CHANGING ENVIRONMENT: GEOLOGICAL PROCESSES WHICH DESTROYED/CREATED RAW MATERIAL DEPOSITS SINCE THE LAST CONTINENTAL GLACIATION

Dusan Hovorka

Bratislava

During the Neolithic/Aeneolithic human population exploited namely two kinds of raw materials of abiotic nature. Man used clays of different genetical types and various quality. The other category of raw materials represents solid rocks of desirable hardness, elasticity, homogeneity and structure. Number of used raw material types in time progressively increased.

Which geological processes influenced the Earth' s surface topography, and namely destruction of known and creation of a new raw material deposits ? In the following I will try to discuss only those of them, which influenced, or could influenced, exploitation of raw materials for chipped and polished implements construction, together with clays for ceramic production (remember: clay is also rock !) i) Changes of topography of mountaineous as well as hilly areas. As gravity permanently act downslope movement of rock masses is documented. When slopes of hills/mountains are steep enough rockfalls are the most characteristic process. In areas formed by sedimentary sequences movements are relatively slow - they are described as landslides. Namely in the outer Carpathians such processes nowadays represent permanent danger for human settlements, roads, railways and the other linear and areal constructions. Both processes, i. e. rockfalls and landslides represent drastic changes of local topography. Pre-existing rock bodies in those processes are hidden under huge masses of moving rock material, but new outcrops of raw materials also appear. i) Another source of topography changes represents rivers and brooks changing of beds. So rock bodies cropping out in original river beds/valleys are covered by newly deposited river sediments. In newly formed river valleys new outcrops of raw materials, appeared. i) After the retreat of the continental icecap from central Europe some 12000-10000 years ago it takes some time till landscape becames covered by thick vegetation. During that time small soil particles, being the substantial part of tillites (material deposited by the moving continental icecap), have been transported by wind - loess originated. It several meters/tens of meters deposits originated before the Neolithic, but some part of this sediment was deposited also after the last glaciation. Areas covered by loess during Neolithic and namely during Aeneolithic became densily populated - loess is very fertile and should be used as raw material for ceramics as well as the settlements construction.

i) In central Europe during the last 10000 years no volcanic activity is documented. Some volcanoes produced lava flows and namely volcaniclastic material during Palaeolithic: on other places in Europe volcanoes were/are active. Volcanic ash was transported by air several tens till hundreds of kilometers distances. Through the Neolithic, when agriculture starts to supply human race by sufficient quantity of food, volcanic ashfalls represent supply of natural fertilizer on one hand, but it covers (like snow in cold winters) whole country. Also at present (in the New Age) volcanic ash for example in the Sunda islands (Indonesia) is highly expected by farmers, though several volcanic eruptions produced huge amount of volcanic ash (Tambora in 15th century) and destroyed existing civilization. Similar destructive effect is documented in 1783 on Island, where thick ash cover drastically diminished number of cattle, and caused real catastrophe among the population of Island. In nearly all textbooks of geology and archaeology explosive eruption of volcan Thera (now Santorini, Cyclade Islands in the Aegean Sea) around 1500 years BC destroyed practically the whole island. High tsunami, earthquakes and the fall of volcanic ash influenced principally the whole eastern Mediterranean. In connection just with this eruption the Minoan culture on island Creta was destroyed. It was burried under several meters thick ash cover.

i) After the last continental glaciation of Europe in the moderate but humid climate explosion of vegetation expanded over practically whole area of the central Europe. In this permanent process many suitable rock-types have been hidden under vegetation cover. To find raw-material bodies and simultaneously to find exploitable outcrops became more-and-more difficult. This situation, among the other aspects, is responsible for the fact, that Neolithic/ Aeneolithic populations used progresivelly more-and-more raw material types.

i) Among natural catastrophes just on the territory of Slovakia and Hungary, which destroyed log-term used place of living we can mention repeated owerflows and rock-falls in the Domica-Baradla cave system. Natural catastrophes caused that after the time-period of the very rich remnants representing the Bükk culture this cave system was never more inhabitet.

i) Among the very slow, but permantly acting geological processes of the Earth s surface belong those of weathering. Products of chemical weathering processes are visible namely on individualized blocks of rock. Patination of stone archaeological artefacts is just the result of discussed processes. On the very end it should be summed up that geological processes fundamentally also influenced environment of Neolithic/Aeneolithic communities and influenced (speeded up) their progressive development.