Rwh. Butler et al., PLIOQUATERNARY MEGASEQUENCE GEOMETRY AND ITS TECTONIC CONTROLS WITHINTHE MAGHREBIAN THRUST BELT OF SOUTH-CENTRAL SICILY, Terra nova, 7(2), 1995, pp. 171-178
Sequence stratigraphy in marine foredeep and thrust-top basins is cont
rolled by the conventional variations in eustatic sea-level and sedime
ntation rate together with tectonics. Vertical motions reflect combina
tions of subsidence due to regional flexure and uplift on local thrust
anticlines which act to modify the volume and shape of accommodation
space together with syn-depositional slopes. Plio-Pleistocene successi
ons on Sicily were deposited in thrust-top and foredeep basins, above
and ahead of evolving structures of the Maghrebian fold and thrust bel
t. Collectively the sediments represent a single megasequence defined
at its base by a maximum flooding surface of earliest Pliocene age fol
lowing reconnection with global sea-level at the end of the Messinian.
The internal stratigraphy of this megasequence consists of Trubi chal
ks, blue marls and a coastal calcarenite package with subordinate sili
ciclastic sand. Plankton biostratigraphy allows these facies to be pla
ced in a chronostratigraphic framework. Regionally the upper assemblag
e progrades away from the orogenic hinterland, recording a tectonicall
y forced regression in response to regional uplift from late Pliocene
times. This uplift may be associated with isostatic unloading in the o
rogenic hinterland due to tectonic collapse of the more internal thrus
t sheets. Prior to this, flexure from orogenic loading is inferred to
have been sufficient for regional subsidence locally to outstrip uplif
t associated with the growth of some thrust structures. For shallow-wa
ter facies the competition between thrust-related uplift and flexural
subsidence can be investigated from the stacking patterns of paraseque
nce sets. For structures developed at greater palaeobathymetries recei
ving fine-grained pelagic sediment, active tectonics may be recognized
from depositional hiatuses.