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!

Rift migration and asymmetric continental margins

Yesterday, our paper on rift migration and formation of asymmetric continental margins was published in Nature Communications. Using high resolution forward numerical models we investigate the influence of extension velocities on the evolution of continental rifts to passive margins. We find a strong correlation between margin width, asymmetry and extension velocity, illustrated by the conjugate South Atlantic passive margins. Our models can explain the highly asymmetric and hyperextended passive continental margins, further, we propose that large amounts of crustal material during the rift migration phase are transferred from one side of the rift to the other, challenging conventional ideas about passive margin formation. This means that large parts of the outer margins off West Africa could actually be composed of crustal material originating from the conjugate Brazilian margin.

(a–e) Fault kinematics of the model. Active faults are shown in red and inactive faults in black. Brittle faults are indicated with solid lines, ductile shear zones with dashed lines. The wide margin is formed through rift migration and sequentially active faulting towards the future ocean. Hence, thick undisturbed pre-salt sediments pre-dating break-up are predicted by our model to be deposited in the landward part of the margin (d,e). The final crustal structure of the model reproduces the strong asymmetry (f) of the conjugate Campos Basin–Angola margins (modified after ref. 5). Note that the geosection is drawn without vertical exaggeration at the same scale as the model (scale bar in the lower right corner is 50 km long). Vertical scale is in seconds two-way travel time (TWT). Source: Brune, Heine, Perez-Gussinye & Sobolev, Nature Communications (http://www.nature.com/ncomms/2014/140606/ncomms5014/full/ncomms5014.html), licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License (http://creativecommons.org/licenses/by-nc-nd/3.0/).

The GFZ Potsdam has also issued a press release related to this [in German].

Citation: Sascha Brune, Christian Heine, Marta Pérez-Gussinyé & Stephan V. Sobolev, 2014, “Rift migration explains continental margin asymmetry and crustal hyper-extension”, Nature Communications, 5, doi: 10.1038/ncomms5014. The paper is openly accessible, licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Update 1 (2014-06-11):

Nature Comms’ Article metrics are a pretty cool indicator for immediate online impact (and I believe future citations). By now a few of the standard science news outlets have picked up the press releases (changing by the minute. Here’s a static (and human) collection of the news around the article (including some of the Altmetric links):

Continents breaking apart

Watch this space for a new paper on the formation of hyperextended margins which should be out in the next week or two. Below a photo from the Gulf of Suez (Hamman Faraun fault block north of Abu Zenima) taken during a field trip a few years back, which illustrates how a continental rift looks like just before continents break apart.

Overview map of the Gulf of Suez (GeoMapApp) with location (red circle) and view direction (red arrow) of the photo below.

Overview map with hillshade relief of the Gulf of Suez region (GeoMapApp) with location (red circle) and view direction (red arrow) of the photo below.

 

A view of the northern Gulf of Suez looking northwest from the Sinai margin towards the African margin. Picture licensed under a Creative Commons Attribution-Share Alike 3.0 license.

A view of the northern Gulf of Suez looking northwest from the Sinai  towards the African margin. This is how the very young South Atlantic could have looked like in the Cretaceous. The photo is taken from the Hamman Faraun fault block north of Abu Zenima (Openstreetmap link) . Picture licensed under a Creative Commons Attribution-Share Alike 3.0 license.

The Saharan Atlantic ocean makes ripples (edited)

Our  “Saharan Atlantic ocean” paper has just been featured in GEOLOGY’s “Research Focus” article in the March issue. The focus article is entitled “Roadmap to continental rupture: Is obliquity the route to success?” is written by Cythia Ebinger and Jolante van Wijk and is available as open access. This is fantastic news!

Update #1,2,3,4,5: So by now, there’s been quite some science (and popular) media buzz with both Sydney Uni and GFZ Potsdam having released press info on our article – it’s been overwhelming. Spiegel Online (one of the largest German online news outlets) & Sueddeutsche Zeitung (also one of the largest papers) reported in Germany even going a bit beyond the standard press release texts. As Sascha and I hoped, our hypothetical “Saharan Ocean” image (see here) facilitated the take up of the story quite a bit.

According to Altmetric, the article is currently ranking as #7 in terms of impact which makes it one of the highest ever scores for articles published in GEOLOGY.

Links here (I’m updating those from time to time):

Why there is no Saharan Atlantic Ocean

Our paper “Oblique rifting along the Equatorial Atlantic ocean: Why there is no Saharan Atlantic Ocean” (Doi: 10.1130/G35082.1) is now available online, I believe a pre-issue publication listing will follow this week. We use plate kinematic and 3D numerical modelling to explain why the Equatorial Atlantic ocean formed in the Early Cretaceous time (around 120-100 Million years ago). Here’s a summary of the paper in simple terms:

Every schoolchild can recognise continents or parts of them based on their shape. But why does Italy look like a boot, why is Australia an island-like continent and what sculpted Africa’s margins? In this study we address the underlying processes that shaped Earth’s continental plates when the last era of supercontinents came to an end, between about 150 and 100 My years ago.

At the time when dinosaur evolution peaked, the southern continents were still united in the supercontinent Gondwana. However, vast continental rift systems comparable to the present East African rift, extended between present-day South America and Africa as well as within the African continent. These rifts are preserved as deep sedimentary basins in the subsurface of the African continent and along continental margins and document processes where continental crust is stretched like chewing gum. The so-called South Atlantic and West African rift systems were about to split the African-South American part of Gondwana North-South into nearly equal halfs, generating a South Atlantic and a Saharan Atlantic Ocean (see Image). In a dramatic plate tectonic twist, however, a competing rift along the present-day South American and African Equatorial Atlantic margins, won over the West African rift, causing it to become extinct, avoiding the break up of the African continent and the formation of a Saharan Atlantic ocean.

Our work elucidates the reasons behind the success and failure of these rift systems by coupling plate tectonic and advanced 3D numerical models of continental lithosphere deformation. We find that rift obliquity acts as a selector between successful and aborted rift systems, explaining why the South and Equatorial Atlantic Ocean basins formed and other rifts became aborted. Our modelling also sheds lights on the dynamics of rifting, suggesting that feedback loops caused a ten-fold acceleration in the velocities of the South American plate once the Equatorial Rift System had sufficiently weakened the last remaining continental bridge between both plates.

One hundred years after the German scientist Alfred Wegener developed first ideas of continental drift, this study provides a new keystone in understanding the rules which govern continental extension and tectonic plate motion ultimately sculpting Earth’s continents into the shapes as we recognise them today.

The  abstract of the paper:

Rifting between large continental plates results in either continental breakup and the formation of conjugate passive margins, or rift abandonment and a set of aborted rift basins. The nonlinear interaction between key parameters such as plate boundary configuration, lithospheric architecture, and extension geometry determines the dynamics of rift evolution and ultimately selects between successful or failed rifts. In an attempt to evaluate and quantify the contribution of the rift geometry, we analyze the Early Cretaceous extension between Africa and South America that was preceded by ∼20–30 m.y. of extensive intracontinental rifting prior to the final separation between the two plates. While the South Atlantic and Equatorial Atlantic conjugate passive margins continued into seafloor-spreading mode, forming the South Atlantic Ocean basin, Cretaceous African intraplate rifts eventually failed soon after South America broke away from Africa. We investigate the spatiotemporal dynamics of rifting in these domains through a joint plate kinematic and three-dimensional forward numerical modeling approach, addressing (1) the dynamic competition of Atlantic and African extensional systems, (2) two-stage kinematics of the South Atlantic Rift System, and (3) the acceleration of the South America plate prior to final breakup. Oblique rifts are mechanically favored because they require both less strain and less force in order to reach the plastic yield limit. This implies that rift obliquity can act as selector between successful ocean basin formation and failed rifts, explaining the success of the highly oblique Equatorial Atlantic rift and ultimately inhibiting the formation of a Saharan Atlantic Ocean. We suggest that thinning of the last continental connection between Africa and South America produced a severe strength-velocity feedback responsible for the observed increase in South America plate velocity.

The associated data for the plate kinematic model is available full and for free as open data from the Datahub.org pages (http://datahub.io/dataset/southatlanticrift) of my earlier South Atlantic paper in Solid-Earth.net. More detailed explanations and animations will follow later.

Lastly, here’s our guess for how the world might look liked like if a Saharan Atlantic ocean had formed:

The world as it might have looked like if the West African Rift system had been "successful" in forming a "Saharan Atlantic Ocean basin". We explain in our paper why this did not happen.

The world as it might have looked like if the West African Rift system had been “successful” in forming a “Saharan Atlantic Ocean basin”. We explain in our paper why this did not happen. Made with GPlates and image manipulation.

Working with plate velocities in GPlates

GPlates v1.3 can display and extract plate velocities. Depending on your work, you might have different requirements for these domains, plus there are a few pitfalls on the way. Currently, there are two three  ways to create velocity domains in GPlates:

  1. Create a global set of points at regular spacing which stay fixed absolute and the plates move across them. This method will report velocities of whatever plate will be on top of these points. This method is generally used when working with global models and when one wants to export boundary conditions for global geodynamic modelling (the CitcomS and Terra mesh generation options). Use  Features → Generate Velocity Point Domains to create a velocity domain setup according to your needs. Note that this also allows to create a regular spaced lon/lat grid of distributed points. The features are gpml:MeshNode features in the GPlates Geological Information Model.

    Adding a global layer of velocity domain points using GPlates' built-in function

    Adding a global layer of velocity domain points using GPlates’ built-in function

  2. Alternatively, you can just go and create a set of points wherever you require them – you might have a few small plates which fall through the cracks when creating the global velocity domains. So here, you just go and create a few point features, assigning them the right properties in the ‘Create Feature’ dialogue. Create and save the layer after you are done. You can automatically assign PlateIDs using GPlates’ cookie-cutting tool afterwards which saves you typing in PlateIDs manually.

    Manually creating a point feature collection where velocities are to be extraced

    Manually creating a point feature collection where velocities are to be extracted

  3. Use QGIS and the Vector toolbox to create a regular spaced point grid in OGR Vector format (ESRI Shapefile, OGR GMT etc) and load that into GPlates, cookie-cut – or rather – assign plate ids and there is a regional, regular-spaced point set which you can use as velocity domains.

    Creating a regular spaced point grid to be used as velocity domain, using QGIS.

    Creating a regular spaced point grid to be used as velocity domain, using QGIS.

One important thing to know is that GPlates utilises layers for different types of data, so here’s a little digression and some background info. This layer business is much like GIS software has vector and raster layers, and other layers which are the result of some computations/combination of other layers – or like image manipulation applications like GIMP or Photoshop. The following layer types exist in GPlates (n.b. ideally a detailed overview of the layers with examples should follow here but currently there is no time, I suppose this might be found in the GPlates documentation somewhere):

  • ReconstructionTree: Rotation files/models are automagically assigned to the yellow layer.
  • ReconstructedGeometries: Essentially all feature data one works with gets stuffed into the green layer type. Shapefiles, standard GPML files (not topologies), OGR GMT files all belong to this layer type.
  • Co-registration: Features related to data mining and association checks are combined in this layer type. This is one example where a layer does not correspond directly to a feature collection (ie a single file on disk). Instead, the user selects a set of seed points (a feature collection) and target geometries/rasters (another feature collection/raster) to generate a new data type.
  • Calculated velocity fields: Another one of of those layers where the layer=feature collection equation breaks down. Here we load a point feature collection and combine it with other data such as topological polygons or static polygons to compute velocities.
  • Resolved topologial networks:   This (brown) layer type is similar to the topological geometries but creates triangulated networks used for deformation.
  • Resolved topological geometries: Topologically closed polygons are created from the combination of a rotation file (ReconstructionTree) and a feature layer (ReconstructedGeometries).
  • Reconstructed Raster: Raster data gets loaded into the red layer type.
  • 3D scalar field: Volume-rendering of scalar fields as, for example, from seismic tomography

Now that this is sorted, let’s generate some velocity fields.

After completing either of those steps above you should have a point layer from which you can now extract velocities. Depending on the way you created these points, the steps to display velocities might differ a bit.

Generating plate velocity vectors:

  1. Create a global velocity domain layer using (1) from above or create your velocity points using method 2 or 3 from above.
  2. Once you have created the velocity domain layer using option (1), GPlates will automatically load a new feature layer with the name of velocity point layer as you specified. If you have  used the “Latitude Longitude” option in GPlates, your default layer name will be something like lat_lon_velocity_domain_SomeIntegervalue and have a green color in the layer window (the ReconstructedGeometry layer). In addition, GPlates will create a aqua turquoise colored layer (the “Calculated Velocity Fields” layer) with the same name. That is where ze aktion happens.
  3. Creating a global velocity domain layer will automagically create a "ReconstructableFeature" layer (green) and a "Calculated Velocity Fields" layer (turquoise) - see arrows. Above, the different layer types are displayed from the drop-down menu.

    Creating a global velocity domain layer will automagically create a “ReconstructableFeature” layer (green) and a “Calculated Velocity Fields” layer (turquoise) – see arrows. Above, the different layer types are displayed from the drop-down menu.

  4. The next thing you need is either a static polygon feature collection set or a topologically closed polygon feature collection and of course a rotation model loaded. The next steps will illustrate why.
  5. Only if you have created your point velocity domain layer manually): Add a new blank “Calculated Velocity Fields” layer throug clicking the big at the top of the layer window.
  6. The key now is to connect the Velocity layer with other feature data. This can be a global polygon data set or a set of static polygons. Open the aqua-colored layer by clicking the little triangle on the left and  under the “Inputs” category you see the headings “Velocity domains” (and your generated velocity domain reconstructable geometry layer is already connected to this. If it is not connected, you need to add it here. This is  the case where you created it manually. Under the “Velocity surfaces” heading, click on the “Add new connection”  field and select the polygon data. If one is set to export velocity boundary conditions for geodynamic modelling this of course requires continuously closed polygons, covering the surface of the Earth at any reconstruction time. Such topologically closed polygon data is provided on the EarthByte website. If you are working regionally, just select whatever polygon feature collection you are working with.
    The "Calculated Velocity Fields" layer unfolded.

    The “Calculated Velocity Fields” layer unfolded.

    Adding regional polygons as surfaces for the velocity calculations

    Adding regional polygons as surfaces for the velocity calculations

  7. In the case that you are using global velocity domain points and polygons, make sure that in the “Velocity and Interpolation options” section,  Calculate velocities is set to “of surfaces” . If you have a set of points that are assigned plate ids, one would want to set this to “of domain points”.
  8. Once you have connected your surface domains with your velocity domains, you should see velocity vectors displayed in the main window. The settings for the vector display can be altered in the layer dialogue.

    Screenshot showing calculated velocities at a set of global domain points. Note that velocities are only displayed where surface polygons overlap with the points.

    Screenshot showing calculated velocities at a set of global domain points. Note that velocities are only displayed where surface polygons overlap with the points.

  9. If needed these vectors can be exported using the “Export…” function under the “Reconstruction” menu in a wide flavour of formats.

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” .