Pleistocene Holocene Deposits Research Articles

Multi-seismic cycle velocity and strain fields for an active normal fault system, central Italy

Vertical offsets of Late Pleistocene–Holocene deposits and landforms are combined with slip-direction indicators on dipping active normal faults in central Italy to produce velocity and strain-rate fields averaged since 12–18 ka for a 5 by 5 km grid. Maximum strain-rates of 0.078 ± 0.0156 ppm/yr, or 0.052 ± 0.01 ppm/yr across a distance of 63,639 m imply maximum NE–SW extension rates of 5.0 ± 1.0 mm/yr or 3.3 ± 0.66 mm/yr depending on whether rates are averaged over 12 ka or 18 ka. The high spatial resolution reveals that strain-rates vary by up to 0.04 ± 0.008 or 0.06 ± 0.012 ppm/yr over a distance of only c. 7 km along the strike of the fault system, again depending on the timescale chosen. For the first time, these data allow a comparison of rates derived over time periods that would contain numerous seismic cycles with those measured with GPS that represent either interseismic strain, or displacements due to a single large earthquake with some interseismic strain. Overall, the rates compare reasonably well with those measured geodetically or derived from seismic moment summations (< 0.12 ppm/yr and generally in the range of 0.10–0.06 ppm/yr; 6.36–3.82 mm/yr). However, the present wide spacing of geodetic sites (30–40 km) means that the small-scale spatial variations in strain-rate since 12–18 ka have not yet been resolved using GPS. This makes it difficult to compare strain measured geodetically with that released during historical earthquakes to assess whether excess strain will be released in an impending earthquake.

High-resolution stratigraphy of the Mediterranean outflow contourite system in the Gulf of Cadiz during the late Pleistocene: The impact of Heinrich events

A detailed, high-resolution stratigraphic analysis of the Mediterranean Outflow contourite system at the continental slope of the Gulf of Cadiz has been carried out through the correlation between a dense network of seismic reflection profiles (sparker, airgun, 3.75 kHz and parametric echosounder — TOPAS), Calypso giant piston and standard gravity cores. From such correlation we determine a stacking pattern constituted by four main seismic units (a–d) that are internally structured into ten subunits. Each subunit shows a single sequence formed by transparent seismic facies at the base to smooth, parallel reflectors of moderate to high amplitude facies at the top, being well correlated in the cores with a coarsening-upward sequence. The latest Pleistocene–Holocene deposits form glacial/interglacial depositional sequences related to cycles with a frequency range below the Milankovitch band that corresponds to millennial timescale climatic changes such as Dansgaard–Oeschger (1.5 ka) and Bond Cycles (10–15 ka). Oxygen isotope records of planktonic foraminifera and the occurrence of ice-rafted debris (IRD) in the most recent contourite subunits show clear evidence of the influence of the North Atlantic climatic conditions, especially the climatic Heinrich events (H) in the slope sedimentation of the Gulf of Cadiz and then in the circulation of the Mediterranean Outflow Water (MOW). The coarser contourite deposits are mostly associated with the Last Glacial Maximum, Younger Dryas and Heinrich events on the central area of the middle slope. During globally cooler conditions, the MOW was denser so that it was more active in deeper areas than today. On the other hand, during warm periods the MOW became less dense favoring an increased intensity of the MOW on the distal area of the upper slope. Therefore, spatial and vertical fluctuations of the MOW contourite system are strongly affected by global climate and oceanographic changes, being clearly influenced by iceberg discharges and probably also, by the resumption of thermohaline circulation in the North Atlantic Ocean during ice melting periods.

History of Sedimentation on the Voring Plateau (Norwegian Sea) during the Last 25 ka

Based on sedimentological, mineralogical, geochemical, and micropaleontological data on the comprehensively investigated Core ASV 1372, the late Pleistocene-Holocene sedimentation history is reconstructed for the Voring marginal plateau (continental margin of the Norwegian Sea). The age model is constructed based on the correlation with several adjacent cores, for which the AMS radiocarbon dates are available. Lithostratigraphic correlation made it possible to compare stratigraphic division of Core ASV 1372 with other cores recovered from the Voring Plateau and the shelf and continental slope off the central Norway. It is concluded that the compositional and structural features of sediments are correlated with paleoclimatic and paleoceanographic changes, variations in provenances, as well as agents and pathways of sedimentary material transport.

Late Pliocene–Quaternary tectonics in the frontal part of the SE Carpathians: Insights from tectonic geomorphology

The Romanian East Carpathians display large-scale heterogeneities along the mountain belt, unusual foredeep geometries, significant post-collisional and neotectonic activity, and major variations in topography, mostly developed in the aftermath of late Miocene (Sarmatian; ∼11 Ma) subduction/underthrusting and continental collision between the East European/Scythian/Moesian foreland and the inner Carpathians Tisza-Dacia unit. In particular, the SE corner of the arcuate orogenic belt represents the place of still active large-scale differential vertical movements between the uplifting mountain chain and the subsiding Focşani foredeep basin. In this key area, we have analysed the configuration of the present day landforms and the drainage patterns in order to quantify the amplitude, timing and kinematics of these post-collisional late Pliocene–Quaternary vertical movements. A river network is incising in the upstream a high topography consisting of the external Carpathians nappes and the Pliocene–Lower Pleistocene sediments of the foreland. Further eastwards in the downstream, this network is cross-cutting a low topography consisting of the Middle Pleistocene–Holocene sediments of the foreland. Geological observations and well-preserved geomorphic features demonstrate a complex succession of geological structures. The late Pliocene–Holocene tectonic evolution is generally characterised by coeval uplift in the mountain chain and subsidence in the foreland. At a more detailed scale, these vertical movements took place in pulses of accelerated motion, with laterally variable amplitude both in space and in time. After a first late Pliocene uplifting period, subsidence took place during the Earliest Pleistocene resulting in a basal Quaternary unconformity. This was followed by two, quantifiable periods of increased uplift, which affected the studied area at the transition between the Carpathians orogen and the Focşani foreland basin in the late Early Pleistocene and the late Middle to late Pleistocene. Both large-scale deformation events affected the western Focşani basin flank, tilting the entire structure with ∼9° during the late Early Pleistocene and uplifted it as a block during the early Late Pleistocene. The late Early Pleistocene tilting resulted in ∼750 m uplift near the frontal monocline and by extrapolation in a presumed 3000 m uplift near the central parts of the Carpathians. The late Middle to late Pleistocene cumulative uplift reaches ∼250 m and correlates with a contemporaneous progradation of the uplifted areas towards the Focşani Basin. The uplifting events are separated by a second Quaternary unconformity. On the whole, the late Pliocene–Quaternary evolution of the Carpathians orogen/Focşani basin structure indicate large-scale differential uplift during the latest stages of a continuous post-collisional orogenic evolution.

AMS radiocarbon dating of the marine late Pleistocene–Holocene sediment cores from the western Ulleung Basin, East/Japan Sea

We present the results on radiocarbon dating of planktonic foraminifera samples from two piston cores collected from the western part of the Ulleung Basin, East/Japan Sea. Until recently, there were no radiocarbon dates from late Quaternary sediments of this location. Eight samples from the Ulleung Basin cores were accelerator mass spectrometry (AMS) 14C-dated, and reservoir-corrected using R-values as 400yr. The results indicate that the cores cover the time interval from the middle stage of marine isotope stage (MIS) 3 through last glacial maximum (LGM) to Holocene, and the average sedimentation rate of the cores vary from 17.61cm/kyr to 19.96cm/kyr. Particularly, it is shown using the calibrated 14C data that in the cores hemipelagic muds (bioturbated and slightly laminated mud facies) were mainly formed during interglacial periods (MIS 1/3), whereas non-hemipelagic muds (laminated and homogenous mud facies) were deposited during glacial period (MIS 2).

Surface faulting in Norcia (central Italy): a “paleoseismological perspective”

We carried out paleoseismological analyses in Norcia, one of the oldest town of central Italy. Four trenches were dug in late Pleistocene–Holocene deposits, across an unmapped, antithetic splay of the Norcia Fault System. The investigated fault runs through the recent settlement of the town, brushing against the middle-age city walls. We found evidence of repeated surface ruptures in the past 20 ky, the last one dated to a period fitting with the 1703 AD, catastrophic earthquake ( M = 6.8). Our data (i) show definitively the late Pleistocene–Holocene activity of the Norcia Fault System, (ii) strengthen the historical accounts describing surface ruptures during the 1703 event in Norcia, (iii) cast light on the seismogenic behavior of the 70-km-long fault system between L'Aquila and Norcia (central Italy) and (iv) predict the occurrence of normal surface faulting inside the municipality of Norcia during future M ≥ 6 earthquakes.

Sedimentological study of the Chernobyl NPP site to schematise radionuclide migration conditions

The approach, methods and results of a sedimentological study of a near-surface stratum of Late Pleistocene-Holocene deposits in the near-zone (5–10 km radius) of the Chernobyl Nuclear Power Plant are presented. Sedimentological analyses are carried out at three levels of detail: regional-, local- and object-scale. The unsaturated zone and unconfined aquifer at the site are composed of two main genetic types of deposits, aeolian and alluvial, including several dynamic facies. Consideration of lithological properties leads to following ranking of the main genetic sediments facies with respect to radionuclide migration retardation potential: aeolian <alluvial channel <alluvial overbank <alluvial abandoned channel. Based on sedimentological interpretations, the geological environment is schematised into a set of typical geological sections possessing different radionuclide retardation potential.

Sedimentary and environmental characteristics of the Gilan–Mazenderan plain, northern Iran: influence of long- and short-term Caspian water level fluctuations on geomorphology

The south–southwestern Caspian coastal lowland in Iran, or the Gilan–Mazenderan plain, is a relatively narrow but long, composite depositional area of late Quaternary age. The Sefid Rud delta, the Anzali Lake (connected to the Caspian Sea by a meandering outlet 3.5 km long) and storm-dominated beaches are its prominent sedimentary features. They are controlled by the present water level of the Caspian Sea at −26.36 m in 2000. The late Pleistocene–Holocene deposits of the lowland, which are covered commonly by a modern loess-origin soil, mainly consist of alternations of marine and non-marine sediments. The marine units form coastal terraces at 19–20 m (I), 2–0 m (II) and −6–−8 m (III) corresponding to the Late Khvalinian and Neocaspian transgressions. The deposits of the youngest terrace (terrace III) that represents a prograding beach–ridge complex are a consequence of several medium-term, cyclic water level oscillations in late Holocene. Just after the initiation of the beach–ridge complex, Lake Anzali that formed by damming of rivers and then by progradation of the complex in time forced to form the outlet of the lake. The nearest medium-term cycle lasted c. 65 years between 1930 and 1995, and the records showed that it included a lot of short-term (c. 4–5 years) and very short-term (week to months) water level oscillations. During the last erratic rise of sea level (1977–1996), the area of Lake Anzali doubled; the delta and the coastal sands including modern beaches were eroded on a width of around 30–100 m. Overall, a steplike morphology, through the repetition of marine and non-marine facies and also water level records of the last 75 years, indicate that the ancient and recent deposition on the coastal lowland has been controlled by long-, medium- and short-term fluctuations of the Caspian Sea level.

Early–Middle Pleistocene eastward migration of the Abruzzi Apennine (central Italy) extensional domain

The evolution of the Apennine arc is related to the flexural retreat of the Adriatic lithosphere plate, the NE migration of the compressive front and the contemporaneous rifting of the Tyrrhenian basin. Evidence of the NE migration of the orogen can also be inferred from the analysis of the intra-Apennine Quaternary extensional tectonics. Stratigraphic and structural data collected along NE–SW transects in the Abruzzi Apennines (central Italy), indeed, indicate that the westernmost normal faults (activated during the Pliocene) have to be considered inactive since the Early Pleistocene (Turano valley fault) or the beginning of the Middle Pleistocene (Salto valley and Liri valley faults). In contrast, the easternmost faults (Campo Imperatore and Mt. Morrone faults) were activated during the Early Pleistocene and are still active, as demonstrated by the displacement of Late Pleistocene–Holocene deposits and landforms. Within the innermost portion of the extensional domain, the Fucino and upper Aterno valley fault systems show persistent activity since the Pliocene. Besides the evidence of a progressively NE-shifted intra-Apennine extension, available data suggest that a period of co-existing activity of the presently inactive and newly activated faults (e.g. Liri valley and Mt. Morrone faults, respectively) occurred during the Early Pleistocene. This indicates that for a few hundred thousand years active faults in the central Apennines were more numerous than in the period of the present tectonic regime. This may have resulted in a reduced activity per fault (lower slip rates) or an increased intra-Apennine extension rate. Quaternary faults in the Abruzzi Apennines generally coincide with pre-existing discontinuities such as old thrust ramps or syn-orogenic normal faults. Based on a simple geometric criteria, i.e. direction, dip, length of the pre-existing discontinuities located east of the investigated area, and assuming a still active NE-migration of the extensional domain, it is possible to hypothesize that the old and presently inactive normal faults of the Maiella and Montagna dei Fiori anticlines may accomodate active extension of the future. The NE-ward shifting of the extensional domain would be, instead, locked if the process of lithospheric flexural retreat which drove the Neogene-Quaternary p.p. structural evolution of the Apennine chain has ended during the Early Pleistocene.

Late glacial, Holocene and modern dinoflagellate cyst assemblages in the Aegean–Marmara–Black Sea corridor: statistical analysis and re-interpretation of the early Holocene Noah’s Flood hypothesis

Understanding of the history of water exchange between the Mediterranean and Black seas has been hampered by the lack of continuous microfossil records for Holocene cores from the Marmara Sea Gateway (Aegean–Marmara–Black Sea corridor), and by the lack of core-top data linking modern microfossil assemblages with sea surface conditions. Based on molluscs, an abrupt transition from freshwater to marine conditions at ca. 7.5 ka has been postulated, with interpretation of this event as the basis for the story of Noah’s Flood. We have re-examined this hypothesis using organic-walled dinoflagellate cysts that show excellent preservation and moderate to high diversity in Pleistocene–Holocene sediments of the Marmara Sea Gateway. Principle component analysis of 16 core-top samples shows that an assemblage dominated by cysts of autotrophic gonyaulacoids distinguishes the hypersaline Aegean–Mediterranean water (salinity 31–38), whereas heterotrophic protoperidinioids characterise the low-salinity Marmara–Black Sea water (salinity ∼14–25). About 150 samples from eight cores, with multiple radiocarbon ages spanning the past ∼33 000 years, show correlatable major changes in cyst assemblages along the Marmara–Black Sea corridor. Variation in length and shape of gonyaulacoid species processes decreases upcore from basal units where there are no-analogue assemblages of cysts with highly variable spine development. It is shown that these variable and no-analogue assemblages correspond to brackish conditions (salinity ∼4–12) when calibrated against δ 18O data and salinity estimates derived from planktonic foraminifera. Salinity reconstructions indicate that the Aegean and Marmara seas were connected by ∼11 ka when the Marmara Sea was a brackish or low-salinity sea (∼12–17) and that the Black Sea was flowing into the Marmara Sea by at least 10.2–9.5 ka. There is no evidence to support either the idea that the Black Sea was a large freshwater lake suitable for farming in the early Holocene or that a sudden (<500-yr) flooding of the Black Sea by a 100-m-high waterfall of Mediterranean water occurred at 7.5 ka. It is shown that there is a need for precise use of salinity terms when reconstructing the history of saline lakes in the context of Neolithic human occupation so that the likelihood of agricultural settlement can be evaluated realistically.

Sedimentary facies and radiocarbon dates of the Nam Dinh-1 core from the Song Hong (Red River) delta, Vietnam

The Song Hong (Red River) delta, which is located on the western coast of the Gulf of Bac Bo (Gulf of Tonkin) in the South China Sea is characterized by three morphological systems that are clearly distinguished spatially: fluvial-, tidal-, and wave-dominated. We obtained a 70-m-long core of sediments (the Nam Dinh-1 core) from the central part of the delta in 1999. This paper presents the first detailed description of sedimentary facies with high-resolution radiocarbon dating for the latest Pleistocene–Holocene sediments of the Song Hong delta. The core sediments were divided into three units on the basis of the sediment facies: in ascending order, Unit 1, fluvial sediments consisting of fining-upward gravels to clay; Unit 2, coarsening-upward marine clay to shelly sand; and Unit 3, coarsening-upward marine clay and laminated sand. Twenty-one radiocarbon dates showed that the core succession was deposited after the Last Glacial Maximum (LGM); the ages were 15–11 cal. kyr bp for Unit 1, 11–9 cal. kyr bp for Unit 2, and 8–0 cal. kyr bp for Unit 3. These data indicate that sediments were deposited in transgressive fluvial/estuarine to regressive deltaic environments formed in the central delta plain of the Song Hong after the LGM in response to sea-level changes.

Late Pleistocene–Holocene deposits of the Rhône inner continental shelf (France): detailed mapping and correlation with previous continental and marine studies

Very‐high‐resolution seismic data acquired on the Rhône continental shelf were used to address the detailed morphology of Late Pleistocene and post‐glacial units (from 18 000 yr BP to the present). Two groups of units can be distinguished. (1) Lower units that are mainly the product of variations in relative sea level. They comprise the last Pleistocene regressive deposits made of alluvial sheets (U0, U1) and, above, transgressive deposits that can be divided into: backstepping transgressive units (U3 and U4a), deposited during the landward retreat of the river mouth and transgressive units (U4b, U4c) laid down during the inundation of the shelf. A prograding littoral/lagoon system (U5/U6) indicating a fluctuation during the rise in sea level caps the transgressive units. This work has emphasized the complexity of these depositional environments, mainly related to a river system situated near the current Petit‐Rhône. (2) Upper units that make up the recent Rhône delta and correspond to the current highstand systems tract (HST) developed since the stabilization of relative sea level. Seven prodeltaic lobes have been identified (U7–U13). Two of them are bilobate (U7 and U8) and date from a period when the delta was split as a result of the fluviatile system being progressively divided into several channels. Other prodeltaic lobes (U9, U10) are stacked in front of the distributary's outlet, recording several periods of outflow. The results show a strong correlation with studies on land. The distribution of recent prodeltaic lobes was constrained by canalization of the Rhône river to prevent the effects of climatic crises or other natural disasters.

Volcano-tectonic activity along structures of the unstable NE flank of Mt. Etna (Italy) and their possible origin

We describe the prehistoric–historic activity of the main and minor volcano-tectonic structures of the northeastern flank of Mt. Etna, giving new data which provide a clearer view of how destabilized volcanoes react to magma pressure and gravity forces. Data are mostly based on new lithostratigraphic surveys and on offset measurements of late Pleistocene–Holocene deposits and historic man-made features. The North-East Rift (NE Rift) is a volcanic rift that has guided mostly explosive, but also secondary effusive, activity since the end of the Pleistocene. Monogenetic cones and explosive craters are strongly elongated and aligned along 66 main surface fractures and several others, hidden, but inferred, from sinkhole alignments. The opening direction is locally oblique, with a left-lateral component in the north-eastern segment of the rift. At the NE tip of the rift, the movements are relieved by the normal left-lateral Pernicana Fault (PF), an 11-km-long structure comprising E–W fault segments connected by right-stepping en échelon faults. Our study demonstrates that the very high slip rates at a centennial scale of these structures are well constrained and similar (NE Rift=0.6–1.8 cm/a, PF=0.5–2.2 cm/a) and have been also recognized in the Latest Pleistocene–Holocene (2.7 cm/a). The E–W Fiumefreddo Fault (FF) has normal left-lateral kinematics and a historic slip rate of 0.1 cm/a. Ripa della Naca Faults strike NE and are covered by unfaulted <15-ka-old lavas. Relative sinking to the SE gives a late Pleistocene slip rate of 0.2 cm/a. Newly recognized NNE- to NE-striking active normal faults interfere at the PF–FF junction zone. The active East-North-East Rift, which is described in detail for the first time, is another volcanic rift affecting the eastern flank of Mt. Etna. This rift shows left-lateral normal motions and has guided the location of several pyroclastic cones since at least the end of the Pleistocene. Stratigraphic and structural data prove the presence of a North–South Rift which has existed across the Mt. Etna summit zone during at least the last 14 ka. Our data coupled with published seismological data indicate that these structures are the surface expressions of the seaward sliding of the eastern flank of Etna along two slip surfaces in a two-component principal stress field, produced by gravity loading and magma intrusion. A shallower slide surface can be activated following dominance of gravity instability triggered by the mass of the volcano flank, or movements can occur along a deeper surface triggered by injection phases, or the two surfaces can move at the same time by a combination of effects. The existence of this double system of deformation can explain several apparently contradictory phenomena, such as discontinuous correlation of deformation, earthquakes and eruptions, and different earthquake foci, focal mechanisms and fault slip rates.

History of Sedimentation on the Yermak Plateau during the Recent 190 ka: Communication 1. Lithology and Mineralogy of Middle Pleistocene–Holocene Sediments

Three cores of bottom sediments obtained from the Yermak Plateau are scrutinized. Age model based on AMS 14C dating and oxygen isotope stratigraphy (OIS) is presented for the reference core PS 2837. Hypothetical stratigraphic models for cores PS 2834 and PS 2859 are based on lithostratigraphic analyses. Detailed layer-by-layer descriptions of all studied sections are given based on grain size distribution and contents of CaCO3, Corg, and heavy minerals.

Application of paleoseismological techniques to the study of Late Pleistocene-Holocene deep-seated gravitational movements at the Mortirolo Pass (central Alps, Italy)

AbstractPaleoseismological techniques have been used to investigate gravitational deformations at the Mortirolo Pass (Valtellina region, central Alps), in order to improve the knowledge on the activation mechanisms and the evolution of deep-seated gravitational slope movements. The deformation has been responsible for mass sliding towards the Valtellina depression through the activation of several-hundred-metre-long shear planes. Minor shear planes dipping towards the mountain played the role of antithetic structures. Four trenches were excavated across scarps representing the surficial expression of shear planes affecting the bedrock and Late Pleistocene-Holocene deposits. The excavations enabled to investigate the stratigraphy of Quaternary deposits and the geometry and kinematics of the shear planes affecting them. Radiocarbon analyses on organic material contained in sediments and paleosols enabled to define a succession of displacement events which occurred during the Late Pleistocene-Holocene. Collected data indicate the persistence of the activity until recent times (last movement related to 1810-1540 cal. BP). A sudden movement has been detected along one of the main shear surfaces (dipping towards the valley) with a vertical displacement of several metres. In contrast, numerous displacements (with lower vertical offset) have been detected along the antithetic shear planes. Different hypotheses have been proposed in the past to define the origin of huge gravitational movements (glacial retreat, uplift of the Alpine chain, fault activity). However, the Late Pleistocene cycles of glacial loading and unloading on the mountain slopes seem to be the most probable factors causing deep-seated gravitational movements in the investigated region. A recent dramatic landslide in an area adjacent to the investigated one (Mt. Zandila-Valpola) testifies to the paroxistic evolution of the large scale gravitational deformations. The densely inhabited Valtellina region is affected by a large number of gravitational structures similar to those of the Mortirolo area. In consideration of the possible effects of the paroxistic activation of these structures, detailed studies on the chronology and kinematics of the deformations through the application of paleoseismological techniques should therefore be encouraged.

過去１３万年間にわたる大阪湾東部沿岸地域の層序，堆積シークエンスと堆積環境

大阪平野西部で採取された住之江コア(A～F孔)を用いて, 大阪湾東部沿岸地域の過去13万年間の層序, 堆積シークエンスおよび堆積環境の検討を行った.その結果, 以下の3項目が明確となった.(1)住之江コアは7つの堆積ユニット(Sm-1～Sm-7)に区分される.このうちSm-7～Sm-5は上町累層(中位段丘堆積層), Sm-4～Sm-2は難波累層(沖積層)に区分される.(2)住之江コアには2つの礫質網状河川システム(Sm-5およびSm-4)ならびに2つの内湾～デルタシステム(Sm-7～Sm-6およびSm-3～Sm-2)が認定される.(3)住之江コアをシークエンス層序学的に解釈するならば, 過去13万年間に3つの第5から第6オーダーの堆積シークエンス(DS1～DS3)の認定が可能である.

High-Resolution Seismic Study as a Tool for Sequence Stratigraphic Evidence of High-Frequency Sea-Level Changes: Latest Pleistocene-Holocene Example from the Korea Strait

ABSTRACT Sequence stratigraphic analysis of high-resolution seismic reflection profiles and sediment data reveals that the latest Pleistocene-Holocene deposits in the Korea Strait shelf off the southeastern Korean Peninsula form a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 kyr) sea-level cycle. Eight depositional systems, each with different seismic facies, constitute the systems tracts. The lowstand systems tract, consisting of sandy mud, forms a deltaic wedge that pinches out updip near or at the relict shelf edge. The transgressive systems tract, consisting mainly of sands, includes six depositional systems: (1) inner-shelf transgressive layer, (2) transgressive estuarine-deltaic complex, (3) transgressive sand ridge, (4) mid-shelf transgressive layer, (5) incised-channel fill, and (6) beach-shoreface complex. Although the transgressive systems tract is widely distributed, it is much thinner than the lowstand and highstand systems tracts. The highstand systems tract is composed of a prodelta-shelf complex consisting almost exclusively of Holocene muds. The distribution and geometry of the systems tracts in the latest Pleistocene-Holocene sequence in the Korea Strait shelf is different from that of Vail's model in that: (1) the lowstand systems tract consists only of the lowstand deltaic wedge, which forms an elongated sediment body along the paleoshelf edge, and (2) the highstand systems tract is completely confined to the inner shelf and forms a nearshore belt parallel to the coastline. High-frequency (20 kyr), high-amplitude (magnitude of about 130 m) sea-level change, together with strong currents flowing northeastward along the southeastern coast of the Korean Peninsula and varying sediment supply, have resulted in this rather unusual stratigraphic architecture.

Fin d'analyse

The relief evolution of several areas of northeastern Brazil has been increasingly related to tectonic events. This is the case for the Paraíba Basin, where an abundance of faults and folds were recorded in Neogene and even Late Pleistocene-Holocene deposits. We tested whether dome-like morphologies in the northern sector of this basin, where geological exposures are scarce, were also formed by tectonic deformation. The work combined limited geological data with qualitative and quantitative analyses of the relief applying the 1 arc-second digital elevation model provided by the Shuttle Radar Topography Mission. The geomorphic indices of basin asymmetry factor (AF), swath topographic profiles, enhanced transverse hypsometry index (THi*) and normalized river long-profiles were used for validating a neotectonic origin for the dome-like morphologies. This interpretation was also supported by other morphological evidence of the dome relief, including: recurving channels featured in radial to recurved trellis patterns; tectonically-controlled drainage sub-basins; high relative relief values related to increased fluvial incision; and anomalous river long-profiles indicative of ungraded rivers. The domic structures were attributed to fault- and fold-related strike-slip deformation during the late Quaternary. This record supports the proposal that the South American passive margin remained under tectonic stress long after the main rifting in the late Jurassic-early Cretaceous.

R-Selected benthic foraminifera with associated bacterial colonies in Upper Pleistocene sediments of the Ross Sea (Antarctica): implications for calcium carbonate preservation

Investigations on foraminifera from Upper Pleistocene–Holocene sediments cored in the continental slope of the western Ross Sea (2383 m water depth) revealed that the record of calcareous assemblages was restricted to a limited time interval (approximately 6 kyr) and characterized by a dominance of phytodetritus-exploiting taxa, such as Alabaminella weddellensis and Epistominella exigua. Rod-shaped calcified, fossil bacteria infest the partially dissolved calcareous foraminiferal surfaces, either as clusters or as isolated cells, suggesting that significant changes (from under- to oversaturated conditions with respect to calcium carbonate) in the chemistry of the seawater developed before the final burial of the foraminiferal tests. We postulate that bacterial activity on a microenvironmental scale (interface and pore water) in the sea floor could influence pore water conditions in such a way as to preserve carbonate in deep marine regions where environmental conditions usually prevent the establishment of carbonate secreting communities.

Paleoenvironmental evidence for latest Pleistocene sea-level fluctuations on the New Jersey outer continental shelf: combining high-resolution sequence stratigraphy and foraminiferal analysis

Foraminiferal assemblages in vibracored sediments within ∼5 m of the seafloor document high-resolution sea-level fluctuations and confirm the complex Quaternary depositional history of the New Jersey margin. Biostratigraphic data have been integrated with ongoing 2-D/3-D high-resolution seismic analyses to interpret paleoenvironments of surficial stratigraphy beneath the modern middle-to-outer shelf. Cluster analysis of foraminiferal assemblages sampled every 20 cm (average) define four sample groups (A–D) dominated by benthic species. Group A, characterized by Cibicides lobatulus, is a middle-to-outer-shelf assemblage (∼60–100 m water depths). Group B is composed of middle-shelf species (∼30–60 m water depths) and is characterized by low abundances and a fairly uniform distribution of foraminifera, which suggests reworking and/or a high rate of sediment accumulation. Group C, dominated by Elphidium excavatum, is an inner-to-middle-shelf assemblage (∼10–40 m water depths). Group D, present in only one core and dominated by Ammonia beccarii, represents marginal marine environments (∼0–10 m water depths, with fluctuations in salinity). In general, the modern sedimentary veneer (i.e., the upper ∼20 cm) is characterized by the deeper-water fauna of group A. Sediments below these modern deposits are characterized by groups B and C, reflecting shallower water depths and variable sediment-accumulation rates on the inner and middle shelf. Taken together, the group succession in the cores suggests an overall SE-to-NW (landward) transgression in these latest Pleistocene–Holocene deposits. Seismic analysis indicates that one core (27) penetrates the flank of a buried channel, including its fill and the pre-channel section. Within the channel, three alternations of groups C and D suggest fluctuations between marginal-marine and middle-shelf paleoenvironments; high-frequency, perhaps very small (<10 m?) changes in base level are indicated. Using previously published AMS 14C dates, these fluctuations can be constrained as having occurred between 45,000 yr B.P. (channel incision) and 12,500 yr B.P. (channel filling), suggesting the non-uniform nature of the last Wisconsinan deglaciation.