Aragonite sea

The alternation of calcite and aragonite seas through geologic time.

An aragonite sea contains aragonite and high-magnesium calcite as the primary inorganic carbonate precipitates. Therefore, the chemical conditions of the seawater must be notably high in magnesium content for an aragonite sea to form. This is in contrast to a calcite sea in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate.

The Early Paleozoic and the Middle to Late Mesozoic oceans were predominantly calcite seas, whereas the Middle Paleozoic through the Early Mesozoic and the Cenozoic (including today) are characterized by aragonite seas.^{[1][2][3][4][5]}

Aragonite seas form due to several factors, the most obvious of these is a high magnesium content. However, the sea level and the temperature of the surrounding system also determine whether an aragonite sea will form.^[6]

Calcite seas occurred at times of rapid seafloor spreading and global greenhouse climate conditions.^[7] Calcite is the predominant mineral in warm, shallow marine environments. Aragonite on the other hand, is the dominant mineral in cool marine water environments.

This trend has been observed by looking at the chemistry of carbonates, dating them and analyzing the conditions under which they were formed. One study has examined the temporal and spatial distribution of limestone-marl alternations in Ordovician, Jurassic and Cretaceous (times of calcite seas). This study concluded that the most abundant of the limestone-marl alternations occurred in settings similar to today's seas which favor aragonite production.^[8]

Citations

1. Wilkinson, Owen & Carroll 1985
2. Wilkinson & Given 1986
3. Morse & Mackenzie 1990
4. Lowenstein et al. 2001
5. Palmer & Wilson 2004
6. Adabi 2004
7. Stanley & Hardy 1999
8. Westphall & Munnecke 2003

References

• Cherns, L., Wright, V.P. (2000). "Missing molluscs as evidence of large-scale, early skeletal aragonite dissolution in a Silurian Sea". Geology. 28 (9): 791–794. Bibcode:2000Geo....28..791C. doi:10.1130/0091-7613(2000)28<791:MMAEOL>2.0.CO;2. ISSN 0091-7613.
• Harper, E.M., Palmer, T.J., Alphey, J.R. (1997). "Evolutionary response by bivalves to changing Phanerozoic sea-water chemistry". Geological Magazine. 134: 403–407. doi:10.1017/S0016756897007061.
• Lowenstein, T.K.; Timofeeff, M.N.; Brennan, S.T.; Hardie, L.A.; Demicco, R.V. (2001). "Oscillations in Phanerozoic seawater chemistry: evidence from fluid inclusions". Science. 294 (5544): 1086–1088. Bibcode:2001Sci...294.1086L. doi:10.1126/science.1064280. PMID 11691988.
• Mohammad, A. (2004). "A re-evaluation of aragonite versus calcite seas". Carbonates and Evaporites. 19 (2): 133–141. doi:10.1007/BF03178476.
• Morse, J.W.; Mackenzie, F.T. (1990). "Geochemistry of sedimentary carbonates". Developments in Sedimentology. 48: 1–707. doi:10.1016/S0070-4571(08)70330-3.
• Palmer, T.J.; Wilson, M.A. (2004). "Calcite precipitation and dissolution of biogenic aragonite in shallow Ordovician calcite seas". Lethaia. 37 (4): 417–427 . doi:10.1080/00241160410002135.
• Palmer, T.J. (1982). "Cambrian to Cretaceous changes in hardground communities". Lethaia. 15 (4): 309–323. doi:10.1111/j.1502-3931.1982.tb01696.x.
• Palmer, T.J., Hudson, J.D., Wilson, M.A. (1988). "Palaeoecological evidence for early aragonite dissolution in ancient calcite seas". Nature. 335 (6193): 809–810. Bibcode:1988Natur.335..809P. doi:10.1038/335809a0.
• Pojeta J., Jr. (1988). "Review of Ordovician pelecypods". U.S. Geological Survey Professional Paper. 1044: 1–46.
• Porter, S.M. (2007). "Seawater chemistry and early carbonate biomineralization". Science. 316 (5829): 1302–1304. Bibcode:2007Sci...316.1302P. doi:10.1126/science.1137284. PMID 17540895.
• Sandberg, P.A. (1983). "An oscillating trend in Phanerozoic non-skeletal carbonate mineralogy". Nature. 305 (5929): 19–22. Bibcode:1983Natur.305...19S. doi:10.1038/305019a0.
• Stanley, S.M.; Hardie, L.A. (1998). "Secular oscillations in the carbonate mineralogy of reef-building and sediment-producing organisms driven by tectonically forced shifts in seawater chemistry". Palaeogeography, Palaeoclimatology, Palaeoecology. 144: 3–19. doi:10.1016/S0031-0182(98)00109-6.
• Stanley, S.M.; Hardie, L.A. (1999). "Hypercalcification; paleontology links plate tectonics and geochemistry to sedimentology". GSA Today. 9: 1–7.
• Wilkinson, B.H. (1979). "Biomineralization, paleooceanography, and the evolution of calcareous marine organisms". Geology. 7 (11): 524–527. Bibcode:1979Geo.....7..524W. doi:10.1130/0091-7613(1979)7<524:BPATEO>2.0.CO;2. ISSN 0091-7613.
• Wilkinson, B.H.; Given, K.R. (1986). "Secular variation in abiotic marine carbonates: constraints on Phanerozoic atmospheric carbon dioxide contents and oceanic Mg/Ca ratios". Journal of Geology. 94 (3): 321–333. Bibcode:1986JG.....94..321W. doi:10.1086/629032.
• Wilkinson, B.H.; Owen, R.M.; Carroll, A.R. (1985). "Submarine hydrothermal weathering, global eustacy, and carbonate polymorphism in Phanerozoic marine oolites". Journal of Sedimentary Petrology. 55: 171–183.
• Wilson, M.A.; Palmer, T.J. (1992). "Hardgrounds and hardground faunas". University of Wales, Aberystwyth, Institute of Earth Studies Publications. 9: 1–131.
• Westphall, H.; Munnecke, A. (2003). "Limestone-marl alternations: A warm-water phenomenon?". Geology. 31 (3): 263–266. Bibcode:2003Geo....31..263W. doi:10.1130/0091-7613(2003)031<0263:LMAAWW>2.0.CO;2. ISSN 0091-7613.