Goldilocks at the dawn of complex life: mountains might have damaged Ediacaran–Cambrian ecosystems and prompted an early Cambrian greenhouse world

Abstract

We combine U–Pb in-situ carbonate dating, elemental and isotope constraints to calibrate the synergy of integrated mountain-basin evolution in western Gondwana. We show that deposition of the Bambuí Group coincides with closure of the Goiás-Pharusian (630–600 Ma) and Adamastor (585–530 Ma) oceans. Metazoans thrived for a brief moment of balanced redox and nutrient conditions. This was followed, however, by closure of the Clymene ocean (540–500 Ma), eventually landlocking the basin. This hindered seawater renewal and led to uncontrolled nutrient input, shallowing of the redoxcline and anoxic incursions, fueling positive productivity feedbacks and preventing the development of typical Ediacaran–Cambrian ecosystems. Thus, mountains provide the conditions, such as oxygen and nutrients, but may also preclude life development if basins become too restricted, characterizing a Goldilocks or optimal level effect. During the late Neoproterozoic-Cambrian fan-like transition from Rodinia to Gondwana, the newborn marginal basins of Laurentia, Baltica and Siberia remained open to the global sea, while intracontinental basins of Gondwana became progressively landlocked. The extent to which basin restriction might have affected the global carbon cycle and climate, e.g. through the input of gases such as methane that could eventually have collaborated to an early Cambrian greenhouse world, needs to be further considered.

Simple Structures and Complex Stories: Potential Microbially Induced Sedimentary Structures in the Ediacaran Serra De Santa Helena Formation, Bambuí Group, Eastern Brazil

“…The interactions between various microbial communities and different types of substrates led to the formation of a variety of microbially induced sedimentary surface textures described in this paper. The abundant MISS in the Serra de Santa Helena Formation are consistent with the interpretation of progressive restriction of the Bambuí basin (Paula-Santos et al 2017; Caxito et al 2021; Guacaneme et al 2022), where typical late Ediacaran and early Cambrian macrofaunas were not present, but benthic microbial assemblages thrived.…”

“…Abundant stromatolites are known from the Bambuí Group, particularly the Sete Lagoas, Lagoa do Jacaré, and upper Serra da Saudade formations (Vieira et al 2007; Santos et al 2018; Uhlein et al 2020). However, eukaryotic fossils and particularly macroscopic animal fossils are rare in the Bambuí Group, either because of their poor preservation (Simonetti and Fairchild 2000; Warren et al 2014), their rarity due to ecologically stressful environment (Caetano-Filho et al 2019, 2020; Hippertt et al 2019; Caxito et al 2021), or inadequate sampling. On the other hand, the presence of microbially induced sedimentary structures in the Serra de Santa Helena Formation indicates extensive development of benthic microbial communities in shallow to moderately deep marine settings, similar to those described in modern environments with intense methanogenesis (Birgel et al 2015).…”

“…The middle Sete Lagoas Formation is substantially younger, because it contains the terminal Ediacaran index fossil Cloudina (550-538 Ma; Warren et al 2014) and a population of detrital zircon grains with ages of ~557 Ma (Paula- Santos et al 2015). More recently, novel in-situ carbonate U-Pb dating provided strong evidence for a hiatus between the lower and middle Sete Lagoas Formation (Caxito et al 2021). Geochronologic (and/or biostratigraphic) data constraining the age of the Serra de Santa Helena and Lagoa do Jacaré formations are rare.…”

Late Cryogenian and late Paleozoic ice ages on the São Francisco craton, east Brazil

“…The two major Neoproterozoic glaciations, with occurrences in many continents, have come to be known as "Sturtian" (~720-660 Ma) and "Marinoan" (~650-635 Ma) glaciations (Condon et al, 2005;Macdonald et al, 2010;Hoffman et al, 2017;Cox et al, 2018). In east Brazil, the glaciogenic Jequitaí Formation is the base of the Bambuí Group (Dardenne, 1978;Dardenne, 2000;Uhlein et al, 2016) and although still controversial, its age is generally assigned to the Marinoan glaciation event (Caxito et al, 2012;Caxito et al, 2021;Alvarenga et al, 2014;Uhlein et al, 2016;Uhlein et al, 2017;Uhlein et al, 2019). The Jequitaí Formation is found in several regions of the São Francisco craton and one area is particularly relevant as it presents outstanding records that served as the basis for the geologic knowledge of the unit: the outskirts of the Água Fria ridge in central Minas Gerais state.…”

Stratigraphy of the Pitangui Synclinorium, northwest of the Quadrilátero Ferrífero mineral province - Brazil: magmatism and sedimentation from Archean to Neoproterozoic

“…Detrital zircon from marls of the basal Sete Lagoas Formation yielded a maximum depositional age (LA-ICPMS) of 593 ± 2 Ma (Paula-Santos et al 2015). Dating calcite crystals (U-Pb LA-ICPMS) from limestones also of the Sete Lagoas Formation, Caxito et al (2021) obtained ages of 615 ± 6 Ma, 608 ± 5 Ma and 607 ± 6 Ma for the base of this formation, and ages of 573 ± 11 Ma, 569 ± 7 Ma and 566 ± 15 Ma for the upper portion, correlating them to the post-Marinoan glaciation event. Furthermore, the recognition of the Cloudina fossil guide in the intermediate portion of the Sete Lagoas Formation certifies an Ediacaran age for this unit (Warren et al 2014).…”