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Additional Information
Ammonites are a group of extinct marine mollusks that occupy the same class that includes octopuses, squids, and nautiluses.
The group Cephalopoda is divided into three subgroups: coleoids (including squids, octopuses and cuttlefishes), nautiloids (the nautiluses) and ammonites.
During their long history, ammonites survived three mass extinctions—most notably the Permian extinction, a global warming that was brought on by volcanic activity about 252 million years ago, and that killed 96 percent of the planet’s marine species. While many species of ammonites died out in that extinction event, scientists believe the survivors diversified explosively in the million years that followed. Ammonites hunted the planet’s seas until they were entirely wiped out by the same cataclysm that claimed the non-avian dinosaurs about 66 million years ago.
The cliffs and foreshore at Folkestone, Kent, England are renowned for their fossils, particularly the ammonites from the Gault Clay formation, which often exhibit remarkably preserved nacreous shells 🐚 The Gault Clay, dating to the Albian stage of the Early Cretaceous epoch (approximately 110–105 million years ago), is a dark blue-grey, soft, and silty mudstone that was deposited in a calm, relatively deep-water marine environment. This specific geological setting is conducive to the exceptional preservation of the original shell material.
Nacre, also known as mother-of-pearl, is the iridescent layer that lined the interior of the ammonite's shell when the creature was alive.
The nacreous layer is composed of tiny tabular crystals of aragonite, a form of calcium carbonate.
In many fossils, the original shell is dissolved or recrystallized, but the conditions in the Gault Clay often allowed for the original aragonite nacre to be preserved, sometimes replaced by pyrite (a process called pyritisation).
This preservation gives the fossilized shells a beautiful iridescent sheen, a characteristic often associated with Folkestone ammonites.
Significance of the Finds Folkestone is considered the type locality for the Gault Clay, making the ammonite finds here scientifically important.
Species Diversity: The Gault Clay contains a rich and diverse marine fauna, including over 100 species of ammonite, many belonging to the families like the Hoplitaceae (e.g., Hoplites, Anahoplites).
Stratigraphy: Ammonites are essential guide fossils for stratigraphy because they evolved rapidly, allowing geologists to accurately date and correlate rock layers (zones) over wide geographical areas. The Gault Clay has been divided into 13 beds, each characterized by specific ammonite marker species.
Collecting: The fossils are primarily found at the base of the slumping clay cliffs and loose among the boulders on the foreshore, especially after storms have scoured the beach. Due to the fragile nature of the aragonite shells and the surrounding clay, collectors must take care in their retrieval and preservation.
