Permian marginal marine carbonates and evaporites in the North Sea and Barents Sea area
Deposition of shallow marine carbonates and evaporites were widespread in the upper Palaeozoic and host resources of economic importance. Carbonate deposition is sensitive to changes in climate and sea water temperature and therefore provide archives for climate changes. This dissertation concerns t...
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| Format: | Book |
| Language: | English |
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Natural History Museum of Denmark, Faculty of Science, University of Copenhagen
2018
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| Online Access: | https://curis.ku.dk/portal/da/publications/permian-marginal-marine-carbonates-and-evaporites-in-the-north-sea-and-barents-sea-area(a8ae9256-c0ed-409e-b453-c386c028b879).html https://soeg.kb.dk/permalink/45KBDK_KGL/fbp0ps/alma99122252324505763 |
| Summary: | Deposition of shallow marine carbonates and evaporites were widespread in the upper Palaeozoic and host resources of economic importance. Carbonate deposition is sensitive to changes in climate and sea water temperature and therefore provide archives for climate changes. This dissertation concerns the deposition and diagenesis of shallow marine carbonates deposited at times of transitional climate and sea water temperature. The study adds to the understanding of the Permian depositional and diagenetic evolution of the northern North Sea and Barents Sea areas and presents two new depositional models. The study is based on detailed descriptions of Permian shelf carbonates and evaporites from Spitsbergen (Arctic Norway) and Utsira High (Norwegian North Sea). The lower Permian Gipshuken Formation in central Spitsbergen, Arctic Norway, consists of 180-300 m interbedded shallow marine carbonates and evaporites. The study presents detailed facies descriptions identified from thin sections and field observations from 16 measured sections along a 70 km SE-NW transect in central Spitsbergen. It has resulted in two depositional models for the lower and upper Gipshuken Formation respectively. The lower Gipshuken Formation was formed by cyclic deposition of shallow subaqueous salina evaporites and shallow marginal marine carbonates on a wide evaporite platform. The cyclic stacking of facies reflect both allocyclic and autocyclic processes controlled by fluctuations in relative sea level, subsidence rate and topography which was closely linked to older N-S oriented lineaments. In the upper Gipshuken Formation 18 facies have been identified belonging to eight facies associations of the outer, mid and inner ramp reflecting deposition on a temperaturestratified ramp. The facies association both reflect differences in depth and wave-energy but also a difference in water temperature. The outer and mid ramp facies associations are characterised by a heterozoan assemblage reflecting cool-water conditions. The inner ramp deposits are dominated by a photozoan assemblage which together with widespread evaporite precipitation and evidence from subaerial exposed surfaces indicate a warm semi-arid climate. The study of the Permian Gipshuken Formation shows that semi-arid climate existed on land and influenced deposition in marginal marine settings while the deeper parts of the Barents Shelf were site of cool-water deposition. It thereby links the Gipshuken Formation to a significant depositional shift in water temperature in the Permian observed across the Barents Shelf and previously thought to be non-depositional in the depositional record of Spitsbergen. Upper Permian Zechstein carbonates have recently been drilled in four exploration wells on Utsira High in the Norwegian North Sea. They provide the first core material from the northern margin of the Zechstein Basin which covered Northwest Europe in late Permian. The present study describes the facies and depositional environment, paragenesis and the stratigraphic relations for the cored Zechstein carbonates, based on detailed core descriptions combined with well log data, analyses of stable isotopes of carbon and oxygen, and petrographic descriptions of 104 thin sections in transmitted and polarized light microscope, cathodoluminescence and scanning electron microscope. Utsira High was in the late Permian a land-attached, shallow carbonate platform located at the northeastern margin of the northern Zechstein Basin close to the Norwegian mainland. The carbonate facies and early diagenesis are similar to Zechstein deposits on the more southerly platforms of NW Europe. The carbonates have been locally comprehensively altered due to subaerial exposure and fresh water infiltration which have altered the porosity and permeability of the carbonates. The late diagenesis of the carbonates is dated to the late Triassic and together with the absence of widespread anhydrite deposition it suggests a more humid climate in line with the upper Permian carbonates of East Greenland |
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