Abdul Rahman Ashraf

Terrestrial Climate Evolution in Northwest Germany Over the Last 25 Million Years

Abstract The first detailed reconstruction of the continental paleoclimate evolution of the Northwest German Tertiary (Late Oligocene to Pliocene) is presented. The paleoclimate data are derived from the paleobotanical record using the coexistence approach, a method recently introduced that employs climatic requirements of the Nearest Living Relatives of a fossil flora. Twenty six megafloras (fruits and seeds, leaves, woods) from the Tertiary succession of the Lower Rhine Basin and neighboring areas are analyzed with respect to ten meteorological parameters. Additionally, two sample sets from Late Miocene to Early Pliocene sediments comprising 396 palynofloras are analyzed by the same method providing a higher temporal resolution. The temperature curves show a comparatively cooler phase in the Late Oligocene, a warm interval the Middle Miocene, and a cooling starting at 14 Ma. The cooling trend persisted until Late Pliocene with a few higher frequency temperature variations observed. From the beginning of Late Miocene to the present, the seasonality increases and climate appears to have been less stable. As indicated by the precipitation data, a Cfa climate with wet summers persisted in NW Germany from Late Oligocene to Late Pliocene. The results obtained are well in accordance with regional and global isotope curves derived from the marine record, and allow for a refined correlation of the Tertiary succession in the Lower Rhine Basin with the international standard. It is shown that the reconstructed data are largely consistent with the continental climate record for the Northern Hemisphere, as reported by various authors. Discrepancies with previous reconstructions are discussed in detail.

Palynological evidence for Miocene climate change in the Forecarpathian Basin (Central Paratethys, NW Bulgaria)

Abstract We reconstruct quantitatively the Middle to Upper Miocene climate evolution in the southern Forecarpathian Basin (Central Paratethys area, Northwest Bulgaria) by applying the coexistence approach to 101 well-dated palynofloras isolated from three cores. The climatic evolution is compared with changes in vegetation and palaeogeography. The Middle Miocene was a period of a subtropical/warm–temperate humid climate with mean annual temperature (MAT) between 16 and 18°C and mean annual precipitation (MAP) between 1100 and 1300 mm. Thereby, during the entire Middle Miocene a trend of slightly decreasing temperatures is observed and only small climate fluctuations occur which are presumably related to palaeogeographic reorganisations. The vegetation shows a corresponding trend with a decrease in abundance of palaeotropic and thermophilous elements. The Upper Miocene is characterised by more diverse climatic conditions, probably depending on palaeogeographic and global climatic transformations. The beginning of this period is marked by a slight cooling and a significant drying of the climate, with MAT 13.3–17°C and MAP 652–759 mm. After that, fluctuations of all palaeoclimate parameters occur displaying cycles of humid/dryer and warmer/cooler conditions, which are again well reflected in the vegetation. Our study provides a first quantitative model of the Middle–Upper Miocene palaeoclimate evolution in Southeastern Europe and is characterised by a relatively high precision and resolution with respect to the climate data and stratigraphy.

The Miocene peat-forming vegetation of northwestern Germany: an analysis of wood remains and comparison with previous palynological interpretations

New methods of sampling, preparing and identifying fossil wood fragments preserved in browncoal are presented and used to aid in reconstructions of the vegetation from the Miocene Lower Rhine Basin (Germany). The technique involves laboratory charring wood specimens followed by routine identification with reflected light microscopy. Problems concerning the taxonomic identification of the fossil wood are discussed. A list of taxa is presented for the Garzweiler Seam and the implications for reconstructing the Miocene palaeoenvironment are discussed with reference to ecological comparisons of extant taxa: the nearest living relative approach. Results indicate a dominance of conifer wood types, mostly representing members of the Taxodiaceae and Cupressaceae; extensive sampling is required of both small (macroscopic) and large fragments to obtain results comparable with palynological assemblages. Up to now, twenty-one taxa of gymnosperms and angiosperms have been recognized from the Garzweiler seam. Data obtained are compared with those from pollen analysis and corroborate the previously identified trend consisting of increasing concentrations of Taxodium towards the upper section of the seam.

Facies and paleogeography of the Tertiary of the Lower Rhine Basin - sedimentary versus climatic control

Based on recent studies, the impact of global sea-level and climate change on the paleogeographic and sedimentary evolution of the Tertiary of the Lower Rhine Basin is analysed. It is shown that major changes in global climate and sea-level, such as the high-stand during the Middle Miocene climate optimum, the extreme low-stands near the base of the Tortonian and within the Messinian, are clearly reflected in the sedimentary succession. Continental climate curves, as reconstructed from Tertiary macrofloras of the Lower Rhine Basin, can be correlated with the marine, long-term isotope record. As shown by the analyses, a warm and humid climate with mean annual temperatures above 13 ° C and mean annual precipitation not below 1000 mm, persisted throughout the Late Miocene to Early Pliocene. Continental, high-resolution, climate data show that Late Miocene alternations of lignites and elastics are rather caused by tectonic and sedimentary processes (such as the repeated migration of the river system) than by major climate changes.

Miocene microflora and palaeoclimate reconstructions from three sites in Bulgaria

In this study we reconstruct quantitatively the Middle to Upper Miocene climate evolution in the southern Forecarpathian Basin (Central Paratethys area, Northwest Bulgaria) by applying the coexistence approach to 101 well-dated palynofloras isolated from three cores. The climatic evolution is compared with changes in vegetation and palaeogeography. The Middle Miocene was a period of a subtropical/warm–temperate humid climate with mean annual temperature (MAT) between 16 and 18°C and mean annual precipitation (MAP) between 1100 and 1300 mm. Thereby, during the entire Middle Miocene a trend of slightly decreasing temperatures is observed and only small climate fluctuations occur which are presumably related to palaeogeographic reorganisations. The vegetation shows a corresponding trend with a decrease in abundance of palaeotropic and thermophilous elements. The Upper Miocene is characterised by more diverse climatic conditions, probably depending on palaeogeographic and global climatic transformations. The beginning of this period is marked by a slight cooling and a significant drying of the climate, with MAT 13.3–17°C and MAP 652–759 mm. After that, fluctuations of all palaeoclimate parameters occur displaying cycles of humid/dryer and warmer/cooler conditions, which are again well reflected in the vegetation. Our study provides a first quantitative model of the Middle–Upper Miocene palaeoclimate evolution in Southeastern Europe and is characterised by a relatively high precision and resolution with respect to the climate data and stratigraphy.