Lower Paleozoic petroleum from southern Scandinavia: Implications to a Paleozoic petroleum system offshore southern Norway

Petroleum occurring in lower Paleozoic rocks is known to be present in southern Scandinavia, northern Poland, and the Baltic states. Oil has been produced from lower Paleozoic reservoirs in Sweden; northern Poland; and the Baltic countries Lithuania, Latvia, and the Russian exclave area of Kaliningrad. The sources for this petroleum are marine, organic-rich muds deposited in the Cambrian, Ordovician, and Silurian. This article concerns geochemical analysis of oils extracted from sandstones and carbonates from the Norwegian Oslo Graben rift and locations in Sweden and describes, in addition, insoluble bitumens collected from lower Paleozoic rocks in the Oslo Graben, locations in Sweden, and from upper Paleozoic rocks in a Norwegian North Sea well. The oils in this study have several geochemical characteristics shared with oils from the Baltic states and northern Poland, and the maturities of the oils are, in general, low. The occurrences of bitumen and migrated petroleum in the Oslo Graben lead us to believe that petroleum also has been generated and expelled in the related offshore Skagerrak Graben, indicating that a Paleozoic petroleum system operated in the Skagerrak Graben. This potential petroleum system has not suffered the degree of uplift, erosion, and destruction of reservoirs experienced by the onshore Oslo Graben, making preservation of any petroleum accumulations in the Skagerrak Graben more plausible. Although speculative, these considerations should interest anyone involved in petroleum exploration in the Skagerrak and the Norwegian-Danish Basin, not the least because of the proximity of Skagerrak and major energy markets in Europe. Copyright ©2007. The American Association of Petroleum Geologists. All rights reserved

A systematic revision of the Ordovician plectambonitoidean brachiopods Chonetoidea and Sericoidea

The revised Treatise on Invertebrate Paleontology, part H: Brachiopoda regards Chonetoidea Jones and Sericoidea Lindström synonymic, on the basis of characters that were considered common to both genera (e.g. ornament type, number of septules). However, some features (e.g. number of septules) discriminate specimens at species level, rather than at generic level as previously thought. Other morphological features, never taken into account or described before, e.g. the position of the ventral diductor scars or the presence of a pair of septules developed anterolaterally to the socket ridges (named praeculmen septules) in Chonetoidea solely, permit a confident separation of the two genera. The ornament is not useful for diagnosing the genera. A review of all species belonging to each genus is made in light of the emended diagnoses of both Chonetoidea and Sericoidea. Based on the internal morphologies of their lophophoral supporting structures and on sedimentological data, Chonetoidea and Sericoidea are interpreted as living in different bathymetric conditions. Chonetoidea was adapted to a more dynamic environment, with higher nutrient levels. Sericoidea needed a wider area for trapping food, in an environment (open water) with three to six times less nutrients than mid to inner shelf environments. The palaeogeographic and stratigraphic distributions of Chonetoidea and Sericoidea indicate the progressive disappearance of Sericoidea and adaptative radiation of Chonetoidea in a palaeoworld where epicontinental seas were shallowing, prior to the end of Ordovician glaciation events which coincided with the extinction of Chonetoidea

Late Ordovician trace fossils from offshore to shallow water mixed Siliciclastic and carbonate facies in the Ringerike Area, Oslo Region, Norway

Upper Ordovician (Rawtheyan-Hirnantian) deposits in the Ringerike area contain 21 ichnogenera of burrows and two ichnogenera of borings. These deposits consist of a lower siliciclastic part and an upper part dominated by carbonates and mixed clastic-carbonate deposits. Sedimentological and geochemical investigations combined with an ichnological analysis in the lower siliciclastic part point to a shallowing from a transitional-offshore partly dysoxic zone to an oxic delta front/upper shoreface facies. The trace fossils belong to the proximal, archetypal, and distal Cruziana ichnofacies. The upper part of the sequence comprises a complex pattern involving patch reefs interfingering with shallow marine deposits of sandstones and crinoidal limestones in the southern area and carbonate mud banks to the north. The carbonate mud banks were subaerially exposed with the development of local coastlines. The overlying transgressive sediments, consisting of sandstones and carbonates, contain an offshore to transitional trace fossil assemblage