Sedimentological Evidence

Introduction


Early Cretaceous


Mid-Cretaceous



Late Cretaceous



Palaeontological
Evidence



Sedimentological
Evidence



Isotopical Evidence



Summary



Glossary



References



Climate Change Home Page




KT Event
Links



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Sedimentological Evidence


Terrestrial Rocks

The lack of evidence of tillites and associated glacial deposits, which are the best indicators of cold climates, suggests a warm Late Cretaceous climate. This is supported by the high sea level at the time, which implies the absence of polar ice sheets.

Further evidence are the substantial evaporite deposits in the Late Cretaceous. Evaporites signify a persistent excess of evaporation over precipitation and occur in subtropical climates.


Marine Rocks

In the Late Cretaceous, sea level was up to 200 m higher than it is at present. Due to this, the continents were well dispersed and marine sediments were forming in abundance. The Late Cretaceous is therefore characterised by marine deposits such as:
  • pelagic oozes,
  • limestones, including chalk,
  • marls,
  • sandstones.
The high sea level created a large shallow marine area where chalk, and other limestones predominate across the Earth. These rocks form in warm, shallow water; further evidence for a warm equable climate throughout the Late Cretaceous. The evidence for a substantial accumulation of fossil fuels (e.g. coal, oil and gas) in the Mid to Late Cretaceous, supports the theory of an extensive shallow submergence at this time.

The chalk productivity essentially stopped at the end of the Maastrichtian as a result of the KT extinction. The onset of clay deposition and possibly low oxygenation at the sea floor caused the geologically instantaneous destruction of these marine habitats.

 


 

| Intro | Early Cretaceous | Mid-Cretaceous | Late Cretaceous |

| Palaeontological Evidence | Sedimentological Evidence | Isotope Evidence |

| Summary | Glossary | Further Reading | Climate Change Home Page | KT Event Links | Back to Bristol Palaeontology Homepage |