Sediments and Sedimentary Processes I (January 15 & 17)

A thorough understanding of geologic time is fundamental in any geology course, and it is especially critical in Sedimentology & Stratigraphy. Because time scales change, I will hand out in class (as part of your first lab) our version of the Geological Time Scale. You will see that I recognize the Ediacaran Period before the Cambrian, and the Paleogene and Neogene instead of the old Tertiary. Remember that geologists make a crucial distinction between relative and absolute time, which is usually calculated radiometrically. Radiocarbon dating is a special case of radiometric dating. (Note that I’m a fan of Wikipedia. If an article there is inaccurate, we can fix it!)

Here’s a page that you may use often this semester: Internet Resources for Sedimentary Geologists (with only a few annoying dead links). It is a bit outdated, but you will still see the range of studies within sedimentary geology, from the interface with chemistry (low-temperature diagenesis) to the combination of sediments and biology (ichnology), along with plate tectonics, radiometric dating, sequence stratigraphy, and paleoenvironmental interpretations.

Our lectures and labs on the fabrics and textures of sediments and sedimentary rocks are not thrilling, although I’ll work hard on them! Here’s a clever graphic for the Udden-Wentworth grain-size scale. The Wikipedia page on grain sizes is very good. (And if it wasn’t, we’d make sure to fix it!)

Middle Triassic marginal marine sequence, southwestern Utah. (Click for larger view.)

Geology in the News —

On New Year’s Day, NASA’s New Horizons spacecraft flew by and photographed the most distant object observed in our Solar System: Ultima Thule. It’s a binary object looking a bit like a snowman. It is apparently reddish in true color. It will take 20 months for all the data collected to be received on Earth. Amazing.

We all know that the asteroid that slammed into the Chicxulub region 66 million years ago generated a huge tsunami that devastated southern North America. Now the global spread of this tsunami has been modeled. May we never see the likes of this in our species’ time!

The Little Ice Age ended more than a century ago, but cold seawater still lingers from that time. Cold waters that were once on the surface of the Pacific have been found very deep, and they’re still sinking. The Earth System responds to climate change on a wide range of time scales.

 

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