Why choose the Colorado Plateau:

 

Evidence of kilometre scale uplift and subsidence at locations remote from any recognised plate boundaries, the existence of mega-sequences of post-rift marine sediments over widespread intra-cratonic areas, and the consideration that pulses of deposition display a clear periodicity and synchronicity over widely dispersed spatial domains, remain largely unresolved issues within current geological theory. One of the finest demonstrations of the repetitive cycles of deposition, uplift, erosion, and again subsidence can be found within the Colorado Plateau. Due to massive uplift experienced over the past 30 Ma or so, followed by the deep incision of the Colorado River and its tributaries over the past 10Ma, rich layers of sedimentary formations going back at least 1,500 Ma have been revealed. Since these deep sediment formations exposed within the cliffs of the Grand and adjacent canyons display clear cycles of continuous deposition separated by at times massive periods of missing time, during which there was either no deposition or whatever deposition might have occurred has been ground away, they provide an important repository of geological evidence against which any theory purporting to explain these cycles of uplift and subsidence should be gauged.   

 

Grand Canyon showing clearly the remarkably horizontal strata including 

the peneplaination at the upper surface 

With this in mind, the following will reappraise the sedimentary records exposed within the Grand Canyon which, as Sloss^5,6,7 repeatedly pointed out, display clear cycles of deposition and non-deposition reflecting kilometre scale cycles of crustal rise and fall. These cycles of deposition and non-deposition and their associated vertical motions still require explanation. This reappraisal of the phasing of the cycles of subsidence and upheaval, burial and exhumation, will in later posts be related in time with the ice- and hot-house cycles of climate that have occurred at periodicities of circa 130 Ma over at least the Phanerozoic (-540 Ma to present)^8,9. Because any sedimentary records within the Grand Canyon^10,11 have been lost from the early Mesozoic (-270 Ma to present) the evidence from the contiguous region of the Grand Staircase leading up to Bryce Canyon will be used to complete the analysis up to at least -40 Ma.

Paria Badlands Western Grand Staircase (photo by Tim Peterson)

A further reason for choosing the Colorado Plateau is that the extensive studies reported by Sloss^5,6,7 have shown the phasing of the periods of deposition and non-deposition at this location, show strong correlations with the records over widely dispersed regions of the USA. And it might be added with extensive regions on other continents.   

 Cross section illustrating the link between the sedimentary deposits of the Grand Canyon and the Grand Staircase leading up to Bryce Canyon. It graphically illustrates the km scale uplifts that have occurred in the past 40Ma and the erosion of the post -270Ma sediments from the Grand Canyon area.