Dark Horizon Marks Intriguing Layer on Mars

HiRISE images reveal an intriguing marker horizon among the rocks near Mount Sharp is Gale Crater, which is more erosion resistant than layers above and below.

IMAGE: The marker horizon (yellow arrow) is darker, smoother, and harder than the sulfate-bearing rocks surrounding it. HiRISE image merged to a Digital Terrain Model (DTM) perspective view showing approximately 1 kilometer of topography across Mount Sharp. Image features three times vertical exaggeration. CREDIT: NASA/University of Arizona

A press release was issued from the Planetary Science Institute that looks at an intriguing darker layer of rocks on Mars at Mount Sharp, near where Curiosity is roving. This layer is “darker, stronger, flatter” than the surrounding sulfate-bearing rocks and has been observed using orbital data from the HiRISE camera onboard the Mars Reconnaissance Orbiter. The layer is also weathering differently than the layers above and below, suggesting is made of a more erosion-resistant rock.

Because of the stand-out nature of this rock layer, geologists refer to it as a “marker horizon”. We use marker horizons on Earth to constrain time-stratigraphic features where we know that the layer formed during one single event or a specific period of time. That layer then marks the rocks below as deposited before the event and therefore [older], and the rocks above as deposited after the event and [younger]. Think of the KT boundary and the iridium that marks “below here are dinosaurs and above here, not so much.”