First Calibration and Application of Leaf Wax n-Alkane Biomarkers in Loess-Paleosol Sequences and Modern Plants and Soils in Armenia

Abstract

Interpreting paleoenvironmental conditions by means of n-alkane biomarker analyses is challenging because results depend on different influencing factors. Thus, regional calibration of n-alkane patterns is needed because of different plant chemo-taxonomic behavior. We investigated for the first-time leaf wax-derived n-alkane biomarkers from modern plants, litter, top soils, and two recently discovered loess-paleosol sequences (LPSs) in Armenia (Lesser Caucasus). Our results on modern samples show a promising discrimination power based on n-alkane chain length nC33 (probably nC31)) for grasses and herbs versus nC29 for deciduous trees, despite the large interplant variability within vegetation groups. In contrast with other Loess records in Europe, where Late Pleistocene environments are ranging from tundra-like (glacial) to deciduous forest habitats (interglacial), our results from two Armenian LPSs suggest a transition from humid-steppe biome or forest-steppe vegetation dominating during interglacial periods, to semi-desert shrubs species more adapted to the enhanced aridity during glacial periods.

Evidence for Middle Palaeolithic occupation and landscape change in central Armenia at the open-air site of Alapars-1

“…Other documented exposures in Armenia with well-developed compound palaeosols and associated biomarker evidence also indicate a relatively warm and stable climate during MIS 5 (e.g., Wolf et al, 2016; Trigui et al, 2019; Richter, 2020). In contrast, during MIS 4–3, when climatic conditions are likely to have been be more arid and less stable in the region (Pickarski et al, 2015b; Stockhecke et al, 2016; Wolf et al, 2016; Trigui et al, 2019; Richter, 2020), hominin occupations at Alapars-1 were more intensive than those documented during MIS 5. Lithic artefact assemblages of the latter document nearly all stages of core reduction, showing an emphasis on blank production, use, and maintenance.…”

“…MIS 5 is regarded in eastern Anatolia as a period of warm, humid climates (Litt et al, 2014, Pickarski et al, 2015a), but despite the resource-rich landscapes that likely resulted, Alapars-1 is only the second site in the region dating to this time interval. Other documented exposures in Armenia with well-developed compound palaeosols and associated biomarker evidence also indicate a relatively warm and stable climate during MIS 5 (e.g., Wolf et al, 2016; Trigui et al, 2019; Richter, 2020). In contrast, during MIS 4–3, when climatic conditions are likely to have been be more arid and less stable in the region (Pickarski et al, 2015b; Stockhecke et al, 2016; Wolf et al, 2016; Trigui et al, 2019; Richter, 2020), hominin occupations at Alapars-1 were more intensive than those documented during MIS 5.…”

“…The occurrence of several Bt–Bk horizons at Alapars-1 may indicate that conditions were warm and humid during MIS 5. Elsewhere in Armenia, there is evidence for the development of similar soil profiles associated with interglacial warmth (see Wolf et al, 2016; Trigui et al, 2019; Richter et al, 2020). Although fragmentary in nature, the evidence from these sequences correlates well with palynological evidence from the long lacustrine sequences at Lake Van, Turkey (Litt et al, 2014) and Lake Urmia, Iran (Djamali et al, 2008; Stevens et al, 2012), where warm and humid interglacial periods dominated by the expansion of open deciduous oak steppe-forest are postulated.…”

Short-term occupations at high elevation during the Middle Paleolithic at Kalavan 2 (Republic of Armenia)

“…During glacial periods, winters were thought to have lasted longer, while summer droughts were more frequent, whereas during interglacials precipitation occurred mainly in spring to early summer [35][36][37]. These hydrological changes impacted distributions of terrestrial biota, such as shifts in the treeline elevation [23,24]. The seasonal distribution of resources currently shapes animal migrations [38][39][40][41][42] and most likely will also then have governed the migrations of animals and the hominins that followed them [43,44].…”

“…However, the majority of the Middle and Upper Paleolithic sites (MP and UP) are dated to~65-30 ka (late Marine Isotope Stages (MIS) 4 up to 2) [4][5][6][7][8][9][10][11][12][13][14][15][16]. The environmental conditions during this time interval indicated by regional long-term climatic records were characterized by abrupt, millennial-scale temperature and precipitation oscillations between cold (stadial) and warm (interstadial) stages [17][18][19][20][21][22][23][24][25]. Two parts of the research area have been widely studied: the Imereti region in Georgia where mainly cave sites were studied, including Ortvale Klde are located at 530 m asl [5,13,26].…”