ERTH 209-02 Earth Sedimentary Rocks Fall 2024 PDF

ERTH 209-02 EARTH Fall 2024 Sedimentary rocks Sedimentary rock classification  There are two major groups of sedimentary rocks:  Chemical (precipitated) - made up of mineral precipitate, chemical or biochemical;  Clastic (detrital) - made up of eroded pieces of ro...

ERTH 209-02 EARTH Fall 2024 Sedimentary rocks Sedimentary rock classification  There are two major groups of sedimentary rocks:  Chemical (precipitated) - made up of mineral precipitate, chemical or biochemical;  Clastic (detrital) - made up of eroded pieces of rock (mineral or rock fragments).  They can co-exist or can be accumulated in distinct sedimentary areas. Sedimentary rock abundance  The clastic rocks are the dominant ones in the Earth’s crust. From Press & Seiver, 1998 Two major characteristics  The clastic sedimentary rocks are composed predominantly of silicate fragments (clasts), such as individual silicate minerals (e.g., quartz) and rock (lithic) fragments (e.g., granite, basalt).  Clasts undergo weathering & erosion, transport, deposition and lithification to form a clastic sedimentary rock (the process of formation is extremely complex). Clastic rock main components  Clasts (c ) and matrix or ground mass (m). Pores  Porosity is the fundamental property of the reservoir rock for hydrocarbons (oil and natural gas).  Pores can be filled with fluids.  According to their size, pores can be macropores (larger than 5 microns) and micropores (smaller than 5 microns). Pore classification  Catenary pores – allow the fluid flow in the subsurface conditions.  Cul-du-sac pores – can be filled with fluids but do not allow the fluids to flow through them.  Closed pores – in general are empty (not always!) and do not allow the fluids to flow. Clastic rock formation cycle Weathering & erosion Transport Deposition ` Lithification From Dolgoff, 1998 Weathering and erosion  Weathering represents the physical and chemical alteration of rocks exposed to the atmospheric influences on the Earth’s surface.  Physical Weathering: bedrock is broken into smaller fragments and the composition of the minerals remains unchanged.  Chemical Weathering: water and dissolved ions react with solid rock to produce materials of different compositions.  Sediment transport Landslides and rockfalls. Eolian transport (transport media = winds and air currents); Glacier transport (transport media = glaciers); Stream and river transport (transport media = continental water). Wave and current transport (transport media = oceanic water). Deposition Detrital Sediments: fragments derived from weathered rocks that were transported by wind, water or ice, and deposited in loose layers at the Earth’s surface. Sediments are formed as the result of deposition.