Sequence Stratigraphy - Trace Fossils as Indicators of Sedimentary Environments - page 179

(sequences KS4-1), and separated by a widespread evaporation event (Middle
Anhydrite) on the top of sequence KS5. Each sequence comprises a TST and
a HST, separated from one another by a maximum accommodation zone includ-
ing the MFS. The six sequences consist of stacked, smaller-scale sequences of
higher frequency with a pronounced shallowing-upward character.
Based on wells from the Iranian South Pars Field in the Persian Gulf, Knaust
(2009) employed core data to supplement the sequence-stratigraphic subdivi-
sion by means of ichnology. A first step of that study was the interpretation
of facies by using sedimentological and ichnological criteria (e.g., trace-fossil
suites, bioturbation index, and ichnodiversity), and their distribution on a
proximal-to-distal transect on the Khuff carbonate platform ( Fig. 12 ):
1. Sabkha and salina : Mudstone, alternating with anhydrite and gypsum, with
breccia, laminated caliche crusts and nodules (pedogenic carbonates, supra-
tidal). Plant roots are common and probably result from the colonization of
cordaitalean trees in a coastal environment.
2. Tidal flat : Dolomitic mudstones with sporadically distributed root traces and
biolaminites dominate in the upper zone. In the lower zone, rooted mudstone
layers are intercalated with oolitic and intraclastic grainstone and packstone
containing Asterosoma and Rosselia (beach sands, sand waves, tidal chan-
nels, tidal deltas, and storm deposits). The degree of bioturbation is high but
the ichnodiversity is moderate.
3. Restricted lagoon : Laminated and homogeneous dolomitic mudstone and
wackestone with scattered pseudomorphs of evaporite minerals and anhy-
drite nodules. The ichnodiversity is low to moderate, including Taenidium ,
Planolites, and Arenicolites, and the degree of bioturbation is moderate.
4. Open lagoon : Mud-dominated lithofacies with wackestone, grainstone, and
packstone interlayers due to washover and storm deposition. Grain-filled
Zoophycos dominate, accompanied by Asterosoma , Siphonichnus , and
Chondrites . The degree of bioturbation and ichnodiversity are moderate
to high, indicating a suitable environment with adequate water circulation.
5. Platform margin : An extensive rim of grainstone and packstone with thin
mudstone interlayers separates the interior platform from the open sea.
The leeward margin of the rim is weakly bioturbated and has a moderate
ichnodiversity. It contains Asterosoma , while toward its central part, root
traces are more abundant. The high-energy foreshore environment on the
seaward side of the margin is dominated by a high to intense degree of bio-
turbation and by a low ichnodiversity with Macaronichnus . Arenicolites
results from opportunistic colonization of sand shoals and sand waves,
whereas Balanoglossites occurs in firm- and hardgrounds.
6. Shoreface/inner ramp : Packstone, grainstone, and mudstone with a low
degree of bioturbation and a moderate ichnodiversity, as well as intensely
mottled event beds. Skolithos dominates, accompanied by Asterosoma
and Cylindrichnus .