Sub-Recent travertine deposits buried by a humiferous palaeosoil of Roman age at Hunor utca, Óbuda – a testimony of man-and-environment interaction from Roman times

Abstract

Travertine beds, covered by a humiferous soil horizon and slope-deposits, alternating with fine alluvial (overbank)
sediments were exposed by an archaeogeological excavation at Hunor Street N° 50, this site is in front of the foothills of
Tábor Hill, at the fringe of the alluvial plain of the Danube and its small tributaries. At the lower and middle part of the
exposed profile, loose and porous travertine tufa beds alternate with grey-coloured calcareous-, silty-, argillaceous mud.
These calcareous layers were apparently deposited by the nearby Árpád Spring. The top of the travertine complex is hard,
shows patchy cementation and serves as the substrate of a rendzina-like, humiferous palaeosoil of Roman Age.
The remnants of the Roman settlement include waste-pits and ceramics. Powdery calcareous coatings and fills found
in root channels of the Roman palaeosoil could be the results of interaction with CaCO3-saturated groundwater (which
to this day is still discharged from the springs). The complete lack of travertine layers above this humiferous paleosoil is,
however, striking. The research indicated that this is the result of a human-induced hydrological change in the vicinity of
the springs. It seems likely that springwater — which formerly flowed away in an uncontrolled way from the orifice —
was collected and canalized in Roman times to contribute to the water-supply of the settlements on the plains. This is also
supported by earlier archaeological observations (PÓCZY 2003). The Roman palaeosoil above the travertine shows that
drainage was improved by the canalization of the spring discharge, so that on top of the former (now dry) travertine
accumulation an incipient humiferous soil could develop. The overlying clastic complex, consists of a moderately
developed humiferous soil matrix and is intimately mixed with fine silty-sandy sediments, intercalated unsorted rock
debris and occasional brick fragments. This suggests that, after having been abandoned by the Romans, the area soon
became the site of alluvial sedimentation again. In this situation the deposition of fine overbank sediments was from time
to time interrupted by an episodic influx of rock debris from the nearby hills (=probably by mass-wasting on the rather
steep slopes). Further consideration is needed to determine whether this sequence also reflects a changing climate at that
time According to GÁBRIS 2003 and others, the observed increase of the discharge of the Danube in Post-Roman times
may have been related to a climatic change which made the atmosphere far more humid than before).