Class Notes (1,100,000)
CA (650,000)
UTSC (30,000)
EESA06H3 (600)
Lecture 9

EESA06H3 Lecture 9: Geologic Time

Environmental Science
Course Code
Nick Eyles

This preview shows page 1. to view the full 4 pages of the document.
Lecture 9 Geologic Time
Strata, the rocks are formed in layers at different geologic time, with the oldest layers at the bottom and the
youngest on top, therefore establishing relative age. In this case, it is quite simple to distinguish the relative ages
because it is in conformable succession
Stratigraphy, a branch of geology concerned with the study of rock layers and layering
Comfortable succession, when layers of rocks are deposited in a continuous succession through time without any
significant break in deposition they are conformable
Unconformable succession (U), deposition is interrupted or there is an episode of erosion between deposition then
the boundary between the older and younger rocks is unconformable, in essence part of the geologic record is
whereas going to other part of the world with tectonics, the rock layers were being bent, folded, turned upside
down something, increasing the difficulty in the establishment of the relative age although with the same
principle because the process of accommodation is being interrupted, leaving gaps In between
The gaps, called unconformity, can then be filled in by searching for other places with a complete
Unconformities are being formed during the episodes of uplift, erosion and non-deposition
o Angular unconformity, is when the unconformity layer is at an angle to the conformable succession
Disconformities (D), sedimentations are not continuous, there can be big storms, or climate change that interrupt the
process of sedimentations for a shorter period of time, they are small pauses of sedimentations
Some of the successions can have more gaps missing than there are sedimentation records preserved, this is
not uncommon
Therefore it is extremely rare to have completely continuous records no matter where you are in the world
Absolute age, is where the guess comes in with the knowledge of chemistry and physics, along with radiometric
age dating
Accommodation, rocks, particularly sedimentary rocks, cannot be formed unless there are some places where they
can accommodate sediments. Creating the space where the sediments can be deposited, ultimately preserving the
sedimentary rocks with all the fossils contained within
A lot of the places on the surfaces are sites of erosion, this is because they are high standing, subjected to
erosion by wind, water, ice and chemically; producing sediments
Accommodation has the sediments accumulate, they are transforming into the basins for seas and oceans after
billion of years but only when the basin is subsiding, usually at the same rate to the sedimentary rate
Index fossils, fossils used to define and identify geologic periods. Index fossils must have a short vertical range,
wide geographic distribution and rapid evolutionary trends.
Index fossils are usually the organisms that was not around for very long or else they would not be accurate in
dictating the geologic time
There are usually fossils contained within the sedimentary rocks, the remains of the past organisms.
o Crinoids, and trilobite are the two most common fossils; the stem of the crinoids tend to break up, end
up in the bioclastic sedimentary rocks
o Ammonites, are the best index fossils, they are older than 200 mya, the age of Jurassic time
o Bony fish, one of the earliest fish being evolved
You're Reading a Preview

Unlock to view full version