33. IGC Excursion 25 B. The Palaeozoic geology of the Oslo Region, The Inner Oslofjord area

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1 Notes to the localities, map and photos 33. IGC Excursion 25 B. Tuesday, August 12th, 2008 The Palaeozoic geology of the Oslo Region, The Inner Oslofjord area J. Fredrik Bockelie (Sagex), Bjørn T. Larsen (DetNorske) & Snorre Olaussen (Eni Norge)

2 Excursion 25 B, The Palaeozoic geology of the Oslo Region, The Inner Oslofjord area Fredrik Bockelie (Sagex), Bjørn T. Larsen (DetNorske) & Snorre Olaussen (ENI Norge) Tuesday, August,12 th. From 08:30 to ~18:00 Number of participant max 50. By boat. Start 08:30 Embark the ship at the key on the west side of the Akershus Castle (towards the City Hall). The ship`s name Nordsol We disembark the ship in the early evening at the same place. Lunch will be served on board. Stop 1 Hovedøya, Oslo Relative sea level changes in the Upper Ordovician, and the Ordovician Silurian boundary. Hirnantian glaciation and Caledonian tectonics. Stop 2 Rambergøya, Oslo Sequence stratigraphy and facies changes in the Upper Ordovician, from the Solvang Formation (middle Katian) to touching the lower Silurian of the Solvik Formation (Rhuddanian). Stop 3 Malmøykalven, Oslo Lower Silurian facies and faunas. The Upper Llandovery Malmøya Formation Stop 4 Stop 5 Stop 6 Ildjenet, Nesodden (no landing) Alvern brygge, Nesodden Ostøya (Bjørnen), Bærum Sailing the ship along the Permian eastern master fault of the Oslo Graben. Pre-Cambrian basement on the footwall to the east and Ordovician sediments on the hanging wall to the west. Landing to see the friction breccia of the Nesodden Fault. Crushed basement rocks, and even Lower palaeozoic sediments (limestones and shales) and Permian ingneous dykes are included into the breccia. Lower Permian debris flow deposits on alluvial fans. Formed on the downfaulted side of the Oslofjorden master fault during the rift climax (Stage 3)

3 Excursion 25 B, The Palaeozoic geology of the OsloRegion, The Inner Oslofjord area

4 Excursion 25 B, The Palaeozoic geology of the OsloRegion, The Inner Oslofjord area OSLO Nesodden Map NGU

5 Stop 1. Hovedøya, Oslo. Slide 1. Relative sea level changes in the Upper Ordovician, and the Ordovician Silurian boundary. Hirnantian glaciation and Caledonian tectonics. Geological map Hovedøya.

6 Stop 1. Hovedøya, Oslo. Slide 2. Relative sea level changes in the Upper Ordovician, and the Ordovician Silurian boundary. Hirnantian glaciation and Caledonian tectonics. Figure to the left show inverted Upper Ordovician strata with small incised valley filled with limestone boulders at the base and mixed siliciclastics and carbonates in upper part. Right figure show the Ordovician /Silurian boundary. Inverted strata. Langøyene and Solvik formations.

7 Stop 2. Rambergøya, Oslo. Slide 1. Facies changes and sequence stratigraphy of the Upper Ordovician Mixed siliciclastic carbonate shoreline deposits with recognizable foreshore deposits. The fisherman is standing on a 2m thick fossilferous limestone conglomerate which cap the section. Upper Ordovician Langøyene Formation. Rambergøya. Stratgraphic up is to the right.

8 Stop 2. Rambergøya, Oslo. Slide 2. Facies changes and sequence stratigraphy of the Upper Ordovician Outcrops in Langøyene Formation on Rambergøya and Langøyene. Sequence stratgraphic subdivison based on the outcrop on Rambergøya. Sequence stratigraphy of the Upper Ordovician into the Silurian, and details in the sedimentology of the Hirnantian Langøyene Formation.

9 Stop 3. Malmøykalven, Oslo. Slide 1. Lower Silurian facies and fauna. Upper Silurian (Wenlock) limestones, the Malmøya Formation. Fossil sea floor. Crinoidal remains in the Malmøya Formation, Malmøykalven

10 Stop 3. Malmøykalven, Oslo. Slide 2. Lower Silurian facies and fauna. Upper Silurian (Wenlock) limestones, the Malmøya Formation. Re

11 Stop 4. Ildjernet/Kavringsund, Nesodden. Slide 1. Rift climax. Large alluvial fans along the east-bounding master fault of the Oslo Graben Photo: FW The displacement along the Nesodden Fault, down in the west, is estimated to about 1 km. The absolute minimum displacement is 400m. The Nesodden peninsula consists of PC-basement, and the downfaulted

12 Stop 4. Iljernet/Kavringsund, Nesodden. Slide 2. Rift climax. the eastbounding master fault of the Oslo Graben The northern part (the Nesodden Fault) of the Oslofjord Master fault follows the western side of the peninsula of Nesodden. The rift climax, stage 3

13 Stop 5. Alværn brygge, Nesodden. Slide 1. A. The Nesodden riftbounding fault, its strike and breccias. Få inn det magnetiske kartet We land on the key at Alværn brygge. North of Alværn a magmatic dyke swarm cut into the Nesodden basement block in a NW-SE direction. This dyke swarm is the continuation from west of the Krikkleiva - Kjaglidalen transfer fault, and the structure and dyke swarm can be followed as a magmatic lineament in the basement.

14 Stop 5. Alværn brygge, Nesodden. Slide 2. A. The Nesodden rift-bounding fault and its breccias. We studies the different types of breccias formed during the rift formation. The PC-basement is brecciated and both Under Palaeozoic limestones and shales are found in the breccia (left picture). And magmatic dykes (Permian) are found fractured into an orthogonal pattern.

15 Stop 5. Ostøya south Bjørnen, Bærum. Slide 1. Sedimentology and sequences in the Upper Ordovician. Permian dyke intrusions. The beach shows a long continous section of the Upper Ordovician stratigraphy from the Vollen Formation to the Venstøp Formation. Age Sandbian to Katian.

16 Stop 6. Ostøya south, Bjørnen, Bærum. Slide 1. Sedimentology and sequences in the Upper Ordovician. Permian dyke intrusions. Permian dykes of different compositions, size and directions intrudes into the sediments in most areas of Bærum. In general we can say that a dyke swarm system I cutting through the whole of Bærum. Closeness to the transfer system.

17 Stop 6. Skogerholmen, Asker. Slide 1. Sedimentology and sequences in the Upper Ordovician. Skjærholmene Formation to Langøyene Formation. Photo: K. Tonstad Oolite Høyerhomen, size of ooides 1-3 mm Alternative stop at Skogerholmen. Type locality for the Skogerholmen Formation.

18 Stop 6. Skogerholmen, Asker. Slide 1. Sedimentology and sequences in the Upper Ordovician. Skjærholmene Formation to Langøyene Formation. Slumping in the sandstones in the Langøyene Formation.