Geology Reference
In-Depth Information
Fig. 16.5.
Systems tracts and microfacies.
The example from the Late Cretaceous of the Sinai (Egypt) demonstrates the
relationships between systems tracts, environmentally diagnostic microfacies criteria and characteristic microfacies types.
From left to right: Sequence boundaries and their features; systems tracts defined by sea level (LST, TST, HST; 1-14; mfs:
maximum flooding surface); facies-diagnostic fossils and microfacies criteria; stratigraphic distribution of prevalent microfacies
types. Modified from Bauer et al. (2002).
Facies of systems tracts
: 1 - HST, marls and limestones with mollusks and echinoderms. 2 - LST, siltstones and shales
with plants and ferruginous ooids. 3/4 - TST/HST, transgressive surface (ts), decrease of quartzose sediments; maximum
flooding surface (mfs), dolomites, limestones and marls with abundant rudists, oysters and corals. 5 - TST, ts, condensed
deposits with abundant ammonites overlain by marls with planktonic foraminifera. 6 - HST, mfs, dolomites and oolitic
limestones. 7 - LST, gypsum, siltstones and shales with plant remains and brackish ostracods. 8 - TST, ts, onset of shallow-
subtidal deposits. 9 - HST, mfs, thick-bedded limestones and dolomites. 10 - LST - siliciclastics. 11 - TST/HST, bioclastic
dolomites and limestones. 12 - LST, marls, shales and siltstones with plants, gypsum, Fe-ooids and caliche. 13 - TST, ts,
onset of carbonates with ooids and reworked grains. 14 - HST, condensation at mfs, dolomites alternating with limestones.
Microfacies types:
Siliciclastic shoreface - S 2. Quartzose bioclastic packstones and grainstones. Lagoon - L 2, bioclastic
packstones and wackestones with mollusks, echinoderms, ostracods, and benthic foraminifera. Shallow subtidal - P 1, peloidal
wackestones and packstones with abundant mollusks. P 2, bivalve floatstones with oysters and rudist fragments. P 3, bioclas-
tic packstone with green algae. P 4, foraminiferal wackestones with miliolids and packstones with bivalves. P 5, winnowed
packstones and grainstones rich in peloids. High-energy subtidal - W 1, bioclastic packstones rich in coated grains. W 2,
winnowed packstones rich in bioclasts. W 3, algal packstones with dasyclads and rhodophyceans, and with coated grains.
W 4, oolitic packstones and grainstones. Deep open-marine environment - B 1, dolomitic wackestones and packstones with
planktonic foraminifera.
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