Kristianstad Basin


The Kristianstad Basin is a Cretaceous-age structural basin and geological formation in northeastern Skåne, the southernmost province of Sweden. The basin extends from Hanöbukten, a bay in the Baltic Sea, in the east to the town of Hässleholm in the west and ends with the two horsts Linderödsåsen and Nävlingeåsen in the south. The basin's northern boundary is more diffuse and there are several outlying portions of Cretaceous-age sediments. During the Cretaceous, the region was a shallow subtropical to temperate inland sea and archipelago.
Though the sediments in the basin range in age from the Barremian to the earliest Maastrichtian, the only accessible strata are from the Late Cretaceous, ranging in age from the Early or early Middle Santonian to the earliest Maastrichtian. A majority of the fossil sites only expose strata of latest Early Campanian age. Fossils from these sites have been collected since the 18th century, but most of the excavations have taken place through commercial quarrying in the 20th century and paleontological expeditions in the 20th and 21st centuries.
The Early Campanian deposits of the Kristianstad Basin preserve fossils of a diverse array of organisms, including algae, brachiopods, bryozoans, molluscs, sea urchins, fish. The Kristianstad Basin has also yielded fossils of several varieties of reptiles, including plesiosaurs, turtles and crocodylomorphs, as well as one of the most diverse mosasaur faunas in the world and the only non-avian dinosaurs known from Sweden.

Geology

Geological background

The Kristianstad Basin is located in northeastern Skåne, the southernmost province of Sweden, extending from Hanöbukten, a bay in the Baltic Sea, in the east to the town of Hässleholm in the west. The basement of the basin is crystalline and deeply weathered bedrock from the Precambrian. Most of this weathering, and the uneven topography of the basement, is due to the warm and moist climate experienced during the Jurassic or Early Cretaceous. The basement is overlaid by approximately 250 metres of mainly shallow water or marine sediments from the Cretaceous, ranging in age from the Barremian to the earliest Maastrichtian. In addition to the aquatic sediments, there are delta plain deposits of late Santonian to earliest Campanian age, overlaid by marine strata of latest Early Campanian age.
The surface of the basement slopes to the south and is cut off by Linderödsåsen and Nävlingeåsen, two horsts that mark the basin's south-western boundary. To the south-east, the basin's margin is marked by the Baltic Sea while the basin's northern margin is more diffuse, with several small outliers of Cretaceous-age sediments.
During the Late Cretaceous, the basement of the basin was subjected to several regressions and transgressions. The sediments within the basin are dominated by fine- to coarse-grained sandy biocalcarenites and more or less consolidated sandstones. Conglomeratic beds are also common, typically consisting of belemnite rostra or bivalve shells and coarse terrigenous clastic rocks. There are also several flint beds in the upper parts of the strata, dating to the early Late Campanian through the earliest Maastrichtian. Dominant sediment types from the Early Campanian are oyster banks, calcarenites and calcareous, glauconitic quartz sands.
Accessible strata exposed in the basin range in age from Early or early Middle Santonian to earliest Maastrichtian. A majority of the fossil sites only expose strata of latest Early Campanian age. With the sole exception of the Ugnsmunnarna site, which is the only large natural outcrop of Late Cretaceous strata in Sweden, the sites within the Kristianstad Basin are the result of commercial kaolin clay/limestone exploitation.
species and belemnite biozones in the Kristianstad Basin, exhibited at "Havsdrakarnas hus" in Bromölla, Sweden
The biozones of the Kristianstad Basin, based on belemnite fossils, are:
The Kristianstad Basin is one of the most prolific and historically famous Mesozoic fossil sites in Scandinavia. The earliest known fossil discoveries within the basin were made by the physician and paleontologist Magnus Bromelius at Ivö Klack and Ignaberga in 1725. Most of the early fossil finds were belemnite fossils, descriptions of which were published by physician and naturalist Kilian Stobæus in 1752, naturalist Göran Wahlenberg in 1821 and zoologist and archaeologist Sven Nilsson in 1826, 1827, 1835 and 1857. Early sedimentological studies were also conducted throughout the 19th and early 20th centuries, prominently by paleontologist and geologist Bernhard Lundgren in 1888 and geologist Alf Lundegren in 1931 and 1934.
The various limestone and kaolin quarries throughout the basin were described in detail by geologist and paleontologist Karl A. Grönwall in 1915, followed by further descriptions by Alf Lundegren in 1931, geologist Lars Bjerning in 1947, geologist Per H. Lundegårdh in 1971, geologists Jan Bergström and Naz Ahmed Shaikh in 1980 and geologists Mikael Erlström and Jan Gabrielson in 1985 and 1992. Throughout the 20th century, quarrying was most intense at Åsen, Axeltorp and Ivö Klack, most of it conducted by the companies Höganäs keramik and Ifö-verken.
Important historical studies conducted on the basin's many invertebrate taxa include those by Bernhard Lundgren, paleontologist J. Christian Moberg in 1884 and 1885, geologist Anders H. Hennig in 1892, 1894 and 1904, geologist and mineralogist Assar Hadding in 1919, Bernhard Lundegren in 1934, paleontologist Gustaf Troedsson in 1946 and 1954, paleontologist Richard Hägg in 1954 and geologist and paleontologist Fritz Brotzen in 1960. Further studies on the invertebrate fauna, as with the more publicized vertebrate fossils, have continued into the 21st century.
Actinopterygian fishes were first described form the basin by Sven Nilsson in 1827, with further studies being conducted by paleontologist John W. Davis in 1890 and by paleontologist Mohamad Bazzi and colleagues in 2016. Though shark teeth have been recovered from the basin since early times, the shark and ray fauna was first studied in detail by paleontologist Mikael Siverson in the 20th century, who in a series of publications from 1989 to 2016, some together with other authors, identified a vast number of species.
Marine reptile fossils, found at Ivetofta, were first described from the basin by Sven Nilsson in 1835. Nilsson's work was followed by further investigations by physicist and chemist Wilhelm Hisinger in 1837, archaeologist and bibliographer Johan Henrik Schröder in 1885 and paleontologist Carl Wiman in 1916. Later studies on marine reptile fossils were also conducted by J. Christian Moberg in 1884 and 1885, Bernhard Lundgren in 1888, Anders H. Hennig in 1910, Alf Lundegren in 1934, Gustaf Troedsson in 1946 and 1954 and prominently in a series of publications of paleontologist Per-Ove Persson, who described several species of mosasaurs and plesiosaurs alongside sea turtles and the crocodylomorph Aigialosuchus, from 1954 to 1996. More recent work on marine reptiles has been conducted primarily by Mikael Siverson and paleontologist Johan Lindgren and paleontologists Elisabeth Einarsson, Benjamin P. Kear, Sven Sachs and Torsten M. Scheyer. Recent dinosaur discoveries, including both non-avian dinosaurs and hesperornithiform birds, have mainly been researched by Johan Lindgren and paleontologist Jan Rees alongside several colleagues.

Depositional environment and paleoecology

During the transgressions experienced during the Late Cretaceous, the inland sea within the Kristianstad Basin remained very shallow, and its northern parts formed an archipelago with several low islands and a number of small peninsulas. The climate was subtropical to temperate and local plant life included low-growing flowering plants, ferns, conifers and deciduous trees.
Most of the area preserved in the Kristianstad Basin was a shallow marine inner shelf environment, as indicated by the present invertebrate fauna. Most of the water was probably less than 40 meters deep, but there were a wide range of environments present. These environments included rocky and sandy beach areas, drowned river valleys and neritic and deeper offshore environments. There were shallow and protected coastal bays as well as coastal waters that were significantly deeper.
Some structures within the rocks of the Basin, combined with the often fragmented and broken condition of the fossils recovered, indicates that the Cretaceous environment was a high-energy environment.
During the Late Cretaceous, the Kristianstad region was home to a diverse marine fauna. The composition of the local fauna was characteristic of shallow marine life of an inner shelf community and included abundant algae, brachiopods, bryozoans, molluscs, sea urchins, serpulids, decapods and sponges. Additionally, fish were also common and fossils of many species of reptiles, most of them marine, have also been found, including mosasaurs, plesiosaurs, sea turtles, crocodylmorphs and a few dinosaurs.

Shorelines of Ivö Klack

Ivö Klack was a small island during the Campanian. Teeth from large lamniform sharks, such as Cretoxyrhina mantelli and Cretalamna appendiculata, are significantly more common at Ivö Klack than they are in other sites, such as Ignaberga. The prominence of large sharks in the area probably derives from large sharks requiring large prey, and large marine reptiles being common at Ivö Klack as well. There are plesiosaur fossils from Ivö Klack with shark bite marks. Modern great white sharks are known to patrol around small islands inhabited by seals, possibly a behavior also present in the similar Cretoxyrhina. Ivö Klack is the only site where fossils of hesperornithiforms, a group of aquatic birds, are present.
Fossil remains of large marine reptiles are also especially common at Ivö Klack. The high diversity of sharks and mosasaurs recovered at Ivö Klack shows that large predators frequented the rocky coastline. There must have been a productive ecosystem, with a diverse invertebrate fauna attracting small nektonic predators, which then in turn attracted larger predators. It is probable that the richness of the environment also made Ivö Klack a nursery and feeding ground for migratory species, similar to rocky shores today. The discovery of the basin's only crocodylomorph at Ivö Klack might indicate that Aigialosuchus preferred to live in coastal waters, where it could lay its egg on adjacent land, rest and heat up, similar to modern crocodilians.

Murky waters of Ã…sen

The Ã…sen site is believed to have been a murky river mouth during the Campanian. Teeth and vertebrae of small-sized Clidastes propython mosasaurs have been found at Ã…sen, which suggests that the area offered some protection against predation by larger mosasaurs and other predators, possibly due to the murky waters produced by some nearby river system. This murky setting also seems to have been preferred by the many species of benthic sharks and rays recovered at Ã…sen. Particularly, Rays significantly more common at Ã…sen than elsewhere. It is probable that they preferred the murky and estuarine environment there, similar to the environments preferred by their modern relatives. The sharks and rays at Ã…sen probably fed on fish and invertebrates, which occur with less diversity at Ã…sen than elsewhere. They might have primarily fed on soft-bodied invertebrates, less likely to be preserved in the fossil record.

Terrestrial life

The few fragmentary dinosaur fossils recovered in the Kristianstad Basin represent the remains of specimens transported out into the sea during floods or storms. Despite being fragmentary, they add to our understanding of the as of yet poorly known dinosaur fauna of the Baltic Shield, which was an isolated landmass during the Late Cretaceous. It is also possible that the recovered dinosaurs were not from the landmass itself, but from the rocky islands of the adjacent archipelago in the Kristianstad Basin itself. Dinosaur fossils recovered from the Kristianstad Basin can be confidently attributed to theropod, ornithopod and leptoceratopsid dinosaurs.
The recovered dinosaurs all represent animals with lengths less than three meters, but this does not necessarily mean that larger dinosaurs were absent; it is equally likely that only small animals were transported out into the sea where they could be fossilized and preserved. When large dinosaurs are excluded, the dinosaur fauna preserved in the Kristianstad Basin resembles that of Campanian–Maastrichtian dinosaur-bearing formations in Canada, which also include small ornithopods and leptoceratopsids.
Fossil wood has been recovered from late Middle Santonian to earliest Campanian-age deposits at Ã…sen, representing the tree genera Pinus, Platanus, Scandianthus, Silvianthemum and Actinocalyx.

Vertebrate fossil content

Fish

Sharks

A majority of the sharks in the Kristianstad Basin were lamniforms and they were either nectonic or nectobenthic. The lamniform shark fauna in the basin represents the most diverse Late Cretaceous lamniform fauna yet discovered. The most common genus of shark found is Carcharias. All shark species found in the Kristianstad Basin were active predators, but many of them only fed on smaller food items such as bony fish and various invertebrates. Large nektonic species, such as Squalicorax kaupi and Cretoxyrhina mantelli, presumably occupied the top of the food web. Bite marks from sharks are relatively common on reptile bones in the Kristianstad Basin.

Holocephali

Rays

Ray-finned fish

Mosasaurs

The Swedish latest Early Campanian mosasaur fauna is one of the most taxon-rich assemblages of mosasaurs known, rivalled only by the Maastrichtian "Mosasaurus shales" fauna of southwestern Niger, the late Maastrichtian Maastricht Formation of the southern Netherlands, the early Maastrichtian Ciply Phosphatic Chalk fauna of southern Belgium and the contemporary Mooreville Chalk fauna of west-central Alabama. The mosasaurs were large, carnivorous reptiles at the top of the food chain and since all the Campanian species are known from several sites, it is likely that all of them lived in the entire basin. The most common mosasaurs were the smaller-sized Clidastes and Eonatator. The high diversity of mosasaurs in the basin can be explained by the dissimilarity in dentition and body size between the species, meaning that they would not have competed with each other for food.

Plesiosaurs

The last comprehensive review of the plesiosaur fauna in the Kristianstad Basin was done by paleontologist Per-Ove Persson in the 1960s and his taxonomy is still used with caution, pending a much-needed new review. Because plesiosaurs are found in all the different environments thought to have existed in the Kristianstad Basin, they are believed to have been present in the entire basin.

Turtles

Though only two taxa have been identified so far, turtle remains are abundant in the Kristianstad Basin. In addition to the fossils described below, indeterminate turtle remains, including limb bones and carapace fragments, have also been recovered from Ivö Klack, Ugnsmunnarna, Ignaberga and Åsen.

Crocodylomorphs

In addition to the remains referred to Aigialosuchus, detached and unidentified crocodylomorph scutes have also been discovered in Campanian-age deposits at Ivö Klack.

Pterosaurs

Possible pterosaur bone fragments have been recovered from earliest Campanian-age deposits at Ullstorp, though they remain unpublished.

Dinosaurs

Non-avian dinosaurs

Fossils of non-avian dinosaurs are exceptionally rare in Scandinavia, and the Kristianstad Basin is the only location in Sweden where dinosaur fossils have been recovered. The only other certain traces of dinosaurs in Sweden are footprints of Late Triassic/Early Jurassic age in northwestern Skåne, made by theropods and thyreophorans. Though theropod teeth were reported from Ivö Klack by Per-Ove Persson in the 1950s, these have since been identified as fish teeth, probably from the genus Protosphyraena. Fossil material conclusively identified as dinosaurian was recovered only relatively recently, with material referred to a leptoceratopsid being described in 2007 and further fragmentary fossils of other groups being recovered during excavations from 2010 to 2013.

Birds

In addition to the fossils described below, indeterminate hesperornithiform remains have also been recovered from Ã…sen.

Cited bibliography