Unit S2 Research Articles

Evolution of the Manabí forearc basin in Ecuador: From the collision of Caribbean oceanic plateau to the build up of the Andes and Coastal Cordilleras

We investigate the evolution of the onshore Manabí forearc basin in Ecuador, which has developed on accreted oceanic terranes. We use 2D seismic profiles to identify 10 seismic units, separated by 9 unconformities. These units were dated by correlation with Ricaurte-1 well and regional stratigraphy. Unit S1 represents the first depocenter developed on the oceanic plateau before accretion. The emplacement of NE-dipping oceanic plateau slices evidencing the accretionary process dated to ∼75 Ma (Unconformity U1), was followed by folds and east-dipping thrusts at the Andes foothills that were eroded by unconformity U2 (56–41.3 Ma hiatus). The large distribution of unit S3 (late Eocene-Oligocene) over the topography inherited from the collision, points to the configuration of the post-collision forearc basin. The geometry of slope front fill and the thickening of unit S4 at the foot of the Andes reveals the building of Andean reliefs during the early Miocene. Unit S5 (17.8–15.9 Ma) is fan-shaped and abuts against the Jama fault, evidencing local extensional. After unconformity U5 (∼16 Ma), differential subsidence causes the installation of a westward-prograding sedimentary platform during the middle to late Miocene (S6 to S8). Since the Pliocene, the uplift of the Coastal Cordillera is related to localized shortening across the Jama and Canandé faults. Enhanced tectonic erosion at the tip of the margin,likely related to the Carnegie ridge subduction, could have led to underplating of offscraped material beneath the Coastal Cordillera, contributing to the uplift and enlargement of the Coastal Cordillera. The Pleistocene eastward tilt of the Santo Domingo fan (unit S10) relates to the Coastal Cordillera uplift. The fan is then deformed along the Andean thrust. This study provides a remarkable example of a forearc basin-fill developed on accreted oceanic terranes and controlled by erosional and underplating subduction processes, reactivation of inherited crustal structures, and the rise of peripheral reliefs.

Palynofloras, palaeoenvironmental change and the inception of the Paleocene Eocene Thermal Maximum; the record of the Forties Fan, Sele Formation, North Sea Basin

The Paleocene–Eocene Thermal Maximum (PETM) has previously been recorded in marine density flow sedimentary rocks of the Forties Member, Sele Formation, North Sea Basin. Two cored well sections with existing δ 13 C records were analysed for their total palynofloras. Using statistically defined microplankton groups and diversity data, the Sele Formation Unit S1 depositional sequence and its maximum flooding surface was identified in both wells. This highlighted that deposition of the Forties Fan complex began significantly earlier than the inception of the PETM in the proximal fan area. Palynofloras from the Central and West Axial fairways of the Forties Fan have previously been used to indicate increased rainfall, erosion and onset of Forties Fan deposition at the PETM inception. However, winterwet floodplain communities typify the coeval East Axial Fairway, whereas the dominance of swamp-derived communities in the West and Central Axial Fairway sediments reflects source palaeogeography overriding the regional winterwet climate signal. Palynofloras reflecting regional increased seasonality and lower moisture availability increase immediately before the PETM CIE onset, but reflect climate warming over the hyperthermal. However, there is no correlation between Forties Fan initiation and the PETM. NE Atlantic margin basin flank uplift in response to synrift volcanism is indicated as the driving mechanism behind Forties Fan inception. Supplementary material : Raw data, DCA graphs for microplankton, pollen and spore data and δ 13 C data for well 22/6-1 are available at https://doi.org/10.6084/m9.figshare.c.6080873

Comparative study on stepped solar distillers internally loaded with different masses of phase change material

This experimental work discusses the thermo-enviro-economic analyses for effect of mass of paraffin wax as phase change material (PCM) on solar distillation in inclined stepped solar still (SSS). Three identically designed SSS units, namely, S1, S2, and S3 respectively, laden with 0.45, 0.90, and 1.35 kg of PCM filled in copper tubes are fabricated and tested at 25 mL/min flow rate. The findings of the experimental study manifested that the performance of SSS unit is significantly improved as the mass of the PCM is increased. The amount of distillate produced by units S1, S2, and S3 are respectively, 1.99, 2.12, and 2.18 kg. The distillate obtained from S3 unit is 8.4% and 2.6% more than S1 and S2 units, respectively. The average values of energy and exergy efficiencies of this unit are evaluated as 31.53% and 2.15%, respectively. This unit is capable to mitigate 8.28 t of CO2 per year which is 7.6% and 2.1% higher than that of units S1 and S2, respectively. Carbon credit earned by units S1, S2 and S3 are respectively, $114.78, $121.58, and $124.23. The carbon credit earned from S3 unit is the highest among tested units which inferred that unit S3 is environmentally friendlier. The total productive cost of environmentally and thermally supreme unit S3 is evaluated as $0.30 which is 6.67% and 3.34% higher than that of S1 and S2 units, respectively. The study shows that the use of PCM in solar distillation has the potential to improve its productivity which helps to eradicate the scarcity of potable water. Highlights The effect of mass of paraffin wax loading on the performance of stepped solar still is presented. Thermo-enviro-economic performance of system is observed to improve with increase in mass of paraffin wax loading. The system loaded with 1.35 kg paraffin wax is found best in environmental conservation and can mitigate 8.28 t CO2 per year. The total productive cost per day of the unit having maximum mass of paraffin wax is $0.30.

Assessment of a solar powered sustainable energy recovery system for cleaner production of concentrated sugarcane juice

A sustainable energy recovery system (SERS) having series of stepped solar stills (units S1, S2 and S3) is examined for cleaner production of concentrated sugarcane juice (CSJ). The supply of overflowing energized sugarcane juice in S2 and S3 units of SERS makes them to operate in active mode that instigate us to perform this experimental work. The performance of SERS based on thermal, environment and economic aspects, is also compared with a simple stepped solar still system (S4S) of equal area (0.75 m2) at 40, 50, and 60 ml/min flow rates. In this modernized strategy of CSJ production, distilled water is collected as waste recovery product with energy and environmental conservation. The performances of SERS and S4S are found optimum at 50 ml/min and SERS is found superior. The maximum brix content for SERS is 27.4oB with distillate output of 3777.1 g. The average values of hc, he, and hr for SERS are respectively, 2.11, 26.01 and 7.13 W/m2 oC. The annual CO2 mitigation, embodied energy, thermal efficiency, and exergy efficiency for SERS are respectively, 14.66 tonnes, 213.1 kWh, 47.84%, and 8.68%. The distillate and total productive costs per day for SERS are found to be $0.016 and $0.74, respectively.

Seismic record of a cyclic turbidite-contourite system in the Northern Campos Basin, SE Brazil

A new mixed turbidite-contourite system is described in the northern Campos Basin, southeastern Brazilian margin. This system is developed in a middle slope setting, and was formed through non-synchronous interaction between the turbidity current and a contour current in the same stratigraphic interval (Miocene). Depositional cycles were differentiated based on diagnostic seismic features. Seismic attributes, seismic facies, and isochron maps were used to identify alternating cycles of downslope and alongslope processes in the study area, along with the intermediate stage with features from both processes (mixed system). Seismic units were then associated with the dominant type of current. Alongslope current activity can be distinguished from the downslope current based on its acoustic characteristics (mainly low root-mean-square (RMS) amplitude values), internal architecture (clinoforms), and external geometry pattern (alongslope trend).On the other hand, downslope gravity currents develop deposits with high-amplitude or chaotic seismic facies, usually higher values of RMS amplitude, channel or channel-lobe features, erosive surfaces, and a basinward depositional trend. The first and oldest seismic unit (S1) was interpreted as a dominantly alongslope system, with vertical aggrading sigmoidal clinoforms and high-frequency, low-amplitude reflections commonly associated with fine-grained sedimentary deposits, typical of a plastered drift, along with a basinward mass transport deposit (MTD) from previous drift instability. Seismic unit S2 represents the intermediate stage where both gravity-driven and along-slope currents act asynchronously. Its is refered to as a mixed turbidite-contourite sequence that shows high-amplitude sediment waves migrating upslope and a moat feature that is carved in its upslope front. The interfingering between high- and low-amplitude reflectors, distal chaotic facies, together with sediment waves and a channel moat, points to a sand-rich deposit reworked by northward-flowing contour currents. Seismic units S3 and S4 show downslope features with chaotic facies (S3) and paleochannels with coarse basal lag deposits (high RMS amplitude values) (S4). In S4, a series of long-lived submarine channels formed. Last, seismic unit S5, referred to as the second plastered drift sequence, is marked by low-amplitude clinoforms that thin basinward. At the seafloor, submarine channel banks (formed at S4) covered by fine sediment deposits (from S5) show asymmetrical features with a slight northward depositional trend, indicating a northward-flowing bottom current, as the deposits are known to pile up in a downcurrent trend. Important information on the paleocurrents' direction was also made based on the final deposits display (e.g. terraces, sediment waves, paleochannels). Research on alternating dominant processes and transitional stages or mixed depositional systems, with both turbidites and contour currents, may provide a better understanding of deep-water depositional processes. Because these processes do not always fit previous depositional models that are mainly described for synchronous systems, new insights on cyclic non-synchronous mixed systems can improve our understanding of how mixed systems are organized through time and space. Being able to determine which were the dominant processes that controlled the sedimentation by indicating periods where the margin was mostly submitted to sediment transfer from continent to the basin and periods where the oceanic currents prevailed by redistributing sediments along the isobaths and replacing the axis of downslope transfer conduits. Setting new models on cyclic deposits and intermediate stages can have a future economic impact on potential hydrocarbon reservoir architecture.

Seismic stratigraphy of late Neogene - Quaternary units and evolutionary model in the inner sector of Bahia Blanca estuary (Argentina)

The Quaternary sedimentary deposit of the inner sector of Bahía Blanca estuary (BBE), Argentina, was studied using high-resolution seismic profiles, core samples and correlation with continental – marine units outcropping in the continent. We interpreted four prominent seismic reflection surfaces and the acoustic basement which together defined five seismic stratigraphic units (S0, S1, S2, S3, S4) and four related systems tracts. Studying those units, we proposed a fourth Stage deposition evolutionary model that took place in a relative sea-level fluctuation context after the Miocene in the BBE area. The first stage contained the deposition of the regressive seismic units S0 and S1. The S0 was determined as an acoustic basement. The top of the S0 erosional surface (SU) was determined and it was formed by subaerial processes during the Late Pleistocene fall in sea-level and the following marine reworking during transgression. The unit was correlated with the oldest continental Miocene loess deposit and was associated with an Early Lowstand Systems Tract (ELST). Unit S1 was associated with a Late Lowstand Systems Tract (LLST). An irregular stratigraphic surface was observed above it. It was inferred as a Maximum Regressive Surface and the Ravinement Surface (RS/MRS) which are related to a maximum regression and subsequent transgression. The S1 unit was correlated with Pliocene-Pleistocene continental deposits. The Miocene - Pleistocene coastline movement in this sector would be associated with both Neogene Andean dynamics and the Last Maximum Glacial. After that, during the second Stage in the Late Pleistocene - middle Holocene the sea-level on the Bahia Blanca coast rose and unit S2 was formed. We interpreted unit S2 as a Transgressive System Tract which developed until the maximum sea-level of the Mid-Holocene. The coastline extension on the continent conformed the Maximum Flooding Surface. After a stabilization period to the mid Holocene, the sea-level started falling, offering conditions for the deposition of the High Stand System Tract (S3 – S4). Following stabilization, the third Stage took place and a progradation unit S3 was deposited overlying the MFS and a minor stratigraphic surface Bedset Boundary (BsB) separated this unit from S4. During the fourth phase, the sea-level continued to fall until the present level and the last HST (S4) was interpreted, which is interpreted as an aggradational – progradational deposit formed in the Middle Holocene to the present day by a change in the rate of sediment supply or energy flux.

EVALUASI KESESUAIAN LAHAN TANAMAN PADI DAN BUAH-BUAHAN BERDASARKAN AGROEKOSISTEM DAN AGROEKONOMI DI DESA TANGGUWISIA DAN JOANYAR, KECAMATAN SERIRIT, KABUPATEN BULELENG, BALI.

Agroecosystem and agroeconomic evaluation of land suitability for fruit and rice agriculture in Tangguwisia and Joanyar Village, Seririt District, Bali, Indonesia. This research was conducted in the Tangguwisia Village and Joanyar Village, Seririt District, Buleleng Regency, Bali, from January to April 2011. The goals of this study were to determine the suitability of land-based agroecosystems and agroeconomies for rice and fruit crops from an agroeconomic perspective and at the level of the subclass, to understand the characteristics and qualities of the land that allow for increased production of rice and fruits and to create thematic maps of land suitability for rice plant, banana, mango, rambutan, durian, and grape in the agriculturally viable area. Land suitability was evaluated in several stages. First, a preparation phase was followed by the classification of land units (S1, S2, S3 and N). Agroecosystems with extremely agriculturally suitable soil were labelled (S1), systems with reasonably suitable soil were labelled (S2), systems with marginally suitable soil were labelled (S3) and systems considered completely unsuitable for agriculture were labelled (N). Sample points were determined and field surveys were conducted followed by soil analysis and data collection. This data was used to determine agroeconomic and agroecosystem suitability, and to make land-use planning recommendations, all of which culminated in the production of a land suitability map. Existing rice agroecosystems S2, S3 and N were found to be suitable for rice, with slope and texture as limiting factors. Land sections S3 and N were found to be suitable for bananas, with rainfall, dry season length, texture, slope and erosion as limiting factors. Land sections S2, S3 and N were found to be suitable for mango agriculture with rainfall, texture, slope, surface rock, and erosion as limiting, banana, mango, rambutan, and durian). S1 was found to be most suitable to the growing of grapes factors. Rambutan and durian cultivation was found to be best suited to the conditions in land unit N, with rainfall and texture as limiting factors. Vines were found to be suitable in section S2, S3 and N, with dry season length, texture, drainage, slope and erosion as limiting factors. Land units S1 and S2 were found to be suitable to the widest variety of crops (rice).

Seismic-based identification and stage analysis of overlapped compound sedimentary units in rifted lacustrine basins: An example from the Bozhong sag, Bohai Bay Basin, China

Using recently acquired three-dimensional seismic data, we summarize typical patterns for seismic-based identification and stage analysis of sedimentary units in the Eocene succession of the southern slope-break belts of the Bozhong sag, Bohai Bay Basin, China. The sedimentary units in the study area are characterized by progradational reflectors and mound-shaped, bidirectional downlapping reflectors in dip and strike directions, respectively. Differential characteristics of a distinct sedimentary unit within one lobe are documented. The major provenance direction is defined and characterized by the largest dip angles of reflectors, the longest transport distance of sediments, and the thickest deposits in comparison to other dip directions—all recognized in this study and serving as typical characteristics for sedimentary unit identification and separation from the overlapped sedimentary complex. This study also summarizes diverse patterns—including collateral and prograding types—of sedimentary unit contact relationships and stage analysis along dip and strike directions. Collateral patterns are composed of three subtypes: superimposed, antithetic, and isolated. Three sedimentary units—S1, S2, and S3—are recognized in the study area. Summarized patterns of sedimentary unit contact relationships indicate that S1 was deposited earliest and S3 latest. The proposed patterns supplement seismic-based sedimentologic studies. This work may serve as a useful reference for sand-body characterization and stage analysis in other basins and similar areas.

Magnetic motion of spherical frictional charged particles on the unit sphere

Mathematically, the sphere unit S² is described to be a 2-sphere in an ordinary space with a positive curvature. In this study, we aim to present the manipulation of a spherical charged particle in a continuous motion with a magnetic field on the sphere S² while it is exposed to a frictional force. In other words, we effot to derive the exact geometric characterization for the spherical charged particle under the influence of a frictional force field on the unit 2-sphere. This approach also helps to discover some physical and kinematical characterizations belonging to the particle such as the magnetic motion, the torque, the potential energy functional, and the Poynting vector.

Seasonal dynamics of bacterial communities associated with antibiotic removal and sludge stabilization in three different sludge treatment wetlands

In this study, antibiotics removal, sludge stabilization and the change in the bacterial community in sludge treatment wetlands (STWs) were investigated in different seasons. Pilot-scale STWs were characterized for sludge stabilization and the fate of antibiotics in surplus sludge applied during different seasons in three different configurations. The three configurations were unit S1 with ventilation, unit S2 with ventilation and reed plantings and unit S3 with reed plantings. The antibiotics used were ciprofloxacin, azithromycin and oxytetracycline and their degradation, degree of sludge stabilization and bacterial community dynamics were monitored. The results showed that the removal of antibiotics and reduction in the amount of organics in the planted units S2 and S3 were higher than those in the unplanted unit S1, especially in summer. The antibiotic removal efficiency in the planted unit S2, which was equipped with aeration tubes, was the highest over the entire test period. Bacterial community was analyzed by IlluminaMiSeq sequencing of the 16SrRNA gene, showed that the presence of plants in STWs enhanced microbial diversity and richness which promote the removal of antibiotics and sludge stabilization. Proteobacteria, Bacteroidetes and Firmicutes were dominant in the bacterial communities, with Thiobacillus, Dechloromonas and Pseudomonas occurring as dominant genera.

Fate of antibiotics in three distinct sludge treatment wetlands under different operating conditions

Sludge treatment wetlands (STWs) have recently been used to treat surplus sludge. However, the distribution of antibiotics involved in the process has not been comprehensively investigated.This study aimed to evaluate the fate of two antibiotics, i.e., ciprofloxacin (CIP) and azithromycin (AZM) in STWs during the treatment of surplus sludge. Three pilot-scale STWs units—S1 with aeration tubes, S2 with aeration tubes and reed planting, and S3 with reed planting—were constructed and operated under feeding followed by resting periods. The results showed that antibiotic content in residual sludge decreased over time and unit S2 performed the best in terms of antibiotic removal. Planting reed considerably improved the antibiotic removal performance of the STWs. Biodegradation and absorption resulted in removal of most of the antibiotics in the test units. Less than 2% of the antibiotics was taken up by plants, whereas <5% of the influent antibiotics left the STW units through the drainage discharge. Overall, STW units contributed to effectively decrease CIP and AZM to 41–72% and 49–84%, respectively.

Physical property characterization of quaternary sediments in the vicinity of the paleo-Seomjin River of the continental shelf of the South Sea, Korea

Thirty-two core samples were collected from the continental shelf area of the South Sea, Korea. They have been used to characterize physical properties in relation to sedimentary units (interpreted from seismic and core data) and to interpret physical property variation as a function of burial depth. The physical property data were readily classified into sedimentary units: Units S1, S2, S3, S4, and S5, in descending order. The variations in physical properties reflect well the relative characteristics of sedimentary units (equivalent to seismic units). Moreover, the relationships between physical properties are well grouped by each sedimentary unit. In addition, the distributions of physical properties match well with the grain size distribution and bathymetry of the study area. In particular, the lithology (e.g., grain size) plays an important role in the variation of physical properties. These results suggest that the physical properties of these sediments are mainly controlled by depositional processes in the vicinity of the paleo-Seomjin River, and that sea-level change specifically was a dominant sedimentary processes in the study area during the Quaternary. In particular, the physical properties of Unit S2 do not show transitional characteristics between Units S1 and S3, although it belongs to the transition zone in sequence order. This finding is attributed to the fact that compared with the sediments of Units S1 and S3, Unit S2 is composed of more coarse-grained sediments with abundant shell fragments.

Aeolian dust supply from the Yellow River floodplain to the Pleistocene loess deposits of the Mangshan Plateau, central China: Evidence from zircon U-Pb age spectra

The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the south bank of the lower reach of the Yellow River provide high-resolution records of Quaternary climate change. In addition, substantial increases in grain-size and accumulation rate have been inferred in the upper part of the loess sequence, above palaeosol layer S2. This study investigates the sources of the long-term dust supply to the MLP and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since S2 (∼240 ka) by using end member modelling of the loess grain-size dataset and single-grain zircon U-Pb dating. Our results indicate that the lower Yellow River floodplain, directly north of the MLP, served as a major dust supply for the plateau at least since the deposition of loess unit L9 and indirectly suggest that the integration of the Yellow River and the disappearance of the Sanmen palaeolake took place before L9 (∼900 ka). The sudden change in sedimentology of the Mangshan sequence above palaeosol unit S2 may result from an increased fluvial sediment flux being transported to the lower reaches of the Yellow River because of tectonic movements (initiated) in the Weihe Basin around 240 ka. Furthermore, sediment coarsening can be explained by the gradual southward migration of the lower Yellow River floodplain towards the MLP since the deposition of palaeosol S2. The migration is evidenced by the formation of an impressive scarp, and is likely caused by tectonic tilting of the floodplain area.

Late Cretaceous onset of current controlled sedimentation in the African–Southern Ocean gateway

During the breakup of Gondwana the Mozambique Ridge, a Large Igneous Province emplaced between 140 and 125Ma, was located in the evolving African–Southern Ocean gateway. Therefore, it represents an archive of the evolving exchange of water masses between the South Atlantic and Indian Ocean via the development of surface, intermediate, and bottom circulation. Two Cretaceous seismic units (S1 and S2a) were deposited on top of magmatic basement separated by a hiatus. Unit S1 mostly shows seismic reflections parallel to the top of the basement and no indications of current activity. The occurrence of several sediment drifts within seismic unit S2a indicates the onset of current controlled sedimentation. Based on our observations we propose deposition under partly euxinic conditions in the area of the Mozambique Ridge until ~100Ma. The onset of a strong shallow circulation affecting deposition at the Mozambique Ridge is inferred by the Late Cretaceous ~25Myr hiatus reported by drilling results and documented in the seismic records, whereas black shales deposited in the nearby deep Transkei Basin indicate a restricted deep circulation at least until ~85–80Ma. We propose that the observed hiatus might be a consequence of a late Early Cretaceous uplift of the Mozambique Ridge and the progressive opening of the Agulhas Passage allowing inflow of surface (Upper Pacific Water, Upper North Atlantic Water) and intermediate water (Intermediate Southern Ocean Water) into the study area. The intense circulation that caused the hiatus seems to have weakened in Campanian times, which is documented by the occurrence of sediment drifts in seismic unit S2a. We suggest that the onset of current controlled sedimentation was caused by palaeogeographic modifications in the Atlantic Ocean along with relocation of circulation pathways. Our results illustrate the crucial role of the African–Southern Ocean gateway in the commencing water mass exchange between the Atlantic and Indian Ocean and highlight the complex interactions that eventually lead to the initiation of a proto–Antarctic Circumpolar Current in Turonian times.

Sequence stratigraphy and evolution history of the continental shelf of South Sea, Korea, since the Last Glacial Maximum (LGM)

High-resolution seismic data (Chirp and Sparker profiles) were used to investigate the sequence stratigraphy and evolution of the continental shelf of the South Sea, Korea, since the Last Glacial Maximum (LGM). Approximately 1950 km of chirp and sparker profiles were acquired. Along with seismic profiling, 30 piston core samples were collected and two previous long drill cores (SSDP-103 and 104) were tied to the seismic data. Our data show nine types of seismic facies on the basis of seafloor morphology and sub-bottom acoustic characters. Based on the analysis of seismic profiles, shelf deposits of the South Sea accumulated after the onset of the LGM can be divided into five sedimentary units; S1 to S5, from top to bottom. Correlation between sediment cores and seismic data suggests that Unit S5 is an incised channel fill formed by fluvial or coastal sediments during the early transgressive stage, accompanied by backstepping of the shoreline. Unit S4 is a transgressive sand layer reflecting the deposition of coarse sediments due to the strong currents and tides, following the rapid retreat of the coastline. Unit S3 represents paleo channel- and basin-fill deposits formed in estuary or delta environments near the inner continental shelf. Unit S2 forms an inner shelf transgressive sand layer including sand ridges. Unit S1 is interpreted as the most recent mud formed during the sea level highstand stage when the sea-level rise ended. Our results show that the sedimentary evolution of the continental shelf of the South Sea, since the LGM, has been closely related to the sea-level changes. The distribution of paleo-channels is associated with the paleo-Seomjin River, local sediment supply, and continental shelf erosion.

Long-term Pleistocene aridification and possible linkage to high-latitude forcing: New evidence from grain size and magnetic susceptibility proxies from loess-paleosol record in northeastern China

Loess deposits are regarded as good indicators of the inception and development of arid and semi-arid climate in central Asia and northern China during the late Cenozoic. In northeastern China extensive loess deposits are found surrounding the Horqin and Otindag sand fields, and they have great potential for reconstructing the long-term aridification history of the region. However, these loess deposits are currently poorly understood. Here, we present a high-resolution magnetic susceptibility (MS) and grain-size record spanning the last 1.0Ma from a 36.6-m-thick loess-paleosol sequence at Niuyangzigou site (NYZG) in NE China. The grain-size record reveals a long-term drying trend in NE China since ca. 1.0Ma, punctuated by two significant abrupt drying events at ~0.65Ma and ~0.3Ma. These results demonstrate a process of stepwise intensification of drying in NE China over the past 1Ma, and lend support to the hypothesis that global ice volume/temperature changes were the major driver of the long-term aridification of Asian dust source areas. However, unlike the widely studied loess deposits on the central Chinese Loess Plateau (CLP), the MS record in paleosol units S1, S2 and S4 from the NYZG site do not show evidence of enhanced monsoon precipitation resulting from decreased global ice volume and the prolonged episodes of interglaciation after the Mid-Pleistocene Transition evident in the ice volume record. We hypothesize that this may be due to differences in the climatic sensitivity of the MS of Chinese loess deposits on a regional scale, rather than to in regional differences in monsoon intensity.

Paleomagnetism from Deception Island (South Shetlands archipelago, Antarctica), new insights into the interpretation of the volcanic evolution using a geomagnetic model

Deception Island shows the most recent exposed active volcanism in the northern boundary of the Bransfield Trough. The succession of the volcanic sequence in the island is broadly divided into pre- and post-caldera collapse units although a well-constrained chronological identification of the well-defined successive volcanic episodes is still needed. A new paleomagnetic investigation was carried out on 157 samples grouped in 20 sites from the volcanic deposits of Deception Island (South Shetlands archipelago, Antarctic Peninsula region) distributed in: (1) volcanic breccia (3 sites) and lavas (2 sites) prior to the caldera collapse; (2) lavas emplaced after the caldera collapse (10 sites); and (3) dikes cutting pre- and the lowermost post-caldera collapse units (5 sites). The information revealed by paleomagnetism provides new data about the evolution of the multi-episodic volcanic edifice of this Quaternary volcano, suggesting that the present-day position of the volcanic materials is close to their original emplacement position. The new data have been combined with previous paleomagnetic results in order to tentatively propose an age when comparing the paleomagnetic data with a global geomagnetic model. Despite the uncertainties in the use of averaged paleomagnetic data per volcanic units, the new data in combination with tephra occurrences noted elsewhere in the region suggest that the pre-caldera units (F1 and F2) erupted before 12,000 year BC, the caldera collapse took place at about 8300 year BC, and post-caldera units S1 and S2 are younger than 2000 year BC.

Characterizing and quantifying iron oxides in Chinese loess/paleosols: Implications for pedogenesis

To accurately decode the paleoclimatic and paleoenvironmental significance of magnetic properties in Chinese loess/paleosols, neoformation of magnetic iron oxides via pedogenesis as well as the relationship between ferrimagnetic (maghemite and magnetite) and antiferromagnetic minerals (hematite and goethite) of both detrital and pedogenic origins should be well determined. To resolve this problem, magnetic iron oxides from a contiguous loess–paleosol sequence (lower part of the loess unit L1, paleosol unit S1, and the upper part of L2) at Luochuan, Center of the Chinese Loess Plateau, were well characterized and quantified by using an integrated approach including chemical dissolution, diffuse reflectance spectroscopy and rock magnetism methods. Results showed that these magnetic minerals have distinct coercivity and dissolution behavior, which is highly grain size-dependent. More specifically, the paleosol is enriched with nano-sized pedogenic hematites with a medium coercivity of ~130mT, which are also preferentially dissolved in a weak reductive environment. In contrast, the coarse-grained micro-sized detrital hematites with a medium coercivity of ~1T are dominant in loess. In addition, these coarse-grained detrital hematites are more stoichiometric than their pedogenic counterparts as evidenced by the higher band position on the diffuse reflectance spectrum. Goethite can be well distinguished from hematite by its higher coercivity (4–7T) at low temperature (10K). The consistent dissolution behavior of goethite for both loess and paleosol samples in citrate–bicarbonate–dithionite solution indicates that goethite could be less relevant to the pedogenic processes. The reductive dissolution of pedogenic maghemite lags the dissolution of pedogenic hematite and fine-grained goethite, which suggests that average grain size of pedogenic maghemite is relatively larger than those of pedogenic hematite and fine-grained goethite. Detrital magnetite is hard to dissolve and ~50% of its initial remanence survived after dissolution. On the basis of these contrasting behaviors, pedogenic hematite, fine grained goethite and maghemite content was further quantified. Our results suggest that single domain pedogenic hematite was produced after initial formation of pedogenic maghemite. This provides direct evidence for the recently proposed pathway in which ferrihydrite is transformed into a transient maghemite-like phase before its final transformation into hematite.

Open System evolution of peralkaline trachyte and phonolite from the Suswa volcano, Kenya rift

Suswa is the southernmost volcanic center in the Central Kenya Peralkaline Province (CKPP) and represents the only salic center to have erupted significant volumes of peralkaline silica-undersaturated lavas and tuffs (trachyte, nepheline trachyte and phonolite). The eruptive products of Suswa can be clearly divided into two series, which correspond closely to the volcano's eruptive history. The earlier series (C1) includes lavas and tuffs that built the initial shield volcano (pre-caldera, unit S1) and erupted during the first caldera collapse (syn-caldera, units S2–S5); these rocks are dominated by peralkaline, silica-saturated to mildly under-saturated trachyte. The later series (C2) includes lavas and tuffs that erupted within the caldera structure following the initial collapse (post-caldera, units S6–S7) and during the creation of a second smaller, nested caldera and central “island block” (ring trench group, RTG, unit S8); these rocks are dominated by peralkaline phonolite. In this study, we combine mineralogical evidence with the results of major-element, trace-element, and thermodynamic modelling to propose a complex model for the origin of the Suswa volcano. From these results we conclude that C1 is the result of protracted fractional crystallization of a fairly “dry” alkali basalt (<1wt.% H2O) under relatively high pressure (400MPa) and low oxygen fugacity (FMQ to FMQ-1). Although C1 appears to be primarily the result of closed system processes, a variety of open system processes are responsible for C2. We propose that crystallization of C1 trachyte resulted in the formation of a syenitic residue, which was assimilated (Ma/Mc=0.1) during a later stage of recharge and differentiation of alkali basalt to produce post-caldera ne-trachyte. Post-caldera (S6-7) phonolites were in turn the result of fractional crystallization of this ne-trachyte. RTG phonolites, however, are the result of feldspar resorption prompted perhaps by magma recharge as evidenced by reverse zoning in alkali feldspar and linear compatible trace element patterns.

Pliocene paleoenvironment evolution as interpreted from 3D-seismic data in the southern North Sea, Dutch offshore sector

A high-resolution 3D-seismic survey from the Dutch offshore sector has been interpreted and subsequently correlated with existing regional seismo-stratigraphic concepts derived from conventional 2D-seismic data sets. The interpreted 13 seismic units have been related to a newly established chrono-stratigraphic framework [Kuhlmann et al., 2006a, b. Chronostratigraphy of Late Neogene sediments in the southern North Sea Basin and paleoenvironmental interpretations. Palaeogeography, Palaeoclimatology, Palaeoecology, 239, 426–455; Integrated chronostratigraphy of the Pliocene–Pleistocene interval and its relation to the regional stratigraphical stages in the southern North Sea region. Netherlands Journal of Geosciences-Geologie en Mijnbouw, 85(1), 19–35] resulting in up-dated age control for the seismic units. The generation of amplitude maps, time slices and isopach maps from the 3D-seismic data enabled detailed spatial and temporal reconstruction regarding the paleoenvironmental and climatological development as depicted by Kuhlmann et al. [2006a. Chronostratigraphy of Late Neogene sediments in the southern North Sea Basin and paleoenvironmental interpretations. Palaeogeography, Palaeoclimatology, Palaeoecology, 239, 426–455]. The lowermost seismic units S1–S4 comprise condensed Middle Miocene to Piacencian sediments, deposited under warm open marine conditions. These sediments show a uniform seismic facies of low-amplitude reflectors. The boundary of seismic unit S4–S5 (around 2.6 Ma) delineates a shift towards generally colder climate conditions that are connected to the onset of Northern Hemisphere Glaciation. Seismic unit S5 includes alternations of warmer and colder periods. During warmer periods, bottom currents generated elongated structures (2.5–4 km long, 300–500 m wide) on the horizon display. These layers show as well shallow gas accumulations with a more regional extent and are related to coarser-grained sediments sealed by clayey sediments of the cold phases. A homogenous seismic facies is characteristic for the colder periods. Within seismic units S6 and S7, internal fore set structures display the regressional trend related to the cooling of this interval. Seismic units S8–S11 display a pattern of unoriented lineaments which was probably caused by icebergs drifting into the North Sea and souring the sea floor. This finding is in accordance with the shallow marine, arctic conditions of this interval. Within these units a bright spot of 3 by 7 km in size, is interpreted to result from shallow gas accumulation related to a grounded iceberg. This feature represents another, more local area of gas accumulation that is closely related to iceberg activity within the study area. The uppermost seismic units S12 and S13 belong to a fluvial, paralic paleo-environment, that is characterised by aggradational seismic reflectors. Pleistocene glacial valleys were recognised in the upper 200 m below sea floor.