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  • General

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  • 使用相对年龄的相关性

    Two photos of unique rock formations from Valley of Fire and Capitol Reef, showcasing sandstone.
     

    How would you correlate two rock units?
    ::你会如何联系两个岩石单位?

    On a  field trip  in the southwestern United States you would see some very unique   layers. You might see a distinctive whitish rock unit that looks like  sand dunes . This rock is the Navajo Sandstone. The first photo is from the  Valley  of Fire near Las Vegas, Nevada. The second is from Capitol  Reef  National Park in Utah. These sites are roughly 250 miles apart. Sand dunes stretched across this part of the country during the Mesozoic.
    ::在美国西南部的一次实地考察中,你会看到一些非常独特的地层。你可能会看到一个与众不同、看起来像沙丘的怪异岩石单位。这块岩石是纳瓦霍沙岩。第一张照片来自内华达州拉斯维加斯附近的火灾谷。第二张照片来自犹他州国会珊瑚礁国家公园。这些地点相距约250英里。在美索索契时,沙丘横跨全国各地。

    Matching Rock Layers
    ::匹配摇滚层

    When rock layers are in the same place, it’s easy to give them relative ages. But what if rock layers are far apart? What if they are on different continents? What evidence is used to match rock layers in different places?
    ::当岩石层位于同一个地方时,很容易给它们相对的年代。 但如果岩石层相距很远呢?如果它们位于不同的大陆上呢?用什么证据来匹配不同地方的岩石层呢?

    Widespread Rock Layers
    ::环状岩层

    Some rock layers extend over a very wide area. They may be found on more than one  continent  or in more than one country. They are matched up by  correlation . For example, the famous White Cliffs of Dover are on the coast of southeastern England. These distinctive rocks are matched by similar white cliffs in France, Belgium, Holland, Germany, and Denmark ( Figure   ). It is important that this chalk layer goes across the English Channel. The rock is so soft that the Channel Tunnel connecting England and France was carved into it!
    ::有些岩石层延伸到一个宽广的区域。 它们可能在一个以上大陆或一个以上的国家发现。 它们相互对应。 例如, 著名的多佛白裂谷位于英格兰东南部海岸。 法国、 比利时、 荷兰、 德国、 丹麦( 图表 ) 与这些独特的岩石相匹配。 这块粉笔层必须穿过英吉利海峡。 岩层非常柔软, 以至于连接英格兰和法国的海峡隧道被刻入其中 !

    Chalk cliffs in Denmark (A) and Dover, U.K. (B) demonstrating widespread rock layers.
     
    Chalk Cliffs. (A) Matching chalk cliffs in Denmark and (B) in Dover, U.K.

    Key Beds
    ::密钥床位

    Like  index fossils ,  key beds  are used to match rock layers. A  key bed  is a thin layer of rock. The rock must be unique and widespread. For example, a key bed from around the time that the dinosaurs went  extinct  is very important. A thin layer of clay was  deposited  over much of Earth’s surface. The clay has large amount of the  element  iridium. Iridium is rare on Earth but common in  . This unusual clay layer has been used to match rock up layers all over the world. It also led to the  hypothesis  that a giant asteroid struck Earth and caused the dinosaurs to go extinct.
    ::像指数化石一样,钥匙床被用来匹配岩石层。钥匙床是一块薄薄的岩石层。岩石必须具有独特性和广度。例如,恐龙灭绝前后的密床非常重要。薄的粘土层沉积在地球表面的许多地方。粘土有大量的元素。在地球上是稀有的,但在地球上是常见的。这种不寻常的粘土层被用来匹配全世界的岩石层。它也导致一个巨型小行星撞击地球并导致恐龙灭绝的假设。

    Using Index Fossils
    ::使用化石指数

    Index fossils are commonly used to match rock layers in different places ( Figure   ). If two rock layers have the same index fossils, then they’re probably about the same age.
    ::指数化石通常用来匹配不同地方的岩石层(图 ) 。 如果两个岩石层具有相同的指数化石,那么它们大概也差不多是同一年代。

    Comparison of rock layers in two areas showing matching index fossils for age correlation.
     
    Using Index Fossils to Match Rock Layers. Rock layers with the same index fossils must have formed at about the same time. The presence of more than one type of index fossil provides stronger evidence that rock layers are the same age.

    Summary
    ::摘要

    • A single rock unit contains the story of the geology of that location. To understand the geology of a region, scientists use correlation.
      ::一个单一的岩石单元载有该地点的地质学故事。为了了解一个区域的地质学,科学家们使用相关性。
    • To correlate rock units, something distinctive must be present in each. This can include an index fossil, a unique rock type, a key bed, or a unique sequence of rocks.
      ::相联的岩石单位, 必须在每块岩石中都存在独特的东西。 这可以包括一种指数化石、一种独特的岩石类型、一种钥匙床, 或者一种独特的岩石序列 。
    • A key bed can be global. An example is the iridium layer that was deposited at the time of the Cretaceous-Paleogene mass extinction.
      ::一个关键床位可以是全球性的。一个例子就是白鲸-白蚁大规模灭绝时沉积的层。

    Review
    ::回顾

    1. What features must the iridium layer at the time of the dinosaur extinction need to be a key bed?
      ::恐龙灭绝时的层必须具备什么特征才能成为关键床?
    1. To be more certain that fossils can be used to correlate rock layers, what is needed?
      ::更确切地说,化石可以用来连接岩石层,需要什么?
    1. What is the process of correlation?
      ::关联的过程是什么?

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

     

     

    1. In what type of rock were the leaf fossils found? How is this type of rock formed?
      ::叶子化石在什么类型的岩石中发现的?这种类型的岩石是如何形成的?
    1. Why is this volcanic ash unique?
      ::为什么火山灰是独一无二的?
    1. How does the lapilli tuff form?
      ::长尾草怎么样?
    1. What does the lapilli tuff allow scientists to do?
      ::怎样才能让科学家们做这些呢?