Distal Floodplain Research Articles

Pleistocene pedogenic carbonates from alluvial paleosols in eastern Sudan reveal a semi-arid and seasonal climate, similar to today

Pedogenic carbonates can provide important information regarding paleoclimatic conditions. Compared with East Africa, Pleistocene pedogenic carbonates in Sudan, particularly calcretes, have received very little attention, particularly with regard to local paleoclimatic reconstructions. Pleistocene alluvial sediments aged from ∼230 to <17 ka were deposited along the middle Atbara River in eastern Sudan. Intercalated in these alluvial deposits are paleosols in which different types of pedogenic carbonates occur. Petrographic, mineralogical and isotopic analyses were performed to reconstruct the regional paleoenvironmental conditions. The investigated pedogenic carbonates are appropriate for paleoclimatic reconstruction because they are free of inherited carbonate and diagenetic modification. The paleosols identified in a previous study as Aridisols/Calcisols contain calcrete horizons that consist of an orthic nodular horizon, sometimes overlain by a laminar horizon. Paleosols identified as Vertisols contain slickensides, and disorthic and septaric nodules. The paleosols show stable carbon and oxygen isotope values ranging between −9.12 and −5.12 ‰, and between −7.25 and −4.09 ‰, respectively. Supporting the previous study, the inferred climatic conditions were arid to semi‐arid, with a mixture of C3 and C4 vegetation cover, and paleoprecipitation greater than 350 mm/yr, similar to that of the present-day, with likely higher rainfall during the formation of Vertisols than Aridisols/Calcisols. The thickness and morphology of Pleistocene calcretes in eastern Sudan are similar to those in East Africa, suggesting similar climatic conditions during their formation. Well-and weakly-developed calcretes in Aridisols formed in distal and proximal floodplains, respectively, whereas well-developed vertic horizon in Vertisols formed in distal floodplains.

Changes in soils and terrestrial landscapes of the Appalachian Basin (Conemaugh, Monongahela, and Dunkard groups), U.S.A., at the onset of the late Paleozoic climate transition

ABSTRACT Changes in global climate from the Late Pennsylvanian to early Permian resulting from the destabilization of ice sheets in the Southern Hemisphere had important effects on terrestrial landscapes around the Paleozoic world. In the northern Appalachian Basin (U.S.A.), evidence for this transition and its effects on terrestrial systems is preserved in numerous paleosols in the Conemaugh, Monongahela, and Dunkard groups that formed in various alluvial environments. Several studies along a 50 km west–east and 40 km north–south transect through southeast Ohio and southwest West Virginia resulted in the recognition of 24 different pedotypes. An up-section shift in pedotypes from Argillisols to Vertisols and Calcisols as well as an overall upward increase in the diversity of pedotypes records a significant change in soil-forming processes and landscapes. The landscapes of the Late Pennsylvanian were largely characterized by well-developed, clay-rich Alfisols of woodland ecosystems on distal floodplains bordered by poorly developed Inceptisols of early successional or marshland ecosystems on proximal floodplains. By the early Permian, these landscapes began to experience strongly seasonal climates and increasingly prolonged dry periods, resulting in the production of pronounced shrink–swell features and well-developed carbonate horizons. These landscapes were characterized by Vertisols and Inceptisols of highly heterogeneous brakeland ecosystems, with rapid changes in sedimentation, hydrology, and vegetation over short distances. Climatic conditions were prone to fluctuations between wet and dry states during the transition, resulting in a highly heterogeneous landscape that changed significantly through time.

Rapid subsidence in the Kathmandu Valley recorded using Sentinel-1 InSAR

ABSTRACT Urban subsidence poses significant challenges for rapidly developing cities. Published InSAR data reveal Kathmandu as a prime example, demonstrating an alarming rate of subsidence during rapid urban expansion. To monitor the spatiotemporal evolution of recent subsidence, we use Sentinel-1 Synthetic Aperture Radar (SAR) data and the LiCSBAS open-source processing package. Vertical surface motion maps from 2015 to present reveal many localized zones with high subsidence rates (>100 mm year−1), while the mountains that surround the valley have experienced slight surface uplift of ~5 mm year−1. The highest subsidence rate is ~200 mm year−1 and occurs in the centre of the Kathmandu metropolitan area. The distribution of subsidence in the valley matches with areas of the Pliocene to recent sediment up to 500 m thick. The deep aquifer compaction is likely to be the main driver of subsidence in the Kathmandu Valley. Time-series data show a dominant linear subsidence signal with weak sinusoidal signal peaks associated with groundwater recharge of shallow aquifers during the monsoon season. Subsidence rates decrease in proximity to the main river channels, likely driven by the seasonal recharge into the distal floodplain. The distribution of subsidence in the Kathmandu Valley has significant implications for future flood risk and infrastructure in the city.

Sedimentary texture of crevasse splays formed by present-day and palaeofloods against the background of floodplain geomorphology and lithofacies exposed in channel cut banks (in the Vistula River valley between Warsaw and Płock, Poland)

Abstract On the floodplain of a sandy, braided river in the Central European Lowland, we studied the sedimentary texture of two crevasse splays, which were: (1) formed due to a levee breach in the 2010 flood, and widely documented by hydrological, bathymetric and LIDAR data, (2) developed under natural conditions when the channel was not embanked by artificial levees (dikes). We compare the sedimentological results with a geomorphological map, a model of the floodplain geomorphology showing different facies of fluvial deposition derived from a meandering river, and deposits in cut banks of the river channel. The statistical parameters of the grain size composition and geomorphic features of the splay, shaped by overbank flow through the broken embankment, are similar to the natural landform. Most of the cut banks (60% of alluvial deposits were mapped there) consist of lithofacies representing proximal floodplain; 30% were distal floodplain (muds), and 10% channel (coarse sand with gravel, pebbles and cobbles). We speculate about the palaeogeography of the Lower Vistula, and the origin of muds and coarse deposits in the banks of the channel. We link these unusual sediments with avulsion, deposition in side arms during ice-jam conditions, and dredging of the channel bottom by suction excavator, which reached the fluvioglacial, suballuvial layer on the bedrock protrusion.

Downstream changes in floodplain sedimentation and their effects on channel avulsion in stream-dominated alluvial fans: The Cretaceous Duwon Formation in the southern Korean Peninsula

Stream-dominated alluvial fans are formed by the periodic channel avulsion running on their surfaces and are characterized by the downstream changes in hydrodynamics of stream flows and flood frequency. The spatial variations in hydrodynamics also control the sedimentation on the floodplain, which is important for sediment dispersal patterns on the stream-dominated alluvial fans as they feed back into channel avulsion processes. To understand the influence of downstream changes in hydrodynamics on the floodplain sedimentation and associated channel avulsion processes, we studied the Cretaceous Duwon Formation in the southern part of the Korean Peninsula. The Duwon Formation unconformably overlies the Paleoproterozoic basements and consists of gravelly braided stream deposits (FA-1), sandy braided stream deposits (FA-2), and calcretes-bearing floodplain deposits (FA-3). Close to the basements, FA-1 shows the radial paleoflow patterns, and the size of sediments and the ratio of channel to floodplain deposits decrease downstream over a relatively short distance (<7 km). This indicates that the Duwon Formation was deposited in the stream-dominated alluvial fans under arid to semi-arid climatic conditions, which can be classified into the proximal, medial, and distal zones.In the medial zone, the floodplain deposits are composed of the underlying, purple-colored sandstones and the overlying, compensational stacked crevasse channel and splay deposits (ca. 19 m thick) with the unsystematic paleoflow directions, finally overlain by the sandy braided stream deposits. In contrast, in the distal zone, the floodplain fines are composed of homogeneous clay and silt with calcretes and vegetation traces. These floodplain fines are interbedded with and overlain by the progradational stacked, coarsening- and thickening-upward trending, crevasse channel and splay deposits (ca. 18 m thick) with the constant paleoflow directions to those of the overlying sandy braided stream deposits. In the medial zone, a relatively large volume of discharge of the stream floods resulted in the frequent overbank flooding via the multiple breaching points and the concomitant growth of alluvial ridges by the combined effects of in-channel bed aggradation and compensational stacked crevasse channel and splay deposits resulted in a shift in the flow pathway of the sandy braided streams. In the distal zone, the floodplain fines containing calcretes and vegetation traces suggest the longer periods of non-deposition, providing sufficient time for the vegetation development. Once the channel levees collapsed, the vegetated channel levees stabilized the breaching point, and the breaching point progressively incised by the multiple flooding events, causing susceptibility to overbank flooding. Crevasse channel flows via the breaching point and associated overbank floodwaters led to a continuous supply of the coarse-grained sediments stacking on the cohesive, vegetated floodplain fines, with an increase in the cross-floodplain topographic gradient. As a result, crevasse channels were able to advance the distal floodplains, resulting in the development of progradational stacking pattern. With the cross-floodplain topographic gradient, the deposition of these erodible overbank flooding sediments on the cohesive, vegetated floodplain fines provided an alternative route for the parent channel, resulting in channel avulsion. Thus, this study suggests that downstream changes in hydrodynamics and associated floodplain sedimentation are important for channel avulsion and hence control the sediment dispersal patterns of coarse-grained sediments on the stream-dominated alluvial fans.

Gzhelian cyclothem development in the western North China cratonic basin and its glacioeustatic, tectonic, climatic and autogenic implications

The Gzhelian Ximing Sandstone–to–No. 8 Coal succession of the Taiyuan Formation in the Linxing gas field and adjacent areas records the complex nested architecture of the Palougou Cyclothem and component cyclothems 2–10 developed in the western North China underfilled cratonic basin. Integrated facies and sequence stratigraphic analysis of core, well log, outcrop, and seismic data reveals architectural variation of the Palougou Cyclothem in the study area from southwestward retrograding incised-valley estuary and lagoon (TST) through upward and northeastward prograding coastal plain to epeiric shelf (HST) into downward and eastward prograding open-coast tidal flat and epeiric shelf with aggrading distributive fluvial system (FSST). The component cyclothems vary in the internal architecture through the Palougou Cyclothem from mixed retrogradational–progradational (R–P; R/P > 1) cyclothems 2–4 in the early TST to retrogradation-dominated (R/P ≫1) cyclothems 5–7 in the late TST, progradation-dominated (R/P ≪1) Cyclothem 8 in the HST, and fluvial aggradation-dominated cyclothems 9 and 10 in the FSST. The Palougou Cyclothem and component cyclothems constrained by conodont-bearing limestone marker beds and radiometric dating have been observed to be substantially synchronized with the Gzhelian interglacial–glacial cyclothem and nested 400-kyr cyclothems in the North American Midcontinent and Donets Basin. The cyclic change in accommodation at the scale of the Palougou Cyclothem and component cyclothems has been ascribed to the third-order interglacial–glacial cycle and fourth-order, long eccentricity (ca. 400 kyr)-driven glacioeustatic fluctuations coupled with the tectonically driven source–to–sink reorganization. The progressively decreasing siliciclastic flux and increasing vegetation through both the Palougou Cyclothem and individual component cyclothems have been ascribed to the third- and fourth-order equatorial seasonally dry–wet climatic cycles coupled with the tectonically driven source–to–sink reorganization, in concert with the Gzhelian third- and fourth-order interglacial–glacial eustatic cycles. Both the transgressive fluvial degradation and the falling-stage fluvial aggradation have been ascribed to a higher-gradient fluvial profile relative to the gradient of the receiving North China epeiric shelf. The autogenic shoreline retreat, advance and channel migration modified the depositional response to the third- and fourth-order sea level rise through time. The termination of the falling-stage fluvial channel belts in the lateral and distal floodplain mires has been ascribed to the sustained fluvial aggradation and autodetachment of the fluvial fan from the syn-depositional shoreline in response to steady fall of relative sea level. This study contributes to a proper understanding of the Gzhelian North China intracratonic cyclothem development in response to the coupled glacioeustatic, tectonic, climatic, and autogenic processes at the third- and fourth-order scales, but also provides a context within which to interpret the symbiotic relationship, and predict the distribution, of superimposed coal–sandstone–shale gas reservoirs, and to investigate the impact of depositional heterogeneities on hydrocarbon generation and migration pathways.

Paleosols of the Maastrichtian dinosaur-bearing Chorrillo Formation (southern Patagonia, Argentina): Paleoenvironmental and paleoclimate implications

The Maastrichtian dinosaur-bearing Chorrillo Formation in southern Patagonia (⁓50° S, Austral-Magallanes Basin, Argentina) is a pedogenically modified fluvial succession, which records sediment deposition at mid–high paleolatitudes in the Southern Hemisphere. In order to reconstruct the paleoenvironment and paleoclimates for the Chorrillo Formation, we performed a paleopedological study (abiotic components) of the unit within a well-defined sedimentological–paleontological context, and considering new paleobotanical data of the unit. Using detailed macro and micromorphological features and clay mineralogy of the paleosols, we show that the Chorrillo Formation paleosols are overall smectite-rich soils with vertic and redoximorphic features (i.e., moderately developed hydromorphic Vertisol-, calcic Vertisol-, poorly developed hydromorphic Vertisol-, Histosol-, and argillic Vertisol-like paleosols). The small-scale or high-frequency stacking of such paleosols indicates that they developed under different hydrologic conditions, and subtle differences in grain-size (parent material) and topographic relief on a distal floodplain. Conversely, the large-scale or small-frequency vertical stacking of different paleosols is linked to avulsion processes. Paleobotanical remains through the Chorrillo succession demonstrates different ecological requirements for the inhabited part of the fluvial floodplain. Abiotic and biotic climate proxies suggest that these paleosols formed under a broadly temperate–warm and seasonally humid climate. Overall, these combined data record environmental and climatic conditions during the uppermost Cretaceous, and preserve a record of Maastrichtian terrestrial conditions in the Southern Hemisphere.

Defining Regional and Local Sediment Sources in the Ancestral Colorado River System: A Heavy Mineral Study of a Mixed Provenance Unit in the Fish Creek-Vallecito Basin, Southern California

The Colorado River has flowed across the dextral strike-slip plate boundary between the North American and Pacific plates since the latest Miocene or earliest Pliocene. The Fish Creek-Vallecito Basin (FCVB) lies on the Pacific Plate in southern California, dextrally offset from the point where the modern Colorado river enters the Salton Trough; it contains a record of ancestral Colorado River sedimentation from 5.3–2.5 Ma. The basin stratigraphy exhibits a changing balance between locally derived (L-Suite) and Colorado River (C-Suite) sediments. This paper focuses on the Palm Springs Group (PSG), a thick fluvial and alluvial sequence deposited on the upper delta plain (between 4.2–2.5 Ma) when the Colorado was active in the area, allowing the detailed examination of the processes of sediment mixing from two distinct provenance areas. The PSG consists of three coeval formations: 1) Canebrake Conglomerate, a basin margin that has coarse alluvial fan deposits derived from surrounding igneous basement; 2) Olla Formation, fan-fringe sandstones containing L-Suite, C-Suite, and mixed units; and 3) Arroyo Diablo Formation, mineralogically mature C-Suite sandstones. Stratigraphic analysis demonstrates that the river flowed through a landscape with relief up to 2000 m. Satellite mapping and detailed logging reveal a variable balance between the two suites in the Olla Formation with an apparent upward increase in L-Suite units before abrupt cessation of Colorado sedimentation in the basin. Stable heavy mineral indices differentiate L-Suite (high rutile:zircon index: RZi 40–95) from C-Suite (RZi: 0–20). Both suites have garnet:zircon index (GZi) and apatite:tourmaline index (ATi) mostly above 50, although many L-suite and mixed Olla samples have much lower ATi (20–50), suggesting that the distal floodplain was wet and the local sediment had a longer residence time there, or went through several cycles of erosion and redeposition. Heavy mineral analysis, garnet geochemical analysis, and detrital zircon U-Pb age spectra allow us to quantify the amount of mixing from different sediment sources. These data show that about 30% of the mixed units are derived from the Colorado River and that up to 20% of the L-Suite is also derived from the Colorado River, suggesting that there was mutual cannibalisation of older deposits by fluvial channels in a transitional area at the basin margin. Although this study is local in scope, it provides an insight into the extent and nature of sediment mixing in a two-source system. We conclude that most ‘mixing’ is actually interbedding from separate sources; true mixing is facilitated by low subsidence rates and the rapid migration of fluvial channels.

Palustrine limestones and calcretes as the sedimentary record of paleoenvironmental changes in a Late Permian semi-arid climate at the SE periphery of the Southern Permian Basin (the Holy Cross Mountains, Poland)

An important part of the Upper Permian (Zechstein) sequence in the Holy Cross Mountains (HCM) in Poland comprises continental carbonate facies where dryland and wetland depositional environments dominated the southeastern part of the Southern Permian Basin. Sedimentological and thin-section microfacies analysis of over 860 m of core from seven wells, supplemented with field observations from several outcrops from the HCM area, has allowed recognition of numerous siliciclastic and mixed silici‑carbonate facies which are related to alluvial fan, proximal and distal floodplains, and ephemeral lacustrine environments. Due to climatic seasonality and subsequent groundwater oscillations, the latter were frequently exposed, causing widespread desiccation cracking and pedogenesis. Continuous aggradation controlled by steady tectonic subsidence allowed the deposition and preservation of thick (> 30 m) units with numerous palustrine intervals. In such a low aggradation rate system, vertical and lateral changes in the continental facies associations reflect the climatic evolution from arid to semi-arid and then to sub-humid environments with enhanced climatic seasonality. These facies changes indicate a gradual increase in the water availability towards the Permian-Triassic boundary, which may support the hypothesis of generally increased wetting at the low-latitudes of Pangea, linked with the development of greenhouse conditions and enhancement of the intertropical convergence zone at that time. Continental carbonates are therefore recognised as high-resolution recorders of palaeoclimate and tectonics.

EARLY EFFECTS OF THE LATE PALEOZOIC CLIMATE TRANSITION ON SOIL ECOSYSTEMS OF THE APPALACHIAN BASIN (CONEMAUGH, MONONGAHELA, AND DUNKARD GROUPS): EVIDENCE FROM ICHNOFOSSILS

ABSTRACT The late Paleozoic transition is well represented by the upper Pennsylvanian to lower Permian Conemaugh, Monongahela, and Dunkard groups of the western Appalachian Basin (U.S.A.). These units contain abundant paleosols possessing suites of ichnofossils that serve as indicators of soil moisture, soil organic content, water table level, precipitation, and landscape stability. Analysis of these units can, therefore, be used to refine the details of how late Paleozoic terrestrial landscapes changed through time. A study along a 50 km west-east and a 40 km north-south transect through southeast Ohio and southwest West Virginia resulted in the recognition of 24 pedotypes with distinct ichnofossil assemblages. Ichnofossils include rhizoliths, Planolites, Palaeophycus, Taenidium, Scoyenia, Macanopsis, Skolithos, Cylindricum, cf. Psilonichnus, Arenicolites, mottles, and coprolites produced by various plants, gastropods, and larval-to-adult soil arthropods. Soil-forming environments include palustrine, levee, proximal to distal floodplain, interfluve, backswamp, marsh, and fen settings. An up-section shift in pedotypes from Argillisols to Vertisols and Calcisols as well as an overall increase in the diversity of pedotypes recorded a change in soil-forming conditions, resulting in a diverse landscape that changed significantly as mean annual precipitation rose and fell. An up-section increase in ichnofossil diversity in the paleosols and changes in ichnocoenoses suggests an increased dependence on the soil as a refuge and as a food resource. Overall, growing instability of the climate during the Pennsylvanian–Permian transition led to a more heterogeneous landscape that helped to promote colonization of a more diverse assemblage of soil organisms.

Litologie a paleopůdy klikovského souvrství ve vrtu 2140 01T1 Dunajovice, třebonská pánev

The 2140 01T1 borehole sampling the Late Cretaceous non-marine strata of the Klikov Formation in the central part of the Třeboň Basin in southern Bohemia provided ~ 70 m thick alluvial succession composed of alternating sandstone and mudstone intervals that overlays deeply weathered crystalline basement. The mudstone interval in the lower part of the Klikov Formation is separated by sandy layers into several 2–4 m thick fining-upward units. The sharp-based sandy layers with fusain, carbonized stems and rip-up clasts of underlying mudstone are interpreted as avulsion deposits. They grade upwards into heterolithic sand-silt sequence and mottled massive mudstone with burrows, rhizohalos and variably developed pedogenic features. Such cyclic arrangement probably reflects autogenic processes on distal floodplain with episodic deposition and upward increasing subaerial exposition and pedogenic overprint. In the middle to upper parts of the Klikov Formation up to 6 m thick channel sandbodies with sharp erosional bases cutting into the underlying laminated sand-silt heteroliths of channel levee deposits occur. The thickness of the single-storey sandbodies corresponds usually to c. 2 m which suggests up to 3 m deep channels during bankfull discharge. The thicker multi-storey sandbodies record channel amalgamation on the alluvial ridge or shallow paleovalley fillings. The sandbodies grade upwards to massive mudstones of abandoned channel fills and floodplain deposits. These floodplain units are up to 8 m thick and consist of variegated massive mudstones interrupted by discrete up to 1 m thick fining upward layers of rippled sandstone representing crevasse splay deposits. Depositional context including preserved levee deposits, abandoned channel fillings and floodplain finegrained deposits suggests rather higher sinuosity of the formative rivers. Palaeosol profiles represent pedogenically modified floodplain fines with gradational bases and sharp erosive top surfaces. At least 10 palaeosols were identified in the measured section, forming mostly discrete profiles up to 2 m thick consisting of several B-horizons that differ in the degree of the soil structure development, colour, mottling, grain size, presence of clay hypocoatings and bioturbation index. The most common Bw horizons form lower parts of the profiles and have no or only a weakly developed angular blocky structure (ABS). The typical mottling is caused by a hierarchical system of vermicular greenish-grey reduction rhizohalos, that may be filled by silt to sand or illuviated clay hypocoatings and probably follow the original plant root system. Some patches have diffuse orange rims of iron oxides, probably represented by goethite. Mudstone of Bsst horizons displays well-developed ABS with rare wedge-shaped peds and contains a number of illuviated clay skins and redox depletions. Vertic features like fine cracks filled by sand are common, and slickensides with clay hypocoatings occur rarely. Mudstones of Bt horizons contain a number of illuviated clay hypocoatings filling root channels or interpedal cracks, while the Bss horizons exhibit well-developed ABS with slickensides and contain a number of vertical cracks filled by sandy grains. Palaeosol profiles represent mainly argillisols and vertic argillisols with transitions to argillic vertisols. Poorly developed argillic to vertic protosols are also common. Palaeosol profiles differ mainly in the degree of structural development/maturity, which is given by various lengths of exposition to similar climatic conditions. Vertical distribution of palaeosols reflects their position in the alluvial landscape with locally specific hydromorphic conditions rather than a distinct climatic trend. Most of palaeosols exhibits downprofile translocation of clay (illuviation) leading to the formation of argillic horizon, which typically develop on stabilized landscape in humid climate with seasonal moisture deficit.

Current and paleo sources of organic material within fluvial features of the meandering Ruda River, Poland

This study aimed to identify differences in organic matter (OM) composition and origin in the main depositional subenvironments within the floodplain of a meandering river in a temperate climate zone. The study analysed organic-rich sediments found within different facies (side bars, natural levees, crevasse splays, palaeochannels, flood basins, and alluvial fans). Quantitative macrofossil analysis of the OM present in proximal floodplain sediments pointed to a dominance of amorphous OM (AOM), the average proportion of which comprised up to 60% of the total OM. During floods, the most significant phenomenon is the deposition of wood and leaf debris; however, these debris are subject to rapid decomposition in sandy layers and, as a result, do not contribute much to the total OM composition. Root and epidermis remain accumulated in situ and, with an average share of more than 10% of the total OM, are an important part of the more fine-grained alluvial layers. The other components were no more than bioindicators. The proximal floodplain is characterised by sponge spicules in the alluvia and mycelia in the epipedons. In addition, diatom remains are often recorded in the flood layers. The average AOM content in the OM found within the distal floodplain was approximately 40%, although a significantly higher proportion of this component was recorded in flood basin sediments. The accumulation of rhizodermis, epidermis, wood, and periderm (with shares ranging from 5% to 22% of the total OM) plays an important role. Less common components that are of indicative value within the distal zone include the remains of mosses, Cladocera, and sporomorphs. OM within the distal floodplain has high preservation potential, and the sediments in this zone are crucial for carbon sequestration processes in river valleys.

Transferring network analysis to the study of potential biogeochemical interactions of phosphorus-relevant elements in floodplain subsoils – A new use case for the Soilscape Network Approach (SNAp)

Subsurface phosphorus (P) loss from deep P stocks in floodplain subsoils can contribute to eutrophication of freshwaters. To date, knowledge on the complex biogeochemical interactions of P in floodplain subsoils is too scarce to enable targeted P management to mitigate subsurface P loss from deep P stocks. We propose using graph theory and the Soilscape Network Approach (SNAp) based on correlations between P-relevant elements to study these complex biogeochemical interactions in the soilscape. Complex interactions of several elements in soils are difficult to investigate from a holistic perspective with conventional data analysis. We translated soil element data from topsoils and subsoils of terrestrial sites, proximal and distal floodplain sites into relational data and analyzed network structure, centrality, and modularity. The results indicate that a higher frequency of groundwater level fluctuations in distal subsoils and proximal topsoils could result in 24–44 % less biogeochemical interaction compared to sites with stable conditions. Impeded microbial processes on the frequently disturbed sites may explain this finding. Our analyses suggest biogeochemical differences between floodplain topsoils and subsoils expressed in 24 % lower and 75 % higher network connectivity in distal and proximal subsoils (respectively). We also found 22 % lower network connectivity in distal than proximal floodplain subsoils, suggesting biogeochemical differences between both soil sections. These findings imply that floodplain P management should not take a whole-floodplain approach but a 3D-approach, which differentiates laterally between floodplain zones and vertically between soil sections. In addition, SNAp indicated that Fe(II) oxides are important in P biogeochemistry of floodplain subsoils but are not the key element. Instead, labile P forms are suggested to have different major associations in distal (Alox, Feox) versus proximal deep P stocks (Alox, Mn, Ca). Our study provides new insights into the biogeochemistry of deep P stocks in floodplain subsoils which require targeted validation by other methods.

Araucariaceous fossil woods from the Upper Triassic Ischigualasto Formation (San Juan Province, Argentina): paleofloristic and paleoclimatic implications

AbstractIn this contribution, fossil woods from the Valle de La Luna Member of the Upper Triassic Ischigualasto Formation at Ischigualasto Provincial Park, San Juan Province, Argentina, are described. The specimens are preserved as silica permineralization in tuffs intercalated with carbonaceous mudstone beds interpreted as distal floodplain facies. The fossil woods were assigned to the new species Agathoxylon argentinum since their anatomy differs from the known Mesozoic Gondwanan species of the genus Agathoxylon. The combination of characters present in the new taxon indicates an affiliation with the conifer family Araucariaceae. Signals of fungal-mediated wood decay were observed, comparable to the activity of basidiomycetes. Spherical structures attached to the walls of the tracheids were recognized and are interpreted as holocarpic chytrid fungi. The growth rings were quantitatively analyzed. Low values of percentage diminution, percentage latewood, and Ring Markedness Index, and a mean percentage skew of +11.5, were obtained, suggesting that the new species was an evergreen gymnosperm. The stratigraphic distribution and taxonomic composition of the Ischigualasto Formation fossil-plant-bearing levels were studied. A vegetation change is recorded in the fossil level bearing Agathoxylon argentinum n. sp., marked by the replacement of the corystosperm genera and a diminution of arboreal corystosperms. This floristic change, in addition to other evidence, indicates humid paleoclimatic conditions for the uppermost part of the Valle de La Luna Member of the Ischigualasto Formation.

Alluvial ichnofacies from Upper Triassic red beds in India: Implications for palaeoenvironment and palaeoclimate

Trace fossils are highly sensitive to the hydrodynamic conditions of depositional systems, substrate, and climate and hence yield information about spatio-temporal changes in palaeoenvironment and palaeoclimate. In this paper, we report alluvial trace fossil assemblages from the Upper Triassic Tiki Formation of the Rewa Basin, central India. Based on detailed facies analysis and architecture, two depositional environments are identified in this formation: (1) perennial braided channel belts and (2) extensive and complex floodplains containing ephemeral small fluvial channels, lakes, and crevasse splay deposits. Upper flow regime primary structures in laterally extensive sandstones encased in the floodplain deposits indicate short-lived high magnitude flood discharge, suggestive of seasonal climates. Trace fossils are sporadically distributed through these facies, generally in suites of low abundance, although in places the bioturbation index is higher. Three major ichnofacies, namely Skolithos, Scoyenia and Mermia are recognized, based on the association of different trace fossils preserved in the channel, crevasse splay of proximal floodplain and pond/lake of distal floodplain deposits, respectively. Vertical Beaconites in palaeosols and an abrupt change from Skolithos to Scoyenia ichnofacies indicate a highly variable water table, controlled by seasonal precipitation. The transitions between the Skolithos, Scoyenia and Mermia ichnofacies reveal that trace fossil preservation was variously controlled by channel abandonment, floodplain dewatering, substrate desiccation or periodic waterlogging of overbank areas. Specifically, increased water discharge over the floodplain during high precipitation, followed by post-flood recovery of hot, dry, low-water table conditions may have been a key controlling factor in shaping the ichnological characteristics of these Upper Triassic red beds.

Paleosols in distal alluvial sequences and their formation mechanisms: Insights from a high-resolution record in a foreland basin during early Miocene (SE France)

The stratigraphic distribution of paleosols provides a framework to investigate the controls on distal alluvial fan architecture. This study focused on paleosol-bound alluvial cycles (PACs) from the southern Digne-Valensole foreland Basin (SE France, early Miocene). We investigated the duration of the paleosol formation and identified the controlling mechanisms on their temporal and spatial distribution. Paleosols formed primarily from fine-grained sediments (65% shale, 16% lime mud). We identified three pedotypes: Calcisols from reddening throughout the weathering profile, Bw horizon overlying Bk horizon; vertic Calcisols with similar features including slickensides; and gleyic Calcisols showing saturated conditions superimposed on well-drained Calcisol features. Duration of Calcisol formation, estimated from the time span of aggrading PACs, was compatible with those from Quaternary Calcisols: median 11 to 29 kyr for maturity Stage II, > 90% of the dataset); range 20–58 kyr for maturity Stage III-IV. The shortest PACs time spans (< 10 kyr) indicate episodic sedimentation in the distal floodplain. Spatially or temporally variable sediment input in the intermediate floodplain prevented the development of paleosols at short time scales, resulting in longer PACs time spans (40 to 70 kyr) in the range of astronomical-related climate cycles. Autogenic processes also controlled the PACs stacking pattern as illustrated by stacked meter scale PACs formed during periods of relative sea-lowering indicative of a regular down-dip slope limiting river entrenchment; or during a period of high base-level in areas of low sediment supply suggesting complete diversion of the flow laterally from the previous course. The age-constrained PACs enabled to document on high-resolution time scales (a few to 100 s of kyr) the interactions between two components of the alluvial architecture, the episodic aggradation and the pedogenic processes that are difficult to determine in fossil alluvial successions. • Paleosol-bound alluvial cycles studied at 10 4 to 10 5 timescales over 3.5 Myr. • Durations of Aquitanian Calcisol formation were comparable to Quaternary ones. • Episodic floodplain aggradation is documented for timescale shorter than 10 kyr. • The potential of paleosol maturity in evaluating climate fluctuations is discussed. • Autogenic controls were identified from stacking pattern of Calcisols.

Insect herbivory on Catula gettyi gen. et sp. nov. (Lauraceae) from the Kaiparowits Formation (Late Cretaceous, Utah, USA).

The Upper Cretaceous (Campanian Stage) Kaiparowits Formation of southern Utah, USA, preserves abundant plant, invertebrate, and vertebrate fossil taxa. Taken together, these fossils indicate that the ecosystems preserved in the Kaiparowits Formation were characterized by high biodiversity. Hundreds of vertebrate and invertebrate species and over 80 plant morphotypes are recognized from the formation, but insects and their associations with plants are largely undocumented. Here, we describe a new fossil leaf taxon, Catula gettyi gen et. sp. nov. in the family Lauraceae from the Kaiparowits Formation. Catula gettyi occurs at numerous localities in this deposit that represent ponded and distal floodplain environments. The type locality for C. gettyi has yielded 1,564 fossil leaf specimens of this species, which provides the opportunity to circumscribe this new plant species. By erecting this new genus and species, we are able to describe ecological associations on C. gettyi and place these interactions within a taxonomic context. We describe an extensive archive of feeding damage on C. gettyi caused by herbivorous insects, including more than 800 occurrences of insect damage belonging to five functional feeding groups indicating that insect-mediated damage on this taxon is both rich and abundant. Catula gettyi is one of the best-sampled host plant taxa from the Mesozoic Era, a poorly sampled time interval, and its insect damage is comparable to other Lauraceae taxa from the younger Late Cretaceous Hell Creek Flora of North Dakota, USA.

Sedimentary evolution of distributive fluvial systems within intraplate tectonic active basins: Case study of the Early Cretaceous Araripina Formation (Araripe Basin, NE Brazil)

The Lower Cretaceous Araripina Formation records deposition in a distributive fluvial system that is a part of the post-rift sequence of the Araripe Basin, NE Brazil. Following the opening of the Brazilian Equatorial Margin, the reactivation of regional faults of the Paleoproterozoic basement resulted in tectonic subsidence and formation of a regional-scale DFS. The Araripina Formation is an up to 40-m-thick succession of rhythmically interbedded sandstone and mudstone, organized in two depositional sequences separated by a regional disconformity. We recognized and grouped nine sedimentary facies into six facies associations that we interpreted as deposits of meandering channels, ribbon channels, minor channels, floodplain, lateral and terminal splays, and distal floodplain. The lower sequence facies associations suggest deposition in the medial to distal part of a distributive fluvial system in a tectonically active, interior basin subjected to episodic flooding. The periodic inundations were responsible for activating ephemeral channels and producing sheetfloods, followed by deposition of lateral and terminal splays in distal flooded areas. Syn-sedimentary deformation structures are present in rhythmite facies (truncating surfaces, load structures, injectite and convoluted folds) in the upper part of the lower sequence. The upper sequence was formed after a period of intense tectonic activity in a large distal floodbasin dominated by suspension. The deposition culminates in an interval with pedogenetic deposits cross-cut by a regional disconformity with the upper Exu Formation. Paleocurrent data from both depositional sequences indicate paleodepositional slope towards southeast and east with source-areas located to the northwest and west. This pattern is similar to that observed in the lower Santana Group and opposite to the westward direction of sedimentary transport in the overlying Exu Formation implying significant change of source region, basin topography and continental paleodrainage in the Araripe Basin after the Albian.

Late Cretaceous palynomorphs from the Golfo San Jorge Basin, Argentina

A lithofacial and palynological study was carried out on the Cañadón Seco Formation in the La Frieda Oeste x-1 well (Golfo San Jorge Basin). According to sedimentological characteristics of the core four main litofacies lithofacies are defined: 1. Cross-bedded sandstones, 2. Interlaminated fine-grained sandstones and mudstones, 3. Shales, and 4. Muddy tuff. The cross-bedded sandstones correspond to channel deposits, which are interpreted as lateral bars (point bars) or attached bars. The interchannel area is dominated by interlaminated fine-grained sandstones and mudstones, together with shales. The former represents sedimentation occurred in proximal floodplain areas, while shales correspond to deposition in distal floodplains, where thin and scarce muddy tuff intercalations indicate ash fall events. The palynological assemblage here analyzed was recovered from the green shales corresponding to distal floodplains areas, probably surrounding temporary water bodies. The floristic assemblage contains abundant fern spores as a dominant group, followed by angiosperm and gymnosperm pollen grains. Bryophyte and lycophyte spores, along with fungal remains, are also present in lower proportions. Based on the taxonomic content of the palynoflora, a Turonian–Coniacian age is suggested for this assemblage. Additionally, some taxa present in the assemblage allow inferring temperate to warm and humid conditions. This new record represents a period of time little known for the evolution of angiosperms in the southern region of Gondwana.

Vliv sedimentačního prostředí na magnetickou susceptibilitu přelivových sedimentů nivy Moravy ve Strážnickém Pomoraví

Four profiles in different sedimentary environments - natural levee, proximal floodplain, distal floodplain, oxbow lake - were sampled to obtain magnetic susceptibility (MS), grain size, organic matter content (LOI) and pH. Relationships between selected parameters (χlf, D50, LOI, pH) were analysed by means of statistical analysis (linear regression, PCA, factor analysis). Principal goal was to investigate how character of individual sedimentary environments and their distance from the active river channel is reflected in the magnetic signal of overbank deposits. A decrease in the magnetic signal with increasing distance from the river channel was shown, confirming that fluvial deposition is a major factor of contamination of floodplain sediments by anthropogenic magnetic particles. The base of elevated values of MS (levee: 80 cm, proximal floodplain: 30 cm) probably corresponds to the turn of the 19th and 20th century and the strongest magnetic signal (levee: 32,5 cm, proximal floodplain: 5 cm) belongs to the 1980s. Statistically significant relationships were found between: χlf and LOI (direct dependence), LOI and D50 (indirect dependence), pH and D50 (direct dependence) when data from all profiles were analysed together.