Mineralogy of a Mudstone at Yellowknife Bay, Gale Crater, Mars

TLDR: Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover, indicating that clay mineral formation on Mars extended beyond Noachian time.

Abstract: Sedimentary rocks at Yellowknife Bay (Gale crater) on Mars include mudstone sampled by the Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, calcium sulfates, iron oxide or hydroxides, iron sulfides, amorphous material, and trioctahedral smectites. The John Klein smectite has basal spacing of similar to 10 angstroms, indicating little interlayer hydration. The Cumberland smectite has basal spacing at both similar to 13.2 and similar to 10 angstroms. The larger spacing suggests a partially chloritized interlayer or interlayer magnesium or calcium facilitating H2O retention. Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars extended beyond Noachian time.

Figures

Table 1: Crystalline and amorphous components (wt%) of the John Klein and Cumberland drill powders, compared with the Rocknest scooped eolian deposit (23).

Table 2: Refined unit-cell parameters for some of the major crystalline phases in the Rocknest soil compared with those for the John Klein and Cumberland mudstone samples.

Fig. 2. X-ray diffraction patterns of mudstone samples. (A) X-ray diffraction patterns for John Klein and Cumberland superimposed. Similarity between the mudstone samples is evident but there are notable differences in the major smectite 001 peaks at 13.2 Å in Cumberland and at 10 Å in John Klein (spacing corrected for Lorentz polarization). Also labeled are reflections at 6 Å for bassanite and 3.5 Å

Table 3: Compositions of major crystalline phases in the Rocknest soil compared with those for the John Klein and Cumberland mudstone samples, based on unit-cell parameters in Table 2.

Fig. 3. Comparison of 02l diffraction bands of John Klein and Cumberland with other smectites. The 2-Theta range is selected to contain the maximum intensity positions (in Å) and profiles of the 02l

Fig. 1. Images of mudstone drill holes and drill powders. (A) shallow (1-cm deep) test drill hole (at left) and sampled drill hole (6.5-cm deep) for John Klein. (B) John Klein drill sample in the scoop

Full text

Mineralogy of a Mudstone at Yellowknife Bay, Gale Crater, Mars
Authors: D.T. Vaniman
1*
, D.L. Bish
2
, D.W. Ming
3
, T.F. Bristow
4
, R.V. Morris
3
, D. F. Blake
4
,
S. J. Chipera
5
, S.M. Morrison
6
, A.H. Treiman
7
, E.B. Rampe
3
, M. Rice
8
, C.N. Achilles
9†
, J.
Grotzinger
8
, S.M. McLennan
10
, J. Williams
11
, J. Bell III
12
, H. Newsom
11
, R.T. Downs
6
, S.
Maurice
13
, P. Sarrazin
14
, A.S. Yen
15
, J.M. Morookian
15
, J.D. Farmer
12
,
K. Stack
8
, R.E.
Milliken
16
, B. Ehlmann
8,15
, D.Y. Sumner
17
,
G. Berger
13
, J.A. Crisp
15
, J.A. Hurowitz
10
, R.
Anderson
15
, D. DesMarais
4
, E.M. Stolper
8
, K.S. Edgett
18
, S. Gupta
19
, and N. Spanovich
15
, MSL
Science Team
‡
Institutions:
1
Planetary Science Institute, Tucson, AZ, 85719, USA
2
Department of Geological Sciences, Indiana University, Bloomington, IN, 47405, USA
3
NASA Johnson Space Center, Houston, TX, 77058, USA
4
NASA Ames Research Center, Moffett Field, CA, 94035, USA
5
Chesapeake Energy, Oklahoma City, OK, 73154, USA
6
Department of Geosciences, University of Arizona, Tucson, AZ, 85721, USA
7
Lunar and Planetary Institute, Houston, TX, 77058, USA
8
Division of Geologic and Planetary Sciences, California Institute of Technology, Pasadena, CA,
91125, USA
9
ESCG/UTC Aerospace Systems, Houston, TX, 77058, USA
10
Department of Geosciences, SUNY Stony Brook, Stony Brook, NY, 11794, USA
11
Institute of Meteoritics, University of New Mexico, Albuquerque, NM, 87131, USA
12
School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287, USA
13
Institut de Recherche en Astrophysique et Planétologie (IRAP), Universite de Toulouse/CNRS,
Toulouse, 31400, France
14
SETI Institute, Mountain View, CA, 94043, USA
15
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
16
Department of Geological Sciences, Brown University, Providence, RI, 02912, USA
17
Department of Earth and Planetary Sciences, University of California, Davis, CA, 95616, USA
18
Malin Space Science Systems, San Diego, CA, 92121, USA
19
Department of Earth Science and Engineering, Imperial College London, SW7 2AZ, UK
*Correspondence to: dvaniman@psi.edu
†
Current address: Department of Geological Sciences, Indiana University, Bloomington, IN,
47405, USA
‡
MSL Science Team authors and affiliations are listed in the supplementary materials.

Abstract
Sedimentary rocks at Yellowknife Bay (Gale Crater) on Mars include mudstone sampled by the
Curiosity rover. The samples, John Klein and Cumberland, contain detrital basaltic minerals, Ca-
sulfates, Fe oxide/hydroxides, Fe-sulfides, amorphous material, and trioctahedral smectites. The
John Klein smectite has basal spacing of ~10 Å indicating little interlayer hydration. The
Cumberland smectite has basal spacing at ~13.2 Å as well as ~10 Å. The ~13.2 Å spacing
suggests a partially chloritized interlayer or interlayer Mg or Ca facilitating H
2
O retention.
Basaltic minerals in the mudstone are similar to those in nearby eolian deposits. However, the
mudstone has far less Fe-forsterite, possibly lost with formation of smectite plus magnetite. Late
Noachian/Early Hesperian or younger age indicates that clay mineral formation on Mars
extended beyond Noachian time.
Introduction
The recent decade of orbiter- and rover-based studies of ancient sedimentary rocks on Mars
has revealed a diverse mineralogy that constrains the nature and timing of early environments in
the history of the planet (1, 2, 3) These studies provide a starting point for considering the
habitability of Mars, based on an understanding of the aqueous geochemistry and mineralogy of
rocks placed within a geologic framework (4, 5). Such an approach has been adopted by the
Mars Science Laboratory (MSL) mission, where the science payload and advanced capabilities
of the Curiosity rover were designed for assessment of past habitability (6).
Mission goals for MSL placed high priority on aqueous-system mineralogy, particularly clay
minerals and sulfate salts (6). The mission concept for the landing site in Gale Crater was to
leave the landing spot quickly and drive to Aeolis Mons, a central mound informally known as
Mount Sharp. Interpretation of Mars Reconnaissance Orbiter CRISM (Compact Reconnaissance
Imaging Spectrometer for Mars) visible-near infrared spectroscopy suggests the presence of
hydrated minerals in sedimentary layers at the base of the mound (7). However, soon after
landing a contact between three different geologic units, one with relatively high thermal inertia,
was recognized within ~450 m of the landing spot, just beyond the alluvial lobe of the Peace
Vallis fan (8). The decision to drive away from Mount Sharp toward this location has provided
early samples of a mudstone that contains both clay minerals and sulfate salts.
The John Klein and Cumberland drill samples were collected from the Sheepbed mudstone
member of the sedimentary Yellowknife Bay formation, which is interpreted as a shallow
lacustrine deposit (8). John Klein and Cumberland are the second and third solid samples,
respectively, collected by the MSL rover Curiosity. The first sample, from an eolian deposit
named Rocknest, is ~60 m west of the mudstone drill locations. The loose Rocknest deposit (9)
had been used to commission Curiosity’s scoop sampling system and the lithified John Klein
sample was used to commission the drill. Curiosity’s sampling system delivers both scooped and
drilled powders to the same set of sieves (10). All scooped or drilled samples were sieved to
<150 µm and portions were analyzed by the Chemistry and Mineralogy (CheMin) X-ray
diffraction (XRD) and X-ray fluorescence (XRF) instrument (11) and the Sample Analysis at
Mars (SAM) quadrupole mass spectrometer/gas chromatograph/tunable laser spectrometer suite
of instruments (12, 13).

CheMin XRD data are the focus of this paper. Although the CheMin XRD instrument is the
prime mineralogy tool carried by Curiosity, constraints on the mudstone mineralogy are provided
by the temperatures at which volatiles are released in SAM evolved gas analyses, particularly
H
2
O release profiles (13). Other instruments on Curiosity provide additional insight into
mineralogy. Mastcam (14, 15) multispectral images are capable of sand-size resolution and
potential identification of certain hydrated minerals using short-wavelength near-IR filters (16).
ChemCam has a narrow laser beam that can target veins and nodules for remote chemical
analysis by laser-induced breakdown spectroscopy (LIBS), with sensitivity to many elements
including hydrogen (17, 18); this capability can aid in constraining mineral compositions where
individual minerals are ~0.5 mm or larger and is particularly sensitive to alkali and alkaline-earth
elements (19). The MSL alpha-particle X-ray spectrometer (APXS) has proven heritage from
previous missions and provides sensitivity to a wide range of common rock-forming elements
(20), although analysis spot resolution is ~1.7 cm diameter, providing a bulk chemical analysis
rather than mineral analysis for most samples. We use the results from APXS to constrain the
composition of the X-ray amorphous components of the mudstone. The Mars Hand Lens Imager
(MAHLI) provides high-resolution images, to 14 µm per pixel, with Bayer pattern color that can
simulate hand-lens or close-up sample analysis (21).
Figure 1 shows Mastcam and MAHLI images of the boreholes and drill powders for John
Klein and Cumberland. Cumberland (Fig. 1C) was targeted after John Klein, in order to analyze
a part of the mudstone with fewer sulfate veins and a greater abundance of resistant concretions,
including nodules and hollow nodules that are regarded as early cementation. The two drill holes
are ~3 m apart. Powders of both mudstone samples are notably gray in color, unlike the reddish
weathering and/or dust evident on the surface of the mudstone. This reddish surface of the
mudstone did not contribute to either drill sample, for the auger does not pass powder into the
sampling system until it is ~1.5 cm into the drill target (10).
Mineralogical Analysis and Quantitative Mineralogy
The X-ray diffraction patterns for John Klein and Cumberland are compared in Fig. 2A. We
quantified the crystalline components, other than smectites, in John Klein and Cumberland
(Table 1) by using whole-pattern fitting and Rietveld analysis (Figs. 2B,C); smectites and the
amorphous component were quantified using a modified version of the FULLPAT program (22).
These methods are described in (23) and elaborated in (24). Conversion of the two-dimensional
images of Debye diffraction rings on the CCD to one-dimensional diffraction patterns was done
in the same manner for Rocknest, John Klein, and Cumberland. For all three samples, we
obtained unit-cell parameters (Table 2) and phase compositions (Table 3) for major phases. The
unit-cell parameter and phase composition data reported for Rocknest, John Klein, and
Cumberland were processed in the same manner and are therefore comparable.
An independent assessment of the abundance of smectite and amorphous material can be
obtained from the fixed or cell-parameter-constrained chemical compositions of the phases listed
in Table 1 and the total sample chemical composition from APXS analysis of the drill tailings.
This approach (24) uses a mass-balance calculation with XRD constraints on crystal chemistry
(25, 26) and, for the present study, model smectite compositions, to estimate the composition of
the amorphous component. Additional constraints on smectite abundance come from SAM

evolved gas analysis, where the amount of H
2
O released at higher temperatures (~400-835 °C)
can be related to dehydroxylation of various clay minerals (13). Within estimated errors these
three methods agree, but in this paper we focus on the XRD estimates (Table 1).
None of the coarse (>mm width) veins that cross the Sheepbed member (8) were sampled for
CheMin and SAM analysis. However, Mastcam near-IR spectral filters are sensitive to hydration
in certain minerals (27), and this method (24) was used to analyze veins where ChemCam and
APXS data indicated that Ca-sulfate phases are present. This allows mapping of inferred gypsum
distributions in the veins that were not sampled for CheMin and SAM analysis.
The sedimentologic context of the mudstone is complex. Observations of the mudstone (8)
lead to interpretation of an early-diagenetic association of nodules, hollow nodules, and raised
ridges that are crosscut by late-diagenetic fractures filled with light-toned Ca-sulfates (S-Ca
association in these veins was identified with ChemCam). Early-diagenetic hollow nodules are
filled with light-toned sulfates only where intersected by late-diagenetic light-toned
microfractures (8, 19). MAHLI images show that the John Klein drill spot had a surface footprint
(1.6 cm diameter) with ~3.9% hollow nodules, ~2.5% solid nodules, and ~14.5% light-toned
sulfate, whereas the Cumberland drill spot had ~8.5% hollow nodules, ~2.2% solid nodules, and
no evident light-toned sulfate. Estimates of light-toned sulfate abundances from pre-drilling
images can be deceptive because their three-dimensional distribution is dependent on variable
occurrence of thin veins that may or may not be visible on the dust-mantled surface. A more
accurate survey of the distribution and abundance of light-toned sulfates is obtained by analysis
of drill-hole wall images (24), at least to the depth exposed (the lower part of each drill hole
contains some debris).
The borehole samples John Klein and Cumberland provide adequate sampling of the
mudstone matrix with a partial sampling of features that are both early-diagenetic (nodules and
hollow nodules) and late-diagenetic (light-toned veins). The drill did not sample any early-
diagenetic raised ridges. The raised ridges were identified in LIBS and APXS analyses as
including an Mg-Fe-Cl rich component; in images they appear to have an isopachous filling of
several layers and may be mineralogically complex (19). Without direct sampling and CheMin
XRD analysis, knowledge of mineralogy in the raised ridges is speculative and is not addressed
here.
Silicates other than Smectites
Several detrital silicate minerals in the mudstone bear a strong resemblance to those found in
the Rocknest eolian deposit (Tables 2, 3). Fe-forsterite, plagioclase, pigeonite, and augite are
generally similar between Rocknest, John Klein, and Cumberland, suggesting similar mafic
sources. Presence of pigeonite indicates mafic sources that were basaltic. However, XRD
analyses of the mudstone samples reveal presence of orthopyroxene as well as clinopyroxenes,
indicating a source of some mafic minerals that is either absent from or very minor in the nearby
eolian deposit.
It is notable that Fe-forsterite is almost absent in Cumberland and its abundance in John Klein
is much lower than in Rocknest. Figure 1B shows that the reddish Rocknest sample coats the

walls of the scoop that is filled with the John Klein drill powder. Testbed operations on Earth
suggest that at least ~4% cross-contamination should be expected between samples. By the time
Cumberland was imaged (Fig. 1D), the red Rocknest powder was almost gone, so the sampling
system had been largely cleared of this contaminant in processing John Klein. Progressive
dilution and a stronger cleaning cycle between John Klein and Cumberland left little if any
Rocknest contamination in Cumberland – and conversely, some of the Fe-forsteritic olivine
present in the John Klein sample might be contamination from the Rocknest sample.
Phyllosilicates
CheMin XRD data reveal the presence of phyllosilicates in John Klein and Cumberland (Fig.
2A). A broad 001 diffraction peak in the John Klein XRD pattern extends from 12 to 9.4 Å,
corresponding with the large interlayer spacing of a 2:1 smectite. This broad range of 001
diffraction is common to a variety of phyllosilicates, but the breadth of this peak (and the lack of
other well-defined peaks, such as an 002 peak at 5 Å) argue against the presence of well-
crystallized phyllosilicates such as mica or illite. Well-defined diffraction peaks for kaolinite or
chlorite-group minerals at 7 Å are absent. A smectite with similar diffraction properties is
present in Cumberland, although the low-angle region includes a second peak ranging from ~12-
17 Å with a maximum at ~13.2 Å. This larger interlayer spacing in the Cumberland XRD pattern
is a noteworthy characteristic.
The interlayer spacing in a smectite, revealed by the broad 001 peak, is affected by the layer
charge, the nature of the interlayer cation(s) (typically K, Na, and/or Ca; less commonly Mg), the
hydration state of the interlayer cations, and the possible presence of chloritic interlayers. The
layer charge and interlayer cation content of a smectite are relatively stable in solid samples, so
changes in interlayer spacing are mostly dependent on relative humidity. Modeling and
experimental studies (28, 29) suggest that if exposed at Mars surface conditions, smectites can go
through diurnal and seasonal hydration cycling, with substantial dependence of the amount of
hydration on the nature of the interlayer cation. For example, Ca-smectite will hold more
interlayer H
2
O than Na-smectite at the same conditions (30). The John Klein and Cumberland
samples inside the body of Curiosity were exposed to higher and less variable temperature (a
diurnal range of 5 to 25 °C) than they were in situ. These temperatures yield very low relative
humidities and dehydration should be favored. The position and breadth of the 001 diffraction
peak in the John Klein sample have not changed over 30 sols of analysis following collection,
but at 10 Å this smectite appears to be largely dehydrated and little or no change would be
expected. The larger 001 spacing in Cumberland has also been static, over 28 sols of analysis;
the preservation of this wider spacing suggests a difference in the interlayer composition of the
smectite in Cumberland compared with John Klein.
Possible explanations for persistent larger interlayer spacing in Cumberland include smectite
having hydrated interlayers with H
2
O molecules retained by high hydration-energy interlayer
cations, possibly Mg
2+
(28) or Ca
2+
(30), and partial pillaring of the interlayer by metal-hydroxyl
groups, as with incipient chloritization (31), that would prevent collapse. The nodule-bearing
portions of the mudstone that were drilled for sampling pass laterally into mudstone with early-
digenetic Mg-rich raised ridges described above. These could be sources of Mg for cation
exchange or incipient chloritization, focused more on Cumberland than on John Klein. Cation

Frequently asked questions

Q1. What is the central process in forming saponitic, trioctahed?

Analogous alteration of Fe-forsterite is the central process in forming saponitic, trioctahedral clay minerals plus magnetite in chondritic meteorites at temperatures <100 °C (60). 

Q2. What are the contributions in "Mineralogy of a mudstone at yellowknife bay, gale crater, mars authors: d.t. vaniman" ?

In this paper, the authors used the Curiosity rover 's X-ray diffraction ( XRD ) and XRF ( X-ray fluorescence ) instrument to sample the sheepbed mudstone from Yellowknife Bay ( Gale Crater ). 

Q3. What is the possible formation of H2 gas as part of this process?

The possible formation of H2 gas as part of this process could be another component of habitability, providing a potential energy source for chemolithoautotrophs. 

Q4. What is the diffraction range of a smectite?

The layer charge and interlayer cation content of a smectite are relatively stable in solid samples, so changes in interlayer spacing are mostly dependent on relative humidity. 

Q5. What is the reason for the existence of bassanite on Mars?

Bassanite in the mudstone is not in equilibrium, but it may persist for long periods because of the unique surface conditions on Mars. 

Q6. What is the main reason for the formation of bassanite on Earth?

In most of these bassanite occurrences on Earth, the associated or precursor Ca-sulfate is gypsum because bassanite is often a product of gypsum dehydration. 

Q7. What is the diffraction band of the smectite?

In addition, a substantial component of smectite classification is in determination of trioctahedral or dioctahedral crystal structure (the range from full to 2/3 occupancy of sites in the octahedral sheet), but this is generally accomplished by analysis of the06l diffraction band at ~1.54 Å (trioctahedral, ~71 2 Co Kα) to ~1.50 Å (dioctahedral, ~73 2Co Kα). 

Q8. What is the interlayer spacing in a smectite?

The interlayer spacing in a smectite, revealed by the broad 001 peak, is affected by the layercharge, the nature of the interlayer cation(s) (typically K, Na, and/or Ca; less commonly Mg), the hydration state of the interlayer cations, and the possible presence of chloritic interlayers. 

Q9. What is the way to determine the stability of bassanite?

Bassanite does not have a stability field at pressures less than 235 MPa (42), far in excess ofthe maximum pressure (~50 MPa) that would be attained if the Sheepbed mudstone had been buried under ~5 km of sediment (a possibility because the mudstone could be exhumed from beneath the 5-km-high stratigraphy of Mt. Sharp). 

Q10. Why is bassanite a rare mineral on Earth?

This is probably because temperatures of anhydrite formation are generally high enough not to favor a metastable bassanite precursor, and hydration of anhydrite is likely to go directly to gypsum. 

Q11. What is the significance of the basal spacing of the clay mineral in Cumberland?

the larger basal spacing of the clay mineral in Cumberland suggests that it is either hydrated or expanded by some form of intercalation. 

Q12. What is the abundance of magnetite in the mudstone?

The abundance of magnetite relative to other crystalline phases in the mudstone, however, is in excess of what would be expected for likely basaltic source rocks; normalized to the igneous detrital minerals the magnetite abundance rises from 2.1 wt% in Rocknest to 8.7 wt% in John Klein and 9.5 wt% in Cumberland. 

Q13. What is the way to explain the absence of a structural modification in clay?

Absence of such clay mineral modification, beyond the proposed incipient chloritization and partial intercalation of Mg-hydroxy interlayers in clay minerals of the Cumberland sample, suggests alteration at temperatures lower than this. 

Q14. What is the type of akaganeite found in the rocknest sample?

Akaganeite at its type locality on Earth (37) occurs as an alteration product of pyrrhotite, a sulfide that is also found in the Yellowknife Bay mudstone but not in the Rocknest sample (Table 1). 

Q15. What is the advantage of X-ray diffraction analysis of clay minerals in terrestrial?

Hydrothermal fluids may induce this change as well (33).X-ray diffraction analysis of clay minerals in terrestrial laboratories has the advantage ofadditional sample processing, such as preparation of oriented mounts, controlled variation of relative humidity, treatment with ethylene glycol, and heat treatment. 

Q16. What is the nature of the amorphous component of the mudstone?

The amorphous component of the mudstone may represent soil or eolian fines accumulatedalong with crystalline detritus in the mudstone, but the nature and origin of the amorphous component is poorly known. 

Q17. What are the other factors required for selective enrichment of magnetite in the Sheep?

Other factors are required for selective enrichment such as free settling of grains in turbulent flow, selective entrainment of grains from a granular bed by flowing water, and shearing of grains in a moving granular dispersion (35).