Philippe Claeys Earth System Sciences. Meteorite in - Dino s out

Transcription

1 Philippe Claeys Earth System Sciences Meteorite in - Dino s out

2 KT Clay Lower Paleocene KT clay KT Clay KT Clay Upper Maastrichtian Contessa, Italy El Guayal, Tabasco, Mexico Raton Basin, Stevns Caravaca, Klint, Danemark Spain US Western Contessa, Interior Italy Worldwide KT boundary is marked by a small clay bed

3 KT Contessa, Italy, Photo A. Montanari Microfossil changes across the boundary clay, no visible changes below

4 This small clay bed contains the famous enrichment in Iridium Ni-rich magnesioferrite spinels Image E. Robin high Fe 3+ /Fe 2+ Ir concentration in ppt or pg/g

5 Iridium, like the other platinum group (PGE) metals is rare at Earth surface, Ir distribution Mantle: 100 to < ppt Asteroid or comet (not differentiated) ± ppt Crust: < 20 ppt Pallasite Clastic sediments: < 100 ppt Carbonates: < 10 ppt & seawater KT boundary: ppt clay Eucrite NWA 1836 Most of Earth's Ir Values in parts per trillion Gibeon Fe km H chondrite but abundant in non-differentiated meteorites

6 The Ir anomaly identified at 112 KT boundary sites KT base Claeys et al., 2002, for an update Goderis et al (GCA)

7 Also, in the clay bed, the presence of shocked minerals forms another evidence for impact. Shocked quartz (SiO 2 ) & zircons with planar deformation features (PDF) = crystallographic response to shock wave propagation Pressure >> 5 Gpa (= millions x atm pressure) Only found in craters & nuclear explosions PDF SEM close up Western US shocked Quartz 5 µm 25 µm

8 KT base, Claeys et al., 2002 Larger & more abundant in Western Interior & Pacific sites

9 El Mulato, NE Mexico KT boundary Paleocene Cretaceous In NE Mexico, the KT boundary is a 4 m thick sandstone bed

10 3 coarse units form the KT boundary around GOM KT boundary ~ 4 m versus ~ 2 cm at distal locations

11 Basal ejecta unit Clay spherules El Mimbral 1 cm Glass core CaO-rich impact glass 1 mm SiO2 wt% At base of unit, clay spherules with aerodynamic shapes: cooled in flight, and a preserved glass core (Spherule update see Belza et al. in press GCA) M i mbral (M exi co) gl ass Bel oc (Ha i ti ) gl ass (from Sigur dsson et al., 1991; I zett, 1991; Koeb er l & Sigu r d sson, 1992 ; Claeys u n p u bli shed ) 45 Yel low glass Black glass 65 70

12 The thick sand cuts the underlying unit Multiple paleocurrent directions NE Mexico Charcoiled plant fragments & shallow marine fossils Result of gigantic tsunami wave(s)

13 Model for the spreading of forest fires through superheading of atmosphere, at distal sites by re-entering ejecta

14 Still Ir anomaly at top

15 Middle to Lower Paleocene carbonate pockets of green spherules, altered glass bombs? Cm-size basement clast in the matrix 20 to 50 m? thick Flow bed or spheroid bed Dolomite breccia with mega-blocks Zone of fractured beds? Upper K Barton Creek dolomite Composite section showing the distal KT boundary ejecta blanket on the Yucatan platform Ejecta blanket: Dolomite-rich diamictite with large blocks, rare shocked quartz and basement clasts

16 Chicxulub crater Proximal KT sites in the Gulf of Mexico region with thick ejecta, tsunami bed & Ir anomaly Ejecta blanket covers most of Yucatan peninsula

17 Wells within the Chicxulub crater Cenote ring UNAM 5 UNAM 7 NASA Shuttle radar topography image At time of impact Yucatan target consisted of ~ 3 km carbonates & evaporites on top of Pan African basement

18 Geophysical imaging of the impact structure Coast line 3 D view of crater morphology based on gravity Elevated central peak ring with magnetic anomaly Seismic reflection profile

19 Cratering process Univ. of Arizona

20 Today Offshore IODP in ? Drilling at Yaxcopoil in 2002 Merida Crater now buried under 1 km of recent sediments

21 Cores from the Yaxcopoil drilling in 2002

22 Isotope genectic link impact glass with Chicxulub melt-rock Yucatan basement

23 After 1 sec. a huge curtain of material was ejected from deep within the structure, composed of solid, molten and vaporized meteorite & target rock. A huge fireball rose out of the crater

24 Modeling Fireball, Ir is spread wordwide Dust CO2 SOx sec. U.ATM km Ejecta L. ATM Target (N. Artemieva) km

25 Fine pulverized dust and S aerosols were injected into the atmosphere, blocking sunlight for up to one entire year the Earth cooled abruptly for a short time. SOx reaction in the atmosphere triggered severe acid rain?

26 Photosynthesis decreased, the whole food chain was affected

27 Sunlight is lost for months Sunlight Returns Extinct Survivors No food Food And the winner is. Extinct No food No sunlight plants die Food available Detritus Survivors (Sheehan 2004)

28 Environmental consequences of the Stress Air blast near impact site Heat from re-entering ejecta Tsunamis near impact site Large earthquakes (> 10 R) Soot from continent-scale wildfires Nitric + H2SO4 acid rain (ph ocean?) Darkness from dust, no photosynthesis Heavy metal poisoning? Cold from dust Sulfur aerosol cooling ( Gt) KT impact Time scale hours hours hours to weeks days to years months months > 6 months years years years to decades Destruction Ozone layer (NOx, Cl, Br) decades? H2O greenhouse ( Gt) CO2 greenhouse ( Gt) Perturbated oceanic cycles > years > years years

29 Consequences of the impact at Chicxulub Fall back ejecta Forest fires temperature Dust, SO X soot Greenhouse CO 2 Darkness Hours days weeks months years decades centuries Time

30 Type and origin of projectile? Chromium system ε 53 Cr CC Fragment of metal-sulphide-rich carbonaceous chondrite recovered from KT boundary in Pacific ocean (Kyte 1998) 2 cm KTB Chrondrites SNC Moon Earth Mn E.C 53 Cr 53 Cr/ 52 Cr = 0 std Earth Meteorites differ due to early planetary Mn/Cr fractionation Shukolyukov& Lugmair (1998) Goderis et al PGE database = CM or CO Asteroidal origin or comet origin?

31 Remember dino s have dominated Earth for >120 millions of years. Without the Chicxulub impact, might they still be here today? Reading: Walter Alvarez T-rex and the crater of doom. Princeton Univ. Press

32 and what has Deccan trap do to with it Recently GSA (2014) Deccan must be involved in K-Pg mass extinction because all other extinction levels associated with LIP (let s not cite him) Mark Richards (UC Berkeley) Chicxulub seismic activity triggered worldwide volcanism, including major Deccan pulse??? + new age for Deccan (~68 Ma) Os isotope traces first volcanism in India, but no association with faunal disturbance in ocean or on land, although warming effect is possible Schulte et al 2010