The Purbeck Group is a distinctive sequence of evaporites, thin sandstones and shelly limestones interbedded with marl and shales.
Sedimentology shows they were deposited in a fluctuation of freshwater, brackish, hypersaline and quasi-marine environments.
Flora and fauna are indicative of variable terrestrial, lacustrine, saline and lagoonal associations.
The climate of the early Purbeck Group was likely similar to the modern Mediterranean and became wetter towards the end of the Berriasian.
While the Purbeck Group was originally known as the informal Purbeck Beds, it can now be divided into the upper Durlston Formation and the lower Lulworth Formation.
The "Upper Purbeck Beds" and a majority of the "Middle Purbeck Beds" are contained within the Durlston Formation, the oldest deposit of which is the Cinder Beds of the Stair Hole Member.
The Cinder Beds have, at times, been considered the Jurassic-Cretaceous Boundary, which would result in the entire Lulworth Formation being latest Jurassic, Tithonian, in age.
However, despite the uncertainties about the age of the beds because of a lack of correlation through fauna or dating, it is generally accepted that the Purbeck Group is entirely earliest Cretaceous in age, with the Lulworth Formation being early Berriasian.
The Purbeck Group is visibly underlain by the Late Jurassic Portland Group in Durlston Bay and has a transitional but locally obscured boundary with the overlying Wealden Group at Peveril Point.

There is a great deal of uncertainty as to the location of the specimens collected from the Lulworth Formation; the only definitive way to test would be to analyse the matrix of each specimen to determine its salinity.
The Purbeck Group has the most diverse ornithischian fauna of any deposit in Dorset, and is one of few Berriasian deposits globally, but is limited almost entirely to cranial or dental material, and tracks.
Owenodon hoggii is the only other named ornithischian from the beds and is known only from a dentary with teeth originally described as a species of Iguanodon.
A femur and dorsal of an intermediate hadrosauriform is also known, along with intermediate ornithopods and ankylosaurs known both from body fossils and from footprints.
Beyond ornithischians, the Lulworth Formation also contains the theropod Nuthetes, amphibians, turtles, lizards, snakes, mammals and crocodilians, and varieties of invertebrates.
Amphibians from the Lulworth Formation include the salamanders Apricosiren and an intermediate batrachosauroidid, the albanerpetontid Celtedens and the frog Sunnybatrachus.
Four taxa of turtles are known, the cryptodires Dorsetochelys, Helochelydra, Hylaeochelys and Pleurosternon.
The Purbeck is one of the most diverse Early Cretaceous deposits globally for lepidosaurians.
The genera Becklesius, Dorsetisaurus, Durotrigia, Paramacellodus, Pseudosaurillus, Parasaurillus, Purbicella, Saurillus, Parviraptor and three unnamed tooth morphologies represent the known squamates, and fossils referred to the rhynchocephalians Homoeosaurus and Opisthias have also been found.

The diverse mammal assemblage includes the small eutherians Durlstodon and Durlstotherium; the non-eutherian peramurans Peramus, Peramuroides, Magnimus and Kouriogenys; the non-eutherian symmetrodonts Spalacotherium, Tinodon and Thereuodon; the non-eutherian dryolestoids Achyrodon, Amblotherium, Dorsetodon, Chunnelodon and Phascolestes; the non-eutherian multituberculates Albionbaatar, Bolodon, Gerhardodon, Plagiaulax and Sunnyodon; the non-eutherian eutriconodonts Trioracodon and Triconodon, the non-mammalian morganucodontan Purbeckodon; and the non-mammalian docodont Peraiocynodon.
Crocodilians from within the Lulworth deposits include Goniopholis gracilidens, Theriosuchus pusillus, Pholidosaurus purbeckensis, dubious remains previously known as Goniopholis tenuidens, and the dubious taxon Macellodus brodiei.
Specific sites within the formation also preserve the primitive snipe flies Simulidium and Pseudosimulium, and the nematoceran flies Eoptychoptera, Brodilka and Eucorethrina.
The Purbeck Group is a distinctive sequence of evaporites, thin sandstones and shelly limestones interbedded with marl and shales. Sedimentology shows they were deposited in a fluctuation of freshwater, brackish, hypersaline and quasi-marine environments. Flora and fauna are indicative of variable terrestrial, lacustrine, saline and lagoonal associations. The climate of the early Purbeck Group was likely similar to the modern Mediterranean and became wetter towards the end of the Berriasian. While the Purbeck Group was originally known as the informal Purbeck Beds, it can now be divided into the upper Durlston Formation and the lower Lulworth Formation. The "Upper Purbeck Beds" and a majority of the "Middle Purbeck Beds" are contained within the Durlston Formation, the oldest deposit of which is the Cinder Beds of the Stair Hole Member. The Cinder Beds have, at times, been considered the Jurassic-Cretaceous Boundary, which would result in the entire Lulworth Formation being latest Jurassic, Tithonian, in age. However, despite the uncertainties about the age of the beds because of a lack of correlation through fauna or dating, it is generally accepted that the Purbeck Group is entirely earliest Cretaceous in age, with the Lulworth Formation being early Berriasian. The Purbeck Group is visibly underlain by the Late Jurassic Portland Group in Durlston Bay and has a transitional but locally obscured boundary with the overlying Wealden Group at Peveril Point.
There is a great deal of uncertainty as to the location of the specimens collected from the Lulworth Formation; the only definitive way to test would be to analyse the matrix of each specimen to determine its salinity. The Purbeck Group has the most diverse ornithischian fauna of any deposit in Dorset, and is one of few Berriasian deposits globally, but is limited almost entirely to cranial or dental material, and tracks. Owenodon hoggii is the only other named ornithischian from the beds and is known only from a dentary with teeth originally described as a species of Iguanodon. A femur and dorsal of an intermediate hadrosauriform is also known, along with intermediate ornithopods and ankylosaurs known both from body fossils and from footprints. Beyond ornithischians, the Lulworth Formation also contains the theropod Nuthetes, amphibians, turtles, lizards, snakes, mammals and crocodilians, and varieties of invertebrates. Amphibians from the Lulworth Formation include the salamanders Apricosiren and an intermediate batrachosauroidid, the albanerpetontid Celtedens and the frog Sunnybatrachus. Four taxa of turtles are known, the cryptodires Dorsetochelys, Helochelydra, Hylaeochelys and Pleurosternon. The Purbeck is one of the most diverse Early Cretaceous deposits globally for lepidosaurians. The genera Becklesius, Dorsetisaurus, Durotrigia, Paramacellodus, Pseudosaurillus, Parasaurillus, Purbicella, Saurillus, Parviraptor and three unnamed tooth morphologies represent the known squamates, and fossils referred to the rhynchocephalians Homoeosaurus and Opisthias have also been found.
The diverse mammal assemblage includes the small eutherians Durlstodon and Durlstotherium; the non-eutherian peramurans Peramus, Peramuroides, Magnimus and Kouriogenys; the non-eutherian symmetrodonts Spalacotherium, Tinodon and Thereuodon; the non-eutherian dryolestoids Achyrodon, Amblotherium, Dorsetodon, Chunnelodon and Phascolestes; the non-eutherian multituberculates Albionbaatar, Bolodon, Gerhardodon, Plagiaulax and Sunnyodon; the non-eutherian eutriconodonts Trioracodon and Triconodon, the non-mammalian morganucodontan Purbeckodon; and the non-mammalian docodont Peraiocynodon. Crocodilians from within the Lulworth deposits include Goniopholis gracilidens, Theriosuchus pusillus, Pholidosaurus purbeckensis, dubious remains previously known as Goniopholis tenuidens, and the dubious taxon Macellodus brodiei. Specific sites within the formation also preserve the primitive snipe flies Simulidium and Pseudosimulium, and the nematoceran flies Eoptychoptera, Brodilka and Eucorethrina.
Echinodon