Amadeus Event

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The Amadeus Event (OAE1c) was an oceanic anoxic event (OAE). It occurred 106 million years ago (Ma), during the Albian age of the Cretaceous period, [1] in a climatic interval known as the Middle Cretaceous Hothouse (MKH). [2]

Contents

Extent and duration

OAE1c lasted for approximately 567 kyr. [3] Environmental conditions across much of the globe facilitated the formation of dysaerobic waters, although OAE1c varied in its nature and magnitude depending on region. Shallow shelf environments in the Gulf of Mexico were unaffected by anoxia. [4]

Causes

The MKH was one of the hottest intervals of the entire Phanerozoic eon, with OAE1c occurring during a particularly warm time known as the Amadeus Thermal Maximum; these conditions were prime for generating anoxic waters. [2] Orbital forcing is considered the most likely cause of OAE1c, as most geochemical changes observed across the OAE1c interval were in lockstep with Milankovitch cycles. [5] Black shale deposition occurs during minima in the axial precession cycle, when waters were less saline and/or warmer. Increased influxes of terrestrial runoff would have induced stratification of the water column, inhibiting mixing of water masses at different depths. Peaks in carbonate deposition occurred during precession maxima, when precipitation and evaporation rates were lower and saline deep water bodies were able to form, preventing stratification. [1] The lack of anomalous osmium enrichments of any significance rules out large igneous province volcanism as a suspected causal factor, which is known to have caused other Cretaceous OAEs like OAE1a and OAE2. [6]

Effects

Unlike many other OAEs across the MKH, the black shales deposited during OAE1c were made up of type III kerogen and consisted primarily of terrestrial organic matter, in contrast to the type II kerogen made up of marine organic matter that the black shales of OAE1a, OAE1b, OAE1d, and OAE2 were composed of. Also unlike other MKH OAEs, no significant radiations or extinctions of radiolarians occurred as a result of OAE1c. [7]

See also

References

  1. 1 2 Galeotti, Simone; Sprovieri, Mario; Coccioni, Rodolfo; Bellanca, Adriana; Neri, Rodolfo (15 January 2023). "Orbitally modulated black shale deposition in the upper Albian Amadeus Segment (central Italy): a multi-proxy reconstruction" . Palaeogeography, Palaeoclimatology, Palaeoecology . 190: 441–458. doi:10.1016/S0031-0182(02)00618-1 . Retrieved 10 June 2023.
  2. 1 2 Scotese, Christopher Robert; Song, Haijun; Mills, Benjamin J. W.; Van der Meer, Douwe G. (April 2021). "Phanerozoic paleotemperatures: The earth's changing climate during the last 540 million years" . Earth-Science Reviews . 215: 1–47. doi:10.1016/j.earscirev.2021.103503 . Retrieved 10 June 2023.
  3. ↑ Liu, Xuan; Zhang, Yi; Han, Kaibo; Batenburg, Sietske J.; Guo, Huifang; Ma, Chao; Yao, Hanwei; Fan, Hanhan; Wu, Qi; Chen, Xi (November 2022). "Chemo- and cyclostratigraphic records of the Albian from the Tethyan Himalaya of southern Tibet, China" . Global and Planetary Change . 218. doi:10.1016/j.gloplacha.2022.103955 . Retrieved 10 June 2023.
  4. ↑ Scott, Robert W.; Rush, Natalie; Hojnacki, Rachel; Campbell, Whitney; Wang, Yulun; Lai, Xin (August 2020). "Albian (Lower Cretaceous) carbon isotope chemozones, Texas Comanche Shelf and Mexican Chihuahua Trough: Implications for OAEs" . Cretaceous Research . 112: 1–19. doi:10.1016/j.cretres.2020.104453 . Retrieved 10 June 2023.
  5. ↑ Tateo, Fabio; Morandi, Noris; Nicolai, Annarita; Ripepe, Maurizio; Coccioni, Rodolfo; Galeotti, Simone; Baudin, Francois (1 March 2000). "Orbital control on pelagic clay sedimentology; the case of the late Albian "Amadeus Segment" (central Italy)" . Bulletin de la Société Géologique de France . 171 (2): 217–228. doi:10.2113/171.2.217 . Retrieved 10 June 2023.
  6. ↑ Matsumoto, Hironao; Coccioni, Rodolfo; Frontalini, Fabrizio; Shirai, Kotaro; Jovane, Luigi; Trindade, Ricardo; Savian, Jairo F.; Koroda, Junichiro (11 January 2022). "Mid-Cretaceous marine Os isotope evidence for heterogeneous cause of oceanic anoxic events". Nature Communications . 13 (1): 239. Bibcode:2022NatCo..13..239M. doi:10.1038/s41467-021-27817-0. PMC   8752794 . PMID   35017487 . Retrieved 13 June 2023.
  7. ↑ Erbacher, Jochen; Thurow, J. (March 1997). "Influence of oceanic anoxic events on the evolution of mid-Cretaceous radiolaria in the North Atlantic and western Tethys" . Marine Micropaleontology. 30 (1–3): 139–158. doi:10.1016/S0377-8398(96)00023-0 . Retrieved 14 June 2023.
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