Sea-level Curve Research Articles

Biostratigraphy, sequence stratigraphy, and paleoecology of the Lower–Middle Miocene of Northern Bandar Abbas, Southeast Zagros basin in south of Iran

The Guri Member is a limestone interval at the base of the calcareous marls of the Mishan Formation. It is the youngest hydrocarbon reservoir of the southeast part of the Zagros sedimentary basin. This Member overlaid siliciclastic rocks of Razak Formation and is overlain by green and gray marls of the Mishan Formation. In order to consider the paleoecology and paleoenvironments of the Lower–Middle Miocene (Guri Member), we have studied biostratigraphy and sequence stratigraphy of the Guri Member based on foraminifer and microfacies in two stratigraphic sections including Dorahi–Homag and Chahestan. A total of 33 genera and 56 species of benthic and planktonic foraminifera were identified in two studied stratigraphic sections. Benthic and planktonic foraminifera demonstrate Aquitanian to Langhian age (Early–Middle Miocene) for this Member at the study area. Studied interval has deposited in four facies association including supratidal, lagoon, coral reef, and open sea on a carbonate ramp. Carbonate rocks of the Guri Member have precipitated in two and three depositional sequences at Chahestan and Dorahi–Homag sections, respectively. Sedimentation of marine carbonates of the Guri Member on siliciclastic deposits reflects a major transgression of sea level at Lower to Middle Miocene that led to creating a new sea in the Zagros basin at that age. Increasing siliciclastic influx along with a sea level fall finally caused burying of the carbonate ramp. Except for the beginning of sedimentation of carbonate at the base of both stratigraphic sections (depositional sequence 1), most of the system tracts are not matched to global sea level curve that reflect local effects of the basin. Distribution of foraminifera suggests precipitation in tropical to subtropical in mesotrophic to oligotrophic and eutrophic to oligotrophic conditions. Based on large benthic foraminifera (porcelaneous large benthic foraminifera and hyaline larger benthic foraminifera), water temperature average was determined between 25 and 30 °C that was confirmed by analyzing oxygen and carbon stable isotopes. Finally, we have utilized achieved data to reconstruction and modeling of paleoecology, paleoenvironments, and sea level changes in the southeast part of the Zagros basin.

Chemostratigraphy (CaCO3, TOC, δ13Corg) of Sinemurian (Lower Jurassic) black shales from the Wessex Basin, Dorset and palaeoenvironmental implications

The Shales-with-'Beef' and Black Ven Marls of the Charmouth Mudstone Formation (Sinemurian) exposed on the Dorset Coast in southern England (Wessex Basin) show stratigraphic variation in carbonate, organic carbon and organic-carbon isotopes. Little environmental significance is attached to the variation of carbonate except in the case of the tabular and nodular limestones interrupting the sequence that probably record stratigraphic condensation and/or sedimentary stillstands that, in an extreme case, were accompanied by sea-floor erosion to produce the bored and encrusted ?Coinstone'. Relatively high total organiccarbon (TOC) contents are present in the laminated mudstones of the lower turneri Zone (upper brooki and lower birch Subzones) and the obtusum Zone (obtusum and stellare Subzones). Basin stratification related to fresh-water influx was the most likely aid to deoxygenation and enhanced preservation of organic matter. The organic-carbon isotope curve (δ13Corg), which shows positive excursions in the upper turneri Zone (upper birchi Subzone) and highest obtusum-raricostatum Zones (highest stellare Subzone, densinodulum and lower raricostatoides Subzones), does not correlate with the TOC stratigraphy and was clearly not controlled by local patterns of organic-matter burial. Long-term (hundreds-of-thousands of years) variations in the carbonisotope (δ13Corg) curve are interpreted as reflecting changing seawater isotopic composition and, in the case of the stratigraphically higher interval, may be related to marine organic-carbon burial on the margins of the proto-Atlantic, as exemplified by the Lusitanian Basin in Portugal. Correlation of the carbon-isotope profile with putative sea-level curves is problematic in detail, although significant local transgressive pulses in the turneri and late raricostatum Zones are approximately coincident with positive δ13Corg excursions.© 2013 Gebruder Borntraeger, Stuttgart, Germany.

Intersection of exogenous, endogenous and anthropogenic factors in the Holocene landscape: A study of the Naples coastline during the last 6000 years

New data on the ancient landscape of Naples (southern Italy) during the middle and late Holocene from geo-archaeological excavations associated with public transport works were used to reconstruct the hill and coastal environment to the west of the ancient Graeco-Roman polis, where remains of human settlements date to the late Neolithic. The rich stratigraphic and archaeological records that emerged from the digs and from previous boreholes were measured and analysed by combining sedimentary facies analysis, tephrostratigraphy and archaeological data. Between the 5th and 4th millennia BP, a rocky profile with a wave-cut platform cutting across pyroclastites emplaced from the surrounding volcanoes was predominant in the coastal landscape. During the 3rd millennium BP, this rocky coast was progressively replaced by a sandy littoral environment primarily due to marine deposition, with a coastline located some hundred meters inland with respect to the modern one. The sedimentary record of the Greek and Roman periods indicates short-term fluctuations of the coastline, leading to the establishment of a backshore environment towards the end of the 6th century AD, when prograding river mouths and lobes of debris flows contributed to the advancing trend of the shoreline. The frequent archaeological remains from these periods indicate a stable settled area since Roman times. The shoreline was still subject to short-lived fluctuations between the 12th and 16th centuries, and attained its present position during the modern era with man-made reshaping of its profile. The construction of Relative Sea Level curves for two coastal sites reveals that the persistence of the foreshore environment in the Naples coastal strip during the 5th and 4th millennia BP was controlled by the counterbalancing effect of either the concurrent eustatic sea level rise or subsidence. On the other hand, the morpho-stratigraphic record for the last two millennia shows a significant correlation between sedimentation rate and settlement history, accounting for the dominant role of the anthropogenic forcing-factor in late Holocene landscape history. In particular, land mismanagement during Late Antiquity seems to have triggered a slope disequilibrium phase, exacerbating soil erosion and increasing the sediment accumulation rate in both foothill and coastal areas. Nonetheless, the environmental changes of the Chiaia coast during the last 2000 years clearly show volcanic–tectonic perturbations influencing coastline development up to the modern era.

Reconstructed Holocene sea level curve from the Akkeshi barrier system in eastern Hokkaido, Japan

An active barrier system is present in Akkeshi Bay and a lagoonal area along the Pacific coast of eastern Hokkaido, Japan. This rare feature consists of a so-called lagoon (the Akkeshi-ko lagoon), a flood tidal delta, a barrier, and a tidal inlet that leads into the outer sea of Akkeshi Bay and the Pacific Ocean. Large oyster reefs were living on the flood tidal delta until their sudden extinction in the early 1980s. The processes involved in the formation of this barrier system during a postglacial transgression period are not well understood. Here, we use sedimentological, paleontological, and radiocarbon dating methods to analyze Holocene drillcore obtained from the Akkeshi fishing port in 2009 and borehole log data previously obtained from public works around the Akkeshi lowlands. The data obtained from both drillcore and borehole logs indicates that: (1) postglacial transgression occurred in this area some 11,400 years ago and reached 50 m below the present sea water level, with the barrier system in the study area established 8800 years ago. (2) The preservation of this barrier system is due to the stable sea level in this area. The sea level has been constant for the past 5500 years, and has led to the development of oyster reefs on the tidal flood delta. (3) The current topographically distinctive barrier system has been affected by sudden uplifts associated with giant earthquakes. These events occur every few hundred years, with the barrier undergoing prolonged but relatively rapid post-earthquake subsidence at about 1 cm/year, as observed after a giant 17th century earthquake.

Evidence for shallow-water ‘Upper Kellwasser’ anoxia in the Frasnian–Famennian reefs of Alberta, Canada

The Frasnian–Famennian extinction witnessed the global devastation of both level-bottom and reef communities in low latitudes. Marine extinctions in offshore level-bottom communities are associated with two widespread, transgressive, anoxic ‘Kellwasser Events’ that support an anoxia–extinction link. Typical Kellwasser facies of bituminous limestones and shales are not obviously recorded in shallow-water settings, and thus, it is unclear whether anoxia played a role in reef losses. We evaluate geochemical, petrographic and facies evidence for oxygen restriction from an extremely shallow-water carbonate platform in Alberta. Sequence stratigraphy places the Frasnian–Famennian boundary at a sequence boundary that tops a laminated mudstone and interrupts carbonate platform deposition. Two transgressive pulses have been identified, one of which is associated with the second, major transgression of T-R cycle IId of the Devonian eustatic sea-level curve. Geochemical proxies indicate that these transgressions were accompanied by influx of dysoxic or anoxic waters. Organic carbon and U enrichment in the Frasnian, particularly just below the Frasnian–Famennian boundary, points to episodic dysoxic conditions that probably persisted into the basal Famennian and were coincidental with the global Upper Kellwasser Event. This study provides the first evidence for the smoking gun of an anoxia-driven extinction in very shallow waters, implicating this potent killer in the demise of the Devonian reefs.

Continental shelf landscapes of the southeastern United States since the last interglacial

The wide, sediment-starved continental shelf and modern coastal areas of the southeastern United States retain well-preserved but scattered remnants of a submerged paleolandscape. This paper presents a conceptual model of stratigraphic deposition and landscape formation since the last interglacial on the continental shelf of South Carolina, with portions of North Carolina, Georgia, and Florida (USA). Data for this study include multibeam bathymetry surveys, sidescan sonar mosaics, high-resolution subbottom profiles, and ground-truth surveys from −250m to the modern tidewater region.Four bathymetric zones are recognized with eleven landforms and landform indicators. The described zones range in depths from the modern shoreline, across the shelf, and over the shelf edge to −250m MSL. Relative sea level curves are presented for the area and discussed in conjunction with cultural and climatic events.The potential for preservation of Paleoamerican sites is high at the shelf edge between −130m and −45m, with Archaic and later occupations likely in depths of less than −25m. Prominent vantage points for Paleoamericans (>11kya) would have existed at the shelf edge, and tidewater resources would have been available nearby for a period of almost 6ka. Rapid transgression rates (>60km/ka) after the sea level rose over the shelf edge make preservation of tidewater sites less likely on the outer and middle shelf. Searches for the earliest Paleoamericans should focus on promontories at the edge of the shelf and along future discoveries of paleoincisions on the shelf. Mapping and delineating this paleolandscape and associated unconsolidated sedimentary deposits interspersed with rocky plains and ledges will continue to be a priority to marine archeologists, coastal managers, fishery scientists, and marine spatial planners over the next several decades.

The flooding of the San Matías Gulf: The Northern Patagonia sea-level curve

Northern Patagonia is characterised by tectonic depressions below present sea level. Some of them are today flooded by the sea; others remain emerged although they are at altitudes of −50m (Bajo del Gualicho), −35m (Salinas Grandes) and −7m (Salina La Piedra). San Matías Gulf also was such an emerged depression below contemporary mean sea level during the Late Pleistocene. It flooded between 11,500 and 11,000years ago, when the sea level surpassed the sill of the gulf (today 50m below mean sea level) during postglacial sea-level rise. In those days, shrublands extended on the slopes of the tectonic depression. In-situ pieces of woods dredged from the bottom of the gulf at depths of 70m gave a conventional age of 11,310±150years BP. We used the wood, together with dated shells from the continental shelf, and shells and organic matter dated from the San Blas, Negro and Chubut coastal plains to construct a sea-level curve. Sea level rise surpassed the present level somewhat before 6000years BP, reaching a maximum stand of +6m. It has since gently diminished towards present sea level.

Carbon and oxygen isotope stratigraphy of the oxfordian carbonate rocks in Amu Darya basin

Based on the detailed research on petrologic and geochemical characteristics of deposition and diagenesis of Oxfordian carbonate rocks in Amu Darya Basin, Turkmenistan, carbon and oxygen isotopes were analyzed. The results show that the paleoenvironmental evolution reflected by the samples with well-preserved original carbon isotopes coincides with the carbon-isotope stratigraphic curve and is almost consistent with the global sea-level curve, the Mid-Oxfordian wide transgression, and the positive carbon-isotope excursion event. The Mid-Oxfordian continuing transgression not only laid the foundation for the development of the Oxfordian reef and shoal reservoirs in Amu Darya Basin but also provided an example for the Oxfordian global transgression and the resulting development of reefs and banks and high-speed organic carbon burial events. The response of oxygen isotopes in diagenetic environment showed that micrite limestones and granular limestones underwent weak diagenetic alteration, and the samples largely retained the original seawater features. Dolomitization and the precipitation of hydrothermal calcites filling solution vugs and fractures before hydrocarbon accumulation occurred in a closed diagenetic environment where the main controlling factor is the temperature, and the diagenetic fluids were from the deep hot brine. The chalkification of the limestones after hydrocarbon accumulation occurred in the oilfield water systems.

A near‐field sea level record of East Antarctic Ice Sheet instability from 32 to 27 Myr

Fossil, facies, and isotope analyses of an early high‐paleolatitude (55°S) section suggests a highly unstable East Antarctic Ice Sheet from 32 to 27 Myr. The waxing and waning of this ice sheet from 140% to 40% of its present volume caused sea level changes of +25 m (ranging from ‐30 to +50 m) related to periodic glacial (100,000 to 200,000 years) and shorter interglacial events. The near‐field Gippsland sea level (GSL) curve shares many similarities to the far‐field New Jersey sea level (NJSL) estimates. However, there are possible resolution errors due to biochronology, taphonomy, and paleodepth estimates and the relative lack of lowstand deposits (in NJSL) that prevent detailed correlations with GSL. Nevertheless, the lateral variations in sea level between the GSL section and NJSL record that suggest ocean siphoning and antisiphoning may have propagated synchronous yet variable sea levels.

Relative sea level during the Holocene in Uruguay

A curve of the relative sea level during the Holocene in Uruguay was constructed based on data from beach storm deposits. The error envelope was too great to register small but significant oscillations, but the number of points used and the coincidence between our data and that from the literature show that in Uruguay the sea level was above the present level approximately 6000years BP and has been declining since then. The non-parametric smoothing technique used favours a smooth declining sea level curve similar to that proposed for the coast of Brazil (different slope).

Sequence and Biostratigraphy of Lower Cenozoic Succession in the Kopet-Dagh Basin, NE of Iran

The main purpose of this paper is the sequence stratigraphy and biostratigraphy of lower Tertiary sediments on the base of larger benthic foraminifera in northeast of Iran (Chehel-Kaman Formation). This formation mainly consists of Limestone, dolomite and interbeds of sand, shale and evaporate sediments. Petrographical studies indicate that these sediments may have been deposited on a shallow carbonate platform ramp and consist of 4 carbonate lithofacies (15 subfacies). These lithofacies may have been deposited in open marine, shoal, lagoon and tidal flat environmental conditions. Sequence stratigraphy analysis led to identification of 4 third-order depositional sequences, bounded by type 2 (within the top of the underlying Pestehleigh Formation) and type 1 sequence boundaries (paleosol). Interpreted sea level curve in this basin can be relatively correlated with global curves during Paleocene time and a with a sea-level fall occurred in the latest Paleocene, followed by a rise in the earliest Eocene. Biostratigraphy study led to the identification of 32 larger benthic Foraminifera genera. The Paleocene/Eocene boundary has been probably recorded as a thin red paleosol horizon (~10 - 15 cm).

Pennsylvanian to Lower Permian (Desmoinesian-Wolfcampian) fusulinid biostratigraphy of Midcontinent North America

Midcontinent North American Middle Pennsylvanian-Lower Permian (Desmoinesian-Wolfcampian) fusulinid foraminiferal species range charts were plotted and new fusulinid zones were defined. The species range charts were plotted together with lithostratigraphic columns and cyclothemic sea level curves in order to compare biostratigraphic, lithostratigraphic, and glacio-eustatic patterns. The fusulinids Beedeina and Wedekindellina appeared during widespread early Desmoinesian transgressions and characterized that interval. The mid-Desmoinesian extinction of Wedekindellina and turnover of Beedeina species coincided with a lowstand followed by a widespread transgression, generally higher sea levels, and changing paleoclimatic patterns. Beedeina went to extinction near the Desmoinesian-Missourian sequence boundary. The earliest Missourian is barren of fusulinids in the Midcontinent, followed by a thin zone of Eowaeringella, and then the appearance of Triticites, which dominated fusulinid faunas through the remainder of the Upper Pennsylvanian. Lower and Middle Missourian Triticites have relatively small tests and plane septa. In the Upper Missourian, Triticites became medium-sized with more complex septal fluting, and Kansanella appeared. In the uppermost Missourian and lower Virgilian, most Triticites are medium-sized and evenly biconvex, and have weak septal fluting. Kansanella gradually declined through the lower Virgilian and disappeared in the lowest middle Virgilian. The middle Virgilian is dominated by medium to large Triticites with complex septal fluting, and Dunbarinella appeared and became locally common. The upper Virgilian has mostly large inflated Triticites and the first Leptotriticites. The uppermost Virgilian (‘Bursumian’) has large Triticites, diverse Leptotriticites, and the first primitive elongate Schwagerina. That fauna extends across the new conodont-based Pennsylvanian-Permian (Virgilian-Wolfcampian) boundary, and the first definitive Wolfcampian (Lower Permian) fusulinids did not appear until the Neva Limestone, which is a couple cycles above the new systemic boundary. Most significant fusulinid biostratigraphic changes correlate with major glacio-eustatic cyclothem boundaries, but not all major cyclothem boundaries have significant faunal turnovers. Fusulinid zonal boundaries that were based on only fusulinid species ranges were found to closely approximate maximum sea level lowstands. Most new genera and species appear in the regressive phases of the next cyclothem, probably because faunal migrations occurred during maximum flooding events, and subsequent highstand system tracts had more paleoenvironmental diversity and thus more niches to fill.

MIDDLE EAST GEOLOGIC TIME SCALE 2013

ABSTRACT During the Aptian 28 to possibly 34 transgressive-regressive “fourth-order” sequences were deposited on the Arabian Plate. The sequences were controlled by sea-level fluctuations with a relative amplitude of 5–20 m. The fluctuations are interpreted as the glacio-eustatic response to orbital-forcing and assumed to have an average duration of 405 Kyr corresponding to the long-eccentricity orbital cycle. The sequences are referred to as “stratons” and calibrated in the orbital time scale of Matthews and Al-Husseini (2010, abbreviated M&H-2010). An independent study by Huang et al. (2010) counted nearly 33 cycles of 405-Kyr in a deep-marine Aptian succession in the Piobicco core in central Italy. The Italian cycles and Arabian stratons can be correlated in GTS 2004 by the position and age of the oceanic anoxic event OAE1a (Selli Interval, ca. 124.5–123.1 Ma). Two lowermost Aptian stratons and at least nine upper Aptian ones show stratigraphic geometries that imply 40–50 m box-like drops in relative sea level. They provide evidence for the formation of an ice sheet, mainly in Antarctica, that held several 10s of meters sea-level equivalent. The ca. 5-Myr-long late Aptian drop started at Global SB Apt 5 (ca. 117.9 Ma), which correlates to a major eccentricity minimum predicted at 118.2 Ma in the M&H-2010 scale. Similar minima are predicted to recur every 14.58 Myr (36 × 405 Kyr), and to cause major glacio-eustatic drops and regional sequence boundaries (SB). The youngest SB 0 is predicted at 1.586 Ma, and SB 8 (118.2 = 1.586 + 8 × 14.58 Ma) is interpreted to have triggered the late Aptian glaciation. The M&H-2010 scale was tested against the high-resolution sea-level curve derived from benthic foraminiferal δ18O isotopes for the late Miocene to Holocene (9.25– 0.0 Ma, Miller et al., 2005, abbreviated Metal-2005). Antarctica’s glacio-eustatic signature is interpreted as high-frequency sea-level fluctuations with a period of 41 Kyr (obliquity) above -20 m relative to present-day sea level. The fluctuations ride up-and-down on longer-period sea-level cycles (transgression-regression) with amplitudes of 20–40 m. The cycles are bounded by prominent lowstands, have durations of 325–545 Kyr, and an average duration of 405 Kyr. Sequence Boundary SB 0 (predicted at 1.586 Ma) is interpreted at 1.54 Ma, and correlated to Calabrian Global sequence boundary Cala1 (1.54 Ma).

The Latrobe Group and the 90-million-year beach

Carbon dioxide geosequestration requires a detailed understanding of the whole sedimentary section, with particular emphasis on topseals and intraformational seals. Hydrocarbon exploration is more focused on reservoirs but requires a similar basin understanding. This extended abstract reviews the knowledge gained from petroleum exploration in the Gippsland Basin to The CarbonNet Project’s exploration program for CO2 storage. The Ninety Mile Beach on the Gippsland coast is a prominent modern-day sand fairway where longshore drift transports sediments north-eastwards along a barrier-bar system, trapping lake systems behind the coastal strip. This beach is only 10,000 years old (dating to the last glacial rise of sea level) but is built on a platform of earlier beaches that can be traced back almost 90 million years to the initiation of Latrobe Group deposition in the Gippsland Basin. Using a recently compiled and open-file volume of merged 3D seismic surveys, the authors show the evolution of the Latrobe shoreline can be mapped continuously from the Upper Cretaceous to the present day. Sand fairways accumulate as a barrier-bar system at the edge of a steadily subsiding marine embayment, with distinct retrogradational geometries. Behind the barrier system, a series of trapped lakes and lagoons are mapped. In these, coal swamps, extensive shales, and tidal sediments were deposited at different stages of the sea-level curve, while fluvial systems prograded through these lowlands. Detailed 3D seismic extractions show the geometry, orientation and extent of coals, sealing shales, fluvial channels, and bayhead deltas. Detailed understanding of these reservoir and seal systems outlines multi-storey play fairways for hydrocarbon exploration and geosequestration. Use of modern basin resource needs careful coordination of activity and benefits greatly from established data-sharing practices.

From an Estuary to a Freshwater Lake: A Paleo-Estuary Evolution in the Context of Holocene Sea-Level Fluctuations, SE Brazil

A sediment core was studied to characterize the influences of Holocene sea-level variations in the Barra Seca River valley, in the Atlantic rainforest, Linhares, Espírito Santo, southeastern Brazil. Biological proxies (pollen, spores, and sponge spicules), 14C dating, granulometry, δ13C, δ15N, C/N and major chemical elements revealed the establishment and the evolution of a paleo-estuary during the interval from ∼7700–585 cal BP. During the interval ∼7700–7000 cal BP, the study site was occupied by a bay-head delta, the inner portion of the paleo-estuary, presenting the most dense mangrove coverage of the entire record. In the interval ∼7000–3200 cal BP, the site was occupied by the central basin, possibly a consequence of the landward migration of the paleo-estuary. This interval presents reduced mangrove coverage, probably due to the permanent flooding of the valley. From ∼3200 cal BP, the marine influence at the site decreased probably as result of the seaward migration of the coast line. From ∼600 cal BP, the modern floodplain and freshwater lake were established. This interpretation is in agreement with the sea-level curves for the southeastern Brazilian coast, except for the fact that evidence of sea levels lower than the present at ∼4000 and ∼2500 cal BP as suggested by some authors were not found.

Constraints on Antarctic Ice Sheet configuration during and following the Last Glacial Maximum and its episodic contribution to sea-level rise

Abstract Marine geological studies provide a record of diachronous expansion and retreat of the Antarctic Peninsula Ice Sheet, West Antarctic Ice Sheet and East Antarctic Ice Sheet during the past c. 30 000 cal yr BP. Retreat of these ice sheets and Antarctica’s contribution to sea-level rise was largely complete by the early Holocene. Estimates of ice sheet thickness, based on maximum grounding depths, range from 640 to 1640 m on the inner continental shelf. Grounding depths on the outer continental shelf equate to minimum thicknesses of 410–950 m. Geomorphic features indicate that retreat from the continental shelf was mostly step-wise around the continent, a result of the different factors that control ice sheet behaviour and the degree to which these factors vary regionally. Thus, the nature of post-LGM (Last Glacial Maximum) sea-level rise was episodic and believed to have been punctuated by rapid pulses triggered by individual ice stream collapse. Most of these pulses would have been of sub-metre magnitudes and below the resolution of existing sea-level curves, but they would have had significant impact on coastal evolution, especially along low-gradient coasts.

The Middle and Upper Eocene sections of the Omsk trough, West Siberian Platform: Palynological, stratigraphic, hydrologic, and climatic aspects

The thorough analysis and correlation of Middle-Upper Eocene sections in the Omsk trough (southern West Siberian Platform) recovered by Borehole 9 in its axial part near the Chistoozernoe Settlement (Novosibirsk region) and Borehole 8 on the southern limb near the Russkaya Polyana Settlement (southern Omsk region) revealed hiatuses at the base and top of the Russkaya Polyana Beds, a lithostratigraphic unit defined in the Lyulinvor Formation based on its substantially fine-grained composition and poor siliceous microplankton fossil remains. The overlying Tavda Formation (Middle-Upper Eocene) is traditionally accepted to consist of two subformations. The last formation was deposited in the West Siberian inner sea isolated from the Arctic basin. Particular attention is paid to eustatic sea level fluctuation especially during the period marked by accumulation of Azolla Beds under considerable desalination of surface waters in the basin. The curve of variations in the open sea factor based on the quantitative ratio between organic-walled phytoplankton fossils and higher plant palynomorphs is correlated with the modified version of the wellknown Vail curve. It is established that the West Siberian sea level experienced a brief rise in the terminal late Eocene prior to its complete desiccation at the Eocene-Oligocene transition because of global regression in response to glaciation in Antarctica.

Relative sea-level changes during the Holocene in Bangladesh

Abstract This paper presents a reconstruction of the Holocene paleo-environment in the central part of Bangladesh in relation to relative sea-level changes 200 km north of the present coastline. Lithofacies characteristics, mangal peat, diatoms and paleophysiographical evidence were considered to reconstruct the past position and C-14 ages were used to determine the time of formation of the relative sea level during the Holocene. With standard reference datum, the required m.s.l. at the surface of five sections was calculated. The relative sea-level (RSL) curve suggests that Bangladesh experienced two mid-Holocene RSL transgressions punctuated by regressions. The curve shows an RSL highstand at approximately 7500 cal BP, although the height of this highstand could not be determined because the transgressive phase was observed in a bioturbated sand flat facies. The curve shows a regression of approximately 6500 cal BP, and the RSL was considerably lower, perhaps 1–2 m, than the present m.s.l. The abundant marine diatoms and mangrove pollens indicate the highest RSL transgression in Bangladesh at approximately 6000 cal BP, being at least 4.5 to 5 m higher than the modern m.s.l. After this phase, the relative sea level started to fall, and consequently, a freshwater peat developed at approximately 5980–5700 cal BP. The abundant mangrove pollens in the salt-marsh succession shows the regression at approximately 5500 cal BP, when it was 1–2 m higher than the modern sea level. The curve indicates that at approximately 5000 cal BP and onwards, the RSL started to fall towards its present position, and the present shoreline of Bangladesh was established at approximately 1500 cal BP and has not noticeably migrated inland since.

Last deglacial relative sea level variations in Antarctica derived from glacial isostatic adjustment modelling

We present relative sea level (RSL) curves in Antarctica derived from glacial isostatic adjustment (GIA) predictions based on the melting scenarios of the Antarctic ice sheet since the Last Glacial Maximum (LGM) given in previous works. Simultaneously, Holocene-age RSL observations obtained at the raised beaches along the coast of Antarctica are shown to be in agreement with the GIA predictions. The differences from previously published ice-loading models regarding the spatial distribution and total mass change of the melted ice are significant. These models were also derived from GIA modelling; the variations can be attributed to the lack of geological and geographical evidence regarding the history of crustal movement due to ice sheet evolution. Next, we summarise the previously published ice load models and demonstrate the RSL curves based on combinations of different ice and earth models. The RSL curves calculated by GIA models indicate that the model dependence of both the ice and earth models is significantly large at several sites where RSL observations were obtained. In particular, GIA predictions based on the thin lithospheric thickness show the spatial distributions that are dependent on the melted ice thickness at each sites. These characteristics result from the short-wavelength deformation of the Earth. However, our predictions strongly suggest that it is possible to find the average ice model despite the use of the different models of lithospheric thickness. By sea level and crustal movement observations, we can deduce the geometry of the post-LGM ice sheets in detail and remove the GIA contribution from the crustal deformation and gravity change observed by space geodetic techniques, such as GPS and GRACE, for the estimation of the Antarctic ice mass change associated with recent global warming.

The impact of the Late Holocene coastal changes on the rise and decay of the ancient city of Histria (southern Danube delta)

Histria (Istros) is one of the earliest Milesian colonies founded on the Black Sea coast during the archaic period (7th c. BC). Its remains are located within what is today the Razelm–Sinoe lagoon system which forms the southern part of the Danube Delta. During its 13 centuries of existence, Histria experienced an environment favourable for a prosperous economy (e.g. fishery, farming, grazing, pottery, marine trades) as indicated by numerous archeological finds from both in situ and elsewhere in the Black Sea and Mediterranean Sea basins. Moreover, it benefited from a strategic position on an open-coast, which was easy to defend. Important environmental changes occurred both during and after the existence of the ancient city, and the most significant are related to major shoreline displacement.This study reports Late Holocene coastal landscape changes, from the open-coast stage to the present-day lagoon system, based on numerical age determination of the paleoshorelines, stratigraphic records by cores in lagoons and beach ridges and topographic surveys. A new chronological framework is established which reports younger ages than previously suggested for the coastal morphosedimentary units of the Histria region. Further, the findings shed new light upon the evolution of the southern part of the Danube delta. The results point to the development of an ancient deltaic lobe (Dunavăţ lobe, 2000–1300 BP, associated with the southernmost Danube distributary) which was situated 10–20 km north of the settlement. The lobe was subsequently reworked by waves, providing sediments which were accumulated downdrift (southward) as a continuous beach ridge plain (Saele–Chituc) in front of the city, leading to its isolation from the sea. The abandonment of Histria (7th c. AD) coincides with the decoupling of the city from the open coast as a consequence of the shoreline progradation. The new beach ridge plain (Saele–Chituc) is affected by intense neotectonic movements which led to the recent drowning of its central part and the formation of Sinoe lagoon; the same processes affected the downdrift part of the Dunavăţ lobe and Histria and Nuntaşi Lakes. The new sea-level curve obtained for the Histria region shows relative stability within the last four millennia, with oscillations within 0 to −2 m of the current level. This contradicts the concept of a marine regression (Phanagorian) which is suggested to have occurred during the 1st millennium BC. However, a few areas containing archeological remains are currently below sea-level owing to local neotectonics.