POLLEN ANALYSIS AT HAGENTHAL-LE-BAS (HAUT-RHIN, FRANCE) AND ARCHAEOLOGICAL SITES IN THE EAST OF SUNDGAU AREA

A stream paleochannel (the Kirchbach) situated in the lower part of the Hagenthal-le-Bas village was spotted during an archaeological survey. One of the aims of this survey was to identify sites suitable for pollen analysis in the Sundgau area, the extreme south of Alsace in the foothills of northern Jura Mountain. The study is part of a research program developed around the Saint Joseph rock shelter, located in the Lutter municipality 8 km southwest of Hagenthal, which was excavated between 2005 and 2011. A 4.5 meter silty organic sequence was found in this paleochannel. The sequence suffered several episodes of flooding and is characterized by a discontinuous sedimentation. Measurements of magnetic susceptibility showed a succession of cycles and peaks of strong values distributed over the entire sequence and correlated with the movements of the stream running in the valley. Twelve radiocarbon dates were performed on this sequence but the construction of an age/depth model was hampered by irregular sedimentation. Nevertheless the estimated age depth model confirmed the existence of a significant gap between ca. 9,000 and 4,000 cal. years BC (about 11,000-6,000 BP). The palynological diagram starts in the middle of the Allerod interstadial, between ca. 11,500 and 11,150 cal. years BC (13,450-13,100 cal. years BP), in a forest environment dominated by pine (Pinus). The end of the Allerod period, i.e. Younger Dryas and early Holocene, was characterized by a stronger stream regime which prevented steady sedimentation. Starting around 9,400-9,300 cal. years BC (ca. 11,400 BP) a long period dominated by pine lasted until around 3,6003,500 cal. years BC (ca. 5,500 BP). From 4,400-4,300 cal. years BC (ca. 6,300 BP), on the sediments disclose some cereal pollen grains together with Artemisia and Rubiaceae pollen. This weak evidence of possible human impact corresponds to the early phase of the Neolithic period, which is however more recent than the oldest occupations detected in the Lutter archaeological site. During the Neolithic period, unambiguous signs of human impact on the environment are regularly found for a whole millennium. After this time, new anthropogenic indicators reappear in the diagram only in the middle of the Iron Age. They remain discreet until the 5th century AD hidden by the pollens from the wet forest which covers the bottom of the valley. Between the 5th-6th and the 12th-13th centuries, various crops, pastures and hay fields occupy the major part of the territory while the nearby hills remain forested. It is likely that this strong farming activity extended over many centuries. Indeed, from 90 cm deep, i.e. in the 14th century, a detrital phase (poor pollen preservation) is found up to the top of the sequence. This detrital phase could result from local effects of the Little Ice Age. However, palynological evidence of a heavy human impact suggests that it rather derives from the huge environmental footprint of medieval and modern agricultural practices in the stream catchment area.