We dedicate this paper to the life and work of Gloria Galeano (1958( -2016, botanist and outstanding palm researcher. ABSTRACTAim We analysed in detail a past marine incursion event in north-western Amazonia and measured its effect on the forest composition. We also determined the sediment provenance in the fluvio-estuarine system and reconstructed the overall floral composition of the Amazon lowland forest during the Miocene climatic optimum.Location A 60-m-thick sedimentary succession situated along the Caquet a River in Colombian Amazonia (0.77°S; 71.97°W).Methods Palynological, geochemical and statistical analyses were performed on samples from organic-rich sediments. ResultsThe lower section was formed by fluvial floodplain deposits of Andean provenance rich in pollen of Malvacipolloides maristellae (aff. Abutilon) and Rhoipites guianensis (aff. Vasivaea). The middle section was formed by fluvial channel and estuarine swamp deposits of central Venezuelan provenance dominated by pollen of Mauritiidites franciscoi (Mauritia). Towards the top, the swamp deposits represent an estuarine floodplain with aquatic biomarkers, marine palynomorphs and mangrove pollen. The succession ended with fluvial floodplain deposits of central to southern Venezuelan origin with R. guianensis as dominant pollen type. Palynological diversity was high throughout the section with Andean-and Venezuelan-derived sediments each with their characteristic taxa. Tropical rain forest taxa, such as Arecaceae, Fabaceae, Sapotaceae, Malpighiaceae and Bombacoideae, were common in these sediments, although taxa adapted to drier conditions also occurred. We provide a 'figshare' link to an image library of selected taxa, as well as the raw counts and processed data. Main conclusionsThe fluvio-estuarine system was of mixed origin with sediments and palynomorphs from the emerging Andes, but also from an area situated in the modern Orinoco Basin. Marine influence was linked to the Venezuelan source area and thus of indisputable Caribbean origin. Overall, a mixed forest with drought-resistant components existed in the drainage system during the Miocene climatic optimum. Our data provide a novel insight into the composition of the tropical lowland forest and the environments in northwestern Amazonia prior to the main uplift of the central and northern Andes.

It remains poorly understood how the composition of leaf wax n‐alkanes reflects the local environment. This knowledge gap inhibits the interpretation of plant responses to the environment at the community level and, by extension, inhibits the applicability of n‐alkane patterns as a proxy for past environments. Here, we studied the n‐alkane patterns of five Miconia species and one Guarea species, in the Ecuadorian Andes (653–3,507 m a.s.l.). We tested for species‐specific responses in the average chain length (ACL), the C31/(C31 + C29) ratio (ratio), and individual odd n‐alkane chain lengths across an altitudinally driven environmental gradient (mean annual temperature, mean annual relative air humidity, and mean annual precipitation). We found significant correlations between the environmental gradients and species‐specific ACL and ratio, but with varying magnitude and direction. We found that the n‐alkane patterns are species‐specific at the individual chain length level, which could explain the high variance in metrics like ACL and ratio. Although we find species‐specific sensitivity and responses in leaf n‐alkanes, we also find a general decrease in “shorter” (C31) chain lengths with the environmental gradients, most strongly with temperature, suggesting n‐alkanes are useful for reconstructing past environments.

Abstract. The relative abundance of n-alkanes of different chain lengths obtained from ancient soils and sediments have been used to reconstruct past environmental changes. However, interpretation of ancient n-alkane patterns relies primarily on modern plant wax n-alkane patterns measured from leaves. Little is still known about how n-alkane patterns, and environmental information therein, might be altered during the process of transfer from leaves into soil. We studied the n-alkane patterns extracted from leaves, necromass, and soil samples from an altitudinal gradient in the tropical Andes to clarify if the n-alkane pattern, and the local environmental information reflected, is altered as the plant source material degrades. We considered the (dis)similarity between n-alkane patterns in soil, necromass, and leaves and specifically explored whether a temperature and/or precipitation signal is reflected in their n-alkane patterns. The n-alkane patterns showed degradation in soil as reflected by a reduced carbon preference index (CPI). The lower CPI in soils as compared to leaves and necromass was significantly correlated with temperature and precipitation along the transect, most likely because of increased microbial activity under warmer and wetter conditions. Despite degradation, all sample types showed a systematic shift in longer vs. shorter n-alkanes when moving up the transect. Further examination revealed the systematic shift correlated with transect temperature and precipitation. Since transect vegetation is constant along the transect, this would appear to indicate the recording of a climatic signal within the n-alkane patterns that is preserved in the soil, albeit that the correlation was weaker there. The study results warrant further research into a possible underlying causal relationship that may lead to the development of n-alkane patterns as a novel palaeoecological proxy.

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<p><strong>Abstract.</strong> Plant wax <i>n</i>-alkane biomarkers obtained from ancient soils and sediments have been used to reconstruct past environmental changes. However, the interpretation of these ancient <i>n</i>-alkane patterns relies primarily on our understanding of modern plant wax <i>n</i>-alkane patterns measured from leaves. Very little is known about how <i>n</i>-alkane patterns might be altered during the process of transfer from leaves into soil. Therefore our interpretations of the ancient <i>n</i>-alkane biomarker signal could be confounded by an unobserved bias caused by degradation processes. Here we present the <i>n</i>-alkane patterns extracted from leaves, necromass and soil samples to clarify whether the <i>n</i>-alkane pattern, the <i>n</i>-alkane signal, and the local environmental information reflected in the <i>n</i>-alkane signal degrade, as the plant source material degrades in the tropical Andes. We find that the <i>n</i>-alkane patterns do degrade, but that the <i>n</i>-alkane patterns and signal remain similar across sample types. We find that the <i>n</i>-alkane patterns primarily reflect changes in longer vs. shorter <i>n</i>-alkanes, captured by the average chain length (ACL) and the C<sub>31</sub> / (C<sub>29</sub> + C<sub>31</sub>) ratio (ratio), regardless of sample type. Additionally, soil sample <i>n</i>-alkanes secondarily reflect changes in carbon preference index (CPI) whereas leaf and necromass <i>n</i>-alkanes do not. We find that in all sample types the primary observed <i>n</i>-alkane signals correlate significantly with the environment, temperature in particular, but that soil <i>n</i>-alkane correlations are muted compared to leaf <i>n</i>-alkanes. The secondary <i>n</i>-alkane signal (CPI) in soils also correlates significantly with the environmental signal, temperature in particular. Our results are an important step towards better understanding the taphonomy of the <i>n</i>-alkane signal in the tropics, and suggest that environmental information is preserved in the <i>n</i>-alkane signal, despite the observed degradation.</p>

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