A) Weathering: physical and chemical

B) Erosion: carrying away weathered products from weathering site

C)Transportation: particles carried to new locations via wind, water or ice

D) Deposition (sedimentation): particles settled out of transporting agent to form layers of sediment on land or under water.

E) Compaction (diagenesis): sediments are buried and compacted due to the weight of overlying sediments accumulating above. Pore waters may be squeezed out.

F) Lithification(diagenesis): can occur concurrently with compaction. Buried sediments are cemented together into rocks.

1. Fig. 7.1: Once rock particles and dissolved ions have been formed by weathering, they are transported via streams, rivers, glaciers or mass wasting to a different location.

2. The solid fragments produced by weathering of pre-existing rocks are called clastic particles.

3. Fig. 7.2: Clastic particles vary widely in composition depending on the composition of the source rock from which they were derived. Clastics also vary widely in size from boulders and cobbles to sand grains and even smaller particles.

4. Accumulations of clastic particles are referred to as clastic sediments, also called siliciclastics because they are composed largely of silicate minerals.

1. Transport of sediments is accomplished mainly by currents of water or air. Currents can modify the transported sediments in three ways:

A) Mineralogy (compositional evolution).

B) Grain sizes

C) Grain shapes

1. Varying intensities of weathering before and/or during transport can produce different sets of minerals in sediments derived from the same parent rock. The greater the intensity or duration of transport, the more likely the sediment will contain only the most chemically stable minerals (i.e. minerals most resistant to weathering).

2. Most chemical weathering is accomplished during the long intermittent periods when the sediment is temporarily deposited before being picked up again by the current (changes in wind or stream velocity; flooding). During these intermittent periods, less resistant minerals in the sediment can be destroyed by chemical weathering.

1. When sediments are carried by a current, dual forces act. These forces consist of the ability of the current to carry a particle versus the tendency of a particle to settle to the bottom of the flow due to the pull of gravity.

2. As a current that is carrying particles of various sizes begins to slow, it can no longer keep the largest particles suspended. The largest particles therefore settle out and are deposited. As the current slows even more, smaller particles settle out.

3. Strong currents (velocities over 50 cm/s) can carry gravel along with coarse and fine detritus. Moderately strong currents (20-50 cm/s), common to most rivers, will carry and deposit sand. Weak currents (<20 cm/s) carry only mud composed of the finest clastic particles.

4. Currents may begin by carrying particles of widely varying sizes, but during transport, variations in current velocity will segregate minerals according to size. This process is called sorting.

5. Poorly sorted sediments were probably not transported very far from their source rock by currents. Well-sorted sediments were either carried long distances by currents and/or were extensively winnowed in place as deposits by currents.

1. An aid to determining whether sediments have been transported long distances is by examining the shapes of individual grains.

2. Fig. 7.3: The prolonged transport of sediment by water and wind current affect the particles in two ways: (1) reduction in particle size and (2) rounding of originally angular fragments. The greater the distance of transport, the smaller and more rounded the grains.

1. Figure 15.11: Glaciers can also carry clastic particles. These solid particles are excavated and picked up by glaciers as the massive ice sheets flow slowly downhill. Once incorporated into the flowing ice, however, these particles cannot settle out and therefore remain unsorted until eventually dumped when the ice melts. Glacial deposits are recognized in the rocks record as a mixture of compositionally heterogeneous, unsorted debris often ranging from boulder to silt sized all mixed together.

2. Dissolved chemical substances are also carried by rivers and generally do not settle out of the current until ultimately being dumped into lakes or oceans. The ocean's high salinity results from all the dissolved chemical substances brought in by rivers.

1. Figure 7.5: Transported sediments are ultimately deposited in lowlands, coastal plains, shallow ocean or deep ocean. These various sites of sedimentation are referred to as sedimentary environments.

2. A sedimentary environment is a geographic location characterized by a combination of geological processes and environmental conditions. Environmental conditions may include the kind and amount of water (ocean, lake, arid land), the topography (lowland, mountain, deep ocean) and extent of biological activity.

Continental Sedimentary Environments may include:

A) Alluvial environments: sediments deposited in and adjacent to river channels.

B) Desert environments: generally arid and controlled by wind action (sand dunes).

C) Lake environments: freshwater and saline lakes.

D) Glacial environments: controlled by moving masses of ice and melt-water streams.

Shoreline environments are dominated by the interactions of waves, tides and currents on sandy shores.

A) Deltaic environments: sediments deposited at sites where rivers enter lakes or the sea.

B) Tidal flat environments: extensive areas that are exposed during low tide and dominated by tidal

currents.

C) Beach environments where strong waves control the distribution of sediments.

Marine environments are those areas of sedimentation beneath the oceans. Sedimentation can occur in shallow water near the beach. Sediment can also be transported by currents to deeper waters much further from shore.

1. The pattern of sedimentation, or how sediments are deposited, depends on the sedimentary environment. Sediments can be deposited as successive horizontal layers, or layers can be at angles to one another. Within a single layer of sediment, individual grains can all be of uniform size or can vary in size. Sedimentary structures tell us much about the environment within which these sediments were deposited.

2. Parallel layers of different grain sizes or compositions indicate successive depositional surfaces possibly indicating changes in depositional processes such as stream velocity, wind strength and/or change in the type of sediment being deposited. In stream deposits, larger grain sizes suggest stronger currents.

3. The pattern of sedimentation giving way to a particular sedimentary structure is strongly linked to the sedimentary environment. Sediments deposited by wave action have a distincly different depositional pattern than do sediments deposited by winds or glaciers.

4. Figures 7.6 & 7.7: Cross bedding consists of bedded material which are inclined at angles due to deposition by wind or water. Cross bedding occurs when grains are deposited on the steeper, downcurrent slopes of sand dunes in deserts or sand bars under water.

5. Graded bedding refers to a sedimentary layer where grains range in size from coarsest at the bottom to finest at the top. Graded bedding reflects a waning (decrease in velocity) of the current that deposited the grains.

6. Figures 7.8 & 7.9: Ripples are small ridges of sand or silt deposited by wind or water currents. The long dimention of ripples occur at right angles to the current direction. The shapes of ripples tell us about the type of current that deposited the sediments.

7. Fig. 7.10: Bioturbation structures are relict burrows or tunnels produced by burrowing organisms in the soft sediment. These structures may be preserved in sedimentary rocks.

8. Fig. 7.11: Bedding sequences are patterns of inter-layering of sandstone, shale and other sedimentary rock types. Bedding sequences may provide clues as to how the sediments were deposited.

1. As sedimentation continues in the various environments, thick piles of sediment of various types may eventually accumulate.

2. As sediments pile up, the increasing weight resulting from the growing thickness of material may evenually cause the crust underlying the sediments to sink, producing a Sedimentary Basin. A sedimentary basin is a large depression within the earth's crust and contains thick accumulations of sediments. As the crust sinks, the basin deepens and more sediment can be deposited.

3. Sedimentary basins are regions of considerable extent (at least 10,000 km2) and are sites were sediments are buried to great depths.

1. Fig. 7.12: When sediments are buried deeper and deeper, they eventually encounter temperatures and pressures high enough for diagenesis to occur. The term diagenesis refers to the physical and chemical changes by which buried sediments undergo alterations and are lithified into rocks.

2. During burial, sediments are gradually compacted due to the increasing weight of overlying sediments. During compaction, grains are squeezed closer together, the pore spaces between grains start to close and fluids within the pore spaces are expelled. Compaction is particularly dramatic in mud that can lose more than half of their water. Compaction can be regarded as an aspect of diagenesis.

3. Compaction is often accompanied by the precipitation of cementing materials.

4. Cementation is a process by which minerals precipitate from pore fluids and bind individual grains together to form a rock. The cement may be quartz, calcite, hematite, etc. The process of converting sediments into rocks is termed lithification.

5. Other possible diagenetic changes include dissolution of more soluble minerals within buried sediments or chemical alteration of clay minerals into other clay minerals (e.g. kaolinite to illite).

1. Table 7.4: Clastic sediments and rocks are classified by their textures, primarily the sizes of grains.

2. Fig. 7.16: Sandstone can be further classified according to composition. End members are quartz, feldspar, rock fragments and clay. Greywackes include a clay matrix.

1. The dissolved products of weathering are eventually precipitated from water (usually seawater) by chemical and biochemical reactions to form chemical sediments. Chemical sediments may include such minerals as calcite, dolomite, gypsum, halite and quartz.

2. Biochemical sediments contain the mineral remains of organisms or minerals precipitated as a result of biological processes. Biochemical sediments are usually composed of calcium carbonate of which calcite/aragonite are the characteristic minerals. Silica can also be precipitated by certain marine organisms.

1. Carbonate sediments and sedimentary rocks are formed from the accumulation of carbonate minerals precipitated either organically or inorganically from seawater. The minerals are either calcium carbonate (calcite, aragonite) or calcium-magnesium carbonates (dolomite). Carbonate formation occurs mostly in warm, tropical regions.

2. Bioclastic particles are sediments composed of fragments or detritus of biologically precipitated calcium carbonate. Bioclastic particles represent a two-stage process. (1) Precipitation of calcium carbonate through biological activity. (2) Break-up of the calcium carbonate, followed by transport and deposition to another location. Bioclastic particles may consist of shells and shell fragments from many different kinds of marine organisms (clams, corals, oysters, brachiopods) and also the detritus of biochemically precipitated carbonate rocks. Bioclastic sediments can be re-cemented together by precipitated calcite to form a bioclastic carbonate rock called a limestone (Fig. 7.20).

3. Limestone can also form inorganically through direct precipitation from seawater.

4. Carbonate environments include certain inland water bodies, the continental shelf, reef colonies along the edge of the continental shelf, and deep sea environments. Carbonate environments are found primarily in warm, tropical climates. Calcium carbonate sand, mud and shell structures are precipitated by warm water marine organisms and certain algae. Calcium carbonate can also form inorganically through direct precipitation from seawater.

5. Most carbonate sediments in shallow marine environments are bioclastic in that they are composed of shells, shell fragments, and clastic material derived from materials precipitated by marine organisms.

6. Much of the biochemical carbonate sediments in the ocean result from microscopic organisms called foraminifera that live in surface waters. These generally free-floating organisms form tiny calcite shells. After the forams die, their shells sink and accumulate on the ocean floor. Accumulation and lithification of these tiny shells forms carbonate rock such as chalk. Figure 6.11: In certain parts of the world, immense chalk cliffs had formed as a result of accumulation and lithification of tiny foram shells over thousands to millions of years.

7. Fig. 7.18: Organic reefs are large carbonate mounds or ridges occurring along the edges of certain continental shelves. Reefs are constructed from the carbonate shells of marine organisms like corals, clams, oysters and other shallow-marine organisms. Reefs typically grow along the edges of continental shelves because these areas are sites of abundant nutrients that upwell from deeper portions of the ocean basin.

8. Calcium carbonate can also be precipitated directly from seawater without the aid of marine organisms. Inorganic precipitation of carbonate sediments results when warm, tropical regions of the ocean become supersaturated with calcium carbonate via the following chemical reaction.

Ca²⁺ + 2HCO₃^- = CaCO₃ + H₂CO₃

9. The rock Dolostone is a Ca-Mg carbonate consisting of the mineral dolomite. Dolomite generally does not form as a primary precipitate from seawater. Instead, dolomite is a product of diagenetically altered carbonate sediments and limestone. The original calcite or aragonite sediment is converted to dolomite soon after deposition by the addition of magnesium ions from seawater passing slowly hrough the pores of the sediment.

2CaCO₃ + Mg²⁺ = CaMg(CO₃)₂ + Ca²⁺

1. Evaporites are minerals that precipitated from evaporating saltwater. Common evaporite minerals are gypsum and halite.

2. Marine evaporites are the chemical sediments and sedimentary rocks formed by the evaporation of seawater in restricted, semi-enclosed inlets or basins.

3. Fig. 7.21: As evaporation proceeds, seawater remaining in the semi-enclosed basin becomes increasingly concentrated in dissolved constituents like Ca²⁺, Na⁺, K⁺, SO₄^2-, CO₃^2- and Cl^-. Eventually the evaporating water becomes supersaturated with respect to these dissolved ions, resulting in precipitation of salts. As evaporation progresses and salinity increases, salts are precipitated in the order gypsum - halite - K-salts.

4. Evaporites can also form in deserts through extensive evaporation of lakes such as the Great Salt Lake of Utah. In the western United States, many large lakes formed at the end of the last ice age 12,000 years ago have since dried up, leaving behind extensive salt deposits.

1. Siliceous sediments and rocks are composed primarily of SiO₂ and may precipitate in the deep sea with the aid of shelled organisms to form opal. Silica can also form through alteration of rocks. Chalcedony is a fibrous variety of microcrystalline quartz and is frequently found lining or filling cavities in rocks. Quartz can also grow within cavities in rocks to form agates.

2. Coal, oil and gas: chemical products resulting from the breakdown of organic matter such as vegetation (coal) and microscopic marine organisms (oil and gas) as a result of burial of the organic matter to higher temperatures and pressures. Vegetation leading to coal primarily grow in swamp environments.

Table 7.5: Chemical and biochemical sediments and sedimentary rocks are classified primarily by their chemical composition.