Palaeoenvironmental Context of Coprolites and Plant Microfossils from Unit II. Azokh 1

Abstract Poor pollen preservation in cave deposits is due to oxidation and increasing scarcity of pollen with distance from the cave entrance. After an attempt to obtain pollen grains from the sediments in Azokh 1 (Lesser Caucasus) failed, two coprolites from Unit II were investigated for their microfossil contents. They contained few diatoms (including the rare Pliocaenicus), even less pollen but numerous phytoliths that were compared with those in selected levels of cave deposits and modern soil from outside. Grass silica short cell phytoliths give evidence of vegetation typical of a temperate climate for Unit II, which included C3 grasses. Not only the coprolites from Azokh are useful but the whole sequence of deposits has good potential for palaeoclimatic reconstruction based on for phytolith studies. The diatoms observed indicate feeding from a relatively moist terrestrial environment and availability of lake and/or running water.

Резюме Для изучения экологической ситуации в процессе возникновения отложений в пещере Азох 1 (Малый Кавказ) химическому анализу были подвергнуты два образца копролитов. Исследование было предпринято после попытки получения пыльцы из мелкозернистого

L. Scott (&)

Department of Plant Sciences, University of the Free State, PO Box 339,Bloemfontein 9300, South Africa

e-mail: scottl@ufs.ac.za

седимента, которая окончилась неудачей по причине продолжительной оксидации и разложения в условиях постоянного изменения влажности в пещере, а также возрастающей нехватки переносимой по воздуху пыльцы от входа в глубь пещеры. В качестве альтернативного источника пыльцы и других микроископаемых элементов были исследованы два копролита, обнаруженных в подразделении II. Они содержали редко встречающиеся виды диатомеи, включая Pliocaenicus sp., немного пыльцы и большое количество фитолитов. Фитолиты в копролитах были сопоставлены с образцами, отобранными из нескольких слоев отложений внутри и из современной почвы за пределами пещеры. Различные типы фитолитов рода Poaceae (силицированные короткие клетки травы) в пределах подразделения II указывают на типичную для умеренного климата растительность, которая включает C3 травы и несколько отличается от современной смешанной флоры. Плотность лесного покрова не может быть определена без дальнейшего изучения нетравяных фитолитов в копролитах и седименте. Последние указывают на то, что мелкозернистая седиментная последовательность в Азох 1 имеет одинаково хороший потенциал для анализа фитолитов в копролитах и, следовательно, для палеоэкологической реконструкции всей последовательности отложений, в том числе и для более обширного региона. Обнаруженные диатомовые водоросли свидетельствуют об относительно влажной почве и наличии озерной или речной воды в качестве источника питания.

© Springer Science+Business Media Dordrecht 2016

Yolanda Fernández-Jalvo et al. (eds.), Azokh Cave and the Transcaucasian Corridor, Vertebrate Paleobiology and Paleoanthropology, DOI 10.1007/978-3-319-24924-7_13

Phytoliths Diatoms MIS 5

287

Introduction

The primary way of reconstructing past vegetation and environments is usually by means of pollen analysis of lakes and swamps but this method is not regularly used in caves. Fine-grained cave deposits often provide little or no information about past climates because concentrations of aerially introduced material like pollen, which is introduced as dust in the cave by air currents or other means, is usually not high. The influx of transported microscopic particles declines progressively deeper into a cave and beyond 20 to 30 m it is very low (Coles and Gilberstone 1994; Navarro et al. 2001; Hunt and Rushworth 2005). Conditions for preservation are often not ideal on cave floors, and considering these constraints both for pollen and phytoliths in fine-grained cave sediments, richer alternative sources may be needed.

Our first attempt at Azokh 1 in the Lesser Caucasus to extract pollen from sediments of Units I and V, at depths of 77 cm and lower in the Azokh cave system, was unsuccessful. After exposure for more than 20 years sediments near the cave opening became dry, crumbly, cracked, bioturbated and oxidized (Fernández-Jalvo et al. 2010) and therefore not suitable for pollen analysis. Other plant microfossil research may still be feasible, and initial investigations indicated that sediments potentially contain phytoliths and starch inclusions (Fernández-Jalvo et al. 2010). A further possible reason for the lack of pollen may be the 40 m distance of the present excavation area to cave entrance, which is removed from aerial pollen sources. Although air currents are relatively active today (Y. Fernandez-Jalvo, personal communication 2006), we do not have evidence that this was the case in the past. Preservation qualities may not be ideal and pollen could also have been destroyed by a combination of highly oxidizing conditions and microbial action in acidic bat guano rich in phosphates, which is present throughout the cave sequence, and by wet-dry cycles in the cave such as recognized in Unit II (Marin-Monfort et al. 2016). Fresh bat guano is rich in pollen, but in fossil layers it could have been decomposed over time (Carrion et al. 2006). Extensive carbonate cementation occurs in some parts of the Azokh 1 excavation, mainly in levels closer to the limestone cave walls, as result of seasonal and drip-water flows, and this could also have played a role in destroying pollen grains. It has been reported that damp areas near cave walls have poorer pollen preservation (Navarro et al. 2001; Carrion et al. 2006).

In view of the paucity of pollen in the Azokh deposits and in order to obtain additional dietary or environmental data, we turned our attention to the coprolites to search for pollen and phytoliths in them for comparison with phytoliths in the surrounding deposits. Coprolittes are biogenic inclusions

that trap plants from outside the cave (Thompson et al. 1980; O’Rourke and Mead 1985; Scott 1987), and they can be useful alternatives as sources for micro-plant remains because their inclusions are sealed off and protected more effectively from adverse sedimentary conditions such as dampness and oxidation. In the long run these conditions, if severe enough can destroy pollen anywhere, also in coprolites, but the chances are that they will survive longer inside a coprolite than in unconsolidated deposits (Navarro et al. 2001; Scott et al. 2003). Coprolites in caves can therefore shed light on prehistoric conditions not only because their shape, size and structure represent prehistoric fauna, but also because their microscopic contents provide clues about past vegetation and climate. Apart from research on hyrax dung deposits in Africa and the Middle East, previous studies of coprolites in Africa and Europe were often based on hyena coprolites (Scott 1987; Carrión et al. 2007) because these coprolites are more frequently found in caves than those of other animals, for example badgers, which are less frequent (Carrion et al. 2005).

Plant microfossils in a coprolite can be derived from an animal’s diet, it’s drinking water, ingested dust, or that which became attached to the dung via air currents soon after defecation. Dung usually traps a representative assemblage of pollen and organic and siliceous dust derived from wide surroundings where the animals were roaming. Dung pellets fossilize in caves to become solid coprolites that preserve their micro-contents under more stable conditions than those in the surrounding fine, looser deposits, which experience local variations of humidity and temperature. As long as coprolites do not disintegrate, their slightly acidic conditions are not necessarily harmful to microscopic inclusions. Coprolites therefore prevent decomposition and destruction of organics, but this can be temporary because the microscopic contents can be lost in the long run if local conditions deteriorate (Scott et al. 2003).

Because significant differences occur in the morphology of microscopic phytolith types produced by the main Poaceae subfamilies (or grass silica short-cell types (GSSC)) (Twiss et al. 1969; Brown 1984; Mulholland 1989; Fredlund and Tieszen 1994), these microfossils in coprolites promised to be an informative tool. Despite the prevalence of ‘multiplicity’ and ‘redundancy’ in GSSC assemblages (Rovner 1971, 1983), i.e. the occurrence of a variety of types in one grass taxon as well as the occurrence of the same type in different taxa, fluctuations in the frequencies of certain types can be still be used to distinguish between the grass subfamilies (Fredlund and Tieszen 1994; Rossouw 2009).

Coprolite fragments of unidentified origin have been found at Unit II and Vu of Azokh 1. Unit II also yielded two complete coprolites (no’s 5153 and 5246) of which 5246, and some obviously derived stone artifacts together with fossils typical of Unit II, were apparently displaced in Unit I