The numbers along the left side of the chart represent depth, with 180 meters being near the surface.
This diagram shows a representation of all the sedimentary beds at Chilga in an area of the basin where our work has been concentrated. Leaf sites are shown in green, fruit and seed localities are in brown, and the red star shows the location of CH 3 toward the top of the column. Also shown in this figure are the dates we have on the deposits – which tell us the age of the fossils. A radiometric (isotope) date on the ash being studied by Juan is 27.36 million years old, and a basalt (solidified lava flow) underlying the sediments is dated at 32.4 million years old. Another technique is called paleomagnetic dating, which uses the precisely-dated pattern of changes in the Earth’s geomagnetic field during geologic history to better constrain the age of sediments. The part of the geomagnetic time scale relevant to Chilga sediments is shown in this diagram – our sediments were most likely laid down during the part of the time scale labeled “C9n”. For more information on dating techniques used here, you can visit http://en.wikipedia.org/wiki/Potassium-argon_dating ,http://en.wikipedia.org/wiki/Argon-argon_dating and http://en.wikipedia.org/wiki/Geomagnetic_reversal .
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