The Origin of Sediments Inside Collapse Dolines of Postojna Karst (Slovenia)

Na kraškem površju Slovenije najdemo več sto večjih udornic. Njihova dna lahko prekrivajo podorni bloki, melišča ali prst. Na ponornem obrobju krasa, kjer voda prenaša večje količine alohtonega materiala, so dna mnogih udornic zapolnjena z ilovnatimi sedimentnimi uravnavami. Podrobneje sem preučil 15 udornic v bližini Postojnskega jamskega sistema. Pokazalo se je, da so ilovnate sedimentne uravnave na istih nadmorskih višinah v večih sosednjih udornicah hkrati. Nivoji sedimentnih uravnav so primerljivi z višinami zapolnitev poplavne ilovice v bližnjih jamskih rovih. Proces sedimentacije in uravnavanja dnov udornic v nivoje je posledica poplav, ki so segale nad dna udornic in so povzročile sedimentacijo ilovnatega materiala in uravnavanje v njihovem dnu. Zato lahko na podlagi nadmorskih višin sedimenta v dneh udornic predvidevamo dinamiko sedimentacije v kraškem podzemlju, hkrati pa lahko na podlagi razvoja jamskega sistema ugotavljamo razvoj udornic. Several hundred collapse dolines are recorded on the Slovenian karst surface. Their fl oors are covered with boulders, scree or a soil layer. In ponor karst areas, where water transports signifi cant amount of allochtonous material, many collapse doline fl oors are made level by deposits of loamy sediment. This discussion relates to a detailed study of 15 collapse dolines near the Postojna cave system. Loamy sediment appears within several neighboring collapse dolines and covers their fl oors at approximately the same altitude. The sediment level preserved in the collapse dolines is commonly at the same elevation as fl ood loam deposits within nearby caves. It transpires that the fl attening of the collapse doline fl oors is a result of fl ooding inside the karst that extended above the original fl oors of the collapse dolines. It is possible to predict some of the sedimentation dynamics inside the karst on the basis of the elevations of the loamy sediments within the collapse dolines. On the other hand, it is also possible to fi nd out about collapse doline development by studying the processes inside cave systems.