Spreading Sea Floor: by Convection or Conviction?
A. A. Meyerhoff
Continental drift by sea-floor spreading and concomitant polar wandering are widely accepted explanations of earth tectonics, of continent distribution, and, therefore, of the locations of sedimentary basins. The formation of petroleum, oil shale, tar sand, and coal is believed to be climate-related. Uranium and thermal springs are thought to form only in specific tectonic environments. Therefore, if continental drift and polar wandering are facts, exploration for new energy resources depends on a thorough knowledge of former continent positions and paleolatitudes.
Many petroleum companies are reevaluating the petroleum potential of continental shelves, slopes, and rises in the light of the spreading-sea-floor hypothesis. For example, if the Atlantic basin were nonexistent before Late Jurassic time (as drift proponents believe), drilling for pre-Late Jurassic objectives in certain areas is senseless. Around the Pacific border toward which the continents allegedly moved, sea-floor spreading would affect profoundly the structural history and petroleum potential.
The concepts of drift and polar movement are equally important in onshore areas. For example, a major petroleum company several years ago used paleomagnetic data to determine ancient latitudes and found that nearly all giant fields for which they had adequate control--Cambrian through Tertiary--are within 20°-25° of the various paleoequators. Although the data available at that time were so few that this conclusion was very poorly supported, the company's staff concluded that exploration in paleolatitudes higher than 40° was not justified. Yet in 1968 major discoveries apparently were made near Prudhoe Bay, northern Alaska, in Mississippian carbonates (41° N paleolatitude) and Triassic sandstone (52° N paleolatitude). Cretaceous oil in the same area is at 80 76; N paleolatitude, and in Tierra del Fuego is at about 60° S paleolatitude.
Arguments favoring drift have been published widely, but facts which refute this concept are published only rarely. Many of the same facts which refute drift also eliminate earth expansion. Many phenomena are not explained by drift. Among them are: (1) the probable restriction of convection currents (if they can exist at all) to the upper mantle low-velocity zone, about 100 to 300 km thick; (2) lack of a driving mechanism for convection; (3) convection-cell geometry in plan view (e.g., several mid-ocean ridges--allegedly the locales of upwelling mantle currents--join or intersect compressional belts--the supposed locales of downturning mantle currents); (4) the steady flow requirement of current convection hypotheses; (5) the distribution of upper mantle density variations determined rom satellite geodesy; (6) the equatorial bulge; (7) lateral chemical composition changes in the upper mantle; (8) preliminary radiometric (K-Ar) dates (obtained in 1968 by the writer from G. D. Afanas'yev of the USSR Academy of Sciences), which range from late Proterozoic (Riphean) through Paleozoic; the dates are from metamorphic rocks of the Mid-Indian-Carlsberg Ridge system; (9) an unexplained Cambrian trilobite fauna from east of the Mid-Atlantic Ridge at 42°21^prime N, 17°12^prime W; (10) the narrow width of high heat-flow bands at mid-ocean ridge crests; (11) the geometric absurdities which result if the linear magnetic anomalies of mid-ocean ridges are assumed to be the combined result of sea-floor spreading and magnetic field polarity reversals (e.g., in the northeast acific, linear anomalies, which supposedly are moving westward from near the North American coast, bend westward 90° in the Gulf of Alaska and parallel the Aleutian Trench. This places the "oldest" anomaly bands closest to the Aleutian Trench! Similar anomalies parallel with the Kuriles cross the Japan Trench into Japan and others in the Arctic strike obliquely across the Mid-Arctic [Gakkel] Ridge); (12) bottom-towed magnetometer studies which sugest that each linear anomaly, whether negative or positive, is itself composed of smaller scale alternate negative and positive linear bands; (13) gravity data from the mid-ocean ridges that fit no convection model; (14) the proved Precambrian, Paleozoic, or Mesozoic ages of most continental rift systems which are known to be continuous with the mid-ocean ridges; (15) the uniform, worldwide thickness and elastic properties of the ocean crust; (16) the earth's thermal gradient which eliminates the possibility that ocean crust is either a polymorphic form of mantle material or serpentinized peridotite; (17) the immaculati: e.g., sea-floor spreading takes place (a) without deformation of sediments in f acture zones which cross mid-ocean ridges, (b) without deformation of ocean-floor sediments, (c) without deformation of sediments beneath continental rises, slopes, and shelves, and (d) without deformation of sediments in trenches adjacent to island arcs; (18) the numerous conflicts between paleomagnetic and paleoclimatic data; (19) the global distribution by age of coals and evaporites (they parallel the present equator); (20) fossil species-diversity gradients which show that many equatorial belts of the past were nearly the same as those of the present; (21) fossil tree-ring distribution which demonstrates parallelism between past and present climatic zones; (22) the distribution of Carboniferous through Cretaceous floras and tetrapod faunas of the Southern Hemisphere; (23) the imposs bility of continental glaciation on a landmass the size of "Gondwanaland"; (24) Rezanov's paleomagnetic results which demonstrate clearly that current paleomagnetic methods for determining ancient polar positions are invalid, and that paleomagnetic data cannot be used to demonstrate continent separation; (25) the combined Ushakov-Talwani et al.-Melson et al. mid-ocean ridge model which explains the ridge topography, linear magnetic anomalies, heat flow, and Sykes' "transform fault" solutions on the basis of known (as opposed to inferred) physical processes; and (26) preliminary results of the JOIDES deep-ocean drilling program.
The data do not eliminate the possibility that some tilting of the rotational pole has occurred in the past, but the same data do suggest that sea-floor spreading and continental drift--as presently conceived--belong more properly in the realm of mythology than in the science of geology. Geologists exploring for future energy resources may find more reward in expending their energies on hypotheses which are more consistent with reality.
AAPG Search and Discovery Article #91051©2012 AAPG Rocky Mountain Section Meeting, Albuquerque, New Mexico, 23-26 February 1969