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The study of pollen spectra from recent and ancient alluvium
Review of Palaeobotany and Palynology
Elsevier PublishingCompany,Amsterdam--Printedin The Netherlands
T H E S T U D Y OF P O L L E N SPECTRA F R O M R E C E N T A N D A N C I E N T ALLUVIUM
M. P. GRICHUK Geographical Institute, M. 1I. Lomonosov Moscow State University, Moscow (U.S.S.R.)
(Received August29, 1966) SUMMARY Studies by Soviet palynologists on spore-and-pollen spectra of Recent and Holocene alluvium have indicated that: (1) spore-and-pollen spectra of river deposits generally correspond to the zonal type of the vegetation cover at the point of sampling and are comparable to the spore-and-pollen spectra of lake and bog deposits; (2) the run-off direction and facies character, as well as other factors of the deposits studied affect the formation of spore-and-pollen spectra; (3) the distribution of spores and pollen grains redeposited from older deposits is governed by only a small number of factors. A comparison of palynological data from old alluvial deposits with the results of geological investigations shows that an intimate relation exists between the vertical distribution of the sediments and past changes of climate and vegetation. A study of the specific features of alluvium accumulation in mountainous, piedmont and plain areas demands: (1) a close correlation of palynological and geological-geomorphological data; (2) a selection of the most promising areas and sequences; (3) repeated traverses of terraces along transverse profiles; (4) an exact recording in the sequence of all traces of lengthy intervals or substantial washouts of the deposits; and (5) a separate interpretation of the results for each facies.
INTRODUCTION
In the plains and mountains of the eastern part of the U.S.S.R. the Quaternary deposits are represented mainly by ancient alluvium. The use of pollen analysis for their study necessitated special methods of investigation. In this connection it is a favourable opportunity to make possible correlations of spectra from the modern alluvium of large rivers crossing different geographical zones as well as with spectra from the alluvium of tributaries located within only one zone. Rev. Palaeobotan. PalynoL, 4 (1967) 107-112
107
STATUS,
PROSPECTS
AND
PROBLEMS
OF
ALLUVIUM
PALYNOLOGY
Surface-sample diagrams have been compiled for a set of regions. They give an idea how the nature of modern vegetation zones is reflected in pollen-andspore diagrams. Some profiles compiled for the Ob Basin in western Siberia are presented as examples in Fig.1 and 2. Onecan see that, notwithstanding the water transport of organic particles, pollen spectra have a zonal representativeness. The similarity to spectra from the alluvium of longitudinal tributaries also signifies little importance for water transport of pollen. Zonal representativeness is preserved in them both in equal part. The comparison between diagrams from surface samples of alluvial deposits and diagrams from the bogs indicates that the transport of pollen by river is equally small. They both can be used with the same reliability
Fig. I. Distribution of vegetation zones in western Siberia and the localities where samples of Recent deposits were taken. I = tundra; 2 = forest tundra; 3 = northern taiga; 4 = middle taiga; 5 = southern taiga; 6 = forests with small-leaved trees; 7 = forest steppe; 8 = steppes; 9 = mountain forest; 10 = sample sites. 108
Rev. Palaeobotan.
Palynol.,
4 (1967) 107-112
c:~
~pha9num
o
~po~es (~o o~ z spo~es) ~o ~o ~o 8o~o ~0 40 ~ so ioo~,
p .... a 9.0 ~0 60~ a~o~estatLon
0
9040
50°j°
steppL~atLon
mL~eO pe~,centage ~0 ~07°
Fig.2. Composition of pollen spectra from Recent alluvium of the river Ob compared with the quantitative composition of the vegetational cover. to distinguish boundaries between zonal types of spectra close to real zonal boundaries on the map. Therefore, the spectra from ancient alluvial deposits can be assumed to reflect in general the types of vegetational cover, which existed during the time of sedimentation, and to indicate time--space relationships of these types. Another aspect in the analysis and comparison of modern spectra and modern vegetation is no less important. It helps to establish a correlation between stratigraphical terms (for example "pollen maximum", "pollen zones") that have a marked importance in vertical sections, and the concepts of zonal types of spectra of present-day vegetation types. It also helps to detect the corresponding stages in diagrams, i.e., phases in the historical development of one zonal vegetational type. It becomes necessary as palaeobotanical data for long-distance correlation and palaeogeographical reconstructions of Quaternary landscapes are being accumulated. Data about the quantitative composition of a vegetation and the corresponding quantitative composition of pollen spectra are important aids to provide a basis for the determination of the distribution of vegetation types in time and space. Fig.2 and 3 show quantity curves for the main components of present-day Rev. Palaeobotan. PalynoL, 4 (1967) 107-112
109
110
Rev. Palaeobotan.
Pulynol.,
4 (1967)
107-112
vegetations in the basin of the river Ob (forest, steppe and bog) and the corresponding curves for the pollen contributions from these groups to surface samples from alluvial deposits and bogs. The similarity between the two kinds of quantitative data is clear. The considerable quantitative deviations of some species (e.g., larch, aspen, fir) complicate the reconstruction of hardwood forests and the determination of the extent of the participation of aspen in forests. The same deviations need considerable correction for the determination of quantitative participation of fir (Abies) in forests. The most noticeable deviation in the quantitative comparison is found in the spectra from woodless regions where long-range air transport of tree pollen, especially pine pollen, increases significantly the percentage of such pollen in the spectra. When rivers fl0w southward from the forest zone to the steppes the percentage of tree pollen in alluvium spectra is deafly exaggerated compared to the quantitative contribution of these trees to the vegetation of the regions lying immediately south of the forest zone (FEDoROVA, 1952). Special study of pollen spectra from different facies of modern alluvium of plain and mountain rivers (PERMYAKOV, 1964; KOTSERUBAand RYBAKOVA,1965; SOKOLOVA,1965; YEVTEYEVA, 1965) indicates that a spectrum from coarse-grained alluvium differs from that from flood-plain alluvium in the same locality by a slightly larger content of coniferous pollen. Thus it is essential to make corrections when interpreting ancient spectra. One sample taken from several tens in modern sandy alluvium contained no less than 60 ~ of pollen grains of species typical of the Oligocene flora of Siberia. Other samples seldom contained the pollen of exotic species, though the rivers of western Siberia scour Oligocene deposits in many localities. One cannot be sure that redeposited pollen has not influenced spectra of Quaternary age. The study of ancient alluvium showed that river erosion seems to have ~taken place with a certain periodicity. During single time intervals, for example the Middle Quaternary, rivers had left thick deposits, showing diagonal bedding,, which have an abundant content of pollen redeposited from Oligocene sediments. Interpreting palaeobotanical data one can state that during the Quaternary Period the same main types of vegetational cover existed, as at present but with different geographical distributions. The following ancient zonal types were less investigated: (1) those peculiar to cold times; (2) coniferous forests with an admixture of broad-leaved tree species; (3) coniferous forests with fir (Abies) as a dominant now occupying a relic and intrazonal position or occurring in a mountain belt where vertical zonality is well expressed (mountain taiga). The ancient pollen spectra of such zonal vegetational types do not have modern analogues and reconstructions are less reliable. The practical application of this method for the investigation of ancient alluvium necessitated the summary of the data on a series of sections from one area and representing a full sequence of historical stages. The presence of inter-
Rev. Palaeobotan. Palynol., 4 (1967) 107-112
111
ruptions is connected with the squamate nature of sequences of fluvial facies of alluvium, which is caused by the fact that flood-plain and lacustrine-alluvial deposits are mutually alternating, and thus constitute only to a lesser degree interruptions in time. The sections of alluvium from mountain regions which often show only episodic sedimentation do not represent comprehensive time scales. In these regions only the study of a large number of sections helps to reconstruct the vegetational history and to make comparisons of this with that in plain regions. The investigation of present-day and ancient alluvial deposits from mountains and plains indicated that pollen-analytical data reflect the peculiarities of the process of alluvium formation and also of the formation of the valleys themselves. The relationships between river regime and climate are clearly exposed. One can see that the predominant part of coarse-grained sediments accumulated during periods of drier climate and increasing warmth, but their thickness varied to a considerable degree in mountain regions due to the tectonic regime. The accumulation of fine-grained flood-plain and lacustrine-alluvial deposits prevails mainly during the periods of intense humidification and increasing cold and is connected with the period of the marked flood-plain-high river regime that can also be apparent in mountains.
CONCLUSION The general conclusion is that application of the pollen-analytical method to the detailed analysis of alluvial deposits, combined with further improvements of pollen analysis will help not ~only to solve the problems of correlation and stratigraphy of ancient alluvial deposits but also to make sound reconstructions of whole landscapes. In addition the method is useful for studying the origin and history of river valleys.
REFERENCES
FEDOROVA, R. V., 1952. Pollen and spore distribution by current waters. Trans. Inst. Geogr., Acad. Sci. U.S.S.R., 52:46-73 (in Russian).
KOTSERUBA,L. A. and RYBAKOVA,N. O., 1965. Palynological characteristics of various facies
of the alluvial deposits in the lower Ob floodplain. Herald Moscow Univ., Ser. IV, Geol., 3:75-80 (in Russian). PERMYAKOV,A. I., 1964. Features of the formation of spore-and-pollen spectra of Recent continental sedimentary deposits (with examples from the Yenisei Basin). Trans. Inst. Geol. Geophys., Siberian Branch, Acad. Sci. U.S.S.R., 25:82-90 (in Russian). SOKOLOVA,N. S., 1965. The Recent spore and pollen spectra of the Ob River alluvium in the Berezovo Village area. Herald Moscow Univ., Set. V, Geogr., 6:65-67 (in Russian). YEVTEYEVA, I. S., 1965. Data of spore and pollen analysis. In: S. S. VOSKRESENSKI(Editor), Geomorphological Studies. Moscow Univ., Moscow, pp.171-187 (in Russian). 112
Rev. Palaeobotan. Palynol., 4. (1967) 107-112
Elsevier PublishingCompany,Amsterdam--Printedin The Netherlands
T H E S T U D Y OF P O L L E N SPECTRA F R O M R E C E N T A N D A N C I E N T ALLUVIUM
M. P. GRICHUK Geographical Institute, M. 1I. Lomonosov Moscow State University, Moscow (U.S.S.R.)
(Received August29, 1966) SUMMARY Studies by Soviet palynologists on spore-and-pollen spectra of Recent and Holocene alluvium have indicated that: (1) spore-and-pollen spectra of river deposits generally correspond to the zonal type of the vegetation cover at the point of sampling and are comparable to the spore-and-pollen spectra of lake and bog deposits; (2) the run-off direction and facies character, as well as other factors of the deposits studied affect the formation of spore-and-pollen spectra; (3) the distribution of spores and pollen grains redeposited from older deposits is governed by only a small number of factors. A comparison of palynological data from old alluvial deposits with the results of geological investigations shows that an intimate relation exists between the vertical distribution of the sediments and past changes of climate and vegetation. A study of the specific features of alluvium accumulation in mountainous, piedmont and plain areas demands: (1) a close correlation of palynological and geological-geomorphological data; (2) a selection of the most promising areas and sequences; (3) repeated traverses of terraces along transverse profiles; (4) an exact recording in the sequence of all traces of lengthy intervals or substantial washouts of the deposits; and (5) a separate interpretation of the results for each facies.
INTRODUCTION
In the plains and mountains of the eastern part of the U.S.S.R. the Quaternary deposits are represented mainly by ancient alluvium. The use of pollen analysis for their study necessitated special methods of investigation. In this connection it is a favourable opportunity to make possible correlations of spectra from the modern alluvium of large rivers crossing different geographical zones as well as with spectra from the alluvium of tributaries located within only one zone. Rev. Palaeobotan. PalynoL, 4 (1967) 107-112
107
STATUS,
PROSPECTS
AND
PROBLEMS
OF
ALLUVIUM
PALYNOLOGY
Surface-sample diagrams have been compiled for a set of regions. They give an idea how the nature of modern vegetation zones is reflected in pollen-andspore diagrams. Some profiles compiled for the Ob Basin in western Siberia are presented as examples in Fig.1 and 2. Onecan see that, notwithstanding the water transport of organic particles, pollen spectra have a zonal representativeness. The similarity to spectra from the alluvium of longitudinal tributaries also signifies little importance for water transport of pollen. Zonal representativeness is preserved in them both in equal part. The comparison between diagrams from surface samples of alluvial deposits and diagrams from the bogs indicates that the transport of pollen by river is equally small. They both can be used with the same reliability
Fig. I. Distribution of vegetation zones in western Siberia and the localities where samples of Recent deposits were taken. I = tundra; 2 = forest tundra; 3 = northern taiga; 4 = middle taiga; 5 = southern taiga; 6 = forests with small-leaved trees; 7 = forest steppe; 8 = steppes; 9 = mountain forest; 10 = sample sites. 108
Rev. Palaeobotan.
Palynol.,
4 (1967) 107-112
c:~
~pha9num
o
~po~es (~o o~ z spo~es) ~o ~o ~o 8o~o ~0 40 ~ so ioo~,
p .... a 9.0 ~0 60~ a~o~estatLon
0
9040
50°j°
steppL~atLon
mL~eO pe~,centage ~0 ~07°
Fig.2. Composition of pollen spectra from Recent alluvium of the river Ob compared with the quantitative composition of the vegetational cover. to distinguish boundaries between zonal types of spectra close to real zonal boundaries on the map. Therefore, the spectra from ancient alluvial deposits can be assumed to reflect in general the types of vegetational cover, which existed during the time of sedimentation, and to indicate time--space relationships of these types. Another aspect in the analysis and comparison of modern spectra and modern vegetation is no less important. It helps to establish a correlation between stratigraphical terms (for example "pollen maximum", "pollen zones") that have a marked importance in vertical sections, and the concepts of zonal types of spectra of present-day vegetation types. It also helps to detect the corresponding stages in diagrams, i.e., phases in the historical development of one zonal vegetational type. It becomes necessary as palaeobotanical data for long-distance correlation and palaeogeographical reconstructions of Quaternary landscapes are being accumulated. Data about the quantitative composition of a vegetation and the corresponding quantitative composition of pollen spectra are important aids to provide a basis for the determination of the distribution of vegetation types in time and space. Fig.2 and 3 show quantity curves for the main components of present-day Rev. Palaeobotan. PalynoL, 4 (1967) 107-112
109
110
Rev. Palaeobotan.
Pulynol.,
4 (1967)
107-112
vegetations in the basin of the river Ob (forest, steppe and bog) and the corresponding curves for the pollen contributions from these groups to surface samples from alluvial deposits and bogs. The similarity between the two kinds of quantitative data is clear. The considerable quantitative deviations of some species (e.g., larch, aspen, fir) complicate the reconstruction of hardwood forests and the determination of the extent of the participation of aspen in forests. The same deviations need considerable correction for the determination of quantitative participation of fir (Abies) in forests. The most noticeable deviation in the quantitative comparison is found in the spectra from woodless regions where long-range air transport of tree pollen, especially pine pollen, increases significantly the percentage of such pollen in the spectra. When rivers fl0w southward from the forest zone to the steppes the percentage of tree pollen in alluvium spectra is deafly exaggerated compared to the quantitative contribution of these trees to the vegetation of the regions lying immediately south of the forest zone (FEDoROVA, 1952). Special study of pollen spectra from different facies of modern alluvium of plain and mountain rivers (PERMYAKOV, 1964; KOTSERUBAand RYBAKOVA,1965; SOKOLOVA,1965; YEVTEYEVA, 1965) indicates that a spectrum from coarse-grained alluvium differs from that from flood-plain alluvium in the same locality by a slightly larger content of coniferous pollen. Thus it is essential to make corrections when interpreting ancient spectra. One sample taken from several tens in modern sandy alluvium contained no less than 60 ~ of pollen grains of species typical of the Oligocene flora of Siberia. Other samples seldom contained the pollen of exotic species, though the rivers of western Siberia scour Oligocene deposits in many localities. One cannot be sure that redeposited pollen has not influenced spectra of Quaternary age. The study of ancient alluvium showed that river erosion seems to have ~taken place with a certain periodicity. During single time intervals, for example the Middle Quaternary, rivers had left thick deposits, showing diagonal bedding,, which have an abundant content of pollen redeposited from Oligocene sediments. Interpreting palaeobotanical data one can state that during the Quaternary Period the same main types of vegetational cover existed, as at present but with different geographical distributions. The following ancient zonal types were less investigated: (1) those peculiar to cold times; (2) coniferous forests with an admixture of broad-leaved tree species; (3) coniferous forests with fir (Abies) as a dominant now occupying a relic and intrazonal position or occurring in a mountain belt where vertical zonality is well expressed (mountain taiga). The ancient pollen spectra of such zonal vegetational types do not have modern analogues and reconstructions are less reliable. The practical application of this method for the investigation of ancient alluvium necessitated the summary of the data on a series of sections from one area and representing a full sequence of historical stages. The presence of inter-
Rev. Palaeobotan. Palynol., 4 (1967) 107-112
111
ruptions is connected with the squamate nature of sequences of fluvial facies of alluvium, which is caused by the fact that flood-plain and lacustrine-alluvial deposits are mutually alternating, and thus constitute only to a lesser degree interruptions in time. The sections of alluvium from mountain regions which often show only episodic sedimentation do not represent comprehensive time scales. In these regions only the study of a large number of sections helps to reconstruct the vegetational history and to make comparisons of this with that in plain regions. The investigation of present-day and ancient alluvial deposits from mountains and plains indicated that pollen-analytical data reflect the peculiarities of the process of alluvium formation and also of the formation of the valleys themselves. The relationships between river regime and climate are clearly exposed. One can see that the predominant part of coarse-grained sediments accumulated during periods of drier climate and increasing warmth, but their thickness varied to a considerable degree in mountain regions due to the tectonic regime. The accumulation of fine-grained flood-plain and lacustrine-alluvial deposits prevails mainly during the periods of intense humidification and increasing cold and is connected with the period of the marked flood-plain-high river regime that can also be apparent in mountains.
CONCLUSION The general conclusion is that application of the pollen-analytical method to the detailed analysis of alluvial deposits, combined with further improvements of pollen analysis will help not ~only to solve the problems of correlation and stratigraphy of ancient alluvial deposits but also to make sound reconstructions of whole landscapes. In addition the method is useful for studying the origin and history of river valleys.
REFERENCES
FEDOROVA, R. V., 1952. Pollen and spore distribution by current waters. Trans. Inst. Geogr., Acad. Sci. U.S.S.R., 52:46-73 (in Russian).
KOTSERUBA,L. A. and RYBAKOVA,N. O., 1965. Palynological characteristics of various facies
of the alluvial deposits in the lower Ob floodplain. Herald Moscow Univ., Ser. IV, Geol., 3:75-80 (in Russian). PERMYAKOV,A. I., 1964. Features of the formation of spore-and-pollen spectra of Recent continental sedimentary deposits (with examples from the Yenisei Basin). Trans. Inst. Geol. Geophys., Siberian Branch, Acad. Sci. U.S.S.R., 25:82-90 (in Russian). SOKOLOVA,N. S., 1965. The Recent spore and pollen spectra of the Ob River alluvium in the Berezovo Village area. Herald Moscow Univ., Set. V, Geogr., 6:65-67 (in Russian). YEVTEYEVA, I. S., 1965. Data of spore and pollen analysis. In: S. S. VOSKRESENSKI(Editor), Geomorphological Studies. Moscow Univ., Moscow, pp.171-187 (in Russian). 112
Rev. Palaeobotan. Palynol., 4. (1967) 107-112