Assessing the Role of Skeletons in Early Paleozoic Carbonate Production: Insights from Cambro-Ordovician Strata, Western Newfoundland

Animals originated in the Neoproterozoic and ‘exploded’ into the fossil record in the Cambrian. The Cambrian also represents a high point in the animal fossil record for the preservation of soft tissues that are normally degraded. Specifically, fossils from Burgess Shale-type (BST) preservational windows give paleontologists an unparalleled view into early animal evolution. Why this time interval hosts such exceptional preservation, and why this preservational window declines in the early Paleozoic, have been long-standing questions. Anoxic conditions have been hypothesized to play a role in BST preservation, but recent geochemical investigations of these deposits have reached contradictory results with respect to the redox state of overlying bottom waters. Here, we report a multi-proxy geochemical study of the Lower Cambrian Mural Formation, Alberta, Canada. At the type section, the Mural Formation preserves rare recalcitrant organic tissues in shales that were deposited near storm wave base (a Tier 3 deposit; the worst level of soft-tissue preservation). The geochemical signature of this section shows little to no evidence of anoxic conditions, in contrast with published multi-proxy studies of more celebrated Tier 1 and 2 deposits. These data help confirm that ‘decay-limited’ BST biotas were deposited in more oxygenated conditions, and support a role for anoxic conditions in BST preservation. Finally, we discuss the role of iron reduction in BST preservation, including the formation of iron-rich clays and inducement of sealing seafloor carbonate cements. As oceans and sediment columns became more oxygenated and more sulfidic through the early Paleozoic, these geochemical changes may have helped close the BST taphonomic window.

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Modeling the marine aragonite cycle: changes under rising carbon dioxide and its role in shallow water CaCO<sub>3</sub> dissolution

Biogeosciences ◽

10.5194/bg-5-1057-2008 ◽

2008 ◽

Vol 5 (4) ◽

pp. 1057-1072 ◽

Cited By ~ 46

Author(s):

R. Gangstø ◽

M. Gehlen ◽

B. Schneider ◽

L. Bopp ◽

O. Aumont ◽

...

Keyword(s):

Carbon Dioxide ◽

Shallow Water ◽

Biogeochemical Model ◽

Subsequent Reduction ◽

Saturation State ◽

Carbonate Production ◽

Mesozooplankton Biomass ◽

Marine Carbonate ◽

Realistic Representation

Abstract. The marine aragonite cycle has been included in the global biogeochemical model PISCES to study the role of aragonite in shallow water CaCO3 dissolution. Aragonite production is parameterized as a function of mesozooplankton biomass and aragonite saturation state of ambient waters. Observation-based estimates of marine carbonate production and dissolution are well reproduced by the model and about 60% of the combined CaCO3 water column dissolution from aragonite and calcite is simulated above 2000 m. In contrast, a calcite-only version yields a much smaller fraction. This suggests that the aragonite cycle should be included in models for a realistic representation of CaCO3 dissolution and alkalinity. For the SRES A2 CO2 scenario, production rates of aragonite are projected to notably decrease after 2050. By the end of this century, global aragonite production is reduced by 29% and total CaCO3 production by 19% relative to pre-industrial. Geographically, the effect from increasing atmospheric CO2, and the subsequent reduction in saturation state, is largest in the subpolar and polar areas where the modeled aragonite production is projected to decrease by 65% until 2100.

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Aragonite is calcite’s best friend at the seafloor

10.21203/rs.3.rs-776722/v1 ◽

2021 ◽

Author(s):

Olivier Sulpis ◽

Priyanka Agrawal ◽

Mariette Wolthers ◽

Guy Munhoven ◽

Matthew Walker ◽

...

Keyword(s):

Calcium Carbonate ◽

Reactive Transport ◽

Transport Model ◽

Deep Ocean ◽

Diffusive Transport ◽

Carbonate Production ◽

Calcium Carbonates ◽

Calcite Dissolution ◽

Calcium Carbonate Dissolution

Abstract In the open ocean, calcium carbonates are mainly found in two mineral forms. Calcite, the least soluble, is widespread at the seafloor, while aragonite, the more soluble, is rarely preserved in marine sediments. Despite its greater solubility, research has shown that aragonite, which could contribute between 10 and 90% to pelagic calcium carbonate production, is able to reach the deep-ocean. If large quantities of aragonite settle and dissolve at the seafloor, this represents a large source of alkalinity that buffers the deep ocean and favours the preservation of less soluble calcite, acting as a deep-sea, carbonate version of galvanization. Here, we investigate the role of aragonite dissolution on the early diagenesis of calcite-rich sediments using a novel 3D, micrometric-scale reactive-transport model combined with 3D, X-ray tomography structures of natural aragonite and calcite shells. Results highlight the important role of diffusive transport in benthic calcium carbonate dissolution, in agreement with recent work. We show that, locally, aragonite fluxes to the seafloor could be sufficient to suppress calcite dissolution in the top layer of the seabed, possibly causing calcite recrystallization. As aragonite producers are particularly vulnerable to ocean acidification, the proposed galvanizing effect of aragonite could be weakened in the future, indirectly boosting calcite dissolution further.

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Inter-Specific and Inter-Individual Trait Variability Matter in Surface Sediment Reworking Rates of Intertidal Benthic Foraminifera

10.21203/rs.3.rs-383583/v1 ◽

2021 ◽

Author(s):

Noémie Deldicq ◽

Laurent Seuront ◽

Vincent M.P. Bouchet

Keyword(s):

Surface Sediment ◽

Benthic Foraminifera ◽

Heat Waves ◽

Critical Role ◽

Individual Variability ◽

Plastic Pollution ◽

Carbonate Production ◽

Sediment Reworking ◽

Species Specific

Abstract Although benthic foraminifera are an important component of meiofauna and contribute to carbonate production and carbon/nitrogen cycles, their role in bioturbation processes remains poorly known. Five dominant intertidal benthic foraminifera were recently classified into functional bioturbator groups according to their sediment reworking mode and intensity. Our study aimed at identifying potential drivers (i.e. size and/or travelled distance) of species-specific surface sediment reworking rate. The travelled distance and surface sediment reworking rate of Haynesina germanica, Cribroelphidium williamsoni, Ammonia tepida, Quinqueloculina seminulum and Miliammina fusca were assessed through image analysis. Our results show that the surface sediment reworking performed by these species is not size-dependent, but dependent on their motility traits through interspecific differences in the travelled distance. Smaller species (i.e. Quinqueloculina seminulum and Haynesina germanica) contribute more to surface sediment reworking than larger ones (i.e. Ammonia tepida, Cribroelphidium williamsoni and Miliammina fusca). These observations stress the critical role of motion behaviour in surface sediment reworking processes by intertidal foraminifera. Finally, we stress that the high inter-individual variability observed in conspecific motion behaviour may be important to decipher the role of foraminifera in sediment bioturbation. Noticeably, the species characterized by a strong inter-individual variability are also the species that have the highest surface sediment reworking rates. This last observation may inform on the species-specific phenotypic plasticity and therefore the potential for the functional role of these species to be maintained in their natural environment. This is particularly relevant in an era of global change where ecosystem balance is increasingly threatened by various stressors such as heat-waves, ocean acidification and plastic pollution.

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