by | Sep 21, 2022 | mainpost, vol23

Enhanced continental weathering activity at the onset of the mid-Cenomanian Event (MCE)

L. Nana Yobo1,

1Department of Geology and Geophysics, Texas A&M University, College Station, TX, USA

A.D. Brandon2,

2Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA

L.M. Lauckner1,2,

1Department of Geology and Geophysics, Texas A&M University, College Station, TX, USA
2Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX, USA

J.S. Eldrett3,

3Shell Global Solutions International B.V., Lange Kleiweg 40, 2288 GK Rijswijk, Netherlands

S.C. Bergman4,a,

4Shell Technological Center, Houston, TX, USA
aPresent address: SCB GeoSciences, Vashon, WA, USA

D. Minisini4,5

4Shell Technological Center, Houston, TX, USA
5Department of Earth, Environmental & Planetary Sciences, Rice University, Houston, TX, USA

Affiliations | Corresponding Author | Cite as | Funding information

Geochemical Perspectives Letters v23 | https://doi.org/10.7185/geochemlet.2231
Received 10 May 2022 | Accepted 29 August 2022 | Published 21 September 2022

Copyright © 2022 The Authors

Published by the European Association of Geochemistry
under Creative Commons License CC BY-NC-ND 4.0

Keywords: mid-Cenomanian, anoxia, weathering, hydrothermal, OAE, osmium isotopes


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Abstract

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information

The emplacement of a Large Igneous Province (LIP) is implicated in the triggering of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE 2). Evidence for a similar initiation mechanism for the mid-Cenomanian Event (MCE) is unclear. In this study, a reconstruction of mid-Cenomanian seawater 187Os/188Os, the first for the Western Interior Seaway, tests the competing roles of LIP versus continental weathering activity in triggering the MCE. The absence of a prolonged unradiogenic Os isotope excursion (low 187Os/188Os) at the onset of the MCE interval argues against LIP involvement in the event’s initiation. Rather, more radiogenic 187Os/188Os at the onset, that continues to rise to the middle of the MCE, indicates that the event was triggered by increased continental weathering. The combination of decreasing 187Os/188Os from the middle of the MCE onward, coincident with a 40Ar/39Ar age of 96.4 Ma of basalts from Ellesmere Island, Canada, is consistent with High Arctic LIP-related volcanic activity that may have contributed to the end of the MCE. These new data on the MCE thus indicate that LIP activity is not always the trigger for carbon cycle perturbation and associated climate change.

Figures and Tables

Figure 1 Comparison of the MCE interval from Iona-1 core with sections from Pueblo and Folkestone. Iona-1 core: δ13C data after Eldrett et al. (2015) and Sweere et al. (2020); biostratigraphic markers and astronomically tuned age model with ages plotted after Eldrett et al. (2015). Pueblo section: 40Ar/39Ar and astronomic ages assigned to the Thatcher bentonite after Batenburg et al. (2016). Folkestone Lydden Spout section: δ13C from Abbot’s cliff section after Paul et al. (1994). Occurrence of planktonic foraminifera R. cushmani after Moghadam and Paul (2000). A second Folkestone section is also plotted from Gale et al. (2008). Dual positive δ13C excursions shaded (MCE 1a and 1b) with a possible phase of initiation (init.).

Figure 2 Palaeogeographic reconstruction of the WIS during the early Turonian showing the location of the Iona-1 core. Modified from Eldrett et al. (2015).

Figure 3 Stratigraphic profile of Osi and C isotope ratios from the MCE interval of the Iona-1 core of West Texas. δ13Corg from Eldrett et al. (2015) and Sweere et al. (2020), Osi and 192Os (this study), Hg concentrations (Sweere et al., 2020). The Osi response is divided into four segments: I, II, III and IV. See text for discussion.

Table 1 Raw measured 187Re/188Os and 187Os/188Os measurements from the MCE interval of the Iona-1 core. Also shown is the calculated Osi values and the Re and 192Os concentrations. *From Sullivan et al. (2020).

Figure 1 Figure 2 Figure 3 Table 1

View all figures and tables





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Introduction

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information


The Mesozoic was characterised by periods of marine anoxia and disruption of the global carbon cycle, termed oceanic anoxic events (OAEs, see Jenkyns, 2010

Jenkyns, H.C. (2010) Geochemistry of oceanic anoxic events. Geochemistry, Geophysics, Geosystems 11, Q03004. https://doi.org/10.1029/2009GC002788

). These periods represent intervals when organic carbon was buried in sediments under oxygen deficient bottom waters, most notably the Cenomanian–Turonian OAE 2 (ca. 94.5 Ma) and Aptian OAE 1a (ca. 124 Ma) (Jenkyns, 2010

Jenkyns, H.C. (2010) Geochemistry of oceanic anoxic events. Geochemistry, Geophysics, Geosystems 11, Q03004. https://doi.org/10.1029/2009GC002788

). Another such event, the mid-Cenomanian Event (MCE) occurring just before OAE 2 (ca. 96.5 Ma), is often referred to as a precursor to OAE 2 (Coccioni and Galeotti, 2003

Coccioni, R., Galeotti, S. (2003) The mid-Cenomanian Event: prelude to OAE 2. Palaeogeography, Palaeoclimatology, Palaeoecology 190, 427–440. https://doi.org/10.1016/S0031-0182(02)00617-X

). Since the first description of the MCE by Paul et al. (1994)

Paul, C.R.C., Mitchell, S.F., Marshall, J.D., Leary, P.N., Gale, A.S., Duane, A.M., Ditchfield, P.W. (1994) Paleoceanographic events in the Middle Cenomanian of Northwest Europe. Cretaceous Research 15, 707–738. https://doi.org/10.1006/cres.1994.1039

, it has remained one of the least studied carbon cycle perturbations. Understanding the change in the biogeochemical processes that set the stage for the onset of the MCE provides insights on the conditions that led to the global expansion of marine anoxia during OAE 2. This is because the MCE is interpreted to signify the onset of major oceanic and climatic reorganisation that ultimately led to OAE 2 (Coccioni and Galeotti, 2003

Coccioni, R., Galeotti, S. (2003) The mid-Cenomanian Event: prelude to OAE 2. Palaeogeography, Palaeoclimatology, Palaeoecology 190, 427–440. https://doi.org/10.1016/S0031-0182(02)00617-X

).

Like OAE 2, the MCE is recognisable by a positive δ13C excursion of 1–2 ‰ (Fig. 1) and recognised globally (see summary in Beil et al., 2018

Beil, S., Kuhnt, W., Holbourn, A.E., Arquit, M., Flogel, S., Chellai, E.H., Jabour, H. (2018) New insights into Cenomanian paleoceanography and climate evolution from the Tarfaya Basin, southern Morocco. Cretaceous Research 84, 451–473. https://doi.org/10.1016/j.cretres.2017.11.006

, and Supplementary Information for additional discussion). Unlike OAE 2 that lasted ∼700–1100 kyr (Jones et al., 2021

Jones, M.M., Sageman, B.B., Selby, D., Jicha, B.R., Singer, B.S., Titus, A.L. (2021) Regional chronostratigraphic synthesis of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) interval, Western Interior Basin (USA): New Re-Os chemostratigraphy and 40Ar/39Ar geochronology. GSA Bulletin 133, 1090–1104. https://doi.org/10.1130/B35594.1

), the MCE was shorter-lived (Fig. 1; ∼150–400 kyr; Eldrett et al., 2015

Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

). Extensive organic matter preservation was less pervasive than during OAE2, with black shale deposition occurring in fewer basins (Coccioni and Galeotti, 2003

Coccioni, R., Galeotti, S. (2003) The mid-Cenomanian Event: prelude to OAE 2. Palaeogeography, Palaeoclimatology, Palaeoecology 190, 427–440. https://doi.org/10.1016/S0031-0182(02)00617-X

; Friedrich et al., 2009

Friedrich, O., Erbacher, J., Wilson, P.A., Moriya, K., Mutterlose, J. (2009) Paleoenvironmental changes across the Mid Cenomanian Event in the tropical Atlantic Ocean (Demerara Rise, ODP Leg 207) inferred from benthic foraminiferal assemblages. Marine Micropaleontology 71, 28–40. https://doi.org/10.1016/j.marmicro.2009.01.002

). Although no two carbon cycle perturbations are the same, many of the local expressions of the global event are observed to be identical (see Jenkyns, 2010

Jenkyns, H.C. (2010) Geochemistry of oceanic anoxic events. Geochemistry, Geophysics, Geosystems 11, Q03004. https://doi.org/10.1029/2009GC002788

). Moreover, because of the unusually high productivity and excess organic carbon burial, coupled with the close proximity in time and associated development of anoxia during the MCE and OAE 2, they are thought to have been triggered by a similar mechanism (e.g., Beil et al., 2018

Beil, S., Kuhnt, W., Holbourn, A.E., Arquit, M., Flogel, S., Chellai, E.H., Jabour, H. (2018) New insights into Cenomanian paleoceanography and climate evolution from the Tarfaya Basin, southern Morocco. Cretaceous Research 84, 451–473. https://doi.org/10.1016/j.cretres.2017.11.006

). Notably, increased magmatic activity from LIP eruptions are favoured to have triggered the onset of OAE 2 (Turgeon and Creaser, 2008

Turgeon, S.C., Creaser, R.A. (2008) Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode. Nature 454, 323–326. https://doi.org/10.1038/nature07076

), OAE 1a and other OAEs (Bergman et al., 2021

Bergman, S.C., Eldrett, J.S., Minisini, D. (2021) Phanerozoic Large Igneous Province, Petroleum System, and Source Rock Links. In: Ernst, R.E., Dickson, A.J., Bekker, A. (Eds.) Large Igneous Provinces. A Driver of Global Environmental and Biotic Changes. Geophysical Monograph 255, John Wiley & Sons, Inc., Hoboken, NJ, and American Geophysical Union, Washington, D.C., 191–228. https://doi.org/10.1002/9781119507444.ch9

). However, unlike OAE 2, where there is consensus on LIP emplacement as a trigger (e.g., Turgeon and Creaser 2008

Turgeon, S.C., Creaser, R.A. (2008) Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode. Nature 454, 323–326. https://doi.org/10.1038/nature07076

; Du Vivier et al., 2014

Du Vivier, A.D.C., Selby, D., Sageman, B.B., Jarvis, I., Gröcke, D.R., Voigt, S. (2014) Marine 187Os/188Os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during Oceanic Anoxic Event 2. Earth and Planetary Science Letters 389, 23–33. https://doi.org/10.1016/j.epsl.2013.12.024

; Sullivan et al., 2020

Sullivan, D.L., Brandon, A.D., Eldrett, J., Bergman, S.C., Wright, S., Minisini, D. (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2). Geochimica et Cosmochimica Acta 285, 257–273. https://doi.org/10.1016/j.gca.2020.04.002

; Nana Yobo et al., 2021

Nana Yobo, L., Brandon, A.D., Holmden, C., Lau, K.V., Eldrett, J. (2021) Changing inputs of continental and submarine weathering sources of Sr to the oceans during OAE 2. Geochimica et Cosmochimica Acta 303, 205–225. https://doi.org/10.1016/j.gca.2021.03.013

), proxy evidence for a direct and causal link between LIP activity during the MCE or significant weathering are limited. Attempts thus far to understand ocean conditions at the onset of the MCE are drawn from reconstruction of seawater ɛNd (Zheng et al., 2016

Zheng, X-Y., Jenkyns, H.C., Gale, A.S., Ward, D.J., Henderson, G.M. (2016) A climatic control on reorganization of ocean circulation during the mid-Cenomanian event and Cenomanian-Turonian oceanic anoxic event (OAE 2): Nd isotope evidence. Geology 44, 151–154. https://doi.org/10.1130/G37354.1

). This can be challenging due to the short residence time of Nd (100–1000 years; Siddall et al., 2008

Siddall, M., Khatiwala, S., van de Flierdt, T., Jones, K., Goldstein, S.L., Hemming, S., Anderson, R.F. (2008) Towards explaining the Nd paradox using reversible scavenging in an ocean general circulation model. Earth and Planetary Science Letters 274, 448–461. https://doi.org/10.1016/j.epsl.2008.07.044

) relative to the global ocean mixing time (1000–2000 years). Thus ɛNd variation may represent regional rather than global seawater trends. On the other hand, δ18O records from various sites globally garner opposing interpretations for cooling (Voigt et al., 2004

Voigt, S., Gale, A.S., Flögel, S. (2004) Midlatitude shelf seas in the Cenomanian-Turonian greenhouse world: Temperature evolution and North Atlantic circulation. Paleoceanography and Paleoclimatology 19, PA4020. https://doi.org/10.1029/2004PA001015

) and against cooling (Ando et al., 2009

Ando, A., Huber, B.T., MacLeod, K.G., Ohta, T., Khim, B.-K. (2009) Blake Nose stable isotopic evidence against the mid-Cenomanian glaciation hypothesis. Geology 37, 451–454. https://doi.org/10.1130/G25580A.1

). Conversely, peak enrichment of Hg concentrations during the MCE indicate that volcanic activity may have sustained part of the event, albeit not at the onset (Scaife et al., 2017

Scaife, J.D., Ruhl, M., Dickson, A.J., Mather, T.A., Jenkyns, H.C., Percival, L.M.E., Hesselbo, S.P., Cartwright, J., Eldrett, J.S., Bergman, S.C., Minisini, D. (2017) Sedimentary Mercury Enrichments as a Marker for Large Igneous Province Volcanism: Evidence from the Mid-Cenomanian Event and Ocean Anoxic Event 2 (Late Cretaceous). Geochemistry, Geophysics, Geosystems 18, 4253–4275. https://doi.org/10.1002/2017GC007153

). These different proxies thus provide different interpretations on whether increased volcanic activity, consistent with other OAEs, and/or enhanced weathering contributed the MCE. To examine this issue further, new Re-Os isotope systematics of the MCE in the Iona-1 core from present day SW Texas, USA (Fig. 2), are presented using 187Os/188Os initial values (Osi) as a proxy for mantle-derived LIP magmatism. This study represents the first attempt to examine the causal mechanisms for the onset of the MCE by constraining the timing of volcanic activity and/or fluctuations in weathering activity during the event.


Figure 1 Comparison of the MCE interval from Iona-1 core with sections from Pueblo and Folkestone. Iona-1 core: δ13C data after Eldrett et al. (2015)

Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

and Sweere et al. (2020)

Sweere, T.C., Dickson, A.J., Jenkyns, H.C., Porcelli, D., Ruhl, M., Murphy, M.J., Idiz, E., van den Boorn, S.H.J.M., Eldrett, J.S., Henderson, G.M. (2020) Controls on the Cd-isotope composition of Upper Cretaceous (Cenomanian–Turonian) organic-rich mudrocks from south Texas (Eagle Ford Group). Geochimica et Cosmochimica Acta 287, 251–262. https://doi.org/10.1016/j.gca.2020.02.019

; biostratigraphic markers and astronomically tuned age model with ages plotted after Eldrett et al. (2015)

Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

. Pueblo section: 40Ar/39Ar and astronomic ages assigned to the Thatcher bentonite after Batenburg et al. (2016)

Batenburg, S.J., De Vleeschouwer, D., Sprovieri, M., Hilgen, F.J., Gale, A.S., Singer, B.S., Koeberl, C., Coccioni, R., Claeys, P., Montanari, A. (2016) Orbital control on the timing of oceanic anoxia in the Late Cretaceous. Climate of the Past 12, 1995–2009. https://doi.org/10.5194/cp-12-1995-2016

. Folkestone Lydden Spout section: δ13C from Abbot’s cliff section after Paul et al. (1994)

Paul, C.R.C., Mitchell, S.F., Marshall, J.D., Leary, P.N., Gale, A.S., Duane, A.M., Ditchfield, P.W. (1994) Paleoceanographic events in the Middle Cenomanian of Northwest Europe. Cretaceous Research 15, 707–738. https://doi.org/10.1006/cres.1994.1039

. Occurrence of planktonic foraminifera R. cushmani after Moghadam and Paul (2000)

Moghadam, H.V., Paul, C.R.C. (2000) Micropalaeontology of the Cenomanian at Chinnor, Oxfordshire, and comparison with the Dover-Folkestone succession. Proceedings of the Geologists’ Association 111, 17–39. https://doi.org/10.1016/S0016-7878(00)80034-6

. A second Folkestone section is also plotted from Gale et al. (2008)

Gale, A.S., Voigt, S., Sageman, B.B., Kennedy, W.J. (2008) Eustatic sea-level record for the Cenomanian (Late Cretaceous)—Extension to the Western Interior Basin, USA. Geology 36, 859–862. https://doi.org/10.1130/G24838A.1

. Dual positive δ13C excursions shaded (MCE 1a and 1b) with a possible phase of initiation (init.).
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Figure 2 Palaeogeographic reconstruction of the WIS during the early Turonian showing the location of the Iona-1 core. Modified from Eldrett et al. (2015)

Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

.
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Results

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information


The Osi ratios are listed in Table 1 and shown in Figure 3. The Os isotope response during the MCE shows a rise prior to and within the onset of the event to more radiogenic Osi during MCE with a peak in values in the middle followed by a decrease to the end of the event. The Osi can be divided into four segments, I-II-III-IV moving up section, based on the carbon isotope excursion (CIE): pre-MCE (I), MCE 1a (II), MCE 1b (III) and post-MCE carbon isotope excursion (IV). Prior to the carbon isotope excursion that marks the onset MCE, Osi values range between 0.8–0.9, similar to previous estimates of pre-OAE2 Osi background values for the WIS (Du Vivier et al., 2014

Du Vivier, A.D.C., Selby, D., Sageman, B.B., Jarvis, I., Gröcke, D.R., Voigt, S. (2014) Marine 187Os/188Os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during Oceanic Anoxic Event 2. Earth and Planetary Science Letters 389, 23–33. https://doi.org/10.1016/j.epsl.2013.12.024

; Jones et al., 2021

Jones, M.M., Sageman, B.B., Selby, D., Jicha, B.R., Singer, B.S., Titus, A.L. (2021) Regional chronostratigraphic synthesis of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) interval, Western Interior Basin (USA): New Re-Os chemostratigraphy and 40Ar/39Ar geochronology. GSA Bulletin 133, 1090–1104. https://doi.org/10.1130/B35594.1

; Sullivan et al., 2020

Sullivan, D.L., Brandon, A.D., Eldrett, J., Bergman, S.C., Wright, S., Minisini, D. (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2). Geochimica et Cosmochimica Acta 285, 257–273. https://doi.org/10.1016/j.gca.2020.04.002

). During the segment I (possibly initiation phase of MCE at 144 m), the Osi values start a shift to more radiogenic values. This increase continues through segment II (which is coincident with the onset of MCE 1a at 142.8 m) up to a peak value of 1.26. After this point (segment III), the Osi begins a gradual decline from 1.26 to 0.65 at 139.86 m. This Osi minima in MCE is coincident with the onset MCE 1b (139.9 m). After the peak CIE in MCE 1b, the Osi values then start to increase. The increase/relaxation continues after the termination of the MCE at 139.27 m, to a new Osi background value of ∼0.9–1 in segment IV.

Table 1 Raw measured 187Re/188Os and 187Os/188Os measurements from the MCE interval of the Iona-1 core. Also shown is the calculated Osi values and the Re and 192Os concentrations.

Depth
(m)		AgeRe
(ppb)		±2σ192Os
(ppt)		Os
(ppt)		±2σ187Os/188Os
measured		±2σ187Re/188Os±2σ187Os/188Os
initial		±2σ
135.2596.1519.230.0614580.605.260.07268925.570.950.05
136.1496.19182.540.471425635.105.010.05255514.100.910.07
137.3196.2543.630.12361421.084.860.04240118.321.000.07
137.8596.28179.450.461295286.535.440.09277526.100.980.13
138.6596.32214.320.612007573.644.430.0121306.801.010.03
138.6596.32217.800.632007553.704.440.0221727.140.950.03
139.2796.3628.330.08281020.864.060.04201719.560.820.07
139.8696.39176.870.461866645.063.680.0318789.450.660.05
139.86*96.39318.002399605.2027370.800.02
140.3996.42159.670.401505622.544.360.0121256.610.940.02
141.1596.45234.120.681897513.865.070.0224718.561.100.03
141.7796.4823.290.0619760.825.210.06245315.701.260.08
141.77*96.4824.0018735.5427401.130.05
142.2796.50145.650.351184703.235.030.03244710.171.090.05
142.4196.51134.591.461214591.994.510.01222224.290.940.05
142.7196.52154.240.191144682.495.460.0226928.221.120.03
142.9496.53186.192.031596132.694.660.01233025.470.910.05
143.3796.56202.790.552067533.604.050.0119626.450.890.02
143.7396.619.710.1113440.343.180.03148518.720.790.06
145.7596.67183.590.4520485411.145.730.10297515.000.930.12
146.4696.70398.071.10238103811.916.280.08333025.510.910.12

*From Sullivan et al. (2020)Sullivan, D.L., Brandon, A.D., Eldrett, J., Bergman, S.C., Wright, S., Minisini, D. (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2). Geochimica et Cosmochimica Acta 285, 257–273. https://doi.org/10.1016/j.gca.2020.04.002.




Figure 3 Stratigraphic profile of Osi and C isotope ratios from the MCE interval of the Iona-1 core of West Texas. δ13Corg from Eldrett et al. (2015)

Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

and Sweere et al. (2020)

Sweere, T.C., Dickson, A.J., Jenkyns, H.C., Porcelli, D., Ruhl, M., Murphy, M.J., Idiz, E., van den Boorn, S.H.J.M., Eldrett, J.S., Henderson, G.M. (2020) Controls on the Cd-isotope composition of Upper Cretaceous (Cenomanian–Turonian) organic-rich mudrocks from south Texas (Eagle Ford Group). Geochimica et Cosmochimica Acta 287, 251–262. https://doi.org/10.1016/j.gca.2020.02.019

, Osi and 192Os (this study), Hg concentrations (Sweere et al., 2020

Sweere, T.C., Dickson, A.J., Jenkyns, H.C., Porcelli, D., Ruhl, M., Murphy, M.J., Idiz, E., van den Boorn, S.H.J.M., Eldrett, J.S., Henderson, G.M. (2020) Controls on the Cd-isotope composition of Upper Cretaceous (Cenomanian–Turonian) organic-rich mudrocks from south Texas (Eagle Ford Group). Geochimica et Cosmochimica Acta 287, 251–262. https://doi.org/10.1016/j.gca.2020.02.019

). The Osi response is divided into four segments: I, II, III and IV. See text for discussion.
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Discussion

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information


The marine Os isotope composition of seawater reflects the relative mass balance of continental crust (187Os/188Os ≈ 1.4) versus mantle-derived basaltic magma/LIP (187Os/188Os ≈ 0.13) inputs into the oceans (Peucker-Ehrenbrink and Ravizza, 2000

Peucker‐Ehrenbrink, B., Ravizza, G. (2000) The marine osmium isotope record. Terra Nova 12, 205–219. https://doi.org/10.1046/j.1365-3121.2000.00295.x

). The seawater 187Os/188Os is used to assess the competing influence of LIP activity and continental weathering at the different stages during MCE. The residence time of Os (∼104 years; Peucker-Ehrenbrink and Ravizza, 2000

Peucker‐Ehrenbrink, B., Ravizza, G. (2000) The marine osmium isotope record. Terra Nova 12, 205–219. https://doi.org/10.1046/j.1365-3121.2000.00295.x

) is longer than the ∼1000 year mixing time of the ocean and allows for a well-mixed ocean. This means that fluctuations in the global seawater Os isotope record are likely preserved in marine sediments and localised variations are minimised.

Iona-1 MCE 187Os/188Os. The Os isotope signature during the MCE in the Iona-1 core indicates that the event was initiated by increased continental weathering, evidenced by the increased supply of radiogenic Os (Fig. 3). This increased supply of radiogenic Os began about 90 kyr before the CIE that marks the onset of MCE 1a interval. This is inconsistent with increased LIP activity as triggering the initiation of the MCE. This is opposite to OAE 2 with respect to the Os proxy response, despite having similar CIE responses. Further support for increased weathering activity at the onset of the MCE comes from the Aquitaine Basin in France, where the presence of clay mineral assemblages (smectite) has been interpreted as possible evidence for weathering of submarine volcanic materials (Giraud et al., 2013

Giraud, F., Reboulet, S., Deconinck, J.F., Martinez, M., Carpentier, A., Bréziat, C. (2013) The Mid-Cenomanian Event in southeastern France: Evidence from paleontological and clay mineralogical data. Cretaceous Research 46, 43–58. https://doi.org/10.1016/j.cretres.2013.09.004

). Additional support of increased weathering is recorded in the ɛNd profile from the Folkstone, UK section, which has a negative excursion likely reflecting increased flux from the surrounding Precambrian continental rocks that have been shown to have lower ɛNd values (Zheng et al., 2016

Zheng, X-Y., Jenkyns, H.C., Gale, A.S., Ward, D.J., Henderson, G.M. (2016) A climatic control on reorganization of ocean circulation during the mid-Cenomanian event and Cenomanian-Turonian oceanic anoxic event (OAE 2): Nd isotope evidence. Geology 44, 151–154. https://doi.org/10.1130/G37354.1

).

After the increase in Osi recorded in segment II, it then follows a gradual decrease towards more unradiogenic values, signifying a shift in the balance of Os sourcing into the ocean. This shift to more unradiogenic Osi can be interpreted in three scenarios: 1 - decreased continental weathering, 2 - increased basaltic magmatism, and 3 - a large meteoric impact. Scenario 3 is ruled out because a significant increase in HSE (Os, Ir, Ru, Pt, Pd, Re), or changes in their chondrite-normalised patterns from continental crust-like to flatter slopes, fingerprinting increased extraterrestrial flux, is not recorded here (Table S-1, Fig. S-1) or in other locations during this interval (Farley et al., 2012

Farley, K.A., Montanari, A., Coccioni, R. (2012) A record of the extraterrestrial 3He flux through the Late Cretaceous. Geochimica et Cosmochimica Acta 84, 314–328. https://doi.org/10.1016/j.gca.2012.01.015

). A decreased weathering rate (Scenario 1) would result in decreased supply of radiogenic Os into the ocean. Alternatively, the rate of weathering may stay constant but outpaced by increased supply of unradiogenic Os such as from the High Arctic LIP (HALIP) in support of Scenario 2. Geochronology data, including a 40Ar/39Ar age of 96.4 ± 1.6 Ma (Estrada, 2015

Estrada, S. (2015) Geochemical and Sr–Nd isotope variations within Cretaceous continental flood-basalt suites of the Canadian High Arctic, with a focus on the Hassel Formation basalts of northeast Ellesmere Island. International Journal of Earth Sciences 104, 1981–2005. https://doi.org/10.1007/s00531-014-1066-x

) shows that the HALIP was active around the time of the MCE and thus may have been the source of the gradual decline of Osi observed. If increased magmatic activity from LIP eruptions were responsible for the shift to unradiogenic Os, a consequent spike in 192Os concentrations can be expected, similar to the spikes of magmatic activity recorded during OAE 2 in the Iona-1 core and elsewhere (see Sullivan et al., 2020

Sullivan, D.L., Brandon, A.D., Eldrett, J., Bergman, S.C., Wright, S., Minisini, D. (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2). Geochimica et Cosmochimica Acta 285, 257–273. https://doi.org/10.1016/j.gca.2020.04.002

). Consistent with Sullivan et al. (2020)

Sullivan, D.L., Brandon, A.D., Eldrett, J., Bergman, S.C., Wright, S., Minisini, D. (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2). Geochimica et Cosmochimica Acta 285, 257–273. https://doi.org/10.1016/j.gca.2020.04.002

, 192Os normalised to TOC is used rather than total Os abundance. This ratio thus represents the unradiogenic Os concentrations from sample to sample that are independent of ingrowth of radiogenic 187Os. This ingrowth since deposition can result in vastly different and increased Os concentrations and can have a large affect on the total abundance of Os in samples of ancient sediments. Therefore, it is used as an indicator of ‘common’ Os (i.e. unradiogenic) contained in the sample. The 192Os concentrations in this segment of the MCE interval show an increase with corresponding decrease in Osi (Fig. 3). However, unlike in OAE 2 where the increase is by factors of 10 or more (Sullivan et al., 2020

Sullivan, D.L., Brandon, A.D., Eldrett, J., Bergman, S.C., Wright, S., Minisini, D. (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2). Geochimica et Cosmochimica Acta 285, 257–273. https://doi.org/10.1016/j.gca.2020.04.002

), the 192Os concentrations in the MCE increases are only about 2 times above background concentration levels. On the other hand, increased Hg concentrations (Scaife et al., 2017

Scaife, J.D., Ruhl, M., Dickson, A.J., Mather, T.A., Jenkyns, H.C., Percival, L.M.E., Hesselbo, S.P., Cartwright, J., Eldrett, J.S., Bergman, S.C., Minisini, D. (2017) Sedimentary Mercury Enrichments as a Marker for Large Igneous Province Volcanism: Evidence from the Mid-Cenomanian Event and Ocean Anoxic Event 2 (Late Cretaceous). Geochemistry, Geophysics, Geosystems 18, 4253–4275. https://doi.org/10.1002/2017GC007153

) recorded in segment III have been used to argue for influence of increased volcanic activity. Although it is challenging to disentangle the competing effect of decreased weathering activity from rising sea level and presumed magmatic activity that was prevalent during this segment, it can be concluded that basaltic magmatic activity may have acted in concert with a sea level transgression recorded during segment III. Since the shift to more unradiogenic Osi did not persist for long (0.14 Myr), and the Osi quickly recovered to background levels following the MCE (Fig. 3), the basaltic magmatic activity that may have supplied the Os was short relative to that observed during OAE 2. If HALIP was the source of unradiogenic Os, the limited circulation of ocean water from the Arctic Ocean southwards to the southern WIS during the MCE (Eldrett et al., 2017

Eldrett, J.S., Dodsworth, P., Bergman, S.C., Wright, M., Minisini, D. (2017) Water-mass evolution in the Cretaceous Western Interior Seaway of North America and equatorial Atlantic. Climate of the Past 13, 855–878. https://doi.org/10.5194/cp-13-855-2017

), may have muted the signal. If so, then a larger magnitude of minimum Osi values at locations closer to the HALIP would be expected.

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Conclusions

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information


The first reconstruction of mid-Cenomanian seawater 187Os/188Os in the WIS can be divided into four chronostratigraphic units (“segments”). The earliest unit (segment I) indicates possible initiation of the MCE. This is followed by segment II which corresponds to a +2 ‰ shift in carbon isotope values. This segment records increased continental weathering fingerprinted by the rise in Osi values and decreasing 192Os/TOC values. Notably, increased continental weathering began 90 kyr before the onset of the CIE recorded at the start of segment II. This is followed by a shift to more unradiogenic Osi with corresponding increased 192Os/TOC and Hg concentrations in segment III which coincides with the onset of MCE 1b. The Osi shortly thereafter in segment IV recovers to background levels of around 1, with both 192Os/TOC and Hg concentrations decreasing. The shift to unradiogenic Osi with increased 192Os/TOC and Hg concentrations in segment III is consistent with an increased supply of unradiogenic Os, likely from a LIP emplacement. This interpretation is also supported by 40Ar/39Ar ages for HALIP of 96.4 ± 1.6 Ma which was active around the time of the MCE. These relationships indicate that whereas the longer OAE2 has a clear signal of initiation from LIP activity, the carbon perturbation at the start of MCE was not initiated in this way and that LIP activity may have been present only in a short time interval towards the end of the event. This shows that smaller events such as the MCE are important as their biogeochemical regimes can continue into bigger events such as OAE2.

top

Acknowledgements

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information


F. Marcantonio is thanked for his assistance in the lab. The manuscript was improved by suggestions of two anonymous reviewers. We also appreciate editorial handling by Claudine Stirling. Funding for this project was made possible by National Science Foundation award EAR 1933302.

Editor: Claudine Stirling

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References

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information

Ando, A., Huber, B.T., MacLeod, K.G., Ohta, T., Khim, B.-K. (2009) Blake Nose stable isotopic evidence against the mid-Cenomanian glaciation hypothesis. Geology 37, 451–454. https://doi.org/10.1130/G25580A.1
Show in context

Thus ɛNd variation may represent regional rather than global seawater trends. On the other hand, δ18O records from various sites globally garner opposing interpretations for cooling (Voigt et al., 2004) and against cooling (Ando et al., 2009).
View in article


Batenburg, S.J., De Vleeschouwer, D., Sprovieri, M., Hilgen, F.J., Gale, A.S., Singer, B.S., Koeberl, C., Coccioni, R., Claeys, P., Montanari, A. (2016) Orbital control on the timing of oceanic anoxia in the Late Cretaceous. Climate of the Past 12, 1995–2009. https://doi.org/10.5194/cp-12-1995-2016
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Pueblo section: 40Ar/39Ar and astronomic ages assigned to the Thatcher bentonite after Batenburg et al. (2016).
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Beil, S., Kuhnt, W., Holbourn, A.E., Arquit, M., Flogel, S., Chellai, E.H., Jabour, H. (2018) New insights into Cenomanian paleoceanography and climate evolution from the Tarfaya Basin, southern Morocco. Cretaceous Research 84, 451–473. https://doi.org/10.1016/j.cretres.2017.11.006
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Like OAE 2, the MCE is recognisable by a positive δ13C excursion of 1–2 ‰ (Fig. 1) and recognised globally (see summary in Beil et al., 2018, and Supplementary Information for additional discussion).
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Moreover, because of the unusually high productivity and excess organic carbon burial, coupled with the close proximity in time and associated development of anoxia during the MCE and OAE 2, they are thought to have been triggered by a similar mechanism (e.g., Beil et al., 2018).
View in article


Bergman, S.C., Eldrett, J.S., Minisini, D. (2021) Phanerozoic Large Igneous Province, Petroleum System, and Source Rock Links. In: Ernst, R.E., Dickson, A.J., Bekker, A. (Eds.) Large Igneous Provinces. A Driver of Global Environmental and Biotic Changes. Geophysical Monograph 255, John Wiley & Sons, Inc., Hoboken, NJ, and American Geophysical Union, Washington, D.C., 191–228. https://doi.org/10.1002/9781119507444.ch9
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Notably, increased magmatic activity from LIP eruptions are favoured to have triggered the onset of OAE 2 (Turgeon and Creaser, 2008), OAE 1a and other OAEs (Bergman et al., 2021).
View in article


Coccioni, R., Galeotti, S. (2003) The mid-Cenomanian Event: prelude to OAE 2. Palaeogeography, Palaeoclimatology, Palaeoecology 190, 427–440. https://doi.org/10.1016/S0031-0182(02)00617-X
Show in context

Another such event, the mid-Cenomanian Event (MCE) occurring just before OAE 2 (ca. 96.5 Ma), is often referred to as a precursor to OAE 2 (Coccioni and Galeotti, 2003).
View in article
This is because the MCE is interpreted to signify the onset of major oceanic and climatic reorganisation that ultimately led to OAE 2 (Coccioni and Galeotti, 2003).
View in article
Extensive organic matter preservation was less pervasive than during OAE2, with black shale deposition occurring in fewer basins (Coccioni and Galeotti, 2003; Friedrich et al., 2009).
View in article


Du Vivier, A.D.C., Selby, D., Sageman, B.B., Jarvis, I., Gröcke, D.R., Voigt, S. (2014) Marine 187Os/188Os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during Oceanic Anoxic Event 2. Earth and Planetary Science Letters 389, 23–33. https://doi.org/10.1016/j.epsl.2013.12.024
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However, unlike OAE 2, where there is consensus on LIP emplacement as a trigger (e.g., Turgeon and Creaser 2008; Du Vivier et al., 2014; Sullivan et al., 2020; Nana Yobo et al., 2021), proxy evidence for a direct and causal link between LIP activity during the MCE or significant weathering are limited.
View in article
Prior to the carbon isotope excursion that marks the onset MCE, Osi values range between 0.8–0.9, similar to previous estimates of pre-OAE2 Osi background values for the WIS (Du Vivier et al., 2014; Jones et al., 2021; Sullivan et al., 2020).
View in article


Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010
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Unlike OAE 2 that lasted ∼700–1100 kyr (Jones et al., 2021), the MCE was shorter-lived (Fig. 1; ∼150–400 kyr; Eldrett et al., 2015).
View in article
Comparison of the MCE interval from Iona-1 core with sections from Pueblo and Folkestone. Iona-1 core: δ13C data after Eldrett et al. (2015) and Sweere et al. (2020); biostratigraphic markers and astronomically tuned age model with ages plotted after Eldrett et al. (2015).
View in article
Palaeogeographic reconstruction of the WIS during the early Turonian showing the location of the Iona-1 core. Modified from Eldrett et al. (2015).
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Stratigraphic profile of Osi and C isotope ratios from the MCE interval of the Iona-1 core of West Texas. δ13Corg from Eldrett et al. (2015) and Sweere et al. (2020), Osi and 192Os (this study), Hg concentrations (Sweere et al., 2020).
View in article


Eldrett, J.S., Dodsworth, P., Bergman, S.C., Wright, M., Minisini, D. (2017) Water-mass evolution in the Cretaceous Western Interior Seaway of North America and equatorial Atlantic. Climate of the Past 13, 855–878. https://doi.org/10.5194/cp-13-855-2017
Show in context

If HALIP was the source of unradiogenic Os, the limited circulation of ocean water from the Arctic Ocean southwards to the southern WIS during the MCE (Eldrett et al., 2017), may have muted the signal.
View in article


Estrada, S. (2015) Geochemical and Sr–Nd isotope variations within Cretaceous continental flood-basalt suites of the Canadian High Arctic, with a focus on the Hassel Formation basalts of northeast Ellesmere Island. International Journal of Earth Sciences 104, 1981–2005. https://doi.org/10.1007/s00531-014-1066-x
Show in context

Geochronology data, including a 40Ar/39Ar age of 96.4 ± 1.6 Ma (Estrada, 2015) shows that the HALIP was active around the time of the MCE and thus may have been the source of the gradual decline of Osi observed.
View in article


Farley, K.A., Montanari, A., Coccioni, R. (2012) A record of the extraterrestrial 3He flux through the Late Cretaceous. Geochimica et Cosmochimica Acta 84, 314–328. https://doi.org/10.1016/j.gca.2012.01.015
Show in context

This shift to more unradiogenic Osi can be interpreted in three scenarios: 1 - decreased continental weathering, 2 - increased basaltic magmatism, and 3 - a large meteoric impact. Scenario 3 is ruled out because a significant increase in HSE (Os, Ir, Ru, Pt, Pd, Re), or changes in their chondrite-normalised patterns from continental crust-like to flatter slopes, fingerprinting increased extraterrestrial flux, is not recorded here (Table S-1, Fig. S-1) or in other locations during this interval (Farley et al., 2012).
View in article


Friedrich, O., Erbacher, J., Wilson, P.A., Moriya, K., Mutterlose, J. (2009) Paleoenvironmental changes across the Mid Cenomanian Event in the tropical Atlantic Ocean (Demerara Rise, ODP Leg 207) inferred from benthic foraminiferal assemblages. Marine Micropaleontology 71, 28–40. https://doi.org/10.1016/j.marmicro.2009.01.002
Show in context

Extensive organic matter preservation was less pervasive than during OAE2, with black shale deposition occurring in fewer basins (Coccioni and Galeotti, 2003; Friedrich et al., 2009).
View in article


Gale, A.S., Voigt, S., Sageman, B.B., Kennedy, W.J. (2008) Eustatic sea-level record for the Cenomanian (Late Cretaceous)—Extension to the Western Interior Basin, USA. Geology 36, 859–862. https://doi.org/10.1130/G24838A.1
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A second Folkestone section is also plotted from Gale et al. (2008).
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Giraud, F., Reboulet, S., Deconinck, J.F., Martinez, M., Carpentier, A., Bréziat, C. (2013) The Mid-Cenomanian Event in southeastern France: Evidence from paleontological and clay mineralogical data. Cretaceous Research 46, 43–58. https://doi.org/10.1016/j.cretres.2013.09.004
Show in context

Further support for increased weathering activity at the onset of the MCE comes from the Aquitaine Basin in France, where the presence of clay mineral assemblages (smectite) has been interpreted as possible evidence for weathering of submarine volcanic materials (Giraud et al., 2013).
View in article


Jenkyns, H.C. (2010) Geochemistry of oceanic anoxic events. Geochemistry, Geophysics, Geosystems 11, Q03004. https://doi.org/10.1029/2009GC002788
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The Mesozoic was characterised by periods of marine anoxia and disruption of the global carbon cycle, termed oceanic anoxic events (OAEs, see Jenkyns, 2010).
View in article
These periods represent intervals when organic carbon was buried in sediments under oxygen deficient bottom waters, most notably the Cenomanian–Turonian OAE 2 (ca. 94.5 Ma) and Aptian OAE 1a (ca. 124 Ma) (Jenkyns, 2010).
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Although no two carbon cycle perturbations are the same, many of the local expressions of the global event are observed to be identical (see Jenkyns, 2010).
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Jones, M.M., Sageman, B.B., Selby, D., Jicha, B.R., Singer, B.S., Titus, A.L. (2021) Regional chronostratigraphic synthesis of the Cenomanian-Turonian Oceanic Anoxic Event 2 (OAE2) interval, Western Interior Basin (USA): New Re-Os chemostratigraphy and 40Ar/39Ar geochronology. GSA Bulletin 133, 1090–1104. https://doi.org/10.1130/B35594.1
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Unlike OAE 2 that lasted ∼700–1100 kyr (Jones et al., 2021), the MCE was shorter-lived (Fig. 1; ∼150–400 kyr; Eldrett et al., 2015).
View in article
Prior to the carbon isotope excursion that marks the onset MCE, Osi values range between 0.8–0.9, similar to previous estimates of pre-OAE2 Osi background values for the WIS (Du Vivier et al., 2014; Jones et al., 2021; Sullivan et al., 2020).
View in article


Moghadam, H.V., Paul, C.R.C. (2000) Micropalaeontology of the Cenomanian at Chinnor, Oxfordshire, and comparison with the Dover-Folkestone succession. Proceedings of the Geologists’ Association 111, 17–39. https://doi.org/10.1016/S0016-7878(00)80034-6
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Occurrence of planktonic foraminifera R. cushmani after Moghadam and Paul (2000).
View in article


Nana Yobo, L., Brandon, A.D., Holmden, C., Lau, K.V., Eldrett, J. (2021) Changing inputs of continental and submarine weathering sources of Sr to the oceans during OAE 2. Geochimica et Cosmochimica Acta 303, 205–225. https://doi.org/10.1016/j.gca.2021.03.013
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However, unlike OAE 2, where there is consensus on LIP emplacement as a trigger (e.g., Turgeon and Creaser 2008; Du Vivier et al., 2014; Sullivan et al., 2020; Nana Yobo et al., 2021), proxy evidence for a direct and causal link between LIP activity during the MCE or significant weathering are limited.
View in article


Paul, C.R.C., Mitchell, S.F., Marshall, J.D., Leary, P.N., Gale, A.S., Duane, A.M., Ditchfield, P.W. (1994) Paleoceanographic events in the Middle Cenomanian of Northwest Europe. Cretaceous Research 15, 707–738. https://doi.org/10.1006/cres.1994.1039
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Since the first description of the MCE by Paul et al. (1994), it has remained one of the least studied carbon cycle perturbations.
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Folkestone Lydden Spout section: δ13C from Abbot’s cliff section after Paul et al. (1994).
View in article


Peucker‐Ehrenbrink, B., Ravizza, G. (2000) The marine osmium isotope record. Terra Nova 12, 205–219. https://doi.org/10.1046/j.1365-3121.2000.00295.x
Show in context

The marine Os isotope composition of seawater reflects the relative mass balance of continental crust (187Os/188Os ≈ 1.4) versus mantle-derived basaltic magma/LIP (187Os/188Os ≈ 0.13) inputs into the oceans (Peucker-Ehrenbrink and Ravizza, 2000).
View in article
The seawater 187Os/188Os is used to assess the competing influence of LIP activity and continental weathering at the different stages during MCE. The residence time of Os (∼104 years; Peucker-Ehrenbrink and Ravizza, 2000) is longer than the ∼1000 year mixing time of the ocean and allows for a well-mixed ocean.
View in article


Scaife, J.D., Ruhl, M., Dickson, A.J., Mather, T.A., Jenkyns, H.C., Percival, L.M.E., Hesselbo, S.P., Cartwright, J., Eldrett, J.S., Bergman, S.C., Minisini, D. (2017) Sedimentary Mercury Enrichments as a Marker for Large Igneous Province Volcanism: Evidence from the Mid-Cenomanian Event and Ocean Anoxic Event 2 (Late Cretaceous). Geochemistry, Geophysics, Geosystems 18, 4253–4275. https://doi.org/10.1002/2017GC007153
Show in context

Conversely, peak enrichment of Hg concentrations during the MCE indicate that volcanic activity may have sustained part of the event, albeit not at the onset (Scaife et al., 2017).
View in article
On the other hand, increased Hg concentrations (Scaife et al., 2017) recorded in segment III have been used to argue for influence of increased volcanic activity.
View in article


Siddall, M., Khatiwala, S., van de Flierdt, T., Jones, K., Goldstein, S.L., Hemming, S., Anderson, R.F. (2008) Towards explaining the Nd paradox using reversible scavenging in an ocean general circulation model. Earth and Planetary Science Letters 274, 448–461. https://doi.org/10.1016/j.epsl.2008.07.044
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This can be challenging due to the short residence time of Nd (100–1000 years; Siddall et al., 2008) relative to the global ocean mixing time (1000–2000 years).
View in article


Sullivan, D.L., Brandon, A.D., Eldrett, J., Bergman, S.C., Wright, S., Minisini, D. (2020) High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2). Geochimica et Cosmochimica Acta 285, 257–273. https://doi.org/10.1016/j.gca.2020.04.002
Show in context

However, unlike OAE 2, where there is consensus on LIP emplacement as a trigger (e.g., Turgeon and Creaser 2008; Du Vivier et al., 2014; Sullivan et al., 2020; Nana Yobo et al., 2021), proxy evidence for a direct and causal link between LIP activity during the MCE or significant weathering are limited.
View in article
Prior to the carbon isotope excursion that marks the onset MCE, Osi values range between 0.8–0.9, similar to previous estimates of pre-OAE2 Osi background values for the WIS (Du Vivier et al., 2014; Jones et al., 2021; Sullivan et al., 2020).
View in article
From Sullivan et al. (2020).
View in article
If increased magmatic activity from LIP eruptions were responsible for the shift to unradiogenic Os, a consequent spike in 192Os concentrations can be expected, similar to the spikes of magmatic activity recorded during OAE 2 in the Iona-1 core and elsewhere (see Sullivan et al., 2020).
View in article
Consistent with Sullivan et al. (2020), 192Os normalised to TOC is used rather than total Os abundance. This ratio thus represents the unradiogenic Os concentrations from sample to sample that are independent of ingrowth of radiogenic 187Os.
View in article
However, unlike in OAE 2 where the increase is by factors of 10 or more (Sullivan et al., 2020), the 192Os concentrations in the MCE increases are only about 2 times above background concentration levels.
View in article


Sweere, T.C., Dickson, A.J., Jenkyns, H.C., Porcelli, D., Ruhl, M., Murphy, M.J., Idiz, E., van den Boorn, S.H.J.M., Eldrett, J.S., Henderson, G.M. (2020) Controls on the Cd-isotope composition of Upper Cretaceous (Cenomanian–Turonian) organic-rich mudrocks from south Texas (Eagle Ford Group). Geochimica et Cosmochimica Acta 287, 251–262. https://doi.org/10.1016/j.gca.2020.02.019
Show in context

Comparison of the MCE interval from Iona-1 core with sections from Pueblo and Folkestone. Iona-1 core: δ13C data after Eldrett et al. (2015) and Sweere et al. (2020); biostratigraphic markers and astronomically tuned age model with ages plotted after Eldrett et al. (2015).
View in article
Stratigraphic profile of Osi and C isotope ratios from the MCE interval of the Iona-1 core of West Texas. δ13Corg from Eldrett et al. (2015) and Sweere et al. (2020), Osi and 192Os (this study), Hg concentrations (Sweere et al., 2020).
View in article


Turgeon, S.C., Creaser, R.A. (2008) Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode. Nature 454, 323–326. https://doi.org/10.1038/nature07076
Show in context

Notably, increased magmatic activity from LIP eruptions are favoured to have triggered the onset of OAE 2 (Turgeon and Creaser, 2008), OAE 1a and other OAEs (Bergman et al., 2021).
View in article
However, unlike OAE 2, where there is consensus on LIP emplacement as a trigger (e.g., Turgeon and Creaser 2008; Du Vivier et al., 2014; Sullivan et al., 2020; Nana Yobo et al., 2021), proxy evidence for a direct and causal link between LIP activity during the MCE or significant weathering are limited.
View in article


Voigt, S., Gale, A.S., Flögel, S. (2004) Midlatitude shelf seas in the Cenomanian-Turonian greenhouse world: Temperature evolution and North Atlantic circulation. Paleoceanography and Paleoclimatology 19, PA4020. https://doi.org/10.1029/2004PA001015
Show in context

Thus ɛNd variation may represent regional rather than global seawater trends. On the other hand, δ18O records from various sites globally garner opposing interpretations for cooling (Voigt et al., 2004) and against cooling (Ando et al., 2009).
View in article


Zheng, X-Y., Jenkyns, H.C., Gale, A.S., Ward, D.J., Henderson, G.M. (2016) A climatic control on reorganization of ocean circulation during the mid-Cenomanian event and Cenomanian-Turonian oceanic anoxic event (OAE 2): Nd isotope evidence. Geology 44, 151–154. https://doi.org/10.1130/G37354.1
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Attempts thus far to understand ocean conditions at the onset of the MCE are drawn from reconstruction of seawater ɛNd (Zheng et al., 2016).
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Additional support of increased weathering is recorded in the ɛNd profile from the Folkstone, UK section, which has a negative excursion likely reflecting increased flux from the surrounding Precambrian continental rocks that have been shown to have lower ɛNd values (Zheng et al., 2016).
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Supplementary Information

Abstract | Introduction | Results | Discussion | Conclusions | Acknowledgements | References | Supplementary Information


The Supplementary Information includes:
  • Stratigraphic Framework
  • Materials and Analytical Method
  • Table S-1
  • Figure S-1
  • Supplementary Information References
    •

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    Figures



    Figure 1 Comparison of the MCE interval from Iona-1 core with sections from Pueblo and Folkestone. Iona-1 core: δ13C data after Eldrett et al. (2015)

    Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

    and Sweere et al. (2020)

    Sweere, T.C., Dickson, A.J., Jenkyns, H.C., Porcelli, D., Ruhl, M., Murphy, M.J., Idiz, E., van den Boorn, S.H.J.M., Eldrett, J.S., Henderson, G.M. (2020) Controls on the Cd-isotope composition of Upper Cretaceous (Cenomanian–Turonian) organic-rich mudrocks from south Texas (Eagle Ford Group). Geochimica et Cosmochimica Acta 287, 251–262. https://doi.org/10.1016/j.gca.2020.02.019

    ; biostratigraphic markers and astronomically tuned age model with ages plotted after Eldrett et al. (2015)

    Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

    . Pueblo section: 40Ar/39Ar and astronomic ages assigned to the Thatcher bentonite after Batenburg et al. (2016)

    Batenburg, S.J., De Vleeschouwer, D., Sprovieri, M., Hilgen, F.J., Gale, A.S., Singer, B.S., Koeberl, C., Coccioni, R., Claeys, P., Montanari, A. (2016) Orbital control on the timing of oceanic anoxia in the Late Cretaceous. Climate of the Past 12, 1995–2009. https://doi.org/10.5194/cp-12-1995-2016

    . Folkestone Lydden Spout section: δ13C from Abbot’s cliff section after Paul et al. (1994)

    Paul, C.R.C., Mitchell, S.F., Marshall, J.D., Leary, P.N., Gale, A.S., Duane, A.M., Ditchfield, P.W. (1994) Paleoceanographic events in the Middle Cenomanian of Northwest Europe. Cretaceous Research 15, 707–738. https://doi.org/10.1006/cres.1994.1039

    . Occurrence of planktonic foraminifera R. cushmani after Moghadam and Paul (2000)

    Moghadam, H.V., Paul, C.R.C. (2000) Micropalaeontology of the Cenomanian at Chinnor, Oxfordshire, and comparison with the Dover-Folkestone succession. Proceedings of the Geologists’ Association 111, 17–39. https://doi.org/10.1016/S0016-7878(00)80034-6

    . A second Folkestone section is also plotted from Gale et al. (2008)

    Gale, A.S., Voigt, S., Sageman, B.B., Kennedy, W.J. (2008) Eustatic sea-level record for the Cenomanian (Late Cretaceous)—Extension to the Western Interior Basin, USA. Geology 36, 859–862. https://doi.org/10.1130/G24838A.1

    . Dual positive δ13C excursions shaded (MCE 1a and 1b) with a possible phase of initiation (init.).
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    Figure 2 Palaeogeographic reconstruction of the WIS during the early Turonian showing the location of the Iona-1 core. Modified from Eldrett et al. (2015)

    Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

    .
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    Figure 3 Stratigraphic profile of Osi and C isotope ratios from the MCE interval of the Iona-1 core of West Texas. δ13Corg from Eldrett et al. (2015)

    Eldrett, J.S., Ma, C., Bergman, S.C., Lutz, B., Gregory, F.J., Dodsworth, P., Phipps, M., Hardas, P., Minisini, D., Ozkan, A., Ramezani, J., Bowring, S.A., Kamo, S.L., Ferguson, K., Macaulay, C., Kelly, A.E. (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. https://doi.org/10.1016/j.cretres.2015.04.010

    and Sweere et al. (2020)

    Sweere, T.C., Dickson, A.J., Jenkyns, H.C., Porcelli, D., Ruhl, M., Murphy, M.J., Idiz, E., van den Boorn, S.H.J.M., Eldrett, J.S., Henderson, G.M. (2020) Controls on the Cd-isotope composition of Upper Cretaceous (Cenomanian–Turonian) organic-rich mudrocks from south Texas (Eagle Ford Group). Geochimica et Cosmochimica Acta 287, 251–262. https://doi.org/10.1016/j.gca.2020.02.019

    , Osi and 192Os (this study), Hg concentrations (Sweere et al., 2020

    Sweere, T.C., Dickson, A.J., Jenkyns, H.C., Porcelli, D., Ruhl, M., Murphy, M.J., Idiz, E., van den Boorn, S.H.J.M., Eldrett, J.S., Henderson, G.M. (2020) Controls on the Cd-isotope composition of Upper Cretaceous (Cenomanian–Turonian) organic-rich mudrocks from south Texas (Eagle Ford Group). Geochimica et Cosmochimica Acta 287, 251–262. https://doi.org/10.1016/j.gca.2020.02.019

    ). The Osi response is divided into four segments: I, II, III and IV. See text for discussion.
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