Eustatic Sea-level Changes Research Articles

Review and Prospects of Studying Methods to Reconstruct Eustatic Sea-level Changes in Deep-time

Review and Prospects of Studying Methods to Reconstruct Eustatic Sea-level Changes in Deep-time

Astronomically forced climate change in the late Cambrian

We report evidence for Milankovitch cycles in two drill cores from the Cambro–Ordovician Alum Shale Formation of Scandinavia. The signal is preserved in elemental abundances recorded at high stratigraphic resolution by core scanning XRF analysis (0.2 mm resolution). The new data enable us to establish a floating timeline calibrated to the stable 405 kyr eccentricity cycle for a ∼8.7 Myr interval across the Miaolingian–Furongian boundary. This interval spans the Steptoean Positive Carbon Isotope Excursion (SPICE), which is recorded in the δ13Corg in the studied drill cores. We calculate the durations of the Olenus Superzone to 3.4 ± 0.2 Myr, the Parabolina Superzone to 1.9 ± 0.3 Myr, the Leptoplastus Superzone to 0.33 ± 0.18 Myr, the Protopeltura Superzone to 0.51 ± 0.20 Myr, and the SPICE event straddling the Paibian and lower main part of the Jiangshanian Stage to 3.0 ± 0.2 Myr. The sedimentation rate shows similar trends at both drilling locations and is inversely correlated to eustatic sea level changes in certain time intervals, opening tantalizing new prospects of using cyclostratigraphic analyses of shales to track eustatic sea level variations. The identification of obliquity cycles enables us to calculate the Cambrian Earth–Moon distance as well as the day length at ∼493 Ma to 368.9 ± 2.3 ⋅ 106 m and 21.78 ± 0.29 hr, respectively.

New age constraints on the duration and origin of the Late Ordovician Guttenberg δ13Ccarb excursion from high-precision U-Pb geochronology of K-bentonites

AbstractPerturbations to the global carbon cycle as recorded in the isotopic compositions of marine deposits have been commonly associated with major shifts in the climate and/or biologic activity, including mass extinctions. The Late Ordovician Guttenberg isotopic carbon excursion (GICE) is a large, globally correlative positive shift (∼3‰) in the carbon isotopic composition of marine carbonates (δ13Ccarb), but its driving mechanism(s) remains ambiguous. This is in large part due to uncertain correlations among Late Ordovician records, as well as complex and poorly constrained temporal relationships of abundant K-bentonite (altered volcanic ash) marker beds deposited in this time interval. Here, we provide new, high-precision U-Pb zircon geochronology by chemical-abrasion–isotope-dilution–thermal ionization mass spectrometry for K-bentonites bounding the GICE in the North American Midcontinent, including robust 206Pb/238U ages (reported with 2σ analytical uncertainty) for two important regional markers: the Deicke (453.35 ± 0.10 Ma) and Millbrig (453.36 ± 0.14 Ma) K-bentonites. The new data from these K-bentonites directly constrain the duration of the GICE to less than 400 k.y. at two well-studied locations in eastern Missouri, United States. The abruptness of the GICE precludes relatively gradual tectonic mechanisms as possible drivers of the excursion and suggests more rapid environmental drivers, such as changes in eustatic sea level associated with pre-Hirnantian glacial activity.

Geological framework of the Bagnoli-Coroglio coastal zone and continental shelf, Pozzuoli (Napoli) Bay

ABSTRACT Bagnoli-Coroglio is a Site of National Interest (SNI) facing the Pozzuoli Bay that has been the place of an industrial activity for more than a century (1854-1985). The modern coastal geology of this area results from the recent evolution of an antecedent volcanic landscape that originated after a caldera collapse following the eruption of Neapolitan Yellow Tuff (NYT) of Campi Flegrei (15 ka). After the NYT eruption, a shallow marine depression formed within the caldera collapse area that underwent progressive filling-up, due to volcaniclastic sediment input from the caldera borders, within a semi-enclosed source-to-sink system. The integrated interpretation of the Digital Terrain Model (DTM) of the Bagnoli-Coroglio area and the high resolution reflection seismic profiles acquired off the Pozzuoli Bay suggests that the present-day coastal plain of Bagnoli-Fuorigrotta and conterminous continental shelf represent the latest infilling phase of the annular depression (caldera ‘collar’) between the structural border of the NYT caldera and the inner caldera resurgent dome. The stratigraphic architecture and morpho-bathymetry of the Bagnoli inner shelf provide a record of the complex interplay between eustatic sea level changes, volcano-tectonic (ground/seafloor) deformation, and supply of volcaniclastic sediments, with associated coastline shifts over the last millennia.

Chronology of Quaternary shoreline progradational sequences related to eustatic sea-level changes: Sedimentation and subsidence in Saronikos Gulf, Greece

The stacking pattern of shoreline progradational sequences in subsiding basins have been used as a chronologic tool in the Mediterranean region. Most previous studies have used a few key seismic lines seaward of deltas, where the record is complicated by deltaic distributary switching. Southeastern Saronikos Gulf, in the western Aegean Sea at the northwestern end of the South Aegean Arc, lacks large river input of sediment. The ENE-WSW and NW-SE trending neotectonic Aegina and Methana basins lie between the tectonically active Gulf of Corinth and the relatively stable Cyclades plateau. New high-resolution seismic profiles from southeastern Saronikos Gulf have been interpreted according to the principles of seismic and sequence stratigraphy. Alpine basement and marine Pliocene sediments have been recognized in the surrounding basin margins and more than 300 m and 150 m of unconsolidated sediments have been mapped in Aegina and Methana basin respectively. Progradational clinoforms that toplap against transgressive surfaces, have been traced along strike, leading to the establishment of a robust chronostratigraphic framework further controlled by sedimentation rates as extracted from cores. Southeastern Saronikos Gulf poses an outstanding example of development of progradational wedges formed within a microtidal, wave dominated regime of low sedimentation rates, between 2.8 cm/ka and 3.2 cm/ka, within the framework of low subsiding basins with rates between 0.03 and 0.31 m/ka. In this environment, more than 180 well preserved shoreline progradational units, with attributes similar to the ones reported from the Aegean and Eastern Mediterranean seas, have been mapped and correlated to sea level lowstands back to 866 ka. Deeper Mid-Pleistocene progradational units are also recognized, tentatively back to 1.4 Ma. Subsidence rate shows a dramatic decrease in the last 1 Ma and significant numbers of faults became inactive during the last 130 ka. In Early-Middle Quaternary, Methana basin was an isolated lake and extended terrestrial areas were shaped in the Poros-Agios Georgios plateau during sea level lowstands. Aegina basin was continuously connected to the Aegean through the Agios Georgios fault valley. This study demonstrates the robustness of chronology based on stacked shoreline progradational sequences and its applicability to determining rates of tectonic subsidence.

Dynamics of the Largest Carbon Isotope Excursion During the Early Triassic Biotic Recovery

The dynamics of the carbon cycle across different timescales is crucial for understanding past and present global climate changes. Following the Permian–Triassic boundary mass extinction (PTBME), the carbon cycle changed profoundly during the following 5.4 Myr, with magnitudes of changes comparable to those of the Precambrian. In pace with the successive cycles of the carbon budget, the recovery of the marine nekton underwent several evolutionary diversification and extinction cycles accompanied by eustatic sea-level changes and profound ecological reorganization of land plants, all indicative of climatic changes. Additional eruptive bursts of the Siberian Large Igneous Province (SLIP) are traditionally called upon as a plausible trigger for these climatic oscillations but firm evidence for coeval SLIP volcanism is still lacking. Based on new precise and accurate U-Pb zircon ages, we establish a high-resolution temporal calibration of the biggest positive carbon isotope excursion (CIE) spanning about 600 kyr in the late Smithian. The age of the Smithian-Spathian boundary (SSB) is established between 249.29 ± 0.06 and 249.11 ± 0.09 Ma. Our oldest U-Pb zircon ages indicate no overlap in time between the middle Smithian onset of the thermal maximum and the youngest available U-Pb zircon ages from SLIP volcanism. The constructed time line also indicates a duration of the global unconformity at the SSB that is compatible with glacio-eustatism. Potential cooling mechanisms such as a volcanic winter, the biological pump and the cessation of volcanism are discussed in the light of this new time line. In the low latitudes, the onset of the positive CIE remarkably predates the temperature drop by some 100 to 125 kyr. However, as long as the magnitude of such offset – if any – is unknown for the high latitudes, relations between the CIE and the cooling will remain an open question associated with largest Triassic extinction of the nekton.

Has Earth ever been ice-free? Implications for glacio-eustasy in the Cretaceous greenhouse age using high-resolution sequence stratigraphy

AbstractControls on high-frequency sequences formed during super-greenhouse conditions in the Late Cretaceous Western Interior Seaway remain equivocal because of the active foreland basin tectonic setting and the lack of direct evidence of polar glaciations to support a glacio-eustatic origin. This paper quantifies eustatic sea-level changes based on high-resolution sequence stratigraphic analysis and improved chronometry of shallow marine deposits of the Late Cretaceous Gallup Sandstone in New Mexico, USA. Backstripping techniques remove tectonic and compactional subsidence and enable quantification of the magnitude of eustatic sea-level change, that allow evaluation of the dominant controls on the high-frequency sequences to resolve the role of orbitally controlled, climate-driven eustasy versus tectonics. Sixty-five parasequences, constituting 29 parasequence sets and 12 sequences are identified in the ∼1.2 m.y. duration of the Late Cretaceous Gallup system. New 40Ar/39Ar dating of bentonites constrains the durations of the individual parasequences, parasequence sets, and sequences, and that these match Milankovitch periodicity, indicating an orbital climate control. The magnitudes of sea-level changes between parasequences range between −28 m and +22 m, which are compatible with hypotheses of both aquifer and glacio-eustasy. Aquifer-eustasy predicts a reciprocal relationship between floodplain cycles and shallow marine sequences, such that aquifer drawdown and falling water tables should correlate to rising sea levels (highstands), whereas increased aquifer storage and rising water tables should correlate to falling sea levels (lowstands). Our preliminary observations show synchronous, versus reciprocal, relationships that may be more compatible with a glacio-eustatic origin. The results of this study support the hypothesis that the Cretaceous greenhouse was marked by high-frequency, low-amplitude glaciations driven by orbital climate cycles, but further work is required to evaluate the contribution of aquifer-eustasy.

Factors controlling facies distribution during the early Late Cretaceous in the Eastern Desert of Egypt: Paleoenvironmental reconstruction and relationship to sequence stratigraphy

In the context of a high-resolution stratigraphic perspective, facies analysis is carried out to interpret the paleoenvironments that prevailed during the Cenomanian–Turonian sedimentation in the Eastern Desert of Egypt. Particular emphasis is placed on the possible reasons for observed changes in the facies distribution. The facies associations indicate that the mixed carbonate and siliciclastic successions were deposited on a long-extended ramp setting with a gentle dip from a proximal position in the south to a distal position in the north. The late Cenomanian transgression covered the study area and formed a shallow fully marine environment, in which the Galala Formation was deposited. The sea-level rose continuously to reach a maximum during the early Turonian, with a deep subtidal setting in which the Maghra El Hadida and Abu Qada formations were deposited at relatively high and low paleo-depths, respectively. Changes in the facies distribution reveal a strong relationship to sea-level fluctuations; each sea-level stage of the studied sequences is characterized by similar facies associations with the same facies arrangements. In addition, at the proximal southern part of the study area, where shallow facies are expected to occur, deep marine facies are instead recorded, which is interpreted here as a tectonic effect of the Syrian arc folding system. Furthermore, the dominant paleoenvironmental perturbations during the Cenomanian–Turonian as represented by major lateral and vertical litho- and biofacies changes also affected the studied facies distribution. Therefore, the Cenomanian–Turonian facies development in northeast Egypt was not only controlled by eustatic sea-level changes as commonly suggested but was also influenced by tectonic and environmental changes.

The Complex Vertical Motion of Intraplate Oceanic Islands Assessed in Santiago Island, Cape Verde

AbstractDated paleosea level markers and eustatic sea level changes are necessary but not sufficient information to calculate vertical motion rates on oceanic islands. Therefore, we use a procedure in which we work progressively back in time to incorporate the more recent vertical motion rates implied by the youngest paleoshorelines into the vertical motion history of all older shorelines. Specifically, we calculate the time‐averaged vertical motion rates required to explain the present‐day elevations of the dated sequence of paleoshorelines on Santiago volcanic island (Cape Verde). We thus obtain a vertical motion history consisting of time‐averaged vertical motion rates spanning the five intervening periods between paleoshoreline formation and the present day: (1) 5.06 to 3.29 Ma—seamount growth or island subsidence because all the rocks in this period are submarine; (2) fast uplift (approximately 0.96 mm/a) from 3.29 to 2.87 Ma, mostly responsible for putting submarine lavas currently close to 410 m altitude; (3) relatively fast subsidence (approximately −0.11 mm/a) between 2.87 and 2.18 Ma; (4) stagnation from 2.18 to 0.811 Ma; and (5) relatively fast uplift (approximately 0.14 mm/a) between 0.811 and 0 Ma. We numerically tested top‐down (volcanic loading) and bottom‐up (lithosphere thinning, underplating, and mantle plume) mechanisms to explain the inferred vertical movements, and we conclude that volcanic loading and crustal underplating are capable of producing the observed subsidence and uplift, respectively.

Chapter 6 The Loyalty Islands and Ridge, New Caledonia

Abstract The Loyalty Ridge lies to the east and NE of the Norfolk Ridge. The three main Loyalty Islands (Maré, Lifou and Ouvéa) emerge from the ridge at the same latitude as Grande Terre. The islands are uniformly composed of carbonate deposits, except for Maré, where Middle Miocene intra-plate basalts and associated volcaniclastic rocks form restricted outcrops. Miocene rhodolith limestones constitute the bulk of the carbonate cover of the three islands. On Maré, these platform accumulations are locally topped by a dolomitic hardground, which, in turn, is covered by Pliocene–Pleistocene coral-bearing formations. These coral reef constructions are preserved as elevated rims over all three islands and define an atoll stage in their development. The Pleistocene–Holocene palaeoshoreline indicators include fringing bioconstructions and marine notches and record both eustatic sea-level changes and tectonic deformation. The ridge has been in the forebulge region in front of the active Vanuatu subduction zone since the Pliocene and each of the three islands has been uplifted and tilted to varying degrees. Offshore, the Loyalty Ridge continues northwards to the d'Entrecasteaux Zone and southwards to the Three Kings Ridge. Although typically volcanic, the nature of the deep Loyalty Ridge remains unknown.

Mid Holocene Sea-Level Changes in and around Dhaka City, Bangladesh

Bengal basin, the largest fluvio-deltaic sedimentary system on Earth, is located in Bangladesh and three eastern states of India. Sediment accumulates in the basin from the Ganges, Brahmaputra, and Meghna (GBM) river systems and is dispersed into the Bay of Bengal, forming the largest submarine fan in the world. The present-day geomorphology is dominated by the extensive Holocene GBM floodplain and delta. The initiation of the modern GBM delta at the onset of the Pleistocene glacial maximum and its evolution to the present configuration are intricately related to Holocene fluvio-dynamic processes, eustatic sea-level changes, and tectonic movements. Quaternary System in Bengal basin has varieties of depositional environment. Sediment characteristics of different geomorphic units are different. Late Quaternary monsoon climatic episodes played the vital role in creating the present morphology of the Madhupur surfaces. During the Holocene, the central part of the basin experienced cyclic transgression and regression phase in several times. This was the evidence by mangrove pollens. The presence of mangrove pollen specially Phoenix paludosa, Avicennia sp, Phoenix sylvestris, Prosopis grandis, Sonneratiopollis sp found in Chatbari, Dubadia and Mirertek area of Dhaka city along with radiocarbon dating indicated that marine influence occurred during Mid Holocene time. Two phases of transgression and regression have been recorded during mid Holocene time. First transgression was noticed around 6500 cal BP and then a subsequent regression of the bay had been observed around 5500-3500 cal BP. This was again followed by another transgression episode around 3500-1500 cal BP. and then a regression during between 1500 cal BP onwards.

Chapter 6 Jubaila–Arab–Hith sequences

Abstract During deposition of the Jubaila-Arab-Hith sequences, the most important Arab-D reservoir, the Arab-C to A reservoirs and the Arab and Hith anhydrite seals were formed. The Kimmeridgian Jubaila-Arab-D transgression (MFS J70) restored and expanded the intrashelf basin geometry. The restored basin was filled by deeper subtidal Jubaila facies, which graded upwards to the Arab-D reservoir facies. In the late stages the Arab-D facies included both basin rim shoal facies and at least one large isolated shoal surrounded by ‘lagoonal’ intrashelf basin remnants interconnected by accessway channels. This differentiation was facilitated by local structural growth of a few metres. The Arab-D reservoir is overlain by the Arab-D anhydrite, deposited initially as gypsum in broad salinas, which blanketed the intrashelf basin region, forming the first major seal. By the end of Arab-D anhydrite deposition, the entire intrashelf basin area had been filled and transformed into a broad evaporite platform. Atop this platform, the Arab-C to -A (MFS J80-100) alternating shallow water carbonate and anhydrite (initially gypsum) intervals were deposited, ending regionally with the thick Hith Anhydrite Formation. The depositional setting for each of the main Jubaila-Arab-Hith sequences is reviewed and illustrated. The evolution of Jubaila-Arab-D reservoir models is discussed. Different interpretations of Jubaila-Arab-D-Hith sequences are compared, including the issue of whether the Arab carbonate-evaporite depositional sequence boundaries should be taken at the top of the carbonate intervals or the top of the anhydrites. Examples are included which illustrate how easterly palaeowind directions were an important factor controlling Arab-D facies variation. A scenario is presented to show how the Late Jurassic Tethys shelf uplift and low angle unconformity coupled with westward structural tilt were important. An alternating balance developed between the evolving land barrier and eustatic sea-level change during deposition of the Arab carbonate–evaporites and the Hith Anhydrite. Carbonates were deposited when the barrier was inundated and evaporites when the barrier was exposed and the area restricted and hypersaline. A major late Tithonian flooding event (MFS J110) formed the top-Hith Manifa carbonate reservoir and brought open marine carbonate mud-rich deposition to the area, continuing without hiatus into the Early Cretaceous.

Benthic foraminifera and Neogene sea level changes in the Pelotas Basin, offshore south Brazil

The Neogene benthic foraminiferal ecostratigraphy of offshore Pelotas Basin has not yet been researched. The benthic foraminifera were examined in twenty-nine ditch cuttings samples from Well 1-SCS-3B, present water depth 200 m. These samples ranged from the Lower Miocene Catapsydrax dissimilis planktonic foraminiferal Zone to the Pliocene Globigerinoides trilobus fistulosus Zone. Only ditch cuttings were available, which allowed us to present just broad paleoenvironmental trends within the studied section. Benthic foraminifera indicate deposition mostly between outer neritic to upper bathyal paleodepths. A peak in uvigerinid relative abundance marks a possible flooding surface or condensed section with a high nutrient flux, low diversity (marked by the Shannon Function H), and sluggish circulation within the Globorotalia mayeri Zone. This peak is bracketed by high abundances of Cibicidoides, which indicate stronger current action than within the condensed section. Biostratigraphic hiatuses within these Cibicidoides-rich intervals are concluded not to indicate subaerial exposure, but to reflect current action sufficiently strong to induce either non-deposition or seafloor scouring. A second possible flooding surface occurs at the top of the section, indicated by a decline in Cibicidoides associated with upticks in Sphaeroidina and Bolivina and a dip in H. The top of this younger maximum flood was not encountered, probably occurring above the studied section. That the timing of these floods differs from those recorded elsewhere in the Pelotas Basin implies that they were tectonically induced, perhaps as distal effects associated with the interaction between the South American and Nazca tectonic plates. Future studies with better quality core samples will add detail to this picture; such studies can incorporate eustatic sea-level changes into the model presented.

MIS 5c Maker Tephra-bearing Beds in the Upper Pleistocene Joso Formation, Shimosa Group in the Sashima and Tsukuba Uplands, Kanto Plain, Japan

Marine and fluvial terraces in the Kanto Plain mostly formed in marine oxygen isotope stage (MIS) 5 under the concurrent influence of eustatic sea-level changes and Kanto basin-forming movements. In the central part of the plain, however, it remains unknown when and how terraces composed of the upper Pleistocene Joso and Kioroshi Formations, Shimosa Group developed. Terrace surfaces are classified by integrating geomorphic, sedimentary facies, and tephra analyses focusing on the southern Sashima and Tsukuba Uplands, including the northwestern Shimosa Upland. Terrace surfaces are classified into levels I to III. Terrace sediments distributed over levels I to II from the top in the Sashima, Tsukuba, and Shimosa Uplands are divided into two formations: Kioroshi Formation composed of beach facies and Joso Formation composed of flood plain and fluvial channel facies.Found in the Joso Formation were tuffaceous silt layer and pumiceous sand layer, including tephra grain correlated with On-Pm1 (c. 96 ka: Aoki et al., 2008) and Nk-Ma (c. 100 ka: Yamamoto, 2012) in the southern Sashima and Tsukuba Uplands, which allow fluvial terraces formed in the Central Kanto Plain after MIS 5c to be identified.

Cenomanian–Turonian drowning of the Arabian Carbonate Platform, the İnişdere section, Adıyaman, SE Turkey

Abstract The Cenomanian–Turonian carbonate ramp in the Adıyaman Region of SE Turkey (Northern Arabian Platform) records an abrupt shift from benthic carbonate deposits to pelagic deposits near the Cenomanian–Turonian boundary event (CTBE) in the İnişdere stratigraphic section and surrounding borehole sections. A positive δ 13 C excursion of up to 2.15% is recorded in carbonate and organic carbon deposited around the CTBE and provides evidence of a direct link between the CTBE and oceanic anoxic events and the demise of the shallow carbonate production in the Derdere Formation. The microfacies analyses, biostratigraphic dating and palaeoenvironmental interpretations suggest that the platform was drowned near the CTBE as a result of changing environmental conditions. The microfacies indicating significant deepening show a contemporaneity to equivalent surfaces globally and thus strongly support an isochronous formation of Cenomanian–Turonian facies by eustatic sea-level changes. Anoxia spreading over the platform drastically reduced the carbonate production as observed in the studied sections and, therefore, resulted in a reduction in carbonate accumulation rates. Regional/local subsidence and a coeval sea-level rise during the late Cenomanian to early Turonian interval were the cause of the drowning of the platform, including regional anoxia at the northern Arabian platform linked to the Cenomanian–Turonian oceanic anoxic event (OAE2).

Cenomanian to Coniacian sea-level changes in the Lower Benue Trough (Nkalagu Area, Nigeria) and the Eastern Dahomey Basin: palaeontological and sedimentological evidence for eustasy and tectonism

Abstract The Benue Trough formed in close relation to the opening of the South Atlantic and experienced sea-level fluctuations of different magnitudes during the Cenomanian to Coniacian interval. We identify depositional environments from outcrop sections and a drilling as control record. Lines of evidence for the interpretation include facies analyses, foraminiferal assemblage composition (P/B-ratio) and the presence of planktonic deep-water indicators. While the analysis of the well data from the Dahomey Basin indicates a continuous deep-water (bathyal) environment, the succession in the Nkalagu area of the Lower Benue Trough evolved in a different and more complex way. Beginning with latest Cenomanian shoreface to shelf deposits, a long period of subsidence lasted until the middle Turonian when pelagic shales and calcareous turbidites were deposited at upper to middle bathyal depths. These conditions continued during late Turonian and Coniacian times. The general deepening trend of the Lower Benue Trough was mainly controlled by tectonic subsidence and was superimposed by eustatic sea-level changes, resulting in periodically changing palaeowater depths. We were able to identify eight sea-level rises and falls that can be attributed to 405 kyr eccentricity cycles. The amplitudes of the sea-level changes were most likely in the range of several tens to a few hundred metres. The deposition of carbonate turbidites at Nkalagu was probably triggered by eustatic sea-level lowstands.

Tectonic processes, variations in sediment flux, and eustatic sea level recorded by the 20 Myr old Burdigalian transgression in the Swiss Molasse basin

Abstract. The stratigraphic architecture of the Swiss Molasse basin, situated on the northern side of the evolving Alps, reveals crucial information about the basin's geometry, its evolution, and the processes leading to the deposition of the siliciclastic sediments. Nevertheless, the formation of the Upper Marine Molasse (OMM) and the controls on the related Burdigalian transgression have still been a matter of scientific debate. During the time period from ca. 20 to 17 Ma, the Swiss Molasse basin was partly flooded by a shallow marine sea striking SW–NE. Previous studies have proposed that the transgression occurred in response to a rise in global sea level, a reduction of sediment flux, or an increase in tectonically controlled accommodation space. Here, we readdress this problem and extract stratigraphic signals from the Burdigalian molasse deposits that can be related to changes in sediment supply rate, variations in the eustatic sea level, and subduction tectonics. To achieve this goal, we conducted sedimentological and stratigraphic analyses of several sites across the entire Swiss Molasse basin. Field investigations show that the transgression and the subsequent evolution of the Burdigalian seaway was characterized by (i) a deepening and widening of the basin, (ii) phases of erosion and non-deposition during Lower Freshwater Molasse (USM), OMM, and Upper Freshwater Molasse (OSM) times, and (iii) changes in along-strike drainage reversals. We use these changes in the stratigraphic record to disentangle tectonic and surface controls on the facies evolution at various scales. As the most important mechanism, rollback subduction of the European mantle lithosphere most likely caused a further downwarping of the foreland plate, which we use to explain the deepening and widening of the Molasse basin, particularly at distal sites. In addition, subduction tectonics also caused the uplift of the Aar massif. This process was likely to have shifted the patterns of surface loads, thereby resulting in a buckling of the foreland plate and influencing the water depths in the basin. We use this mechanism to explain the establishment of distinct depositional settings, particularly the formation of subtidal shoals wherein a bulge in relation to this buckling is expected. The rise of the Aar massif also resulted in a reorganization of the drainage network in the Alpine hinterland, with the consequence that the sediment flux to the basin decreased. We consider this reduction in sediment supply to have amplified the tectonically controlled deepening of the Molasse basin. Because the marine conditions were generally very shallow, subtle changes in eustatic sea level contributed to the formation of several hiatuses that chronicle periods of erosion and non-sedimentation. These processes also amplified the tectonically induced increase in accommodation space during times of global sea level highstands. Whereas these mechanisms are capable of explaining the establishment of the Burdigalian seaway and the formation of distinct sedimentological niches in the Swiss Molasse basin, the drainage reversal during OMM times possibly requires a change in tectonic processes at the slab scale, most likely including the entire Alpine range between the Eastern and Central Alps. In conclusion, we consider rollback tectonics to be the main driving force controlling the transgression of the OMM in Switzerland, with contributions by the uplift of individual crustal blocks (here the Aar massif) and by a reduction of sediment supply. This reduction of sediment flux was likely to have been controlled by tectonic processes as well when basement blocks became uplifted, thereby modifying the catchment geometries. Eustatic changes in sea level explain the various hiatuses and amplified the deepening of the basin during eustatic highstand conditions.

Rapid subsidence and preservation of fluvial signals in an otherwise wave-reworked delta front succession: Early-mid Pliocene Orinoco continental-margin growth, SE Trinidad

Outcrops of the early-mid Pliocene Orinoco Delta succession on the Atlantic-facing Trinidad continental margin demonstrate facies and stratigraphic architecture of a shelf margin developed in a setting of high sediment supply (Orinoco River) and unusually rapid, sediment accumulation/subsidence (averaging >1 km/My). The studied Moruga clastic wedge of the Orinoco margin consists of a series of topset to deepwater clinoforms with channelized sandstones, river- and mixed-process delta front, wave-dominated delta front, shoreface, prodelta-offshore transition-shelf, upper-slope turbidite channels and mass-transport deposits. The succession is sand-prone and generally consists of coarsening- and thickening-upward delta-front lobes with hummocky/swaley and wave-ripple stratified sandstones indicating dominant storm wave reworking of the delta, particularly when the delta lobes had reached outer shelf sites after long shelf transits. The lower parts of distributary channels are well preserved and characterized by cross-bedded to parallel-laminated sandstones with mud clast lags. The upper parts of channel fills were wave reworked during transgressions, creating hummocky/swaley cross-stratified strata. River-dominated and mixed-process (wave and tide) delta-front deposits occur commonly within stacked, coarsening-upward units. The river-dominated delta front deposits exhibit parallel-laminated to current ripple-laminated intervals with normally graded thin beds changing upward to parallel and low-angle cross lamination, but mixed-process delta front deposits also contain wave and bidirectional current ripples as well as discrete intervals of hummocky/swaley cross-stratification. The preservation of the channel-base as well as river- and mixed-process delta-front deposits in the otherwise storm wave-dominated Atlantic-facing setting suggests some sheltering of the coastal morphology, and possibly low-frequency of large storms, but it is more likely that the unusually rapid subsidence (at rates competing well with Icehouse rates of eustatic sea-level change) and burial of deposits may have prevented the fluvial and tidal signals from being completely reworked by the storm waves in the studied outcrop area. This study demonstrates an example of how the interactions of river-, tide- and wave-generated facies impacted stratigraphic architecture of a rapid subsiding shelf margin built by shelf-edge deltas with high sediment supply.

Pliocene–Pleistocene sedimentary and geomorphologic development of the Vasilikos river catchment, S Cyprus, in relation to uplift of the Troodos ophiolite and climate-related changes

AbstractThe Pleistocene development of the Vasilikos River exemplifies the interaction of focused, tectonically induced surface uplift and climate-influenced changes. The resulting sediments are well exposed in Vasilikos Quarry and in the main river catchment further east. An important erosional surface incises the highest-level (oldest) fluvial conglomerates, down into Late Pliocene – Early Pleistocene open-marine mudrocks (Nicosia Formation), allowing integration with the circum-Cyprus sedimentary–geomorphic development (F1–F4 stages). To determine where the quarry deposits lie in relation to the Vasilikos river catchment, the fluvial deposits were mapped and valley profiles were constructed, revealing four main episodes, each associated with incision and distinctive fluvial deposition. Source lithology strongly influenced channel morphology, infill and adjacent slope-sediment (colluvium) composition. Palaeosols, particularly red-brown terra rossa, developed on abandoned fluvial terraces and adjacent hillslopes, especially overlying F3 surfaces. The combined evidence allows close correlation of the Vasilikos river and quarry deposits. Relatively coarse (chalky conglomerate/breccia) and fine-grained colluvium (calcareous silt – Cyprus harvara) developed especially on lower hillslopes following incision (mainly above F2 and F3 surfaces). Based on regional comparisons, overall sediment aggregation ended during the Early Pleistocene. The F1–F2 surfaces and deposits are inferred to be Middle Pleistocene, the F3 ones later Middle Pleistocene and the F4 ones near the Middle–Late Pleistocene boundary. Geomorphology and deposition were tectonically forced during strong, focused Early–Middle Pleistocene surface uplift. Coarse clastic ruff-off and palaeosol development (terra rossa) and related sediment aggradation are inferred to have increased during warm, humid periods. Late Pleistocene geomorphology and deposition were more influenced by climatic change, with semi-perennial streamflow, rapid sediment aggradation and palaeosol (terra rossa) development during warm, humid periods (interglacials). Cooler (glacial) periods enhanced fluvial-incision, sediment-bypassing and hillslope colluvial processes (e.g. frost shattering, downslope creep and mass flow) when sediment transport (bypassing) exceeded sediment supply. Neotectonic faulting affected the catchment but did not greatly affect geomorphology or sediment supply. Although climate / climate change (and eustatic sea-level change) had an important influence, tectonics is interpreted as the fundamental driver of geomorphological development and fluvial sedimentation, with implications for other areas, regionally to globally.

Depositional sequences and sea-level changes of the upper Maastrichtian-middle Eocene succession in central Jordan: Evidence from foraminiferal biostratigraphy and paleoenvironments

The qualitative and quantitative analyses of the foraminiferal assemblages from the upper Maastrichtian -middle Eocene succession at Jabal Ghuzayma section (central Jordan) is utilized to evaluate the biostratigraphic framework and the prevailing paleoenvironments. Nine planktonic biozones (CF3, P4c, P5, and E3-E8) were recognized covering the upper Maastrichtian to the middle Eocene. Field observations as well as foraminiferal biostratigraphy and paleoenvironments led to identify five 3rd depositional sequences bounded by four sequence boundaries. Two of these sequence boundaries have long-lasting time gaps across the Cretaceous/Paleogene (K/Pg) and the Paleocene/Eocene (P/E) unconformities. These longtime gaps are linked to the tectonic deformation of the Syrian Arc System (SAS) during the convergence and collision of the Eurasian/Arabian plates. The intera- Ypresian and Ypresian/Lutetian (Y/L) boundaries exhibit a sharp change in microfaunal content suggesting distinctive paleoenvironmental turnover which may be enhanced primarily to the eustatic sea-level changes.