Eustatic Sea-level Changes Research Articles

Ediacaran-Ordovician tectonic and geodynamic drivers of Great Unconformity exhumation on the southern Canadian Shield

The Great Unconformity erosion surface between Paleozoic sedimentary rocks and Archean-Proterozoic basement has been related to erosion occurring during Snowball Earth glaciations, eustatic sea level fluctuations, and a range of tectonic and/or geodynamic mechanisms. Each class of mechanism predicts distinct timing and spatial patterns of exhumation. Snowball Earth glacial erosion is limited to 717-635 Ma and concentrated in narrow ice streams on continental margins. Sea-level related erosion is unconstrained in time but also spatially limited to continental margins. Tectonic and geodynamic mechanisms, in contrast, can result in exhumation distributed more broadly in time and space. We combine new zircon and apatite (U-Th)/He thermochronology data (ZHe, AHe) with independent paleodepth information from a continental interior location in southeastern Ontario, Canada to constrain the timing, magnitude, and regional pattern of exhumation associated with the Great Unconformity along a ∼650 km-long transect across the southern Canadian Shield. Here, the unconformity is defined by Middle Ordovician carbonates atop Archean-Proterozoic basement. ZHe analyses for seven basement samples display a range of dates from 960 ± 20 Ma to 37.5 ± 0.9 Ma that correlate negatively with radiation damage. AHe dates are ∼300-200 Ma and generally consistent across samples regardless of radiation damage. Independent evidence supports emplacement of both the 590 +2/-1 Ma Grenville dikes and the 577 ± 1 Ma Callander Complex in the study region at depths ≥6 km. The combined data require ≥6 km of exhumation between ca. 590-577 Ma and 470 Ma in the middle of our transect, with multi-km erosion up to ≥5 km elsewhere in the study area, well after the ca. 717-635 Ma Snowball Earth glaciations. These outcomes expand the spatial extent of an Ediacaran to early-Paleozoic exhumation signal previously inferred elsewhere across the Shield to ∼1.1 million km2. Thick Ediacaran successions on the Laurentian margins are complementary depositional signals of this erosion. The enormous spatial extent of Great Unconformity exhumation across the continental interior of the Canadian Shield is incompatible with glacial erosion and eustatic sea-level change as the primary causes. Instead, we attribute exhumation to tectonic and geodynamic mechanisms, which may include isostatic rebound, dynamic topography, plume activity associated with the Central Iapetus Magmatic Province, rifting during opening of the Iapetus Ocean, and development of the Transcontinental Arch.

Middle Jurassic syn-sedimentary tectonics and palaeoenvironmental evolution in the eastern part of the Alborz Mountains (N Iran)

The facies variations in the Middle Jurassic deposits of northern Iran (northeastern Neotethys) were studied in two stratigraphic sections (Tapal and Kalariz) in the eastern part of the Alborz Basin to reconstruct the palaeoenvironmental evolution in this region. Six different palaeoenvironments were recognized based on alternation of sedimentary facies in the four formations of the studied sections (upper part of the Fillzamin, Dansirit, Dalichai and lower part of the Lar formations). The upper Fillzamin Formation (lower Bajocian) records a gradual shallowing-upward sequence from seaward to landward margin of a prodelta environment in the study area. This shallowing trend terminated with the Mid-Cimmerian tectonic event and unconformity, which is characterized by a thin limonite layer at the base of the Dansirit Formation in the Tapal section. The Dansirit Formation (lower upper Bajocian) represents heterolithic marginal marine, sand and gravel bars and terrestrial environments. The subsequent deposits of the Dalichai Formation (upper Bajocian–Callovian) represent a deepening sequence, which is associated with the appearance of pelagic strata and ammonitico rosso facies in the upper part of the formation. The ammonitico rosso facies, which is related to the development of pelagic swells in the rift basin, gives direct evidence of an extension phase and presence of a swell/trough system in the region. The rifting and subsidence are attributed to the opening of the South Caspian Basin (north of the Alborz region). The lack of correlation between the sea-level changes recorded by the upper Bajocian strata of the sections and the long-term eustatic sea-level changes suggest tectonic influence on the facies variations and sea-level fluctuations in the Alborz region. From the upper Bajocian upwards, a deepening trend in the studied sections can be correlated with the global sea-level changes, while tectonic (rifting and subsidence) overprinted the eustatic sea-level rise.

An overview of grey mullet (Mugilidae) global occurrence and species-rich ecoregions, with indications of possible past dispersal routes within the family.

This review examines the published literature on the distribution and species richness of the family Mugilidae around six continents as well as their phylogenetic relationships in a time-calibrated tree. Three mugilid species-rich regions were identified globally, namely the Coral Triangle, southern Asia and southern Africa, all of which have between 16 and 18 morphologically recognized species. Two of the species hotspots are tropical, and only southern Africa incorporates temperate waters. The centre of mugilid evolution and then global dispersion appears to be located in the tropical waters of the Indo-Pacific. Speciation within the family was promoted mainly by plate tectonics, eustatic sea-level changes, tropical climate and high habitat diversity within this region. The number of these tropical species that radiated out to the coastal waters of Africa and America was clearly less than the number that remained in the central Indo-Pacific region. Nonetheless, access by tropical mugilid species was greater to Africa than the Americas because of the direct tropical and subtropical coastal connectivity to the former continent. This enabled more tropical mugilids to reach Africa than America, with the latter probably relying on Palaeocene "island hopping" or "rafting" to move eastwards across the Pacific Ocean. In addition, tropical mugilids were able to access warm western and central African coastal waters from the Pacific prior to the closure of the Tethys Sea gap in the eastern Mediterranean and prior to the development of the cool Benguela Current upwelling off the southwest African coast, and from America through at least two transatlantic rafting events.

Paleoenvironment, sequence stratigraphy, and sea level change in the upper Maastrichtian–Danian boundary interval in Gabal Aras, east Qena, Nile Valley, Egypt

The Cretaceous–Paleogene (K–Pg) boundary interval at Gabal Aras, Qena region (part of the southern Tethyan margin) was investigated in detail for calcareous nannofossil and foraminiferal (planktonic and benthonic) assemblages to characterize the surface and bottom sea water conditions. The K–Pg boundary is marked by a minor hiatus expressed by the absence of the lowermost Danian P0 and Pα planktonic foraminiferal zones. Benthonic foraminifera assemblages indicate moderately oxygenated bottom sea waters associated with oligo-mesotrophic conditions during early late Maastrichtian, and mesotrophic conditions during the latest Maastrichtian. The benthonic foraminiferal assemblage reflects a decrease in the food supply in the bottom sea water during the early Danian, while well-oxygenated and oligotrophic conditions dominated during late Danian. The late Maastrichtian surface water witnessed a general cooling trend that was interrupted by a warming episode that could correspond to the Late Maastrichtian Warming Event (LMWE). Acme of Thoracosphaera associated with increased abundance of Neobiscutum romeinii were observed within the upper part of NP1 Zone indicating stressful surface water conditions. The increase of the epifaunal foraminiferal taxa and the occurrence of Cruciplacolithus primus throughout NP2 and NP3 zones reflect a progressive return to normal marine conditions. In the framework of sequence stratigraphy, two third-order depositional sequences covering the K–Pg boundary interval were identified, interpreted, and correlated. The obtained sea-level curve was evaluated to assess whether it was controlled by the eustatic sea-level changes, regional tectonics, or both these factors.

Revisiting paleoenvironmental changes on the Upper Yangtze Block during the Ordovician-Silurian transition: New insights from elemental geochemistry

Temporal and spatial patterns of paleoenvironmental change on the Upper Yangtze Block during the Ordovician-Silurian transition remain debatable and somewhat self-contradictory. The present study is a reassessment of how regional and global events may have influenced the paleoenvironmental evolution of the Upper Yangtze Block. Abundances of redox-sensitive trace elements, including Mo and U, suggest a general ascending stratigraphic pattern from the oxic to anoxic (euxinic) conditions during Late Katian time. High-resolution fluctuations of redox conditions may reflect frequent eustatic sea-level changes. The Kuanyinchiao Bed accumulated under less reducing conditions during the climax of Hirnantian glaciation. Post-glacial transgression during the latest Hirnantian to Early Rhuddanian was accompanied by the re-establishment of euxinic bottom-water conditions. Authigenic MoU covariation and Mo/TOC values of the studied stratigraphic successions suggest that the Upper Yangtze Shelf Sea was weakly to moderately restricted. Patterns of Cd/Mo and Co (ppm) × Mn (wt%) values suggest that the study area of the basin did not experience persistent upwelling. Instead, only seasonal upwelling occurred on the outer shelf, which is somewhat analogous with the modern Cariaco Basin. Terrestrial inputs, as reflected by Si/Al values, correspond with periods of diminished sedimentation rates and the establishment of anoxic conditions. Uplift associated with the Kwangsian Orogeny during latest Hirnantian to the early Rhuddanian time caused an increase in sedimentation rates in the eastern region of the study area. Strong covariance of Baxs and Eu/Eu* suggests that paleoproductivity was enhanced by regional hydrothermal events. Our results suggest that redox conditions and clastic inputs during deposition of the Ordovician-Silurian transition succession of the Upper Yangtze shelf were linked to climatically-induced sea-level fluctuations whereas the spatial gradient of redox conditions and clastic inputs from inner shelf to outer shelf was strongly controlled by paleogeography and orogenic movements.

Geochemistry of Foraminifera in the Marginal Seas of the Sunda Shelf: A Review

Foraminiferal geochemistry applies geochemical elements embedded in foraminiferal calcites through bioaccumulation to interpret and reconstruct past oceanic climate histories. Due to its extensive variability and abundance, foraminifera is the easiest to retrieve and the best indicator of marine productivity and ocean temporal changes. In this review, we discuss the development of foraminiferal geochemistry studies in Southeast Asia, analyzing its current status and potential areas to be developed, namely, the Sunda Shelf. The Sunda Shelf is one of the world’s largest low-latitude shelves, bordered by marginal seas and sensitive to sea-level changes. The shelf response towards changes in ocean salinity affected the isotopic signals in foraminiferal calcites, which can indicate sea-level changes ideally. The Sunda Shelf has the potential to be developed as a study area for eustatic sea-level changes as it is located far from major glaciation centers; hence through this review, we aim to highlight the potential of exploring the application of geochemical elements in foraminifera as an indicator for sea-level changes. To date, literature on foraminiferal geochemistry in this region is very limited, thus inhibiting progress in such studies. A comprehensive summary of past studies in this region is provided to give a general overview of the direction of foraminiferal geochemistry studies and serve as guidelines for future research.

Biostratigraphy and lithofacies of the Middle-Upper Devonian in the Ayazovo oil field (North-Eastern of Bashkiria)

Research subject. Oil-bearing deposits of the Middle-Upper Devonian in the Ayazovo oil field located in the north-east of Bashkiria. Materials and methods. A detailed description and subdivision of the section were carried out based on the borehole cores of the Rustamovskaya area using biostratigraphic and lithofacial analysis, micropalaeontology of spores and conodonts. Results. The sediments of the Pashian, Timan, Sargaevo, Domanic and Mendym horizons are identified, their lithofacial features are described, and sedimentation conditions are determined. Conclusions. The studied succession of the Devonian sediments demonstrates cyclical changes in terrigenous and carbonate shelf sedimentation environments caused by eustatic sea level change and complicated by the tectonic events associated with the formation of uplifts and troughs of the Kama-Kinel system at the end of the Frasnian.

Sedimentary modulation of magnetic mineral records in the Central Bengal Fan

Submarine fan sediments are essential archives for understanding the interaction between continental weathering and climate change, but decoding multiple geological and environmental factors in such highly dynamic sedimentary environments is challenging. Here we present a high-resolution magnetic mineral record spanning the past ∼40 ka from the central Bengal Fan. Comprehensive rock magnetic and electron microscopic analyses are conducted to understand the origins of different magnetic mineral components in response to sedimentary and paleoclimate processes. Detrital magnetite and titanomagnetite are the dominant magnetic minerals in Bengal Fan sediments, whose abundance and grain size are primarily controlled by eustatic sea-level change. Increased Himalaya terrestrial input during Heinrich events is documented during sea-level low stand, but magnetic mineral variations and climate events are decoupled due to enhanced Indian hemipelagic sediment input since the last deglaciation sea-level rise. In addition, we identify an enriched biogenic magnetite layer near the Fe-redox boundary in the studied Bengal Fan sediment core, possibly related to relatively mild post-depositional diagenesis. Massive detrital inputs in the submarine fan sediments dilute the contribution of biogenic magnetite to the bulk magnetic record. Our results contribute to an integrated source-to-sink understanding of magnetic mineral components in continental margin submarine fans, which helps to construct multi-proxy Quaternary paleoclimate and paleogeography records in typical submarine fan deposits.

A synopsis of the Ordovician System in its birthplace – Britain and Ireland

Abstract Rock successions in Britain and Ireland, and more especially those in Wales, were instrumental in the founding and naming of the Ordovician System, and the Anglo-Welsh series established both initially and subsequently were used widely as a standard for Ordovician chronostratigraphy. Although now largely superseded in the global scheme of series and stages, they retain their local and regional importance. The Ordovician System in Britain and Ireland documents the history of a segment of the Earth's crust that incorporated opposing peri-Gondwanan and peri-Laurentian/Laurentian margins of the Iapetus Ocean during its closure, and is accordingly complex. The complexity arises from the volcanic and tectonic processes that accompanied oceanic closure coupled with the effects of eustatic sea-level changes, including the far-field effects of the Late Ordovician glaciation. For the past three decades, Ordovician successions in Britain and Ireland have been discussed in terms of terranes. Here we review Ordovician successions in each terrane, incorporating the results of recent research and correlating those successions via biostratigraphical schemes and radiometric dates to the global Ordovician series and stages.

Holocene Glaucony from the Guadiana Shelf, Northern Gulf of Cadiz (SW Iberia): New Genetic Insights in a Sequence Stratigraphy Context

Glaucony occurrences have been reported both from exposed transgressive and overlying highstand system tracts. However, its occurrences within highstand deposits are often invoked as the result of underlying condensed section reworking. Detailed textural, mineralogical and geochemical reports of glaucony grains in highstand deposits remain elusive. The northern Gulf of Cadiz shelf (SW Iberia) offers a unique opportunity to investigate late Holocene glaucony authigenesis in a well-documented time-stratigraphic context, where transgressive deposits are locally exposed on the seafloor and are laterally draped by highstand muddy deposits. In this study, glaucony grains extracted from a core retrieved from a highstand muddy depocenter off the Guadiana River were investigated by means of digital microscopy, X-ray diffraction (XRD), and electron microscopic methods (FESEM-EDX and TEM-HRTEM). To better constrain the glaucony origin (autochthonous vs. allochthonous) in highstand muddy deposits, glaucony grains from surficial samples—taken from exposed transgressive deposits—were also investigated. Glauconitization in the studied core can be largely attributed to the replacement of faecal pellets from c. ~4.2–1.0 cal. ka BP. Both XRD and TEM-HRTEM analyses indicate that glaucony consists mainly of an R1, with a minor presence of R0, smectite-rich (nontronite) glauconite-smectite mixed-layer silicate, made up of 35–75% glauconitic layers and 65–25% of interstratified smectite layers. At the mineral lattice level, minor individual 7Å layers (berthierine) were also identified by HRTEM. Shallow radial cracks at the pellet surface, along with globular and vermiform-like biomorphic to low packing density lamellar-flaky nanostructures, mineralogical properties, and K-poor content (average 0.4 atoms p.f.u.) indicate a scarcely mature glauconitization process, attesting to formation of the grains in situ (autochthonous). Glaucony grains from exposed transgressive deposits, i.e., in the tests of calcareous benthic foraminifera, do not share a genetic relationship with the grains investigated in the highstand deposits, thus supporting the autochthonous origin of glaucony within the highstand deposits. Our combined dataset provides evidence of a multiphase history for autochthonous glaucony formation in the Guadiana shelf, as its genesis is traced to both transgressive and highstand conditions. While eustatic sea-level changes favoured glaucony formation under transgressive conditions, factors such as protracted low sediment supply and the establishment of a strong nutrient-rich upwelling system in the study area promoted glaucony development during late Holocene highstand conditions.

Late Pleistocene evolution of Robe Range, southern Australia – The timing and carbonate source dynamics of coastal dune development

Robe Range is a coastal barrier that extends for over 155 km along the modern coastline of the Coorong Coastal Plain in southern Australia, a region renowned as preserving one of the world's longest records of Quaternary eolian dune deposition. Previous research has shown that the late Pleistocene dune development in this barrier structure is linked with sea-level highstands, particularly warm interstadials of marine isotope stage (MIS) 5. To better understand the principal depositional phases and sediment provenance of the dune successions of Robe Range, we use a combination of amino acid racemization analyses on the foraminifer Lamellodiscorbis dimidiatus and optically stimulated luminescence dating of associated quartz sand. The new and previously published optical dating results indicate that phases of dune formation correlate with MIS 5c–a (ca. 105–75 ka) and early in MIS 3 (ca. 61–53 ka). More importantly, the distribution of the extent of amino acid racemization on single-foraminifers reveals that the overall barrier successions have complex sources of carbonate sediment, principally derived from contemporaneous inner shelf temperate carbonate factories and reworked skeletal grains from the erosion of older marginal marine successions. The regional narrowing of the Bonney Shelf restricted the degree of lateral changes of the shoreline in response to the glacial–interglacial cycles, in contrast to the wider Lacepede Shelf to the north. The characteristics of offshore shelf topography allow wind-driven onshore transport and delivery of bioclastic sand from mixed-age carbonate sources to onshore coastal dunes during lower sea levels, particularly in association with the intensified wind regime of early MIS 3. This points to other factors influencing coastal dune emplacement besides simply glacio–eustatic sea-level changes, and relates to the availability of biogenic particles and the delicate balance between shelf topography and wind regimes during the interstadials of the late Pleistocene.

Controls on carbonate-siliciclastic relationships in quaternary deposits of the Midyan coast of the Gulf of Aqaba, Saudi Arabia

Quaternary deposits of the Midyan coast of Saudi Arabia include coral-bearing limestones interbedded with sheet-flow siliciclastic sands and gravels, interpreted as braid-delta fan deposits. The limestones and their contained faunas provide evidence of periodic local stabilization of gravel surfaces and effective starvation of siliciclastic supply. Some indicate growth and deposition in waters a metre or so deep whereas others were substantially deeper. An additional group reflects initial deposition in shallow waters with resedimentation downslope by storm or other ‘delta-front’ processes. The surfaces of the fans provided morphological and environmental analogues to fore- and back-reef situations in which corals, calcareous coralline algae, molluscs, and echinoderms flourished, but in this area did not form independent reefs. The dominant controls on the changes from siliciclastic- to carbonate-dominated deposition were not transitional, and primarily related to channel and fan-lobe migration rather than tectonic or eustatic sea level changes. Similar variations in the distribution of siliciclastic sediments may control carbonate occurrence in other mixed sequences.

Temporal and spatial distribution of Precambrian red beds and their formation mechanisms

Red beds are irrefutable evidence of important geological events; understanding their formation mechanism and sedimentary environment provide insights about Earth's history and the evolution of life. In this paper, Precambrian red beds from over 70 outcrops in nearly 30 regions in different countries are statistically assessed using their lithology, sedimentary environment, and spatio-temporal distribution. Twelve sets of red beds are identified, five of which are distributed globally; the other sets are regional or local. The depositional environments for red beds are varied. They include terrestrial (aeolian, alluvial, and fluvial) and shallow marine environments (dominantly, tidal and glacial marine), as well as the transition areas from shallow to deep-water environments. While the former two are dominant environments, the latter has fewer occurrences – most of which are concentrated in strata of the Ediacaran Period. Red beds are lithologically diverse; terrestrial red beds are mainly composed of conglomerate and sandstone, while shallow marine red beds primarily consist of siltstone, mudstone, and carbonate rocks. The formation of red beds is directly controlled by the concentration of dissolved Fe and O2 content, and penecontemporaneous geological events. Here, they are sorted into two groups based on their chronological coupling with glaciations, the assembly and breakup of supercontinents, eustatic sea-level changes, the flourishing of photoautotrophs like cyanobacteria, as well as δ13C and 87Sr/86Sr isotope anomalies. The formation of the first group of red beds is closely related to the Paleoproterozoic and Neoproterozoic glaciations, the Great Oxidation Event, and the Neoproterozoic Oxygenation Event. Much of the dissolved Fe scavenged from seawater during oxygenation events precipitated into banded iron formations (BIF). The transmittance of light through water reduced during glaciations. It prevented the production of O2 and limited Fe2+ oxidation – which worked as a protector for oceanic Fe re-accumulation. The melting of glaciers improved the availability of light which restarted the production of photosynthetic O2 that aided the formation of red beds. The formation of the second group of red beds was aided by supercontinent fragmentation that created many shallow margin habitats for photoautotrophs, facilitating O2 production. The appearance of this group of red beds coincides with and is geochemically supported by pulses of O2 increase recorded by Cr and C isotopes, as well as by iron speciation data. Future research should examine how Precambrian red beds can be used to systematically decode paleoenvironment changes.

Early Eocene carbon isotope excursions in a lignite-bearing succession at the southern edge of the proto-North Sea (Schöningen, Germany)

Abstract. Situated at the southern edge of the proto-North Sea, the lower Eocene Schöningen Formation of the Helmstedt Lignite Mining District, Lower Saxony, Germany, is characterized by several lignite seams alternating with estuarine to brackish interbeds. Here, we present carbon isotope data for bulk organic matter (δ13CTOC), total organic carbon content (%TOC), and palynomorphs from a 98 m thick sequence of the Schöningen Formation in combination with a new robust age model, which is based on eustatic sea level changes, biostratigraphy, and a correlation with existing radiometric ages. Based on the δ13CTOC data we observe six negative carbon isotope excursions (CIEs) reflecting massive short-term carbon cycle perturbations. A strong CIE of −2.6 ‰ in δ13CTOC values in the Main Seam and the succeeding marine interbed can be related to the Paleocene–Eocene Thermal Maximum (PETM). The subsequent CIE of −1.7 ‰ in δ13CTOC values may be correlated with the Eocene Thermal Maximum 2 (ETM2) or slightly older events preceding the ETM2. High-amplitude climate fluctuations including at least four minor CIEs with a maximum negative shift of −1.3 ‰ in δ13CTOC in the upper part of the studied section are characteristic of the Early Eocene Climatic Optimum (EECO). Palynological analysis across the Main Seam proved that shifts in δ13CTOC values are correlated with changes in the peat-forming wetland vegetation, specifically the change from a mixed angiosperm and gymnosperm flora to angiosperm-dominated vegetation at the onset of the PETM. The PETM-related CIE shows a distinct rebound to higher δ13CTOC values shortly after the onset of the CIE, which is recognized here as a common feature of terrestrial and marginal marine PETM records worldwide and may reflect a stepwise injection of carbon into the atmosphere.

Holocene relative sea level changes in the Västervik‐Gamlebyviken region on the southeast coast of Sweden, southern Baltic Sea

We reconstruct the Holocene shore displacement of the Västervik‐Gamlebyviken area on the southeast coast of Sweden, characterised by a maritime cultural landscape and archaeological significance since the Mesolithic. Sediment cores were retrieved from four lake basins that have been raised above sea level due to the postglacial land uplift and eustatic sea level changes after the melting of the Fennoscandian Ice Sheet. The cores were radiocarbon dated and analysed for loss on ignition and diatoms. The isolation thresholds of the basins were determined using LiDAR data. The results provide evidence for the initiation of the first Littorina Sea transgression in this area at 8.5 thousand calibrated years before present (cal. ka BP). A relative sea level rise by ∼7 m a.s.l. is recorded between 8.0 and 7.5 cal. ka BP with a highstand at ∼22 m a.s.l. between 7.5 and 6.2 cal. ka BP. These phases coincide with the second and third Littorina Sea transgressions, respectively, in the Blekinge area, southern Sweden and are consistent with the final deglaciation of North America. After 6.2 cal. ka BP, the relative sea level dropped below 22 m a.s.l., and remained at ∼20 m a.s.l. until 4.6 cal. ka BP coinciding with the fourth Littorina Sea transgression in Blekinge. From 4.6 to 4.2 cal. ka BP, the shore displacement shows a regression rate of 10 mm a−1 followed by a slowdown with a mean value of 4.6 mm a−1 until 1.6 cal. ka BP, when the relative sea level dropped below 3.3 m a.s.l. The Middle to Late Holocene highstand and other periods of minor sea level transgressions and/or higher salinity between 6.2 and 1.7 cal. ka BP are attributed to a combination of warmer climate and higher inflow of saline waters in the southern Baltic Sea due to stronger westerlies, caused by variations in the North Atlantic atmospheric patterns.

Quaternary Beach Dunes in Daryanah Area NW of Al Jabal al Akhdar, NE Libya.

The present study has shown that the Quaternary beach dunes of Daryanah area are composed of four distinctive lithological facies, these are the planer cross bed calcarenite facies, lenticular calcarenite facies, massive calcarenite, and alluvial deposits facies. The planer cross-bedding and the lenticular bedding are interpreted to reflect aeolian deposits. The massive calcarenite is thought to have been accumulated in shallow marine. The interbedded calcarenites and alluvial deposits interpreted to represent cycles of prograding alluvial system associated with Eustatic sea-level changes. The paleo-winds in the area were mostly unimodal blowing between 290°and 330°, which were influenced by the escarpment position and orientation. The age of these deposits has been attributed to Early Pleistocene (Calabrian) based on its occurrence above the sea level and correlation with previous studies.

Paleoenvironmental reconstruction, paleoecology and sequence stratigraphy of some Nummulites buildups in Egypt

The present study deals with microfacies analysis, paleoecology and sequence stratigraphy of the Lower–Middle Eocene rocks in central Nile Valley and west-central Sinai. Four rock units were marked (Minia, Darat, Samalut and Maghagha formations). Eight facies belts were interpreted including lagoon, back bank, main bank, fore bank and open marine outer bank facies and deposited on a gently dipping platform ramp. This ramp might be further divided to three main faunal associations depending on the depth of the water and associated fauna. Four major depositional sequences (DS1–DS4), reflecting third-order cycles and separated by two prominent sequence boundaries (SB1 and SB2) were marked. The record of these sequences reflects the changes in eustatic sea level plus the regional tectonism in the area. Every sequence includes facies associations, which constitute lowstand and/or transgressive and highstand systems tracts. Based on faunal elements and facies analysis, the water salinity, water temperature, nutrients, substrate, water depth and hydrodynamic behavior were discussed. The fine-grain size of the deposits, the loss of good connectedness and the occluding of the Nummulite tests by other minerals could give rise to low reservoir potential. The sedimentation was affected by the tectonic activity of the Syrian orogeny. Moreover, both external and internal mechanisms have controlled the carbonate sedimentation, basin construction and sequence bounding surfaces.

Late Pleistocene Geomorphic Evolution of Cephalonia Island, Western Greece, Inferred from Uplifted Marine Terraces

Combined with eustatic sea-level changes, uplifted Quaternary marine terraces provide insight into the tectonics of coastal areas. Cephalonia Island lies 35 km off the western coast of mainland Greece and 15 km northeast of the Hellenic subduction zone. Late Pleistocene eustatic sea-level oscillations and the long-term tectonic movements are imprinted on the landscape of the southern part of the island, in the form of seven uplifted marine terraces. In the present study we aim to identify and map in detail these terraces, applying Digital Elevation Model analysis, utilizing Geographic Information Systems techniques and extensive fieldwork. The GIS-based analysis combined with field geomorphological observations revealed a sequence of seven marine terraces at the southern part of the main island ranging in elevation between 4 m and 176 m asl. Microscope, petrological and microgeomorphological analyses on two caprock samples suggest strong marine influence during the deposition of the sediments covering the marine terraces. The age of the formation of the 32 m marine terrace was assigned to the MIS 3e, based on OSL dating of a caprock sample, and an average uplift rate of 1.4 ± 0.35 mm a−1 was calculated for the last 61 ± 5.5 ka. Assuming a uniform uplift rate for the Late Pleistocene allowed us to correlate the marine terrace with the sea-level highstands and constrain their ages.

Trench floor depositional response to glacio-eustatic changes over the last 45 ka, northern Hikurangi subduction margin, New Zealand

ABSTRACT Glacio-eustatic cycles lead to changes in sedimentation on all types of continental margins. There is, however, a paucity of sedimentation rate data over eustatic sea-level cycles in active subduction zones. During International Ocean Discovery Program Expedition 375, coring of the upper ∼110 m of the northern Hikurangi Trough Site U1520 recovered a turbidite-dominated succession deposited during the last ∼45 kyrs (Marine Isotope Stages (MIS) 1–3). We present an age model integrating radiocarbon dates, tephrochronology, and δ18O stratigraphy, to evaluate the bed recurrence interval (RI) and sediment accumulation rate (SAR). Our analyses indicate mean bed RI varies from ∼322 yrs in MIS1, ∼49 yrs in MIS2, and ∼231 yrs in MIS3. Large (6-fold) and abrupt variations in SAR are recorded across MIS transitions, with rates of up to ∼10 m/kyr occurring during the Last Glacial Maximum (LGM), and <1 m/kyr during MIS1 and 3. The pronounced variability in SAR, with extremely high rates during the LGM, even for a subduction zone, are the result of changes in regional sediment supply associated with climate-driven changes in terrestrial catchment erosion, and critical thresholds of eustatic sea-level change altering the degree of sediment bypassing the continental shelf and slope via submarine canyon systems.

Miocene organic-rich layers of the Saouef Formation (Oriental Tunisia); insights into temporal and spatial variability of environmental conditions during deposition

Miocene organic-rich sediments (coal and carbonaceous clays) from the La Falaise section of the Saouef Formation have been investigated by organic petrographic, palynofacies and organic geochemical approaches. The results are compared with data obtained during a previous study of the nearby Saouef section. The sedimentary succession is built up by repetitive sedimentary sequences (i.e., parasequences) deposited during progradation and retrogradation, respectively. The coal, or carbonaceous layers, developed during the establishment of clay-dominated sedimentation.The organic-rich layers within the samples, containing high amounts of mineral matter, are dark brown, with a stratified texture and are classified as humic coal. Microscopically, the huminite group dominates the maceral composition of the carbonaceous clays and lignite (av. 75% mmf). The variable degrees of the tissue preservation index (TPI) and highly fluctuating vegetation index (VI) values provide evidence for different contributions of vascular plants vs. herbaceous vegetation and macrophytes, to peat formation. Higher contributions of macrophytes (e.g., reed grasses) to peat accumulation at La Falaise are concluded, based on n-alkane distributions. High mineral matter contents and changing gelification index (GI), and ground water index (GWI) values, found in both sections, provide evidence for rheotrophic hydrogeological conditions, and peat formation within wet forest swamp to inundated marsh environment. The low sulphur contents attest to peat formation within a freshwater environment and the relative proportions of ββ to (ββ + αβ)-C31 hopanes argue for slightly acidic conditions. In comparison to the results of the Saouef section (average pH of 5.6), a lower pH (4.2) is revealed from the average hopane isomerization ratio of the La Falaise samples.The palynofacies investigation of the La Falaise deposits indicates the dominance of phytoclasts over amorphous organic matter (AOM) in most of the samples and suggests good preservation of the higher plant remains. In contrast, increased degradation of plant tissues under oxygen-deficient conditions is concluded from the enhanced proportions of AOM found in several of the previously investigated Saouef samples. The molecular analysis of hydrocarbons from all the samples indicated the dominance of n-alkanes and hopanoids. The obtained pristane/phytane ratios argue for sub-oxic conditions during peatification at La Falaise, whereas data from our previous study of the Saouef section provided evidence for a reducing environment. Terpenoid hydrocarbon compositions reveal highly variable contributions of conifers and angiosperms to peat formation, consistent with previous findings at the Saouef sampling site. The presence of polycyclic aromatic hydrocarbons (PAHs), as well as fusinite, provides evidence for mire or forest fires.The comparison of the results from lignite of both sections of the Saouef Formation indicate comparable, highly variable conditions during peat accumulation, probably governed by eustatic sea level changes. The peatlands most likely developed due to the establishment of flood basins situated between alluvial ridges. The obtained regional differences are suggested to reflect slightly different hydrological conditions and associated vegetation cover in the peatlands.