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Explore the classification, formation, and unique features of sedimentary rocks, including the processes of lithification and erosion. Discover the various types of sedimentary rocks through clastic, organic, and chemical formations. Gain insights into field geology tools and techniques used by geologists.
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What are Sedimentary Rocks? • What are sediments? • How do sediments form sedimentary rocks? • Where do sedimentary rocks form?
sedimentary rocks usually come from SEDIMENTS (mud, sand, pebbles, etc.) sediments are pressed into layers (strata) General Features
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
sediment comes from the weathering and erosion of other rocks wind and water move sediment Formation
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
clastic rocks come from broken pieces of other rock (as was just described) they are further classified according to their pieces Types of Sedimentary Rocks:1. Clastic
conglomerates have large, round, pieces (see last slide) breccias have large, angular pieces clastic rocks from smaller pieces can be sandstones or mudrocks Shale Clastic Rocks ctd.
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 2. Organic 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 3. Chemical Rocks
FIELD GEOLOGY • Tools of a Geologist • Grain size scale • Roundness scale • Hand lens • Field notebook • Make good observations and notes
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?