DR2013151
F. Balsamo et al.
ON LINE DATA REPOSITORY MATERIAL
ANALYTICAL METHODS
Field work included detailed structural and diagenetic alteration mapping and in situ
permeability
measurements.
Laboratory
analyses
included
petrographic,
microstructural, mineralogical (X-ray diffraction, XRD) and laser diffraction grain size
analyses. Color photographs of the three selected field sites (Fig. DR1) are provided to
be compared with line-drawings in Figure 3.
In situ permeability
Permeability measurements were performed in undeformed and faulted sand(stone)s by
a TinyPerm II Portable Air Permeameter manufactured by New England Research
(NER). This has a 5 mm nozzle and provides reliable permeability values from 10-4–101
Darcy (Rotevatn et al., 2008). Due to the very high permeability of medium to coarse
sandy layers of the Barreiras sandstone, the calibration of TinyPerm II has been
extended in NER laboratory by measuring the effective permeability of two parallel
plates with known separation. By varying the separation up to 4.5 mm, the calibration
was extrapolated to TinyPerm numbers as low as 7.5. Results are plotted in Figure DR2
for 10 measurements at each flow condition, illustrating the degree of scatter in
TinyPerm number for a given flow resistance. For the very high permeabilities, the
scatter implies a greater uncertainty for a single measurement, but on average, the
calibration equation holds to the limit of about 5000 Darcy. Measurement sites in the
field were carefully scraped with a putty knife to remove weathering effects and gently
brushed to remove dust. A silicon tip formed a seal to prevent air leakage from the minipermeameter nozzle. Data in the undeformed sands were acquired by multiple
clustered measurements in an area of about 1 m2. Fault zone permeability
measurements were acquired in vertical sections of multiple spots oriented parallel to
the fault strike and foliations in fault cores and mixed zones. Measurements in damage
zones were acquired both across joints and deformation bands, and in the virtually
undeformed lithons between them. Where dense iron oxide precipitation occurs in a
structural domain, permeability was measured in the adjacent, non-pervasively
cemented parts.
Laser diffraction granulometry
About 400–500 g of material was collected for grain size analyses after removal of
the weathered surface material. A total of 54 samples were analyzed for grain size data,
including 19 undeformed and 35 faulted sandstones. We used a Mastersizer 2000 laser
diffraction particle size analyzer manufactured by Malvern Instruments, with an
analytical size range of 0.2–2000 μm. All samples were sieved at 1700 μm to account
for the shape anisotropy of coarser particles. Representative subsamples were obtained
by a Quantachrome sieving riffler and rotary sample splitter. Analyses were performed
using the Hydro MU wet dispersion unit, decalcified water as the dispersant liquid
(refraction index 1.33), and 1.544 and 0.01 as the refraction index and adsorbent
coefficient of quartz grains, respectively. A wide variety of standard operating
procedures (SOP) is available and can be set up to aid sample disaggregation and
dispersion (Blott et al., 2004). Among the parameters that influence the final analytical
results are the velocity of centrifugal pumping, the length of measurement time, and the
intensity and duration of ultrasonication. Samples in this study can be grouped into two
categories: loose sands and very fine-grained silt. We conducted preliminary tests on:
(1) undeformed medium-grained loose sand; and (2) faulted, tectonically compacted
clay-rich silt, to investigate the effects of these technical factors and minimize
instrumental bias (Fig. DR3). Pump speed velocity significantly influences the reading of
particle size distributions, as indicated by the asymmetric bell-shaped trend of mean
volumetric diameters (Dm) for the undeformed medium sand (Fig. DR3A). At low pump
speed, the mean diameters are characterized by low values, which rapidly increase with
increasing pump speed up to about 450 μm at 1100 revolutions per minute (rpm). After
the peak values, the mean diameters tend to decrease dramatically with increasing
pump speed, and then stabilize at plateau values of about 300 μm at 1800 rpm. This
indicates that a low pump speed causes the sedimentation of coarser grains at the
bottom of the tank, slow motion in the recirculation unit and measuring cell, producing
initial measurements biased towards the finer particles. Recirculation of coarser
particles improves with increasing pump speed, but the highest values are related to the
inefficient recirculation and stagnation of coarser particles in the measuring cell. With
increasing pump speed, diameters reach plateau values, and the grain-water dispersion
is assumed to flow properly within the recirculation system. Based on the results of
these tests, we selected a standard velocity of 2000 rpm for all samples. Three
precision tests (involving 100 sequential measurement runs on the same subsample
aliquot) were performed on medium sand by using 2000 rpm and 5 s, 10 s, and 20 s of
measurement run time (Fig. DR3B). Results show that the mean diameter of the
medium sand is not significantly affected by variation in run time. Longer measurement
run times slightly reduce data scattering and provide very similar granulometric curves
with respect to the 5 s trend, whereas a greater number of measurement runs favors the
progressive decrease of mean diameter values due to the longer sample recirculation
time, which eventually favors grain fragmentation. As a consequence, we used a
measurement run time of 5 s to minimize sample biasing induced by longer recirculation
times, and the number of measurement runs for each sample analysis was set at 25 in
order to minimize the destructive mechanical impact on grain sizes induced by
progressive particle collisions during sample recirculation (Fig. DR3C). Ultrasonication
tests were performed at the minimum, intermediate and maximum ultrasound power
(i.e. 2, 5, 10 and 20 μm of probe tip displacement) on tectonically compacted, clay-rich
silt, due to the problems of disaggregation and measurement of these types of samples
using only the recirculation system. Ultrasonication significantly impacts on the mean
diameter of such very fine-grained faulted material by enhancing grain disaggregation,
as indicated by the rapid decrease in mean grain size values from 160–180 μm, up to
15–35 μm, particularly with the highest ultrasonication power (Fig. DR3D). The lower
mean grain size values were reached by using 20 μm of probe tip displacement (US 20)
after 10 measurements (i.e. after ~60 s of ultrasonication). Comparison between the
initial curve and the curve after 10 measurements with US 20 (see the two curves in the
box of Fig. A2D), suggests that grains disaggregate rather than fragment, as indicated
by the change in the shape of the curves without significant shifting of the coarser and
finer tails. Accordingly, we only used 1 minute of ultrasonication (US 20) for very finegrained, tectonically compacted faulted materials. Finally, we tested sample
reproducibility by repeating 25 measurement runs under the same analytical conditions
(2000 rpm, 5 s measure run time) on five different subsample aliquots for mediumgrained sand (Fig. DR3E). Results show that the different granulometric curves are
almost indistinguishable from one another.
Statistical parameters, such as mean grain size and grain size span were calculated.
The span values represent the measurement of the width of the distribution (i.e. the
sorting degree) computed by Malvern Mastersizer 2000 software as (percentile 0.9 –
percentile 0.1) / (percentile 0.5). Narrower distributions mean better sorting, and smaller
span values.
Microstructural analysis
Representative undeformed and faulted samples were impregnated with blue epoxy,
and a total of 26 oriented thin sections were analyzed under a standard petrographic
microscope. The thin sections of faulted samples were oriented parallel to the
slickenlines and orthogonal to the mesoscale foliation in the fault zone.
XRD analysis
XRD analyses were performed on 15 representative samples to determine the
mineral assemblage of undeformed sandstone, faulted sandstone, and iron oxide
deposits. The same amount of bulk materials (~2 g) of all samples was examined. Airdried random mounts were analyzed using a Scintag X1 (CuKα radiation, solid state
detector, spinner) X-ray diffractometer from 2–80o °2θ, at a scan speed of 2 o/min, a
step size of 0.02 °2θ and a count time of 0.6 s at 40 kV and 30 mA. Because the
amount of analyzed material was the same, the relative amount of different mineral
phases was estimated in the undeformed samples by measuring the area below each
peak with image analysis, and comparing the measured area with the total area below
all peaks in the same diffractogram.
REFERENCE CITED
Blott, S.J., Croft, D.J., Pye, K., Saye, S.E., and Wilson, H.E., 2004, Particle size
analysis by laser diffraction, in Pye, K., and Croft, D.J., eds., Forensic
Geoscience: Principles, Techniques and Applications: Geological Society of
London Special Publication 232, p. 63–73.
Rotevatn, A., Torabi, A., Fossen, H., and Braathen, A., 2008, Slipped deformation
bands: A new type of cataclastic deformation bands in western Sinai, Suez rift,
Egypt:
Journal
of
Structural
Geology,
v.
30,
p.
1317–1331,
doi:10.1016/j.jsg.2008.06.010.
DATA REPOSITORY FIGURE CAPTION
Figure DR1. Field photographs showing the diagenetic alteration patterns in field site 1
(A), 2 (B) and 3 (C).Line drawings are shown in Figure 3.
Fig. DR 3. Extended calibration of TinyPerm portable minipermeameter to air
permeability values of 5000 Darcy.
Figure DR3. Preliminary tests performed to determine the best standard operating
procedure for grain-size determination with laser diffraction granulometry in the granular
materials analyzed. (A) Pump speed velocity test for the medium sand (rpm –
revolutions per minute). (B) Measurement precision tests for medium sand at 2000 rpm
and 5 s, 10 s. and 20 s of measurement run time. (C) Measure precision test showing
the consistency of the first 25 measurements for medium sand at 2000 rpm and 5 s of
measurement run time. (D) Ultrasonication test for the fine-grained clay-rich silt showing
the progressive decrease in mean grain size with increasing time and power of
ultrasonication. Note the black squares (US 20) showing the abrupt decrease in mean
grain size in the first 10 measurements. (E) Reproducibility test for medium sand
showing the range variability of grain-size distribution curves indicated by the gray area
around the continuous line.
(A) Site 1
(B)
Site 2
(C) Site 3
On line Dara Reposity material.
Figure DR1.
too fast
Inability to
distinguish
too slow
Mean diameter (mm)
500
A
400
300
200
100
0
0
B
350
Mean diameter (mm)
1000 2000
3000 4000
Pump speed velocity (rpm)
5s
250
10 s
350
250
350
20 s
250
0
Mean diameter (mm)
500
20
40
60
80
Measure run number
100
C
400
5s
300
y = -0.3277x + 317.44
R2 = 0.0991
200
100
0
0
200
5
10
15
20
Measure run number
D
clay silt
180
Mean diameter (mm)
sand
measure 1
(US 20)
measure 10
(US 20)
160
25
140
no US
120
US 2
100
US 5
US 10
80
US 20
60
40
20
0
0
10
40
60
80
Measure run number
100
E
average curve
(n= 125 analyses)
range of variability
8
Volume percent
20
6
4
2
0
0.1
1
10
100 1000 10000
Log grain size (mm)
Data Repository
Fig DR3