Lecture: Sedimentary Rocks

Formed through lithification of accumulated sediments

Vital economic resources, essential for energy, industry and construction Groundwater and hydrocarbon reservoirs Environmental and climate records are preserved in sedimentary rocks Fossil archives

Clastic sedimentary rocks Chemical sedimentary rocks Organic sedimentary rocks

Formed from fragments of other rocks Ex. sandstone

Formed from precipitation of new minerals from ions in solution Ex. limestone

Composed of carbon-rich remains of organisms Ex. coal

• Weathering: breakdown of igneous, metamorphic, or older sedimentary rocks into solid particles and dissolved ions • Transport/Erosion: movement of sediment by gravity, water, wind, or ice • Deposition: settling of sediment in lakes, rivers, oceans, deserts or glacial environments • Lithification: Transformation of sediments into solid rock through compaction and cementation • Diagenesis: post-depositional changes that alter the texture and composition of the rock • Later uplift or sea level fall if we want to see the sedimentary rocks on land

The type of particle size depends on whether the sediment will travel by wind Very small particles are more likely to rise and be transported farther by wind than larger particles

Sediment transported by ice are mostly poorly sorted with different particle sizes

The bigger particles like gravel are closer to the ocean floor

As the water loses energy it drops heavier particles first

Cementation and compaction

Squeezing layers together

Hardening the sediments, cement (glue) all the sediments together

Particle size - indicating energy levels in the depositional environment Particle shape - determines transport history rounded grains suggest long transport distances, while angular grains indicate minimal transport Composition Sorting - uniformity of grain sizes

Higher energy shows more coarse-grained particle size While low energy show more fine-grained size

The uniformity of grain sizes Poorly sorted is when there is a wide range of different size particles Well sorted mean there are nearly all the same size

Whether the particle have sharps angle or rounded/smooth

Whether the particle has a sphere shape

Rounded gravel-sized particles from high energy environments like fast rivers and shorelines

Angular fragments indicating short transport

Composed of sand-sized grains

Most abundant sedimentary rock Made of silt and clay-sized particles Forms in calm water Poorly cemented

Inorganic processes: evaporation and chemical reactions OR Biochemical processes: Organisms extract minerals to build shells, which accumulate after death