based on the study’s results, the total rock layers measured in the study area were 15 m. Facies found in the stratigraphic path of the study area are floatstone facies, rudstone facies, allochemic sandstone facies, polymict conglomerate facies. The type of deposition environment of limestone and allochemic sandstone in the study area is on the foreslope, while the conglomerate facies is included in the fan delta deposition environment. Overall, the sedimentation dynamics in this area are in a high energy environment, indicating that the facies that developed were deposited with a sediment gravity flow mechanism.The results of the analysis of fossils found Cyclammina cancellata sp., Orbulina universa sp., Globigerina bulloides sp., and Trilobatus immaturus sp., which indicates the limestone in the study area was deposited in the Late Pleistocene to early Holocene.

Strong variation of near-surface seismic anisotropy in Taiwan and its geological implications

We report on the near-surface (< 500 m) seismic structure (Vp, Vs, and Vs anisotropy) of Taiwan using the empirical Green's functions of body waves between vertical station pairs at 60 borehole sites. The near-surface anisotropy in metamorphic rocks and Miocene or older sedimentary strata are mostly categorized as orogeny-parallel anisotropy (OPA), and sites exhibiting stress-aligned anisotropy (SAA) are located in areas with late Quaternary sedimentary deposits or in alluvial coastal plains. The results show that there is a significant variation of the anisotropy strength even within the same geological unit. Since all the major geological units of Taiwan are well sampled by borehole arrays, and drilling data for 52 sites are available, this provides a unique opportunity to investigate the geological implications of strong variations in near-surface anisotropy. The investigation indicates that (1) near-surface anisotropy caused by structural fabric is generally stronger than that resulting from the alignment of stress-induced open cracks, (2) SAA strength in sedimentary rocks, igneous rocks, and gravel sediments is generally higher than that in fine-grained sediments, and (3) the sites with the strongest OPA (> 30%) are located in mountain ranges and the mean OPA strength of these sites is significantly higher than that of foothills, suggesting that foliated metamorphic rocks lead to stronger OPA than do dipping sedimentary strata. The results also suggest that the fluid-saturation of micro-cracks is not a necessary condition for the occurrence of the SAA mechanism in the near-surface depth range.

Fluvial aggradation and incision in the Brazilian tropical semi-arid: Climate-controlled landscape evolution of the São Francisco River

Large rivers are dynamic systems whose evolution depends on both internal and external forcing, particularly tectonics, sea level, and climate. Associating fluvial responses to a specific driver is a complex task that has been debated for a long time. Thus, rivers that flow exclusively under tectonically stable areas and without direct influence of relative sea level changes are suitable targets to understand how large fluvial systems responded to past climate changes. The São Francisco River is one of the largest cratonic rivers across South America, and its late Quaternary sedimentary deposits record the fluvial landscape evolution in a thousand-year timescale. The São Francisco River flows northward over different climate zones, with its upper course in a semi-humid setting, but with most of its watershed under semi-arid conditions. To understand the controls on sediment erosion, transport, and storage from uplands to lowlands, we investigated a 200-km section of the medium course of the São Francisco River in northeast Brazil. Several geomorphological zones were characterized, mapped, and dated by optically stimulated luminescence (OSL). Two zones are represented by degraded terraces with lakes, but no preserved alluvial features: (zone 1) high-level terrace (87.7 ± 12.7 ka) and (zone 2) low-level terrace (65.5 ± 5.3 to 39.3 ± 4.3 ka). Three zones comprise the active confined aggradational plain, with features such as scroll bars and abandoned channels: (zone 3) older meander belt (18.1 ± 1.6 ka); (zone 4) young meander belt (15.5 ± 1.5 to 9.5 ± 1.0 ka), and (zone 5) modern channel belt (0.4 ± 0.1 to 0.3 ± 0.1 ka). Zone 6 comprises an eolian dune field composed of parabolic dunes with two phases of active sedimentation (45.1 ± 5.2 to 25.5 ± 4.4 ka and 14.3 ± 2.6 to 5.2 ± 1.4 ka). Sediment deposition ages allowed the recognition of at least four phases of fluvial aggradation (⁓90 ka; ⁓66 to 39 ka; ⁓18 to 9 ka and ⁓0.3 ka to recent), three phases of incision (⁓85 to 66 ka; ⁓39 to 18 ka and ⁓9 to 1 ka), and two phases of dune field stabilization (⁓25 to 15 ka and ⁓5 ka to recent). Development of the eolian dune fields occurred during drier conditions, when the inland activity of trade winds reworked sediments deposited on the fluvial plain. We interpret the incision events as having been set in motion by an increase of fluvial discharge in the upper catchment area, produced by rainfall intensification due to activity of the South Atlantic Convergence Zone (SACZ). The aggradation and incision phases on the São Francisco River during the last 100 ka are therefore likely controlled by multi-millennial precipitation changes, possibly related to precession cycles. The events of high sedimentation rate in the São Francisco river mouth are partially correlated with incision phases in its middle course. This suggests that sedimentation in plains of large plateau rivers can be decoupled from the coastal area.

Geology of the Macao Special Administrative Region (China)

ABSTRACT A 1:12,000 geological map of the Macao Special Administrative Region has been produced through detailed field work supported by petrographic, mineralogical, geochronological and geochemical data obtained in previous studies. This map aims to represent a reliable tool to understand the geological evolution of the region and for management of the territory. The geology of Macao is dominated by two groups of Jurassic granitic rocks belonging to an intrusive suite located along the coast of Southeast China: Macao Group I (MGI: 164.5 ± 0.6 to 162.9 ± 0.7 Ma) and Macao Group II (MGII: 156.6 ± 0.2 to 155.5 ± 0.8 Ma), including the associated microgranite, aplite and pegmatite dikes and quartz veins. Remnants of the metasedimentary wall-rock are present as Devonian xenoliths enclosed within the granites. Younger Jurassic to Cretaceous andesite to dacite dikes (150.6 ± 0.6 to <120 Ma) intrude the granitic rocks. Additionally, Quaternary sedimentary deposits cover the older lithologies.

Processes and characteristics of hydrogeochemical variations between unconfined and confined aquifer systems: a case study of the Nakdong River Basin in Busan City, Korea.

This study is to assess the hydrogeochemical characteristics of groundwater at the deltaic region of the Nakdong River Basin in the Busan Metropolitan City of Korea. The study area is covered by the Quaternary sedimentary deposits and the Cretaceous granites associated with unconformity. The thick sedimentary deposits consists of two aquifers, i.e., unconfined and confined aquifers on the basis of clay deposit. Groundwater samples were collected from seven boreholes: two from unconfined aquifer and five from confined aquifer systems during the wet season of 2017year. ORP and DO indicates thatthe groundwater of the unconfined aquifer exists in the oxidization condition and that of the confined aquifer pertains in the reduction condition. Piper's trilinear diagram shows CaSO4 type for groundwater of the unconfined aquifer, and NaCl type for that of the confined aquifer. Ionic concentrations of groundwater increase in the confined aquifer because of direct and reverse ion exchange processes. Carbonate weathering and evaporation are other mechanisms in the water-rock interaction. Saturation indices of dolomite and calcite are observed as oversaturated, while halite reveals undersaturation. Hierarchical cluster analysis (HCA) exhibitsthat cluster 1 and cluster 2 represents the properties of groundwater in unconfined and confined aquifers, respectively. Factor analysis shows that groundwater of the confined aquifer is much influenced by seawater, and includes heavy metals of iron and aluminum. Groundwater samples in unconfined and confined aquifers are located at the rock weathering and evaporation zones in the Gibbs diagram. Inverse geochemical modeling of PHREEQC code suggests that carbonate dissolution and ion exchange of major ions are the prevailing geochemical processes. This comprehensive research provides the distinguished hydrogeochemical characteristics of groundwater in confined and unconfined aquifer systems of the Nakdong River Basin in Busan City, Korea.

Morphometrical analysis of Ceiba Mill. (Bombacoideae, Malvaceae) pollen: a sacred plant of the Mayan (Mesoamerican) civilisation

Ceiba, is a large tree used for ornamental landscaping in tropical regions of the world. It is found in tropical areas, including Mexico, Central America, South America, the Caribbean, West Africa, and Southeast Asia. The present work communicates the detailed pollen morphology of four Ceiba species growing in India including one hybrid, C. speciosa (A.St.-Hil.) Ravenna, C. insignis (Kunth) P. E. Gibbs & Semir, C. x insignis (cross between C. insignis and C. speciosa) and C. pentandra (L.) Gaertn., using Field Emission Scanning Electron Microscope (FESEM), Confocal Laser Scanning Microscope (CLSM) and Light Microscope (LM) to highlight the taxonomic characterization of these species and document finer morphological details to correlate them with other Ceiba spp., growing around the world. Pollen grain is 4-5-colporate, brevicolpate; sub-oblate to prolate-spheroidal to sub-prolate; sexine reticulate (muri provided with scattered spinuloid excrescences, lumina reticolumellate) and mostly thicker than nexine. The multivariate principal component analysis (PCA) was applied on Ceiba and Bombax ceiba to numerical data obtained from pollen morphometry which clearly revealed a significant variation between different genus and species. A pollen key, based on these micromorphological data (especially pollen aperture and size of muri), is also presented for the Ceiba and B. ceiba. The study provides an analogue for precise identification of Ceiba pollen grains recovered in Quaternary and pre-Quaternary sedimentary deposits in India and other tropical and subtropical regions of the world. Besides, pollen preservation, evolutionary trend and palaeoecology are the other important implications of this study.

Sedimentological and geomorphological characteristics of Quaternary deposits in the Planica-Tamar Valley in the Julian Alps (NW Slovenia)

ABSTRACTWe present a geomorphological map on a scale of 1:15,000, with detailed sedimentological descriptions, and a general relative spatio-temporal depositional reconstruction of Quaternary sediments in the Planica-Tamar Valley (NW Slovenia). After the Last Glacial Maximum, the retreating Quaternary glacier deposited large amounts of glacial sediments. These were followed by Holocene sediments, which differ in their sedimentological characteristics, transport mechanisms, and morphology. These sediments are deposited as sedimentary bodies with complex depositional geometries. They form areas of active, partly active, and inactive sedimentation in response to local/regional climate and bedrock geology. Previous research of the valley was mainly focused on bedrock mapping, while almost completely neglecting Quaternary deposits. This work is the first broader analysis of Quaternary sedimentary deposits in the research area, which offers an insight into the complex geomorphological and sedimentological processes, which shape the current mountainous landscape.

First record of Annonaceae wood for the Neogene of South America, Amazon Basin, Brazil

ABSTRACT: The relief of the regions of Manaus and Itacoatiara, Central Amazon, is supported by Neogene siliciclastic rocks, bounded at the base and top by lateritic paleosols and covered by quaternary sedimentary deposits from the Solimões-Amazon river system. This unit is informally assigned to the Novo Remanso Formation, consists of usually reddish and ferruginized sandstones, conglomerates and pelites, with few identified fossil records, a fact that has hindered its stratigraphic position, and the paleoenvironmental reconstruction of the last phase of the Amazon Basin settling. This study describes, for the first time, the occurrence of fossil wood in outcroppings of the left bank of the Amazon River, where anatomical and morphological data has enabled its characterization to the species level. Thus, the data marks the record of the Annonaceae in South America, as well as the depositional processes related to incorporation of organic material in the sandy layer and the fossilization processes that allowed its preservation. In an unprecedented way, this study has described Duguetiaxylon amazonicum nov. gen and sp. and provided information on the anatomical and systematic character, as well as data on plant-insect interaction, and a better understanding of the family.

Mapping Neogene and Quaternary sedimentary deposits in northeastern Brazil by integrating geophysics, remote sensing and geological field data

Neogene and late Quaternary sedimentary deposits corresponding respectively to the Barreiras Formation and Post-Barreiras Sediments are abundant along the Brazilian coast. Such deposits are valuable for reconstructing sea level fluctuations and recording tectonic reactivation along the passive margin of South America. Despite this relevance, much effort remains to be invested in discriminating these units in their various areas of occurrence. The main objective of this work is to develop and test a new methodology for semi-automated mapping of Neogene and late Quaternary sedimentary deposits in northeastern Brazil integrating geophysical and remote sensing data. The central onshore Paraíba Basin was selected due to the recent availability of a detailed map based on the integration of surface and subsurface geological data. We used airborne gamma-ray spectrometry (i.e., potassium-K and thorium-Th concentration) and morphometric data (i.e., relief–dissection, slope and elevation) extracted from the digital elevation model (DEM) generated by the Shuttle Radar Topography Mission (SRTM). The procedures included: (a) data integration using geographic information systems (GIS); (b) exploratory statistical analyses, including the definition of parameters and thresholds for class discrimination for a set of sample plots; and (c) development and application of a decision-tree classification. Data validation was based on: (i) statistical analysis of geochemical and airborne gamma-ray spectrometry data consisting of K and Th concentrations; and (ii) map validation with the support of a confusion matrix, overall accuracy, as well as quantity disagreement and allocation disagreement for accuracy assessment based on field points. The concentration of K successfully separated the sedimentary units of the basin from Precambrian basement rocks. The relief–dissection morphometric variable allowed the discrimination between the Barreiras Formation and the Post-Barreiras Sediments. In addition, two units of the latter (i.e., PB1 and PB2) previously mapped in the field were promptly separated based on Th concentration. A regression analysis indicated that the relationship between geophysical and geochemical values obtained for the PB1, PB2 and Barreiras Formation is significant (R-squared = 0.91; p-value <0.05). Map validation presented a high overall accuracy of 84%, with a coefficient of quantity disagreement of 12% and a coefficient of allocation disagreement of 8%. These results indicate that the methodology applied in the central onshore Paraíba Basin can be successfully used for mapping the Barreiras Formation and Post-Barreiras Sediments in other areas of the Brazilian coast. The ability to rapidly and precisely map these units using such methodology could reveal their geographic distribution along the northeastern coast of Brazil.

Late Quaternary fluvial terrace evolution in the main southern Amazonian tributary

Late Quaternary sedimentary deposits from Amazonian lowlands are important geological archives for understanding the origin, evolution and controls of the largest fluvial drainage basin on Earth. Climate has been most often claimed as the main factor affecting river evolution in this region. An increasing volume of publications have also highlighted tectonics as a relevant control. This work investigates the late Quaternary evolution of the Madeira River, the biggest southern tributary of the Amazonas Basin and a major waterway in South America, with the goal of discussing the factor with highest potential of influence on its development in space and time. The approach consisted of carrying out a detailed morphological, sedimentological and chronological characterization of terrace deposits. Three terraces were recognized, which record sandy/pebbly channel, muddy channel/oxbow lake, point bar, floodplain, as well as crevasse channel, crevasse splay and levee deposits. The topographically highest terrace T1 formed in the time interval before 43,500 and 31,696–32,913calyrs BP, the intermediate terrace T2 between 25,338–26,056 and 14,129–14,967calyrs BP, and the lowest terrace T3 between 12,881–13,245 and 3158–3367calyrs BP. These terraces are the testimony of successive downcutting and sediment aggradation. Episodes of terrace erosion and deposition cannot be fully accommodated within the framework of fluctuating river base level tied to Late Pleistocene–Holocene global or regional climate fluctuations. Changes in tectonic subsidence rates might have played an important role in the equilibrium state of this particular fluvial system.

Radon levels in groundwaters and natural radioactivity in soils of the volcanic region of La Garrotxa, Spain

Groundwater radon level and soil radionuclide concentration have been measured in the volcanic region of La Garrotxa (Catalonia, Spain) to further research on the origin and dynamics of high radon levels over volcanic materials found in this region. Water samples from different aquifers have been collected from wells and springs and the water radon levels obtained have been lower than 30 Bq l−1. Soil samples have been collected from different geological formations (volcanic and non-volcanic), being Quaternary sedimentary deposits those that have presented the highest mean values of 40K, 226Ra and 232Th concentrations (448 ± 70 Bq kg−1, 35 ± 5 Bq kg−1 and 38 ± 5 Bq kg−1, respectively). Additionally, indoor/outdoor terrestrial radiation absorbed dose rate in air have been measured to better characterize the region from the radiological point of view. Terrestrial radiation absorbed dose rates measurement points have been chosen on the basis of geological and demographical considerations and the results obtained, from 27 to 91 nGy h−1, show a clear relation with geological formation materials. The highest terrestrial gamma absorbed dose rate is observed over Quaternary sedimentary deposits as well. All these results help to better understand previous surveys related with indoor and outdoor radon levels and to reinforce the hypotheses of a radon transport through the fissure network.

Pliocene–Quaternary evolution of the continental shelf of central Vietnam based on high resolution seismic data

The continental shelf of central Vietnam is characterized by complex geological structures in a strike-slip setting and thus by unique morphology compared to other parts of the Vietnam shelf. Studying the Pliocene–Quaternary sediments in this area allows the processes that control the stratigraphic evolution to be highlighted. In this paper, we present new results derived from high resolution seismic data that reveal the geological evolution of the continental shelf of central Vietnam during the Pliocene–Quaternary. Our results demonstrate that the continental shelf of central Vietnam is narrow relatively to other parts of the Vietnam shelf. The evolution of the shelf during the Pliocene–Quaternary was controlled by the pre-Pliocene rifting process. However, fault systems below the present shelf were not strongly active during the Pliocene–Quaternary period, except for several listric faults in the slope. Nonetheless, Quaternary volcanic activities occurred widely both offshore and onshore, especially near the major faults. The Pliocene–Quaternary sedimentary deposits were subdivided into 7 units based on unconformities as result of marine regression corresponding to glacial cycles. Sedimentary environments during this period consist of coastal plain, fluvial, nearshore and shelf environments. Most of the Holocene sediments were trapped nearshore while the outer shelf is characterized by abundant lag gravels as a result of rapid sea level rise between ∼20 and 8ka.

East-west extension in the NW Indian Himalaya

Research Article| September 01, 2010 East-west extension in the NW Indian Himalaya Esther Hintersberger; Esther Hintersberger * 1Institut für Geowissenschaften, Universität Potsdam, Karl-Liebknecht-Strasse 24, 14476 Potsdam, Germany *E-mail: estherh@geo.uni-potsdam.de Search for other works by this author on: GSW Google Scholar Rasmus Ch. Thiede; Rasmus Ch. Thiede † 1Institut für Geowissenschaften, Universität Potsdam, Karl-Liebknecht-Strasse 24, 14476 Potsdam, Germany †Current address: ETH Zürich, Geologisches Institut, NO E 45, Sonneggstrasse 5, 8092 Zürich, Switzerland; e-mail: rasmus.thiede@erdw.ethz.ch Search for other works by this author on: GSW Google Scholar Manfred R. Strecker; Manfred R. Strecker § 1Institut für Geowissenschaften, Universität Potsdam, Karl-Liebknecht-Strasse 24, 14476 Potsdam, Germany §E-mail: strecker@geo.uni-potsdam.de Search for other works by this author on: GSW Google Scholar Bradley R. Hacker Bradley R. Hacker # 2Institute for Crustal Studies, University of California, Santa Barbara, California 93106-9630, USA #E-mail: hacker@geol.ucsb.edu Search for other works by this author on: GSW Google Scholar GSA Bulletin (2010) 122 (9-10): 1499–1515. https://doi.org/10.1130/B26589.1 Article history received: 01 Dec 2008 rev-recd: 01 Jun 2009 accepted: 01 Jul 2009 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 Esther Hintersberger, Rasmus Ch. Thiede, Manfred R. Strecker, Bradley R. Hacker; East-west extension in the NW Indian Himalaya. GSA Bulletin 2010;; 122 (9-10): 1499–1515. doi: https://doi.org/10.1130/B26589.1 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 Explaining the presence of normal faults in overall compressive settings is a challenging problem in understanding the tectonics of active mountain belts. The Himalayan-Tibetan orogenic system is an excellent setting to approach this problem because it preserves one of the most dramatic records of long-term, contemporaneous shortening and extension. Over the past decades, several studies have described extensional features, not only in the Tibetan Plateau, but also in the Himalaya. For a long time, the favored model explained the function of the Southern Tibetan detachment system, a major fault zone in the Himalaya, as a decoupling horizon between the regime of crustal shortening forming the Himalayan wedge to the south and the extensional regime of the Tibetan Plateau to the north. However, in recent years, increasing evidence has shown that N-S–trending normal faults in the Central Himalaya crosscut not only the Southern Tibetan detachment system, but also the Main Central thrust.Here, we present new structural data and geologic evidence collected within the NW Indian Himalaya and combine them with previously published seismicity data sets in order to document pervasive E-W extension accommodated along N-S–trending faults extending as far south as the footwall of the Main Central thrust. We conducted a kinematic analysis of fault striations on brittle faults, documented and mapped fault scarps in Quaternary sedimentary deposits using satellite imagery, and made field observations in the Greater Sutlej region (Spiti, Lahul, Kinnaur) and the Garhwal Himalaya. Studies of extensional features within the regionally NW-SE–trending NW Indian Himalaya provide the advantage that arc-parallel and E-W extension can be separated, in contrast to the Central Himalaya. Therefore, our observations of E-W extension in the Indian NW Himalaya are well suited to test the applicability of current tectonic models for the whole Himalaya. We favor the interpretation of E-W extension in the NW Indian Himalaya as a propagation of extension driven by collapse of the Tibetan Plateau. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Sedimentação e deformação tectônica cenozoicas na porção central da Bacia Potiguar

Neogene and Quaternary sedimentary covers occur along the Brazilian coast and have been frequently described together as a single unit. The study of Brazilian sedimentary basins concentrates on their rift phase, whereas the post-rift phase has been considered a tectonic quiescent period. In the Potiguar basin, although post-rift Cretaceous units are well investigated, the Neogene and Quaternary sedimentary covers, as well as their identification and differentiation, are still poorly known. A few previous studies have demonstrated that post-rift sedimentary units with no apparent deformation have a complex deformation pattern in all scales of observation. The study of this deformation, however, did not include Neogene and Quaternary units. The main aim of the present study is the characterization of Neogene and Quaternary sedimentary units that outcrop in the central part of the Potiguar Basin, State of Rio Grande do Norte, Brazil, and related tectonics. The study has concentrated on the description of the Barreiras Formation and overlying Quaternary alluvial, marine, and aeolian deposits at 1:100,000 scale. Facies analyses, grain size studies, and luminescence dating were carried out. Ten informal and formal lithostratigraphic sedimentary units were described, in addition to the Precambrian crystalline basement. The main results indicate that several Quaternary alluvial deposits were previously mapped as the Miocene Barreiras Formation. It was possible to locate the new boundaries of the Quaternary sedimentary deposits and their stratigraphic relationships with older units. In addition, it was possible to identify the major fault systems in the basin that show NW- and NE-trending directions, which coincide with macro landforms. It follows that these major fault systems, mainly the NW-trending system, control the deposition of Neogene and Quaternary sedimentary units.

Definição de níveis aceitáveis baseados no risco para hidrocarbonetos no Município de Porto Alegre segundo a metodologia RBCA

O presente estudo definiu valores de NABR (Níveis Aceitáveis Baseados no Risco) para hidrocarbonetos no Município de Porto Alegre, de acordo a metodologia RBCA, adotando-se dados hidrogeológicos dos compartimentos Embasamento Cristalino alterado e Depósitos Sedimentares Quaternários. Os parâmetros de exposição adequados à população do município, bem como dados de toxicidade dos compostos selecionados, foram definidos a partir de fontes bibliográficas e bancos toxicológicos disponíveis. As tabelas de referência geradas são, em geral, mais restritivas para o Embasamento Cristalino em relação aos Depósitos Sedimentares. Comparados às tabelas de referência da Cetesb, os valores correspondentes a Porto Alegre são inferiores, resultando na necessidade de investigações ambientais mais detalhadas em áreas impactadas por hidrocarbonetos.

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.

Electrical resistivity tomography investigations in the ufita Valley (southern Italy).

Several Electrical Resistivity Tomography (ERT) surveys have been carried out to study the subsurface structural and sedimentary settings of the upper Ufita River valley, and to evaluate their efficiency to distinguish the geological boundary between shallow Quaternary sedimentary deposits and clayey bedrock characterized by moderate resistivity contrast. Five shallow ERTs were carried out across a morphological scarp running at the foot of the northeastern slope of the valley. This valley shoulder is characterized by a set of triangular facets, that some authors associated to the presence of a SW-dipping normal fault. The geological studies allow us to interpret the shallow ERTs results obtaining a resistivity range for each Quaternary sedimentary deposit. The tomographies showed the geometrical relationships of alluvial and slope deposits, having a maximum thickness of 30-40 m, and the morphology of the bedrock. The resistivity range obtained for each sedimentary body has been used for calibrating the tomographic results of one 3560m-long deep ERT carried out across the deeper part of the intramountain depression with an investigation depth of about 170 m. The deep resistivity result highlighted the complex alluvial setting, characterized by alternating fine grained lacustrine deposits and coarser gravelly fluvial sediments.

Liquefaction Susceptibility Mapping in Boston, Massachusetts

The Boston, Massachusetts, metropolitan area has experienced several historic earthquakes of about magnitude 6.0. A compilation of surficial geologic maps of the Boston, Massachusetts, metropolitan area and geotechnical analyses of Quaternary sedimentary deposits using nearly 3,000 geotechnical borehole logs reveal varying levels of susceptibility of these units to earthquake-induced liquefaction, given the generally accepted design earthquake for the region (M6.0 with 0.12 g Peak Ground Acceleration (PGA)). The majority of the boreholes are located within the extensive downtown artificial fill units, but they also allow characterization of the natural deposits outside the downtown area. The geotechnical data were complemented with surficial geologic mapping, combining published and unpublished geologic maps, aerial photographic interpretation, and soil stratigraphy data from an additional 12,000 geotechnical boring logs. Susceptibility maps were developed based on liquefaction-triggering threshold ground motions, which were determined using the borehole data. We find that much of the non-engineered artificial fill that underlies the downtown Boston area is, when saturated, highly susceptible to liquefaction during seismic loading. Holocene alluvial and marsh deposits in the region are also moderately to highly susceptible to liquefaction. Much of the outlying area is underlain by Pleistocene and Quaternary glacial and glaciofluvial deposits, which have low to moderate susceptibility to liquefaction. This study provides data needed to effectively manage liquefaction hazards in the Boston area, and it will assist in characterizing seismic hazards, mitigating risks, and providing information for urban planning and emergency response.

The place of aeolian coversands in the geomorphic evolution of the southern Cape coast, South Africa

The complex geomorphology of South Africa’s southern Cape coastal belt comprises Gondwana components and a suite of Quaternary sedimentary deposits, superimposed on the older landscape. Of these, the Wilderness aeolianites have previously been reported. This paper is the second of two which focus on the inland coversands. It has a three-fold purpose. Firstly, it provides new information on the sedimentology and geomorphic context of the coversands. Secondly, it suggests a temporal setting for the emplacement of the coversands. Thirdly, the relationship between the coversands, landscape evolution, the Wilderness aeolianites, and the potential of the coversands to serve as indicators of environmental change are examined. The description is preceded by a synopsis of the development of the southern Cape coastal belt. The gross geomorphology of the region was well established by the Middle Pleistocene, but that landscape has been modified since then, and into the Holocene, by sea level and climatic fluctuations. Evidence for southern Cape Quaternary sand deposits predating MIS 5 is only now emerging. The coversands examined in this paper are demonstrated to be both temporally and spatially discrete from the younger coastal aeolianite deposits. A Middle Pleistocene age is tentatively ascribed to the coversands.

Preserving the palaeoenvironmental record in Drylands: Bioturbation and its significance for luminescence-derived chronologies

Luminescence (OSL) dating has revolutionised the understanding of Late Pleistocene dryland activity. However, one of the key assumptions for this sort of palaeoenvironmental work is that sedimentary sequences have been preserved intact, enabling their use as proxy indicators of past changes. This relies on stabilisation or burial soon after deposition and a mechanism to prevent any subsequent re-mobilisation. As well as a dating technique OSL, especially at the single grain level, can be used to gain an insight into post-depositional processes that may distort or invalidate the palaeoenvironmental record of geological sediment sequences. This paper explores the possible impact of bioturbation (the movement of sediment by flora and fauna) on luminescence-derived chronologies from Quaternary sedimentary deposits in Texas and Florida (USA) which have both independent radiocarbon chronologies and archaeological evidence. These sites clearly illustrate the ability of bioturbation to rejuvenate ancient weathered sandy bedrock and/or to alter depositional stratigraphies through the processes of exhumation and sub-surface mixing of sediment. The use of multiple OSL replicate measurements is advocated as a strategy for checking for bioturbated sediment. Where significant OSL heterogeneity is found, caution should be taken with the derived OSL ages and further measurements at the single grain level are recommended. Observations from the linear dunes of the Kalahari show them to have no bedding structure and to have OSL heterogeneity similar to that shown from the bioturbated Texan and Florida sites. The Kalahari linear dunes could therefore have undergone hitherto undetected post-depositional sediment disturbance which would have implications for the established OSL chronology for the region.