Regional Geology TGB4140
Spring Semester 2008
Instructor: Allan Krill (email@example.com) Mobil telephone: 91897197
or office phone 73594803 (which transfers to the same mobil telephone if
not answered.) Please contact me with any questions or problems.
course is being totally redesigned this year, with new reading materials,
exercises and field trips. More information will be posted throughout the semester in the course blog below this page. I am sorry that the description of the course in the Studiehåndbok is not correct!
(In Spring 2009, this course will be taught by a guest lecturer.)
Prerequisites: We will assume a background knowledge of
geology, and encourage you to review the introductory textbook Earth, Portrait
of a planet.
Language: English. The reading material is
mostly in Norwegian, but the lectures and field trips are in English. It is possible for students who are not fluent
in Norwegian to take this course.
Syllabus / Pensum:
Landet blir til, Norges geologi
(Table of contents)
Geological maps of Norway (online 1:250000)
Plus various other materials, some on the internet.
Lectures/Labs (Øvinger): Mondays 815-10 and Tuesdays 1415-17 Room G1. Ground floor of the building Geologi. (Note: the rooms B22 and B3 were too small, and the lectures are now moved to G1.)
Lecture times Tuesday have been changed to 1415-17.
Exercises (Øvinger): The scheduled lab times (Tuesdays 1415-16) will be used for lectures.
Field Trips: There will be three main field trips:
Oslo Four days, probably Tuesday 29.April-Friday 2.May. (With Prof. Hans Arne Nakrem and Prof. Atle Mørk)
Oppdal One long day, date not set. (Tuesday 15.April)
Outer Trondheimsfjord One long day, date not set. (Friday 18.April 700-1800)
The dates of these trips
must be agreed upon, but because of winter snow, they may be late in the semester (probably April-May.)
Grades: The final grade will be based on written work and quizzes during the
semester (50%) and a final exam (50%.) Dates and times will be arranged. (Thursday 15.May)
Preliminary list of students (39):
AnneVilberg. If your name is not on this list, and you are planning to take the course, please contact me firstname.lastname@example.org.
STEINBERGET Course blog: Here I will write various notes about the course, and will update the page throughout the semester.
To find this page easily, remember the web address: http://steinberget.com
Textbook: I have not taught this course from a book before, but rather from journal articles, field trip guides and maps. Using this book will have some advantages and some disadvantages. I will add some extra material, besides the book, as the semester progresses.
I plan to only deal with the first 9 chapters of the book, up to page 327. (We may deal with more of this book.) Chapter 1 is only a preface, and chapter 2 (up to page 61) is mostly a review of Introductory Geology (Geologi innføring). We will try to cover this chapter in the first lecture or two.
This is an excellent book, but my comments are often critical. This should help you understand that all geological products are either defective or debatable. My negative comments do no mean I think poorly of this book. Remember two of my favorite expressions: "It is easier to be critical than correct." "The only geological map without any mistakes is a completely white paper. As soon as you put some marks on it, there will be some mistakes."
Grades: As mentioned in the course outline above, 50% of the grade will be based on a final exam. There will
probably be a written part as well as an oral part of the final exam. I now think that 30% of the grade will be based on two quizzes (15% each) and 20% will be based on 4 short abstracts to be written during the semester (5% each).
Abstracts: To give practice in library research, English scientific writing, and oral presentation, each student will write and present four research abstracts during the semester. These abstracts will be maximum 3000 characters (including spaces.) Topics will be assigned,
or students will choose topics of personal interest from the book "Landet Blir Til." It will be easy to find interesting topics (not from chapters 1 or 2). You might find mistakes in the text that could be corrected; historical details or alternative interpretations that could be added; map details that could be added. Each student will select such topics, write abstracts and present them to the class (about 3-minute presentations.) These abstracts may be rewritten after I give comments and suggestions, and the best 4 abstracts from each student will count toward 20% of the grade. Here are examples, two abstracts (3000 characters each) that I have recently written.
EXTRA FIELD TRIP TUESDAY 8. JANUAR KL 1315-1530 Instead of a lecture on Tuesday. We meet outside of the Berg-building and leave in my minibus at 1315. We drive across town to Rotvoll, to look at what I call the "Rotvoll ophiolite fragment".
Here is a map of the Rotvoll area.
The first outcrop is at the intersection of Øvre (Nedre) Grilstadkleiva and Ranheimsvegen, and the others are along the shore at the northernmost point of the map (north of Rotvoll alle.) Each student will take notes and write an abstract in English (max. 3000 characters.) Several students were not on the trip. If the ground stays snow-free we will arrange a trip for the remaining students in week 3.
Lecture 1: Monday jan. 7. Read all of Chapter 1, p.10-19. Some trivial comments here.
P. 13. Parargraph 5, mentions Olaf Holtedahl. He was Norway's greatest "regional geologist" in the 20th century. His popular geology book "Hvordan landet vårt blev til" was excellent, with versions in 1931, 1951, 1968 (not just 1951 as mentioned.) His professional version "Norges Geologi" in 1953 is a masterpiece, and then in 1960 he edited a version in English by many authors, Geology of Norway.
P.15 line 2, "geofarer" are "geohazards".
The facsimile on page 15 reads as follows: Geologia Norwegica. det er: En kort Undervisning om det viit-begrebne Jordskelff Som her udi Norge skeede mesten ofuer alt Syndenfields, den 24. Aprilis udi nærværende Aar 1657. sampt Physiske, Historiske oc Theologiske fundament oc grundelige Beretning om Jorskelffs Aarsager og Betydninger. Forfattet ved Mickel Pedersøn Escholt, Aggersh. He was a priest at Akershus. It is the first scientific book printed in Norway, and one of the first books actually printed in Norway (rather than in Denmark).
The book was translated to English in 1663: Geologia Norvegica. Or, a brief instructive remembrancer, converning that very great and spacious earthquake, which hapned almost quite through the South part of Norway: upon the 24th day of April, in the year 1657. also Physical, Historical, and Theological Grounds and Reasons concering the causes and significations of earthquakes. Translated ("Englished") by Daniel Collins. This work is thought to be
the origin of the word Geology (Geologia) as the science of the earth.
P.16, parag.1, Says that like all "stories", it is important to start at the beginning, with Precambrian. I disagree. It is ok, but not obvious to start with the oldest rocks to understand geology. Could start with the youngest, and least deformed, and then move back to the more difficult and strange older rocks. Could start with the Oslo area, which is least deformed as it is outside of the Caledonian range. This book takes Norwegian geology in a historical sequence, and that is Ok, but not the only way to do it.
Par.2.Paleozoikum in this book is translated as oldtiden and this is common, but unfortunate. The word Paleozoikum means old-lifeforms-time, not old-time. The Zo is the same as the word Zoo, and has to do with life or fossils, and I think that is important. (In 1870 Kjerulf used the terms ny-livets tid = kainzoiske tid, middel-livets tid = mesozoiske tid, gamle-livets tid = palæozoiske tid.)
P.19, It says this book is a "dugnadsarbeid." It has many authors, unlike the Norges geologi by Holtedahl in 1953. "Storybooks" are not usually written as dugnad (imagine Harry Potter being written as a dugnad.) But encyclopedias are by many authors. Multi-authored works have some advantages and some disadvantages, obviously.
Lecture 2 will be Monday Jan.14 815-10. Before lecture 2, look at pages 22-61, and write a few notes about
what you would like me to discuss in the lecture. If you don't have the book yet, you should get it from Tapir (or from me
for 360 kr.) as soon as possible.
The impressive photos of Norwegian scenery in this book are not there just for decoration. There is a geological reason for each picture, and we should try to learn where and what is important with each one using Google maps and NGU maps. Here are links to NGU geologic maps for the photos in chapters 1 and 2.
Page 12 Værøy.
Page 22 Nesna.
Page 30 Bitihorn.
Page 39 Besseggen.
Page 41 Fræna.
Page 42 Alta canyon.
Page 42 Hårteigen.
Page 43 Lyngen.
Note: The lectures will be in English, and the teaching location is changed to G1 because of the large number of students.
Lecture 2. Monday Jan. 14.
I am sure that everyone would benefit from reviewing the material in Introductory Geology. You will need to know this to follow along in Regional Geology. Most students have had many more geology courses, but I will only require that you know Intro Geology, but know it well.
Probably the best way to review, is too check this list of words, and look up the ones that you don't know in your old textbook: Words for oral exam 2007.
Here are the tests from 2007, in Norwegian and English to help encourage you to review.
Quiz 1 of 4 2007 Intro Geol.
Quiz 2 of 4 2007 Intro Geol.
Quiz 3 of 4 2007 Intro Geol.
Quiz 4 of 4 2007 Intro Geol.
Final exam 2007 Intro Geol.
We have now covered up to page 31, and you should read these pages carefully. Here are my comments and some important terms:
P. 25 The scale of the pie-slice of earth is completely inconsistent: note km distances on right edge.
P.26, find Thingvellir and Reykjavik on a map. The anomaly ages shown here (1, 2, 4, 8, 12) indicatefast spreading from 0-2 million years, slow spreading 2-4 Ma, faster 4-8 Ma, and still faster 8-12Ma. But such variation of spreading is just a technical mistake on the diagram, and is not geologically accurate. The bottom diagram incorrectly shows a layer of melt below the lithosphere. Such a layer is not really present (or S-waves would not pass into the mantle.)
P.27 Map of plates, shows 3 types of plate boundaries. These are called kollisjonsgrense (should be called konvergerende grense, because subduction is not collision), spreading boundary (ok) and Transform fault (ok). But on p. 30 the transform faults are called glidegrenser, and this is not a useful term. The figure text says that the midocean ridge appears to be dislaced by the faults. The use of the word "apparently" is important, because they were never actually displaced by faults -- they only "appear" to be. The rift was offset by these appearant faults already at the initial break-up of the continent.
Read p. 29 about J. Tuzo Wilson, and the Wilson-cycle. He showed that the "Atlantic" ocean has opened and closed more than once. An ocean here closed in Precambrian time to form the Grenvillian mountains. Another ocean (the Iapetus ocean) opened in Cambrian time and closed in Silurian time to form the Caledonian mountains. Yet another ocean (the Atlantic) is opening now.
P.30 Understand the terms Subduction (use the Norwegian term subduksjon, not "synkesone" or "nedføringssone".) The word "oppstuvningssone" is usually called melange, or accretionary wedge. Ophiolite is oceanic crust, about 7 km thick (well illustrated on p 26) now lying on continental crust. P.31 Hot spots are here called varmeflekker (ouch.) Note that Iceland is a hot spot, that was earlier under the Færoe Islands and the coast of Greenland, before the full opening of the North Atlantic.
Lecture 3. Tuesday Jan. 15, 1415-16. P.31. We need to clarify some English and Norwegian terms. Igneous rocks (sometimes called magmatic rocks) have been called eruptive bergarter for about 100 years in Norwegian (from 1870 to 1970). Now most people call them magmatiske bergarter. This book tries something new. It equates English volcanic with Norwegian eruptive but this is not common. Norwegians use the terms dypbergarter, gangbergarter, dagbergarter but these terms are only for popular geology, not for scientific geology, where we use the terms plutonic rocks (plutonske ba.) and volcanic rocks (vulkanske ba.)
P.32. this book seems to use the terms acidic (ca. 75% SiO2), intermediate (65%), basic (55%), ultrabasic (45%) and basic, but these terms are out of date. You should use the terms silisic/felsic, intermediate, mafic, ultramafic.
P.33. To this rock diagram, you need to add the following volcanic rock names: trachyte (=syenite), latite (=monzonite), basalt, andecite, rhyolite. Add also diabase=dolerite, which are dike rocks.
P.34 study these rock pictures. You should be able to identify many of the rocks and minerals in such pictures without reading the figure text. P. 35 excellent diagram, showing the variation in a map according to level of erosion. In the Oslo region, in Permian the map would have looked like b, but now with ablout 2 km of erosion, it looks like c or d. Other parts of norway are more like d, e, f... :)
P.36. Textook diagrams. In fig. c there should be no reverse component. In g, note the folds make some bed upside down. Upside down beds due to flat-lying recumbent folds are very important in Norwegian regional geology, and there is no other diagram showing them here. Note that the thrust fault of g actually removes parts of the blue and green layers! This is not common: thrust faults should double layers, not remove them! In this case, the layers are removed, because the dip of the layers is steeper than the tip of the thrust fault. This is a very special situation.
P. 37. Very difficult map and block diagram to read. Because they green colors for two different layers (should have chosen another color) and the upper green layer is dark green on the block diagram but light green on the map. (The green on the NW corner of the map is the wrong green.) Also difficult because several of the folds plunge toward the middle of the map, while others continue with no plunge. This is very unusual. But the map and diagram are in agreement. Note the symbols used for folds and dips of layers.
P.38 Good diagram showing typical section through a thrust- and fold-mountain range. Here movement is from left to right (in Noregian example from northwest to southeast.) The right part is called the "front," "foreland," or "external" zone, the left is called the "internal" zone or "interior" (not called the "back".) Note the symbols for thrust faults: teeth marks on the map point in the direction of down dip. Both triangles and tick-marks can be used. They do not point in the direction of movement, but only indicate the direction of dip (like strike-and-dip/ strøk-fall marks.) Note that the higher thrust nappes have been transported farther than lower nappes (yellow has been thrust more than blue, brown more than yellow, green more than brown. Norwegian/English words: skyvedekke-thrust nappe, skyveforkastning-thrust fault, utgående-ourcrop, stedegent-autochthon (not transported.)
Colors on this diagram, and on many Norwegian maps follow these Norwegian conventions: Pale brown, beige, grey, pale orange are usually for Precambrian basement. Green is for pelitic rocks, ie. clay- or argillaceous- rocks such as shale, slate, and schist. Blue is for calcareous rocks (also called carbonate rocks), such as limestone, dolomite, marble. Yellow is for psammitic-, sandy-, arenaceous rocks) such as sandstones, conglomerates. Brown is for mafic rocks, such as basalt, diabase, gabbro, greenstone, amphibolite. Other colors, not shown here are red, pink for felsic igneous rocks (granite). Violet is often used for ultramafic rocks.
You should read all of Chapter 2. I have lectured now up to page 38.
FIELD TRIP (FOR GROUP 2) FRIDAY 18. JANUARY 1215-1415. For those who have not been to Rotvoll ophiolite fragment with the first group. Meet outside the Berg-building, to go to Rotvoll in my minibus. Snow is not predicted, but if it snows, we will cancel the trip. I got a message from Beate that she has a double lecture in Petrofysikk Friday 12-14, and should not have a field trip at this time. Do others have this problem? If, so we can schedule a third trip to Rotvoll for another day. Send me an email if you have a problem with this field trip.
Precise weather report for Trondheim. I checked the area Thursday: there is no snow or ice at Rotvoll, and the weather prediction is for dry weather.
There are two students who can't be along on Friday, so we will arrange a third trip for next week. Therefore, if the trip on Friday is also a problem for you, send me an SMS or email that you will not be coming along.
Guidelines for writing a good abstract An abstract is a short report. The main purpose of a report is to present something new and original: new observations/data and new interpetations. The abstract starts with a title, your name and address, and then an introduction to the problem/topic/area. Then it should give some important background information, establishing things that the reader probably already knows. This gives you credibility. That is, it convinces the reader that you have the necessary background and understanding to report on this subject. Then comes the most important part: your new observations or data. This should include specific facts, usually something quantitative. The facts should be reproducible; that is, the reader should get enough information that he can check your facts, by going to the field area, or by repeating the experiments himself. Then there should be an interpretation, to show that you are scientifically mature enough to understand your new data and make sense out of it. The data and interpretation are the real purpose of the abstract, so keep this in mind and keep the introduction modest.
No one writes a good abstract on the first try, or in a hurry. You have to write it and then shorten it as you rewrite it. You can show it to others, and show it to me to get help. We will write 4 abstracts in this class and they will be graded in the end. But this is not a test, but a learning experience, so get the help you need (but not more help than you need.) I don't know if it helps, but here are examples of two abstracts (3000 characters each) that I have recently written.
The first of the four abstracts must be written on our study of the rocks of the field trip to Rotvoll. There is no deadline, but the sooner that you do it, the better it will be. Turn it in and I will read it and give you feedback so that you can improve it. I will grade your final abstract at the end of the course, and the sensor will do the same.
Lecture 4 Monday, Jan.21.
P. 38 Figure shows a sequence of thrust nappes, which we call a tectonostratigraphy. The book calls it a dekkelagpakke, but in Norwegian we also say tektonostratigrafi. Terms autochthon (autokton/stedegen) and allochton (allokton/skjøvet) are also important in Norwegian regional geology.
P. 39 Mylonite is typically darker than the parent rock (protolith) because dark minerals are evenly distributed. (It is the same with bread: if you add a cup of whole-wheat flour to white bread dough, it darkens the bread. If the whole wheat flower is is fine-gound, it darkens it more than if it is course-ground or whole grain.)
We drew the outcrop on p. 51. Try doing it again. Note the amphibolite was strongly foliated and folded, then cut by felsic magma in top right corner, and cut by felsic dikes in the center of the outcrop. Note the xenoliths of amphibolite in the granitic dikes. Drawing outcrops helps you to study them and understand them. Make sure you know the rocks on this page, and on this list: rock names in introductory geology.. Not only the rock names, but you also need to know the compostion of each rocks (main minerals), how the rock is formed, and what its metamorphic equivalents are. You find much of this information in the Introductory textbook, on page 156 (Fig 6.18) and
page 220 (Fig 8.17).
As exercise 1, all students must draw/"map" the rocks on p.51 (on full A4 page.). There are 15 students who have not yet done this, so do it as soon as possible and show it to me.
Lecture 5 Tuesday Jan.22. P.53, three interesting meteorites Gardnos, Mjølnir, Chicxulub. Know their times and locations.
P.56 lower diagram: a regressive sequence, where a delta is building the land out into what was earlier water. P.59 diagram: sequence shows thin transgressive deposits, above are thick regressive deposits, then another thin transgressive sequence and another thick regressive sequence. Make sure that you can understand and read such sequences in such diagrams. Check an introductory geology book or ask for help if you need it.
P.58 about early Norwegian geologists. In my opinion, Keilhau was very slow to understand things, even though explained to him personally by other geologists such as Leopold von Buch and Charles Lyell. His lectures were sometimes published and they seem boring and useless. Theodore Kjerulf was brilliant, quickly understanding and explaining things perfectly.
P.57. Understand the meaning of Lithostratigraphy, Biostratigraphy and Chronstratigraphy. This book overlooks a very important one: Tectonostratigraphy, a sequence of thrust nappes.
Chapter 3. Precambrian. Archean gneisses are mostly TGG, very little K, and what little there was went mostly into biotite, not K-feldspar. P.67 map shows the exposed Archean rocks and the covered Precambrian (Arechean + Proterozoic) cratons and shields. A shield is an exposed area, a craton is the shield plus the exposed area. Note the craton of "Baltika-Øst Europa (no official name for this) does not include western Europe.
P.68. Note all rocks in Scandinavia older than 2000 Ma are in the north, and it is hard to determine which of these are Archean (ie older than 2500 Ma). There is a lot of uncertainty about how to draw a map of this kind. Different geologists have very different opinions. We should learn this one. Note that ages generally get younger to the southwest, as if continental material were being added to an Archean "core" throughout the Precambrian.
P.70 Isotopic dating is very important in regional geology, especially the problem of "blocking temperature" and "open system behaviour" which are not discussed here at all. Read about this in the Introductory Geology text Marshak.
FIELD TRIP (FOR GROUP 3) Thursday 24. JANUARY. We agreed on the time 930-1130, but I forgot that Stine can't come at that time. If we change the time to 915-1115 she can come. Let's change the time. For those of you taking this trip, please send me an email to let me know if you can come at 915 instead of 930. TRIP POSTPONED, DUE TO SNOW! THERE IS A CENTIMETER OF SNOW ON THE ROCKS WE WILL LOOK AT, AND MORE IS EXPECTED. SORRY WE WILL HAVE TO WAIT A WEEK OR TWO!
Lecture 6 Monday, Jan.28. We covered p.72-82 in some detail.
Read the abstract here
abstract of Karasjok paper.
and compare the scetch map with the map on p.72. Note that thrust faults are not shown on most published maps of Precambrian rocks, even though there is evidence for thrusting. (strange habit of Scandinavian geologists.)
The "plate-tectonic" interpretation here
figures from Karasjok paper.
is a typical attempt, but not completely convincing. Similar models of rifting (ocean opening) and collision (closing) shown in figure p.77. Time of rifting is ca. 2500-2060, closing from ca. 2060-1880.
Features to be familiar with here: Raisædno gneiss, Kautokeino gsb, Jergol gneiss, Karasjon gsb. Tana Migamtite belt, Lapland granulite belt, Inari block, PPP-gsb,Sørvaranger gneisses. Note the general rock types of these units (see the folding geological map.)
Another greenstone belt is the Bjørnevann group in Sørvaranger, with Banded Iron Formataion (BIF).
Note "basal conglomerate" of PPP belt, figure p.75. Cobbles are derived from the basement. Most of the greenstone belts have a basal conglomerate (Karasjok, PPP, Bjørnevann.) They are typical for transgressive sequences.
Lecture 7 Tuesday, Jan.29. (Lecture in Norwegian today.) P.74 Began with all students drawing this outcrop. Note the black xenolith with sharp angular contacts (center left side). Note the pink spots are feldspar phenocrysts (lower right and upper left sides.) There is a late felsic dike, not really a pegmatite (with lens cap for scale.) All these rocks can be comagmatic, ie from same magma. Xenolith is earliest mafic minerals, dark parts are main magma composition, felsic parts are late melt that fill late fractures as the rock body cracks.
p.81 We skip over Alta and Raipas, as this is left to be discovered in Field course for structural geology (and very little described here.)
p.84 Mention that many Precambrian rocks are not Caledonized. There are normal faults, with displacements of 2-3 km. You can find some of these shown on map p. 86, and you should be able to decide which block has moved up and which has moved down on most of the faults.
P.85 Supracrustal (don't call them overflatebergarter, but rather suprakrustale ba.) rocks on Ringvassøya are called Ringvassøya Greenstone Belt. Their contacts are shown several places with thrust fault teeth on the map, but this is Caledonian thrusting, not Precambrian. Note the dip of thrusts is to North(west).
Map.86, Mauken window has been called Måselv window in older books. A window is always surrounded by thrust rocks, not by other deposits. Erosion through a thrust nappe makes a window. There are lots of them, see map p.90,
Lofoten is uplifted by a huge fault in Vestforden, not shown on nap p.89. Note Archean rocks, and deep crustal rocks of Lofoten: mangerite, charnockite, gabbro, anorthosite. Such rocks are high temperature and more common at great depth in crust. Lofoten is a mystery, because these rocks were hardly Caledonized, even though they are so far to the west. Maybe because they are such dry rocks, they could not recrystallize in Caledonian conditions. They are dark rocks: even the feldspars are dark brown colored, typical for many granulites, charnockites, anorthosites.
Map p.90 of windows. The windows along the Swedish border (Rombaken, Tysfjord, Nasafjell, Børgefjell) are uplifted but not very Caledonized. The western windows Høgtuva, Sjona, Vikna are mobilized (Caledonized) in Silurian time. Note Archean rocks not found south of Lofoten.
P.92 Map of fault contacts in S. Norway. The best know and first discovered was no.1: "Mylonite zone." also no. 4,5 are well described, and separate high grade metamorphic rocks from others. No.6 was discovered in about 1985 and will probably be undiscovered by about 2085. It is a fault of the short-lived type. There is not general agreement about the relative direction of these faults. Different geologists have different interpretations. Probably mostly reverse faults, related to E-W compression, all very steeply dipping.
Map p.94 Supracrustals of Telemark (see also map p. 98) are very well preserved. Other supracrustals on this map are mostly highly deformed gneisses. Note all the intrusions, especially the ones about 1000-920 Ma. These are from the Sveconorwegian Orogeny, called the Grenvillian in North America.
P.101 Gaustatoppen. Highest mountain in the neighborhood. Find it using google.com maps, and find a geological map of it using NGU.com.
Map p.104 Note the igneous rocks Iddefjord granite in east, very boring rock, with no fractures or stripes. But good for making monoliths (p.105 where the stripes are bird shit, not foliation.) Note also the Egersund or Rogaland intrusives, very unusual rocks (anything but boring.) More detailed map p.107. Both Iddefjord and Egersund are late Sveconorwegian age.
Lecture 8 Monday, Feb.04. Jotunheimen has the highest mountains in Norway, and is geologically very famous for the Jotun Nappe Complex. There is gabbro, anothosite, charnockite and other rocks. Read about them p. 110. These rocks are not differentiated on the maps in this book, either the folding map, or the map on p. 113. You should go to an NGU map and try to find these different rocks.
Here I will just point out a few general patterns. The highest nappe includes the rocks from the deepest crustal levels, in granulite facies metamorphism. The lower nappe is from shallower levels, but these also are thrust over Late Precambrian sparagmites, which are thrust over Paleozoic phyllites, which were thrust over the basement. Jotun was basement somewhere in the far Northwest, before being thust to the southeast. It was earlier thought of as a Caledonian "mushroom fold" or Caledonian intrusive complex, but became one of the first accepted examples of thrusting in Norway. In the lecture I said that the upper Jotun gabbros are older than the younger ones, but I think this is not correct. The ages are mixed.
Note that similar rocks are found in Bergen arcs (no 22 on folded map.)
The Western Gneiss Region (WGR) includes Precambrian gneisses and Caledonian cover nappes, mostly strongly "Caledonized" (folded and metamorphosed together.) It is a "window" or a view through the high nappes that have been removed here. The Jotun Nappe Complex is a "klippe" or erosional remnant of nappes that were over the WGR. There are lots of Precambrian plutonic rocks (granite) in the WGR, but almost no Caledonian plutonic rocks. The WGR subducted, and subduction-related plutonic rocks are found in the higher rocks (Laurentia-Greenland) but not it the WGR.
There are lots of ultramafic bodies in the WGR, often 100-1000 m in diameter, and looking like huge orange pumpkins in the landskape, since u-m rocks often weather orange and almost no grass grows on them. U-m rock can only come from the mantle, and these have sometimes been called "canon balls" shot from the mantle. Most ultramafic rocks in the the crust occur as serpentine rocks (serpentine has lots of H2O, absorbed during metamorphism at high crustal levels.) In the WGR many of the u-m rocks contain olivine and pyroxene, which may be original mantle minerals, or may be high grade minerals related to subduction metamorphism of the WGR.
Find some of these on a NGU map of Norway, for example around Tafjord. "Olivinstein" on this "vector" map.
"31" on this "raster" map.
I want you to explore these maps and be familiar with both "Raster" and "Vecter" types. The legend for the Raster maps is hard to find. You need to click on the word TEGNFORKLARING and then click on the map for the area of interest (so that you get the correct Tegnforklaring/legend for that exact area.)
(The subtitle on p.117 "Eldgamle (arkeiske?) bergarter fra jordens mantel" is completely inappropriate, because no one thinks these rocks are actually Archean. The mantle is Archean, but not the rocks and minerals that came from it in younger times: they have all been recrystallized during mantle convection before being torn away and emplaced into the crust.)
Kapittel 4. Late Precambrian regions. The supercontinent of Late Precambrian (=Neoproterozoic) time is called Rodinia. Learn the time scale p.60: You need to know both Old terms and Modern terms (in parentheses): Late Precambrian = (Neoproterozoic). It is divided into Riphean = (Kryogen) and Vendian (Ediacran). See table p.125, left edge.
Map p. 124 shows Caledonian rocks, which are mostly Late Precambian, and mostly thrust to SW. The amount of thrusting decreases to the northeast, and east of Tanafjorden there is no longer any thrusting.
P.125. Here are tables showing the stratigraphic sequences of the Tanafjord-Varangerfjord region (18 formations) and the Barentshav region (8 formations). Formation names such as these are typical in regional geology. Anyone working in a new region, or visiting them on a field trip, should memorize the sequence of formation names immediately, so that as they learn about the rocks, they have a "framework" for understanding them. But very few geologists do this, or are able to do it.
Most people have great difficulty memorizing such a sequence, because they have never learned the scientific way to memorize. They memorize by instinct: repeating the words over and over again. But usually, they don’t memorize things, because it is so difficult and boring.
If you learn how to memorize a stratigraphy, you will have a great advantage in later geological work. So here I will memorize these 18 formations for you.
You make silly mnemonic associations for each name, and silly links between the names. I do this in two steps below, but with practice you can do it in only one step. For the list of 18 formations, here are my recommendations (sorry, only in Norwegian, since these place names are mostly Norwegian words.):
Breivik (en Brei-vik),
Stahpogieddi (moset Stappe-gjedde),
Mortens-nes (Mortens nese),
Ny-borg (en ny borg),
Smal-fjord (en smal fjord),
Gras-dal (en gresskled dal),
Haknalacearru (“Håkon-Allah cheer u),
Gamasfjell (et Gammes-fjell),
Dakkovarre (innfyll til tacos: Taco-vare),
Stange-nes (en Nese lang som en stange),
Grønn-nes (en Nese som er grønn),
Ekker-øy (ei Øy som består av en stor Åker),
Gol-nes-elv (en Elv med gule neser som flytter i seg),
Padde-by (en By for padder),
Anders-by (en Annerledes by),
Fugle-berget (et Berg med fugle reir),
Klubbnesen (en Nese formet som en Klubb),
Veidnesbotn (Veid-nes-bot, en ulovlig stor Veid nese, som bøtelegges).
For me, these are visual mnemonic associations, something that I can laugh about. Maybe they will work for you. You would probably think of other associations, if I had not done it for you here.
Now link them together in a chain, with silly connections. Begin at the bottom of the stratigraphy. (Now I need to write in Norwegian, for simplicity.) For Veid-nes-bot, jeg tenker på en stor nese, som blir veid og så får en bot, fordi den er så stor. Dommeren som gir bot i rettsaken, bruker en Klubb for slå nesen. En klubb da slår et fugleberg. Fuglene på fugleberget synes det er litt trangt der og vil ha en andre by (Anders-by). En andre by er en Padde-by. Paddene bor i en elv med mange gule neser som flytter i: Gul-nes-elv. I elven er det en flat åker som et øy, dvs Åkerøy (Ekkerøy). I åkeren vokser det grønne neser: Grønnes. Noen grønne neser er så lang som stanger: Stangenes. Stangene er bra som fyll i tacos: Taco-vare. Man serverer tacos i en Samisk gamme på Gamasfjell. Kong Håkon-Allah bor på Gamasfjell, "Håkon-Allah-kjær u". Håkon Allah ser ned på den gressaktige Grasdal. Grasdal ligger ved den smale Smalfjord. Ved Smalfjord er det en Ny-Borg. Mortens-nese stikker nysgjerrig inn i borgen. Morten Stapper en moset gjedde inn i nese si. Gjedde liker å svømme i en Brei vik.
When you have such a chain link of silly visual images, you can remember the stratigraphy both upward and downward. Then as you read or learn about the details of these rocks, you can keep track of them, and maybe fit them into your chain. If any students have a better way to memorize such stratigraphies, we would like to hear how you do it. I will expect all students to memorize this table, and several other regional stratigraphies in this regional geology course.
Lecture 9 Tuesday Feb.05.
Understand and memorize the map on p. 124. Here are the elements to know, vertically (in tectonostratigraphy), and geographically (on the map.) (from SE to NW, or bottom to top: Basement, Dividal, Gaissa, Laksefjord, Kalak, Silurian. These names are easy to remember. Dividal is a valley in Trøms that cuts through the nappes (divides) down into the basement. It exposes the Cambrian Dividal formation. The range of mountain tops along the Caledonian front in Finnmark are called "Gaissa" (a Same-word) Rastigaissa is the highest. Toward the coast are the fjords, among others Lakesfjord. Out in the ocean is floating a Clock (Kalak). These rocks are all Neoproterozoic, and above them all come the Silurian rocks. The nappe movement for all these was in Silurian, not Neoproterozoic.
Here is an NGU map from the 1970s. The Lapland granulite belt is colored orange in this map (I mapped many wide stripes in it, that are shown on newer maps, and in the pink northeast corner of this map.) The Dividal group is colored green and the Gaissa arkoses are colored yellow. Note that the yellow arkoses form mountains called "Gaissa."
In Tanafjord-Varanger area: from E to W (bottom to top) Vadsø, Tanafjord, Vestertana, in the Barents Sea: Barentshav, Løkvikfjell. There is slight angular unconformity between Kryogen and Ediacaran, both north and south of Trollfjord-Komagelv fault.
Now memorized the names on stratigraphic table of p. 125. We did the first part, now we do the Barentshav region: Kongsfjord (think of a Kong, owning a fjord), Båsnæringen (think of the Kongs fjord being divided up in Båser), Båtsfjord (think of a boat in each Bås), Tyvjofjell (think of a Tyv stealing a Båt), Sandfjord (the Tyv sinks in quicksand), Styret (a bicycle has also sunk and only the Styret is visible), Stordalselva (the Styret is steering up the Stor-dals-elva), Skidnefjell (the source of the river is a Skitten fjell.)
Remember the group names as Barents sea (below) and Løkvikfjell (a Løk floating above, at the top of the sea.)
When you have gotten all these names memorized, THEN you are ready to read the chapter and see if there is anything interesting and worth remembering. Having the maps and stratigraphy memorized gives you a framework to sort and understand all the details. We cannot be expected to remember all these details, but should find some of them that are interesting enough to remember. (It is too bad that there is no map here showing the location of these formations or these groups. A map like on page 136 would have been useful here.)
Note that south of the Trollfjord-Komagelv fault the rocks are mostly non-marine, or shallow marine, with a basal conglomerate, and with two tillites. North of the fault the rocks are mostly deep marine.
The Troll-Komag fault was "discovered" in the early 1970s and and for 30 years afterward, it was thought to be a great strike slip fault, with the Barents Sea rocks moved thousands of kilometers. Now most think there is only slight strike slip movement, and it is mostly a normal fault (north down.)
Read what the book says about these areas.
Read about Snowball Earth, maybe best on Wikipedia.
The Varanger Ice age was first discovered here (Mortensnes fm.) by Reusch, and is called the Reusch Moraine. He described it well in 1891. Reusch 1891
Read about it on p. 128, and about the other rocks (not Ediacara fossils.)
The Seiland Igneous Complex is one of Norway's most exciting regions, but is very poorly presented here. I am proud to have been the first (1987) to suggest that it was rift-related (Page 1,
4) and now, only 20 years later, most people are starting to agree. But no rift interpretation is mentioned on page 134-135 (a rift possibility is mentioned on page 207, probably written by another dugnad author.) I think that the layered gabbros, ultramafic rocks, syenites, karbonatites, and mafic dike swarms of the Seiland region are what you would find 20 km under the Oslo region. In Seiland the continental rifting was Late Precambrian and is eroded down 20km. In Oslo it was Permian, and eroded only 2 km.
Read what the book says about these rocks.
Field trips and exams. We need to agree on dates. Here is the calender for spring semester 2008.
The field trip to Oslo has already been decided as April 29 to May 2, since we will combine it with the course Historical Geology/Paleontology. From Oslo, many students are going directly to England until May 10.
Here is the list of students to Oslo. If you see anything wrong here, let us know immediately!
I suggest that we take the field trip to Oppdal in three separate minibus trips of about 13 students each. That way the students will get more attention from the leader (me), and the rocks will get more attention from the students (you.) Two trips can go while 14 students are in England.
We could have our Final exam (50%) on Thursday May 15. That way we can be finished with the course early and can concentrate on other exams.
I suggest we have our first Quiz (15%) on Tuesday Feb. 19.
and our second Quiz (15%) on Tuesday April 8.
Lecture 10 Monday Feb.11.
More on the Neo Proterozoic rocks of Norway. P.134. Layered plutonic rocks like these are commonly formed in rifts, mid-ocean ridges, and hot spots, where there are no compressional deformation forces. They are not usually related to collisional processes. P.135, note that the picture shows two deformed dikes, not sills. The dikes were originally vertical and cross-cutting, but have now been deformed by simple shear to be horizontal and more or less parallel (concordant) with the deformed sandstone layering. The sandstone layers are flattened and do not show the originally cross-bedded arkose structure. These rocks are extremely deformed and difficult to understand. There are swarms of such dikes in Finnmark, and Oppdal and near Åre in Sweden. All from continental rifting, and first magmatism of Iapetus ocean.
P. 136 Map shows the Hedmark basin of Sparagmite region. We need to memorize the stratigraphy (p. 138) and see how that stratigraphy is found on the map (east and west parts). You should be able to determine the relative movement of the faults (ie. normal faults) and note that there is over 130 km of movement on the thrusts (the rocks were deposited outside of the map area, and thrusted into place in Devionian time.) To memorize the stratigraphy, try this: Brøttum (Brød-tom, tom for brød), Biskopås (go to the bishop to get bread), Biri (Beer, the bishop is drinking), Ring (drop a Ring into the beer), Moelv (Mo-cow, with ring in its nose), Ekre (åker, a field where the cow is feeding), Vangsås (Van Gogh? paints the field?) Note the Brøttum is deep marine turbidites, like the Kongsfjord fm at base of Barents Sea group. In Eastern stratigraphy, the Brøttum is same age as the Rendal fm, which are non-marin sands, just in the Southern part of Varanger peninsula. There are some interesting similaries here, (is the IMF fault similar to the Trollfjord-Komagelv fault?) Note that the Biskopås conglomerate is a turbidite conglomerate, not shallow water. In the old days, people thought all conglomerates were shallow water high energy deposits, but now we know that they can form from deep marine turbidites also.
Read and think about the stratigraphy and geology that is described in the book. Remember any parts that are interesting, but don't try to memorize it all.
The Valdres basin is west of the map area of p. 136. It is more deformed and famous for the Bygdin "Walking stick conglomerate."
Lecture 11 Tuesday Feb.12.
Here is an article in English for the students who can't read our Norwegian textbook.
Chapter 5 is about the "Cambrosilur/Cambro-Silurian." This is a common Norwegian term, with an interesting history. The term "Ordovician" was not used in Norway until about 1920. Until that time, the Ordovician was called "Under Silurian" as opposed to "Over Silurian." The terms come from British geology and British geologists. The British geologist Sedgwick invented the term Cambrian and used it for all the rocks above the Precambrian and all the way up to the Devonian. The geologist Murchison invented the term Silurian and used it for all the rocks below the Devonian and all the way down to the Precambrian. the same rocks (the Norwegian Kjerulf followed this usage in 1870.) After 50 years of disagreement - where should the boundary between Cambrian and Silurian be placed?, the geologist Lapworth used graptolite fossils to create a period he called the Ordovician in 1879. This was made international in 1906, but not really used in Norway until about 1920. I like to keep track of these names, and I do it like this: SeDGwick liked Cambrian, and he also would have liked CambriDGe. Murchison liked Silurian. Lapworth came along and put a patch/Lapp or "Ordovician" across the border between "Cambrian" and "Silurian".
I am very fond of fossils, but you can skip pages 151-163 (Take the course Historical Geology and Paleontology for these pages.)
Kjerulf began the numbered stratigraphy in about 1854, and had 8 etasjer, 1: sparagmites and basal conglomerate, 2: alum shale and other shales/carbonates, 3,4,5,6,7,8 for other sediments, overlain by sandstones (eventually number 10). The numbers were developed/expanded with a,b,c, alfa, beta, gamma, etc. for 100 years. They are handy, but not recommended for serious correlation and facies study. For that we use formation names with type localities, and these new formation names need to be learned before reading about Oslo or visiting it in a field trip.
Set of linked mnemonics for learning the formation names of p. 164:
Precambrian basement, overlain by basal conglomerate (etasje 1) and alun shale (etasje 2.) Read about the horrible alum shale: rusty, black, carbon-rich, radioactive causing radon gas and cancer, swelling due to gypsum-formation, sulfuric acid forming, with stink-balls (concretions). No one forgets this rock (et.2) or the basal conglomerate (et.1). Higher units are harder to remember. Here is a quick suggestion of mnemonics: Bjørkåsholm formation (think of a hill with 3 birch trees sliding across the slippery alum shale), Tøyen fm. (think of a jogger grabbing a birch tree and Tøying ut), Huk fm. (the jogger crouches down in a Huk position), Elnes fm. (in the Huk position, the jogger's nose becomes electric and glows), Voll fm. (a Volley ball comes flying in and hits the Electric Nose), Arnestad fm. (the Volley ball comes flying in from Arne-stad), Frognerkil fm. (Frogner park is a place that Arne lives, ie. Arnestad.), Nakkholm fm. (Frogner park is a good place for Naked sunbathing), Solvang fm. (when Naked sunbathing you get sun/Sol on your lap/Fang), Venstøp fm (to mass-produce friends to come sit on your Sol-Fang, you invent a Venn-støperi), Grimsøy fm. (a Venn-støperi sounds like something from a Grims fairy tale story), Skjerholm fm. (a point on the island Grimsøy cuts waves that hit the island Sjær-holm), Skogerholm fm. (not only waves but huge logs get cut on Sjærholm), Husbergøy fm. (the cut logs are made into houses on berg-øy. There are 5 houses because this is etasje 5.) Langøyene fm. (if you live on Husbergøy, you need a long path to your island, and this path is a string of long islands, or Langøyene.) Solvik fm. (on the Langøyene there is a sunny Sol-vik.) Rytteråker fm. (7 horse-riders/Rytter ride on a field (åker) near the sunny Sol-vik.) Vik fm. (The top half of the Y in Rytteråker reminds you of the letter V in Vik.) Skinnerbukt fm. (the V of Vik is formed by two train rails or Skinner.) Malmøya fm. (ore/Malm is taken out of the mine in train cars on rails or Skinner, so it is natural that Malm is over Skinner. Malm is etasje 8, because the number 8 looks like a dumbbell/manual.) Steinsfjorden fm. (you throw 9 small stein of malm into the fjord.) Sundvoll group. A Sund-voll is a good place for a group of 10 people to stand when throwing 9 stein in the fjord.
When you know these 24 formation names, the geology is then more manageable and interesting. Read the descriptions on p 164-177.
Most unusual is the Langøyene fm. at the top of the Ordovician. At this time, sea level dropped because of glaciation in Sahara Africa. It was the only time from etasje 1-9 that the rocks were exposed to air, and there was erosion forming the well-known calcite sandstone (kalksandstein) and even conglomerate of etasje 5b. This is shown as yellow sand on geologic maps, but they put this yellow sand layer in the wrong place (Solvik!) on p.164. Etajse 10 is also non-marine sandstone, called Sundvoll group, also called Ringerike sandstone, also called "Old Red Sandstone." It was the filling up of the shallow sea by sands eroded from the Caledonian mountains forming to the west. It is uppermost Silurian age.
Lecture 12 Monday Feb.18. On Chapter 9 Introduction to the Oslo region. (We will go back to Chapters 6,7,8 later.)
Here is an article in English for the students who can't read our Norwegian textbook.
P.288 The diagram of a graben may be confusing. The base of the diagram is drawn flat, instead of showing the vertical displacements. It shows a simple Horst but not a simple Graben. It does not mention the term half graben. Graben shaped blocks sink, and horst-shaped blocks rise, just as blocks of wood with such shapes would sink and rise if floating in water. The deformation is expensional, but the vertical displacements make the crust thinner. Now we think that most large normal faults become more shallow at depth, something that is called listric. P.297 shows how these are usually drawn today.
The map p.288 shows the Oslo area. There are three common terms: Oslo Region (Oslofelt), Oslo rift, Oslo graben. These are generally not used the same. Oslo Region (Oslofelt) is used as a general term for the area with rocks younger than Precambrian. Oslo Rift is a term that emphasizes the Permian structural setting, with Permian faulting, deposition, and igneous activity. Oslo Graben is not a recommended term, because there is not a specific Oslo graben. See p.295: there are four grabens, of which the Vestfold and Akershus grabens are the most important and should be remembered. On the map p 288, note that within the Oslo Region, the Intrusive rocks are most abundant, and these are felsic and intermediate. Mafic intrusive rocks (gabbros) are only tiny spots. Volcanic rocks are mostly mafic and intermediate, and are less abundant. Cambro-Silurian sedimentary rocks are least.
Quiz 1 will be Tuesday Feb.19, 1415. It will only take 30-45 minutes, not two hours. I will ask about igneous, metamorphic, sedimentary rocks (names, compositions), and about topics discussed in lecture from chapters 2,3,4. You should know the stratigraphies and maps that we have dealt with. You can read or write in either English or Norwegian on the quiz. It counts 15% of the total grade, so the difference between an A (95%) and a D (55%) is only 6% of the total grade. So don't ruin your week reading for this quiz. The grading system is something like this: 100-90=A, 90-80=B, 80-60=C, 60-50=D, 50-40=E, 40-0=F. In May, an external grader will judge the difficulty of the questions, before the final grades are decided.
Here is the Quiz 1, with no answers. (It is much easier to ask such questions than to answer them :)
Here are the grading scores of Quiz 1
Research proposal. As the second piece of original writing in this class, you must write a proposal to do a library research project on the Mandal-Ustaoset fault (see p. 92, 94, 98, 99). Our book does not explain the evidence for this fault, or how it is known that it goes al the way from Mandal to Ustaoset, and where it might continue north of Ustaoset. You may write only 2000 characters/spaces, plus a budget that you hope will be approved.
For the proposal you should only use information available in the book Norge blir til. You must convince the reader/referee that this is an interesting and important topic to research. If your proposal is accepted, you will then try to find relevant geologic information in other sources.
For the budget, you must specify how many hours you expect to work on this research, and how much your time is worth. You should break down your time into searching, reading, and writing, and document your costs, maybe by calculations based on your monthly expenses and monthy work load. Your budget should be realistic and not inflated. You are not going to do field work, just a few hours of reading and writing.
The proposals with budget must be in English on a single A4 page. They will be copied, and each student will judge 3 different proposals, and rank them 1,2,3.
Deadline for delivering proposals will be Tuesday March 11, at 1300.
Lecture 13 Monday March 3. Chapter 9 Oslo region.
P.294 Diagram of compositions found in the Oslo magmatism. Sur=silisic (actually acid, but the term acid is outdated), basisk=mafic (basic is outdated), ultrabasisk=ultramafic. You should know from these diagrams which rocks are silisic, intermediate and mafic. The "ultramafic" rocks are not actually called ultramafic. They have low SiO2, but do not have high enough Fe and Mg for ultramafic rocks. They have high Na and K, instead of such high Fe and Mg. The size of the colored areas show the variation in chemistry, not the volumes or amounts of these rocks in the Olso area. There are very few gabbros, but this diagram shows a huge gabbro field, because there is a variety of compositions. Learn the relative positions of Granite=rhyolite, Nordmarkite=Trakyte, Larvikite(=Rhomb Porphyry), Gabbro=Basalt=Basanite, on these diagrams.
P295 Diagram, note the rift has 4 grabens, two middle ones are important: Vestfold grabem. Akershus graben. Bordered by faults on one side only, Oslofjord fault and Randsfjord fault. These make a "scissors fault". You should be able to draw E-W cross sections across each of these grabens. P296 shows landscape of Oslofjord fault.
Look at cross sections p.297, 298, 301. Nearly all normal faults are shown as curving (litric).
P301 note crust and mantle (ie lithosphere) is thinned at Oslo rift because of stretching. There is no known line between "upper" crust and "lower" crust, but lower crust is probably a bit darker (more mafic.) Melting is caused by uplift, decompression melting.
Lecture 14 Tuesday March 4. Chapter 9 Oslo region.
Diagrams and maps on p.302, 303 are very useful. Also p 321 and this map: Geologic map of Oslo region
You need to look at all these in comparison to each other and the maps on other pages to put this information together! Such maps, stratigraphic columns and tables are the best way to present regional geology.
I discussed these things in some detail in the lectures.
P. 302, note in Skien that the area of preserved lava is tiny, but the amount of B1 basalt lava was huge. Same at Jeløya. There was much more B1 basalt that was eroded away other places. In the columns, note the general pattern: violet colors (mafic) at the base, more brown colors (intermediate) in the middle, more red colors (felsic) toward the top. Do you see how this makes sense according to Bowens reaction series? Then vulcanism died out and there was more sandstone (yellow.)
Stage 1 (stadium 1) Figure p 303 shows the Asker group, above the folded Caledonian sediments (peneplane) and below the B1 basalt. Things to note (memorize): Names Asker = Kolsås, Tanum, Skaugum. Discordances: between all formations. These were all thought to be non-marine, until microfossils (F) and crinoids (star) were found in a few thin limestones. See map p.304. Volcanic material in conglomerates starts appearing in Skaugum. There must have been lava flows other places...but not preserved today.
Stage 2. Rift vulkanism, with Skaugum and B1. P.303 table, p307, 307 maps.
Stage 3. "klimax" RP lavas coming from fissures (dikes) indicates crustal extension. Extensional faults form, larvikite batholiths in south of rift. Look at RPs p 312, and this page showing various forms, which can be mapped in detail based on appearance. Drawings of the rhomb porphyries
Stage 4. (next klimax?) "avslapning" p321 Central volcanos indicated by calderas, Oslo-essexites (small gabbros), and explosion breccias, all show that extension is now mostly over (still some dikes formed) Two granite batholiths in center of rift
Explanation of Bærum caldera
Stage 5. (nest klimax?) Many syenite, nordmarkite and granite batholiths in north of rift.
Stage 6. A few small granites, and few dikes still forming.
Dividing Oslo development into these 6 stages is traditional, with 3=klimax and with 5=batholith stage. But now it is clear that batholiths occured in 4 stages, "Phase 1,2,3,4" so the stage concept is weakened.
Diagrams p304, 307, 308, 311, 313, 316, 317, 319, 320, 321 are also all excellent and should be understood in relation to the lectures I gave.
You should probably print out the three pdf pages above and add them to your book.
Oslo is a world class example of a rift, so learning about the Oslo region is actually learning about rifts.
Lecture 15 Monday March 10. Chapter 6 Iapetus ocean and Caledonides.
Caledonides form over half of Norway, and they are one of the world's classic mountain ranges. Since they are so old (400 million years) they are deeply eroded, and we see a deeper level of an orogen (= mountain range) than one sees in the Alps. Just as the Oslo rift is effectively divided into Stages, the Caledonides are divided into allochthon (=allokton, dekkeserie.) You must learn the fundamentals of these, so that you can think of any part of the Caledonides by what allochthon it is in. The book is not so clear on this, so I explained it in lecture. You can read this on these pages: p 182 first paragraph, p.200 map, p.202 map (very helpful), p 205 map. There is discussion of these (but not so clear) on pages 199-200.) To simplify, we can say that the allochthon originally lay to the west, but were then stacked up on each other and then up on the continent Baltica. The easiest allochthon to identify is the Upper Allochthon, because this is the Iapetus Ocean, that is the ophiolites. It is very important to identify where and if there are ocean fragments in a mountain range. This is the "suture" the seam between the two original continents that collided to form the orogen. If there are no ophiolites, there was probably no continental collision. Himalaya, Alps, Appalachians, Caleodonides, Urals all have sutures. (Greenstone belts in Finnmark can be thought of as sutures.) No suture really in the Pyrenees or the Hercynian mountains of central and western Europe, although I think geologists would like to create them.
Here are the ways to identify which allochthon you are dealing with:
Uppermost allochthon: continental crust now lying above the Upper Allochthon. Can think of these as Laurentia.
Upper Allochthon: Iapetus ocean. Ophiolite (ultramafites, gabbros, dikes, pillow lavas, turbidites, and metamorphic equivalents such as amphibolite, schist, gneiss.) Deep marine sediments, but not shallow marine as in Oslo.
Middle Allochthon: Continental crust, non-marine sediments (sparagmites) and shallow marine rocks that were involved in the rift margin of Iapetus. They are the western margin of Baltica, near where Iapetus formed. The easiest clue for identifying the rift-involvement is the occurrence of Neoproterozoic mafic dikes and intrusions such as Seiland.
Lower Allochthon: Same as Middle, but not rift involvement.
Parautocthon: Same as Lower, but very "local" types of rock, and assumed very short thrust distances, less than maybe 50 km.
Autochthon: Same as above, but no clear proof of thrust displacement. Oslo region is mostly Autochthon, getting into Parautochthon as you move north to Hedmark basin.
With this background, read about ophiolites and other things, p 182-190.
Tuesday March 11. Evaluation of Man-us proposals and of this geology course
Evaluering av faget
25 studenter leverte evalueringer. Det er tydelig at faget kan forbedres på mange måter. Dette var som forventet, fordi pensum og forelesningene kjøres for første gang i år, og det er en del startvanskeligheter. Håper ingen var tilbakeholden med kritikk. Det er ingen frykt for "hevn"! Takk for nyttige tilbakemeldinger.
Field trip to Brekstad
is planned for April 1. Postponed, sorry! Because of late snow, and lectures in Historical Geology and Structural Geology.
Quiz 2 is planned for April 8. Will cover Chapters 5 and 9, lectures 11, 12, 13, 14. (also general questions about rocks, as in Quiz 1)
Final exam is planned for Thursday May 15.
Lecture 16 Monday March 31. Chapter 6 Iapetus ocean and Caledonides.
Figure on p 190 is very uncertain and unclear. Iapetus ocean crust is difficult to interpret today, because almost all of it has been subducted. First study p.29 where a simple example is given. A new ocean opens. When it gets wide and old and cold, part of it is heavy enough to subduct. But why is some of the ocean crust put up on land as ophiolites? There is no clear answer to this today. Maybe ophiolites are emplaced as the first subduction is started (some crust goes down, but a little gets pushed up?) Now back to p.190. The first section is 500 Ma, because the rocks of ophiolites are all isotopically dated at 485-495 Ma (when the rocks formed on sea floor, not when they were thrust as ophiolites). Top diagram shows subduction of Balticaand formation of island arc. This is a suggestion, but cannot be completely correct. What ocean is being subducted here? Baltica cannot subduct and form an island arc. Some eclogites in Sweden (in the Seve nappe) have given isotopic dates of about 500 Ma. It we accept those dates, this drawing tries to show how deep eclogites could have formed. The bottom 3 diagrams are more reliable. But even here, there are complications and problems.
Map p. 185 is helpful. Note the green is all Iapetus, and represents a sort of wide suture. Pink rocks of coastal Nordland are above (Uppermost allochthon) the opiolites; all other rocks are below them (Middle allochthon and lower.) The dark green is mafic rock, of oceanic crust. Here is a joke that I heard at an international geology meeting in the late 1970s: Question: "What is an ophiolite?" Answer: "A mafic rock that has been studied by a geologist from Bergen." (Bergen was, and still is, the Norwegian university most eager to interpret ophiolites.) Most geologists in the world at this time only called a rock ophiolite if there was ultramafic, overlain by gabbro, then sheeted dikes, then pillow lavas. But Norwegian geologists call any part of this sequence an "ophiolite fragment." Here on this map they are called "ophiolite complex."
Lecture 17 Tuesday April 1. On Caledonide mountains. P. 196. Bulldozer image shows a wedge of snow, thickest near the collision (west) and thinner (east). This is correct, but there is even a wedge that forms during sedimentation, well before the collision. the sediments in the east (forland) are thin, nonmarine and shallow marine deposits. Oslo stratigraphy is about 1500 meters thick, but to the east in Sweden the same rocks are much thinner, and to the west, the Cambro-silurian rocks of the Upper Allochthon are maybe 10 times thicker. Turbidites are in general the thickest deposits in mountain ranges, as they formed in deep water off the shelf, "the final resting place" for sediments.
Eclogite is evidence of deep level, high pressure metamorphism, 50 km or more. They were originally thought of as "cannon balls" shot up from the mantle, but now we know that they were gabbros and other crustal rocks, and that the entire crust was pushed down to this level and then brought up again. Not only eclogite, but also micro diamonds show that the depth was up to 100 km in some western parts (west of Ålesund.) Map on page 221 shows ecologites in Western Gneiss Region. The temperature of the basement in Oslo may have reached 100 degrees in the collision. In Valdres it was probably 200 degrees, west of Jotunheimen it was 500 degrees, and to the far west it was 800 degrees. The eastern part of the Western Gneiss Region was depressed to 40 kilometers, and the western part at least 60 km. These temperatures and pressures are deduced mainly by minerals that formed. Collision was Silurian, about 425-410 million years ago. The collision began in the west (highest allochthon) and proceded to the east, finally reaching Oslo in the early Devonian.
Map p.200 is important. Cross sections p.201 try to show evidence of shortening. Everyone should be able to explain some evidence of thrusting. Evidence is NOT based on mylonites (well shown on p.200). It is based on stratigraphy, or tectonostratigraphy. We can simplify and explain the thrust evidence in three parts of Norway.
Southern Caledonides: Cambro-Silurian rocks of Oslo are authochthonous, and since older Neoproterozoic sparagmites lite over them, these must be allochthonous. Since Middle Proterozoic Jotun gabbros lie over sparagmites, they too must be thrust.
Central Caledonides: From our field trips we know that Risberget gneisses lie over Åmøtsdal sandstones, this must be due to thrusting. Sætra sandstones with dike swarms lie over Risberget, this must be from thrusting. Blåhø marine sediments and mafic volcanics, all in high metamophic grade, lie over Sætra continental sandstones, in lower metamorphic grade, this must be from thrusting. A metamorphic break between the Blåhø and Trondheim nappe complex (Støren) nappe indicates thrusting.
Northern Norway. See map and tectonostratigraphic column, p.205. Note that each nappe (Laksefjord, Gargia, Skillefjord, Nalgannas,..) has Precambrian basement that is lying on younger rocks below. This is proof of thrusting. We always decide where important thrusts are by the stratigraphy, age, and metamorphism, not by the presence of mylonites.
Pages 210-219 are can be skipped over.
Lecture 18 Monday April 7. On Caledonide mountains. P.205 mafic dikes in Kalak sandstones. Now deformed to parallel layers, but originally cross cutting, like Sætra dikes in Oppdal field trip and Vestranden-Fosen field trip. These dikes are evidence of rifting of the margin of Baltica, and make the Kalak and Sætra and Risberget all Middle Allochthon. Risberget has gabbro and anorthosite (as seen on field trip) and so does the Jotun Nappe, so it too is Middle Allochthon.
Silly map on p.205 has two legends, with two different color schemes! Magerøy rocks are turbidites, deep marine, and therefore Upper Allochton. Kalak are Middle, and those below are Lower, or Parauthochthonous. We will not go into stratigraphic details in this class, so we will not distinguish between Lower Allochthon and Parautochthon. Those differences are based on thickness and facies of sediments before thrusting. Not explained here.
P.220-225 are well worth reading. Much of this is discussed elsewhere in these blog notes and on the field trips. You can skip p.226-229.
Quiz 2 Tuesday April 8, 1415-15. The quiz will be on chapters 5 and 9, and the map and diagram pages that I handed out and put on this blog (see Lecture 14).
There will be no questions about fossils. But you should memorize the formation names on p 164, and understand the table on p. 321. Chapter 9 is much more important than chapter 5 on this quiz. Quiz 2
Here are the grading scores of Quiz 1
Here are the grading scores of Quiz 1 and 2
Lecture 19 Monday April 14. On Devonian. After the collision, there was collapse. Collision is compressional, with southeastward vergence or movement of higher layers. The collapse was extensional, with southwestward vergence. Fig. p.234 and p. 234 show this. Note that back-gliding in Devonian occured partly on the earlier thrust planes, and partly on new fault surfaces. Now we think there are a lot of Devonian extensional faults in Norway (p. 238) but this idea first began in the middle 1980s with the Devonian basins of western Norway. Map p.244 shows the Devonian sediments in a basin. The largest basin (Hornelen) is similar to this but has more sediment: 25000 meters of continuous, nonmarine sandstone and conglomerate, all dipping to the east (see picture p 244, diagram p.248, photos p.249, 250. It was impossible to explain how so much sediment could be deposited in a mountain basin. 25000 meters of horizontal sediment would extend down to the lower crust. And at a geothermal gradient of 20 degrees per kilometer, this sediment would be 500 degrees, or middle grade metamorphic. The rocks of Hornelen and other basins are only about 100-200 degrees.
They were thought to be thrust to the southwest in a late phase of collision. But then it was shown that they were deposited as shown in diagram p.249. They were deposited flat, and rotated as they were pulled westward across a curving basal extensional fault (listric normal fault) while new sediments were being deposited flat above them. Read the text. These things are seen and discussed in some detail on the field trip to Vestranden-Fosen.
Oppdal Field Trip Tuesday 15.April 900 Leaving from parking place outside of lecture room. Will return about 1900. Everyone should write an abstract of about 3000 characters on some part of this trip. It should be written with the sensor in mind, that is, for a person who was not along on the trip. You should introduce the trip and the area, and then tell some details about one (or more) of the stops. You do not need to use any literature, but only things that are on the maps and guide, and what you saw on the trip. This is one of the four abstracts that will be graded; each one counts as 5% of the final grade. If you have not written 4 abstracts (Rotvoll, Man-Us fault, Oppdal, Vestranden-Fosen), then you should write one for the Oslo trip.
Oppdal field trip guide text
Oppdal geologic map
Oppdal location map
Vestranden-Fosen field trip Friday April 18. 700-1800.
Everyone should write an abstract of about 3000 characters on some part of this trip. It should be written with the sensor in mind, that is, for a person who was not along on the trip. You should introduce the trip and the area, and then tell some details about one (or more) of the stops. You do not need to use any literature, but only things that are on the maps and guide, and what you saw on the trip. This is one of the four abstracts that will be graded; each one counts as 5% of the final grade. If you have not written 4 abstracts (Rotvoll, Man-Us fault, Oppdal, Vestranden-Fosen), then you should write one for the Oslo trip.
Vestranden-Fosen field trip text
Vestranden-Fosen location map
Vestranden-Fosen geologic map
No more lectures in this class. Next official meeting is the Oslo field trip.
Field trip to Oslo Tuesday April 29 - May 2. Bus 0500 from NTNU
Airport bus: We are renting a bus to take everyone from NTNU (outside the Geology guilding) to Værnes airport. The bus departure time will be kl. 0500 ! If you take a Flybuss to the airport, you will have to pay for it yourself (I called the bus company and they cannot let us go for free on the Flybuss.) I will bicycle with my backpack to NTNU. If you bicycle Tuesday morning we can lock your bike indoors so it is not stolen while you are away. Professor Atle Mørk will be taking a Taxi from Fagerlia-Ila-Leutenhaven-NTNU, and can pick up a few students. Send me a message if you would like to sit in his Taxi. From NTNU the bus can go down to Solsiden kjøpesenter and pick up students there, so that you do not have to go up the hill with your heavy bag. Would this help? Send me a message so I know if you are planning this. We can only stop one place to pick up students, because there is not enough time for more stops.
If you miss the bus, you must take a taxi or a flybuss to the airport. We cannot wait for anyone. I will not be along on the bus to the airport. I need to take my minibuss to a technical control in Hommelvik, so I will take the train to Værnes and meet you there.
Put these telephone numbers in your mobile phone: Allan 91897197, Atle 41514490.
At the youth hostel in Oslo, we will not rent a towel or sheets for the bed. You need to bring this yourself (if you are going to England afterward, we will bring your sheets back to Trondheim for you.) If you rent them at the youth hostel, it will cost Kr 70.
First meeing in Oslo Our tour bus leaves from Gardermoen airport and goes to Hotell Opera (right next to Oslo S) to pick up Professor Hans Arne Nakrem and several Trondheim students who have been in England. Students should be there by 0830 to make sure you get picked up by our bus.
Questions from students that deserve an answer to everyone:
Etter de siste ekskursjonene fikk jeg litt mer forsåelse ang hva som
egentlig skjedde da kaledonidene ble dannet og kom til å tenke på
Rotvoll turen vår. På Rotvoll så vi jo flere mafiske ganger i
bergartene, betyr det at det er en del av midtre allokthon? Eller er
det bare bergartene i vestre gneis region som det gjelder for? Rotvoll
er vel en del av trondheims regionen sammen med f eks støren nappe? Er
forresten Trondheim en egen region på samme måte som wgr?
I tillegg lurer jeg på hva sparagmitt egentlig er. Har forstått det er
en bruddstykke bergart, men er det bare sandstein? Og hvorfor er den
brutt opp? Pga metamorfose eller mekansik forvitring?
Middle allochtthon must be rocks that are originally from Baltica, not Iapetus. They are rifted or margin of Baltica. Dikes in continental rocks are an indication of rifting. But dikes in gabbro or dikes in marine sediments or dikes in pillow lavas can be an indication of oceanic crust and not continental crust, so that is Upper Allochthon. Trondheim region and Western Gneiss Region and Sparagamite region, are all accepted names for regions. There are many more regions in Norway. Trondheim region is also called the Trondheim Nappe complex, and consists of many nappes, all of Upper Allochthon. Two nappes are the Støren nappe in the west and the Köli nappe in the east, and our book/map puts these together as the Köli nappe. Many people think the Köli is below the Gula is below the Støren. Others think the Köli is same as Støren. "Sparagmite" is a confusing term. It is used for all the continental (non marine) Neoproterozoic sediments of Norway. It is also used for "arkose" (but this use is incorrect, because we now say arkose and not sparagmite.) The classic "Sparagmite region" is the yellow area on geologic maps north of Oslo. Sparagmite was used a hundred years ago as a term meaning arkose, but that is no longer used now. In general, arkoses have mostly feldspar and some quartz, but not rock fragments. If there are tiny rock fragments as sand grains in a sandstone it is called "lithic arkose" or "greywacke."
>> jeg sitter med rapporten fra Fosenekskursjonen, og har et par
>> -Granitt bollene i konglomeraten på Døsvik.Hvorfor var ikke de
>> forkastet, mens de fleste andre bollene var det?
>> -Det som evt var diabas ved Botngård.Hvilket skyvedekke tilhørte det?
>> Var det også evt Upper Allochthon som helt vest på Ørlandet?
> Jeg er ikke helt sikkert at jeg forstår hva du spør om. Du må spør igjen
> hvis jeg misforstår.
> Granittbollene på Døsvik er forkastet. Det ble avsatt på Lerberen
> granitt og begge ble forkastet, og nå ligger på et lavere nivå enn de
> gjorde da de ble avsatt. De begge tilhører Upper Plate.
> På Botngård var det antagelig metadioritt som hadde blitt grønn (ikke
> diabas). Jeg tror at den tolkes i dag som Støren nappe og er i Upper
> Allochthon. De er i Lower Plate i Devon deformasjon. Helt vest på
> Ørlandet er det gneiser som vi tror er høyere (samme nivå som Døsvik og
> Lerberen.) Alle disse er antagelig Uppermost Allochthon, fra vest for
> Iapetus før overskynving. Gneis der er kanskje ikke høy metamorf
> gneis, men magmatiske bergarter som ble omdannet til gneis under
> magmatisk intrusjon. Fremtidig forskning må jobbe mer med dette
> problemet, fordi det er problematisk å ha gneis i Upper Plate. Ikke
> bare vest på Ørlandet men hele Hitra og Frøya og Smøla er gneisaktig
> magmatiske bergarter, og antagelig alt sammen fra Uppermost Allochthon
> i Silur kollisjon og fra Upper Plate i Devon kollapse.
> Håper det hjelper. Send spørsmål igjen hvis jeg ikke har svart på det du
> egentlig var ute etter.
> Nå skal jeg prøve å forbedre ekskurjonsguide på nett, ved å bruke
> begrepet Upper Plate/Lower Plate. Det vil kanskje hjelpe folk.
Exam. Written part (30% of grade) and oral part (20%), Thursday 15.May in auditorium KJL2. (Kjelhuset, entrance "e" on this map)
and go up the stairs.
Written Part 1: 900-945. (Break from 945-1000) Part 2: 1000-1045.
Oral Part 3: 11-1800 for Norwegian students.
For foreign students, oral exam will be Friday 16.May, from 900-1300. We should have about 30 minutes for the foreign students, to discuss other topics of the course. (If any are not available Friday, we can arrange it for Thursday after the others.)
The order of oral exams is not alphabetical, but made from a random order of names provided by Heiko and Rossana. The preliminary time schedule is here. Students may switch times with each other if they agree to changes.
The written exam will be like the quizzes. You will have to memorize a lot of names, places, rocks, and geological ages (not numerical ages.) It is harder to ask questions that require deeper understanding and can be answered easily, but I will try. There will also be questions from the field trips, but if you were not on a field trip, you can choose a question from a trip you were on instead.
The oral exam is not to ask you a lot of specific questions. It is to hear you "talk geology" for 5 minutes, to hear how you understand and explain things. We don't want to hear something that you have planned in detail, so we will have to ask you some questions to get you talking about something unexpected. Many students are nervous, but we will try to help you relax and talk.
We will have the folding geologic map and a stack of about 20 color figures/pictures, from the big book, and maybe other geology pictures. We will not ask exact questions from these, but may point to something and ask you to explain it.
There is a rule at Norwegian universities that oral exams should be "open to the public" (most people seem to ignore this rule.) That means that other students are allowed to be in the room and try to hear what you say. You can talk quietly, so they can't hear you, or you can talk loud so that you have "witnesses" to how you did, and your witnesses can help assure that your grade was fair.
The sensor (Arne Solli, one of the authors of the folding map) and I will give a grade immediately after each oral exam, but you will not learn your grade for a few weeks. We have given oral exams to a few hundred students in Regional geology over the past 20 years, and we can quickly and independently decide grades. Our grades usually come out very similar to each other, but not always. We will give a letter grade (A, A-, B+, B...) and later we will convert the letters to numbers, and the average of your two numbers counts 20% of your final grade.
Exam results will be posted here (without names) as they are available.
Exam page 1
Exam page 2
Exam page 3
Results oral exam
The external grader gave scores for the 4 abstracts. He also decided the boundary between different grades, based on my list of scores, and his own control of the 2 written quizzes and the 3-page exam.
Final results and grades
Your grade will be sent to you by NTNU, but it takes many days. If you are not sure where you are on this list, send me an email or SMS and I will send you your result.