Free Multi-Width Graph Paper from http://incompetech.com/graphpaper/multiwidth/ A measured section is a graphical representation of the rock layers in outcrop. It is a means by which geologists collect, interpret, and distribute data. Although graphical in nature, the patterns, shapes, and symbols used in the construction of the measured section are a powerful means of condensing a large amount of written data into a concise package. Measured sections have many parts and follow a particular format. By following a certain set of guidelines, it is easy for one geologist to interpret the data from another geologist’s research. The rules. 1. Measured sections are constructed from the bottom up. This is based on two simple ideas. A.) We can easily describe the strata as we walk up the mountain or along an outcrop. B.) We want to follow the Principle of Superposition when describing the geology (i.e. oldest layers on the bottom of the diagram). 2. All measured sections contain a legend. The legend is the explanation of all the symbols used in your measured section. A legend will include lithology, fossils and sedimentary structures. If you’ve drawn it in your section, it needs to be explained in the legend (see attached list of commonly used symbols). You may have to create your own symbols for certain features (just make sure they are sensible). 3. All measured sections have a scale bar. We draw the measured section to scale to create an accurate representation of the geology. The scale bar is represented either as a continuous set of tick marks on the edge of the column, or as a short line that denotes the unit of length. The metric system is the preferred unit of measurement, although some geologists will use both metric and English units. 4. Grain sizes are listed as letters along the bottom of a measured section. The width of the unit is drawn to correlate to the dominant grain size in the layer. For example, if a rock layer is dominated by coarse sand, the graphical representation of this unit would have it drawn to the coarse sand limit. This will be demonstrated. C = clay, s = silt, vf = very fine sand, f = fine sand, m = medium sand, c = coarse sand, vc = very coarse sand, and g = gravel. This scale can be changed to incorporate other size divisions as needed. Units that are a mixture of grain sizes can be drawn between the two dominant sizes. For example, mudstones can be represented as a line between clay and silt. 5. All measured sections have a title. We want to know what and where the section is. 6. All measured sections have a date. You may measure a section several times during your research. Each time may provide new observations. Your (dated) measured sections can show the evolution of your hypotheses as new data are included. 7. Your name. Well, duh….. Use the attached rock descriptions and data to draft a measured section. Use your measured section to answer the following questions. 1. Which depositional environments is/are represented by your measured section? Which unit(s) represent which environment? 2. Is this a shallowing or deepening upward sequence? Why? 3. Is this a transgressive or regressive sequence? Why? Field Data for the JG Locality (a geologically unstable area in Relbma, NW) The vertical scale for this measured section is 10 squares = 1 meter Unit 1:1.8 m thick: brownish-yellow fine sandstone and siltstone with occasional thin stringers of mudstone. Heavily bioturbated, with trace fossils. Erosive contact with… Unit 2: 0.9 m thick: yellowish white, medium to coarse sandstone with cross bedding. Current directions for the cross bedding trend 240, then 60 degrees. Shell hash layer at the base. Sharp contact with… Unit 3: 1.4 m thick: yellowish white, medium sandstone with large scale (40 cm +) cross beds trending 70 degrees. Some bivalve (pelecypod) shells. Slightly eroded contact with… Unit 4: 1.5 m thick: yellowish white, medium to fine sandstone beds interlayered with dark siltstone. Sandstone beds range from 10 to 20 cm in thickness and comprise half the volume of this unit. Sandstone beds fine upward from medium to fine sand, and contain rare fossil root traces. Siltstones contain occasional trace fossils. Gradual contact with… Unit 5: 0.8 m thick: siltstone, heavily bioturbated. Lenses of yellowish-white as fine, ripple-bedded sandstone. Gradual contact with… Unit 6: 0.6 m thick: brown to black mudstone, heavily bioturbated, with common bivalve shells, trace fossils, and rare root structures. Gradual contact with… Unit 7: 0.3 m thick: black mudstone, heavily bioturbated, with frequent root structures. Gradational contact with… Unit 8: 0.3 m thick: coal. Top of section is truncated by erosion. Example measured section https://www.geological-digressions.com/measuring-a-stratigraphic-section/ From: https://www.geological-digressions.com/crossbedding-some-common-terminology/ Section 2: Questions 1) Explain the difference between asymmetrical ripples and symmetrical ripples. What type of environment did each form in? 2) Explain the formation of mud cracks from unaltered sediment to a lithified rock (how do they form and are preserved)? 3) Pick 2 structures identified in lab to explain how sedimentary structures can be used to determine original up direction (geopedal
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