Harald Stollhofen

Abstract The analysis of geochemical palaeoclimate and palaeosalinity proxy elements Ti, Mg, and Al, derived from X-ray fluorescence (XRF) scans of Olduvai Beds I and II from Olduvai Gorge Coring Project (OGCP) borehole Cores 2A and 3A, provides a record of cyclic variation between ~1.3 Ma and ~2.0 Ma. The boreholes were drilled into the depocentre of the Olduvai Basin between Fifth and FLK Faults, where Palaeolake Olduvai was most persistent and deepest. During most of Bed I the lake was particularly deep and probably meromictic, preserving high TOC contents and commonly preserving fine lamination due to lack of bioturbation. Accretion rates were also high during Bed I, when rates of basinal subsidence were maximal due to crustal stretching, associated with basaltic volcanism, towards the end of bimodal Ngorongoro volcanism. Basaltic magma effusive activity is manifested as tuffs, scoriaceous layers and the Bed I Basalt complex lava flows. A magnesium anomaly is recorded in the claystone geochemistry at this time and deposition of dolomite and limestone beds are restricted to this syn-volcanic phase of basin history. During Bed I deposition, accretion rates (0.23 mm/yr) were high enough to permit recognition of cycles with an average periodicity of 22.3 kyr corresponding to the Earth's precession. Only the high values during the Mg anomaly are adequate for the application of the palaeosalinity proxy element ratio Mg/Al. But Ti counts provide a cyclic record in both Bed I and Bed II. During Bed II deposition, the accretion rate was much slower (0.058 mm/yr) and cyclicity averaged 40.4 kyr, corresponding to Earth's orbital obliquity. The Bed II interval corresponds to MIS Stages 40 to 64. Coincidence of precessional and obliquity minima at 1.8 Ma explains the superdrought that affected the basin at the time of emplacement of Tuff IF, when the lake was dried out. The aridity of the sequence containing Tuff IA is also associated with a precessional minimum. The cyclic record suggests that three Bed I Basalt flows were extruded at ~1.94 Ma during a time span lasting between 6 kyr and 15 kyr.

. The exposed Variscan basement in Central Europe is well-known for its complex structural and lithological architecture resulting from multiple deformation phases. We study the southwestern margin of the Bohemian Massif, which is characterized by major and long-lived shear zones, such as the Pfahl and Danube shear zones, extending over > 100 km and initiated during Variscan tectonics. We integrate Bouguer gravity anomaly and LiDAR topographic data analyses and combine our results with available data and observations from low-temperature thermochronology, metamorphic grades, and granite intrusion depths to detect patterns of basement block segmentation and differential uplift. Three NW-SE striking basement blocks are bordered by the Runding, Pfahl, and Danube shear zones from the northeast to the southwest. Basement block boundaries are indicated by abrupt changes in measured gravity patterns and metamorphic grades. By applying high-pass filters to gravity data in combination with lineament analysis, we identified a new NNW-SSE striking tectonic structure (Cham Fault), which further segments known basement blocks. Basement blocks that are segmented by the Cham Fault differ in the abundance and spatial distribution of exposed late Variscan granites and are further characterized by variations of apparent thermochronological age data. Based on our observations and analyses, a differential uplift and tectonic tilt model is proposed to explain the juxtaposition of different crustal levels exposed at the surface. Block segmentation along the NW-SE striking Pfahl and Runding shear zones most likely occurred prior, during, and after late-orogenic granite emplacement at ca. 320 ± 10 Ma, as some of the granites are cross-cut by the shear zones while others utilized these structures during magma ascent and emplacement. In contrast, activity and block segmentation along the Cham Fault occurred after granite emplacement as the fault sharply truncates the granite inventory. Our study provides evidence for intense and continuous fault activity during late and early post-orogenic times and highlights the importance of tectonic structures in the juxtaposition of different crustal levels and the creation of complex lithological patterns in orogenic terrains.

Archaeological excavations at EF-HR and HWK EE allow reassessment of Bed II stratigraphy within the Junction Area and eastern Olduvai Gorge. Application of Sequence Stratigraphic methods provides a time-stratigraphic framework enabling correlation of sedimentary units across facies boundaries, applicable even in those areas where conventional timelines, such as tephrostratigraphic markers, are absent, eroded, or reworked. Sequence Stratigraphically, Bed II subdivides into five major Sequences 1 to 5, all floored by major disconformities that incise deeply into the underlying succession, proving that simple "layer cake" stratigraphy is inappropriate. Previous establishment of the Lemuta Member has invalidated the use of Tuff IIA as the boundary between Lower and Middle Bed II, now redefined at the disconformity between Sequences 2 and 3, a lithostratigraphic contact underlying the succession containing the Lower, Middle, and Upper Augitic Sandstones. HWK EE site records Old...

This paper reports the results of renewed fieldwork at the HWK EE site (Olduvai Gorge, Tanzania). HWK EE is positioned across the boundary between Lower and Middle Bed II, a crucial interval for studying the emergence of the Acheulean at Olduvai Gorge. Our excavations at HWK EE have produced one of the largest collections of fossils and artefacts from any Oldowan site, distributed across several archaeological units and a large excavation surface in four separate trenches that can be stratigraphically correlated. Here we present the main stratigraphic and archaeological units and discuss site formation processes. Results show a great density of fossils and stone tools vertically through two stratigraphic intervals (Lemuta and Lower Augitic Sandstone) and laterally across an area of around 300 m(2), and highlight the confluence of biotic and abiotic agents in the formation of the assemblage. The large size and diversity of the assemblage, as well as its good preservation, qualify HWK...

Herein we introduce a newly recovered partial calvaria, OH 83, from the upper Ndutu Beds of Olduvai Gorge, Tanzania. We present the geological context of its discovery and a comparative analysis of its morphology, placing OH 83 within the context of our current understanding of the origins and evolution of Homo sapiens. We comparatively assessed the morphology of OH 83 using quantitative and qualitative data from penecontemporaneous fossils and the W.W. Howells modern human craniometric dataset. OH 83 is geologically dated to ca. 60-32 ka. Its morphology is indicative of an early modern human, falling at the low end of the range of variation for post-orbital cranial breadth, the high end of the range for bifrontal breadth, and near average in frontal length. There have been numerous attempts to use cranial anatomy to define the species Homo sapiens and identify it in the fossil record. These efforts have not met wide agreement by the scientific community due, in part, to the mosaic ...

The discovery of fossil rooted tree stumps in lowermost Lower Bed I from the western Olduvai Basin, Tanzania, age-bracketed by the Naabi Ignimbrite (2.038 ± 0.005 Ma) and Tuff IA (1.88 ± 0.05 Ma), provides the first direct, in situ, and to date oldest evidence of living trees at Olduvai Gorge. The tree relicts occur in an interval dominated by low-viscosity mass flow and braided fluvial sediments, deposited at the toe of a largely Ngorongoro Volcano-sourced volcaniclastic fan apron that comprised a widely spaced network of ephemeral braided streams draining northward into the Olduvai Basin. Preservation of the trees occurred through their engulfment by mass flows, post-mortem mold formation resulting from differential decay of woody tissues, and subsequent fluvially-related sediment infill, calcite precipitation, and cast formation. Rhizolith preservation was triggered by the interaction of root-induced organic and inorganic processes to form rhizocretionary calcareous root casts. Phytolith analyses were carried out to complete the paleoenvironmental reconstruction. They imply a pronounced seasonality and indicate a wooded landscape with grasses, shrubs, and sedges growing nearby, comparable to the low, open riverine woodland (unit 4c) along the Garusi River and tributaries in the Laetoli area. Among the tree stump cluster were found outsized lithic clasts and those consisting of quartzite were identified as Oldowan stone tool artifacts. In the context of hominin activity, the identification of wooded grassland in association with nearby freshwater drainages and Oldowan artifacts significantly extends our paleoenvironmental purview on the basal parts of Lower Bed I, and highlights the hitherto underrated role of the yet poorly explored western Olduvai Gorge area as a potential ecologically attractive setting and habitat for early hominins.

... The heavy mineral assemblage comprises mainly zircon, apatite and monazite, and minor amounts of hornblende, sphene, rutile, tourmaline and garnet only. ... Alban-, Raumberg-,Hesselberg-, Odernheim-, Kappeln-, Gaugrehweiler-and Humberg-Tuffs (cf. Fig. ...

ABSTRACT The Carboniferous-Permian Dwyka Group in southern Namibia is subdivided into four upward-fining deglaciation sequences, each of which is capped by fine-grained glaciolacustrine or glaciomarine deposits. Both the second and the third deglaciation sequences are associated with mudstone units that are particularly widespread-the Ganigobis Shale Member and the Hardap Shale Member. An abundance of marine macrofossils and ichnofossils and extrabasinally derived fallout tuff horizons characterize these mudstones and provide the basis for an integrated high-resolution biostratigraphic and tephrostratigraphic framework. Juvenile magmatic zircons separated from tuff horizons at the base of the Ganigobis Shale Member (top deglaciation sequence II) yield (206)Pb/(238)U sensitive high-resolution ion microprobe (SHRIMP) ages of 302.3 +/- 2.1, 302.0 +/- 3.0 Ma, and 299.5 +/- 3.1 Ma, whereas a tuff associated with the upper part of the Hardap Shale Member (top deglaciation sequence III) reveals a SHRIMP age of 297.1 +/- 1.8 Ma. Since macrofaunal occurrences reveal the Hardap Shale Member to be a correlative of the Gondwana-wide Eurydesma transgression, this datum is an important age calibration for a well-established global event. Tuff beds sampled next to the boundary between the glacial Dwyka Group and the postglacial Ecca Group yield SHRIMP ages of 290.9 +/- 1.7 Ma and 288.5 +/- 1.6 Ma, providing an age proxy for the end of the late Paleozoic ice age in southern Africa.

In the late phase of the Variscan orogenic evolution crustal extension caused formation of numerous intermontane basins starting in Namurian time, locally already in Viséen time. The localization of the basins frequently made use of older tectonic features. During this late Variscan crustal extension the Saar-Nahe Basin also formed. During its long activity that ended in Lower Permian time the basin got filled only by terrestrial sediments, volcanic rocks and tephra deposits fed from vents inside the basin, and some fed from external sources. Originally the basin had a fill approximately 10,000 m thick. However, synsedimentary migration of the depocentre and pre-Triassic erosion resulted in a presently preserved thickness of the fill of only c. 6,500 m. The lithostratigraphic sequence of the largely Lower Permian Rotliegend Group of the Saar-Nahe Basin is divided into two subgroups. The Glan Subgroup starts with the Remigiusberg Formation and ends with the Thallichtenberg Formation;...

ABSTRACT This study presents a reconstruction of the tectonic history of an Upper Rotliegend tight gas field in Northern Germany. Tectonism of the greater study area was influenced by multiple phases of salt movement, which produced a variety of salt-related structural features such as salt walls, salt diapirs as well as salt glaciers (namakiers). A sequential 2D retro-deformation and stratal backstripping methodology was used to differentiate mechanisms inducing salt movement and to discuss their relation to regional tectonics. The quantitative geometric restoration included sedimentary balancing, decompaction, fault-related deformation, salt movement, thermal subsidence, and isostasy to unravel the post-depositional tectonic overprint of the Rotliegend reservoir rock. The results of this study indicate that reactive salt diapirism started during an Early Triassic interval of thin-skinned extensional tectonics, followed by an active diapirism stage with an overburden salt piercement in the Late Triassic, and finally a period of intensive salt surface extrusion and the formation of salt glaciers (namakiers) in Late Triassic and Jurassic times. Since the Early Cretaceous, salt in the study area has been rising by passive diapirism.

... CARMEN BE KRAPF*,1, IAN G. STANISTREET† and HARALD STOLLHOFEN* *Geologisches Institut der RWTH Aachen, Wüllnerstrasse 2, 52056 Aachen, Germany; and †Department of Earth Sciences, University of Liverpool, Brownlow Street, PO Box 147, Liverpool L69 3BX ...

The Karoo-Etendeka depositories in northwestern Namibia can be subdivided into (1) a Carboniferous-Permian, (2) a Triassic-Jurassic and (3) a Cretaceous megasequence, recording successive extensional periods, separated by time-stratigraphic gaps. Close to the present-day Atlantic coastline the Karoo Supergroup is only represented by the Permian succession in the Huab area. This is disconformably overlain by the Lower Cretaceous Etendeka Group. Further east, the Karoo succession becomes successively more complete, but correlation with the main Karoo Basin in South Africa and the Brazilian Paraná Basin indicates major gaps in the sedimentary record. The gaps can be attributed to the combined effects of the long-lived South Atlantic rift evolution and orogenic pulses derived from the Samfrau active margin.

The Late Permian/Early Triassic succession of the Central European Basin (CEB) was repeatedly affected by tectonic pulses associated with the earliest phases of Tethyan and Arctic-North Atlantic rifting. Effects of differential tectonic subsidence are particularly well recorded by unconformities, which form widespread sequence boundaries. In the lowermost Triassic the Hardegsen Unconformity (H-unconformity) represents the most prominent unconformity that can be

A bstract Effects of the earliest Tethyan and Arc-tic-North Atlantic rifting phases on the Early Triassic succession of the Central Eu-ropean Basin are particularly well recorded by unconformities, which form widespread sequence boundaries. Stratigraphic loss related to these unconformities may comprise entire Lower and Middle Buntsandstein formations most obviously developed in areas occupied by fault-controlled intra-basinal highs (swells). Analysis of 3D-seismic data and well logs combined with high-resolution sedimentological logging of drillcores at the western margin of the Ems Trough (NW Ger-many) reveals details of synsedimentary tec-tonic control on sequence development. Early Triassic extensional faulting of basement blocks provided stepwise addition of accommodation for continental sequences by growth faulting along north-south trending fault zones blocks on the flanks of the East Netherlands High. This process is most evident during the development of the Hardegsen Unconformity, which is characterized by an amalgamation of succeeding unconformity surfaces in areas of structurally controlled intrabasinal highs. The mainly aeolian to playa-type sedimentary fa-cies of the Middle Buntsandstein succession suggests very low intrabasinal relief and implies a constant reworking and levelling of the palaeo-surface. Consequently, the development and preservation of stratigraphic units is primarily determined by the potential accommodation provided by synsedimentary tectonics.

ABSTRACT The Olduvai Gorge palaeoanthropological site, in northern Tanzania, encompasses about two million years of earth history. The sedimentary facies of Palaeolake Olduvai have been used to reconstruct lake transgressions and regressions, up to total drying out, interpreted to reflect wet/dry climate cycles. Although multidisciplinary research has been conducted during the past decades to reconstruct the palaeoenvironments and palaeolandscapes of the Gorge, very few focused on the DK site located about 2 km farther east in the Gorge. We present here a vegetation study at DK for Bed I, the oldest stratum, based upon the phytolith and diatom recovery of the basalt lava to Tuff IB stratigraphic interval. These results have been analysed in relation to the different facies in which they occur: sandy diamictite, sandstone, sandy waxy claystone, waxy claystone, and sandy diatomite. The phytolith results from diamictite samples indicate a similar vegetation composition during these more arid periods. Conversely, waxy claystone and sandy waxy claystone samples show a higher diversity in the vegetation composition. The diatoms were indicative of a fresh water pool environment. Thus the DK site would have provided plant foods for hominins, such as fruits from trees and shrubs and starch-rich rhizomes and tubers from sedges and reeds. Overall, the results at DK site present a different vegetation landscape in comparison to previously published phytolith results from other Olduvai stratigraphic levels and regions.

Its location on a tectonically relatively stable passive margin and its degree of interaction with the sea make the Horingbaai fan-delta, NW Namibia, an exceptional record of coastal activity, providing insights into the response of ephemeral fluvial systems to changes in climate, sea level and continent-scale uplift. The fan comprises upper, middle and lower segments. The upper fan and middle fan are dominated by a braided river system; only in the upper fan are fluvial sediments interleaved with hyperconcentrated flow deposits. Plio-Pleistocene sea level highstands have left marine terraces on the fan surface which enable correlation with the offshore marine record and provide timelines to constrain fan growth. The bulk of fan-delta progradation took place at ∼2.7-2.4 Ma, between the formation of a widespread erosional surface incising the middle Pliocene Karpfenkliff and Kamberg Formations, but prior to the emplacement of the warm-water fauna-bearing late Pliocene "Oyster Terrace" (∼ 2.4-2.2 Ma), an equivalent of the +30 mP (marine terrace package) in coastal southwestern Africa. Major fan progradation is contemporaneous with widespread regional uplift (~12 ± 5 m/Ma) and climate change in southwestern Africa, the latter associated with intensification of northern hemisphere glaciations. Younger fan growth phases are weaker and constrained by b10 m asl marine terrace bodies that yield mostly cold-water fauna, corresponding to the onset of strong glacial/interglacial climatic fluctuations superimposed on a general aridification trend and the introduction of colder sea-surface temperatures after 2.2 Ma.

Single-grain geochemical composition of volcaniclastic sandstones can be a potential tool to improve correlations of mixed pyroclastic/epiclastic deposits. To test this, trachytic tuffs of the paleoanthropologically important FLK, FLK N, and FLK NN sites of Pleistocene Olduvai Gorge Bed I (Tanzania) are used as an established tephrostratigraphic framework against which to test volcaniclastic sandstone correlations. Fluvio-lacustrine sandstones and tuff samples were collected from eight archeological trenches between Tuffs IB and ID across a 500-m transect, including Leakey's famousZinjanthropus(FLK) and OH 7/OH 8 (FLK NN) sites. A previously Tephrostratigraphy unknown, thin, fine, mineralogically unique, black trachyandesitic fallout ash was discovered below Tuff IC. Compositions of individual augite, feldspar and titanomagnetite grains from sandstones between Tuffs IB and IC reveal some IB-equivalent material, and a new compositional assemblage distinct from the sandwiching mar...

ABSTRACT This study focuses on the reservoir characteristics of a Permian tight gas field in the Southern Permian Basin, Eastern Frisia, Germany. To improve the understanding of the reservoir, 3D seismic, wireline and core data were compared with a reservoir analogue in the Panamint Valley, United States. Depositional environments of the Permian Upper Rotliegend II include perennial saline lakes, coastal parallel sand belts comprising wet, damp and dry sand flats and aeolian dunes with interdune deposits. Polygonal patterns at different scales were observed on seismic horizon slices in the reservoir intervals and the overlying Zechstein. Outlines of superordinate polygons coincide with interpreted faults. Similar polygonal networks were identified on modern dry lakes in the western United States. The kilometre-long, up to 1.20 m deep open fissures in the Panamint Valley are interpreted to originate from the combined effects of synaeresis and tectonics. Subsequently, the fissures were filled with aeolian sediment. Vegetation growth confined to the lineaments indicates enhanced fluid circulation. Such fissures systems may serve as weakness zones and fault grain and impact reservoir quality in terms of hydraulic connectivity of reservoir compartments. For the Rotliegend reservoirs, original porosities and permeabilities of these zones were reduced to a minimum by enhanced cementation along the fluid migration pathways. Permeability barriers and reservoir compartmentalization, which can be clearly depicted on seismic attribute volumes, are a potential result of this development.