GEOL 1302 - Lab 07 - SedStructDepoEnv.docx

GEOL 1302 Lab 07 Sedimentary Structures and Depositional Environments In this lab, you are going to identify several depositional features and depositional environments, and connect them with sedimentary rock types. You are also going to review and work on sedimentary structures. Please submit your worksheets to your instructor. Helpful Websites: http://reynolds.asu.edu/glg103/sed_env_start.htm https://geo.libretexts.org/Bookshelves/Geology/Book%3A_An_Introduction_to_Geology_(Jo hnson_Affolter_Inkenbrandt_and_Mosher)/05%3A_Weathering_Erosion_and_Sedimentary_ Rocks/5.04%3A_Sedimentary_Structures You also find very useful information in your textbook. 1

Depositional Features and Environments The numbered images displayed in the lab show various depositional environments. Place each feature in the correct row and complete the information in the table. Image Number Depositional Feature/ Environment Major Environment (Continental, Transitional, or Marine) Typical Rock Types 1 Alluvial Fan Continental Conglomerate, sandstone, and siltstone 2 Braided River Continental Gravel and sand 3 Delta Marine Sand and gravel 4 Dune Continental Quartz and feldspar 5 Glacial Moraine Continental Gravel and sand 6 Meandering River Continental sandstone, mudstone, and conglomerate 7 Playa Lake Continental clay, silt, sand, gravel 8 Reef Marine Limestone 9 Sandy Beach Marine Quartz 10 Swamp Continental shale, sandstone, limestone 11 Tidal Flat Transitional mud and sand 12 Turbidity Current Marine sand, gravel, mud, and silt Environments: Alluvial Fan, Braided River, Delta, Dune, Glacial Moraine, Meandering River, Playa Lake, Reef, Sandy Beach, Swamp, Tidal Flat, Turbidity Current 2

Sedimentary Structures Match the sedimentary structures listed below with the environment in which they are likely to form. Place the correct letter in the empty space. 1. Asymmetrical ripples Wave-washed shoreline 2. Mudcracks Dried-up lake 3. Graded bedding Desert dune 4. Symmetrical ripples Turbidity current 5. Varves Glacial lake 6. Crossbeds (large-scale) River Environments: (A) Turbidity current, (B) Desert dune, (C) Dried-up lake, (D) Glacial lake, (E) River, (F) Wave-washed shoreline 4

Sedimentary structures allow geologists to resolve the history of an area when rocks have been deformed. For example, mudcrack “V”s open toward younger strata, and the shape of ripple marks can also be used to determine which side of a layer is the upper one. Here, the youngest layer is in the center of the fold. What about the picture below? Where is the youngest, where the oldest layer located? Describe how you came up with your answer. The youngest is going to be conglomerate and the oldest is going to be at the bottom right. I came up with this answer because the structures tell going from youngest to oldest by placement. 5