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

Description

Exceptional Multi-Ammonite Fossil Block from the Jurassic Coast

This remarkable Arnioceras and Promicroceras multi block fossil originates from the world-famous Black Ven Marls, part of the Lower Lias Formation on the Jurassic Coast of Dorset, UK—a UNESCO World Heritage Site celebrated for its rich and well-preserved marine fossils. The specimen was discovered by our own team members, Alister and Alison, on 08 October 2025, and has been professionally cleaned, prepared, and treated by Alison to museum-quality standards. The photograph shows the actual specimen you will receive; it is a carefully chosen, 100% genuine fossil, complete with a Certificate of Authenticity.

Scale cube = 1 cm. Please see photos for full sizing.

Geological Context and Formation

This fossil block was unearthed from the Black Ven Marls Member of the Charmouth Mudstone Formation, dating to the Lower Jurassic (Sinemurian Stage, approximately 199–190 million years ago). During this time, the area now known as Lyme Regis, Dorset, was covered by a warm, shallow epicontinental sea—ideal for ammonites and other marine life. The fine-grained marl and shale deposits created a low-oxygen environment that allowed exceptional fossil preservation. These strata are particularly known for yielding multiple ammonite species within the same matrix, reflecting subtle ecological and temporal variations within the Sinemurian seas.

Scientific and Taxonomic Details

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

These two genera represent distinct but overlapping ammonite lineages within the early Jurassic seas. Their co-occurrence in a single block provides a valuable insight into biozonal overlap within the Arnioceras semicostatum and Promicroceras planicosta biozones, characteristic of the Sinemurian succession in southwest England.

Morphological Characteristics

The Arnioceras specimens are recognised by their moderately evolute shells, strong radial ribs, and a slightly compressed whorl section, giving them a distinctly ribbed and symmetrical appearance. In contrast, Promicroceras exhibits a small, tightly coiled shell with fine ribbing and smooth sutures, displaying the delicate, ornate beauty for which this genus is prized by collectors. Together, these ammonites form a stunning natural composition, contrasting robust sculptural texture with fine, intricate detail. Their arrangement in a shared matrix highlights both their palaeoecological association and aesthetic appeal.

Depositional and Palaeoenvironmental Significance

The Black Ven Marls are among the most scientifically important Lower Jurassic sites in Europe. These marine sediments were deposited in a low-energy shelf environment, where fine mud and calcareous material settled gently on the seabed. Periodic anoxic events limited scavenging, ensuring the exceptional preservation of ammonites and associated fauna. Fossils from this locality are often used for biostratigraphic correlation throughout northwest Europe, helping geologists date rock layers with remarkable precision.

Collector’s and Display Value

This Arnioceras and Promicroceras multi block is not only a scientifically significant specimen but also a visually striking piece ideal for collectors, educators, and enthusiasts alike. Its origin from the iconic Jurassic Coast at Lyme Regis—home of Mary Anning and countless historic discoveries—adds historical prestige and educational value. Each fossil from this site tells a story of ancient oceans and evolutionary history, making this piece a captivating display for both private and professional collections.

Authenticity and Preparation

Every fossil we sell is guaranteed 100% genuine, responsibly collected, and legally obtained. Your specimen comes with a Certificate of Authenticity, verifying its origin and preparation. It has been meticulously cleaned, stabilised, and conserved to preserve both its natural integrity and aesthetic presentation.

This multi-ammonite block from the Lower Lias is a timeless reminder of life from the early Jurassic seas—a unique, irreplaceable piece of Britain’s geological heritage.