| Belemnite Marl | Black Ven Marl | Down Cliff Sands | Eype Clay Bed | |
| Green Ammonite Bed | Junction Bed | Shales with Beef | Thorncombe Sands | Three Tiers Bed |
![]()
Originally known as the Black Marl Beds.
Black Ven Marls on Black Ven
The Black Ven Marls (averaging 43m in thickness), are a succession of blue-black mudstones and shales containing the occasional limestone bands and nodules. Although the colour is due to the presence of finely disseminated iron pyrite, it does not denote that the sea-bed, at the time of the formation of theses beds, was always in an anaerobic state.
This bed is best examined to the east of Charmouth, between Evan's Cliff and Stonebarrow Hill, where these marls appear above the Birchi Tabular Bed (Bed 76a).
Birchi Tabular Bed (Bed 76a)
The Hummocky Bed forms an intermittent sloping shore platform or foreshore ledge called Hawkfish Ledge, that is revealed at low tide.
At 11m and 15m above the base of this division are the calcareous concretions belonging to the Lower Cement Bed (Bed 80) and the Upper Cement Bed (Bed 82 - sometimes called the Pavior Bed). At 17.6m above the base is the Flatstone Bed (Bed 83d). This is well renowned for its fine specimens of the Asteroceras turneri ammonite, which are preserved in yellow and brown calcite. Above this bed the remaining shales are richly fossiliferous with ammonites, Rhynchonellids and some insect and fish remains.
The Coinstone Bed (Bed 89) at 0.8m above the nodules marks the top of the Obtusum Zone.
The horizons forming bed 83, are collectively known as the 'Obtusum Shales'.
Although formed during a time when the sea level was fairly deep and often anoxic
, the Coinstone Stone bed, the Stellare Nodule Bed (Bed 88f) were formed during a time when the sea had shallowed quite significantly, combined with erosion leading to some non-sequence occurring.
Black Ven Marl as found between Lyme Regis and Charmouth:
Black Ven Marl as found between Charmouth and St. Gabriel's Mouth:
The 0.5m thick Pentacrinite Bed (Bed 84b), is hard to find but has well preserved fossils of the crinoid Pentacrinites fossilis. The Pentacrinite stems, with their distinctive star shapes were known in the past as 'St. Cuthbert's Beads'. About 10m about the Flatstone Bed (Bed 83d)is a line of nodules called the Stellare Nodules (Bed 88f). 2.1m below the nodules is the Limestone with Brachiopods Bed (Bed 87) containing Rhynchonellids and bivalves.
The Hummocky Bed (Bed 103), 13.7m above the Coinstone Bed (Bed 89) is taken as the top of the Black Ven Marls division. This bed contains the ammonite Echioceras. The Watch Ammonite Bed (Bed 99) is 4m below the Hummocky bed and also contains the ammonite Echioceras.
Echioceras raricostatum
The ammonite Asteroceras obtusum is also known as the Obtuse Star Ammonite, the Asteroceras stellare is also known as the True Star Ammonite and the Microderoceras birchi is known locally as both the Tortoise ammonite and the White Ammonite. Other ammonites found in this bed include Oxynoticeras oxynotum and Echioceras raricostatum.
|
Zone |
Sub-zone | Fossils |
| Echioceras raricostatum | aplanatum (non-sequence) | - |
| macdonnelli (non-sequence) | - | |
| Echioceras raricostatoides | 98-104 | |
| Eoderoceras bispinigerum | 93-97 | |
| Oxynoticeras oxynotum | Oxynoticeras lymense | 90-92 |
| Bifericeras bifer (non-sequence) | - | |
| Oxynoticeras simpsoni (non-sequence) | - | |
| Asteroceras obtusum | Eparietites denotatus (non-sequence) | - |
| Asteroceras stellare | 85-89 | |
| Promicroceras planicosta | 83-84 | |
| Arietites Turneri | Microderoceras birchi | 74g-82 |
| Bed | Bed name | Geology | Fossils found |
| 104 | - | - | - |
| 103b | Hummocky Limestone Bed | 3" nodular
limestone with irregular upper surface originally classified as the lowest member of the Belemnite Marl division |
Epideroceras exheredatum |
| 103a | 1" | Echioceras latidorsatum Echioceras raricostatoides Lobothyris radstockiensis |
|
| 102 | - | 3' black conchoidal marl | Gleviceras sp Echioceras raricostatoides Echioceras microdiscus Echioceras costidomus Echioceratoides aff vellaticum Rhynchonella sp |
| 101 | - | 4" irregular flint-like limestone nodules | Pleurechioceras sp |
| 100 | - | 9' 8" black conchoidal marl | Echioceras cf neum Echioceras cf laevidomus Echioceras cf microdiscus Echioceras cf costidomus Echioceras cf raricostatoides Echioceras cf zieteni Echioceratoides cf prorsum Deroceras sp Crucilobiceras sp Æquipecten priscus Inoceramus faberi Nuculana galathea Ostrea sp Oxytoma in quivalve Plagiostoma giganteum |
| 99 | Watch Ammonite Stone Bed | 1' lenticular & impersistant limestone with an upper coating of grey friable marl | Gryph a Gleviceras aff glevense Echioceras cf neum Echioceras cf costidomus Echioceras crassum Echioceras cf elegans Echioceras aff elegans Echioceras raricostatoides Echioceras cf zieteni Echioceras cf rhodanicum Echioceratoides sp Pleurechioceras congruens Crucilobiceras ornatilobatum Pecten sp Plicatula spinosa Trochus sp Rhynchonella triplicata fronto |
| 98 | - | 5" black conchoidal marl | Echioceras crassum Echioceras cf zieteni Homechioceras simile Homechioceras cf spiratissimus |
| 97 | - | 5'6" black conchoidal marl, FeS & beef seams | Gleviceras cf greenoughi Gleviceras sp Deroceras sp aff armatum Deroceras sp |
| 96b | due to the FeS band this bed, it is sometimes known as the Metal-Bed | 3'6" black conchoidal marl with strong FeS band at 3' from base | Gleviceras sp Deroceras armatum Deroceras aff armatum Leptonotoceras ? sp Deroceras obesum Oxynoticeras ? sp Inoceramus faberi |
| 96a | - | 1' black conchoidal | Eoderoceras aff bispinigerum |
| 95 | - | 5" conchoidal marl & small
limestone nodules arranged vertically. Pyrite nodules in cylinders |
Eoderoceras rhomboidale |
| 94 | - | 5'3" black conchoidal marl | Eoderoceras bispinigerum Eoderoceras proximum Eoderoceras aff bispinigerum Eoderoceras sp Oxytoma in quivalve |
| 93c | - | 1'8" black marl | Crucilobiceras aff
densinodulum Æquipecten priscus Oxytoma in quivalve |
| 93b | - | 1" beef and FeS | Crucilobiceras Eoderoceras aff bispinigerum Crucilobiceras densinodulum Crucilobiceras sp |
| 93a | - | 1'1" black marl | Gleviceras sp Crucilobiceras sp Æquipecten priscus Inoceramus faberi Oxytoma in quivalve |
| 92 | Oxynoticeras Lymense Bed | 2" beef and FeS | Gleviceras sp Eoderoceras aff bispinigerum Crucilobiceras densinodulum Oxynoticeras lymense Oxynoticeras wingravei Oxynoticeras reynesi Oxynoticeras cf dennyi Belemnites sp Æquipecten priscus Oxytoma in quivalve |
| 91 | - | 10" black shaly marl | No fossils found in this bed |
| 90c | - | 4' black conchoidal marl | - |
It is thought that there may be a
non-sequence bed at this point...
| Bed | Bed name | Geology | Fossils found |
| 89 | Coin Stone Bed (Coin Stone Ledge) |
5" parallel sided impersistant nodular limestone with pittings and borings on upper surface | Promicroceras sp Cymbites sp Plagiostoma giganteum Fish remains |
|
|
|||
| 88f | Stellare Nodular
Bed
forming the Mumbles reef |
1' regular compressed spherical nodules | Asteroceras stellare Promicroceras sp Inoceramus faberi |
|
|
|||
| 88e | - | 10" pale marl | No fossils found in this bed |
| 88d | - | 3" pale marl with 4-5 beef strings | No fossils found in this bed |
| 88c | - | 4-8" irregular limestone nodules | No fossils found in this bed |
| 88b | - | 18" small irregular limestone nodules in pale marl | No fossils found in this bed |
| 88a | - | 18" bedded marl | No fossils found in this bed |
| 87 | Limestone with Brachiopods Bed
originally called the Upper Cement Bed after Thomas Wright |
10" tabular limestone | Xipheroceras aff dudressieri Cymbites ? Asteroceras ? sp Promicroceras aff planicosta Cymbites l vigatus Epopioceras sp Belemnites sp Plagiostoma giganteum Rhynchonella cf lineata Piarorhynchia gryphitica juvenis Tropiorhynchia sp |
|
|
|||
| 86g | - | 4" conchoidal marl | No fossils found in this bed |
| 86f | - | 2" indurated marl | No fossils found in this bed |
| 86e | - | 2" conchoidal marl | No fossils found in this bed |
| 86d | - | 4" small irregular nodules in conchoidal marl | No fossils found in this bed |
| 86c | - | 2'10" conchoidal marl & occasional beef | Asteroceras aff margaritoides Asteroceras aff stellare Cymbites neglectus |
| 86b | - | 4" strings of beef in conchoidal marl | No fossils found in this bed |
| 86a | - | 3" conchoidal marl | No fossils found in this bed |
| 85 | Mudstone Bed | 2-4" occasional small lenticular nodules in conchoidal marl sometimes containing zinc sulphide crystals | Eparnioceras flavum Eparnioceras semicostatum Xipheroceras dudressieri Xipheroceras aff dudressieri Xipheroceras cf rasinodum Xipheroceras sp Asteroceras margaritoides Asteroceras aff margaritoides Asteroceras aff stellare Asteroceras sp Promicroceras aff planicosta Promicroceras aff perplanicosta Promicroceras aff capricornoides Promicroceras sp Cymbites l vigatus Cymbites neglectus Cymbites sp Inoceramus faberi Scelidosaurus harrisoni |
| 84e | - | 3-9" conchoidal marl | Asteroceras sp |
| 84d | - | 3" occasional small nodules in conchoidal marl | Fish remains Xipheroceras aff dudressieri |
| 84c | - | 5'6" conchoidal marl, paper shales & beef | No fossils found in this bed |
| 84b | Pentacrinite Bed | 1' paper shales, beef, FeS and 1" crinoid remains | Pentacrinite fossilis Extracrinus briareus |
|
|
|||
| 84a | - | 3'8" paper shales, beef, FeS and lignite | No fossils found in this bed |
| 83i | - | 5' 4" paper shales, occasional bedded shales and beef | Asteroceras sp Promicroceras aff perplanicosta |
| 83h | 5" bed formally known as Stonebarrow
Flatstone Bed or Upper Flatstone Bed. Recent geological surveys have since failed to find this bed |
||
| 83g | - | 1' bedded conchoidal marl | No fossils found in this bed |
| 83f | Woodstone Bed | 2' paper shales & lenticular limestone nodules | Asteroceras obtusum |
| 83e | - | 2' bedded conchoidal marl | No fossils found in this bed |
| 83d | Flatstone Bed (Lower Flatstone Bed) |
18" paper shales & lenticular limestone nodules | Xipheroceras aff dudressieri Asteroceras obtusum Promicroceras aff precompressum Cymbites aff l vigatus Chalamys calva |
| 83c | - | 18" conchoidal marl | No fossils found in this bed |
| 83b | - | 10-12" hardened shales | No fossils found in this bed |
| 83a | - | 3'6" conchoidal marl & occasional nodules | Chalamys calva |
| 82 | Upper Cement Bed (Pavior Bed) forming Dover Ledge reef |
1' impure & irregular limestone | Promicroceras sp Chalamys cf lohbergensis |
|
|
|||
| 81q | - | 6-8" conchoidal marl | No fossils found in this bed |
| 81p | - | 1-6" very irregular limestone with stellate nodules | No fossils found in this bed |
| 81o | - | 5" conchoidal marl with cruciform & stellate nodules | No fossils found in this bed |
| 81n | - | 3'6" conchoidal marl | No fossils found in this bed |
| 81m | - | 1" indurated marl | No fossils found in this bed |
| 81l | - | 2'3" conchoidal marl | No fossils found in this bed |
| 81k | - | 2" strong indurated marl | No fossils found in this bed |
| 81j | - | 3" conchoidal marl & beef with layer of FeS | Promicroceras sp Promicroceras capricornoides Promicroceras pyritosum Microderoceras inexpectans |
| 81i | - | 15" conchoidal marl & beef with layer of FeS | Promicroceras sp Promicroceras capricornoides Promicroceras pyritosum Microderoceras inexpectans Arietites sp |
| 81h | - | 1" strong indurated marl | No fossils found in this bed |
| 81g | - | 3" conchoidal marl | No fossils found in this bed |
| 81f | - | 2" indurated marl with flattened nodules | No fossils found in this bed |
| 81e | - | 5" conchoidal marl | No fossils found in this bed |
| 81d | - | 2" indurated marl | No fossils found in this bed |
| 81c | - | 3' conchoidal marl | Microderoceras cf inexpectans |
| 81b | - | 1" indurated marl | No fossils found in this bed |
| 81a | 4" conchoidal marl | No fossils found in this bed | |
| 80 | Lower Cement Bed
forming Black Rock reef |
1' tabular persistent limestone [actually an argillaceous |
Promicroceras cf capricornoides Promicroceras aff pyritosum Promicroceras sp capricornoides |
|
|
|||
| 79 | - | - | - |
| 78 | Blocky Marlstone | 3" blocky indurated marl | Promicroceras cf capricornoides Promicroceras pyritosum |
| 77b | - | 13' conchoidal marl (coarser above/finer below) | Promicroceras pyritosum Promicroceras capricornoides Belemnites acutus |
| 77a | - | 0.5" beef seam with pyritised ammonite layer on upper surface | Promicroceras capricornoides Microderoceras inexpectans Cymbites neglectus Squamirhynchia belemnitica Rhynchonella sp |
| 76g | - | 1.5" conchoidal marl | Cymbites suncostulatus Arietites cf turneri |
| 76f | - | 4" small flat nodules of indurated marl & impurities | Promicroceras sp Arietites sp |
| 76e | - | 7" conchoidal marl | Arietites cf turneri |
| 76d | - | 5" larger flat nodules of indurated marl & limestone | No fossils found in this bed |
| 76c | - | 3" conchoidal marl | Arietites cf turneri Plagiostoma giganteum |
| 76b | forms Mouth Rocks at extreme low tide under Stonebarrow | 1-2' paper shales & conchoidal marl | Pholidophorus sp Promicroceras capricornoides Promicroceras perplanicosta Cymbites l vigatus Arietites cf turneri Microderoceras birchi Plagiostoma giganteum Inoceramus faberi |
|
|
|||
| 76a | Birchi Tabular Bed | 1' irregular tabular to lenticular limestone with FeS on upper surface | Promicroceras capricornoides Cymbites l vigatus Cymbites cf semicostulatus Arietites turneri Microderoceras birchi |
![]()
The Black Rock Reef.
Formed by the Lower Cement Bed (Bed 80).
This can only be seen if the shingle has been removed from the
beach under Stonebarrow Hill.
![]()
The Black Rock Reef seen at a low spring tide. The 'beach section' is covered by shingle.
![]()
The Lower Cement Bed (Bed 80) provides an easy marker along Evans Cliff
and Stonebarrow Hill.
![]()
Lower Cement Bed (Bed 80) as found in-situ along Evans Cliff and Stonebarrow Hill.
![]()
Birchi Tabular Bed (Bed 76a) provides an easy marker along the Black Ven cliff face,
just to the west of Charmouth.
![]()
A partially uncovered Flatstone from the Flatstone Bed (Bed 83d).
![]()
The relationship between the Birchi Tabular Bed (Bed 76a) in this division, and
the lower Birchi Nodular Bed (bed 75a), from the Shales with Beef division.
![]()
The top of the Shales with Beef division meeting the bottom of the Black Ven Marl just to the west of Charmouth. The constant erosion reveals new part of the beds every time there is a landslip.
![]()
Black Ven Marl when it gets wet!
In this state it cannot support any weight, hence the landslips.
All images copyright © Graeme Caselton
|
![]()