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| Titel |
Lacustrine Geomorphology on Titan; Glimpses into the Evolution of Titan's Polar Landscapes over Multiple Timescales |
| VerfasserIn |
A. G. Hayes, W. E. Dietrich, M. M. Manga, A. Lucas, O. Aharonson |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250069165
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| Zusammenfassung |
| Titan’s hydrocarbon lakes and seas express a range of morphologic characteristics that
suggest a rich history of change operating on seasonal, millennial, and geologic timescales.
We will present a review of observed lacustrine morphologies, describing both the
distribution of and interaction between lake basins, shoreline features and fluvial drainage
networks found in the North and South Polar Regions. While Cassini has directly
observed seasonal variation in the southern lakes, longer timescale variations must be
inferred from the interaction between geologic features. Features interpreted as
topographic benches in the north and paleoshorelines in the south suggest base level
changes on millennial timescales while the orientation between sea shorelines and
nearby drainage networks implies regional variations over geologic timescales. A
process-based study of these relationships reveals important information pertaining to
the paleoenvironment, paleohydrology, and topographic evolution of Titan’s polar
landscapes.
Lakes are found both with and without associated drainage networks, have shoreline
transitions varying from sharp to diffuse, include a variety of plan-form shapes ranging from
near-circular to highly-irregular, and have surface areas than span from the limits of detection
(~ 1Â km2) to more than 105Â km2. The largest seas in the north, including Ligeia, Kraken
and Punga Mare, accommodate shallow bays where upland channels terminate into
well-developed drowned river valleys, thus showing a transition from well drained to
swamped topography without sedimentation keeping pace with the rising relative base level.
Nearby fluvial systems include drainage networks that run parallel to sea shorelines,
suggesting the existence of a widespread drainage system that predates the large-scale,
and apparently non-uniform, down-dropping of topography responsible for sea
formation. Similar morphologic relationships are observed in the lowest portions of the
south, revealing boundaries that may represent paleoshorelines which encompass
areas comparable to their northern counterparts. Here we also see evidence of a
pulse of channel incision (due to relative base level lowering) that has propagated
across a pre-existing less dissected plain sloping away from the advancing channel
network.
While the larger seas are morphologically consistent with drowned topography
the smaller lakes, which have median area of 77 ± 20Â km2, originate through
other processes. The formation mechanisms responsible for these features are not
well understood. Where available, topographic data suggests empty lake basins
are steep-sided and 150-300Â m in depth. Proposed mechanisms for creating these
depressions include impact, volcanic, dissolution and/or solution-based processes. Glacial
and most periglacial processes are likely thermodynamically restricted. However,
each of the currently proposed mechanisms has significant problems. The irregular
shape of many lakes, the non-stochastic size distribution, and the concentration
in polar regions argues against impact and volcanic-based processes. The karstic
dissolution model requires the upper crust to contain a substantial amount of material
that is soluble in liquid hydrocarbon and solution-based processes (e.g. gnamma
holes) required an efficient method of removing weakened material. As part of
our review of lacustrine morphology, each of these formation mechanisms will be
discussed in the context of the distribution, shape and structure of the observed lakes. |
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