Geology Reference
In-Depth Information
Fig. 18.13
(
a)
Sedimentary section through Unit 2 of Cycle 5
of Eichenseer (
1988
) of the Alevolina Limestone in the village
of Serraduy (Fig.
18.10
). (
b
) Outcrop image of bioclastic tidal bar
deposits in the upper tidal channel indicated in (
a
). (
c
) Detail of the
tidal bar deposits in the upper tidal channel showing large-scale
inclined stratifi cation (master bedding surfaces) and the erosive
tidal channel base. (
d
) Bottomsets of cross-stratifi ed sets with
mud-draped laminae formed in an inlet channel and mouthbar
succession (cf. Eichenseer
1988
) underneath the upper tidal
channel
18.4.4 Tidal Bars of the Ametlla Formation
currents fl owing towards the NW. Tidal currents were
defl ected by the Gilbert-type delta lobe front along the
NW-SE oriented paleoshoreline, reworking the lobe
front.
The tidal bars appear to have developed during
the transgressive phase of sedimentary cycles (López-
Blanco
1996a
; Olariu et al.
2011
; Michaud
2011
) in
response to delta lobe abandonment after sediment deli-
very to the delta ceased. The ensuing high-frequency
(10s of millenia) relative sea-level rise initiated favou-
rable conditions for a period of reworking of the
Gilbert-type delta lobe front by tidal currents and
the formation of tidal bars similar to headland tidal
banks (cf. Michaud
2010
) that subsequently drowned
or, in some cases, became moribund. In the latter case,
they are capped by mudstone. In the former case, when
the bars became stationary, carbonate buildups devel-
oped on top (Michaud
2010
; several examples in the
Esdolomada Member).
The lowermost three sandstone units of the Pallaresa
mbr are dominantly composed of tide-infl uenced,
delta-front mouth bars (Dreyer and Fält
1993
) .
Sandstone unit 4 was studied in more detail (Dreyer
1994
) and is composed of three parts. The lower part
was deposited in a tide-dominated estuarine environ-
ment during fl ooding (early transgressive stage) of a
previously created incised valley with a pronounced
unconformity at the base (Dreyer
1994
) . Units formed
by stacked cross-stratifi ed sets are up to 4 m thick and
separated by fi ne-grained sandstone (Dreyer and Fält
1993
) resemble the compound dunes of the Baronia
Fm. In the data presented, however, no specifi c infor-
mation is provided enabling the assessment of the
progradation direction of the master bedding surfaces
in relation to paleofl ow directions of superposed
cross-stratifi ed sets. It is therefore unclear whether the
