Heterozoan carbonates: When, where and why? A synthesis on parameters controlling carbonate production and occurrences
Résumé
n modern and Phanerozoic times, heterozoan carbonates group a large array of depositional environments from the poles to the tropics. This global assessment reviews the critical parameters and controlling factors of heterozoan carbonates: (i) stratigraphic and global distributional trends, (ii) oceanographic and trophic relationships, and (iii) biological and sedimentary processes. Well-documented case studies (n = 129) have been investigated when facies and stratigraphic attributes were available, and when environmental settings, such as oceanography, climate and paleogeography were clearly identified. These case studies occur during specific periods of time in the sedimentary record, e.g. Late Ordovician, Early Carboniferous, Early Permian and Neogene, while they are absent during others, e.g. Triassic and Jurassic. Periods during greenhouse to icehouse transitions, and those with active thermohaline circulation, are particularly conducive for heterozoan carbonates. Based on global oceanographic patterns and existing ecological and hydrodynamic regime classifications (Hallock, 2001; Pedley and Carannante, 2006; James and Jones, 2015), a process-based classification scheme is proposed that distinguishes two main heterozoan carbonate systems: (i) a highly productive system characterized by suspension-feeding biota and (ii) an oligo-mesotrophic, warm-temperate system characterized by red algal and seagrass derived biota. Eight depositional models are proposed that combine (i) the source of energy for metabolic activities that allow the carbonate-producing biota to thrive and (ii) hydrodynamics and physiography of the depositional system that control the sediment accumulation. The local and platform scale based profiles can be used to complement the facies approach of James and Jones (2015)