Relative Sea-level Lowering Research Articles

Correlation of Seismic Data and Sediment Cores From the Seabed in the Medieval Harbour at Avaldsnes, Norway

ABSTRACTThis interdisciplinary study demonstrates the successful integration of non‐destructive geophysical methods and sediment core analyses for mapping the seabed in the historical harbour at Avaldsnes in south‐west Norway. In the Medieval Period, this was a royal manor, with the harbour as a central hub for the Hanseatic League in the 14th to 15th centuries. The use of an Autonomous Surface Vehicle (ASV) mounted with two distinct sub‐bottom profiler (SBP) systems facilitated the acquisition of high‐resolution seismic data, providing efficient imaging of the seafloor and subsurface layers. Sequence of fifteen sediment cores allowed for the description and dating of stratigraphy and the depositional environment. In combination, these methods provided a multidimensional understanding of the distribution of subsea sediments in the harbour, while preserving most of the archaeological context. The analysis revealed organic‐rich sediments, primarily consisting of fine detritus gyttja, accumulated over the last 1700 years, trapping certain archaeological features. Deposition of the soft sediments likely commenced due to a lower relative sea level, possibly accompanied by intensified land‐use and harbour activity. The study identified several minor anomalies in the seismic data, potentially representing artefacts of archaeological importance. An anomaly of significant size might correspond to a buried shipwreck or harbour structure. By providing a comprehensive understanding of sediment dynamics and human‐environment interactions in the harbour, the research contributes to the preservation and management of an important cultural heritage site.

Sea level changes and sequence stratigraphy of the Lower-Middle Jurassic Quse and Sewa formations in the Qiangtang Basin, central Tibet: Geochemical and palynological perspectives

ABSTRACT Sequence stratigraphy is a commonly used approach to understand basin-fill history and the occurrence of conventional reservoir and/or probable source rocks. Reconstructing a sequence stratigraphic framework in carbonates, marls, and organic-rich mudstones is challenging due to environmental, petrophysical, and sedimentological variations that can be subtle, whereas seismic data may be lacking or of limited use. For this reason, incorporation between palynological analysis and chemostratigraphic profiles is becoming increasingly common to facilitate sequence stratigraphic reconstruction. This study investigates the Quse (lower Toarcian) and Sewa formations (upper Bajocian-Bathonian) in the Bilong Co section from the Qiangtang Basin of central Tibet. Eighty-three rock samples were analysed for their whole-rock inorganic geochemical composition, of which 25 rock samples were tested for palynological and palynofacies analyses. The palynological composition defined two associations for the study section. The lower part of the Bilong Co section consisted is dominated by a moderate to high abundance of opaque phytoclasts versus low to moderate amorphous organic matter (AOM) content with a high concentration of sphaeromorphs pollen grains, revealing deposition of this interval at times of low relative sea level in fluvio-deltaic settings. The middle to upper parts of the section comprised of significantly high AOM content versus low phytoclasts and high content of sphaeromorphs pollen grains, but with increasing the relative abundance of dinoflagellate cysts, indicating a phase of high sea level. Chemostratigraphic variations relevant to changes in relative sea level delineated the subdivision of the Quse and Sewa formations into two and three third-order transgressive-regressive sequences, respectively. The collision between the Lhasa and Qiangtang blocks during the Early-Middle Jurassic is suggested to control consequent subduction and sea level highstand, especially during deposition of the Sewa Formation. Geochemical proxies that relate to shelf carbonate production are calcium, strontium, whereas proxies that relate to siliciclastics include titanium, zirconium, manganese, aluminium, and silicon, other redox-sensitive proxy like uranium is also implemented. This indicates that chemostratigraphic proxies are a promising tool for the interpretation of sea level cyclicity in terms of systems tracts and bounding surfaces.

Climate-induced denudation of the Eastern Ghat during the Holocene: A multi-proxy study from Chilika Lagoon (India)

A Holocene sediment record from Chilika Lagoon, India, suggests that changes in climate control denudation and weathering rate change. We assessed climate variability in the region and through time using multiproxy data comprising biotic and abiotic proxies. Mangrove and its associate assemblages suggest a backwater estuarine environment between ∼7.8 and 6 ka B.P. Depleted δ13Corg values during ∼7.8 to 5.5 ka B.P. indicate dominance of C3 vegetation, suggesting a warmer climate and strengthened monsoon. Enhanced δ13Corg and absence of pollen/spores are observed in the sediment layers deposited after ∼5 ka B.P., indicating arid climatic conditions with a dominance of C4 photosynthesizing plants and a relative lowering of sea level. Paleodenudation rates estimated using 10Be(meteoric)/9Be ratios varied between 556 ± 35 to 242 ± 15 t.km−2.yr−1. Phases of intense denudation occurred during 7.8–6.7 and 2.2–1 ka B.P., corresponding to Holocene Climatic Optimum and Medieval Climatic Anomaly, respectively. The degree of chemical weathering appears to have gradually increased from the early to late Holocene and correlates well (negatively) with the denudation rate. A gradual increase in the degree of chemical weathering from the early to late Holocene suggests an increase in the residence time of minerals in the weathering zone as the monsoon weakened.

10Be exposure age dating of Late Quaternary relative sea level changes and deglaciation of W Jura and NE Islay, Scottish Inner Hebrides

ABSTRACTNew 10Be exposure age dating and geomorphological mapping of emerged shoreline features in W Jura and NE Islay throw new light on the regional pattern of ice sheet deglaciation and late-glacial relative sea level change. We conclude that the oldest and highest emerged shorelines in this area were produced ~15.7–16.3 ka, shortly after ice sheet deglaciation ~16.5 ka. It is envisaged that the first incursion of marine waters into coastal areas took place close to a former ice sheet margin that oscillated in position across this part of the Scottish Inner Hebrides. The first evidence of late-glacial marine sedimentation following deglaciation consists of emerged marine terrace fragments and unvegetated gravel beach ridges, the former represented by a prominent glacio-isostatically tilted shoreline that declines in altitude NE to SW, from ~40 m above ordnance datum (OD) in NW Jura to ~19 m OD in central Islay. In W Jura, north of Loch Tarbert, spectacular staircases of up to 55 unvegetated gravel beach ridges were formed shortly after regional deglaciation, possibly within 1 ka. A preliminary estimate of the average rate of relative sea level lowering across W Jura between deglaciation and the Younger Dryas is in the order of ~7 mmyr−1. Geomorphological evidence from Shian Bay, W Jura, indicates a truncation of the late-glacial beach ridge staircases by a large 480-m-long beach ridge (the Colonsay Ridge) at ~14.9 ka, when former relative sea level was at ~18 m OD. This ridge may represent the product of either a stillstand in the progressive lowering of relative sea level during the late-glacial or a reversal. This raises the intriguing possibility of an association between ridge formation and the timing of the well-established global meltwater pulse 1A between ~14.65 and ~14.8 ka.

Late-Holocene sea levels from vermetids and barnacles at Ponta do Papagaio, 27° 50′S latitude and a comparison with other sectors of southern Brazil

The height difference between paleo-vermetids and present homologous bioconstructions remains as the best Mid- to Late-Holocene paleo-sea level indicator on the Brazilian coast. The vertical range of the vermetid bioconstructions and, consequently, their precision as a sea-level indicator, varies from ±0.1 to ±1.0 m according to local conditions such as wave energy exposure and tidal range. However, live vermetid bioconstructions are scarce or do not occur at several places south of 23°S latitude, which has led to the use of other bioconstructions (e.g. Phragmatopoma caudata) as a homologous reference level, adding uncertainties to the paleo-sea level reconstructions. At the Southeast Brazilian coast, from 25° 30′ S to 28° 37′ S latitude, the precision varies from ±0.5 to ±1.0 m. At the Ponta do Papagaio headland, at 27°50′38″- 44″ S latitude, the occurrence of the subfossil barnacle Tetraclita stalactifera included in the remains of Holocene vermetids (Petaloconchus varians (d'Orbigny, 1839)) bioconstructions allowed the authors to adopt the living fringe of this barnacle species as a homologous reference level and thereby improve the accuracy of paleo-sea level reconstructions (error margin of only ± 0.5 to ± 0.3 m). The paleo-sea level obtained at Ponta do Papagaio by this method varied between +2.4 and 0.8 m. The resultant relative sea-level curve is included in the empiric sea-level envelop previously determined for the Brazilian coast, south of 28°S latitude, and matches with the far-field eustatic sea-level models. It is also similar to other curves defined for Southern Brazil regions such as Laguna-Imbituba (Santa Marta Cape surroundings, 85-40 km to South from Ponta do Papagaio), São Francisco do Sul (180 km North) and Paraná (220–260 km North). However, the height of 2.4 ± 0.3 m at 4 ky BP at Ponta do Papagaio is similar to the two cited regions to the North, but higher than the one at Laguna-Imbituba for the same period. This difference may not be significant, as it is within the ±1.0 m error margin adopted in the inference of the paleo-sea level at Laguna-Imbituba. If it is significant, it can be attributed to a local lowering of relative sea-level by thermosteric and dynamic effects of the Santa Marta Cape coastal upwelling strengthening at the epoch of maximum sea-level. This work also suggests further quantification of the living vertical distribution of vermetids and other species used as reference species (e.g. Tetraclita stalactifera, Phragmatopoma caudata), under different bedrock morphology, wave exposure and oceanographic conditions, as a necessary way to improve the precision of paleo-sea level reconstructions.

Holocene filling of a narrow estuary in a regressive coast: The Paleo-Kinu Bay region, central Japan

Estuaries are typical depositional systems of transgressive coasts; however, depositional systems with similar geometry also occur on regressive coasts. Such “regressive estuaries” are found in areas of Asia, South America, and Australia that have experienced relative sea-level lowering since the middle Holocene. Regressive estuaries form in incised valleys that were drowned by the last deglacial sea-level rise and receive relatively little riverine sediment discharge. The largest estuary in Japan, with a length of 120 km and a width of 10 km, is in the Paleo-Kinu Bay region. A partly unfilled wave-dominated estuary developed in this region prior to the artificial diversion of the Tone River during the 17th century. In this study, we document the Holocene filling of the Paleo-Kinu Bay on the basis of 14 sediment cores and 171 radiocarbon dates. Unfilled wave-dominated estuary at 7–4 ka has more pronounced wave-built morphologic elements than at 4–0 ka. As a result of sea-level lowering and weakening of tidal currents at 4–0 ka, the bay mouth became narrowed by lateral accretion of sandy tidal river sediments and the central basin was filled by progradation of muddy bayhead delta sediments. The acceleration of the bay mouth narrowing and central basin infilling similar to what happened during 4–0 ka in the Paleo-Kinu Bay region have not been identified in transgressive estuaries, but are common features of regressive estuaries.

SEQUENCE STRATIGRAPHY, PALAEOGEOGRAPHY AND PETROLEUM PLAYS OF THE CENOMANIAN – TURONIAN SUCCESSION OF THE ARABIAN PLATE: AN UPDATED SYNTHESIS

In order to facilitate the search for new play concepts and exploration opportunities, a sequence stratigraphic synthesis of the Cenomanian–Turonian interval of the Arabian Plate has been compiled. The synthesis is based on published datasets which have been analysed within a temporal framework constrained by biostratigraphy and isotope stratigraphy. The high stratigraphic resolution allows the palaeogeography of the study area to be mapped within 3rd order depositional sequences, and the relative influence of eustacy and tectonics on basin development to be evaluated. This significantly improves the prediction of stratigraphic architecture and depositional morphology at the scale of the entire tectonic plate.Conceptual models informed by outcrop and subsurface observations have been applied to characterize the development of intrashelf basins in depositional settings that are either isolated from siliciclastics (symmetric intrashelf basin model) or influenced by siliciclastics (asymmetric intrashelf basin model). The application of a sequence stratigraphic model across regional well log transects facilitates an understanding of stratigraphic architecture and acts as an important control for the generation of a new suite of gross depositional environment (GDE) maps. These maps characterize the palaeogeography at a previously unprecedented resolution and scale during both periods of high relative sea level (maximum flooding surface and highstand systems tract) and low relative sea level (lowstand systems tract). The maps are complemented by sequence isopachs which reveal changes in accommodation through time and space.This approach helps characterize the preserved distribution and stratigraphic configuration of petroleum systems elements. In the Shilaif (UAE), Natih (Oman) and Sarvak (Iran) intrashelf basins, condensed, organic‐rich carbonate source rocks were deposited in restricted, anoxic conditions. These basins resulted from differential aggradation of the carbonate platform during the transgressive systems tract. Grainy, rudist‐debris –rich carbonate reservoir rocks developed along the margins of the intrashelf basins during highstand progradation. Claystones in the overlying sequence may form intraformational seals and were deposited during retrogradation of the shoreline associated with sea‐level rise.By contrast in the Najaf intrashelf basin (Iraq), there is a significant siliciclastic component sourced from the Arabian Shield. This influx resulted in a mixed carbonate‐siliciclastic ramp depositional system on the proximal, western margin of the basin, and an apparent absence of organic‐rich intervals within the central basin succession. Grainy carbonate reservoir rocks are restricted to the eastern margin and are charged by older source rocks within the underlying stratigraphy.The GDE maps record the configuration of these petroleum systems elements within the Cenomanian–Turonian interval and form the basis for play screening. The Cenomanian–Turonian interval is punctuated by the major mid‐Turonian unconformity which is a tectonostratigraphic boundary of considerable geological and economic significance. In the southern and eastern part of the Arabian Plate, this unconformity has a differential erosion profile that facilitates a subcrop play with exploration potential. Identifying subtle stratigraphic traps is challenging, but by combining GDE facies with the mapped preservation limit for each sequence, it is possible to identify areas where rudist‐rich reservoir facies with potential karst enhancement are overlain by a regional claystone seal, high‐grading areas with subcrop trap potential.

Sedimentology and lithofacies of organic-rich Namurian Shale, Namur Synclinorium and Campine Basin (Belgium and S-Netherlands)

Organic-rich Namurian A mudstone is the main potential shale gas play in Belgium and neighboring countries. In order to reveal the regional depositional setting and its influence on lithofacies and origin of organic matter, this study investigates lithofacies, depositional processes and mechanisms controlling organic matter accumulation based on analysis of sedimentary structures, grain size, mineralogy, optical petrography, pyrite framboid diameter, total organic carbon and gamma log in five wells from Namurian A mudstone in Belgium and the southern part of the Netherlands. These mudstones, located in the Namur Synclinorium and Campine Basin, consist of an organic-rich mudstone succession that was deposited in the epicontinental basin within the Variscan foredeep within a moderate deep water environment below storm wave base in a distal shelf to basin floor setting under mainly euxinic and anoxic conditions with occasional dysoxic and oxic conditions. These sediments were deposited through various processes, including turbidity currents, debris flows, pelagic suspension settling with minor contribution of bottom currents, slumping processes and storm events. Lithofacies stacks generate repeated regressive and transgressive units. In the Campine Basin and the western Namur Synclinorium, 3 regressive units are characterized by basal lithofacies derived from pelagic suspension settling changing upward to lithofacies derived from mainly turbidity currents and debris flows while 2 transgressive units are characterized by basal lithofacies derived from mainly turbidity currents and debris flows changing up to lithofacies from pelagic suspension settling. In contrast in the eastern Namur Synclinorium which reflects a more proximal depositional setting, only 2 regressive units were identified. They are characterized by basal lithofacies derived from turbidity currents and debris flows changing upward to lithofacies from debris flows, bottom currents and slumping processes. 2 transgressive units were also identified. The first unit is characterized by basal breccia from karstification while in the second unit, lithofacies evolve from debris flows and slumping processes changing upward to lithofacies deposited from turbidity currents, debris flows and bottom currents. Overall, carbonate and silica dominated lithofacies from pelagic suspension settling with minor input from debris flows were deposited during high relative sea-level under euxinic to anoxic conditions. Quartz-rich lithofacies from debris flows and turbidity currents with minor input from pelagic suspension settling and bottom currents were deposited during intermediate relative sea-level under anoxic conditions. In contrast, clay, silt and carbonate-rich lithofacies from turbidity currents, debris flows, bottom currents, slumping processes and storm events were deposited during low relative sea-level under anoxic to dysoxic conditions with occasional oxic conditions near the basin margin. The highest total organic carbon observed in lithofacies from intermediate relative sea-level is caused by relative high primary marine productivity with dominant marine organic matter, low siliciclastic dilution and excellent preservation under anoxic conditions. Organic matter accumulation is low in lithofacies deposited during high and low relative sea-level. During high relative sea-level, it was controlled by clay mineral content, organic matter consumption and carbonate dilution, while during low relative sea-level, it was controlled by water redox conditions and siliciclastic dilution.

Mid- to late-Holocene analysis of the influence of the La Plata River plume on the southwestern Atlantic shelf: A paleoenvironmental reconstruction based on lipid biomarkers and benthic foraminifera

A combined analysis of sedimentological, molecular, and microfossil proxies was used to determine paleoclimatic and paleoceanographic variations and assess sediment transport pathways along the last c.a. 6300 years in a sedimentary record collected on the inner shelf of the southwestern Atlantic Ocean. The combined use of terrestrial and marine proxies enables a more complete environmental perspective of the La Plata River plume influence on the southwestern Atlantic shelf, regarding the relationship between climate, productivity, as well as hydrodynamic. Variations in marine productivity, lipid biomarkers of terrestrial plants, diagnostic geochemical indices, and sea-surface temperature point to three phases within the core. The first interval (6300–5200 cal yr BP) was characterized by low marine and terrigenous organic matter input, with pulses of phytodetritus indicated by benthic foraminifera. These features suggested dry climatic conditions over the southeastern portion of South America, with the influence of sediments from the adjacent continent and, on a smaller scale, transported from the Argentinian shelf due to the high relative sea level. The second interval (5200–2800 cal yr BP) was distinguished by a slight increase in marine productivity and terrigenous input, indicating a transition period with an increase of total rainfall influenced by an intensified South American Monsoon System (SAMS) and the modern El Niño-Southern Oscillation (ENSO) phenomenon. These features, associated with the changes in wind patterns and the lower relative sea level, suggest the onset of the influence of the La Plata River (LPR) plume over the southern regions of the Brazilian continental shelf for the last 6300 cal yr BP. The last interval (2800–890 cal yr BP) had the highest contents of marine and terrigenous proxies, suggesting less climatic variability, as the long-term intensification of the SAMS and a further increase in the amplitude of the ENSO resulted in the modern establishment and dominant influence of the LPR plume on the core site. Variations in sea-surface temperature up to 3.3°C were related to the influence of the LPR plume on the shelf off southern Brazil.

New relative sea-level (RSL) indications from the Eastern Mediterranean: Middle Bronze Age to the Roman period (~3800-1800 y BP) archaeological constructions at Dor, the Carmel coast, Israel.

This article presents new archaeological observations and multidisciplinary research from Dor, Israel to establish a more reliable relative sea level for the Carmel Coast and Southern Levant between the Middle Bronze Age and the Roman period (ca. 3500-1800 y BP). Our record indicates a period of low relative sea level, around -2.5 m below present, from the Middle Bronze Age to the Hellenistic period (ca. 3500-2200 y BP). This was followed by a rapid rise to present levels, starting in the Hellenistic period and concluding during the Roman period (ca. 2200-1800 y BP). These Roman levels agree with other relative sea-level indications from Israel and other tectonically stable areas in the Mediterranean. Several relative sea-level reconstruction models carried out in the current study provide different predictions due to their parameters and do not model the changes observed from field data which points to a non-isostatic origin for the changes. Long-term low stable Iron Age relative sea level can be seen in Dor, where Iron Age harbor structures remain around the same elevation between ca. 3100-2700 y BP. A similar pattern occurs at Atlit, the Iron Age harbor to the north used continuously from ca. 2900 y BP to the beginning of the Hellenistic period (ca. 2200 y BP). An examination of historical and archaeological sources reveals decline and occasional disappearance of Hellenistic sites along the coast of Israel at ca. 2200 y BP (2nd century BCE), as in the case of Yavneh Yam, Ashdod Yam, Straton's Tower, and tel Taninim. In Akko-Ptolemais, the large harbor installations built in the Hellenistic period were never replaced by a substantial Roman harbor. The conclusions of this research are thus relevant for the sea-level research community and for the historical analyses of the Israeli and South Levantine coastline.

High-resolution chemostratigraphy in carbonate mudstones: Salina A-1 carbonate (Silurian), Michigan Basin, U.S.A.

Portable Energy-Dispersive X-Ray Fluorescence spectrometry (PXRF) is routinely used to identify stratigraphic variations in the elemental chemistry of fine-grained siliciclastics. The application of this approach in carbonates is limited, however. In this study, over 9000 PXRF analyses from nine drill cores are used to document cm-scale variations in the carbonate mudstones of the A-1 Carbonate (Silurian) in the Michigan Basin. High-resolution elemental data are integrated with petrographic and mineralogical observations to evaluate the extent to which: (i) basin-center mudstones in the A-1 Carbonate (A-1C) have spatially correlative elemental signatures (i.e. chemofacies), and (ii) elemental variations reflect temporal changes in relative sea-level and sedimentation.Spatially correlative variations in concentrations less than 5 wt% of Si, Al, K, and S are observed throughout the A-1C. Higher concentrations of Si, Al, and K are associated with more abundant siliciclastic minerals as determined petrographically and with x-ray diffraction, and are thus interpreted to reflect intensification of siliciclastic sedimentation caused by relative sea-level fall. Associated S increases reflect a higher abundance of anhydrite, which is interpreted as diagenetically altered gypsum deposited during periods of low relative sea-level. Chemofacies successions for siliciclastic and evaporite proxy elements indicate four transgressive-regressive cycles. Collectively, these data show that variations in the minor, non-carbonate sediment fraction within the A-1C are regionally correlative suggesting that siliciclastic and evaporite deposition responded in tandem to basin-wide controls on sedimentation. The observed relationship between siliciclastics and evaporites further exemplifies the broader utility of quantifying the elemental signatures and non-carbonate mineral compositions in carbonate-dominated strata to constrain sequence stratigraphic interpretations. These findings add to a growing body of work that demonstrates the utility of PXRF to generate reliable geochemical data sets and highlights the importance of integrating elemental and mineral data in sedimentological interpretations.

Understanding the Internal Variability of Mudstones: Dark Mudstone of the Campano- Maastrichtian Mamu Formation as Case Study

The objective of this research work was to investigate approximately 6m of Campano-Maastrichtian dark mudstone outcropping at Uzebba, Benin Flank, SW Anambra Basin using sedimentological, geochemical, mineralogical, and palynofacies techniques. Our findings show that the mudstone succession can be subdivided into 3-broad units from bottom to top. Unit 1 is characterized by weak to moderate bioturbation, high quartz content (≥50 %) as well as grained dominated microfabric with planar to wavy laminations. Unit 2 has the lowest particle size, zero to mild bioturbation, low quartz content as well as matrix dominated microfabric with thin to indistinct laminations, which are mostly planar. Unit 3 show intermediate particle size, weak to moderate bioturbation, moderate quartz content as well as grain dominated microfabric with much thicker laminations than units 1and 2 that vary from wavy to curved. Geochemical and palynofacies proxies for detrital influx and paleoproductivity are congruent. They show that units 1 and 3 received significant detrital contribution as well as high terrestrial paleoproductivity under low relative sea level, which promoted the development of good petrophysical and geomechanical properties suitable for gas shale development. Conversely, Unit 2 received less significant detrital contribution as well as increased marine paleoproductivity under higher relative sea level. 
 Keywords: Detrital influx, paleoproductivity, unconventional reservoirs, Benin flank

Geochemistry and palynology of the upper Albian at the Abu Gharadig Basin, southern Tethys: Constraints on the oceanic anoxic event 1d

The mid‐Cretaceous period was a time of abnormal polar temperature warming and consequent global oceanic anoxia that enhanced the widespread accumulation of organic matter‐rich marine sediments. The current contribution focuses on the late Albian oceanic anoxic subevent 1d (OAE 1d) that represents a period of increased perturbation of the global carbon cycle. Palynological and geochemical investigations, including TOC/Rock‐Eval pyrolysis and stable carbon isotope of organic matter (δ13CTOC), were conducted for the upper part of the Kharita Formation from the Abu Gharadig Basin, north Western Desert, Egypt, to (a) confirm the age of this unit, (b) assess the depositional environments and prevalent redox conditions, and (c) confirm the occurrence of the OAE 1d within the sedimentary record in this part of the southern Tethys. Based on the TOC content and Rock‐Eval pyrolysis parameters, the organic matter in the upper Kharita Formation is expected to have a limited hydrocarbon generation potential consisting of gas only. The sedimentation patterns and role of continental weathering and runoff influx were assessed through trace element ratios and relationships. Redox conditions were interpreted based on Stotal–TOC relationship, Stotal–TOC–Fetotalternary plot, Rock‐Eval S2, trace element proxies and relationships (including Cr vs. V + Ni, V/Cr vs. Stotal, and Stotal/Fe vs. Mn/Stotal). The ratio of TOC/Ptotalwas implemented to assess both marine primary productivity and oceanic anoxia during this period. Biostratigraphic constraints showed that the upper part of the Kharita Formation spanned a late Albian age (Cretacaeiporites densimurusInterval Zone). Results showed that the OAE 1d was characterized by organic matter deposition during dysoxic‐suboxic to anoxic redox conditions in a fluvio‐deltaic to shallow marine depositional environment in this part of the Tethys. A low to moderate primary productivity was also prevalent during a fairly high rate of sediment accumulation. Regional correlation of positiveδ13CTOCexcursion during the OAE 1d throughout the Tethys and Atlantic oceans matched well, in several parts, with the current study interval that confirm the global distribution of the OAE 1d. In this region of the southern Tethys, an overall collapse of water column stratification during the OAE 1d principally related to decreased terrestrial input at low relative sea level, as evidenced from freshwater algaePediastrumand pteridophyte sporeCrybelosporites pannuceus; however, orbital forcing likely induced monsoonal activity at low‐latitudes in the SE, N, and W Tethys.

Postglacial evolution of marine and lacustrine water bodies in Bunger Hills

AbstractUnglaciated coastal areas in East Antarctica provide records of past ice sheet and glacier fluctuations and subsequent environmental conditions. In this paper we review lithological, geochemical, diatom and radiocarbon data from sediment records from inland and epishelf lakes in Bunger Hills, East Antarctica. While some hilltops were unglaciated during the Last Glacial Maximum, till deposits in lake basins indicate infilling by glacier ice prior to the Holocene. Proglacial sedimentation occurred in lakes during the early Holocene. Around 9.6 kabp, deposition of marine sapropel started under relatively warm climate conditions. Inland lakes were affected by high clastic input from meltwater runoff untilc.7.9 kabp, when deposition became highly organic and biogenic proxies indicate a period of cooler conditions. Epishelf lakes experienced a decrease in water exchange with the ocean and increased freshwater input around 7.7 ± 0.2 kabpand after 2.2 kabp. This probably resulted from grounding line advances of the bounding glaciers, which could be either controlled by relative sea level (RSL) lowering and/or climate-driven glacier dynamics. The absence of marine sediments in the postglacial record of Algae Lake indicates that Holocene RSL probably reached a maximum at or below 10 m above present sea level.

Medieval relative low sea-level indications from the Peloponnese and the Aegean Sea

This research is an interdisciplinary study of changes in relative sea level (RSL) in the Peloponnese and the Aegean Sea during the last 1000 years that links archaeological sea-level indicators, from medieval constructions and historical accounts with geological processes. Site survey was conducted in the south Peloponnese, Crete and Paros Island. The study evaluates the 'functional height' of the archaeological remains and dates them based on archaeological and historical records. The archaeological indicators were compared to other indications made by previous studies and to the predicted RSL. The results correlate with the RSL indications in previous studies, but they are below the predicted curve. The difference can be attributed to both the Glacial Isostatic Adjustment (GIA) and to tectonic contributions, which are in agreement with other studies in the area. The current study calculates a low RSL of about −1.3m in the south Peloponnese of the 5th century CE, rising gradually to about −0.5 m at the 15th century. In the Cyclades Plateau RSL of −1.2m is estimated for the end of 13th century, climbing to −0.7m by the beginning of the 16th century. The archaeological sea-level indicators in the south Peloponnese and the Aegean Sea confirm the low medieval sea levels found in other Mediterranean sites.

Cenomanian–Turonian depositional history of a post–Gondwana rift succession in the West Beni Suef Basin, Egypt

The structural and stratigraphic evolution of rift basins has been documented globally from modern systems, outcrop and subsurface datasets. Extensive fragmentation and break-up of Gondwana during the Cretaceous created a complex suite of rift basins in the Northern Africa. The Beni Suef rift basin straddles the River Nile and is infilled by a thick Mesozoic–Tertiary succession. Cenomanian–Turonian deposition commenced with the sandstone-dominated Bahariya Formation. Depositional environments transitioned stratigraphically from fluvial-marine to shallow marine and finally to mixed clastic and non-clastic shelfal deposits of the Abu Roash Formation. Sedimentation styles were tectonically controlled showing transgressive-to-regressive depositional cycles developed over the Gondwana rift systems. Cycles were controlled by short-lived, small-scale tectonic oscillations of the platform, resulting in four depositional sequences. Deposition environments in the Cenomanian transitioned from shallow marine to deeper marine shelfal deposits and finally to a coastal environment. During Late Cenomanian–Early Turonian, rapid platform submergence resulted in a transgressive facies succession, topped by deltaic deposits. In the Middle–Upper Turonian, two sequences formed with an intervening short-lived period of lower relative sea level. Relative sea-level oscillations were partly in phase with the global sea-level changes, controlled by local tectonics induced by the fragmentation of Gondwana during the Late Cretaceous.

Climatic and anthropogenic impacts on the Ría de Vigo (NW Iberia) over the last two centuries: A high-resolution dinoflagellate cyst sedimentary record

A high-resolution dinoflagellate cyst record spanning the period of ~1830–2012 CE from Ría de Vigo (Atlantic margin of NW Iberia) is presented. Changes in concentrations and percentages of dinoflagellate cysts and freshwater algal spores reflect climatic and anthropogenic influences on the ria, i.e. coastal inlet formed by the partial submergence of a river valley. Statistical analyses (PCA and clustering) were used to identify the main patterns of change in the cyst assemblages. The cyst record was compared with reconstructed and measured instrumental environmental data (NAO, temperatures, mean sea level, etc.) to support (palaeo)reconstructions. Four main phases were identified: the first phase (~1830–1855 CE) of lower relative sea level (RSL), temperatures and precipitations represents the last stages of the LIA (Little Ice Age); the second phase (~1855–1910 CE) is interpreted as a transition between the colder LIA and the wetter and warmer conditions that prevailed through the 20th century; the third phase (~1910–1975 CE) is characterized by strong river inputs and water stratification in the ria; and the fourth phase (~1975–2012 CE) reflects impacts of anthropogenic warming and pollution. The anthropogenic signal consists of increases in heterotrophic cyst proportions and cysts diversity, as well as of a marked decline of potentially toxic Lingulodinium machaerophorum. Increasing organic matter content, nutrients and industrial wastes have likely caused detrimental impacts on the autotrophic dinoflagellates, by increasing turbidity and toxicity. The B5-cyst record and its comparison with previously published data suggest that increased concentrations of L. machaerophorum in the 20th century were mainly related to river flow variations, that in turn were primarily driven by NAO changes, rather than cultural eutrophication. We also report high abundances of Peridinium ponticum in our record, determining that this species is not exclusive to the Black and Marmara Seas and has much wider natural distribution.

Land–sea coupling of early Pleistocene glacial cycles in the southern North Sea exhibit dominant Northern Hemisphere forcing

Abstract. We assess the disputed phase relations between forcing and climatic response in the early Pleistocene with a spliced Gelasian (∼2.6–1.8 Ma) multi-proxy record from the southern North Sea basin. The cored sections couple climate evolution on both land and sea during the intensification of Northern Hemisphere glaciation (NHG) in NW Europe, providing the first well-constrained stratigraphic sequence of the classic terrestrial Praetiglian stage. Terrestrial signals were derived from the Eridanos paleoriver, a major fluvial system that contributed a large amount of freshwater to the northeast Atlantic. Due to its latitudinal position, the Eridanos catchment was likely affected by early Pleistocene NHG, leading to intermittent shutdown and reactivation of river flow and sediment transport. Here we apply organic geochemistry, palynology, carbonate isotope geochemistry, and seismostratigraphy to document both vegetation changes in the Eridanos catchment and regional surface water conditions and relate them to early Pleistocene glacial–interglacial cycles and relative sea level changes. Paleomagnetic and palynological data provide a solid integrated timeframe that ties the obliquity cycles, expressed in the borehole geophysical logs, to Marine Isotope Stages (MIS) 103 to 92, independently confirmed by a local benthic oxygen isotope record. Marine and terrestrial palynological and organic geochemical records provide high-resolution reconstructions of relative terrestrial and sea surface temperature (TT and SST), vegetation, relative sea level, and coastal influence. During the prominent cold stages MIS 98 and 96, as well as 94, the record indicates increased non-arboreal vegetation, low SST and TT, and low relative sea level. During the warm stages MIS 99, 97, and 95 we infer increased stratification of the water column together with a higher percentage of arboreal vegetation, high SST, and relative sea level maxima. The early Pleistocene distinct warm–cold alterations are synchronous between land and sea, but lead the relative sea level change by 3000–8000 years. The record provides evidence for a dominantly Northern Hemisphere-driven cooling that leads the glacial buildup and varies on the obliquity timescale. Southward migration of Arctic surface water masses during glacials, indicated by cool-water dinoflagellate cyst assemblages, is furthermore relevant for the discussion on the relation between the intensity of the Atlantic meridional overturning circulation and ice sheet growth.

Discriminating between the roles of late Pleistocene palaeodischarge and geological‐topographic inheritance in fluvial longitudinal profile and channel development

AbstractThis paper investigates the influences of palaeohydrology and geological‐topographic inheritance in shaping the channel of the lower River Suir, southeast Ireland. Results of acoustic surveys of the lower River Suir and Waterford Harbour reveal two scales of pseudo‐cyclic river bedforms. Longitudinal elevation profiles of the geological topography (undulating bedrock and till‐mantled bedrock) bounding the present floodplain swath reveal pseudo‐cyclicity in that terrain too. Spectral and statistical analyses are used to quantify the cyclicity of the long profile and geological‐topographic series. These methods show that the dominant cyclicity of the long profile reflects autocorrelation more than inheritance of cyclicity from the bounding geological topography. The cyclicity of the long profile mainly reflects a hydraulic control on pool‐spacing, although some cyclicity probably has been inherited from the geological‐topography. Channel‐forming palaeodischarge is estimated based on the dominant pool‐spacing revealed by spectral analysis, validated using relationships between meander wavelength, channel cross‐sectional geometry and hydraulically‐informed discharge reconstruction. The palaeodischarge estimates are in close agreement and are two orders of magnitude greater than present flood maxima. Significantly, these palaeodischarge estimates also agree closely with palaeodischarge calculated for the submerged Pleistocene palaeochannel that extends across the near‐shore continental shelf from Waterford Harbour. The pool‐sequence of the lower Suir and the submerged palaeochannel represent a former land‐system that was active during a period of low relative sea level during the last glacial. More broadly, the paper offers insights into the landscape evolution of formerly glaciated regions that experienced very wide discharge variability during and after the transition from glacial to interglacial regimes, in a context of complex relative sea level change. Copyright © 2017 John Wiley & Sons, Ltd.

Organic biomarker records spanning the last 34,800 years from the southeastern Brazilian upper slope: links between sea surface temperature, displacement of the Brazil Current, and marine productivity

Collective assessment of marine and terrigenous organic biomarkers was performed on a sediment core spanning the last 34,800 years on the upper slope southeast of Brazil to verify the signatures of climatic variations in sea surface temperature (SST), marine productivity, and the flux of terrigenous material in this region. This evaluation is based on marine and terrigenous proxies including alkenones, chlorins, aliphatic hydrocarbons, n-alcohols, and fatty acids. This first report of organic biomarker data for this region confirms a correlation between SST, changes in terrigenous organic matter flow into the ocean, and marine productivity over the last 34.8 ka as a response to the displacement of the Brazil Current. Conditions prevailing during marine isotopic stage (MIS) 3 may be considered intermediate between the last glacial maximum (LGM) and the Late Holocene. For MIS 2, a period of low relative sea level, it was verified that the lowest SSTs were associated with the LGM and higher marine productivity. SST increased by up to 4.4 °C between the LGM and the Holocene. This reveals synchronicity between SST on the southeastern Brazilian upper slope and the North Atlantic Ocean SST records reported in earlier studies.