Stevns Klint, Denmark: Uppermost Maastrichtian chalk, Cretaceous–Tertiary boundary, and lower Danian bryozoan mound complex

Abstract

Stevns Klint is a 14.5 km long coastal cliff south of Copenhagen, Denmark. It is a classical Cretaceous–Tertiary boundary locality and constitutes the type locality of the Danian Stage together with the nearby Faxe quarry. The irregular coastal topography, the presence of numerous old quarries in the upper, Danian part of the cliff section, and the inaccessibility of parts of the coast makes it difficult to construct an exact geological profile of the whole length of the cliff. Until now the only profile is a fine engraved pen drawing from a boat by Puggaard in 1853. We present a new profile of the cliff constructed on the basis of multi-model photogrammetric mapping of a long series of overlapping photographs taken from a small airplane. This was supplemented by photography and observations from a boat and from the beach. The exposed succession is about 45 m thick and is subdivided into a series of new lithostratigraphic units. It shows the stratigraphic evolution from the uppermost Maastrichtian, across the Cretaceous–Tertiary boundary and into the lower Danian. The position of the boundary varies from about 5 m below to about 30 m above present day sea level. The irregular relief has been interpreted as due to Paleogene folding but it actually represents a depositional sea-floor topography. The lower part of the succession comprises about 25 m of upper Maastrichtian benthos-rich chalk of the newSigerslev Member showing irregular low-amplitude mounded bedding outlined by thin layers of nodular flint, passing upward into benthos-poor, gently wavy to almost horizontally bedded chalk poor in flint. The member is capped by a double incipient hardground and a prominent marker band of nodular flint, occurring 30–50 cm beneath the upper hardground can be followed along the length of the cliff. The upper hardground is overlain by uppermost Maastrichtian bryozoan chalk wackestone deposited in low asymmetrical mounds of the new Højerup Member. It is 4–5 m thick in the southern part of the cliff, thins gradually to the north, and has wedged out almost completely at the northern end of the cliff. The new Sigerslev and Højerup Members form the top part of the Maastrichtian Tor Formation in the Stevns Klint area. It is overlain by the new lowermost Danian Fiskeler Member (P0 foraminifer Zone) which drapes the troughs between the mound crests and wedges out gradually towards the margins of the troughs. It is generally about 5–10 cm thick and passes gradually upwards into the strongly burrowed new Cerithium Limestone Member (Pα–P1a Zones), which is up to 60 cm thick. The Fiskeler and Cerithium Limestone Members form the new Rødvig Formation. An erosional hardground surface truncates the top of the Cerithium Limestone Member and the intervening crests of the uppermost Maastrichtian mounds of the Højerup Member. The surface is overlain by lower Danian bryozoan packstone–rudstone mound complexes (foraminifer zones P1b–P1c , local coccolith zones 2–3, Nannoplankton Zones D2–D3). The internal architecture of the mounds is outlined by thick black flint layers and the mounded bryozoan limestone belongs to the new Korsnæb Member of the new Stevns Klint Formation. Up to 20 m of bryozoan limestone are preserved beneath the Quaternary deposits, forming the top of the cliff succession. The new photogrammetric profile may serve as an excursion guide, as a basis for detailed sedimentological study, and for biostratigraphical, geochemical and palaeomagnetic sampling. Finally, it illustrates the geometry, dimensions and architecture of one of the finest carbonate mound complexes known.