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You are here: Story of the Jurassic Coast > Geology > Environmental Stories
The Mesozoic Era saw dramatic changes in environmental conditions, culminating in mass extinction events as well as catalysing exceptional biodiversity.
Environmental changes through the Mesozoic can be broadly categorised into the three main temporal periods, the Triassic, Jurassic and Cretaceous. Within each of these periods, subtle alterations within the main environmental story were present.
The Triassic Period was characterised by hot, desert conditions that began during the preceding Permian Period. During this time, The Jurassic Coast, was located close to the equator within the supercontinent Pangaea, creating considerably warmer environmental conditions. Triassic rocks are dominated by sandstones and muds, coloured red by iron minerals that oxidised in the arid environment.
The Jurassic Period was dominated by marine conditions. Jurassic rocks of sequences of clay, sandstone, then limestone, are characterised by several cycles of sea level rise and gradual fall. The Jurassic ended with a fall in sea level exposing the area as a low-lying coastal landscape.
The Cretaceous Period began with coastal swamp, lagoon, forest and salt flat environments but these were replaced by a large river system and sea level rise towards the middle of the Cretaceous. This sea level rise led to a return of marine conditions. As the continents continued to drift, the Jurassic Coast moved further away from the equator and closer to its present position, creating slightly cooler seas. Sea levels peaked at roughly 200 m higher than those seen today. This high sea level led to the formation of chalk rocks, comprised largely of fossilised plankton.
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