Glacio-eustatic Sea-level Changes Research Articles

Orbital-scale stratigraphy and high-resolution analysis of biogenic components and deep-water oxygenation conditions in the Japan Sea during the last 640 kyr

Paleoceanographic conditions in the Japan Sea changed drastically during the Late Quaternary in association with orbital and suborbital cycles and glacio-eustatic sea level changes. However, few studies have examined long-term sediment records older than 160 ka because of the lack of long and continuous cores and the difficulty in constructing high-resolution age models. In this study, we first constructed an orbital-scale stratigraphy of the sediments covering the last 640 kyr by comparing the SPECMAP ∂ 18O curve and the ∂ 18O curve of planktonic foraminifera ( ∂ 18O pf) in the Japan Sea together with the combination zones of dominant planktonic foraminifera species. Then, we reconstructed temporal variations in biogenic silica (BioSil) and biogenic carbonate (BioCarb) contents calculated from high-resolution major element analysis data determined by an XRF microscanner. In order to evaluate the deep-water oxygenation conditions, we also defined excess S as the difference between the content of S in the sediments and that for normal marine sediments calculated from the organic carbon content (C org) estimated from lightness ( L ⁎) by assuming a total sulfur content (S total)/C org ratio of 0.36, and examined its variability. BioSil shows orbital-scale variation and is generally low except during interglacial maxima when global sea level was high enough to allow a strong influx of the Tsushima Warm Current. BioCarb shows orbital- and suborbital-scale variations and tends to be higher in dark layers deposited during glacial stages, whereas the relationship is reversed during interglacial stages. The low BioCarb in dark layers deposited during interglacial stages is probably due to dissolution of biogenic carbonate caused by the increase in surface productivity as a result of the strong influx of nutrient rich East China Sea Coastal Water and consequent increase in surface productivity and decomposition rate of organic matter in the intermediate water. Excess S tends to be higher in thicker dark layers deposited during glacial maxima when the sea level dropped below − 90 m compared to adjacent light layers, suggesting development of euxinic deep-water conditions during these periods. The results demonstrated the presence of orbital- and suborbital-scale variations in BioSil and BioCarb and their association with dark and light layers in the Japan Sea that reflect variations in the nature and strength of inflow through the Tsushima Strait controlled by both climatic and sea level changes, whereas higher excess S reflects the development of euxinic deep-water condition during glacial maxima in association with glacio-eustatic sea level drops below − 90 m during the last 640 kyr.

Sedimentary manganese metallogenesis in response to the evolution of the Earth system

The concentration of manganese in solution and its precipitation in inorganic systems are primarily redox-controlled, guided by several Earth processes most of which were tectonically induced. The Early Archean atmosphere–hydrosphere system was extremely O 2-deficient. Thus, the very high mantle heat flux producing superplumes, severe outgassing and high-temperature hydrothermal activity introduced substantial Mn 2+ in anoxic oceans but prevented its precipitation. During the Late Archean, centered at ca. 2.75 Ga, the introduction of Photosystem II and decrease of the oxygen sinks led to a limited buildup of surface O 2-content locally, initiating modest deposition of manganese in shallow basin-margin oxygenated niches (e.g., deposits in India and Brazil). Rapid burial of organic matter, decline of reduced gases from a progressively oxygenated mantle and a net increase in photosynthetic oxygen marked the Archean–Proterozoic transition. Concurrently, a massive drawdown of atmospheric CO 2 owing to increased weathering rates on the tectonically expanded freeboard of the assembled supercontinents caused Paleoproterozoic glaciations (2.45–2.22 Ga). The spectacular sedimentary manganese deposits (at ca. 2.4 Ga) of Transvaal Supergroup, South Africa, were formed by oxidation of hydrothermally derived Mn 2+ transferred from a stratified ocean to the continental shelf by transgression. Episodes of increased burial rate of organic matter during ca. 2.4 and 2.06 Ga are correlatable to ocean stratification and further rise of oxygen in the atmosphere. Black shale-hosted Mn carbonate deposits in the Birimian sequence (ca. 2.3–2.0 Ga), West Africa, its equivalents in South America and those in the Francevillian sequence (ca. 2.2–2.1 Ga), Gabon are correlatable to this period. Tectonically forced doming-up, attenuation and substantial increase in freeboard areas prompted increased silicate weathering and atmospheric CO 2 drawdown causing glaciation on the Neoproterozoic Rodinia supercontinent. Tectonic rifting and mantle outgassing led to deglaciation. Dissolved Mn 2+ and Fe 2+ concentrated earlier in highly saline stagnant seawater below the ice cover were exported to shallow shelves by transgression during deglaciation. During the Sturtian glacial-interglacial event (ca. 750–700 Ma), interstratified Mn oxide and BIF deposits of Damara sequence, Namibia, was formed. The Varangian (≡ Marinoan; ca. 600 Ma) cryogenic event produced Mn oxide and BIF deposits at Urucum, Jacadigo Group, Brazil. The Datangpo interglacial sequence, South China (Liantuo–Nantuo ≡ Varangian event) contains black shale-hosted Mn carbonate deposits. The Early Paleozoic witnessed several glacioeustatic sea level changes producing small Mn carbonate deposits of Tiantaishan (Early Cambrian) and Taojiang (Mid-Ordovician) in black shale sequences, China, and the major Mn oxide–carbonate deposits of Karadzhal-type, Central Kazakhstan (Late Devonian). The Mesozoic period of intense plate movements and volcanism produced greenhouse climate and stratified oceans. During the Early Jurassic OAE, organic–rich sediments host many Mn carbonate deposits in Europe (e.g., Úrkút, Hungary) in black shale sequences. The Late Jurassic giant Mn Carbonate deposit at Molango, Mexico, was also genetically related to sea level change. Mn carbonates were always derived from Mn oxyhydroxides during early diagenesis. Large Mn oxide deposits of Cretaceous age at Groote Eylandt, Australia and Imini-Tasdremt, Morocco, were also formed during transgression–regression in greenhouse climate. The Early Oligocene giant Mn oxide–carbonate deposit of Chiatura (Georgia) and Nikopol (Ukraine) were developed in a similar situation. Thereafter, manganese sedimentation was entirely shifted to the deep seafloor and since ca. 15 Ma B.P. was climatically controlled (glaciation–deglaciation) assisted by oxygenated polar bottom currents (AABW, NADW). The changes in climate and the sea level were mainly tectonically forced.

Carbonate Diagenesis Controlled by Glacioeustatic Sea-Level Changes: A Case Study from the Carboniferous-Permian Boundary Section at Xikou, China

ABSTRACT The platform-facies carbonate rocks of the Carboniferous-Permian boundary strata are well developed and outcropped in Xikou ( ), Zhenan ( ) County, Shaanxi ( ) Province, China. The carbonate diagenesis in the Carboniferous-Permian boundary section at Xikou contains many processes with conspicuous effects, including micritization, cementation, mechanical and chemical compaction, neomorphism, and dissolution. Based on mineralogical composition and microfabrics, the diagenetic environments are distinguished into marine, near surface meteoric and burial environments. Detailed petrographical observation of abundant thin sections integrated with previous studies on sequence stratigraphy reveals that the carbonate diagenesis in the Carboniferous-Permian boundary section is related to the relative stratigraphic position of the rocks in the high-frequency cycles and controlled by the glacioeustatic sea-level changes. There are distinctive differences in diagenetic patterns between the lower transgressive sequence and the upper regressive sequence in a cyclothem. The diagenesis in the lower transgressive sequence is mainly characterized by pressure dissolution and recrystallization of mudstone and wackstone in a burial environment, and the diagenesis in the upper regressive sequence by cementation and leaching of freshwater in a meteoric environment.

Constraints on Pennsylvanian glacioeustatic sea-level changes using oxygen isotopes of conodont apatite

Research Article| April 01, 2006 Constraints on Pennsylvanian glacioeustatic sea-level changes using oxygen isotopes of conodont apatite Michael M. Joachimski; Michael M. Joachimski 1Institute of Geology and Mineralogy, University of Erlangen, Schlossgarten 5, 91054 Erlangen, Germany Search for other works by this author on: GSW Google Scholar Peter H. von Bitter; Peter H. von Bitter 2Department of Natural History, Palaeobiology Section, Royal Ontario Museum, and Department of Geology, University of Toronto, 100 Queen's Park, Toronto M5S 2C6, Canada Search for other works by this author on: GSW Google Scholar Werner Buggisch Werner Buggisch 3Institute of Geology and Mineralogy, University of Erlangen, Schlossgarten 5, 91054 Erlangen, Germany Search for other works by this author on: GSW Google Scholar Author and Article Information Michael M. Joachimski 1Institute of Geology and Mineralogy, University of Erlangen, Schlossgarten 5, 91054 Erlangen, Germany Peter H. von Bitter 2Department of Natural History, Palaeobiology Section, Royal Ontario Museum, and Department of Geology, University of Toronto, 100 Queen's Park, Toronto M5S 2C6, Canada Werner Buggisch 3Institute of Geology and Mineralogy, University of Erlangen, Schlossgarten 5, 91054 Erlangen, Germany Publisher: Geological Society of America Received: 24 Aug 2005 Revision Received: 05 Dec 2005 Accepted: 14 Dec 2005 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2006) 34 (4): 277–280. https://doi.org/10.1130/G22198.1 Article history Received: 24 Aug 2005 Revision Received: 05 Dec 2005 Accepted: 14 Dec 2005 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michael M. Joachimski, Peter H. von Bitter, Werner Buggisch; Constraints on Pennsylvanian glacioeustatic sea-level changes using oxygen isotopes of conodont apatite. Geology 2006;; 34 (4): 277–280. doi: https://doi.org/10.1130/G22198.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Conodonts from U.S. Midcontinent cyclothems were studied for oxygen isotopes in order to constrain Pennsylvanian glacioeustatic sea-level fluctuations. Pennsylvanian deposits of the Midcontinent United States are composed of cyclic alternations of thin transgressive limestones, offshore gray to black phosphatic shales, and thick regressive limestones, a sequence that is underlain and overlain by nearshore to terrestrial shales with paleosols and coal beds. Glacioeustatic sea-level fluctuations are considered the primary cause for the formation of these cyclothems. Oxygen isotope analyses of conodont apatite from the black (20.1 ± 0.5‰, Vienna standard mean ocean water [VSMOW]) and gray shale units (20.5 ± 0.5‰, VSMOW) show lowest average δ18O values, whereas conodont elements from the regressive (21.0 ± 0.3‰, VSMOW) and transgressive limestone units (21.1 ± 0.6‰, VSMOW) are enriched in 18O. The maximum change in δ18O of conodonts from the black shale and carbonate units from individual cyclothems is 1.7‰. The 1.7‰ difference in δ18O compares relatively well to Pleistocene interglacial-glacial changes in δ18O of equatorial surface-dwelling foraminifers and suggests that Pennsylvanian glacioeustatic sea-level changes may have been of comparable amplitude. However, since the Pennsylvanian glacial maxima are represented by terrestrial sediments and are not documented in the conodont oxygen isotope record, Pennsylvanian glacioeustatic sea-level changes were probably larger than the 120 m fluctuations recorded for the Pleistocene glaciations. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Permo-Carboniferous climate: Early Pennsylvanian to Late Permian climate development of central Europe in a regional and global context

Abstract A well-justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of Pangaea reveal new insights into the northern Pangaean climate development influenced by palaeogeography, palaeotopography, glacio-eustatic sealevel changes and ocean currents. The overall Permo-Carboniferous aridization trend was interrupted by five wet phases. These are linked to the Gondwana icecap. The aridization and weakening of wet phases over time were not only caused by the drift of northern Pangaea to the arid climatic belt, but also by the successive closure of the Rheic Ocean, which caused the expansion of arid/semi-arid environments in the Lower/Middle Permian. The end of the Gondwana glaciation rearranged ocean circulation, leading to a cold, coast-parallel ocean current west of northern Pangaea, blocking moisture coming with westerly winds. The maximum of aridity was reached during the Roadian/Wordian. The Trans-Pangaean Mountain Belt was non-existent. Its single diachronous parts never exceeded an average elevation of 2000 m. The maximum elevation shifted during time from east to west. The Hercynian orogen never acted as an orographic east-west barrier, and the Inter-Tropical Convergence Zone was widely displaced, causing four seasons (dry summer/winter, wet spring/autumn) at the equator and a strong monsoon system.

Latest Chesterian (Carboniferous) initiation of Gondwanan glaciation recorded in facies stacking patterns and brachiopod paleocommunities of the Antler foreland basin, Idaho

Stacking patterns of facies and brachiopod communities of Latest Chesterian (Middle Carboniferous) units of east-central Idaho record an increase in the frequency and amplitude of sea level changes. Water depth, as inferred from lithology and paleoecology, provides the basis for quantifying sea level fluctuations. The Surrett Canyon Formation is dominated by thick sequences of subtidal carbonates. The Arco Hills Formation consists of thin parasequences of mixed carbonate and siliciclastic lithologies, representing sea level changes up to 50 m in amplitude, bounded by flooding surfaces. Overlying the Arco Hills, the Bluebird Mountain Formation (very fine-grained quartz arenite, dolomite, and unfossiliferous limestone) records a major lowstand just below the mid-Carboniferous boundary. Increased amplitude and frequency of sea level changes in the Antler foreland basin initiated at the C. naviculus/ A. unicornis conodont zone boundary which occurs at the base of the Arco Hills Formation. These are interpreted as 4th-order glacio-eustatic sea level changes related to the onset of Gondwana glaciation comparable to those seen in the Illinois Basin, Alaska, and elsewhere.

Ecological analysis of benthic ostracods in the northern Japan Sea, based on water properties of modern habitats and late Cenozoic fossil records

The ecology of ostracods in the northern Japan Sea is well documented. These ostracods can be grouped in two assemblages: (1) the Tsushima Warm Current Surface Water Assemblage (TWSA, northern), which lives in an environment where summer temperatures reach up to about 20 °C, winter temperatures up to about 5 °C. Several species in this assemblage, e.g., Loxoconcha optima and Pontocythere subjaponica tolerate seasonally low temperatures, and lived in the region since the early Pleistocene; (2) the Japan Sea Intermediate Proper Water Assemblage (JSI-PA), which lives at greater depths (lower shelf to upper slope). This assemblage lives under stable conditions, with a small annual range in temperature (0–5 °C). The assemblage has a relatively low diversity, contains species such as Acanthocythereis dunelmensis and Robertsonites spp., and has been present in the area since the Pliocene. These data indicate that the presently living species either tolerate seasonally low temperatures (TWSA, northern) or tolerate stable, but very low temperatures (near 0 °C), and therefore, they could survive the Pleistocene environmental fluctuations in the Japan Sea caused by glacio-eustatic changes in sea level. Our data document the survival of ostracod species during past climate change, and thus can be used to speculate on the effect of possible future climate change on the faunas. We predict that some of the cryophilic species in the Japan Sea cannot be expected to survive global warming for more than 2 centuries.

Basin physiography and tectonic influence on sequence architecture and stacking pattern: Pleistocene succession of the Canoa Basin (central Ecuador)

Facies, shell bed features, and sequence stratigraphic framework for the shallow-marine Pleistocene upper Canoa and Tablazo Formations are presented, based on outcrop data from the southern coast of Cabo San Lorenzo, Ecuador. Sediments of this succession exhibit a distinct cyclic pattern, consisting of a stack of eight depositional sequences (cyclothems) likely developed under the main control of orbitally induced sea-level changes. As a rule, within the studied interval an idealized cyclothem is composed of a transgressive systems tract (TST) and a highstand systems tract (HST), whereas deposits attributable to the lowstand and falling-stage systems tracts are not present. Transgressive lithosomes may be defined by estuarine deposits interposed between the sequence boundary and the ravinement surface (back-barrier wedge) and by upward fining shoreface to inner-shelf facies successions above the ravinement (backstepping shelf wedge). Separated by an expanded siliciclastic core, hiatal shell concentrations occur at the base (onlap shell beds) and the top (backlap shell beds) of the transgressive shelf wedges, and some occur at the base of highstand systems tracts (downlap shell beds). On the basis of sedimentary facies, geometry, taphonomy, and paleoecology of shell beds, and the nature of the transition between siliciclastic and mollusk-bearing sediments, cyclothems were classified into two main types that show dependence upon paleoshoreline morphological configuration: sheltered (in the upper Canoa Formation) and exposed (in the Tablazo Formation). Notwithstanding the different synsedimentary tectonic and climatic regimes, the Ecuadorian cyclothems share basic patterns of condensation and facies assemblages with other roughly coeval cyclothemic successions around the world. This suggests that (1) hiatal shell bed development is not just a temperate-latitude phenomenon; (2) a global process, such as glacio-eustatic sea-level change, is the primary mechanism of control for the general architecture of sequences; and (3) specific paleogeographic settings play an important role by determining the taphonomic and paleoecologic characteristics of key shell beds, the nature of their contacts with the encasing sediments, and the type of the component set of facies. At a multicycle time scale, tectonics influenced the long-term trend of the relative sea-level changes and consequently the large-scale stratigraphic organization. Owing to the continued tectonic uplift of the area, successive high-frequency depositional sequences are nested to form a longer-order falling-stage sequence set.

The effects of glacio-eustatic sea-level change on Pleistocene cold-water ostracod assemblages from the Japan Sea

The Pleistocene palaeo-habitats and the extinction history of cold-water ostracods in the Japan Sea are recorded in its coastal strata. The presence of now-extinct species in the Omma Formation of central Japan (1.5 Ma) indicates that such species predominated in a shallow, open sea environment. The tolerance ranges of these species as to water temperature and salinity are inferred to have been narrower than those of most extant cold-water species in the same families that live in shallow open water, as well as in brackish inner bays. The horizons in the Omma Formation with peak relative abundances of now-extinct species differ from the horizons with peak abundances of living Japan Sea species. We therefore suggest that the now-extinct species were adapted to optimum temperature and salinity conditions that differ from those in the modern Japan Sea. The observation that few now-extinct species survived after 0.4 Ma may be explained by the hypothesis that physicochemical properties of the water masses changed. We argue that, during the glacial periods with increased amplitude (0.9–0.4 Ma), the salinity decreased as the result of glacio-eustatic changes and the closure of shallow straits owing to low sea levels, causing the extinctions.

Ytterholmen revisited – implications for the Late Wenlock stratigraphy of Gotland and coeval extinctions

The latest Cyrtograptus lundgreni graptolite Chron (Late Wenlock, middle Silurian) is characterized globally by the Mulde Event faunal extinctions and glacio-eustatic sea-level change. Only in the last decade has it been recognized as one of the most severe extinction events of the Silurian Period. A section spanning the Slite Group-Halla Formation boundary on the islet Ytterholmen off main Gotland (Sweden) is unique in that strata through the extinction interval are preserved within a reef complex. The importance of Ytterholmen is twofold: First, based on conodonts, lithology and stratigraphic boundaries, the stratigraphy of the Slite Group-Halla Formation boundary interval on eastern Gotland is now fully understood, in ascending order: Slite ‘g’ (c. 12–20 m), Atrypa “reticularis” Beds (c. 0.5 m), Fröjel Formation (c. 0.5 m), and the Halla Formation. The boundary between the Fröjel and Halla formations is an unconformity as previously reported across most of the main island. Second, correlation of the Ytterholmen section with the Mulde Event reference profile on western Gotland for the first time enables study of this event in very shallow interior areas of the carbonate platform. Here, the c. 1 m thick extinction interval (including the Atrypa “reticularis” Beds and the Fröjel Formation) is characterized by mass-occurrences of an atrypid brachiopod, deposition of fine siliciclastic material and termination of the reef complex. Correlation with the East Baltic and Podolia, Ukraine, suggests that similar reef termination occurred contemporaneously throughout the basin. Small patch-reefs occurring immediately above the unconformity on Ytterholmen are among the earliest Mulde Event post-extinction reefs reported from the Baltic basin.

Water temperature, salinity ranges and ecological significance of the three families of Recent cold-water ostracods in and around the Japan Sea

Water temperature (T) and salinity (S) ranges for the modern distribution of relict species of cold-water ostracods in and around the Japan Sea are summarized. These results provide new information on the ecology of species in the Omma-Manganji ostracod fauna and their survival through Pleistocene environmental changes. Fourteen representative species of this fauna belonging to the three families Hemicytheridae, Cytheruridae and Eucytheridae are discussed. The summer T-S habitat requirements were divided into three species groups: (a) Japan open sea-inner bay (0–20°C, 30–341; 9 species); (b) Japan-Alaska open sea (around 5°C, 31–341; 1 species); (c) Japan open sea (0–20°C, around 341; 4 species). The winter T-S of these three species groups falls in a single range of 0–5°C and 30–341. Their summer T-S conditions are characterized by a wide range either for T or S or both. The summer T range of most species reflects the Tsushima Warm Current water in summer. The winter T range of all the species corresponds to the coldest Japan Sea Intermediate-Proper Water through the year. The large T range difference between summer and winter is a remarkable character of most species. It is clear that most of these species examined here also live in temperatures as high as 20°C, but are generally cold-water species as a whole. The winter low T (less than 5°C) is considered to be critical for the survival of all of these species. These species were interpreted as having survived the cyclic environmental changes between glacial and interglacial periods by expansion or contraction of their distribution. Group (a) species can inhabit various T-S environments in summer. Furthermore, they can probably breed and maintain their populations, even in small areas such as the restricted inner bay, when suitable open sea conditions were lost. Group (b) species have only recently migrated to the low T-S region in the Northeast Pacific, and low T regions of deeper areas of the eastern Japan Sea where only a few species live. Group (c) species invaded the newly appearing T-S condition in the shallow-open areas of the Japan Sea, and have flourished, replacing the extinct species during the Pleistocene. Their wide T-S tolerance is considered to be the most advantageous factor for survival through the Pleistocene environmental fluctuations in the Japan Sea, linked with the glacio-eustatic sea-level changes.

Pliocene–Pleistocene sequences bounded by subaerial unconformities within foramol ramp calcarenites and mixed deposits (Salento, SE Italy)

Nine discrete, metre-scale sequences, of Early Pliocene to Middle Pleistocene age, were deposited in the small Novoli graben (Salento peninsula, Puglia, S-Italy). They consist of carbonate and mixed carbonate-siliciclastic sediments, deposited on a slowly subsiding foreland ramp. Skeletal concentrations and intervening less fossiliferous intervals have been examined to provide information on major environmental parameters and infer the dynamics of their changes. Taphonomic and palaeoecological analyses indicate that storm-induced waves and currents, reduced sediment input, and settling behaviour of components were the main factors controlling the features of the various shellbed types. The concentrations were formed below fair-weather wave base in low-stress inner-to-outer shelf environments and are often associated with surfaces or intervals that are characterized by sedimentary condensation. Vertical change in the fossil content within individual cycles indicates water depth changes that were parallel to climatic fluctuations, hence may result from glacio-eustatic sea-level changes. Most sequences are bounded by subaerial, karstic unconformities. Because of the regional setting of low subsidence rate, the record of the relative sea-level fluctuations is incomplete. Episodes of subaerial exposure and concomitant effects of vadose diagenesis are documented by: (i) diagenetic changes leading to hardening of unconformity horizons; (ii) local subvertical solution pits developed in the vadose zone below unconformity surfaces; (iii) networks of polygonal cracks below unconformities; and (iv) infilling of solution pits and polygonal cracks with vadose silt and marine sediment inwashed during transgressions following the subaerial stages. Lower sequences are characterized by tighter cementation and significant increase in moldic and vuggy porosity, due to superimposition of the diagenetic effects of repeated high-amplitude sea-level fluctuations.

Rift structure, evolution, and earthquakes in the Gulf of Corinth, from reflection seismic images

Continental extension is forming the Gulf of Corinth across the strike of earlier Alpine evolution. Here, we present the first deep reflection sections with pre-stack depth-migration processing across the deep basin of the Corinth active rift, which image structures unpredicted by current models. Resolving the infill as a pile of layers that are broken by faults allows one to follow their subsidence and deformation history. Variation among the profiles suggests that southern normal faults control the rift in a time progression from the east towards its western tip. On the central, Derveni–Itea transect, a 3-km widening of the basin accrued since the initiation of this control that is marked by an unconformity between the two main sedimentary units. This is estimated to have occurred 0.5–0.6 Myr ago, assuming the glacio-eustatic sea-level changes have controlled the stratigraphy of sediments deposited as a succession of layers on the subsiding hangingwall, as they did on the southern footwall in forming the famous flight of marine terraces of Corinth. A roll-over anticline and crestal collapse graben are diagnostic of the control by a normal fault of dip varying with depth. The deeper low-angle part of this bi-planar fault is indeed imaged as a reflector in the basement. The occurrence of the collapse with a breakaway at the steep southern basin-bounding fault of the hangingwall slab can be estimated 0.12–0.2 Myr ago, with a marked increase in extension rate that brought it to its present fastest value over 10 mm/yr. The low-angle part of the active fault might also have controlled earlier evolution upslope and in the basin. When compared with inferences from earthquake studies, this low-angle active fault may not appear to be seismogenic but may participate to the seismic cycle, possibly in a conditionally stable regime. Active faults seen as sea-bottom scarps merely accommodate deformation of its subsiding hangingwall. The footwall of the low-angle faults, which current seismicity shows to be in extension, appears then as being pulled out from beneath the rift, in a motion towards the rolling-back slab that causes the Hellenic subduction retreat.

Analysis of the postglacial deposits of the Rhône shelf (golfe du Lion). Implementation to the study of the late Quaternary depositional sequences

Abstract Postglacial deposits of the Rhône shelf have been studied from high-resolution seismic data and Kullenberg piston cores. They are organised into a set of transgressive units or parasequences backstepping from the outer shelf to the subaerial deltaic plain. On the deltaic plain, they are overlain by the prograding deltaic parasequences deposited at the end of the Holocene sea level rise. At regional scale, given the short time span covered by the late Quaternary deposits, tectonic subsidence has played a minor role and sediment deposition on the Rhône shelf was chiefly controlled by glacio-eustatic sea level changes (120 m between the maximum lowstand and present highstand). Progradational phases correspond to periods of reduced rate of eustatic sea level rise while the flooding surfaces bounding the regressive units form during periods of increasing rate of sea level rise and landward shoreline migration. At local scale, location, geometry, nature of deposits, and lateral variations of the stratigraphic pattern are controlled by the interaction between eustasy and local factors as sediment supply, antecedent morphology and ocean dynamics. Seaward of the Rhône river, terrigenous input was important during deglaciation and transgressive deposits extend continuously from the outer shelf to the inner shelf along the retreating path of the paleo-Rhône river mouth. Laterally, on either side of the Rhône incised valley, because of the reduced sediment supply, parasequences only develop on the outer shelf and inner shelf : the combination of the very low inherited gradient of the mid/outer shelf and a very high rate of sea level rise favoured a very rapid migration of the shoreline from outer to inner shelf. Ocean dynamics has been controlled, as in present time, by the E to SE prevailing waves that are the only ones which can develop on an extended fetch. The westward alongshore drift accounted for the development of parasequences west of the incised valley. The sandy material needed for the construction of the outershelf parasequence was supplied by wave-reworking and westward long-shore drift of deposits from the Rhône delta front and the uppermost forced regressive unit. The decreasing sand content of parasequences from outer shelf to inner shelf results from flattening of the equilibrium river profile that led to a decrease in competence and a change in the character of the sediment caliber (relative increase of suspension load). The underlying Pleistocene depositional sequences comprise both lowstand prograding units, that characterize most of the Mediterranean shelves, and intercalated units which are analogs of the postglacial transgressive deposits here presented.

Quaternary transgressive and regressive depositional sequences in the East China Sea

Based on the interpretation more than 4000 km sparker single channel seismic profiles and the comparison with Borehole DZQ4 on the outer shelf of the East China Sea (ECS), the seismic sequences, sedimentary facies and pa-leo-sedimentary environment are studied to establish the chronology framework and discuss the Quaternary transgressive and regressive sequences of the ECS shelf as well as their response to glacio-eustatic sea-level changes. The sea level of the ECS fluctuated with global climate changes in the Quaternary. During the sea level rise, the Pacific tidal wave impacted actively on the ECS continental shelf and the re-ciprocating tidal currents in NW-SE direction formed tidal sand ridges, which represent large transgressive deposits visible on the seismic profiles. In response to sea level fall, the Yangtze River deltas prograded seaward and built massive subaqueous deltas to form regressive sequences on the seismic profiles. Alternative transgression and regression sequences were vertically distributed on the ECS shelf with the frequent eustacy in the Quaternary. The gentle slope of the ECS shelf makes it possible for the coastline to migrate hundreds of kilometers forth and back on the shelf because of tens of meters sea level changes, in the meanwhile, the Yangtze River discharged large amounts of sediments into the ECS resulting in large-scale subaqueous deltas and tidal sand ridges. There have developed 3 stages of tidal sand ridges and 4 stages of deltas on the ECS shelf since oxygen isotope stage 8.

Discrimination of Local and Global Effects on Upper Mississippian Stratigraphy, Illinois Basin, U.S.A.

ABSTRACT Interpretive cross sections based on detailed descriptions of 33 outcrops and cores are used to better understand the relative effects of tectonics, eustasy, tides, and climate on Upper Mississippian (middle Chesterian) stratigraphy in the tectonically active, tide-dominated Illinois basin. The cross sections show that five mixed carbonate-siliciclastic, high-frequency sequences in the Bethel through Glen Dean formations can be correlated around the outcrop belt through areas with very different subsidence histories. The sequence boundaries are marked by paleosols and incised valleys and can be correlated basin-wide within a framework of distinctive marker beds. Because of its updip position, lowstand systems tracts are not preserved in the Illinois basin. The transgressive systems tracts generally consist of one or two parasequences that are typically composed of tidally influenced quartz sandstone filling incised valleys at the base overlain by open-marine skeletal limestone, shallow-marine shale, and heterolithic siliciclastic tidal-flat deposits. The maximum flooding surface (MFS) for the sequences is picked at the base of the deepest water limestone facies. Highstand systems tracts are composed of 1 to 6 regressive parasequences that consist of basal offshore skeletal limestone capped by laterally extensive shale and heterolithic siliciclastic tidal-flat facies. The basin-wide extent of the sequence boundaries and maximum flooding surfaces across tectonic highs and lows suggests that the sequences were produced by eustatic sea-level changes rather than local tectonics or autogenic processes. The sequences were likely produced by moderate- to high-amplitude (30-100 m) fourth-order ( 400 ky) glacio-eustatic sea-level changes driven by the transition from the greenhouse conditions of the Early Mississippian to the icehouse conditions of the late Paleozoic. The lateral extent and frequency of component parasequences suggests that they were likely produced by fifth-order sea-level changes (10-100 ky). The sequences may be bundled into third-order composite sequences, but the third-order signal is obscured by the magnitude of the fourth-order sea-level changes a feature typical of ice-house stratigraphies. The sequences can be used as time slices to identify spatial and temporal variations in differential subsidence between the Cincinnati Arch and the more rapidly subsiding Basin Interior. Episodes of high and low differential subsidence occurred every two to three sequences. These subsidence variations had a major impact on lithofacies distribution and onlap and offlap geometries in sequences and parasequences. The occurrence of some widespread seismically disturbed beds suggests that active faulting occurred during deposition. Normal faulting appears to have occurred during periods of high differential subsidence and reverse faulting during periods of low differential subsidence. Differential subsidence and related normal and reverse faulting may have occurred in response to phases of thrust loading and quiescence in the Appalachian orogenic belt to the east. Even in this tectonically active setting, however, it is the eustatic signal that generates basin-wide, mappable stratigraphic sequences.

Palaeoceanographic records related to glacio-eustatic fluctuations in the Pleistocene Japan Sea coast based on ostracods from the Omma Formation

Six palaeo-water depth oscillations in response to glacio-eustacy during ca. 1.5–1.25Ma were recognized based on the changes of ostracod assemblages from the coastal sediments of the Omma Formation in the Noto Peninsula on the coast of the Japan Sea in central Japan. This is the first report of glacio-eustatic sea-level changes from the shallow-coastal sediments between ca. 1.5 and 1.3Ma, and the process of stepped intensification of the magnitude of the sea-level change is illustrated clearly for the first time.Shallow cold-water and relatively deeper warm-water fossil assemblages appear alternatively in the Omma Formation. This mode of occurrence indicates that sea-level rise occurred repeatedly in parallel with a marine climatic warming. These palaeo-water depth changes occurred with a periodicity of a few tens of thousands of years, and the six sea-level rises can be assigned to oxygen isotope stages 49–39, when compared with the oxygen isotope fluctuation curve from the North Atlantic deep-sea sediments records. The first three sea-level changes probably correlate with stages 49, 47 and 45, and had a magnitude of fluctuation of 10–20m. This was followed by stages 43, 41 and 39, with a magnitude of fluctuations of 50–60m for stage 43 and 70–80m for stage 39. The process of intensification of the amplitude is reflected in the increase of the thickness of warm water influx into the Japan Sea at high sea-level stand during this period, which developed from 20–30m into ca. 100m.

Pulsed uplift estimated from terrace elevations in the coast of Rome: evidence for a new phase of volcanic activity?

The most recent phase of activity from the Roman volcanoes, since 45 ka, has been interpreted to be the waning stage of the older explosive activity that peaked between 550 and 250 ka. Yet substantial regional uplift from approximately 250 ka suggests that magma chambers beneath the area are growing rather than shrinking. We have estimated the uplift history of the region using radioisotopically and paleomagnetically constrained coastal terrace elevation data that allow us to correlate these terraces with marine oxygen isotopic stages 1–22. Elevations have been corrected for glacio-eustatic sea-level change. Our study shows that over the last million years, regional uplift of coastal terraces occurred in pulses that preceded volcanic activity at roughly 800 ka (in the Monti Sabatini) and 600 ka (in the Alban Hills). The recent pulse of uplift since 250 ka occurred primarily during a period of relative volcanic dormancy that lasted from 250 to 45 ka. We hypothesize that the most recent volcanic activity since 45 ka may reflect the completion of magma chamber recharge, suggesting the start of a new volcanic epoch. It is also possible that the local tectonic stress field changed recently from one dominated by transpression to one dominated by extension, allowing magma to more easily reach the surface via normal faults.

The ‘Tortonian salinity crisis’ of the eastern Betics (Spain)

The late Miocene depositional history of the Lorca and Fortuna basins, both occupying an internal position in the eastern Betics of Spain, is marked by a regressive sequence from open marine marls, via diatomites and evaporites, to continental sediments. Based on facies similarities, these evaporites have often been correlated to the well-known Mediterranean evaporites of the Messinian salinity crisis, although this correlation was never substantiated by reliable chronological data. In this paper, we present an integrated stratigraphy of this regressive sequence which shows that the evaporites of the Lorca and Fortuna basins are entirely of late Tortonian age and as such have no relation with the Messinian salinity crisis. The main phase of basin restriction, resulting in deposition of diatomites and evaporites, took place at 7.8 Ma, while the last marine deposits (massive evaporites of the Lorca basin) are dated at 7.6 Ma. Consequently, this ‘Tortonian salinity crisis’ of the eastern Betics had a duration of approximately 200 kyr, while continental deposition prevailed throughout the entire Messinian as also revealed by the fossil mammal record. The ‘Tortonian salinity crisis’ of the eastern Betics is obviously related to a local phase of basin restriction caused by uplift of the metamorphic complexes at the basin margins, probably in concert with strike-slip activity along SW–NE trending fault systems. The development of a submarine sill is of crucial importance for the increase in salinity because it allows marine waters to continuously enter the basin at the surface while it restricts or prevents the outflow of dense saline waters at depth. Furthermore, we show that evaporite and diatomite cyclicity in these restricted basins is predominantly related to precession controlled circum-Mediterranean climate changes and that glacio-eustatic sea level changes only play a minor role. It is remarkable that the lithological sequence of the Tortonian salinity crisis mimics in many aspects that of the Messinian salinity crisis. This suggests that the diatomaceous facies is an essential part of the lithological sequence associated with basin restriction.

Sedimentary Successions Formed by Fifth-Order Glacio-Eustatic Cycles in the Middle to Upper Quaternary Formations of the Oga Peninsula, Northeast Japan

ABSTRACT The northern coast of the Oga Peninsula is a type locality for Quaternary sedimentary exposures on the Sea of Japan side of northeast Japan. Middle to late Pleistocene shallow marine to nonmarine sediments are continuously exposed on sea cliffs along the Anden Coast. These sediments have been mapped and classified into nine sedimentary facies, based on grain size, sedimentary structures, intensity of bioturbation, and associated fossils. The depositional environments and paleo-water depths of each facies have been estimated, based on comparison with the present sub-bottom sedimentary features observed in coastal systems around the Oga Peninsula. On the basis of sedimentary facies analysis, variations in the depositional depth through time have been reconstructed and correlated with the SPECMAP 18O curve, using four marker tephras as time controls. The two curves generally agree between approximately 80 and 450 ka, suggesting that the sedimentary cycles at the Anden Coast faithfully record 5th- and 6th-order glacio-eustatic sea-level changes. Peak-to-peak comparison between the reconstructed depositional depth curve and the 18O curve reveals that (1) unconformities are formed during the late eustatic sea-level falls and/or the following lowstands, (2) transgressive lag deposits are mainly formed below wave base, (3) deepening-upward successions, which sometimes occur below the ravinement surfaces, are formed in the inner part of estuary or barrier-island environments where wave action was minor, (4) shoaling-upward successions formed during eustatic sea-level falls are deposited under the influence of intense wave action in a strand plain-coastal plain system, and (5) the characteristic combination of thinner deepening-upward successions and thicker shoaling-upward successions reflects the asymmetric pattern of glacio-eustatic sea-level changes and/or lower sediment supply during transgression.