Figure 40. (A) Model shows evolution of the shelf margin at The Elbow (ages > 125 ka modified from Lidz, 2004). Horizontal scale and vertical exaggeration apply to features at and seaward of shelf margin based on the seismic profile that crossed normal to the margin (Fig. 39A; Lidz et al., 2003). Shelf features are based on the Marker G core transect across two coral ridges (Fig. 34A) and are not drawn to scale. Note landward expansion (dotted lines) of the Pleistocene shelf-margin reef. This type of development is called a backstepped reef complex (Lidz, 2004). Also note Holocene infilling of the backreef trough that led to a backfilled progradation of the outer shelf (Lidz, 2004). Buried outlier reefs on the upper-slope terrace are ~5-12 m high. Their crests are ~35-38 m below present sea level. Up arrows indicate six of the seven periods of sea-level highstands that produced coral reef ecosystems on the Florida shelf in the last 325 ka. Small, downward-curving arrows indicate backfilling of troughs by landward-transported sediments. Ls = limestone. ka = thousands of years. Holocene = the most recent 10 ka. Q1-Q5 Units = names assigned by Perkins (1977) to the five marine sections that compose the bedrock. Marine-isotope substages refer to periods of time that correspond to major changes in the paleotemperature record (Fig. 37A, 37B). Curved arrows indicate landward sediment transport and infilling of backreef troughs. (B) The Elbow presently exhibits a progradational-margin profile. Renewed development of outlier reefs on terrace features (white areas) would produce multiple reef complexes. When buried, the complexes would form a coalesced reef-complex margin (Lidz, 2004).