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

Description

Exceptional Promicroceras Calcite Multi-Ammonite Block from the Jurassic Coast

This stunning Promicroceras Calcite multi block fossil originates from the Black Ven Marls, part of the Lower Lias Formation on the iconic Jurassic Coast of Dorset, UK, a UNESCO World Heritage Site famous for its world-class fossil deposits. The specimen was discovered by our team members, Alister and Alison, on 08 October 2025, and has been expertly cleaned, prepared, and treated by Alison to museum-quality standards. The photo shows the actual specimen you will receive, ensuring complete authenticity and transparency.

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

All of our fossils are 100% genuine specimens, and each comes complete with a Certificate of Authenticity, verifying its origin, geological context, and preparation.

Geological Context and Formation

This fossil block comes from the Black Ven Marls Member of the Charmouth Mudstone Formation, dating to the Lower Jurassic (Sinemurian Stage, approximately 199–190 million years ago). These fossil-rich sediments were deposited in a calm, shallow sea, part of the early Jurassic marine environment that once covered southern England.

The marls and clays at Black Ven, near Lyme Regis, are globally recognised for their exceptional fossil preservation, formed under low-oxygen conditions that prevented decay and allowed delicate shells to mineralise over millions of years. The result is an exquisite calcite replacement, where the original shell material of the ammonite was gradually transformed into translucent, honey-coloured calcite, revealing fine ribbing and chamber detail under natural light.

Scientific Classification

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

The genus Promicroceras is among the most distinctive of early Jurassic ammonites and is widely distributed throughout Sinemurian strata in the UK and Europe. Fossils of Promicroceras define the Promicroceras planicosta biozone, a key stratigraphic interval used internationally by geologists to date early Jurassic marine deposits. Its abundance and fine preservation make it one of the most studied ammonite taxa of the Lower Lias.

Morphological Description

Promicroceras ammonites are small, finely detailed shells typically measuring between 10–25 mm in diameter. They display a tightly coiled, involute shell with a narrow umbilicus and delicate, regular ribbing that radiates gracefully across the flanks. The ribs terminate evenly across the venter without interruption, giving the shell an elegant radial symmetry.

This multi-ammonite fossil block preserves several Promicroceras individuals naturally grouped together, representing a snapshot of early Jurassic marine life. Each ammonite exhibits a remarkable degree of detail, and the calcite mineralisation enhances the aesthetic appeal by creating a subtle golden glow and crystalline texture within the chambered shell structure.

Such specimens capture not only the artistry of natural mineralisation but also the ecological dynamics of the early Jurassic seabed.

Depositional Environment and Palaeontological Significance

The Black Ven Marls were deposited in a low-energy, offshore environment, where fine sediments slowly accumulated on the seabed. Periodic oxygen depletion limited biological activity, allowing fossils to remain undisturbed. These conditions produced some of the best-preserved Lower Jurassic ammonites known to science.

Ammonites like Promicroceras were nektonic cephalopods, closely related to modern squids and nautiluses. They lived in open marine waters, moving by jet propulsion and preying on small planktonic organisms. Their chambered shells served as buoyancy devices, allowing them to control depth with precision. Because they evolved rapidly and were widespread, ammonites are invaluable index fossils, allowing geologists to correlate rock layers across vast regions with exceptional accuracy.

The preservation quality of this multi-ammonite block demonstrates the unique palaeoenvironmental stability of the Black Ven area during the Sinemurian stage. It provides a tangible link to a time when life in the seas was recovering and diversifying after the major extinction event that ended the Triassic Period.

Collector’s and Display Value

This Promicroceras Calcite multi block fossil is both scientifically important and visually striking. Its natural grouping of multiple ammonites, combined with the lustrous calcite crystallisation, makes it an ideal piece for collectors, educators, or display in a home or museum setting. The fossil’s origin from Lyme Regis, the historic birthplace of palaeontology, adds historical and cultural depth—this is the same coastline famously explored by Mary Anning in the early 19th century.

Every specimen is carefully stabilised and professionally finished to ensure long-term preservation while maintaining its natural integrity.

A truly exceptional example of an authentic Lower Jurassic Promicroceras Calcite multi-ammonite fossil, combining natural beauty, geological heritage, and scientific value from the heart of the Jurassic Coast.