GULF OF MEXICO 



69 



Howe (1936, p. 82) called attention to the great 

 sinking in the rou;ion of the Mississippi Delta 

 which he believed amounted to about 30,000 feet 

 since the beginning of the Tertiary. He believed 

 the Gulf coast is an active geosyncline resulting 

 from the weight of the sediments brought down by 

 the Mississippi River. Evidence of the sinking 

 of the Mississippi Delta was also presented by 

 Russell (1936, pp. 167-169) in his study of the 

 physiography of the region. Russell and Fisk 

 (1942, pp. 56-59) questioned the "strength" 

 of the earth's crust and concluded that the crust 

 appeared "weak" as it jnelded and subsided "at 

 essentially the same rate that the deposits 

 thickened." 



Meyer (1939, p. 206) did not subscribe to the 

 sedimentary -load theory and among various ob- 

 jections stated that the "epochs of reversal of 

 movement in the geosyncline, indicated by un- 

 conformities, shoreline migrations, entrenched 

 streams, submarine canyons, and the elevated 

 beach at Corpus Christi, are opposed to the basic 

 tenets of the sedimentary-load theory." 



Meyer also used the argument that the ocean 

 deeps, which are structural troughs, could not have 

 been caused by the weight of accumulating sedi- 

 ments. He suggested that the Mexican Basin 

 and the Gulf coast geosyncline may be related 

 structures and that the Gulf coast geosyncline 

 was a "similar structural and topographic basin in 

 early Tertiary time when the strand-line was far 

 inland. After this basin had come into existence, 

 it offered an opportunity for the accumulation of 

 thousands of feet of sediments. The weight of 

 the first several thousand feet of Tertiary deposits 

 may have been sufficient to overcome the in- 

 herent strength of the crust and to cause further 

 sinking" (op. cit., p. 206). 



Storm (1945, p. 1330) considered the Gulf coast 

 geosynclinal trough as a well-marked feature 

 indicating considerable subsidence. He believed 

 that, if subsidence continued at a fixed position 

 and if sediment filled this trough and passed over 

 it, there should be some sign of sinking inland and 

 drainage should have caused deposition over the 

 axis of the syncline. Such indications were lack- 

 ing, and he therefore believed that the shape of 

 the trough was a composite of past and present. 

 He showed that sediments are accumulating prin- 

 cipally on the seaward flank of the trough which 

 pushes the bottom of the flank downward while 



the landward flank rises slightly. Thus, the 

 trough tends to move seaward with continued 

 sedimentation. 



Glaessner and Teichert (1947, p. 586) thoroughly 

 reviewed the subject of gcosynclines and con- 

 cluded that the origin of gcosynclines is still 

 unknown. Observed facts are too often over- 

 shadowed by an author's "attitude to one or the 

 other of the current and mutually exclusive 

 hypotheses of mountain building and of the 

 origin of continents on which no finality has yet 

 been reached. Concerning the actual mechanism 

 of the formation of gcosynclines it would seem that 

 the school of Gulf coast geologists has produced 

 such weighty arguments in favor of subsidence 

 under load that the operation of the factor can no 

 longer be doubted. On the other hand, there is 

 evidence for 'autonomous' uplift and subsidence 

 of parts of the crust which would make it possible 

 for sedimentary accumulations to be formed as a 

 result of active subsidence and uplift rather than 

 of passive depression under the load of shifting 

 products of erosion." 



Bornhauser (1947, pp. 706-711) observed that, 

 since the Tertiary transgressions affected the 

 whole northern border of the Gulf of Mexico, 

 diastrophic movements must have been the 

 primary cause of the transgressions. He agreed 

 that the subsidence of the Mississippi embayment 

 and the Gulf coast geosyncline caused the Ter- 

 tiary transgressions of those areas, and the sub- 

 sidence was due to diastrophic movements. 

 Bornhauser "has not found clear evidence to 

 support the idea that the weight of the sedi- 

 mentary column is the deciding factor for subsi- 

 dence. On the contrary, all facts and evidences 

 seem to point toward the conclusion that the 

 formation of the Mississippi embayment is a 

 tectonic incident closely related to the structural 

 history of the Gulf of Mexico which underwent 

 considerable epeirogenic movements during the 

 Tertiary." 



The idea of a Gulf of Mexico neutral plate was 

 introduced by Suess and substantiated by Schu- 

 chert who considered it to be the foreland of the 

 Antdles. Bornhauser accepted this neutral plate 

 and suggested that the northern border of the 

 plate may have formed the submarine plateau of 

 southeast Mississippi, at least during earlier Ter- 

 tiary. Deeper synclines separated this plateau 



