12th February.docx - 12th February Pages of earth\u2019s Past Sedimentary Rocks Drilling into the bottom of the North Sea we encounter o Soft mud and loose

12th February.docx - 12th February Pages of earthu2019s...

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12 th February Pages of earth’s Past: Sedimentary Rocks Drilling into the bottom of the North Sea, we encounter: o Soft mud and loose sand, silt, pebbles, and shells. Then: o Similar materials that are more solidified. Then: o Fragments of solid rock. Cemented sand and silt. Pottery-like clay. Cemented shells. Crystalline masses of salt. The drill reveals a transition. o Soft sediment changes into cemented sedimentary rock. o This change occurs as burial depth increases Sedimentary Rock: o Forms at or near Earth’s surface in one of several ways. Cementing loose clasts (fragments) of preexisting rock. Cementing together loose shells and shell fragments. Accumulation of organic matter from living organisms. Precipitation of minerals dissolved in water. Sedimentary rocks form layers like the pages of a book. o The layers record a history of ancient environments. o The layers occur only in the upper part of the crust. Sedimentary rocks cover underlying basement rock. Geologists define four classes of sedimentary rock: o Clastic—loose rock fragments (clasts) cemented together. o Biochemical—cemented shells of organisms. o Organic—carbon-rich remains of once living organisms. o Chemical—minerals that crystallize directly from water. Physical and chemical weathering provide the raw material for all sedimentary rocks. Detrital (or clastic) sedimentary rocks consist of: o Detritus (loose clasts). Mineral grains.
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  • Fall '09
  • ALFONSOMUCCI
  • clastic sedimentary rocks,  Pottery

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