Plots for overbank deposits
appear more often to consist of two superimposed plots, as in Figs 5 and 6.
Channels, levees, overbank deposits
, and depositional lobes are among the chief architectural elements covered.
The distinct and remarkable facies pattern and associated depositional environments are characterized by yellow brown siltstone offlood plains, massive silica rich off-white to cream colored sandstones ofbeach environment, gray colored sandstones ofdeltas, variegated colored and thinly bedded to alternate laminated sandstone, siltstone and clays of tidal flats as well as massive brown and maroon colored gypsiferous clays of overbank deposits
. Moreover, small scale and locally developed shallow lagoons and estuaries are characterized by thinly bedded and white to buff colored gypsiferous carbonaceous sandstone which is overlain by brown siltsone/claystone with Oyester bank development.
The lack of thick, homogeneous channel sandstone and conglomerate units and a high proportion of overbank deposits
suggest deposition in an anastomosing river system (Miall 1992).
The units are: 1) 7Aa, glacial till over bedded sedimentary rocks (DRASTIC designation); 2) 7Ad, glacial till over sandstone; 3) 7Af, sand and gravel interbedded in glacial till; 4) 7Ba, outwash; 5) 7D, buried valley; 6) 7Eb, alluvium without overbank deposits; 7) 7Ec, alluvium over bedded sedimentary rocks.
of Index Settings Ranges Calculations 7Aa-Glacial Till Over Bedded Sedimentary Rocks 78-150 37 7Ad-Glacial Till Over Sandstone 79-158 33 7Af-Sand&Gravel Interbedded in Till 88-152 23 7Ba-Outwash 107-179 19 7D-Buried Valley 111-179 26 7Eb-Alluvium Without Overbank Deposits 95-160 35 7Ec-Alluvium Over Bedded Sedimentary Rocks 90-138 5
Sedimentology and facies architecture of overbank deposits
of the Mississippi River, False River Region, Louisiana.
C3 facies is interpreted as overbank deposits produced by the waning flow strength of sandy to muddy sheetfloods through crevasse splays, whereas C4 facies indicates a flood basin origin in a well drained oxygenated environment.
The vertical and l teral stacking of the multistorey sandstone bodies in relation to overbank deposits indicates periodic avulsion of the channel belt (Allen, 1965, 1978; Bridge and Leeder, 1979), which suggests an increase in the drainage network in the source area (Kumar et al., 2004).
In contrast to previous workers, no evidence supportive of meandering streams (such as lateral-accretion surfaces, point-bar deposits, or extensive overbank deposits
) were observed.