And Some Concluding Remarks from Colorado Plateau Geology

A reconstruction of the sedimentation records of the Grand Canyon region reveals a strong correlation between the timing of the recommencement of deposition cycles above major unconformities and the transition from global ice-house climates to hot-house. This has been explained in terms of sea level rises accompanying the melting of surface ice. The massive thermal capacity of oceans, their currents, convective mixing and tidal flows provide a more effective heat transfer mechanism for the outflow of geothermal heat energy. An increased geothermal gradient resulting from the rising geothermal heat flux has the effect of thinning the lithosphere, possibly through a process of phase change, re-magmafication, at the lower lithosphere boundary. Increased average density of the lithosphere column will then result in continuing subsidence as sediments are added from above and lower lithosphere is removed. Furthermore, this circa 130 Ma cycle of pulses in sedimentation, in phase with the onset of hot-house climate conditions, appears to be related to similarly timed pulses of uplift and mountain building observed to coincide with the onset of ice-house periods. I will return to this latter process in subsequent posts. 

With hot- and ice-house conditions known to have had global reach also starts to explain the often-noted synchronicity of burial and exhumation events over widely dispersed geographic domains that are often remote from any plate tectonic recognised active tectonic zones. Additionally, the high levels of temperature change at a given crustal depth, associated with the periodic thickening and thinning of crust, will induce massive cycles of horizontal thermal strain and deformations. Restraint, of these thermally induced strains could in turn account for many of the observed fracture patterns during tension cycles or folding and metamorphism during compression cycles.

While the evidence from the Colorado Plateau cannot be regarded as conclusive, it does appear to support a model in which very long-term climate cycles could be providing an important contribution to the clear geological evidence of ups and downs of both continental and oceanic lithosphere. Could this be at least a partial answer to the challenge laid down at the 2017, William Smith Meeting at the Geological Society London?