Grain Size Proxies Research Articles

Desert-oasis evolutionary process in the Tarim Basin since ∼ 2.2 ka B.P. during the late Holocene and their environmental implications

Oases, serving as ideal locations for human settlements in arid regions, exhibit extreme sensitivity to regional climatic fluctuations. Consequently, the oasis deposition sediments play a pivotal role in the study of regional paleoenvironmental changes and the exploration of prehistoric human-environment interactions. The YSD and STM sections, both typical aeolian-lacustrine sections located at the edge of the Tarim Basin, were investigated in this study. By analyzing optically stimulated luminescence (OSL) dating results and grain-size proxy indicators, the environmental evolution patterns in the Tarim Basin since approximately 2.2 ka BP were reconstructed. Additionally, the parametric end-member analysis on the grain-size data was conducted to explore the environmental significance revealed by each end-member. The research findings indicate that: (1) ∼ 2.2–1.8 ka B.P., sediment morphology and grain-size parameters indicate that the climate in the Tarim Basin recorded by the STM section was relatively dry, with rivers gradually receding and frequent sand-drift activities. During the development of the YSD section (∼1.67–1.5 ka B.P.), the environmental conditions in the Tarim Basin transitioned to a relatively humid phase, with the Yarkand River experienced multiple episodes of natural diluvial deposition. The grain-size data of two sections both comprise five sedimentary dynamic components, serving as sensitive indicators of regional humidity conditions and winter monsoon intensity. (2) The oasis development in the Tarim Basin during the late Holocene (particularly refers to between ∼ 2.2 ka B.P. and ∼ 1.4 ka B.P.) exhibits a significant positive correlation with temperature records. (3) Environmental changes and human activities jointly regulate the spatial and temporal distribution and number of archeological sites during the development of both sections. However, the dominance of the two factors varied across different historical periods.

Palaeoenvironmental evolution of the Badain Jaran Desert hinterland during the Early to Middle Holocene: A multi-proxy reconstruction on Taoerlegetu paleolake, northwest China

In this paper, we examine the Early to Middle Holocene evolution of a prominent group of ground-water fed lakes in the southeastern hinterland of the Badain Jaran Desert (BJD) of northwest China. Specifically, we describe a sediment profile record from the Taoerlegetu (TR) palaeolake basin using multiple proxies of total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ13Corg, grain size and mineral composition based on a well-dated trench profile. As C/N values suggest that sedimentary organic matter mainly originated from aquatic plants, δ13Corg values can be used as a qualitative proxy for water level because aquatic plants in different biotopes (water depth) have different δ13C values. Our results show that from 10.9 to 9.1 cal kyr B.P., water level rose slowly, and aquatic macrophytes occupied the lake basin. From 9.1 to 5.5 cal kyr B.P., water level reached an even higher level and phytoplankton replaced macrophytes as the major contributor to organic matter. The humid episode of the lakes in the hinterland of the BJD in the early Holocene might be related to the increased groundwater supply from the northeast region of the Tibet Plateau. These findings are consistent with earlier studies of lacustrine and peat sediments found in periphery of the modern lake group, which indicate that their geographic extent may have been larger in the past. A relative drought period recorded in the studied succession from 8.5 to 8.0 cal kyr B.P. marks an interval of reduced ground-water transport from the Tibet Plateau. This interval probably corresponds to the “8.2 ka cold event” and provides evidence that this widespread climate episode influenced groundwater processes across inland Asia.

Sedimentary Rock Magnetic Response to Holocene Environmental Instability in the Pearl River Delta

Located on the northern coast of the South China Sea, the densely populated Pearl River Delta has experienced the combined effects of sea-level change, monsoon-driven discharge, and especially human activity, since the late Holocene. However, how these factors have regulated the regional environmental and sedimentary evolution remains unclear. To better understand these processes, we conducted a high-resolution rock magnetic investigation of the Holocene sediments of core DS01, drilled in the vicinity of the West River channel in the head area of the Pearl River deltaic plain. The magnetic grain-size proxy of the ARM/κlf ratio (the ratio of anhysteretic remanent magnetization to low-field magnetic susceptibility) indicates a long-term fining trend of the magnetite grain size, which may be a response to an increase in the weathering intensity in the Asian monsoon region during the Holocene. An interval with an enhanced concentration of magnetic minerals (mainly magnetite and hematite) occurred during 7.7–4.8 kyr BP (calendar years before 1950), coinciding with a period of delta progradation. During the marine transgression in the early Holocene, two similar intervals of magnetic enrichment may reflect regional hydrodynamic shifts associated with cooling events at ∼9.5–9.3 kyr BP and 8.2 kyr BP. The subsequent 4.2 kyr BP cooling event possibly induced a cold and dry environment in the sediment source area. From ∼800 yr BP onward, there was a major increase in the sedimentary magnetic mineral content, likely in response to intensified agricultural and industrial activities.

Carbon isotope and sequence stratigraphy of the upper Isachsen Formation on Axel Heiberg Island (Nunavut, Canada): High Arctic expression of oceanic anoxic event 1a in a deltaic environment

Abstract The Early Cretaceous oceanic anoxic event (OAE) 1a documents a major perturbation of the global carbon cycle with severe consequences for the ocean-climate-biosphere system. While numerous studies over the past decades have provided a relatively detailed picture of the environmental repercussions of OAE 1a at low and mid-latitudes, studies from high latitudes, in particular the High Arctic, are limited. In this study, we present a high-resolution carbon isotopic and sequence stratigraphic framework for the lower to lower upper Aptian interval of the Isachsen Formation of the High Arctic Sverdrup Basin (Canada). These data enable us to precisely locate the stratigraphic position of OAE 1a in a deltaic sedimentary environment. The carbon isotope record allows, for the first time, identification of the different carbon isotope segments (CISs) of OAE 1a in the Sverdrup Basin and thereby correlation of the High Arctic record with sections from lower latitudes. Based on this improved chemostratigraphy, we revise the age of upper Paterson Island, Rondon, and Walker Island Members, important regional lithostratigraphic marker units. Whole-rock geochemical data record two episodes of marine incursion into the Sverdrup Basin during OAE 1a (CISs Ap3 and Ap6), which are interpreted as regional maximum flooding surfaces. This information is used in conjunction with detailed sedimentological logs and geochemical grain-size proxies to refine the sequence stratigraphic framework for the upper Isachsen Formation. We propose that transgressive-regressive cycles in the Sverdrup Basin were controlled mainly by the combined effects of eustatic sea-level changes and regional tectonic uplift, potentially related to the emplacement of Alpha Ridge, which culminated at ca. 122 Ma during CIS Ap9.

Holocene hydroclimate in the source region of the Yellow River: A new sediment record from Lake Gyaring, NE Tibetan Plateau

Abstract The environmental history of the source region of the Yellow River (SRYR) is vital for understanding its hydrological response to climate processes in the alpine northeastern Tibetan Plateau (TP). In this study, we present the first sediment core record from Lake Gyaring, one of the largest fresh lakes in SRYR, using proxies of total organic carbon, total nitrogen, C/N ratio, δ13Corg, chlorophyll a, and grain size, to discuss the environmental variations over past 10 kyr. The results show that sedimentary organic matter mainly originated from the aquatic macrophytes and phytoplankton, the relative abundance of which can serve as a qualitative indicator of lake level changes of Lake Gyaring. From 10 to 6.2 cal kyr B.P., the notable expansion of macrophytes was favored by the warm conditions and an enlarged littoral zone due to lake-level decline. The abrupt cooling between 8.9 and 8 cal kyr B.P. led to temporal lake-level rises that significantly reduced macrophyte primary production. After 6.2 cal kyr B.P., the lake turned to be phytoplankton-dominated following the cooling trend and stepwise increase in lake level. The inferred climate pattern in the lake catchment with an overall dry early to mid Holocene and moister mid to late Holocene disagrees with the Asian monsoon variations. This phenomenon is well recognized by the lake-level records from most of the northeastern TP lakes, implying that strong evaporation in semi-arid lake catchments could have outweighed the increased regional precipitation during early to mid Holocene and vice versa for mid to late Holocene.

Lithological correction of chemical weathering proxies based on K, Rb, and Mg contents for isolation of orbital signals in clastic sedimentary archives

The extraction of palaeoenvironmental (palaeoclimatic) signals from the chemical composition of siliciclastic sediments is valuable for the reconstruction of past environments, particularly in continental basins. Here we test novel weathering proxies, which are less sensitive to lithological control than the previously used raw element ratios K/Al, K/Ti, and K/Rb: (1) local enrichment factors of K/Al, Mg/Al, and K/Rb, i.e., the element ratios corrected for grain size- and matrix composition using local background functions (Al/Si, Fe, and Ca as explanatory variables) and ordinary regression and (2) robust regression residuals of those element ratios based on isometric log-ratio coordinates of the most relevant “lithogenic” elements (Ca, Fe, Rb, Si, Zr) in the chemical composition. Chemical weathering proxies can be obtained from departures of chemical composition of sedimentary profiles from relationships with other chemical elements, in particular those with grain-size control. The resulting weathering proxies were examined for the Miocene deposits from the Most Basin, the Czech Republic, which recorded one of the major warm episodes of the Cenozoic time – the Miocene Climatic Optimum. The performance of weathering proxies has been checked by (1) comparison of individual proposed proxies in one drill core HK930, (2) detailed analysis of orbital signals in the relevant compositional functions in HK930; and (3) lateral correlation of three cores HK930, DU7, and DO565 of the same basin. The novel proxies show lateral stability and orbital signatures of short eccentricity, obliquity, and precession, confirming their usefulness in palaeoenvironmental studies. Corrections for grain-size and carbonate contents should help to isolate climatic content from the weathering proxies, although in the studied sediments it weakened the precession component in the orbital signal, as grain-size proxies and other compositional data also carried orbital signals. We propose to consider these proxy ideas in palaeoclimatic reconstructions based on chemical weathering proxies.

Sea-level and climate signatures recorded in orbitally-forced continental margin deposits over the last 1 Myr: New perspectives from the Bohai Sea

Sediment accumulation in continental margins during the Quaternary Period was substantially influenced by both sea-level fluctuations and climate changes. However, the response of sediment accumulation to these changes on an orbital timescale, remains poorly understood, for two main reasons: the scarcity of sedimentary records with a high-resolution chronology, and the difficulty in distinguishing the role of sea-level from regional climate signals. Here we present the results of sediment color reflectance (c*), grain size and total organic carbon (TOC) content of core BH08 (212.4 m in length, spanning the last ~1 Myr) recovered from the Bohai Sea, China. The chronology of core BH08 on the orbital timescale is constrained by both magnetostratigraphy and astronomical tuning. Sedimentary facies analysis suggests that the sedimentary sequence is dominated by the alternation of a deltaic system and floodplain deposition. Principal components analysis of the grain-size data reveals two principal components (PCs), including PC1, reflecting the 31–500 μm fraction, and PC2, reflecting the 18–66 μm fraction. Comparison of sample scores on PC1, PC2 and c* with the alternation of sedimentary environments reveals that PC1 and c* reflect cycles of deltaic and floodplain deposition at ~100-kyr and ~40-kyr periodicities, while PC2 exhibits a ~20-kyr periodicity, in addition to the ~100-kyr and ~40-kyr cycles. We infer that PC1 and c* are mainly sea-level dependent, whereas PC2 is controlled by the combination of changes in monsoon climate and sea level. We suggest that Milankovitch-scale monsoon climate fluctuations controlled the sediments supply to the Bohai Sea during the last ~1 Myr, while the redistribution of sediments by marine processes (e.g., tidal currents) has partially obscured the monsoonal signal in the grain-size proxy (e.g., PC1) which instead is sensitive to sea-level change. Our results provide an example of the influence of climate and sea-level on sediment accumulation in a shallow continental margin setting influenced by monsoonal climate in an icehouse world.

A 2000 year record of palaeofloods in a volcanically-reset catchment: Whanganui River, New Zealand

Palaeofloods in the Whanganui River, North Island, New Zealand are investigated using floodplain sedimentary archives at two locations in the lower Whanganui catchment. The ca. AD 232 Taupo volcanic eruption transformed the lower valley of the Whanganui River, emplacing a substantial volume of volcanogenic mass flow material and providing a new starting point for subsequent alluvial sedimentation. At Atene a high–resolution archive of flood sediments is preserved in a valley meander cutoff in the lower reaches of the Whanganui Gorge, where a ~9 m core was extracted. At Crowley House further down valley, two ~5 m cores were also extracted from a terrace-confined floodplain. Organic material from these cores allows the timing of floods at these sites to be constrained using 11 radiocarbon dates (ten from Atene, one from Crowley House). Flood magnitudes are reconstructed using XRF core-scanned geochemistry as a proxy for flood unit grain size. An age-depth model at Atene identifies three distinct phases of sedimentation with above average flood activity recorded at 1450–1125, 950, 650–500, and 400–325 cal. yr BP, which can be linked to the El Nino Southern Oscillation (ENSO) and strengthening of the Southern Hemisphere Westerly Wind circulation. Large floods also cluster in the late 1800s, reflecting a combination of enhanced storminess and land cover change, which also resulted in deeper erosion of regolith in the catchment, revealed by cosmogenic analysis at Crowley House. Climatic and non-climatic drivers are responsible for floods in the Whanganui catchment over the past ~2000 years, with the largest floods occurring during La Nina and positive Southern Annular Mode conditions. The timing of the largest single flood in the Whanganui in this period is consistent with the volcanic-resetting event itself of AD 232. This study demonstrates the close relationship between regional climate variability in the south-western Pacific Ocean and the occurrence of extreme floods in New Zealand, and the importance of using multi-centennial length hydrological series for effective flood risk assessment.

A 4000-year record of hydrologic variability from the Olympic Mountains, Washington, USA

Sedimentological and geochemical analyses of gravity and piston cores retrieved from Lake Quinault, Washington, reveal an ~4000-year flood-dominated depositional record. Individual flood event layers are identified by combining core stratigraphy, sedimentology, and the ratio of incoherent to coherently scattered x-ray radiation ( inc/coh) from µXRF (x-ray fluorescence) core scans. The inc/coh time series is used as a proxy for sediment grain size and, in combination with radiocarbon-anchored core age–depth models, enables the reconstruction of late-Holocene hydrologic variability for the Quinault River catchment. Decadal to centennial variability in inc/coh is interpreted to reflect trends in ocean-atmosphere teleconnections favorable for the formation of land-falling atmospheric rivers along the Pacific Ocean flank of the Olympic Mountains. Such processes likely modulate the rate of flooding and may explain notable increases in the frequency of flood event layers observed during the periods 2350–2450 cal. yr BP and the most recent century (AD 1910–2010). Understanding past hydrologic variability has important implications for the landscape and ecosystem response of Olympic Mountain catchments to future climate warming.

Optical dating of Holocene paleosol development and climate changes in the Yili Basin, arid central Asia

Optically stimulated luminescence (OSL) dating was conducted on the K-feldspar and quartz fractions of a Holocene loess-paleosol sequence in the Yili Basin, in the core area of arid central Asia (ACA). Age overestimation using the post-IR IR (pIR50IR170) signals from feldspar was observed for paleosols, because of poor bleaching prior to deposition. Therefore, a reliable age framework for the studied section was established using OSL dating of coarse-grained quartz, combined with a Bacon age model. A total of 18 OSL ages were obtained from a 2.5-m-loess/paleosol sequence with age range of 17.4–0.4 ka. Magnetic and grain-size proxies were used to reconstruct environmental changes during the studied interval, and the results indicate that paleosol development commenced at ~6 ka in the Yili Basin, which is consistent with previous studies in the Xinjiang region. Dust accumulation rates (DARs) and end-member analysis (EMA) of the grain-size frequency distributions were used to infer variations in the Westerlies during the Holocene, and the results suggest that the Westerlies were the main source of excess moisture in ACA during the studied interval.

Magneto-biostratigraphic age models for Pleistocene sedimentary records from the Ross Sea

Abstract The Ross Sea is one of the major sites of formation for Antarctic Bottom Water (AABW), a key component of the global ocean overturning circulation. However, there is currently a lack of high quality stratigraphic records documenting how this water mass flows from the continental shelf into the abyssal ocean, and specifically how this pathway is affected by changes in ice sheet cover on the Ross Sea continental shelf through Pleistocene glacial-interglacial cycles. Over the course of two expeditions in 2015 and 2016, a suite of cores from the upper continental slope to the abyssal plain was obtained by the Korea Polar Research Institute from the R/V Araon. The age of these cores ranges from Holocene to the latest Pliocene, and they hold the potential to document a source-to-sink record of AABW transfer into the abyssal Pacific Ocean. The cores are located in regions with distinct differences in bottom water energy, with high-energy cascading water masses on the upper slope creating the potential for erosional hiatuses, passing downslope into a lower energy setting. To decipher the complex environmental records and allow core-to-core correlation, robust chronostratigraphies are essential. Here, we present age models for four of these cores, based on correlation between their magnetostratigraphy and the geomagnetic polarity timescale, resulting in sedimentation rates between 1.5 cm/ky and 0.5 cm/ky. Rock magnetic data indicate the remanence is carried by magnetite with an almost ubiquitous contribution of high coercivity fraction that is not demagnetised by 100 mT. We demonstrate that a reliable magnetostratigraphy is established for each of these cores, and magnetic properties can be used to identify potential hiatuses in the cores and as a proxy for sedimentary grain-size.

ARCiS framework for exoplanet atmospheres

Context. Understanding of clouds is instrumental in interpreting current and future spectroscopic observations of exoplanets. Modeling clouds consistently is complex, since it involves many facets of chemistry, nucleation theory, condensation physics, coagulation, and particle transport. Aims. We aim to develop a simple physical model for cloud formation and transport, efficient and versatile enough that it can be used, in modular fashion for parameter optimization searches of exoplanet atmosphere spectra. In this work we present the cloud model and investigate the dependence of key parameters as the cloud diffusivity K and the nuclei injection rate Σn. on the planet’s observational characteristics. Methods. The transport equations are formulated in 1D, accounting for sedimentation and diffusion. The grain size is obtained through a moment method. For simplicity, only one cloud species is considered and the nucleation rate is parametrized. From the resulting physical profiles we simulate transmission spectra covering the visual to mid-IR wavelength range. Results. We apply our models toward KCl clouds in the atmosphere of GJ1214 b and toward MgSiO3 clouds of a canonical hot-Jupiter. We find that larger K increases the thickness of the cloud, pushing the τ = 1 surface to a lower pressure layer higher in the atmosphere. A larger nucleation rate also increases the cloud thickness while it suppresses the grain size. Coagulation is most important at high Σn. and low K. We find that the investigated combinations of K and Σn. greatly affect the transmission spectra in terms of the slope at near-IR wavelength (a proxy for grain size), the molecular features seen at approximately μm (which disappear for thick clouds, high in the atmosphere), and the 10 μm silicate feature, which becomes prominent for small grains high in the atmosphere. Conclusions. Clouds have a major impact on the atmospheric characteristics of hot-Jupiters, and models as those presented here are necessary to reveal the underlying properties of exoplanet atmospheres. The result of our hybrid approach – aimed to provide a good balance between physical consistency and computational efficiency – is ideal toward interpreting (future) spectroscopic observations of exoplanets.

Checklist for the use of potassium concentrations in siliciclastic sediments as paleoenvironmental archives

Weathering indices quantify the release of mobile elements from source units of soils and sediments. They have been employed in geosciences for more than three decades, but their performance in sedimentary archives can still be improved by deciphering other forcing factors than climatic. From the most common alkali and alkaline earth metals included in the weathering indices, K seems to be most suitable for deciphering paleoclimate records of temperate to subtropical non-arid climates, assuming the interpretation respects the complex of controlling factors on sediment geochemistry. As a case study, normalised K concentrations in siliciclastic sediments of the Most Basin (Miocene period, central Europe) are revisited here and variations compared with modern fluvially transported solids. Existing knowledge on manifold controls of K concentrations in sediments is summarised and used to propose list of possible controlling factors, in particular Al/Si and Zr/Rb as grain-size proxies, Ti/Al as provenance proxy relevant for K concentration in parent rocks, and K/Rb as a measure for possible effects of metasomatism. The K/Al or K/Ti element ratios may be efficient in chemostratigraphic correlations in siliciclastic basins and efficient proxies for chemical weathering in the source area. The proposals in this work should stimulate future studies to overcome the underrepresentation of continental sediments in paleoclimate reconstructions.

Impacts of Material Engineering Properties on Slope Wash and Stability in Fine-Grained Bedrock Slopes at Fossil-Bearing Sites, Badlands National Park, South Dakota, USA

Engineering properties of bedrock materials at Badlands National Park were used to develop models for Park managers to assess slope erosion and stability for fossil resource protection. Six fully instrumented sites were used to document slope conditions. Bedrock consisted of Oligocene White River Group rocks. Bulk erosion rates correlated to grain size with silty-sandy materials producing higher mass erosion rates as a function of the silt-to-clay ratio and plastic index. Data indicated that as grain size decreased, plastic index increased leading to a decrease in erodibility. These parameters were used to construct a grain-size proxy, ψ, that was substituted for grain size, D, in Bagnold’s entrainment equation and provided significant improvement in calculation of critical entrainment velocities for fine-grained materials. Hydraulic analyses of slope and pediment surface processes indicated surface roughness was a controlling factor and materials washed from rough steep slopes were effectively transported across smooth low-angle pediments with slope-to-pediment angle ratios of nearly 6:1. Slope stability modeling of ten slopes produced high factors of safety for all slopes, even under saturated conditions and was attributable to clay cohesion. All results were used to construct models that predicted years until net slope erosion equaled 2.5 cm (1 inch). Using these results, Park managers were advised to visit erosion-prone sites on a 1- to 6-year schedule, based on site geology and slope aspect, to adequately protect critical fossil resources from destruction.

Mineralogy and geochemistry of modern Yellow River sediments: Implications for weathering and provenance

This study illustrates the textural, mineralogical and geochemical signatures of sediments from the upper Yellow River. Sediments of major tributaries have also been examined to study the influence of provenance, weathering intensity, and hydraulic sorting on the spatial compositional variability of sediments. Similarly to floodplain sediments, riverbed deposits are strongly depleted in MgO and Na2O, and enriched in CaO and Si2O relative to the upper-continental-crust standard. The pattern of rare earth elements (REE) indicates LREE enrichment and negative Eu anomaly (Eu/Eu* = 0.54–0.68). Low CIA (Chemical Index of Alteration) values indicate that the sediments from the trunk-river channel, floodplain, and major tributaries have not experienced intense chemical weathering in arid to semi-arid climatic conditions. The distribution of chemical elements shows a significant increase of Zr and Hf with coarsening of grain-size, whereas Rb, Ni, and V are associated with finer sediment fractions supplied by adjacent dune fields and tributaries. The Al/Si ratio (a proxy for grain size) correlates positively with CIA, Fe2O3, MgO, and K2O, but not with Na2O, reflecting grain-size control. Clay mineral assemblages in the upper Yellow River and in tributaries draining the Loess Plateau (e.g., Qingshui and Zuli Rivers) are dominated by illite and chlorite, whereas the abundance of smectite characterizes the middle reaches of the Yellow River and the Ten tributaries draining the Ordos Plateau.

Climate change in arid central Asia since MIS 2 revealed from a loess sequence in Yili Basin, Xinjiang, China

K-feldspar pIRIR dating was used to establish a chronological framework for the KS15-05 loess section in the Yili Basin, northern Xinjiang Province, China, in arid central Asia. The reliability of the dating results was verified from the luminescence characteristics and internal checks. The chronology was used to calculate mass accumulation rates (MARs) for the section and the paleoclimatic proxies of grain size and magnetic susceptibility were also analyzed. The high dust accumulation patterns during the last glacial maximum in Yili Basin are consistent with those of the Chinese Loess Plateau (CLP). On a millennial-scale, the Bølling-Allerød (B/A) interstadial is clearly reflected in the KS15-05 section by the variation of the 2–10 μm grain-size fraction, suggesting the influence of the Westerlies which dominate the modern atmospheric circulation of the region. However, the B/A interstadial is poorly recorded in grain-size records of the CLP and this disparity may provide additional information about the nature of the transmission of climate signals from the North Atlantic region to Asia. Specifically, the zonal transmission of the B/A warm signal to the CLP may have been obscured by the cooling effect of High-latitude cold air to the north of the CLP.

Pleistocene climate change inferred from multi-proxy analyses of a loess-paleosol sequence in China

The aeolian loess blanketing the Chinese Loess Plateau (CLP) is sensitive to climate change in monsoonal East Asia. Here, we present a multi-proxy climatic record from a Pleistocene loess-paleosol sequence from the Lantian Basin on the southern margin of the CLP. The measurements include magnetic susceptibility and related magnetic properties, bulk median grain-size, color reflectance, and the color-inferred hematite versus goethite ratio (Hm/Gt). A long-term aridification and cooling trend during the interval from ca 2.22–0.43 Ma is indicated by two magnetic grain-size proxies, corresponding to the global climatic cooling of the late Cenozoic. In addition, at least four intervals of climatic extremes are evident in the record of Hm/Gt ratio: at 1.71–1.65 Ma, 1.26–1.24 Ma, 0.94–0.86 Ma, and 0.62–0.48 Ma. These intervals are characterized by distinct regional climates, which contrast with the global climatic conditions represented in marine sediments. For example, a relatively arid climate is documented from 1.71 to 1.65 Ma, which was rapidly succeeded by a relatively humid climate which is associated with the earliest hominin (with an age of ca 1.63 Ma) in the Lantian Basin.

Pseudo-outcrop Visualization of Borehole Images and Core Scans

A pseudo-outcrop visualization is demonstrated for borehole and full-diameter rock core images to augment the ubiquitous unwrapped cylinder view and thereby to assist non-specialist interpreters. The pseudo-outcrop visualization is equivalent to a nonlinear projection of the image from borehole to earth frame of reference that creates a solid volume sliced longitudinally to reveal two or more faces in which the orientations of geological features indicate what is observed in the subsurface. A proxy for grain size is used to modulate the external dimensions of the plot to mimic profiles seen in real outcrops. The volume is created from a mixture of geological boundary elements and texture, the latter being the residue after the sum of boundary elements is subtracted from the original data. In the case of measurements from wireline microresistivity tools, whose circumferential coverage is substantially less than 100%, the missing circumferential data is first inpainted using multiscale directional transforms, which decompose the image into its elemental building structures, before reconstructing the full image. The pseudo-outcrop view enables direct observation of the angular relationships between features and aids visual comparison between borehole and core images, especially for the interested non-specialist.

Brief sea‐level fall event and centennial to millennial sea‐level variations during Marine Isotope Stage 19 in Osaka Bay, Japan

ABSTRACTDetailed sea‐level variation was investigated for Marine Isotope Stage (MIS) 19, based on diatom and grain size analyses of a marine sequence in a core of the Osaka Group. Diatom sea‐level proxies represent precession‐related signals correlated with highstands MIS 19.3 and 19.1, and lowstand MIS 19.2. Astronomical tuning shows the marine sequence has a uniform accumulation rate of about 60 cm ka−1. A rapid sea‐level fall event was found in the earliest MIS 19, demonstrated by several independent sea‐level proxies of diatom and grain size. This event began with a rapid sea‐level drop, followed by a gradual recovery, at about 783–782 ka. A maximum abundance of pelagic diatom taxa at a core depth of 402.20 m evidently shows the highest sea‐level peak in MIS 19, supported by many other proxies. Based on the diatom data, sea‐level change across MIS 19.1 is characterized by centennial to millennial fluctuations. The sea‐level fall event began just after the onset of a cooling event previously reported from the same core. Observations of a comparable sea‐level fall signal in many deep‐sea core records suggest the event is global.

Paleoclimatic record from Chumbur-Kosa section in Sea of Azov region since Marine Isotope Stage 11

oess–paleosol sequences preserve records of climatic change during the Quaternary, which is important for paleoclimate study. In this study, a loess-palaeosol sequence from the Chumbur-Kosa (CK) site in the Sea of Azov region was investigated to reconstruct climatic variability during the Marine Isotope Stage (MIS)11- MIS 1, using proxies of grain size (GS), magnetic susceptibility (χlf and χfd(%)), carbonate content (CaCO3%) and soil color. The results enabled formulation of a detailed description of the climatic characteristics related to each individual layer. The sequence indicates that the paleoclimate shifted progressively towards increasingly cooler, somewhat drier conditions. The CK section may thus be ideal for reconstructing climatic conditions during the Middle and Late Pleistocene in the Sea of Azov region. However, the χlfvalue of paleosol S2 in the CK profile indicates different characteristics from the other paleosol layers, dilution of carbonate resulting from carbonate leaching in L2 may be the main reason for the decrease in magnetic susceptibility. Furthermore, through simple analysis part of the environmental evolution process in the Sea of Azov region and Serbia during Middle and Late Pleistocene cycles. The climate cycle expressed by χfd(%)and χlfvariations show similar patterns, with rapidly alternating cold and warm intervals. Nevertheless, although the two areas had different climatic regimes, geographical settings, and loess source areas, both exhibited similar climate change trends since the MIS 11.