Fluvial Succession Research Articles

Magnetic susceptibility as a possible correlation tool in Quaternary alluvial stratigraphy

Correlation of the fluvial magnetic susceptibility (MS) record of borehole Devavanya‐1 in the Körös Basin (eastern Hungary) with Chinese aeolian MS records (Jingbian, Lingtai) and the marine δ18O record from the Equatorial Pacific (V28‐239) is established here based on cross‐correlations and singular spectral analysis. A basin‐scale well‐to‐well correlation based on magnetic susceptibility records was also performed involving unpublished cores. To refine the age model, a Monte Carlo simulation was conducted using the Chinese Jingbian section as a tuning target. Spectral analysis of the tuned record revealed c. 400, c. 100 and c. 41 ka cycles over the 2.5 million years of the Quaternary fluvial succession. To ensure a complementary palaeoclimate proxy, the full width at half maximum of smectites was measured as a facies‐independent indicator of weathering intensity. This investigation was carried out on a subset of samples involved in MS measurements representing a c. 400 ka time interval across the top of the Olduvai subchron. A phase‐shift between MS and weathering intensity recorded in the clay mineralogy indicates different response times of the considered proxies. The fluvial MS record is determined by the climatic control on delivery and preservation of magnetic minerals, mainly of magnetite. Under cold‐and‐dry climate these minerals were released owing to frost shattering in the adjacent hinterlands and were transported to alluvial plains in the early postglacial periods thanks to the increasing discharge of rivers. With further warming the weathering‐sensitive magnetic minerals soon disappeared from the soils of the catchment area and thus from the fluvial load. As a result, in fluvial successions early postglacial warmings are expressed by the occurrences of MS maxima (magnetic episodes), while the palaeotemperature maximum and the subsequent cooling remain concealed within the tract of low MS values. The early postglacial magnetic episodes may serve as ideal stratigraphical markers in regional and global correlations.

Detrital mode and whole-rock geochemistry of the Miocene-Pliocene fluvial succession, Pishin Belt, Pakistan: implications on provenance and source area weathering in peripheral foreland basins

Detrital mode and geochemical composition of sandstones and mudstones of the Miocene Dasht Murgha Group (DMG) and Pliocene Malthanai Formation (MF) of the Pishin Belt, northwestern Pakistan, have been examined to identify their provenance and source area weathering. Sandstones of the Dasht Murgha Group and Malthanai Formation are lithic to sublitharenites, rich in quartz, and metamorphic and sedimentary lithic fragments, indicating a recycled orogenic source. LmLvLs plots show that the Dasht Murgha Group is rich in sedimentary and metamorphic lithic fragments (Lm35Lv18Ls47), while samples of the Malthanai Formation are overwhelmingly rich in sedimentary fragments (Lm14Lv10Ls76). Eocene Nisai Formation and Oligocene Khojak Formation within the Pishin Belt were mainly providing the sedimentary/metasedimentary detritus. High content of monocrystalline quartz (DMG 28.21 %; MF 30.7) and higher SiO2/Al2O3 ratios in sandstones (DMG 9.86; MF 11.98) also indicate high maturity of sandstones due to recycling of source terrain in collision orogens. High Cr/Ni (DMG 5.23; MF 6.17) and moderate Cr/V (DMG 3.96; MF 3.88) ratios suggest significant contributions from mafic and ultramafic detritus derived from Muslim Bagh-Zhob Ophiolite. Malthanai Formation has higher CIA and CIW values (68.96 and 77.53) than Dasht Murgha Group (63.87 and 70.93); however, they both indicate low to moderate weathering intensities. Dasht Murgha Group and Malthanai Formation have higher ICV values which indicate abundance of aluminous silicates, hence, showing moderate weathering of the source area. In A-CN-K diagrams, the samples make linear trend towards illite which suggests that the sediments were derived from a tectonically active source going through non-steady-state weathering, where the detritus has been derived from different zones of weathering profiles.

Uranium distribution as a proxy for basin-scale fluid flow in distributive fluvial systems

We infer system-scale fluid flow in the Late Jurassic Salt Wash fluvial succession (SW USA) by plotting uranium deposit distribution against sedimentological data, using uranium distribution as a proxy for subsurface fluid flow. More than 90% of uranium deposits in the Salt Wash occur where sandstone forms 40–55% and sand-rich channel-belts form 20–50% of the succession, which coincides with changes in channel-belt connectivity and gross-scale architecture. The paucity of uranium below these cut-off values suggests that fluid flow is related directly to predictable downstream fining and facies variations in distributive fluvial systems. Supplementary material: A summary table of location data, key trends and the amalgamation ratio method is available at https://doi.org/10.6084/m9.figshare.c.2849581 .

River response to climate and sea level changes during the Late Saalian/Early Eemian in northern Poland – a case study of meandering river deposits in the Chłapowo cliff section

Abstract Fluvial sediments in the Chłapowo cliff section were studied in order to reconstruct their palaeoflow conditions and stratigraphical position. Lithofacies, textural and palaeohydraulic analyses as well as luminescence dating were performed so as to achieve the aim of study. Sedimentary successions were identified as a record of point bar cycles. The fluvial environment probably functioned during the latest Saalian, shortly after the retreat of the Scandinavian Ice Sheet. Discharge outflow was directed to the northwest. The river used the older fluvioglacial valley and probably was directly connected to the Eem Sea. Good preservation and strong aggradation of point-bar cycles were related to a rapid relative base level rise. The meandering river sediments recognised showed responses to climate and sea level changes as illustrated by stratigraphical, morphological and sedimentological features of the strata described. The present study also revealed several insights into proper interpretation of meandering fluvial successions, in which the most important were: specific lithofacies assemblage of GSt (St, Sp) → Sl → SFrc → Fm (SFr) and related architectural elements: channel/sandy bedforms CH/SB → lateral accretion deposits LA → floodplain fines with crevasse splays FF (CS); upward-fining grain size and decreasing content of denser heavy minerals; estimated low-energy flow regime with a mean depth of 1.6–3.3 m, a Froude number of 0.2–0.4 and a sinuosity of 1.5.

Sedimentology and alluvial architecture of the Bajo Barreal Formation (Upper Cretaceous) in the Golfo San Jorge Basin: Outcrop analogues of the richest oil-bearing fluvial succession in Argentina

This study addresses the sedimentology, architecture and dimensions of fluvial deposits in the Bajo Barreal Formation (Upper Cretaceous) in the Codo del Senguerr anticline, Golfo San Jorge Basin, Argentina. The stratigraphic framework of the 450–650 m thick alluvial succession was carried out through description and interpretation using 18 detailed sedimentary logs along a 4.5 km wide exposure, where 314 fluvial channels were analysed. The Bajo Barreal Formation is a high-accommodation fluvial succession, dominated by fine-grained floodplain deposits, with isolated-to-vertically stacked, sheet-like, low-sinuosity or braided fluvial channels of limited lateral mobility clustered in several coeval channel belts, in which fluvial channels were relocated by avulsion. The Lower Member consists of reworked ash-fall materials preserved in floodplain areas (78%), floodplain sandstones (4%) and fluvial channels (18%). The mean thickness of sandbodies is 2.96 m (n = 118) and mean true width is 112 m (mean W:T = 43), with thicker and wider sandbodies in upper levels of the Member. The Upper Member consists of grey siltstones and mudstones preserved in extensive lowland areas (78%) and fluvial channels (19%), with scarce preservation of sandstones in the proximal floodplain (3%). Fluvial channels are narrow low-sinuosity sheets with comparable thickness (mean = 3.21 m, n = 196), but greater width than those of the Lower Member (mean width = 147 m, mean W:T = 50). Paleoflow data from 298 fluvial sandbodies indicates a paleoflow direction toward the SE (Az. 112°). Rivers flowed parallel to inherited early Cretaceous normal faults and are oriented to high-angle (>70°) to the current axis of the Codo del Senguerr anticline, suggesting that the uplift of the anticline occurred after the deposition of the formation. The variation in geometry of fluvial channels in both Members of the Bajo Barreal Formation could help in planning and developing primary and/or enhanced oil recovery projects in nearby oilfields, and provide data necessary for modelling the subsurface connectivity of hydrocarbon reservoirs.

Paleobiogeoclimatic scenarios of the Late Quaternary inferred from fluvial deposits of the Quadrilátero Ferrífero (Southeastern Brazil)

The Quadrilátero Ferrífero is an important mineral province in Southeastern Brazil and has one of the largest iron ore reserves in the world. Previous work in this region has indicated that the formation of fluvial successions with duricrusts coincided with drier/cooler climatic phases alternating with moister/warmer periods during which the formation of fluvial successions without duricrusts occurred. For the construction of this proposal, ages of fluvial sediments obtained through Optically Stimulated Luminescence (OSL) were associated with data from the literature on paleobioclimatic scenarios. Therefore, using these observations as a starting point, this paper aims to investigate evidence of bioclimatic oscillations obtained directly from the fluvial successions and discuss its influence on the geomorphogenis of local river valleys. For this purpose, phytolith, carbon isotope and granulometric analyses were carried out, as well as dating of sediments using OSL and of soil organic matter through radiocarbon. The results show that in the oldest depositional succession (DS1 — about 34ka) the predominant phytoliths are those of bulliform polyedric, elongate, acicular and globular granulate types and δ13C values are typical of C3 plants. On the other hand, despite having a similar phytolith assemblage (abundance of bulliform polyedric, elongate, bulliform cuneiform, acicular, globular psilate and bilobate flat/concave types), the fluvial successions associated with significant conglomeratic duricrusts (DS2 and DS3) present a dominance of δ13C values characteristic of C4 plants. The Bi index indicates water stress in all the successions, and the Ic index suggests decreasing temperatures with depth in DS3. Thus, the three fluvial successions indicate a savanna-like environment, but depositional successions DS2 (∼27ka) and DS3 show drier/cooler climatic conditions when compared to DS1 and to the present-day regime. Both scenarios evolved under conditions of the Last Glacial period, but DS2 and DS3 were formed closer to the Last Glacial Maximum, and therefore under the strong influence of the lower temperatures during this period. These drier/cooler conditions in steep valleys with unprotected hillslopes may have been decisive for the formation of relatively thicker layers of gravel and sand, which later became duricrusts. The results indicate that climate has also played an important role in the regional hydrosedimentological dynamics, given the variations in vegetation influencing the abandonment of fill terraces and formation of nested floodplains.

Mesozoic tectonostratigraphic evolution of the North Carnarvon Basin unlocked using regional 3D seismic

Interpretation of regional scale merged 3D seismic data sets covering the North Carnarvon Basin has for the first time enabled a detailed description of Mesozoic stratigraphic and structural features on a basin scale. Isoproportional slicing of the data enables direct interpretation of Triassic depositional environments, including contrasting low-stand and high-stand fluvial channel complexes, marginal marine clastic systems and reef complexes. Channels vary dramatically between sinuous-straight single channels within low net:gross floodplain successions, to broad channel belts within relatively high net:gross fluvial successions. The latter can be traced from the inboard part of the basin to the outer areas of the Exmouth Plateau. 3D visualisation and interpretation has demonstrated the huge variety of structural styles that are present, including basement-involved extensional faults, detached listric fault complexes, polygonal faults, and regional scale vertical strike-slip faults with flower structures. Fault trends include north–south, north–northeast to south–southwest, and northeast–southwest, with deformation events occurring mainly between the Rhaetian and Valanginian. Extensional and compressional deformation has created multiple horsts, three-way fault closures, fold belts and associated four-way anticlinal traps. Wrench tectonics may also explain pock-mark trains with the interpreted transfer of over-pressure from Triassic to Early Cretaceous levels. The use of regional scale merged 3D seismic data sets is now shedding light on tectonostratigraphic features on a basin scale that were previously unrecognised or enigmatic on 2D seismic or local 3D seismic data sets.

Soft sediments deformation structures: Implication for draining of Paleo-Kathmandu Lake

Kathmandu basin is one of the Quaternary intermontane basins in the central Nepal Himalaya. It is bounded by several faults on both southern and northern margins. The basin is filled with Plio-Pliestocene terrestrial sediments and their characteristics indicate four types of unconsolidated successions within the basin. These are before lake succession, during lake succession, draining stage lake succession and fluvial succession. Late Pleistocene aged Sunakothi Formation crops out along the southern part of the basin. It is a typical fluviolacustrine delta succession that extended from 1390 m in the southern margin to nearly 1300 m toward center of the basin. It is composed by poorly consolidated sand, gravelly sand, silt and mud beds. Various soft-sediment deformation structures occur in the formation, especially in fine- to medium –grained sands, silts and mud: load structures, flame structures, clastic dikes (sand dike), disturbed layers, convolute beds, slumps and synsedimentary faulting. The deformation mechanism and driving force for the soft-sediment deformation are related, essentially, to gravitational instability, dewatering, liquefaction and brittle deformation. Field data and the wide lateral extent of the structures as well as regional geological data show that most of the deformation is related to seismicity and the structures are interpreted as seismites. In addition, there have also been experimental studies undertaken by various authors within the different sedimentary basin.
 Soft-sediments deformation structure in Kathmandu basin are mainly considered to be part of the initial diagenetic changes of the sediments and include: Slump structure which occurred on the slope like delta-front area, dewatering structures which occurred by the processes of upward escape of water commonly due to loading, load structures which occurred due to density contrasts between sand and underlying wet mud. The existence of seismites in the Sunakothi Formation is evidence of continuing tectonic activity in the study area during the late Pleistocene and is a main factor for draining of the Paleo- Kathmandu lake water.

Unconformity‐bounded stratigraphy in the Plio‐Pleistocene continental record: new insights from the Alessandria Basin (NW Italy)

AbstractCombined stratigraphic and bio‐magnetostratigraphic analyses on a fluvial sequence from the southern margin of the Alessandria Basin (at the junction between the Alps and the Apennines) provide evidence for the first documentation of a late Piacenzian–Gelasian continental record in northern Italy. The basin experienced general growth at the margins and ongoing subsidence in the depocentre, during overthrusting onto the Po Foreland Basin. The studied fluvial succession is 25–30 m thick and can be divided into three units (MRZ1, MRZ2 and MRZ3) delimited by erosional unconformities (S1, S2 and S3). The MRZ1 and MRZ2 units (shallow to confined braided systems) are chronologically restricted between 2.8 and 2.58 Ma based on bio‐magnetostratigraphic analyses. The overall stratigraphic framework indicates deposition and erosion during the progressive uplift of the Alps/Apennines system. The frequency of unconformities and sedimentary changes, compared to other coeval successions of other syn‐orogenic basins of northern and central Italy, suggests the interaction between high‐amplitude global cold stages and tectonic deformation. Tectonic climax occurred in the Gelasian, as revealed by the 450‐ to 600‐ka‐long hiatus associated with the S3 unconformity, whereas the subsequent deposition of the MRZ3 unit (meandering alluvial system) including a Gelasian magnetic reversal points to the fading of tectonic activity. The stratigraphic reconstruction provided in this study enriches the current knowledge of the European continental biota: the absence of thermophilous elements in the MRZ1 carpoflora reflects the late Piacenzian cooling phase after 2.8 Ma, whereas the persistence of several extra‐European taxa in MRZ3 (e.g. Ampelopsis cf. ludwigii, Boehmeria lithuanica, Cryptomeria rhenana) rules out an age younger than 1.4 Ma. The freshwater mollusc assemblage of MRZ2 shows the occurrence of Pomatias elegans and Tournouerina belnensis, identified for the first time in the Pliocene of northern Italy. Copyright © 2015 John Wiley & Sons, Ltd.

Palaeoenvironment of braided fluvial systems in different tectonic realms of the Triassic Sherwood Sandstone Group, UK

Fluvial successions comprising the fills of sedimentary basins occur in a variety of tectonic realms related to extensional, compressional and strike-slip settings, as well as on slowly subsiding, passive basin margins. A major rifting phase affected NW Europe during the Triassic and resulted in the generation of numerous sedimentary basins. In the UK, much of the fill of these basins is represented by fluvial and aeolian successions of the Sherwood Sandstone Group. Additionally, regions that experienced slow rates of Mesozoic subsidence unrelated to Triassic rifting also acted as sites of accumulation of the Sherwood Sandstone Group, one well-exposed example being the eastern England Shelf. The fluvial depositional architecture of deposits of the Sherwood Sandstone Group of the eastern England Shelf (a shelf-edge basin) is compared with similar fluvial deposits of the St Bees Sandstone Formation, eastern Irish Sea Basin (a half-graben). The two studied successions represent the preserved deposits of braided fluvial systems that were influenced by common allogenic factors (climate, sediment source, delivery style); differences in preserved sedimentary style principally reflect their different tectonics settings. Analysis of lithofacies and architectural elements demonstrates that both studied successions are characterized by amalgamated channel-fill elements that are recorded predominantly by downstream-accreting sandy barforms. The different tectonic settings in which the two braided-fluvial systems accumulated exerted a dominant control on preserved sedimentary style and long-term preservation potential. On the eastern England Shelf, the vertical stacking of pebbly units and the general absence of fine-grained units reflect a slow rate of sediment accommodation generation (18–19.4m/Myr). In this shelf-edge basin, successive fluvial cycles repeatedly reworked the uppermost parts of earlier fluvial deposits such that only the lowermost channel lags tend to be preserved. By contrast, in the eastern Irish Sea Basin of west Cumbria, the rate of sediment accommodation generation was substantially greater (119m/Myr) such that space was available to preserve complete fluvial cycles, including silty drape units that cap the channelized deposits.

First record of Ginkgo-related fertile organs (Hamshawvia, Stachyopitys) and leaves (Baiera, Sphenobaiera) in the Triassic of Brazil, Santa Maria formation

This paper describes new ginkgophytes recently discovered in a new exposure of the original type section of the Passo das Tropas Member, Santa Maria Formation, linked to Paraná Basin succession. The well-preserved fossils come from a very fine red laminated mudstone representing a lacustrine interval, within a broader low-sinuosity fluvial succession. The material occurs in a Dicroidium-dominated assemblage and is represented by the leaves Baiera and Sphenobaiera, accompanied by the fertile structures Hamshawvia and Stachyopytis. Cuticle fragments preserved on leaf impressions of Sphenobaiera schenkii show xeromorphic features. The geology, paleogeography and paleoclimate of the Passo das Tropas Member (PTM), Santa Maria Formation, is discussed. By comparing these ginkgophytes with those from other Gondwanan assemblages, the Brazilian deposits earlier assigned to Anisian–Ladinian age can now be extended to the Carnian age.

Quantification of a Distributive Fluvial System: The Salt Wash DFS of the Morrison Formation, SW U.S.A.

Abstract Recent analysis of modern aggradational continental sedimentary basins reveals that sedimentation patterns are dominated by distributive fluvial systems (DFSs). The Salt Wash Member of the Late Jurassic Morrison Formation has previously been described as a fan-shaped fluvial system. This study characterizes facies variations across the Salt Wash DFS to quantitatively test predicted trends in conceptual DFS models. Notable proximal-to-distal trends include a change in total thickness of the fluvial succession from 174 m to 40 m, and an average grain size from coarse sand to silt, while the percentage of sand decreased from 70% in the proximal region to 8% in the distal region. The proportion of amalgamated channel-belt deposits decreased from 67% to 0%, while floodplain facies and lacustrine deposits increase (38% to 94% and 0.1% to 7% respectively). A downstream decrease in average channel-belt thickness (15 m to 3.8 m, from thickest to thinnest) and average story thickness (7.7 m to 2.3 m, from thickest to thinnest) is also recorded. Significant downstream changes in deposit architecture were also noted, with proximal regions dominated by stacked channel-belt deposits with a high degree of amalgamation. Distal deposits are dominated by floodplain muds and sheet sandstones and sparse ribbon channels, with little to no amalgamation of channel deposits. This study provides quantified information for an ancient DFSs with the aim of providing a dataset that can be used for objective comparison between different DFSs, as well as providing numerical data to aid resource exploration and modelling efforts.

Relicts of the Pleistocene Po Plain on the Western and Southern slopes of Turin Hill (NW Italy)

A detailed geological survey of the Southern slope of Turin Hill reveals a Pleistocene terraced fluvial succession consisting of flat surfaces separated by scarps with associated fluvial clayey–silty and gravelly sediments. This succession is not linked to the present N–S hilly streams, but is instead related to major Pleistocene W–E rivers. The collected regional data suggest an ancient trend of the Po River flowing across Turin Hill, prior to its present course to the north of the hill. The Pleistocene terraced fluvial succession of the Western slope of Turin Hill is also mapped, based on a previous survey to allow a full reconstruction of the ancient rivers. The collected regional data and the petrographic analysis show that this succession is related to an ancient tributary of the Po River (Dora Riparia River). Wide saddles of the same river have been mapped on the main watershed between the two slopes of Turin Hill. The capping of soils less evolved with decreasing elevation over the fluvial sediments and landforms indicates that the whole terraced succession covers a large time range (Middle–Upper Pleistocene). The reported geologic successions and the current morphology of the relief result from the uplift and deformation of the Pleistocene Po Plain and the Dora Riparia Plain that were shaped at the south of Turin Hill. The proposed age/elevation relationships for the mapped terraces suggest a remarkable uplift of Turin Hill during the late Quaternary.

A meta-study of relationships between fluvial channel-body stacking pattern and aggradation rate: Implications for sequence stratigraphy

A quantitative comparison of 20 literature case studies of fluvial sedimentary successions tests common assumptions made in published models of alluvial architecture concerning (1) inverse proportionality between channel-deposit density and floodplain aggradation rates, and (2) resulting characteristics of channel-body geometries and connectedness. Our results do not support the relationships predicted by established stratigraphy models: the data suggest that channel-body density, geometry, and stacking pattern are not reliable diagnostic indicators of rates of accommodation creation. Hence, these architectural characteristics alone do not permit the definition of accommodation-based “systems tracts” and “settings”, and this calls into question current sequence stratigraphic practice in application to fluvial successions.

Facies architecture and sequence stratigraphy of an early post-rift fluvial succession, Aptian Barbalha Formation, Araripe Basin, northeastern Brazil

The Barbalha Formation (Aptian) records deposition in a fluvial and lacustrine environment accumulated in an early post-rift sag basin. Characterization of the facies architecture and sequence stratigraphic framework of the alluvial succession was carried out through detailed description and interpretation of outcrops and cored wells. The development of depositional sequences in this unit reflects variation in the accommodation-to-sediment supply (A/S) ratio. Two depositional sequences, showing an overall fining-upward trend, are preserved within the succession. The sequences are bounded by regional subaerial unconformities formed during negative A/S ratio, and may be subdivided in Low-accommodation Systems Tracts (LAST) (positive A/S ratio close to zero) and High accommodation Systems Tracts (HAST) (A/S ratio between 0.5 and 1). Sequence 1, with a minimum thickness of 100m, is characterized by amalgamated, multi-storey, braided fluvial channel sand bodies, defining a LAST. These are interlayered with crevasse splay and floodplain deposits toward the top, passing to open lacustrine deposits, defining a HAST. Sequence 2, with minimum thickness ranging from 50 to 90m, overlies the organic-rich lacustrine deposits. At the base, this sequence is composed of amalgamated, multistorey braided fluvial channel sand bodies (LAST), similar to Sequence 1, overlain by well-drained floodplain with fixed fluvial channel deposits, interpreted as an anastomosed fluvial system, which are in turn capped by lacustrine deposits, both grouped in a HAST. Paleocurrent data on fluvial deposits of sequences 1 and 2 show a consistent paleoflow to the SE. Sedimentological evidence indicates humid to sub-humid climatic conditions during deposition of sequences 1 and 2. Accumulation of fluvial sequences 1 and 2 was mainly controlled by tectonics. Variation in A/S ratios must be related to tectonic subsidence and uplift of the basin.

Tectonic activation, source area stratigraphy and provenance changes in a rift basin: the Early Cretaceous Tucano Basin (NE‐Brazil)

AbstractChanges in sandstone and conglomerate maturity in tectonically active basins can be considered either as the product of climatic change or of tectonic restructuring of the feeder drainage system. Besides these regional controls, changes in the configuration of local sources can expressively affect basin fill composition. The Early Cretaceous fluvial successions of the Tucano Basin, a rift basin in northeastern Brazil related to the South Atlantic opening, contain one such case of abrupt change in maturity, marked by the passage from pebbly sandstone and conglomerate rich in quartz and quartzite fragments (Neocomian to Barremian São Sebastião Formation) to more feldspathic pebbly sandstone and conglomerate bearing pebbles of varied composition (Aptian Marizal Formation). Systematic analysis of stratigraphic and spatial variation in palaeocurrents and composition of pebbles and cobbles from both units, integrated with the recognition of fluvial and alluvial fan deposits distribution, revealed an abrupt decrease in maturity during the passage from the São Sebastião Formation to the Marizal Formation. This change is explained by exhumation of basement rocks and erosional removal of originally widespread Silurian to Jurassic sandstone and conglomerate units which were a major source of reworked vein quartz and quartzite pebbles to the São Sebastião Formation. Basin border faults activation during the deposition of the Marizal Formation caused adjacent basement uplift above the local erosional base level at the basin borders, whereas during the São Sebastião Formation deposition, the basin border fault scarps probably exposed mineralogically mature sedimentary units. The proposed model has important implications for interpreting changes in sediment maturity in rift basin successions, as similar results are expected where activation of basin border faults occurs after the erosional removal of older sedimentary or volcanic units that controlled syn‐rift successions composition.

Lithofacies, depositional environments and stratigraphic architecture of the Wajid Group outcrops in southern Saudi Arabia

ABSTRACT The Wajid Group is a Palaeozoic siliciclastic succession of southern Saudi Arabia. In the outcrop belt it is ca. 500 m thick, whereas in the subsurface, the thickness increases to more than 4,500 m. The siliciclastic sediments have great reservoir potential for hydrocarbons and for groundwater. Although they represent one of the most important aquifers of the Arabian Peninsula, neither their sedimentologic, lithostratigraphic, nor their reservoir characteristics are satisfactorily known. In this study, a detailed description of lithology and sedimentology is given and the Wajid Group sediments are interpreted in terms of depositional environment and facies architecture. Thirteen lithofacies (LF 1 to LF 13) have been recognised, most of them composed of different subfacies. These lithofacies are grouped into 9 lithofacies associations (LF-A1 through LF-A9). LF-A1 through LF-A3 and LF-A7 represent shallow-marine siliciclastic environments. The remaining lithofacies associations describe periglacial environments of the Hirnantian (Late Ordovician) and Permian Gondwana glaciations. Except for a few pro-glacial fluvial deposits, fluvial successions and aeolian sediments are absent in the outcrops of the Wajid Sandstone. Five formations are recognised in the Wajid Group: the Dibsiyah, Sanamah, Qalibah, Khusayyayn, and Juwayl formations. They are all separated by major unconformities. The Dibsiyah Formation represents a vast sand-sheet complex with core and margin facies formed under shallow-marine conditions. These marine conditions enabled an abundant fauna to proliferate and leave its traces in the form of Skolithos piperock and Cruziana sp. A late Cambrian to Early Ordovician age is inferred for these deposits from regional considerations. The Sanamah Formation records the Late Ordovician Hirnantian glaciation with coarse sandstones and conglomerates. A variety of glacier-induced sedimentary structures are present. The internal succession is composed of three major sediment packages reflecting three ice advance-retreat cycles. The latest of these cycles is overlain by a few metres of marginal-marine sediments of the Qalibah Formation. The Khusayyayn Formation was deposited probably during Early Devonian times. It also represents a sand-sheet environment characterised by the dominance of mega-scale and giant cross beds and bed sets. A marine depositional environment is assumed from scarce Skolithos sp., and because nearly all indicators of a braided river system are absent. The Juwayl Formation of Permian age was deposited at the interface of the Late Palaeozoic Gondwana ice shield with a large lake that may have covered most of southern Arabia and adjacent areas. Proglacial sandstones and conglomerates were deposited close to the glaciers, whereas fine-grained sediment with dropstones, boulder pavements and a wide spectrum of soft-sediment deformation are characteristic of the lake environment. While the two glacial successions and the Khusayyayn Formation can rather confidently be attributed to the geological time scale, either through seismic correlation or biostratigraphically, the Dibsiyah Formation has not yet been biostratigraphically well dated.

Stratigraphic continuity and fragmentary sedimentation: the success of cyclostratigraphy as part of integrated stratigraphy

Abstract The Milankovitch theory of climate change is widely accepted, but the registration of the climate changes in the stratigraphic record and their use in building high-resolution astronomically tuned timescales has been disputed due to the complex and fragmentary nature of the stratigraphic record. However, results of time series analysis and consistency with independent magnetobiostratigraphic and/or radio-isotopic age models show that Milankovitch cycles are recorded not only in deep marine and lacustrine successions, but also in ice cores and speleothems, and in eolian and fluvial successions. Integrated stratigraphic studies further provide evidence for continuous sedimentation at Milankovitch time scales (10 4 years up to 10 6 years). This combined approach also shows that strict application of statistical confidence limits in spectral analysis to verify astronomical forcing in climate proxy records is not fully justified and may lead to false negatives. This is in contrast to recent claims that failure to apply strict statistical standards can lead to false positives in the search for periodic signals. Finally, and contrary to the argument that changes in insolation are too small to effect significant climate change, seasonal insolation variations resulting from orbital extremes can be significant (20% and more) and, as shown by climate modelling, generate large climate changes that can be expected to leave a marked imprint in the stratigraphic record. The tuning of long and continuous cyclic successions now underlies the standard geological time scale for much of the Cenozoic and also for extended intervals of the Mesozoic. Such successions have to be taken into account to fully comprehend the (cyclic) nature of the stratigraphic record.

Important Dinosaur-dominated footprint assemblages from the Lower Cretaceous Tianjialou Formation at the Houzuoshan Dinosaur Park, Junan County, Shandong Province, China

Multiple track-bearing levels in Lower Cretaceous fluvial successions at the Houzuoshan Dinosaur Park also known as the “Junan Geological Park of Dinosaurian Relic” in Junan County, Shandong Province, China, have recently become globally famous for the unique vertebrate footprints they yield. These include Shandongornipes, the first zygodactyl bird track reported from the fossil record, Dromaeopodus, the first reported trackway of a large dromaeosaur, and a new ichnospecies of Minisauripus. However, these important trackways represent only a small part of the vertebrate track record at the Houzuoshan Dinosaur Park site. Herein we describe the entire ichnofaunas representing 12 discrete mapped assemblages (surfaces) at 20 different stratigraphic levels. In total we have recorded more than 360 footprints comprising at least 130 individual trackways, belonging to eight named ichnogenera of which five (Grallator sensu lato, Asianopodus, Minisauripus, Velociraptorichnus and Dromaeopodus) are attributed to non-avian theropods, one (Ornithopodichnus) to an ornithopod and two (Shandongornipes and Koreanaornis) to birds (avian theropods). This remarkable track record allows us to characterize the ichnofaunas as one of the most distinctive and diverse yet reported from the entire Mesozoic. The ichnofauna is heavily theropod-dominated representing almost ∼90% of the total trackways, with Asianopodus the most ubiquitous track type occurring at 18 of the 20 (or 90%) of the observed levels and representing ∼74% of all trackways. None of the other track types occur at more than 5 levels or represent more than 8.3% of the trackways. Such theropod-domination is consistent with patterns noted for other Lower Cretaceous ichnofaunas from China.

Spatial and Temporal Changes In Geometries of Fluvial Channel Bodies From the Triassic Snadd Formation of Offshore Norway

Abstract During the Triassic, the Barents Sea Basin was gradually filled by a low-gradient prograding alluvial to deltaic plain, sourced from the Ural and Caledonian mountain belts in the southeast and stretching over 1000 km to Spitsbergen in the north. Progradation was made possible by high sediment yield and large trunk river systems on the scale of modern continental drainage systems. Analysis of six 3D seismic volumes from the southwest Barents Sea samples the Middle to Late Triassic Snadd Formation at various locations along an oblique depositional dip profile. By investigating spatial variability and stratigraphic evolution, this study reveals a variety of fluvial seismic geomorphological features, including point-bar systems and ribbon channel sandstone bodies. The fluvial part of the Snadd Formation is dominated by channel bodies up to 20 km wide that decrease in size to hundreds of meters over a distance of 300 km in a proximal–distal direction. There is a significant change in channel body geometries towards the top of the formation, with a decrease in maximum width from 20 to 5 km and maximum thickness from 58 to 40 m. In addition, there is an upward decrease in the channel-to-overbank ratio, and more elongated sandstone bodies have been identified in the upper part of the formation. Temporal changes are interpreted to reflect an allogenic response to changes in the hinterland, whereas spatial changes were governed by autogenic processes. This new regional understanding of the fluvial succession of the Snadd Formation provides insight into the architecture of ancient large-scale fluvial systems.