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, [ QR o= T 1) - (=S =T [} QYA T\ o 1151 (o] oA = TeTo) 40 =T (RN o (o] {1 [=E- S F-T IR A/ 13 To [ 1TV o T=1) (ON =~ N (Nole &y A M- TR\ V] 172 Stratigraphy and Lithologic Correlation Cambrian Strata in the Grand Canyon For the diagram below showing Cambrian strata in the Grand Canyon area, answer the following questions. T 2 2. LN Cross-section of Cambrian sedimentary rocks exposed in the Grand Canyon. Red line 0 marks the top of the Low Cambrian Olenellus trilobite zone, and red line G marks the Middle Cambrian Glossopleura trilobite zone. (From Levin, H., 2013, The Earth Through Time (10* edition), figure 10-12, p. 285. This material is reproduced with permission of John Wiley & Sons, Inc.). Adapted from Mckee, E. D., 1945, Cambrian Stratigraphy of the Grand Canyon Region, Washington, Carnegie Institute, Publication 563. leveled 1. Label the position of the unconformity. 2. What type of ity is wisz_nonconformity . What does the vertical sequence of rock types indicate about sea level changes? e sequence or a regressive sequence? _LIANSQression . What is the most likely depositional environment of the Tapeats Sandstone in this sequence? each or deeper water . What is the most likely depositional environment of the Bright Angel Shale in this viroment Notice the two red lines, one labeled O and the other labeled G. These lines indi- cate the times at which two different trilobite species (Olenellus and Glossopleura) lived, along with their geographic distribution. These trilobites are index fossils or indicators of very specific intervals of geologic time. Olenellus lived during the Early Cambrian and Glossopleura lived during the Middle Cambrian. These red lines can be considered time lines. Is this a transgressi IS o sequence? 6. What is the age of the Bright Angel Shale in the western part of this diagram? early cambrien Olenellus trilobites. 7. What is the age of the Bright Angel Shale in the eastern part of this diagram? —mid-eambrien-Glossopleura trilobites. . By examining these trilobite distributions, we can see that the Bright Angel Shale is diachronous (it is older in some areas and younger in others). Is the Bright ® Angel Shale older in the east or older in the west?