Geology Reference
In-Depth Information
16.4 Recognizing Ancient Cool-
Water Carbonates
by characteristic grain associations and supported by
paleontological data, and (2) mineralogical and diage-
netic criteria.
The criteria and constraints of recent shelf and reef
carbonates were discussed in Sect. 2.4.4 (see Pl. 4). A
promising method based on grain association analysis
to distinguish cold-water from warm-water limestones
was described in Sect. 12.2. The present chapter sum-
marizes the diagnostic criteria of ancient cold-water
carbonates and presents a case study.
Our knowledge of ancient cold-water limestones is
predominantly based on the study of Ordovician, Car-
boniferous and Permian as well as Cenozoic shelf car-
bonates, and Tertiary reef carbonates.
Compositional criteria.
The common compositional
criteria of cold-water shelf limestones are the abun-
dance of sand- and gravel-sized bioclasts, sometimes
associated with litho- and intraclasts and peloids. Car-
bonate mud formed by physical and chemical degra-
dation of skeletons or pelagic admixtures occurs in dif-
ferent quantities. Biodegradation of skeletal grains is
high. Some grains, characteristic of shallow-marine
warm-water carbonates, e.g. ooids and aggregate grains,
are almost or completely absent.
16.4.1 Microfacies Criteria of Non-Tropical
Cold-Water Shelf and Reef Limestones
The major differences of tropical warm-water carbon-
ates and nontropical cold-water carbonates are listed
in Tab. 2.2. Ancient cold-water shelf carbonates are
characterized by (1) compositional criteria expressed
Fig. 16.15.
Cool
-water bryozoan limestone.
During the Late Cretaceous and Cenozoic cool-water bryozoan mounds formed
in mid- to high-latitudinal settings. An impressive example are extended belts of asymmetric bryozoan mounds consisting of
skeletal floatstones, packstones and wackestones. The mounds originated below the photic zone on the outer shelf and upper
slope. Composition, facies types and geometry of the mounds exhibit great similarity with Neogene cool-water carbonates of
the Great Australian Bight (Surlyk 1997). The sample is a skeletal packstone consisting predominantly of cyclostome bryo-
zoans. Early Tertiary (Early Danian): Stevns Klint, Denmark.
