Fluvial, inertia‐dominated deltaic deposition in the Namurian (Carboniferous) of northern England

Abstract

The Namurian (Upper Carboniferous) Scar House Beds of Yorkshire, northern England, are an example of a fluvial‐dominated deltaic sequence that cannot be adequately described using existing classification schemes for deltas. For substantial periods of the Scar House delta history, inertial processes and hyperpycnal mixing prevailed in the river mouth area due to repeated, frequent flooding in the distributary system. This generated voluminous density currents which deposited their sandy loads in successively stacked lobes beyond the river mouth bar in the prodelta area. The position of a lobe was directly controlled by the position of an active river mouth. Only during periods of low discharge in the distributary system did homo‐ and hypopycnal mixing take place. In these periods, frictional and buoyant forces operated, and sand was deposited from tractional sheet flow on the mouth bar while mudstone was laid down in the otherwise density‐current‐dominated prodelta. Because of the dominantly hyperpycnal mixing mode, the river effluent experienced a low lateral spread causing an elongate delta lobe to form that in geometry can be compared with some recent and ancient ‘bar finger’ sands. Important differences exist in terms of dominant depositional processes however. Most other ‘bar finger’ sands were controlled by a hypopycnal mixing mode and buoyant forces (e.g. South Pass, Mississippi), while the Scar House delta was controlled by hyperpycnal mixing and inertial forces. This study shows that similar sand‐body geometries can be generated from different river mouth processes. In the future, particularly in the field of hydrocarbon exploration, there may be a need to classify deltas both in terms of geometry and dominant river mouth processes. In that respect, the Scar House Beds represent a fluvial, inertia‐dominated elongate delta.

The Evolution of Lacustrine Environments on Mars: Is Mars Only Hydrologically Dormant?

“…Finally, if the channel water density is less than the lake density, the sediment load is transported further away. Because of the tendency of these sediments to be carried as a buoyant plume, the resulting deltas are also called buoyancy-dominated mouth bars (Harris 1989, Pulham 1989, Martinsen 1990.…”

Lacustrine basin to delta evolution in the Zagorje Basin, a Pannonian sub-basin (Late Miocene: Pontian, NW Croatia)

“…The incision of the distributary mouth-bar by a large channel during catastrophic flood and related deposition of sand lobes on the pro-delta by issuing sustained hyperpycnal flows has been proposed to be the dominant process in the Namurian Scar House delta by Martinsen (1990). In the Zagorje Basin, however, similar flows were not common, whereas frictional forces were dominant.…”

“…9), and also other sand accumulations in pro-delta and/or basin-floor areas produced either by sustained hyperpycnal flows or short-lived turbidity currents. Otherwise, sustained hyperpycnal flows generated by river floods may deposit sandy lobes on lacustrine pro-deltas (Gustavson et al 1975;Martinsen 1990) and sandy lobes and fans on lake basin floor (e.g. Buatois and Mangano 1995, with references).…”

Cyclic facies architecture as a key to depositional controls in a distal foredeep: Campanian Mesaverde Group, Wyoming, USA

“…A similar rapid mouth bar to strandplain transition is documented for the underlying massive littoral sandstone between sections 1 and 2. There is not much indication for the presence of dip-elongated bar finger sandstones or prodelta lobes suggesting fluvial-dominated delta progradation (Coleman and Prior, 1982;Martinsen, 1990). Obviously, these mouth bar sands were constantly reworked by surf zone flow dynamics and redistributed by storm-enhanced longshore currents.…”