Biometry of Upper Cretaceous (Cenomanian-Maastrichtian) coccoliths - a record of long-term stability and interspecies size shifts

Biometric measurements of Mesozoic coccoliths (coccolith length and width) have been used in short-term biostratigraphic, taxonomic and palaeoecologic studies, but until now, not over longer time scales. Here, we present a long time-series study (∼ 30 million years) for the Upper Cretaceous, which aims to identify broad trends in coccolith size and to understand the factors governing coccolith size change over long time scales. We have generated biometric data for the dominant Upper Cretaceous coccolith groups, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa and Watznaueria, from 36 Cenomanian–Maastrichtian (100.5–66 Ma) samples from Goban Spur in the northeast Atlantic (DSDP Site 549). These data show that the coccolith sizes within Prediscosphaera, Retecapsa and Watznaueria were relatively stable through the Late Cretaceous, with mean size variation less than 0.7 μm. Within the Broinsonia/Arkhangelskiella group there was more pronounced variation, with a mean size increase from ∼ 6 μm in the Cenomanian to ∼ 10 μm in the Campanian. This significant change in mean size was largely driven by evolutionary turnover (species origination and extinctions), and, in particular, the appearance of larger species/subspecies (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) in the early Campanian, replacing smaller species, such as Broinsonia signata and Broinsonia enormis. Shorter-term size fluctuations within Broinsonia/Arkhangelskiella, observed across the Late Cenomanian–Turonian and Late Campanian–Maastrichtian intervals, may, however, reflect changing palaeoenvironmental conditions, such as sea surface temperature and nutrient availability. / Les dimensions des coccolithes du Mésozoïque (longueur et largeur) ont été utilisées dans des études biostratigraphiques, taxonomiques et paléoécologiques sur le court-terme mais jusqu’à présent, jamais sur le long-terme. Ici, nous présentons l’étude d’une série chronologique à échelle de temps longue (∼ 30 millions d’années) du Crétacé supérieur, visant à identifier les tendances générales de leur taille et de comprendre les facteurs gouvernant les changements de taille des coccolithes sur une échelle de temps longue. Nous avons généré des données biométriques pour les groupes de coccolithes dominants au Crétacé supérieur, Broinsonia/Arkhangelskiella, Prediscosphaera, Retecapsa et Watznaueria, sur 36 échantillons du Cénomanien–Maastrichtien (100,5–66 Ma) provenant du Goban Spur dans l’Atlantique Nord-Est (DSDP Site 549). Ces données montrent que la taille des coccolithes appartenant aux groupes Prediscosphaera, Retecapsa et Watznaueria fut relativement stable durant tout le Crétacé supérieur, avec une variation de la taille moyenne inférieure à 0,7 μm. Au sein du groupe Broinsonia/Arkhangelskiella, les variations furent plus prononcées, avec une augmentation de la taille moyenne de ∼ 6 μm au Cénomanien jusqu’à ∼ 10 μm au Campanien. Ce changement significatif de la taille moyenne fut largement dû aux processus évolutifs (spéciations et extinctions), et en particulier à l’apparition d’espèces/sous-espèces plus larges (Broinsonia parca parca, Broinsonia parca constricta, Arkhangelskiella cymbiformis) au Campanien inférieur, remplaçant des espèces plus petites, telles que Broinsonia signata et Broinsonia enormis. Cependant, les fluctuations à court-terme au sein du groupe Broinsonia/Arkhangelskiella, observées aux transitions Cénomanien–Turonien et Campanien–Maastrichtien, pourraient refléter un changement des conditions paléoenvironnementales, telles que la température superficielle des eaux océaniques et la disponibilité en nutriment

Early Cretaceous biogeographic and oceanographic synthesis of Leg 123 (off Northwestern Australia)

Biogeographic observations made by Leg 123 shipboard paleontologists for Lower Cretaceous nannofossils, foraminifers, radiolarians, belemnites, and inoceramids are combined in this chapter to evaluate the paleoceanographic history of the northwestern Australian margin and adjacent basins. Each fossil group is characterized at specific intervals of Cretaceous time and compared with data from Tethyan and Southern Hemisphere high-latitude localities. Special attention is given to the biogeographic observations made for the Falkland Plateau (DSDP Legs 36 and 71) and the Weddell Sea (ODP Leg 113). Both areas have yielded valuable Lower Cretaceous fossil records of the circumantarctic high latitudes. In general, the Neocomian fossil record from DSDP and ODP sites off northwestern Australia has important southern high-latitude affinities and weak Tethyan influence. The same is true for the pelagic lithofacies: radiolarian chert and/or nannofossil limestone, dominant in the Tethyan Lower Cretaceous, are minor lithologies in the Exmouth-Argo sites. These observations, together with the young age of the Argo crust and plate tectonic considerations, suggest that the Argo Basin was not part of the Tethys Realm. The biogeography of the Neocomian radiolarian and nannofossil assemblages suggests opening of a seaway during the Berriasian that connected the circumantarctic area with the Argo Basin, which resulted in the influx of southern high-latitude waters. This conclusion constrains the initial fit and break-up history of Gondwana. Our results favor the loose fit of the western Australian margin with southeast India by Ricou et al. (1990), which accounts for a deeper water connection with the Weddell-Mozambique basins via drowned marginal plateaus as early as the Berriasian. In fits of the du Toit-type (1937), India would remain attached to Antarctica, at least until the late Valanginian, making such a connection impossible. After the Barremian, increasing Tethyan influence is evident in all fossil groups, although southern high-latitude taxa are still present. Biogeographic domains, such as the southern extension of Nannoconus and Ticinella suggest paleolatitudes of about 50°S for the Exmouth-Argo area. Alternatively, if paleolatitudes of about 35° are accepted, these biogeographic limits were displaced northward at least 15° along Australia in comparison to the southern Atlantic. In this case, the proto-circumantarctic current was deflected northward into an eastern boundary current off Australia and carried circumantarctic cold water into the middle latitudes. Late Aptian/early Albian time is characterized by mixing of Tethyan and southern faunal elements and a significant gradient in Albian surface-water temperatures over 10° latitude along the Australian margin, as indicated by planktonic foraminifers. Both phenomena may be indicative of convergence of temperate and antarctic waters near the Australian margin. High fertility conditions, reflected by radiolarian cherts, are suggestive of coastal upwelling during that time

Cenomanian/Turonian benthic foraminiferal faunas of the Demerara Rise depth transect (ODP Leg 207)

Abstrac

Biogeodynamics of Cretaceous marine carbonate production

We have compiled stratigraphic ranges of genera of calcareous nannofossils, calcispheres, planktonic foraminifers, larger benthic foraminifers, corals and rudists bivalves, and species of dasycladalean green algae. These taxa comprise the main planktonic and benthic carbonate producers of the Cretaceous, a period of exceptionally high sea level and palaeotemperatures that was characterized by unique assemblages of benthic carbonate producers and the significant rise in pelagic carbonate sedimentation. The autecology, physiological control on calcification, and carbonate-production potential of these groups is summarized. The observed diversity patterns are compared with proxy data of Cretaceous climate and seawater chemistry to elucidate the effect of environmental change on carbonate production and sedimentation. Two characteristic patterns are recognized. Diversity of calcareous nannofossils, calcispheres, planktonic foraminifers and corals trace the evolution of Cretaceous sea-level, while the diversity of dasycladalean algae, larger benthic foraminifers, corals and rudist bivalves show significant reductions at the level of oceanic anoxic events (OAEs). Benthic carbonate producers except for corals thus appear to have been more vulnerable to environmental change, and these general patterns appear to be unrelated to the autecology of the taxa investigated. The expansion of suitable habitats during episodes of high sea level and high temperatures appears to have been a more important control of diversity in calcareous nannofossils, planktonic foraminifers, and corals than changes in seawater chemistry. Aragonitic or aragonite-dominated benthic carbonate producers are most affected during extinction events related to OAEs, and there is a general trend of decreasing aragonite dominance throughout the Cretaceous. This is compensated by the extensive formation of calcitic hemipelagic chalk since the Cenomanian. The trend of decreasing aragonite dominance is independent of the level of biological control on calcification in the different taxa affected. The demise of aragonitic or aragonite-dominated carbonate producers at OAE1a (early Aptian) and OAE2 (Cenomanian–Turonian boundary interval) may be related to short episodes of reduced seawater carbonate-saturation caused by short-lived injections of CO2 from large igneous provinces that initiated OAEs. For OAE1a, this scenario also explains the retreat of carbonate platforms to low latitudes in the early Aptian, as sea-surface water typically has a higher carbonate saturation in warm, lower than in cooler, higher latitude waters. The gradual decrease of aragonite throughout the Cretaceous matches model simulations of seawater carbonate-saturation. An increase in the relative number of azooxanthellate coral genera following OAE1a and OAE2 suggests a disruption of photosymbiosis in the course of these global events due to high temperatures. However, the relative numbers of azooxanthellate genera continued to increase during the Late Cretaceous, when global temperatures declined. Due to the short residence time of major nutrients in seawater, these may have affected carbonate-producing ecosystems regionally. The recent patterns of benthic carbonate production being highest in oligotrophic environments cannot confidently be extrapolated to the Cretaceous. Our database records ranges of genera at the substage level. Higher-resolution stratigraphical studies of neritic carbonate sequences are required to understand what aspect of environmental change in the sequences are required to understand what aspect of environmental change in the sequence of events that unfolded in the context of OAEs caused the demise of benthic carbonate producers

The Wunstorf Drilling Project: Coring a Global Stratigraphic Reference Section of the Oceanic Anoxic Event 2

No abstract available. <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.4.05.2007" target="_blank">10.2204/iodp.sd.4.05.2007</a

Early Cretaceous Biogeographic and Oceanographic Synthesis of Leg 123 (off Northwestern Australia)

Biogeographic observations made by Leg 123 shipboard paleontologists for Lower Cretaceous nannofossils, foraminifers, radiolarians, belemnites, and inoceramids are combined in this chapter to evaluate the paleoceanographic history of the northwestern Australian margin and adjacent basins. Each fossil group is characterized at specific intervals of Cretaceous time and compared with data from Tethyan and Southern Hemisphere high-latitude localities. Special attention is given to the biogeographic observations made for the Falkland Plateau (DSDP Legs 36 and 71) and the Weddell Sea (ODP Leg 113). Both areas have yielded valuable Lower Cretaceous fossil records of the circumantarctic high latitudes. In general, the Neocomian fossil record from DSDP and ODP sites off northwestern Australia has important southern high-latitude affinities and weak Tethyan influence. The same is true for the pelagic lithofacies: radiolarian chert and/or nannofossil limestone, dominant in the Tethyan Lower Cretaceous, are minor lithologies in the Exmouth-Argo sites. These observations, together with the young age of the Argo crust and plate tectonic considerations, suggest that the Argo Basin was not part of the Tethys Realm. The biogeography of the Neocomian radiolarian and nannofossil assemblages suggests opening of a seaway during the Berriasian that connected the circumantarctic area with the Argo Basin, which resulted in the influx of southern high-latitude waters. This conclusion constrains the initial fit and break-up history of Gondwana. Our results favor the loose fit of the western Australian margin with southeast India by Ricou et al. (1990), which accounts for a deeper water connection with the Weddell-Mozambique basins via drowned marginal plateaus as early as the Berriasian. In fits of the du Toit-type (1937), India would remain attached to Antarctica, at least until the late Valanginian, making such a connection impossible. After the Barremian, increasing Tethyan influence is evident in all fossil groups, although southern high-latitude taxa are still present. Biogeographic domains, such as the southern extension of Nannoconus and Ticinella suggest paleolatitudes of about 50°S for the Exmouth-Argo area. Alternatively, if paleolatitudes of about 35° are accepted, these biogeographic limits were displaced northward at least 15° along Australia in comparison to the southern Atlantic. In this case, the proto-circumantarctic current was deflected northward into an eastern boundary current off Australia and carried circumantarctic cold water into the middle latitudes. Late Aptian/early Albian time is characterized by mixing of Tethyan and southern faunal elements and a significant gradient in Albian surface-water temperatures over 10° latitude along the Australian margin, as indicated by planktonic foraminifers. Both phenomena may be indicative of convergence of temperate and antarctic waters near the Australian margin. High fertility conditions, reflected by radiolarian cherts, are suggestive of coastal upwelling during that time

Calcareous nannofossil data and magnetostratigraphy from the Atlantic and Tethys Oceans - An integrated approach to approximate the Jurassic/Cretaceous (J/K) boundary in low-latitudinal pelagic and hemipelagic sequences.

The Tithonian \u2013 Early Berriasian interval is characterized by a major calcareous nannofossil speciation event: several Cretaceous genera and species first appear and rapidly evolve (Bralower et al., 1989). Progressive increases in diversity, abundance and degree of calcification (Nannofossil Calcification Event \u2013 NCE; Bornemann et al., 2003) have also been documented. Integrated magneto- and calcareous nannofossil biostratigraphy across the Jurassic/Cretaceous (J/K) boundary have been independently investigated in Tethyan land sections (Torre de Busi and Foza, Southern Alps) and at Atlantic Ocean DSDP sites (534A, Blake Bahama Basin and 105, Hatteras Basin). Calcareous nannofossil biostratigraphy, absolute and relative abundances have been obtained using three different techniques: random settling slides (Geisen et al., 1999), simple smear slides and ultra-thin sections (7-8 \ub5m thick). Similar variations in nannofloral abundance and composition, including the NCE, have been documented in both Atlantic and Tethys oceans (low latitude associations). All known calcareous nannofossil Zones and corresponding Subzones, following the biostratigraphic scheme of Bralower et al. (1989), have been recognized: NJ-19b; NJ-20a, NJ-20b; NJK-A, NJK-B, NJK-C across J/K boundary, NJK-D; NK-1 In the Middle Tithonian the nannoliths taxa C. mexicana minor, C. mexicana mexicana, and P. beckmannii increase significantly in abundance (Bornemann et al., 2003; Tremolada et al., 2006): the maximum relative abundance is reached between the calcareous nannofossil Zone NJ-20B and early NJK-A (Atlantic Ocean) or NJK-B (Tethys Ocean), followed by a decrease through NJK-A and NJK-B. Nannoconids appear and rapidly evolve across the J/K boundary reaching high relative abundances in the lowermost Berriasian (from calcareous nannofossil Subzone NJK-C to NK-1). Quantitative and morphometric studies have identified new potential events. Relative abundances of the placolith genera Watznaueria and the nannolith genera Conusphaera show opposite trends, while morphometric analysis show a size increase of placoliths, nannoliths and nannoconids during NCEs both in the Atlantic and Tethyan sections: calibration with magnetostratigraphy indicate that these trends are useful as additional bio-horizons for locating the J/K boundary. Calcareous nannofossil zonations and abundance variations of tethyan Torre de Busi section have also been correlated with calpionellid biostratigraphy, which has been investigated on the same samples used for the calcareous nannofossil study. It has been possible to identify the Chitinoidella, Crassicollaria and Calpionella Zones across the J/K boundary (Remane, 1986;Pop, 1994b and Reh\ue1kov\ue1 and Michal\uedk, 1997). Six polarity chrons (from CM22 to CM17) have been identified in DSDP site 534A, and in the tethyan land sections. The speciation of highly-calcified and dissolution resistant calcareous nannofossil forms, and related remarkable abundance and size increases, and the relative trends between genera Watznaueria and Conusphaera could provide new reliable stratigraphic tools for the approximation of the J/K boundary in low latitudinal pelagic and hemipelagic sequences in the Atlantic and Tethyan Oceans. In conclusion integrated stratigraphy, derived from the correlation among several calcareous nannofossils events, capionellid zonation and magnetostratigraphic events, can be used to characterize the J/K boundary interval, and is believed essential for defining the Jurassic/Cretaceous boundary particularly in the absence of orthostratigraphic markers (e.g. ammonites). References: Bornemann, A., Aschwer, U. and Mutterlose, J., 2003. The impact of calcareous nannofossils on the pelagic carbonate accumulation across the Jurassic-Cretaceous boundary. Palaeogeography Palaeoclimatology Palaeoecology, 199(3-4): 187-228. Bown, P.R. and Cooper, M.K.E., 1998. Jurassic. In: P.R. Bown (Editor), Calcareous nannofossil stratigraphy. British Micropalaeontological Society Publications Series. Kluver Academic Publishers, Dordrecht, Boston, London, pp. 34-85. Bown, P.R., Lees, J.A. and Young, J.R., 2004. Calcareous nannoplankton evolution and diversity through time. In: H. Thierstein and J.R. Young (Editors), ), Coccolithophores - From Molecular Processes to Global Impact. Springer, Berlin, pp. 481-508. Bralower, T.J., Monechi, S. and Thierstein, H.R., 1989. Calcareous nannofossil Zonation of the Jurassic-Cretaceous Boundary Interval and Correlation with the Geomagnetic Polarity Timescale. Marine Micropaleontology, 14: 153-235. Geisen, M., Bollmann, J., Herrle, J.O., Mutterlose, J. and Young, J.R., 1999. Calibration of the random settling technique for calculation of absolute abundances of calcareous nannoplankton. Micropaleontology, 45(4): 437-442. Erba, E. and Quadrio, B., 1989. Biostratigrafia a Nannofossili Calcarei, Calpionellidi e Foramminiferi planctonici della Maiolica (Titoniano superiore - Aptiano) nelle Prealpi Bresciane (Italia settentrionale). Riv. It. Paleont. Strat. 93(1): 3-108 Danelian, T. and Johnson, K.G., 2001. Patterns of biotic changes in Middle Jurassic to Early Cretaceous Tethyan radiolaria. Marine Micropaleontology 43: 239-260 Pop, G., 1994b. Calpionellid evolutive events and their use in biostratigraphy. Rom. J. Stratigraphy, 76: 7-24. Reh\ue1kov\ue1, D. and Michal\uedk, J., 1997: Evolution and distribution of calpionellids- the most characteristic constituents of Lower Cretaceous Tethyan microplankton. Cretaceous Research, 18: 493-504 Remane, J., 1986: Calpionellids and the Jurassic-Cretaceous boundary. Acta Geologica Hungarica, 29: 15-26 Rais, P., 2007. Ph.D. Thesis Roth, P.H., 1983. Jurassic and Lower Cretaceous calcareous nannofossils in the western North Atlantic (site 534): biostratigraphy, preservation, and some observation on biogeography and paleoceanography. Init. Rep. DSDP 76: 587-621 Tremolada, F., Bornemann, A., Bralower, T.J., Koeberl, C. and van de Schootbrugge, B., 2006. Paleoceanographic changes across the Jurassic/Cretaceous boundary: The calcareous phytoplankton response. Earth and Planetary Science Letters, 241(3-4): 361-371. Weissert, H. and Channell, J.E.T., 1989. Tethyan carbonate carbon isotope stratigraphy across the Jurassic/Cretaceous boundary: an indicator of decelerated global carbon cycling?. Paleoceanography 4(4): 483-49

Cretaceous large igneous provinces: from volcanic formation to environmental catastrophes and biological crises

The Cretaceous Period was marked by the formation of numerous Large Igneous Provinces (LIPs), several of which were associated with geologically rapid climate, environmental, and biosphere perturbations, including the early Aptian and latest Cenomanian Oceanic Anoxic Events (OAEs 1a and 2, respectively). In most cases, magmatic CO2 emissions are thought to have been the major driver of climate and biosphere degradation. This work summarises the relationships between Cretaceous LIPs and environmental perturbations, focussing on how volcanism caused climate warming during OAE 1a using osmium-isotope and mercury concentration data. The new results support magmatic CO2 output from submarine LIP activity as the primary trigger of climate warming and biosphere stress before/during OAE 1a. This submarine volcanic trigger of OAE 1a (and OAE 2), two of the most climatically/biotically severe Cretaceous events, highlights the capacity of oceanic LIPs to impact Earth's environment as profoundly as many continental provinces. Cretaceous magmatism (and likely output of CO2 and trace-metal micronutrients) was apparently most intense during those OAEs; further studies are needed to better constrain eruption histories of those oceanic plateaus. Another open question is why the Cretaceous Period overall featured a higher rate of magmatic activity and LIP formation compared to before and afterwards

Magnetobiostratigraphic Synthesis of Leg 123: Sites 765 and 766 (Argo Abyssal Plain and Lower Exmouth Plateau)

During ODP Leg 123, Sites 765 and 766 were drilled to examine the tectonic evolution, sedimentary history, and paleoceanography of the Argo Abyssal Plain and lower Exmouth Plateau. At each site, the quality of magnetostratigraphic and biostratigraphic records varies because of complicating factors, such as the predominance of turbidites, the presence of condensed horizons, or deposition beneath the CCD. Based primarily on the presence of nannofossils, the base of the sedimentary section at Site 765 was dated as Tithonian. A complete Cretaceous sequence was recovered at this site, although the sedimentation rate varies markedly through the section. The Cretaceous/Tertiary boundary is represented by a condensed horizon. The condensed Cenozoic sequence at Site 765 extends from the upper Paleocene to the lower Miocene. A dramatic increase in sedimentation rate was observed in the lower Miocene, and a 480-m-thick Neogene section is present. The Neogene section is continuous, except for a minor hiatus in the lower Pliocene. The base of the sedimentary section at Site 766 is Valanginian, in agreement with the site's position on marine magnetic anomaly Mil. Valanginian to Barremian sediments are terrigenous, with variable preservation of microfossils, and younger sediments are pelagic, with abundant well-preserved microfossils. Sedimentation rate is highest in the Lower Cretaceous and decreases continually upsection. Upper Cenozoic sediments are condensed, with several hiatuses