Marine Sequences Research Articles

Glacier Peak and mid‐Lateglacial Katla cryptotephras in Scotland: potential new intercontinental and marine‐terrestrial correlations

ABSTRACTUsing contiguous high resolution sampling methods, we report the detection of a Glacier Peak volcanic ash from North America in Lateglacial Interstadial lake sediments in western Scotland. It occurs in close proximity to the Icelandic Borrobol and Penifiler tephras, but is distinguishable by its rhyolitic major‐element composition that is consistent with the earliest set G layer, one of a number of mid‐Interstadial Glacier Peak eruptions dated between 13.71 and 13.41 cal ka bp. Another cryptotephra layer present in these same Interstadial sediments has a rhyolitic composition consistent with the Icelandic Katla source. However, it is in a stratigraphic position below the widespread mid‐Lateglacial Stadial Vedde Ash from Katla, which is also present in these cores. The Katla layer is stratigraphically well defined, suggesting primary airfall, and is compositionally similar to a mid‐Interstadial rhyolitic tephra reported from a North Atlantic marine sequence south of Iceland dated to ~13.6 ka. The detection of Glacier Peak G in the European tephrostratigraphy will permit direct high‐precision correlation of mid‐Interstadial palaeoenvironments between North American and European terrestrial sequences. Any correlation between the new Katla layer and similar marine layers remains provisional, though if verified would permit similar correlation between North Atlantic marine and European terrestrial records.

Age and depositional environment of the Xiaheyan insect fauna, embedded in marine black shales (Early Pennsylvanian, China)

The Early Pennsylvanian Xiaheyan entomofauna (Ningxia, China) is among the earliest assemblages of winged insects known so far, and therefore provides an essential input on deciphering the early diversification of this group. Despite its evolutionary significance, both the age and depositional environment remained poorly constrained. Here, we present high-resolution documentation of litho- and biofacies, biostratigraphy and geochronology of the up to 100 m thick type section. Accordingly, the insect-bearing strata are of latest Bashkirian (latest Duckmantian) to middle Moscovian (Bolsovian) age. The sediments, lithostratigraphically assigned to the Yanghugou Fm., represent a regressional marine sequence formed at the southern margin of the Qilian Inland Sea. Intercalations of crevasse channels and splays that laterally interlock with marine black shales and bioclastic limestones point to deposition in an interdelta bay. Ground-touching waves provoked the erosion of muds at shallow depths leading to mass mortalities among mollusc communities due to rising anoxia, turbidity and water turbulence. In addition, bottom currents transported mud intraclasts towards the basin, where sinking insects that reached the bay via winds and surface currents were buried sub-contemporaneously with bivalves below the storm wave base. Observed differences in insect preservation and assemblage composition across the sequence are found to correlate with lithology and are best explained by distance from land, and the action of events inducing insect carcasses to sink, such as storms. The proposed taphonomic model represents a new fossilization pathway from land to sea and provides new directions for prospecting Paleozoic deposits in the search for insects.

Correlation of carbon isotope stratigraphy and paleoenvironmental conditions in the Cretaceous Jehol Group, northeastern China

ABSTRACTThe Jehol Biota represents an important phase in the history of biological evolution on Earth. Two sites with Aptian Jehol Biota, located in western Liaoning Province and in northern Hebei Province, northeastern China, have generated a major debate about the relationships between their fossil-bearing layers, resulting in confusions about their stratigraphic correlation and biogenetic sequence. We have applied carbon isotope analysis of total organic carbon to provide new data relevant to this debate and have re-examined the connection between volcanism and carbon cycle perturbations, with consideration of the paleoenvironmental conditions. The rare earth element data show that the provenances of the Jehol Group in western Liaoning and northern Hebei were similar and derived mainly from the underlying andesite. Constrained by the radiometric age, the δ13Corg curve suggests that the Dadianzi Formation in northern Hebei is comparable to the three lacustrine layers of the Yixian Formation (ranging from the Jianshangou Bed to the Jingangshan Bed) in western Liaoning. These layers are highly correlated with the early Aptian marine sequence in Oceanic Anoxic Event 1a (OAE 1a), implying that a possible teleconnection (possibly related to a large igneous province) existed between oceanic and terrestrial realms. We also propose that the Xiguayuan Formation above the Dadianzi Formation in northern Hebei is equivalent to the Huanghuashan Breccia Bed at the top of the Yixian Formation in western Liaoning. Moreover, the δ13Corg and element geochemical data suggest that the carbon cycle perturbation and the paleolimnological environments were distinctly influenced by the effects of volcanic CO2 during the early Aptian.

Organic carbon isotopes in terrestrial Permian-Triassic boundary sections of North China: Implications for global carbon cycle perturbations

Abstract The end-Permian mass extinction (ca. 252 Ma) represents the most severe biotic crisis of the Phanerozoic, and it was accompanied by profound environmental perturbations, especially to the global carbon cycle, as indicated by sharp negative carbon isotope excursions (CIE) in both carbonates (δ13Ccarb) and organic matter (δ13Corg). To date, carbon isotope records are mostly from marine Permian-Triassic transitional sequences with relatively few high-resolution carbon isotope profiles having been generated for terrestrial facies. Terrestrial Permian-Triassic sequences suitable for high-resolution carbon isotope study are rare globally and are difficult to correlate with better-studied marine sequences. However, carbon isotope records from continental facies are essential to a full understanding of global carbon cycle changes during the Permian-Triassic transition. Here, we present bulk δ13Corg profiles for three terrestrial sections in North China representing Permian-Triassic transitional beds. These profiles exhibit similar patterns of secular variation defining three stages: (1) a pre-CIE interval, (2) a CIE interval, characterized by a rapid negative shift of 1.7‰–2.2‰ within the middle part of the Sunjiagou Formation, and (3) a post-CIE interval. The similarity of the CIE in all three study sections facilitates correlations among them, and its presence in the Permian-Triassic transitional beds suggests that it is equivalent to the negative CIE at the Permian-Triassic boundary in the Meishan global stratotype section and point (GSSP) and in coeval marine and terrestrial sections globally. The end-Permian CIE was probably triggered by a massive release of 13C-depleted carbon from volcanogenic sources leading to elevated atmospheric pCO2, although oceanic sources of CO2 cannot be ruled out at present.

Cross correlation of CIELAB color reflectance data from archive photographs and line-scan images of sediment

AbstractArchive color photographs—particularly of sites where sediment is no longer available—are an underused resource that potentially contains detailed paleoenvironmental information. To investigate this potential, two sets of digital images were taken, at different times, of loess, glaciolacustrine, and deep-sea sediments. The first image set was taken using standard digital cameras. Lighting conditions and sediment surface preparation varied, in a similar way to characteristics likely to be encountered in archive photographs. The second image set was taken by a high-resolution, line-scan camera with an integrated light source. CIELAB (Commission Internationale de l'Eclairage) color reflectance data were obtained from both image sets and analyzed by cross correlation. Of the three reflectance parameters (L*, a*, and b*), L* reflectance is the most compromised by differences in ambient lighting or moisture content. Textural distinctions appear to be an important factor influencing the cross correlations and produce multiple, relatively weak solutions for the glaciolacustrine sediments, whereas the texturally uniform loess and deep-sea sediments produce a single, best-fit solution. Comparison of a* reflectance records from an undated marine sequence with a chronologically constrained sequence from the same site indicates the potential to apply color reflectance to produce preliminary age models.

First geochronological constraint for the Palaeoproterozoic Lomagundi-Jatuli δ13C anomaly in the Tandilia Belt basement (Argentina), Río de la Plata Craton

Geochronological data of Palaeoproterozoic carbonates with δ13C values between +5‰ and +16‰ suggest that the positive carbon isotope excursion of the global Lomagundi-Jatuli event (LJE) occurred mostly between 2220 and 2060 Ma.In the southern portion of the Río de la Plata Craton, the LJE was recorded in calcite-diopside marble of the Tandilia Belt basement. The marble was found at the San Miguel area as part of a metamorphic rock assemblage, mainly composed of gneisses and migmatites, formed during the Transamazonian Orogeny. The latter represents the maximum magmatic and metamorphic activity in the Tandilia Belt basement. The marble, derived from a calcareous-siliciclastic sedimentary marine sequence, was intruded by leucogranites that provoked the San Miguel skarn formation.First U-Pb LA-ICP-MS age of 2206 ± 14 Ma, obtained from titanites of the skarn, also placed the metasomatic processes into the Transamazonian Orogeny. In addition, this age corresponds to the minimum age for the marble’s protolith deposition which matches with the beginning of the LJE worldwide. These new data would favor the correlation between the San Miguel marble and the Montevideo Formation marble of the Tandilia Terrane (Uruguay), within the Río de la Plata Craton, and not with the Paso Severino Formation of the Piedra Alta Terrane, which is at least 60 Ma younger.New δ13C determinations in calcite crystals from the marble allowed the lowest and the highest carbon values (+3.19‰ and +6.90‰, respectively) to be obtained. The lowest values are within the range of normal marine carbonates (between −5‰ and +5‰), despite having been altered by contact metamorphism, while the highest values are typical of the LJE carbonates. In this sense, the early deposition of the carbonate protolith within the LJE, together with the effect of post-depositional metamorphic processes would justify the wide range of values shown by the isotopic ratios of C.

The Devonian-Cretaceous fossil record of “conchostracans” of Africa and their paleobiogeographic relationships with other Gondwanan faunas

The main objective of this work is to present a survey of the fossil record of “conchostracans”, a group of continental (also occasionally from brackish and marine sequences) fossil invertebrates, recorded from Africa, to explore relationships among these taxa and those recorded from other paleocontinents, and to assess the potential for the African “conchostracan” records to provide insight on paleobiogeographic connections within Gondwana. This work is focused on “conchostracans” (laevicaudatans, spinicaudatans and cyclestheriids), because “conchostracans” are one of the most widely documented groups in the Phanerozoic continental sequences. A clear signal of taxonomic change is recovered within the African fauna. Leaiids, lioestheriids and palaeolimnadiids characterize African Paleozoic-Triassic strata, whereas afrograptids, fushunograptids and palaeolimnadiopseids characterize African Mesozoic strata. The relationship among African and other Gondwanan taxa is considered, and the potential for “conchostracans” as paleobiogeographic indicators is evaluated. Biogeographic analysis is based on the compiled data about the African “conchostacans” fossil record with specific consideration of some emblematic groups (Leaiidae, Paleolimnadidae, Vertexiinae, and Afrograptidae). Key dispersal pathways may have operated. During the Devonian to Triassic, records suggest four different faunal interchanges between Africa and Australia, Europe, South America, and India. During the Jurassic to Cretaceous, records suggest five different faunal interchanges between Africa and South America, Europe, Asia, India and Antarctica marked by different emblematic taxa.

Dinoflagellate cysts and Foraminifera of the Upper Jurassic Lopsiya River sections, Nether-Polar Urals, NW Western Siberia (Russia)

The Upper Jurassic Lopsiya River sections (Nether-Polar Urals) represent the most complete stratigraphical marine sequence throughout Russia. It is characterized by a continuous succession of Kimmeridgian to Lower Volgian deposits and is defined by rich faunal associations including ammonites, belemnites, and bivalves. The Lopsiya River sections were previously studied in detail with palaeontological, lithological, and litho-geochemical purposes. Furthermore, assemblages rich in palynomorphs and foraminifers were found in the currently studied successions of the Lopsiya River sections. It results the establishment of the uppermost Oxfordian to Lower Volgian foraminiferal zones, as well as the Kimmeridgian dinoflagellate cyst zones and palynological assemblage. Then, the Upper Jurassic dinoflagellate cyst and foraminiferal biostratigraphical zonations have been calibrated against the ammonite zones. Finally, current results on the Lopsiya River sections have been compared with biostratigraphic data of the Kimmeridgian dinoflagellate cyst assemblages from northwestern Europe, Russian Platform, and Arctic Siberia. The studied foraminiferal and dinoflagellate cyst assemblages of the Upper Jurassic successions of the Lopsiya River sections hold high potential of correlations, especially for the Kimmeridgian strata.

Geochemical, mineralogical and statistical characteristics of arsenic in groundwater of the Lanyang Plain, Taiwan

High arsenic concentrations (average 0.1 mg/L) of groundwater were found in Lanyang plain of Taiwan. In this study, 39 groundwater samples from 23 wells were collected and 14 hydro-geochemical parameters were analyzed. Factor analysis was applied to determine major influence factors of the arsenic enriched groundwater quality, and PHREEQC was used to calculate the distribution of aqueous species and saturation index of which affected the hydrogeochemistry of groundwater. 393 geological core samples from 9 drilling wells were collected and analyzed the contents of total arsenic and iron. Moreover, core samples associated with high arsenic concentration groundwater were selected, mineralogical phases were analyzed using X-ray fluorescence (XRF), high resolution X-ray photoelectron (XPS) and scanning electron microscope and energy dispersive spectrometer (SEM-EDS). Results of the arsenic enrichment factor determined by factor analysis indicated that infiltration of the organic and nitrogen pollutants from anthropogenic activities to shallow groundwater, and the reductive dissolution from iron oxyhydroxides in the deep aquifer were the main processes of arsenic release to groundwater from the sediment. Total arsenic and iron contents of the core samples were well correlated in marine sequences. The presence of clay layer within the subsurface may increase in the As contamination in groundwater aquifer. However the time for As release from clay layer to lower aquifer may require tens or hundreds years to complete under natural environment condition. Surface analyses of core sample performed by XPS showed that arsenic was adsorbed or co-precipitated with non-crystalline iron oxyhdroxides and sulfides. After a long term burial of sediment, microbial metabolism of organic matter creates a more reducing environment, arsenic may then be gradually released from iron oxyhydroxides by reductive dissolution or desorption to aqueous phase. The framboidal-diagenetic type phase was identified by XPS and the groundwater is supersaturated with respect to pyrite and orpiment determined by PHREEQC are suggesting sulfide minerals co-precipitate As. Arsenic in sediments is released into groundwater primarily by the reductive dissolution of As-bearing Fe-oxyhydroxides in reducing environment in the Lanyang plain.

Pelmatozoan “rooting grounds” from the Early Devonian (late Emsian) Heckelmann Mill Fossil-Lagerstätte (Lahn Syncline, Rhineland-Palatinate, SW-Germany): morphological, palaeoenvironmental and taphonomic aspects

An exceptionally rich occurrence of pelmatozoan holdfasts from the Early Devonian Heckelmann Mill Lagerstatte in the Lahn Syncline is documented. Two distinct holdfast morphotypes are described, a larger one with clearly separated radicles and a smaller one showing interpenetration of radicles. Both types served to anchor the animals on soft substrates and are designated as terminal dendritic radice holdfasts broadly similar in morphology to those of the crinoid Eucalyptocrinites. Occasional turbidity currents or mud-flows, possibly released by seismic events or severe storms, affected the Heckelmann Mill biota. These either “mowed down” these pelmatozoans or, more probably, triggered their autotomy. Only their “roots” were preserved in situ by obrution. Such a scenario is furthermore indicated by the taphonomy of associated biota. The depositional environment is tentatively interpreted as a storm influenced outer shelf within the photic zone and below average storm wave base. Additionally, reports of early land plants from fully marine sequences known to yield pelmatozoan tree root-like holdfasts should be treated with caution when based upon sterile axes alone.

Recent Geomorphological Evolution and 3D Numerical Modelling of Soft Clastic Rock Cliffs in the Mid-Western Adriatic Sea (Abruzzo, Italy)

Geomorphological evolution, erosion and retreat processes that affect the rocky coasts of the mid-western Adriatic Sea (Abruzzo, Central Italy) are the subject of this research. This coastal sector, one of the few examples of clastic soft rock coasts in the Mediterranean Sea, is characterized by active, inactive and paleo cliffs, as well as coastal slopes, composed of the clayey-sandy-arenaceous-conglomeratic marine sequence (Early-Middle Pleistocene) covered by continental deposits (Late Pleistocene-Holocene). This study provides geomorphological and 3D modelling stability analyses of the cliffs of Torre Mucchia, Punta Lunga, Punta Ferruccio (Ortona, CH) and Punta Aderci (Vasto, CH), which are popular tourist sites included in natural reserve areas. They are representative of two main types of active cliffs on soft clastic rocks: cliffs on sandstone and cliffs on conglomerate with notches. In order to evaluate the processes and factors that induce cliffs to retreat and their recent evolution, the research was based on a DEM analysis (LIDAR 2 × 2 m data), aerial photos and an orthoimages interpretation, detailed geological–geomorphological surveys, and a structural analysis; field and remote investigations were combined with numerical modelling with a FLAC3D calculation code. Geological and geomorphological field data provided reliable 3D models, and FLAC3D numerical analyses allowed the definition of the most critical and/or failure areas, and the evaluation of the controlling factors, evolution mechanisms of the slopes and the sliding kinematics of gravitational instability phenomena. Different retreat mechanisms have been observed all along the investigated coastal sectors, induced by gravitational processes due to coastal erosion cycles at the foot of the cliffs, and controlled by lithological features and joints systems. The geomorphological analysis combined with the 3D modelling (i) showed that the retreat process of the cliffs is connected to translational slides and rockfalls (cliffs on sandstone), combined rockfalls, and topples (cliffs on conglomerate), largely controlled by main joints; (ii) defined the most critical areas along the cliffs. These results are of great interest in the assessment of hazard connected to potential sliding on the cliffs. Their implementation within Geographical Information Systems provides a valuable contribution to the integrated management of coastal areas, strongly improving the identification and prediction of landscape changes and supporting a new geomorphological hazards assessment, in areas of high tourism, as well as natural and cultural landscape value.

Preliminary tephrochronological study of the Yezo Group (uppermost Albian–basal Campanian) in north Japan

The Yezo Group, exposed in north Japan, is a Cretaceous siliciclastic marine sequence accumulated in the active Asian continental margin of the northwest Pacific. This group is regarded as an important Cretaceous reference sequence in Japan because the detailed age of the group has been determined by numerous studies of bio- and chemostratigraphies, in addition to the radiometric dating of tuffs. Here we preliminarily establish a tephrostratigraphy in the middle–upper parts of the Yezo Group (uppermost Albian–basal Campanian interval) based on the trace-element composition of apatite contained in tuffs to improve the regional stratigraphic correlation of the Cretaceous sequences in the northwest Pacific region. The results demonstrate that the Cl, Mg, Mn, Fe, Y and Ce contents of apatite are useful to discriminate and correlate individual tuffs in the Yezo Group. The correlation of tuffs among distant areas in Hokkaido, Japan revealed three widely traceable (within a distance of several hundreds of kilometers) tuffs intercalated in the lower Cenomanian, Turonian/Coniacian boundary and the Santonian/Campanian boundary. Correlation of the tuffs also solves the local biostratigraphic problem where the datum plane of age-diagnostic fossils is sometimes diachronous across areas, which is attributed to the sporadic occurrences of fossils and/or different depositional settings.

Basin evolution, configuration styles, and hydrocarbon accumulation of the South Atlantic conjugate margins

The basins of the South Atlantic passive margins are filled with early rifting stage lacustrine sediments (Barremian, 129–125 Ma), transitional lacustrine and marine sediments (Aptian, 125–113 Ma), and drift stage marine sediments since early Cretaceous (Albian, 113 Ma). The South Atlantic margins can be divided into three segments by the Rio Grande Fracture Zone and the Ascension Fracture Zone according to variations in the basin evolution history and configuration style. The lacustrine shale and marine shale source rocks are developed in the rift stage and drift (post-rift) stage in the South Atlantic passive margins, respectively. The southern segment of the margins is dominated by the lacustrine sedimentary filling in the rifted stage overlain by a thin marine sag system as a regional seal, where the hydrocarbons are mainly accumulated in the structural-stratigraphic lacustrine reservoirs formed in the rift stage. The middle segment developed salty rift-sag-type basins with rift and sag systems and with salt deposited in the transitional intercontinental rift stage, where the lacustrine shale in the lower part of the rifted lacustrine sequence and the marine shale in the lower part of the sag sequence formed in the marine post-rift stage are high-quality source rocks. This segment in the middle is mainly dominated by pre-salt lacustrine carbonate and post-salt marine turbidite plays. The northern segment is characterized by sag-type basins with a narrowly and locally distributed rifted lacustrine system and its overlying widely distributed thick marine sag systems. Gravity-flow (mostly turbidite) marine sandstones as good reservoirs were extensively developed in the sag stage due to the narrow shelf and steep slope. The post-rift marine shales in the lower part of the sag sequence are the main source rocks in the northern segment and the hydrocarbons generated from these source rocks directly migrated to and accumulated in the deep marine turbidite sandstones in the same sag sequence formed in the drift stage. From southern segment to northern segment, source rocks and hydrocarbon accumulations tend to occur in the stratigraphically higher formations. The hydrocarbon accumulations in the southern segment are mainly distributed in the rifted lacustrine sequence while that in the northern segment primarily occur in the post-rift marine sequence.

The Blake Geomagnetic Field Event recorded in a sequence of marine and continental facies outcropping in the coast of Buenos Aires province, Argentina

Different authors have suggested that there is a relationship between Quaternary geomagnetic field events and climate variability. Considering that in a recent paper a detailed stratigraphic study in a section of the coast of Claromecó (Buenos Aires province) indicates Late Pleistocene paleoclimatic changes, a paleomagnetic study was performed in the same stratigraphic succession. The analyzed sedimentary section belongs to “Belgranense” unit that is composed of continental and marine deposits. According to previously published dates and stable isotope results presented in this paper, it is proposed that 6 facies (sedimentary units) of the Claromecó section developed during the interglacial Marine Isotope Stage 5 (MIS 5). These units are presumably coeval with one of the best known geomagnetic field events, the Blake Event, occurred during the MIS 5, between ca. 120 and ca. 115 ka. The studied units from the base to the top are: 1) diagenetic wackestones with clasts of sand, 2) pedogenized loessian deposits, 3) lower marine wackestones, 4) lower tidal channel deposits, 5) upper marine wackestones and 6) upper tidal channel deposits. The section is capped by a continental gravity flow much younger than MIS 5. Different facies record distinct characteristic remanent magnetizations (ChRM) suggesting that these have a not modern origin. Low-field thermomagnetic curves and hysteresis loops were performed for all the sedimentary facies that provide magnetic remanences. Special sediment magnetism experiments were made for the units with reverse and/or oblique reverse components including isothermal remanent magnetization and anhysteretic remanent magnetization to perform the Lowrie-Fuller test. In these units opaque minerals were identified using polished and thin sections together with scanning electron microscopy analysis. According to all the results it is interpreted that the Blake Geomagnetic Field Event was recorded in the pedogenized loessian deposits with magnetite crystals generated during pedogenetic processes, and in extracellular biogenic magnetite crystals in the lower marine wackestones. The reverse and/or oblique reverse ChRM components were recorded before the lower tidal channel deposits, which have normal polarity directions. The Blake Geomagnetic Field Event was recorded in Claromecó during last interglacial MIS 5, however a direct correlation cannot be made between the recorded transitional polarity and a marine transgression corresponding to an important melting of ice sheets during this marine isotope stage. The magnetic components recorded in the studied sequence could be used as a stratigraphic tool to help identify “Belgranense” unit in Argentina or correlative sedimentary facies outcropping in South America.

Establishing a high‐resolution stratigraphy in the Holocene marine sequence of the ancient Theodosian harbor of Istanbul with the help of dendrochronology

AbstractSalvage excavations in the Theodosian harbor (Yenikapı‐Istanbul) have uncovered diverse archaeological objects including 36 shipwrecks and various Byzantine period wooden docks. The sequence of these docks provided a unique opportunity to obtain a high‐resolution stratigraphy. The new approach is based on stratigraphic interpretation of deformation patterns created by the posts in soft sediments, combined with dendrochronological dating of the posts. Dendrochronology offers the potential to date the posts to within one calendar year of felling, a level of precision and accuracy rare in sedimentological analysis. The posts, most of them Quercus, were rammed during six different time periods. The first period is associated with posts cut in 528 AD. The second and third periods are dated by posts cut in 583 and 594 AD, respectively. The fourth‐period dates within 8–10 years of 639 AD. The fifth period could be dated only roughly to between 690 and 770 AD. The last period produced a possible placement of after 778 AD. This new approach helps to establish a high‐resolution stratigraphy. Furthermore, it provides information about sedimentation history and specific anthropogenic events.

A Late Carboniferous–Early Permian back‐arc basin in the southeastern Central Asian Orogenic Belt: Constraint from sedimentological and geochronological investigations of the Shoushangou Formation in the central Inner Mongolia

The Solonker Suture Zone was formed during the closure process of the Paleo‐Asian Ocean (PAO). In order to better constrain its tectonic setting and evolution history in the Late Carboniferous–Early Permian, we conducted an integrated study of the Shoushangou Formation in the central Inner Mongolia, involving the sedimentological features, depositional age, and detrital zircon populations. Our results indicate that the Shoushangou Formation was deposited in ca. 320–280 Ma, overlain by the Dashizhai Formation with ages of ca. 280–274 Ma, and the 330‐ to 280‐Ma detrital age data almost serve as the entire age component of this formation. Also, its stratigraphic reconstruction shows a coarsening‐upward marine sequence upwards, which is characterized by sandstone turbidites with a Bouma sequence and the numerous tuff involvements in the lower strata, showing a deep marine environment and synchronous volcanism. Integrating previous data and our results, with a gradually deepening water depth and a geographic variation, detrital zircon age spectra from the Late Carboniferous–Early Permian sequence show distinct differences, and a marked shift of multiple resources to a single source occurred in the Late Carboniferous–Early Permian. These clues suggest an active marginal setting and a northward‐dipping subduction during this period in the north side of the PAO, and we further attribute such a source variation to the spreading of a marine back‐arc basin after the amalgamation of the Uliastai Active Continental Margin with the Northern Accretionary Orogen. The Shoushangou Formation was the direct depositional response to such a back‐arc basin.

Biostratigraphic Analysis of the Cretaceous Abeokuta Group in the Eastern Dahomey Basin, Southwestern Nigeria

Shales of the Abeokuta Group in the Dahomey Basin yielded abundant foraminiferal tests. The study investigated sediments from three wells that were drilled for petroleum exploration: Well – X located in the offshore deep water, Orimedu-1 and Ise-2 in the coastline region to establish their Cretaceous biostratigraphic units through planktonic foraminiferal zonation. Calcareous benthonic foraminifers occur abundantly and consistently throughout the sequences in the three wells while planktonic foraminifera are more abundant in the Well X than those in the Orimedu-1 and Ise-2.The identified planktonic foraminiferal species are: Rotalipora greenhornesis, Rotalipora cushmani, Dicarinella primitiva, Praeglobotruncana helvetica, Marginotruncana sp. Heldbergella delrionensis, Helbergella planispira, Hedbergella simplex, Whitenella inonata, Whitenella baltica, Globotruncana aegytiaca, Globotruncana sp., Heterohelix reymenti, Heterohelix moremani, Heterohelix globulosa, Abathomphalus mayaroensis and occurrence of Orthokarstenina oyea, Ammobaculites corprolithiformis, Ammobaculities sp and Bolivina sp. Calcareous benthonic foraminiferal species were more abundant than the planktonic species in Orimedu-1 and Ise-2 wells. The benthonic species decrease drastically in the well-X offshore deep water where the planktonic species were most abundant. This trend may suggest an increasing water depth from near coastline to offshore regions in the Cretaceous times.Six planktonic foraminiferal zones were recognised across the three exploratory wells. These include Rotalipora greenhornesis (middle – late Cenomanian), Helvetoglobotruncana helvetica (early – late Turonian), Marginotruncana pseudolinneiana (late Turonian), Marginotruncana renzi (Coniacian – Santonian), Globotruncana calcarata (late Santonian – early Campanian) and Globotruncana aegytiaca (Maastrichtian) Zones. The Rotalipora greenhornesis and Praeglobotruncanae helvetica Zones (Cenomanian – Turonian) were correlated with the standard zones in the Tethyan regions.The Well-X indeed penetrated older Cenomanian to Turonian intervals in the investigated wells, thereby confirming the presence of older marine sequences in the Eastern Dahomey Basin contrary to previous suppositions.

The glacier-influenced marine record on high-latitude continental margins: synergies between modern, Quaternary and ancient evidence

Abstract Major glaciations or ‘ice ages’ are known to have affected the Earth's surface over the past three billion years. The best preserved records of these glaciations are often found in high-latitude continental margin settings where sediment has been delivered to, and then accumulated at, the edge of the ice sheet in thick glacier-influenced marine sequences. The composition and geometry of these deposits and the related assemblages of glacial landforms provide a wealth of information about the environmental setting during successive cycles of glaciation and deglaciation, including ice-dynamic and oceanographic processes. Here, we discuss modern (present day), Quaternary (last 2.6 myr) and ancient (last 1 gyr) high-latitude continental margin settings, and then contrast the methodologies used and glacier-influenced deposits and landforms most often identified for each time period. We use examples from the literature to identify synergies, as well as to note differences, between studies of glacier-influenced sediments from ancient to modern environments.

Marine Isotope Stage 4 in Australasia: A full glacial culminating 65,000 years ago – Global connections and implications for human dispersal

Over the last four decades of palaeoclimate research, significant emphasis has been placed on the Last Glacial Maximum (LGM) spanning 26.5–19 thousand years ago (ka), a period that saw significant (∼125 m) sea-level reductions and major ice caps adorning large parts of the Northern Hemisphere. Here, we present evidence for another major glacial period spanning 71–59 ka (Marine Isotope Stage 4: MIS4) from a well-dated marine sequence offshore South Australia. The astronomically-tuned chronology of this deep-sea core is confirmed using single-grain optically stimulated luminescence dating (OSL), providing confidence in our high-resolution age model. Our approach to the study of our MD03-2607 core has been to employ many different proxies. These are: δ18O of both planktic and benthic foraminifera for stratigraphic purposes, faunal counts of planktonic foraminifera to reconstruct the position of oceanic fronts and currents, alkenone palaeothermometry, XRF core scanning to determine the presence of aeolian dust, and εNd isotope to identify fluvial discharge over the core site. We compare our new proxy findings with other archives for mainland Australia and Tasmania.Our multi-proxy palaeoclimate reconstructions are consistent with other marine, terrestrial and cryosphere archives across the Southern Hemisphere and suggest, for the first time, that MIS 4 was almost as dramatic as the LGM. During MIS4, global sea-level was reduced by ∼100 m, glaciers across Australasia were more significant compared to the LGM, and sea-surface temperatures were much reduced. These glacial conditions uniformly peaked around 65 ka. Global comparisons show major glacial conditions and vegetation shifts elsewhere during MIS4, but many are poorly dated. The significant environmental changes taking place during this glacial period were paralleled by waves of human dispersal across Eurasia and the earliest evidence of human occupation in northern Australia at 65 ka.

Sea level-controlled sediment transport to the eastern Arabian Sea over the past 600 kyr: Clay minerals and Sr[sbnd]Nd isotopic evidence from IODP site U1457

Long marine sequences deposited in the Arabian Sea are suitable to study the orbital sensitivity of sediment dynamics from a source-to-sink perspective. The clay mineralogy and SrNd isotopic compositions have been analyzed for the detrital fraction of sediments from IODP Site U1457 located in the Laxmi basin, eastern Arabian Sea to constrain the sediment sources and reconstruct a high-resolution record of sediment export to the Indus deep-sea fan over the past 600 kyr. The 87Sr/86Sr ratio (varying from 0.7154 to 0.7255) and εNd (varying from −12.9 to −9.5) imply a mixing of sediments derived from not only the Indus River but also the rivers draining the Deccan Traps. The variations in the smectite/(illite + chlorite) ratio combined with SrNd isotopes permit the reconstruction of past changes in the relative proportions of sediments derived from the Indus River (mainly illite, chlorite and kaolinite) and the Deccan Traps (smectite). The wavelet and cross-spectral analyses further reveal that sediment transport to the eastern Arabian Sea since 600 kyr is mainly dominated by sea-level variations in the eccentricity (100-kyr) band, while the Indian summer monsoon might contribute moderately to the precession (23-kyr) band. The εNd and turbidite frequency indicate that more turbidite events are associated with Indus River-sourced sediments at IODP Site U1457 during sea-level lowstands, which might reflect a reconnection of deep-sea channels to the Indus River mouth and/or reworking of previously deposited Indus River sediments located northward.