Eustatic Sea-level Fall Research Articles

Carbon cycle perturbations and environmental change of the middle permian and Late Triassic Paleo-Antarctic circle

During the middle Permian through the Triassic, Tasmania moved from paleo-latitudes of 78° to 69°S, wedged between Antarctica and Australia, within the paleo-South polar circle. During this time, significant global carbon cycle disturbances triggered major environmental and climatic changes and mass extinction events globally. The Bicheno-5 core from Eastern Tasmania, Australia, provides the opportunity to examine middle Permian and Upper Triassic sediments from the paleo-Antarctic, using high-resolution organic carbon isotope (δ13CTOC) chemostratigraphy, pXRF, and sedimentology, combined with new palynological data integrated with the existing radiometric age model. While there is a significant unconformity in the Upper Permian to the middle Triassic associated with eustatic sea-level fall as a result of regional uplift in eastern Australia, three distinct carbon isotope excursions (CIEs), characterized by negative shifts of up to − 6 ‰ were identified; the middle Permian Guadalupian Carbon Isotope Excursions (G-CIE), the Carnian Pluvial Episode (CPE), and the mid-Norian Event (MNE). These three events highlight a significant climate shift through glacial and interglacial cycles to warmer non-glacial intervals in the Late Triassic, with evidence of the polar record of the Carnian Pluvial Episode and the mid-Norian Event, which are poorly studied in the Southern Hemisphere, specifically within the Paleo-Antarctic circle.

Integrated multi-proxy source-to-sink analysis of Late Barremian (Lower Cretaceous) clastic systems in the Essaouira-Agadir Basin

This study investigates the provenance of the continental and marine Late Barremian clastics of the Bouzergoun Formation, exposed in the Essaouira-Agadir Basin (EAB). Thin section petrography, Scanning Electron Micrography, heavy minerals analysis, and detrital zircon dating were conducted and integrated with a large dataset of published Low-Temperature Thermochronology (LTT) studies to reconstruct the associated source-to-sink system(s). The results constrain the source and size of the system, and composition of deposited clastics, and investigate the mechanism for delivery of coarse clastics into the offshore domain, a key target for hydrocarbon exploration.The homogeneity of rock composition fingerprints throughout the basin indicates a common provenance for both the northern and southern studied transects. Hinterland analysis based on LTT data identifies the Western Meseta and Massif Ancien de Marrakech (MAM) regions as the only possible source candidates exhuming during the Late Barremian, confirmed by detrital zircon geochronology. Heavy mineral populations reveal partly recycled sediment including a probable igneous source. Rock fragment populations comprise limestones, sandstones, and volcanic composition, which correlate with lithologies of the MAM.The integration of all data suggests a best-fit model for the Late Barremian of a source-to-sink system of moderate size (200–300 km long), dominantly sourced from the MAM (western High Atlas). This provided a sand-rich mix of sediment resulting from the erosion of exhuming Triassic continental basins, with associated clays from the weathering of basalts and Triassic/Jurassic mudstones.Late Barremian eustatic sea level fall, together with regional uplift in the hinterland, is interpreted to have resulted in a forced regression that allowed the system to prograde towards the slope margin, offering enhanced potential for sand delivery into the deep offshore domain. Seismic imaging offshore provides tentative interpretation of synchronous high reflectivity deepwater channels located in structural lows controlled by diapiric salt movement.The Mesetian domain was likely undergoing denudation at the same time and shedding clastic-rich sediments to the northern part of the EAB, beyond the studied region. Sediment supply from the MAM may be mixed with the Mesetian sands to the northern part of the EAB and tentatively in the offshore Essaouira.

Geomorphologic control on the evolution of Middle-Late Miocene submarine channels in the Southern Taranaki Basin, New Zealand

The Clifdenian-Tongaporutuan interval in the Southern Taranaki Basin experienced significant activity by turbidity flows during the Middle to Late Miocene, resulting in the formation and burial of several submarine channels. The chronological evolution of these channels is difficult to prove due to their architectures, repeated cut-and-fill, stacking patterns, erosive and erosional natures, and spatial-temporal interactions. In this study, high-quality 3D seismic reflection data from three industrial seismic reflection surveys, combined with five exploration industrial standard wellbore data, were used to analyze the geomorphologic controls on the evolution of fourteen channels within the Clifdenian-Tongaporutuan interval (Middle to Late Miocene) of the southern Taranaki Basin. Our seismic geomorphological analysis, which included seismic facies, slicing, and seismic attribute techniques, revealed that the channels can be classified into two main groups: isolated and amalgamated stacks. These groups may further include high sinuosity-meandering, low sinuosity-meandering, and straight channels. Additionally, gamma-ray logs indicated cylindrical, bell, and serrated trends of sandstone within a thick shale interval, indicating the presence of submarine channels in the study area. Furthermore, the complex spatial interactions of the channels, including architectural variation, and their temporal evolution reflect the activities of different turbidity flow regimes and the interaction with seafloor topography. These interactions, along with a balance between waxing and waning energy phases, influenced the evolution, architecture, and scale of the channels. Importantly, the eustatic sea-level fall in the late Waiauan at approximately 13 Ma, increased clastic sediment supply (climate) and tectonic activities related to rifting and contraction in the Middle Miocene played a significant role in shaping the channels. The workflow, integrated analysis, findings, and the unique case study area presented in this study contribute to research on submarine channels and provide insights into seismic geomorphology, seismic attributes, paleoenvironment reconstruction, the Taranaki Basin, climate, sea-level, and tectonics.

Stratigraphic architecture and fluvial interpretations of the Upper Cretaceous (Turonian?) Middendorf Formation, Chesterfield County, South Carolina, U.S.A.

ABSTRACT The Upper Cretaceous (Turonian?) Middendorf Formation is a sand-rich stratigraphic unit of fluvial origin that forms a large aquifer in the U.S. Atlantic Coastal Plain. In Chesterfield County (South Carolina), which is the site of the type locality, the formation ranges in thickness from 66.5 to > 119.7 meters. The base of the formation is an unconformity above Paleozoic metasiltstone, and the upper contact is an unconformity above which lies sand of the Quaternary Pinehurst Formation. Outcrops display the following five facies assemblages: 1) sandstone to conglomeratic sandstone (fluvial bar and channel deposits), 2) beds of alternating laminae of sandstone and mudstone (fluvial overbank or floodplain deposits), 3) ≥ 1 m-thick beds of clay (swamp deposits, floodplain deposits, and/or sediment that accumulated in abandoned fluvial channels), 4) 0.2–0.5 m-thick planar to slightly undulatory beds of framework-supported sandstone with a mud matrix (traction-dominated current deposits at the top of fluvial bars, upper-flow-regime bedform deposits in subsidiary fluvial channels, or coarse-grained overbank deposits), and 5) sandstone to conglomeratic sandstone cemented by iron (interpreted as fluvial bar and channel deposits, with the iron cement being a diagenetic “groundwater ferricrete” that formed via the circulation of shallow groundwater and the oxidation of iron-bearing minerals). Kaolinite in various forms is pervasive throughout the formation and is interpreted as an early diagenetic phenomenon that formed by prolonged postdepositional weathering and flushing by meteoric water under a warm and humid paleoclimate. The fluvial system that formed the Middendorf Formation prograded into the area from the west or northwest from uplifted margins of Mesozoic rift basins and/or the Appalachian Mountains. This progradation was a response to a base-level fall and the sediment accumulated during base-level lowstand and subsequent early transgression. In Chesterfield County, the Middendorf Formation can be subdivided into three fining-upward sequences. Each sequence consists predominantly of medium to coarse sand with a greater abundance of gravel in the lower part of the sequence and a greater abundance of clay and silt beds in the upper part. Each sequence is interpreted as either a response to autogenic processes or a response to allogenic sea-level changes, specifically a higher-order (higher-frequency) progression from relative lowstand conditions to early transgression whereby coarse sand and gravel (e.g., fluvial bar and channel deposits) were preserved during initial lowstand conditions and a greater proportion of mud and finer-grained sand (floodplain deposits) were preserved during subsequent early transgression. The Middendorf Formation is correlative with several other kaolinite-rich fluvial sandstones in North America including the Raritan Formation in New Jersey, the Tuscaloosa Formation of the eastern Gulf of Mexico (Alabama, Mississippi, Louisiana), the Woodbine Formation of the central Gulf of Mexico (Texas), and the Frontier Formation of Wyoming. The accumulation and preservation of these formations occurred in response to a Turonian eustatic sea-level fall and subsequent transgression, and the early diagenetic kaolinite in these formations is attributed to similar warm and humid paleoclimate conditions.

Reconstruction of Tournaisian-Viséan tectonic and climatically induced event histories of the Mobarak carbonate platform along depositional strike in the northeastern margin of Gondwana: Constraints from high-resolution cycle and sequence stratigraphy

Cyclic successions are one of the most important types of deposits in the carbonate platform of the Mississippian (Tournaisian-Viséan) in Gondwanan and Laurussian margins. The importance of climatically induced events impact on the amplitudes and frequencies of sea-level fluctuations in Mississippian of Iran is significant because the beginning, extent, duration, and significance of periods of climatically induced events in northern margin of Gondwana are not well recognized. A high-resolution sequence architecture in integration with paleoenvironmental reconstruction and foraminiferal biozonation from the Tournaisian-early Visean carbonate successions of the Mobarak Formation in Alborz basin along depositional strike (E-W- a distance of c. 340 km) suggests a mosaic-like pattern of deposition and compartmentalization of the depositional settings (homocline ramp to distally steepened ramp). According to the recognized facies, the stacking pattern of high-frequency cycles across the platform, and major accommodation events recognized on the correlated Fischer plots, six 3rd-order sequences (DS1–DS6) were identified. Detailed analysis on high-frequency cycles representing a highly variable number of shallowing-upward cycles, types, thicknesses, and facies heterogeneity along depositional strike. A combination of the episodic tectonic events along faults interacting with autocyclic processes, and inherited topographic irregularities are suggested as the driving mechanism for the cycle development. Six stages of Mobarak carbonate platform evolution based on understand the interplay of autocyclic and allocyclic controls are recognized in a hierarchical 3rd-order sequence stratigraphic framework and a chronological order: (1) early Hastarian corresponds to post-glacial transgressive episode with progressive backstepping of facies belts of early TST of DS1 throughout the region; (2) middle to late Hastarian corresponds to a major transgressional phase of DS1 following global temperature rise superimposed on different subsidence/uplift rates with the deformation of the platform along depositional strike; (3) Hastarian–Ivorian boundary corresponds to TST of DS2 with facies heterogeneity along depositional strike related to continuation of different subsidence/uplift rates. The absence of any systematic changes in the amplitude and period of cyclicity or lowstand deposits and subaerial surfaces during this phase shows the lack of influence of mid-Tournaisian glaciation and concurrent eustatic regression in northern margin of Gondwana. (4) early to middle Ivorian coincides with the RST of DS2 and TST of DS3 showing by remarkable topographic irregularities in the basin physiography and change in the position of the depocenter axis from a E–W trend to the center; (5) late Ivorian-early Moliniacian coincides with the RST of DS3 and DS4 showing by the Late Tournaisian thermal period and eustatic rise superimposed on uplift and subaerial exposure of the western part and subsidence in the central and eastern parts of the basin; (6) Moliniacian coincides with DS5-DS6 sequences showing by change from fault-related topography to major tilted fault-block topography accompanied by eustatic sea-level fall caused indirectly by the Viséan and Serpukhovian glaciations phases.

Seismic constraints for ice sheets along the northern margin of Beringia

Beringia today is a partly submerged Arctic region bordered by the Lena River in East Siberia and the Mackenzie River in North America. Whilst emergent at times of eustatic sea-level fall, the northern Beringian Margin was affected by the repeated growth and decay of regional ice sheets. The size and dynamism of these ice sheets are a subject of some debate that can be addressed using geophysical data, which reveal widespread evidence for glacial processes on the continental shelves. We use published and reprocessed 2D multichannel seismic reflection data from the northern margins of Beringia between 147° E to 149° W to investigate their glacially deposited sediments in detail. Deposition of up to 450 m of sediments caused the shelf break to migrate basinward by up to 13 km between 165° E and 161° W. On the Kucherov Terrace (175° E to 176° W) the data show evidence for erosion by grounded ice in water depths of 1200 m. Deposits in the Northwind Basin, between 165° W and 161° W, are separated by continuous reflections indicating at least 3–5 glacial advances. However, the continental slopes of the western East Siberian Sea and the Beaufort Sea lack the thick glacial deposits found in the intervening region. Overall, the volume of glacial deposited sediments along the margins of Beringia are significantly smaller than the reported amounts along the Norwegian and Greenland margins. Therefore, we suggest a less dynamic and fewer number of glaciations of Beringia compared to other glaciated margins during the Quaternary. • Evidence for multiple glacial advances along the northern rim of Beringia. • Erosion by ice sheets only to water depths of 1200 m. • Three main depocenters of glacial deposits along the Beringian margin.

Eustatic sea-level fall and global fluctuations in carbonate production during the Carnian Pluvial Episode

In this paper, sea-level fluctuations during the Carnian Pluvial Episode (CPE) are investigated. A revision of published data from multiple successions worldwide indicates a sea-level drop that occurred in different geodynamic settings after the onset of the first of multiple carbon-isotope perturbations that characterize the CPE. New stable isotope data, zircon U-Pb geochronology, carbonate petrology, conodont and foraminifer biostratigraphy from the Carnian of the Sichuan Basin and comparison to the well-dated coeval successions of the Dolomites allow pinpointing with unprecedented precision this sea-level fall and determine that it occurred after the onset of the first, but prior to the third negative δ13C shift of the CPE. These lines of evidence indicate that such sea-level oscillation was eustatic. Facies analysis and sequence stratigraphy of units deposited during the ensuing sea-level rise in the Sichuan and Dolomites, further show that a Tethys-wide crisis of microbial carbonate production and drowning of carbonate platforms were followed by a recovery of marine calcification, widely testified by the deposition of oolitic bodies. Whereas a Tethys-wide recovery of microbial carbonate production is documented at the end of the Carnian, this increase in chemical calcification occurred earlier, at the beginning of the Tuvalian, and suggest that global transformations in carbonate systems coincident with the CPE were complex and share commonalities with other times in the geological record when a similar evolution was linked to ocean acidification.

Evolution of a Miocene canyon and its carbonate fill in the pre-evaporitic eastern Mediterranean

Extensive canyons, excavated into the margins of the Levant Basin during the Oligocene–Miocene, are interesting case-studies for canyon fills in carbonate settings. The carbonate Pattish Formation, developed along the margins of the pre-evaporitic Messinian Beer Sheva Canyon in Israel, was investigated using both onshore seismic imaging and field data. The canyon has three main seismic facies of fill (1) Subparallel reflections mimicking the canyon´s morphology; (2) chaotic reflections overlying the subparallel ones, and (3) sigmoidal reflections, locally with sharp edges at the canyon margins. The first seismic facies corresponds to the pelagic marls of the Bet Eshel Formation. The other two seismic facies are, respectively, equivalent to bioclastic calcarenite clinobeds with slumps and channels, and to coral–stromatolite reefs and reef slopes of the Pattish Formation observed at outcrop. There were three phases of canyon development: (1) slope incision and headward erosion due to tectonic uplift and eustatic sea-level fall during the Early Oligocene, and large slope failure during the latest Middle Miocene; (2) platform incision and connection with a fluvial system in the Late Miocene related to falling sea level and tectonic uplift; and (3) canyon filling first by pelagic marls at the centre of the canyon, followed by calcarenite clinobeds at the canyon flanks formed by gravity flows. Finally, carbonate production at the margins of the canyon resulted in reefs and associated slopes prograding towards the canyon axis. The late canyon filling phase ended with the deposition of evaporites during the Messinian Salinity Crisis.

Middle Miocene short-lived Tethyan seaway through the Zagros foreland basin: Facies analysis and paleoenvironmental reconstruction of mixed siliciclastic-carbonate deposits of Mishan Formation, Dezful Embayment, SW Iran

Integrated sedimentological and petrographical analyses have been used for paleo-environmental reconstruction of mixed siliciclastic-carbonate deposits of Mishan Formation (late Burdigalian-Serravallian) in the Dezful Embayment within the Zagros foreland basin. The carbonate deposits alternated with marl layers consisting of open marine, restricted to semi-restricted subtidal lagoon and tide-related facies associations with organic buildups deposited within tropical to subtropical warm water multi-factory platform including euphotic and meso-oligophotic factories. The siliciclastic deposits comprise progradational tide-influenced delta deposits including prodelta, delta front and delta plain facies associations. The lack of wave related structures and the absence of the shelf type evidence together with tide-related deposits within the carbonate facies and prograding delta deposits indicate a tide-dominated mixed siliciclastic-carbonate homoclinal ramp with the development of organic buildups. These sediments deposited within the short-lived Tethyan seaway resulted from Middle Miocene Climate Optimum through the Zagros foreland basin. Predominant heterozoan skeletal grains and alternation of marl layers with carbonate sediments indicate high nutrient and sediment flux from adjacent highlands. Carbonate tidal deposits within the siliciclastic sediments suggest that the tidal currents have provided suitable ecological conditions for carbonate production by supplying nutrients for heterotrophic organisms and pumping clear water from the ocean. Shallowing upward trend from marine carbonates and marls to prograding siliciclastic paralic and non-marine deposits of the Mishan Formation within the studied area can be linked to the eustatic sea-level fall in response to the Middle Miocene Climate Transition which led to the closure of Tethyan seaway in the Dezful Embayment.

Lagoonal carbonate deposition preceding rifting-related uplift: evidence from the Bartonian–Priabonian (Eocene) of the northwestern Gulf of Suez (Egypt)

Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene. This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian–Priabonian succession cropping out in this area. Bartonian–Priabonian carbonate deposits in five stratigraphic sections constitute, from base to top, the Gebel Hof, Observatory, Sannur, Qurn, and Wadi Hof Formations. These formations contain four local assemblage zones of larger benthic foraminifers. Analyses of litho-, bio-, and microfacies in the succession resulted in the recognition of 12 lithofacies types. These litho-facies are represented by packages of lime-mudstones, wackestones, packstones, pack- to grainstones, grainstones, rudstones, boundstones and dolomites. These lithofacies have been grouped into four genetically-related facies associations that represent, respectively, tidal flats/shallow subtidal, restricted-shelf/lagoonal, shoal bar, and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting. The vertical transitions of these facies associations, representing facies changes through time, imply fluctuations of the regional sea level. The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises; the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity. The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian–Priabonian.

Nitrogen isotope evidence for a redox-stratified ocean and eustasy-driven environmental evolution during the Ordovician–Silurian transition

The Ordovician-Silurian (O/S) transition was a critical geological interval, during which significant biological events and dramatic environmental changes occurred. Extensive research has proven that changes in the ocean environment are one of the main causes of events that affect the biosphere. However, the redox structure and related geochemical evolution of the ocean during the O/S transition remain under debate. N isotopes are thought to have significant potential for further elucidating the oceanic redox structure and related geochemical evolution during the O/S transition, and are an effective supplement to the former environmental proxies of bottom sediments. This study presents high-resolution N isotope data from a well-sequenced drill core across the O/S transition from the Lower Yangtze Platform, South China, showing an interesting isotopic variation with high δ 15 N values (+1‰ to +4‰) during the Late Katian to Hirnantian ages of the Ordovician and much lower values (−1‰ to +1‰) during the Rhuddanian Age of the earliest Silurian. This δ 15 N variation is mostly controlled by ocean redox conditions and the corresponding changes in the nitrate reservoir. Combined with previously reported δ 15 N data, a redox-stratified ocean with a relatively deep redox transition zone was reconstructed according to the distribution of δ 15 N profiles across different palaeogeographic locations. The lower δ 15 N values and more reducing conditions in deep water sections demonstrate that glacio–eustatic fall, rather than increased upwelling, was likely the main driver of the global redox change during the Late Ordovician. Furthermore, a global δ 15 N decrease during the Late Katian may be associated with the debated Boda warm event, and the up to six positive δ 15 N excursions observed during the Hirnantian might suggest the cyclicity of the glaciation process. • δ 15 N can be correlated globally during the Ordovician-Silurian (O/S) transition. • Oceanic δ 15 N was controlled by water redox conditions during the O/S transition. • Positive δ 15 N excursions with a low δ 15 N baseline support a redox-stratified ocean. • δ 15 N records indicate Hirnantian redox evolution driven by eustatic sea-level fall. • Global δ 15 N variations correspond with a Boda warm event and multistage Hirnantian glaciation.

The Devonian-Carboniferous Boundary At Guar Sanai, Kampung Guar Jentik, Perlis: An Updated Map And Stratigraphic Section

The Sanai Hill B outcrop, exposed at Kampung Guar Jentik, Beseri district, Perlis, exposes one of the best-preserved Devonian-Carboniferous boundary successions in Malaysia. A new geologic map for the locality is presented, which is based on better exposure of the outcrop due to active quarrying, and was constructed using a combination of aerial drone imagery, three-dimensional photogrammetry, Google Earth satellite imagery and traditional field methods. The sedimentary strata include the Silurian Mempelam Limestone, the Lower Devonian Timah Tasoh Formation, the Upper Devonian Sanai Limestone, the Lower Carboniferous Telaga Jatoh Formation and the Lower Carboniferous Chepor Member of the Kubang Pasu Formation. The Devonian-Carboniferous boundary is marked by the contact between the Sanai Limestone and the Telaga Jatoh Formation. It shows an abrupt change from carbonate to siliceous (chert) deposition, with the contact represented by a paraconformity. This unconformity can be correlated to the Devonian-Carboniferous unconformity in the Kanthan Limestone of Perak. It can also be identified in many sections throughout the Western Belt, including in southern Thailand, Langkawi, Kedah, Perak and the Selangor-Kuala Lumpur area. The unconformity can be linked to a eustatic sea level fall at the end of the Devonian. N-S trending imbricate reverse faults and repeated sections have been interpreted as evidence for collisional tectonics associated with the Late Triassic Indosinian Orogeny. E-W trending normal faults mark a Tertiary extensional phase.

Environmental constraints on the distribution of matground and mixground ecosystems across the Cambrian Series 2–Miaolingian boundary interval in Iran: A case study for the central sector of northern Gondwana

The stratigraphic architecture, changes of depositional systems in lateral and vertical extent, and 3D-stacking pattern of second- and third-order sequences of the Cambrian successions on the northern Gondwanan margin indicates a distinct sea-level fall in the Alborz Zone and Central Iran corresponding with global sea-level fluctuations. The peak of the sea-level fluctuations is located at the boundary between the Lalun Formation and the base of the overlying Mila Group. A vertical trend from gradual sea-level rise during the Cambrian Series 2 (recorded as thick transgressive deposits of the Lalun Formation) to transgressive valley-fill system at the base of the Fasham Formation and overlying highstand subtidal carbonates (carbonate platform of the Deh-Sufiyan Formation) can be observed. This trend is paralleled by a change from mixgrounds with metazoan body fossils to microbial matgrounds and microbial boundstones (thrombolites and stromatolites). The general increase in vagile bilaterian metazoans led to a distinct proliferation in ichnofossils in the Lalun Formation indicating a considerable increase in progressive ecospace utilization and tiering complexity. These are associated with biodiffusion, sediment reworking and bioirrigation so that matgrounds were disrupted and mixed layer substrates developed. A proliferation of microbes took place at the base of the Mila Group, which is regarded as a reaction to unfavourable environmental conditions and considerable challenges for metazoans. Consequently, a dramatic degradation of marine bottom communities followed the major eustatic sea-level fall at the Cambrian Series 2–Miaolingian boundary interval and led to the decrease in ichnodiversity, bioturbation intensity, depth of bioturbation and burrow size at the base of the Mila Group. The amount of biogenic mixing significantly decreased, and eventually sedimentary mixed layers disappeared.

Late Miocene and Early Pliocene coastal deposits from the Canary Islands: New records and paleoclimatic significance

The Canary Islands offer an outstanding context for paleoclimatic studies because their volcanic nature and the presence of datable lava flows, their antiquity, the existence of marine deposits and their location in the NE Atlantic. New records of Miocene and Pliocene coastal deposits are registered in the eastern Canary Islands, 100 km off the NW African coast.Late Miocene marine deposits are conglomerates and sandstones assigned to the Tortonian through a new 40Ar/39Ar age (9.60 ± 0.05 Ma) of an overlying lava flow at the Janubio site in Lanzarote Island. These deposits contain littoral-intertidal and intertropical genera of fossils, e.g. the gastropod Nerita and the coral Siderastrea, they are almost horizontal and were elevated up to 36 m in height by regional or local tectonics, yielding a relatively low rate of uplift of ~3.75 m/Ma.Furthermore, Early Pliocene coastal deposits studied, are mainly marine conglomerates and sandstones and derived aeolianites that are spread over the south of Lanzarote and the west of the Jandía peninsula of Fuerteventura Island. No associated lava flow permits their dating, but they contain marine fossils of littoral and intertropical genera, as the gastropods Nerita and Persististrombus and the coral Siderastrea. They are all inclined toward the coast in the form of a large layer elevated up to 70 m a.s.l., in a surrounding geological environment with gypsum and aeolianites that indicate a eustatic sea-level fall with a regressive effect in the area. These deposits, previously attributed to the Quaternary, are now assigned to the Zanclean because of its similarity in lithology, appearance and fossil content with deposits in western Fuerteventura and NE Gran Canaria.The nearby existence of paleosols with particular structures indicates the start of climatic seasonality in the region; and the only possible time interval in a global context (record of deep-sea oxygen isotopes and sea-level history) fits in the most notable Pliocene global climatic change (~4 Ma) that is registered in the Canary Islands by mean of these coastal and aeolian deposits.

Integrated stratigraphy of the Eocene-Oligocene deposits of the northern Caucasus (Belaya River, Russia): Intermittent oxygen-depleted episodes in the Peri-Tethys and Paratethys

The sedimentary succession along the Belaya River (North Caucasus) provides a record of middle Eocene to Miocene sediments. This time interval is well known for its important climatic transitions (e.g., Middle Eocene Climate Optimum (MECO) and Eocene-Oligocene Transition (EOT)), and changes in basin configuration from Peri-Tethys to Paratethys. The Belaya section contains two intervals marked by oxygen-depleted sediments; the Eocene Kuma Formation of the Peri-Tethys and the Oligocene Maikop Group of the Paratethys. Both are considered important source rocks for hydrocarbon exploration in the Black Sea and Caspian Sea. We present integrated stratigraphic results of the Belaya River section using calcareous nannoplankton biostratigraphy, magnetostratigraphy and 40Ar/39Ar dating. Furthermore, we investigate the geochemical character of the sediments using X-ray fluorescence (XRF) and stable carbon and oxygen isotopes. A middle Eocene age for the lower part of the succession is established from nannoplankton biostratigraphy. The Kuma Formation is dated between 42.1 and 38.4 Ma based on the assumption of constant sediment accumulation rates. A negative oxygen isotope excursion in the middle part of the Kuma Formation could be related to the MECO (~40 Ma). The onset of the Maikop Group is dated around the base of chron C13n at an age of ~33.7 Ma, close to the Eocene-Oligocene boundary. Based on geochemical results, we show that the Kuma Formation and Maikop Group correspond to two different episodes of intensified oceanic oxygen depletion in the succession. We hypothesise that oxygen-depletion as recorded in the Kuma Formation is linked to an increased nutrient input in the open marine Peri-Tethys due to widespread volcanism in the Neotethys subduction zone, while oxygen-depletion as recorded in the Maikop Group is linked to basin restriction caused by the eustatic sea-level fall straddling the Eocene – Oligocene boundary triggering stratified conditions in the semi-isolated Paratethys Sea.

An extraterrestrial trigger for the mid-Ordovician ice age: Dust from the breakup of the L-chondrite parent body.

The breakup of the L-chondrite parent body in the asteroid belt 466 million years (Ma) ago still delivers almost a third of all meteorites falling on Earth. Our new extraterrestrial chromite and 3He data for Ordovician sediments show that the breakup took place just at the onset of a major, eustatic sea level fall previously attributed to an Ordovician ice age. Shortly after the breakup, the flux to Earth of the most fine-grained, extraterrestrial material increased by three to four orders of magnitude. In the present stratosphere, extraterrestrial dust represents 1% of all the dust and has no climatic significance. Extraordinary amounts of dust in the entire inner solar system during >2 Ma following the L-chondrite breakup cooled Earth and triggered Ordovician icehouse conditions, sea level fall, and major faunal turnovers related to the Great Ordovician Biodiversification Event.

Constraining Mesozoic early post-rift depositional systems evolution along the eastern Central Atlantic margin

Extensive Mesozoic outcrops exposed in the Aaiun-Tarfaya Basin, in the Atlantic margin of Morocco, have been overlooked for decades. Original subdivisions and dating of rocks, performed more than five decades ago, have survived until today virtually without any update. In the north eastern margin of the basin, key Mesozoic sections have been revisited. Its coastal position next to the Variscan Anti-Atlas Orogen allows insight into the interplay between local tectonics and eustasy during deposition of sedimentary sequences on passive margins. High-resolution stratigraphy and sedimentology have allowed for an improved understanding of the depositional systems and evolution during the early opening of the Atlantic and provided a valuable control point recording the syn- and early post-rift evolution of the basin. Three formations are described: (i) a basal continental red bed unit unconformably overlying the Palaezoic Variscan basement of the Ifni Inlier; (ii) a unit dominated by intertidal clastics and microbial carbonates, and (iii) a shallow marine unit comprising mixed siliciclastic-carbonates. Despite the sedimentological affinity of these outcrops to Triassic or Lower Jurassic deposits elsewhere in Morocco, these units had previously been assigned an Early Cretaceous age, based on limited non-conclusive fossil fauna and basin-scale lithostratigraphic correlation. New collections of macrofauna have yielded a Bathonian age for the upper part of the succession and a possible Triassic/Early Jurassic for the lower part. The whole succession displays an overall transgressive trend not consistent with the eustatic Bathonian sea-level fall. Local post-rift tectonic pulses exhuming the Western Anti-Atlas coupled with eustasy are responsible for increased sediment supply at this time. Enhanced tectonic subsidence, overcoming sea-level fall, is interpreted to be the main driver for creation of accommodation and preservation of this sequence. Resumed sedimentation on structural heights offshore suggests exhumation of the Western Anti-Atlas ceased by the early Callovian, reducing clastic input to the region and allowing the development of a carbonate platform. Variable regional exhumation and local tectonics along the Moroccan margin during the early post-rift stage influenced the highly variable nature of clastic vs carbonate deposition, thickness distribution and depositional environments at this time.

Characterization and discrimination of paleokarst breccias and pseudobreccias in carbonate rocks: Insight from Ordovician strata in the northern Tarim Basin, China

Ordovician carbonates in the central and southern Halahatang area of the Tarim Basin host highly productive hydrocarbon reservoirs. Previous studies suggest that the Yingshan and Yijianfang Formations (the primary producing intervals) have been extensively karstified. However, the current author has not observed significant karst features in the formations based on the detailed study of 380 m long cores from 16 wells. In the current study, true breccias are only identified in two wells in the Lianglitage Formation, including crackle and mosaic breccias as well as chaotic, clast-supported breccias. The breccias are interpreted as karst-related breccias that formed in near-surface environments during pre-Silurian subaerial exposure, and timing of karstification probably coincided with eustatic sea-level fall caused by the middle Katian glaciation. Widespread “karst features” of the Yijianfang and Yingshan Formations identified as breccias or sediment-filled cavities in many previous studies are actually only a mottled fabric (pseudobreccia) caused by selective diagenetic alteration and infiltration of bitumen in the deeper subsurface. The color difference between pseudoclasts and pseudomatrix does not reflect a mixture of clasts and cave sediments, but instead is characterized by distinct, nevertheless commonly subtle, variations in the limestone texture and whether bitumen is present. One the basis of core and thin section observations, SEM (scanning electron microscope) and XRD (X-ray diffraction) analyses, the author presents criteria to distinguish karst breccias and pseudobreccias that can be applied to other similar carbonate deposits. Discrimination between karst breccias and nodular limestones is also presented. Differentiation of karst and pseudokarst features serves not only an academic interest, but also has important applications for the exploration and development of carbonate reservoirs.

Mut Havzası’nda Deniz Düzeyi Değişimlerinin Sedimantasyon Üzerindeki Kontrolü: Geç Serravaliyen-erken Tortoniyen Kazınma Vadisi Dolgusu

Early–middle Miocene reefal limestones are overlain disconformably by late Serravallian– early Tortonian incised valley-fill deposits of Dağpazarı formation in the Mut Basin. Dağpazarı formation is composed of mudstone, siltstone, sandstone and conglomerates. Facies associations of the formation are: fluvial, lagoon, shoal-water delta, shoreface, beach and barrier island deposits. Loxoconcha tumida Brady and Loxoconcha sp. in the gray mudstones indicate the freshwater influence and decrease in salinity. Hemicyprideis sp. documents brackish water conditions. The shoreface sandstones alternating with the lagoonal mudstones, and oyster-rich beach deposits in different levels of the sequence indicate episodes of marine connections. The age of the Dağpazarı formation is provided by the planktonic foraminifera from the marine mudstones and marls below and above the formation, and corresponds to the MMi8–MMi10 biostratigraphic interval, which spans the late Serravallian–early Tortonian. Late Serravallian eustatic sea-level fall caused to the quick shallowing of the Mut Basin and subaerial exposure of the reefal limestones at the basin margin. Thus, the incised valley, formed upon the reefal limestones of the Mut formation. This incised valley reflects a regional forced regression and unconformity. The Dağpazarı formation was deposited within this incised valley following an early Tortonian relative sea-level rise.

Tectonic and eustatic controls on the spatial distribution and stratigraphic architecture of late early Cambrian successions at the northern Gondwana margin: The siliciclastic-carbonate successions of the Lalun Formation in central Iran

Abstract The lower Cambrian Lalun Formation of the Tabas Block, Central Iran, allows to generate a sequence stratigraphic model which characterises the sedimentary evolution and improves palaeoenvironmental interpretation of sedimentary successions along the northern margin of the Prototethys. This formation provides a key for understanding processes that took place during the late early Cambrian in Iran and is the best representative for the complex mosaic of mixed siliciclastic-carbonate systems which illustrate the development and evolution of fluvial and tide-dominated estuarine systems adjacent to an open coast during this interval in the region. Detailed facies analysis allows to differentiate five vertically-stacked groups of facies associations (fluvial facies associations; estuarine facies association; open coast tidal flat facies association; carbonate ramp facies association; and delta facies association) in the uppermost interval of the Lalun Formation. The conceptual depositional models for the siliciclastic-carbonate successions of the Lalun Formation are summarised in a sequence stratigraphic framework, including three third-order depositional sequences (braided fluvial systems; incised-valley fill; and carbonate ramp and tide-influenced delta systems). The data suggest that the Central Iranian Microcontinent broke up during latest Neoproterozoic–early Cambrian times, resulting in the Proto-/Palaeotethys rifting, with considerable differential subsidence recognizable from the reactivation of faults in the early Cambrian which led to new syn-rift successions. The mosaic pattern of deposition observed among the studied sections suggests a compartmentalization of the depositional setting as a result of the interplay between tectonics, sediment supply, and eustasy. Abrupt lateral changes in facies and thickness within the sequences depositional sequences suggest that deposition was controlled by repeated tectonic downdrop and uplift as a consequence of local syndepositional, extensional fault movements. Tectonic activities in the studied region controlled sedimentation and accommodation as well as the position of depocentres within the basin, and the stratal geometries within the sequences. However, the stratigraphic architectural style of the depositional sequences and the asymmetrical trend of the transgressive and regressive second-order sequences imply that the deposition of the late early Cambrian successions is at least partly a result of eustatic sea level changes and cannot be linked exclusively to differential subsidence due to fault movements. Our study indicates that stratigraphic relationship between carbonate and siliciclastic facies in the depositional sequences was also controlled by subsidence/uplift in the hinterland and the areas of siliciclastic input rather than climatic changes. The late early Cambrian depositional environments evolved from braided rivers and an incised valley system (lowstand) to transgressive incised-valley-fill successions which are capped by transgressive open coast tidal flat and carbonate open marine facies. Depositional history of the formation terminated with a regression that ceased with progradation of tide-influenced delta systems. The stratigraphic evolution described in this study documents an eustatic sea-level fall interposed between the top of the Lalun Formation and the base of transgressive tidal bars of the overlying Fasham Formation reflecting the complex (sub-)globally recognizable regressive–transgressive event at the lower–middle Cambrian boundary interval, which led to the establishment of an extensive middle–late Cambrian carbonate platform in present-day northern and central Iran.