Wheeler Diagrams from The Mini Basin (by Matt Kuchta)
Small basin (built from instructions by T. Hickson, Univ. of St. Thomas) run with relatively constant sediment input, but variations in base level to produce variations in sedimentary “packages” which are then traced onto a graph of lateral extent vs. time (wheeler diagram).
kinks, bends, fractures, fillings.. oh my.. (by Ale*)
Many of the iron-rich layers in this outcrop show extremely fine lamination. In this example there are four couples of pink and brown bands at the base, followed by a few whitish bands and then an overall lighter pattern before ending up in the black cherts. If one looks to the right, it is possible to see a discontinuity, a microfault, that breaks the bands. Across the fault, the bands have different thicknesses, but they are consistent in number and order. It looks like that when the bands were folded, they expanded towards the outside the bend. The cracks have been filled likely with calcite, but they stop at the edge of the iron layer: you can not follow the cracks into the chert, indicating that the iron was already a solid rock when the chert, above and below, was plastic enough to flow following the deformation.
Banded Iron Formations
Fuente: Flickr / greenriver
Draft, delta building and stratigraphy, Emriver Em4 model. (by Steve Gough)
Here we build a delta, then lower base level so the channel cuts through it. We then used vertical slicing to reveal some very nice stratigraphy. There are four sizes of color coded particles, the material is melamine plastic (density 1.6). You can see Gigapan images of the stratigraphy.
Stratigraphy of Kasimov Crater Fill (by Lunar and Planetary Institute)
This image shows layered sedimentary rocks and ripples that fill and surround Kasimov crater. These layered deposits may have formed through the accumulation of sediment that was transported into this crater by blowing wind. The crater interior contains a sequence of layers that are remnants of the material that originally infilled the crater. These sediments form an extensive deposit that once covered the floor of the surrounding larger crater.
All this geological activity has made me dig out my master geology notebook from college. Describing that book is more than one post can handle, so here’s my notes from Sedimentation and Stratigraphy.
Basically, we were allowed to have one notecard worth of notes for each major test, and to use all three notecards for the final. I condensed all my best notes from the master notebook onto these, and aced every one. This is everything that you would need to know to pass a University of Mary Washington Sedimentation and Stratigraphy course.
111. AGES OF GEOLOGY: Early Geologists Grasped Essentials.
Altho subsequent investigations have multiplied extensively the number of geological periods, … yet the first general division into three great eras [primary, secondary, and tertiary] was nevertheless founded upon a broad and true generalization. In the first stratified rocks in which any organic remains are found, the highest animals are fishes, and the highest plants are cryptogams; in the middle periods reptiles come in, accompanied by fern and moss forests; in later times quadrupeds are introduced, with a dicotyledonous vegetation. So closely does the march of animal and vegetable life keep pace with the material progress of the world, that we may well consider these three divisions, included under the first general classification of its physical history, as the three ages of nature; the more important epochs which subdivide them may be compared to so many great dynasties, while the lesser periods are the separate reigns contained therein.
— AGASSIZ Geological Sketches, ser. i, ch. 1, p. 15. (H. M. & Co., 1896.)
Blogger’s note: The geologic timescale has a pretty cool history. It all started with humans gradually realizing fossils are the remains of ancient life. The Law of Superposition (layers of rock are formed in a time sequence, oldest on the bottom; originally thought to be a result of the biblical great flood) was another crucial concept. The first steps towards our modern relative geologic timescale were made once the above two and uniformitarianism were combined to separate out the past into eons in the late 18th century. Now, we have this monstrosity, made accurate in recent years by the use of radiometric dating.
(I’d like to clarify that my main issue with the geologic timescale as it stands is that the names are frequently confusing and difficult to learn. No, I don’t have any better ideas.)
The photo above shows the eye-catching Painted Hills Unit in the John Day Fossil Beds National Monument of Oregon. These conspicuous layers represent different claystone deposits laid down about 25 million years ago when this area was a floodplain. Over time, erosion has exposed the ochre, orange and apricot layering. The coloration of the claystone strata seem to change with changing light conditions and moisture levels. Photo taken on May 18, 2010. Credit: Paul Marcellini. (via EPOD)
Seismites in outcrop of Pleistocene lake bed deposits, SE California. (by Marli Bryant Miller)
Seismites, sediment disturbed by the shaking from an earthquake, preserved in a layer of Pleistocene ash and sand of the Tecopa Lakebeds. Photo is about 30 cm across.
Fuente: Flickr / marlimiller