Always a privilege this week to see the ‘ammonite pavements’ in Lyme Regis on the Jurassic Coast in Dorset, UK. Above are some of my photographs of hundreds of large ammonites exposed at low tide.
Thought provoking to imagine as you walk over the fossilised sea floor of 200 Million years ago, when the UK was roughly where North Africa is today, in a large epicontinental sea.
These Blue Lias rocks are packed with giant Arietites Ammonites. This assemblage may have been caused by rapid cementation after a storm. Sea level and climate changes probably influencing the cycles of organic rich bituminous shales, marls and limestone layers. Shallower water depths favouring limestone deposition.
The timing of diagenesis dissolution and cementation may explain why some ammonites only have the outer whorl preserved (those cemented on top of layers) whilst the inner whorls were crushed and are not preserved. Whereas, those within beds generally have both inner and outer whorls uncrushed and preserved.
Fossilised lignite / driftwood is also common (see below).
More Here and papers on ammonite preservation and here
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