Search

Given the substantial groundwater level declines in the Central Valley of California, there is an urgent need to supplement the recharge of the groundwater systems by implementing managed aquifer recharge. With approximately 170 km3 (140 million acre-feet) of available groundwater storage space, water deemed to be excess during wet years could be spread on the ground surface at selected locations allowing it to move downward to recharge the underlying aquifer system. Along the eastern edge of the Central Valley there are large paleovalleys that can act as fast paths expediting the downward movement of water. These paleovalleys, incised and then filled with coarse-grained materials—sand, gravel, cobbles—at the end of the last glacial period, are referred to as incised valley fill (IVF) deposits. An IVF deposit has been mapped at one location in the Kings River alluvial fan, with others proposed to exist in the fans of major rivers. If located, these deposits would be optimal sites for managed recharge. In this study, we assessed the use of a helicopter-deployed geophysical method to efficiently locate IVF deposits throughout the Central Valley. We acquired 542 line-kilometers of airborne electromagnetic (AEM) data in the Kings River alluvial fan, with dense line-spacing over the Kings River IVF deposit which had been mapped as ∼2 km wide, extending over 20 km into the Central Valley, from the ground surface to a depth of 30 m. The IVF deposit was unambiguously imaged in the AEM data as an extensive linear feature that was more electrically resistive than the surrounding materials due to the high percentage of coarse-grained sediments. This study provides the evidence to support the rapid adoption of the AEM method to locate IVF deposits along the eastern edge of the Central Valley. These deposits provide valuable natural infrastructure for recharging California’s groundwater.

U-shaped and V-shaped palleovalleys and paleodepressions are identified on multifrequency seismic data in near-surface section (NSS) within three study areas in Vostochno-Prinovozemelsky area. Valleys of the Late Cretaceous and Quaternary ages and of different genesis are found in the first area of study. The palleovalleys of the Late Cretaceous age are V-shaped and U-shaped by their characteristic morphological properties and are likely formed as a result of the rivers erosional activity. Genesis of the buried valleys filled with Quaternary glacial sediments is usually connected to glacial plucking of the Late Quaternary glaciation, and they are similar to U-shaped paleovalleys. The tunnel valleys of Quaternary age that most likely were formed as a result from impact of ice sheet located to the east of the Novaya Zemlya archipelago in the Late Quaternary age were observed in the second study area. In contrast to the first two sites, isometric depressions of Quaternary age and controversial genesis were observed in the third one. The direction of the identified paleovalleys in some cases coincides with the submarine valleys indicated on the USSR Northern Seas submarine valleys map (Lastochkin, 1977) and the Kara Sea geomorphological map (Miroshnikov et al., 2021). [ABSTRACT FROM AUTHOR]

Lake Seliger has been always classified as a former glacial water body, a remnant of a vast proglacial lake, which has existed since the disappearance of the last glacial Ice Sheet in the territory 18–19 thousand years ago. The study was focused on areas of southern pools of the lake looking like underflooded meandering river channels. Bottom sediments were drilled in three such areas and ground penetrating radar profiling was carried out on two areas. Lake silt, several meters thick, was found to overlay coarse sand, which is most likely of riverine origin. A feature in favor of this is a characteristic asymmetrical bed profile in the supposed parts of ancient river bends and the time of transition from active flow to the regime of stagnant water body since 14.5 thousand years ago: in that time, glacier edge already lied far from here, and glacial melt water did not penetrate into this area. The inundation of segments of river valleys and their transformation into lake pools was provoked by damming of the Selizharovka River, which originally flowed out from Lake Seliger near Ostashkov Town. About 14.5 thousand years ago, the rapidly growing delta of the Krapivenka River, a left tributary of the Selizharovka, started growing rapidly, damming the latter river. In the period of 2 thousand years, the damming effect extended over the entire 15-km segment of the valley and reached the source of the river in Lake Seliger. In the Holocene, the level rise continued, though at a lesser rate. The total rise of lake level was 7–8 m, which caused flooding of the lower reaches of the valleys of rivers emptying into the lake and transformed them into estuaries. It is shown that glacioisostatic deformations of the Earth crust could not reverse the flow from Seliger into the Baltic Basin. After the disappearance of the most recent glacier, Lake Seliger and its tributaries have always belonged to the Volga Basin; this is to be taken into account in the reconstruction of the Volga runoff and the water balance of the receiving water body (the Caspian Sea). [ABSTRACT FROM AUTHOR]

Given the substantial groundwater level declines in the Central Valley of California, there is an urgent need to supplement the recharge of the groundwater systems by implementing managed aquifer recharge. With approximately 170 km ^3 (140 million acre-feet) of available groundwater storage space, water deemed to be excess during wet years could be spread on the ground surface at selected locations allowing it to move downward to recharge the underlying aquifer system. Along the eastern edge of the Central Valley there are large paleovalleys that can act as fast paths expediting the downward movement of water. These paleovalleys, incised and then filled with coarse-grained materials—sand, gravel, cobbles—at the end of the last glacial period, are referred to as incised valley fill (IVF) deposits. An IVF deposit has been mapped at one location in the Kings River alluvial fan, with others proposed to exist in the fans of major rivers. If located, these deposits would be optimal sites for managed recharge. In this study, we assessed the use of a helicopter-deployed geophysical method to efficiently locate IVF deposits throughout the Central Valley. We acquired 542 line-kilometers of airborne electromagnetic (AEM) data in the Kings River alluvial fan, with dense line-spacing over the Kings River IVF deposit which had been mapped as ∼2 km wide, extending over 20 km into the Central Valley, from the ground surface to a depth of 30 m. The IVF deposit was unambiguously imaged in the AEM data as an extensive linear feature that was more electrically resistive than the surrounding materials due to the high percentage of coarse-grained sediments. This study provides the evidence to support the rapid adoption of the AEM method to locate IVF deposits along the eastern edge of the Central Valley. These deposits provide valuable natural infrastructure for recharging California’s groundwater.

Bortolin, E.; Weschenfelder, J., and Cooper, A., 2019. Holocene evolution of Patos Lagoon, Brazil: The role of antecedent topography. Journal of Coastal Research, 35(2), 357–368. Coconut Creek (Florida), ISSN 0749-0208. The Patos Lagoon in Rio Grande do Sul, Brazil, is part of the largest barrier lagoon system in the world. It is enclosed by a 400-km-long composite late Pleistocene/Holocene sandy barrier and has a single tidal inlet. The modern lagoon is shallow (average < 5 m) and is dominated by silt deposition. More than 1000 km of shallow seismic data (3.5 kHz) indicate that the lagoon is underlain by several shore-normal incised valleys separated by interfluves. Each incised valley existed as an individual estuary since its first flooding during the mid-Holocene. The infill of these valleys contains a basal fluvial unit, a central estuarine mud unit, and locally developed tidal sand bodies associated with former tidal inlets. The contemporary lagoonal sediments form a blanketing upper unit. Ultimately, the interfluves were drowned and the contemporary lagoon was formed by the coalescence of the incised valley estuarine systems in the late Holocene. This expansion of accommodation space coincided with a dramatic reduction in vertical sedimentation rates. Seismic profiling reveals the contemporary sandy spits, and their subaqueous extensions coincide with the location of former interfluves, indicating that inherited topography exerts major control over the location and development of lagoon-marginal spits. [ABSTRACT FROM AUTHOR]

A network of cross-shelf paleovalleys has been recognized over the paleo-inner shelf off the Gilão-Almargem Estuary, a small fluvial drainage system that presently receives minor sediment supply in the eastern Algarve shelf, northern margin of the Gulf of Cadiz (SW Iberian Peninsula). This study is aimed at determining the driving controls that triggered substantially different paleohydrological conditions and sedimentary dynamics of ancient fluvial systems in this margin. We focus on evidences of secondary controls on valley genesis and evolution, superimposed to primary glacio-eustatic control such as antecedent geology, low fluvial supply and changing hydrodynamic regimes. The architecture and spatial distribution of these paleovalleys were interpreted based on a grid of seismic profiles with different resolutions. Likewise, a sediment core obtained in a distal position of the paleovalley system provided information about sedimentary processes during the most recent stage of valley infilling. The chronostratigraphic framework was constructed based on regional seismic horizons defined in previous studies and complemented with two AMS 14C dates obtained from bivalve shells. The inner shelf paleovalley system is composed of several incised valley features which exhibit a remarkable similar internal architecture. These inner valley features exhibit two major incision phases (from oldest to youngest; IP 2 and IP 1) that are thought to constitute a simple paleovalley system formed during the last glacial cycle. The origins of the incision are considered to be different. The older one is related to fluvial incision during the sea-level fall leading into the Last Glacial Maximum, whereas the recent one is interpreted as the result of tidal scour during the postglacial transgression. Their corresponding infillings are interpreted, respectively, as estuarine bay-fill deposits and estuary-mouth sands. Overlying the paleovalley infilling, a distinctive reflective unit is in agreement with the generation of coastal barriers and related depositional systems. The formation of the paleo-inner-shelf paleovalley system was strongly conditioned by antecedent geology, which strongly limited the generation of wide incised valleys and determined the amount of incision landward of a well-defined break of slope. Its postglacial infilling was mainly estuarine in nature, likely involving the development of a dendritic system, with numerous barriers interrupted by tidal inlets and channels in a mixed estuarine system with low fluvial supply. • Inner-shelf valleys interpreted as a simple system formed during the last glacial cycle. • The valleys infilling records the occurrence of wave- and tide-dominated processes. • Incised valley formation was strongly determined by antecedent geology. • The infilling took place under high rates of sea-level rise and low fluvial supply. • The system comprised an estuarine system with multiple barriers and inlets. [ABSTRACT FROM AUTHOR]

This study reviews the available information for over 1200 Australian salt lakes including in areas that have little or unreliable data. Publicly available groundwater hydrogeochemical datasets for the Australian arid zone are particularly sparse, inconsistent and of variable quality. Many datasets in the vicinity of salt lakes only report salinity or total dissolved solids, with no data for constituent cations and anions, and no appreciation of the hydrological and geomorphic evolution of the lakes. To overcome these limitations and to provide a broad-scale context, we developed mineral systems models to assess the potential of Australian salt lakes for potash, lithium and boron deposits. These models show that an important control on the potential of salt lake systems to form economic deposits of potash, lithium or boron is hydrogeological connectivity between leachable source rocks and the lakes. The assessment of the mineral potential was carried out in two stages. The first stage selection was based on the presence of favourable source rocks in the salt lakes’ catchments. The mean values of concentration in each catchment were derived from whole rock, sediment and groundwater geochemical datasets by averaging the values in samples (separately for each of the three datasets) located in the catchment and assigning this value to the catchment's salt lakes. The second stage selection was carried out by analysing available chemical data of groundwater in proximity to the salt lake systems delineated in the first stage. As a result, six regions were identified as having the highest potential, for potash in particular, but also for lithium and/or boron deposits. These are: the Lake Frome/Central Gawler Region of South Australia; two regions in the Northern Territory: the central western region extending into Western Australia, and the Lake Woods region; and, in Western Australia, the Lake Disappointment region, the north east Yilgarn and south east Yilgarn regions. [ABSTRACT FROM AUTHOR]

The first Holocene stratigraphic record of river-channel occupation and switching between the Brahmaputra–Jamuna and Old Brahmaputra paleovalleys is presented here. Motivated by the Brahmaputra River's historic avulsion from the Old Brahmaputra channel to its present-day Jamuna course, we have obtained sediment and radiocarbon samples from 41 boreholes along a 120 km transect crossing these two braided-river valleys. The stratigraphy along this transect reveals sand-dominated Holocene channel systems, each bound by remnant, mud-capped Pleistocene stratigraphy. Using sediment lithology and bulk strontium concentration as a provenance indicator, we define the geometry and channel-occupation history of each paleovalley. The western Brahmaputra–Jamuna valley is broad and somewhat deeper compared with the Old Brahmaputra valley, the latter actually comprising a composite of two narrower sub-valleys bifurcated by an antecedent topographic remnant. The gently sloped valley margins (slope: 0.002 to 0.007) and high width-to-thickness ratio (W/T: ~ 1000) of the Brahmaputra–Jamuna valley suggest that it was filled primarily through lateral channel migration and the reworking of braidbelt and overbank deposits. Conversely, the two Old Brahmaputra sub-valleys have comparatively steeper valley margins (slope: 0.007 to 0.022) and lower width-to-thickness ratios (W/T: ~ 125 and ~ 250), indicating that these were filled primarily through vertical aggradation of channel sands. We attribute this disparity in valley geometry and fill processes to the different occupation histories for each valley. In this case, the much larger Brahmaputra–Jamuna valley represents the principal, if not singular, river course during the last lowstand of sea-level, with a prominent gravel lag underlying the valley. In contrast the smaller Old Brahmaputra valleys do not appear to have been present, or at least well developed, at the last lowstand. Rather these courses were first occupied during the early Holocene transgression, and we infer that the river had been previously excluded from this region by the relatively higher elevation between the Madhupur Terrace and the Shillong Massif. We also demonstrate that the Brahmaputra River experienced 3–4 major avulsions during the Holocene, with considerably longer occupation times within the principal Brahmaputra–Jamuna valley. Together these observations indicate that occupation history and antecedent topography have been important controls on river course mobility and avulsion behavior. [ABSTRACT FROM AUTHOR]

For work materials used multispectral satellite imagery Landsat (7 channels), medium spatial resolution (14,25-90 m) and a digital elevation model (data SRTM).For interpretation of satellite images and especially their infrared and thermal channels allocated buried paleovalleys pre-paleogene age. Their total length is 228 km. By manifestation of the content of remote sensing paleovalleys distinctly divided into two types, long ribbon-like read in materials and space survey highlights a network of small lakes. By the nature of the relationship established that the second type of river paleovalleys flogs first. On this basis, proposed to allocate two uneven river paleosystem. The most ancient paleovalleys first type can presumably be attributed to karst erosion, blurry chalk and carbon deposits foundation. Paleovalleys may include significant groundwater resources as drinking and industrial purposes. Also we can control the position paleovalleys zinc and bauxite mineralization area and alluvial deposits include uranium mineralization valleys infiltration type and placer gold. Direction paleovalleys choppy, but in general they have a north-east orientation, which is controlled by tectonic zones of the foundation. These zones are defined as the burial place themselves paleovalleys and position of karst cavities in areas interfacing with other structures orientation. The association of mineralization to the caverns in the beds paleovalleys could generally present conditions of formation of mineralization and carry it to the «Niagara» type. The term is obviously best reflects the mechanism of formation of these ores. [ABSTRACT FROM AUTHOR]

Abstract: Holocene shallow (0.5–4.5 m, rarely more) and Pliocene–Pleistocene deep (>25 m) placers occur within the China tectonic depression. The shallow placers are associated with the formation of the present-day drainage valleys of the China River under permafrost conditions, and the deep ones are localized within the preglacial paleovalleys of the river basin. An integrated geological and geochemical study was carried out at ten shallow commercial placers, eight of which are classified as poorly studied and “unconventional.” Placers are considered “unconventional” based on their technological characteristics (commercial gold is small (−0.25 to +0.1 mm), thin (−0.1 mm), and micron-sized or “bound” (invisible)), geomorphologic conditions of formation, confinement to the oxidized zone of active permafrost, significant portion of fine hydrogenic gold, and several other minor features. The formation of shallow “unconventional” placers is controlled by the conditions of active permafrost. Under aerobic conditions, suprapermafrost waters form an oxidized zone, in which iron hydroxides impart a yellowish reddish color to water-bearing rocks. Long-lived geochemical barriers (biogenic, reduction, electrochemical, sorption, and others), including gravitational differentiation, play an important role in the concentration of small and thin gold. Alluvial deposits in Meso-Cenozoic tectonic depressions, such as the China basin, are the most promising in terms of “unconventional” placers. The main factors favoring the formation of these localities and the criteria for their assessment are large feeding sources of gold (mainly carbonaceous and sulfide) mineralization, endogenic and exogenic dispersion aureoles with thin and invisible gold; increased thickness of the suprapermafrost active layer and its temporal and spatial stability, contributing to the formation and functioning of oxidized horizons with the accumulation of ferric hydroxide and hydrogenic gold; specific morphologic varieties of hydrogenic gold, which are the fundamental criterion for primary gold mineralization with migratable metal; fine-clastic clay-rich composition of recent alluvial or alluvial-talus sediments, produced by water reworking of ancient gold-bearing weathering crusts; and development of broad floodplains filled with Holocene sediments and their junction with talus-solifluction erosional slopes. [Copyright &y& Elsevier]

Abstract: Ancient fluvial valley systems are long recognized as important features in the stratigraphic record, but emerged as a specific focus of attention with publication of first-generation sequence-stratigraphic concepts. This paper reviews current understanding of paleovalley systems from the perspective of Quaternary analogs and experimental studies. Paleovalley systems can include distinct mixed bedrock–alluvial, coastal-plain, and cross-shelf segments. Mixed bedrock–alluvial segments are long-lived, cut across bedrock of significantly older age, and have an overall degradational architecture. By contrast, coastal-plain and cross-shelf segments are non-equilibrium responses to high-frequency cycles of relative sea-level change: most coastal-plain and cross-shelf segments form as a geometric response to relative sea-level fall, as river systems cut through coastal-plain and inner shelf clinothems, and extend basinward to track the shoreline. After incision and cross-shelf extension, lateral channel migration and contemporaneous channel-belt deposition creates a valley-scale feature. Coastal-plain and cross-shelf paleovalley widths are set by the number of channel-belt sandbodies deposited during this time. Paleovalley systems play a key role in source-to-sink sediment routing. Early views included the model of incision and complete sediment bypass in response to relative sea-level fall. However, this model does not stand up to empirical, theoretical, or experimental scrutiny. Instead, there is a complex dynamic between incision, deposition, and sediment export from an evolving valley: periods of incision correspond with sediment export minima, whereas periods of lateral migration and channel-belt construction result in increased flux to the river mouth. Sediment export from evolving valleys, and merging of drainages during cross-shelf transit, play key roles in sediment transfer to the shelf-margin and genetically-linked slope to basin-floor systems. Connection between the river mouth and the shelf margin likely occurs for different periods of time depending on gradient of the river and shelf, as well as amplitude of high-frequency sea-level changes. Late Quaternary analogs and experimental studies provide an alternative sequence-stratigraphic interpretation for paleovalley systems. In coastal-plain paleovalleys, basal valley-fill surfaces meet criteria for an unconformity and a classically-defined sequence boundary: however, this surface is mostly everywhere of the same age as overlying fluvial deposits, and does not correspond to a long period of incision and sediment bypass. In cross-shelf paleovalleys, the basal contact between fluvial and deltaic or shoreface deposits is commonly interpreted as a sequence boundary, but is not an unconformity characterized by incision and sediment bypass. Instead, this surface is a facies contact that separates genetically-related fluvial and deltaic strata: the surface that correlates to the basal valley-fill surface within the coastal-plain paleovalley dips below cross-shelf prograding deltaic and/or shoreface strata, which are fed by deposition within the evolving valley itself, and should be the downlap surface. Many issues deserve attention in the future. We have stressed understanding the inherent scales and physical processes that operate during the formation and evolution of paleovalley systems. We also suggest the relative roles of allogenic forcing vs. autogenic dynamics, and the potential significance of high-frequency isostatic adjustments should be topics for future discussion. [Copyright &y& Elsevier]

Abstract: Pennsylvanian cycles in the Northern Appalachian Basin (NAB) were historically considered to result from delta-lobe switching, and more recently from sea-level fluctuation with sandy deltas prograding during highstand. These interpretations are revised using new data from cores and outcrop exposures. Thick (>5m) channel deposits with a marked erosion surface at their base cutting down across previous cycles are re-interpreted as incised valley fill (IVF) deposits in paleovalleys, because the basal erosion surfaces are widespread, and thus reflect a record of lowstand. Most common are simple paleovalleys that contain mainly sandy fluvial deposits. Compound paleovalleys with sequence boundaries above the basal erosion surface, contain terrestrial, estuarine, and marine deposits. Early to late highstand deposits in interfluvial parts of the cycles are dominated by shale and mudstone, with paleosols, coals, and local non-marine limestone, which reflect floodbasin to lacustrine conditions. These reinterpretations are applied to previously and newly recognized cycles in ascending order: Upper Kittanning, Lower Freeport, Upper Freeport Leader (new), Upper Freeport, Piedmont (new), Mahoning, Mason interval (locally includes Upper New Galilee in the north), and Brush Creek, across a 300-km arc in the Northern Appalachian Basin. These deposits accumulated in a ‘high shelf’ setting that experienced fewer marine transgressions, and were interrupted by more frequent exposure and downcutting, in contrast to the thicker and more complete succession with more numerous marine units in the Midcontinent. Magnitudes of highstand transgressions into this basin, deduced from the up-dip extent of marine and brackish fossil assemblages, were greatest for the Brush Creek, less so for the Upper Kittanning and Mahoning, and least for the Lower Freeport, Upper Freeport Leader, Piedmont, and Mason. The anomalous basin-wide fresh-water roofshales and equivalents of the Upper Freeport coal may reflect ponding of fresh water to the north by an elevated area that prevented marine encroachment at the southern opening of the basin along the Kentucky–Ohio border. Maximum thicknesses of IVF deposits in each cycle are used as a proxy for estimating the minimum depth of lowstand incision preceding transgression. While the thickness of IVF deposits in most cycles ranges from 6 to 20m, the two thickest are 30+ m thick, one associated with the pre-Mahoning paleovalley and the other with the immediately post-Mahoning paleovalley. The extent of transgression of each cycle in the NAB is roughly equivalent to those of their age-correlative major marine cyclothems (Pawnee through Swope) in the Midcontinent. Moreover, the amount of incision between them is also roughly equivalent to the amount of regression between each of the roughly coeval cyclothems in the Midcontinent, with the deepest incisions in the NAB (pre-Mahoning and post-Mahoning) corresponding to the greatest southward withdrawals of the sea in the Midcontinent (Memorial and Seminole/Hepler) during this same interval. [Copyright &y& Elsevier]

Buried river channels and valleys have proven to be valuable economic and agricultural resources. Often they are ecologically important refugia and in some instances, such as in the Sahara Desert, serve as dramatic reminders of the climatic changes that have taken place. Here we report the determination of a fluvial landscape that is substantially buried under the Simpson Desert using a digital elevation model (DEM) specifically derived for this purpose. The DEM is a grid of ground-level elevation points with a spacing of 9 s in longitude and latitude (∼250 m). It was calculated by applying the ANUDEM gridding algorithm to national spot height elevation data taken from 1:100 000 scale topographic maps. The ANUDEM algorithm includes a drainage enforcement algorithm that has been found to reliably discern drainage structure from minimally sampled point elevation data in central Queensland and broad-scale paleodrainage structure in Western Australia. To avoid erroneously high-elevation information, source elevation data were only selected from between dunes in the Simpson Desert region, providing a more accurate basis for determination of the general surface topography and its underlying paleodrainage structure that existed prior to the development of the dunefields. The DEM reveals the broader, low-frequency topography in the Simpson Desert, reflecting the landscape buried up to 35 m below the sand surface. The paleodrainage analysis is in good agreement with data from the Shuttle Radar Topographic Mission (SRTM). It is now possible to trace a network of topographic lows that are likely to represent paleochannels through the driest desert in Australia and plot the former courses of the world's oldest rivers prior to their burial. [ABSTRACT FROM AUTHOR]

Abstract: Ancient paleovalley fills are typically interpreted in the rock record using over-generalized models without carefully considering modern analogs, especially in light of recent discoveries. It is now known that many Quaternary paleovalleys are compound in origin, exhibit considerable stratigraphic complexity, contain multiple incisions, and can be orders of magnitude larger than their putative ancient counterparts. Compound paleovalley fills in the Lower Pennsylvanian New River Formation (NRF) are directly comparable to these Quaternary analogs, stimulating a paradigm shift in the interpretation of ancient paleovalleys. In the NRF, multiple laterally- and vertically-juxtaposed fill successions, separated by incision surfaces, record high-frequency fluvial responses to external controls within lower-order sequences. Lowstand incision and sediment bypass, as predicted in sequence stratigraphy, is largely discounted by the available evidence and the definition of regional sequence boundaries is not straightforward. The identification of genetic sequences may be the most effective approach to understanding the NRF and, by inference, many other ancient paleovalleys. Results from this study of the NRF promote a revised model for ancient paleovalleys that incorporates: 1) the pre-eminence of compound architecture, 2) periodic episodes of incision and subaerial exposure occurring in response to high-frequency changes in climate or relative sea level, 3) fluvial downcutting as the primary cause of paleovalley incision, although some sediments are still preserved in a net-erosional regime, and 4) composite, time-transgressive sequence boundaries that may be difficult or impossible to correlate regionally. [Copyright &y& Elsevier]

The lithology and stratigraphy of Holocene fine-grained sediments were studied in buried paleovalleys on the coastal shelf of the East Korean Bay. The typical natural setting of recent nepheloid near-continental sedimentation in the near-mouth area is defined. It is established that the silting apron and transit-linear settings are untypical of recent sedimentation. Their formation was determined by paleoclimatic changes during the Holocene. [ABSTRACT FROM AUTHOR]

Since the idea of the Pliocene Kosciusko Uplift in the Southeastern Highlands of Australia was first introduced, there has been considerable debate about the validity of this Cenozoic uplift event. Until the mid 1990s, most researchers argued that most highland relief was present by the Cretaceous. Since the late 1990s, there has been a paradigm shift that extensive young Cenozoic uplift created much of the high relief. In this paper, we synthesise Cenozoic stratigraphic and structural data from the East Victoria Highlands to assess the timing and origin of uplift. New high-resolution radar topography data indicate extensive east-northeast- and northeast-trending vertical and horizontal fault block displacement of the Cenozoic volcanic and sedimentary paleovalley infill. We suggest that regional uplift and exhumation of the East Victoria Highlands took place along these faults, initiated during the Late Eocene to Early Oligocene, and movements continue to the present day. By a combination of block faulting and epeirogenic uplift the divide migrated 40 km north reaching the present position by Pliocene time. Paleocurrent, lateral stream and magnetic basaltic valley flow directions indicate northward paleoflow directions for many of the Eocene - Oligocene valleys even those south of the present divide. Paleovalleys close to the Gippsland Basin show southward flow directions. The uplift that began in the Eocene causing valley cut and infill, eroded an Early Cenozoic paleoplain surface. Remnants of Late Eocene to Oligocene ligneous sediments are preserved as sub-basaltic, lowland valley, fluvio-lacustrinal sediment on this surface. Three large low-gradient paleodrainage systems that begin south of the present divide flowed north over 100 km to the Murray Basin where they are overlain by younger sediments. In contrast, paleodrainage systems flowing south from the present coastal escarpment to Gippsland, were shorter and steeper. The similarities of palynofacies of this infill to the adjacent basins suggest the valleys were low-relief/low-altitude paleodrainage systems that extended over the East Highlands. Based on our palynology results from Mt Hotham (present-day height 1800 m), previous macrofossil estimates of 800 m maximum Eocene relief could be overestimates of the paleo-height. Due to Cenozoic uplift, the strata (where present) are preserved as hilltop deposits and flows tilted away from the present divide. The Late Eocene to Pliocene uplift is probably primarily responsible for the topographic relief of the present East Victoria Highlands, is of the order of several hundreds of metres to a kilometre, and commenced in the Late Eocene at a divide closer to the Gippsland Basin than at present. This uplift continues to the present day as shown by the active seismicity in the area. [ABSTRACT FROM AUTHOR]

• Amazon rivers can be used to test the claimed tectonic origin for large rivers. • This is the case of the Juruá River, the longest and most winding Amazon River. • Surface and subsurface data allowed to reconstruct its geological evolution. • The connection of this river with three paleovalley morphologies has been found. • Intraplate tectonics led the Juruá River to change during the Holocene-Pleistocene. Understanding the factors that controlled the development of large rivers lacks information from modern and ancient analogues. The Amazonian basin contains several of the largest rivers on Earth, with many having tectonic control. The study of these rivers can contribute to test the claim that large rivers have a tectonic forcing. Addressing the evolution of the Juruá River is relevant, since this is the longest Amazonian river that parallels the Solimões Megashear Zone, a major NE-striking structure with a long history of reactivation of faults and folds even in the Cenozoic. This work discusses the geological evolution of the Juruá River along the Pleistocene-Holocene based on digital elevation models, integrated with subsurface data (well log and seismic reflection). The goal was to characterize some ancient large river valleys in forested areas of Amazonia and to analyze whether they might be related to previous paths of the Juruá River. A physical connection was found between this river and three elongated belts (i.e., PV1, PV2, and PV3) with low topographic and dissection values and surfaces marked by sinuous to meandering strings or curved lines. These characteristics led to relate the belts to ancient Juruá River valleys, an interpretation also suggested by the correspondence between paleovalley morphologies and subsurface Pleistocene-Holocene deposits with concave-up erosional bases. A tectonic hypothesis could explain the development of these paleovalleys around drainage basins with an annular pattern associated with a large convex-up relief, which we relate to rock upwarping by folding. Reconstructing the geological evolution of the Juruá River can introduce new data in discussions focused on the origin of large tropical rivers and on the neotectonic history of the South American intraplate. [ABSTRACT FROM AUTHOR]