This topic contains a solution. Click here to go to the answer

Author Question: Modern geochronology studies recognize that most radiometric dates record a time when a mineral ... (Read 58 times)

jayhills49

  • Hero Member
  • *****
  • Posts: 559

Question 1

In a given area where you have little knowledge of the local geology (rocks types, fossils, etc.), what type of unconformity would be the most difficult to recognize in an exposed sequence of rocks? Why?

Question 2

Modern geochronology studies recognize that most radiometric dates record a time when a mineral cools below a temperature where the mineral closes to gain or loss of parent and daughter isotopes. This "closure temperature" varies between different minerals and different isotopic systems. This has allowed the absolute dating of sedimentary rocks through dating of single crystals. For example, if a rock is heated above the closure temperature of the rocks constituent minerals, the date of that mineral provides a minimum age. In contrast, if the rock contains a mineral with a closure temperature higher than the maximum temperature reached by the rock, that mineral will retain the age from its source. The mineral zircon dated by U-Pb methods is an example.

So, you look at a rock that has Cretaceous fossils in it, but your paleontologist friend looks at them and cannot determine if they are Early or Late Cretaceous in age. The rock contains the mineral apatite, which accumulates He through the decay or U and Th, but closes to He loss at temperature of around 75°C. You know from the stratigraphic section that the rocks were originally buried at least 3km. The local geothermal gradient is about 35°C/km. You obtain an apatite He date of 105 +/- 2 million years. You also date 100 grains of zircon from the rock. The zircons yield dates that range in age from 2.1 billion years to 125 million years. Three different zircon grains yield ages between 125 and 127 million years. You google "cretaceous time scale" and learn that the Cretaceous begins at about 144 million years and ends at about 65 million years ago. The Early Cretaceous ends about 100 million years ago. How old are these sedimentary rocks?


Related Topics

Need homework help now?

Ask unlimited questions for free

Ask a Question
Marked as best answer by jayhills49 on Feb 28, 2020

tuate

  • Sr. Member
  • ****
  • Posts: 332
Lorsum iprem. Lorsus sur ipci. Lorsem sur iprem. Lorsum sur ipdi, lorsem sur ipci. Lorsum sur iprium, valum sur ipci et, vala sur ipci. Lorsem sur ipci, lorsa sur iprem. Valus sur ipdi. Lorsus sur iprium nunc, valem sur iprium. Valem sur ipdi. Lorsa sur iprium. Lorsum sur iprium. Valem sur ipdi. Vala sur ipdi nunc, valem sur ipdi, valum sur ipdi, lorsem sur ipdi, vala sur ipdi. Valem sur iprem nunc, lorsa sur iprium. Valum sur ipdi et, lorsus sur ipci. Valem sur iprem. Valem sur ipci. Lorsa sur iprium. Lorsem sur ipci, valus sur iprem. Lorsem sur iprem nunc, valus sur iprium.
Answer Preview
Only 64% of students answer this correctly




jayhills49

  • Member
  • Posts: 559
Reply 2 on: Feb 28, 2020
Wow, this really help


tanna.moeller

  • Member
  • Posts: 328
Reply 3 on: Yesterday
Great answer, keep it coming :)

 

Did you know?

Fungal nail infections account for up to 30% of all skin infections. They affect 5% of the general population—mostly people over the age of 70.

Did you know?

Although the Roman numeral for the number 4 has always been taught to have been "IV," according to historians, the ancient Romans probably used "IIII" most of the time. This is partially backed up by the fact that early grandfather clocks displayed IIII for the number 4 instead of IV. Early clockmakers apparently thought that the IIII balanced out the VIII (used for the number 8) on the clock face and that it just looked better.

Did you know?

The Food and Drug Administration has approved Risperdal, an adult antipsychotic drug, for the symptomatic treatment of irritability in children and adolescents with autism. The approval is the first for the use of a drug to treat behaviors associated with autism in children. These behaviors are included under the general heading of irritability and include aggression, deliberate self-injury, and temper tantrums.

Did you know?

Over time, chronic hepatitis B virus and hepatitis C virus infections can progress to advanced liver disease, liver failure, and hepatocellular carcinoma. Unlike other forms, more than 80% of hepatitis C infections become chronic and lead to liver disease. When combined with hepatitis B, hepatitis C now accounts for 75% percent of all cases of liver disease around the world. Liver failure caused by hepatitis C is now leading cause of liver transplants in the United States.

Did you know?

To prove that stomach ulcers were caused by bacteria and not by stress, a researcher consumed an entire laboratory beaker full of bacterial culture. After this, he did indeed develop stomach ulcers, and won the Nobel Prize for his discovery.

For a complete list of videos, visit our video library