RED BEDS FORMATION REVISITED
Formerly BRGM (Bureau de Recherches Géologiques et Minières)
Question : Red beds are aeolian sands or « sand waves » deposited by large floods ?
What do we know about the origin of our red beds , 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.). 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 ) were authigenic and formed in depth long after sedimentation. Glennie et al. 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., )
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 ) 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.
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.
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?
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
 Red beds sur Wikipedia : http://en.wikipedia.org/wiki/Red_bed
 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)
 Freeman W.E. and Visher, G.S. “Stratigraphic analysis of the Navajo Sandstones”, Journal of Sedimentary Petrology Vol.45 and 47, p.475-497
 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
 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.
 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.