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Molluscs in loess, their paleoecological significance and role in geochronology — Principles and methods
Quaternary lmernalional, Vols. 7/8, pp. 71-79, 1990.
1040-618~90 $0.00 + .50 © 1991 1NQUA/PergamonPress plc
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M O L L U S C S IN LOESS, THEIR P A L E O E C O L O G I C A L SIGNIFICANCE AND ROLE IN G E O C H R O N O L O G Y m PRINCIPLES AND M E T H O D S V. Lo~ek
~eskoslovenskd akademie v~d, Geologicky~ ~stav, 165 O0 Praha 6-Suchdol, Rozvojov~ 135, Czechoslovakia
The malacofauna of genuine wind-blown loess consists of a minor number of tolerant species occurring mostly in high amounts and reflecting open habitats with poorly developed calcareous soils. It shows a rather uniform character in space and time distinctly differing from all present-day assemblages of the temperate zone, and thus indicating a very peculiar environment characteristic of the loess steppe. In protected areas, particularly on valley slopes, the loess covers alternate with intercalations of slope sediments and soils including several other types of snail assemblages reflecting environmental changes in the course of the Quaternary climatic cycle. Among these malacocoenoses the interglacial faunas are of prime biostratigraphic importance. They are associated with strongly weathered forest soils and indicate woodland environments under very damp and warm climatic conditions. Transitional steppe and taiga assemblages occur in buried chernozem soils and in various slope sediments, e.g. in the pellet sands, overlying the interglacial soils and corresponding to early glacial periods. Although the fauna of proper loess shows a monotonous composition, it is possible to distinguish several types of loess assemblages corresponding to minor facies changes of loess environments in time and space; these are, for example, the Pupilla, Helicopsis striata and Columella faunas of Central Europe. A peculiar marshland fauna characterizes the so-called swamp-loess deposited in ephemeral swamps. In the marginal zones of the loess belt there occur also faunas partly differing from those of typical loess; this is true particularly of the Mediterranean region. The most important contribution provided by molluscan faunas from the loess series is the evidence of the maximum number of climatic cycles during the Quaternary period.
LOESS AND LOESS SERIES AS LOCALITIES OF MOLLUSC FINDS, TREATMENT OF THEIR PALEOMALACOLOGICAL CONTENTS
older loesses, soils and slope sediments and commonly contain an admixture of weathered bedrock. Their fossil assemblages include, therefore, 3 main components: (1) autochthonous - - species inhabiting the accumulation area; (2) parautochthonous - - shells transported together with the slope material from its catchment area; (3) aUochthonous - - redeposited fossil shells from reworked older sediments and soils. The autochthonous and parautochthonous components thus correspond to malacocoenoses living in the sedimentation and catchment area, and the allochthonous one represents an allogene admixture, mostly recognizable by its fossilization. Soils yield shells only when they are primarily calcareous which applies to carbonate chernozems and rendzinas. Their fauna is predominantly autochthonous being incorporated into the soil horizon by bioturbation leading to gradual redeposition of the soil material in situ (Lo~ek, 1964; Evans, 1972). An assemblage from a fossil soil thus commonly corresponds to a much longer period of time than that from a loess horizon of the same thickness. The soil can also include older fossil shells coming from its parent material. These generally differ by their fossilization. Weathered brown and red soils are decalcified so that shells are only exceptionally preserved, e.g. in calcareous fills of burrows or at places where such soils grade into calcareous colluvia. The evidence presented here demonstrates that loess provides a rich autochthonous snail material which is well preserved and can be easily obtained by washing with numbers which allow a statistical treatment. Other members of the loess series are in general considerably poorer. The shells are commonly preserved in frag-
In view of its CaCO3 content and quiet sedimentary environment loess provides suitable conditions for fossilization of molluscan shells. In general, loesses include numerous well-preserved shells which used to be distributed throughout the loess covers in both the vertical and horizontal sense. The richest malacofauna occurs in loesses situated in the valleys of large lowland rivers, whereas loesses on plateaus are most commonly poor in species or malacologically sterile. Molluscs can be preserved only in proper, i.e. calcareous loess, whereas in lime-deficient eolian loams the shells are rapidly corroded and dissolved, apart from the fact that such sedimentary environments might be primarily poor in snails. Thus the occurrence of fossil molluscs is often regarded as one of the characteristic features of genuine loess. In protected areas, particularly on valley slopes, the loesses form complicated sequences including intercalations of non-ioessic origin such as slope sediments and soils. These alternate with loess covers in successions of regular pattern called loess series (Kukla, 1961, 1975). Their fossil assemblages differ, however, from those of loess in several aspects. Loess thanatocoenoses predominantly consist of individuals which formerly lived in the sedimentation area in question. They are thus markedly autochthonous and broadly correspond to original malacocoenoses living in areas where the loess formed. Slope sediments generally consist of redeposited 71
72
v. Lo~ek
merits only and the assemblages often represent a mixture of different elements. Nevertheless, some of these non-loessic faunas are biostratigraphically very important which is particularly true of interglacial faunas. In the case of such horizons it is therefore appropriate to take much more voluminous soil samples than from the loess. The loess malacofauna has received attention mainly in the European loess belt and in the U.S.A. However, most previous works do not distinguish those records from proper loess from those collected in non-loessic horizons of the loess series, apart from the fact that a number of important species were not recognized. For this reason, our review is mostly based on records from the area situated between the French coast and the Ukraine, where after World War II large-scale investigations of loesses and loess malacofaunas have been made, throwing light on sedimentological and coenological details which are not available from other regions so far (Fink et al., 1976; Kukla, 1975, 1977; Lo~.ek, 1964, 1965a, 1972, 1976; Mazenot, 1956; Melni~uk, 1974; Puiss6gur, 1983 and others). MOLLUSCAN ASSEMBLAGES OF TRUE LOESS AND NON-LOESSIC MEMBERS OF THE LOESS SERIES The malacocoenoses of true wind-blown loess consist of a minor number of species occurring mostly in high amounts and showing the following environmental requirements (Lo~.ek, 1965a): (a) They are confined to open habitats or are able to live in such habitats. (b) They are resistant to major temperature and partly also moisture fluctuations. A number of them live at present in very cold regions. (c) They prefer, or are able, to live on poorly developed fresh calcareous soils. (d) They are comparatively independent of vegetation - - dendrophile elements are absent. Although the loess fauna shows a specific monotonous composition, it is possible to distinguish, in accordance with changes in abundance, presence or absence of certain species, several characteristic types of loess assemblages which could be grouped into three main categories (Table 1): (1) Pupilla fauna - - called after the genus PupiUa represented by several species such as P. muscorum (L.), P. sterri (Vth), P. loessica (L~k) and P. alpicola densegyrata (L~k) which dominate this most widespread loess assemblage (Fig. 1). Besides Pupillas, Succinea oblonga (Drap.) (Fig. 4), Trichia hispida (L.) agg., Vallonia tenuilabris (A. Br.) (Fig. 3) and locally also further species such as Helicopsis striata (Miill.) (in dry areas) are abundant. The Pupilla fauna may be regarded as basic assemblages of the loess malacofauna forming the basis of further, more specialized loess assemblages. (2) Columella fauna - - its index species is the arctoalpine element Columella columella (Mart.) (Fig. 2)
still living in high calcareous mountains of Central Europe and in the subarctic zone. Another index species is Vertigo parcedentata (A. Br.) (Fig. 2), only recently discovered living in the subarctic zone of Eurasia. Vallonia tenuilabris (A. Br.) (Fig. 3) is frequent. In many sites various tolerant, more hygrophile snails occur: Arianta arbustorum (L.), Euconulus fulvus (Miill.), Nesovitrea hammonis (Str.) and Vitrea crystallina (Miill.), whereas Helicopsis striata (Miill.) is absent or sparse. There appear also several interesting accidental elements as Vertigo modesta (Say) (D. V6stonice, Stillfried) or V. pseudosubstriata (L~k), recently discovered alive in the high mountains of Central Asia. Among Pupilla species, P. loessica (L~k) and P. a. densegyrata (L~k) play a prominent role. (3) Helicopsis striata fauna (= Striata f.) - - after H. striata (Miill.), an important steppe element, represents in its strict sense the warmest and driest (xerothermic) facies of the loess fauna and predominantly consists of species still living in Central Europe and showing no racial differences in comparison with modern populations: Pupilla muscorum (L.), P. triplicam (Stud.) as well as Vallonia costata (Miill.) which occurs in other loess assemblages only sparsely. Columella and the above Vertigo species are absent, whereas P. loessica (L~.k), P. a. densegyrata (L~.k), VaUonia tenuilabris (A. Br.) and even Trichia hispida (L.) or Succinea oblonga (Drap.) occur only exceptionally and in small amounts. In older, particularly Early Pleistocene Striata faunas, further demanding species such as Granaria frumentum (Drap.) and Chondrula tridens (Miill.) (Fig. 5) appear, which corroborates the xerothermic character of the Striata fauna (e.g. Krems). Locally, however, assemblages may occur which are dominated even by other species, e.g. by Trichia hispida (L.), Succinea oblonga (Drap.), Arianta arbusforum (L.) or, in the neighborhood of the Danube River, Trichia striolata (C. Pfr). The above types of malacofaunas form the main body of loess assemblages and show gradational differences in relation to environmental conditions (Lo~ek, 1972a). The Columella fauna represents the coldest and relatively hygrophile facies, the Helicopsis (Striata) fauna is rather xerothermic, whereas the Pupilla fauna corresponds to the most common median state. They grade into one another, although in certain horizons they are typically developed. Molluscan assemblages from the non-loessic members of the loess series show a differentiation corresponding to sedimentary or soil-forming environments in question. Loessified slope sediments commonly separating the members of pedocomplexes generally include assemblages resembling the Striata fauna of loess. Pellet sands (= Lehmbr6ckelsand) overlying the pedocomplexes are characterized by mixed faunas whose main body corresponds to a drier facies of the Pupilla fauna with abundant Helicopsis striata (Mfill.) comprising the autochthonous and parautochthonous
Catinella arenaria (B.-Chant.) Columeila columella (Mart.) Pupilla loessica (L~k) Pupilla alp. densegyrata (L~.k) Pupiila muscorum (Linn6) Truncatellina cylindrica (F6r.) Vailonia costata (M011.) Vallonia pulchella (M011.) Vallonia tenuilabris (A. Br.) Vertigo parcedentata (A. Br.) Vertigo pygmaea (Drap.) Cochlicopa lubricella (Porro) Euomphalia strigeUa (Drap.) Cochlicopa lubrica (M011.) Deroceras sp. Euconulus fulvus (M011.) Nesovitrea hammonis (Str6m) Trichia hispida (L.) agg. Trichia plebeia (Drap.) Clausilia dubia (Drap.) Orcula dolium (Drap.) Succinea oblonga (Drap.) Succinea sp.
(+)
(~) (~) (+) (+) (+) (+)
(+) (+) +
Woodland/open country - - xeric habitats
Woodland/open country - - mesic or indifferent
Mesic rocks, Stony habitats
Woodland/open country - - damp habitats
(+)
(+)
+
(G)
G ++ ++
(~) (+)
++ ++ ++ +
(+)
+
(+) 5
8
1
10 - -
7
- -
5
9
--
7
3
5
264
--
42
--
--
--
--
--
--
- -
--
39 --
- -
--
24 8
--
--
---
3 1 13 21
5
1
1
1
--
- -
(~K
57 7 183 10
--
--
--
- -
MI
130
55
1
304 40 182
7
46
VH
Localities
47
3 14 12
--
!?
|
14
2
3
8
8
8
LI M O
m
1
4
17
- -
42
389 27
71
94
30
127
1
LE
Biostratigraphic data: + - - characteristic loess species, + + - - index loess species, ( + ) - - local or accidental loess species, G - - species surviving the pleniglacial out o f the loess belt, (G) - - ditto, as relict, (!) - - eurythermic warm phase species.
Localities: MI - - Milanovce, Slovak Danubian Lowland (youngest loess, Columella f.), (~K - - Brno-t~erven~, kopec, Moravia (Late Biharian loess, Columella f., V H - Velk~, Hubenov, N. Bohemia (youngest loess, Pupiila f.), L I - Litohlavsk~, ml~'n near Beroun, Central Bohemia (youngest loess, poor Pupilla f.), M O - - Moravany on V~ih, S.W. Slovakia (Early Weichselian loess, Striata f.), L E - - Litom61~ice, eastern brickyard, N. Bohemia (upper chernozem o f Stillfried A, Tridens f.).
Open habitats in general
Granaria frumentum (Drap.) Helicopsis striata (M011.) Chondrula tridens (M011.) Pupilla sterri (Voith) Pupilla triplicata (Studer)
+
(+)
Steppe, xerothermic rocks
Bradybaena fruticum (M011.)
(~)
Species
Woodland, locally open habitats
Ecological groups
Biostratigraphic data
T A B L E 1. Malacofaunas from loess
"-...I
r~
g-
o.
74
v. Lotek
FIG. 3. Vallonia tenuilabris (A. Br.). F1G. 1. Loess species of Pupilla: (a) P. muscorum (L.), typic, (b) large loess race of P. muscorum, (c) Pupilla Ioessica (L~,k), (d) P. alpicola densegyrala (L~k).
S ...,//
\
,N
' // b
FIG. 2. (a) Columella columella (Mart.), (b) Vertigo parcedentam (A. Br.).
FIG. 4. (a) Succinea oblonga (Drap.), (b) Catinella arenaria (B.-Chant.).
Molluscs in Loess
75
are lacking. Such assemblages are called Tridens fauna. At the base of the most intensively developed early glacial soils an assemblage with Bradybaena fruticum (M/ill.) and Euomphalia strigella (Drap.) occurs - - the Fruticum fauna. It corresponds to a rather temperate parkland and represents the warmest facies of glacial malacofauna. Similar malacocoenoses characterize the transition between glacials and interglacials. POSITION OF INTERGLACIAL FAUNAS
FIG. 5. Chondrula tridens (Miill.).
Interglacial malacofaunas only occur in the loess series rather exceptionally, but they deserve more attention in view of their major biostratigraphic importance. Autochthonous or parautochthonous occurrences are confined to calcareous deposits locally preserved at the boundary between weathered brown soils and the underlying loess (Lo~.ek, 1965b). These correspond to early stages of warm phases and thus include fully developed interglacial assemblages only in interglacials with an early start of the thermal optimum, e.g. in the Eemian. Further records come from buried channels, burrow fills or from scree intercalations. Allochthonous interglacial shells often occur in pellet sands overlying the pedocomplexes as an admixture in various glacial assemblages. They can be distinguished not only on the basis of species identification but also by their state of preservation. ZONAL DIFFERENTIATION OF THE LOESS MALACOFAUNA
FIG. 6. Lymnaea glabra (Miill.) (All scales in mm).
components, whereas the allochthonous shells came from the reworked material of older loesses, slope sediments and soils. Therefore, steppe species as Chondrula tridens (M011.) or Granaria frumentum (Drap.) appear rather frequently. In a number of sites an admixture of interglacial species is present. Carbonate chernozems of early glacial warm oscillations include assemblages similar to the Striata fauna, but with high amounts of the steppe species Chondrula tridens (M011.) (Fig. 5) as well as with further less tolerant elements as Cochlicopa lubricella (Porro), TruncateUina cylindrica (F6r.) or Granaria frumentum (Drap.). By contrast, index species of loess as e.g. PupiUa loessica (l.~k) or Vallonia tenuilabris (A. Br.)
Typical loesses with well-developed characteristic malacofauna are concentrated in a zone situated in the middle latitudes of the North Hemisphere. In the marginal zone of this loess belt the richness of malacofauna decreases as shown by the records e.g. from northern France (Puiss6gur, 1983) as well as from various Mediterranean loess sites (Brunnacker and LoZek, 1969; Mazenot, 1956). However, the Mediterranean loess faunas are much more regionally differentiated and include a number of local species. In Central Europe a regional loess zonation has been described by Fink (1965). A completely developed sequence of loess series assemblages is only characteristic of dry loess regions, whereas in humid regions the malacofaunal sequence remains reduced to assemblages of proper loess, first of all to the thickest cover of the late pleniglacial, since the early glacial and early pleniglacial are represented by rather monotonous solifluction deposits which are malacologically sterile, and from the soils only the weathered interglacial soil remains well preserved, however, also being sterile. The assemblages of late pleniglacial loess are depauperized in comparison with those from the dry region and commonly contain higher amounts of several more hygrophile species, e.g. Arianta arbustorum (L.). In the transitional region the malacofaunal sequences are more differentiated than in the humid region, but they are less complete than in the dry region. Intergla-
V. L o ~ k
76
T A B L E 2. Malacofaunas from local loess facies and loess-like ioams Localities Ecological groups
Biostratigraphic data
Species
Monachoides incarnata (Miill.)
Woodland
(+)
Semilimax kotulai (West.) Vitrea crystallina (Miill.)
+ + (+)
Helicopsis striata (Miill.) Pupilla sterri (Voith) Pupilla triplicata (Studer)
L i m e s t o n e xeric rocks
(G)
Chondrina clienta (West.)
O p e n habitats in general
++ ++ ++ +
Columella columella (Mart.) Pupilla alp. densegyrata (L~k) Pupilla loessica (L~k) Pupilla muscorum (Linn6) Vallonia costata (M011.) Vallonia tenuilabris (A. Br.) Vertigo parcedentata (A. Br.)
W o o d l a n d , locally open habitats
Steppe, xerothermic rocks
G
(+) ++ ++ W o o d l a n d / o p e n country - - mesic or indifferent
(+) (+) (+) (+) +
(+) Mesic rocks, stony habitats
Woodland/open country - - d a m p habitats Marshlands, banks
(+)
Cochlicopa lubrica (Miill.) Deroceras sp. Euconulus fulvus (M011.) Nesovitrea hammonis (Str6m) Trichia hispida (L.) agg. Trichia plebeia (Drap.) Clausilia dubia (Drap.) Helicigona achates (Rossm.)
+
Succinea oblonga (Drap.)
(+)
Succinea putris (Linn6) Vertigo genesii (Gredler)
G
PO
BA
KO
SR
(~A
--
1
.
.
.
.
--
1
.
.
.
.
- -
143
VO
--
47
x
- -
--
12
--
18
s
- -
- -
12
.
.
1
.
.
--
32 -. . . -53 232 43 -3 - -
.
- -
3 209 --
29
--
8
- -
93
--
1?
--
- -
2
.
.
8 .
15
--
- -
16
.
.
--
2
.
.
5
--
- -
1?
--
.
.
.
.
--
s
302
s
--
s
-- -
.
- -
--
.
3?
. .
2 --
65 69 323 ---
x
--
.
- -
97
s s s x s
.
--
3
.
--
- -
.
. .
-. 763 -8
16
.
.
.
+
1431 39
s
X
--
Ancylus fluviatilis (M011.)
Moving water Various, mainly small water bodies
(+)
Pisidium casertanum (Poli)
.
.
.
.
s
17
Moving/stagnant water
(+)
Lymnaea ovata (Drap.)
.
.
.
.
x
55
.
.
.
.
. .
. .
. .
. .
.
.
.
.
.
.
.
.
S
.
.
.
.
S
Stagnant water
Periodic swamps
(+)
Bathyomphalus contortus (L.) Gyraulus acronicus (F6r.) Gvraulus albus (MOll.) Pisidium obtusale (Lamarck)
(+) (+) (+) (+)
Gyraulus rossmaessleri (Auers.) Anisus leucostomus (Mill.) Lymnaea occulta (Jack.) Aplexa hypnorum (Linn6) Valvata pulchella (Studer)
(+)
.
.
.
S
. .
--
197 l0 S
.
.
3
-3 3
.
.
.
.
.
3
.
.
.
.
.
2
Localities: PO - - Portelet, Isle of Jersey (Weichselian pleniglacial loess, poor Columella f., R o u s s e a u and Keen, 1989), B A - - Barovfi Cave, Moravia~ Karst (Early Weichselian pleniglacial cave loess, rich Pupilla f.), K O - Kobyla Hill near Kon~prusy, B o h e m i a n Karst (rock shelter, loess-like loam witl7 frost debris, Weichselian late pleniglacial, poor Pupilla f.), SR - - Srbsko, B o h e m i a n Karst (early Tardiglacial sandy loess in footslope positio~ d o m i n a t e d by V. costata), (~A - - ~akovice, N of Praha (Weichselian floodplain loess, Columella f. affected by moist environment), V O - - Vojkovice o~ Vltava, Central B o h e m i a (Weichselian late pleniglacial s w a m p loess, Columella f.). Biostratigraphic data: ! - - characteristic species of warm phases. See Table 1. A p p r o x i m a t e n u m b e r of specimens: + - - high, x - - m e d i u m , s - - low ((~akovice).
cial records are rather numerous (Rhine and Vfih Valleys, areas of Krems, etc.). Furthermore, local facies of loesses (Table 2) and other members of the loess series have to be briefly discussed. In hilly regions with steep topography they are usually affected by adjacent outcrops of bedrock as documented by the so-called white loess in marl areas, sandy loesses in sandstone districts, or loesses rich in frost debris coming from rocks producing large
amounts of fine fragments. In such areas local loess species most commonly occur, e.g. Vestia turgida (Rssm.) in Carpathian or Neostyriaca corynodes (Held) in Alpine foothills, Orcula dolium (Drap.) in the peripheral zone of both mountain ranges or Clausilia dubia (Drap.) in a broad area of midEuropean uplands. Accidental loess species as Semilimax kotulai (West.) or Vertigo modesta (Say) are also present. To this group also belong cave loesses,
Molluscs in Loess developed locally even in areas where typical surface loess is absent. A particular facies is represented by the floodplain loess deposited on valley floors and thus affected by the activity of water streams. In such sites moisture-loving species such as Vertigo genesii (Grd.), Cochlicopa lubrica (M011.), Zonitoides nitidus (Miill.), Succinea putris (L.), Lymnaea truncatula (M011.) and some most tolerant Pisidia including P. stewarti (Preston) appear.
MOLLUSCAN FAUNA OF SWAMP LOESS
In flat lowland areas (e.g. Pannonian Basin, Rumanian Danube Lowland) loesses include intercalations with rich assemblages of tolerant inhabitants of ephemeral waters, e.g. Lymnaea ovata (Drap.), L. glabra (Mtill.) (Fig. 6), L. diluviana (And.), probably L. occulta (Jack.), Planorbis planorbis (L.), Anisus leucostomus (Mill.), A. vortex (L.), Gyraulus acronicus (F6r.), Valvata pulchella (Stud.), Bithynia leachi troscheli (Paasch), etc., and terrestrial marsh species as Pseudotrichia rubiginosa (A. Sch.), Zonitoides nitidus (Miill.), Succinea putris (L.), locally also Oxyloma cf. elegans (Rs.) and Vertigo pygmaea (Drap.). The swamp loess malacofauna represents autochthonous assemblages of shallow ephemeral swamps which temporarily developed on loess plains with limited drainage. The underlying and overlying loess strata include a common terrestrial loess fauna. There are also swamp equivalents of non-loessic members of the loess series, very rich in snails. Rich occurrences of aquatic and marsh species in loess complexes have repeatedly given rise to speculations of fluvial or limnic origin of the loess, but this assumption is erroneous, since the species in question are characteristic of temporary periodic marshes. ASSEMBLAGES OF LOESS EQUIVALENTS OUT OF THE LOESS BELT PALEOMALACOLOGICAL CORRELATIONS The composition of loess malacofauna is controlled not only by climate but also by environmental conditions within the loess zone which ranges up to certain elevations only, in Central Europe approximately to 300-350 m above sea level. In general, loess areas have a weak to fiat relief and deep loamy substrate. They have, even during periods without loess formation, a fauna which is generally different from that living in higher areas with steeper relief and numerous outcrops of solid bedrock. During the loess formation the non-loessic areas had their specific assemblages consisting in part of several species also common in loess and in part of species which survived the pleniglacial out of the loess zone. In such areas the loess is mostly replaced by fine-sized screes developed often as cryoclastic debris with various proportions of dust-rich matrix. These only include fossil shells in areas rich in CaCO3, particularly
77
in karstlands. A number of loess species occur such as Columella columella (Mart.), VaUonia tenuilabris (A. Br.), and most Pupilla species associated with nonIoessic elements, e.g. Vertigo alpestris (Aid.), Vitrina pellucida (M011.) and other Vitrinids as well as in protected mountain areas Pyramidula rupestris (Drap.), Chondrina clienta (West.) and Ch. tatrica (L~k) and even Helicigona cingulella (Rssm.) (Lo~ek, 1980). Survival of several Carpathian endemites as Cochlodina cerata (Rssm.), Monachoides vicina (Rssm.) or Helicigona faustina (Rssm.) seems to be very probable. In this connection it is worth noting that the youngest loess, deposited in the late Weichselian pleniglacial, has the widest distribution extending far into the periphery of the loess belt where other loess horizons are replaced either by lime-deficient dust loams or cryoclastic debris. These marginal loesses generally include a Columella fauna in depauperized facies and represent, at least within the Last Glacial, the loess optimum (Lo~ek, 1988). MOLLUSCS AS INDICATORS OF ENVIRONMENTAL CONDITIONS DURING LOESS FORMATION
The malacofaunal indication of loess forming environments is based partly (1) on the knowledge of environmental requirements of particular loess species as observed at the present time and partly (2) on the total structure of loess malacocoenoses. (1) The main body of species constituting the assemblages of genuine loess live also at present over most of the temperate zone of Eurasia and partly of North America. However, their present demands are extremely variable, often greatly confronting as shown, e.g. by a comparison of the present demands of Columella columella (Mart.), Trichia hispida (L.), Pupilla triplicata (Stud.) or Succinea oblonga (Drap.), let alone those of local loess species which in particular areas represent an important component of loess assemblages as, e.g. Clausilia parvula (F6r.), Vestia turgida (Rssm.) or Trichia striolata (C. Pfr). (2) Characteristic loess communities thus consist of species which at present commonly belong to highly differing assemblages occurring in very different habitats. There is no analog of loess malacocoenoses within the modern fauna of Europe, apart from some peculiar communities living in extreme habitats which rather resemble the loess fauna. Moreover, the loess assemblages include a number of elements living at present in the Far North or in Central Asia, whose environmental requirements are poorly known so far. These observations and several further lines of evidence indicate that the environments during the loess formation showed specific features which differed markedly from those in other phases of the Quaternary climatic cycle inclusive of the present time. This peculiar environment is reflected also by the shell form of most loess species which differ in various
78
v. Lo~ek
details from modern populations as e.g. the small forms Quaternary and latest Pliocene which include a number of Trichia, several forms of Pupilla muscorum (L.) as of species absent from younger ioesses as e.g. Granaria frumentum (Drap.) agg. or specific forms of Vertigo well as Clausilia dubia (Drap.). In order to understand this apparent chaos we must and Pupilla, whereas several species frequent in the emphasize the features which are common to all loess younger part of the Pleistocene such as e.g. Trichia species as summarized in the section discussing mollus- hispida (L.) agg., have not been recorded (Fink et al., can assemblages of the loess series. Most loess species 1976). The chief difficulty in wider application of loess have a wide distributional range (eurosiberian, palearc- assemblages to Quaternary biostratigraphy is the scartic to holarctic). Species with restricted range including city of older loess records which makes it impossible to several endemites appear only locally or regionally in establish a reliable characteristic of loess assemblages from different time periods. loess assemblages. It will be obvious from the forgoing that the loess Among various assemblages from the loess series, fauna is characterized by a number of common features interglacial faunas are of prime importance being much which provide a solid basis to reconstruct environmen- richer in species and showing more changes with time. tal conditions controlling the loess formation (Lo~ek, Thus, in certain regions they can characterize particular 1965a, 1976). Except for assemblages of loessified slope interglacials both by the presence of various index sediments which resemble the loess faunas, assembla- species and by specific combinations of particular ges from non-loessic members of the loess series are elements: in Central Europe the last Interglacial has a markedly different. In this context it is worth noting fully developed woodland fauna with Drobacia banathat several loess species also occur in these non-ioessic tica (Rssm.), whereas in the penultimate Interglacial assemblages, but in races identical with those living at only Helix pomatia (L.) faunas, poor in species, have present and not with forms prevailing in loess. been recorded (Lo~ek, 1969; Hor~i~ek and Lo~ek, All malacological lines of evidence indicate that the 1988). loess formed in steppes with a sufficiently developed However, the snail faunas from loess and loess series herb cover supporting a comparatively rich snail fauna are of essential importance to a detailed subdivision of requiring an appropriately humid and warm vegeta- the Quaternary climatic cycle, since the sequence of tional period. This was, naturally, very short, since the malacofaunas throughout the loess series enables the climate was in general very severe, with marked aridity, course of this cycle to be established in a completeness so that no mature soils could form and the accumulat- having no analog in other continental deposits (Kukla, ing eolian dust was only converted into a carbonate raw 1977). Malacology provides evidence of the following soil, which process (= Ioessification) considerably phases: Interglacial (usually non-subdivided), Early affected the characteristic loess structure. The loess Glacial (subdivided into cold to warm oscillations), ecosystem documented by molluscan fauna has no Pleniglacial (in many cases subdivided in detail). By modern analog in Europe and it remains to be seen, contrast, the Late Glacial is recorded only exceptionwhether such analogs exist, e.g. in highly continental ally. areas of North and Central Asia, where several index The importance of malacofauna increases in areas species of loess, extinct in Europe, are still living. In where loess series from several cycles occur in superChina the differences between the loess assemblages position or overlie other stratigraphically important and the interglacial and modern fauna seem to be less sediments as river terraces or glacial deposits. In such pronounced (Chen et al., 1982). Concerning the loess cases molluscs provide fundamental biostratigraphic fauna of North America, there are some parallels, e.g. criteria to the subdivision of the Quaternary based on the assemblages with Columella alticola (Ing.), Pupilla regular alternation of cold and warm phases. In a (spp.), etc. in the Late Wisconsin loess (Taylor, 1965), similar manner they can be applied in the case of fully but in general, the situation seems to be different from subdivided loess series as demonstrated by the course that in West Eurasia, as previously summarized by of the Last Glacial whose youngest loess has a Shimek (1930), who found only minor differences Columella fauna with Vertigo parcedentata (A. Br.), between the loess communities and modern malaco- whereas early pleniglacial loesses include Pupilla coenoses of the Mississippi Valley. Therefore, he faunas and loess-like intercalations within the early considers the loesses interglacial, although he does not glacial complex Striata faunas. deny their eolian origin. The most important contribution of malacostratigraphy is the evidence of the maximum number of climatic cycles, i.e. of the full number of cold/warm oscillations BIOSTRATIGRAPHIC SIGNIFICANCE OF THE within various periods of time (Fink and Kukla, 1977). LOESS MALACOFAUNA These are mostly not preserved in other sedimentary The malacocoenoses of proper loess show a rather environments which leads to simplifications of Quateruniform character in space and time. Thus they attain nary climatic stratigraphy (Lo~ek, 1972b). For instonly limited application in terms of detailed biostrati- ance, in the non-glaciated region of Central Europe a graphy of the Quaternary. As matters now stand, we considerably higher number of climatic phases of first can distinguish the assemblages occurring in Late and order can be documented than in adjacent glaciated Middle Pleistocene loesses from those of the Early areas, where many traces of climatic fluctuations have
Molluscs in Loess
been destroyed by the glaciation. The mid-European loess belt is thus the very area where malacofaunas from well-differentiated loess series enabled the socalled full subdivision (Vollgliederung of Soergel, 1939) of the Quaternary to be established and former schematic conceptions based on glacial deposits to be reassessed and completed. REFERENCES Brunnacker, K. and LoI:ek, V. (1969). LOss-Vorkommen in Siidostspanien. Zeitschrift far Geomorphologie, 13(3), 297-316. Chen, D., Lu, Y.C. and An Z.S. (1982). Snail assemblages in loess strata and their environmental implication. In: Proceedings of the third National Quaternary Conference, China, pp. 7-15. Science Press, Beijing. Evans, J.G. (1972). Land Snails in Archaeology. Seminar Press, London, 436 pp. Fink, J. (1965). The Pleistocene in Eastern Austria. The Geological Society of America, Special Paper, 84, 179-199. Fink, J. and Kukla, G.J. (1977). Pleistocene climates in Central Europe: At least 17 interglacials after the Olduvai Event. Quaternary Research, 7, 363-371. Fink, J., Fischer, H., Klaus, W.. Ko~i, A., Kohl, H., Kukla, J., Lo~ek, V., Piffl, L. and Rabeder, G. (1976). Exkursion durch den 6stereichischen Teil des n6rdlichen Alpenvorlandes und den Donauraum zwischen Krems und Wiener Pforte. Mineilungen der
Kommission fiir Quartiirforschung der Osterreichischen Akademie der Wissenschaften, 1, 113 pp. Horfi~:ek, I. and Lo~ek, V. (1988). Palaeozoology and the MidEuropean Quaternary past: scope of the approach and selected results. Rozpravy ~eskoslovenskd akademie vdd, l~ada MPV, 98(4), 102 pp. Kukla, J. (1961). Survey of Czechoslovak Quaternary: Quaternary sedimentation cycle, lnstytut Geologiczny, Prace, 34-Czwartorzed Europy ~rodkowej i Wschodniej, !, 145-154. Kukla, J. (1975). Loess stratigraphy of Central Europe. In: Butzer. K.W. and Isaac, G.L.L. (eds), After the Australopithecines, pp. 99-188. Mouton Publishers, The Hague. Kukla, J. (1977). Pleistocene land-sea correlations. I. Europe. Earth-Science Reviews, 13, 307-374.
79
Lo~ek, V. (1964). Quart~irmoilusken der Tschechoslowakei. Rozpravy l~lst~edniho astavu geologick~ho, 31, 374 pp. Lo~'ek, V. (1965a). Das Problem der L6ssbiidung und die und die L6ssmollusken. Eiszeitalter und Gegenwart, 16, 61-75. Lo~ek, V. (1965b). The relationship between the development of soils and faunas in the warm Quaternary phases. Sbornik geologickpch v#d, A-Antropozoikum, 3, 7-33. Lo~.ek, V. (1969). Uber die malakozooiogische Charakteristik der pleistoz/inen Warmzeiten mit besonderer Beriicksichtigung des letzten lnterglazials. Berichte der Deutschen Gesellschafi far Geologische Wissenschaften, 14(4), 439--469. Lo~'ek, V. (1972a). Le loess et ies formations assimil6es: corr61ation entre l'Europe Centrale et la France par la faune de Mollusques.
In: Proceedings of the Eighth INQUA Congress. Etudes sur le Quaternaire dans le Monde, pp. 597-606. Paris. Lo~'ek, V. (1972b). Zum Problem der Zahl der quart~iren Klimaschwankungen. Quartiir, 22, 1-16. Lo~ek, V. (1976). Klimaabh~ingige Zyklen der Sedimentation und Bodenbildung wiihrend des Ouartiirs im Lichte malakozoologischer Untersuchungen. Rozpravy ~eskoslovensk~ akademie v~d, ~'. MPV, 86(8), 97 pp. Lo~.ek, V. (1980). Quaternary molluscs and stratigraphy of the Ma~arnfi cave. ~eskoslovensky~ Kras, 30, 67-80. Lo~ek, V. (1988). Slope deposition in karst environments of Central Europe. ~eskoslovensky~ Kras, 39, 15-33. Mazenot, G. (1956). Recherches sur les faunes malacologiques du loess r6cent wiirmien et de divers limons terrestres holoc~nes dans ie sud-est de ia France. Bulletin mensuel de la Sod~td Linn~enne de Lyon, 25, 9-24, 41-56, 73--85. Mel'ni~uk, I.V. (1974). Fauna molljuskov antropogenovych po~v Ukrainy. In: Paleopedologija, pp. 128--138. Naukova Dumka, Kiev. Puiss6gur, J.-J. (1983). Pleistocene malacologicai faunas of Normandy. In: Lautridou, J.P. (ed.), The Quaternary of Normandy, pp. 151-160. IGCP 24 Normandy Meeting, September 1982, Rouen. Shimek, B. (1930). Land snails as indicators of ecological conditions. Ecology, 11(4), 673--686. Soergel, W. (1939). Das Diluviale System. Fortschritte der Geologie und Palaeontologie, 12(39), 1--8, 155--292. Taylor, D. (1965). The study of Pleistocene nonmarine mollusks in North America. In: Wright, H.E. and Frey, D.G. (eds), The Quaternary of the United States, pp. 597--611. Princeton University Press, Princeton NJ.
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M O L L U S C S IN LOESS, THEIR P A L E O E C O L O G I C A L SIGNIFICANCE AND ROLE IN G E O C H R O N O L O G Y m PRINCIPLES AND M E T H O D S V. Lo~ek
~eskoslovenskd akademie v~d, Geologicky~ ~stav, 165 O0 Praha 6-Suchdol, Rozvojov~ 135, Czechoslovakia
The malacofauna of genuine wind-blown loess consists of a minor number of tolerant species occurring mostly in high amounts and reflecting open habitats with poorly developed calcareous soils. It shows a rather uniform character in space and time distinctly differing from all present-day assemblages of the temperate zone, and thus indicating a very peculiar environment characteristic of the loess steppe. In protected areas, particularly on valley slopes, the loess covers alternate with intercalations of slope sediments and soils including several other types of snail assemblages reflecting environmental changes in the course of the Quaternary climatic cycle. Among these malacocoenoses the interglacial faunas are of prime biostratigraphic importance. They are associated with strongly weathered forest soils and indicate woodland environments under very damp and warm climatic conditions. Transitional steppe and taiga assemblages occur in buried chernozem soils and in various slope sediments, e.g. in the pellet sands, overlying the interglacial soils and corresponding to early glacial periods. Although the fauna of proper loess shows a monotonous composition, it is possible to distinguish several types of loess assemblages corresponding to minor facies changes of loess environments in time and space; these are, for example, the Pupilla, Helicopsis striata and Columella faunas of Central Europe. A peculiar marshland fauna characterizes the so-called swamp-loess deposited in ephemeral swamps. In the marginal zones of the loess belt there occur also faunas partly differing from those of typical loess; this is true particularly of the Mediterranean region. The most important contribution provided by molluscan faunas from the loess series is the evidence of the maximum number of climatic cycles during the Quaternary period.
LOESS AND LOESS SERIES AS LOCALITIES OF MOLLUSC FINDS, TREATMENT OF THEIR PALEOMALACOLOGICAL CONTENTS
older loesses, soils and slope sediments and commonly contain an admixture of weathered bedrock. Their fossil assemblages include, therefore, 3 main components: (1) autochthonous - - species inhabiting the accumulation area; (2) parautochthonous - - shells transported together with the slope material from its catchment area; (3) aUochthonous - - redeposited fossil shells from reworked older sediments and soils. The autochthonous and parautochthonous components thus correspond to malacocoenoses living in the sedimentation and catchment area, and the allochthonous one represents an allogene admixture, mostly recognizable by its fossilization. Soils yield shells only when they are primarily calcareous which applies to carbonate chernozems and rendzinas. Their fauna is predominantly autochthonous being incorporated into the soil horizon by bioturbation leading to gradual redeposition of the soil material in situ (Lo~ek, 1964; Evans, 1972). An assemblage from a fossil soil thus commonly corresponds to a much longer period of time than that from a loess horizon of the same thickness. The soil can also include older fossil shells coming from its parent material. These generally differ by their fossilization. Weathered brown and red soils are decalcified so that shells are only exceptionally preserved, e.g. in calcareous fills of burrows or at places where such soils grade into calcareous colluvia. The evidence presented here demonstrates that loess provides a rich autochthonous snail material which is well preserved and can be easily obtained by washing with numbers which allow a statistical treatment. Other members of the loess series are in general considerably poorer. The shells are commonly preserved in frag-
In view of its CaCO3 content and quiet sedimentary environment loess provides suitable conditions for fossilization of molluscan shells. In general, loesses include numerous well-preserved shells which used to be distributed throughout the loess covers in both the vertical and horizontal sense. The richest malacofauna occurs in loesses situated in the valleys of large lowland rivers, whereas loesses on plateaus are most commonly poor in species or malacologically sterile. Molluscs can be preserved only in proper, i.e. calcareous loess, whereas in lime-deficient eolian loams the shells are rapidly corroded and dissolved, apart from the fact that such sedimentary environments might be primarily poor in snails. Thus the occurrence of fossil molluscs is often regarded as one of the characteristic features of genuine loess. In protected areas, particularly on valley slopes, the loesses form complicated sequences including intercalations of non-ioessic origin such as slope sediments and soils. These alternate with loess covers in successions of regular pattern called loess series (Kukla, 1961, 1975). Their fossil assemblages differ, however, from those of loess in several aspects. Loess thanatocoenoses predominantly consist of individuals which formerly lived in the sedimentation area in question. They are thus markedly autochthonous and broadly correspond to original malacocoenoses living in areas where the loess formed. Slope sediments generally consist of redeposited 71
72
v. Lo~ek
merits only and the assemblages often represent a mixture of different elements. Nevertheless, some of these non-loessic faunas are biostratigraphically very important which is particularly true of interglacial faunas. In the case of such horizons it is therefore appropriate to take much more voluminous soil samples than from the loess. The loess malacofauna has received attention mainly in the European loess belt and in the U.S.A. However, most previous works do not distinguish those records from proper loess from those collected in non-loessic horizons of the loess series, apart from the fact that a number of important species were not recognized. For this reason, our review is mostly based on records from the area situated between the French coast and the Ukraine, where after World War II large-scale investigations of loesses and loess malacofaunas have been made, throwing light on sedimentological and coenological details which are not available from other regions so far (Fink et al., 1976; Kukla, 1975, 1977; Lo~.ek, 1964, 1965a, 1972, 1976; Mazenot, 1956; Melni~uk, 1974; Puiss6gur, 1983 and others). MOLLUSCAN ASSEMBLAGES OF TRUE LOESS AND NON-LOESSIC MEMBERS OF THE LOESS SERIES The malacocoenoses of true wind-blown loess consist of a minor number of species occurring mostly in high amounts and showing the following environmental requirements (Lo~.ek, 1965a): (a) They are confined to open habitats or are able to live in such habitats. (b) They are resistant to major temperature and partly also moisture fluctuations. A number of them live at present in very cold regions. (c) They prefer, or are able, to live on poorly developed fresh calcareous soils. (d) They are comparatively independent of vegetation - - dendrophile elements are absent. Although the loess fauna shows a specific monotonous composition, it is possible to distinguish, in accordance with changes in abundance, presence or absence of certain species, several characteristic types of loess assemblages which could be grouped into three main categories (Table 1): (1) Pupilla fauna - - called after the genus PupiUa represented by several species such as P. muscorum (L.), P. sterri (Vth), P. loessica (L~k) and P. alpicola densegyrata (L~k) which dominate this most widespread loess assemblage (Fig. 1). Besides Pupillas, Succinea oblonga (Drap.) (Fig. 4), Trichia hispida (L.) agg., Vallonia tenuilabris (A. Br.) (Fig. 3) and locally also further species such as Helicopsis striata (Miill.) (in dry areas) are abundant. The Pupilla fauna may be regarded as basic assemblages of the loess malacofauna forming the basis of further, more specialized loess assemblages. (2) Columella fauna - - its index species is the arctoalpine element Columella columella (Mart.) (Fig. 2)
still living in high calcareous mountains of Central Europe and in the subarctic zone. Another index species is Vertigo parcedentata (A. Br.) (Fig. 2), only recently discovered living in the subarctic zone of Eurasia. Vallonia tenuilabris (A. Br.) (Fig. 3) is frequent. In many sites various tolerant, more hygrophile snails occur: Arianta arbustorum (L.), Euconulus fulvus (Miill.), Nesovitrea hammonis (Str.) and Vitrea crystallina (Miill.), whereas Helicopsis striata (Miill.) is absent or sparse. There appear also several interesting accidental elements as Vertigo modesta (Say) (D. V6stonice, Stillfried) or V. pseudosubstriata (L~k), recently discovered alive in the high mountains of Central Asia. Among Pupilla species, P. loessica (L~k) and P. a. densegyrata (L~k) play a prominent role. (3) Helicopsis striata fauna (= Striata f.) - - after H. striata (Miill.), an important steppe element, represents in its strict sense the warmest and driest (xerothermic) facies of the loess fauna and predominantly consists of species still living in Central Europe and showing no racial differences in comparison with modern populations: Pupilla muscorum (L.), P. triplicam (Stud.) as well as Vallonia costata (Miill.) which occurs in other loess assemblages only sparsely. Columella and the above Vertigo species are absent, whereas P. loessica (L~.k), P. a. densegyrata (L~.k), VaUonia tenuilabris (A. Br.) and even Trichia hispida (L.) or Succinea oblonga (Drap.) occur only exceptionally and in small amounts. In older, particularly Early Pleistocene Striata faunas, further demanding species such as Granaria frumentum (Drap.) and Chondrula tridens (Miill.) (Fig. 5) appear, which corroborates the xerothermic character of the Striata fauna (e.g. Krems). Locally, however, assemblages may occur which are dominated even by other species, e.g. by Trichia hispida (L.), Succinea oblonga (Drap.), Arianta arbusforum (L.) or, in the neighborhood of the Danube River, Trichia striolata (C. Pfr). The above types of malacofaunas form the main body of loess assemblages and show gradational differences in relation to environmental conditions (Lo~ek, 1972a). The Columella fauna represents the coldest and relatively hygrophile facies, the Helicopsis (Striata) fauna is rather xerothermic, whereas the Pupilla fauna corresponds to the most common median state. They grade into one another, although in certain horizons they are typically developed. Molluscan assemblages from the non-loessic members of the loess series show a differentiation corresponding to sedimentary or soil-forming environments in question. Loessified slope sediments commonly separating the members of pedocomplexes generally include assemblages resembling the Striata fauna of loess. Pellet sands (= Lehmbr6ckelsand) overlying the pedocomplexes are characterized by mixed faunas whose main body corresponds to a drier facies of the Pupilla fauna with abundant Helicopsis striata (Mfill.) comprising the autochthonous and parautochthonous
Catinella arenaria (B.-Chant.) Columeila columella (Mart.) Pupilla loessica (L~k) Pupilla alp. densegyrata (L~.k) Pupiila muscorum (Linn6) Truncatellina cylindrica (F6r.) Vailonia costata (M011.) Vallonia pulchella (M011.) Vallonia tenuilabris (A. Br.) Vertigo parcedentata (A. Br.) Vertigo pygmaea (Drap.) Cochlicopa lubricella (Porro) Euomphalia strigeUa (Drap.) Cochlicopa lubrica (M011.) Deroceras sp. Euconulus fulvus (M011.) Nesovitrea hammonis (Str6m) Trichia hispida (L.) agg. Trichia plebeia (Drap.) Clausilia dubia (Drap.) Orcula dolium (Drap.) Succinea oblonga (Drap.) Succinea sp.
(+)
(~) (~) (+) (+) (+) (+)
(+) (+) +
Woodland/open country - - xeric habitats
Woodland/open country - - mesic or indifferent
Mesic rocks, Stony habitats
Woodland/open country - - damp habitats
(+)
(+)
+
(G)
G ++ ++
(~) (+)
++ ++ ++ +
(+)
+
(+) 5
8
1
10 - -
7
- -
5
9
--
7
3
5
264
--
42
--
--
--
--
--
--
- -
--
39 --
- -
--
24 8
--
--
---
3 1 13 21
5
1
1
1
--
- -
(~K
57 7 183 10
--
--
--
- -
MI
130
55
1
304 40 182
7
46
VH
Localities
47
3 14 12
--
!?
|
14
2
3
8
8
8
LI M O
m
1
4
17
- -
42
389 27
71
94
30
127
1
LE
Biostratigraphic data: + - - characteristic loess species, + + - - index loess species, ( + ) - - local or accidental loess species, G - - species surviving the pleniglacial out o f the loess belt, (G) - - ditto, as relict, (!) - - eurythermic warm phase species.
Localities: MI - - Milanovce, Slovak Danubian Lowland (youngest loess, Columella f.), (~K - - Brno-t~erven~, kopec, Moravia (Late Biharian loess, Columella f., V H - Velk~, Hubenov, N. Bohemia (youngest loess, Pupiila f.), L I - Litohlavsk~, ml~'n near Beroun, Central Bohemia (youngest loess, poor Pupilla f.), M O - - Moravany on V~ih, S.W. Slovakia (Early Weichselian loess, Striata f.), L E - - Litom61~ice, eastern brickyard, N. Bohemia (upper chernozem o f Stillfried A, Tridens f.).
Open habitats in general
Granaria frumentum (Drap.) Helicopsis striata (M011.) Chondrula tridens (M011.) Pupilla sterri (Voith) Pupilla triplicata (Studer)
+
(+)
Steppe, xerothermic rocks
Bradybaena fruticum (M011.)
(~)
Species
Woodland, locally open habitats
Ecological groups
Biostratigraphic data
T A B L E 1. Malacofaunas from loess
"-...I
r~
g-
o.
74
v. Lotek
FIG. 3. Vallonia tenuilabris (A. Br.). F1G. 1. Loess species of Pupilla: (a) P. muscorum (L.), typic, (b) large loess race of P. muscorum, (c) Pupilla Ioessica (L~,k), (d) P. alpicola densegyrala (L~k).
S ...,//
\
,N
' // b
FIG. 2. (a) Columella columella (Mart.), (b) Vertigo parcedentam (A. Br.).
FIG. 4. (a) Succinea oblonga (Drap.), (b) Catinella arenaria (B.-Chant.).
Molluscs in Loess
75
are lacking. Such assemblages are called Tridens fauna. At the base of the most intensively developed early glacial soils an assemblage with Bradybaena fruticum (M/ill.) and Euomphalia strigella (Drap.) occurs - - the Fruticum fauna. It corresponds to a rather temperate parkland and represents the warmest facies of glacial malacofauna. Similar malacocoenoses characterize the transition between glacials and interglacials. POSITION OF INTERGLACIAL FAUNAS
FIG. 5. Chondrula tridens (Miill.).
Interglacial malacofaunas only occur in the loess series rather exceptionally, but they deserve more attention in view of their major biostratigraphic importance. Autochthonous or parautochthonous occurrences are confined to calcareous deposits locally preserved at the boundary between weathered brown soils and the underlying loess (Lo~.ek, 1965b). These correspond to early stages of warm phases and thus include fully developed interglacial assemblages only in interglacials with an early start of the thermal optimum, e.g. in the Eemian. Further records come from buried channels, burrow fills or from scree intercalations. Allochthonous interglacial shells often occur in pellet sands overlying the pedocomplexes as an admixture in various glacial assemblages. They can be distinguished not only on the basis of species identification but also by their state of preservation. ZONAL DIFFERENTIATION OF THE LOESS MALACOFAUNA
FIG. 6. Lymnaea glabra (Miill.) (All scales in mm).
components, whereas the allochthonous shells came from the reworked material of older loesses, slope sediments and soils. Therefore, steppe species as Chondrula tridens (M011.) or Granaria frumentum (Drap.) appear rather frequently. In a number of sites an admixture of interglacial species is present. Carbonate chernozems of early glacial warm oscillations include assemblages similar to the Striata fauna, but with high amounts of the steppe species Chondrula tridens (M011.) (Fig. 5) as well as with further less tolerant elements as Cochlicopa lubricella (Porro), TruncateUina cylindrica (F6r.) or Granaria frumentum (Drap.). By contrast, index species of loess as e.g. PupiUa loessica (l.~k) or Vallonia tenuilabris (A. Br.)
Typical loesses with well-developed characteristic malacofauna are concentrated in a zone situated in the middle latitudes of the North Hemisphere. In the marginal zone of this loess belt the richness of malacofauna decreases as shown by the records e.g. from northern France (Puiss6gur, 1983) as well as from various Mediterranean loess sites (Brunnacker and LoZek, 1969; Mazenot, 1956). However, the Mediterranean loess faunas are much more regionally differentiated and include a number of local species. In Central Europe a regional loess zonation has been described by Fink (1965). A completely developed sequence of loess series assemblages is only characteristic of dry loess regions, whereas in humid regions the malacofaunal sequence remains reduced to assemblages of proper loess, first of all to the thickest cover of the late pleniglacial, since the early glacial and early pleniglacial are represented by rather monotonous solifluction deposits which are malacologically sterile, and from the soils only the weathered interglacial soil remains well preserved, however, also being sterile. The assemblages of late pleniglacial loess are depauperized in comparison with those from the dry region and commonly contain higher amounts of several more hygrophile species, e.g. Arianta arbustorum (L.). In the transitional region the malacofaunal sequences are more differentiated than in the humid region, but they are less complete than in the dry region. Intergla-
V. L o ~ k
76
T A B L E 2. Malacofaunas from local loess facies and loess-like ioams Localities Ecological groups
Biostratigraphic data
Species
Monachoides incarnata (Miill.)
Woodland
(+)
Semilimax kotulai (West.) Vitrea crystallina (Miill.)
+ + (+)
Helicopsis striata (Miill.) Pupilla sterri (Voith) Pupilla triplicata (Studer)
L i m e s t o n e xeric rocks
(G)
Chondrina clienta (West.)
O p e n habitats in general
++ ++ ++ +
Columella columella (Mart.) Pupilla alp. densegyrata (L~k) Pupilla loessica (L~k) Pupilla muscorum (Linn6) Vallonia costata (M011.) Vallonia tenuilabris (A. Br.) Vertigo parcedentata (A. Br.)
W o o d l a n d , locally open habitats
Steppe, xerothermic rocks
G
(+) ++ ++ W o o d l a n d / o p e n country - - mesic or indifferent
(+) (+) (+) (+) +
(+) Mesic rocks, stony habitats
Woodland/open country - - d a m p habitats Marshlands, banks
(+)
Cochlicopa lubrica (Miill.) Deroceras sp. Euconulus fulvus (M011.) Nesovitrea hammonis (Str6m) Trichia hispida (L.) agg. Trichia plebeia (Drap.) Clausilia dubia (Drap.) Helicigona achates (Rossm.)
+
Succinea oblonga (Drap.)
(+)
Succinea putris (Linn6) Vertigo genesii (Gredler)
G
PO
BA
KO
SR
(~A
--
1
.
.
.
.
--
1
.
.
.
.
- -
143
VO
--
47
x
- -
--
12
--
18
s
- -
- -
12
.
.
1
.
.
--
32 -. . . -53 232 43 -3 - -
.
- -
3 209 --
29
--
8
- -
93
--
1?
--
- -
2
.
.
8 .
15
--
- -
16
.
.
--
2
.
.
5
--
- -
1?
--
.
.
.
.
--
s
302
s
--
s
-- -
.
- -
--
.
3?
. .
2 --
65 69 323 ---
x
--
.
- -
97
s s s x s
.
--
3
.
--
- -
.
. .
-. 763 -8
16
.
.
.
+
1431 39
s
X
--
Ancylus fluviatilis (M011.)
Moving water Various, mainly small water bodies
(+)
Pisidium casertanum (Poli)
.
.
.
.
s
17
Moving/stagnant water
(+)
Lymnaea ovata (Drap.)
.
.
.
.
x
55
.
.
.
.
. .
. .
. .
. .
.
.
.
.
.
.
.
.
S
.
.
.
.
S
Stagnant water
Periodic swamps
(+)
Bathyomphalus contortus (L.) Gyraulus acronicus (F6r.) Gvraulus albus (MOll.) Pisidium obtusale (Lamarck)
(+) (+) (+) (+)
Gyraulus rossmaessleri (Auers.) Anisus leucostomus (Mill.) Lymnaea occulta (Jack.) Aplexa hypnorum (Linn6) Valvata pulchella (Studer)
(+)
.
.
.
S
. .
--
197 l0 S
.
.
3
-3 3
.
.
.
.
.
3
.
.
.
.
.
2
Localities: PO - - Portelet, Isle of Jersey (Weichselian pleniglacial loess, poor Columella f., R o u s s e a u and Keen, 1989), B A - - Barovfi Cave, Moravia~ Karst (Early Weichselian pleniglacial cave loess, rich Pupilla f.), K O - Kobyla Hill near Kon~prusy, B o h e m i a n Karst (rock shelter, loess-like loam witl7 frost debris, Weichselian late pleniglacial, poor Pupilla f.), SR - - Srbsko, B o h e m i a n Karst (early Tardiglacial sandy loess in footslope positio~ d o m i n a t e d by V. costata), (~A - - ~akovice, N of Praha (Weichselian floodplain loess, Columella f. affected by moist environment), V O - - Vojkovice o~ Vltava, Central B o h e m i a (Weichselian late pleniglacial s w a m p loess, Columella f.). Biostratigraphic data: ! - - characteristic species of warm phases. See Table 1. A p p r o x i m a t e n u m b e r of specimens: + - - high, x - - m e d i u m , s - - low ((~akovice).
cial records are rather numerous (Rhine and Vfih Valleys, areas of Krems, etc.). Furthermore, local facies of loesses (Table 2) and other members of the loess series have to be briefly discussed. In hilly regions with steep topography they are usually affected by adjacent outcrops of bedrock as documented by the so-called white loess in marl areas, sandy loesses in sandstone districts, or loesses rich in frost debris coming from rocks producing large
amounts of fine fragments. In such areas local loess species most commonly occur, e.g. Vestia turgida (Rssm.) in Carpathian or Neostyriaca corynodes (Held) in Alpine foothills, Orcula dolium (Drap.) in the peripheral zone of both mountain ranges or Clausilia dubia (Drap.) in a broad area of midEuropean uplands. Accidental loess species as Semilimax kotulai (West.) or Vertigo modesta (Say) are also present. To this group also belong cave loesses,
Molluscs in Loess developed locally even in areas where typical surface loess is absent. A particular facies is represented by the floodplain loess deposited on valley floors and thus affected by the activity of water streams. In such sites moisture-loving species such as Vertigo genesii (Grd.), Cochlicopa lubrica (M011.), Zonitoides nitidus (Miill.), Succinea putris (L.), Lymnaea truncatula (M011.) and some most tolerant Pisidia including P. stewarti (Preston) appear.
MOLLUSCAN FAUNA OF SWAMP LOESS
In flat lowland areas (e.g. Pannonian Basin, Rumanian Danube Lowland) loesses include intercalations with rich assemblages of tolerant inhabitants of ephemeral waters, e.g. Lymnaea ovata (Drap.), L. glabra (Mtill.) (Fig. 6), L. diluviana (And.), probably L. occulta (Jack.), Planorbis planorbis (L.), Anisus leucostomus (Mill.), A. vortex (L.), Gyraulus acronicus (F6r.), Valvata pulchella (Stud.), Bithynia leachi troscheli (Paasch), etc., and terrestrial marsh species as Pseudotrichia rubiginosa (A. Sch.), Zonitoides nitidus (Miill.), Succinea putris (L.), locally also Oxyloma cf. elegans (Rs.) and Vertigo pygmaea (Drap.). The swamp loess malacofauna represents autochthonous assemblages of shallow ephemeral swamps which temporarily developed on loess plains with limited drainage. The underlying and overlying loess strata include a common terrestrial loess fauna. There are also swamp equivalents of non-loessic members of the loess series, very rich in snails. Rich occurrences of aquatic and marsh species in loess complexes have repeatedly given rise to speculations of fluvial or limnic origin of the loess, but this assumption is erroneous, since the species in question are characteristic of temporary periodic marshes. ASSEMBLAGES OF LOESS EQUIVALENTS OUT OF THE LOESS BELT PALEOMALACOLOGICAL CORRELATIONS The composition of loess malacofauna is controlled not only by climate but also by environmental conditions within the loess zone which ranges up to certain elevations only, in Central Europe approximately to 300-350 m above sea level. In general, loess areas have a weak to fiat relief and deep loamy substrate. They have, even during periods without loess formation, a fauna which is generally different from that living in higher areas with steeper relief and numerous outcrops of solid bedrock. During the loess formation the non-loessic areas had their specific assemblages consisting in part of several species also common in loess and in part of species which survived the pleniglacial out of the loess zone. In such areas the loess is mostly replaced by fine-sized screes developed often as cryoclastic debris with various proportions of dust-rich matrix. These only include fossil shells in areas rich in CaCO3, particularly
77
in karstlands. A number of loess species occur such as Columella columella (Mart.), VaUonia tenuilabris (A. Br.), and most Pupilla species associated with nonIoessic elements, e.g. Vertigo alpestris (Aid.), Vitrina pellucida (M011.) and other Vitrinids as well as in protected mountain areas Pyramidula rupestris (Drap.), Chondrina clienta (West.) and Ch. tatrica (L~k) and even Helicigona cingulella (Rssm.) (Lo~ek, 1980). Survival of several Carpathian endemites as Cochlodina cerata (Rssm.), Monachoides vicina (Rssm.) or Helicigona faustina (Rssm.) seems to be very probable. In this connection it is worth noting that the youngest loess, deposited in the late Weichselian pleniglacial, has the widest distribution extending far into the periphery of the loess belt where other loess horizons are replaced either by lime-deficient dust loams or cryoclastic debris. These marginal loesses generally include a Columella fauna in depauperized facies and represent, at least within the Last Glacial, the loess optimum (Lo~ek, 1988). MOLLUSCS AS INDICATORS OF ENVIRONMENTAL CONDITIONS DURING LOESS FORMATION
The malacofaunal indication of loess forming environments is based partly (1) on the knowledge of environmental requirements of particular loess species as observed at the present time and partly (2) on the total structure of loess malacocoenoses. (1) The main body of species constituting the assemblages of genuine loess live also at present over most of the temperate zone of Eurasia and partly of North America. However, their present demands are extremely variable, often greatly confronting as shown, e.g. by a comparison of the present demands of Columella columella (Mart.), Trichia hispida (L.), Pupilla triplicata (Stud.) or Succinea oblonga (Drap.), let alone those of local loess species which in particular areas represent an important component of loess assemblages as, e.g. Clausilia parvula (F6r.), Vestia turgida (Rssm.) or Trichia striolata (C. Pfr). (2) Characteristic loess communities thus consist of species which at present commonly belong to highly differing assemblages occurring in very different habitats. There is no analog of loess malacocoenoses within the modern fauna of Europe, apart from some peculiar communities living in extreme habitats which rather resemble the loess fauna. Moreover, the loess assemblages include a number of elements living at present in the Far North or in Central Asia, whose environmental requirements are poorly known so far. These observations and several further lines of evidence indicate that the environments during the loess formation showed specific features which differed markedly from those in other phases of the Quaternary climatic cycle inclusive of the present time. This peculiar environment is reflected also by the shell form of most loess species which differ in various
78
v. Lo~ek
details from modern populations as e.g. the small forms Quaternary and latest Pliocene which include a number of Trichia, several forms of Pupilla muscorum (L.) as of species absent from younger ioesses as e.g. Granaria frumentum (Drap.) agg. or specific forms of Vertigo well as Clausilia dubia (Drap.). In order to understand this apparent chaos we must and Pupilla, whereas several species frequent in the emphasize the features which are common to all loess younger part of the Pleistocene such as e.g. Trichia species as summarized in the section discussing mollus- hispida (L.) agg., have not been recorded (Fink et al., can assemblages of the loess series. Most loess species 1976). The chief difficulty in wider application of loess have a wide distributional range (eurosiberian, palearc- assemblages to Quaternary biostratigraphy is the scartic to holarctic). Species with restricted range including city of older loess records which makes it impossible to several endemites appear only locally or regionally in establish a reliable characteristic of loess assemblages from different time periods. loess assemblages. It will be obvious from the forgoing that the loess Among various assemblages from the loess series, fauna is characterized by a number of common features interglacial faunas are of prime importance being much which provide a solid basis to reconstruct environmen- richer in species and showing more changes with time. tal conditions controlling the loess formation (Lo~ek, Thus, in certain regions they can characterize particular 1965a, 1976). Except for assemblages of loessified slope interglacials both by the presence of various index sediments which resemble the loess faunas, assembla- species and by specific combinations of particular ges from non-loessic members of the loess series are elements: in Central Europe the last Interglacial has a markedly different. In this context it is worth noting fully developed woodland fauna with Drobacia banathat several loess species also occur in these non-ioessic tica (Rssm.), whereas in the penultimate Interglacial assemblages, but in races identical with those living at only Helix pomatia (L.) faunas, poor in species, have present and not with forms prevailing in loess. been recorded (Lo~ek, 1969; Hor~i~ek and Lo~ek, All malacological lines of evidence indicate that the 1988). loess formed in steppes with a sufficiently developed However, the snail faunas from loess and loess series herb cover supporting a comparatively rich snail fauna are of essential importance to a detailed subdivision of requiring an appropriately humid and warm vegeta- the Quaternary climatic cycle, since the sequence of tional period. This was, naturally, very short, since the malacofaunas throughout the loess series enables the climate was in general very severe, with marked aridity, course of this cycle to be established in a completeness so that no mature soils could form and the accumulat- having no analog in other continental deposits (Kukla, ing eolian dust was only converted into a carbonate raw 1977). Malacology provides evidence of the following soil, which process (= Ioessification) considerably phases: Interglacial (usually non-subdivided), Early affected the characteristic loess structure. The loess Glacial (subdivided into cold to warm oscillations), ecosystem documented by molluscan fauna has no Pleniglacial (in many cases subdivided in detail). By modern analog in Europe and it remains to be seen, contrast, the Late Glacial is recorded only exceptionwhether such analogs exist, e.g. in highly continental ally. areas of North and Central Asia, where several index The importance of malacofauna increases in areas species of loess, extinct in Europe, are still living. In where loess series from several cycles occur in superChina the differences between the loess assemblages position or overlie other stratigraphically important and the interglacial and modern fauna seem to be less sediments as river terraces or glacial deposits. In such pronounced (Chen et al., 1982). Concerning the loess cases molluscs provide fundamental biostratigraphic fauna of North America, there are some parallels, e.g. criteria to the subdivision of the Quaternary based on the assemblages with Columella alticola (Ing.), Pupilla regular alternation of cold and warm phases. In a (spp.), etc. in the Late Wisconsin loess (Taylor, 1965), similar manner they can be applied in the case of fully but in general, the situation seems to be different from subdivided loess series as demonstrated by the course that in West Eurasia, as previously summarized by of the Last Glacial whose youngest loess has a Shimek (1930), who found only minor differences Columella fauna with Vertigo parcedentata (A. Br.), between the loess communities and modern malaco- whereas early pleniglacial loesses include Pupilla coenoses of the Mississippi Valley. Therefore, he faunas and loess-like intercalations within the early considers the loesses interglacial, although he does not glacial complex Striata faunas. deny their eolian origin. The most important contribution of malacostratigraphy is the evidence of the maximum number of climatic cycles, i.e. of the full number of cold/warm oscillations BIOSTRATIGRAPHIC SIGNIFICANCE OF THE within various periods of time (Fink and Kukla, 1977). LOESS MALACOFAUNA These are mostly not preserved in other sedimentary The malacocoenoses of proper loess show a rather environments which leads to simplifications of Quateruniform character in space and time. Thus they attain nary climatic stratigraphy (Lo~ek, 1972b). For instonly limited application in terms of detailed biostrati- ance, in the non-glaciated region of Central Europe a graphy of the Quaternary. As matters now stand, we considerably higher number of climatic phases of first can distinguish the assemblages occurring in Late and order can be documented than in adjacent glaciated Middle Pleistocene loesses from those of the Early areas, where many traces of climatic fluctuations have
Molluscs in Loess
been destroyed by the glaciation. The mid-European loess belt is thus the very area where malacofaunas from well-differentiated loess series enabled the socalled full subdivision (Vollgliederung of Soergel, 1939) of the Quaternary to be established and former schematic conceptions based on glacial deposits to be reassessed and completed. REFERENCES Brunnacker, K. and LoI:ek, V. (1969). LOss-Vorkommen in Siidostspanien. Zeitschrift far Geomorphologie, 13(3), 297-316. Chen, D., Lu, Y.C. and An Z.S. (1982). Snail assemblages in loess strata and their environmental implication. In: Proceedings of the third National Quaternary Conference, China, pp. 7-15. Science Press, Beijing. Evans, J.G. (1972). Land Snails in Archaeology. Seminar Press, London, 436 pp. Fink, J. (1965). The Pleistocene in Eastern Austria. The Geological Society of America, Special Paper, 84, 179-199. Fink, J. and Kukla, G.J. (1977). Pleistocene climates in Central Europe: At least 17 interglacials after the Olduvai Event. Quaternary Research, 7, 363-371. Fink, J., Fischer, H., Klaus, W.. Ko~i, A., Kohl, H., Kukla, J., Lo~ek, V., Piffl, L. and Rabeder, G. (1976). Exkursion durch den 6stereichischen Teil des n6rdlichen Alpenvorlandes und den Donauraum zwischen Krems und Wiener Pforte. Mineilungen der
Kommission fiir Quartiirforschung der Osterreichischen Akademie der Wissenschaften, 1, 113 pp. Horfi~:ek, I. and Lo~ek, V. (1988). Palaeozoology and the MidEuropean Quaternary past: scope of the approach and selected results. Rozpravy ~eskoslovenskd akademie vdd, l~ada MPV, 98(4), 102 pp. Kukla, J. (1961). Survey of Czechoslovak Quaternary: Quaternary sedimentation cycle, lnstytut Geologiczny, Prace, 34-Czwartorzed Europy ~rodkowej i Wschodniej, !, 145-154. Kukla, J. (1975). Loess stratigraphy of Central Europe. In: Butzer. K.W. and Isaac, G.L.L. (eds), After the Australopithecines, pp. 99-188. Mouton Publishers, The Hague. Kukla, J. (1977). Pleistocene land-sea correlations. I. Europe. Earth-Science Reviews, 13, 307-374.
79
Lo~ek, V. (1964). Quart~irmoilusken der Tschechoslowakei. Rozpravy l~lst~edniho astavu geologick~ho, 31, 374 pp. Lo~'ek, V. (1965a). Das Problem der L6ssbiidung und die und die L6ssmollusken. Eiszeitalter und Gegenwart, 16, 61-75. Lo~ek, V. (1965b). The relationship between the development of soils and faunas in the warm Quaternary phases. Sbornik geologickpch v#d, A-Antropozoikum, 3, 7-33. Lo~.ek, V. (1969). Uber die malakozooiogische Charakteristik der pleistoz/inen Warmzeiten mit besonderer Beriicksichtigung des letzten lnterglazials. Berichte der Deutschen Gesellschafi far Geologische Wissenschaften, 14(4), 439--469. Lo~'ek, V. (1972a). Le loess et ies formations assimil6es: corr61ation entre l'Europe Centrale et la France par la faune de Mollusques.
In: Proceedings of the Eighth INQUA Congress. Etudes sur le Quaternaire dans le Monde, pp. 597-606. Paris. Lo~'ek, V. (1972b). Zum Problem der Zahl der quart~iren Klimaschwankungen. Quartiir, 22, 1-16. Lo~ek, V. (1976). Klimaabh~ingige Zyklen der Sedimentation und Bodenbildung wiihrend des Ouartiirs im Lichte malakozoologischer Untersuchungen. Rozpravy ~eskoslovensk~ akademie v~d, ~'. MPV, 86(8), 97 pp. Lo~.ek, V. (1980). Quaternary molluscs and stratigraphy of the Ma~arnfi cave. ~eskoslovensky~ Kras, 30, 67-80. Lo~ek, V. (1988). Slope deposition in karst environments of Central Europe. ~eskoslovensky~ Kras, 39, 15-33. Mazenot, G. (1956). Recherches sur les faunes malacologiques du loess r6cent wiirmien et de divers limons terrestres holoc~nes dans ie sud-est de ia France. Bulletin mensuel de la Sod~td Linn~enne de Lyon, 25, 9-24, 41-56, 73--85. Mel'ni~uk, I.V. (1974). Fauna molljuskov antropogenovych po~v Ukrainy. In: Paleopedologija, pp. 128--138. Naukova Dumka, Kiev. Puiss6gur, J.-J. (1983). Pleistocene malacologicai faunas of Normandy. In: Lautridou, J.P. (ed.), The Quaternary of Normandy, pp. 151-160. IGCP 24 Normandy Meeting, September 1982, Rouen. Shimek, B. (1930). Land snails as indicators of ecological conditions. Ecology, 11(4), 673--686. Soergel, W. (1939). Das Diluviale System. Fortschritte der Geologie und Palaeontologie, 12(39), 1--8, 155--292. Taylor, D. (1965). The study of Pleistocene nonmarine mollusks in North America. In: Wright, H.E. and Frey, D.G. (eds), The Quaternary of the United States, pp. 597--611. Princeton University Press, Princeton NJ.