Paleoecology and sedimentology of the Upper Cretaceous (Campanian), marine strata at Åsen, Kristianstad Basin, Southern Sweden, Scania

Detta är en Master-uppsats från Lunds universitet/Geologiska institutionen

Sammanfattning: The Campanian marine strata from Åsen, north east part of the Kristianstad Basin (southern Sweden) contain a most diverse vertebrate and invertebrate marine fossil assemblages. A diverse fossil fauna was collected from Campanian deposits from a ca. 4.15m thick section during June-August 2010-2012. The succession is divided into two zones, the latest early Campanian Belemnellocamax mammilatus Zone and early latest Campanian Belem-nellocamax balsvikensis Zone. The B. mammilatus Zone is further divided into distinct units; the Coquina bed, the Green sand bed and the Oyster bank. The B. balsvikensis Zone is divided into Balsvikensis Green and Balsvikensis Yellow. A total of 169 kg material was sorted and the invertebrate fauna collected includes brachiopods, bivalves, belemnites, bryozoans, barnacles, sea urchins and corals with fair amount of vertebrate bones and teeth, and even coprolites. The succession also contains charcoal fragments but most of them are encountered in the lowermost part representing the latest early Campanian marine strata. A quantitative fossil analysis was performed by weight per-centage of the fossils to assess the variation between the different beds of the studied locality. XRF analysis of the sediment samples were performed for elemental analysis of the different beds showing that silica (Si) and calcium (Ca) are the elements constituting the main part of the sediments. Further it is noted that Si and Ca show an inverse relationship through the whole succession. Si shows a decreasing trend all through the succession with highest val-ues in the samples from the terrestrial flood plain deposits and lowest values within the B. balsvikensis Zone. Ca on the other hand, shows the opposite trend with highest values in the B. balsvikensis Zone. XRF analyses of the bel-emnites were further made for temperature proxy based on variations in Sr/Ca ratio between different beds in the sequence. These revealed that the average Sr/Ca values and trend of the belemnites from different beds of the Cam-panian strata show increasing average values of Sr/Ca from the B. mammillatus Zone to the B. balsvikensis Zone. However, as analyses on aragonite were not perfomred furtehr interpretations are out of scope of this study. Char-coal fragments were studied in Scanning Electron Microscopy (SEM) and binocular microscope for identification, and in order to distinguish the source of the charcoal. This study revealed the presence of mainly conifer wood but with some angiosperm wood present. A stratigraphical log was compiled based on the fossil content and sedimen-tological results from the field study. The amount of pelagic fossil fauna and inoceramids identified suggests high sea levels, also the high faunal diversity and the XRF Sr/Ca of the belemnites suggests warm climates and high primary productivity during the latest early Campanian at Åsen. A sea level drop is inferred by the high amount of benthic communities and steinkern identified in the B. balsvikensis Zone, further, the size of the fossil fauna, the presence of the cold water carbonate producing fossil fauna suggest cooling sea temperatures during the early late Campanian at Åsen

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