Abstract
The middle Miocene was a key period in Earth’s history as climate changed from one of the warmest phases of the Cenozoic Era, the Miocene Climatic Optimum (MCO), to colder conditions with the establishment of permanent ice sheets on Antarctica. This climate change had a profound impact on terrestrial ecosystems affecting vegetation worldwide. However, the scarceness of detailed pollen data at short-scale resolution for this time period precludes us from a deep understanding of environmental and vegetation changes at millennial-scales. Here, we present palynological data from a new sedimentary sequence from the Gracanica open cast mine (Bugojno Basin, Bosnia and Herzegovina), which shows significant changes in the environment and lake sedimentation, probably related with orbital-scale climate dynamics during the middle Miocene. This study also shows that high-amplitude climate variations characterised the middle Miocene climatic optimum (MCO; ~ 16.8–14.7 Ma). Statistical analysis and sedimentary rates suggest that eccentricity- and precession-dominated orbital-scale variability is recorded in the studied core. Warmest conditions are registered at the base of the studied section that could be correlated with an eccentricity maximum at the end of the MCO. A cooling trend is recorded since then and until the top of the sedimentary sequence, with coldest maxima, tentatively correlated with a minimum in eccentricity and insolation. Smaller-scale cyclical climatic events (i.e. warm-dry vs. cold-humid) observed in the vegetation and corresponding with lake-level variations are observed in this study that seems to be related with precession cyclicity. This study suggests that sedimentation in this lake basin lasted for about 200 kyr and was strongly conditioned by climate at the beginning of the middle Miocene climate transition.
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