The morphological characteristics and evolutionary development of rock labyrinths on Earth (in sandstone, volcanics, and carbonates) are compared with those on Mars. On Earth rock labyrinths originate as parallel, an echelon, or intersecting narrow grabens, or develop where fault and joint networks are selectively eroded. Labyrinths frequently contain both downfaulted and erosional elements. Closed labyrinths contain depressions; open labyrinths do not, they are simple part of a fluvial network generally of low order. As closed labyrinths made up of intersecting grabens or made up of connected erosional depressions are extremely common on Mars, the research focussed on an understanding of these labyrinth types. Field investigations were carried out in Canyonlands National Park, Utah, and in the Chirachahua Mountains of Arizona. Martian labyrinths were investigated using Viking orbiter images. In addition, research was undertaken on apparent thermokarst features in Lunae Planum and Chryse Planitia where closed depressions are numerous and resemble atlas topography

Brook, G. A.

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AThe Origin and Evolution of Terrestrial and
	
cuz'
Martian Rock Labyrinths,/
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Final Technical Report
	
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NASA NSG 7539
George A. Brook
The overall objective of the research was to compare the morphological
characteristics and evolutionary development of rock labyrinths on Earth--
in sandstone, volcanics, and carbonates--with those on Mars. On Earth
rock labyrinths originate as parallel, en echelon, or intersecting narrow
g rabens, or develop where fault and joint networks are selectively eroded.
Labyrinths frequently contain both downfaulted and erosional elements.
Closed labyrinths contain closed depressions; open labyrinths do not,
they are simply part of of a fluvial network generally of low order. As
closed l abyrinths made up of intersecting grabens or made up of connected
erosional depressions are extremely common on Mars, the research focussed
on an understanding of these labyrinth types. Field investigations were
carried out in Canyonlands National Park, Utah, and in the Chiracahua
Mountains cC Arizona. Martian laybrinths were investigated using Viking
orbiter imi ►ges. In addition, research was undertaken on apparent
thermokarst features in Lunae Planum and Chryse Planitia where closed
depressions are numerous and resemble alas topography.
Open Labyrinths
Open labyrinths on Earth are well developed in a limestone/sandstone/
shale sequence at Bryce Canyon, Utah; in sandstones at Arches and Canyonlands
National Parks, Utah; and in volcanic rhyolites in the Chisos Mountains of
Texas and Chiracahua Mountains of Arizona. In each area the labyrinths
form part of a stream channel network. Linear, joint-controlled
(NISA -CH- 175511) TIS OSIGIS AND EVOLUTION
OF TBRESSZSIAL ANC dIHTIAN SCCK LABYiINTHS
Final Tecbni,_al Report (Geczgia Univ.)	 9 p
hC Av1/MF AU1	 CSCL 03A
N85-22326
Unclas
G3/91 14515
2channel segments, which often intersect at ri g ht angles, box valleys,
and buttes are characteristic landform elerreiits. Open terrestrial
labyrinths develop ;n fractured rocks where chemical and mechanical
weathering followed by denudation operate preferentially in joints,
which represent lines of increased secondary permeability. Labyrinths
are most common in areas of steep hydraulic gradient and so they tend
to be located back from steep fault or erosional scarps, and at steep
valley headwalls. Sapping with suffosion of weathered detritus are the
si g nificant processes bringing about headward extension of open labyrinth
networks. Open labyrinths are also quite common on Mars and closely
resemble their terrestrial counterparts. For example, Viking images
664.408-664A13 reveal a well-developed labyrinth in Kasei Vallis.
Martian networks appear to erode headward by loss of frozen volatiles
at the valley headwall--a process akin to sapping of liquid water on
Earth. As the frozen volatiles are concentrated in the more weathered
fracture zones, headward retreat is directed along criss-crossing struc-
tural weaknesses.
Closed Labyrinths
1.	 Erosional
Erosional closed labyrinths on Earth are most frequently formed by
solution of karst rocks. Examples in other rock types are relatively
rare. The Channelled Scablands of eastern Washington in basalt, and
the Antarctic Wright Dry Valley labyrinth in dolerite are the only known
deep erosional labyrinths in non-carbonate rocks. The Channelled Scablands
were produced by catastrophic flood erosion. A similar origin has been
3suggested for the Wright Valley labyrinth although other hypotheses includina
glacial erosion, subglacial meltwater erosion, and salt weathering followed
by deflation of the weathered products have been proposed. A significant
difference between karst labyrinths and the Wright Valley and eastern
Washington labyrinths is that the latter show preferential development of
elroAgated depressions in one major direction suggesting a subaerial
formation by a moving medium such as water or ice. Significantly,
morphologically similar labyrinths are present in localized parts of
the Martian outflow channels.
Terrestrial closed erosional labyrinths in karst and in volcanic rocks
appear to contain the same relief elements: pits, streets, platea,
towers, and marginal plains. Furthermore, there is a simple developmental
sequence (Fig. 1). Strings of elliptical, vertical-walled pits develop
in intersecting fracture systems. Pits gradually enlarge and coalesce
so .-hat steep-walled linear depressions or streets are formed. As
streets deepen and widen, intervening rock ridges are dissected and
ultimately destroyed. Angular closed depressions called platea are
produced which frequently contain residual rock towers. As platea increase
in number and size, the landscape is reduced to a series of isolated rock
towers separated by broad marginal plains.
Closed erosional labyrinths on Mars are generally much larger than
those on Earth but have virtually identical form. In the southeast portion
of Memnonia Southeast Quadrangle, for example, a depression 90 km long and
10-15 km wide has developed = n the old cratered surface. The eastern one-
third of the depression is formed of two intersecting craters; the western
two-thirds is an angular platea with residual rock towers 0.5-10 km in
A.
t
r. ^ - ____ -
4
Fig. 1. Stages in the evolution of closed erosional labyrinths
on Earth and Mars. During early stages strings of pits
(catenas) develop in vertical fractures (A). By enlarge-
ment and coalescence along the f ractures strings of pits
are converted to intersecting networks of streets (B and
C). As streets deepen and widen the intervening rock
ridges are dissected and ultimately destroyed. Replacing
them are large closed depressions called platea (D and
E). As platea expand rock towers are left which rise from
a marginal plain (F).
ORIGINAL PAGE
BUCK AND WHITE PHOTOGRAPH
s5
diameter. l!alls of the platea are structurally controlled. West of the
depression are strings of elliptical pits (catenas) developed in regional
fractures.
Strings of pits or catenas, the first stage of closed erosional
labyrinth development, are found on upland surfaces surroundin g
 Noctis
Latyrinthusand Valles Marineris. South of Coprates Chasma and
parallel to it are three catenas, the largest is 350 km long. Other
strings occur east of Ophir Chasma and south of Tithonius Chasma. All
are developed in regional fractures. There is no doubt that the strings
of pits eventually evolve into narrow linear troughs equivalent to the
streets of labyrinth karst. Where parallel troughs develop it is also
apparent that slope recession gradually erodes the intervenin g upland
surfaces. This has occurred in Coprates Chasma, at the western end of
the Chasma a plateau remnant 60 km long and 5 km wide is preserved as the
crest of a narrow ridge separating two troughs. Where Coprates Chasma
joins Eos and Capri Chasma, a second rid g e is in a more advanced stage of
evolution; receding slopes have intersected so that no plateau remnants
remain. If some Martian troughs have developed in the manner described,
they can be regarded as huge platea foim ed by erosion acting along
vertically and horizontally persistent regional fractures which surround
the Tharsis uplift. Closed erosional labyrinth relief is also evident
in many areas of fretted terrain. For example in Nylosyrtis Mensae
catenas on the ancient cratered uplands are clearing evolving into
elon g ated trou g hs equivalent to streets.
2. Structural
Structural labyrinths fotm ed of intersecting grabens are by far the
largest and most common labyrinths on Nars. Noctis Labyrinthus is
6the classic example. It is a network of grabens tens of km wide and hundreds
of km long at the summit of the Tharsis-Syria Rise. The labyrinth is
1,000 km across. A terrestrial labyrinth, similar in many respects to
parts of Noctis Labyrinthus, has developed in the Grabens District of
Canyonlands National Park, Utah. Numerous parallel and en echelon
g rabens 100-600 m wide, 0-100 m deep, and several km long, have floors
covered by stream alluvium, aeolian deposits, and rubble derived from
graben wall collapse.
Field and aerial photographic studies indicate that prior to graben
development a surface stream system drained the region northwards into
the Colorado River. Block faulting disrupted this drainage. The streams
were diverted into the closed grabens, the water was absorbed by the
unconsolidated sediments covering the floors, and eventually it escaped
underground along zones of high secondary permeability in the bedrock--
namely the normal faults that criss-cross the region. Our field investi-
gations have revealed numerous locations where around water in the sediments
covering the depression floors is draining underground into faults. This
water emerges elsewhere in springs. Water frequently sinks into the
faults at the graben side walls or whereone or more faults intersect near
the centers of Graben floors. The sinking points are frequently marked
by subsidence depressions where the surficial sands have subsided into
subsurface cavities. The largest depressions are 10-15 m deep. Subsurface
cavities are believed to originate by the solution of the calcareous
matrix of the sandstone bedrock. Leadina into the subsidence depressions
are shallow (1-5 m deep) valleys with steep sides and headwalls. These
valleys were almost certainly produced by groundwater sapping in the
7surficial sands with suffosion of the finer particles underground. Signi-
ficantly, collapse or subsidence depressions are also numerous in the graben
floors of Noctis Labyrinthus, Mars, attesting to the existence of subsurface
cavities in this region also.
Oriqin of the Closed Labyrinths
The strikin g morphologic and Evolutionary similarities between labyrinth
karst on Earth and closed erosional labyrinths on Mars, and the similarities
between the karst-modified Grabens landscape of Canyonlands National Park,
Utah, and parts of Noctis Labyrinthus, Mars, sungest that the Martian
terrains were produced by surface collapse into subsurface cavities produced
by chemical denudat.)n in the sub-permafrost around water zone over millions
of years, or that cc'lapse resulted from localized permafrost degradation.
In the latter case the labyrinths would be thermokarst features. Alterna-
tively a combination of both processes could be responsible for the labyrinth!
of Mars.
A model for the development of topography like that of Noctis Labyrinthu!
is presented in Fig. 2. The model assumes that permafrost degradation at
depth occurs preferentially along fractures becaise of increased geothermal
heat flow. This causes compaction of volcanic ash layers and eventually
leads to subsidence of the surface. Instability of volcanic ash layers
overlain by basalt causes scarp retreat by mass wasting so that troughs
and depressions grow in size. The finer sediments of the volcanic ash
layers are removed by wind and re-deposited at the Martian poles.
V
81DROCK
F BRICCIA
8
	 I
Stage 1: Fault neat Flux
Stage 2: Thaw 'Lone Coalescence anu 1st Generation Pits
Stage 3: Daughter Hollows and Grandaughter Catenas
Can.. , or. _r.zansion and .;o_io.^ ,i;anaoru;ent
Fig. 2. Topographic Development in Noctis Lab rinthus
as a Result of Permafrost Degradation
OR IGINALBLACK AND WW1
MWOGRAP^1
.J
PUBLISHED ABSTRACTS AND THESES
THESES
Heywood, N. C. (1984). Physiugraphy of the Martian West Equatori
Uplift. M.A. Thesis, University of Georgia, 153 p. (Major
professor George A. Brook)
PUBLISHED ABSTRACTS
Brook, G. A. (1979). Terrestrial and Martian Rock Labyrinths. Decennial
Meeting of Plantary Geology Principal Investigators, Providence.
NASA Technical Memorandum 80339, pp. 42-46.
	
Brook, G. A. (19000).	 Pits, Streets, Platea, Towers, and Marginal Plains
on Mars. NASA Technical Memorandum 81776, pp. 57-59.
Brook, G. A. (1981). The Martian Fretted Terrains: Examples of
Therrokarst Labyrinth Topography. NASA Technical Memorandum
82385, 359-372.
Brook, G. A. (1981). A Small Scale Terrestrial Analog of Martian Pitted
and Etched TE , rrain. Geol. Soc. of America, Abstracts with Programs.
p. 417.
Brook, G. A. (1981). Eolian Erosion of Poorly Consolidated Sedimentary
Blankets on Mars: A Small-Scale Terrestrial Analog. RASP,
Technical Memorandum 84211, 235-237.
Brook, G. A. (1981). Comparison Between flartian Troughed and Fretted
Terrains and Terrestrial Labyrinths. Association of American
Geographers, Annual Conference, Los Angeles, California. Program
Abstracts, p..78.
Brook, G. A. (1981). The Origins of Martian Fretted and Troughed
Terrain. Papers Presented to the Third International Colloquium
on Mars, Pasadena, CA. Lunar and Planetary Institute, Contribution
441, 31-33.
	
Brook, G. A. (1982). 	 Ice-Wedge Polygons, Baydjarakhs, and Alases in
Lunae Planum and Chryse Planitia, Mars. NASA Technical Memorandum
•	 85127, 265-267.


The origin and evolution of terrestrial and Martian rock labyrinths

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