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Fig. 18.12 Schematic illustration of the early transgressive stage in the inferred paleogeographical development of the T-G-A
Basin during deposition of the Ametlla Fm (modifi ed after Dreyer and Fält 1993 )
18.4.3 Tidal Bars of the Esdolomada
Member
ebb-oriented dunes of up to 50 cm height; oppositely
directed cross strata (fl ood currents) were subordinate.
The dunes are part of thick (up to 12 m) bioclastic
(grainstone) tidal bedforms, interpreted as bars (cf. Pool
1983 ; Eichenseer 1988 ; Fig. 18.13 ) based on the
observation that cross-bedded sets show paleocurrent
directions oriented obliquely to the accretion surfaces.
The bars formed in tidal channels with a deeply scoured
base and often covered by a lag of coralgal breccias
derived from adjacent patch reefs. The bars contain
several accretionary units with superposed dunes
separated by discontinuity planes. Southward at short
distances (200 m), small ebb tidal delta lobes with
dominant WSW current directions developed, which,
in places, contain double mud drapes; the existence of
barrier islands, however, is not reported but inferred.
The lateral equivalent of these tidal channel deposits east
of Coll del Vent are formed by lagoonal to shallow-
water bay deposits with occasional patch reefs. The
succession is overlain by a coralgal reef and subse-
quently wide-spread shallow water nodular limestones
of the Serraduy Fm.
Tidal bars, in this case transgressive shore parallel
sandstone bodies, were developed in front of retrogra-
dational fan-delta lobes and mouth bars of the lower
part of the Esdolomada Mbr and are either attached to
or detached (offshore) from the sandy delta lobe front.
Underneath the El Villar Limestone (Fig. 18.4 ), a well-
developed detached example (Fig. 18.14 ) is exposed
near Roda de Isábena. This is formed by slightly
inclined (1.6-4.6°) master bedding surfaces and con-
tains stacked sets of high-angle (average dip angle 21°)
cross-stratifi cation up to 70 cm thick (Olariu et al.
2011 ). The crest of this bar is oriented sub-parallel to
the tidal paleocurrent and to the nearby paleo-shore-
line; the bar was built by oblique accretion, migrating
transverse to the tidal currents towards the SW; it has a
width to length ratio of approximately 1:10 (Olariu
et al. 2011 ). Other examples, higher in the stratigraphy,
also lack wave-generated structures and generally
migrated obliquely towards the W driven by ebb-tidal
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