Promicroceras Calcite Ammonite Fossil Nodule Lyme Regis Jurassic UK Lower Lias Black Ven Marls Natural Crystal Authentic Specimen

Description

Promicroceras Calcite Ammonite Nodule – Jurassic Coast, Dorset

This exceptional Promicroceras calcite ammonite nodule is a genuine fossil specimen from the renowned Black Ven Marls of Charmouth, Lyme Regis, along the iconic Jurassic Coast in Dorset, UK. Dating to the Lower Lias of the Early Jurassic period, approximately 199–190 million years ago, this fossil beautifully combines natural preservation with crystalline mineralisation.

Carefully chosen for its quality and display appeal, this ammonite is preserved within its original nodule, often referred to as a “natural concretion,” which has protected the fossil for millions of years. The internal chambers of the ammonite display attractive calcite crystal growth, enhancing both its scientific and aesthetic value. The exact specimen shown in the photographs is the one you will receive and includes a Certificate of Authenticity lifetime guarantee generic card.

Geological Context – Black Ven Marls and Lower Lias Formation

The Black Ven Marls form part of the Lower Jurassic Lias Group, a sequence of alternating clay and marl layers deposited in a shallow marine environment covering southern Britain during the Early Jurassic. These sediments are famous for their exceptional fossil preservation, particularly ammonites, which are abundant and diverse within this formation.

This specimen is typically associated with the Sinemurian stage, a time of significant ammonite diversification. Promicroceras is well known from the Promicroceras planicosta Biozone, making it an important index fossil for dating Lower Jurassic strata.

The formation of nodules within the marls played a crucial role in preservation. These calcareous concretions formed early during diagenesis, encapsulating organic remains and protecting them from compaction and erosion.

Fossil Identification – Promicroceras (Order: Ammonitida)

Promicroceras is a classic Early Jurassic ammonite belonging to the order Ammonitida and is commonly placed within the family Arietitidae and superfamily Psiloceratoidea. It is one of the most recognisable ammonites from the Lower Lias due to its distinctive morphology and widespread occurrence.

This genus is particularly important in biostratigraphy, as it defines a key ammonite biozone used by geologists to correlate rock layers across Europe.

Morphology and Notable Features

This specimen exhibits the characteristic features of Promicroceras, enhanced by natural calcite mineralisation:

• Tight, evolute coiling with clearly visible whorls
• Strong, regular ribbing across the shell surface
• Well-preserved chamber structure within the nodule
• Calcite crystal infill within the internal chambers
• Natural nodule matrix providing both protection and visual contrast

The calcite crystals formed as mineral-rich waters permeated the buried shell, filling the chambers and crystallising over time. This process creates a unique interplay between fossil structure and mineral growth, making each piece one of a kind.

Depositional Environment and Fossil Formation

During the Early Jurassic, the area around Lyme Regis was submerged beneath a warm, shallow sea rich in marine life. Ammonites such as Promicroceras thrived in these waters, playing a vital role in the marine ecosystem.

After death, the shell settled on the seabed and became buried by fine sediments. In certain conditions, early cementation of the surrounding sediment formed a nodule around the fossil. This nodule protected the ammonite from compression and preserved its three-dimensional structure.

Over millions of years, groundwater carrying dissolved minerals infiltrated the chambers, depositing calcite crystals and enhancing the fossil’s internal features.

Scientific and Collecting Significance

Promicroceras is one of the most important index fossils of the Lower Jurassic, making specimens highly desirable for both collectors and educational purposes. Fossils from the Jurassic Coast are globally recognised for their quality and historical importance, with Lyme Regis being one of the most significant fossil localities in the world.

Calcite-filled nodules are especially prized, as they preserve both the external shell morphology and internal chamber structure in remarkable detail.

Authenticity and Presentation

This fossil is a 100% genuine specimen and includes a Certificate of Authenticity lifetime guarantee generic card. The fossil shown in the photographs is the exact piece you will receive.

Full sizing is available via the listing photographs, allowing you to clearly assess the scale and detail of the specimen before purchase.

Perfect for Collectors, Display, or Study

This Promicroceras calcite ammonite nodule is an outstanding example of Jurassic fossil preservation, combining scientific importance with natural beauty. Ideal for fossil collectors, geology enthusiasts, or as a unique display piece, it represents a genuine and fascinating piece of Earth’s ancient marine history from the famous Jurassic Coast.