Mid-Cenomanian Event

Short description: Oceanic anoxic event during the middle Cenomanian

The Mid-Cenomanian Event (MCE) was an oceanic anoxic event that took place during the middle Cenomanian, as its name suggests, around 96.5 Ma.[1]

## Contents

* 1 Timing
* 2 Causes
* 3 Effects
* 4 See also
* 5 References

## Timing

Approximately 400 kyr before the MCE occurred a major negative δ13C excursion.[2] Geochronological analysis of the Iona-1 core from the Eagle Ford Group of Texas shows the MCE lasted from 96.57 ± 0.12 Ma to 96.36 ± 0.12 Ma.[3] A positive δ13C excursion of a rather small magnitude (1%) defines the MCE.[4][5] The MCE δ13C excursion had two pulses, designated MCE Ia and MCE Ib, respectively.[6] The magnitude of MCE Ib's δ13C shift was greater than MCE Ia's.[7]

## Causes

Orbital forcing is considered the chief cause of the MCE by many scientists. It is believed that the MCE occurred during the simultaneous occurrence of nodes in the obliquity, orbital eccentricity, and axial precession Milankovitch cycles. A coincidence in all three nodes would occur once every 2.45 Myr, a timeframe consistent with the occurrence of the Cenomanian-Turonian boundary event (OAE2) about 2.4 Myr after the MCE.[8] Within the MCE, a 10,784 year anoxia cycle, governed by 80–100 yr, 200–230 yr, 350–500 yr, ~1650 yr, and 4843 yr cycles, can be detected by examining the timing of various miscellaneous biogeochemical fluctuations, revealing that a pattern of variability in solar irradiance reminiscent to that observed during the Holocene governed geobiological events of a smaller timeframe and their geological expression within the MCE.[1]

A second hypothesis postulates volcanic activity from a large igneous province (LIP) as the MCE's main cause. Various LIPs have been held responsible for initiating the MCE, including the High Arctic Large Igneous Province (HALIP), the Caribbean Large Igneous Province (CLIP), the Madagascar Large Igneous Province, and the Ontong-Java Plateau. Both overall concentrations of mercury and ratios of mercury to total organic carbon increased during the MCE interval, suggesting volcanism played a major role in the development of MCE anoxia.[9] The absence of unradiogenic osmium enrichments during the MCE interval has been invoked as evidence against a volcanic cause, on the other hand.[10]

## Effects

The carbon cycle perturbation associated with the MCE was not intense enough to cause a major extinction event, as was the case with the much more severe disturbance that led to OAE2.[11] Nevertheless, many marine creatures underwent noticeable declines and turnovers, particularly calcitic benthos.[12]

A change in ammonoid composition and abundance has been observed across the MCE. Up until MCE Ia, planispiral ammonoids, in particular the genus Schloenbachia, dominated the waters of the Vocontian Basin. During and after MCE Ib, heteromorph ammonoids, especially Sciponoceras, predominated.[13]

A pronounced turnover among calcareous nannofossils ensued in equatorial waters over the MCE's duration. Prior to the MCE, the nannofossil Biscutum constans was very abundant thanks to high nutrient availability in the upper parts of the photic zone. During the MCE, Rhagodiscus asper decreased in relative abundance. After the MCE, taxa that preferred less eutrophic surficial waters, such as Eprolithus floralis, became more abundant.[14]

Foraminiferal abundance was tied to the 100 kyr eccentricity cycle. During the middle to upper parts of this cycle, planktic foraminifera increased in abundance. Blooms of Gavelinella reussi and G. berthelini were typical of the upper parts of the cycle. The common occurrence of plano-convex Rotalipora characterised the eccentricity cycle's lows.[11] The long eccentricity cycle governed the influx of Boreal Ocean foraminifera into the much warmer Tethys Ocean.[15]

## See also

* Selli Event
* Paquier Event
* Amadeus Event
* Breistroffer Event

## References

1. ↑ 1.0 1.1 Ma, Chao; Hinnov, Linda A.; Eldrett, James S.; Meyers, Stephen R.; Bergman, Steven C.; Minisini, Daniel; Lutz, Brendan (9 November 2021). "Centennial to millennial variability of greenhouse climate across the mid-Cenomanian event". Geology 50 (2): 227–231. doi:10.1130/G48734.1.
2. ↑ Coccioni, Rodolfo; Galeotti, Simone (15 January 2003). "The mid-Cenomanian Event: prelude to OAE 2". Palaeogeography, Palaeoclimatology, Palaeoecology 190: 427–440. doi:10.1016/S0031-0182(02)00617-X. Bibcode: 2003PPP...190..427C. https://www.researchgate.net/publication/223718129. Retrieved 22 January 2023.
3. ↑ Eldrett, James S.; Ma, Chao; Bergman, Steven C.; Lutz, Brendan; Gregory, F. John; Dodsworth, Paul; Phipps, Mark; Hardas, Petros et al. (September–December 2015). "An astronomically calibrated stratigraphy of the Cenomanian, Turonian and earliest Coniacian from the Cretaceous Western Interior Seaway, USA: Implications for global chronostratigraphy". Cretaceous Research 56: 316–344. doi:10.1016/j.cretres.2015.04.010. https://www.sciencedirect.com/science/article/abs/pii/S0195667115000622. Retrieved 13 June 2023.
4. ↑ Paul, C. R. C.; Mitchell, S. F.; Marshall, J. D.; Leafy, P. N.; Gale, A. S.; Duane, A. M.; Ditchfield, P. W. (December 1994). "Palaeoceanographic events in the Middle Cenomanian of Northwest Europe". Cretaceous Research 15 (6): 707–738. doi:10.1006/cres.1994.1039. https://www.sciencedirect.com/science/article/abs/pii/S0195667184710391. Retrieved 12 June 2023.
5. ↑ Asadi Mehmandsoti, Elham; Asadi, Ahmad; Daneshian, Jahanbakhsh; Woods, Adam D.; Loyd, Sean J. (15 September 2021). "Evidence of Mid-Cretaceous carbon cycle perturbations and OAE2 recorded in Cenomanian to middle Campanian carbonates of the Zagros fold–thrust belt basin, Iran". Journal of Asian Earth Sciences 218. doi:10.1016/j.jseaes.2021.104863. ISSN 1367-9120. https://www.sciencedirect.com/science/article/pii/S1367912021002017. Retrieved 26 September 2023.
6. ↑ Andrieu, Simon; Brigaud, Benjamin; Rabourg, Thomas; Noret, Aurélie (September–December 2015). "The Mid-Cenomanian Event in shallow marine environments: Influence on carbonate producers and depositional sequences (northern Aquitaine Basin, France)". Cretaceous Research 56: 587–607. doi:10.1016/j.cretres.2015.06.018. https://www.sciencedirect.com/science/article/abs/pii/S0195667115300215. Retrieved 12 June 2023.
7. ↑ Hennhoefer, Dominik; Al-Suwaidi, Aisha; Bottini, Cinzia; Helja, Emina; Steuber, Thomas (16 May 2018). "The Albian to Turonian carbon isotope record from the Shilaif Basin (United Arab Emirates) and its regional and intercontinental correlation". Sedimentology 66 (2): 536–555. doi:10.1111/sed.12493. https://onlinelibrary.wiley.com/doi/abs/10.1111/sed.12493. Retrieved 13 June 2023.
8. ↑ Mitchell, Ross N.; Bice, David M.; Montanari, Alessandro; Cleaveland, Laura C.; Christianson, Keith T.; Coccioni, Rodolfo; Hinnov, Linda A. (1 March 2008). "Oceanic anoxic cycles? Orbital prelude to the Bonarelli Level (OAE 2)". Earth and Planetary Science Letters 267 (1–2): 1–16. doi:10.1016/j.epsl.2007.11.026. Bibcode: 2008E&PSL.267....1M. https://www.sciencedirect.com/science/article/abs/pii/S0012821X07007546. Retrieved 2 January 2023.
9. ↑ Scaife, J. D.; Ruhl, Micha; Dickson, Alexander J.; Mather, Tamsin A.; Jenkyns, Hugh C.; Percival, Lawrence M. E.; Hesselbo, Stephen C.; Cartwright, J. et al. (1 November 2017). "Sedimentary Mercury Enrichments as a Marker for Submarine Large Igneous Province Volcanism? Evidence From the Mid-Cenomanian Event and Oceanic Anoxic Event 2 (Late Cretaceous)". Geochemistry, Geophysics, Geosystems 18 (12): 4253–4275. doi:10.1002/2017GC007153.
10. ↑ Nana Yobo, L.; Brandon, A. D.; Lauckner, L. M.; Eldrett, J. S.; Bergman, S. C.; Minisini, Daniel (21 September 2022). "Enhanced continental weathering activity at the onset of the mid-Cenomanian Event (MCE)". Geochemical Perspectives Letters 23: 17–22. doi:10.7185/geochemlet.2231. https://www.geochemicalperspectivesletters.org/article2231/. Retrieved 14 June 2023.
11. ↑ 11.0 11.1 Mitchell, S. F.; Carr, I. T. (February 1998). "Foraminiferal response to mid-Cenomanian (Upper Cretaceous) palaeoceanographic events in the Anglo-Paris Basin (Northwest Europe)". Palaeogeography, Palaeoclimatology, Palaeoecology 137 (1–2): 103–125. doi:10.1016/S0031-0182(97)00087-4. https://www.sciencedirect.com/science/article/abs/pii/S0031018297000874. Retrieved 14 June 2023.
12. ↑ Rodriguez-Lázaro, Julio; Pascual, Ana; Elorza, Javier (December 1998). "Cenomanian events in the deep western Basque Basin: the Leioa section". Cretaceous Research 19 (6): 673–700. doi:10.1006/cres.1998.0125. ISSN 0195-6671. https://www.sciencedirect.com/science/article/pii/S0195667198901252. Retrieved 26 September 2023.
13. ↑ Giraud, Fabienne; Reboulet, Stéphane; Deconinck, Jean François; Martinez, Mathieu; Carpentier, André; Bréziat, Clément (November 2013). "The Mid-Cenomanian Event in southeastern France: Evidence from palaeontological and clay mineralogical data". Cretaceous Research 46: 43–58. doi:10.1016/j.cretres.2013.09.004. https://www.sciencedirect.com/science/article/abs/pii/S0195667113001353. Retrieved 12 June 2023.
14. ↑ Hardas, Petros; Mutterlose, Jörg; Friedrich, Oliver; Erbacher, Jochen (December 2012). "The Middle Cenomanian Event in the equatorial Atlantic: The calcareous nannofossil and benthic foraminiferal response". Marine Micropaleontology 96-97: 66–74. doi:10.1016/j.marmicro.2012.08.003. https://www.sciencedirect.com/science/article/abs/pii/S0377839812000849. Retrieved 12 June 2023.
15. ↑ Petrizzo, Maria Rose; Gale, Andy S. (28 November 2022). "Planktonic foraminifera document palaeoceanographic changes across the middle Cenomanian carbon-isotope excursion MCE 1: new evidence from the UK chalk". Geological Magazine 160 (2): 372–392. doi:10.1017/S0016756822000991. https://www.cambridge.org/core/journals/geological-magazine/article/planktonic-foraminifera-document-palaeoceanographic-changes-across-the-middle-cenomanian-carbonisotope-excursion-mce-1-new-evidence-from-the-uk-chalk/12CC74F3C1F850A012333CC8C1318FA7. Retrieved 14 June 2023.

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