Enhanced continental weathering activity at the onset of the mid-Cenomanian Event (MCE)
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Abstract
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 |
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Introduction
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, 2010Jenkyns, 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, 2003Coccioni, 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, 2003Coccioni, 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., 2021Jones, 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., 2015Eldrett, 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, 2003Coccioni, 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., 2009Friedrich, 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, 2010Jenkyns, 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., 2018Beil, 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, 2008Turgeon, 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., 2021Bergman, 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 2008Turgeon, 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., 2014Du 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., 2020Sullivan, 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., 2021Nana 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., 2016Zheng, 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., 2008Siddall, 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., 2004Voigt, 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., 2009Ando, 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., 2017Scaife, 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.top
Results
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., 2021Jones, 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., 2020Sullivan, 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) | Age | Re (ppb) | ±2σ | 192Os (ppt) | Os (ppt) | ±2σ | 187Os/188Os measured | ±2σ | 187Re/188Os | ±2σ | 187Os/188Os initial | ±2σ |
135.25 | 96.15 | 19.23 | 0.06 | 14 | 58 | 0.60 | 5.26 | 0.07 | 2689 | 25.57 | 0.95 | 0.05 |
136.14 | 96.19 | 182.54 | 0.47 | 142 | 563 | 5.10 | 5.01 | 0.05 | 2555 | 14.10 | 0.91 | 0.07 |
137.31 | 96.25 | 43.63 | 0.12 | 36 | 142 | 1.08 | 4.86 | 0.04 | 2401 | 18.32 | 1.00 | 0.07 |
137.85 | 96.28 | 179.45 | 0.46 | 129 | 528 | 6.53 | 5.44 | 0.09 | 2775 | 26.10 | 0.98 | 0.13 |
138.65 | 96.32 | 214.32 | 0.61 | 200 | 757 | 3.64 | 4.43 | 0.01 | 2130 | 6.80 | 1.01 | 0.03 |
138.65 | 96.32 | 217.80 | 0.63 | 200 | 755 | 3.70 | 4.44 | 0.02 | 2172 | 7.14 | 0.95 | 0.03 |
139.27 | 96.36 | 28.33 | 0.08 | 28 | 102 | 0.86 | 4.06 | 0.04 | 2017 | 19.56 | 0.82 | 0.07 |
139.86 | 96.39 | 176.87 | 0.46 | 186 | 664 | 5.06 | 3.68 | 0.03 | 1878 | 9.45 | 0.66 | 0.05 |
139.86* | 96.39 | 318.00 | 239 | 960 | 5.20 | 2737 | 0.80 | 0.02 | ||||
140.39 | 96.42 | 159.67 | 0.40 | 150 | 562 | 2.54 | 4.36 | 0.01 | 2125 | 6.61 | 0.94 | 0.02 |
141.15 | 96.45 | 234.12 | 0.68 | 189 | 751 | 3.86 | 5.07 | 0.02 | 2471 | 8.56 | 1.10 | 0.03 |
141.77 | 96.48 | 23.29 | 0.06 | 19 | 76 | 0.82 | 5.21 | 0.06 | 2453 | 15.70 | 1.26 | 0.08 |
141.77* | 96.48 | 24.00 | 18 | 73 | 5.54 | 2740 | 1.13 | 0.05 | ||||
142.27 | 96.50 | 145.65 | 0.35 | 118 | 470 | 3.23 | 5.03 | 0.03 | 2447 | 10.17 | 1.09 | 0.05 |
142.41 | 96.51 | 134.59 | 1.46 | 121 | 459 | 1.99 | 4.51 | 0.01 | 2222 | 24.29 | 0.94 | 0.05 |
142.71 | 96.52 | 154.24 | 0.19 | 114 | 468 | 2.49 | 5.46 | 0.02 | 2692 | 8.22 | 1.12 | 0.03 |
142.94 | 96.53 | 186.19 | 2.03 | 159 | 613 | 2.69 | 4.66 | 0.01 | 2330 | 25.47 | 0.91 | 0.05 |
143.37 | 96.56 | 202.79 | 0.55 | 206 | 753 | 3.60 | 4.05 | 0.01 | 1962 | 6.45 | 0.89 | 0.02 |
143.73 | 96.61 | 9.71 | 0.11 | 13 | 44 | 0.34 | 3.18 | 0.03 | 1485 | 18.72 | 0.79 | 0.06 |
145.75 | 96.67 | 183.59 | 0.45 | 204 | 854 | 11.14 | 5.73 | 0.10 | 2975 | 15.00 | 0.93 | 0.12 |
146.46 | 96.70 | 398.07 | 1.10 | 238 | 1038 | 11.91 | 6.28 | 0.08 | 3330 | 25.51 | 0.91 | 0.12 |
*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.
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Discussion
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, 2000Peucker‐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., 2016Zheng, 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, 2015Estrada, 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., 2020Sullivan, 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., 2020Sullivan, 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., 2017Scaife, 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., 2017Eldrett, 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.top
Conclusions
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.
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Acknowledgements
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
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
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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).
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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).
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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).
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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
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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).
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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).
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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).
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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.
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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).
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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).
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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).
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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).
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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
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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.
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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
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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.
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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
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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).
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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
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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).
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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
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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).
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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).
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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).
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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).
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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).
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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.
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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).
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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
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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).
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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.
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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
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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).
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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.
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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).
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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
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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).
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From Sullivan et al. (2020).
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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).
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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.
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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.
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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
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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).
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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).
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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
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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
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.
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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
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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).
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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
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