Over the last decades luminescence dating techniques have been developedthat allow earth scientists to determine the time of deposition ofsediments. In this contribution we review: 1) the development of themethodology; 2) tests of the reliability of luminescence dating onNetherlands’ sediments; and 3) geological applications of the method in theNetherlands. Our review shows that optically stimulated luminescence datingof quartz grains using the single aliquot regenerative dose method yieldsresults in agreement with independent age control for deposits ranging inage from a few years up to 125 ka. Optical dating of quartz has successfullybeen applied to sediments from a wide range of depositional environmentssuch as coastal dunes, cover sands, fluvial channel deposits, colluvialdeposits and fimic soils. These results demonstrate that optical dating is apowerful tool to explore the natural archive of the Netherlands’subsurface.

The vegetation of the northern Upper Rhine Graben (southwestern Germany) is reconstructed for the end of the Lateglacial and the Holocene by means of palynological analyses in combination with AMS 14c dating. Analogous to adjacent lowland areas, the Younger Dryas climatic deterioration did not result in a complete deforestation of the area and open pine woodlands with locally birch stands and shrubs persisted. A subdivision of the Younger Dryas period, into a humid first phase, followed by a dry second phase was also reflected in our records. For the Holocene, the pollen diagrams show two regionally different vegetation developments, related to substrate and variations in annual precipitation: in the south the ‘classical’ succession of pine then hazel is followed by other deciduous trees, whereas in the northern part, pine kept its dominance far into the Subboreal.

An inventory of the available surficial data on active faults in Italy has been compiled by gathering all the available information on peninsular Italy (project by CNR, National Group for the Defense against Earthquakes), the central-eastern Alps and the Po Plain (EC ‘PALEOSIS’ project). Such information has been summarised in maps (reporting surficial expressions of faults with length L≥11 km) and in a table where fault parameters relevant for seismic hazard assessment (e.g. slip rates, recurrence intervals for surface faulting events, etc..) have been reported. Based on the geological characteristics of the Italian territory, a fault has been considered as active if it shows evidence of Late Pleistocene-Holocene displacements. Active faults in Italy are distributed throughout the entire Apennine chain, in the Sicilian and Calabrian regions and in some Alpine sectors, but knowledge is not homogeneously distributed through the territory. The largest amount of data is related to the central Apennines. In contrast, fault geometries and parameters are less well defined in the southern Apennines, Sicily and Calabria, where investigations have started more recently. Knowledge is sparse in the northern Apeninnes, where data necessary to define fault parameters are lacking and also the chronology of the activity has to be considered cautiously. Abundant blind faulting in the Po Plain hinders the detection of active faults by means of the classical surficial investigations and therefore the present knowledge is limited to the Mantova fault. Blind faults and the peculiar recent geological history of the Alpine areas, which is strongly conditioned by the erosional and depositional activity during and after the last glacial maximum, also hinder the identification of active faults in the central-eastern Alps. Some faults in this Alpine sector are believed to be active, but data on their segmentation are still missing. Available information indicates that Italian active faults are usually characterised by slip rates lower than 1 mm/yr. Recurrence intervals for surface faulting events are longer than 1,000 years in the central and southern Apennines. This review on the Italian active faults represents the first step to produce a map of the major seismic sources in Italy, which in turn will result from the merge of surficial data with seismological and geological subsurficial data. The available knowledge gathered in this paper indicates those areas where data are presently sparse. It should be, therefore, possible to better plan future geomorphological and paleoseismological investigations.

A unique complex of multiphased Holocene drift sands and paleosols, with at least two lacustrine phases, was discovered during a major sanitation project in the Laarder Wasmeren area near Hilversum, the Netherlands. The complex could be studied in detail, highly facilitated by the excellent and large-scale exposure of the various deposits and soils. OSL dating was used to establish ages of the phases, where possible differentiating between time of deposition and time of burial by taking into account the potential effects of bioturbation. Pollen analysis served to reconstruct the vegetation during the various phases.

A first minor phase of aeolian activity already started before approx. 5,000 BC, followed around 4,000 BC by a second phase and a rather massive third phase around 3,000 BC. After a long phase of soil formation, the latest, massive drift sand phase started around the 14th to 15th century. It clearly represents the classic drift sand phase that started in the Late Middle Ages in the Netherlands. Sand drifting followed on soil forming phases during which the vegetation became increasingly dominated by ericaceous plants and culminated in heathlands. The first three aeolian phases and associated heathlands are much older than generally assumed for heathland and drift sand to occur in the Netherlands. Moreover, podzolisation was found to have started very early, true podzols already occurring before 4,000 BC.

Around 3,000 BC groundwater in the area reached a maximum altitude of about 230 cm +NAP, resulting in local open water in the area. This rise is probably linked to the development of the Dutch coastal area, where at that time peat accumulated and drainage was poor, inducing a rise of the groundwater level in ‘het Gooi’. This groundwater level fell later on, to never reach this altitude again. The Groot Wasmeer was formed by local stagnation on a slowly permeable podzol and already reached a level of 320-325 cm +NAP by 400 BC, which more or less equals its 20th century level.

The results demonstrate that earlier concepts on the occurrence and age of aeolian phases, podzols and heathland vegetations in the Netherlands are far too schematic, and that early, pre-agricultural cultures may already have had an impact on the stability of fragile cover sand landscapes, e.g. through burning. Results are in line with those from several contemporary studies on early prehistoric cultures and their impact in river dune areas in the Central and Eastern Netherlands.

The Zechstein salt in the Dutch part of the North Sea Basin played a key role in the generation of successful petroleum plays. This is not only because of its sealing capacity, but also because the salt occurs in structures that provide lateral and vertical traps. The structural styles of areas with thick salt and those with none- or thin salt are completely different during phases of extensional or compressional tectonics. This indicates that, indirectly, the depositional thickness of the main Zechstein salt is essential in regulating the loci of the Dutch petroleum systems. In this paper we aim at quantifying current ideas on the relationship between 1) depositional salt thicknesses; 2) structural style of the main structural elements identified in the Dutch subsurface; 3) timing of deformation; and 4) thickness of the overburden. By finalisation of TNO's subsurface mapping program (see Kombrink et al., this issue), several data products are available that allow evaluation of these relationships. The depositional thickness of the salt was estimated using iterative smoothing of the present day thickness, the results of which account both for regional thickness variations and volume preservation (99%). Fault-distribution analysis shows that faults are only able to penetrate salt with a depositional thickness of <300 m, a transition that demarcates the division between thin- and thick-skinned salt tectonics. In the southern offshore where the salt is thin or absent, the overburden shows the same fault pattern throughout the stratigraphic sequence. In the northern realm, where salt is thicker than 300 m, the salt layer acted as decollement and sub- and supra salt strain are dissimilar. A strong genetic and temporal relationship exists between periods of regional tectonism, halokinetic intensity and thickness distribution of the Zechstein overburden. This relationship is further proven by burial history analysis across two selected profiles in the northern offshore. The analysis focuses on the vertical distribution of the salt by taking into account the depositional and erosional history of the salt overburden, without a-priori defined periods of salt flow. The results corroborate the notion that platforms and highs experienced less extension during the major phases of Jurassic rifting and further suggest that the absence of a thick Jurassic overburden precludes major salt flow during this tectonic phase. Main salt flow was triggered during the Sub-Hercynian and later phases of compression resulting in salt pillow geometries. In the basinal areas, where the Jurassic succession is thickest, salt diapirs and walls formed that are almost exclusively linked to major subsalt faults. Main salt flow occurred during Late Kimmerian rifting, whereas some minor structuration occurred during Sub-Hercynian inversion.

Floodplain topography and related hydraulic patterns of overbank flow constitute a major control on the amounts and patterns of sediment deposition on floodplains. We studied the differences in sediment deposition at two scales along two river branches of the lower River Rhine in the Netherlands: the Waal and IJssel River. Human alterations like levelling and embankment construction have severely impacted the floodplains along the Waal River branch (average discharge: 1500 m3·s‒1), whereas the relatively wide floodplains along the IJssel River (average discharge: 250 m3·s‒1) still exhibit their characteristic ridge-and-swale topography and natural levees. We found that, in general, the amounts of sediment deposited sediment decreases with increasing distance to the sediment source. Clay and organic matter content generally increase with decreasing floodplain elevation. These trends are, however, far less pronounced in the Waal River floodplains than in the IJssel River floodplains. Sediment deposited on the IJssel River floodplains also contains significantly more sand than the sediment deposited on the Waal River floodplains, probably because of the absence of minor embankments along the IJssel River and its higher sinuosity. Furthermore, during inundation the individual Waal River floodplains receive more sediment per unit area than the IJssel River floodplains. At the scale of the river branch, however, the conveyance losses in the Waal River are less than in the IJssel River, because of the larger surface area of the floodplains along the IJssel River relative to its water and sediment discharge during flood events. This discrepancy stresses that both the individual floodplain sections and the total river branch should be taken into account when studying the role of overbank deposition as part of a river’s sediment budget.

Alluvial architecture has been subject of many studies because of theoccurrence of natural resources in ancient fluvial successions. This paperprovides an overview of the current state of research on alluvialarchitecture with special reference to Holocene fluvio-deltaic settings.Several examples from modern fluvio-deltaic areas, especially the HoloceneRhine-Meuse delta (the Netherlands) and the Lower Mississippi Valley(U.S.A.), are used to illustrate the architectural elements that can bedistinguished in fluvial successions and to show the influence of thevarious controls on alluvial architecture (base level, climate, tectonism,aggradation, avulsion, and compaction). Avulsion is regarded as a principalprocess in the formation of fluvio-deltaic sequences, because it determinesthe location and number of active channels on the floodplain. The avulsionmechanism is still subject of debate, though. A brief description of theevolution of process-based alluvial-architecture models is given. Thesemodels simulate the proportion and distribution of coarse-grained channelbelts in fine-grained overbank deposits. The major drawback of thepresent-day alluvial-architecture models is the lack of (three-dimensional)quantitative field data to test and validate them. The paper concludes withthe suggestion to collect more architectural data from natural fluvialsettings, to improve simulation of channel-belt geometry inalluvial-architecture models, and to implement new data and knowledge offluvial processes into models.

Middle Jurassic - Early Cretaceous strata are a target for oil and gas exploration in the Dutch offshore. During the initial stages of the ‘Late Jurassic’ offshore exploration, various oil fields and a few gas fields were discovered of which only one, the F3-FB field, proved to be economically viable. In the Northern Offshore of the Netherlands, latest Middle Jurassic (Callovian) - earliest Cretaceous (Ryazanian) strata are mostly limited to the Dutch Central Graben and Terschelling basins. Outside the Dutch Central Graben and the Terschelling Basin only thin veneers of these strata occur on the fringing highs such as the Schill Grund High and the Step Graben. The geology of this non-marine to shallow marine succession is complex. The combination of lateral facies changes, repetitive log and facies characteristics in time, sea-level and climate changes, salt tectonics and structural compartmentalisation hamper straightforward seismic interpretation and log correlation. The large number of lithostratigraphic units defined in the Stratigraphic Nomenclature of the Netherlands illustrates the complexity of this time-interval.

In recent years, new biostratigraphic techniques and newly acquired stratigraphic data led to the identification of a series of events which can be related to the tectonic, climatic, environmental and stratigraphic development of the ‘Late Jurassic’ in the Dutch Central Graben and Terschelling basins. Based on these data, three stratigraphic sequences can be recognized. Sequence 1 (Callovian - earliest Kimmeridgian) records the initiation of the Dutch Central Graben, Sequence 2 (early Kimmeridgian - early Portlandian) that of the initiation of the Terschelling Basin. During sequence 3 (late Portlandian - Ryazanian) the Dutch offshore was draped by a regional transgression. These insights have directly impact on the exploration potential, which is discussed in two play concepts. The first is a strat-trap play in the fluvial/paralic sediments of Sequence 1 in the lows between the graben boundary and salt domes. The second example is the Spiculite play, which comprises a bioclastic sandstone reservoir at the top of a dome with a 4-way dip closure. These two examples highlight the necessity of understanding the paleoenvironment and geography for assessing the future exploration potential.

Solar activity, as manifested by its many equatorial as well as high-latitude components of short-term variability is regulated by the Sun’s dynamo. This constitutes an intricate interplay between the solar toroidal and poloidal magnetic field components. The dynamo originates in the tachocline, which is a thin layer situated about 200,000 km beneath the solar surface. The dynamo is a non-linear system with deterministic chaotic elements, hence in principle unpredictable. Yet there are regularities in the past behaviour, such as the Grand Maxima (example: the recent high maximum of the 2nd half of the 20th century) the Grand Minima (e.g. the Maunder Minimum between 1650 and 1710) and the Regular Oscillations such as those between 1730 and 1923. Their occurrences are described by a phase diagram in which a specific point can be identified: the Transition Point. This diagram plays an essential role in determining the future solar activity. Guided by its quasi-regularities and by recent measurements of the solar magnetic fields we find that the Sun is presently undergoing a transition between the past Grand Maximum and a forthcoming period of Regular Oscillations. We forecast that this latter period will start in a few years and will continue for at least one Gleissberg cycle and that the next solar maximum (expected for 2014) will be low (Rmax ~ 68).

We discuss the heliospheric drivers of Sun-climate interaction and find that the low-latitude magnetic regions contribute most to tropospheric temperatures but that also the influence of the - so far always neglected - polar activity is significant. Subtraction of these components from the observed temperatures of the past 400 years shows a residual series of relative peaks and dips in the temperature. These tops and lows last for periods of the order of the Gleissberg cycle. One of these is the recent period of global warming, which, from this point of view, is not an exceptional period.

The Groningen gas field has shown considerable compaction and subsidence since starting production in the early 1960s. The behaviour is understood from the geomechanical response of the reservoir pressure depletion. By integrating surface movement measurements and modelling, the model parameters can be constrained and understanding of the subsurface behaviour can be improved. Such a procedure has been employed to formulate new compaction and subsidence forecasts. The results are put into the context of an extensive review of the work performed in this field, both in Groningen and beyond. The review is used to formulate a way forward designed to integrate all knowledge in a stochastic manner.

Within the Cenozoic sedimentary section of the Roer Valley Graben ten seismostratigraphic units have been identified. They are closely related to the lithological framework which makes it possible to recognize diem also on well logs in this region. The Lower Tertiary seismic units, representing mainly marine sediments, have a uniform development mat can be correlated over large distances into the German part of the Roer Valley Graben. The marine to continental Upper Tertiary and Quaternary seismic units display a more complex development due to lateral facies changes (including prograding delta systems) and rift tectonics.

Reactive-transport models contribute significantly to the field of modern geosciences. A general mathematical approach to solving models of complex biogeochemical systems is introduced. It is argued that even though mathematical models for reactive-transport simulations can be developed at various levels of approximation, the approach for their construction and application to the various compartments of the hydrosphere is fundamentally the same. The workings of coupled transport-reaction systems are described in more detail by means of examples, which demonstrate the similarities in the approach. Three models of the carbon dynamics in redox-stratified environments are compared: porous media flow problems in a coastal sediment and in a contaminated groundwater system; and a surface flow problem in a eutrophic estuary. Considering the interdisciplinary nature of such models, a Knowledge Base System for biogeochemical processes is proposed. Incorporation of the proposed knowledge base in an appropriate modeling framework, such as the Biogeochemical Reaction Network Simulator, proves an effective approach to the modeling of complex natural systems. This methodology allows for construction of multi-component reactive-transport models applicable to a wide range of problems of interest to the geoscientist.

The youngest representatives of ‘true’ (= non-tegulated) inoceramid bivalves (Inoceramidae) are described from intervals 3-6 of the Vijlen Member (Gulpen Formation), of late early and early late Maastrichtian age, as exposed at quarries and temporary sections in northeast Belgium (CPL SA-Haccourt and CBR-Lixhe quarries) and the Aachen area (Germany), i.e. the extended type area of the Maastrichtian Stage. In total, twelve taxa are recognised from levels which are correlative with the Calcaire à Baculites of Manche (France), as well as with the Tercis les Bains section in southwest France, the Wisła (Vistula) River sections (central Poland) and the Western Interior of the United States. Associated cephalopods allow a detailed correlation between biozones based on those groups and on inoceramid bivalves.

This paper presents an overview of a provisional lithostratigraphical framework for the Quaternary and Neogene deposits of Great Britain (England, Scotland and Wales) (onshore). The objective is to provide a workable framework to aid future Quaternary mapping and research, and a stratigraphical scheme capable of use in a wide variety of applications. Using the full hierarchy, a supergroup, group and subgroup lithostratigraphy, based upon the primary mapping unit, the formation, is proposed. It is recommended that some classes of lithogenetically-defined deposits which, at present cannot be accorded formational status, should be assigned informally to one of the proposed groups or subgroups. The framework distinguishes one superficial deposits supergroup within which seven groups are defined: i) Crag Group, marine deposits (Late Pliocene to Early Pleistocene); ii), Dunwich Group, fluvial deposits (pre-Anglian/pre-Elsterian); iii) Residual Deposits Group; iv) British Coastal Deposits Group, coastal and marine deposits (Anglian to Holocene); v) Britannia Catchments Group, fluvial, organic and mass movement deposits (Anglian to Holocene) within broadly defined catchment areas related to Late Devensian to present-day physiography; vi) Albion Glacigenic Group, glacigenic deposits (pre-Devensian/pre-Weichselian), and vii) Caledonia Glacigenic Group, glacigenic deposits (Devensian/Weichselian). North of the Devensian (Weichselian) ice-sheet limit, a series of glacigenic subgroups are defined geographically for the two glacigenic groups on the basis of mappable formations of till. The subgroups include associated formations of glaciofluvial and glaciolacustrine deposits. Consequently some of the glacigenic water-lain units may extend beyond the Devensian limit. Catchment subgroups of the Britannia Catchments Group are proposed for formations and lithogenetic units defined within broad present-day physiographic regions by major river drainage systems that have developed since Middle Pleistocene time. Lithostratigraphical description and correlation of formations will aid the refinement of the proposed framework and enable the development of lithostratigraphical maps and three-dimensional models. As well as offering a unified framework for onshore Quaternary and Neogene deposits the proposed supergroup, group and subgroup structure may prove useful for a wide range of regional applications (e.g. hydrological, hydrogeological, engineering).

Ground surface dynamics is one of the processes influencing the future of the Wadden Sea area. Vertical land movement, both subsidence and heave, is a direct contributor to changes in the relative sea level. It is defined as the change of height of the Earth's surface with respect to a vertical datum. In the Netherlands, the Normaal Amsterdams Peil (NAP) is the official height datum, but its realisation via reference benchmarks is not time-dependent. Consequently, NAP benchmarks are not optimal for monitoring physical processes such as land subsidence. However, surface subsidence can be regarded as a differential signal: the vertical motion of one location relative to the vertical motion of another location. In this case, the actual geodetic height datum is superfluous.

In the present paper, we highlight the processes that cause subsidence, with specific focus on the Wadden Sea area. The focus will be toward anthropogenic causes of subsidence, and how to understand them; how to measure and monitor and use these measurements for better characterisation and forecasting; with some details on the activities in the Wadden Sea that are relevant in this respect. This naturally leads to the identification of knowledge gaps and to the formulation of notions for future research.

The coversands along the Bree fault escarpment, NE Belgium, were investigated by a combined dating approach including infrared optically stimulated luminescence (IRSL), thermoluminescence (TL) and radiocarbon methods. Four trenches were excavated cutting the fault scarp near the village of Bree in northeast Belgium. Altogether 17 luminescence samples and seven radiocarbon samples were investigated in order to set up a more reliable and precise chronological frame for the local coversand stratigraphy and the timing of Late Quaternary earthquake events. The chronological results indicate at least five accumulation periods for the coversand units in the area of interest. The oldest coversands were deposited during Saalian or Early Weichselian followed by coversands deposited during the Early and/or Middle Weichselian. At least three coversand units can be distinguished for the time span of the Late Weichselian to Holocene. Significant TL age underestimation of more than 20% compared to IRSL was found for samples from Trench 4. Most of the IRSL age estimates are in agreement with radiocarbon dates from the same section.

Recent core drillings, carried out during water-economic exploration in the area of Mannheim/Ludwigshafen/Schifferstadt (Rhine-Neckar region, Germany), have produced a more differentiated stratigraphic division of the Pleistocene sediments of the northern Upper Rhine Graben. Pollen analytical investigations as well as malacological, heavy mineral, palaeomagnetic and lithological research have led to a stratigraphic reinterpretation of the gravel layers and intermediate horizons. Based on the results of the pollen analyses, the Mannheim interglacial period in the upper intermediate horizon (Oberer Zwischenhorizont, OZH) cannot be assigned to the Eemian as stated earlier. The occurrence of Fagus, Celtis and Azolla, along with the results of malacological analyses, indicate a Cromerian age for the Mannheim Interglacial. In addition, a pollen sequence from a different interglacial in the core sediments from Schifferstadt could also be assigned to the Cromerian. The Schifferstadt Interglacial is divided into a lower optimum phase with high values of Ulmus, Quercus and Corylus while Carpinus is completely absent, and an upper optimum phase with low values of Carpinus. Fagus is absent in the whole sequence. The OZH comprises not only the two interglacial pollen sequences described above but also parts of at least four Middle Pleistocene Interglacials. In the lower part of the drillings in Schifferstadt and Ludwigshafen, which are assigned to the Early Pleistocene, pollen assemblages with Fagus are likely to correlate with parts of the Tiglian A substage. There is a clear change to a Tertiary type of pollen flora at 91 m at Schifferstadt and at 186 m in Ludwigshafen.

During its maximum extension, the Saalian ice cap reached into the central Netherlands, where glacier tongues excavated over 100 m deep basins in the unconsolidated Middle and Early Pleistocene sediments. The basins are filled by relatively thick successions of Late Saalian, Eemian and Weichselian sediments. The fill of the Amsterdam glacial basin is among the best known and studied in the Netherlands. The Late Saalian sediments consist mainly of warves and ill-bedded clays and silts with, along its southern margin, influxes of sands from the surrounding ice-pushed ridges. During deposition of these sediments, the Amsterdam basin formed part of a large lake extending into the present North Sea. Draining of this lake at the end of the Late Saalian left small, shallow pools at the site of the glacial basins.

Late Saalian and Eemian sediments are probably separated by a short break, although sedimentation may have been continuous in the deepest part of the basin. The Eemian deposits consist in main lines of a thin, diatom-rich sapropel at the base, overlain by an up to 30 m thick clay-rich sequence covered by a wedge of sand that measures more than 20 m in the northern part of the basin and that peters out southwards. As appears from the fauna, most of the clays were deposited in a lagoonal setting shielded behind a threshold and/or barrier. The rate of sediment supply was low so that lagoonal conditions were maintained over a long timespan. Sands derived from the surrounding ice-pushed ridges and transported by longshore drift and tidal currents formed a spit at the northern margin of the basin, which moved southward after eustatic sea-level rise stabilized and the lagoon was filled by clay. Loading of this clay-rich sequence by the spit and its washover fans induced subsidence, however, because of compaction, so that marine conditions were maintained until after the Eemian highstand. Fluvial and eolian sediments of Weichselian age, locally reaching a thickness of almost 10 m, eventually levelled the Amsterdam glacial basin.

More than 400 samples for paleobotanical and sedimentological investigations were collected from Late Pliocene and earliest Pleistocene beds in the open-cast lignite mine Hambach. They were analysed to obtain information about the paleoecology and paleoclimate of this time interval. The sedimentation type changed from a high-energy meandering fluvial system to floodplain, swamp and oxbow lake sedimentation. The typical Tertiary floral elements decreased with the onset of increasingly cooler climatic conditions and disappeared at the beginning of the Pleistocene to be substituted by a impoverished and coldadapted flora. These combined litho- and biostratigraphic investigations led to an improved and reproducible separation of Late Pliocene from Early Pleistocene deposits.

Evidence-based interpretations of fluvial evolution, and especially of river-terrace formation, have advanced significantly in recent decades, with a notable contribution made by activities of the Fluvial Archives Group. Well-dated river-terrace sequences provide frameworks for the understanding of landscape evolution, since they record valley-floor levels that were higher in the past, attributable, from their patterns of occurrence, to regional uplift. The role of climate fluctuation during the Quaternary is also paramount, since this has been an important driver of the varied fluvial activity that has given rise to the staircases of terraces that characterise the temperate latitudes. This approach is contrasted with a more theoretical methodology for using rivers as recorders of landscape evolution, again with an emphasis on uplift, based on the concept of the formation of knickpoints at particular base levels and their migration upstream. Although different timescales can be explored by the two methods, the concept of headward-migrating knickpoints implies a mechanism for incision that is difficult to reconcile with the formation of the broadly parallel river terraces that are observed in many systems. Knickpoints can frequently be observed to coincide with gorge reaches, where river valleys are constricted as a result of resistant bedrock and/or the effects of localised active crustal deformation. This raises the possibility that knickpoints have generally formed in response to factors of local geology rather than migrating from downstream.