Correlación de registros paleoambientales y ocupacionales en los últimos 14 ka de Cueva Mayor en Atapuerca (Burgos, España)

Abstract

The Atapuerca Mountains are located in the proximity of Sierra de la Demanda, 15 km east of Burgos, between the Ebro and Duero basins (Fig.1). The aim of this study is to correlate the environmental signals recorded on two sites (Galería de Estatuas and El Portalón) of the Atapuerca karst system called Cueva Mayor (Fig. 2), during the last 14 kyr. During this interval, in Galería de Estatuas, the development of speleothems with laminar precipitates (flowstones) and dripping (stalagmites) was dominant. Several climatic oscillations and human occupation episodes during the Late Pleistocene and Holocene have been detected from the petrological characterization of a stalagmite (Fig. 3; Table I). The result shows variations in crystal growth (Lám. I, fig. 1-4) related to different formation conditions: water availability, carbonate saturation, seasonality and occupation of the cavity. On the other hand, the stratigraphic sequence of El Portalón starts in the Upper Pleistocene (30 kyr BP) and it records human occupation, with varying intensities, from the Mesolithic to the Middle Ages. Its pollen sequence shows a strong contrast between the relatively open landscapes at the beginning, and the further development of the woodlands, progressively becoming more significant during the Holocene (Fig. 4, 5). The main component in the phases of climatic optimum is the pine forest associated with temperate taxa, while declines are characterized by the development of xeric taxa and open areas that facilitate erosion under cold and arid conditions (Table II). The correlation of both sites (14-2 kyr BP) provides that, for the range between 13.9 and 12.8 kyr BP, there were warm and humid conditions in general, without a marked seasonality. There was an increasing forest cover due to the development of both mesophilic and riparian taxa, indicating an increase in the values of both precipitation and temperature. In this period, human occupation has not been detected yet. A major erosion event (with a possible flood event) and subsequent occupation of the cave by bats (a level of guano) in both studied areas marks the Pleistocene-Holocene transition (12.8-5.9 kyr BP). Around the 5.9 kyr BP, environmental conditions ranged around a climatic optimum but with a marked seasonality, evidenced by the alternation of sparite-micrite in the stalagmite and typical vegetation of wet conditions, with a development of mesophilic and Mediterranean taxa, alternating with dry conditions associated with a slight increase in xeric taxa. In addition, Neolithic occupations with presence of remains of macrofauna, bone industry, stone industry, ceramic production and traces of cereals, related to the beginning of agriculture in the area, are found in Level 9 of El Portalón in these chronologies (6.1 and 6.07 kyr BP). The environmental conditions became drier from the 4.2 kyr BP with a decrease in the woodlands and nitrophilous taxa, and a slight increase in xeric taxa. This increase of aridity could be potentially amplified by the impact of human activity and the consequent alteration of the landscape in the region (deforestation and agriculture), as evidenced by a greater number of ash layers in the stalagmite of the Gallery of Statues, reaching chronologies after 3.1 kyr BP. Human presence in El Portalón is also the most intense and continuous from the Calcolithic period (4.4 kyr BP, Level 7 / 8) to the Middle Bronze Age (3.3 kyr BP, Level 3). After this level there is a stratigraphic-cultural gap that affects the Late Bronze Age, resuming the sequence in an Iron I and some sporadic occupations of high imperial times and the Middle Age (Levels 2 and 1).