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)

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 ,12th. 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 Ildjenet, Nesodden

(no landing)

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.

Stop 5 Alvern brygge,

Nesodden

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.

Stop 6 Ostøya (Bjørnen),

Bærum

Lower Permian debris flow deposits on alluvial fans. Formed on the

downfaulted side of the Oslofjorden master fault during the rift climax

(Stage 3)

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4

5

6

Excursion 25 B,

The Palaeozoic geology of the OsloRegion, The Inner Oslofjord area

Excursion 25 B,

The Palaeozoic geology of the OsloRegion, The Inner Oslofjord area

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OSLO

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3

4

5

6

Nesodden

Map

NGU

Geological map Hovedøya.

Stop 1. Hovedøya, Oslo. Slide 1. Relative sea level changes in the Upper

Ordovician, and the Ordovician – Silurian boundary. Hirnantian glaciation and

Caledonian tectonics.

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.

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.

Stop 2. Rambergøya, Oslo. Slide 2. Facies changes and sequence

stratigraphy of the Upper Ordovician

Sequence stratigraphy of the Upper Ordovician into the Silurian, and details in the sedimentology of the

Hirnantian Langøyene Formation.

Sequence stratgraphic subdivison

based on the outcrop on

Rambergøya.

Outcrops in Langøyene Formation on Rambergøya and

Langøyene.

Fossil sea floor. Crinoidal remains in the Malmøya Formation, Malmøykalven

Stop 3. Malmøykalven, Oslo. Slide 1. Lower Silurian facies and fauna. Upper

Silurian (Wenlock) limestones, the Malmøya Formation.

Stop 3. Malmøykalven, Oslo. Slide 2. Lower Silurian facies and fauna. Upper

Silurian (Wenlock) limestones, the Malmøya Formation.

Re

Stop 4. Ildjernet/Kavringsund, Nesodden. Slide 1. Rift climax.

Large alluvial fans along the east-bounding master fault of the Oslo Graben

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

islands of Ordovician folded marine sediments. The formed early in Permian time during the rift climax, stage 3

Photo

: F

W

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

Stop 4. Iljernet/Kavringsund, Nesodden. Slide 2. Rift climax. the east-

bounding master fault of the Oslo Graben

Stop 5. Alværn brygge, Nesodden. Slide 1. A. The Nesodden riftbounding

fault, its strike and breccias.

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.

Få inn det magnetiske kartet

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.

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.

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.

Stop 6. Skogerholmen, Asker. Slide 1. Sedimentology and sequences in the

Upper Ordovician. Skjærholmene Formation to Langøyene Formation.

Alternative stop at Skogerholmen. Type locality for the Skogerholmen Formation.

Photo: K. Tonstad

Oolite Høyerhomen, size of ooides 1-3 mm

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.