A clay-sequence from Lake Götesjön in the south-western part of the Lake Vänern basin has been investigated with respect to the foraminiferal and ostracod faunas and δ
18
O
c
and δ
13
C
c
. The ...sequence covers the middle/late Younger Dryas and the early part of the Preboreal chronozones. The conditions were severe during the Younger Dryas due to sea ice cover and a proximal position to the ice. The faunal assemblages indicate arctic glaciomarine conditions with a reduced salinity and the marine conditions ceased at c. 9700
14
C-years BP. In the late Younger Dryas an increased ice retreat raised the salinity of the bottomwater. This was due to the formation of reaction currents with marine water entering the basin at the bottom as a response to a surface freshwater flowing out from the basin. A period with improved marine conditions is recorded in the Early Preboreal. The transition from the Younger Dryas to the Preboreal is recorded as a lowering in the δ
18
O
c
due to increased input of meltwater and higher δ
13
C
c
as a consequence of a more intensive mixing of water masses and a less extensive sea ice cover. The Vedde Ash is found in the lower part of the sequence and AMS radiocarbon datings of bivalves suggest a marine reservoir age in the area of 800-900 years during the Younger Dryas. The final drainage of the Baltic Ice Lake had only limited effects on the marine environment in the south-western part of the Vänern basin.
Istraživanje u hrvatskom dijelu Sjevernog Jadrana započelo je 1970. godine snimanjem 2D seizmike te istraživačkim bušenjem. Do 1995. načinjeno je više od 16 000 km 2D seizmičkih profila te 80 ...bušotina. Tijekom ranih 80-ih godina XX. stoljeća otkriveno je nekoliko plinskih polja koja su kasnije postigla značajnu proizvodnju ugljikovodika. Ležišta plina nalaze se u nekonsolidiranim ili tek slabo konsolidiranim pijescima pleistocenske starosti taloženim u Padskoj depresiji (litostratigrafski pripadaju formaciji Ivana prema hrvatskoj, odnosno formacijama Ravenna i Carola po talijanskoj podjeli). Zamke su strukturnog i strukturno-stratigrafskog tipa, uglavnom oblikovane procesom diferencijalne kompakcije te, manjim dijelom, boranjem, nasljeđivanjem oblika mezozojskog paleoreljefa te bočnom promjenom facijesa. Plin je biogenog podrijetla, nastao i nakupljen uglavnom „in situ“, a sastavljen prevladavajuće od metana s vrlo malim udjelom dušika.
Zbog nedostatka infrastrukture u početku proizvodnje te tehnoloških problema zbog kontrole kretanja pijeska u ležištu, razrada sjevernojadranskih polja započela je 1996., kada je, za to vrijeme, primijenjena vrlo napredna kontrola proizvodnje iz pijesaka. Većina proizvodnih bušotina tako je opremljena dvostruko, tj. opremom za visoki protok vode (engl. high rate water pack) i/ili kontrolu kretanja pijeska (engl. FracPack sand control technique). Ta tehnologija se pokazalo vrlo uspješnom kod crpljenja iz nekonsolidiranih ležišta. Primjena kontrole pijeska potaknula je partnere (INA i ENI) da zajednički ulože (preko tvrtke INAgip) u novi ciklus istraživanja i proizvodnje. Tako je od 1996. snimljeno približno 5000 km2 3D seizmike, izbušeno 12 novih istraživačkih bušotina te otkriveno dodatnih 7 plinskih polja. Radom tvrtke INAgip otkriveno je ukupno 105 plinskih ležišta u 9 plinskih polja, načinjeno preko 40 proizvodnih bušotina, instalirano 19 proizvodnih platformi te dosegnuta prosječna proizvodnja oko 30 000 boe/day.
A local varve chronology from southeast Sweden between the town of Karlskrona in the province of Blekinge and Hultsfred in the province of Småland is presented. The chronology covers approximately ...800 varve-years. The glaciolacustrine varves were deposited in the Baltic Ice Lake during the Late Weichselian deglaciation. The study includes 60 connected and 56 unconnected varve series and shows that the ice recession rates vary between 75-125 m/year and 250-340 m/year in the southern and northern parts of the area, respectively. An abrupt change from thin to thick clay varves was found in the northern part of the area. The change has been correlated with a similar change of silty varves in the bottom bed of one of the delta plains close to the highest shoreline. This change in the meltwater deposition has been hypothetically correlated with the transition between the Older Dryas (GI-1d) and Alleröd (GI-1c) chronozones, or around 13,750 GRIP years.
This thesis presents palaeoenvironmental data from equatorial Africa covering two important time intervals; i) the warming period forming the Pleistocene/Holocene transition and ii) the last ...millennium. The Empakaai Crater, in northern Tanzania contains a lake from where sediment cores, spanning two time-slices 14.8-9.3 ka and 800-2000 AD, have been studied. Palaeoecological and palaeohydrological reconstruction is based on a multitude of proxies from the sediments, representing both catchment environment and the lakes aquatic ecosystem response. Between 14.8 and 10 ka the catchment vegetation and lake hydrology responded to both regional climate changes and local environment, but with different amplitude and frequency, reflecting temporal and spatial lags between the two systems. However, at c 10 ka both lake conditions and catchment vegetation showed drastic changes towards drier conditions. The record covering the last millennium reveals environmental changes related to climate and human activities. The catchment’s vegetation was affected by frequent fires, most probably human induced, while near shore vegetation responded to lake level fluctuation associated with rainfall variability. About 15 km from Empakaai Crater is an extensive abandoned irrigation system, the Engaruka complex, which was in active use between c 1400 AD and 1840 AD. By comparing a number of social and environmental factors potentially influencing the societal development at Engaruka it is shown that wet climate conditions have had positive effects on the societal development but also that dry climate conditions were not always disastrous to the society. The resemblance of the pollen taxa present is strong between the two time slices and pollen representing catchment conditions respond in similar manner in both records. The lake conditions are however very different between the two periods Thus the lake responds to both long and short term changes of variable amplitude, while the catchment vegetation seems to responds to high amplitude, low frequency changes.
In this thesis the Weichselian history of northern Sweden is investigated, with emphasis on vegetation and climate during ice-free intervals. The main method used has been pollen analysis of ...sediments from pre-Late Weichselian landforms. To interpret fossil pollen assemblages, comparisons with modern pollen spectra were made. Modern pollen data were retrieved through monitoring of annual pollen deposition at seven sites in northern Sweden, from the boreal forest to above the present forest-line of birch. Eight years of pollen monitoring is described and put in a larger context through comparison with monitoring data from Iceland, Svalbard, Norway and Finland. A study of sediment cores from the Riipiharju esker shows evidence of two ice free phases during the Weichselian glacial; Tärendö I and Tärendö II. The Tärendö II ice free interval includes large climatic shifts, previously not recognized, from relatively warm conditions with Betula as the dominating pollen taxon to cold conditions with dominance of Artemisia and Gramineae and back to warmer conditions again. Correlation alternatives of the north Swedish ice free intervals Tärendö I and II are: 1/ Brörup (MIS 5c; c. 105-93 ka BP) and Odderade (MIS 5a; c. 85-74 ka BP), respectively, or 2/ Odderade and early Middle Weichselian time (MIS 3; c. 59-40 ka BP). Of these, alternative 2 is regarded as the most likely. Interstadial sediments deposited in a Veiki moraine plateau during downwasting of a pre-Late Weichselian ice sheet include only Betula dominant pollen spectra, showing that the climate during formation of the Veiki moraine was relatively warm. According to stratigraphical correlation there are three possible alternatives for Veiki moraine formation. Either it was formed during 1/ early Tärendö I, 2/ early Tärendö II, or 3/ late Tärendö II. Alternative 3 implies growth of an intermediate ice sheet reaching the eastern limit of Veiki moraine distribution during the cold phase of Tärendö II.
Vibrocore 9303 was drilled at a water depth of 35 m in the southern Kattegat and penetrated 10 m of Holocene and Late Weich-selian sediments. The ostracods recorded from 11 samples of this core in ...the time between c. 11,500 and 10,500 BP are dominated by Elofsonella concinna, Sarsicytheridea punctillata, Cytheropteron dimlingtonensis, Roundstonia globulifera, Acanthocythereis dunelmensis, Sarsicyther-idea bradii, Cytheropteron macchesneyi, Robertsonites tuberculatus, freshwater spp., and Heterocyprideis sorbyana. Most of these species are autochthonous (not freshwater spp.) based on their population age structures. The maximum bottom-water temperature probably ranged from 8 to 12 °C during summer. The palaeoenvironment was probably marine sublittoral with depths exceeding 10-15 m. The time interval between c. 10,900 and 10,650 BP is marked by (1) an increase in ostracod species diversity, (2) a decrease in dominance of the three most abundant ostracod species, (3) a replacement of A. dunelmensis by C. macchesneyi and (4) freshwater species become more abundant. These changes may possibly be due to an increased niche availability and/or sea-level changes associated with a stronger influence of freshwater to the in situ environment. However, the changes in species composition are statistically insignificant according to a bootstrap correspondence analysis.
Na području Sjevernog Jadrana nalaze se neogenske i kvartarne naslage razmjerno velikih debljina. Odlagane su u nekoliko depresija unutar Jadranskoga bazena, od kojih je najveća Padska. Današnje ...granice te depresije pružaju se unutar talijanskog i hrvatskog podmorja Jadrana gdje su pliocenske i pleistocenske sekvencije hemipelagičkog taloženja prekidane progradacijama delte rijeke Po, a u manjoj mjeri i rijeka Adige i Piave. Ti sedimenti sadrže važna ležišta značajnih količina prirodnog plina, te su dobro istraženi na području više talijanskih i hrvatskih plinskih polja dubokim bušotinama, kao i nizom različitih metoda snimanja podzemlja, uglavnom refleksijskom seizmikom. Slijed pliocenskih i pleistocenskih sedimenata može debljinom doseći i 6 000 m, a podijeljen je u odgovarajući sustav litostratigrafskih jedinica ranga formacija. Dok su na talijanskoj strani kenozojske naslage do mezozojske podine razrađene na dvanaest formacija, na hrvatskoj strani do sada je izdvojena samo jedna. To je formacija Susak koja obuhvaća sve stijene unutar kenozoika. Stoga se u hrvatskom dijelu Sjevernoga Jadrana predlaže uvođenje sljedećih litostratigrafskih jedinica u rangu formacija: formacija Dinaridi (mezozojske stijene), formacija Susak (paleocenske-miocenske stijene), formacija Istra (pliocenske naslage) i formacija Ivana (pleistocenske i holocenske naslage).
Sedimentological studies rarely reveal direct information about abrupt climatic changes. The interpretations of climatic changes, for instance at the end of the Pleistocene, are mainly based on ...fossils (in the Pleistocene deposits particularly on pollen) of species that are known to flourish within specific temperature ranges. The relatively scarce generally accessible literature data on the response of glaciofluvial and glaciolacustrine sedimentation to abrupt climatic change is based mainly on research of deposits formed at the Pleistocene/Holocene transition, which need, however, not necessarily reflect a representative climatic change (it may have been exceptionally fast). Such data, in combination with theoretical considerations, provide some insight in the tendencies that such sediments might show during climate changes. Yet, it is not well possible to determine during which timespan most of such climatic changes took place. More insight might be obtained by a structured analysis of well chosen sedimentological sections, in combination with detailed and accurate dating of such sections.
This is the first pollen stratigraphical investigation of late Weichselian deposits in the area which was situated close to the late Weichselian Fennoscandian ice sheet margin and the Baltic Ice Lake ...shore during the Allerød-Younger Dryas climatic transition. Pollen analyses were carried out on varved clay sequences, covering a time span of 350 years of an AMS radiocarbon-dated 800-year varve chronology, and on two lacustrine sequences. The Allerød-Younger Dryas pollen zone boundary has been defined at the local varve year 2000. The pollen zone boundary coincides with an apparent drop of AMS radiocarbon ages from c. 11,000 to 10,800-10,600
14
C years BP. The Allerød, Younger Dryas, and Preboreal climatic events are distinguished in the pollen records of the lacustrine sites. Pollen and macrofossil evidence and AMS radiocarbon dates at these sites indicate that the area was deglaciated during the Allerød. Soon after the deglaciation Betula pendula/pubescens immigrated. At the Allerød/Younger Dryas transition the vegetation changed to a herb tundra indicating cooler and/or drier conditions. The Younger Dryas/Preboreal boundary is characterised by a vegetation change from a herb tundra to a park tundra with tree birch. Later in the Preboreal the vegetation became more dense and was dominated again by Betula pendula/pubescens.
