Why and How are Caves “Organized”: Does the Past Offer a Key to the Present

Povzetek

Prenekatere jame v karbonatnih sekvencah (in morda tudi drugod) izkazujejo opazno prostorsko organizacijo, pri čemer je poudarjeno kopičenje rovov v prostoru (drugega nad drugim). Mnoge starejše razlage tega zgoščevanja vključujejo “recentno” dogajanje in medsebojne vplive. Nove ideje, ki temeljijo na proučevanju “denudiranih” ali ”brezstropih” jam, pripisujejo velik pomen pojavom in odnosom, ki so sicer znani že dolgo, a so jih raziskovalci puščali ob strani kot “neznačilne”, “nepomembne” ali celo “nemogoče”, ob enem pa jih interpretirajo na novo. Tako je potrebno nekatere uveljavljene razlage trodimenzionalnega kopičenja rovov popolnoma prevetriti. Opazovanja ne podpirajo privzetka, da vsaka stratigrafska (lezika) ali tektonska (razpoka) nezveznost že sama po sebi odpira vodi pot in in je zato samodejno žarišče nastajanja kraških kanalov. V svojem prvotnem, “pred-jamskem” stanju - ko so posamezne votline v kamnini zgolj možne - karbonatne gmote niso nujno hidrološko aktivne, niti niso geološko homogene. Nova opazovanja in prevrednotenje starejšega znanja nakazujejo, da se “začetje” bodočih rovov odvije samo na majhni podmnožici vseh lezik, ki so priviligirane že v začetku in že od kraja odrejajo smernice bodočemu razvoju kanalov. Spoznanje te temeljne vloge kaže možno pot k razumevanju organizacije jamskih sistemov in kliče po podaljšanju spelogenetske časovne lestvice prav v čas diageneze.

Many caves within carbonate (and perhaps other) rock sequences display marked spatial organization, particularly a tendency to group within vertical clusters. Most past explanations of clustering involve “recent” effects and interactions. New ideas, based on study of “denuded” or “unroofed” caves, acknowledge but reinterpret features and relationships that were observed long ago and commonly dismissed as “atypical”, “irrelevant” or “impossible”. Some traditional explanations of vertical clustering must now be re-assessed. Assumptions that any stratigraphical (bedding plane) or joint/fault fissure in carbonate rock provides (or provided) a de facto route for fluid transfer, and hence a focus for void development, are not confirmed by observation. Primitive pre-cave, but potentially cavernous, carbonate masses are not inevitably active hydrologically; nor are they geologically homogeneous. New evidence, and re-evaluation of earlier observations, implies that dissolutional void “inception” is related to a minor subset of all stratigraphical partings, which dominate initially, imprinting incipient guidance for later cave development. Recognition of this fundamental role provides a possible key to understanding the organization of cave systems and necessitates acceptance of an expansion of speleogenetic timescales back to the time of diagenesis.