Upper Tagus loess formation and the marine atmosphere off the Iberian margin
A
Table 2. Analytical data for luminescence age calculation: sample codes, radionuclide concentrations, total dose rates, equivalent doses,
and OSL ages.
Laboratory code U [ppm]* Th [ppm]*® K [wt.%]” Total dose rate D [Gy/ka]“ Equivalent Dose ED [Gy] Luminescence Age [ka]
Fuentiduena section
HUB 470 4.16 + 0.30 9.12+0.97 1.17+0.12
HUB 471 4.42+ 0.35 12.93+1.16 1.29+0.13
BT 949 5.86+ 0.60 14.22+2.00 1.48 + 0.15
BT 950 3.97+0.57 14.57+1.88 1.36 +0.14
BT 1364 4.48 + 0.39 38.84+1.27 1.40+0.14
BT 1365 3.81+0.41 11.11+1.37 1.34+0.13
BT 1366 53.44+ 0.48 13.01+1.48 1.34+ 0.13
BT 1367 3.88+0.38 8.25+1.25 1.07+0.11
BT 1368 5.97+ 0.42 10.49 +1.39 0.97+0.10
A3 section
HUB 472
BT 1369
BT 1370
BT 1371
BT 1372
BT 1373
BT 1374
Paraiso section
BT 1375
BT 1376
BT 1377
BT 1378
BT 1379
BT 1380
BT 1381
BT 1382
BT 1383
BT 1384
BT 1544
"Determined by thick source o-counting.
'Determined by ICP-OES.
“For total dose rate calculation, cosmic dose rates were considered according to Prescott and Hutton (1994). An interstitial water content of 5 + 3% was used for
all samples except for samples BT 1375, BT 1381, BT 1383, BT 1384, and BT 1544 (8% + 3%)
lower values are linked to a group of samples belonging to
PS-2, the paleosol formed during the lower MIS 3 in Paraiso
section. All other samples plot below an yır of —1.5*1078
m’kg7! and lack evidence of a pedogenic influence. The ana-
Iyzed samples thus reveal a clear pattern of magnetic
enhancement due to pedogenic effects resulting from climate
control (Fig. 12, left side). The initial magnetic values of
loess in central Spain (detrital background susceptibility:
XB=2.5*107® m’kg”') show a higher dispersion and are
lower (Fig. 12, right side) than the values at Semlac (Roma-
nian Banat, Xp =1.6*107’ m’kg”'), which are assumed to
represent the average geochemical composition of the earth’s
crust (Buggle et al., 2014; Zeeden et al., 2016). This lowering
of the background susceptibility very likely resulted from a
dilution effect through dominantly diamagnetic mineral frac-
ons dominated by quartz and feldspars as well as calcite or
dolomite (carbonate contents 30-50%), or even gypsum that
was inherited from the evaporate marls and Tagus River
deposits. However, when looking each different loess section
‚Fig. 13), it becomes clear that the sections start from different
initial magnetic values between Xg=1.4 and 3.9*107®
N ’kg-! while showing the same vector for pedogenic enrich-
ment. The gradient from lower Xp to higher Xp corresponds
more or less to the gradient shown in Fig. 9, which means
hat lower Xp values (A3 section) relate to more coarse-
zrained deposits that were only transported short distances
ınd are rich in calcite and dolomite. In contrast, higher Xp val-
Jes (Villarubia section) relate to finer-grained material with
longer transport distances, which exemplifies the combined
effect of grain sizes and mineralogical composition (content
of diamagnetic particles) on magnetic susceptibility.
Magnetic parameters (Yır, Xra» and s-ratio) plotted for the
Fuentiduena and Paraiso sections (Figs. 2, 9) reveal follow-
.ng patterns: (i) marl deposits at the base of the section show
very low values for all parameters. (ii) Sediments deposited
during MIS 5 (SU-3 and SU-4) are linked to highest values
for all magnetic parameters, indicating high contents of fer-
romagnetic minerals (s. 1.) and superparamagnetic particles.
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