Causes and consequences of calcareous nannoplankton evolution in the Late Jurassic : implications for biogeochronology, biocalcification and ocean chemistry.

Abstract The Jurassic was a time of important changes in the ocean/continent configuration: important reorganization of oceanic and climatic condition are underlined by a most remarkable widespread shift from mostly siliceous to mainly calcareous sedimentation. The beginning of Late Jurassic was a time of exceptionally low carbonate accumulation rates, while the uppermost Jurassic is characterized by high sedimentation rates and the deposition of calcareous nannofossil oozes. During the Late Jurassic calcareous nannoplankton experienced a progressive increase in diversity, abundance and degree of calcification, culminating in the Middle Tithonian \u2013 Lower Berriasian interval. Upper Callovian \u2013 Lower Berriasian sections from the Southern Alps (Northern Italy) have been analyzed for calcareous nannofossil biostratigraphy; selected sections (Southern Alps )and the DSDP Site 534 A (Atlantic Ocean) were investigated for calcareous nannofossil relative and absolute abundances and to derive paleo-fluxes. Data were compared with litho-magnetostratigraphy, calpionellid biostratigraphy, where available, and information on the tectonic, palaeoceanographic and palaeoclimatic regime. Biostratigraphic investigations led to revise the biostratigraphic schemes available for Late Jurassic, and a new scheme is proposed for Tethyan Realm. Quantitative investigations and derived paleo-fluxes show a calcareous nannofossil increase in diversity, abundance and calcification, inducing a major change in pelagic sedimentation from predominantly siliceous (lower part of the Rosso ad Aptici) to mostly calcareous (Rosso ad Aptici \u2013 Maiolica transition and Maiolica). In particular, an impressive speciation started in the Tithonian, including the first occurrence and early diversification of nannoliths and nannoconids. The increase in abundance of coccoliths and nannoliths affected the ocean carbonate system, especially because of the high rates of some nannolith calcification. These nannoplankton evolutionary events (NCEs) occurred during times of low spreading rates, low pCO2, low Mg/Ca ratio, cool climatic conditions and relatively oligotrophic oceans. Available data suggest that calcareous phytoplankton was stimulated by environmental stability rather than perturbations. This is consistent with modern coccolithophorid distribution, showing highest diversity and abundance as well as calcification in stable oligotrophic oceanic areas. A precise stratigraphic control allows to model the Late Jurassic nannofossil speciation episode and the abundance increase of high-calcified genera (Conusphaera, Polycostella, Faviconus, Nannoconus), evaluating environmental causes and consequences of evolution. The results suggest that the Late Jurassic nannoplankton evolution was mostly controlled by the following factors: A) a decrease in pCO2 due to decreased spreading rate and/or increased weathering rate (87Sr/86Sr); B) a decrease in oceanic Mg/Ca ratio values promoting low Mg-CaCO3 and CaCO3 biomineralization (nannofossils fertilization sensu Stanley, 2006); C) cool climatic condition (Price, 1999). The Tithonian time interval provides examples of accelerated intra- and inter-generic evolutionary rates (a speciation event) during a time period of environmental stability, in absence of coeval environmental change evidences. It provides an excellent opportunity to investigate nannoplankton evolutionary behaviour, and on the basis on the achieved stratigraphic and time framework, evolutionary trends of calcareous nannoplankton were quantified: example of Philetic Gradualism, Punctuated Equilibrium and Punctuated Gradualisms as well were described

Change in the earth system and calcareous nannofossil evolution: does any linkage exist? An example from the Late Jurassic Tethys Ocean

In the Late Jurassic calcareous nannoplankton experienced a progressive increase in diversity, abundance and degree of calcification, culminating in the Middle Tithonian \u2013 Berriasian interval (Calcareous Nannofossils Zone NJK and NK1 \u2013 Bralower et al., 1989). Were there any linkages between calcareous nannoplankton evolution and geologic, palaeoceanographic or palaeoclimatic events? Upper Oxfordian - Berriasian selected sections from the Southern Alps (N Italy) have been analyzed for calcareous nannofossil biostratigraphy, relative and absolute abundances and palaeofluxes. Data were compared with litho-magneto-chemostratigraphy and available information on the tectonic, palaeoceanographic and palaeoclimatic regime. A calcareous nannofossil increase in diversity, abundance and calcification occurred, inducing a major change in pelagic sedimentation from predominantly siliceous (Radiolarite fm. and lower part of the Rosso ad Aptici fm.) to mostly calcareous (upper part fo Rosso ad Aptici fm. and Maiolica fm.). In particular, an impressive speciation started in the Tithonian, including the first occurrence and early diversification of nannoliths and nannoconids. The increase in abundance of coccoliths and nannoliths affected the ocean carbonate system, especially because of the high rates of some nannolith calcification. These nannoplankton evolutionary events occurred during times of low spreading rates, low pCO2, low Mg/Ca ratio, cool climatic conditions and relatively oligotrophic oceans. Available data suggest that calcareous phytoplankton was stimulated by environmental stability rather than perturbations. This is consistent with modern coccolithophorid distribution, showing highest diversity and abundance as well as calcification in stable oligotrophic oceanic areas. A precise stratigraphic control allows to model the Late Jurassic nannofossil speciation episode and the abundance increase of high-calcified genera (Conusphaera, Polycostella, Faviconus, Nannoconus), evaluating environmental causes and consequences of evolution. Preliminary results suggest that the Late Jurassic nannoplankton evolution was mostly controlled by the following factors: A) a decrease in pCO2 due to decreased spreading rate and/or increased weathering rate (87Sr/86Sr); B) a decrease in oceanic Mg/Ca ratio values promoting low Mg-CaCO3 and CaCO3 biomineralization (nannofossils fertilization sensu Stanley, 2006); C) cool climatic condition (Price, 1999)

I sistemi carbonatici giurassici della Sardegna orientale (Golfo di Orosei) ed eventi deposizionali nel sistema carbonatico giurassico-cretacico della Nurra (Sardegna nord-occidentale)

This field trip gives a panoramic of the facies association and sedimentological-stratigraphic evolution of Jurassic-Cretaceous depositional systems of eastern (Golfo di Orosei) and western (Nurra) Sardinia. Carbonate deposition in western Sardinia occurred in an epeiric sea during Jurassic and Cretaceous whereas carbonates of the eastern Sardinia figure out a complex depositional settings with intraplatformal basins facing the Alpine Tethys from a basal transgression in the Bajocian to Berriasian. The presence of partly coeval succession allows a comparison between these two depositional systems and highlights relation with global and regional events. The Jurassic-Cretaceous carbonate succession of Sardinia shows similarities with coeval succession of the Provencal-Pyrenean domain (Nurra), nevertheless differences, both in terms of facies characters and distribution and range of stratigraphic gaps, occur between the successions of eastern Sardinia. These differences can be ascribed to different paleogeographic and depositional settings

Calcareous nannofossil quantitative data from the Tithonian-Berriasian interval: implications for the Jurassic/Cretaceous boundary

The Jurassic/Cretaceous (J/K) boundary time interval is characterized by a major calcareous nannofossil speciation episode: several Cretaceous genera and species appear and rapidly evolve. Nannoliths, and especially nannoconids, show a progressive increase in diversity, abundance and degree of calcification through time, which have been documented in both Atlantic and Tethys oceans (Nannofossil Calcification Event \u2013 NCE, Bornemann et al., 2003; NCEs, Casellato, 2009). Calcareous nannofossil biostratigraphy, relative and absolute abundances have been investigated on selected Tethyan land sections (Southern Alps, Northern Italy) in order to integrate calcareous nannofossil events with the polarity chron sequence and, partly, with calpionellid biostratigraphy. Analyses have been performed on un-heated magneto-core end-pieces, using both simple smear slides and ultra-thin sections (7-8\ub5m thick). Calcareous nannofossil absolute abundances, performed on ultra-thin sections, have been also investigated on the DSDP Site 534 from Central Atlantic Ocean, in order to compare nannofossil patterns in different paleogeographic settings and to point out their supraregional importance. All calcareous nannofossil zones and subzones proposed for the Tithonian-Berriasian interval (NJ-19; NJ-20a, NJ-20b; NJK-A, NJK-B, NJK-C, NJK-D; NK-1, Bralower et al. 1989) have been recognized. Quantitative studies indicate that nannolith taxa (firstly F.multicolumnatus, then C.mexicana, finally P.beckmannii) increase significantly in abundance, size and calcification degree gaining lithogenetic proportion (NCE1, Casellato 2009): the abundance acmes are reached in discrete steps between calcareous nannofossil Zones NJ-20 and NJK-A. Nannoconids rapidly evolve across the J/K boundary, reaching lithogenetic abundances from calcareous nannofossil Subzone NJK-C upward (NCE2, Casellato 2009), when highly calcified conical morphotypes (N.wintereri, N.steinmannii minor, N.kamptneri minor) appear. This event correlates with the middle CM19n to the CM18r interval and the \u2018explosive\u2019 appearance of small globular Calpionella alpina (C.alpina \u201cacme\u201d). Calcareous nannofossil quantitative studies permit to identify additional potential events, characterized by an increase in size, calcification degree and abundance of nannoliths. Calibration with magnetostratigraphy indicates that these trends could be very useful as new bio-horizons in identifying the lower Upper Tithonian and for locating the J/K boundary. The speciation of highly calcified nannoconids and their remarkable increase in volume and abundance, increase the stratigraphic resolution of the J/K boundary time interval. 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. 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. Casellato C.E. (2009) - Causes and consequences of calcareous nannoplankton evolution in the Late Jurassic: implications for biogeochronology, biocalcification and ocean chemistry. PhD Thesis, 116 pp., Universit\ue0 degli Studi di Milano, Scuola di Dottorato \u201cTerra, Ambiente e Biodiversit\ue0\u201d, Dottorato di ricerca in Scienze della Terra, Ciclo XXI

Calcareous nannofossil biostratigraphy and paleoceanography of the "Toarcian Oceanic Anoxic Event at Colle di Sogno (Southern Alps, Northern Italy)

We present calcareous nannofossil biostratigraphy and abundances for the Upper Pliensbachian-Lower Toarcian interval, including the Toarcian Oceanic Anoxic Event (T-OAE), represented by the Fish Level at Colle di Sogno (N Italy). In addition to biohorizons identifying NJT 5 and NJT 6 nannofossil zones, the first occurrences of C. superbus and D. striatus constrain the onset and the end of the T-OAE, respectively. We propose the last occurrence of M. jansae as additional event to approximate the end of the T-OAE at lower latitudes. Quantitative data highlight the "Schizosphaerella decline" marking the Pliensbachian/Toarcian boundary and the "Schizosphaerella crisis" at the onset of the T-OAE as supplementary biohorizons. S. punctulata and M. jansae constitute most of the micrite in the interval below the Fish Level, which is marked by an increase in abundance of small coccoliths remaining abundant in the overlying interval, with limited contributions of S. punctulata, while M. jansae disappears. Principal Component Analysis implemented nannofossil paleoecological and paleoenvironmental reconstructions. The latest Pliensbachian was characterized by stable oligotrophic conditions favourable to calcification at low pCO2 levels promoting the proliferation of deep-dwelling and highly-calcified S. punctulata. During the earliest Toarcian an initial pulse of continental run-off introduced terrigenous material favouring the intermediate-dweller M. jansae and the low-salinity adapted Calyculus. Higher nutrient concentrations and ocean acidification magnified during the T-OAE, stimulatying mesotrophic low-calcified coccolith-producers and suppressing k-strategist deep- to intermediate-dwellers. After the T-OAE, partial recovery of calcareous nannoplankton indicates still perturbed conditions. Ecosystem modifications anticipated the T-OAE of -1 million years with species origination and major changes in assemblages

Does environmental stability stimulate species renovation?

The Tithonian-Berriasian time interval is characterized by a major calcareous nannoplankton speciation episode: several coccolith and nannolith genera and species first appear and rapidly evolve, reaching a high diversity, abundance, and calcification degree. The history of calcareous nannoplankton indicates that times of accelerated rates of radiations (or extinctions) generally correlate with global changes in the geosphere, hydrosphere and atmosphere suggesting that evolutionary patterns are intimately linked to environmental modifications (Roth, 1989; Bown et al., 2004; Erba, 2006). Nevertheless, the Tithonian-Berriasian interval provides examples of intra- and intergeneric accelerated evolutionary rates (an origination event) during a time period of general environmental stability, in absence of coeval environmental change evidence. The Tithonian - Early Berriasian can be regarded as a \u201cquiet\u201d interval as far as the C cycle is concerned; the \u3b413C curve shows a gradual minor decline after the Oxfordian anomalies and prior to the Valanginian event. The Tithonian-Berriasian speciation episode provides an excellent opportunity to study modo and tempo of calcareous nannoplankton evolution relative to absent environmental change, which is believed to be instrumental for driving biological evolution. Nannofossils have been investigated in sections from the Tethys and Atlantic oceans in order to discriminate among local, regional or global causes, and to verify possible diachroneity in calcareous phytoplankton evolution and/or in response to global changes. Calcareous nannofossil species richness, first and last occurrences and relative abundance were achieved. Different evolution modes have been proposed since Darwin\u2019s Evolutionary Theory: Phyletic Gradualism (Darwin, 1859), Punctuated Equilibrium (Gould & Eldredge, 1977) and Punctuated Gradualism (Malmgren et al., 1984). Phyletic gradualism holds that new species arise from slow, steady transformation of populations providing gradational fossil series linking separate phylogenetic species. Punctuated gradualism implies long-lasting evolutionary stasis interrupted by rapid, but gradual phyletic transformation without lineage splitting. Punctuated equilibrium explains the appearance of new species by rapid speciation occurring in small peripheral isolated populations, followed by migration to other areas where fossil sequence usually shows a series of sharp morphological breaks. The Tithonian-Berriasian nannoplankton speciation episode is characterized by the first occurrence of several new nannolith genera (Conusphaera, Polycostella, Pseudolithraphidites and Lithraphidites, Nannoconus, Assipetra, Braarudoaphaera and Micrantolithus), few new coccoliths genera (Umbria, Rhagodiscus, Cruciellipsis) and several coccoliths and nannolith new species. Most new species rapidly evolved generating related new species or subspecies, often in a time interval shorter than two millions of years, providing examples of all speciation modes. The appearance of highly calcified nannoplankton and its evolution in the Tithonian-Berriasian interval were possibly controlled by abiotic factors, such as seawater chemistry (Mg/Ca ratio and pCO2) and temperature (cool climatic episode). On the other hand this speciation episode corresponds to an interval of environmental stability, probably favoring diversification and expansion of calcareous nannoplankton, adapted to oligotrophic oceans. Nannoliths seem to have experienced all three evolutionary modes, while coccoliths provide examples for only two of them. Evolutionary patterns in the studied interval permit the following considerations: at specific level both nannoliths and coccoliths gradually evolve in time intervals of more that 1 Ma, while at generic level a rapid speciation is most common. Bown, P.R., Lees, J.A., Young, J.R. (2004). Calcareous nannoplankton evolution and diversity through time. In: Thierstein, H.R., Young, J.R. (Eds.), Coccolithophores. From Molecular Processes to Global Impact. Springer-Verlag, Berlin, pp. 481 \u2013 508. Darwin, C. (1859). L\u2019Origine delle specie. In: L\u2019Evoluzione. Newton, 1994 Erba, E. (2006). The first 150 million years history of calcareous nannoplankton: Biosphere - Geosphere interaction. Paleogeogr. Paleoclimatol.Paleoecol. 232, 237-250. Gould, S.J. & Eldredge, N. (1977). Punctuated equilibria: the tempo and mode of evolution reconsidered. Paleobiology 3:115-151. Malmgren, B.A., Berggren, W.A. & Lohmann, G.P. (1984). Species formation through Punctuated Gradualism in Planktonic Foraminifera. Science 225, 317-319. Roth, P.H. (1989). Ocean circulation and calcareous nannoplankton evolution during the Jurassic and Cretaceous. Palaeogeogr. Palaeoclimatol. Palaeoecol. 74, 111 \u2013 126. Stenseth, N.C. & Maynard Smith, J. (1984). Coevolution in ecosystems: rred queen evolution or stasis? Evolution 38, 870-880. Van Valen, L. (1973). A new evolutionary law. Evolutionary Theory 1:1-30