Abstract
The Bell Island and Wabana groups together comprise a ca. 150-m-thick succession of interbedded clastic and
chemical sedimentary rocks composed of eight distinct lithofacies that accumulated along the northern margin
of the Rheic Ocean. Lithofacies stacking patterns indicate that deposition occurred during a marine transgression
with superimposed small-scale sea level fluctuations producing at least six parasequences. Parasequences containing
ironstone are 10 to 20-m-thick and composed of hummocky cross-stratified sandstone interbedded
with organic-rich mudstone and phosphatic Fe-silicate-bearing siltstone,which is overlain by hematitic granular
ironstone capped by an erosive flooding surface.
This lithofacies association is interpreted to record the deposition of upwelling-related ironstone on a stormdominated
shelf. The close relationship between Fe-silicates and phosphorite typical of upwelling systems
suggests that Fe was delivered from deep, anoxic, nutrient-rich seawater that also stimulated high surface productivities.
The result was the precipitation of authigenic sedimentary apatite in anoxic organic-rich sediments
that accumulated near the upwelling front. The gradual advection of Fe-rich waters away from the upwelling
front, initiated precipitation of Fe-silicate coated grains and cements in suboxic pore-waters. Iron pumped
into shallower environments through advection and Fe-redox cycling is interpreted to have precipitated Fe-
(oxyhydr)oxide grains in sediment of the oxygenated middle shelf. These coated grains were subsequently
concentrated by fairweather and storm currents on the shoreface to create granular economic Fe deposits.
We challenge conventional models of Paleozoic ironstone deposition that rely on a continental source of Fe by
proposing a hydrothermal source that supplied Fe2+ to the shelf through upwelling. It also highlights the potential
connection between the delivery of anoxic, ferruginous seawater to the margins of the Rheic Ocean and the
Early Ordovician extinctions that punctuated the beginning of the Great Ordovician Biodiversification Event.
chemical sedimentary rocks composed of eight distinct lithofacies that accumulated along the northern margin
of the Rheic Ocean. Lithofacies stacking patterns indicate that deposition occurred during a marine transgression
with superimposed small-scale sea level fluctuations producing at least six parasequences. Parasequences containing
ironstone are 10 to 20-m-thick and composed of hummocky cross-stratified sandstone interbedded
with organic-rich mudstone and phosphatic Fe-silicate-bearing siltstone,which is overlain by hematitic granular
ironstone capped by an erosive flooding surface.
This lithofacies association is interpreted to record the deposition of upwelling-related ironstone on a stormdominated
shelf. The close relationship between Fe-silicates and phosphorite typical of upwelling systems
suggests that Fe was delivered from deep, anoxic, nutrient-rich seawater that also stimulated high surface productivities.
The result was the precipitation of authigenic sedimentary apatite in anoxic organic-rich sediments
that accumulated near the upwelling front. The gradual advection of Fe-rich waters away from the upwelling
front, initiated precipitation of Fe-silicate coated grains and cements in suboxic pore-waters. Iron pumped
into shallower environments through advection and Fe-redox cycling is interpreted to have precipitated Fe-
(oxyhydr)oxide grains in sediment of the oxygenated middle shelf. These coated grains were subsequently
concentrated by fairweather and storm currents on the shoreface to create granular economic Fe deposits.
We challenge conventional models of Paleozoic ironstone deposition that rely on a continental source of Fe by
proposing a hydrothermal source that supplied Fe2+ to the shelf through upwelling. It also highlights the potential
connection between the delivery of anoxic, ferruginous seawater to the margins of the Rheic Ocean and the
Early Ordovician extinctions that punctuated the beginning of the Great Ordovician Biodiversification Event.
| Original language | English |
|---|---|
| Pages (from-to) | 1-15 |
| Number of pages | 16 |
| Journal | Sedimentary Geology |
| Volume | 379 |
| Early online date | 3 Nov 2018 |
| DOIs | |
| Publication status | Published - Jan 2019 |
Access to Document
Fingerprint
Dive into the research topics of 'Sedimentology and oceanography of Early Ordovician ironstone, Bell Island, Newfoundland: Ferruginous seawater and upwelling in the Rheic Ocean'. Together they form a unique fingerprint.Projects
-
Basins, stratigraphy and sedimentary processes
Brunt, R. (PI), Redfern, J. (PI), Huuse, M. (PI), Schroeder, S. (PI), Hodgetts, D. (PI), Hollis, C. (PI), Kane, I. (PI), Jerrett, R. (PI), Taylor, K. (PI), Flint, S. (PI), Gawthorpe, R. (PI), Bowman, M. (PI) & Bulot, L. G. (PI)
Project: Research