Heterozoan carbonates: When, where and why? A synthesis on parameters controlling carbonate production and occurrences

Abstract

In 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).

Evidence for seasonality in early Eocene high latitude sea-surface temperatures

“…Heterozoan assemblages can occur within a wide spectrum of trophic levels and climatic zones but are generally swamped by rapidly growing photozoan material in tropical environments. Heterozoan assemblages are therefore typical, but not exclusively reflective, of temperate to polar environments where summer SSTs remain cooler than 24°C (Michel et al, 2018).…”

Are local dominance and inter-clade dynamics causally linked when one fossil clade displaces another?

“…Surprisingly, cheilostome origination rates have no detectable relationship to cyclostome origination or extinction rates, given the weights of the null model (columns 1, 3, model A). These results suggest consideration of additional factors such as potential key innovations (23,24) or environmental and ecological changes (14,25), that could reveal relationships to pulses of cheilostome radiation. Between rates of cheilostome and cyclostome extinction, a feedback model has the highest model weight (column 2, model D).…”

The seagrass skeletal assemblage from modern to fossil and from tropical to temperate: Insight from Maldivian and Mediterranean examples

“…The green algae, mainly halimedaceans, characterize the Maldive and Eocene seagrasses, while coralline red algae are dominant in the Mediterranean and in the Oligocene. Generally, the type and the efficiency of carbonate factories are controlled by various factors, including light availability, hydraulic energy, trophic conditions and Ca/Mg ratios (James, 1997;Mutti & Hallock, 2003;Pomar et al, 2004;Westphal et al, 2010;Mateu-Vicens et al, 2012;Michel et al, 2018). Classically, heterozoan skeletal assemblages represent neritic carbonate production in high latitudes, in cold to temperate settings and at lower latitudes, in tropical to subtropical environments where nutrient input, and consequently light penetration, does not support mixotrophic and photoautotrophic production at shallow-water depths, except for coralline algae.…”

“…Classically, heterozoan skeletal assemblages represent neritic carbonate production in high latitudes, in cold to temperate settings and at lower latitudes, in tropical to subtropical environments where nutrient input, and consequently light penetration, does not support mixotrophic and photoautotrophic production at shallow-water depths, except for coralline algae. In this context, Michel et al (2018) indicated two major specific environmental conditions for the heterozoan carbonate factory: (i) planktonic-rich waters; and (ii) a subtle combination of light penetration and hydrodynamic levels. Conversely, for oligotrophic, tropical and subtropical ecosystems, carbonate production is dominated by the photozoan assemblage, with abundant corals, large benthic foraminifera and green algae (James, 1997;Halfar et al, 2004;Pomar et al, 2004;Michel et al, 2018).…”

“…During greenhouse periods this assemblage is limited and often associated with local environmental disturbance such as terrigenous and nutrient influx. For a complete review of skeletal association terminologies, see Fl€ ugel (2004) and Michel et al (2018).…”