Carbonate Depositional Environments - Microfacies of Carbonate Rocks - page 35

Table 2.2. Main features of modern (warm-water) and non-tropical (cool- and cold-water) carbonates (based on Leonard et
al. 1981, Nelson 1988, Rao 1997). Bold-type criteria are of specific value in microfacies studies of ancient non-tropical
limestones.

Tropical carbonates Nontropical carbonates

Latitude 30° N - 30° S beyond 30° N and 30°S

Environment Platform; shelf Open shelf; ramp

Tectonics Stable Stable to unstable

Terrigenous input Low Low to high

Geometry of buildups Attached and isolated plat- Homoclinal and distally

forms with marginal rims steepened ramps

Mean water temperature > 23 °C <20 °C

Salinity Normal to hypersaline Normal (to reduced)

Carbonate saturation Supersaturated to saturated Saturated to undersaturated

Water circulation Restricted to open Open

Accumulation rates 50 to >1000 cm/1000 a >1 to >10 cm/1000 a

Reefs Common to abundant Rare to absent

Algal mats Common Absent

Biodegradation Common to abundant Abundant, strong

Carbonate content >90% 50-100%

Texture Muds, sands, gravels Sands, gravels, muds

Carbonate mud Common to abundant Rare to abundant

Origin of allochthonous mud Disintegration of algae, Physical and chemical

microbial degradation of skeletons

Ooids Common Absent

Aggregate Grains Common Absent

Peloids Common Rare or absent

Intra/Lithoclasts Common Rare to common

Calcareous red algae Common to abundant Abundant

Rhodoids Common Abundant

Calcareous green algae Abundant Very rare

Stromatolites Common to abundant Rare

Seaweed (brown algae) Rare Abundant

Seagrass Abundant Less common

Zooxanthellate corals Abundant Rare

Azooxanthellate corals Rare Common to abundant

Coral growth forms Diverse Solitary and fasciculate

Benthic foraminifera Common, high-diversity Abundant, low-diversity

Bryozoans Rare to common Abundant

Bivalves Common and diverse Abundant and diverse

Vermetid gastropods Rare Common

Serpulid worms Rare to common Common

Barnacles Rare Common to abundant

Echinoderms Common Abundant

Siliceous sponges Rare to common Common to abundant

Skeletal grain associations Few Diverse

Biotic diversity High Moderate to high

Equatability Low High

Association with non-carbonates Rare Rare to abundant

Glauconite Rare Common

Phosphorite Rare Common

Biogenic silica Rare Rare to common

Low-Mg calcite Rare to common Common to abundant

High-Mg-calcite Abundant Abundant to common

Aragonite Abundant Rare

Dolomite Common Rare

Early sea-bed lithification Common to abundant Less common

Diagenetic trends Constructive Destructive