Geology Reference
In-Depth Information
Fig. 18.10
Simplifi ed geological map of the present-day Tremp-
Graus Basin showing the location of the outcropping Alveolina
Limestone and the Roda, Capella and Pano Fms (modifi ed after
Serra-Kiel et al.
1994
, who used data from Fonnesu
1984
, Samsó
1988
and Tosquella
1988
, and Cuevas Gozalo
1989
) . The
box
indicates the area in part covered by Fig. 19.11a
Mutti et al. (
1972,
1973,
1975
) divided the forma-
tion into three units (lower, middle and upper). The
lower and upper units consist of a series of tabular sand-
stone bodies characterised by an upward-coarsening
grain-size profi le and a sigmoidal geometry of accre-
tion surfaces (Mutti et al.
1985
b
; Olariu et al.
2008a
) .
The upper unit of the Baronia Fm is interpreted to have
been deposited in shallower water, subject to stronger
tidal currents than the lower unit (Mutti et al.
1985b
) .
Wonham (
1993
) divided the Baronia Fm into two
low-order sequences. The lower sequence is com-
posed of a transgressive estuary succession with barri-
ers at the mouth of the estuary developed above an
erosional unconformity formed by lowstand fl uvial
incision. A tripartite estuarine facies distribution was
recognized with ebb-tidal delta deposits in the distal
western part of the basin and bay-head delta bars in
the proximal astern part of the basin. Higher-order
relative sea-level changes resulted in repeated basin-
ward shifts of facies and a successive broadening of
the estuary in time. The estuary deposits are overlain
by a relatively thin (up to 12 m) succession of trans-
gressive offshore and shelf deposits. The upper
sequence is also formed by a tide-dominated estuary
overlying an unconformity formed by lowstand fl uvial
incision (Wonham
1993
). The wide estuary had no
barriers at its mouth and was fi lled with compound
cross-stratifi ed beds formed by ebb- and fl ood-directed
cosets containing tidal bundles; water depths were
interpreted to decrease from about 20 m at the base to
5-10 m at the top. The transgressive estuary fi ll is
overlain by a retrogradational set of lower shoreface
and offshore deposits (Wonham
1993
) .
The Ametlla Fm (Mutti et al.
1972,
1973
; Figs.
18.4
,
18.5
and
18.11
) rests conformably on the offshore
siltstones of the Passarella Fm. It is informally