Hi Bill
Silvestru can't know as much about karst as he says he does if he makes these
statements. With respect to karst landscapes, many of these are of great
age. For example, many caves in Devonain limestone in eastern Australia have
been partly filled by Eocene basalts. In addition there are numerous
examples from many parts of the world of ancient karst landforms within
geological strata. Three examples follow.
ORDOVICIAN PALAEOKARST, QUEBEC
Desrochers and James (1988) described two major palaeokarst unconformities
from the Middle Ordovician rocks of Mingan Island, Quebec. The first of
these is at the top of the Early to Middle Ordovician Romaine Formation, a
succession of dolomitised limestones, containing mud banks, patch reefs, and
intertidal (sabkha) cycles. The unconformity is exposed over a 75 km length.
The post Romaine unconformity is very flat with almost no relief. However,
gentle tilting of the underlying strata means that up to 30 m of the
succession have been eroded from the easternmost exposures, resulting in a
slight angular unconformity. Most of the Whiterockian is missing along this
surface. The post Romaine surface shows numerous small scale features that
indicate that the erosion occurred subaerially by solution erosion. These
features include dolines, rundkarren, kamenitzas, and planar surfaces.
Dolines in the top of the Romaine are up to 3 m deep and 5-30 m across.
Discrete breccia bodies underlie some dolines; the dissolution that formed
them led to the collapse of overlying beds to form the doline.
Rundkarren at the top of the Romaine are 10-40 cm in width and 5-30 cm deep.
Their length varies from a few metres to more than 15 m. Kamenitzas on the
post Romaine surface are 20-80 cm across and 5-30 cm deep. They are
scattered across the surface and are not underlain by breccias.
MADISON AND LEADVILLE PALAEOKARST (MISSISSIPPIAN), WYOMING
The Madison Palaeokarst is developed on the top of the Middle Mississippian
Madison Limestone (Sando 1988) over a distance of at least 800 km in each
direction. The This surface was transgressed from the west during the Late
Mississippian into the Early Pennsylvanian by the Amseden Formation. Local
relief, excluding dolines, is 5 m and regional erosional relief is 60 m.
Isopachs of the basal Darwin Sandstone Member of the Amseden Formation define
a west-draining dendritic palaeovalley system. Elsewhere, karst towers up to
30 m high and palaeovalleys up to 140 m deep are developed along the same
surface on the laterally equivalent Leadville Limestone (de Voto 1988).
Perpendicular and horizontal joints are common in the uppermost preserved 32
m of the Madison Limestone and descend down from the unconformity surface.
The enlarged joints vary from a few cm to 30 cm in width. They define
reticulated networks. Red terrigenous sediments fill the enlarged joints.
The enlarged joints that intersect the surface resemble grikes. The largest
solution enlarged joints form a continuum with the smallest caves.
Large vertical cavities that have demonstrated continuity with the top of
Madison unconformity are up to 27 m deep and 15 m wide. Overhangs and
re-entrant walls are present, and angular blocks of the limestone occur in
the doline fill of red sandstone, siltstone, and shale. Those developed in
the Leadville Limestone in Colorado are larger, 10-500 m across and up to 75
m deep. A structural control on their distribution is evident.
Irregularly shaped cavities varying from less than 30 cm to more than 3 m
across and lacking obvious connection with the unconformity are interpreted
as caves. They occur at depths of up to 60 or 105 m below the preserved top
of the Madison. Circular, semi-circular, and elliptical cross sections have
been observed. No decoration is present on the walls of the caves. This,
combined with their predominantly horizontal orientation, suggests that they
are largely phreatic features. Angular blocks of the enclosing rock occur in
the cases that are mainly filled by red sandstone. Similar features beneath
the Leadville unconformity are locally interconnected with the dolines.
Infill of the palaeokarst features consists of fine to coarse grained, red
coloured, terrigenous sediment. These are considered to represent the
earliest stages of the overlying Darwin Sandstone Member. Depositional
environment is interpreted as being fluvial, given the palaeovalley filling
nature of the Darwin Sandstone.
The Molas Formation occurs discontinuously and only in the lowest parts of
the palaeotopography developed on the upper part of the Leadville Formation,
such as between karst towers. It is up to 30 m thick in the topographic lows
and thins on the flanks. Where dolines are present the Molas Formation can
occur as much as 50 m below the preserved top of the Leadville Formation. The
Molas Formation is clay rich in the upper part with angular chert and
limestone fragments and grades down into unaltered bedrock. Lithologies very
similar to the Molas Formation also occur in solution enlarged joints and
bedding planes. Considerable variability occurs in the upper part of the
Formation. It varies from haematitic to grey to carbonaceous. The Molas
Formation is interpreted as a residual palaeosol varying from a terra rossa
where haematitic, as gley soils where grey, and organic rich where
carbonaceous.
ORDOVICIAN KNOX UNCONFORMITY, APPALACHIANS
The Knox unconformity is developed on the 200-1200 km thick carbonates of the
Upper Knox-Beekmantown Groups of Virginia and Tennessee (Mussman et al.
1988). It is equivalent to the Post Romaine unconformity in Quebec. In
southwest Virginia the Knox is marked by an angular unconformity between the
Canadian and the Chazyan, with the entire Whiterockian missing. The
stratigraphy is more conformable in northern Virginia and the upper part of
the Whiterockian is present overlying the Knox surface. Sedimentation before
and after formation of the unconformity is consistent with arid or semi arid
conditions. The contact changes from a disconformity in the south east to an
angular unconformity in the north west, with the angular discordance reaching
a maximum of 12 degrees. The amount of section removed by erosion is a few
metres in northern Virginia to 140 m in south west Virginia. Palaeokarst
features include knolls, dolines, caves, microfacies, and geochemistry.
Cross-cutting features that extend down from the unconformity are interpreted
as dolines. These are narrow, breccia-filled bodies, 3-35 m wide and up to
65 m deep. Typically vertical in orientation, some extend horizontally at
depth. The clasts consist of carbonate and chert blocks derived from the
host rock in a matrix of quartz and detrital dolomite. There is no
decoration on the walls.
Bedrock highs along the Knock Unconformity locally reach 30 m above the
surrounding surface, not including dolines. The highs are draped by thin (30
cm typically) breccias which thicken in the lows between them to 70 m,
including dolines.
Thin, sheet like to pod like bodies up 12 m long and 2 m wide occur up to 35
m beneath the unconformity and are filled by detrital dolomite. These are
likely to be filled caves. The contact between the wall rocks and the fill
is sharp, with local breccias in the fill near the contact. The walls are
undecorated. The fill is brown, and occasionally layered or conglomeratic.
Aragonitic fossils and other grains are partly to completely dissolved.
Carbonate marine muds that were also probably originally aragonitic have
undergone patchy recrystallisation. Pendant and meniscus cements, which can
form only in zones of partial saturation, are found locally beneath the
unconformity. Deeper in the succession only blocky calcite, consistent with
precipitation in the phreatic zone, is present.
Ordovician marine carbonates such as those that under and overlie the Knox
unconformity, have oxygen isotope values of –5 to –6. The crystallised
marine muds have values –8.3 to –8.8 and early cements –8.8 to –11.6. These
values are consistent with reaction with rainwater, which is rich in
isotopically light oxygen. Sources of oxygen other than sea water and rain
water (such as hydrothermal fluids or deep groundwater) are much heavier.
FORMER JUGOSLAVIA
None of the caves in the palaeokarst systems mentioned above contain
spleothems. However, at Knezopolije (near Mostar) mining for bauxite within
the Mesozoic limestone succession has revealed that the bauxite fills a
palaeokarst topography that includes decorated caves. These caves had both
vertical and horizontal sections and were decorated with cascades and
stalagmites (Bardossy 1982).
Silvestru is wrong. There are many karst features in the geological record
of great antiquity. These occur at all scales, from the large scale
dendritic drainage systems in the Leadville Limestone, to the medium scale
karst towers (also at Leadville) and almost ubiquitous dolines, to the small
scale rundkarren and kamenitzas in the Romaine surface. Furthermore, these
surfaces are associated with palaeosols and the petrographic and geochemical
features characteristic of subaerial exposure.
BARDOSSY, G. 1982. Karst bauxites. Developments in economic geology 14.
Elsevier, Amsterdam, 441p.
DE VOTO, R. H. 1988. Late Mississippian paleokarst and related mineral
deposits, Leadville Formation, central Colorado. In JAMES, N. P. and
CHOQUETTE, P. W. 1988 (eds). Paleokarst. Springer-Verlag, New York, p
278-305.
DESROCHERS, A. and JAMES, N. P. 1988. Paleozoic surface and subsurface
paleokarst: Middle ordovician carbonates, Mingan Islands, Quebec. In JAMES,
N. P. and CHOQUETTE, P. W. 1988 (eds). Paleokarst. Springer-Verlag, New
York, p 183-210.
MUSSMAN, W. J., MONTANEWZ, I. P. and READ, J. F. 1988. Ordovician Knox
paleokart unconformity, Appalachians . In JAMES, N. P. and CHOQUETTE, P. W.
1988 (eds). Paleokarst. Springer-Verlag, New York, p 211-228.
SANDO, W. J. 1988. Madison Limestone (Mississippian) paleokarst: a geologic
synthesis. In JAMES, N. P. and CHOQUETTE, P. W. 1988 (eds). Paleokarst.
Springer-Verlag, New York, p 256-277.
respectfully
Jon
Bill Payne wrote (in part):
> As an example of why I find this Journal refreshing, I seem to remember
> seeing on this list a statement to the effect that paleokarst proves long
> ages. From the "Summary and conclusion" of the article on "Paleokarst"
> in the Journal:
>
> "From the Proterozoic to Mesozoic, all paleokarst features seem to have
> been reduced to local minor surface features.
>
> During the Mesozoic, it is claimed that major karst features formed only
> in some parts of Europe (namely Yugoslavia). The other regions of the
> earth, even when karstification conditions were much better than today,
> seem to have produced nothing but bauxite ore deposits in minor surface
> karst features.
>
> Similarly, the Tertiary produced little, if any, aerial paleokarst, even
> though karstification conditions were supposedly good enough and long
> enough to generate a complex and widely developed surface and subsurface
> karst.
>
> The Quaternary, the shortest era according to evolutionary geology, has
> managed to make up for it all. In this 'short' period, karstification
> processes have been able to generate the grandiose karst features we see
> all over the world today, from the equatorial to polar regions.
>
> It is clear that there must have been a major qualitative change in the
> gnensis of landforms, especially karst landforms, at the end of the
> Tertiary.
>
> A logical inference from this change is that true karstification
> processes, like the ones we are witnessing today (which after all are the
> ones that inspired the very idea of karstification), only occurred in the
> Quaternary. All previous karst-like features represent protokarst
> (incipient or incomplete karst) or pseudokarst." (from Silvestru, Emil,
> Paleokarst - a riddle inside confusion, CEN Tech. J., v 14(3): pp100-108,
> 2000)
>
> The paper contains 37 references, only one of which appears to be from a
> creationist source (another CEN Tech. J. article). Silvestru has a
> Masters and Ph.D from Babes-Bolyai University of Cluj, Transylvania,
> Romania, where he has worked as an associate professor in karst
> sedimentology. "A world authority on the geology of caves, he has
> published 26 scientific papers, six abroad. He was until recently the
> head scientist at the first speleological institute in the world, the
> Emil Racovitza Speleological Institute founded in Cluj, Romania in 1920."
>
> Comments anyone?
>
> Bill Payne
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