What You Need and
“Things To Be Aware Of”
Park safely uphill and walk down the footpath to GZ. Stay on the
footpath and only cross the road to the rock wall if you are
confident you can do so safely. The co-ords are approximate as you
will have to walk up and down the street - no single spot affords a
perfect view.
Background
Stratigraphy is the branch of geology that is associated
with the study of strata (rock layers). Strata are often
sedimentary in nature - eroded sediment that has been transported
by rivers to lakes or the ocean where the accumulated sediment is
compacted and concreted (lithified) to rock over time. The oldest
layers of rock are the lowest stratum and the youngest are
uppermost. This provides a means for the relative dating of fossils
found within the rock. Volcanic igneous rock can also form strata
where different layers of lava are erupted across the landscape
over time.
Each distinct layer is usually assigned to a "formation" name
usually based on a town, river, mountain, or region where the
formation is exposed or first characterised. In Dunedin we have,
Roslyn dolerite, Leith Valley andesite, Abbotsford mudstone,
Fairfield greensand and Haast schist. Stratigraphic columns are
diagrams used to depict vertical location of rock units or strata
in a particular area. Stratigraphic columns reveal the sequential
formation of sedmentary rocks, igneous lava/magma flows and other
geological events. They are often obtained by drilling core samples
of rock.
A Stratigraphic Column - Thanks:
www.esp.cr.usgs.gov/info/meve/
Logging
Requirements
0. Preface any email with GC2FF19 Stone Street
Stratigraphy in the subject line and title and clearly note the
question number and answer. You don't need to wait for a
confirmation email to log but you might be asked for more info if
your answers are slim.
1. Draw a stratigraphic column of the scene at Stone Street. You
may need to walk up and down the road to appreciate the full
extent. In your column you should show the two main rocks present
and their:
- Names
- Approximate ages
- Approximate thickness
Most Dunedin residents will recognise the upper rock and may
have walked through one of two different tunnels dug through the
lower rock.
Email your stratigraphic column to me at: gcstegan@gmail.com
Bonus question: Which suburb is the lower rock named after? 3
Points.
Key
Sources
MS Nucleus lessons on Stratigraphy
Wikipedia article on Lithostratigraphy
2010 Stegan’s
EarthCache Masters Programme
Since it is not very feasible for many NZers to easily get more
than two states for the earthcache.org masters programme and
therefore not get past Bronze I’m running my own one on a
number of Earthcaches that I plan to release this year (all things
being equal) with the following points system:
5 points: First to find
3 points: 2nd to find
1 point: Logging a find
1-5 points: Special bonus questions.
Shared points for joint finds.
At the end of 2010, I’ll issue certificates for 1st, 2nd
and 3rd and the first place getter will be awarded a geocoin. If I
feel richer and/or it looks like this is popular I’ll upgrade
the prizes.
Updated information and Leaderboard at: Stegan’s
Earthcache Programme