1. 2. The tortuosity of the pathways. Tortuosity is a measure of how much a pathway deviates from a straight line. The path that fluid takes through a granular material is governed by how individual pore spaces are connected. The greater the tortuosity the lower the permeability because viscous resistance is cumulative along the length of the pathway. Porosity and Permeabilty

2. Pathway diameter and tortuosity are controlled by the properties of the sediment and determine the sediment’s permeability. The units of permeability are Darcies (d): 1 darcy is the permeability that allows a fluid with 1 centipoise viscosity to flow at a rate of 1 cm/s under a pressure gradient of 1 atm/cm. Permeability is often very small and expressed in millidarcies ( ) Porosity and Permeabilty 2. The Tortuosity of the Pathways.

3. a) Sediment Controls on Permeability i) Packing Density Smaller pathways reduce porosity and the size of the pathways so the more tightly packed the sediment the lower the permeability. Tightly packed sediment has smaller pathways than loosely packed sediment (all other factors being equal). Porosity and Permeabilty

4. ii) Porosity In general, permeability increases with primary porosity. The larger and more abundant the pore spaces connected, the greater the permeability. Pore spaces must be well connected to enhance permeability. Porosity and Permeabilty

5. Shale, chalk and vuggy rocks (rocks with large solution holes) may have very high porosity but the pores are not well linked. The discontinuous pathways result in low permeability. Fractures can greatly enhance permeability but do not increase porosity significantly. A 0.25 mm fracture will pass fluid at the rate that would be passed by13.5 metres of rock with 100 md permeability. Porosity and Permeabilty

6. iii) Grain Size Unlike porosity, permeability increases with grain size. The larger the grain size the larger the pore area. For spherical grains in cubic packing: Pore area = 0.74d 2 Porosity and Permeabilty

7. A ten-fold increase in grain size yields a hundred-fold increase in permeability. iv) Sorting The better sorted a sediment is the greater its permeability. In very well sorted sands the pore spaces are open. In poorly sorted sands fine grains occupy the pore spaces between coarser grains. Porosity and Permeabilty

8. v) Post-burial processes Like porosity, permeability is changed following burial of a sediment. In this example permeability is reduced by two orders of magnitude with 3 km of burial. Cementation Clay formation Compaction Pressure solution All act to reduce permeability Porosity and Permeabilty

9. b) Directional permeability Permeability is not necessarily isotropic (equal in all directions) Fractures are commonly aligned in the same direction, greatly enhancing permeability in the direction that is parallel to the fractures. Porosity and Permeabilty

10. Variation in grain size and geological structure can create directional permeability. E.g., Graded bedding: grain size becomes finer upwards in a bed. Fluid that is introduced at the surface will follow a path that is towards the direction of dip of the beds. Porosity and Permeabilty

11. Provenance of a Sediment Transport Distance

12. The Classification of Clastic Sedimentary Rocks Based on Type A very basic classification of all sedimentary rocks is based on the type of material that is deposited and the modes of deposition.

13. ConglomerateA rudite composed predominanty of rounded clasts. Rounded clasts may indicate considerable distance of transport from source. Limestone clasts will become round a short distance from their source whereas quartzite will require much greater transport). Rudites are classified on the basis of particle shape, packing and composition. Classification of Rudites

14. Generally indicates that the clasts have not traveled far from their source or were transported by a non-fluid medium (e.g., gravity or glacial ice). A rudite composed predominantly of angular clasts. Breccia http://homepage.smc.edu/robinson_richard/rocktest/igneous_web/pages/breccia.html

15. Commonly refers to sediment deposited from glaciers or sediment gravity flows, particularly debris flows. Diamictite: A rudite composed of poorly sorted, mud to gravel-size sediment, commonly with angular clasts. Classification of Rudites

16. Orthoconglomerate (clast-supported conglomerate) Classification of Rudites

17. Orthoconglomerate with open framework.

18. Paraconglomerate (matrix-supported conglomerate) Typical of the deposits of debris flows or water flows in which gravel size clasts were not abundant in comparison to the finer grain sizes. A conglomerate in which most clasts are not in contact; i.e., the matrix supports the clasts.

19. Classification of Rudites

20. Polymictic conglomerate A conglomerate in which clasts include several different rock types. Classification of Rudites

21. Oligomictic conglomerate A conglomerate in which the clasts are made up of only one rock type. Classification of Rudites

22. Intraformational conglomerate A conglomerate in which clasts are derived locally from within the depositional basin (e.g., clasts composed of local muds torn up by currents). Deposition in an environment where muds accumulated. Classification of Rudites

23. CONGLOMERATES The term 'Conglomerates is used as a general class name for sedimentary rocks that contain a substantial fraction (at least 30 percent) of gravel- size (>2 mm) particles as shown in figure A. They are common in stratigraphic successions of all ages and make up less than l% by weight of the total sedimentary rocks (Garrels and McKenzie, 1971), and they are closely related to sandstones in terms of origin and depositional mechanisms. Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter, figure B ). The spaces between the large angular fragments are filled with a matrix of smaller particles and a mineral cement that binds the rock together. In current discussion, breccias are not distinguished from conglomerates. A B Classification of Rudites

24. Classification on the basis of clast type (igneous, metamorphic, sedimentary) is made on next slide. Clastic Sedimentary Rocks CONGLOMERATES

25. Clastic Sedimentary Rocks CONGLOMERATES Types of Sedimentary Rocks Classification Gravel-size framework grains touch each other and form a supporting framework are called clast-supported conglomerates. Clast-poor conglomerates that consist of sparse gravels supported in a mud/ sand matrix are called matrix- supported conglomerates or diamictites.

26. Clastic Sedimentary Rocks CONGLOMERATES Types of Sedimentary Rocks Classification Genetic classification of conglomerates proposed by Pettijohn 1975, is given. Major TypesSubtypesOrigin of Clasts Epiclastic Conglomerate and Breccia Extraformational Conglomerate and Breccia Intraformational Conglomerate And Breccia Breakdown of older rocks of any kind through the processes of weathering and erosion; deposition by fluid flows (water, ice) and sediment gravity flows. Penecontemporaneous fragmentation of weakly consolidated sedimentary beds; deposition by fluid flows and sediment gravity flows. Volcanic Breccia Pyroclastic Breccia Auto Breccia Hyaloclastic Breccia Explosive volcanic eruptions, either magmatic or phreatic (steam) eruptions; deposited by air- falls or pyroclastic flows. Breakup of viscous, partially congealed (thick) lava owing to continued movement of the lava. Shattering of hot, coherent magma into glassy fragments owing to contact with water, snow, or water-saturated sediment (quench fragmentation). Cataclastic Breccia Landslide and Slump Breccia Tectonic Breccia: Fault, Fold, Crush Breccia Collapse Breccia Breakup of rock owing to tensile stresses and impact during sliding and slumping of rock masses. Breakage of brittle rock as a result of crustal movements. Breakage of brittle rock owing to collapse into an opening created by solution or other processes. Solution BrecciaInsoluble fragments that remain after solution of more soluble material; e.g., chert clasts concentrated by solution of limestone. Meteorite Impact BrecciaShattering of rock owing to meteorite impact.

27. Clastic Sedimentary Rocks CONGLOMERATES