1. Sedimentary Rock Classification

2. Rock cycle

3. What are Sedimentary Rocks?  What are sediments?  How do sediments form sedimentary rocks?  Where do sedimentary rocks form?

4. General Features  sedimentary rocks usually come from SEDIMENTS (mud, sand, pebbles, etc.)  sediments are pressed into layers (strata)

5. Ernst Tinaja Big Bend National Park

6. Ernst Tinaja  Thin-bedded orangish rock = Del Rio Clay,  Stratigraphically just below the Buda Limestone  The massive white rock below the Del Rio is the Santa Elena Limestone  Time lapse between the deposition of the Santa Elena and the Del Rio = unconformity

7. Formation  sediment comes from the weathering and erosion of other rocks  wind and water move sediment

8. Formation ctd.  once sediments are settled, lithification (making a rock) begins  lithification can involve two main processes:  compaction: sediments are pressed together by weight, and water is forced out  cementation: minerals deposit out of water and “cement” together sediments

9. Rock Cycle

10. Types of Sedimentary Rocks: 1. Clastic  clastic rocks come from broken pieces of other rock (as was just described)  they are further classified according to their pieces

11. Clastic Rocks ctd.  conglomerates have large, round, pieces (see last slide)  breccias have large, angular pieces  clastic rocks from smaller pieces can be sandstones or mudrocks  Shale

12. 2. Organic Rocks  form directly or indirectly from living material (despite our definition of minerals)  example: limestone is calcium carbonate from the shells of dead clams and oysters

13. 3. Chemical Rocks  form by chemical processes (not regular compaction)  Limestone: a. grainstone b. boundstone  “evaporites” form when water evaporates, leaving just minerals  ex: gypsum, halite, and even some limestone are from evaporating water

14.  Tools of a Geologist Grain size scale Roundness scale Hand lens  Field notebook Make good observations and notes FIELD GEOLOGY

15. Summary Questions  What might tip you off that you’re looking at a sedimentary rock?  What are two ways that limestone can form?  How are chemical rocks different from other sedimentary rocks?