Jindrich (1969) and Basan (1973) 

 provide more specific discussion of 

 the Holocene sediment environments 

 in the lower Keys gulf side, an area 

 only briefly discussed by Enos 

 (1977). Figure 29 illustrates the 

 depositional environments outlined 

 by Jindrich (1969). The majority of 

 carbonate sediment accumulation is 

 due to the sediment-trapping effects 

 of the marine grass Thalassia testu - 

 dinum and the calcareous green alga 

 Halimeda opuntia . The sediment 

 consists primarily of Halimeda , mol- 

 lusks, foraminifera, and Pleistocene 



limestone rock fragments (Jindrich 

 1969). In the Barracuda Keys, to 

 the ENE of Jindrich's study area 

 and still to the gulf side of the 

 lower Keys, Basan (1973) identified 

 a similar pattern of carbonate 

 sedimentation containing the same 

 four major components described by 

 Jindrich (1969) and in the same 

 relative abundance. Studies by 



Landon (1975) and Kissling (1977) 

 contain more recent and supplemental 

 research on carbonate sediments in 

 the lower Keys' seaward region, out 

 to and including the shallow slope. 



KEY 



WEST 



INTERIOR 



SHELF L AGOON 



STARVED LAGOON SUBTIDAL GRASSY BANK 



INTERTIDAL 

 BARRIER BELT 



OUTER 

 PLATEAU 



GULF OF 

 MEXICO 



oTthd 



After JnrJricri ,1969 



Figure 29. Depositional environments in the lower Keys (adapted from 

 Jindrich 1969). 



Holocene sediment investiga- 

 tions in the distal island groups 

 west of Key West (Boca Grande Group, 

 Marquesas Keys, and Dry Tortugas) 

 are rather scarce. For the area 

 including the Marquesas and Boca 

 Grande groups the only study found 

 which addresses recent sediments was 

 Davis' (1942) work describing the 

 general topography of the Sand Keys 

 (name attributed to all three distal 



island groups). Davis (1942) de- 

 scribes these two island groups as 

 low, calcareous sand and marl ridges 

 emerging from a shallow limestone 

 bank representing an extension of 

 the lower Keys oolitic facies of 

 the Miami Limestone. The composi- 

 tion of the calcareous sediment is 

 similar to banks on the lower Keys' 

 gulf side, as previously discussed 

 (Jindrich 1969, Basan 1973). 



67 



