References used in Mass Extinction Posts

Veizer, J. et alia. (2000): Evidence for Decoupling of Atmospheric CO2 and Global Climate During the Phanerozoic eon. Nature, 408, 698-701.

Shaviv, N. J. and Veizer, J. (2003): Celestial Driver of Phanerozoic Climate? GSA Today, July, 4-10.

Hallam, A. (1998): Mass Extinctions in Phanerozoic Time. In Grady, M. M. et alia (ed) Meteorites: Flux with Time and Impact Effects. Geol Soc. London, Special Publication, 140, 259-274.

Alvarez, L. W. (1980): Extraterrestrial Cause for the Cretaceous-Tertiary Extinction. Science, 208, 1095-1108.

Raup, D. M. (1992): Large-body Impact and Extinction in the Phanerozoic,#. Paleobiology, 18. 80-88.

Matthew, E. C. et al (2019): Flood Basalts and Mass Extinctions. Annu. Rev. Earth Planet Sci. 47, 275-303

 

 

Relating Mass Extinction Events to Phanerozoic Climate Cycles

 

As current climate concerns recognise, it is likely that both faunal and floral life will experience considerable environment stress during periods of rapid climate change. So perhaps the observed sudden changes in the fossil records that came to form the basis of the geological period boundaries could have at least a part of their explanation in terms of these correlations with the rates of change in the climate.      

This suggests that high rates of climate changes might also be a contributing cause of the observed “mass extinction events” (MEE). A reasonably well supported summary of the recorded MEE is provided in Figure 2, adapted from the entry in Wikipedia. This shows the percentage extinctions of readily fossilized marine genera (these are the ones that have hard calcite shells). Especially over the past 300 Ma, where the fossil records are a little more complete, the relationship is quite uncanny. For example, the three most extreme MEE occur at: -250 Ma which falls on the Permian-Triassic boundary (P/T); -200 Ma on the Triassic-Jurassic boundary (T/J); -66 Ma on the Cretaceous-Paleogene boundary (K/Pg) – all associated with very rapid (in geological terms) decreases in Earth temperature. Even the relatively minor MEE at -150 Ma corresponds with the Jurassic-Cretaceous (J/K); and near the -35 Ma the Paleogene-Neogene (Pg/N) boundary.

Earlier MME are a little more difficult to separate but the well recorded events at: -445 Ma (O/S) is very close to the Ordovician-Silurian boundary; and -485 Ma (Cm/O) close to the Cambrian-Ordovician boundary; the -500 Ma and -520 Ma events occur either side of the Cambrian-Ordovician boundary

Fig 2 The percentage extinctions of readily fossilized marine genera (vertical axis) shown by the vertical blue bar chart related to the geological period boundaries over the phanerozoic eon.

One of the commonly advanced explanations for MEE events has been sudden drops in sea level – regression events. And noting that one of the primary drivers for drops in sea level is the indirect sucking-up of sea water into the ice sheets and permafrost, that characterise periods of icehouse climate, it might be anticipated that the periods at which Earth climate is experiencing rapid temperature reduction as it moves into an ice-house period would fall into this category, including - the Cm/O, D/C, P/T, T/J, K/Pg MEE. It is interesting to observe that in his discussion of mass extinctions, Hallam (1998) attributed a significant cause for Newell’s six MEE to sea level regression at each of the Cm/O, O/S, D/C, P/T, T/J, K/Pg MEE (see Fig 5 Hallam (1998). With the exception of the O/S MEE at -450Ma these assessments agree. However, the O/S MEE, along with the C/P. J/K Pg/N can be seen in Fig 3 to all occur at periods when Earth temperature is experienceing sudden drops. All of this suggests a very strong possibility that sudden and extreme climate change could have been responsible for most of the observed MEE over the past 500Ma.  

 There have been several other explanations for MEE in the past. There is some evidence of a strong correlation between recorded flood basalt eruptions and at least some of the periods when MEE occur. For example, the widespread MEE recorded at the P/T (-250 Ma) and T/J (-200 Ma) and K/Pg (-66 Ma) boundaries all coincided with times when massive flood basalt events occurred (see Matthews et al 2019) usually creating large igneous provinces. As discussed in earlier posts (ref needed), periods of rapid cooling of the lithosphere, occurring for example when climate moves from hot-house conditions to ice-house, would be expected to increase the predominance of tension induced thermal fractures of the lithosphere and the often associated release of magma through volcanism and release of flood basalts. And of course it is at these times that sea level regressions will be at their extreme linking both the regression and flood basalt explanations to their underlying cause from major changes of climate.  

Another possible cause, discussed by Alvarez et al (1980), is that of bolide impact events. It is generally accepted that the only credible possibility of a bolide impact being the cause is that of the K/Pg event, but even that is ambiguous (Raup 1991) so that Bolide impacts are generally dismissed as likely explanations - See Hallam,(1998). 

      

Fig 3. Summarises the links between MEE, the geological period boundaries and their possible unified causal link to periods of rapid climate change.

In the posts relating to the evidence for the Colorado Plateau, I concentrated upon the moments in time at which regions of the Earth's surface experienced a renewed pulse of sedimentation. This provided a fairly precise time signal at which a possibly very long periods of missing time, a so called unconformity, came to an end. Over what would have been very long periods when fossil bearing sediments were eroded during these unconformity missing times, starts to expain why so many of the recorded MEE seem to correspond with the transitions from hot-house to ice-house conditions. Perhaps some of these may have been rather slower extinctions of species than the step functions of Figure 2 suggest!   

Relating Mass Extinction Events to Phanerozoic Geological Period Boundaries

 

What I have noticed while thinking about Phanerozoic climate cycles, in the context of vertical tectonics, is the interesting correlation between Earth climate and the times that have been adopted by geologists to mark the transition from one geological period to the next. These correlations seem to relate to periods when Earth climate is experiencing a rapid transition from icehouse to hothouse conditions and vice-versa. There also seem to be some correlations between the periods when Earth climate is experiencing extreme heat or extreme cold, although in most cases a more sensitive measure of time varying climate shows these generally involve short bursts of very rapid climate change. On reflection, there is some logic in an expectation that many species of flora and fauna will find it difficult to adapt to major changes in their natural environments, occasioned by rapidly changing climatic conditions. And given that it is the sudden changes in the nature of the fossil records, observed in differing locations over the Earth, that have been used to define these period boundaries, there would be a reasonable expectation for a correlation to exist between climate cycles and the geological period boundaries.  

These correlations can be seen in Fig 1. The proxies for climatic conditions have been taken from Veizer et al (2000). The various curves show data from the oxygen isotope analysis of fossil calcite marine deposits at varying levels of time sensitivity, allowing the ocean temperatures to be estimated at the time of deposition. For example, the light green curve marked as 5/10 indicates sampling window of 5 Ma that are averaged over a 10 Ma period. Using the abbreviated period boundaries, so that Cm/O indicates the boundary between the Cambrian and Ordovician periods at -485 Ma, it can be seen from Fig 1 that Earth climate is emerging from an extended period of hothouse conditions into icehouse conditions at each of the Cm/O, D/C, T/J, and K/Pg period boundaries. Most of the other period boundaries during the Phanerozoic can be seen to occur at times of rapid change in climate during either a hot-house or ice-house period. For example, the P/Tr boundary relates to very rapid decreases in temperature during the late-Paleozoic hothouse climate conditions. The O/S boundary lies at a point in time when temperature decreases suddenly during the mid-Paleozoic icehouse climate conditions - it is also a time of massive decreased temperature. Similarly, the J/K transition is associated with some sharp swings in Earth temperature during the mid-Mesozoic icehouse conditions. Note, the periods when Earth is experiencing ice-house climate connditions are shown by the blue bars at the top.      

Fig 1 plotting climate cycles and geological periods based upon an adaptation of Veizer’s Fig 1 (Nature 408, 698-701, 2000) correlating geological period boundaries with rapid changes in Earth climate. See text for details. The light blue shading indicastes periods and paleolatidudes of ice rafted debris during period when ice sheets existyed at the poles. The purple shading represenrts the frequency histogrammes of other glacial deposits.  

References in Analysis of Colorado Plateau Geology

1. William Smith Meeting 2017: Plate Tectonics at 50, Geological Society London, 3 October, 2017. https://www.geolsoc.org.uk/wsmith17 
2. Green, P et alia (2017) Kilometre-scale burial and exhumation of passive margins and continental interiors: an overlooked consequence of plate tectonics? Paper presented in session 8, William Smith Meeting 2017: Plate Tectonics at 50, Geological Society London, 3 October, 2017
3. Green, P et alia. 2018 Post-breakup burial and exhumation of passive continental margins:Seven propositions to inform geodynamic models, Gondwana Research, 53 (2018), 58–81.

4. Hutton, J (1795) Theory of the Earth, vol. 1, Edinburgh.
5. Sloss, LL, Krumbein, WC, Dapples, EC (1949) Integrated facies analysis, appearing in Longwell, CR, Sedimentary facies in geological history, GSA Bulletin, 39, 91-124.
6. Sloss, LL (1963) Sequences in the cratonic interior of North America, GSA Bulletin, 74, 93-114.
7. Sloss, LL (1964) Tectonic Cycles of the North American Craton, in Symposium on cyclic sedimentation: Kansas Geological Survey, ed. Merriam, D. F., Bulletin 169, 449-459.
8. Shaviv, N. J. and Veizer, J. (2003): Celestial driver of Phanerozoic climate? GSA Today, July, 4-10.
9. Shaviv, N. J. (2002): The spiral structure of the milky way, cosmic rays, and ice age epochs on Earth, New Astronomy, 8, 39-77.
10. Beus, S. S. and Morales, M. (ed) (2003) Grand Canyon geology, NY: Oxford University Press, 2^nd Edition, see contributions from Beus, S. S., Blakey, R. C. et alia.
11. Timmins, J. M. and Karlstrom, K. E. (ed) (2012) Grand Canyon geology: Two biion years of Earth’s history, GSA Special Paper 489, see contributions from Blakey, R. C., Middleton, L. T., Timmons, J. M., Karlstrom, K. E. et alia.   
12. Sprinkel, D. A., Chidsey, D. C., Anderson, P. B. (ed) (2003) Geology of Utah’s parks and monuments. Utah Geological Association Publication 28, 2^nd Ed., see paper by Sprinkel, D. A.    
13. Croll, J. G. A. (2007): A new hypothesis for Earth lithosphere evolution, New Concepts in Global tectonics, Newsletter, 45, December 34-51.
14. Croll, J G A (2011) Some Comments on Lithosphere Evolution, paper presented at Frontiers Meeting, Geological Society London, 14 November, 2011.
15. Illis, B. (2009): Searching the Paleo Climate record for estimated correlations: temperature CO2 and sea level, see Kalenda et al..  
16. Kalenda, P, Neumann et al. (2011) Tilts, global tectonics and earthquake prediction, research monograph, in press.

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?  

Some Further Comments on what the Colorado Plateau Tells Us

The most recent posts have been based upon the rejected paper submitted to what was a new publication venture by UCL in 2019. This paper attempted to use the fascinating geology exposed within the canyons and the geomorphology of the Colorado Plateau and contiguous areas to assess whether a hypothesised mechanism for explaining the well recognised and often massive rises and falls of continental and oceanic lithosphere might have any relevance. This afterall is an area of geology that seems to be very poorly covered within the current prevailing paradigm of plate tectonics. And as noted at the start of this new burst of blogging activity, these posts, like the paper on which they have been derived, have concentrated on the sedimentary sequences of the Grand and Bryce Canyon areas simply because they are so clearly exposed and thoroughly researched. Furthermore, as the stratigraphic geometry shown in Fig 4 of the 8^th August post seems to demonstrate, the Grand Canyon area in particular has recently, and certainly post hypothesised "breakup", been subject to major uplift and what on the face of it seem to be ice sheet erosions. Earlier sequence stratigraphy also suggests that this area has been subject to repeated cycles of ice- and hot-house climate cycles and consequently what appears to be a direct correlation of tectonic activity and climate. But clearly the massive erosion occurring during the ice-house phases must produce in contiguous areas equally massive accumulations of ice erosion deposits, suggesting a counter-phasing of deposition in areas contiguous with those directly affected by the growth of ice-sheets – and of course vice versa during the erosion of possibly uplifted areas during hot-house climatic conditions.   

From the direct evidence of the Grand Canyon, along with the reported synchronicity over craton-wide and even continent-wide areas noted by Sloss and others, there appears to be strong evidence of a causal link between cycles of uplift and erosion during ice-house global climate, and subsidence and deposition during hot-house climatic conditions. It is therefore surprising that the thermo-geodynamics underpinning these links have not been more thoroughly investigated. If as suggested there is a causal link between at least vertical tectonics and global climate cycles this could significantly add to our ability to explain other important aspects of global tectonics. As opined at the 2017 meeting at the Geological Society of London the current version of the mobilist concepts do not adequately explain the all too clear evidence within the Colorado Plateau of cyclic ups and downs of the lithosphere. Nor do these concepts account for the seemingly strong evidence that these ups and downs seem to occur in a regular cyclic pattern. Changing climatic domains exposed within the sedimentary record are currently accounted for by invoking major latitudinal movements of continents. By looking at Earth climate records it seems clear that these records can be equally accounted for without the need to move continents around quite so much!

Fig 12. Crossection covering the area between Brian Head and the Grand Canyon. 

Horizontal scale 20 times verttical scale to emphasise vertical tectonic motions.  

Fig 12 is a redrawn cross-section linking the relatively high point at Brian Head down through the Grand Staircase to the incision of the Grand Canyon created by the recent (geologically speaking) erosion by the Colorado River. The vertical scale is exaggerated by around 20 fold relative to the horizontal scale to emphasise some of the important tectonic features. First, is the massive regional uplift of the sedimentary sequences covering the 500 Ma from the Cambrian sequences of the Tonto Group (-525 Ma) through to the residual late Mesozoic sequences of the Grand Staircase (-40 Ma). Not shown clearly at the left of the Brian Head is a steeply sloping fault within which the sedimentary sequences beneath Brian Head have been uplifted by around 2 km relative to the matching sequences to the left (name?). Furthermore, at some time after -40 Ma the post Cambrian sequences in the Grand Canyon area have been domed-up by as much as 2.2 km relative to the area beneath Brian Head. Whatever induced these post -40 Ma massive relative motions clearly involved tremendous tectonic forces. It is worth noting that this 4 km depth of sediments would have been laid down horizontally and remained so up to some time after -40 Ma when a process of erosion kicked-in.

Geothermal Mechanism for Epeirogenic Uplift

Previous studies have noted the close link between periods of mountain building with climate cycles^14,15,16. Recorded periods of mountain building¹³ are summarised by the bar charts at the top of Fig 9. The 4 recorded periods of widespread mountain building during the Phanerozoic, often occurring synchronously over widely dispersed geographical domains, are shown to correspond closely with the periods of ice-house climate conditions. Tentative explanations for how ice-house conditions could result in spurts of uplift required for mountain building and subsequent erosion have again focused on how changes in surface disposition of ice and water could influence the rate of geothermal heat loss as expressed by the geothermal flux^13,14. Reductions in the geothermal heat flux caused by the insulating effects of the development of deep surface ice sheets and permafrost would result in a lowering of the geothermal gradient and a concomitant increase in lithosphere thickness brought about by aggradation, due to phase change at the lower lithosphere-mantle boundary. Associated reductions in average density within the lithosphere and mantle could then be expected to result in regional uplift of the crust. This is summarised in Fig 11.

                   (a)                                  (b)                                  (c)      

Fig 11 Mechanism for epeirogenic uplift and sediment erosion based upon (a) the high geothermal gradient due to high heat flux into the overlying ocean during hot-house conditions which with (b) the development of thick ice-sheets and permafrost after transition to ice-house climate reduces the geothermal heat flux which over a few Ma (c) readjusts to a lower geothermal gradient and increased crustal thickness through aggradation of lower crust while crust continues to rise during ice erosion. 

 A variant and perhaps more prevalent situation than that of the above model for epeirogenic uplift and sediment erosion would be as follows. Again starting with the situation of Fig 11a which depicts a high geothermal gradient due to high heat flux into the overlying ocean during hot-house conditions, a lowering of mean sea level (msl) at the onset of an ice-house period might expose the previous sea bed to sub-aerial conditions - the situation of Figure 11b but without the overlying ice sheet. This would be  followed by a long term thickening of the crust due to a lowering of the geothermal heat flux as indicated in Fig 11c - again without the overlying ice sheet but as a result of the reduced heat flow into the overlying atmosphere. This lowered geothermal gradient and associated thickening of the lithosphere over a few Ma Fig 11c would result from phase changes and consequent aggradation of lower crust. 

It might be observed that such a mechanism for the raising of a previous, largely horizontal, seabed helps to explain why so frequently vertical tectonics produces uplifted peneplains. Frequently, as I hope later posts will describe, mountain building results from erosion of such uplifted peneplains.