Sandy Braidplain Research Articles

The Quaternary sedimentary history and dynamics of the deep-water margin off the Hudson Strait ice stream

Sites of ice-stream discharge to the continental slope build trough-mouth fans from glacigenic debris flows (GDFs), subglacial meltwater flows, and suspended sediment. Thus, past ice configurations may be interpreted from the sedimentological record. This study links the records in cores, high-resolution seismic profiles, and multibeam swath bathymetry of Hatton Slope and Fan to the changing glaciological history in Hudson Strait, one of the largest ice streams of the late Pleistocene Laurentide Ice Sheet. 14C-AMS dates, X-ray fluorescence geochemical profiles, and oxygen isotopes in sixteen cores document sediment supply during the last glacial cycle, and earlier history is interpreted from seismic data. The Frobisher Bay slope sector has a long record of GDF deposits from severe glacial periods between MIS 6 and 22, with little impact of meltwater discharge. Mass-transport events and aggrading gravel-floored valleys dominate the northern Hatton slope sector. The central slope sector shows the greatest shelf break progradation by till deposition, with kilometre-spaced gullies heading at 700–730 mbsl from the last major grounding of the ice-stream on the upper slope during Heinrich event 3 (H3). The gullies pass downslope into ∼5 km wide valleys, which have been sites of sediment bypass since widespread meltwater flow in MIS 6 and show little aggradation since MIS 16. Intervening >50 m high ridges show alternating levee accretion and erosion by shallow mass-transport events. Downslope on Hatton Fan, GDFs are common and fill wide erosional channels that lead to the sandy braid plain of the central Labrador Sea. The channels of the southern sector and Saglek Slope have channeled turbidity currents down the NAMOC, and stratified contourite deposits accumulated on the fan. Over the MIS 1–3 period widely represented by cores, ice was grounded in Hatton Basin and on the upper slope to 700 m water depth only immediately prior to H3. Older and younger H events had a floating ice-shelf in Hatton Basin, and sedimentation was dominated by the retreat of that ice shelf to Resolution Island. Distal cores show no systematic difference between the H1–top H3 interval and the base H3–H5 interval. Given the supply of carbonate detritus of consistent composition back to at least H5, any MIS 3 deglaciation of Hudson Bay would require improbably high growth rates of ice sheets in the centre of the continent.

Facies and architecture of a coarse-grained alluvial-dominated incised valley fill: a case study from the Oligocene Gebel Ahmar Formation, Southern Tethyan-shelf (northern Egypt)

Exposures of multistorey, alluvial deposits from the Oligocene Gebel Ahmar Formation in the Cairo-Suez province (north Eastern Desert, Egypt) show the architecture of an up to 35m thick continuously prograding fluvial/alluvial filling of an incised valley. The Oligocene base level fall resulted in cannibalization of the Eocene bedrock. Subsequent baselevel rise created accommodation space that was filled by deposition of four stacked storeys: lower storeys (1-2) of low sinuosity sandy braid plains and upper storeys (3-4) of gravelly braid plain. These braid plains were sourced from exposed Upper Cretaceous-Eocene and Paleozoic-Lower Cretaceous siliciclastic successions to the south. These successions dominate the Galala-Araba inverted structures. The sandy braid plain channel belts mainly downstream accretion (DA), downstream oblique accretion(DLA), lateral accretion (LA), sandy bedforms (SB), channel (CH), and Hollow (HO) elements, while the gravelly braid plain consists mainly of gravel bars and sheets (GB), gravel-sandstone foresets (GSF), gravel-sand couplets (GSC), and scour pool filling (SPF) architectures. Incised valley incision is potentially linked to a global drop of sea level caused by glaciation, although hinterland tectonism (i.e. Late Cretaceous-Paleogene tectonic inversion and Late Eocene-Oligocene crustal updoming in the source terrains) as well as Late Oligocene-Miocene rifting play a significant role in the subsequent filling. The hinterland tectonism as well as the climate controls the sediment supply. The understanding of the nature of the Oligocene incised valley fill helps in the constrain potential down depositional dip hydrocarbon reservoirs in Nile Delta, East Mediterranean basins, and similar settings in passive continental margins.

Stratigraphy, petrography and dispersion of the lower Permian syn-eruptive deposits in the Viar Basin, Spain

This paper presents a stratigraphic, petrographic and sedimentologic analysis of felsic syn-eruptive deposits of the southernmost Permian basin in Europe (Viar Basin), an inner-orogenic, transtensional half-graben located between two major geotectonic zones of the Iberian Variscan Belt, SW Spain. The syn-eruptive deposits of the Viar Basin represent a mappable lithostratigraphic unit, that is herein named the Los Canchales Formation. This unit forms a wedge-shaped body bounded by alluvial–fluvial deposits (red layers) that are in gradational contact. The stratigraphic architecture of the Los Canchales Formation is complex with frequent facies changes and interfingering among pyroclastic rocks, resedimented–volcaniclastic rocks and sedimentary rocks. Abundant fossil flora is also recorded. A wax–wane cycle of volcanic activity is recognized during the syn-eruptive period. Two short-lived volcanic episodes were recorded including ignimbrites and a possible phreatomagmatic event. Explosive volcanism generated pyroclastic flow, surge and ash-fall deposits, in cases collapsing the drainage network. They also modified the vegetation and created a new depositional setting with four successive sedimentary environments: vegetated floodplain, ephemeral sandy braidplain, palustrine environment and again vegetated floodplain. Input of pyroclasts followed a NW to SE longitudinal–axial dispersal pattern.

A model of alluvial megafan sedimentation: Ganga Megafan

Abstract Ganga Megafan is one of several megafans, developed in the northern and central part of the Ganga Plain, that formed during the middle Late Pleistocene under conditions of higher sediment-water discharge and higher regional slopes than today. Incision by the Ganga River exposes 15–30 m thick megafan deposits in the valley walls and cliffs. Ganga Megafan deposits can be separated into four zones: Zone I — Gravelly braided streams; Zone II — Sandy braid plain; Zone III — Anastomosing channel plain; and Zone IV — Meandering channels with broad interfluve areas. Deposits of each zone show distinct facies associations. Palaeocurrents fan from SW to SE and E, while the grain size decreases from proximal to distal fan. At present, fan-building activity is highly subdued and is restricted only to the northernmost 5–10 km wide belt of Piedmont plain.

River ice and its role in limiting woodland development on a sandy braid-plain, Milk River, Montana

Abstract Previous research shows an anomalous absence of plains cottonwood (Populus deltoides) woodlands along a 30 km sandy braid-channel reach of the Milk River upstream of the Fresno Dam in northern Montana, USA. This absence contrasts to well-wooded, meandering reaches upriver and downriver of the braid-plain. Our field measurements show that mechanical ice breakups and ice floes physically damage most plains cottonwood saplings and small trees along the braid-plain. Between 1911 and 1998, mechanical ice breakups occurred in 50% of the years of record. Of these, 12% were greater than bankfull discharge and followed dramatic temperature increases and subsequent snowpack melting in the headwaters. We suggest that the absence of cottonwood woodlands on the braid-plain is associated with low bank heights, wide channels, and low channel sinuosity in the braiding reach through which overbank river ice moves more easily compared to the meandering reaches. Ice blocks rafted onto the braid-plain have repeatedl...

Sedimentology of a Devonian fault‐bounded braidplain and lacustrine fill in the lower part of the Skrinkle Sandstones, Dyfed, Wales

The Upper Devonian to Lower Carboniferous Skrinkle Sandstones of the Pembroke Peninsula are predominantly continental deposits from the post‐Caledonian synrift succession at the southern margin of the Upper Palaeozoic Welsh Landmass. The lower part of the Sandstones record deposition in the 30 × 10 km Tenby–Angle fault block, from which a 6‐ to 68‐m‐thick interval is described and interpreted as a lacustrine deposit succeeded by a high‐energy sandy braidplain succession. The lacustrine deposit is dominated by red mudstones and ripple cross‐laminated sandstones. Interbedded quartzose sandstones form a coarsening‐upward sequence from the red mudstones in the basin centre, suggesting a deltaic origin, and a smooth‐fronted braidplain delta model is proposed. The sequence introduces the braidplain succession, composed of groups of horizontal/low‐angle laminated and trough cross‐bedded sandstones. These are compared with recent ephemeral stream and sheetflood sediments and their characteristics used to depict a system of mutually erosive sheetflood and channel bodies, the latter produced during the rising and falling stages of flood events, which alternate to produce a thick multistorey sandstone. Palaeocurrent data indicate an axial drainage system from the north‐west, running parallel to the main faults of the area. This is supported by the maturity and sandy nature of the sediments. Basin closure towards the south and the postulated Bristol Channel Landmass is inferred.

Influence of tectonism and climate on lithofacies distribution and sandstone and conglomerate composition in the Archean Beaulieu Rapids Formation, Northwest Territories, Canada

The 0.2–1 km thick Archean Beaulieu Rapids Formation is a late-orogenic, tectonically-controlled sedimentary sequence overlying the Beaulieu River volcanic belt unconformably on the west and bordering the major, N-trending Beniah Lake fault on the east. Local porphyry stocks, characteristic of late-orogenic successions, were emplaced along strike of the fault. Four lithofacies comprise the Beaulieu Rapids Formation: (1) the 20–320 m thick conglomerate I; (2) the 10–305 m thick siltstone–sandstone; (3) the 20–120 m thick conglomerate II; and (4) the 40–320 m thick quartz-rich sandstone. Lithofacies stacking displays two distinct, large-scale, fining-upward sequences represented by the 300–375 m thick conglomerate I and sandstone–siltstone (sequence A), and the 300–400 m thick conglomerate II and quartz-rich sandstone (sequence B). Fining-upward sequences, a bounding unconformity, and the Beniah Lake fault are compelling indicators of tectonic influence on sedimentation. Conglomerate I was deposited by debris flows, traction currents, and sheetfloods on the proximal, medial, and distal portions of alluvial fans or fan deltas, respectively. The overlying siltstone–sandstone contains two distinct lithological units. A sandstone-dominated unit formed from fluvial dune migration and overbank deposition in a sandy braidplain setting with scattered ponds, whereas sedimentary structures in the siltstone-dominated unit are consistent with lacustrine deposition. A second phase of tectonic uplift produced sequence B. Conglomerate II was deposited in a proximal braided stream setting characterized by abundant longitudinal gravel bars. The quartz-rich sandstone developed from dune migration on a sandy braidplain. Mineralogy and textures reflect high sediment influx, limited transport distance, local sources, and climatic influence. Clast populations in conglomerate indicate a prevalent mafic volcanic source, whereas sandstones contain prominent quartz (av. 76%) with subordinate feldspar (13%) and lithic fragments (11%). The disparity between clast and sandstone composition is a function of chemical weathering, typical of a humid climate. Source areas are restricted to the mafic-dominated Beaulieu River volcanic belt, the >2.8 Ga gneisso-plutonic Sleepy Dragon Complex, and fault-related porphyry stocks. The humid, weathering-aggressive Archean climate was responsible for destroying labile minerals and lithic fragments in proximal source rocks rich in plagioclase, accounting for the high quartz component in the sandstones. The Beaulieu Rapids Formation is similar to modern strike–slip basins that form along major fault zones in terms of basin geometry, faulted and unconformable contacts, lithological units, and sedimentary facies stacking and organization. Fault-controlled basins of this nature commonly develop during the last stage of terrane accretion on Archean cratons.

Abstract: Reservoir Limiting Factors and Enhancement in a Sandy Braidplain Reservoir, Lower Cretaceous Cadomin Formation, Northeastern British Columbia 

Abstract: Reservoir Limiting Factors and Enhancement in a Sandy Braidplain Reservoir, Lower Cretaceous Cadomin Formation, Northeastern British Columbia 

Sedimentology of the upper cretaceous red beds of Angostura Colorada formation in the western sector of the Northpatagonian Massif, Argentina

Detailed sedimentological analysis of the Angostura Colorada Fm. (Upper Cretaceous) in the Comallo Jacobacci Gastre areas of the western sector of the North Patagonian Massif has enabled the definition of three members based on sedimentary structures, paleocurrents, grain size, compositional characteristics and lithofacies associations. These members are: lower (alluvial fan), middle (sandy braidplain) and upper (flood plain) developed within a rift sequence. Compositionally, two alternating source rocks are shown in the geological record, a continental block and recycled orogen provenance for the lower and middle members (Jacobacci area) and magmatic arc provenance for the middle (Gastre area) and upper members. This is interpreted as a progressive magmatism towards the K-T boundary during the rising of the Andean Cordillera to the west. The granitic provenance is attributed to igneous bodies of Paleozoic age to the N and SW of the study area. The smectite-zeolite rich clay mineral association of the upper member is interpreted as product of alteration of thick pyroclastic deposits. The paleogeography of this unit includes two different paleodepositional systems, to the SW an alluvial fan system running from the SW to the NE, to the NE a sandy braided river running from the NW to the SE, perpendicular to the previous one in a wide paleovalley. Later flood plain and lacustrine shaley deposits developed to the east which are equivalent to the Alamitos Fm. This distribution of paleodepositional systems is coherent with the main structural trends within the study area. A late Campanian age is assigned to this unit.

Triassic sandy braidplain and aeolian sedimentation in the Sherwood Sandstone Group of the Sellafield area, west Cumbria

SUMMARY During the Permo-Triassic the Sellafield area formed part of the eastern margin to the East Irish Sea Basin. Basin-margin alluvial fan, shallow marine and coastal mudflat sedimentation created a locally thick Permian succession. Triassic sediments are represented by the Sherwood Sandstone Group, which comprises the St Bees, Calder and Ormskirk sandstone formations. The basal few metres of the St Bees Sandstone are characterized by sheetflood sandstones, interbedded with playa-mudflat deposits. These pass upwards into thick, multistorey fluvial sandbodies, formed on sandy braidplain. Rare aeolian units are interbedded with the channel facies. The top of the St Bees Sandstone is sharply defined and represents the regional abandonment of the fluvial system. The overlying Calder Sandstone Formation is coarser grained and dominated by aeolian sediments, with dune and interdune facies recognized. These sands were blown into the area from the east. Minor episodes of fluvial reworking punctuated aeolian deposition and the top of the Calder Sandstone is represented by a fluvially deposited unit. The lower part of the overlying Ormskirk Sandstone is of aeolian facies and can be distinguished from the Calder Sandstone by its finer grain size. The two formations can also be differentiated using geophysical logs, as aeolian and fluvial sandstones have diagnostic geophysical log characteristics allowing recognition of different sedimentary facies associations.

Alternating Braidplain and Lacustrine Deposition in a Strike-Slip Setting: The Pennsylvanian Boss Point Formation of the Cumberland Basin, Maritime Canada

ABSTRACT The Boss Point Formation was deposited in the Cumberland Basin of southeastern New Brunswick and northern Nova Scotia during the early Pennsylvanian. The basin is bounded to the northwest and south by strike-slip faults, active during the Pennsylvanian. The Boss Point comprises two main fades associations: sandy braidplain (BFA) and muddy lacustrine (LFA), the abrupt alternation of which allows 16 depositional megacycles to be defined. The LFA forms units 50 m thick that rest sharply but nonerosively on braidplain sandstone. In some instances the contact can be traced for over 12 km perpendicular to paleoflow. Commonly dunes and ripples are preserved in relief beneath lacustrine mudstone, implying rapid but very low-energy flooding of t e braidplain. The BFA comprises multistory channel sandbodies 90 m thick, separated from the underlying LFA by sixth-order surfaces with up to 15 m of erosional relief. The erosion surfaces are commonly overlain by spectacular mudstone breccias and boulders that reflect deep erosion and rotational slumping into channels cut into, and sometimes right through, lacustrine deposits. BFA packages are internally partitioned by fifth-order erosion surfaces into individual channel-fill units, commonly about 5 m thick. The BFA is dominated by trough-cross-bedded fine to lower medium sandstone. Conglomerate, pebbly sandstone, and ripple-laminated and planar-laminated sandstone are minor components. Rare mud-filled abandoned channels suggest a mean width and de th of > 160 m and 4.8 m, respectively. The dominance of trough cross-bedding suggests relatively deep channels, whose banks may have been maintained by a dense vegetation cover. Repeated channel avulsion and flood-related erosion resulted in a rock record dominated by deep-channel and flood-stage deposits; bartop facies were rarely preserved. Channel dimensions, lateral consistency of facies, paucity of muddy channel plugs, and regionally consistent paleoflow suggest deposition on a braidplain. The distribution of conglomerates indicates a local gravel source area in the Caledonia Highlands to the northwest, but much of the sand is likely to have been sourced far to the southwest. The Boss Point falls into two sharply disjunct paleoflow domains, one directed to the north and northeast and the other to the east and southeast, separated by the Harvey-Hopewell fault zone. The absence of an adequate watershed between the two domains strongly suggests tectonic juxtaposition involving ?several tens of kilometers of sinistral offset.

Fluvial processes and cyclicity in terminal fan deposits: an example from the Late Devonian of southwest Ireland

The Gun Point Formation is a sandstone-dominated sequence, approximately 1.5–2.5 km thick, which forms part of a major (> 6 km) Late Devonian alluvial basin fill succession in southwest Ireland. It is interpreted as the deposits of a southerly flowing terminal fan system which operated under a semi-arid climate. The proximal zone was characterized by low-sinuosity gravelly feeder channels which passed downstream into a medial zone dominated by a sandy braidplain. Further south, in the distal zone, phases of high-energy flood activity were centred on transient, low-sinuosity ephemeral channels and were separated by more quiescent periods of shallow sheetflooding, subaerial exposure and non-deposition.Sedimentary parameters such as set thickness, coset thickness, channel sand body density and maximum sand body thickness all exhibit regular cyclic fluctuations with a periodicity of 160–180 m. The cycles are interpreted as evidence of regular discharge variations which may have been a response to the 412 ka orbital eccentricity cycle. A second periodicity of approximately 700 m has also been detected and is thought to reflect long-term variations in basin subsidence.

Depositional and sequence stratigraphic framework of the Lower Cambrian Zabriskie Quartzite: Implications for regional correlations and the Early Cambrian paleogeography of the Death Valley region of California and Nevada

The Lower Cambrian Zabriskie Quartzite in the Death Valley region of California and Nevada records deposition in both nearshore marine and terrestrial environments and represents two genetically distinct depositional units. The lower unit, defined by the Resting Springs Member, is a highstand-systems tract in which sandy braidplain deposits prograded over storm-influenced inner-shelf mudstone and sandstone. The top flooding surface of that systems tract is a sequence boundary (type 2). The upper unit, defined by the Emigrant Pass Member, is the lowermost deposit of a transgressive systems tract in which nearshore marine sediments progressively overstep/onlap the sequence boundary cratonward. It is herein suggested that in the Death Valley area the top of Lower Cambrian Grand Cycle B is coincident with this sequence boundary. This work shows that nonmarine deposition characterized much of the southwestern margin of cratonic North America during Early Cambrian time ( Bonnier-Olenellus zone). The stable tectonic setting and consistently low-latitudinal position of Laurentia during this time preclude tectonism and climactic variation, and associated changes in sediment flux, as principal forcing mechanisms of relative sea-level change. Consequently, eustatic variation was the probable first-order causative mechanism for systems-tract and facies development. The relative sea-level changes indicated in this study can be used to further aid the construction of global sea-level curves.

Braidplain Evolution in the Pennsylvanian South Bar Formation, Sydney Basin, Nova Scotia, Canada

ABSTRACT The South Bar Formation is a 1 km-thick alluvial succession in the Pennsylvanian Morien Group of the Sydney Basin, Nova Scotia that fines upward from conglomerate to pebbly sandstone to sandstone facies assemblages. The conglomerate assemblage comprises mainly massive to horizontally stratified conglomerate and planar cross-stratified sandstone, attributed to deposition in proximal braided rivers confined between bedrock ridges. The sandstone assemblage shows uniformity of facies and paleocurrents across the basin, and is interpreted as a distal braidplain deposit; the pebbly sandstone assemblage is transitional between the other two. Both sandstone assemblages are dominated by trough cross-stratified sandstone formed by dune migration in channel tracts about 4 m deep. This succession differs markedly from Platte River and Icelandic sandy braidplain deposits, which are mainly planar cross-stratified sands formed by broad, shallow flow. The South Bar sandstones are more like South Saskatchewan River deposits, but differ in 1) greater abundance of trough sets and 2) rarity of planar sets and other components of shallow water channel fill. These features are ascribed to 1) inheritance of relatively deep channels from confined upstream reaches, 2) maintenance of deep flow in active tracts by local confinement between temporary banks, and 3) rapid avulsive abandonment of active tracts, which inhibited development of channel-fill sequences. Evidence for local temporary confinement is preserved as in situ and slumped channel-margin mudrock units. Lateral and vertical transitions from the upper South Bar Formation to the mud-rich Waddens Cove and Sydney Mines Formations are ascribed to changes in channel pattern from braided to meandering. The former is attributed to decreased slope, the latter to eustatic rise in sea level.

PARAGLACIAL AEOLIANITES: POTENTIAL NEW HYDROCARBON RESERVOIRS, GIDGEALPA GROUP, SOUTHERN COOPER BASIN

Facies analysis of core from the Gidgealpa Group has led to the first recognition of sandstones of aeolian origin in the Cooper Basin. The aeolian suite was recognised in core from the Merrimelia Formation penetrated by wells within the Merrimelia field.The Merrimelia 5 aeolianites occur in core between 8603 and 8659 ft drill depth. These were correlated to similar facies in core from Merrimelia 1 between 9649 and 9674 ft drill depth, where other lithotypes of the suite were identified.Gamma ray-sonic log response over cored aeolianite intervals can be correlated to Merrimelia 13, where similar aeolian sediments are interpreted for an uncored interval of Merrimelia Formation.The overall glacigenic nature of the Merrimelia Formation is well documented but this discovery records the first aeolian suite in the Gidgealpa Group and may also document the first subsurface example of cold-climate aeolianites.The aeolianites are porous, poorly cemented, coarse and fine grained sandstones dominated by parallel lamination. Sharp, planar truncation surfaces divide the suite into units composed mainly of translatent wind ripple lamination with minor amounts of sandflow bedding. Primary depositional dip (post-compaction) varies between 0° and 25° suggesting preservation of dune lee-slope strata. Local deformation of avalanche foresets is also visible in the core.The gamma ray-sonic logs of the thick (1190 ft (363 m)) Merrimelia Formation in Merrimelia 5 indicate thick (760 ft (232 m)) porous sandstones. These originate from distal aeolian and distal sandy braidplain environments. In core from Merrimelia 1, aeolianites are interbedded with proximal outwash fan conglomerates. Also gamma ray-sonic logs of the interval indicate thinning of the aeolianite sands. These two observations indicate a nearby depositional edge to the aeolianites.A low interval transit time on sonic logs is characteristic of the porous aeolianite sand. This response produces an identifiable change in seismic reflections where the sands are developed, which allows mapping of the sand distribution from seismic data.A 6 to 8-km wide band of aeolianite sand facies trending southeast — northwest has been mapped. This porous aeolianite sand facies is interpreted to pass laterally into outwash fan, braidplain and interdune deposits.Potential hydrocarbon traps may occur at the top of the aeolianites, or within them beneath intraformational seals formed by muddy interdune facies. The recognition of an aeolian suite at Merrimelia indicates the potential for similar facies development elsewhere in the southern Cooper Basin. Locally these could form important reservoirs beneath the level of existing production.