17:15 〜 18:45
[HQR06-P07] Luminescence vs Biotic dating methods in Late Quaternary stratigraphy
★Invited Papers
Since the late '40radiocarbon and U/Th methods have been widely used to provide precise ages of Pleistocene/Holocene, continental to marine, sedimentary successions worldwide. The major stratigraphic assumption is that the time elapsed since the death of organisms such as corals, shells, plants and (in some cases) bones found in sedimentary bodies correspond to the age of the strata depositions. The luminescence method, instead, provides the age since quartz and/or feldspar grains were hidden by the sunlight and buried in a sedimentary strata. Thus, this method should directly calculate the age of a depositional events. Despite the enormous influences of the lumines-cence method in provide geochronological framework to build up stratigraphical succession worldwide the scientific community still required the combine use of different geochronological methods to support and confirm the luminescence derived ages.
We present two case studies where luminescence and biotic methos (radiocarbon and/or U/Th) have been applied on Late Quaternary to Holocene marine and continental successions producing "apparent" geological inconsistencies.
The first case study is represented by the relict beach deposits of Sardinia island (Mediterrane-an Sea) considered important sites of Marine Isotopic Stage (MIS) 5e (ca. 125 ka). The succession filling marine terraces, ischaracterizedbytwosuperimposedunitswithabbundantcoralstowardthe top. Traditional U/Th dating have been performed on corals for more than 30 years dating all the suc-cessions to the MIS5e (ca. 125 ka). Newly performed luminescence analysis instead, dated the lower unit to the MIS 5e (ca. 130ka) and the upper unit containing coral fragments to the following MIS 5c (ca. 100 ka) substage. Despite the methods provide a different chronological framework both are accurate and reliable. Thus the resultant interpretation is that the luminescence method is dating the age of the strata deposition (MIS5c) whereas U/Th provide the age of the death of corals (MIS5e) that were reduced in fragments and reworked from the underlain unit toward the top.
The second case study is represented by the distal alluvial fan deposits developed along the flank of the Famara cliff (Lanzarote island, CanaryArchipelago). The succession from the bottom up is dominated by a ritmitic alternation of sand-sheet and muddy pond-like strata rich in shell-snails cut at the top by a relatively thick gravelly channel body. The succession is dated both using luminescene and radiocarbon on fine sediments and snails respectively. The resultant chronologi-cal framework clearly appear as a geological nonsense despite these both methods are accurate and the ages "in theory" fully reliable. The age reversal cannot be explained considering a post-death reworking of the snails and a robust geochronological framework cannot be established for the studied succession.
We present two case studies where luminescence and biotic methos (radiocarbon and/or U/Th) have been applied on Late Quaternary to Holocene marine and continental successions producing "apparent" geological inconsistencies.
The first case study is represented by the relict beach deposits of Sardinia island (Mediterrane-an Sea) considered important sites of Marine Isotopic Stage (MIS) 5e (ca. 125 ka). The succession filling marine terraces, ischaracterizedbytwosuperimposedunitswithabbundantcoralstowardthe top. Traditional U/Th dating have been performed on corals for more than 30 years dating all the suc-cessions to the MIS5e (ca. 125 ka). Newly performed luminescence analysis instead, dated the lower unit to the MIS 5e (ca. 130ka) and the upper unit containing coral fragments to the following MIS 5c (ca. 100 ka) substage. Despite the methods provide a different chronological framework both are accurate and reliable. Thus the resultant interpretation is that the luminescence method is dating the age of the strata deposition (MIS5c) whereas U/Th provide the age of the death of corals (MIS5e) that were reduced in fragments and reworked from the underlain unit toward the top.
The second case study is represented by the distal alluvial fan deposits developed along the flank of the Famara cliff (Lanzarote island, CanaryArchipelago). The succession from the bottom up is dominated by a ritmitic alternation of sand-sheet and muddy pond-like strata rich in shell-snails cut at the top by a relatively thick gravelly channel body. The succession is dated both using luminescene and radiocarbon on fine sediments and snails respectively. The resultant chronologi-cal framework clearly appear as a geological nonsense despite these both methods are accurate and the ages "in theory" fully reliable. The age reversal cannot be explained considering a post-death reworking of the snails and a robust geochronological framework cannot be established for the studied succession.