Tutorial 1B Fossilization ERTH 1091 You have a chunk of coarse-grained conglomer

Question

Tutorial 1B Fossilization ERTH 1091 You have a chunk of coarse-grained conglomerate and a chunk of fine-grained marine mudstone. Which is more likely to have abundant fossils, and why? a. b. A geologist found dinosaur bones and human bones in the same layer of fine-grained sandstone. What is a reasonable conclusion that the geologist might make as the presence of these unlikely companions? c. Suppose that a geologist had collected several suites of fossils from a quarry in Nova Scotia (or anywhere else, for that matter!). Given the ranges of each fossil (without knowing exact ages), and knowing that these fossils were all collected from the same rock unit, what is the age of this rock unit? (assume the fossils are autochthonous) Sample 1 Ordovician-Permian Sample 2 Silurian-Mississippian Sample 3 Cambrian-Triassic Sample 4 Devonian-Recent Sample 5 Ordovician-Jurassic Sample 6 Mississippian-Recent d. An index fossil is one that existed over a relatively short time period, in other words, one that is relatively good at narrowing down the age of a r 600 million years-they are not good index fossils!). Which of the above samples in questions (c) is the best index fossil in this group? ock (jellyfish have been around for

Explanation / Answer

a. The porosity present in coarse grain sedimentary rocks is comparatively more than the fine grained rocks, considering they are from the same environment. Therefore conglomerate which have particles of greater size have more fossils as compared to mud stone composed of clay sized particle.

b. Now both of the fossil are from different age, hence it is only possible if there is intrusion of older layer containing fossils of dinosaurs into the recent sandstone later having human bones in it.

c. Most of the samples are from Mississippian and Silurian time, hence the age is from 323 million years to 444 million years.

d. Index fossil are those which occur for short period of time and in the data above sample 2 is having the least period hence we can call it as a index fossil.

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