Sequence Stratigraphy - Trace Fossils as Indicators of Sedimentary Environments - page 178

trough cross-stratified and current-rippled sandstones and pebbly sandstones
( Fig. 9 C and D), with lesser horizontal planar parallel-laminated sandstone beds
( Boreen and Walker, 1991; MacEachern and Pemberton, 1994; Pattison, 1991;
Pattison and Walker, 1994 ). Ichnological suites are sporadically distributed and
are commonly associated with pauses in deposition. Ichnogenera are restricted
mainly to dwelling structures such as Ophiomorpha irregulaire , Ophiomorpha
nodosa , Rosselia , Cylindrichnus , Diplocraterion, and Skolithos . Mudstone
interbeds, where present, may contain isolated Planolites . Most beds show
BI

1-2 (cf. MacEachern and Gingras, 2007 ).
The flood-tidal delta deposits interfinger with bay deposits and are character-
ized by stacked current and combined flow ripple-lamination, commonly
capping horizontal planar parallel-lamination ( Pattison, 1991; Pattison and
Walker, 1994 ). These flood-tidal deposits form composite bedsets attributable
to wavy bedding. Trace fossils are sporadically distributed and bioturbation
intensities are variable (BI

0, with zones of BI

¼ ¼

0-4), but ichnological suites show higher diversi-
ties than apparent in the sandy bay-head deltas, and contain higher proportions of
more fully marine elements ( MacEachern and Gingras, 2007; MacEachern and
Pemberton, 1994 ). Constituents include Ophiomorpha irregulaire , Rosselia ,
Diplocraterion , Palaeophycus , Skolithos , Chondrites , Planolites, and very rare
Phycosiphon .
Much of the delay in recognizing that the Viking Formation at Crystal and
Willesden Green constituted parts of estuarine incised-valley complexes lay in
the focus, at the time, on purely sedimentological criteria. Physical sedimento-
logical characteristics are most pronounced in channel deposits (fluvial, distrib-
utary, and tidal), the flood-tidal delta deposits, and the sandy bay-head deltas.
Discriminating the central-basin deposits from the open-marine parasequences
largely relies on ichnological characterization, which was only coming to be
appreciated in the late 1970s. Many bay fills were routinely regarded to be part
of the underlying marine parasequences and the presence of softground and
firmground omission suites went unrecognized.

¼

3.3 Carbonate Platform, Khuff Formation, Middle East
The Middle Permian to Early Triassic Khuff Formation and their correlative
formations in the Middle East comprise giant gas accumulations, and thus have
been of increasing economical and reservoir technical interest. Good subsurface
data coverage combined with superb outcrops has guided the regional correla-
tion and has led to a reasonable understanding of the depositional environments
and paleogeographic situation. In addition to the biostratigraphic delineation, a
sequence-stratigraphic framework for the Khuff Formation was established
early and has been subject of some refinement (see review in Al-Husseini
and Matthews, 2010 ).
Accordingly, six long-period sequences have been identified, subdivided into
the Lower Khuff Formation (sequences KS6-5) and the Upper Khuff Formation