CHEMICAL SEDIMENTARY ROCKS Prepared by Dr. F. Clark Department of Earth and Atmospheric Sciences, University of Alberta August 06.

Slides:



Advertisements
Similar presentations
Rocks made of bits & pieces of other rocks.
Advertisements

SEDIMENTS & SEDIMENTARY ROCKS
Content Composition of Earth Crust Minerals Groups Silicates Structures Silicates Minerals Nonsilicate Minerals.
Sediments and Sedimentary Rocks. Significance for Climate and CCS Form at the surface, so directly influnced by Earth’s climate, provide the climate record.
Rocks made of bits & pieces of other rocks.
Sedimentary Rocks Sedimentary Rocks - Those rocks that form from the aggregation of sediments that have been transported, deposited, and later lithified.
THE LANGUAGE OF THE EARTH – PART II SEDIMENTARY ROCKS.
Earth Systems 3209 – Unit 3. The Rock Cycle  Why study sedimentary rocks? Economic use, fossils and earths history.  5% of Earths crust is sedimentary.
The Rock Cycle. Sedimentary Processes 1 2) & 3) Sediments are transported and deposited 4.
Sedimentary Rocks. What is a sedimentary rock? Sedimentary rocks are products of mechanical and chemical weathering They account for about 5 percent (by.
Sedimentary Rocks Chapter 4 Section 4.
Sedimentary Rocks.
Rocks B. Sedimentary Rocks.
Do You Remebmer? Sedimentary Rocks Chapter 6. What Are Sediments? ______________________ In order of decreasing size.
Biogenic and Chemical Sedimentary Rocks
SEDIMENTARY ROCKS. FORMATION OF SEDIMENTARY ROCKS Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface.
What is a metamorphic rock?
Earth Science 14.3 Seafloor Sediments
INTRODUCTION TO SEDIMENTARY ROCKS Prepared by Dr. F. Clark Department of Earth and Atmospheric Sciences, University of Alberta August 06.
Geology 12 Presents. Sedimentary Rocks 95% of the Earth’s volume is igneous and metamorphic rocks but 75% of the Earth’s surface is covered by sediments.
Copyright © 2014 All rights reserved, Government of Newfoundland and Labrador Earth Systems 3209 Unit: 3 Earth’s Materials Reference: Chapters 2, 3, 6,
Sedimentary Rocks. Basic Geologic Principles Principle of Superposition: Younger sedimentary and volcanic rocks are deposited on top of older rocks. Principle.
Sedimentary Rocks Chemical Sedimentary Rocks Limestone Limestone Chert – Silica Chert – Silica Evaporites Evaporites Organic Rocks Organic Rocks Coal Coal.
Chapter 29 Minerals and the Environment. LIST EVERYTHING THAT IS IN A PENCIL.
U Chemical sedimentary rocks v derived from material carried in solution to lakes/seas v evaporation and precipitation from solution to form “chemical.
Chapter 6 Sedimentary rocks.
Marine Sediments Chap 5.
How do Sedimentary Rocks Form? By J. Piccirillo. For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn.
Sedimentary Rocks Chapter 6. What Are Sediments? Loose particulate material In order of decreasing size.
Rock Cycle. Sedimentary Rocks Fossil source rock Made from weathered and eroded igneous and metamorphic rocks Indicate past climates/environments Petroleum,
SEDIMENTARY ROCK Mod E. U.3 L.3. Definition Rock that forms when sediments are compacted and cemented together.
Sedimentary Rocks Chapter 4 Section 4. Sedimentary Rocks Sediments are loose materials like rock fragments, mineral grains, and bits of shell. Sediments.
Sedimentary Rocks Sedimentary rocks form when sediments harden into rocks 3 main kinds clastic, chemical and organic Most of Earth’s crust is covered by.
Sedimentary Rocks Rocks made from sediments. The majority of rocks seen on the earth’s surface are sedimentary rocks.
SEDIMENTARY ROCKS A Brief Review.
Sedimentary Rocks.
Every stone a story, like a rosary. ---Joan Osborne
Lithification/ Diagenesis
Sedimentary Rocks Rocks made of bits & pieces of other rocks.
Salt Water. Properties of Salt Water  Salinity is the amount of dissolved salts in water  The salinity of the oceans averages 35 ppt (parts per thousand)
SEDIMENTARY ROCKS.
Sedimentary Rocks Rocks made of bits & pieces of other rocks.
Warm Up 2/10/09 Which regions are thought to be the most level places on Earth? a. mid-ocean ridges c. continental slopes b. deep-ocean trenches d.
SEDIMENTARY ROCKS. TERMS Weathering : breakdown of pre-existing rock – Physical or chemical breakdown Erosion: transport of sediment on Earth’s surface.
Minerals A naturally occurring, homogeneous inorganic solid substance having a definite chemical composition and characteristic crystalline structure,
SEDIMENTARY ROCKS What are sediments? They are “loose” rock particles.
Chapter 6 Section 3 Sedimentary Rock. Formation Sediment (small particles of sand, clay, or pebbles) get cemented together.
Chapter 2: Matter and Minerals
Rocks made of bits & pieces of other rocks.
Sedimentary Rocks.
Sedimentary Rocks.
SEDIMENTARY ROCKS.
What is a sedimentary rock?
Sedimentary Rocks Detrital rocks Material is solid particles
Sedimentary Rocks.
How Rocks are Formed: Sedimentary
SEDIMENTARY ROCKS.
Weathering of ________ Calcium Carbonate _______
Biogenous Sediment Biogenous sediments (bio = life, generare = to produce) are sediments made from the skeletal remains of once-living organisms. These.
Unit 3 - Rock Types Sedimentary Rocks.
SEDIMENTARY ROCK Mod E. U.3 L.3.
Objectives Define the term mineral.
Rocks made of bits & pieces of other rocks.
Rocks made of bits & pieces of other rocks.
Sedimentary Rocks (Origin & Formation).
Made from an accumulation of various types of sediments
Marine Sediment Classification
Rocks made of bits & pieces of other rocks.
SEDIMENTARY ROCK Mod E. U.3 L.3.
How they form, how they are classified, and why they are important.
Presentation transcript:

CHEMICAL SEDIMENTARY ROCKS Prepared by Dr. F. Clark Department of Earth and Atmospheric Sciences, University of Alberta August 06

INTRODUCTION Chemical sedimentary rocks would be those whose grains formed by direct precipitation or crystallization from water, without organic influence or mediation. This latter qualification is somewhat problematic, given that most bodies of water have organisms which will influence the chemistry of that water at least to some extent. There is one volumetrically and economically significant group of sedimentary rocks of non-controversial chemical origin, the so-called evaporites. As their name implies, they form by evaporation of concentrated sea or saline lake water.

EVAPORITES As a body of sea water or a saline lake experiences net evaporation, the concentration of the ions dissolved in that water rises until the saturation point of various materials is exceeded, and minerals precipitate or crystallize. Many of these minerals are economically significant, such as gypsum, halite, and potash salts from sea water, and epsom salts, borax and trona from saline lakes. The first minerals to form as the water evaporates are carbonates, which we have covered already under biochemical sedimentary rocks. They are generally volumetrically minor components of evaporite mineral assemblages.

Gypsum. This is hydrated calcium sulphate; the sulphates are the second major group to form as sea water evaporates. Such large crystals as these are frequently formed by precipitation from saturated groundwater circulating through near-surface sediment deposits and soils, rather than precipitation from sea water. Note the clarity of these large crystals, which have a Mohs hardness of 2.

Gypsum – the Effect of Crystal Size Both photos illustrate the effect on opacity that crystal size has. These evaporite samples consist of thousands of individual small crystals, whose edges and grain boundaries dominate the optical effects and render the samples opaque, even though gypsum is transparent to translucent. The right sample is from the Devonian age Elk Point Group of the Western Canada Sedimentary Basin.

Anhydrite. This is calcium sulphate without the bound molecular water that defines gypsum. In this sample it is white. This is less likely to form as a primary evaporite mineral, because the presence of water makes gypsum formation more likely. It is possible to dehydrate gypsum after its initial formation, or as apparently happened in this case, for anhydrite to form in a carbonate host rock.

Halite – Rock Salt, NaCl Halite forms third in the sequence of evaporation of sea water, and in a closed system would account for approximately 75% of all the solids that will form. It may be mined conventionally, or as suggested by the core sample on the right, can be recovered from bore holes by circulation of water in the subsurface and evaporation of the resulting brines at surface. The salty taste is distinctive.

Sylvite. This is potassium chloride (KCl), and unlike halite, has a distinctly bitter taste. Its other properties are similar to those of halite. The fourth group to form from the evaporation of sea water is a complex assemblage, whose most useful member is sylvite. It is found in the potash deposits of Saskatchewan, and is a major component in fertilizer production. It forms when 98% of the water is lost.

CHERT – PROBLEMATIC ORIGIN Chert, a microcrystalline or cryptocrystalline form of silica (SiO 2 ), can originate either by organic means or not. There are two principal groups of organisms that secrete siliceous skeletons whose accumulation can result in the formation of bedded chert. Radiolarians are microscopic plankton that are less than 1 mm in size. As well, there are some sponges whose spicules (tiny hard parts that support the tissues) are siliceous. These groups first appeared in the Cambrian, so older rocks (>544 million years old) hypothetically can’t be biochemical. Even younger chert may be chemical in origin, forming during diagenesis as nodules and beds, usually in carbonates.

Chert. Chert has many properties in common with quartz. It has a hardness of 7, and samples exhibit conchoidal fracture. There are many coloured varieties of chert, ranging from white through yellow and pale green to black, depending on trace elements and their chemical state (e.g. red for oxidized and green for reduced iron).

Chert from Western Canada The occurrence of chert as beds or bands, especially in carbonate sections, is quite common in the rocks of the Western Canada Sedimentary Basin. From left to right we see examples from the Mississippian Rundle Group, the Pennsylvanian Kananaskis Formation, and the Permian Ishbel Group. Not only is chert common in these rocks, but when they are weathered after uplift during building of the Rocky Mountains, they form a rich source of the common chert pebbles and sand grains seen in Cretaceous age siliciclastic units.