Post‐Variscan tectonics in eastern Anti‐Atlas (Morocco)

New field data integrated by fission‐track (FT) analysis unravel an innovative scenario for the post‐Variscan evolution of the eastern Anti‐Atlas. This area, unaffected by Meso‐Cenozoic tectonics according to most workers, is crosscut by crustal faults bearing evidence of a polyphase deformation history. Apatite FT ages, ranging between 284 and 88 Ma, point to fast Neogene exhumation and unravel contrasting cooling paths across major faults. Results show that the study area was buried beneath 2 km of allochthonous Variscan units, now eroded. The eastern Anti‐Atlas acted as the southern shoulder of the Atlasic rift in the Mesozoic, and underwent a dextral transpressional structuring of Neogene age followed by sub‐meridian shortening. The southern front of Atlasic deformation is therefore located inside the Anti‐Atlas region, and it is still active.     

Geological structure and composition of the Curonian Spit (Baltic Sea)

The paper presents new data on geology of the Curonian Spit based on results of the study of data on the engineering-geological transect compiled during the construction of gas pipe in the Russian sector of the spit. The data show that, along with eolian sand, peat deposits recovered in both its Russian and Lithuanian sectors make up a significant portion of the spit (data on the Lithuanian sector are adopted from the available literature). Based on new data, existing concepts on geology, paleogeography, geoecology, and stability of the Curonian Spit are discussed and refined.     

Post‐Last Glacial Maximum glacier fluctuations in the southern Écrins massif (westernmost Alps): insights from 10Be cosmic ray exposure dating

Only a few chronological constraints on Lateglacial and Early Holocene glacier variability in the westernmost Alps have hitherto been obtained. In this paper, moraines of two palaeoglaciers in the southern Écrins massif were mapped. The chronology of the stabilization of selected moraines was established through the use of ¹⁰Be cosmic ray exposure (CRE) dating. The equilibrium line altitude (ELA) during moraine deposition was reconstructed assuming an accumulation area ratio (AAR) of 0.67. Ten pre‐Little Ice Age (LIA) ice‐marginal positions of the Rougnoux palaeoglacier were identified and seven of these have been dated. The ¹⁰Be CRE age of a boulder on the lowermost sampled moraine indicates that the landform may have been first formed during a period of stable glaciers at around 16.2±1.7 ka (kiloyears before AD 2017) or that the sampled boulder experienced pre‐exposure to secondary cosmic radiation. The moraine was re‐occupied or, alternatively, shaped somewhat before 12.2±0.6 ka when the ELA was lowered by 230 m relative to the LIA ELA. At least six periods of stable ice margins occurred thereafter when the ELA was 220–160 m lower than during the LIA. The innermost dated moraine stabilized at or before 10.9±0.7 ka. Three ¹⁰Be CRE ages from a moraine of the Prelles palaeoglacier indicate a period of stationary ice margins at or before 10.9±0.6 ka when the ELA was lowered by 160 m with respect to the end of the LIA. The presented ¹⁰Be CRE ages are in good agreement with those of moraines that have been attributed to the Egesen stadial. Assuming unchanged precipitation, summer temperature in the southern Écrins massif at ~12 ka must have been at least 2 °C lower relative to the LIA.     

Sources and pathways of natural and anthropogenic hydrocarbons into the natural dump Arkona Basin (southern Baltic Sea)

 Surface sediments, suspended particulate matter and fluffy-layer material, collected in the Arkona Basin and the Pomeranian Bay during 1995–1997, as well as air particulate matter, collected on the island of Rügen during August 1995, were analysed for total organic carbon content, saturated and polycyclic aromatic hydrocarbons (PAH). The resulting concentrations and distributions of these compounds and molecular PAH ratios are discussed in terms of matrix, origin of the organic matter and seasonal variations. The data show that the Oder river can be identified as a major source for PAH transported into the southern part of the Arkona Basin. A strong atmospheric input of PAH is noted for the central and northern part of the basin. In general, anthropogenic and bacterially degraded hydrocarbons bound to organic carbon-rich and small particles are mainly deposited in the basin center, whereas their natural counterparts accumulate mainly on the basin flanks covered by coarser grained sediments. Received: 2 March 1999 · Accepted: 8 June 1999     

Groundwater discharge to the Gulf of Finland (Baltic Sea): ecological aspects

The Gulf of Finland lies in the eastern part of the Baltic Sea. The surface area is 29,700 km² and the average depth of the basin is 38 m. Groundwater discharge to the Gulf of Finland equals 0.6 km³/year and this discharge is composed of many different chemical compounds. Groundwater discharge into the Gulf of Finland is dispersal. The coastal area of the Gulf of Finland can be divided into four zones with different geological, hydrogeological and discharge properties. The amount of direct groundwater discharge to the sea may be estimated using several geological and hydrogeological methods.     

Post‐Variscan exhumation of the Central Anti‐Atlas (Morocco) constrained by zircon and apatite fission‐track thermochronology

The origin of the Anti‐Atlas relief is one of the currently debated issues of Moroccan geology. To constrain the post‐Variscan evolution of the Central Anti‐Atlas, we collected nine samples from the Precambrian basement of the Bou Azzer‐El Graara inlier for zircon and apatite fission‐track thermochronology. Zircon ages cluster between 340 ± 20 and 306 ± 20 Ma, whereas apatite ages range from 171 ± 7 Ma to 133 ± 5 Ma. Zircon ages reflect the thermal effect of the Variscan orogeny (tectonic thickening of the ca. 7 km‐thick Paleozoic series), likely enhanced by fluid advection. Apatite ages record a complex Mesozoic–Cenozoic exhumation history. Track length modelling yields evidence that, (i) the Precambrian basement was still buried at ca. 5 km depth by Permian times, (ii) the Central Anti‐Atlas was subjected to (erosional) exhumation during the Triassic‐Early Cretaceous, then buried beneath ca. 1.5 km‐thick Cretaceous‐Paleogene deposits, (iii) final exhumation took place during the Neogene, contemporaneously with that of the High Atlas.     

Sea‐level change in the Irish Sea since the Last Glacial Maximum: constraints from isostatic modelling

Models of glacio‐hydroisostatic sea‐level change have been published for the British Isles that are broadly consistent with the observational evidence, as well as with glaciological constraints. It has been argued, however, that the models fail to represent sea‐level change along the Irish Sea margins and in southern Ireland for the post‐deglaciation period. The argument rests on the interpretation of the depositional environment of the elevated ‘Irish Sea Drift’ on both sides of the Irish Sea: whether this is terrestrial or glaciomarine. The isostatic models for the British Isles are consistent with the former interpretation in that sea‐levels on either side of the Irish Sea, south of about the Isle of Man, are not predicted to have risen above present sea‐level at any time since the deglaciation of the Irish Sea. This implies that ice over both the Irish Sea and Ireland was relatively thin (ca. 600–700 m over Ireland). If the glaciomarine interpretation of the elevated Irish Sea Drift is correct, then the maximum ice thickness over central and southern Ireland would have to reach 2000 m, exceeding that over Scotland. Furthermore, for the resulting sea‐level change to be consistent with the Holocene evidence, this thick ice sheet could not have extended to the eastern side of the Irish Sea. Nor could it have been very thick at its northern and western limits. If such an ice model is extreme and incompatible with glaciological observations then the alternative is to accept the interpretation of the Irish Sea Drift as terrestrial in origin. Copyright © 2001 John Wiley & Sons, Ltd.     

Changes in the inflow of saline water into the Bornholm Basin (SW Baltic Sea) during the past 7100 years – evidence from benthic foraminifera record

The Baltic Sea (~393 000 km²) is the largest brackish sea in the world and its hydrographic and environmental conditions are strongly dependent on the frequency of saline water inflows from the North Sea. To improve our understanding of the natural variability of the Baltic Sea ecosystem detailed reconstructions of past saline water inflow changes based on palaeoecological archives are needed. Here we present a high‐resolution study of benthic foraminiferal assemblages accompanied by sediment geochemistry (loss on ignition, total organic carbon) and other microfossil data (ostracods and cladocerans) from a well‐dated 8‐m‐long gravity core taken in the Bornholm Basin. The foraminiferal diversity in the core is low and dominated by species of Elphidium. The benthic foraminiferal faunas in the central Baltic require oxic bottom water conditions and salinities >11–12 PSU. Consequently, shell abundance peaks in the record reflect frequent saline water inflow phases. The first appearance of foraminiferal tests and ostracods in the investigated sediment core is dated to c. 6.9 cal. ka BP and attributed to the first inflows of saline and oxygenated bottom waters into the Bornholm Basin during the Littorina Sea transgression. The transgression terminated the Ancylus Lake phase, reflected in the studied record by abundant cladocerans. High absolute foraminiferal abundances are found within two time intervals: (i) c. 5.5–4.0 cal. ka BP (Holocene Thermal Maximum) and (ii) c. 1.3–0.75 cal. ka BP (Medieval Climate Anomaly). Our data also show three intervals of absent or low saline water inflows: (i) c. 6.5–6.0 cal. ka BP, (ii) c. 3.0–2.3 cal. ka BP and (iii) c. 0.5–0.1 cal. ka BP (Little Ice Age). Our study demonstrates a strong effect of saline and well‐oxygenated water inflows from the Atlantic Ocean on the Baltic Sea ecosystem over millennial time scales, which is linked to the major climate transitions over the last 7 ka.     

Dating early Holocene palaeoseismic event(s) in the Gulf of Bothnia, Baltic Sea

Hutri, K.-L., Heinsalu, A., Kotilainen, A. T. & Ojala, A. E. K. 2007 (January): Dating early Holocene palaeoseismic event(s) in the Gulf of Bothnia, Baltic Sea. Boreas , Vol. 36, pp. 56–64. Oslo. ISSN 0030–9483.
Deformation structures in submarine Holocene sediments caused by palaeoseismicity have recently been found in the Olkiluoto area, Gulf of Bothnia, Baltic Sea, within old fracture zones of bedrock. In this study, the palaeoseismic event(s) was dated and the palaeoenvironment was characterized using palaeomagnetic, biostratigraphical and lithostratigraphical methods, thereby enhancing the reliability of the chronology. The variations in the inclination and declination of the Olkiluoto sediment core showed very good correlation with the palaeosecular variations recorded in the annually laminated long lake sediment record from Lake Nautajarvi in central Finland. Combined litho-, bio- and palaeomagnetic stratigraphy revealed an age estimation of 10 650 to 10 200 cal. yr BP for the palaeoseismic event(s), which coincides with postglacial bedrock faulting in northern Fennoscandia.     

Biomarkers for aerobic methanotrophy in the water column of the stratified Gotland Deep (Baltic Sea)

Filter samples from the oxic zone and suboxic zone of the physically stratified water column and sediment samples of the Gotland Deep, Baltic Sea, were analyzed for bacteriohopanepolyol (BHP) and phospholipid fatty acid (PLFA) concentrations. In total, eight BHPs were identified, with the greatest diversity in the suboxic zone. There, 35-aminobacteriohopane-31,32,33,34-tetrol (aminotetrol) and 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), whose concentrations decreased concurrently from the lower to the upper suboxic zone, indicated type I methanotrophic bacteria and thus aerobic oxidation of methane. The presence and activity of type I aerobic methanotrophic bacteria was further supported by the presence of ¹³C-depleted PLFAs, specifically 16:1ω8c and 16:1ω5c (δ¹³C as low as −41.2‰). However, the relative amount of methanotroph-specific compounds was low (aminopentol, <0.2% of total BHPs; 16:1ω8c, ca. 0.5% of total PLFAs), suggesting a minor contribution of aerobic methanotrophic bacteria to the particulate organic matter. The distinctive BHP pattern in the suboxic zone, including aerobic methanotroph biomarkers and a tentative marker for a pelagic redoxcline [putative 22S isomer of the ubiquitous 22R-bacteriohopanetetrol (BHT)], was mirrored in the sediment samples. Our data indicate that a major portion of the sedimentary hopanoids of the Gotland Deep is sourced from the suboxic part of the water column via an effective but unknown transport mechanism.     

Late Glacial fluvial response of the Niers‐Rhine (western Germany) to climate and vegetation change

The Niers valley was part of the Rhine system that came into existence during the maximum Saalian glaciation and was abandoned at the end of the Weichselian. The aim of the study was to explain the Late Pleniglacial and Late Glacial fluvial dynamics and to explore the external forcing factors: climate change, tectonics and sea level. The sedimentary units have been investigated by large‐scale coring transects and detailed cross‐sections over abandoned channels. The temporal fluvial development has been reconstructed by means of geomorphological relationships, pollen analysis and ¹⁴C dating. The Niers‐Rhine experienced a channel pattern change from braided, via a transformational phase, to meandering in the early Late Glacial. This change in fluvial style is explained by climate amelioration at the Late Pleniglacial to Late Glacial transition (at ca. 12.5 k ¹⁴C yr BP) and climate‐related hydrological, lithological and vegetation changes. A delayed fluvial response of ca. 400 ¹⁴C yr (transitional phase) was established. The channel transformations are not related to tectonic effects and sea‐level changes. Successive river systems have similar gradients of ca. 35–40 cm km^?1. A meandering river system dominated the Allerød and Younger Dryas periods. The threshold towards braiding was not crossed during the Younger Dryas, but increased aeolian activity has been observed on the Younger Dryas point bars. The final abandonment of the Niers‐Rhine was dated shortly after the Younger Dryas to Holocene transition. Traces of Laacher See pumice have been found in the Niers valley, indicating that the Niers‐Rhine was still in use during the Younger Dryas. Copyright © 2005 John Wiley & Sons, Ltd.     

Long-term Changes and Controlling Factors of Phytoplankton Community in the Gulf of Riga (Baltic Sea)

Trends in phytoplankton monitoring data (1976–2008) from the Gulf of Riga were investigated and linked to environmental factors. Annual means of spring phytoplankton biomass correlated to phosphorus input from land and shifts between diatoms and dinoflagellates were attributed to potential Si limitation and time of sampling relative to the spring phytoplankton succession. The summer phytoplankton biomass, which more than doubled over the study period, was related to the abundance of summer copepods that similarly declined. Cyanobacterial blooms proliferated in summer and the proportion of diatoms similarly declined when the winter–spring inorganic N/P ratio was low. The chlorophyte proportion in summer increased over the study period, and this was linked to increasing temperatures favoring their higher growth rates. The dinoflagellate proportion appeared to decrease with temperatures above a threshold of 15.5°C. Although nutrient inputs and their ratios are important factors for the phytoplankton community, this study suggests that climate change and overfishing could be equally important.     

Early Last Interglacial palaeoenvironments in the western Baltic Sea: benthic foraminiferal stable isotopes and diatom‐based sea‐surface salinity

Knudsen, K. L., Jiang, H., Kristensen, P., Gibbard, P. L. & Haila, H. 2011: Early Last Interglacial palaeoenvironments in the western Baltic Sea: benthic foraminiferal stable isotopes and diatom‐based sea‐surface salinity. Boreas, 10.1111/j.1502‐3885.2011.00206.x. ISSN 0300‐9483. Stable isotopes from benthic foraminifera, combined with diatom assemblage analysis and diatom‐based sea‐surface salinity reconstructions, are used for the interpretation of changes in bottom‐ and surface‐water conditions through the early Eemian at Ristinge Klint in the western Baltic Sea. Correlation of the sediments with the Eemian Stage is based on a previously published pollen analysis that indicates that they represent pollen zones E2–E5 and span ～3400 years. An initial brackish‐water phase, initiated c. 300 years after the beginning of the interglacial, is characterized by a rapid increase in sea‐surface and sea‐bottom salinity, followed by a major increase at c. 650 years, which is related to the opening of the Danish Straits to the western Baltic. The diatoms allow estimation of the maximum sea‐surface salinity in the time interval of c. 650–1250 years. After that, slightly reduced salinity is estimated for the interval of c. 1250–2600 years (with minimum values at c. 1600–2200 years). This may be related to a period of high precipitation/humidity and thus increased freshwater run‐off from land. Together with a continuous increase in the water depth, this may have contributed to the gradual development of a stratified water column after c. 1600 years. The stratification was, however, particularly pronounced between c. 2600 and 3400 years, a period with particularly high sea‐surface temperature, as well as bottom‐water salinity, and thus a maximum influence of Atlantic water masses. The freshwater run‐off from land may have been reduced as a result of particularly high summer temperatures during the climatic optimum.     

An illustrated key and (palaeo)ecological primer for Postglacial to Recent Ostracoda (Crustacea) of the Baltic Sea

Frenzel, P., Keyser, D. & Viehberg, F.A. 2010: An illustrated key and (pala6e6o)ecological primer for Postglacial to Recent Ostracoda (Crustacea) of the Baltic Sea. Boreas, Vol. 39, pp. 567–575. 10.1111/j.1502‐3885.2009.00135.x. ISSN 0300‐9483 This synopsis of Baltic Sea brackish water Ostracoda gives an overview of all known Recent species for the first time. It also includes Holocene taxa now extinct in the area. There are 131 species, two of which are recorded only from Yoldia stage (Preboreal) sediments. The illustrated key is based exclusively on valve morphology, providing a taxonomical base for geoscience and biological studies using ostracods from the Baltic Sea area. A list of ecological tolerances and preferences as well as the latitudinal distribution of all species is intended as a reference for palaeoenvironmental analyses. Salinity, temperature and oxygen tolerance values as well as preferences for latitudinal distribution, water depth and energy, habitat and substrate are given. The data are based on quantitative sampling in the southern, central and western Baltic Sea and on information gained from literature.     

Soft-sediment deformation of Late Pleistocene sediments along the southwestern coast of the Baltic Sea (NE Germany)

A 1,460-m-long profile of a Late Glacial subglacial, glacio-fluvial, glacio-limnic and glacio-deltaic sequence exposed at a cliff section on Usedom Island (SW Baltic Sea coast) is described. The sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting. Soft-sediment deformation is encountered and is associated with changes in lithology. These deformations include liquefaction, slumping, and faulting. As the most plausible cause, earthquake-induced shaking is discussed. The associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound. As the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out, no large earthquakes are anticipated for northern Germany, although in conclusion the lithosphere of the North German Basin has to be regarded as weakened by repeated ice loading and deloading.     

Lost Foraging Opportunities for East Asian Hunter‐Gatherers Due to Rising Sea Level Since the Last Glacial Maximum

This paper explores how changes in sea level and biome distribution may have affected the habitats occupied by hunter‐gatherers in East Asia. Using a model‐based reconstruction of changing sea level from the Last Glacial Maximum (LGM) to present day, our analysis reveals that the exposure of a large continental shelf during the LGM sea level lowstand created a wealth of wooded, estuarine, and coastal biomes that could have been exploited intensively by Late Pleistocene hunter‐gatherers. Models explaining hunter‐gatherer subsistence changes and migrations in this period should take into account the large area that has been lost to rising sea level since the LGM.     

Regressions and transgressions of the Baltic basin reflected by a new high-resolution deglacial and postglacial lithostratigraphy for Arkona Basin sediments (western Baltic Sea)

Seismoacoustic profiles from the Arkona Basin show a late Pleistocene and Holocene succession of several distinct reflectors. The physical, sedimentological, mineralogical and geochemical properties of more than 30 sediment cores were analysed in order to assign these reflectors to specific sedimentary discontinuity layers. Additionally, AMS ¹⁴C data and biostratigraphic information were gathered. Based on this multi‐proxy approach, seven lithostratigraphic units (AI, AII, B to F) were distinguished. These consist of fine‐grained clay, silt and mud, and are separated from each other by thin basin‐wide traceable sandy layers (S_ab‐S_ef). The most sensitive parameter to mark the lithostratigraphic boundaries is the weight percentage of the grain‐size fraction >63μm. In addition, some of the quartz‐grain‐dominated sandy layers cause the strong reflection lines recorded in seismoacoustic profiles. The sandy layers are interpreted to reflect enhanced hydrodynamic energy induced by episodes of basin‐wide water‐level low‐stand conditions. These low stands resulted from water‐level drops that occurred frequently during the Baltic Sea's history and presumably affected the entire Baltic basin. The thick fine‐grained units AI, AII to F, in which coarser material is absent, represent water‐level high‐stands. We conclude that the units AI and AII are Baltic Ice Lake sediments deposited before and after the Billingen‐1 regression, respectively. We assign the most prominent sandy layer S_ab to the final drainage of the Baltic Ice Lake (Billingen‐2), whereas the sandy layers between units B, C., D and E are related to the Yoldia Sea and Ancylus Lake regressions of the Baltic Sea's history. The uppermost fine‐grained unit F with its high organic carbon content contains marine sediments deposited after the Littorina Transgression. The macroscopically well‐visible sediment colour change from reddish/brown‐to‐grey, previously interpreted as a regional stratigraphic boundary, varies from core to core. It has been shown by our new data that this colour change has a diagenetic origin, and thus does not represent a stratigraphic boundary. Previous subdivisions therefore have to be revised.     

Post‐impact event bed (tsunamite) at the Cretaceous–Palaeogene boundary deposited on a distal carbonate platform interior

We show crucial evidence for the Cretaceous–Palaeogene (K–Pg) boundary event recorded within a rare succession deposited in an inner‐platform lagoon on top of a Mesozoic, tropical, intra‐oceanic (western Tethys) Adriatic carbonate platform, which is exposed at Likva cove on the island of Bra? (Croatia). The last terminal Maastrichtian fossils appear within a distinct 10–12 cm thick event bed that is characterised by soft‐sediment bioturbation and rare shocked‐quartz grains, and is interpreted as a distal tsunamite. Directly overlying this is a 2 cm thick reddish‐brown clayey mudstone containing planktonic foraminifera typical of the basal Danian, and with elevated platinum‐group elements in chondritic proportions indicating a clear link to the Chicxulub asteroid impact. These results strongly support the first discovery of a “potential” K–Pg boundary tsunamite on the neighbouring island of Hvar, and these two complementary sections represent probably the most complete record of the event among known distal shallow‐marine successions.     

Holocene environmental history of the Ångermanälven Estuary,northern Baltic Sea

The Baltic Sea has experienced a complex geological history, with notable swings in salinity driven by changes to its connection with the Atlantic and glacio‐isostatic rebound. Sediments obtained during International Ocean Drilling Program Expedition 347 allow the study of the effects of these changes on the ecology of the Baltic in high resolution through the Holocene in areas where continuous records had not always been available. Sites M0061 and M0062, drilled in the Ångermanälven Estuary (northern Baltic Sea), contain records of Holocene‐aged sediments and microfossils. Here we present detailed records of palaeoecological and palaeoenvironmental changes to the Ångermanälven Estuary inferred from diatom, palynomorph and organic‐geochemical data. Based on diatom assemblages, the record is divided into four zones that comprise the Ancylus Lake, Littorina Sea, Post‐Littorina Sea and Recent Baltic Sea stages. The Ancylus Lake phase is initially characterized as oligotrophic, with the majority of primary productivity in the upper water column. This transition to a eutrophic state continues into the Initial Littorina Sea stage. The Initial Littorina Sea stage contains the most marine phase recorded here, as well as low surface water temperatures. These conditions end before the Littorina Sea stage, which is marked by a return to oligotrophic conditions and warmer waters of the Holocene Thermal Maximum. Glacio‐isostatic rebound leads to a shallowing of the water column, allowing for increased benthic primary productivity and stratification of the water column. The Medieval Climate Anomaly is also identified within Post‐Littorina Sea sediments. Modern Baltic sediments and evidence of human‐induced eutrophication are seen. Human influence upon the Baltic Sea begins c. 1700 cal. a BP and becomes more intense c. 215 cal. a BP.