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Cretaceous-Paleogene Boundary 2 (Caravaca, Spain Stratigraphy (Boundary…
Cretaceous-Paleogene Boundary 2
Agost, Spain Stratigraphy
Impact layer - brownish
with iron oxides (oxidised)
Dark carbonate layer
- dark since
carbonates died off
Light carbonate layer
- carbonate content gradually increase as new carbonates radiate
Carbonates
with time
Impact killed off most carbonates
sharp drop across boundary
Stepwise recovery
into Paleogene
Carbonates recovered after few kyr
to stability
Almost switched entire plankton off
Never as abundant as before in Maastrichtian
Only select few survived & radiated
Caravaca, Spain Stratigraphy
Spikes at boundary
- iridium, chromium
Upper Maastrichtian Layer
(before impact) - carbonate rich
Ejecta Layer
-
thin tectite rich
layer
Boundary Clay
-
ocean with little life
first ~10 kyr after impact
mass kill of plankton
reflects Strangelove ocean
Carbonate layer
- Incoming new Paleocene plankton (forams)
Why did plankton suffer so much?
Debated to this day
Aerosols triggered global warming ?
Photosynthesis inhibited by dust ?
Planktic Foram Species abundance
Many species before impact
Impact killed all but one or two
Survivors spike at boundary
- free to bloom
Response of other groups ? Coccolithophores
Phytoplankton - photosynthesising algae
Nanofossils
Flourished from Triassic (like forams)
Radiation ~10 kyr after wiped out at boundary
Some extinct, some survived & flourished
Microfossils allow trace exact boundary
Dinosaurs much harder to find
Microfossils found throughout oceans
Ocean Evolution
Stable ocean before impact
Darwinian evolution
Gradual evolution with time
Stasis - in equilibrium
Mass extinctions fundamentally change understanding of evolution
'Punctuated' rapid evolution after
Adaptive radiation
survivors rapidly adapt to new conditions
begin to radiate
a few kyr after impact
Tsunami Layers El Mulato, Mexico
Huge ripples abundant at boundary
Recognised as
tsunamite
layer
Ripples record variable palaeocurrent
Sedimentation disturbed at impact site
Huge waves sloshing around basin
Redistribution of sediment
Sandstone bed interrupts
sed below boundary
Recognised as
tsunamite
layers
Abundant tectites at bottom of layer
Iridium at top of unit
Schmidt Interpretation
One Impact
Impact occurred
Tectites deposited
as vaporised rock lithifies & returns to Earth
3. Tsunami arrives
forming megaripples
3. Iridium layer forms as ashfall settles
Some claim there were 2 impacts...there was only one