Mysterious rock layer in Gale Crater on Mars awaits study by Curiosity rover

(ORDO NEWS) — Scientists have been studying deposits in Gale Crater on Mars for years using orbital data, but thanks to the Curiosity rover passing over these deposits, we can also get close observations and detailed measurements of rocks, similar to the field work of geologists on Earth.

A new paper led by Planetary Institute Senior Scientist Katherine Weitz takes a fresh look at a mysterious feature seen from orbital images of Mount Sharp, a 5.5-kilometer mound in Gale Crater: a darker, thicker, evener, smoother rock layer or weathering horizon , which stands out against the background of sulfate-bearing rocks in which it occurs.

Since the dark horizon can be distinguished from the orbital data from the surrounding brighter sulfate-bearing rocks, it can be traced across much of Mount Sharp and marks a period of time in the crater, hence it is called a “marker horizon”.

A marker horizon appears as one or more layers of rock or a weathered zone that differs in appearance from the sulfate-bearing rocks in which it is located. Marker horizons are also found on Earth, with volcanic ash being a common marker horizon as it can differ from surrounding deposits and can be traced across variable landscapes.

Geologists can use marker horizons as temporal stratigraphic features, i.e. they form during a single event or period of time, so by tracing a marker horizon over large areas, we can always know which rocks were deposited before or after it in the stratigraphy.

“In Gale Crater, during the deposition of sulfate-bearing sediments, some event occurred that led to the appearance of a different type of rock.

The marker horizon differs in appearance from the sulfate-bearing rocks above and below it, indicating a short-term change in the environment, for example, a drier period , or perhaps a regional event such as an explosive eruption from a nearby volcano that deposited ash over a large area, including Gale Crater,” Weitz said.

“We used orbital data collected by the High Resolution Imaging Science Experiment (HiRISE), Context Camera (CTX), and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instruments on the Mars Reconnaissance Orbiter (MRO) to locate a marker horizon on Mount Sharp and to study its appearance and composition.

We found that the marker horizon varies in height by 1.6 km throughout Mount Sharp, that it slopes from 1 to 5 degrees from the center of Gale Crater, and has a mafic composition similar to others basaltic materials, including aeolian sands,” said Weitz, lead author of “Orbital Observations of the Gale Crater Marker Horizon,” published in Geophysical Research: Planets.

“We have studied several different mechanisms for the formation of a marker horizon. It may have been composed of the same materials as the sulfate-bearing rocks above and below it, but became harder and more resistant to erosion either during formation or subsequently by the action of water carrying minerals to it.

The marker horizon could also be sandstone or a deposit that formed when Gale Crater was drier compared to the sulfate period.Another possibility is that the horizon contains volcanic ash that was deposited when a nearby volcano erupted into the Martian atmosphere. , which later hardened.

All of these possible origins require the presence of at least some water to cause cementation to harden at the horizon,” Weitz said.”Our orbital observations currently favor sulfate or volcanic ash, but we will have to wait until the Curiosity rover reaches the horizon in the coming months to determine which is the most plausible origin.”

Closer observations will allow scientists to better understand why the marker horizon is so different from nearby sulfate outcrops.

We are fortunate that the Curiosity rover plans to reach the marker horizon in the coming months as it climbs Mount Sharp through sulfate-bearing rocks, providing valuable ground measurements that can be used to evaluate various origin scenarios.” meters from the marker horizon, moving from the Greenheugh region to the shaly-sulphate transition region.

Curiosity’s study of the marker horizon will allow a detailed analysis of the sedimentological properties, including grain sizes, any inconsistencies, internal structures, textures and chemical composition, “said Weitz,

‚ÄúThese observations and measurements that Curiosity can make are very important in order to distinguish between several proposed formation scenarios. Of course, Mars may surprise us, and it may turn out that the origin of the marker horizon may be the result of something that we didn’t assume from the orbital data set,” Weitz said.

“Only when Curiosity begins its own exploration of the marker horizon will there be enough data to unravel the origin of this enigmatic area and help us better understand the intriguing history of the Gale Crater sediments.”


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