Promicroceras Calcite Ammonite Fossil Lower Lias Black Ven Marls Jurassic Coast Charmouth Dorset UK

Description

Authentic Promicroceras Calcite Ammonite Fossil

This beautiful Promicroceras Calcite Ammonite Fossil is an authentic specimen from the Black Ven Marls, Lower Lias Formation, discovered on the Jurassic Coast at Stonebarrow Cliff, Charmouth, Lyme Regis, Dorset, UK. Dating to the Lower Jurassic period (approximately 195–200 million years ago), this ammonite represents one of the most recognisable and iconic species from the early Jurassic seas.

Your specimen was discovered by our own team members, Alister and Alison, on 23 October 2025, and has been expertly cleaned, prepped, and treated by Alison to enhance its natural detail and preserve its stunning calcite crystal structure. The photo shows the exact fossil you will receive, ensuring full transparency and authenticity.

Geological Context and Origin

The fossil originates from the Black Ven Marls Member of the Charmouth Mudstone Formation, part of the Lower Lias Group, which forms the foundation of the UNESCO World Heritage-listed Jurassic Coast. The Charmouth and Stonebarrow cliffs are among the most famous fossil localities in the world, historically studied since the time of Mary Anning in the early 19th century.

These deposits were laid down in a low-energy, offshore marine environment, where fine-grained clay and mud accumulated on the seabed. The environment was often anoxic (low in oxygen), allowing for exceptional preservation of marine life. Over millions of years, mineral-rich fluids percolated through the sediments, gradually replacing the original aragonite shell with translucent calcite, giving this fossil its distinctive glassy appearance.

The layers from which this specimen was recovered belong to the Sinemurian Stage of the Early Jurassic, specifically within the Promicroceras planicosta Zone, named for this very genus — an index zone used globally for Lower Jurassic stratigraphy.

Scientific Classification

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Cephalopoda
• Subclass: Ammonoidea
• Order: Ammonitida
• Superfamily: Psiloceratoidea
• Family: Promicroceratidae
• Genus: Promicroceras
• Age: Early Jurassic (Sinemurian Stage)
• Formation: Black Ven Marls, Lower Lias
• Locality: Stonebarrow Cliff, Charmouth, Lyme Regis, Dorset, UK

Promicroceras is one of the most important index ammonites of the Lower Jurassic, used by geologists to precisely date the surrounding rock layers. Its wide distribution and distinct morphology make it a key fossil for both scientific study and collectors.

Morphological Features and Preservation

This Promicroceras ammonite displays the classic tightly coiled, planispiral form characteristic of the genus. It has a small, finely detailed shell with crisp, radiating ribs that cross the whorls in gentle, symmetrical arcs. The ribs are slender and evenly spaced, creating a delicately sculpted surface that catches the light beautifully.

The fossil exhibits striking calcite mineralisation, giving it a natural glass-like translucency when viewed under light. In some areas, faint golden or honey-toned hues can appear within the calcite crystals, a hallmark of high-quality preservation from the Black Ven Marls. The scale cube (1 cm) shown in the photo provides accurate size reference; full measurements are included in the accompanying images.

This is a museum-grade display specimen, highly representative of the fine calcite-preserved ammonites found along the Charmouth stretch of the Jurassic Coast.

Palaeobiological and Scientific Significance

Promicroceras lived during the early Jurassic, when the seas around southern England were warm and shallow, supporting an abundance of marine life. These small ammonites were free-swimming cephalopods, related to modern squids and cuttlefish, with chambered shells that allowed them to regulate buoyancy. They likely fed on small crustaceans and plankton, propelling themselves through the water using jet propulsion.

The exceptional preservation of Promicroceras in calcite makes these fossils invaluable for both collectors and scientists. They reveal intricate details of early ammonite shell structure and growth patterns, helping palaeontologists understand the early evolution of the Ammonitida following the Triassic–Jurassic extinction event.

Authenticity and Provenance

All of our fossils are 100% genuine specimens and come complete with a Certificate of Authenticity. Each piece is responsibly sourced and professionally prepared by our team to ensure it retains its natural beauty and integrity. No casts or artificial enhancements are ever used — the fossil you see is the true geological specimen, exactly as discovered and prepared.

This Promicroceras Calcite Ammonite Fossil is an outstanding example of Britain’s Jurassic heritage — a perfect combination of scientific importance, natural artistry, and historical significance from the legendary Jurassic Coast of Lyme Regis, Dorset.