Eustatic Sea-level Fluctuations Research Articles

Sequence stratigraphy and a revised sea-level curve for the Middle Devonian of eastern North America

The well-exposed Middle Devonian rocks of the Appalachian foreland basin (Onondaga Formation; Hamilton Group, Tully Formation, and the Genesee Group of New York State) preserve one of the most detailed records of high-order sea-level oscillation cycles for this time period in the world. Detailed examination of coeval units in distal areas of the Appalachian Basin, as well as portions of the Michigan and Illinois basins, has revealed that the pattern of high-order sea-level oscillations documented in the New York–Pennsylvania section can be positively identified in all areas of eastern North America where coeval units are preserved. The persistence of the pattern of high-order sea-level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea-level oscillation, as opposed to autocylic controls, such as sediment supply, which would be more local in their manifestation. There is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to Milankovitch orbital variations, with the short and long-term eccentricity cycles (100 kyr and 405 kyr) being the dominant oscillations in many settings. Relative sea-level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism, given that the Middle Devonian appears to record a greenhouse phase of Phanerozoic history. These new correlations lend strong support to a revised high-resolution sea-level oscillation curve for the Middle Devonian for the eastern portion of North America. Recognized third-order sequences are: Eif-1 lower Onondaga Formation, Eif-2: upper Onondaga and Union Springs formations; Eif–Giv: Oatka Creek Formation; Giv-1: Skaneateles, Giv-2: Ludlowville, Giv-3: lower Moscow, Giv-4: upper Moscow–lower Tully, and Giv-5: middle Tully–Geneseo formations. Thus, in contrast with the widely cited eustatic curve of Johnson et al. (1985), which recognizes just one major transgressive–regressive (T–R) cycle in the early–mid Givetian (If) prior to the major late Givetian Taghanic unconformity (IIa, upper Tully–Geneseo Shale), we recognize four T–R cycles: If (restricted), Ig, Ih, and Ii. We surmise that third-order sequences record eustatic sea-level fluctuations of tens of meters with periodicities of 0.8–2 myr, while their medial-scale (fourth-order) subdivisions record lesser variations primarily of 405 kyr duration (long-term eccentricity). This high-resolution record of sea-level change provides strong evidence for high-order eustatic cycles with probable Milankovitch periodicities, despite the fact that no direct evidence for Middle Devonian glacial sediments has been found to date.

Tectonically driven carbonate ramp evolution at the southern Tethyan shelf: the Lower Eocene succession of the Galala Mountains, Egypt

The succession of the Galala Mountains at the southern Tethyan margin (Eastern Desert, Egypt) provides new data for the evolution of an isolated carbonate platform in the Early Eocene. Since the Late Cretaceous emergence of the Galala platform, its evolution has been controlled strongly by eustatic sea-level fluctuations and the tectonic activity along the Syrian Arc-Fold-Belt. Previous studies introduced five platform stages to describe platform evolution from the Maastrichtian (stage A) to the latest Paleocene shift from a platform to ramp morphology (stage E). A first Early Eocene stage F was tentatively introduced but not described in detail. In this study, we continue the work at the Galala platform, focussing on Early Eocene platform evolution, microfacies analysis and the distribution of larger benthic foraminifera on a south-dipping inner ramp to basin transect. We redefine the tentative platform stage F and introduce two new platform stages (stage G and H) by means of the distribution of 13 facies types and syn-depositional tectonism. In the earliest Eocene (stage F, NP 9b–NP 11), facies patterns indicate mainly aggradation of the ramp system. The first occurrence of isolated sandstone beds at the mid ramp reflects a post-Paleocene-Eocene thermal maximum (PETM) reactivation of a Cretaceous fault system, yielding to the tectonic uplift of Mesozoic and Palaeozoic siliciclastics. As a consequence, the Paleocene ramp with pure carbonate deposition shifted to a mixed carbonate-siliciclastic system during stage F. The subsequent platform stage G (NP 11–NP 14a) is characterised by a deepening trend at the mid ramp, resulting in the retrogradation of the platform. The increasing deposition of quartz-rich sandstones at the mid ramp reflects the enhanced erosion of Mesozoic and Palaeozoic deposits. In contrast to the deepening trend at the mid ramp, the deposition of cyclic tidalites reflects a coeval shallowing and the temporarily subaerial exposure of inner ramp environments. This oppositional trend is related to the continuing uplift along the Syrian Arc-Fold-Belt in stage G. Platform stage H (NP 14a–?) demonstrates the termination of Syrian Arc uplift and the recovery from a mixed siliciclastic carbonate platform to pure carbonate deposition.

Sedimentology, architecture, and sequence stratigraphy of coarse-grained, submarine canyon fills from the Pleistocene (Gelasian-Calabrian) of the Peri-Adriatic basin, central Italy

The Plio-Pleistocene stratigraphic record of the Peri-Adriatic basin (eastern central Italy) is well exposed along the uplifted western margin of the basin and consists of a series of coarse-grained slope canyon fills encased in a thick succession of hemipelagic mudstones. This study deals with the detailed sedimentology, stratal architecture, and sequence-stratigraphic interpretation of two of these submarine canyon-fills (namely CMC1 and CMC2) exposed at Colle Montarone. These strata contain widespread evidence of gravity-driven sedimentation processes, with high- and low-density turbidity currents, slumps and cohesive debris flows being responsible for most of the sediment transport and deposition. Beds are organised into four recurrent lithofacies, each corresponding to a specific deep-water depositional element: (i) clast-supported conglomerates (channel complexes); (ii) thin-bedded sandstones and mudstones (levee-overbank); (iii) very thinly-bedded mudstones (tributary channels); (iv) pebbly mudstones and chaotically bedded mudstones (mass-transport complexes). One of the most conspicuous attributes of the canyon-fill sediments exposed at Colle Montarone is their pronounced cyclic packaging, resulting from several pulses of erosion and fill. The lithofacies listed above combine to form a number of discontinuity-bound stratal packages, or high-frequency depositional sequences, each characteristically having an overall fining-upward character. Within sequences, systematic vertical trends in their constituent lithofacies define two main stratigraphic motifs, namely Motif-1 and Motif-2, which are typical of CMC1 and CMC2, respectively. Each sequence is deemed to reflect cyclical changes in volume, composition, and rheology of sediment gravity flows entering the canyons and comprises a basal unconformity (sequence boundary), succeeded by a high net-gross channel-levee complex (lowstand systems tract), overlain by a succession of either a low net-gross heterolithic deposits (early transgressive systems tract, Motif-1 sequences) or mass-transport deposits (transgressive to falling stage systems tract, Motif-2 sequences). Given the severe Icehouse climatic regime during the Pleistocene, the cyclic arrangement is most reasonably attributed primarily to repeated glacio-eustatic fluctuations in global sea level, which regulated the flux of terrigenous clastic sediment to the slope and basin-floor settings. Results from this paper are directly applicable to the oil and gas industry when making predictions of reservoir and seal relationships within slope turbidite systems developed during periods of high-frequency, eustatic sea-level fluctuations.

Controls on stratigraphic architecture in contemporaneous delta systems from the Eocene Roda Sandstone, Tremp-Graus Basin, northern Spain

The Eocene Roda Sandstone of the Spanish Pyrenees is comprised of two coeval coarse-grained delta systems which share correlatable surfaces but show a markedly different internal facies architecture. The two deltas developed contemporaneously with the differences in internal architecture attributed to basin morphology and the role of two, distinct sediment sources, while the correlatability of the larger-scale packages indicates an external, allocyclic control. As such the Roda Sandstone provides the possibility to address the relative roles of different parameters known to interact and control stratal architecture. The Roda Sandstone crops out at the NE-margin of the Tremp-Graus Basin, a “piggyback” basin initiated in Palaeogene times in the foreland of the Southern Pyrenees. The study area (∼ 30 km 2) is composed of the well-understood and well-exposed parts of the Roda Sandstone cropping out along the Isabena Valley, and the less-worked and less-exposed outcrops to the north along Barranco de Ricans and Barranco de Codoñeras. Data for this study include a combination of conventional sedimentology data coupled with analyses of 3D Virtual Outcrop Models. Based on these methods 8 different facies associations have been distinguished. Their distribution suggests that the Roda Sandstone is composed of two different but coeval delta systems and their linked subenvironments; a Gilbert-type delta outcropping along Isabena Valley, and a shoal-water fan delta along Barranco de Ricans and Barranco de Codoñeras. Along the Isabena Valley the outcrops of the Gilbert-type deltaic system are composed of at least 6 distinct packages (Roda U–Z) characterized by texturally mature, delta-front sandstones separated by offshore mudstones. The stacked basinward-stepping architecture of the Roda U–Y units here represents a minimum of 3 major phases of SW-directed progradation, capped by hardground horizons formed during the subsequent flooding phases. Tidally-modified delta-front deposits found in the distal exposures of Roda Y represent the redistribution of the delta toeset by W–NW directed ebb-tidal currents, active during advanced stages of progradation of the Gilbert-type delta. The more gentle sloping shoal-water fan-delta system found in Barranco de Ricans and Barranco de Codoñeras, is characterized by progradational to aggradational stacking of texturally immature wave-modified mouth-bar sandstone packages separated by offshore mudstones. The zone of interference between the Gilbert-type and shoal-water delta is dominated by wave-reworked sediments deposited as shoreface, barrier and spit deposits. Biostratigraphic dating suggests that the Roda Sandstone was deposited during a 3rd order relative sea level cycle as a shelf-margin systems tract. However, the stacking of the individual Roda U–Y units demarcated by offshore mudstones, both within the Gilbert-type and the shoal-water deltaic systems, suggest that 4th order fluctuations occurred. These 4th order units are physically correlatable between the two deltaic systems, which implies that both deltas responded synchronously to a combination of regional subsidence and eustatic sea level fluctuations. The differing internal architecture, such as the steeply-dipping, textural mature, foreset beds of the Gilbert-type delta versus the more gentle sloping, textural immature mouth-bars of the shoal-water fan-delta, are controlled by different hinterland characteristics and intrabasinal topography.

Flank Margin Cave Development in Carbonate Talus Breccia Facies: An Example from Cres Island, Croatia

Plava Grota, Cres Island, Croatia, is a flank margin cave developed in a coastal setting in talus breccia facies. The internal cave geometry of small entrances, intersecting adjacent chambers, remnant dissolutional bedrock pillars, and low arches matches diagnostic features used to separate flank margin caves from epigenic stream caves on one hand, and sea caves on the other. Plava Grota is found, along with adjacent smaller caves, solely in a breccia facies that is most probably of Pleistocene age. This breccia is comprised of clasts derived from diagenetically mature, or telogenetic, Cretaceous carbonate rocks. The clasts are loosely cemented by vadose calcite cements. The breccia facies provide a three-dimensional porosity and permeability structure that behaves hydraulically in a manner similar to the high primary porosity and permeability of young eogenetic carbonate rocks in settings such as the Bahamas or Puerto Rico, and the many flow paths found in highly-tectonized telogenetic carbonate rocks in New Zealand. Plava Grota is the first described flank margin cave from the coastal carbonate rocks of the Adriatic Sea. According to present sea-level position in relation to the cave, fresh-water springs in and adjacent to the cave, general tectonic subsidence of the area and Quaternary eustatic sea-level fluctuations, we propose the hypotheses that the cave was primarily formed during the MIS 5e sea-level highstand.

Stratigraphic significance and resolution of spectral reflectance logs in Lower Devonian carbonates of the Barrandian area, Czech Republic; a correlation with magnetic susceptibility and gamma-ray logs

Spectral reflectance (SR) is a relatively novel technique which is used as a proxy for organic carbon and siliciclastic input in carbonate sediments, in particular in core research. This study summarizes results from high-resolution outcrop SR logging of a Lower Devonian distal ramp carbonate section of the Barrandian area, Czech Republic. The SR data were correlated with parallel petrophysical and geochemical data with an aim to improving their cyclostratigraphic and event stratigraphic interpretation potential and the gaps SR data can fill. Transgressive–regressive trends, indicated by facies stacking patterns, CaCO 3 data and spectral gamma-ray (GRS) logs, are well correlated in the regional context and point to third-order eustatic sea-level fluctuations. Peak regressions of the TR cycles are sensitively marked by CIE L* a* b* parameters and percent reflectance in colour bands. The SR and magnetic susceptibility (MS) data are markedly cyclic on a more detailed scale. Their inferred periods vary between 49.2 and 205 kyr indicating that they may have been forced by orbital cycles in the Milankovitch band. The SR and MS cycles are either in phase or out of phase. The latter cycles point to a strong diagenetic forcing of the colour cyclicity. Hematite concentration cycles, inferred from SR signal in the Pragian red hemipelagic carbonates, are interpreted as reflecting changing bottom oxygenation and subsurface redox gradients during early diagenesis. The CIE L* parameter was found to be related to the presence of diagenetic hematite, which indicates that cyclostratigraphic analysis of simple greyscale data can be affected by considerable error due to chromacity. Although the CIE L* parameter is partly correlated with CaCO 3 concentrations, the MS data are not, which suggests that the MS signal can be significantly influenced by diagenetic minerals and its cyclostratigraphic interpretation can be potentially misleading. The SR data, backed up by GRS, MS and CaCO 3 data indicate that the red colour in the Pragian hemipelagic limestones originated from early diagenetic hematite precipitation under the conditions of an oxygenated ocean floor. This suggests that deep-sea bottom oxygentation may have been in operation during the early Devonian, which is traditionally perceived as a typical greenhouse period. The SR data can be obscured in several m thick zones of elevated CIE L* and other colour changes (“leaching zones”) related to postdepositional alteration along subvertical faults, however, this fault-related telogenic alteration has little influence on the MS signal. The combined use of SR and MS has a synergic effect and can significantly improve the interpretation of their respective cyclic signals, particularly in relation to the diagenetic overprint and possible carriers of the MS.

Lithologic and diagenetic attributes of the Sharwayn (Maastrichtian) and Umm Er Radhuma (late Paleocene–Eocene) formations and their significance to the K-T unconformity, Jabal Samhan area, Dhofar, Sultanate of Oman

The boundary separating Maastrichtian Sharwayn Formation from late Paleocene Eocene Umm Er Radhuma (UER) Formation in Dhofar, southern Oman, is characterized by a regionally extensive unconformity. The Jabal Samhan escarpment, north of Marbat-Sadh transect, preserves this unconformable boundary. This paper addresses the lithologic and diagenetic differences of the strata across the boundary and discusses their significance and link to the development of the upper Maastrichtian to lower Paleocene unconformity. The upper part of the Sharwayn Formation is characterized by lower thickly bedded, bioclastic, and peloidal mudstone to wackestone lithofacies overlain by a thick ledge (~5.5 m) of medium to coarse crystalline, (sucrosic) dolostone. Poorly preserved outlines of the framework grains suggest an original peloidal and bioclastic grainstone texture for the dolostone unit. The contact with the overlying UER Formation is sharp. The UER Formation is characterized by thickly bedded, bioclastic mudstone to wackestone overlain by coarse-grained, foraminiferal grainstone. The dolomitization process of the dolomite unit at the top of the Sharwayn Formation is envisaged to a shallow subsurface mixed meteoric and sea water diagenetic realm. This interpretation is supported by an inferred timing of dolomitization of latest Maastrichtian (post-Sharwayn Formation) to early Paleocene (pre-EUR Formation), preservation (although poorly recognizable) of the original depositional texture and diagenetic features that postdate the sucrosic dolomite. Pervasive dolomitization of the dolomite unit was controlled by its original grainstone texture, which permitted efficient percolation of the dolomitizing fluids. Correlation between the reference section of the formation and the section studied in this work raises the thickness of the formation to 28.5 m (relative to a thickness of 22 m at the reference section). Analysis of the new composite section suggests that deposition of the formation took place in a shallowing-upward setting where low-energy subtidal sediments (the lower limestone unit) were succeeded by a high energy sand shoal (upper dolomitized unit).This shallowing-upward succession is attributed to a third-order sea-level drop. The later is also recognized in many parts of the Arabian Peninsula, as well as globally, and interpreted as eustatic sea-level fluctuation.

Tectonic controls on nearshore sediment accumulation and submarine canyon morphology offshore La Jolla, Southern California

CHIRP seismic and swath bathymetry data acquired offshore La Jolla, California provide an unprecedented three-dimensional view of the La Jolla and Scripps submarine canyons. Shore-parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons. These shore-parallel patterns allow the impact of local tectonic deformation to be separated from the influence of eustatic sea-level fluctuations. Based on stratal geometry and acoustic character, we identify a prominent angular unconformity inferred to be the transgressive surface and three sedimentary sequences: an acoustically laminated estuarine unit deposited during early transgression, an infilling or “healing-phase” unit formed during the transgression, and an upper transparent unit. Beneath the transgressive surface, steeply dipping reflectors with several dip reversals record faulting and folding along the La Jolla margin. Scripps Canyon is located at the crest of an antiform, where the rocks are fractured and more susceptible to erosion. La Jolla Canyon is located along the northern strand of the Rose Canyon Fault Zone, which separates Cretaceous lithified rocks to the south from poorly cemented Eocene sands and gravels to the north. Isopach and structure contour maps of the three sedimentary units reveal how their thicknesses and spatial distributions relate to regional tectonic deformation. For example, the estuarine unit is predominantly deposited along the edges of the canyons in paleotopographic lows that may have been inlets along barrier beaches during the Holocene sea-level rise. The distribution of the infilling unit is controlled by pre-existing relief that records tectonic deformation and erosional processes. The thickness and distribution of the upper transparent unit are controlled by long-wavelength, tectonically induced relief on the transgressive surface and hydrodynamics.

Correlation of TL layers for the synchronous paleoceanographic events in the East Sea (Sea of Japan) during the Late Quaternary

TL layers (i.e., dark mud layers), either thin or thick, as determined by the L* values with lithologic observation, are distinct paleoceanographic signatures in the East Sea (Sea of Japan), which were formed in response to the global eustatic sealevel fluctuations between interglacials and glacials during the Late Quaternary. These lithologic markers were consistently correlated among the three sediment cores (MD01-2407, 05GCRP21, and KR05-09PC1) collected from the Oki Ridge of the southern Yamato Basin, the South Korea Plateau of the northern Ulleung Basin, and the Matsumae Plateau of the northeastern Japan Basin, respectively. Reconstruction of age models for cores 05GCRP and KR05-09PC1 was aided in a good way by the AMS 14C ages of planktonic foraminifera and identification of the tephra layers, and mainly by lithostratigraphic correlation with TL layers of well-dated core MD01-2407, based on the L* values. The correlation of TL layers among the three sediment cores was remarkable, indicating that the East Sea (Sea of Japan) experienced the synchronous and basin-wide scale paleoceanographic events during the Late Quaternary. Our study exemplifies the significant usefulness of these lithologic markers for further Late Quaternary paleoceanographic investigation.

Mechanism and geochemical implications of the Late Holocene organic carbon burial event: an example from the southwest coast of India

Carbonaceous clay found in the palaeo-deposits of Meenachil River basin was analysed for the total organic carbon, nitrogen and textural characters. Radiocarbon dating of this clay formation and the embedded carbonized wood fragments was also done. The values obtained for the organic carbon, nitrogen and C/N ratio of the carbonaceous clay exhibited a very remarkable range, suggestive of different environmental conditions of formation. It is evident from the present study that since the lignin and cellulose are the dominant components of terrestrial higher plants, allochthonous and submerged organic matter have high C/N ratio. The radio carbon dating of the sediment and wood samples suggested that the palaeo-deposits of Meenachil River basin were formed as result of many transgrassive–regressive episodes, which had started even before the formation of Vembanad Lake. The formation of carbonaceous clay, as found sandwiched in palaeo-deposits, was due to the global eustatic sea-level fluctuations and tectonism.

Fluvial-estuarine reinterpretation of large, isolated sandstone bodies in epicontinental cyclothems, Upper Pennsylvanian, northern Midcontinent, USA, and their significance for understanding late Paleozoic sea-level fluctuations

The Upper Pennsylvanian Indian Cave Sandstone (ICS) in southeastern Nebraska is herein reinterpreted as three multistory incised valley fills and one single-storey channel fill, altogether representing at least two different intervals of time. ICS lithosomes are linear bodies, as much as 2000 m wide and 30 m thick, incised into pre-existing cyclothems, and have relatively steep sides and flat bases. They include crudely fining-upwards successions of trough cross-bedded sandstones, interpreted as tidally-influenced fluvial deposits, overlain by upper estuarine heterolithic facies, with local coals, and a restricted trace fossil assemblage. The vertical facies succession suggests sediment accumulation in a regime of gradually increasing accommodation, i.e., during rising relative sea level. The basal erosion surfaces of ICS bodies can be traced out onto the adjacent interfluves where they correspond to well-developed paleosols, indicating sequence boundaries. Furthermore, the sequences defined herein can be correlated closely with recently published sequence stratigraphic frameworks from the region, suggesting that the ICS bodies record repeated, fifth-order (Milankovitch band), relative sea-level fluctuations of a minimum of 30 m during latest Pennsylvanian time Significantly, this estimate is half or less of those made by many other studies. Such a local quantification of relative sea-level change provides a critical constraint on eustatic sea-level fluctuation during the late Paleozoic Gondwanan Ice Age.

Dispersivity and distribution coefficients in marine sediments using3Hand226Ra

Continental aquifers flow along topographic gradients toward coastlines in many geologic environments. Wherever aquifers intersect coastlines, ground water mixes with seawater infiltrated in marine sediments. In this mixing zone, sediment-pore fluid interactions create geochemical gradients that migrate back and forth on short (e.g., tides, waves) and long time scales (e.g. seasonal and eustatic sea level fluctuations). We focus on sorption and ion exchange characteristics of radium in these mixing zone sediments using laboratory column experiments. Previous studies have shown salinity affects radium sorption, but this process has not been investigated in porous sediments where solution ionic strength may fluctuate over a range of time scales. Additionally, different sediment types present within this subsurface zone may act as temporally and spatially variable source/sink sites for Ra. These sediments may have been underestimated in Ra mass balances for estimating coastal ground water fluxes. We performed microcosm sediment column experiments to examine Ra behavior and quantify the source/sink capacity of sediments. Longitudinal dispersivity results indicate local flow field variability was minimal during experiments. Radium desorption from sediments occurs rapidly (within 60 to 120 minutes) with exposure to solution and is generally high in the shallow portion of the subterranean mixing zone.

A pre-cursor extensive Miocene reef system to the Rowley Shoals reefs, Western Australia: evidence for structural control of reef growth or natural hydrocarbon seepage?

Numerous Miocene reefs and related carbonate build-ups have been identified in the Rowley Shoals region of the central North West Shelf, offshore Western Australia. The reefs form part of an extensive Miocene reef tract over 1,600 km long, which extended northward into the Browse and Bonaparte basins and southward to North West Cape in the Carnarvon Basin—comparable in length to the modern Great Barrier Reef. Growth of the vast majority of these Miocene reefs failed to keep pace with relative sea-level changes in the latest Miocene, whereas reef growth continued on the central North West Shelf to form the three present-day atolls of the Rowley Shoals: Mermaid, Clerke and Imperieuse reefs. In the Rowley Shoals region, scattered small build-ups and local reef complexes were first established in the Early Miocene, but these build-ups were subsequently terminated at a major Mid Miocene sequence boundary. Widespread buildups and atoll reefs were re-established in the Middle Miocene, and the internal stacking geometries of the reefs appear to relate to distinct growth phases that are correlated with eustatic sea-level fluctuations. These geometries include: a basal aggradational buildup of early Middle Miocene age; a strongly progradational growth phase in the late Middle to early Late Miocene that constructed large reef atolls with infilling lagoon deposits; and a back-stepped aggradational growth phase that formed smaller reef caps in the early–latest Late Miocene. Growth of the majority of the reefs ceased at a major sea-level fall in the Late Miocene (Messinian), and only the reefs of the present-day Rowley Shoals (Mermaid, Clerke and Imperieuse reefs, as well as a drowned shoal to the southwest of Imperieuse Reef) continued to grow after this event. Growth of the Rowley Shoals reefs continued to keep pace with Pliocene-Recent sea-level changes, whereas the surrounding shelf subsided to depths of 230–440 m. We conclude that initial reef growth in the Rowley Shoals region was controlled by transpressional reactivation and structuring of the Mermaid Fault Zone during the early stage of collision between the Australian and Eurasian plates. During this structural reactivation, seabed fault scarps and topographic highs likely provided ideal sites for the initiation of reef growth. The subsequent growth and selective demise of the reefs was controlled by the interplay of eustatic sea-level variations and differential subsidence resulting from continued structural reactivation of the Mermaid Fault Zone. In contrast to models proposed in other regions, there is no direct evidence that active or palaeo hydrocarbon seepage triggered or controlled growth of the Rowley Shoals reefs or their buried Miocene predecessors.

Constraints on the amplitude of Mid-Pliocene (3.6–2.4 Ma) eustatic sea-level fluctuations from the New Zealand shallow-marine sediment record

Ice-volume calibrations of the deep-ocean foraminiferal delta18O record imply orbitally influenced sea-level fluctuations of up to 30m amplitude during the Mid-Pliocene, and up to 30 per cent loss of the present-day mass of the East Antarctic Ice Sheet (EAIS) assuming complete deglaciation of the West Antarctic Ice Sheet (WAIS) and Greenland. These sea-level oscillations have driven recurrent transgressions and regressions across the world's continental shelves. Wanganui Basin, New Zealand, contains the most complete shallow-marine Late Neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100ka sea-level cycle since ca 3.6Ma. This paper presents a synthesis of faunally derived palaeobathymetric data for shallow-marine sedimentary cycles corresponding to marine isotope stages M2-100 (ca 3.4-2.4Ma). Our approach estimates the eustatic sea-level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation. The sea-level estimates are consistent with those from delta18O curves and numerical ice sheet models, and imply a significant sensitivity of the WAIS and the coastal margins of the EAIS to orbital oscillations in insolation during the Mid-Pliocene period of relative global warmth. Sea-level oscillations of 10-30m were paced by obliquity.

Triassic ammonoids of Northeast Asia: Diversity and evolutionary stages

The history of Triassic ammonoids in the Siberian Province of the Boreal Paleobiogeographic Realm is recorded in detail in sections of Northeast Asia. In this region there are known at present 123 Triassic ammonoid genera of 41 family and 3 orders. Six stages and 14 substages are defined based on main levels of taxonomic restructuring of Triassic ammonoids, changes in their genera and families diversity, and changes in percentage of endemic and cosmopolitan taxa in assemblages. Each stage and substage is characterized by individual taxonomic composition of ammonoids, dominant groups, trends of changes in taxonomic diversity, and percentages of endemic and cosmopolitan taxa. Boundaries of ammonoid evolution stages coincide as a rule with boundaries of series and stages, whereas boundaries of evolutionary substages match those of substages. In the history of Triassic ammonoids of Northeast Asia, the periods of a rather monotonous fauna represented mainly by cosmopolitan or panboreal taxa (early Induan, early Olenekian, early Anisian, late Anisian, early Carnian, early and middle Norian) alternated with periods, typical of which were higher rates of taxa origination and endemism of ammonoids (late Induan, late Olenekian, middle Anisian, Ladinian, late Carnian). Changing degree of cosmopolitism and endemism of Triassic ammonoid faunas from Northeast Asia is shown to be connected with global eustatic sea-level fluctuations and climatic changes.

Petrographic and seismic evidence for the depositional setting of giant turbidite reservoirs and the paleogeographic evolution of Campos Basin, offshore Brazil

The paleogeographic evolution of Campos Basin, a major oil province of Brazil, during the deposition of its giant turbidite reservoirs, was reinterpreted based on the integration of quantitative sandstone petrography and structural analysis of regional 3D seismic data. The major detrital compositional trends indicate that the geodynamic evolution of the continental margin, rather than global eustatic sea-level fluctuations, has exerted the main control on sand supply to the deepwater systems. This control was imposed by the interaction of three geodynamic processes: (i) escarpment retreat of the coastal mountain ridges, (ii) mantle plume-related dynamic uplift and magmatic activity, and (iii) tectonic reactivation of major basement fault-zones. The pattern of distribution of compositional and textural parameters within the turbidite sequences indicated that the sand supply to deepwater was also constrained by high-frequency stratigraphic processes of the climate Milankovitch band. This new approach to the controls on the formation of the sand-rich, deepwater systems in Campos Basin has a key importance for the generation of realistic models for the exploration of new turbidite reservoirs and for the optimized development of producing turbidite oilfields in such a world-class hydrocarbon province. The proposed integrated methodology can help to unravel the controls on the deposition of deepwater sand-rich, deepwater reservoirs in other divergent margin settings.

Cenomanian rocks in the Sinai Peninsula, Northeast Egypt: Facies analysis and sequence stratigraphy

Five stratigraphic sections of the Cenomanian rocks exposed in the Sinai Peninsula are described and interpreted on the basis of field observations and facies analysis in order to reconstruct their depositional environments and sequence stratigraphic framework. Based on their lithologic characteristics, the Cenomanian successions consist of mixed siliciclastic–carbonate rocks. The Cenomanian successions are dominated by carbonate production in the northern and eastern parts of the study area. Siliciclastic supply increases southward. Detailed petrographic investigations made it possible to recognize several clastic and carbonate facies types. The facies recognized and their related palaeoenvironments document a lateral transition between inner- and mid ramp settings. The inner-ramp setting occurs in the south and west central Sinai where the peritidal flat, lagoonal, high-energy shoals facies dominate. The mid-ramp setting is assumed to have developed in the north and east central Sinai where intertidal and low-energy subtidal facies interfingers with a few storm-influenced deposits occur. The main factors controlling ramp deposition were eustatic sea-level fluctuations combined with environmental influences such as autochthonous carbonate productivity and siliciclastic supply. In terms of sequence stratigraphy, the Cenomanian successions in Sinai exhibit two superimposed depositional sequences, each of which shows retrogradational (transgressive systems tract) and aggradational to prograditional (highstand systems tract) packages of facies. The retrograditional facies display a predominance of subtidal carbonate facies, whereas the prograditional and aggradational facies show an increase of peritidal carbonates and siliciclastic deposits.

Calcareous nannofossil surface sediment assemblages from the Sicily Channel (central Mediterranean Sea): Palaeoceanographic implications

Quantitative analysis of 67 calcareous nannofossil assemblages from surface sediments recovered in a wide area across the Sicily Channel has been carried out in order to improve the interpretation of palaeontological data based on this planktonic group in a key area for Mediterranean palaeoceanographic studies. The investigation focused on three case studies that demonstrate the high potentiality of such a combined approach, taking into account the recent distribution of taxa or groups of taxa on the sea floor and the palaeontological record. The distribution of reworked specimens over the northern Sicily Channel sea floor validates the role of southern Sicily as a source region for reworked nannofossils and the role of rivers as their carrier. Eustatic sea-level fluctuations can be considered to be the main factor that influenced the abundance variations in sedimentary sequences of this area. The distribution of Florisphaera profunda can be explained in terms of topography (positive correlation) and mesoscale oceanographic circulation. In particular, its significant anti-correlation to the amount of chlorophyll-A deduced by satellite imagery validates the use of this species as a proxy for palaeoproductivity reconstructions. Finally, high abundance values of G. oceanica are confined to the westernmost part of the Sicily Channel, coinciding with a water mass salinity minimum. In particular, abundances of up to about 10% were observed in the westernmost part of the African Margin, suggesting the importance of the Atlantic Tunisian Current, whose activity is more pronounced in winter. The comparison of data of this species between 135 and 110 kyr BP, inside and outside the Channel, led us to deduce that the physical transport in almost unmodified waters of Atlantic origin might be the most important factor for its significant occurrence.

Neogene evolution of the mixed carbonate‐siliciclastic system in the Gulf of Papua, Papua New Guinea

This paper outlines the evolution of the late Cenozoic mixed carbonate‐siliciclastic depositional system in the Gulf of Papua (GoP), using seismic, gravity, multibeam bathymetry, well data sets, and Landsat imagery. The deposition of the mixed sedimentary sequences was influenced by dynamic interplay of tectonics, eustasy, in situ carbonate production, and siliciclastic sediment supply. The roles of these major factors are estimated during different periods of the GoP margin evolution. The Cenozoic mixed system in the GoP formed in distinct phases. The first phase (Late Cretaceous–Paleocene) was mostly driven by tectonics. Rifting created grabens and uplifted structural blocks which served later as pedestals for carbonate edifices. Active neritic carbonate accumulation characterized the second phase (Eocene–middle Miocene). During this phase, mostly eustatic fluctuations controlled the large‐scale sedimentary geometries of the carbonate system. The third phase (late Miocene–early Pliocene) was characterized by extensive demise of the carbonate platforms in the central part of the study area, which can be triggered by one or combination of several factors, such as eustatic sea level fluctuations, increased tectonic subsidence, uplift, sudden influx of siliciclastics, or dramatic changes in environmental conditions and climate. The fourth phase (late Pliocene‐Holocene) was dominated by siliciclastics, which resulted in the burial of drowned and/or active carbonate platforms, although some platforms still remain alive until present‐day.

The Canaries: an important biogeographical meeting place

The Canaries: an important biogeographical meeting place