TY - JOUR
T1 - Hollow carbonate pebbles in Neogene conglomerates, central Israel
T2 - Paleogeographic and stratigraphic implications
AU - Sass, Eytan
AU - Kafri, Uri
PY - 1998
Y1 - 1998
N2 - The present study describes the occurrence of hollow pebbles that are found in late Cenozoic conglomerate beds in two localities in central Israel. This extends our previous study of a similar occurrence in northern Israel, and demonstrates that this phenomenon is not as rare as formerly believed. The hollow pebbles, and related rimmed (but whole) pebbles, are characterized by their hard calcitic rims. It has been found that the affected pebbles had originally consisted of either porous dolomites or chalks, and that the lithified rims are due to calcitization (dedolomitization in the case of dolomite precursors, cementation and neomorphism in the case of chalks). The conglomerates which include the hollow (and related) pebbles occur as calcite-cemented lenticular beds that alternate with argillaceous mudstone beds. We propose that this association is not coincidental, and is closely related to the conditions and circumstances that governed the formation of the hollow pebbles. Accordingly, the calcitization of the "suitable" pebbles' rims, which coincided with the cementation of the conglomerates, is attributed to anaerobic microenvironments that prevailed in the mudstones and underlying conglomerates. Dissolution of the pebbles' interiors, which affected only part of the rimmed pebbles, reflects a reversal from calcite supersaturation to undersaturation. We attribute this change to the emergence of the area from the fluviatile aquatic environments, and to the consequent establishment of oxidizing conditions in the vadose zone. The described scenario of lithological association and hollow pebble formation is also linked to the paleogeographic setting. Thus, the alternations of conglomerate and mudstone beds reflect fluviatile environments of shifting channels and overbank deposits which characterize flat and widespread floodplains. Sedimentological and stratigraphic analysis of the data suggests that the two studied conglomerate-bearing sequences, one in the higher Shefela (foothills), the other in the lower Shefela, correlate with the Bet Nir Formation, of Miocene age. This interpretation is linked to the portrayed evolution of a widespread peneplain in the area during the Middle Miocene. Subsequently, the area has been subjected to younger tectonism and to degradation and aggradation processes which largely erased the previous record.
AB - The present study describes the occurrence of hollow pebbles that are found in late Cenozoic conglomerate beds in two localities in central Israel. This extends our previous study of a similar occurrence in northern Israel, and demonstrates that this phenomenon is not as rare as formerly believed. The hollow pebbles, and related rimmed (but whole) pebbles, are characterized by their hard calcitic rims. It has been found that the affected pebbles had originally consisted of either porous dolomites or chalks, and that the lithified rims are due to calcitization (dedolomitization in the case of dolomite precursors, cementation and neomorphism in the case of chalks). The conglomerates which include the hollow (and related) pebbles occur as calcite-cemented lenticular beds that alternate with argillaceous mudstone beds. We propose that this association is not coincidental, and is closely related to the conditions and circumstances that governed the formation of the hollow pebbles. Accordingly, the calcitization of the "suitable" pebbles' rims, which coincided with the cementation of the conglomerates, is attributed to anaerobic microenvironments that prevailed in the mudstones and underlying conglomerates. Dissolution of the pebbles' interiors, which affected only part of the rimmed pebbles, reflects a reversal from calcite supersaturation to undersaturation. We attribute this change to the emergence of the area from the fluviatile aquatic environments, and to the consequent establishment of oxidizing conditions in the vadose zone. The described scenario of lithological association and hollow pebble formation is also linked to the paleogeographic setting. Thus, the alternations of conglomerate and mudstone beds reflect fluviatile environments of shifting channels and overbank deposits which characterize flat and widespread floodplains. Sedimentological and stratigraphic analysis of the data suggests that the two studied conglomerate-bearing sequences, one in the higher Shefela (foothills), the other in the lower Shefela, correlate with the Bet Nir Formation, of Miocene age. This interpretation is linked to the portrayed evolution of a widespread peneplain in the area during the Middle Miocene. Subsequently, the area has been subjected to younger tectonism and to degradation and aggradation processes which largely erased the previous record.
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AN - SCOPUS:0012355557
SN - 0021-2164
VL - 47
SP - 19
EP - 28
JO - Israel Journal of Earth Sciences
JF - Israel Journal of Earth Sciences
IS - 1
ER -