Clay mineral assemblages of Mesozoic pelagic and flysch sediments of the Lombardian Basin (Southern Alps): implications for palaeotectonics, palaeoclimate and diagenesis

Deconinck, J.-F.; Bernoulli, Daniel

doi:10.1007/bf01828765

Cited by 30 publications

(17 citation statements)

References 19 publications

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“…In the Maiolica limestones, there is a general increase in detrital clay upsection (H. Weisseft, personal communication, 1993) which is manifest by an increase in frequency and thickness of dark interbedded clay-rich layers. In the Maiolica at Breggia, Deconinck and Bernoulli [1991] have noted upsection increases in the percentage of chlorite and illitc in the clay mineral assemblage. We therefore attribute the the enhanced upsection paramagnetic signal to clay minerals, rather than to superparamagnetic grains.…”

Section: Magnetite Bearing Tethyan Limestones (Maiolica Formation)mentioning

confidence: 92%

Comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones

Channell¹,

McCabe²

1994

J. Geophys. Res.

128

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For white magnetite‐bearing Mesozoic pelagic limestones from Italy which carry a “primary” magnetization, the values of Mrs/Ms and Hcr/Hc generally lie in the pseudo‐single domain (PSD) field of the Day et al. (1977) plot. The logarithmic plot of Mrs/Ms against Hcr/Hc gives a straight line (R = 0.814) with slope and intercept close to the empirical mixing line of Parry (1982) for single domain (SD) and multidomain (MD) magnetite. For one of the white pelagic limestone formations (Maiolica Formation), samples with hysteresis ratios closer to the MD field display increased paramagnetic susceptibility and are from the upper part of the formation characterized by increased detrital clay. We therefore associate the increased MD magnetite with increased detrital influx. For pinkish and reddish varieties of the Italian pelagic limestones, the presence of hematite is manifest by high saturation fields, a wide range of Hcr/Hc, and “wasp‐waisted” hysteresis loops attributed to the mixing of magnetite and high‐coercivity authigenic hematite. The hysteresis ratios for a collection of Paleozoic and Mesozoic remagnetized magnetite‐bearing limestones from Britain, Nevada, Alaska and the Appalachians lie mainly outside the PSD field and appear to follow a power law trend. Following Jackson et al. (1993), the high values of Hcr/Hc and the characteristically “wasp‐waisted” hysteresis loops can be interpreted in terms of a fine‐grained subspherical high‐coercivity SD magnetite mixed with a high proportion of superparamagnetic magnetite. The slope and intercept of the power law relationship for Mrs/Ms and Hcr/Hc in the remagnetized limestones are distinct from those observed for the Italian limestones, and may provide a means of fingerprinting magnetite of “primary” as opposed to diagenetic origin.

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Section: Magnetite Bearing Tethyan Limestones (Maiolica Formation)mentioning

confidence: 92%

Comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones

Channell¹,

McCabe²

1994

J. Geophys. Res.

128

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“…Up‐section the silica content decreases and the red argillaceous limestones with chert bands are rich in aptychi (Rosso ad Aptici member). Several clay intercalations of pure smectite composition are interpreted as devitrified volcanic ash layers (Deconinck & Bernoulli, ). The whole Selcifero Lombardo Formation yielded rich radiolarian assemblages that allowed detailed dating (Baumgartner et al ., , ,c; Kocher, ; Baumgartner, ).…”

Section: Geological and Palaeogeographic Settingmentioning

confidence: 97%

Mesozoic radiolarites – accumulation as a function of sea surface fertility on Tethyan margins and in ocean basins

Baumgartner

2013

Sedimentology

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Radiolarites, commonly comprising chert‐shale couplets, feature prominently in the Mesozoic stratigraphy of the Neotethyan realm. The origin and significance of these deposits, especially with regard to understanding palaeoproductivity in that region, remains controversial. This study examines transport processes and accumulation rates of radiolarians/radiolarites, as well as the chronology of radiolarite sedimentation based on revised data from the Southern Alps and new data from the Balagne Nappes, Alpine Corsica. Results suggest that the spatio‐temporal distribution of carbonate and silica on Tethyan margins was governed by extensive lateral transport of radiolarian tests from topographic highs to basins. Palaeoclimatic, rather than palaeotectonic, changes seem to have triggered changes in surface fertility which, in turn, brought about major facies changes observed in Tethyan marginal basins: Regional platform demise – possibly due to eutrophication and onset of radiolarite deposition in the Early Bajocian – can be correlated with a positive shift in the carbon isotope curve, whereas platform recovery and the end of radiolarite accumulation correlates with a gradual decline in δ13C‐values. The existence of a vigorous trans‐Pangaean, equatorial current system that could have produced regional upwelling is questioned because of evidence for Middle Jurassic to Early Cretaceous oligotrophic conditions in the Proto‐Caribbean and the Central Atlantic. The ‘Caribbean River Plume Model’ is proposed as a possible alternative to upwelling in the Jurassic Western Tethys. Dissolved nutrients may have been dispersed in low salinity lids that originated from river plumes of rivers from tropical Africa and warm‐temperate Eurasia. Vast areas of the pre‐Late Cretaceous world ocean must have accumulated radiolarites at low rates (<4 g cm−2 10−3years) represented by the condensed, long‐lived (>50 Myr) radiolarite sections observed in many Circumpacific terranes. Radiolarian chert and claystone could be the normal pelagic sediment during Ordovician to Early Cretaceous time in far‐offshore, open oceanic settings, where dilution by terrigenous material and periplatform shallow‐water carbonates was absent.

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“…The size of the osmium-isotope excursion is an order of magnitude greater than that characterizing the PETM. Locally, as in southern Switzerland, pelagic sediments show a dramatic 'spike' in the abundance of kaolinite in lower Toarcian sediments, equally suggestive of enhanced continental weathering (Deconinck & Bernoulli 1991).…”

Section: Rapid Warming At the Onset Of The Early Toarcian (Jurassic) Oaementioning

confidence: 98%

Evidence for rapid climate change in the Mesozoic–Palaeogene greenhouse world

Jenkyns

2003

Philosophical Transactions of the Royal Society of London. Seri

449

308

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The best-documented example of rapid climate change that characterized the socalled 'greenhouse world' took place at the time of the Palaeocene-Eocene boundary: introduction of isotopically light carbon into the ocean-atmosphere system, accompanied by global warming of 5-8• C across a range of latitudes, took place over a few thousand years. Dissociation, release and oxidation of gas hydrates from continental-margin sites and the consequent rapid global warming from the input of greenhouses gases are generally credited with causing the abrupt negative excursions in carbon-and oxygen-isotope ratios. The isotopic anomalies, as recorded in foraminifera, propagated downwards from the shallowest levels of the ocean, implying that considerable quantities of methane survived upward transit through the water column to oxidize in the atmosphere. In the Mesozoic Era, a number of similar events have been recognized, of which those at the Triassic-Jurassic boundary, in the early Toarcian (Jurassic) and in the early Aptian (Cretaceous) currently carry the best documentation for dramatic rises in temperature. In these three examples, and in other less well-documented cases, the lack of a definitive time-scale for the intervals in question hinders calculation of the rate of environmental change. However, comparison with the Palaeocene-Eocene thermal maximum (PETM) suggests that these older examples could have been similarly rapid. In both the early Toarcian and early Aptian cases, the negative carbon-isotope excursion precedes global excess carbon burial across a range of marine environments, a phenomenon that defines these intervals as oceanic anoxic events (OAEs). Osmium-isotope ratios ( 187 Os/ 188 Os) for both the early Toarcian OAE and the PETM show an excursion to more radiogenic values, demonstrating an increase in weathering and erosion of continental crust consonant with elevated temperatures. The more highly buffered strontium-isotope system ( 87 Sr/ 86 Sr) also shows relatively more radiogenic signatures during the early Toarcian OAE, but the early Aptian and Cenomanian-Turonian OAEs show the reverse effect, implying that increased rates of sea-floor spreading and hydrothermal activity dominated over continental weathering in governing sea-water chemistry. The Cretaceous climatic optimum (late Cenomanian to mid Turonian) also shows evidence for abrupt cooling episodes characterized by episodic invasion of boreal faunas into temperate and subtropical regions and changes in terrestrial vegetation; drawdown of CO 2 related to massive marine carbon burial (OAE) may be implicated here. The absence of a pronounced negative carbon-isotope excursion preceding the One contribution of 14 to a Discussion Meeting 'Abrupt climate change: evidence, mechanisms and implications'.

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Clay mineral assemblages of Mesozoic pelagic and flysch sediments of the Lombardian Basin (Southern Alps): implications for palaeotectonics, palaeoclimate and diagenesis

Cited by 30 publications

References 19 publications

Comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones

Comparison of magnetic hysteresis parameters of unremagnetized and remagnetized limestones

Mesozoic radiolarites – accumulation as a function of sea surface fertility on Tethyan margins and in ocean basins

Evidence for rapid climate change in the Mesozoic–Palaeogene greenhouse world

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