Problem 2: Dating Rocks with Fossils Fossils can provide important information a

Question

Problem 2: Dating Rocks with Fossils Fossils can provide important information as to the age of the rocks they were found in and the timing of geologic events. In many instances they can improve our understanding of the order of events based on relative age dating principles and provide information on missing time. The geologic ranges of 12 different dinosaur genera are given below. Use this nformation to answer the following questions. Be as precise as possible when providing relative ages, dividing each period into Early, Middle, and Late. Refer to Lecture 4 for more details. Herrerasourus Riojasaurus Dilophosaurus Cetiosourus Stegosaurus Allosaurus Oviraptor

Explanation / Answer

Problem 2:

1. a) Cetiosaurus.

b) Megalosaurus, Stagosaurus, Allosaurus.

2. a) Early Jurassic

b) Middle Jurassic

c) Late Jurassic

Answer 14 : Megalosaurus, Stegosaurus, Allosaurus.

Explanation : Apart from Brachiosaurus, fossils of Megalosaurus, Stegosaurus and Allosaurus are found from Late Jurassic times. So if we find all these fossils together in a rock, we can identify its age to be Late Jurassic.

Answer 15 : Early Jurassic

Explanation : The rocks were tilted after the deposition of the unit I which from its fossil record is found to have been deposited during Early Jurassic times.

Answer 16 : Middle Jurassic

Explanation : The layer C, from its fossil record is found to be of Late Jurassic age while the underlying tilted I layer is of Early Jurassic (from it's fossil content). So, the time gap represented by the contact between C and the underlying tilted layers is Middle Jurassic.

Answer 17 : Late Jurassic.

Explanation : The fault did not cut through the layer G but it cut across the unit K. So, it was formed before the deposition of unit G, which from its fossil content is found to be Early Cretaceous in age. So the fault must be formed before Early Cretaceous, that is during Late Jurassic.

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