Early Neoproterozoic origin of the metazoan clade recorded in carbonate rock texture

Abstract

Early Neoproterozoic reefs (older than 779, younger than 1083 Ma) contain a carbonate rock texture, already familiar from sponge-rich Phanerozoic limestones, characterized by authigenic Ca carbonate and irregular, secondary voids containing internal sediment (polymud fabric). In Holocene sediment, this texture develops by calcifi cation of degrading extracellular collagenous matrix (ECM) of siliceous sponges. ECM calcifi cation of siliceous sponges is evident throughout the Phanerozoic, and the related polymud fabric is a diagnostic petrographic feature of Phanerozoic sponge-rich carbonate mudmounds. The authigenic Ca carbonate of polymuds is interpreted to result from connective tissue calcifi cation just beneath the seafl oor, that, in a kind of taphonomic race, takes place at the same time as tissue oxidation and associated void formation. It is intriguing that ECM is a fundamental character of the metazoan clade, and so the presence in Early Neoproterozoic rocks of a texture directly associated with it implies the existence of metazoan-grade organisms at that time. This observation pushes back the earliest geological evidence for animals by about 200 m.y. The timing corroborates results of an integrated phylochronology and supports the concept of a biosphere that persisted through the snowball Earth interval.

Carbonate mounds: From paradox to World Heritage

“…In the Mackenzie Mountains, north-western Canada, coalescing small microbial reefs of Neoproterozoic age (1100-780 Ma) of the Little Dal Group, each 1-8 m thick, had built composite, three-dimensional reefs up to 500 m in height and 3 km in diameter (Wood, 1999). Neuweiler et al (2009) found that the reefs of the Little Dal Group contain a carbonate rock texture, already familiar from sponge-rich Phanerozoic carbonate mud mounds. It is characterized by authigenic calcium carbonate and irregular, secondary voids containing internal sediment with a so-called polymud fabric.…”

“…That very same year however, Neuweiler et al (2009) pushed back evidence of the earliest animals by some 200 Myr. In the Mackenzie Mountains, north-western Canada, coalescing small microbial reefs of Neoproterozoic age (1100-780 Ma) of the Little Dal Group, each 1-8 m thick, had built composite, three-dimensional reefs up to 500 m in height and 3 km in diameter (Wood, 1999).…”

Exploring a link between Atlantic coral mounds and Phanerozoic carbonate mudmounds: Insights from pore water fluorescent dissolved organic matter (FDOM), Pen Duick mounds, offshore Morocco

“…In recent years, one line of research on ancient sponge-rich carbonate mudmounds gained substantial momentum through the rediscovery of a modern, calcifying siliceous sponge (Wiedenmayer, 1978;Neuweiler and Burdige, 2005;Neuweiler et al, 2007Neuweiler et al, , 2009a. Highly reactive, freshly produced humic compounds (Ziechmann, 1994) originating from sponge tissue degradation-exudation contribute to a permineralizing interstitial fluid as a dissolved to colloidal phase.…”

“…3). Such a feature is subordinately present in many marine pore waters (Coble, 1996;Burdige et al, 2004) but becomes important in aqueous extracts of fluorescent sedimentary rocks (Neuweiler et al, 2009a). Peak Geol.-A is considered to derive from the alteration of refractory, marine FDOM (peak A in Fig.…”

“…Peak Geol.-A is considered to derive from the alteration of refractory, marine FDOM (peak A in Fig. 3), either through thermal maturation (material that experienced burial diagenesis; Neuweiler et al, 2009a) or due to a late stage of microbial biodegradation in modern sediments (Kisand et al, 2008). Peaks P1 and P2 form part of two emission bands (P1-P1* and P2-P2* in Fig.…”