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RED BEDS FORMATION REVISITED

Jan SNOEP  

 (1929 - 2011) 

Formerly BRGM   (Bureau de Recherches Géologiques et Minières)


Horizontal sandstone beds with cross bedding , Escalante River basin  , Utah

Question : Red beds are aeolian sands or « sand waves » deposited by large floods ?


Introduction

What do we know about the origin of our red beds[1] , the beautiful reddish coloured rocks you see everywhere on the Colorado Plateau in the USA and in many other places ? These  well known red beds occur on all continents   and they were formed in various  geological periods . The oldest are Proterozoic ( 1.5 billion years) and the most recent ones are of Miocene age (6 million years). They are red by fine disseminated hematite iron oxide impregnating their clay minerals. They can be fine grained clay stones  , siltstones, sandstones and conglomerates or even lime stones.  Unfortunately, there is no place on   Earth where we can see them  being formed so that  all theories about their origin are in fact based on speculation.  Present tropical soils are often red, but never over thousands of meters thick as in the old formations. In tropical countries red  laterites composed of iron oxide  are common,  but they were never seen in the old red beds. So how were they formed ?  The red  Martian deposits show much similarity with the terrestrial red beds, which adds to the riddle .


The standard opinion about their origin

For various reasons they are always  considered of continental origin, deposited as continental alluvium deposited  as dunes,  by flash floods, braded rivers or  as alluvial fans on slopes . The fine grained red beds are interpreted as “playa” deposits, which are common in the low flat lands in deserts. The scarcity of typical marine vestiges and the occurrence of pollen and other vegetative matter are another reason for excluding a marine origin. Only during the Cretaceous period we find red beds with many marine fossils.  Are these reasons enough for classifying most of them as of continental  ?  In fact  there is room for many objections, with which most geologists are familiar.


 The objections against a continental origin

How come that the huge evaporite accumulations, which are commonly associated with red beds , are considered of marine origin by nearly all ? The typical continental evaporites like trona etc. should be abundant, but they were never described  in  the old red beds.  Laterally  and vertically they can transit into typical marine   lime stones and marls without intermediate  beach deposits. So they   show  no  transition between the  continental and the marine environment.( Chinle formation Colorado Plateau ). They are usually very well stratified like a “layer cake” with layers spreading over tens of kilometres or more. This  type of bedding is uncommon on the present continents.


 Could they all be in fact tidal flat deposits ?

This seems hardly to  make  any sense, as we know the present tidal flats as clay, silt and sand deposits on most deltas. They are never red and  always full of marine or littoral life, which we do not see in the old  red beds. Is it possible, that marine life was absent when the  red beds were deposited.? Only facies and extensive bedding are similar to  present tidal deposits. New astronomic information may give an explanation


Were the tides in the past different from today ?

So far practically no research was done along these lines by the geologists. They took for granted, that the tides were always the same as the present ones. However recent astronomic studies on the Moon orbit came up with the conclusion, that  the orbit must have been strongly eccentric during various periods  in the geological past  (Garrick-Bethel et al.[4]). Resonance between orbits of Venus and Jupiter are considered to have been the cause which could explain the eccentricity increase of the Moon orbit. No signs of more recent repetitions of this phenomena have been mentioned so far. A more eccentric orbit of the Moon involves that during  part of the month the moon was much closer to the Earth than today and in part much farther away. If their conclusions are right, then very strong tides alternated with very  weak  tides during certain epochs.  If the red beds are the vestiges of giant tides,  it is not a coincidence, that red bed periods generally showed also strong volcanic activity, as strong tidal waves distorted also the Earth crust. These periods are considered to show a frequency between 20 an 30 MY.


 Can we see vestiges of giant tides in the past?

  As a matter of fact there are many signs of very frequent tsunami like waves in the past.  The first effect of the violent tidal inflow would have been a very destructive abrasion ,  flattening out the relief  of  large areas on the planet and covering them with very thick siliciclastic (sandy) sediments like we know them from the red beds. The huge Permian abrasion  and the following  Triassic plane of the West European basin going from Warsaw to London,  and the Karroo basin in South Africa  are  good examples. All continents show  similar  basins considered as “continental” . But how come, that the  old  sediments  are  red ? The answer could be, that   the  present tidal inflows are  weak and compatible with life, but  daily  tidal waves  of tens of meters high are incompatible with life, so that no organic matter could develop to create a reducing environment as we see everywhere today. The  violent  tides must have made the oceans muddy over vast areas so that no sunlight could   penetrate   in the surrounding oceans,  explaining  the absence of all marine life. The most severe extinction of marine  life  (95 %)  happened during the Permo-Triassic period, which is represented by  red beds all over the Planet.   As a result of the absence of life, the sediments were deposited under strong oxidizing   conditions  . Moreover as  new  seawater invaded daily the continents over very large distances,  conditions were favourable  for the formation of brines and evaporites. Microscopic work by various  sedimentologists on red bed  drill cores  deep under the North Sea, and also some paleo-magnetic studies  have shown, that the iron oxides of hematite (Wyles [6]) were authigenic and formed in depth  long after  sedimentation.  Glennie et al.[5]   Later studies on hematite formation showed, that  the presence of brines, oxygen and a higher temperature by burial  are enough for dissolving all ferrous iron from the iron containing minerals of the sediments. Under these conditions hematite becomes soluble  and  crystallizes when temperature decreases , when, after deep burial, the sediments came nearer the surface,  producing  the typical red colour by precipitation of hematite.  This process explains also why we never see any enrichment of iron in red beds. Some palaeomagnetic studies showed, that hematite formed over  a  very long period, long after sedimentation, which is in agreement with the  fore going ..(Beck, M.E. et al., [2])


 Are there more arguments for giant tidal waves in the past?

Every geologist knows, that in the past huge volumes of sediments were deposited on the continents (about 60 %  of all sediments are lying on the continents), and that today sediments accumulate mostly on the border of the continents in the well known present deltas . The volumes of the latter are hundreds of times smaller than the ones on the continental basins of which some  can  reach  a stunning  volume of 15 million cubic  kilometres. (Cambrian-Ordovician of North Africa ) . The deltas as we know them today are rare in older formations. Today practically no sediments are formed on the continents, so  it can be assumed that on the continents other much more violent phenomena were active in the past.


Aeolian deposits or sand waves ?

Most large flat bedded  old sandstones are generally considered of aeolian origin in spite of the absence of dune crests, as we see them in the  present deserts. They show very often unidirectional cross bedding (see figure above)  interpreted as wind blowing with a constant speed over  very  large epochs in the same direction. During the sixties  and  the seventies there was a strong debate about the  origin of these beds of the Navajo sandstones, as some geologist invoked sand waves, which are common in shallow seas  with strong tides , as a more probable origin .( Freeman and Visher  [3]) In fact their constant bedding , their   absence of crests  , the constant angle of their cross bedding and the very little change over long periods  in the direction of he cross bedding,    fit perfectly with  the facies of present  marine sand waves in a tidal environment.  


Alluvial or marine conglomerates ?

Though there is much  confusion  between the two,  there is a big difference between the conglomerates, which are  very common in the old formations and the present ones which  we see on the continents.  In the old ones  the pebbles are mostly matrix supported and hardly touching   each other and spread over very wide areas   , whereas the  present river deposits are always channelled and show  pebbles  often lying on top of each other with very little matrix.  The old ones show a striking similarity with the recent ones left by the  tsunamis, or with the pebbles lying on the bottom of the English Channel or deposited by the Scabland floods in the State of Washington. They always   represent   the result of  large floods over wide areas. as  we  can expect  in case of giant tides.


 Detrital feldspars

Present  alluvium  does not show      the presence of  detrital  feldspars. They are too fragile. They are most of the time transformed into clays  in   most soils before entering the streams.  In case of the absence of vegetation   in deserts they   may  enter into the alluvial system, but they are then destructed very quickly  during repeated  transport  and we never see them in deltas . How do we explain  their  very common occurrence in the red beds ?  There can be no doubt, that they can only be deposited very quickly after  erosion  and  after  limited  transport.  Only violent erosion or abrasion, unknown today, can   be   the  origin, so that the huge tidal waves may   have been the answer.


 Other consequences

If  ever   this violent  past  is accepted, then  we may have another interpretation for several of the  major extinction  periods of the past.  The worst one  between the Permian and the Triassic, both periods of abundant red beds, wiped out as much as  95 % of all marine life.  The amazing development of very large hind legs and long necks  and their over all gigantic  size of  many species of  dinosaurs,    could also have been  their  Darwinistic  defence against frequent  major floods. Their grave yards show nearly always burial by floods. It is perhaps no coincidence, that most of the surviving reptiles can swim or fly. It is possible that these floods where also responsible for their extinction? 


Conclusion

 It is understood, rather  arbitrarily, by most sedimentologists, that tides have never changed  during the history of the planet, in spite of the proof, that at present the Moon distance from the Earth increases by a few centimetres per year. But since recent work on the history of the orbit of the Moon indicates major variations in the past,  there  is plenty of  reason for  reflection about  the possible role of  tides, much more violent during certain periods in the past than today and  its  possible role on abrasion,  sedimentation and  life on  our planet .  Since at present tides are  mostly  weak but vary strongly geographically,  much  stronger tides must have changed  enormously   in time and space. The varying changes in the distances between continents   must have contributed   also to strong variations in tidal intensity by resonance. They may complicate  even  more    the study of the history of our planet. If these considerations  are   taken  into account as a serious possibility,  it is felt that there is still a very wide domain for additional research.


More details in the site    www.redbeds-geology.com


Reference

 [1] Red beds sur Wikipedia : http://en.wikipedia.org/wiki/Red_bed

 [2] Beck, M.E. Jr.   , Russell F. Burmester and Bernard A. Housen, The red bed controversy revisited: shape analysis of Colorado Plateau units suggests long magnetization times, Science Direct Vol.362 , Issues 1-4 , Febr 2003 p.335- 344  (http://myweb.facstaff.wwu.edu/bernieh/reprints/beck-tecto-03.pdf)

[3] Freeman W.E. and Visher, G.S. “Stratigraphic analysis of the Navajo Sandstones”,  Journal of Sedimentary Petrology Vol.45 and 47, p.475-497

[4] Garrick-Bethell I., Jack Wisdom, Maria T. Zuber 2006 I.,Evidence for a Past High-Eccentricity Lunar Orbit, Science, Vol.  313. no. 5787, p. 652 – 655

(http://web.mit.edu/iang/www/pubs/high_eccentricity_science_2006.pdf)

 [5] Glennie, K.W., Mudd, G.C., Nagtegaal, P.J.C., 1978, Depositional environment and diagenesis of Permian Rotliegendes Sandstones in Leman Bank and Sole Pit areas of the UK southern North Sea, J. Geol. Soc. Lond., Vol. 135, 1978 p.25- 34.

 [6] Wylkes J. L.,Manning, Hematite solubility in NaCl and CaSiO3-bearing aqueous fluids at 10 kbar and 800 C, American Geophysical Union, Fall Meeting 2005, abstract #V31C-0619.


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