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Fig. 18.14 ( a ) A tidal bar at the base of the Esdolomada Mbr on
the E side of the Isábena River SE of Roda de Isábena. Note the
sheet-like geometry and well-developed slightly inclined (1.6-4.6°
towards the SW) master bedding surfaces. This sandstone body
migrated laterally (i.e., transverse to the tidal currents) towards
the SW. ( b ) Detail of ( a ) showing stacked sets of high-angle
(average 21°) cross stratifi cation formed by dunes that migrated
in a NW direction, that is approximately coast-parallel
sandstone bodies represent tidal bars (sensu Mutti
et al. 1985b ) or compound tidal dunes (sensu Olariu
et al. 2008a ) .
This estuarine valley fi ll is overlain by mouth bar
deposits of a bay-head delta (middle part of unit 4)
which prograded towards the NW. The delta was
initially fl uvially dominated and infl uenced by tidal
processes but transformed into a tide-dominated delta
that prograded out into offshore inner shelf sediments
during the later stages of the transgression (upper part
of unit 4). No barrier further to the west is reported that
created a back-barrier lagoon into which the bay-head
delta prograded. The described characteristics illustrate
that a certain degree of uncertainty is associated with the
published interpretations and that the tide-infl uenced and
tide-dominated depositional setting was characterized
by a high degree of spatial and temporal variability of
facies and sedimentary processes (Dreyer 1994 ) .
The overlying sandstone units 5 (Fig. 18.15a, b ) and
6 were formed by tide-dominated, near-shore to inner
shelf 'sandbar complexes' during the late transgressive
stage with common large-scale sigmoidal cross-strati-
fi ed sets of up to 5 m thick. Average foreset dip angle
is 23° to the west (Dreyer and Fält 1993 ) which is
comparable to the dip angle observed in the tidal bar at
the base of the Esdolomada Member (Olariu et al.
2011). Compound sets, up to 30 m thick and up to
3 km long, most probably have their long axis oriented
parallel to the regional tidal fl ow direction (Dreyer and
Fält 1993 ). These characteristics tend to classify these
bodies as tidal bars, although a lack of relevant obser-
vational data prevents the distinction between tidal
bars and compound tidal dunes.
18.4.5 Tidal Bars Versus Compound Tidal
Dunes in the Baronia Formation
Tidal sandstone bodies of the lower part of the
Baronia Fm in the T-G-A Basin (Mutti et al. 1985b ;
Fig. 18.16a-d ) have long served as a well-documented
and classical example of shelf tidal bars in front of a
delta (Dalrymple 1992 ; Mellere and Steel 1996 ; Willis
2005 ). Recent work (Olariu et al. 2008a ) on the lower
unit of the Baronia Fm, however, led to the conclusion
that the tidal sandstone bodies were formed by com-
pound tidal dunes deposited in a narrow, approximately
10 km wide, sea that extended farther eastward than
the eastern closure of the present-day Ager Basin.
The tabular sandstone bodies are generally 4-6 m (but
up to 10 m; Fig. 18.16a-c ) thick and display an alignment
transverse to paleofl ow. They continue over 100s of
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