3.3 Shallow Seas
In some areas these elongate sand bodies resemble the
sand ridges and sand-ridge fields described from modem
shelf seas (e.g., Tillman and Siemers 1984). Sands entering
the basin are distributed either direct1y from the river delta
by longshore transport and storm flow, or from the foreshore zone by downwelling storm currents into deeper water (Fig. 3.22c and d).
The seaward prograding sands consist of several faeies units (Fig. 3.22b and d, from top to bottom):
Cross-bedded sands of the strand plain.
- Relatively coarse grained, cross-stratified sands of
the upper shoreface (surf zone) with sand waves.
Fine-grained, amalgamated sands of the middle
shoreface with hummocky cross stratification.
3.3.6 Summary (Siliciclastic Shelf Sediments)
The faeies models described here (Figs. 3.20
and 3.21) represent "regressive" sequences
formed by a prograding coastline during constant sea level. Most of these models imply
coarsening- and thickening-upward sequenees
(in view ofthe sandstone beds).
Exceptions to these roles are the high-energy
models (Fig. 3.21h and i). The low-energy models (Fig. 3.21fand g) with an upward-decreasing
proportion of bio genie eonstituents may be referred to as sequenees with "upward-decreasing
bio genies ".
Fig. 3.22. Large-scale distribution and faeies association of widely extended shallow-sea sandstones in
the Cretaeeous North American seaway. a General
paleogeographic situation. b Cross section of Upper
Cretaceous shale and sands tone formations, Book
Cliffs, Utah, displaying shoreface and shelf sandstones prograding step-wise seaward over shelf
muds. c,d Models of sand distribution at wave-domi- Very fine grained, graded shelf sands
(tempestites) altemating with muds.
133
These storm deposits may rest on a submarine erosion surface characterized by lag deposits and channel fills (Fig. 3.22b and e). Such an erosion surface is
not necessarily associated with a relative sea-Ievel
fall (cf. Sect. 7.3), but mayaIso be caused by waning
sediment supply in an unsteadily subsiding basin.
Many other examples of ancient shelf sands may be interpreted in a similar way (e.g., Reineck and Singh 1980;
Matthews 1984; Tillman et al. 1985; Knight and McLem
1986; Morton and Nummedal 1989; Aigner and Dott 1990;
Johnson and Baldwin 1996). In any case, the interplay between subsidence, sediment accumulation, and sea-Ievel
changes is of eminent importance for the thickness and
vertical and lateral facies association of such sands.
The low-energy models mainly represent epicontinental seas. The storm-dominated, tidedomir,ated, and current-dominated models (Fig.
3.20d, e and Fig. 3.20h, i) are typical of shelf
seas. Model i is restricted to shelf seas.
- These simple facies models ean be modified by
additional factors. Of these, relative sea-Ievel
changes are most important in controlling the
facies architeeture of shelf and epicontinental
sea sediments over longer time spans (cf. Sect.
7.3)
nated, prograding deltas. River mouth sand is distributed by littoral eurrents and storm flow (c), and redistributed by a storm-driven inner-shelf transport
system (d). e Coastal retreat, sediment trapping in
lagoons, shoreface and shelf erosion as a result of
transgression (insufficent sediment supply for
prograding). (After Swift et al. 1987)
In some areas these elongate sand bodies resemble the
sand ridges and sand-ridge fields described from modem
shelf seas (e.g., Tillman and Siemers 1984). Sands entering
the basin are distributed either direct1y from the river delta
by longshore transport and storm flow, or from the foreshore zone by downwelling storm currents into deeper water (Fig. 3.22c and d).
The seaward prograding sands consist of several faeies units (Fig. 3.22b and d, from top to bottom):
Cross-bedded sands of the strand plain.
- Relatively coarse grained, cross-stratified sands of
the upper shoreface (surf zone) with sand waves.
Fine-grained, amalgamated sands of the middle
shoreface with hummocky cross stratification.
3.3.6 Summary (Siliciclastic Shelf Sediments)
The faeies models described here (Figs. 3.20
and 3.21) represent "regressive" sequences
formed by a prograding coastline during constant sea level. Most of these models imply
coarsening- and thickening-upward sequenees
(in view ofthe sandstone beds).
Exceptions to these roles are the high-energy
models (Fig. 3.21h and i). The low-energy models (Fig. 3.21fand g) with an upward-decreasing
proportion of bio genie eonstituents may be referred to as sequenees with "upward-decreasing
bio genies ".
Fig. 3.22. Large-scale distribution and faeies association of widely extended shallow-sea sandstones in
the Cretaeeous North American seaway. a General
paleogeographic situation. b Cross section of Upper
Cretaceous shale and sands tone formations, Book
Cliffs, Utah, displaying shoreface and shelf sandstones prograding step-wise seaward over shelf
muds. c,d Models of sand distribution at wave-domi- Very fine grained, graded shelf sands
(tempestites) altemating with muds.
133
These storm deposits may rest on a submarine erosion surface characterized by lag deposits and channel fills (Fig. 3.22b and e). Such an erosion surface is
not necessarily associated with a relative sea-Ievel
fall (cf. Sect. 7.3), but mayaIso be caused by waning
sediment supply in an unsteadily subsiding basin.
Many other examples of ancient shelf sands may be interpreted in a similar way (e.g., Reineck and Singh 1980;
Matthews 1984; Tillman et al. 1985; Knight and McLem
1986; Morton and Nummedal 1989; Aigner and Dott 1990;
Johnson and Baldwin 1996). In any case, the interplay between subsidence, sediment accumulation, and sea-Ievel
changes is of eminent importance for the thickness and
vertical and lateral facies association of such sands.
The low-energy models mainly represent epicontinental seas. The storm-dominated, tidedomir,ated, and current-dominated models (Fig.
3.20d, e and Fig. 3.20h, i) are typical of shelf
seas. Model i is restricted to shelf seas.
- These simple facies models ean be modified by
additional factors. Of these, relative sea-Ievel
changes are most important in controlling the
facies architeeture of shelf and epicontinental
sea sediments over longer time spans (cf. Sect.
7.3)
nated, prograding deltas. River mouth sand is distributed by littoral eurrents and storm flow (c), and redistributed by a storm-driven inner-shelf transport
system (d). e Coastal retreat, sediment trapping in
lagoons, shoreface and shelf erosion as a result of
transgression (insufficent sediment supply for
prograding). (After Swift et al. 1987)