Geology Reference
In-Depth Information
Fig. 18.28 ( a - d ) Planar bedded and laminated inclined hetero-
lithic facies of the lowermost parasequence in sequence 2.1
(Fig. 18.25 ) of the Pano Fm developed above a major unconfor-
mity. Erosive surfaces separate subsequent units of inclined het-
erolithic strata ( white arrow in a ). The deposits are interpreted to
have been formed in a tidally-dominated part of an (restricted)
embayment (cf. Donselaar 1996a, b ) and are formed by hetero-
lithic (mud and very fi ne sand) deposits with double mud drapes
( white arrows in b ) at the base and neap-spring cyclicity ( black
arrows in d ). Regular vertical decrease and subsequent increase
of bed thickness is interpreted to indicate spring to neap tide
cycles with the thinnest beds formed during neap ( black arrow
in b ; white arrows in d ). Some layers have a deformed base
( white arrow in c ). (After Donselaar 1996b . With permission)
18.6
Summary
formation of compound tidal dune fi elds and large tidal
bars in the foredeep in relatively deep water (at least up
to 40 m). Conditions were favourable for circulating
and amplifi ed outward fl owing tidal currents. No major
axially draining fl uvial systems existed, but instead
locally fed relatively small shoal-water fan deltas and
larger (a) Gilbert-type delta(s) developed along the
northern basin margin, dominantly located in struc-
turally controlled areas of the coastline. Additionally,
a large offshore compound tidal dune fi eld was present
in the south-eastern part of the basin as a result of
suffi ciently strong and confi ned tidal currents fl owing
E-W in a narrow sea.
The overfi lled shelf stage became manifest during
the Late Ypresian to Late Lutetian during which
modest tidal amplifi cation occurred in shallow water
(up to 10 m), in-shore parts of delta distributaries
and the subaqueous part of the delta top. A shelf
formed behind the developing oblique lateral ramp of
Lower Eocene tidalites in the T-G-A Basin in the
southern Pyrenees (Spain) were deposited in response
to developing thrust related folds and blind ramps
which determined the position of facies belts and
focussed and enhanced tidal currents. Two distinct
stages of basin confi guration can be recognised which
share a general basin outline typifi ed by a relatively
narrow (up to 60 km) and long (up to 200 km in total)
semi-enclosed sea which had an open connection to
the Atlantic ocean in the west. They differ, however,
signifi cantly in water depth distribution, basin fl oor
topography and coastal morphology. The two stages are
directly related to two different confi gurations of basin
dimensions favourable for resonant amplifi cation and
dominantly controlled by thrust sheet development.
The underfi lled foredeep stage occurred during
the Early Ypresian and was a period favourable for the
 
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