Sheet flood

Fluvial Deposition or precipitation in valleys and channels, or deposition or alteration by sheet-flood action... 

The overall depositional environment of the Middle Lunde Member represents a distal alluvial plain or terminal basin (Nystuen et al 1989 Steel Ryseth, 1990 Nystuen Fait, 1995). Depressed areas were flooded by ephemeral sheet floods, leaving blankets of sand, silt and mud of high lateral extent. During certain periods these depressions could turn into shallow temporal lakes in which laminated, current-ripple laminated and wave-ripple laminated mud and silt aggraded. Drying up of these shallow lakes gave rise to frequent desiccation cracks, distorted lamination and mud flakes. The episodic flooding promoted the infiltration of suspended clay particles into the sand blankets. 

Typically, mechanically infiltrated clays are originally detrital smectites formed under semi-arid weathering conditions (see Keller, 1970 Walker et al., 1978). This is evidenced by the dominance of smectitic clays in the mudstone samples and in the mud intraclasts. Infiltrated coatings and derived chloritized rims are conspicuous, particularly in medium-grained sheet-flood sandstones (up to 2.7 vol%). 

Although both cores display floodplain mudstones and sheet-flood sandstones, the Middle Lunde samples in 34/7-A-3H are dominated by fine- to medium-grained sheet-flood sandstones. The elevated initial porosity and permeability of these sandstones compared with the mudstones, siltstones and very fine to fine-grained sandstones has perhaps allowed larger amounts of mechanically infiltrated clays, which are preserved as smectitic coatings and/or transformed into chloritic or C/S and I/S rims in the sandstones. 

Sheet flood (also sheetflood) 1)A broad expanse of moving, often storm-generated, water that spreads as a shallow, continuous uniform film over a large area. 2) A flow or the process of water movement in which the fluid is not concentrated in a discrete channel or defined river banks. 

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