Editing Ordovician (section)

== Geochemistry ==
[[File:Anomalodonta gigantea Waynesville Franklin Co IN.JPG|thumb|External mold of Ordovician [[Bivalvia|bivalve]] showing that the original [[aragonite]] shell dissolved on the sea floor, leaving a cemented mold for biological encrustation ([[Waynesville Formation]] of Franklin County, Indiana).]]
The Ordovician was a time of [[calcite sea]] geochemistry in which low-magnesium [[calcite]] was the primary inorganic marine precipitate of [[calcium carbonate]].<ref name="JonesEtAl2019">{{cite journal |last1=Jones |first1=David S. |last2=Brothers |first2=R. William |last3=Ahm |first3=Anne-Sofie Crüger |last4=Slater |first4=Nicholas |last5=Higgins |first5=John A. |last6=Fike |first6=David A. |date=9 December 2019 |title=Sea level, carbonate mineralogy, and early diagenesis controlled δ13C records in Upper Ordovician carbonates |journal=Geology |volume=48 |issue=2 |pages=194–199 |doi=10.1130/G46861.1 |s2cid=213408515 |doi-access=free }}</ref> [[Carbonate hardgrounds]] were thus very common, along with calcitic [[ooid]]s, calcitic cements, and invertebrate faunas with dominantly calcitic skeletons. Biogenic [[aragonite]], like that composing the shells of most [[Mollusca|molluscs]], dissolved rapidly on the sea floor after death.<ref name="Stanley1998">{{Cite journal | last1 = Stanley | first1 = S. | last2 = Hardie | first2 = L. | doi = 10.1016/S0031-0182(98)00109-6 | title = Secular oscillations in the carbonate mineralogy of reef-building and sediment-producing organisms driven by tectonically forced shifts in seawater chemistry | journal = [[Palaeogeography, Palaeoclimatology, Palaeoecology]] | volume = 144 | issue = 1–2 | pages = 3–19 | year = 1998 | bibcode = 1998PPP...144....3S | doi-access = free }}</ref><ref name="Stanley1999">{{cite journal |last=Stanley |first=S. M. |author2=Hardie, L. A. |year=1999 |title=Hypercalcification; paleontology links plate tectonics and geochemistry to sedimentology |journal=GSA Today |volume=9 |pages=1&ndash;7 }}</ref>

Unlike Cambrian times, when calcite production was dominated by microbial and non-biological processes, animals (and macroalgae) became a dominant source of calcareous material in Ordovician deposits.<ref name=Munnecke2010/>