Download PDF - Speleogenesis

40
NCKRI Special Paper No. 1
confined conditions of sluggish rising forced flow and
homogenous hydraulic heads. Less dense and more
aggressive water tends to occupy the uppermost position in
the available space geometry, producing upward-directed
imprints such as rising wall channels, ceiling half-tubes,
and cupolas. Buoyancy currents begin from feeders –
points from which water entered a cave or a particular
story. Buoyant dissolution morphologies comprise a
continuous series, well recognizable in caves where the
original morphology was not much disrupted or obscured
by later water table and vadose development, breakdown
processes, or sedimentation. The morphologic suite of
rising flow is best represented in limestone caves where
thermal waters were involved, and in gypsum caves where
the gypsum strata are underlain by an aquifer with
relatively low solute load.
Dead ends, abrupt changes in morphology and
partitions
Some morphologic features in caves, such as blind
terminations of passages (dead ends), abrupt changes in
size and morphology, and various kinds of bedrock
partitions (vertical or horizontal) were always regarded as
odd and puzzling by researchers accustomed to “lateral”
speleogenetic thinking. They are difficult to explain within
the conventional speleogenetic concepts of caves formed
by lateral flow or by dissolution at the water table. These
features are sometimes considered as attributive to sulfuric
acid speleogenesis (e.g. Hill, 2003a, 2006, Hose and
Macalady, 2006) but in fact, these are very common for
most hypogenic caves regardless of the dissolution
chemistry involved and host rock composition. These
features are perfectly consistent with rising transverse
speleogenesis; lateral changes simply indicate largely
independent rising development of numerous transverse
segments (flow paths), and vertical changes indicate
variations in initial porosity structures across a vertical
section.
Blind terminations of passages are inherent elements
in almost all maze caves (see cave maps throughout this
book) and complex 3-D caves. In most cases they are
“dead ends” only from a “lateral” perspective but in the
transverse flow scheme they are open either to recharge
(feeders from below; Plate 2, A-D; Plate 5, A-C) or to
discharge (outlets to above). The transverse speleogenesis
mechanism allows even a single, laterally isolated fracture
to enlarge to a passable size by vertical flow through its
entire length, but the passage will remain blind-terminated
(pinching out) laterally at both ends (Figure 31-A).
Partitions are thin separations between adjacent
passages or chambers made up of bedrock or various kinds
of planar resistant structures exhumed by dissolution, such
as lithified fill of fractures or faults and paleokarstic
bodies. They are common in many densely packed maze
caves, where bedrock separations between passages are
commonly thin (Plates 12 and 13). In the Western
Ukrainian mazes, bedrock separations (“pillars”) between
adjacent passages may be less than a meter thick (Plate 12,
C though G). Sometimes they are only a few centimeters
thick so that a “window” can be broken by a punch. When
water table overprint was locally noticeable on transitional
stages, thin partitions can be easily truncated by
dissolution at the water table (Plate 12, E-G).
Another type of partition is represented by projections
of lithified fracture fill exposed by dissolution. They may
largely or completely partition rather large passages (Plate
13). Common in some mazes of the western Ukraine, such
partitions are quite fragile (being only a few centimeters
thick). The fact that they remain intact, and passage
morphology remains uniform on both sides of such
partitions, indicates a homogenous head field within a
mature cave system and an overall transverse flow pattern.
Horizontal partitions by more resistant beds in a stratified
sequence may create multi-story cave systems, where
passages of different stories are closely spaced in a vertical
cross-section (e.g. Endless and Dry caves in the Guadalupe
Mountains, New Mexico, USA; Archeri Cave in the Minor
Caucasus, Armenia; Coffee Cave in the Roswell Basin,
New Mexico, USA, Stafford et al., 2008). Osborne (2003)
described partitions of various kinds in Australian caves
and recognized that caves containing vertical and subvertical
partitions are likely to be formed by per ascensum
speleogenetic mechanisms.