Physical Geology 1330 Dr. Mike Murphy 116-S&R 1 [email protected] Lecture 9: Sedimentary Rocks 333-S&R-1 9/30/02 www.uh.edu/~mamurph2/homepage.html Today’s Outline (1) Types of Sedimentary Rocks Detrital Chemical (2) Turning Sediment into Sedimentary Rock (3) Sedimentary Environments (4) Sedimentary Structures Sedimentary Rock (a) Rock resulting from the consolidation of loose sediment that has been derived from previously existing rocks and accumulated in layers (detrital or clastic) (b) Rock formed by the precipitation of minerals from solution by either organic or inorganic processes (chemical) From Source to Sedimentary Rock (1) 4 steps to forming sedimentary rocks (2) (3) deposition (4) lithification diagenesis Lithification – the processes by which sediment is turned into sedimentary rock Compaction Cementation Detrital Sedimentary Rocks classified on the basis of: (1) (2) Sedimentary Textures include: (1) (2) (3) Size Ranges Common Detrital Rock (mm) Particle Name Sediment Name Name > 256 Boulder Conglomerate 64-256 Cobble Gravel or Breccia 4-64 Pebble 2-4 Granule 1/16 to 2 Sand Sand Sandstone 1/256 to Shale or mud 1/16 Silt Mudstone <1/256 Clay Lithification of Sandstone A. After Deposition B. Compaction C. Cementation Roundness and Distance of Transport Distance transported Angular Rounded Grain Sorting Well Sorted Poorly Sorted Porosity – percent void space Permeability – a measure of the ease by which fluid may flow through the rock Lithification of Shale A. Wet Mud B. Weight of New Sediment C. Splitting Surfaces Chemical Sedimentary Rocks form from transported as dissolved material that is precipitated by inorganic or organic processes Precipitation occurs in two ways – Organic (Biochemical) – Inorganic – Evaporation and Chemical Activity Depositional Environments – Places where sediments accumulate. Each environment produces a characteristic sedimentary rock. Two primary categories: Continental - Marine - Beaches (shores) are considered transitional between continental and marine. Alluvial Fan – River (Fluvial) Delta – Continental Margin (Continental Shelf and Slope) Deep Sea – Common Sedimentary Environments Fig. 7.5 Sedimentary Structures – features exhibited in sedimentary rocks that form from processes occurring in the environment, such as, wind or moving water. They provide evidence for the depositional environment in which the sedimentary rocks were deposited. Bedding planes - Cross-bedding – Ripple Marks – Mudcracks – Fossils – Bioturbation - .