Earth’s sedimentary crust

Does it not seem contrary to the principle of isostacy that an ocean floor, after receiving a load of 15,000 feet of sediment, should rise up to form mountains 15,000 feet above sea level? Kuenan says (Marine Geology, p. 548) that “there are no indications in stratigraphy that true ocean bottom has ever been transformed into continental masses.”

Exactly opposite results are presumed to have occurred as regards highlands alleged to have formerly existed off continental margins where ocean waters now are. As we have seen, they are said to have constituted the sources of sediments which filled certain inland geosynclines. It is claimed that after such off-shore mountains were peneplained, they subsided and became ocean floor. Contrarywise, as to geosynclines in inland areas, it is alleged that after the sediments in them accumulated to depths of from 10,000 to 50,000 feet, the synclinal areas were uplifted to form immensely high mountain ranges!

If there is any truth in the theory of isostacy, if continental platforms stand above sea level because they are constituted of sialic material, if ocean floors remain submerged because they are simatic, how could off-shore mountain ranges, especially after denudation, subside to become and remain ocean floor? On the contrary, how could an ocean bottom, as Mr. Henry calls it, after receiving a load of 15,000 feet of sediment, rise up to form a mountain range 15,000 feet above sea level? How and why could forces which compelled sialic land platforms gradually to subside from 10,000 to 50,000 feet below sea level, thereafter reverse their direction to uplift the same areas to great heights above sea level?

Flat statements, like several which have been quoted, that mountainous land areas formerly existed off-shore of present continental platforms where now deep ocean waters flow, illustrate conclusions often reached a priori in efforts to pinpoint sources from which sediments for certain areas could have come. There is no actual, definite evidence that deep, off-shore ocean floors ever existed as mountain ranges on the continental blocks.

Permanence of Continents

The assumption that portions of continental platforms were alternately depressed to depths of from 10,000 to 50,000 feet below sea level and thereafter were uplifted to great heights above sea level, conflicts with accpted ideas about permanence of land areas. For instance, Nevin points out that wherever the “old cornerstones” of the continents have been exposed by erosion, they are found to be igneous and metamorphic rocks; that

these nuclear masses or shields seem to have come into existence in the Archeozoic and since then have remained almost continuously above water. … By inference, the basement underlying the areas masked by sediments—about two-thirds of the continental areas—is composed of this same type of rock.

He concludes that “the facts point clearly to the very old age and permanence of the continental blocks. . . .”

Nevin goes on to say that “on the continents there is an almost complete absence of deep-sea sediments.” He states that if the continents had ever been ocean floors, evidence of deep-sea oozes should be found. He asks:

If continents are permanent features, because of their relatively light density, how was it possible to submerge a considerable part of them to great depths?

Daly says (Our Mobile Earth, p. 129) that “geologists know of no case where regional uplift of a mile or so has soon been followed by subsidence of the same region and of the same order.” According to Kuenan (Marine Geology, p. 126), it is held that

if oceanic floors are never elevated to form part of continental masses, the opposite process, the subsidence of sialic areas to oceanic depths, cannot then be reasonably assumed.

It is said that no interval of geologic time is known when at least the majority of continental areas was not above sea level. If all of North America was never submerged, how can we explain why all of it, with the possible exception of portions of the Canadian Shield area, is or has been covered with sedimentary rocks from Pre-Cambrian time upward? Was all the continent covered with sediment which came from an earlier, much more elevated Canadian Shield of igneous rock only? Could sediments from that single source be transported to such great distances and distributed so efficiently as to cover all the remainder of the continent? Did sedimentary rocks in Mexico and Central America also come from the Canadian Shield, or did they come from mountains which formerly existed off-shore to the west where the deep Pacific now is, or to the east from mountains now lying beneath deep Caribbean waters?

Whence came sediments of stratified rocks which generally underlie South America, Australia, Africa, Europe, Asia and probably Antarctica and Greenland? Can we believe they came from former mountain ranges which, after being denuded to supply sediments for the continents, subsided thousands of feet to form present floors of oceans, which surround all land platforms? Certainly, sediments for world-wide stratified rocks could not have been derived from the regional, infrequent shield areas where igneous, subcrustal rocks of basement complex are exposed.

Down-Warping

Daly believes that “each geosynclinal prism has developed in consequence of prolonged down-warping of the Earth’s crust” (op. cit., p. 220). He presumes that lateral squeezing forces thereafter caused “crumpling” of the prism; and that “after a long interval of time—millions of years—broad up-warping of the fold-thrust belt occurred” (p. 239). Just why “down-warping” should be a prerequisite for “up-warping” caused by lateral pressure is not explained. It would seem that lateral squeezing forces, acting upon a down-warped prism would more probably exaggerate the syncline, rather than reverse the direction and create instead an anticline.

Either horizontal or anticlinal strata lying upon Earth’s outer shell, if squeezed between opposite horizontal forces, obviously would be forced upward in the direction of least resistance. But if the strata were down-warped in a syncline, the vertical components of the horizontal forces would be downward, not upward. To this writer it seems more probable, as was suggested earlier, that the formation of mountain ranges, which has predominantly occurred parallel with and contiguous to oceanic or mediterranean shores, was due to the following forces: the superimposed weight of additional water and sediments accumulating on ocean floors, generated down-thrust of the floors upon Earth’s subcrustal simatic magma, thereby compelling up-thrust of contiguous marginal areas of lighter sialic continental platforms in order to maintain terrestrial equilibrium.

Tagged on: , , , ,