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Matthias Paetzel, Sogn og Fjordane University College (Norway)
Hans Schrader, Sogn og Fjordane University College (Germany)
Jaap S Sinnighe Damste, Royal Netherlands Institute for Sea Research (Netherlands)
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The Present is the Key to the Past (James Hutton 1726-1797). Smear slides of Recent (0-500 years) successive laminae (n=75) are investigated for a variety of sediment parameters in the anoxic sediments of the Kyllaren fjord (KF), Western Norway. The same technique is used to analyze Jurassic, Toarcian, weathered black shale lamination (n=75) of the Hawsker Bottoms (HB), England.
Similarities include the ratio of the organic versus mineral fraction (KF 55:45, HB 57:43%), the ratio of the marine organic matter versus the terrestrial organic matter fraction (KF 62:38, HB 79:21%), the concentration of framboidal pyrite (KF: 25, HB 19%), the grain size of the total material including aggregates (KF sand 68%, HB sand 59%) and the mineral grain size (KF sand and silt 27%, HB sand and silt 23%).
Differences include carbonaceous and other precipitates (KF 0, HB 18%), skeletal remains (KF diatoms 4% and coccoliths 0%, HB diatoms 0% and coccoliths 15%) and andesitic basaltic glass, i.e. volcanic ashes (KF 0%, HB 6%). Precipitates may occur in the Hawsker Bottoms due to weathering processes or diagenetic alteration. Andesitic basaltic glass indicates volcanic activity in this area during sedimentation. The elevated amount of coccoliths suggests more open marine conditions in the Hawsker Bottoms than in the Kyllaren fjord basin.
The comparison to Recent Kyllaren sediment signals allows an interpretation of the sedimentological and hydrographical processes leading to the Toarcian black shale formation. Both sediment deposits are formed during hemipelagic shallow water conditions with reasonable high productivity and continuous supply of terrestrial material, including nutrients. The good preservation of the marine organic matter fraction and the occurrence of framboidal pyrite suggest oxygen deficient bottom water conditions throughout most of the time of deposition. Similarities of the water column of these two systems have earlier been described comparing the record of biomarkers and geochemical processes.
The Recent lamination record of the Kyllaren fjord thus reveals a key to the past formation of the Hawsker Bottoms Jurassic black shale deposit.
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