30 Subsurface Geologic Methods 



Examples of Modern Fades Changes 



Revelle and Shepard ^^ show in figure 11 the general distribution of 

 sediments and rock bottom off the coast of southern California. The types 

 of these recent sediments fall into four categories: (1) sand, (2) sand and 

 mud, (3) mud, and (4) calcareous. The distribution of these deposits is 

 to a considerable extent controlled by submarine topography, "The ridges 

 and saddles, whatever their depth and distance from shore, have notably 

 coarser sediments than the depression and troughs." (See fig. 11) The 

 distribution of the calcareous deposits in the area are extremely variable. 



Tracey -^ et al in their studies of the Bikini reef discuss the distribu- 

 tion of corals and algae of the more important types and the relationship 

 of channels, caverns, pools, and detrital deposits. They recognize a number 

 of distinct facies zones roughly parallel to the reef front. It is stated 

 that "Differences in the composition of the reef surface and in organic 

 growth are also observable laterally — along lines parallel to the reef 

 front — but these differences are less striking than the banding." Specific 

 facies of the reef include (1) a marginal zone on the windward side (Litho- 

 thamnium abundant), (2) a coral-algal zone (inside the marginal zone), 

 (3) a reef flat (forms the major part of the reef and consists of eroded 

 coral and algae with some foraminiferal sand), (4) a beach, and (5) 

 lagoonal. 



As ancient reefs in carbonate sections are now being seriously con- 

 sidered by oil companies in their exploration programs, modern reef 

 development and distribution should be carefully and systematically 

 analyzed. 



Lowman ^^ in a worthy contribution has discussed the modern facies 

 of the Gulf Coast region. 



Examples of Ancient Facies Changes 



Many examples of ancient facies changes may be cited. One of the 

 classic examples of lateral variations in strata is that reported on by 

 King -^ within the Permian of the Guadalupe and Glass Mountains (fig. 

 10) , of west Texas and New Mexico. Three well-defined facies are recog- 

 nized in the Guadalupe series: (1) shelf (back-reef), (2) marginal (reef), 

 and (3) basinal. The shelf facies is represented by limestone, evaporites, 

 and minor amounts of sandstone. The marginal facies is dominated by 

 the Capitan reef limestone. Sandstones, shales, and occasional thin lime- 

 stones comprise the basinal facies. 



^Revelle, R., and Shepard, F. P., Sediments of} the California Coast: Recent Marine Sediments, 

 a Symposium: Am. Assoc. Petroleum Geologists, p. 245-281, 1939. 



^^ Tracey, J. I., Ladd, H. S., and Hoffmeister, J. E., Reefs of Bikini, Marshall Islands: Geol. Soc. 

 America Bull., vol. 59, pp. 861-878, 1948. 



^Lowman, S. W., Sedimentary Facies in. Gulf Coast: Am. Assoc. Petroleum Geologists Bull., vol. 

 33, no. 12, pp. 1939-96, Dec. 1949. 



^' King, P. B., Permian of West Texas and Southeastern New Mexico: Am. Assoc. Petroleum Geolo- 

 gtsts Bull., vol. 26, no. 4, pp. 535-763, 1942. 



