273 FLINT, A. G. 1988. "Sharp-Based Shoreface Sequences and 'Offshore 

 Bars' in the Cardium Formation of Alberta: Their Relationship to Relative 

 Changes in Sea- Level," Wilgus , C. K. , Hastings, B. S., Kendall, C. G., 

 Posamentier, H. W. , Ross, C. A., and Van Wagoner, J. C, eds . , Sea-Level 

 Changes: An Integ;rated Approach . Special Publication No. 42, Society of 

 Economic Paleontologists and Mineralogists, Tulsa, OK, pp 357-370. 



Under conditions of stable sea-level, the progradation of a wave- 

 dominated clastic shoreface will give rise to a coarsening-upward sequence, 

 reflecting an increase in the frequency and volume of sand transport with 

 time. Core and well -log data from the Cardium Formation (Turonian) of Alberta 

 reveal two types of shelf -to-shoreface sequences: (1) gradational -based 

 sequences that steadily coarsen upward from thin-bedded, wave-rippled 

 sandstone and mudstone through hummocky cross-stratified (HCS) sandstone and 

 mudstone into mud-free, swaley cross-stratified (SCS) sandstone capped by a 

 root bed, and (2) sharp-based sequences that consist of SCS sandstone, which , 

 near the base, may contain large mudstone intraclasts, sharply overlying thin- 

 bedded sandstone and mudstone: The HCS interval is thin or absent. Log cross 

 sections show that the changes from a gradational to a sharp-based sequence is 

 accompanied by a lowering of both the top and bottom of the SCS sandstone, 

 relative to upper and lower markers. Simultaneously, the SCS sandstone may 

 thin from 15 to 18 m to as little as 6 m. The sharp base, the presence of 

 intraclasts, and the relative lowering o the SCS unit suggest deposition 

 during a rapid fall of relative sea- level during which the shoreface prograded 

 over an erosion surface cut into the inner shelf by fair-weather wave scour. 



Tens of kilometers seaward of Cardium shoreface sandstones lies a 

 series of shore-parallel, lenticular bodies ("offshore bars") of conglomeratic 

 muddy sandstone. The lenticular bodies rest on regional erosion surfaces that 

 can be traced landward into slightly older shoreface deposits. The 

 conglomerates are here interpreted as lowstand shoreface deposits, which lie 

 on erosion surfaces cut into the shelf by wave scour during a relative sea- 

 level fall. The stratigraphic and lithologic relationships demonstrable from 

 the Cardium Formation suggest that a number of sharp-based "offshore bar 

 sandstones" in other parts of the Western Interior Seaway may also be more 

 satisfactorily explained as lowstand shoreface deposits. (Author). 



274 POAG, C. W. 1973. "Late Quaternary Sea-Levels in the Gulf of Mexico," 

 Transactions. Gulf Coast Association of Geological Society . Vol 23, 

 pp 394-400. 



The definitive data for late Quaternary sea-levels in the Gulf of Mexico 

 primarily are based on the presence of submerged shoreline depositional fea- 

 tures. The accompanying few radiocarbon dates are inadequate to clearly de- 

 fine the chronology of stillstands and regressions during the "post glacial" 

 rise. During the last three years new evidence has been gathered from wavecut 

 terraces and erosional unconformities present on submerged banks near the edge 

 of the northern Gulf continental shelf. At least 26 distinct levels can be 

 recognized between 2 and 223 m, and there are numerous additional minor ones. 

 Most have been interpreted as having resulted from eustatic changes, but it is 

 now clear that tectonic and isostatic movements are also involved. Renewed 

 study of the geomorphology , sedimentology , and stratigraphy of the bank 



125 



