Ribbon sandstones in the Pennsylvanian Waddens Cove Formation, Sydney Basin, Atlantic Canada: the influence of siliceous duricrusts on channel‐body geometry

Abstract

Channelized bodies up to 9 m thick in the Pennsylvanian Waddens Cove Formation show low width: thickness ratios (8:1 to 14:1), up to four vertically stacked storeys, and deep incision into associated floodplain strata. The presence of lateral accretion sets up to 6 m thick indicates that the migration of bank‐attached bars was a major channel‐filling process. The progressive rise in elevation of the basal part of the accretion surfaces where the sets adjoin the steeply inclined sides of the channel bodies shows that the channel floor aggraded progressively as the bars approached the channel sides. In planform, the river system probably showed a low‐sinuosity, incised valley within which the channel followed a more sinuous and partially confined course. The alluvium surrounding the channel bodies includes sandstone sheets attributed to crevasse splay and levee accumulation. The upper strata of many sheet's and some channel bodies contain siliceous duricrusts (ganisters) which formed by pedogenic lithification of sandy material commencing shortly after the landforms became inactive. The channel bodies contain duricrust‐bearing slumpblocks and show stepped margins over duricrusts. The stepped nature of the banks suggests that duricrusts were an important factor in confining the reach, and we suggest that channel‐body geometry was influenced, although not necessarily controlled, by the presence of the lithified layers. Alternation in the Waddens Cove Formation of grey, coal‐bearing zones with red, duricrust‐rich zones is attributed to water‐table fluctuation in response to base‐level changes. The low width: thickness ratios and aggradation mode'of the channel bodies may in part reflect channel incision and subsequent aggradation resulting from these allocyclic events.

Morphometric convergence between Proterozoic and post-vegetation rivers

“…Channel entrenchment and sinuosity may have been enhanced by the local occurrence of cohesive palaeosol horizons ( Fig. 3d ), which provided bank stability 35 , or by confinement betwgeen aeolian landforms 36 . Channel forms in the Ellice Formation have thicknesses comparable to that of the tallest bar slip-faces observed therein ( Table 1 ), indicating limited bed aggradation, as expected in mobile channels capable of lateral migration 15 .…”

Hydrological and sedimentary analyses of well-preserved paleofluvial-paleolacustrine systems at Moa Valles, Mars

“…Low bank erodibility often means that anabranching rivers are spatially stable. Similar to arid environments on Earth, duricrust formation on Mars [ Moore and Jakosky , ; Arvidson et al , ] can be an important cause of channel confinement [ Tricart , ; Friend et al , ; Gibling and Rust , ], which, in combination with low stream power, could explain the lateral stability of individual anabranching channels. On the other hand, because of a large presence of excess ejecta craters (EE) resulting from impacts into ice‐rich surface deposits [ Black and Stewart , ; Kadish and Head , ], permafrost seems to be the best explanation for the channel confinement.…”

Recognizing products of palaeoclimate fluctuation in the fluvial stratigraphic record: An example from the Pennsylvanian to Lower Permian of Cape Breton Island, Nova Scotia

“…). The formation is up to 840 m thick and comprises sandstone, red mudstone, thin coals and siliceous palaeosols deposited in an alluvial plain setting where incised fluvial channel bodies were partially confined by the silica‐cemented palaeosols (Gibling & Rust, ). The Bolsovian to Asturian Sydney Mines Formation overlies the South Bar Formation in the west and the Waddens Cove Formation in the east.…”

“…Fluvial deposits that preserve an abundance of FTSS structures have traditionally been restricted to arid alluvial fan systems (Blair & McPherson, ), ephemeral rivers (Tunbridge, ; Dreyer, ; Luttrell, ; North & Taylor, ) and pre‐vegetation rivers (Røe & Hermansen, ; Hjellbakk, ; Fralick, ; Eriksson et al ., ; Long, ). Froude transcritical to supercritical structures are, however, observed within perennial rivers both in modern settings and in ancient deposits (Shaw & Kellerhals, ; Gibling & Rust, ; Browne and Plint, ; Alexander & Fielding, ; Fielding, ; Fielding et al ., ).…”