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Home , Cementation (geology), Conglomerate (geology), Maturity (sedimentology), Rudite, Sandstone, Sediment

Chapter 5 and

Conglomeratic is also known as . Skim through the section entitled “Composition”, but concentrate on the information about textural characteristics and classification of conglomerates. Make sure that you understand the characteristics and depositional environments of the 5 types of conglomerate listed across the bottom of Figure 5.5.

There is a lot of information about microscopy of . We’ll be doing some of this, but don’t try to understand it just by reading about it. You will soon figure out what to look for with practice.

It’s very important to become familiar with the Udden-Wentworth scale (Figure 5.13) for classifying clastic rocks. You will come across lots of references to Ф (phi) units, so you need to understand how they relate to grain diameter. The relationship is as follows:

– Ф D= 2 (where D=diameter in mm)

(The minus sign is critical. For example if Ф = –2 , D = 22 = 4, so the diameter is 4 mm. Conversely, if Ф = 2, D = 2-2 = 1/(22) = ¼, or 0.25 mm)

The minus sign is used so that Ф values for the more common (ie. small) grain sizes will be positive, rather than negative.

Ф (phi) -10 -9 -8 -7 -6 -5 -4 -3 -2 mm 1024 512 256 128 64 32 16 8 4 (>256 mm) (>64 mm) (>4 mm)

Ф (phi) -1 0 1 2 3 4 mm (dec.) 2 1 0.5 0.25 0.125 0.063 mm (fract.) 2 1 1/2 1/4 1/8 1/16 (> 0.063 mm)

Ф (phi) 5 6 7 8 9 10 mm (dec.) 0.031 0.016 0.008 0.004 0.002 0.001 mm (fract.) 1/32 1/64 1/128 1/256 1/512 1/1024 (> 0.004 mm) (no lower limit)

You should read through the information on the use of statistical techniques to study distribution, but don’t worry if its not totally clear. We will do some of this in the lab.

Classification of sandy and sandstones is very important to understanding their history. We will talk about chemical and mechanical

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 , which is what Figure 5.19A is all about. The important things to remember are as follows:

Rock fragment content decreases with maturity content decreases with maturity Chemical maturity content increases with maturity (clay & silt) content decreases with maturity Degree of increases with maturity Mechanical maturity Degree of rounding increases with maturity

Figure 5.20 is a depiction of the most commonly used classification scheme for sandstones, so make sure that you understand what it means. The “Percent matrix” axis is a measure of how much silt and clay sized material the sandstone has, where an ranges from 0 to 15% and a wacke ranges from 15 up to 75%. (A rock with more than 75% fine material is considered to be a .)

The triangular part of the diagram allows us to specify the proportions of quartz, and rock fragments that make up the framework grains (as opposed to the matrix and cement).

In case you’re not familiar with ternary (ie. triangular) diagrams, here is a generic example with a few points plotted (the numbers are the proportions of A, B and C in per cent):

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004

And the following is an example of the sandstone diagram, with the corners labelled: Quartz, Feldspar and Rock fragments, and the names of the arenite fields:

The last part of the chapter discusses the characteristics and genetic environments (, transportation and ) of the various types of sandstone.

Chapter 6

Mudrocks (a.k.a. ) include all sediments with at least 75% silt and/or clay sized fragments. They are the most abundant of the sedimentary rocks, but as pointed out, they are not very well understood, partly because they are not well exposed. We can see this clearly around Nanaimo. Most of the rocky , ridges and cliffs around us are made up of sandstone and conglomerate, while the soft and boggy valleys are underlain by mudrocks. Many of the Gulf Islands are almost entirely composed of sandstone, while mudrocks are typically hidden beneath the intervening straits and bays.

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 If you have done Geology 312 (and still remember any of it!) you will already have some understanding of the mineralogy of clays, and their significance to a wide range of geological issues.

When and rocks get broken down into very small pieces virtually the only two types of minerals that remain chemically stable are quartz and the clay minerals. Fine silt is typically a mixture of quartz and clay minerals, but clay- sized material (<0.004 mm) is almost entirely made up of a variety of clay minerals. It is important, therefore, to have some understanding of the various clay minerals, what makes them different and under what conditions they form.

You might find the following classification scheme useful:

Name Properties The three main textural types of mudrock: mudrock with over 68% of the particles larger than clay size (feels gritty) mudrock with 35 to 68% of the particles larger than clay size claystone mudrock with at least 66% clay-sized particles (feels slick) Various other categories: any mudrock that has fissility (tendency to split into layers) black any mudrock that has sufficient organic material to make it black in “shale” colour ferruginous any mudrock that has sufficient oxidized iron to make it red in “shale” colour bentonite bentonite rich rock (typically forms from volcanic ash that has accumulated under water) calclutite mudrock

Don’t worry about the section entitled “Proterozoic mudrock ”, or Figures 6.11 and 6.12.

Chapter 7

Any changes that take place within sedimentary rocks from the time of the accumulation of sediments up until the onset of (if there is any) are referred to as diagenesis. These processes include the following:

• • (as described in Ch. 4 under ) • soft- deformation (as described under sedimentary structures) • and de-cementation • alteration of clay minerals • alteration of organic matter

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 Make sure that you understand what these various processes are, why they happen and how it can affect the rocks.

The most complex diagenetic changes are related to the alteration of clay minerals, and many of these processes are not very well understood. Some of the transformations are summarized below.

increasing temperature Æ smectite Æ mixed-layer (interlayers of smectite and illite) Æ illite kaolinite Æ illite (if K is present) or Æ chlorite (if Mg is more abundant) illite Æ

Chapters 8 to 13 include descriptions of a variety of different depositional environments or facies models. As noted in the introduction to Chapter 8, these models are deliberate idealizations of the environments and the rocks that form within them. While models are very useful for understanding what we see in the rocks, they are never perfect and there are always many exceptions. We need to be careful not to let the models constrain and colour what we observe.

There are many, many depositional environments, and I’m not expecting you to understand all of the features of all of them. We will be concentrating on a few important ones.

Chapter 8 Terrestrial sedimentary environments

The term “terrestrial” refers to any sedimentary environment on land as opposed to within the oceans. It includes -blown (aeolian) deposits, alluvial fans (and talus deposits), and all and deposits. Prothero and Schwab did not include glacial deposits in the 1st ed. and don’t give them a lot of room in the 2nd, so we’ll cover those a bit in here – and we’ll look at lots out in the field.

Alluvial fan deposits are quite common in areas where there is active normal faulting producing rising blocks. A good example is the Basin and Range area of the southwestern US.

A braided fluvial system exists wherever a river has more sediment than it can carry. This happens wherever there is rapid , because of recent uplift, or glaciation (eg. in many mountainous parts of BC) or volcanism

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 (eg. at Mt. St. Helens where there is abundant pyroclastic debris from the 1980 eruption) – or some combination of these factors. Make sure that you understand the differences between longitudinal bars (L-bars) and transverse bars (T-bars). The former tend to be rich in , while the latter are finer (sandy), and are typically cross-bedded (see Appendix A of the lab manual).

Mature flowing across broad tend to . These systems produce a variety of deposits. Cross-bedded point- are common, but a number of other deposit types are likely to be present, as summarized under “Diagnostic features of meandering fluvial systems”. The flood plains of meandering rivers are good environments for the accumulation of .

Make sure that you understand the material on lacustrine and aeolian environments, particularly the summaries of “Diagnostic features …” at the end of each section.

Several types of sedimentary deposits are formed under glacial conditions. The ice itself creates a unique type of deposit known as glacial , which is a mixture of fragments ranging in size from very fine clay to very large . The primary characteristic and diagnostic feature of till is that its components are unsorted and unstratified. This is because they have been transported by ice (either within or underneath the ice), and not by water or wind1. are commonly quite clay-rich (but they always have larger fragments as well). Lodgement till is formed from material that is moved along at the base of the ice, and is typically very well compressed (by the weight of the ice), almost to the point of in some cases. Ablation till is comprised of materials that have been moved within or on top of the ice and then deposited when the ice melts. All tills have the property of being poorly sorted and comprised of fragments that are not well rounded.

There is normally a lot of water around a - especially at its leading edge – and also a lot of sediments, because the is typically very steep, and because of the erosive power of the ice. Various types of stratified sediments are deposited in several different environments. Glaciofluvial deposits have many of the features of the deposits of braided . Glaciolacustrine deposits have many of the features of other lacustrine deposits – fine grained

1 Another name for a glacial till is diamicton, which implies a range (dia) of grain sizes. Tills typically comprise a mixture of material ranging in size from clay to boulders

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 and well laminated - except that their organic levels are typically very low. Dropstones are found in glaciolacustrine (and some marine) sediments, but not in normal lacustrine sediments. The photo at the front of Chapter 5 is a dropstone in marine sediments. They are also found in lacustrine sediments, but are not normally that large.

Chapter 9 Coastal environments

Coastal environments include deltas, , tidal flats and barrier complexes. They are dominated by clastic (rather than carbonate) because there is almost always abundant input of terrigenous material near to shore.

A characteristic feature of delta deposits is that different materials are deposited in different parts of the delta at the same time. The resulting deposits are stratified, but, as shown on Figure 9.2, each such layer does not represent a specific time. Instead, the time planes are parallel to the depositional surface. In reference to Figure 9.2, one could talk about “lithostratigraphic” units, such as the offshore clay, the prodelta silty clay and the delta front and sands. It is very important to be aware, however, that the “chronostratigraphic” units in this diagram are separated by the time planes, and that each of these units includes some of each of these different sediment types. We’ll talk more about versus chronostratigraphy later on.

Ensure that you understand the differences in delta characteristics as a function of the controlling factors, sediment supply, tidal flows and wave action (eg. Figure 9.3).

Deltas are even more significant than meandering rivers as the depositional environments for coal deposits.

Please read through the material on peritidal and barrier environments, making sure that you understand the “Diagnostic features ..”.

Chapter 10 Clastic marine and pelagic environments

Chapter 10 covers clastic sedimentation processes that take place on continental margins (shelves, slopes and continental rises), and also in the deep oceans (abyssal plains).

Please read through the material on clastic shelf deposits, making sure that you understand the “Diagnostic features ..”.

The continental slope and rise environment is particularly important, both because these types of sediments are abundant world wide, and also because

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 this is the interpreted environment of most of the Nanaimo Group - which we will be looking at in some detail.

The main features of the submarine fan environment are described in Box 10.1, and Figure 10.14A [10.15A], and are summarized in the table below. The submarine fan environment was originally described by Mutti and Ricci Lucchi in 1972; although some of the sedimentological features were described earlier by Bouma (1962). The designations of Bouma (TABC etc.) represent sediments formed in a environment, as described on Figure 10.13 [10.14] (and the Appendix of the lab manual). They include sequences with multiple repetitions of fining-upward beds, each representing one event. Please don’t confuse the facies letters (A, B, C etc.) of the table below with the letters (TABC etc.).

Facies* description Bouma position conglomerate and coarse feeder channels on shelf A T ) sandstone, 1 to 2 m bedding A (± E and slope medium to coarse sandstone, B T slope and inner fan lenticular ABCE fine to medium sandstone, thin C T middle fan shale partings ABCDE very fine to fine sandstone, siltstone D T mostly outer fan and mudstone BCDE deposits from similar to D, but the sand layers are E T channels in upper and thinner and coarser BCDE middle fan F slump, slide or olistostrome slope and upper fan outer fan and abyssal G T E

A seismic profile and the interpreted geological features of the present-day Amazon River fan are shown on the figure to the right. In this case there is evidence of at least three vertically stacked submarine fan complexes, with an intervening (DF) deposit beneath the upper fan complex.

Idealized cross-sections of the inner, middle and outer parts of a fan complex are shown on the figure below.

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004

The word pelagic2 means the open ocean, and in the context of sedimentary rocks it refers to any sediments that are made up of material that settles out of deep ocean water. For the most part these include clay particles (derived from the ), as well as calcareous and siliceous skeletal material derived from planktonic organisms. Pelagic sediments cover virtually the entire ocean floor. As shown on Figure 10.17 [10.16], and the figure here, they include the following types:

2 In your reading you will also encounter the term hemipelagic, literally: half-pelagic. These are clay-rich sediments with a significant component of coarser terrigenous material. They are restricted to the shelves and near-shore parts of the .

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004

Type Composition and distribution Clay kaolin: in tropical regions illite: in temperate regions chlorite: in polar regions smectite: close to ridges Calcareous ooze v. fine CaCO3 shell material: in tropical to temperate latitudes at water depths under 4000 m v. fine SiO2 shell material: in tropical and near-polar latitudes, mostly deep water Terrigenous and Clastic and hemipelagic sediments of shelf and near-shore Continental margin abyssal regions Glacial glacial and ice-rafted sediments in polar regions

CaCO3 has a low solubility in near-surface ocean water (and is typically present at supersaturation levels), but becomes more and more soluble with depth. At depths greater than between 3500 and 4500 m (depending on other factors) CaCO3 becomes so soluble that it is unlikely to be preserved. This is the carbonate compensation depth (CCD), and it has a major influence on the sea floor sediment distribution. As a consequence of this factor, calcareous pelagic sediments are essentially absent from the deepest parts of the ocean floor.

Chapter 11 Carbonate rocks

Make sure that you understand the differences between the three main carbonate minerals , and . Many organisms make their shells out of aragonite, but most of that aragonite is eventually transformed into calcite. the dolomite is not typically made by any organisms. Most dolostone is formed from by diagenetic processes.

Don’t stress out about the section on carbonate , but do remember that: “The precipitation of limestone is promoted by any process that removes dioxide from water”, and also by biological factors. The processes that lead to precipitation of carbonate are summarized by the 7 points on page 218 [236].

Limestone is classified primarily on the basis of the proportions of its allochemical and orthochemical carbonate components; where allochemical includes carbonate grains that came from elsewhere, and orthochemical includes carbonate (and some grains) that formed in situ. Limestone dominated by allochemical grains is called micrite, while that dominated by orthochemical crystals is called sparite. Various other textural features, such as limestone clasts, bioclasts, and peloids, are used in the standard classification initially devised by R.L. Folk – which is the one that we’ll stick with. See Figure 11.1 and the associated text.

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 Make sure that you understand the stuff on limestone diagenesis, and dolomitization.

Chapter 12 Carbonate environments

Limestones typically accumulate in shallow marine environments where the water is clear (because of limited clastic input) and warm (that is primarily between 30º S and 30º N under current conditions).

Make sure that you understand the characteristics and typical rock types of the three environments described:

Environment Characteristics within the intertidal zone, typically with well-developed tidal peritidal channels, commonly hypersaline with deposits as well from the low-tide line to between 100 and 200 m, oolitic and subtidal shelf pelletal textures are common high-productivity areas near the edges of carbonate banks, reefs skeletal fragments are common

Chapter 13 Other biogenic sedimentary rocks

I only want you to read about bedded and nodular deposits. ( are cool, but we have to draw the line somewhere.)

The source of most of the silica in the oceans is the hydration weathering of minerals other than quartz, for example:

+ + Na-feldspar + H Æ kaolinite + Na + dissolved silica (H4SiO4))

Be sure that you understand the differences (in features and origin) between bedded and nodular chert.

Chapter 14 Chemical and non-epiclastic sedimentary rocks

We will only be looking at the parts of this chapter that deal with iron-rich sediments and . Don’t worry too much about the part entitled Solution Geochemistry, we’ll refer to that as needed.

Iron exists in two main ionic states, namely the reduced ferrous form (Fe2+) and the oxidized (rusty) ferric form (Fe3+). Ferrous iron is quite soluble, while ferric

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004 iron is quite insoluble. Banded iron formation (BIF – alternating bands of chert and iron minerals) only exists in old rock, and it is generally believed that this is because the atmosphere was anoxic up until around 2 b.y. years ago, and that, under those conditions, most iron was in the more soluble ferrous form.

As shown on Figure 14.2, the most popular model for BIF formation involves a stratified ocean and an atmosphere with low, but increasing oxygen levels. The deep water would have been anoxic and Fe-rich, while the shallow water would have been slightly oxic and iron-poor. Deposition of chert was probably continuous, but periodic vertical mixing of the ocean water would have led to oxidation of the bottom waters and deposition of bands of iron-rich sediments.

Deposition of evaporite minerals requires evaporation of seawater to around 20% of its original volume, and of fresh water to a much greater extent. There is no evidence that the oceans themselves have ever been significantly depleted by evaporation, so this process must take place in restricted basins that get separated from the rest of the ocean. This can happen on various scales, from small near-shore shelves, to huge basins.

Make sure that you understand the origin of concentric zoning in evaporite deposits, and be sure to read about the Messinian deep-marine evaporites in the Mediterranean.

Malaspina University-College – GEOL 201 – Sedimentary Geology – May 2004