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HYPOGENIC CAVE FEATURES
Figure 36. Maps of typical caves in the Turonian limestone.
Network maze patterns commonly develop at two or three levels.
Cave entrances are artificial. Broken lines on the Aneva Cave plan
are rifts at the bottom of passages. Combined from Frumkin and
Fischhendler (2005) and Frumkin and Gvirtzman (2006).
A few papers describing karst and caves in Saudi
Arabia, Qatar and other regions of the Arabian Peninsula
(e.g. Amin and Bankher, 1997; Peters et al., 1990; Sadiq
and Nasir, 2002; Hussain et al., 2006) give strong evidence
in favor of a hypogenic transverse origin of karst features,
although not interpreting them in this way. The vast
regional multi-story (eleven aquifers) artesian system
comprises alternating sulfate, carbonate and clastic beds
within the Mesozoic and Cenozoic Arab, Hith, Silaiy,
Aruma, Umm Ar Radhuma, Rus, Dammam and Hofuf
formations. This offers extremely suitable conditions for
transverse speleogenesis. Numerous caves are mainly
fissure- and slot-like passages or clusters of passages
(“ghar” caves); some are clear rectilinear mazes. None of
the caves show any genetic relationship with the surface.
The regional artesian system discharges via numerous
springs at the Gulf area, many of them being vertical pits
(“ayns”) through which groundwater rises from horizontal
passage clusters at the base (Hötzl et al., 1978). Amin and
Bankher (1997) and Sadiq and Nasir (2002) implied that
karst and caves in the area were formed epigenetically
during past humid epochs of the Plio-Pleistocene. Hussain
et al. (2006) suggested that network caves in the Upper
Miocene calcareous sandstone in the Jabal Al Qarah area
(Figure 37), which are being truncated now by
denudational lowering, have developed due to weathering
and enlargement of the fracture systems. The photographs
in this paper show, in fact, very characteristic
morphologies of confined maze caves, now in the process
of un-roofing. It is argued here that, based on available
information about regional litho- and hydrostratigraphy,
hydrogeology, and cave patterns and morphology, the
dominant mode of karst development in that region is
probably hypogenic transverse speleogenesis. Numerous
deep collapse sinkholes described in the region (e.g. Amin
and Bankher, 1997; Sadiq and Nasir, 2002), some with
unexplored caves at the base, are clearly related to
regionally operating contemporary artesian speleogenesis
rather than to presently inactive epigenic cave systems
formed during past epochs of humid climates, as
commonly assumed for the region.
A hypogenic transverse origin could be assigned to
Magharet Qasir Hafeet Cave in the Jebel Hafeet ridge in
the United Arab Emirates, described by Waltham and Fogg
(1998). The cave has rift-like passages at depths of almost
100 m, connected to the surface through a series of vertical
joints and shafts of apparently rising morphology. It occurs
at the crest of an eroded anticline, in limestones that were
confined by a clay-marl sequence in the past. Although
initially a conventional phreatic origin was suggested for
this cave (Waltham and Fogg, 1998), the possibility of per
ascensum hydrothermal origin has been later
acknowledged (Waltham and Jeannin, 1998).
Figure 37. Plan view and cross-sections (insets) of Jabal Al Qarah
caves formed in the calcareous sandstone of the Upper Miocene
Hofuf Formation, northeastern Saudi Arabia (adapted from Hötzl et
al., 1978, and Hussain et al., 2006).
Africa
Hydrothermal caves in massive Cretaceous limestones,
including complex 3-D and network maze systems, are
reported from northern Algeria (Collignon, 1983, 1990)
and northern Namibia (Martini and Marais, 1996). Quinif
and Dupuis (1989) described the artesian karst system of
Ziaka in Zaire. Ziaka Cave is an emergence of the system
explored by divers. It has the characteristic morphology of
confined caves with numerous cupolas. The piezometric
surface of the aquifer is higher than the base level of the
Kwilu River.
Maze caves are common throughout the Transvaal
Basin in South Africa, in the carbonates of the Malmani
Subgroup of late Archaean age (2.5-2.6 billion years).
Sterkfontein Cave is the best documented example
(Martini et al., 2003), well known for the hominin fauna
found in a breccia fill. It is also an informative example of
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