Paleo River Research Articles

Possible Mechanisms for Tsunami‐Like Surge Deposits Due To the Chicxulub Impact at the K‐Pg Boundary at the Tanis Site, North Dakota

AbstractAt Tanis, a unique bi‐directional sediment package occurs precisely at the Cretaceous‐Paleogene (K‐Pg) boundary, recording the first hours of the Paleogene in uncommonly fine temporal detail. The impact ejecta‐bearing sediment package was rapidly emplaced by two massive, ∼10‐m‐high, potentially impact‐triggered surges, that inundated a steep, deeply incised paleo river valley from the direction of the contemporaneous Western Interior Seaway (WIS). Intermingling of fresh‐ and salt‐water fossils at Tanis, coeval brackish water indicators in the nearby region, and historical tsunami observations, suggest that the WIS paleoshoreline was nearby Tanis at K‐Pg time. The interpreted timing for deposition (including ejecta infall) of ∼1–2‐hr immediately post‐impact precludes a direct tsunami from the Chicxulub impact site, which would have required much more than 10 hr to reach Tanis. Seismic waves from the Mw ∼ 11 Chicxulub earthquake, arriving just minutes post‐impact, might have triggered the surge, for example, via seismic excitation of large water waves in the WIS, as proposed by DePalma et al. (2019, https://doi.org/10.1073/pnas.1817407116). Here, we explore this mechanism via a simple mathematical model of seismic excitation and propagation of a water wave into a shallow river and upstream. Matching the observations implies a relatively long source process time of many minutes, such as generated by Chicxulub crater rebound processes, in order to explain sufficient upriver amplitudes and advective transport. Atmospheric waves due to the expanding Chicxulub ejecta curtain might have provided a smaller, secondary contribution during triggering. Thus, the mechanism(s) for the surges at Tanis are now better‐constrained, yet remain incompletely resolved.

Analysis of Gravel Shapes Along the Khazir River, North of Iraq

This research work deals with the analyses of the shape and size of gravels within the terrace deposit of the Khazir River in the north of Iraq. The degree of gravels’ roundness and flatness indicates that they were transported in wet climate conditions during the deposition of the Bai Hassan Formation of the Pliocene-Pleistocene age. Typical increasing roundness and decreasing flatness along the channel (downstream) refer to the stable flow of the paleo River of Khazir. The higher degree of roundness and flatness of the studied 500 pebbles among the terraces came from the already rounded pebbles of the Bai Hassan Formation, and are not due to the rolling of the sediments of the river that were deposited as terraces along the banks. This case is the only acceptable clue for the origin of the rounded and flattened pebbles that were found in the studied terraces; otherwise, the pebbles wouldn’t be having such roundness and flatness. The aim of this research work is to indicate the roundness and flatness of the gravels within the terrace deposits along the Khazir River.

The Prospecting Value of the Fractional Granulometric Analysis in the Study of Diamond-Bearing Placers

The article presents the novel data of fractional granulometric testing on the Syuzevskaya diamond placer located in the northern part of the Chikman-Nyar depression. The geological section was studied to a depth of 42,0 m. 18 samples weighing up to 200 kg each were taken, selected sectionally at two-meter intervals and graded into 10 granulometric classes on the gamma-Baturin scale. The obtained results have important search value: 1) the curve of the debris distribution by size is typical for the mature alluvium of the foothill river; 2) the paleo river alluvium is formed by a high dynamics flow and is fairly well sorted by size, which is a favorable sign for the concentration of large diamonds and indicates a slight dilution with non-diamond-bearing detrital material; 3) the presence of a typical mature alluvium in the paleovally indicates a long time of its existence, which is also a favorable search sign for industrial diamond placers. The methodology and results of the study can be used at various stages of the exploration cycle for placer minerals, including diamonds, all over the world.

Late Mesozoic sandstone volumes recorded in Gulf of Mexico subsurface depocentres: Deciphering long‐term sediment supply trends and contributions by paleo river systems

AbstractQuantitative assessment of terrigenous sediment flux to the deep basin has mainly been limited to the Cenozoic Era, given challenges with reconstruction of more ancient source to sink systems. Subsurface mapping in the northern Gulf of Mexico basin, where there is a robust database of wells and seismic data, allows estimation of sand‐size grain volumes within 12 chronostratigraphically defined Late Mesozoic supersequences. Five subsurface depocentres with thicknesses of >400 m are identified, revealing a history of sediment routing via major fluvial axes (paleo rivers) southward from a mid‐continent drainage divide. The interpreted paleo‐rivers are further confirmed by compilation and synthesis of published and novel detrital zircon provenance data showing combinations of age peak subsets that vary considerably between depocentres. This study quantifies sediment volumes within each depocentre by inverting porosity over defined gross rock volumes derived from subsurface well logs and 2D seismic mapping. Two temporal trends of progressively increasing grain volume can be related to climatic effects on fluvial discharge and sediment delivery to the depocentres: (1) Late Jurassic to Early Cretaceous (Oxfordian to early Aptian) and (2) Late Cretaceous (Late Aptian to Coniacian). The first temporal trend probably reflects the local climate becoming less arid with northward drift of the North American Plate into higher latitudes. The second trend mirrors increasing Cretaceous paleotemperatures and rising global sea levels. This second trend is also marked by increased shelf margin bypass of sand indicated by deep basin drilling. Partitioning of Late Mesozoic grain volume by fluvial axes shows that the Paleo‐Apalachicola and Paleo‐Mississippi rivers, sourced from Appalachian basement terranes, generated the largest and longest terrigenous sediment flux into the Gulf of Mexico basin in the Late Mesozoic. Overall, Late Mesozoic siliciclastic grain volumes are estimated to be an order of magnitude less than those previously documented for the Cenozoic Era.

Groundwater arsenic content related to the sedimentology and stratigraphy of the Red River delta, Vietnam

Arsenic (As) is highly toxic and over 100 million people living on the floodplains of Asia are exposed to excessive groundwater As. A very large spatial variability over small distances has been observed in the groundwater As concentrations. Advances in the prediction of the As distribution in aquifers would support drinking water management. The application of remote sensing of geomorphic paleo river features combined with geological, geophysical and archeological data and available groundwater As measurements may be used to predict groundwater As levels in rural areas, as shown by the example from the Red River delta, Vietnam. Groundwater in sediments deposited in the marine environment is low in As, probably due to the precipitation of As in sulfide minerals under anoxic conditions. Groundwater As levels in freshwater alluvial deposits in undisturbed floodplain areas are slightly increased and the highest As concentrations are associated with meander belts. The meander belts remain clearly visible in remote sensing and may well reflect the youngest preserved alluvial sediments. High As levels in the meander belt aquifers are probably related to the availability of highly reactive organic matter and consequent reduction of iron oxyhydroxides and As release. Furthermore, given similar hydrogeological conditions, the extent of flushing of As from the youngest alluvial sands is limited compared to the older Pleistocene sands. Even within abandoned meander belts a high spatial variability of As concentrations was observed. The younger channel belts (<1 ka BP) and old Holocene aquifers below undisturbed floodplain environments deposited during a period with high sea level host groundwater enriched in As. Low As groundwater is found in sandy channel belts deposited during the regression of the sea and in Pleistocene islands preserved within the floodplain. The decisive influence of the depositional environment of the aquifer sediments on groundwater As content is revealed.

Thermokarst Lagoons: A Core-Based Assessment of Depositional Characteristics and an Estimate of Carbon Pools on the Bykovsky Peninsula

Permafrost region subsurface organic carbon (OC) pools are a major component of the terrestrial carbon cycle and vulnerable to a warming climate. Thermokarst lagoons are an important transition stage with complex depositional histories during which permafrost and lacustrine carbon pools are transformed along eroding Arctic coasts. The effects of temperature and salinity changes during thermokarst lake to lagoon transitions on thaw history and lagoon deposits are understudied. We analyzed two 30-m-long sediment cores from two thermokarst lagoons on the Bykovsky Peninsula, Northeast Siberia, using sedimentological, geochronological, hydrochemical, and biogeochemical techniques. Using remote sensing we distinguished between a semi-closed and a nearly closed lagoon. We (1) characterized the depositional history, (2) studied the impact of marine inundation on ice-bearing permafrost and taliks, and (3) quantified the OC pools for different stages of thermokarst lagoons. Fluvial and former Yedoma deposits were found at depth between 30 and 8.5 m, while lake and lagoon deposits formed the upper layers. The electrical conductivity of the pore water indicated hypersaline conditions for the semi-closed lagoon (max: 108 mS/cm), while fresh to brackish conditions were observed beneath a 5 m-thick surface saline layer at the nearly closed lagoon. The deposits had a mean OC content of 15 ± 2 kg/m3, with higher values in the semi-closed lagoon. Based on the cores we estimated a total OC pool of 5.7 Mt-C for the first 30 m of sediment below five mapped lagoons on the Bykovsky Peninsula. Our results suggest that paleo river branches shaped the middle Pleistocene landscape followed by late Pleistocene Yedoma permafrost accumulation and early Holocene lake development. Afterward, lake drainage, marine flooding, and bedfast ice formation caused the saline enrichment of pore water, which led to cryotic talik development. We find that the OC-pool of Arctic lagoons may comprise a substantial inventory of partially thawed and partially refrozen OC, which is available for microbial degradation processes at the Arctic terrestrial-marine interface. Climate change in the Arctic leading to sea level rise, permafrost thaw, coastal erosion, and sea ice loss may increase the rate of thermokarst lagoon formation and thus increase the importance of lagoons as biogeochemical processors of former permafrost OC.

Mud-capped dredge pits: An experiment of opportunity for characterizing cohesive sediment transport and slope stability in the northern Gulf of Mexico

Mud-capped dredge pits (MCDPs), defined as sand borrow sites from paleo river channels with cohesive sediment-capped walls, are used for northern Gulf of Mexico (NGoM) coastal restoration projects due to lower cost than more distal restoration resources. MCDP evolution, including infilling and pit wall slope stability, is poorly understood in relation to sandy borrow areas. We present and interpret bathymetric data from Sandy Point MCDP, which was constructed in 2012 about 20 km northwest of Southwest Pass, the most active Mississippi River distributary, in water depths of ∼11 m. Repeat bathymetric surveys show the pit is infilling ∼54 cm (or volumetrically 200,000 m3) per year, which is on the same order as seasonal-scale and an order of magnitude higher than the decadal-scale vertical accretion rates observed seaward of Southwest Pass. This infilling rate is higher than predicted based solely on excavated volume when compared with other dredge pits in sandy substrate, sediment-starved settings. MCDP infill is volumetrically dominated by far-field (here defined as river plume or shelf bed resuspension) sediment, with only ∼9% of pit infill from pit wall failure. Geomorphic comparison of Sandy Point MCDP walls with Southwest Pass mudflow gully walls shows that the MCDP is oversteepened relative to natural depression features in this setting; the convergence of MCDP and mudflow gully gradients towards a common value (4–5°) may represent an “angle of repose” in lieu of decadal-scale forcings. Findings from this experiment of opportunity show that MCDPs (1) are effective sediment traps, (2) have steep but relatively laterally stable walls (3) do not represent significant risk to infrastructure in a 3-year time scale, and (4) are predicted to infill within about 2 decades provided a proximal sediment source exists.

Abrupt emergence of a large pockmark field in the German Bight, southeastern North Sea

A series of multibeam bathymetry surveys revealed the emergence of a large pockmark field in the southeastern North Sea. Covering an area of around 915 km2, up to 1,200 pockmarks per square kilometer have been identified. The time of emergence can be confined to 3 months in autumn 2015, suggesting a very dynamic genesis. The gas source and the trigger for the simultaneous outbreak remain speculative. Subseafloor structures and high methane concentrations of up to 30 μmol/l in sediment pore water samples suggest a source of shallow biogenic methane from the decomposition of postglacial deposits in a paleo river valley. Storm waves are suggested as the final trigger for the eruption of the gas. Due to the shallow water depths and energetic conditions at the presumed time of eruption, a large fraction of the released gas must have been emitted to the atmosphere. Conservative estimates amount to 5 kt of methane, equivalent to 67% of the annual release from the entire North Sea. These observations most probably describe a reoccurring phenomenon in shallow shelf seas, which may have been overlooked before because of the transient nature of shallow water bedforms and technology limitations of high resolution bathymetric mapping.

Possible causes of methane release from the East Arctic seas shelf

We analyze data on methane concentration in the water and lower atmosphere over the shelf of the East Siberian Arctic Seas, which were obtained using marine, terrestrial, and satellite observations. Our study is targeted towards attribution of the enhanced concentrations of methane above the latitudinal-mean, which have been detected at selected locations of these seas. We compare two hypothesis, which attribute it to the effect of modern changes of the sub aquatic permafrost, and to geological factors (tectonics, presence of fault zones and paleo river beds in the study region). Our analysis showed that the methane concentration in sea water are directly related to the distance to the nearest fault zone or paleo river bed, where permafrost is absent and bottom sediments are perforated allowing methane to escape from the deep layers containing gas hydrates. This result indicate that the enhanced emission of methane, which was observed at selected locations of the shelf, is not related to the modern climate change. Earlier study, which was based on mathematical modeling, did not find intensive development of taliks as well as other processes that lead to increased gas permeability of the bottom sediments. Taken together, these results reject the hypothesis of methane catastrophe on the East Siberian Arctic Seas shelf over the foreseeable future.

Eocene and Neogene volcanic rocks in the southeastern Nechako Basin, British Columbia: interpretation of the Canadian Hunter seismic reflection surveys using first-arrival tomography

Geological investigation of the near-surface in the southeastern Nechako Basin is difficult. Shallow seismic reflection imaging is poor due in part to an extensive cover of Eocene and Neogene volcanic rocks. Outcrops of these volcanic rocks, and the primarily Cretaceous bedrock, are commonly obscured by Quaternary deposits and vegetation. Estimates of near-surface P-wave velocity are derived from the tomographic inversion of seismic first-arrivals, an effective tool when seismic imaging is poor. Tomographic model velocities are in agreement with sonic logs and laboratory samples, except for those from the Neogene Chilcotin Group. Cretaceous sedimentary rocks have velocities of ∼2800–4200 ms–1. The Eocene Endako and Ootsa Lake groups, which have velocities of ∼3000–4200 ms–1, are not distinguishable based on velocity. The velocity, the character (density, focus, and penetration depth) of rays, and ties with well and surface geology constrain the subsurface extent of the Endako Group adjacent to well b-82-C. The Chilcotin Group typically exhibits velocities (∼2400–3000 ms–1) lower than corresponding velocities from sonic logs (4500–5200 ms–1) and laboratory measurements (5000–5200 ms–1). These low model velocities may be due to the presence of high porosity, brecciated rocks near to the surface, in comparison with the other measurements that have focussed on lower porosity massive lavas. The lowest mean velocities, located to the southeast, are related to anomalously thick, high porosity, breccia-rich deposits of Chilcotin Group. This conclusion is consistent with the interpretation that the Chilcotin Group is thicker in paleo river valleys.

Reconstruction of paleo river systems and distribution of sedimentary facies of Shanxi and lower Shihezi formations in southern Ordos basin

Abstract The study area is located in the south of Huanxian county, in Yan'an and Puxian counties and to the north of Xi'an. The Shanxi and lower Shihezi formations are important gas-bearing formations. Given our analysis of the direction of rivers, the contents of stable heavy minerals and of feldspar of palaeo river systems, the study area is divided into six palaeodrainage patterns corresponding to six feldspar regions and six sedimentary facies regions. On this basis, the distribution of sedimentary facies was also analyzed. During the Shanxi stage, a delta front was deposited in the Huanxian region and delta plains and fronts were deposited in the Pingliang, Chunhua-Yaoxian and Hancheng-Chengcheng regions. In the Yan'an-Daning region, only a delta front was developed. The distribution of sedimentary facies in the earlier Shihezi stage originated from the Shanxi stage. A delta front was developed in the Huanxian region while a delta plain and front developed in the Pingliang-Zhenyuan region during the same time. Lakes originated only in the Zhenyuan-Huanxian-Huachi-Zhengning and Daning-Jixian zones. This analytical method shows that different palaeodrainage patterns can be effectively distinguished in order to forecast sedimentary facies.

On geo-basis of river regulation —A case study for the middle reaches of the Yangtze River

From the point of view that people have to obey the river’s geo-attributes in the river regulation, the definition and the meaning of the geo-attributes of a river are discussed. The geo-basis of the river regulation of the middle reaches of the Yangtze River is expounded in five aspects, including the structural geomorphology environment of flood storage and discharge, the distribution characteristics of subsidence and the sedimentation areas of Dongting Basin, the history evolution of Jianghan Basin, the function of Jianghan Basin and Dongting Basin as the flood water detention areas of Jingjiang River reach in ancient time, and the geological characteristic of Jingjiang River reach. Based on the geo-attributes of the middle reaches of the Yangtze River, some ideas about the middle reach regulation of the Yangtze River are put forward: to process the interchange between the lakes and diked marsh areas in Dongting Basin, to canal the new river route as the flood diversion channel of Jingjiang River reach with the paleo river, to recover the function of Jianghan Basin as flood detention area of the middle reaches. And we should take into consideration the geo-environment of the whole Yangtze River in the river regulation of middle reaches.

Facies Architecture of Flexural Margin Lowstand Delta Deposits in Lake Edward, East African Rift: Constraints from Seismic Reflection Imaging

Abstract Lake Edward is single half-graben rift basin unique in the East African Rift System as a result of its connection to Lake George via the Kazinga Channel, a paleo–river valley which is incised into the flexural margin of the lake. Using recently acquired normal-incidence seismic reflection data and thirty-three lake-bottom sediment samples, we examine the consequences of this hydrologic connection for understanding depositional processes and facies development along the flexural margin of Lake Edward. Three depositional sequences were defined in the study area based on top and bottom discordances of seismic reflections. Climatically induced changes in lake level appear to have forced sequence development. Sequence I deposits indicate that highstand conditions prevailed earlier in the Pleistocene. Evidence for high-frequency lake-level change comes from lowstand delta clinoforms in two separate stratigraphic intervals on the flexural margin. An older lowstand event occurred during Sequence II time and reduced lake level by at least ~ 37 m. A younger lowstand event occurred during the deposition of Sequence III and reduced lake level by ~ 18 m. Clastic sedimentation on the flexural margin of Lake Edward is strongly modified by inflow from the Kazinga Channel and Lake George during periods of lowered lake level. We suggest that the presence of an incised valley at the margin of the rift controls the stratigraphic development of clinoforms diagnostic of lowstand deltaic sedimentation. The morphology and orientation of these clinoforms suggest that discharge from Lake George during arid periods utilized the Kazinga Channel to transport sediment toward the exposed flexural margin of Lake Edward. Dipping reflections in sigmoid-oblique clinoforms suggest that these flows were capable of transporting sediment loads that included coarse grain sizes. Deposition by this process occurred several times during the late-Quaternary history of Lake Edward, and represents an important modern analogue for linked incised valley-lacustrine delta sequences in the stratigraphic record.

Deglacial and Holocene evolution of the Vietnam shelf: stratigraphy, sediments and sea-level change

On the Vietnam Shelf more than 1000 miles of shallow high-resolution seismics were analyzed to unravel post-glacial evolution in a tropical, siliciclastic environment together with 25 sediment cores from water depths between 21 and 169 m to determine stratigraphy, distribution and style of sedimentation. Fourty-seven samples were dated with the AMS- 14C technique. The shelf was grouped into three regions: a southern part, a central part, and a northern part. On the broad Southern Shelf, sedimentation is influenced by the Mekong River, which drains into the SCS in this area. Here, incised valley fills are abundant that were cut into the late Pleistocene land surface by the Paleo-Mekong River during times of sea level lowstand. Those valleys are filled with transgressive deposits. The Holocene sedimentation rate in this low gradient accommodation-dominated depositional system is in the range of 5–10 and 25–40 cm/ky at locations sheltered from currents. The Central Shelf is narrow and the sedimentary strata are conformable. Here, numerous small mountainous rivers reach the SCS and transport large amounts of detrital sediment onto the shelf. Therefore, the Holocene sedimentation rate is high with values of 50–100 cm/ky in this supply-dominated depositional system. The broad Northern Shelf in the vicinity of the Red River Delta shows, as on the Southern Shelf, incised valleys cut into the Pleistocene land surface by paleo river channels. In this accommodation-dominated shelf area, the sedimentation rate is low with values of 5–10 cm/ky. Where applicable, we assigned the sampled deposits to different paleo-facies. The latter are related to certain intervals of water depths at their time of deposition. Comparison with the sea-level curve of [Hanebuth, T.J.J., Stattegger, K., Grootes, P., 2000. Rapid flooding of the Sunda Shelf; a lateglacial sea-level record. Science, 288: 1033–1035.] indicates subsidence on the Central Shelf, which is in agreement with the high sedimentation rates in this area. In contrast, data from the Northern Shelf suggest tectonic uplift that might be related to recent tectonic movements along the Ailao Shan–Red River Fault zone. Data from the Southern Shelf are generally in agreement with the sea-level curve mentioned above.