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The formation of the Oligocene « calcaires à Astéries » in the region of « Entre-deux-Mers » is affected by a karstification with subhorizontal caves that drained rivers from swallow-holes to resurgences. Observations in quarries show that ghost-rock alterites are present. This paper describes the ghost-rocks in the quarry of Piquepoche exploiting the Frontenac stone. We have studied horizontally developed ghost-rocks with vertical extensions still containing the residual alterite. They can be badly consolidated calcarenites up to soft material which has been sampled. Speleogenesis is reviewed in the frame of the mechanical erosion of the alterite of a horizontal ghost-rock followed by an incision by free-flowing waters which form a passage with promontories and potholes. Finally, we show that ceiling anastomoses can form by ghost-rock karstification.
Unusual speleothems resembling giant mushrooms occur in Cueva Grande de Santa
Catalina, Cuba. Although these mineral buildups are considered a natural heritage, their
composition and formation mechanism remain poorly understood. Here we characterize
their morphology and mineralogy and present a model for their genesis. We propose that
the mushrooms, which are mainly comprised of calcite and aragonite, formed during four
different phases within an evolving cave environment. The stipe of the mushroom is an
assemblage of three well-known speleothems: a stalagmite surrounded by calcite rafts
that were subsequently encrusted by cave clouds (mammillaries). More peculiar is the
cap of the mushroom, which is morphologically similar to cerebroid stromatolites and
thrombolites of microbial origin occurring in marine environments. Scanning electron
microscopy (SEM) investigations of this last unit revealed the presence of fossilized
extracellular polymeric substances (EPS)—the constituents of biofilms and microbial
mats. These organic microstructures are mineralized with Ca-carbonate, suggesting that
the mushroom cap formed through a microbially-influenced mineralization process. The
existence of cerebroid Ca-carbonate buildups forming in dark caves (i.e., in the absence
of phototrophs) has interesting implications for the study of fossil microbialites preserved
in ancient rocks, which are today considered as one of the earliest evidence for life on
Earth.
Limestone caves in New Zealand can be divided into two distinct groups : those developed in the nearby flat-lying limestone of Oligocene age, and those formed in the strongly folded Mt. Arthur Marble of Upper Ordovician age. Caves formed in Oligocene limestone are typically horizontal in development, often having passages at several levels, and are frequently of considerable length. Those formed in Mt. Arthur Marble have mainly vertical development, some reaching a depth of several hundred feet. Previous research into the formation and geological history of New Zealand cave systems is discussed briefly, and the need for further work is emphasised.
Because of the ease of its exploration, the Punchbowl-Signature system (Map reference 677587, Army 1/50,000 Sheet 8627-IV, Goodradigbee) is the most frequently visited of the Wee Jasper caves though it contains even less calcite decoration than does Dip Cave. On the other hand, the system is of considerable scientific interest, both biological and geomorphological. Biologically the interest centres on the long-term investigations of the colony of Bentwing Bats (Miniopterus schreibersii blepotis), initiated by G. Dunnet, sustained and enlarged by D. Purchase. On the geomorphological side, though it is now a dry inactive system like Dip Cave, it possesses a morphology which reveals much of the history of its excavation by a former underground river and so contrasts with its neighbour in the same geological formation only a mile away where there are many difficulties in the way of interpretation of its evolution (Jennings, 1963a).
Caves in the coastal aeolian limestone of Western Australia show two major types of morphology due to different groundwater conditions. The first type comprises linear caves with streams, and develops on a watertable which has pronounced relief because of an undulating impervious substratum. Cave systems of this type are thought to start developing as soon as coherence begins to appear in unconsolidated dunes, and develop rapidly by collapse while the dunes are still weakly cemented, to assume more stable mature forms when the rock is strongly cemented.
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