Ordovician ironstone of the Iberian margin: Coastal upwelling, ocean anoxia and Palaeozoic biodiversity

Pufahl, Peir K.; Squires, Alexandra D.; Murphy, J. Brendan; Quesada, Cecilio; Lokier, Stephen W.; Álvaro, J. Javier; Hatch, Jason

doi:10.1002/dep2.113

Cited by 24 publications

(31 citation statements)

References 140 publications

(233 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The link between ironstone deposition and maximum flooding is observed in other Paleozoic ironstones (Young, 1992;Todd et al, 2019;Pufahl et al, 2020). The MFS marks the deepest water facies in a sequence and the change from retrogradational to progradational parasequence stacking (Catuneanu et al, 2011;Catuneanu, 2019).…”

Section: Sequence Stratigraphymentioning

confidence: 88%

“…Such low rates of clastic sedimentation stabilize the zone of authigenesis beneath the seafloor (cf. Föllmi, 2016) and permit waves to rework precipitating authigenic muds and coated Fe grains into granular deposits (Todd et al, 2019;Pufahl et al, 2020;Matheson and Frank, 2021).…”

Section: Sequence Stratigraphymentioning

confidence: 99%

“…Because Eu anomalies are not produced by other REE + Y sources they are considered a robust indicator of hydrothermal input (Derry and Jacobsen, 1990;Olivarez and Owen, 1991;Danielson et al, 1992;Bau and Dulski, 1999;Bayon et al, 2015). The opening Rheic Ocean was ideal for the production and ponding of hydrothermally derived ferruginous seawater (Figure 11; Todd et al, 2019;Pufahl et al, 2020). Mid-ocean ridges discharged hydrothermal Fe as Avalonia rifted from Gondwana.…”

Section: Seawater Redox Conditions and Fe Sourcementioning

confidence: 99%

“…Colours reflect facies: blue clastic rich F1 and F3, green F5, brown F6, red F7, red crosses F7 from drill core. The delivery of ferruginous seawater to continental shelves via coastal upwelling is analogous to the Precambrian when widespread anoxia allowed hydrothermal Fe to concentrate in the global ocean (Pufahl et al, 2020;Matheson and Pufahl, 2021). In the Neoarchean and Paleoproterozoic, the combination of a large Fe reservoir that was periodically tapped by upwelling along favourably positioned continents produced aerially extensive iron formations (Gross, 1983;Bekker et al, 2010;Pufahl, 2010;Pufahl et al, 2020).…”

Section: Seawater Redox Conditions and Fe Sourcementioning

confidence: 99%

“…Modern upwelling systems such as the Humboldt and Benguela current regions along the coasts of Peru and southern Africa, respectively, are characterized by this triad of sedimentary deposits (Suess and Von Huene, 1990;Wefer et al, 2002). Modelling of surface currents in the Rheic Ocean suggest upwelling in this narrow seaway was driven by east-blowing winds and Ekman transport along the southern margin of Avalonia, which formed the northern side of a cyclonic gyre (Figure 11; Pohl et al, 2016;Todd et al, 2019;Pufahl et al, 2020).…”

Section: Depositional Modelmentioning

confidence: 99%

See 4 more Smart Citations

Middle Ordovician Upwelling-Related Ironstone of North Wales: Coated Grains, Ocean Chemistry, and Biological Evolution

et al. 2021

Self Cite

View full text Add to dashboard Cite

Middle Ordovician phosphatic ironstone of the Welsh Basin provides new insight into the paleoenvironmental significance of ironstone and Ordovician ocean chemistry. Deposition occurred in a back-arc basin along the southern margin of Avalonia as the Rheic Ocean opened to the south. Ironstone is interpreted to have accumulated as part of an aggradational parasequence on a storm-dominated shelf with coastal upwelling. This parasequence has a laminated pyritic mudstone base that grades upward into variably bioturbated mudstone and coated grain-rich, intraclastic ironstone, which is overlain in turn by cross-stratified grainstone composed entirely of coated Fe grains. A coarser clastic parasequence composed of more proximal lithofacies rests conformably above and suggests the contact between the two parasequences is a maximum flooding surface marking the onset of highstand conditions. Lithofacies associations suggest that sustained coastal upwelling created a wedge of nutrient-rich, ferruginous seawater on the middle shelf that stimulated high surface ocean productivities. Large, coated Fe grains (granule size) composed of discontinuous and concentric carbonate fluorapatite, hematite, and chamosite cortical layers record fluctuations in pore water Eh that are interpreted to have been related to changes in upwelling intensity and intermittent storm reworking of the seafloor. Results support an emerging model for Ordovician ironstone underpinned by the development of ferruginous bottom water that was periodically tapped by coastal upwelling. Expanding, semi-restricted seaways such as the Rheic Ocean were ideal locations for the ponding of this anoxic, hydrothermally enriched seawater, especially during the early Paleozoic when the deep ocean was variably and inconsistently oxygenated. The coincidence of ironstone depositional episodes with graptolite diversification events suggests that, in addition to Fe, the sustained supply of upwelling-related P may have driven the radiation of some planktonic ecosystems during the Great Ordovician Biodiversification Event. Concomitant minor extinctions of benthic trilobites occurred as these ferruginous waters impinged on the shelf.

show abstract