Palaeosol Development Research Articles

Modelling the paleopedological development of loess/palaeosol sections using discriminant function analysis of compositional geoscience data, case study in Eastern Croatia

Previous studies on the mineralogical differentiation of Pleistocene loess/palaeosol sections focused on the description and source material of four loess/palaeosol sections located on the eastern border of Croatia along the Danube: Zmajevac, Zmajevac I, Erdut and Šarengrad. The authors demonstrated the decreasing influence of the Danube and the increasing influence of the rivers draining the Central Bosnian Mountains of the Dinaric Ophiolite Zone both important source areas for aeolian sediments at the southern edge of the Carpathian Basin that transport material from the Central Bosnian Mountains. The aim of this research is to identify the palaeoclimatic factors that influenced the pedogenetic development of the studied palaeosols. The model was created based on the research results of the same four loess/palaeosol sequences in Eastern Croatia. This model can also be applied in other locations to determine the influence of certain climatic factors on the degree of pedogenetic development of individual palaeosols. The loess/palaeosol sequences were divided into eight comprehensive groups (horizons) based on their genesis, degree of pedological development and/or position in the soil profiles. The explanation of the typical patterns occurring between the studied horizons is based on the construction of a Discriminant Function Model (DFM) resulting from the analysis of the compositional data (CoDa) of the geochemical (major and trace elements) and granulometric (grain size) data of the loess/palaeosols in combination with external variables such as weathering coefficients and chemical soil properties. In the final phase, the DFM was transformed from structural (mathematical) to functional (process) terms. This revealed that three main themes dominate the formation of Pleistocene loess/palaeosol sequences: 1) the separation of well-developed palaeosols from parent material; 2) the separation of automorphic palaeosols from hydromorphic soils exposed to post-pedogenic waterlogging conditions; and 3) the differentiation of horizons (soils and alluvium) formed by the redeposition (by water or mudflows) of previously deposited aeolian material, regardless of whether and to what extent it was exposed to post-sedimentary pedogenesis.

Flow depth estimates and avulsion behaviour in alluvial stratigraphy (Willwood Formation, Bighorn Basin, Wyoming, USA)

AbstractThe size and geometry of river channels play a central role in sediment transport and the character of deposition within alluvial basins across spatiotemporal scales spanning the initiation of grain movement to the filling of accommodation generated by subsidence. This study compares several different approaches to estimating palaeoflow depths from fluvial deposits in the early Palaeogene Willwood Formation of north‐west Wyoming, USA. Fluvial story heights (n = 60) and mud plug thicknesses (n = 13) are statistically indistinguishable from one another and yield palaeoflow depth estimates of 4 to 6 m. The vertical relief on bar clinoforms (n = 112) yields smaller flow depths, by a factor of ca 0.3, with the exception that the largest bar clinoforms match story heights and mud plug estimates. This observation is consistent with modern river data sets that indicate unit bar clinoforms do not capture the reach‐mean bank‐full flow depths except in rare circumstances. Future studies should use story heights (i.e. compound bar deposits) and mud plugs to estimate bank‐full flow depths in alluvial strata. Additionally, the thickness of multi‐storied fluvial sandbodies (n = 102) and overbank cycles composed of paired crevasse splay and palaeosol deposits (n = 45) were compared. The two depositional units display statistically indistinguishable mean and median values. Building upon previous depositional models, these observations suggest basin rivers aggraded approximately one flow depth prior to major avulsion. This avulsion process generated widespread crevasse splay deposition across the floodplain. Once the main river channel stem was reestablished, overbank flooding and palaeosol development dominated floodplain settings. The depositional model implies river aggradation autogenically generated topography in the basin that was effectively filled during the subsequent avulsion. This constitutes a meso‐timescale (103–104 years) compensational pattern driven by morphodynamics that may account for the high completeness of fossil and palaeoclimate records recovered from the basin.

Climatic and tectonic effects on the origin and evolution of the Dereiçi travertines (the Başkale Basin, Eastern Türkiye), and neotectonic implications

The Başkale Basin is located in the easternmost part of Türkiye, within a tectonically active area, and located at the intersection of Europe, Asia and the Middle East. In this study, the Dereiçi travertines, one of the most important products of neotectonism in the basin, were investigated sedimentologically, mineralogically and geochemically. To understand the neotectonic evolution of the travertine succession, the sequence was studied from bottom to top as regards morphology, lithofacies and U/Th dates. Crystalline crust, coated gas bubbles, shrub, paper-thin raft and palaeosol lithofacies have been detected in the Dereiçi travertines, which are morphologically of layer type, two ridge types and terrace type. The Dereiçi travertines commenced to precipitate at the intersection of the Işıklı and Ilıcak faults at 255.56 ±9.01 ka, and their deposition continues today. Travertine deposition paused twice between 198.31 ±18–143.07 ±1.5 ka and 96.73 ±8.34–61.59 ±5.4 ka, when palaeosol development took place. According to field and laboratory studies, the Dereiçi travertines developed under climate and tectonic control. The Işıklı and Ilıcak faults played active roles in the development of the travertines. As the travertine ages are linked to movement on both faults, the age of the Işıklı Fault should be 255.56 ±9.01 ka or earlier, and that of the Ilıcak Fault should be 143.07 ±1.5 ka or earlier.

Sartanian (MIS 2) ice wedge pseudomorphs with hydromorphic pedosediments in the north of West Siberia as an indicator for paleoenvironmental reconstruction and stratigraphic correlation

Within the glacier-free scenario of the MIS 2 (Sartanian cryochron) environment in the north of West Siberia, it is important to search for the new regional paleoecological records and stratigraphic markers for this period. We studied large ice-wedge pseudomorphs filled with gleyic pedosediments developed on the high river terraces in the Nadym and Taz rivers basins as a tracer of the surface cryogenic and pedogenic processes during MIS 2. Field morphological observations and measurements, palynological analysis and radiocarbon dating of organic matter from soils and pedosediments were performed. Two sets of paleoecological indicators were discriminated: pseudomorph geometry evidence of the processes and conditions of ice wedge formation during the Last Glacial Maximum whereas the paleopedological and paleobotanic results from the fills recorded the environments of ice wedge melting at the end of MIS 2. Paleotemperatures 7–10 °C lower than at present are inferred during the major part of Sartanian, even at its end continuous permafrost persisted providing development of swampy tundra vegetation and cryohydromorphic palaeosols. We propose to define Taz-Nadym cryopedogenic horizon as a representative regional unit for MIS 2 and to correlate it with synchronous cryogenic and palaeosol units in Central and Eastern Europe.

Palaeosols in an Upper Pliocene fluvial to shallow marine succession (Valdelsa Basin, Central Italy): A sequence-stratigraphic perspective

The present study provides an example of how palaeopedology and facies analysis may be integrated for the interpretation of a cyclothemic succession in the Upper Pliocene (Piacenzian) of the Valdelsa Basin (central Italy). The stacking of facies and intervening bounding surfaces, including palaeosols, outline a hierarchy of elementary (EDS) and composite (CDS) depositional sequences within the unconformity-bounded stratigraphic units (S4-S6 synthems) which compose the succession. The focus of the study is on synthem S4 and the transition to synthem S5. Synthem S4 records the development of a distal alluvial plain dominated by floodbasin mudstone with subordinated channelized sandstone (S4 1 ), followed by the incision of a fluvial valley aggraded by the cyclical stacking of braided and low sinuosity channelized conglomerate and sandstone (S4 2 ). Synthem S5 includes lower shoreface sandstone and inner shelf mudstone related to a major transgression which affected the study area during the late Piacenzian. Evidence of soil-forming processes is well preserved within sub-unit S4 1 where five palaeosols (PS4a-e) are stacked within the facies architecture of EDS1 c-d , both being defined as transgressive to high stand tracts. Increasing palaeosol development was observed within both EDSs, while palaeosols were generally thicker and more closely stacked within EDS1 d . Palaeosols were interpreted as marking minor cycles of accommodation space creation within EDS1 c , while marking a better defined high stand tract in EDS1 d . Increasing upward soil development was observed within each EDS, with generally better developed soils in EDS S41d. The unconformable transition from S4 to S5 is marked by a thin veneer of slope deposits, bearing pedogenic carbonates reworked from a missing PS4f palaeosol, formed during the shaping of the erosional surface separating sub-units S4 1 and S4 2 . The results of this study indicate that: 1) the sedimentary and pedogenic processes recorded in the channelized facies and palaeosols in the floodbasin facies of sub-unit S4 1 , are coherent with a palaeoenvironmental setting dominated by seasonal climate; 2) the facies-palaeosol architecture of S4 synthem corresponds to those described in sequence-stratigraphic models applied to continental successions. The pedo-sedimentary signature of the major sea-level fluctuation recorded in the transition between S4 and S5 synthem differs from these models. In this case a well-developed and drained palaeosol, expected to record the maximum regressive surface shaped during the falling stage of sea level, is missing. This difference is related to a rapid fall and subsequent rise of relative sea level which marked the transition between S4 and S5 synthems. • Palaeosol and facies analysis coherently restore a Piacenzian fluvial system. • A seasonal climate controlled sediment dispersal and weathering. • Palaeosols are key-surfaces in the cyclical fluvial facies architecture. • Cyclothemic stack of palaeosols partially fits sequence-stratigraphic models. • Major sequence boundary lacks a well developed palaeosol.

A tale of two signals: Global and local influences on the Late Pleistocene loess sequences in Bulgarian Lower Danube

In Central and Eastern Europe, research has been focused on loess associated with a plateau-setting, which preserves distinct and well-developed loess and palaeosol units linked to orbital scale changes. This has led to the view that during the last glacial period the Middle and Lower Danube predominantly experienced dry continental climates and supported steppic environments. However outside of the typical plateau setting, some authors have reported a presence of embryonic palaeosols within loess units suggesting sufficient moisture for short-term pedogenesis, and therefore either large scale moisture delivery systems and/or influence of local climatic and/geomorphic factors. Here the palaeoenvironmental and palaeoclimatic history is reconstructed based on two loess-palaeosol profiles in Slivata, North Bulgaria. The site is located in proximity to both the Carpathian and Balkan Mountains and rest on the Danube river terrace. To understand the timing of sediment deposition and dust fluxes chronological approaches combining quartz optically stimulated luminescence (OSL), feldspar post infrared-infrared stimulated luminescence (pIR-IRSL), and tephra correlation were applied. The results are coupled with high-resolution particle size and magnetic susceptibility analysis to provide an overview of past environmental conditions at the site. Finally, zircon U–Pb ages are used to understand potential changes to sediment delivery patterns, in the context of the site development.The investigated profile at Slivata 2 preserves a loess-palaeosol record spanning 52–30 ka, with a very complex sedimentary sequence that switches between periods of enhanced dust flux and sediment accumulation, and palaeosol development. The Slivata 2 sequence is also punctuated by multiple thin “palaeosol” like units that are interpreted as colluvial “soil” deposits on the basis of sedimentology, provenance, and geochronology, indicating a highly variable and dynamic landscape responding to the surrounding environment. The chronology shows very rapid sediment accumulation at Slivata 1 during LGM, with mass accumulation rates similar to sites in the Carpathian Basin, suggesting strong winds and high sediment supply rates. Yet LGM loess is punctuated by a thin palaeosol, which developed between 20–19 ka. This coincides with a temporary glacial retreat in the Carpathian Mountains and higher moisture availability in Eastern Carpathians, and therefore points to localised influences on loess-palaeosol development. Moreover data from Slivata 1 shows soil development and by extension landscape and climate stabilisation shortly prior to 14 ka. The pre-Holocene onset of pedogenesis at Slivata supports ecological and glacial evidence of weak Younger Dryas from the South Carpathian Mountains.Lastly this paper provides a geochemical analysis of the thin tephra horizon preserved in the Slivata 2 profile, which was correlated to the Cape Riva/Y-2 tephra. Consequently Slivata is the most northerly terrestrial site found to contain this tephra horizon, which has implications for the understanding of the size of the Santorini's Cape-Riva/Y-2 explosion. The identification of the Cape Riva (Y-2) tephra horizon and new remodelled age of 21.92 ± 0.56 cal ka BP provides a new tephrostratigraphic marker for eastern European LGM loess.

Millennial-scale climate variability recorded in Late Pleistocene coastal deposits of Formentera Island (Balearic Archipelago, Western Mediterranean)

Pleistocene aeolian deposits interbedded with marine deposits, colluvial deposits and palaeosols are observed in area of Es Copinar, Caló d'es Mort and Es Ram-s’Estufadors in Formentera Island. The sedimentary succession outcropping along the south-eastern coast of the island is characterized by a well-exposed high-resolution succession representing the main climate and geomorphological changes that occurred in this part of the western Mediterranean during the late Pleistocene. In this study we present the sedimentology and stratigraphy of carbonate sandstone, marine deposits, breccias and the aeolian-alluvial interaction deposits and silty facies, which allow describing ten major sedimentary units. Optically stimulated luminescence (OSL) dating and the biochronostratigraphic fauna from the marine deposits indicate that their deposition took place during the Last interglacial-glacial cycle, and their succession recorded Heinrich and Dansgaard-Oeschger events (DO). In this sense, dryer and cold Heinrich events led to the formation of extensive coastal dune fields when the sea level dropped. On the other hand, relatively warmer and wetter DO events drove the development of palaeosols and the aeolian-alluvial interaction deposits.

Pliocene–Pleistocene sedimentary and geomorphologic development of the Vasilikos river catchment, S Cyprus, in relation to uplift of the Troodos ophiolite and climate-related changes

AbstractThe Pleistocene development of the Vasilikos River exemplifies the interaction of focused, tectonically induced surface uplift and climate-influenced changes. The resulting sediments are well exposed in Vasilikos Quarry and in the main river catchment further east. An important erosional surface incises the highest-level (oldest) fluvial conglomerates, down into Late Pliocene – Early Pleistocene open-marine mudrocks (Nicosia Formation), allowing integration with the circum-Cyprus sedimentary–geomorphic development (F1–F4 stages). To determine where the quarry deposits lie in relation to the Vasilikos river catchment, the fluvial deposits were mapped and valley profiles were constructed, revealing four main episodes, each associated with incision and distinctive fluvial deposition. Source lithology strongly influenced channel morphology, infill and adjacent slope-sediment (colluvium) composition. Palaeosols, particularly red-brown terra rossa, developed on abandoned fluvial terraces and adjacent hillslopes, especially overlying F3 surfaces. The combined evidence allows close correlation of the Vasilikos river and quarry deposits. Relatively coarse (chalky conglomerate/breccia) and fine-grained colluvium (calcareous silt – Cyprus harvara) developed especially on lower hillslopes following incision (mainly above F2 and F3 surfaces). Based on regional comparisons, overall sediment aggregation ended during the Early Pleistocene. The F1–F2 surfaces and deposits are inferred to be Middle Pleistocene, the F3 ones later Middle Pleistocene and the F4 ones near the Middle–Late Pleistocene boundary. Geomorphology and deposition were tectonically forced during strong, focused Early–Middle Pleistocene surface uplift. Coarse clastic ruff-off and palaeosol development (terra rossa) and related sediment aggradation are inferred to have increased during warm, humid periods. Late Pleistocene geomorphology and deposition were more influenced by climatic change, with semi-perennial streamflow, rapid sediment aggradation and palaeosol (terra rossa) development during warm, humid periods (interglacials). Cooler (glacial) periods enhanced fluvial-incision, sediment-bypassing and hillslope colluvial processes (e.g. frost shattering, downslope creep and mass flow) when sediment transport (bypassing) exceeded sediment supply. Neotectonic faulting affected the catchment but did not greatly affect geomorphology or sediment supply. Although climate / climate change (and eustatic sea-level change) had an important influence, tectonics is interpreted as the fundamental driver of geomorphological development and fluvial sedimentation, with implications for other areas, regionally to globally.

High‐resolution stratigraphy of a Quaternary fluvial deposit based on magnetic susceptibility variations (Jászság Basin, Hungary)

Quaternary fluvial succession of the Jászság Basin (Hungary) was investigated, challenging the stratigraphical potential of ‘early postglacial fluvial magnetic susceptibility episodes' recognized earlier in the Körös Basin. Low field magnetic susceptibility (MS) was measured in four boreholes from the basin centre and margins, representing channel and flood‐plain environments. Statistical distributions of MS data contain significant sets of outliers, regardless of facies conditions. The downhole distribution of these outliers produces magnetic susceptibility cycles. Supported by magnetic susceptibility cycles, high‐resolution facies correlations were performed reflecting a steady palaeohydrographical situation in the area, with a trunk river to the southeast and tributaries to the northwest. SEM‐EDX data revealed that ferromagnetic grains are responsible for the outlying MS values. The heterogeneous association of magnetite indicates a catchment area with volcanic and metamorphic rocks, while the group of small (<5 μm) magnetite octahedrons originated from nearby rhyolitic tuff formations. Magnetic grains were transported along channel belts, while small (<2 μm) magnetic particles were floated onto flood‐plains attached to clays. Climatic control is indicated by peaks at ~100 ka frequency in spectra of MS records and was also detected in palaeosol development and in flood frequency using the spectra of measured colour (~100 ka) and logged resistivity (~100 ka, ~41 ka), respectively. The climate‐dependent MS signal traceable far into the basin in both channel and flood‐plain environments can be summoned when the Quaternary fluvial succession of the Pannonian Basin is investigated, assuming some sources of magnetite in the catchment areas. According to the concept of ‘fluvial magnetic susceptibility episodes’, the early postglacial escape and spreading of the magnetite fraction control the MS signal that can support mapping of the unconformable Quaternary base and building of high‐resolution models of aquifers.

Coupled stalagmite – Alluvial fan response to the 8.2 ka event and early Holocene palaeoclimate change in Greece

We explore the expression of early Holocene climatic change in the terrestrial Mediterranean of southern Greece. A regional palaeoclimate record from stable isotope and trace element geochemical proxies in an early Holocene (~12.4 ka to 6.7 ka) stalagmite is compared to the timing of palaeosol (entisol) development on an early Holocene alluvial fan located <100 km from the stalagmite site. Radiocarbon dated entisol development records fan abandonment surfaces, which can be coupled to the stalagmite climate signal. Variations in δ13C best record the main elements of palaeoclimatic change, more negative values indicating soil carbon input to karst groundwater under wetter conditions. The wettest conditions begin around 10.3 ka, coincident with the start of sapropel 1 deposition in the eastern Mediterranean. The widely documented northern hemisphere ‘8.2 ka event’ of cooler and drier conditions has a muted δ18O climatic signal in common with other stalagmite climate records from the wider Mediterranean. However, less negative δ13C values do record a period of episodic dryness between ~8.8 and ending at 8.2 ka. Wetter conditions re-established after 8.1 ka to the end of the record. The oldest alluvial fan entisols were developing by ~9.5 ka, and a prominent rubified entisol developed ~8.3 to 8.4 ka, indicating pedogenesis within dating error of the 8.2 ka event. The speleothem record of episodic dryness between ~8.8 and 8.2 ka, combined with other regional proxies, is consistent with the notion that precipitation patterns in Greece may have changed from predominantly winter frontal to summer convective during this period. Palaeosol formation on the alluvial fan may have been an allocyclic response to this change. It is plausible that fan-channel incision, driven by temporary development of a ‘flashier’ summer rainfall regime, isolated large areas of the fan surface allowing onset of prolonged pedogenesis there.

Holocene aeolian stratigraphic sequences in the eastern portion of the desert belt (sand seas and sandy lands) in northern China and their palaeoenvironmental implications

This paper presents the environmental history and its responses to palaeoclimatic changes since the start of the Holocene in the eastern portion of the desert belt (sand seas and sandy lands) in northern China by comparing the aeolian sand-palaeosol sequences and their palaeoclimatic proxies. The optically stimulated luminescence (OSL) ages of the aeolian sand-palaeosol sedimentary sequences and a series of palaeoenvironmental proxies show that: (1) The large-scale dune landscape currently in the Kubuqi Sand Sea was formed during the Holocene in general; and the palaeosol was generally developed during the period of 4–2 ka, indicating conditions favorable for vegetation growth, soil development, and organic carbon accumulation due to increased precipitation or effective moisture and weakened aeolian activities; the large-scale expansion of dunes in the recent 2 ka is closely linked to human activities. The variable discharge of the Yellow River with diversions for irrigation may have resulted in a more consistent supply of aeolian particles for dune field expansion. (2) The dune landscape of the Hunshandake Sandy Land was likely formed around 12 ka, and before this, the western part of the Hunshandake Sandy Land would have been covered by a single large lake; it was obviously wetter than today in the sandy land during the period of 9.6–3 ka and the palaeosols were developed at the same time. But the aeolian activities have not been completely dormant in this long-lasting wetter epoch; because the Holocene wetter period was likely time-transgressive across the region. (3) The palaeosol of the Hulunbuir Sandy Land began to develop as early as 14.5 ka, probably continuing until the last 2 ka. The palaeosol development of various dune fields in the eastern portion of the desert belt (sand seas and sandy lands) in northern China is spatially heterogeneous, and even the palaeosol development time in different locations within each sandy land is inconsistent. During the middle Holocene (especially the 7.5–3.5 ka), all the sandy lands were stabilized in general and the intensity of aeolian activities was significantly weakened. The number of palaeoenvironmental records in the eastern portion of the desert belt (sand seas and sandy lands) in northern China has increased rapidly in the past decade, but the amount of published data still does not match the vast extent of the dune fields. It does require much more in-depth palaeoenvironmental studies for a full understanding of the relationship between aeolian activities and climate change in northern China.

Factors governing the pattern of glacier advances since the Last Glacial Maxima in the transitional climate zone of the Southern Zanskar Ranges, NW Himalaya

The present study investigates the relics of glacier advances and retreats in the transitional climatic zone of the Southern Zanskar Range, NW Himalaya in response to the temporal changes in the Indian Summer Monsoon (ISM) and mid-latitude westerlies. The study identifies four glacier advances which are named from the oldest to youngest as the Southern Zanskar Glacier Stage-4 (SZS-4) to SZS-1. The SZS-4 remains undated, however based on the existing chronology of the stratigraphically equivalent moraines/trimlines in the region; it is conjectured to the Marine Isotope Stage-4 (MIS-4). The optical chronology obtained during the present study dates the SZS-3 to 22.8 ± 1.9–19.1 ± 1.9 ka which corresponds to the Last Glacial Maxima (LGM). The SZS-2 is dated to 15.7 ± 1.3–14.3 ± 1.3 ka (late Glacial period) whereas, based on the chronology of the recessional moraines (4.9 ± 0.4–4.5 ± 0.3 ka) the youngest SZS-1 is assigned to ∼6 ka (mid-Holocene). The snout proximal moraines are attributed to the Little Ice Age (LIA)/historical times. The pulsating deglaciation associated with each advance since the LGM is represented by the recessional moraines and outwash gravel terraces. The older gravel terrace is dated between 10.8 ± 0.9 and 6.5 ± 0.5 ka and is attributed to SZS-2 deglaciation which is also manifested by the deposition of sandy facies in a relict lake sequence (6.7 ± 0.6 ka) and development of palaeosol (5.6 ± 0.5 ka). We propose that the glacial advances were triggered by the millennial scale cooling events during the periods of strengthened westerlies and thus, suggest a synoptic scale coupling with the Northern Atlantic. The deglaciation is suggested to occur during the warmer ISM dominated phases. The late Holocene climatic instability that followed the recession of SZS-1 is manifested by the development of rhythmites (3.8 ± 0.5 ka), loess (2.5 ± 0.2 ka), and palaeosol (2189 ± 296 cal yr BP).

Facies and palaeosol analysis in a progradational distributive fluvial system from the Campanian–Maastrichtian Bauru Group, Brazil

AbstractThe Upper Cretaceous Bauru Group in south‐east Brazil consists of alluvial strata whose characteristics and distribution indicate a fluvial system developed in a semi‐arid to arid climate. Sections exposed within a 90 000 km2 study area in Minas Gerais State (in south‐eastern Brazil) were evaluated using facies and palaeosol analysis to formulate depositional and pedogenic models that may account for geomorphic and climate features. From east to west, the study succession records a gradual decrease in grain size, an increase in the width/thickness ratio in channels, a decrease in the lateral and vertical connectivity of channel deposits, and an increase in overbank deposits. The fluvial architecture indicates a braided channel belt, ephemeral ribbon–channels, and an unconfined fluvial facies from east to west in the study area. The lateral and vertical distribution of facies, stratigraphic architecture and palaeocurrent data suggest proximal, medial and distal portions of a progradational distributive fluvial system. The sedimentary dynamics were marked by the building and abandonment of channels related to processes of aggradation, vegetation growth and palaeosol generation. Macromorphological and micromorphological analyses have identified pedological and mineralogical features that indicate an arid to semi‐arid climate with a provenance from the north‐eastern part of the basin (Alto Paranaiba Uplift). From the proximal to the distal portions of the distributive fluvial system, the palaeosol development is different. In the proximal portion, the palaeosols are absent or poorly developed, allowing a possible general comparison with the present soil order: Inceptisols and Aridisols. In the medial portion of the fluvial system, the palaeosols are well‐developed and characterized by Bt, Btk, C and Ck horizons (Alfisols, Aridisols, Inceptisols and Entisols). Poorly drained to well‐drained palaeosols from the base to the top in the distal plain (Aridisols and Inceptisols) are associated with geomorphic and hydromorphic changes in the fluvial system due to progradational evolution. The genetic relationship between the fluvial architecture and the palaeosols enhances the understanding that the sedimentation and pedogenesis that occurs in different portions of the distributive fluvial system are related to the tectonic and climatic evolution of the basin.

Constraining the timing of palaeosol development in Iranian arid environments using OSL dating

Abstract The ages of palaeosols in arid environments in Iran are constrained using the optically stimulated luminescence (OSL) signal from quartz. The luminescence properties of quartz OSL and K-feldspar infrared stimulated luminescence (IRSL) at 50 °C (IR50) and post-IR IRSL at 290 °C (pIRIR290) signals are compared to investigate the degree of bleaching of quartz OSL in individual samples at the time of deposition. A comparison between the quartz OSL and K-feldspar IR50 ages shows that 12 out of 15 samples were probably well-bleached prior to deposition. The 17 OSL ages constrain at least four broad phases of sediment deposition and soil formation on the central Iranian plateau: (i) prior to, and (ii) during, mid/late MIS 5 (at Isfahan and Lar), (iii) MIS 3 (at Bam, Mahan and probably Isfahan) and (iv) MIS 1 (at Rayen and Jiroft). In summary, there is no convincing evidence for palaeosol formation during MIS 4 and MIS 2; however pedogenesis does appear to have taken place during all other marine isotope stages over the last full glacial-interglacial cycle.

Climate and soil moisture content during development of the first palaeosol in the southern Loess Plateau

SummaryThe scientific problems concerning Quaternary soil water content and the water cycle have not been researched. This study examined the soil water content and depth of distribution of gravitational water in the south Loess Plateau during development of the first palaeosol layer (S1) by methods such as field investigation, electron microscopy, energy spectrum analysis, chemical analysis, and so on. The purpose was to reveal the climate, water balance and vegetation type at the time when S1 developed. The depth of migration of CaCO3 and Sr were 4.2 m below the upper boundary of the S1 palaeosol, and the depth of weathered loess beneath the argillic horizon was 4.0 m. Ferri‐argillans developed well in the argillic horizon and their depth of migration was 1 m below the argillic horizon. These findings suggest that the climate during the last interglacial was subtropical and humid, and the soil‐water balance was positive. Gravitational water was present to a depth of least 4.2 m from the top of S1, and the water content was adequate for tree growth. The chemical weathering index showed that this palaeosol has been moderately weathered.Highlights We studied the palaeo-water content index during development of the first palaeosol. Soil water balance during development of S1 palaeosol in the south Loess plateau was positive. Available water content was 14% during development of S1 palaeosol. We suggest that a subtropical climate and forest vegetation prevailed.

OSL dating of a mega-dune in the eastern Lake Qinghai basin (northeastern Tibetan Plateau) and its implications for Holocene aeolian activities

Abstract Aeolian sediments are widely distributed in the Lake Qinghai basin of the northeastern Tibetan Plateau (TP), but the history of aeolian activities in the basin is indistinct, and the underlying impacting factors are still poorly understood. In this study, depositional history of a mega-dune from the eastern Lake Qinghai basin was determined by optically stimulated luminescence (OSL) dating. The results show that nearly 30 m thick of sands accumulated during the interval of 7-6 ka, followed by soil formation during the last ∼5 ka. Together with previously published OSL ages of aeolian sediments, the Holocene aeolian activity in the Lake Qinghai basin was reconstructed as following: (1) The temporary aeolian activity appears to be characterized with a pattern of strengthened intensity during the first half of Holocene but relatively lowered intensity with a gradual decreasing trend afterward; (2) The interval of 7-6 ka in the middle Holocene witnessed a transition from dune activation towards stabilization; (3) A very low sand accumulation rate during the period of 5-3 ka and the contemporaneous extensive palaeosol development imply the least aeolian activity at that period. We inferred that the Holocene aeolian activity in the Lake Qinghai basin was mainly controlled by sediment supply, which was in turn modulated by the lake-level change of Lake Qinghai. Large amounts of sand were available, when the lake level dropped and then beach sands could exposure for deflation.

Integrated sedimentology and ichnology of Late Jurassic fluvial point‐bars – facies architecture and colonization styles (Lourinhã Formation, Lusitanian Basin, western Portugal)

AbstractIntegrated sedimentological and ichnological case studies of ancient meandering river systems have, for the most part, focused on the deposits of the fluvial–tidal transition zone; much less emphasis has been placed on the purely fluvial realm above the landward limit of tidal effects. This problem needs to be addressed so that in future the defining sedimentological and ichnological criteria assigned to ancient fluvial reaches are sufficiently well‐established to enable their separation from the down‐dip fluvial–tidal transition zone. Accordingly, a case study has been carried out on a well‐exposed meander belt deposit from the Late Jurassic Lourinhã Formation of the Lusitanian Basin, western Portugal (Praia Do Valmitão, Ribamar). Analysis indicates that the meander belt here comprised mixed‐load fluvial channels traversing a vegetated floodplain subject to a seasonal winter wet/summer dry palaeoclimate. This setting facilitated the development of both calcic palaeosols and shallow lakes on the adjacent floodplain. Critically, there is no evidence of the effects of tidal modulation on bedding structures, thereby establishing purely fluvial conditions. Heterolithic point‐bar deposits generated in this setting are bioturbated extensively by a trace fossil assemblage dominated by the meniscate traceTaenidium barretti, withSkolithos linearis,Planolites beverleyensisandCylindricumisp. also recognized. A number of factors suggest that theTaenidium barrettiproducer in this case was a subaquatic organism living in an active fluvial channel setting (i.e. not colonizing subaerially exposed channel‐margin/floodplain deposits). Accordingly, there are some implications for current ichnofabric/ichnofacies models in the continental realm. Firstly,Taenidium‐dominated ichnofabrics need not necessarily be confined to colonization beneath subaerially exposed surfaces; they might also be produced within submerged substrates. Secondly, there is scope to extend the range of theScoyeniaichnofacies to include active fluvial channels and not simply those channels that were inactive or abandoned.

Beyond the gorge: Palaeoflood reconstruction from slackwater deposits in a range of physiographic settings in subtropical Australia

The application of palaeoflood hydrology in Australia has been limited since its initial introduction >30years ago. This study adopts a regional, field-based approach to sampling slackwater deposits in a subtropical setting in southeast Queensland beyond the traditional arid setting. We explore the potential and challenges of using sites outside the traditional physiographical setting of bedrock gorges. Over 30 flood units were identified across different physiographical settings using a range of criteria. Evidence of charcoal-rich layers and palaeosol development assisted in the identification and separation of distinct flood units. The OSL-dated flood units are relatively young with two-thirds of the samples being <1000years old. The elevation of all flood units have resulted in estimated minimum discharges greater than the 1% annual exceedance probability. Although these are in the same order of gauged flood magnitudes, >80% of them classified as ‘extreme event’. This study opens up the renewed possibility of applying palaeoflood hydrology to more populated parts of Australia where the need for improved estimation of flood frequency and magnitude is now urgent in light of several extreme flood events. Preliminary contributions to improve the understanding between high magnitude floods and regional climatic drivers are also discussed. Recognised regional extreme floods generally coincide with La Niña and negative IPO phases, while tropical cyclones appear to be a key weather system in generating such large floods.

Morphological, pedological, and sedimentary evolution on the fringe of the southwestern European drylands during the Late Pleistocene and Holocene: Evidence of climate and land use changes

Late Quaternary alluvial sedimentary units in the Guadiana Menor River valley, a tributary of the Guadalquivir River in southern Spain are described based on geomorphological mapping, sedimentological analysis, palaeosol development, and radiocarbon chronology. Four infill units in the valleys were differentiated with surfaces at +45 (MU1), +70 (MU2), +8–6 (MU3), and +10m (MU4) above the riverbed. Each unit is capped by a palaeosol.Unit MU1 (Late Pleistocene: >43.5–34calkyrBP) consists of gravel and sand in channels and bars in braided river systems distally evolving to silty clays in the floodplain with vertic and clayic calcisols. It is capped by dark clays with gleysol development representing wetland environments in endorheic basins. Channelized gravels alternating with sandy silts make up unit MU2 (34–24calkyrBP), capped by a gypsisol and interpreted as a semi-arid alluvial fan distally evolving to playa-lake depositional systems. Unit MU3 (5600–2700calyrBP), extending along the valley bottom, is represented by gravels and sand distally evolving to a red and white laminated rhythmite of silt and clay deposited in the playa. Unit MU4 (600–700calyrBP) is scattered and represented by centimetre-thick gravels and sand sheet layers deposited by sheet flows in semi-arid constrained alluvial fans.Alternating intervals of alluvial aggradation (>43.5–24kyrBP, 5700–2700calyrBP, Late Middle Ages) and fluvial incision (24–6calkyrBP, 2700calyrBP to 1200AD, 1500AD to present) are interpreted as valley responses to climate variations and changes in land use. Two regional geomorphological changes are recorded in the sediments: (1) climate-induced aridification after 34calkyrBP with an arid climax after 24calkyrBP before the incision linked to the last glacial period, and (2) two human-forced aggradation stages (5600–2700calyrBP and 1200–1400AD) interrupting the Late Pleistocene to Early Holocene incisional trend.

Heterogeneous distribution of trace fossils across initial transgressive deposits in rift basins: an example from the Springhill Formation, Argentina

In the Lago San Martin region (Santa Cruz Province, Argentina), the Springhill Formation (50–100 m thick) overlies the syn-rift El Quemado Complex, showing outcrops with wedge geometry. Four sedimentological sections were measured in the field, and three depositional palaeoenvironments were interpreted. The Springhill Formation starts with fluvial deposits, characterized by channel-fills and floodplains with palaeosol development, passing transitionally to a coastal plain and, finally, to marine sedimentation. The initial sandy transgressive deposits (Facies Association 9) are the main focus of this study, in which 10 ichnogenera (Arenicolites, Bergaueria, Cylindrichnus, Diplocraterion, Macaronichnus, Palaeophycus, Planolites, Ophiomorpha, Rosselia and Skolithos) are described. Two ichnoassociations (foreshore and shoreface) were defined, and their distribution was controlled by the local palaeoenvironmental conditions, mainly energy, bathymetry and grain size of sediments. A highly bioturbated surface (BI = 4) was recognized in Section 1 showing a limited occurrence and disappearing over short distances perpendicular to the palaeoshoreline. This surface shows a sharp sub-horizontal gently undulating top contact with a bioturbation thickness between 15 and 25 cm. This type of surface has limited usefulness as a key correlative surface, because it is spatially restricted in rift basins due to the tectonic activity, which creates high accommodation space rates. A more accurate characterization of the initial transgressive deposits of the Springhill Formation – which is the most important reservoir in southern Patagonia – could provide new ideas to solve problems in sub-surface studies.