The oceanic anoxic event of The oceanic anoxic event of the Cenomanien-Turonienthe Cenomanien-Turonien

boundaryboundary

(Furlo, northern Apennines)(Furlo, northern Apennines)

Olivier Jacquat

Under the direction of

Prof. Föllmi and Dr. Adatte

Institute of geology, Neuchâtel

What we will see today :What we will see today :

• Overview of the C/T boundaryOverview of the C/T boundary

• Travel to Furlo (Italy)Travel to Furlo (Italy)

• Biozonation with foraminiferaBiozonation with foraminifera

• X-ray analysis on rock and clayX-ray analysis on rock and clay

• Isotope vs TOC in a modelling Isotope vs TOC in a modelling

• PhosphorusPhosphorus

• ConclusionsConclusions

CENOMANIAN-TURONIANANOXIC EVENT (OAEII)

The most extensive of the Mid CretaceousBio-events (93,5 Mioa).

Coincides with highest sea-level of thePhanerozoic (Transgression).

Coincides with highest global warmingof the last 115 Ma.

One of the biggest source rocks of theworld (e.g. Venezuela, Brazil).

Large positive global carbon-isotopeexcursion in both carbonate and organic matter, caused by a major perturbation of the carbon budget dueto extensive burial of OM in black shales.

This burial led to 40-80% reduction inPCO2 levels (below 500ppmv)

Rapid increase in accumulation OM rateswhere euxinic conditions reaching thephotic zone resulted in excellentpreservation of OM

Modest extinction event (7% of families,26 % of genera.(From Kaufman & Hart, 1995)

Preservation model

(Demaison, Shimkus et (Demaison, Shimkus et alal.).)

Productivity model (Caron, Kühnt et (Caron, Kühnt et alal.).)

e.g. Black sea

e.g. upwelling zone

“ enhanced productivity or/and better preservation?”

-enhanced OM accumulation in equatorial zones, high TOC relatively high sed. rate

-Slope environments (Cassis), low TOC high sed. rate

-Continental margin basin and deep sea, very high TOC values, but extremely low sed. rate. (Italy, Spain)

TOC accumulation rates inGrams per square meter and year

Kuhnt et al., 1990

Kuhnt et al., 1990

Main featuresMain features- Second order mass extinction- Second order mass extinction

-Widespread anoxiaWidespread anoxia

-Huge sea-level transgression-Huge sea-level transgression

-Global warming, but possible short cooling-Global warming, but possible short cooling

-Reduced Sr isotopes values-Reduced Sr isotopes values

-Increase in oceanic crustal productionIncrease in oceanic crustal production coincident with those perturbations due tocoincident with those perturbations due to large mantle plume related volcanic provinceslarge mantle plume related volcanic provinces over a period of 2-3Ma. Enriched trace-elementsover a period of 2-3Ma. Enriched trace-elements

-Increased COIncreased CO22

Hallam and Wignall, 2000

-∂-∂1313C positive excursionC positive excursion

-Disruption of the biosphere at CTB due to Disruption of the biosphere at CTB due to oceanic crust production (trace metal release),oceanic crust production (trace metal release), sea level transgression and disruption ofsea level transgression and disruption of circulation patterns. circulation patterns.

- Greenhouse was put in reverse by the increased- Greenhouse was put in reverse by the increased productivity, removal of C from the productivity, removal of C from the atmosphericatmospheric reservoir and buried as organic carbon in blackreservoir and buried as organic carbon in black shalesshales

CTB OAE IICTB OAE IIPossible scenarioPossible scenario

Estimation of the productivity at CTBEstimation of the productivity at CTB??????

- Warming, increase in CO2, runaway Warming, increase in CO2, runaway greenhouse climate, increase in greenhouse climate, increase in productivity contributing to anoxia andproductivity contributing to anoxia and mass extinction. mass extinction.

Hallam and Wignall, 2000

Late Cenomanien paleo-environements :

Modified from Dercourt et al., 1993

Furlo: Paleo-depth: 1000m, pelagic conditions, sluggish circulation,reduced sedimentation rate during CTB event (0.20 [cm/Ky])

Geographic situation of Furlo :

Furlo section :

Dominance of mudstones withplanktic foraminifera of “K” type;specialized, complex and large forms (e.g. R. cushmani), withscarce radiolarian inputs

Biofacies of the CTB at Furlo :

Dominance of radiolarian sands and laminated OM, diatoms, plankticforaminifera of “r” type;small opportunistic and low O2

tolerant forms (e.g.Heterohelix)

Dominance of mudstones withplanktic foraminifera of “K” type;specialized, complex and large forms (e.g. Dicarinella), withscarce radiolarian inputs

Biostratigraphy :

CEN

OM

AN

IAN

TU

RO

NIA

N?

R.c

ush

mani

W.a

rcheocr

eta

cea

H.h

elv

eti

ca

No c

arb

onate

s

200 μm

200 μm

200 μm

Where is the boundary ?

Premature disappearance of R.cushmanidue to dissolution ?

Isotope analysis help us !

Chemo-stratigraphy of the CTB :

Satisfactory correlation withthe well dated Pueblo section

Timing of the CTB event can be constrained using ∂13Corg peaks

Disappearance of R. cushmani (well before the first ∂13C peak) is an artifact probably due to intensive dissolution process.

Mineralogy : bulk rock :

a) Bonarelli depleted in carbonates

b) Quartz and Opal increase.

Mineralogy : clay (fraction 2μ) :

Nature and amount of organic matter at Furlo :

Marine

Terrestria/ altered

well preserved OM, of marine origin, in the entire B.E

Higher OM coincides with ∂13C maxima in the upper part of the Bonarelli level

Productivity vs Preservation : Mass Accumulation rate :

TOC [%]MAR TOC [g/m2/ky]

MAR[g/m2/ky]

Significant decrease in TOC mass accumulation rate in the topof the Bonarelli Event (artifact due to an overestimate time of theinterval CTB-FAD of H. helvetica??)

MAR TOC :0.1-0.25 [g/m2/y]

Very low MAR TOCdue to lowsed. rate

TOC :2-20%

Productivity vs Preservation Modelling

Productivity versus Preservation : Stella modelling results

A) 3-4 x increase of productivity

A)

B)

B) High TOC for the same productivity; betterpreservation due to increased anoxia, higherHI

C)

C) Decreased MAR TOC for the same productivity, but higher HI (Decreased PCO2 ?,miscalculation of the timing: Tragic use of helvetica FAD ????)

Phosphorus :

Bound to OM

>Preservation

Bound to skeletal matter

>Productivity

MAR[g/m2/ky]

P[mg/g]

Phosphorus

speciation !

Remarks :Remarks :

• Model based on present data Model based on present data (sarmiento (sarmiento et et al.)al.)

• A more precise knowledge of CO2 A more precise knowledge of CO2 interactions is requiredinteractions is required

• Model = simplification of the environmentModel = simplification of the environment

• Quantitative approach, test of qualitative.Quantitative approach, test of qualitative.

Other productivity proxies such as Phosphorus and Ba must be usedOther productivity proxies such as Phosphorus and Ba must be usedfor a better understanding of the CTB events.for a better understanding of the CTB events.

Depending on local conditions, additional factors may have to beDepending on local conditions, additional factors may have to becarefully examined. Therefore, productivity modelling must becarefully examined. Therefore, productivity modelling must beapplied in every kind of local setting.applied in every kind of local setting.

Isotopic and MAR TOC fluctuations can be resolved by the modelling Isotopic and MAR TOC fluctuations can be resolved by the modelling if ages are well constrained (do not use FAD of H. helvetica!).if ages are well constrained (do not use FAD of H. helvetica!).

Increased productivity cannot be the only factor for high MAR TOC,Increased productivity cannot be the only factor for high MAR TOC,preservation is also important.preservation is also important.

CONCLUSIONSCONCLUSIONS

Italian deep-sea sections can be chemostratigraphically Italian deep-sea sections can be chemostratigraphically correlated when usual biostratigraphic markers are lacking !correlated when usual biostratigraphic markers are lacking !These sections are condensed but rather complete.These sections are condensed but rather complete.

Thank you !Thank you !

Bibliography :

-Caron M., Robaszynski F., Amédro F., Baudin F., Decochnik J.-F., Hochuli P., Von Salis-Perch Nielsen K. & Tribovillard N., (1999) Estimation de la durée de l'événement anoxique global au passage Cénomanien/Turonien. Approche cyclostratigraphique dans la Formation Bahloul en Tunisie centrale. Bull. Soc. géol. France, 170, 2, 145-160

-Demaison G. J. and GT. Moore (1980) Anoxic environments and oil source bed genesis, Organic Geochemistry, 2, Issue 1, 9-31.

-Kuhnt W. and Wiedmann J. (1995) Cenomanian-Turonian source rocks: Palaeobiogeographic and paleoenvironmental aspects. In: Palaeogeography, palaeoclimatology and source rocks (Edited by A.Y. Huc), AAPG Studies in Geology 40, 213-231.

-Shimkus K., Trimonis E. (1974) Modern sedimentation in Black Sea. Degens ET, Ross DA (eds) The Black Sea-geology, chemistry and biology. AAPG member, 20, 249-278.