Andrea Mindszenty*
Department of Applied and Environmental Geology, 
Eötvös Loránd University, Budapest
*http://iris.elte.hu/geo/aaa/dep/applied/mind.htm

On the controversial nature of paleosols related to shallow marine carbonate depositional environments
(povzetek PDF )

Recognition of the importance of exposure related features in shallow water carbonate sequences dates back to the late fifties–early sixties. They have raised interest first among sedimentologists working in carbonate diagenesis, then, as soon as the obvious implications in petroleum geology were recognized the study of paleosols/paleokarst and the related porosity evolution began to receive considerable industrial support. 
    Paleosols occurring in shallow marine carbonate sequences are generally divided into two main groups: 
(a) paleosols related to long-lasting (tectonically controlled) exposure at major regional unconformities, 
(b) intraformational paleosols occurring in cyclically organized sequences where marine sedimentation is repeatedly interrupted by shorter or longer episodes of non-deposition and subaerial exposure (of either intrinsic or extrinsic control). 
    Representatives of the first group are bauxites, terrae rossae and certain calcretes. They have received attention mainly from scholars of paleokarst and bauxites and much less from soil scientists proper. The reason for that is probably that they are soil derived sediments rather than in situ soils. Because of the long exposure and the associated usually mature paleorelief they are often used as paleotopographic indicators in areas which abound in such deposits. Esteban & Juhász (1990) proposed that in any given area bauxitic paleosols should be considered as antagonists to hydrocarbon accumulations, because they would efficiently plug all available karstic porosity and because their presence is indicative of a subsidence history unfavourable for petroleum generation – a suggestion still open to criticism. 
    Paleosols of the second group are not very attractive for the soil scientist either. They do not show spectacular horizonation and are often heavily altered by early diagenetic interaction with marine pore waters. Their presence indicative of subaerial exposure, and their mineralogy – predominantly argillaceous or calcimorphic – considered as indicative of humidity or aridity, respectively, is, however, highly informative for the sedimentologist. When occurring in long enough sequences they are likely to record even subtle climatic changes whereas their degree of development is considered as indicative of the time spent in the zone of pedogenesis. All this qualifies them as excellent markers for both cyclostratigraphy and sequence stratigraphy (e.g. Strasser, 1994, D’Argenio et al.,1997, Chen et al., 2001) 
    Intraformational paleosols were last reviewed by Wright (1994) who emphasized the need to understand better “the real nature of exposure periods at paleosol-capped discontinuity surfaces”. In fact, though such discontinuity surfaces have been in the focus of cyclostratigraphy for quite some time, debates concerning the ultimate cause of the subaerial exposure they are associated with, are far from being settled, as yet. Latest evidence presented by Enos & Samankassou (1998), Strasser & Hillgärtner (1998), Mindszenty & Deák (1999), Immenhauser et al. (2000) and others questioned even the exclusive role of subaerial exposure in bringing about some of the alterations associated with those discontinuity surfaces. This suggests, that notwithstanding all the knowledge hitherto collected on carbonate-related paleosols, there are quite a number of open questions still awaiting for answer and rendering the whole issue controversial.