CHAP. 34] THE PLEISTOCENE RECORD 901 



important difficulties of sampling and analytical techniques exist. If these diffi- 

 culties can be sufficiently minimized in the future, K-A dating may produce 

 the much-needed absolute time scale for the continental Pleistocene beyond the 

 range of i^C. 



3. Marine Stratigraphy 



A. Marine-Epicontinental Stratigraphy 



The repeated formation of extensive ice sheets on the continents during the 

 glacial ages and their disappearance during the intervening interglacials 

 (Greenland and Antarctic ice sheets excluded) has resulted in repeated glacial- 

 eustatic oscillations of sea-level through much of the Pleistocene. The ampHtude 

 of these oscillations is believed to have been at least 130 m and possibly con- 

 siderably more. Thus, sea-level is believed to have reached at least 100 m below 

 the present level during the last glacial maximum (Main Wiirm or classical 

 Wisconsin), and to have risen to at least 8 m and possibly 30-35 m above the 

 present level during the last or the previous interglacial age. 



In tectonically stable or slowly subsiding areas of the continental margin, 

 where terrigenous sedimentation is appreciable or abundant, the repeated 

 oscillations of sea-level created sequences of alternating marine and continental 

 sediments. Some such sequences have been sampled by means of borings and 

 have been described in some detail. The section of the Lower Versilia (northwest 

 shore of Tuscany) described by Tongiorgi (1936) and Blanc (1937) pictures 

 rather clearly the sea-level changes during the last glacial age (Early and Main 

 Wiirm) and after. Following the end of the last interglacial age, the sea-level 

 decreased to below 90 m, and continental sand 14-m thick was deposited (Early 

 Wiirm). The sea-level then rose to — 61 m and marine sand with seeds of Vitis 

 vinifera was deposited (Early Wiirm-Main Wiirm interval). A new lowering of 

 sea-level occurred, during which a layer of continental sand 29-m thick was 

 deposited (Main Wiirm). This sand contains predominant oak pollen at the 

 base, replaced upward by Abies and then by Pinus mugo and Pinus silvestris. 

 The sequence thus indicates a progressive, marked cooling. Eventually sea- 

 level rose to its present position and additional marine and continental sands, 

 peat and clays were deposited. Carbon- 14 analysis of a peat cobble, apparently 

 reworked from the Pinus level, gave an age of 18,350 years (Broecker et al., 

 1956). 



A succession of marine transgressions and regressions, presumably controlled 

 by glacial-eustatic movements, was reconstructed by Pfannenstiel (1952) for the 

 coast of Syria and Israel. The sea-level was found to have been lowered to at 

 least — 89 m during the Early Wiirm, in agreement with what was found in the 

 Versilia. In addition, the sea-level appears to have oscillated repeatedly during 

 the time of high sea-level defined as the Tyrrhenian Age with maxima at + 30- 

 35 m, -f 15 m and + 6 m, separated by minima of less than + 10 m and less than 

 + 2 (all in order of decreasing age). Evidence of sea-level positions during the 

 Early Wiirm-Main Wiirm interval and during the Main Wiirm is apparently 



