Sedimentary rock quiz

Sedimentary Rock Identification Study Guide

General Quiz Information

  • Quiz Format
    • Similar format to mineral and igneous rock identification quizzes.
    • Bring device to take an online quiz.
    • Approximately 15 questions: True/False and Multiple Choice.
    • Recommendations:
    • Read over lab materials and charts for understanding.
    • Visit the ALMNH in Smith Hall, second floor, to view rock samples.
    • Look up examples of each type of sedimentary rock.

Definition of Sedimentary Rock

  • Sedimentary Rocks: Formed by the weathering of pre-existing rocks, transportation of solid or dissolved weathering products by various agents (e.g., water, ice, wind), and eventual deposition or precipitation in a variety of environments (e.g., mountain peaks to ocean basins).

Sedimentary Rock Formation Steps

Step 1: Weathering
  • Weathering: The process by which rocks are broken down into smaller fragments.
    • Physical Weathering: Rock materials are physically broken down into smaller pieces due to mechanical processes, often influenced by temperature changes (daily or seasonal).
    • Chemical Weathering: The internal structure of minerals within a rock is altered or damaged by weathering agents, such as water, often down to the atomic scale.
    • Erosion: The slow destruction of materials and the removal of those materials to another location by transporting agents (like water, wind, ice, or gravity).
  • Key Distinction: There is no movement involved in the process of weathering, whereas erosion involves movement.
Step 2: Transportation
  • Transportation: The significant movement of weathered and eroded fragments, primarily by water or wind processes.
  • Processes during Transportation:
    • Rounding: The smoothing of sediment grains due to abrasion during transport. The longer the grains are transported, the smoother they become.
    • Sorting: The separation of sediment according to grain size by transporting agents. This reflects the environmental energy conditions:
    • Larger grain sizes indicate higher energy environments.
    • Smaller grain sizes indicate lower energy environments.
    • Sediment size generally decreases with increased transport distance; longer transport results in finer grains.
Step 3: Deposition
  • Deposition: Occurs when there is a change in the energy conditions of the transporting agent (e.g., a river), leading to the settling of the ‘sedimentary load’ out of the water column and onto the riverbed.
  • Steno’s Laws:
    • Law of Original Horizontality: Sediment is typically deposited in horizontal layers (beds).
    • Principle of Superposition: In undisturbed rock layers, the oldest rocks are at the bottom, and the youngest rocks are on top.
Step 4: Lithification
  • Lithification: The process by which the transported and deposited fragments or grains become cemented together after burial and compaction.
    • Without lithification, material remains as loose sediment rather than forming sedimentary rock.
    • Sediment: Described as loose, solid particles until lithified.

Types of Sedimentary Rock

  • Four Main Types:
    1. Clastic: Rocks formed from the accumulation of rock fragments (clasts).
    • Examples: Shale, Sandstone.
    1. Chemical: Formed by the crystallization and precipitation of sediments from natural water solutions.
    • Examples: Dolostone, Chert.
    1. Biochemical: Formed from organic processes and may contain significant amounts of biological material.
    • Examples: Limestone, Chalk.
    1. Organic: Created from organic-rich debris or sediment that has been buried, compacted, and lithified over time.
    • Examples: Peat, Coal.

Clastic Grain Sizes

  • Grain Size Classification (diameter in mm):
    • Boulder: >256 mm
    • Cobble: 64-256 mm
    • Pebble: 4-64 mm
    • Granule: 2-4 mm
    • Very Coarse Sand: 1-2 mm
    • Coarse Sand: 0.5-1 mm
    • Medium Sand: 0.25-0.5 mm
    • Fine Sand: 0.125-0.25 mm
    • Very Fine Sand: 0.063-0.125 mm
    • Silt: 0.0039-0.063 mm
    • Clay: <0.0039 mm

Clastic Rock Types

  • Breccia:

    • Characteristics:
    • Large grains (e.g., pebbles).
    • Angular grains.
    • Poorly sorted.
    • Environment: Terrestrial.

  • Conglomerate:

    • Characteristics:
    • Large grains (e.g., pebbles).
    • Rounded grains.
    • Poorly sorted.
    • Environment: Terrestrial.

  • Sandstone:

    • Characteristics:
    • Sand-sized grains.
    • Clastic composition.
    • Environment: Terrestrial or shallow marine.

  • Shale:

    • Characteristics:
    • Very small particles (invisible to the naked eye).
    • Composed primarily of mud and clay-sized grains.
    • Usually dark gray to black, layered, and fissile.
    • May contain organic material.
    • Environment: Terrestrial or marine.

Biochemical Rock Types

  • Coquina:

    • Characteristics:
    • Composed of shell fragments.
    • Reacts with acid (presence of Calcium Carbonate).
    • Environment: Shallow marine.

  • Fossiliferous Limestone:

    • Characteristics:
    • Contains fossils and reacts with acid (calcium carbonate).
    • Environment: Shallow marine.

  • Microcrystalline Limestone:

    • Characteristics:
    • Crystalline appearance, often gray.
    • Similar in appearance to Chert but DOES react with acid (calcium carbonate).
    • Environment: Deep marine.

  • Chalk:

    • Characteristics:
    • Soft texture, can be scratched by a fingernail.
    • Reacts with acid (calcium carbonate) and composed of dissolved shells of micro-organisms.
    • Environment: Deep marine.

Chemical Rock Types

  • Chert:

    • Composition: Microcrystalline quartz.
    • Characteristics:
    • Resembles microcrystalline limestone but does NOT react with acid.
    • Can be gray or reddish.
    • Environment: Deep marine or terrestrial.

  • Rock Salt:

    • Composition: Primarily halite.
    • Note: Often associated with evaporite environments (merchandise such as Himalayan salt lamps).

  • Rock Gypsum:

    • Characteristics:
    • Similar to mineral gypsum, sometimes has a fibrous appearance.
    • Can be scratched with a fingernail.
    • Note: Evaporite characteristics.

Organic Rock Types

  • Coal:
    • Characteristics:
    • Shiny appearance and black color.
    • Composed of decomposed plant matter and fossilized carbon.
    • Environment: Terrestrial.
    • Note: Formed via processes of compaction and lithification of organic materials over significant time periods.