GEO- Sedimentary Rocks

GEOL 1101 – The Dynamic Earth = Review Questions for Lecture Test 2 Topic 9 – Sedimentary Rocks 1. What is sediment? How does it differ from sedimentary rock? Sediment is a term used to describe loose materials (i.e., rock fragments, mineral grains, and bits of shell) that accumulate on the surface of the Earth ● Material can be moved by wind, water, ice, or gravity ● Material is derived from pre-existing rocks that are weathered and eroded away Sedimentary rock forms when sediment is buried and subsequently lithified, or when minerals precipitate out of solution 2. What are clastic sedimentary rocks? How do they differ from chemical sedimentary rocks? ● Clastic sedimentary rocks form via burial and cementation of sedimentary clasts ● Chemical sedimentary rocks form via burial of plant/animal remains, or by mineral precipitation 3. What are the names of the different clastic sedimentary rocks that we are focusing on in this course? Describe their characteristics. Any sedimentary rock that is made up of clasts is a clastic sedimentary rock. ● Common examples include conglomerate, breccia, sandstone, siltstone, and shale. Conglomerate - Dominated by well-rounded clasts, granule size and larger ● significant proportion of the clasts are larger than 2 mm ● form in high-energy environments such as fast-flowing rivers, where the particles can become rounded. Breccia - Dominated by angular clasts, granule size and larger ● typically form where the particles are not transported a significant distance in water, such as alluvial fans and talus slopes. Sandstone - is mostly made up of sand grains but also include finer material—both silt and clay. ● Arenite - “clean sandstone”, meaning less than 15% silt and clay. ○ Quartz sandstone - arenites dominated by sand, greater than 90% quartz ■ grains larger than 1/16th mm ○ Arkose - Dominated by sand, greater than 10% feldspar ■ more than 10% feldspar ■ more feldspar than rock fragments, feldspathic arenites or arkosic arenites ○ Lithic wacke - dominated by sand, greater than 10% rock fragments, greater than 15% silt and clay ■ more than 10% rock fragments ■ more rock fragments than feldspar, ■ “Lithic” means “rock.” Lithic clasts are rock fragments, as opposed to mineral fragments. ● Wacke - dominated by sand, greater than 10% rock fragments, greater than 15% silt and clay

○ Quartz wacke, lithic wacke, and feldspathic wacke are used with limits similar to those on the arenite diagram. ○ Another name for a lithic wacke is greywacke . Siltstone - visible particles Shale - shale Greater than 75% silt and clay, thinly bedded 4. What are the three main solid components of clastic sedimentary rocks? Produce a sketch that shows all of these components. Clastic sedimentary rocks are normally made up of three solid components: framework grains, matrix grains, and cement. 5. What are the primary mechanisms of sediment transport? Sediment transport is accomplished via gravity, water (rivers and streams), wind and/or ice. 6. How can grain size help us determine the energy level associated with a sedimentary system? Grain size can help us determine the energy level of the medium transporting the grains: ● Large grains (i.e., pebbles) can only be transported by strong currents ● Small grains (i.e., silt) generally fall out of suspension during quiet times Energy level could be linked to gradient discharge, or flow rate (depending on the environment) 7. What does clast sphericity and roundness tell us about the history of sediment transport? Grain shape consists of two elements: roundness and sphericity ● Roundness: a measure of how rounded (or how angular) grain surfaces are ● Sphericity:a measure of how closely the grain shape approximates a sphere in 3D

11. What are limestone textures based on? Limestone Textures In limestones calcite minerals can be present in three distinct forms: ● Carbonate grains (e.g., ooids and skeletal fragments) ● Microcrystalline calcite (mud with silt-and clay-sized calcite crystals) ● Sparry calcite (coarser-grained calcite crystals) Note that it is possible to have all three components present in the same rock! 12. What are the different kinds of carbonate grains that are present in limestones? Describe where they come from. Carbonate grains can be classified into four different types based on shape, internal structure, and origin: Carbonate clasts, skeletal particles, ooids, and pellets 13. What is the Folk classification? How does it differ from the Dunham classification?

Folk’s classification is a carbonate rock classification that primarily focuses on the dominant type of allochem present within a rock, as well as the material that is present between the allochems (e.g., micrite vs. sparry calcite). Key advantage : Very easy-to-understand scheme that helps a researcher rapidly characterise depositional processes. Key disadvantage : Lacks the quantitative information needed to characterise the energy levels or flow velocities of currents active in that environment. Dunham’s classification focuses on the relative proportion of micrite and allochems rather than honing in on the specific type of allochem. The size range of the allochems is also considered. (Ai Gen) The Folk classification and the Dunham classification are both systems used to categorise carbonate rocks, ( rocks formed from carbonate minerals like calcite or dolomite.) Folk's classification is simpler and focuses on identifying the main components within the rock, like grains of sand or shell fragments, and the material that holds them together. Folk’s is easy to understand and quickly gives an idea of how the rock was formed. However, it doesn't provide detailed information about the energy levels of the environment where the rock formed. While Dunham's classification looks at the proportion of different components in the rock, like the amount of fine-grained material (micrite) compared to larger pieces (allochems). It also considers the size range of the allochems. This classification provides more detail about the rock's composition, but it's a bit more complex to understand. Folk's classification is like looking at the big picture of what's in the rock, while Dunham's classification is like zooming in to see the details of how much of each component is present. 14. Provide three examples of pre-depositional sedimentary structures, and explain what they tell you about the history of a rock. Grooves, Gutter Casts, and Tool Marks - Grooves, gutter casts, and tool marks are types of sole marks. They mainly form as a result of a detrital object (e.g., a stick) being dragged along at the base of a current. Flutes - (or flute casts) are also sole marks. They form when a highly erosive current creates a scour in the underlying bed (the scour is later filled with sediment). 15. Provide three examples of syn-depositional sedimentary structures, and explain what they tell you about the history of a rock.

17. Why are sedimentary rocks important? List and describe three different uses for sedimentary rocks. Groundwater Aquifers - Porous and permeable units (i.e., sand-rich units or sandstones) make good groundwater aquifers, whereas less porous and permeable units (i.e mud or mudstones) represent effective aquitards. How much water is underground anyway? Natural Disaster Risk Mitigation Oil and Gas Reservoirs