1. Sedimentary Structures Objective: To examine examples of sedimentary structures and describe how they formed. The following samples are examples of sedimentary structures: 913S, LB1: Lamination/bedding 2: lamination/bedding, cross-lamination (cf. cross bedding) 10. Bedding, cross-lamination 7 and 9. Ripple marks 6, L54-3. Desiccation cracks (mud cracks) These structures are discussed in section 5.6 in the text, and were also discussed in class. Ripples can be formed by unidrectional fluid flow (water or wind)(i.e., a current, such as a river) or by oscillating waves (water). The former form asymmetrical ripples and the latter forms symmetrical ripples. Desiccation cracks were not discussed in class. These are the structures that you can see in dried-up muddy sediments, and are characteristic of environments that periodically flood and deposit mud, and then dry up (desiccate). An example would be a flood plain adjacent to a river. They can be used in paleoenvironmental analysis, as can the other structures I discussed in class. Mud cracks would not, for example, form in a muddy environment in a lake bottom or the deep sea. See also Figure 5.16 in the text. (a) In general, why does lamination or bedding develop? l.e., what does it represent (2) (b) Explain what cross lamination/bedding represents (how does it form?). (4) (c) Name an environment where cross lamination/bedding forms. (1) (d) What feature of sample 9 suggests that it represents a beach environment? (2)