# Hesseltal Formation

The Hesseltal Formation or Blackcoloured Formation is a Late Cretaceous (late Cenomanian to early Turonian) geological formation from northern Germany. It consists of lithified marls and limestone, with a unique series of black shales deposited in anoxic conditions during the Cenomanian-Turonian boundary event.
It provides an important record of the fauna of the proto-North Sea basin. The formation's diversity of fossil fish is thought to be due to a consequence of an expanding oxygen minimum zone that caused mass mortalities among different communities of fish, including both those associated with warm surface waters and those associated with colder waters from upwelling. The anoxic conditions allowed for detailed preservation of some of these fish, including bony fish with their stomach contents preserved and even a few partial body fossils of cartilaginous fish. Fossil ammonites with preserved soft parts are also known.
The formation's deposition also documents the Plenus Cold Event, an enigmatic, brief but severe cooling event that occurred during the otherwise rapid global warming from the Cenomanian-Turonian boundary event, possibly as a consequence of changing ocean circulation.

## Paleobiota

Most fish are documented in Diedrich (2012) and a species list from Amalfitano et al (2020).

### Bony fish

| Genus | Species | Location | Material | Notes |
| Apateodus | A. striatus | | | An ichthyotringid aulopiform. |
| Armigatus | A. brevissimus | | | An ellimmichthyiform clupeomorph. |
| Anomoeodus | A. angustus | | | A pycnodont. |
| Anomoeodus | A. muensteri | | | A pycnodont. |
| Aulolepis | A. typus | | | A ctenothrissiform. |
| Apsopelix | A. anglicus | | | A crossognathid crossognathiform. |
| Bananogmius | B. ornatus | | | A plethodid tselfatiiform. Preserved with Clupavus in the stomach. |
| Belonostomus | B. cinctus | | | An aspidorhynchid. |
| Cimolichthys | C. levesiensis | | | A cimolichthyid aulopiform. |
| Clupavus | C. maroccanus | | | A basal ostariophysian. The most common fish of the formation. |
| Cylindracanthus | C. cf. minor | | Rostral fragment | A fish of uncertain affinities. |
| Dercetis (=Leptotrachelus) | D. sp. | | | A dercetid aulopiform. |
| ?Dixonanogmius | D. sp. | | | A plethodid. |
| Elopopsis | E. microdon | | | A pachyrhizodontid crossognathiform. |
| Enchodus | E. lewesiensis | | | An enchodontid aulopiform. |
| Enchodus | E. venator | | | An enchodontid aulopiform. |
| Hoplopteryx | H. lewesiensis | | | A trachichthyiform. |
| Ichthyodectes | I. sp. | | | An ichthyodectid. |
| Ichthyotringa | I. africana | | | An ichthyotringid aulopiform. |
| Njoerdichthys | N. dyckerhoffi | Galgenknapp Quarry, Hohne Quarry | | A pycnodont. |
| Osmeroides | O. lewesiensis | | | An osmeroidid elopiform. |
| Pachyrhizodus | P. subulidens | | | A pachyrhizodontid crossognathiform. |
| Pachyrhizodus | P. sp. | | | A pachyrhizodontid crossognathiform. |
| Paranursallia | P. gutturosa | | | A pycnodont. |
| Protosphyraena | P. sp. | | | A billfish-like pachycormid. |
| "Pycnodus" | "P." scrobiculatus | | | A pycnodont. |
| Rhamphoichthys | R. taxidiotis | DIMAC Quarry | | A billfish-like plethodid. |
| Rharbichthys | R. ferox | | | An aulopiform. |
| Rhynchodercetis | R. sp. | | | A dercetid aulopiform. |
| Protostomias | P. maroccanus | | | A dragonfish-like teleost. |
| Tselfatia | T. formosa | | | A plethodid. |
| Xiphactinus | X. sp. | | | An ichthyodectid. |

### Chondrichthyans

| Genus | Species | Material | Notes |
| Cantioscyllium | C. decipiens | | A nurse shark. |
| Carcharias | C. sp. | | A sand shark. |
| Chiloscyllium | C. greenei | | A bamboo shark. |
| Cretalamna | C. appendiculata | | An otodontid shark. |
| Cretascyliorhinus | C. aff. destombesi | | A scyliorhinid shark. |
| Cretodus | C. semiplicatus | | A pseudoscapanorhynchid shark. |
| Cretoxyrhina | C. denticulata | | A cretoxyrhinid shark. |
| Cretoxyrhina | C. mantelli | | A cretoxyrhinid shark. |
| Diprosopovenator | D. hilperti | Partial body fossils | A pseudoscyliorhinid shark (formerly Paraorthacodus sp.) |
| ?Eostriatolamia | ?E. subulata | | A sand shark. |
| Heterodontus | H. caniculatus | | A bullhead shark. |
| Heterodontus | H. polydictyos | | A bullhead shark. |
| Paranomotodon | P. angustidens | | A thresher shark. |
| Protolamna | P. acuta | | A pseudoscapanorhynchid shark. |
| Protolamna | P. sokolovi | | A pseudoscapanorhynchid shark. |
| Pseudoscyliorhinus | P. schwarzhansi | | A pseudoscyliorhinid shark |
| Posadaia | P. nolfi | | A sand shark. |
| Pseudospinax | P. pusillus | | A bamboo shark. |
| Ptychodus | P. decurrens | Articulated specimen, teeth | A ptychodontid shark. |
| Ptychodus | P. mammilaris | Articulated specimen, teeth | A ptychodontid shark. |
| Polyacrodus | P. polyptychus | | A hybodontid shark. |
| Scapanorhynchus | S. raphiodon | | A goblin shark. |
| Squalicorax | S. falcatus | | A crow shark. |
| Squatina (Cretascyllium) | S. cranei | | An angelshark. |
| Squatirhina | S. westfalica | | A ray of uncertain affinities. |
| Turoniabatis | T. ornata | | A ray of uncertain affinities. |

### Reptiles

| Genus | Species | Location | Material | Notes |
| Coniasaurus | C. crassidens | DIMAC quarry | Dentary, teeth | A dolichosaurid squamate |
| Dolichosaurus | D. longicollis | DIMAC quarry | Dorsal vertebra | A dolichosaurid squamate |
| Mosasauroidea indet. | | DIMAC quarry | Articulated tail | The oldest articulated mosasaur remains from Europe. |