Arnioceras Calcite Multi Block Ammonites Fossil Lower Lias Lyme Regis Dorset UK

Description

Magnificent Arnioceras Calcite and Multi-Ammonite Block from the Jurassic Coast

This exceptional Arnioceras Calcite and multi block fossil ammonite originates from the Black Ven Marls, part of the Lower Lias Formation on the world-famous Jurassic Coast of Dorset, UK — a UNESCO World Heritage Site celebrated for its abundance of marine fossils and geological importance. The specimen was discovered by our team members, Alister and Alison, on 08 October 2025, and has been professionally cleaned, prepared, and treated by Alison to showcase the fine detail and natural calcite preservation.

The photo shows the actual specimen you will receive, ensuring complete transparency and authenticity.

Scale cube = 1 cm. Please refer to the photograph for full sizing information.

All of our fossils are 100% genuine specimens and include a Certificate of Authenticity confirming provenance and preparation.

Geological Context and Formation

This specimen was recovered from the Black Ven Marls Member of the Charmouth Mudstone Formation, within the Lower Jurassic (Sinemurian Stage, approximately 199–190 million years ago). These layers form part of the Lower Lias, a geological sequence renowned for its finely laminated mudstones and marls, deposited in a calm, shallow marine environment during the early Jurassic Period.

The sediments accumulated on a sea floor characterised by low-oxygen conditions, preventing decay and scavenging, thus enabling the exquisite preservation of ammonite shells and other marine organisms. The calcite mineralisation within this specimen has naturally replaced the original aragonitic shell, creating a captivating golden hue and crystalline lustre that highlights every rib and whorl of the ammonites.

Scientific Classification

• Genus: Arnioceras
• Order: Ammonitida
• Superfamily: Psiloceratoidea
• Family: Arnioceratidae
• Formation: Lower Lias (Black Ven Marls)
• Geological Stage: Sinemurian
• Locality: Black Ven, Lyme Regis, Dorset, UK

This specimen belongs to Arnioceras, a genus of early Jurassic ammonites widely distributed throughout Europe. It is a biostratigraphic index fossil typical of the Arnioceras semicostatum biozone, a globally recognised marker used by geologists to identify the lower Sinemurian stage. Specimens like this one play an important role in understanding faunal succession and evolutionary recovery following the Triassic–Jurassic extinction event.

Morphology and Preservation

The Arnioceras ammonite is easily recognised by its strongly ribbed, moderately evolute shell with ribs radiating from the umbilicus and extending cleanly across the flanks to the venter. The ribs are consistent and robust, giving the shell an elegantly sculpted form. The whorls are slightly compressed, providing symmetry and balance that make the species particularly attractive to collectors.

In this multi-ammonite fossil block, several Arnioceras individuals are preserved together, capturing a moment from the Lower Jurassic sea floor where these cephalopods once thrived. The calcite infilling and replacement illuminate the internal chamber structures, producing a subtle crystalline glow under light — a natural work of art formed over 190 million years ago. The fossil surface exhibits exceptional definition, displaying fine growth lines and the complex sutures typical of ammonites from this horizon.

Depositional Environment and Palaeontological Significance

The Black Ven Marls represent a low-energy, offshore marine setting within a gently subsiding basin. The periodic alternation of marl and clay layers records subtle changes in sediment input and sea level, providing a detailed archive of early Jurassic marine conditions.

Ammonites such as Arnioceras were nektonic predators, living freely in the upper water column and feeding on smaller planktonic organisms. Their rapid evolution and widespread distribution make them excellent zone fossils for correlating rock sequences across Europe and beyond. The Sinemurian Stage in which these fossils occur marks an important phase in the radiation of early Ammonitida, with Arnioceras representing a transitional form between earlier psiloceratids and later, more ornate ammonite lineages.

Collector’s and Display Appeal

This Arnioceras Calcite and multi block ammonite fossil is both scientifically valuable and visually striking. Its combination of crystalline calcite preservation, fine ribbing, and multi-specimen composition makes it a perfect piece for display or educational use. Each ammonite is naturally framed in the original marl matrix, preserving the authentic character of the fossil’s geological setting.

Originating from Black Ven, Lyme Regis — the same iconic cliffs explored by Mary Anning, whose discoveries revolutionised palaeontology — this specimen embodies the enduring legacy of British fossil collecting. It has been meticulously stabilised, cleaned, and treated to museum standards by Alison, ensuring both durability and beauty.

A rare opportunity to own an authentic Lower Jurassic Arnioceras Calcite fossil block, discovered and prepared by our team — a genuine piece of the Earth’s ancient oceans, perfect for collectors, educators, and enthusiasts alike.