STRATIGRAPHIC STACKING OF SEDIMENTARY SUCCESSIONS ON MARS – A REFLECTION OF BASE LEVEL FLUCTUATIONS?

The origin of stratification surfaces is a fundamental matter of concern to stratigraphers. Numerous field studies have driven home the fact that an understanding of stratigraphic omission surfaces is just as important as an appreciation of rock volumes and facies. The logical outcome of this development was the concept of sequence stratigraphy that provides us with a coherent conceptual framework to understand stratigraphic packaging in chronostratigraphic terms.

High resolution images from the Mars Orbiter Camera (MOC) show an abundance of layered strata in Mars that are most likely of sedimentary origin. Examination of MOC images shows that these successions consist of stacked packages of strata that can be distinguished on the basis of albedo, uniformity vs. variability of layer thickness, erosion characteristics, and internal features that may be due to penecontemporaneous mass movements or may even reflect bounding surfaces in thick aeolian strata.

On Earth, such stratigraphic partitioning of rock volumes would depend on the interplay between sediment flux, sedimentation rate, and base level change. The resulting sequences or packages are the fundamental building blocks of regional stratigraphic architecture. In areas like the Colorado Plateau, the thickness of first order sequences (Sloss sequences) would range in thickness from less than 100 to several hundred meters. Stratigraphic packaging at that scale is clearly visible on air photos that have been converted to fall into the resolution range (5-20 meters per pixel) of MOC images. MOLA data acquired with MOC images indicate that stratigraphic packages on Mars are in a similar thickness range as observed for first order sequences on Earth.

By analogy with Earth, we presume that base level change is a dominant cause for stratigraphic stacking on Mars. While there is only scant evidence for crustal processes (e.g. sea floor spreading) that could have caused significant base level variations, fluctuations of polar ice cap volume might be a viable alternative. Mars is more distant from the sun than Earth, and thus ice caps might have been a common feature during its early history and exerted control over water volumes of ocean and lake basins.