Jörg Lang

The Middle Pleistocene tunnel valley at Schöningen as a Paleolithic archive

Schöningen represents one of the key sites for Lower Paleolithic archaeology in central Europe, where a Middle to Late Pleistocene sedimentary succession, locally up to 45 m thick, has been preserved in an Elsterian tunnel valley. After deglaciation, the tunnel valley remained underfilled and provided the accommodation space for Holsteinian interglacial deposition and also kept the artifact-bearing strata below base level for subsequent erosion. The Holsteinian (MIS 9) succession consists of laterally and vertically stacked lacustrine delta systems, which were controlled by repeated lake-level changes. In the face of changing climatic and environmental conditions the long-lived interglacial lake provided an attractive site for animals and early humans. Artifacts were deposited on the subaerial delta plain and became embedded during lake-level rise. Although the area was considerably affected by erosion and glacitectonic deformation during the subsequent Saalian glaciation, the artifact-bearing Holsteinian strata were preserved in the deeper part of the tunnel valley. Tunnel valleys should be regarded as potential archives for interglacial deposits, which may contain important Paleolithic sites. Tunnel valleys may provide accommodation space and also have a high preservation potential. Interglacial lakes situated within underfilled tunnel valleys represented attractive sites for animals and early human hunter-gatherers.

Depositional architecture and sequence stratigraphic correlation of Upper Ordovician glaciogenic deposits, Illizi Basin, Algeria

Abstract Upper Ordovician glaciogenic deposits are profoundly important as hydrocarbon reservoirs across North Africa, such as within the Illizi Basin of SE Algeria. In this study we present a new sedimentological and sequence stratigraphic model for Upper Ordovician glaciogenic deposits based on the analysis of core descriptions and wireline logs from 25 wells in the Tiguentourine Field. Within the glaciogenic succession, two ice advance–retreat cycles can be defined, consisting of glaciomarine ice-contact fan deposits and tillites. Deposits of the marine ice-contact fan systems generally show a retrogradational stacking pattern from ice-proximal to ice-distal deposits. This pattern is attributed to the deposition in front of a retreating ice sheet. The proximal marine ice-contact fan deposits consist of massive or low-angle cross-bedded pebbly sandstone. They are interpreted as the deposits of turbulent, high-energy plane-wall jets, emerging from subglacial meltwater conduits. These jet-efflux deposits are up to 60 m thick and interbedded with deposits of cohesive and non-cohesive debris flows. The jet-efflux deposits are overlain by fine-grained, thick-bedded massive sandstone. These mid-fan deposits build up the bulk of the glaciomarine fans and are interpreted as deposits of underflows, generated at the point of flow-detachment, where marine meltwater jets become buoyant and large volumes of sediment fall-out from suspension. In the upper part of the fan succession massive sandstones pass upwards into mud-prone massive sandstones, interpreted as deposits of cohesive sandy debris flows. The most ice-distal deposits are muddy sandstones and mudstones deposited by waning low-density turbulent flows and suspension fall-out. The best reservoir properties within the glaciogenic succession are attributed to the proximal and medial deposits of the ice-contact fans such as coarse-grained jet-efflux deposits and sustained high-density turbulent flow deposits. However, the mud content within the massive sandstones is highly variable and influences the reservoir quality. Both glacial depositional sequences infill 60–175 m deep, elongated depressions, which are interpreted as subglacial tunnel valleys. These tunnel valleys acted as depocentres for the glaciomarine fan deposits. After final deglaciation and post-glacial transgression, organic-rich shale was preferentially deposited in underfilled tunnel valleys.

Depositional Architecture and Sequence Stratigraphy of Upper Ordovician Glacigenic Deposits, Illizi Basin, Algeria

DEDICATED: GLACIATIONS In the subsurface of North Africa, Upper Ordovician glacigenic deposits form economically important hydrocarbon reservoirs. These glacigenic reservoirs are characterised by lateral and vertical facies changes as a result of deposition in a range of complex ice-contact and proglacial settings. In this study we present a new sedimentological and sequence stratigraphic model for Upper Ordovician glacigenic deposits of the Tiguentourine Field, Illizi Basin. The Lower Palaeozoic succession of the Illizi Basin may be subdivided into pre-, syn- and post-glacial deposits. The glacigenic deposits comprise tillites and glacimarine fan deposits, which were deposited during different stages of ice advance or retreat. Tillites represent deposits of the glacial maximum, while retrogradational glacimarine fans were deposited during the glacial retreat. The deposits of two ice-advance-retreat cycles are correlated across the study area. The best reservoir properties within the glacigenic succession are attributable to the proximal and medial deposits of the subaqueous ice-contact fans.

A Sequence Stratigraphic Model for Ordovician Glacial Deposits, Illizi Basin, Algeria

Well data from the Cambrian to Silurian succession of the Illizi Basin, Algeria, were interpreted to derive a depositional model and correlate the wells in a sequence stratigraphic framework. The succession contains thick glacimarine deposits of the Late Ordovician glaciation. The preglacial deposits show a retrogradational stacking pattern of terrestrial and shallow marine deposits. The synglacial succession is dominated by subaqueous fan deposits. Glacimarine depositional sequences were controlled by advance and retreat cycles of the glacier. Two glacial advance and retreat can be correlated across the study area. The postglacial succession was deposited on the shelf, infilling the residual glacial topography.