Promicroceras Calcite Multi Block Ammonite Fossils Lower Lias Lyme Regis Dorset UK

Description

Beautiful Promicroceras Calcite Multi-Ammonite Block from the Jurassic Coast

This stunning Promicroceras Calcite multi block fossil comes 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 known globally for its rich fossil heritage and exceptional geological exposures. The specimen was discovered by our team members, Alister and Alison, on 07 October 2025, and has been professionally cleaned, prepared, and treated by Alison to ensure a visually striking and scientifically accurate presentation.

The photo shows the actual specimen you will receive, not a stock image. Scale cube = 1 cm; please refer to photos for full sizing information.

All of our fossils are 100% genuine specimens and come complete with a Certificate of Authenticity, verifying their provenance and quality.

Geological Context and Formation

This fine specimen originates from the Black Ven Marls Member of the Charmouth Mudstone Formation, deposited during the Lower Jurassic (Sinemurian Stage, approximately 199–190 million years ago). At this time, southern England was submerged beneath a warm, shallow sea that formed part of the early Jurassic epicontinental system. The calm marine conditions and fine-grained sedimentation of the Black Ven Marls provided ideal circumstances for fossil preservation, with low-oxygen seabeds preventing scavenging and decay.

These marls and clays, rich in carbonate minerals, allowed for the calcite replacement of ammonite shells, giving rise to the exquisite crystalline lustre and soft golden hue characteristic of Promicroceras Calcite specimens from this locality. The Jurassic Coast exposures of Black Ven, near Lyme Regis, are among the most scientifically significant fossil-bearing sites in Europe, providing a detailed record of marine evolution following the Triassic–Jurassic extinction event.

Scientific Classification

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

Promicroceras is a small but highly distinctive ammonite genus that occurs abundantly within early Sinemurian strata. Fossils of this genus are commonly associated with the Promicroceras planicosta biozone, a key stratigraphic marker used globally to define a precise interval of early Jurassic time. Their presence helps geologists establish detailed chronostratigraphic frameworks for the Lower Lias sediments across Europe and beyond.

Morphological Description

The Promicroceras ammonite is renowned for its delicate and intricately coiled morphology, typically measuring between 10–25 mm in diameter. It displays a tightly involute shell with a narrow umbilicus and finely ribbed flanks. The ribs extend from the inner whorls to the outer venter in a smooth, radial pattern, giving the fossil an elegant, symmetrical appearance.

In this particular multi-ammonite block, several Promicroceras specimens are preserved together, illustrating the species’ natural clustering and environmental distribution. The calcite mineralisation has filled or replaced the original aragonitic shell material, resulting in a lustrous, semi-transparent finish that beautifully accentuates the ribbing and internal chamber structure. When viewed under natural or artificial light, the crystalline surfaces shimmer subtly—testament to millions of years of geological transformation.

Palaeoenvironment and Depositional History

The Black Ven Marls were deposited in a low-energy offshore environment, where fine muds and silts accumulated on a relatively stable sea floor. Occasional anoxic events limited bioturbation, allowing for the exceptional preservation of ammonites, bivalves, and other marine fauna. The fine laminations within the marls are evidence of slow, steady sedimentation under oxygen-poor conditions, ideal for fossilisation.

Ammonites like Promicroceras were free-swimming cephalopods that occupied the upper levels of the Jurassic sea, preying on small plankton and crustaceans. Their rapid evolutionary turnover and widespread distribution make them invaluable index fossils, crucial for correlating rock layers throughout the Jurassic sedimentary record. This specimen provides a rare opportunity to view multiple ammonites in natural association, representing a true palaeoecological snapshot of early Jurassic marine life.

Collector’s and Display Significance

This Promicroceras Calcite multi block fossil from Lyme Regis is both a scientifically significant and visually captivating piece. Its natural arrangement of multiple ammonites, combined with the fine calcite crystal preservation, makes it ideal for both collectors and educational displays. The fossil has been carefully stabilised and conserved using professional techniques to ensure long-term preservation without altering its natural integrity.

Originating from the same historic cliffs explored by Mary Anning, this specimen continues the legacy of fossil discovery along the Jurassic Coast—a region that has shaped our understanding of prehistoric marine life.

A genuine and timeless example of early Jurassic beauty, this Promicroceras Calcite multi block fossil perfectly captures the artistry of nature and the heritage of one of Britain’s most celebrated fossil localities.