The Key-Time-slice series of paleogeographic maps for North America was completed in June, 2013. The maps represent a complete redo of the previous North American series; map size and resolution were increased by nearly twice and new data from the geologic literature were used in map preparation. Their detail and image size make them some of my most detailed maps. The maps were compiled from many sources (see references) and are based on many different tectonic models; numerous compromises between varying models were necessary, especially models of terrane accretion. Particular attention was paid to making sure that tectonic and geologic events between adjacent time slices made geologic, geographic (space issues), and tectonic sense. The 36 time slices mark a reduction from the 90+ maps in the original North American series but this strategy was considered to be a necessity of time as most maps in the new series took 40 – 60 hours each to complete. The time slices average 15 m. y. between maps and only two time slices are more than 20 m. y. apart.
All of the features on the maps are palinspastically restored — that is, the positions of various terranes and blocks are shown in their presumed location during a given time slice. Note that state lines are not deformed, a common method of showing palinspastic restorations in many publication; rather state-county lines are minimized until the time slice at which the terrane arrives at its present location for a given area. Terrane-block motion is shown (restored) relative to the interior stable craton of North America. By not deforming state lines, the paleogeography shows more clearly and without confusing lines. The attached reference list includes all the references used in making all of the maps in the two North American series (SW North America; Key time slices).
- Maps are rasterized pixel images, not shape files (nor are they based on shape files)
- Paleogeographic and paleotectonic elements (thrust belts, volcanic centers, paleo-shorelines, dune fields, basin geometry, facies maps, etc.) are plotted from the geologic literature and redrawn, repositioned, or reprojected on the base maps for the given time slices. This information is then used to construct the paleogeography
- Paleogeography is cloned or painted using Photoshop®; cloned images are mostly from GeoMapApp, a marine geoscience, global topography data system (http://www.geomapapp.org/)
- Cloned modern Earth DEM images from GeoMapApp are selected as modern analogues to the paleo-features they are chosen to represent; most DEM images have been re-colored, resized, and/or re-shaped in Photoshop®
- All map elements, both internal to North America and fringing or exotic, are palinspastically restored to each given time slice using recent data from literature
- Paleoclimate patterns, shown via hues of greens vs browns and tans, are generalized; pre-Siluro-Devonian(> 400 Ma) maps are uniformly drab, reflecting lack of significant continental vegetation
- Paleogeographic map time slices are tied to a given age based on stratigraphic/biostratigraphic correlation. This age is converted to time in millions of years (Ma) before present (thousands – Ka for Pleistocene) using the time scale of Ogg, et al., 2008. The time range given in parentheses suggests an error bar or range of time over which the given map is valid. Not all tectonic and stratigraphic features shown on a given map can be correlated to a given instant or short range of time and the parenthetical ages reflect this uncertainty
Paleogeography of North America – Map Projection Data
Map projection and political boundaries from:
Garrity, C. P., and Soller, D. R., 2009, Database of the map by J. C. Reed, Jr. and others (2005): US Geological Survey data series 424 (DVD)
- Map_Projection_Name: Transverse Mercator
- Scale_Factor_at_Central_Meridian: 0.926000
- Longitude_of_Central_Meridian: -100.000000
- Latitude_of_Projection_Origin: 0.000000