Short-term fluctuations in vegetation and phytoplankton during the Middle Eocene greenhouse climate: a 640-kyr record from the Messel oil shale (Germany)

Abstract

The Palaeogene was the most recent greenhouse period on Earth. Especially for the Late Palaeocene and Early Eocene, several superimposed short-term hyperthermal events have been described, including extremes such as the Palaeocene-Eocene Thermal Maximum. Major faunal and floral turnovers in the marine and terrestrial realms were recorded in association with these events. High-resolution palynological analysis of the early Middle Eocene maar lake sediments at Messel, near Darmstadt, Germany, provides an insight into the dynamics of a climax vegetation during the Middle Eocene greenhouse climate in a time span without significant climatic excursions. Numerical techniques like detrended correspondence analysis and wavelet analysis have been applied to recognize cyclic fluctuations and long-term trends in the vegetation through a time interval of approximately 640 kyr. Based on the numerical zoning of the pollen diagram, three phases in the development of the vegetation may be distinguished. Throughout these phases, the climax vegetation did not change substantially in qualitative composition, but a trend towards noticeably less humid conditions probably in combination with a drop of the water level in the lake may be recognized. A shift in algal population from the freshwater dinoflagellate cyst Messelodinium thielepfeifferae to a dominance of Botryococcus in the uppermost part of the core is interpreted as a response to changes in acidity and nutrient availability within the lake. Time series analyses of pollen assemblages show that variations in the Milankovitch range of eccentricity, obliquity and precession can be distinguished. In addition, fluctuations in the sub-Milankovitch range are indicated. This demonstrates that floral changes during steady depositional conditions in the Middle Eocene of Messel were controlled by orbital forcing.

Virtopsy of the controlled decomposition of a dormouse Eliomys quercinus as a tool to analyse the taphonomy of Heterohyus nanus from Messel (Eocene, Germany)

“…The finding horizon of Heterohyus within the Middle Messel formation belongs to the "Late phase" (Lenz et al 2011) of sedimentation of this period. The climate became drier near the end of this phase, and raising evaporation might have been connected with lower water levels (Lenz et al 2011).…”

“…A monsoonal and high Ca climate with a mean annual temperature of about 22°C has been suggested for Messel by Grein et al (2011), Lenz et al (2011) and Mai (1995). The finding horizon of Heterohyus within the Middle Messel formation belongs to the "Late phase" (Lenz et al 2011) of sedimentation of this period.…”

“…They are alternating with horizons where fine layers of siderite precipitated and horizons with phosphate minerals occurred. They were deposited during a long-term stable meromictic phase of the lake (Goth 1990), which lasted about 640 ky (Lenz et al 2011). …”

“…The light layers were mainly built up by algae (Tetraedron minimum), the dark autumn/winter layers primary consists of terrigenous pelitic material, mainly smectites (Goth 1990;Lenz et al 2011;Weber 1991). The rock accumulation rate is estimated by Goth (1990) with 0.15 mm/year and 0.14 mm/year by Schulz et al (2002).…”

Quantitative analysis of biogeochemically controlled density stratification in an iron-meromictic lake

“…Sediments in some meromictic lakes have been undisturbed for thousands of years and hence the varved sediments represent excellent climate archives and fossil deposits (e.g. Walker Kozma and Kupetz, 2008). and Likens, 1975;Lenz et al, 2011). Meromictic lakes have been identified in many mining regions on earth where stratification limits the vertical transport of undesirable substances (e.g.…”