GLG Physical Geology Bob Leighty Sedimentary Rocks & Processes

These lecture notes are very similar to the ones I use in my traditional classes. You’ll find they are loaded with imagery and streamlined text that highlight the most essential terms and concepts. The notes provide a framework for learning and, by themselves, are not meant to be a comprehensive source of information. To take advantage of the global knowledge base known as the Internet, I have included numerous hyperlinks to external web sites (like the Wikipedia, USGS, NASA, etc.). Follow the links and scan them for relevant info. The information from linked web sites is meant to supplement and reinforce the lecture notes – you won’t be responsible for knowing everything contained in them. As a distance learning student, you need to explore and understand the content more independently than in a traditional class. As always, I will help guide you through this learning adventure. Remember, Dr. Bob if you have any questions about today’s lecture Leave no questions behind! Explore and have fun! These notes and web links are your primary “lecture” content in this class. Additionally, various articles are assigned each week to supplement this “lecture” information. I believe you’ll have enough information to reference without having to purchase a costly textbook.

Sedimentary Rocks

 Features that form when sediment is deposited  Can provide important clues in sedimentary rocks Sedimentary Structures Sedimentary Rocks

 Water-laid sediments are originally deposited in horizontal layers (beds) bedding forming today  Bedding = layering in sedimentary rocks Bedding bedding in rocks Bedding Sedimentary Structures Sedimentary Rocks

 A bed with particles that decrease in size upwards Sedimentary Structures Sedimentary Rocks Graded Bedding > Represents waning flow after a flood event

How do graded beds form? Sedimentary Structures Sedimentary Rocks Graded Bedding

ripple marks in sandstone (ancient currents) currents forming ripple marks in sand today  Small ridges in sand/mud formed by currents (wind or water) Ripple Marks  Asymmetrical ripples are useful in telling current direction Sedimentary Structures Sedimentary Rocks

 Tilted layers within a single bed bed Cross Bedding  Represent the cross section of ancient sand dunes  Useful in telling current direction & “up” direction Sedimentary Structures Sedimentary Rocks

Sedimentary Structures Sedimentary Rocks How do cross beds form? Cross Bedding

cross bedding in sandstone (ancient sand dunes) cross bedding forming in a sand dune today Cross Bedding Sedimentary Structures Sedimentary Rocks

desiccation cracks forming in mud today desiccation cracks in mudstone (ancient mud cracks)  Wet, fine-grained sediment is exposed to air, dries, & shrinks Desiccation Cracks (Mud Cracks) Sedimentary Structures Sedimentary Rocks

Trace Fossils  Tracks, trails, burrows - Reworking of soft sediment by organisms  Can describe critters & their movement and behavior Sedimentary Structures Sedimentary Rocks

continental marine transitional Depositional Environments Sedimentary Rocks

Depositional Environments Sedimentary Rocks

sediment  Lithification – Compaction & cementation after deposition Lithification sedimentary rock Turning Sediment Into Rock Sedimentary Rocks

Clastic texture (made of pieces)Chemical texture (crystalline) sedimentary rock sediment gravel conglomerate carbonate mud limestone Turning Sediment Into Rock Sedimentary Rocks

Sedimentary breccia Clastic Rocks Sedimentary Rocks Gravel-sized pieces Conglomerate

Quartz Sandstone (“clean”) Clastic Rocks Sedimentary Rocks Arkose Arkose (“dirty”) Graywacke Sand-sized pieces Sandstone

MudstoneMudstone (Siltstone, Shale) Clastic Rocks Sedimentary Rocks Mud-sized pieces

Carbonate rocksCarbonate rocks (CaCO 3 ) Carbonate rocks LimestoneLimestone, DolomiteDolomite Chemical Rocks Sedimentary Rocks

ChertChert (SiO 2 ) Chert Chemical Rocks Sedimentary Rocks

Evaporites Chemical Rocks Sedimentary Rocks Rock gypsum, Rock salt

Coal Biochemical Rocks Sedimentary Rocks  Unoxidized, organic-rich (carbon) remains of plant material

>Interpretation: low-energy deposition in shallow water, floods, exposed to the atmosphere River Flood Plain  Common “flood plain” rocks = mudstone, sandstone >Ripple marks, graded beds, mud cracks, abundant land plant & critter fossils Interpreting Sedimentary Rocks Sedimentary Rocks

River Flood Plain Permian Hermit Formation (Grand Canyon)  Example of a “flood plain” rock formation: Interpreting Sedimentary Rocks Sedimentary Rocks

Sand Dunes >Interpretation: wind deposited dunes (desert or beach) > X-beds, ripple marks, sparse critter trace fossils  Common “sand dune” rocks = quartz sandstone Interpreting Sedimentary Rocks Sedimentary Rocks

Sand Dune Permian Coconino Sandstone (Grand Canyon)  Example of a “sand dune” rock formation: Interpreting Sedimentary Rocks Sedimentary Rocks

Shallow Marine >Interpretation: mostly low-energy deposition in a shallow (0-135 m) ocean >X-beds, ripple marks, graded beds, marine fossils  Common “shallow marine” rocks = limestone, sandstone, mudstone Interpreting Sedimentary Rocks Sedimentary Rocks

Shallow Marine  Example of “shallow marine” rock formations: Mississippian Redwall Limestone Permian Kaibab Limestone Cambrian Muav Limestone Interpreting Sedimentary Rocks Sedimentary Rocks

WWW Links in this Lecture > Bedding - > Graded bedding - > Ripple marks - > Cross-bedding - > Trace fossil - > Depositional environment - > Lithification - > Sedimentary breccia - > Conglomerate - > Sandstone - > Arkose - > Graywacke - > Mudstone - > Carbonate rock - > Limestone - > Dolostone - > Chert - > Evaporite - > Coal - Sedimentary Rocks