Preliminary report on a mid-19th centuryCannabispollen peak in NE Spain: Historical context and potential chronological significance

Abstract

Cannabis sativa L. (hemp) was introduced in Europe from Asia Minor during classical Greek and Roman times. Since then, hemp pollen abundances between 10% and 80% in Late Holocene sediments have been considered indicative of the local or regional cultivation and/or retting of this plant. In this paper, a unique pollen peak of >60% recorded in Lake Montcortès (pre-Pyrenean foothills, NE Spain) is evaluated as a potential chronostratigraphic marker. Previously, this pollen peak was dated to ad 1757 using a depth–age model based on AMS14C dates from sedimentary macrofossils, but a recent calibration of the model using varve counting has refined the date of the hemp pollen maximum to ad 1839. This date coincides with an outstanding socio-political shift from feudalism to liberalism in Spain and the corresponding dismantling of the royal navy, the main consumer of hemp fibre. These events produced a well-documented decline in Cannabis cultivation across the Iberian Peninsula. The sharpness of the Cannabis pollen peak, its accurate dating using annual varves and its almost exact coincidence with outstanding and widespread historical events suggest that this palynological landmark could be used as a chronostratigraphic marker for recent centuries. This possibility, as well as the geographical extent of this potential datum, should be confirmed with further studies.