Hesseltal Formation

{{Short description|Geological formation in Germany}}

{{Infobox rockunit

|period=Late Cretaceous

|age={{fossil range|95|92|Late Cenomanian-Early Turonian}}| type= Geological formation| unitof=Planerkalk Group| prilithology = Marl, limestone| otherlithology = Black shale

| country = Germany|extent=North Rhine-Westphalia
Lower Saxony|namedby=Hiss, Kaplan & Wiese|year_ts=2007}}

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.{{Cite web |title=PBDB Strata Results |url=https://paleobiodb.org/classic/displayStrata?group_hint=&group_formation_member=Hesseltal |access-date=2024-06-17 |website=paleobiodb.org}}{{Cite journal |last1=Voigt |first1=Silke |last2=Aurag |first2=Aissa |last3=Leis |first3=Florian |last4=Kaplan |first4=Ulrich |date=2007-01-15 |title=Late Cenomanian to Middle Turonian high-resolution carbon isotope stratigraphy: New data from the Münsterland Cretaceous Basin, Germany |url=https://www.sciencedirect.com/science/article/pii/S0012821X06007485 |journal=Earth and Planetary Science Letters |volume=253 |issue=1 |pages=196–210 |doi=10.1016/j.epsl.2006.10.026 |bibcode=2007E&PSL.253..196V |issn=0012-821X|url-access=subscription }}{{Cite journal |last=Diedrich |first=Cajus G. |date=2013-04-01 |title=Facies related phylostratigraphy of the benthic neoselachian Ptychodus from the Late Cretaceous (Cenomanian/Turonian) of the Pre-North Sea Basin of Europe |url=https://www.sciencedirect.com/science/article/pii/S0195667112001590 |journal=Cretaceous Research |volume=41 |pages=17–30 |doi=10.1016/j.cretres.2012.10.007 |bibcode=2013CrRes..41...17D |issn=0195-6671|url-access=subscription }}{{Cite journal |last1=Hetzel |first1=Almut |last2=März |first2=Christian |last3=Vogt |first3=Christoph |last4=Brumsack |first4=Hans-Jürgen |date=2011 |title=Geochemical environment of Cenomanian - Turonian black shale deposition at Wunstorf (northern Germany) |url=https://doi.org/10.1016/j.cretres.2011.03.004 |journal=Cretaceous Research |volume=32 |issue=4 |pages=480–494 |doi=10.1016/j.cretres.2011.03.004 |bibcode=2011CrRes..32..480H |issn=0195-6671|url-access=subscription }}{{Cite journal |last1=van Helmond |first1=N. a. G. M. |last2=Sluijs |first2=A. |last3=Sinninghe Damsté |first3=J. S. |last4=Reichart |first4=G.-J. |last5=Voigt |first5=S. |last6=Erbacher |first6=J. |last7=Pross |first7=J. |last8=Brinkhuis |first8=H. |date=2015-03-18 |title=Freshwater discharge controlled deposition of Cenomanian–Turonian black shales on the NW European epicontinental shelf (Wunstorf, northern Germany) |url=https://cp.copernicus.org/articles/11/495/2015/ |journal=Climate of the Past |language=English |volume=11 |issue=3 |pages=495–508 |doi=10.5194/cp-11-495-2015 |doi-access=free |bibcode=2015CliPa..11..495V |issn=1814-9324}}

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.{{Cite book |last1=Hunt |first1=Adrian P. |url=https://books.google.com/books?id=C_MoCgAAQBAJ |title=Vertebrate Coprolites: Bulletin 57 |last2=Milàn |first2=Jesper |last3=Lucas |first3=Spencer G. |last4=Spielmann |first4=Justin A. |date=2012 |publisher=New Mexico Museum of Natural History and Science |language=en}} Fossil ammonites with preserved soft parts are also known.{{Cite journal |last1=Klug |first1=Christian |last2=Riegraf |first2=Wolfgang |last3=Lehmann |first3=Jens |date=2012 |title=Soft–part preservation in heteromorph ammonites from the Cenomanian–Turonian Boundary Event (OAE 2) in north–west Germany |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2012.01196.x |journal=Palaeontology |language=en |volume=55 |issue=6 |pages=1307–1331 |doi=10.1111/j.1475-4983.2012.01196.x |bibcode=2012Palgy..55.1307K |issn=0031-0239}}

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.