Tag Archives: Magnetic chrons

Updated geological time scale color palettes

While it has been a little break over the summer on this blog, I have nevertheless been able to make a few updates related to the geological time color palettes (see this link for the original post). I have added the GTS2004 palettes (epochs and ages) and also the SEPM95 timescale. The color palettes (or *.cpt files) are designed for use with the Generic Mapping Tools (GMT) but can also be loaded in GPlates. On cpt-city, other formats are also available:

The gradients on cpt-city are usually available in each of the following file formats:

  • Generic Mapping Tools, GMT (cpt)
  • CSS3 gradients (c3g)
  • GIMP (ggr)
  • Gnuplot palette files (gpf)
  • POV-Ray colour map headers (inc)
  • PaintShop Pro’s native format (having the extension PspGradient), which can also be read by Photoshop (psp)
  • The SAO format DS9 (sao)
  • Scalar vector graphics gradients (svg)

Both palettes are still incomplete and require the extension back in geological time or adding eons or epochs. You can find the files on my BitBucket repository (https://bitbucket.org/chhei/gmt-cpts/). Any contribution to extend the individual files or add new timescales (or formats such as for QGIS) will be greatly appreciated!

The world in (geological) colors

The color palettes I described in my recent post can also be used with GPlates to color loaded features. Here are three examples which use the static polygon dataset which comes with GPlates. The first is using the GTS2012 chronostratigraphic time scale to color the static polygons by epoch and fill the polygons:

The world colored by geological epoch.

The world colored by geological epoch, filling the static polygons.

The second is just using the same data set and color the line features by geological era:

Coloring the polygons by era in GTS2012 colors.

Coloring the polygons by era in GTS2012 colors.

And the last is a bit Bauhaus-y by coloring everything in black and white according to the Gee & Kent geomagnetic polarity time scale (not that this would make a lot of sense, but as we can do it…):

The world in normal polarity and reverse polarity according to the Gee & Kent geomagnetic polarity timescale.

The world in normal polarity and reverse polarity according to the Gee & Kent geomagnetic polarity timescale (using the filled static polygons).

That planet looks way to boring -  hemispherical view of the Earth colored according to a normal (white) and reverse (black) geomagnetic polarity. Again using the Gee & Kent 2007 timescale.

That planet looks way to boring – hemispherical view of the Earth with the static polygons colored according to a normal (white) and reverse (black) geomagnetic polarity. Again using the Gee & Kent 2007 timescale.

In order to color loaded features by age (and timescale) just add the colorpalettes to the “Draw style” settings (Features -> Manage colouring) like this:

The geological age color palettes can be added to the Draw style (Manage colouring).

The geological age color palettes can be added to the Draw style (Manage colouring).

Once the new colour palettes are available, they can be assigned to the individual layers either through the layer window or through “Features -> “Manage colouring” .

Geological colors

Making maps with GMT is fun (well, some might argue…), what is not fun is to find color palettes for GMT (*.cpt files) which have the “official” colors for geological time periods coded up against absolute ages as proposed by various geological time scales. The International Commission on Stratigraphy has all their time scales on their webpage, downloadable as PDF files. The different stages are assigned color values according to what apparently the Commission for the Geological Map of the World (CGMW) has proposed. At some stage they even produced a PDF which had both, RGB and CMYK color values for the different subdivisions of the time scale (could not find this anymore when I recently searched for it), but now they only have a giant image on their website which specifies the color assignment.

Such a color assignment is very helpful if you want to make maps in vectorgraphics illustrations by hand and you only have a few polygons to color in. It becomes a massive pain, however, if you want to automate map making, for example, when generating a sequence of paleo-tectonic maps using GMT. So what is needed here is to have that color information not locked up in an image file or as unstructured text, but rather as data file where an RGB value is assigned to a stage/period/eon (as categorical color palette) so that one can use this information in other applications – such as GMT or GPlates, but potentially also QGIS or ArcGIS or Inkscape/GIMP/Photoshop.

The same goes for information about magnetic polarity chrons which are used in plate tectonic reconstructions – a simple assignment of normal/reverse magnetisation to either white or black colors using a certain geomagnetic polarity timescale.

Here are some examples of how the color scales look like when plotted with GMT’s psscale:

GTS 2012 - Eons

GTS 2012 – Eons

GTS 2012 - Eras

GTS 2012 – Eras

GTS 2012 - stages

GTS 2012 – stages

And the geomag timescale plotted is here:

Snapshot of Gee and Kent (2007) magnetic polarities plotted using the GeeK07.cpt file

Snapshot of Gee and Kent (2007) magnetic polarities plotted using the GeeK07.cpt file

I have made a set of CPT files (available as Git repository on my BitBucket site) for the GTS 2012, GTS 2004, and Exxon 88 geological time scales as well as the Gee and Kent (2007) geomagnetic polarity time scale. The files are available under a Creative Commons Share-Alike Attribution License. A zip archive of the data can be downloaded directly through this link. The files should also be incorporated into the fantastic CPT-CITY website over the next weeks.

If you feel like contributing to this work, just fork the Git repository or send me text snippets for the color scales by email.