Equatorward phytoplankton migration during a cold spell within the Late Cretaceous supergreenhouse

Oceanic Anoxic Event 2 (OAE2), a ~600 kyr episode close to the Cenomanian-Turonian boundary (ca. 94 Ma), is characterized by widespread marine anoxia and ranks amongst the warmest intervals of the Phanerozoic. The early stages of OAE2 are, however, marked by an episode of 25 widespread transient cooling and bottom water oxygenation: the Plenus Cold Event. This cold spell has been linked to a decline in atmospheric pCO2, resulting from enhanced global organic carbon burial. To investigate the response of phytoplankton to this marked and rapid climate shift we examined the biogeographical response of dinoflagellates to the Plenus Cold Event. Our study is based on a newly generated geochemical and palynological dataset from a high-latitude Northern Hemisphere site, Pratts 30 Landing (western Alberta, Canada). We combine this data with a semi-quantitative global compilation of the stratigraphic distribution of dinoflagellate cyst taxa. The data show that dinoflagellate cysts grouped in the Cyclonephelium compactum-membraniphorum morphological plexus migrated from highto mid-latitudes during the Plenus Cold Event, making it the sole widely found (micro)fossil to mark this cold spell. In addition to earlier reports from regional metazoan migrations during the Plenus 35 Cold Event, our findings illustrate the effect of rapid climate change on the global biogeographical dispersion of phytoplankton.


Introduction
The Cenomanian-Turonian boundary interval (ca.94 Ma) was an episode of extreme warmth, with tropical and midlatitude sea surface temperatures exceeding 35 • C (e.g., Huber et al., 2002;Forster et al., 2007;Van Helmond et al., 2014a).This interval corresponds to Oceanic Anoxic Event 2 (OAE2), during which an increase in the production of organic carbon and a reduction in the oxygen content of seawater resulted in unusually high organic matter content of marine sediments (e.g., Schlanger and Jenkyns, 1976;Jenkyns, 2010).The OAE2 interval is stratigraphically marked by a positive carbon isotope excursion in all active carbon reservoirs, resulting from elevated organic carbon burial rates (e.g., Tsikos et al., 2004).
The early stages of OAE2 are characterized by a shortlived (ca.40 kyr; Jarvis et al., 2011) (Jefferies, 1963) and δ 13 C carb (low-resolution data (dots and dotted line) derived from Pearce et al., 2009; high-resolution data (solid line) derived from Paul et al., 1999) for the Cenomanian-Turonian boundary reference section at Eastbourne, combined with occurrences of Boreal fauna (Gale and Christensen, 1996).On the right side the ranges of the different definitions for the Plenus Cold Event are indicated.
recorded in several marine paleotemperature records (e.g., Gale and Christensen, 1996;Forster et al., 2007;Sinninghe Damsté et al., 2010).It was first recognized as the cooccurrence of Boreal fauna with a positive oxygen isotope excursion of about 1.5 ‰, recorded in biogenic calcite from beds 4-8 of the Plenus Marl in mid-latitude shelf sites of northwestern Europe (Gale and Christensen, 1996).This interval was termed the "Plenus Cold Event" (PCE; Fig. 1), after the Boreal belemnite Praeactinocamax plenus (Blainville).Subsequently, the PCE was restricted only to Bed 4 of the Plenus Marl, being the sole bed containing abundant Boreal fauna (Voigt et al., 2006;Fig. 1).Bed 4 corresponds precisely to the upper trough and second build-up of the carbon isotope excursion, the upper part of the Metoicoceras geslinianum ammonite zone and basal Whiteinella archaeocretacea planktonic foraminifer zone (Gale et al., 2005).More recently, Jarvis et al. (2011) extended the PCE down to beds 2 and 3 of the Plenus Marl (Fig. 1), based on a positive excursion in carbonate oxygen isotopes.
The PCE interval is characterized by a 3-7 • C cooling of sea surface temperatures in the proto-North Atlantic and the European shelf (e.g., Forster et al., 2007;Sinninghe Damsté et al., 2010;van Helmond et al., 2014avan Helmond et al., , 2015)).In several regions, such as the Western Interior Seaway (Eldrett et al., 2014) and proto-North Atlantic (e.g., Forster et al., 2007), the stratigraphic position of the PCE is characterized by minima in sediment organic carbon content and redox-sensitive element concentrations, which indicates improved oxygenation of bottom waters (e.g., van Helmond et al., 2014b).Furthermore the stratigraphic position of the PCE coincides with a decline in atmospheric pCO 2 (e.g., Kuypers et al., 1999;Sinninghe Damsté et al., 2008;Barclay et al., 2010), which is thought to be a consequence of enhanced sequestration of organic carbon in sediments during the early stages of OAE2 (e.g., Barclay et al., 2010;Sinninghe Damsté et al., 2010).The incursion of Boreal fauna into lower latitudes has only been documented for the European shelf.A causal relation between pCO 2 drawdown, sea surface cooling, bottom water oxygenation and the PCE has been proposed (e.g., Forster et al., 2007;Sinninghe Damsté et al., 2010;Jarvis et al., 2011;van Helmond et al., 2014b).
Previously, it remained unclear as to whether the migration of Boreal fauna was related to a migration of multiple components of marine food webs.Recently, van Helmond et al. (2014avan Helmond et al. ( , 2015) ) showed that the first consistent presence (FCP; presence of multiple specimens in consecutive samples) of dinoflagellate cysts (dinocysts) belonging to the Cyclonephelium compactum-membraniphorum morphological plexus (Ccm; see below for a detailed discussion on taxonomic status) in two sections on the proto-North Atlantic and European shelf coincided with a cooling of sea surface temperatures at the stratigraphic level of the PCE.To test whether Ccm was truly a high-latitude taxon and whether widespread migration of these dinoflagellates occurred during the PCE, we studied a high-latitude site in northwestern Alberta, Canada (Pratts Landing), and compiled a global distribution of Ccm across OAE2, calibrated using biostratigraphy and carbon isotope stratigraphy.

Stratigraphic setting of the Pratts Landing section
In northwestern Alberta and northeastern British Columbia, upper Cenomanian and Turonian strata of the Kaskapau Formation form a thick, mudstone-dominated and northeastward-thinning wedge that spans the foredeep of the Western Canada Foreland Basin (Varban and Plint, 2005).Well-exposed sections in the Rocky Mountain Foothills on the western margin of the foredeep can be correlated with sections in the Peace River Valley, located close to the forebulge.Correlation has been established by using abundant, publicly accessible wireline log data (Fig. 2).Detailed correlation through a grid of 756 wireline logs showed that 28 allomembers, bounded by marine flooding surfaces, could be mapped across the foredeep (Varban and Plint, 2005).In the western part of the foredeep, exemplified by the section at Mount Robert (Figs. 2, 3), nearshore and shoreface sandstones form stacked successions that prograded only 20-40 km seaward from the preserved basin margin; shoreface progradation was limited by a consistently high rate of flexural subsidence (Varban andPlint, 2005, 2008).Traced eastward from Mount Robert, successive allomembers become thinner and finer-grained, and some allomembers (e.g., allomembers 7, 9, 10) pinch out completely before reaching outcrop in the Peace River Valley, exemplified by the section at Pratts Landing (Figs. 2, 3).The section at Pratts Landing, which is the focus of this study, is located on the northern bank of the Peace River (56 • 01 14 N, 118 • 48 47 W; Fig. 4) and comprises stacked siltier-and sandier-upward successions, capped, at a prominent flooding surface, by weakly bioturbated, organic-rich claystones and silty claystones characterized by a very high radioactivity (i.e., boundary of allomembers 6 and 8; Figs. 3, 5).Outcrop spectral gamma ray profiles allow the Pratts Landing section to be correlated with confidence to nearby wireline logs (Fig. 3).
In the west, the Cenomanian-Turonian boundary was recognized at the top of Kaskapau allomember 6 at Mount Robert, based on the distribution of inoceramid bivalves (Fig. 3).At that section, late Cenomanian Inoceramus ex gr.pictus (Sowerby) is widely distributed through allomembers 2 to 6, whereas Mytiloides puebloensis (Walaszczyk and Cobban) is present 2 m above the allomember 6-7 contact, indicating that the lowest zone of the Turonian is present in the lower part of allomember 7 (cf.Kennedy et al., 2000).The upper bounding surface of allomember 6 can be traced, through well logs, for 220 km eastward to Pratts Landing, where it corresponds to the sharp basal surface of a gypsumcemented silty claystone.That sharp surface, separating al-   lomembers 6 and 8, corresponds to an abrupt increase in radioactivity, and lies 25 cm below the first appearance of the early Turonian inoceramids Mytiloides goppelnensis (Badillet and Sornay) and Mytiloides kossmati (Heinz; Figs. 3, 5).The wireline log correlation shows that, at Pratts Landing, all of allomember 7 is missing, and the earliest Turonian zone of M. puebloensis also appears to be unrepresented, emphasizing the hiatal character of the allomember 6-8 boundary (Fig. 3).

British Columbia Alberta
During the Late Cretaceous, the study site was located at ∼ ±5 61 • N (van Hinsbergen et al., 2015; paleolatitude.org), on the eastern flank of the foredeep, about 160 km from the contemporaneous western shoreline of the Western Interior Seaway (Varban andPlint, 2005, 2008).We generated carbon isotope and dinoflagellate cyst data across about 23 m of upper Cenomanian to lower Turonian strata, based on stable carbon isotope stratigraphy and inoceramid biostratigraphy (Figs. 3,6).

Stable isotope geochemistry
The carbon isotope composition of bulk organic carbon (δ 13 C org ) was measured at 20 cm intervals across OAE2 in order to constrain its exact position, and at 50 cm intervals for the remainder of the section.Analyses were performed in the Stable-Isotope Biogeochemistry Laboratory of the School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario, Canada.In total, 77 samples were treated with 3 N HCl to remove carbonates, rinsed with demineralized water, freeze-dried and powdered.Between 1 and 3 mg of powdered sediment sample was weighed in tin capsules and then put in a rotating carousel for subsequent combustion in an elemental analyzer.After purification of the gas sample it was passed through a SIRA II Series 2 dualinlet isotope-ratio mass spectrometer to determine the stable carbon isotopic composition of organic matter.Carbon isotope ratios were measured against an international standard, NBS-21.The analytical reproducibility, based on replicate samples, was better than 0.1 ‰.

Palynological processing
Dinocyst abundances were determined for 21 samples, covering the entire section, using standard palynological methods.About 5 g of freeze-dried sediment was processed following a standardized quantitative method (e.g., Sluijs et al., Sampled interval (Fig. 6) Figure 3. Regional cross section (located in Fig. 2) showing how allomembers of the Kaskapau Formation can be correlated across the foredeep from Mount Robert to Pratts Landing.Cross section is condensed from more detailed lines in Varban and Plint (2005).The Cenomanian-Turonian boundary is shown as a broken line at the top of allomember 6.Note how allomember 7 laps out eastward onto allomember 6, and that both allomembers 6 and 8 become increasingly radioactive towards the east.Spectral gamma ray profiles taken at Pratts Landing confirm the correlation of the various stratal units at outcrop with their equivalents in subsurface.The inset stratigraphic logs show more detailed representations of the lithological successions, gamma ray profiles, and the distribution of inoceramid bivalves at Mount Robert and Pratts Landing.Detailed legend in Fig. 6.
2003), which involves the addition of a known amount of Lycopodium marker spores (Stockmar, 1971).To dissolve carbonates and silicates, HCl (∼ 30 %) and HF (∼ 38 %) were added, respectively.After centrifugation, acids were discarded.The remaining residues were sieved over a 15 µm nylon mesh and the > 15 µm fraction was mounted on slides for analysis by light microscopy.Samples were counted to a minimum of 250 dinocysts, which were identified to genus or species level at 500× magnification, following the taxonomy of Fensome and Williams (2004).All samples and slides are stored in the collection of the Laboratory of Palaeobotany and Palynology, Utrecht University, the Netherlands.All data (δ 13 C org and palynology) are listed in the Supplement (Table S1).

Taxonomy and literature survey
Originally the cysts Cyclonephelium membraniphorum (Cookson and Eisenack, 1962), which was renamed Cauveridinium membraniphorum (Masure in Fauconnier and Masure, 2004), were differentiated from Cyclonephelium compactum (Deflandre and Cookson, 1955), based on the generally higher and structurally ordered crests and membranes of C. membraniphorum.Additionally, cysts of C. membraniphorum form a series of funnel-shaped structures bordering unornamented mid-dorsal and mid-ventral areas.However, the apparent morphological variation regarding ornamentation within the two species exceeds the defined difference between the two species.Therefore, it was proposed to refer to the dinocyst morphological complex Cyclonephelium compactum-membraniphorum, rather than separating both species (Marshall and Batten, 1988).We agree that the two species are members of a morphological continuum and therefore group all these morphotypes of this continuum from our study site and the literature under the Cyclonephelium compactum-membraniphorum morphological plexus (Ccm) (Fig. 7; Table 1).For the compilation of the global biogeographical distribution of Ccm prior to, during and after OAE2, a literature survey was conducted.(Fig. 6).The Cenomanian-Turonian boundary is placed at 15.3 m, at the sharp base of a 20 cm thick, heavily gypsum-cemented silty claystone lacking macrofauna (Fig. 5).The base Turonian marker inoceramid species Mytiloides puebloensis was not found, but the succeeding inoceramid zone, characterized by M. goppelnensis and M. kossmati, starts approximately 25 cm above the basal surface (Fig. 3).Ccm is a general constituent (1-4 %) of the dinocyst assemblage at Pratts Landing throughout the section, i.e., also below the onset of OAE2 (Fig. 6).

Dinocyst biogeography
All localities (n = 35) with reported cysts of Ccm (i.e., Cauveridinium membraniphorum, Cyclonephelium membraniphorum, Cyclonephelium compactum and/or Cyclonephelium compactum-membraniphorum) are listed in Table 1 and shown in Fig. 8.The first common presence (FCP) of Ccm could only be determined for 20 of the localities as a result of poor stratigraphic constraints and only qualitative reporting of Ccm at the other 15 localities.
Recent dinocyst biostratigraphic studies from the East Coast Basin, New Zealand, show that the FCP of Ccm was ca.500 kyr before the onset of OAE2 (Schiøler and Crampton, 2014).At northern high latitudes, notably Pratts Landing and the Norwegian Sea (Radmacher et al., 2015), Ccm is a consistent constituent of the dinocyst assemblage throughout the late Cenomanian.In contrast, at most Northern Hemisphere mid-latitude sites, Ccm has not been reported before OAE2, with the exception of a few spot occurrences at Eastbourne and Iona-1 (Pearce et al., 2009;Eldrett et al., 2014).Crucially, Ccm was never a consistent constituent of midlatitude dinocyst assemblages before OAE2.This indicates that Ccm had a high-latitude biogeographical distribution in both hemispheres before OAE2.
Five Northern Hemisphere shelf sites in Europe and North America, namely Pratts Landing, Iona-1 (southwestern Texas, USA), Bass River (New Jersey, USA), Eastbourne (East Sussex, UK) and Wunstorf (Lower Saxony, Germany), were selected to compare established biozonation, high-resolution records of δ 13 C, and the relative abundances of Ccm (Fig. 9; Pearce et al., 2009;Eldrett et al., 2014;van Helmond et al., 2014avan Helmond et al., , 2015)).Maximum relative abundances of Ccm (i.e., > 10 %) are recorded during the first maximum in the OAE2 characterizing carbon isotope excursion (point "A" -cf.Voigt et al., 2008), at Pratts Landing (Figs. 6, 9).At the same stratigraphic position, Ccm becomes abundant at several other Northern Hemisphere mid-latitude sites, for example the southern part of the Western Interior Seaway, the proto-North Atlantic shelf, the European shelf, and the Tethys (Figs. 8, 9; Table 1).Despite a spot occurrence at point "A", the FCP of Ccm seems somewhat delayed at Eastbourne (i.e., Plenus Marl Bed 7 -Fig.9; Pearce et al., 2009); this is a local phenomenon, because in other English Chalk sections (e.g., Dodsworth, 2000) the FCP of Ccm coincides with that of other Northern Hemisphere mid-latitude sites.

Ecology
At Bass River and Wunstorf the FCP of Ccm precisely correlates with a drop in sea surface temperature (van Helmond et al., 2014a(van Helmond et al., , 2015)), leading to the suggestion that the dinoflagellate taxon that produced Ccm migrated to these sites in response to climatic cooling.We therefore suggest that sea surface temperature was the primary control on the biogeo-graphical distribution of Ccm outside high-latitude regions.For the Shell Iona-1 core the FCP of Ccm coincides with a minimum in organic carbon, redox-sensitive elements and relatively high abundances of benthic foraminifera and trace fossils indicative of a period of improved oxygenation of bottom waters (Eldrett et al., 2014).This is in agreement with previous observations for the interval showing PCE-related cooling of sea surface temperature in the proto-North Atlantic (Forster et al., 2007;Sinninghe Damsté et al., 2010;van Helmond et al., 2014b).The sustained presence of Ccm after the PCE at all sites, except Bass River (Fig. 9), suggests that, in addition to sea surface temperature, other environmental and paleoceanographic factors became dominant in determining the distribution of Ccm once it had occupied niches at lower latitudes.For example, salinity, (enhanced) nutrient availability and proximity to the shoreline may have been important (Harris and Tocher, 2003).Preservation of palynomorphs, e.g., dinocysts, is variable within sections and between sections but unrelated to the occurrences of certain species.
The migration of Ccm towards lower latitudes in response to cooling resembles dinoflagellate migration events during other periods of marked climatic change.Dinocysts referable to the Arctic Paleogene taxon Svalbardella were encountered in mid-and low latitudes during the most pronounced Oligocene glaciations (ca. 30-25 Ma;van Simaeys et al., 2005).In contrast, during the Paleocene-Eocene Thermal Maximum, tropical species of the dinocyst genus Apectodinium moved from low toward high latitudes in response to peak warmth (Crouch et al., 2003;Sluijs et al., 2007).Studies across the Cretaceous-Paleogene boundary indicate initial high latitude to equatorial dinoflagellate migration at the boundary, followed by a reverse migration.This presumably took place in response to impact-related initial climatic cooling followed by a return to warmer conditions (Brinkhuis et al., 1998;Galeotti et al., 2004;Vellekoop et al., 2014).
The biogeographical expansion of Ccm towards the Equator seems to be a relatively strong response to a moderate change in sea surface temperature (ca.3-5 • C).The southward migration of Ccm over relatively large distances, i.e., 20-30 • of latitude southwards, may have been amplified by the flatter meridional temperature gradients across OAE2 (e.g., Sinninghe Damsté et al., 2010).Compared to the present day, which is characterized by a much steeper meridional temperature gradient, relatively small changes in temperature in the mid-Cretaceous and early Paleogene may have had a much larger impact on the distribution of marine organisms.

A new stratigraphic marker
Most of the Cretaceous is covered by the Normal Superchron C34n (ca. 126-84 Ma;Gradstein et al., 2012)  fore relies on biostratigraphy and carbon isotope stratigraphy (Gale et al., 2005) as well as on recent advances in astrochronology (e.g., Meyers et al., 2012;Eldrett et al., 2015).Pelagic sediments are often carbonate-poor, because the calcite compensation depth was relatively shallow during OAE2, complicating planktonic foraminifer and calcareous nannofossil biostratigraphy (e.g., Erba, 2004).Consequently, carbon isotope stratigraphy is the main stratigraphic tool for OAE2 because the positive carbon isotope excursion is recognized in all active carbon reservoirs (Tsikos et al., 2004).Calibration of carbon isotope stratigraphy with bioevents is, however, essential to establish detailed stratigraphic frameworks.
The coincidence of the FCP of Ccm with the base of the W. archaeocretacea and the upper part of the M. geslinianum zones close to the first maximum in the positive carbon isotope excursion (point "A"; Fig. 9) suggests that dinoflagellate migration probably occurred within thousands to 10 000 years.The FCP of Ccm thus represents a useful biostratigraphic marker, being, to date, the only widely found microfossil to mark the PCE, except at high latitudes.

Conclusions
A global compilation of dinocyst assemblage records combined with new data from a high-latitude site spanning OAE2 illustrates the migration of dinoflagellates, which pro-duced the dinocyst morphological complex Ccm, from highlatitudes to mid-latitudes during the early stages of OAE2 (latest Cenomanian).The first consistent presence of this taxon at mid-latitudes correlates with the stratigraphic position of the Plenus Cold Event, following its original definition by Gale and Christensen (1996) (Eldrett et al., 2014).(b) Pratts Landing (this study).(c) Bass River (van Helmond et al., 2014a); open symbols are δ 13 C org derived from Bowman and Bralower (2005).(d) Eastbourne (Pearce et al., 2009); high-resolution δ 13 C carb data derived from Paul et al. (1999).(e) Wunstorf -relative abundances of Ccm from van Helmond et al. (2015), δ 13 C org from Du Vivier et al. (2014) and δ 13 C carb from Voigt et al. (2008); a red cross marks a barren sample.Age is from the astronomically tuned age model for the Shell Iona-1 core (Eldrett et al., 2015).Dashed line represents the first maximum in the carbon isotope excursion, point "A" (cf.Voigt et al., 2008).Solid lines represent the Cenomanian-Turonian boundary.The blue shaded area represents the Plenus Cold Event according to its original definition (Gale and Christensen, 1996), the cooling in reconstructed sea surface temperatures at Bass River and Wunstorf (van Helmond et al., 2014a(van Helmond et al., , 2015)), and the (re)oxygenation of bottom waters in the Shell Iona-1 core (Eldrett et al., 2014).Note: the sections are plotted using different depth scales.van de Schootbrugge.Carbon isotope stratigraphy was carried out by Darren R. Gröcke and João Trabucho-Alexandre.Inoceramid biostratigraphy was carried out by Ireneusz Walaszczyk.Regional stratigraphy was compiled by A. Guy Plint.Compilation of the global biogeographical distribution of Ccm was carried out by Niels van Helmond, Henk Brinkhuis, Martin A. Pearce and James S. Eldrett.Niels van Helmond and Appy Sluijs prepared the manuscript with input from all authors.

Figure 1 .
Figure 1.Biozonation, lithology, Plenus Marl beds(Jefferies, 1963) and δ 13 C carb (low-resolution data (dots and dotted line) derived fromPearce et al., 2009;  high-resolution data (solid line) derived fromPaul et al., 1999) for the Cenomanian-Turonian boundary reference section at Eastbourne, combined with occurrences of Boreal fauna(Gale and Christensen, 1996).On the right side the ranges of the different definitions for the Plenus Cold Event are indicated.

Figure 2 .
Figure 2. Map of northwestern Alberta and adjacent British Columbia showing distribution of well logs, cores and outcrops used to establish the regional stratigraphic framework that forms the basis for the present study.Outcrop sections at Mount Robert in the west and Pratts Landing in the east are correlated via wireline well logs (gamma ray and resistivity pairs).
io n a l d is c o n fo rm it y

Figure 4 .
Figure 4. Map showing the southern part of Alberta.The study site at Pratts Landing is located on the Peace River about 70 km east of the Alberta-British Columbia border.Inset map shows details of the Peace River area in the vicinity of the town of Fairview, with the outcrop locality and access roads indicated.

Figure 5 .
Figure 5. Field photographs of the Pratts Landing site.Photograph (a) shows an overview of upper part of the section showing resistant, gypsum-cemented ledge that marks a sharp erosional boundary between two claystone units.Immediately above the boundary there is a large increase in the uranium content of the sediment.The early Turonian inoceramid bivalves Mytiloides goppelnensis and Mytiloides kossmati appear 25 cm above the erosion surface.Photograph (b) shows an overview of the lower part of the section showing highly bioturbated silty sandstone of Kaskapau allomember 6, sharply overlain, at a major flooding surface (13.6 m level in Fig. 6) by thinly bedded claystones.Rocks embracing the Plenus Cold Event are represented by a 1.4 m thick, shallowing (sandier)upward succession bounded above by a major flooding surface.The Cenomanian-Turonian boundary, marked by a resistant ledge, lies at the 15.3 m level.Note that all of Kaskapau allomember 7 is absent at the erosion surface marking the Cenomanian-Turonian boundary, as illustrated in Fig. 3.
, hampering application of magnetostratigraphy.Stratigraphic correlation for the Cenomanian-Turonian boundary interval there-N.A. G. M. van Helmond et al.: Equatorward phytoplankton migration during a Cretaceous cold spell

Table 1 .
Voigt et al., 2008)alities where cysts of Cyclonephelium compactum-membraniphorum morphological plexus (Ccm) have been reported across the Cenomanian-Turonian boundary interval.In the fourth and fifth column an "X" marks whether the first consistent presence (FCP) of Ccm was before OAE2 or whether it was associated with the first maximum in the positive carbon isotopic excursion (CIE), point "A" (cf.Voigt et al., 2008).Question marks indicate that the FCP could not be determined accurately, resulting from insufficient supporting information, e.g., high-resolution carbon isotope stratigraphy or unquantified abundances of Ccm.Localities further discussed in the article are in bold.WIS: Western Interior Seaway.
At Pratts Landing the OAE2 interval is recorded between 10.2 and 16.8 m, based on a 2 ‰ positive shift in δ 13 C org Biogeosciences, 13, 2859-2872, 2016 www.biogeosciences.net/13/2859/2016/ Compilation of the first consistent presence (FCP) of Cyclonephelium compactum-membraniphorum morphological plexus (Ccm) across Oceanic Anoxic Event 2. Numbers in white boxes refer to localities compiled in Table1.Letters in orange boxes refer to the sites selected for comparison of established biozonation, high-resolution records of δ 13 C and the relative abundances of Ccm (Fig.9) also compiled in Table1.The Mollweide projected paleogeographic map for the Cenomanian-Turonian boundary interval was generated at http://www.odsn.de/odsn/services/paleomap/paleomap.html.Continental plates are in light gray.Dry land in dark gray after Scotese (2001).