Figure 1. Location map of the study site (red star). The yellow
shaded area is the distribution range of the Loess Plateau,edited from
Kukla and An (1989).
2 Geological settings and sample
collection
2.1 Geological settings
The loess-paleosol section is located at the Luoyang Beiyao
archaeological site(34°42′24″N,112°28′46″E) on the southeast edge of
the Chinese Loess Plateau (Figure 1). The Beiyao site lies on the
third-grade loess accumulation terrace on the south bank of the Luo
River in Luoyang. The terrace is about 20m higher than the modern river
bed, and the loess section is 16.7m long from bottom to top. Grain size
and magnetic susceptibility data combined with optical luminescence
(OSL) and AMS 14C datings showed that the loess
section has covered the last two glacial-interglacial cycles (Du et al.,
2011). At present, the mean annual temperature and annual precipitation
are 14.2℃ and 546 mm, respectively. The study area is located in a
typical monsoonal region. Northerly wind prevails and climate is cold
and dry in winter, while southerly wind dominates in summer with hot and
rainy condition. A large number of stone artifacts were found in the
Beiyao section at depth of 6.5~7.5m and
11~13m, indicating that there were prehistoric human
activities.
The magnetic susceptibility and median particle size curves showed
synchronous changes, and had a good correspondence with the marine
oxygen-isotope stage (MIS) curve (Tang et al. , 2017). Therefore,
in this study, we sub-divided the loess section to various oxygen
isotope stages according to the grain size and magnetic susceptibility,
referring to AMS 14C and OSL datings.
2.2 Collection of land snail
fossils
During the sampling process at the Beiyao site, 1m × 1m × 10cm volume
loess (or paleosol) was continuously excavated downward, and the snails
in each horizon were collected by screening and washing using water and
a 0.5 mm sieve. The identification and statistics of the snail fossils
used in this study were completed by Yan Wu. Throughout the section,
there were 1911 cold-aridiphilous Cathaica pulveratrix (C.
pulveratrix ) and 241 sub-humidiphilous Metodontia yantaiensis(M. yantaiensis ) (Wu, 2011). When the fossil fragments were
counted as Quaternary loess snail individuals, the calculation method
developed by Puisségur (1976) was used to convert the fragments into
snail fossil individuals and sum them as the total number of
individuals. The conversion formula (Puisségur, 1976) is as followed:
Number of individuals = number of fragments/5 - number of fragments/5 ×
conversion factor
The conversion factor varies with the number of snail fossil fragments.
When the number of snail fossil fragments is <50, 50-75,
75-100, and >100, the conversion factor is 10%, 20%,
33%, and 50%, respectively. Except for few fossils due to the strong
pedogenesis at 6.8-7m, most of the section is rich in snail fossils. In
this study, we used complete shell of land snails for stable isotope
analysis. Totally, there are 577 C. pulveratrix shells from 59
horizons, and 97 M. yantaiensis shells from 15 horizons.