Sedimentary Wedge Research Articles

Early to middle Miocene ice sheet dynamics in the westernmost Ross Sea (Antarctica): Regional correlations

The present-day morpho-stratigraphy of the Ross Sea is the result of Cenozoic tectonic and cryospheric events, and constitutes a key record of Antarctica's cryospheric evolution. An enduring problem in interpreting this record in a broader regional context is that the correlation between eastern and western Ross Sea stratigraphy has remained uncertain due to the limited number of drill sites. We correlate the glacial-related features observed on a dense network of seismic reflection profiles in McMurdo Sound with those identified in the Nordenskjöld and Drygalski Basins, as well as the basins farther east in the central Ross Sea. We present an improved correlation of the regional patterns of early to middle Miocene ice-sheet variance across the Ross Sea constrained by new evaluation of seismic facies and age models from one site recovered by the Antarctic Drilling Project (ANDRILL) in the southwestern most part of McMurdo Sound. We also integrate this correlation with the recently published seismic framework in the central Ross Sea. The formation of U-shaped valleys during the early Miocene in McMurdo Sound, together with prograding sedimentary wedges in the western-most basins, and the central Ross Sea, suggest two major phases of overall advance of a marine-terminating ice sheet between ~18 Ma and ~17.4 Ma. Widespread formation of turbiditic channel-levee systems in McMurdo Sound and rapid sediment deposition in Nordernskjöld Basin point to subsequent ice-sheet retreat between ~17.4 Ma and ~15.8 Ma, coinciding with the onset of the Miocene Climate Optimum (MCO; ~17–14.5 Ma). However, the carving of troughs and formation of irregular morphologic features suggest that an extensive ice sheet still remained along the western Ross margin at ~17.4 Ma and a brief episode of ice-sheet advance occurred at ~16.8 Ma in the earliest interval of the MCO. Subsequent marine-based ice sheet advance during the Middle Miocene Climate Transition (MMCT, ~14.0–13.8 Ma) is indicated by widespread erosional features. Our results reconcile the semi-continouous seismic and drill core stratigraphy of the offshore Ross Sea continental shelf with inferences of ice sheet dynamics from continuous far-field deep sea and sea level records, as well as the highly discontinous (and heavily debated) onshore records of pre-MMCT glaciation and aridification of the Transantarctic Mountains at 14 Ma. • Core-log-seismic correlation allows regional correlation of the Ross Sea record • 2 major advances of marine-terminating ice sheet occurred between 18 and 17.4 Ma • Ice sheet retreated at the onset of the Miocene Climate Optimum • Short-term ice-sheet advance occurred at ~16.8 Ma • Widespread marine-based ice sheet correlates to the Miocene Climate Transition

Structure, geochronology, and petrogenesis of Permian peraluminous granite dykes in the southern Chinese Altai as indicators of Altai−East Junggar convergence

How and at which thermal conditions the convergence between the Chinese Altai and East Junggar operated remain poorly understood. This issue is addressed in the current study by focusing on the timing and petrogenesis of syntectonic granite dykes from the representative areas of Fuyun (convergent front) and Kalasu-Aletai (Chinese Altai interior). It is shown that Fuyun and Kalasu-Aletai dykes are fractionated I- and S-type granites, with zircon and monazite U-Pb ages of 300−291 Ma and 281−265 Ma, respectively. Geochemically, the Fuyun dykes have lower contents of aluminous (ASI: 0.97−1.13) and light rare earth element-enriched features, while the Kalasu-Aletai dykes have ASI = 1.01−2.17 and show overall flat rare earth element patterns with tetrad effects. The Fuyun dykes exhibit less evolved Sr-Nd isotopic characteristics (87Sr/86Srinitial: 0.7039−0.7048, εNd(t): + 5.7 to + 6.1) with respect to those of the Kalasu-Aletai dykes (87Sr/86Srinitial: 0.6978−0.7183, εNd(t): −7.6 to +3.0). The Fuyun and Kalasu-Aletai dykes are geochemically compatible with isotopically less evolved East Junggar arc components and heterogeneous Ordovician wedge sediment of the Chinese Altai, respectively, implying genetic links. We propose that the late Paleozoic Chinese Altai−Junggar convergence created a local perturbation of weak mantle beneath the southern Chinese Altai, causing partial melting of the underthrusting East Junggar and the overriding Altai components successively. The resulting magmas were emplaced along northward propagating syn-tectonic tensional fractures perpendicular to the Chinese Altai−East Junggar deformation front that serves as an excellent indicator of the convergent-shortening process.

Eustasy in the Aptian world: A vision from the eastern margin of the Iberian Plate

Eustatic controls on Early Cretaceous (Aptian) sedimentation in the western Tethys are discerned in outcrops of carbonate platforms that developed in the Maestrat rift basin located at the eastern margin of the Iberian Plate. The relative sea-level fluctuations with a dominant eustatic contribution investigated had estimated magnitudes of between 50 and 60 m in <0.9 My and ≥115 m in <3 My, and occurred respectively during the late early and early late Aptian. The major relative sea-level falls of mainly eustatic nature were recorded as forced regressive sedimentary wedges or as incised valleys carved into highstand carbonate platforms, whereas the subsequent sea-level rises back-filled the incised topographic lows created, or favoured the development of lowstand platforms. The finding of 50–115 m amplitude fluctuations of Aptian age is of relevance in that show magnitudes of relative sea-level fall in the order of that recorded during the last glacial maximum in the late Pleistocene ( c . 120 m). The current knowledge on Cretaceous climate history shows an Earth with non-uniform greenhouse conditions. However, geological evidence of temporary icehouse states with ice-cap magnitudes close to late Pleistocene scales during the Aptian is absent, or at least has not been reported so far. Thus, although falling within the glacio-eustatic domain, the driving processes of these widespread drops and subsequent rises in relative sea level remain a mystery. Finally, this paper is an example of how sequence stratigraphy can be applied to carbonate successions, and of how this methodology indeed permits to unravel ancient relative sea-level fluctuations which controlled carbonate production and accumulation. • Eustatically-driven changes in accommodation deciphered • The Aptian world recorded a strong eustatic signal • Development of incised valleys during the Aptian

The interplay between deformation and deposition in a Pleistocene push moraine: New insight from structural interpretation and area-depth-strain analysis of the growth strata

There are many examples suggesting that push moraine formation requires building up of the proglacial wedge and then post-depositional folding and/or faulting. Only a few studies have been carried out on syntectonic deposition and erosion within proglacial sediment wedges; however, the resulting growth strata were determined based on the high variability in thickness and occurrence of erosional unconformities across the deformed sequence. This study shows how structural interpretation and the area-depth-strain (ADS) balancing method of the growth strata can be applied to better understand the interplay between deformation and deposition within an evolving push moraine primarily composed of a folded sequence of a glaciofluvial fan. This approach, together with analysis of the onlap/overlap relationships, allowed us to determine the relative rate between deposition and deformation. Moreover it provides an insight into the topography of the push moraine that may be inherited not only from the geometry of deformation structures but also from depositional processes controlling the spatial distribution and thickness variation of the growth strata. This study also gives an opportunity to reconstruct the ranges of probable parameters to quantitatively describe the heavily eroded push moraine in terms of the primary topography, height and relative time frame within which it formed. In addition, the probable thermo-hydro-mechanical properties of the deformed strata are interpreted in terms of drained/undrained conditions of volume strain evidenced by structural data and possibilities of lateral flow from beneath synclines into anticlines indicated by ADS-based balancing.

Bolide impact effects on the West Florida Platform, Gulf of Mexico: End Cretaceous and late Eocene

Abstract This study documents seismic reflection evidence that two different bolide impacts significantly disrupted stratigraphic and depositional processes on the West Florida Platform (Gulf of Mexico). The first impact terminated the Late Cretaceous Epoch (Chicxulub impact, Mexico; ca. 66 Ma; end-Maastrichtian age). The second took place in the late Eocene (Chesapeake Bay impact, Virginia, USA, portion of the Chesapeake Bay; ca. 35 Ma; Priabonian age). Both impacts produced far-reaching seismic shaking and ground roll followed by an impact-generated tsunami, the effects of which are evident in the seismostratigraphic record. The Chicxulub seismic shaking caused collapse and shoreward retreat of the Florida Escarpment and widely disrupted (faulting, folding, slumping) normal flat-lying shelf beds. The associated tsunami currents redistributed these shelf deposits and mixed them together with collapse debris from the escarpment to form a thick wedge of sediments along the base of the escarpment. The Chesapeake Bay impact created a mounded sedimentary deposit near the outer edge of the late Eocene ramp slope. This deposit also has a bipartite origin. A lower layer is marked by en echelon faulting created in situ by seismic shaking, whereas an upper layer represents sediments redistributed from the late Eocene shelf and upper ramp slope by tsunami-driven bottom currents (debris flows, contour currents, slumps). This is the first report of seismic effects from the Chesapeake Bay impact in the Gulf of Mexico. These results further demonstrate that large-scale marine bolide impacts have widespread effects on the stratigraphic and depositional record of Earth.

Holocene morpho-stratigraphic evolution of a compound submarine deltaic system in front of the shelf-incising Almanzora and Garrucha Canyons (Palomares margin, southeastern Iberia)

The Holocene morpho-stratigraphic evolution of a compound submarine deltaic system linked with the Antas and Almanzora Rivers on the narrow (< 5 km) shelf along the Palomares margin (southeastern Iberia) has been reconstructed from the integrated analysis of geomorphology, seismo-stratigraphy and sedimentology. The shelf morphology is characterized by a 3–4 km wide deltaic body off the Almanzora River, where seafloor undulations and gullies are present. Larger and more incised gullies, crescent-shaped bedforms and pockmarks are recognizable at or close to the head of shelf-indenting canyons associated with the Almanzora-Garrucha canyon system.The seismo-stratigraphy displays a strong and irregular basal reflector overlain by a sedimentary wedge, showing variable thicknesses (1–25 m) and seismic characteristics along and across the shelf. The main depocenter of this wedge is not located off the Almanzora River mouth (i.e., the main sedimentary input in the study area) but along the southern shelf encompassing the Almanzora and Antas Rivers. Grain-size and sand compositional analyses show that silty sand with high terrigenous content (mostly quartz and mica) is mainly found on the submarine deltaic body. In contrast, sandy silt with variable ratios between terrigenous and biogenic contents is retrieved from the canyon head and associated gullies as well as from the surrounding mid-outer shelf.The evolution of the Antas-Almanzora compound delta has been divided into three evolutionary stages, mainly driven by the interplay between paleo-topography and riverine and marine processes and modulated by sea level changes during the Holocene. The origin of the present-day morphological features is also discussed, again highlighting a complex interaction between sedimentary gravity flows (mainly flash flood-generated hyperpycnal flows), storm-waves and shelf currents, fluid seepage and retrogressive slope failures.

A stratigraphic record from syn to post subduction sedimentation in Marlborough, New Zealand, and implications for Gondwana breakup

Sediments that accumulate within marine basins at convergent plate margins can provide important insights into the evolution and tectonic stability of the subduction wedge. Long-term sediment dispersal and stratigraphic patterns can also be influenced by geodynamic reconfigurations of the plate margin, such as changes in plate dip or velocity, or the subduction of anomalous oceanic crust. An understanding of tectonic context and complexity is therefore critical for any interpretation of convergent margin stratigraphy. Unfortunately, ongoing subduction and wedge deformation tends to obscure or destroy the stratigraphic record of such events as sediments become progressively incorporated into the wedge.The Awatere Valley in New Zealand's South Island contains well-preserved forearc stratigraphic record that accumulated within coastal-plain and marine basins during the final stages of East Gondwana subduction. We assign seven facies associations (FA) to characterise post-subduction units, showing that a transition from syn to post-subduction deposition is contained within largely marine strata from the New Zealand Urutawan to Ngaterian stages (c. 108 to 95 Ma). In contrast to previous accounts of deposition within nascent rift-basins, restored basin geometries are most consistent with those of terraced subduction wedges. We find no evidence that extension affected deposition prior to 95 Ma. Our results instead document a transition from highly deformed sedimentary wedge (pre 108 Ma) to largely undeformed sedimentary cover units (∼100 Ma) that is predominantly gradational.Up to 2 km of basin fill documents a relative sea-level (RSL) rise and fall between 108 and 95 Ma. A period of relative sediment starvation during the Urutawan (108–103 Ma) was abruptly terminated by synchronous mass-wasting, including the remobilisation of metre-scale blocks and rafts, that signals a dramatic increase in depositional energy relative to preceding patterns. Within the context of a large RSL fluctuation, diminishing compressional tectonism and forearc volcanism (from 98 Ma), this increase is anomalous and appears to signal a significant change in underlying subduction dynamics.

The origin of mysterious deep holes in the upper and central Sydney estuary, Australia

‘Deep holes’ (DHs) were first reported in the upper and central Sydney estuary in 1973 and speculation as to the origin of these features has continued since that time. The present study established that DHs were not ‘holes’, but preserved sections of the main paleo-channel and that they formed as a result of multiple processes over an extended period. The 17 DHs discovered were the product of fluvial erosion, sediment starvation and tidal action and could be classified into four Types based on bathymetric and seismic attributes. Type A DHs contained four sedimentary units, which fully, or partially filled the paleo-valley; Type B holes exhibited a deep, eroded paleo-channel and a thick remnant sediment wedge on one flank; Type C exhibited a rocky, sediment-free flank and a mainly sediment-free base; Type D DHs were genetically different in not being associated with the main paleo-channel.Extensive erosion of Pleistocene estuarine clay and overlying fluvial sediment produced deep paleo-valleys in the upper and central sectors during long periods of Pleistocene sea-level low stand. Major erosion took place where stream velocities increased in narrow parts of the sinusoidal upper paleo-valley and where the paleo-channel was restricted by protruding headlands of the central section. During recent sea-level high stands, sediment supply from small adjoining sub-catchments in the upper estuary was minimal and bedload from the major paleo-channel was confined to the headwaters of the catchment, which resulted in sediment starvation and hole preservation. In the present high sea-level period, remnant parts of the deep, paleo-channels are being preserved by increased tidal velocities in the same localities as in the past, preserving the DHs observed today.

Textures, provenances, and transport patterns of sediment on the inner shelf of the East China Sea

Although many studies have been carried out on the mud wedge in the inner shelf of the East China Sea (ECS), the sediment sources and seismic textures of the mud wedge are still unclear and remain controversial. Therefore, this study utilizes grain size and clay mineral analyses of surficial sediment samples and high-resolution sub-bottom seismic profile interpretation to identify the provenance and texture of these mud wedge sediments. The results show that sediment sources on the inner shelf of the East China Sea are mixed by the Yangtze River, small mountainous rivers along the Zhejiang-Fujian, and western Taiwan coasts. The sediments derived from the Ou and Min rivers are mainly concentrated in the shallowest shelf area within a water depth of 20 m which is located north of the Min River Estuary. Their contribution to the estuaries and coastal areas reflects the different sediment transport patterns of the two small mountainous rivers. The thickness of the Holocene mud wedge between Hangzhou Bay and Taizhou Bay is greater than 20 m at a water depth of approximately 10 m. The cause of this phenomenon is possibly related to the presence of the Zhoushan Islands, which are distributed along the Zhejiang coast and appear to effectively trap sediments from the Yangtze River, facilitating sediment accumulation. The findings of this study will help improve our understanding of the sediment transport and deposition mechanism of deposition on the inner shelf of the East China Sea.

Effects of contemporaneous orogenesis on sedimentation in the Late Cretaceous Western Interior Basin, northern Utah and southwestern Wyoming

AbstractThree drivers of subsidence are recognized in the Western Interior Basin: Mesozoic–early Cenozoic flexure adjacent to the thin‐skinned, eastward propagating Sevier Orogeny, Late Cretaceous–Eocene flexure associated with thick‐skinned Laramide Uplifts and Late Cretaceous dynamic subsidence. This study combines outcrop lithofacies, palaeocurrent measurements, detrital zircon geochronology, biostratigraphy, stratigraphic correlations and isopach maps of Coniacian–Maastrichtian (89–66 Ma) units to identify these subsidence mechanisms impact on basin geometry and stratigraphic architecture in the northern Utah to southwestern Wyoming segment of the North American Cordillera. Detrital zircon maximum depositional ages and biostratigraphy support that the Maastrichtian Hams Fork Conglomerate was deposited above the Moxa unconformity in the wedgetop and foredeep depozones. The Moxa unconformity underlies the progradational Ericson Formation in the distal foredeep. The Hams Fork, however, is younger than the Ericson Formation, and instead equivalent to upper Almond Formation. Therefore, the hiatus associated with the Moxa unconformity continued for several million years longer in the fold belt and proximal basin than in the distal foredeep, with Ericson Formation‐equivalent strata onlapping the Moxa unconformity towards the west. Regional thickness patterns record and constrain the timing of the transition from Sevier to Laramide‐style tectonic regimes. From 88 to 83 Ma (upper Baxter Formation) a westward‐thickening stratigraphic wedge characterized the foredeep developed by lithospheric flexure by thrust‐belt loading. Nevertheless, the presence of &gt;500 m of subsidence &gt;200 km from the thrust front suggests a long‐wavelength subsidence mechanism consistent with dynamic subsidence. By 83 Ma (Blair Formation) the long‐wavelength depocentre shifted away from the thrust belt, with no evidence of a Sevier foredeep. This depocentre continued migrating eastward during the early‐mid Campanian (ca. 81–77 Ma). The late Campanian–Maastrichtian (ca. 74–66 Ma) is marked by narrow sedimentary wedges adjacent to the Wind River, Granite and Uinta Mountain uplifts and attributed to flexural loading by Laramide deformation.

Tectono‐stratigraphic evolution of the offshore western Niger Delta from the Cretaceous to present: Implications of delta dynamics and paleo‐topography on gravity‐driven deformation

AbstractThe interaction between sedimentary wedge dynamics and paleo‐fracture zones is investigated offshore western Niger Delta lobe (WNDL) to reconstruct the evolution of the delta from the Cretaceous to present. This was achieved through detailed regional seismic interpretation, calibrated with well data. Our results suggest that high sedimentation rates in the WNDL since the Serravallian–Tortonian triggered the migration of the ‘Oligocene‐Tortonian extensional zone’ and gravity spreading seawards (from a present‐day onshore to a present‐day offshore position), with extensional, translational and contractional deformation. An additional increase in sedimentation rate since the early Pliocene, further accelerated gravity spreading and the development of the present‐day contractional front. A five‐stage tectono‐stratigraphic evolution of the offshore WNDL from the late Cretaceous to present is proposed. Paleo‐topographies formed by the Charcot and Chain Fracture Zones exerted depositional control on the stratigraphic architecture of the offshore WNDL from the Cretaceous to Serravallian. Differential subsidence on both sides of the relict Charcot and Chain transform faults is responsible for the segmentation of gravity‐driven deformation of the eastern and western Niger Delta lobes. In addition, a comparison of the stratigraphic architecture of the eastern Niger Delta lobe (ENDL) and WNDL demonstrates a similar overall progradation and sediment bypass to the deep basin during the Pliocene. During the Pleistocene, the two lobes show a distinct evolution and architecture: the ENDL shows an overall retrogradation and sediment sequestration on the shelf, whereas the WNDL displays an overall progradation and sediment bypass. This study documents long‐term and large‐scale control of delta dynamics and paleo‐topography on gravity‐driven deformation of the offshore eastern and western Niger Delta lobes, and similar analysis could be applied in the reconstruction of other passive margin basins.

Peculiarities of Tertiary petroleum systems evolution under prograding shelf environment on the continental margin of the East Siberian Sea

The upper part of the sedimentary cover within the East Siberian Sea shelf comprises Cenozoic clinoform deposits, which accumulated in passive continental margin settings. In the Eastern Arctic, the productivity of clinoform deposits has been proved on the Alaska North Slope and in the Beaufort–Mackenzie Basin. Considering that Cenozoic clinoform deposits are widely represented in the Russian part of the Eastern Arctic, they undoubtedly attract considerable interest from the standpoint of hydrocarbons prospecting. However, despite increasingly closer attention to this interval of the sedimentary section, it is still poorly understood due to its complicated geology. The lack of drilled wells in the region imposes a considerable limitation on an understanding of sedimentary basins development. In this situation, geophysical data become the primary source of information for building geologic models in the Russian sector of the Eastern Arctic. An assessment of hypothetical Cenozoic petroleum systems of the East Siberian Sea is the main objective of this paper. It is to be said research performed under high uncertainty of input data. The results obtained from basin analysis and numerical modeling indicate the possibility that an active petroleum system may exist in the Cenozoic sedimentary wedge of the East Siberian Sea. The outlook for the clinoform complex largely depends on the source rock maturity, i.e., higher prospects should be expected in areas where the prograding wedge has maximum thickness. Considering all factors (reservoir quality prediction, proximity to a hydrocarbon kitchen, timing), the Eocene–Oligocene part of the sedimentary section appears to offer the greatest promise within the study area. Here, predominantly oil accumulations may be expected at a depth of 2.5–3.5 km below sea bottom.

Interference between Apennines and Hellenides foreland basins around the Apulian swell (Italy and Greece)

The analysis of a set of public seismic reflection profiles allows to unravel the evolution of a segment of the Adria Plate in the Salento offshore, i.e., the Apulian swell (southeastern Italy). The study area was and still is shrinking in the foreland of two orogens and related opposed subduction zones, i.e., the southern Apennines and the Hellenides. The two thrust belt fronts of the opposite and converging orogens become very close (up to 150 km) giving rise, in the Salento offshore, to one of the largest lithospheric anticlines in the world. In this area, the deposits of the Hellenides foreland basin migrated towards W-SW at least from the Oligocene due to the E-NEward flexure of the Adria Plate in the northeastern part of the Ionian sea (i.e., on the area of the future Apulian swell). The same area, arching, was involved in the eastward roll-back of Adria Plate at least from the early Pleistocene, and the sedimentary wedge of the south Apennines foreland basin migrated towards E-NE beginning to occupy the outermost part of the Hellenides foreland basin. Therefore, the two related foredeeps overlapped in time, interfering during Quaternary. From late Early and Middle Pleistocene the area coinciding with the culmination of the arc began to uplift, forming the Apulian swell. While uplifting, the Apulian swell was affected by regularly-spaced normal faults, and became a threshold for sediments coming from the two opposite orogens. Two different narrow depocenters, well separated from each other, represent today the Apennines and Hellenides foredeeps, respectively.

Wedge Plasticity and Fully Coupled Simulations of Dynamic Rupture and Tsunami in the Cascadia Subduction Zone

AbstractInelastic wedge deformation likely plays an important role in the generation of tsunami and ocean acoustic waves in accretionary subduction margins. In an elastic dislocation model, whether or not the fault breaks the trench has a significant effect on seafloor deformation and resulting tsunami. However, this boundary condition is less important when significant inelastic deformation in the overriding wedge occurs, because large seafloor uplift can occur with little or no slip at the trench. Here we incorporate wedge plasticity in fully coupled dynamic rupture and tsunami simulations for a buried fault in the Cascadia subduction zone with realistic fault geometry, bathymetry, and velocity structure. A linearized Eulerian approach is verified and used to simulate gravity waves in the ocean. Our coupled models show that the inelastic deformation of wedge sediments can significantly contribute to seafloor uplift, producing tsunami heights at least twice as large as in purely elastic simulations, whilst generating weaker ocean acoustic and seismic waves. Inelastic wedge deformation is therefore an important mechanism to consider in tsunami hazard assessment in the Cascadia subduction zone. These results have important implications for tsunami generation and early warning in accretionary and other sediment‐filled margins worldwide.

The evolution of slate microfabrics during progressive accretion of foreland basin sediments

Here, we study slate microfabrics from the exhumed accretionary wedge of the central European Alps and focus on the development of foliation. High-resolution micrographs from novel BIB-SEM imaging and Synchrotron X-ray Fluorescence Microscopy are analysed with 2D auto-correlation functions to quantify the geometry and spacing of slate microfabrics along a metamorphic gradient covering the outer and inner wedge (200–330 °C). The sedimentary layering primarily controls the morphology of the slate microfabrics. However, from outer to inner wedge, a fabric evolution is observed where diagenetic foliations gradually transform to secondary continuous and spaced foliations. With increasing metamorphic grade, the amount of recrystallized phyllosilicate grains and their interconnectivity increase, as does clast/microlithon elongation (aspect ratios up to 11), while foliation spacing decreases to <20 μm. This foliation evolution under non-coaxial deformation involves a combination of mechanical rotation of phyllosilicates, fracturing, and fluid-assisted pressure-dissolution-precipitation creep. The latter is the dominant deformation mechanism at T > 230 °C and accommodates background strain in the inner wedge. The evolving microstructural anisotropy is interpreted to lead to strain weakening by structural softening and may provide preferential fluid pathways parallel to the foliation, enabling the dehydration of large rock volumes in accretionary sediment wedges undergoing prograde metamorphism.

Marine carbonate factories: Review and update

AbstractThe carbonate factories model, as defined at the beginning of the century, provides a subdivision of marine carbonate sediment production‐systems based on the style of carbonate precipitation. The main factors controlling marine carbonate precipitation are light, water temperature, nutrients, salinity, substrate and carbonate saturation. Site‐specific controls influencing the systems comprise ocean currents, upwelling and non‐upwelling systems, ocean‐atmosphere systems, atmospheric systems, shallow‐water dynamics, and terrestrial sediment and water input.Each factory has its own sediment‐production window linking optimal sediment production with selected environmental controls. Sediment production in the tropical factory (T‐factory) is light and temperature‐dependent and negatively impacted by nutrients. Sediment production and export depends on the size of the shallow‐water areas within the photic zone. The cold‐water‐coral factory (CWC‐factory) is nutrient‐dependent, but light‐independent. Sediment production relates to nutrient supply enabling the growth of the cold‐water corals. The cool‐water factory (C‐factory) displays a strong link to nutrients and water temperature, with parts that are light‐dependent, for example, sediment production in kelp dominated environments. The sediment mineralogy and sediment production area within the high‐energy hydrodynamic zone govern sediment distribution with sediment behaviour comparable to siliciclastics. The microbial/mud‐mound factory (M‐factory) is nutrient‐dependent and to some extent temperature and light‐independent. Sediment production and export is referred to here as slope shedding and links to the main sediment production on the upper slope. The planktic factory (P‐factory) depends on variations in light, temperature and nutrients resulting in fluctuating pelagic fall‐out.Platform morphologies and slope profiles are also factory specific: T‐factories show a rimmed flat‐topped platform with adjacent exponential slopes or a carbonate ramp morphology; CWC‐factories display mound morphologies with steep slopes; C‐factories are associated with open shelf systems and Gaussian shaped slope profiles; while M‐factories are characterized by individual steep‐sided mounds or flat‐topped platforms with deepened margins and a linear shaped slope profile. The P‐factory provides biotic grains to all environments and at times, like for the Cretaceous, may dominate sedimentation patterns in the basin realm.The sequence stratigraphic patterns substantially differ between factories. The T‐factory being light‐dependent is characterized by higher sediment production when the platform tops are flooded (highstand shedding). It displays decoupled sediment wedges with the partial infill of accommodation in the shallow‐water realm and major sediment export towards the slopes and surrounding basins. The CWC‐factory is marked by in situ production and deposition with limited sediment export forming single CWC spots or sediment accumulation ridges. The C‐factory has a siliciclastic equivalent style of sediment distribution with lowstand‐dominated, shelf edge wedges and a shaved‐off shelf during sea‐level highstands. Slope shedding marks the M‐factory in which sediment production occurs within the upper slope realm of the flat‐topped platforms both during highstands and lowstands in sea‐level. This allows for fairly continuous sediment production exhibiting minor impact of sea‐level changes, but with progradation, aggradation and retrogradation of the system being only limited by local environmental changes. P‐factory sediment production may vary in accordance with variations in sea‐level, providing time‐lines and systems tracts boundaries in the pelagic realm.In summary, each factory is branded by an individual set of features, for example, production window, sediment production and export, morphologies and slopes. It is this unique set of variables marking each factory that determines the factory‐dependent response to small‐scale and large‐scale environmental changes through space and time as shown in the sequence stratigraphic development.

Insights into the tectonostratigraphic setting of the Southern Appalachians during the Blountian tectophase from an integrated geochemical analysis of magmatic phenocrysts in the Ordovician Deicke K-bentonite

We evaluate competing hypotheses regarding tectonic models of the early Taconic Orogeny in the Southern Appalachians during the Blountian tectophase with new geochemical data obtained from analyses of apatite and zircon phenocrysts, and melt and mineral inclusions therein, from the Ordovician Deicke K-bentonite (453.35 ± 0.10 Ma). Apatite geochemistry confirms that samples from different locations represent the same eruptive event, and zircon geochemistry and UPb geochronology (including several Grenville-age inherited detrital cores) confirm an evolved magma of continental-arc composition, with the trace-metal geochemistry of magmatic Taconic-age rims on Deicke zircons pointing to a provenance of continental crustal igneous rock melts, specifically a granitic melt with a high level of differentiation, rather than a melt that was mantle-derived, or strongly mantle-influenced. Melt inclusions within Deicke phenocrysts are dacitic (apatite) to rhyolitic (zircon), differences that imply an evolving Deicke magma during its eruption.Our data 1) indicate multiple crustal events, and 2) are tectono-chemical evidence supporting an arc-trench subduction system where subducting preexisting sedimentary rocks were subsequently incorporated into the melt during or prior to collision. Indonesia provides modern analogs: the Banda Arc system, where Australian continental crust is jamming the subduction zone in association with the development of a foreland basin and a sedimentary wedge; the New Guinea – western Melanesian region, with its orogenic highlands and associated foredeep; and the Sumatra –Toba system, where subduction-related explosive volcanism has generated enormous caldera-forming eruptions above continental crust basement. Thus, a model for closure of the Iapetus Ocean involving subduction of older passive margin sediments as part of an island-arc collision with the Laurentian passive margin is acceptable, but models based on a back-arc basin are not compatible with our data.

Early and middle Miocene ice sheet dynamics in the Ross Sea: Results from integrated core-log-seismic interpretation

Abstract Oscillations in ice sheet extent during early and middle Miocene are intermittently preserved in the sedimentary record from the Antarctic continental shelf, with widespread erosion occurring during major ice sheet advances, and open marine deposition during times of ice sheet retreat. Data from seismic reflection surveys and drill sites from Deep Sea Drilling Project Leg 28 and International Ocean Discovery Program Expedition 374, located across the present-day middle continental shelf of the central Ross Sea (Antarctica), indicate the presence of expanded early to middle Miocene sedimentary sections. These include the Miocene climate optimum (MCO ca. 17–14.6 Ma) and the middle Miocene climate transition (MMCT ca. 14.6–13.9 Ma). Here, we correlate drill core records, wireline logs and reflection seismic data to elucidate the depositional architecture of the continental shelf and reconstruct the evolution and variability of dynamic ice sheets in the Ross Sea during the Miocene. Drill-site data are used to constrain seismic isopach maps that document the evolution of different ice sheets and ice caps which influenced sedimentary processes in the Ross Sea through the early to middle Miocene. In the early Miocene, periods of localized advance of the ice margin are revealed by the formation of thick sediment wedges prograding into the basins. At this time, morainal bank complexes are distinguished along the basin margins suggesting sediment supply derived from marine-terminating glaciers. During the MCO, biosiliceous-bearing sediments are regionally mapped within the depocenters of the major sedimentary basin across the Ross Sea, indicative of widespread open marine deposition with reduced glacimarine influence. At the MMCT, a distinct erosive surface is interpreted as representing large-scale marine-based ice sheet advance over most of the Ross Sea paleo-continental shelf. The regional mapping of the seismic stratigraphic architecture and its correlation to drilling data indicate a regional transition through the Miocene from growth of ice caps and inland ice sheets with marine-terminating margins, to widespread marine-based ice sheets extending across the outer continental shelf in the Ross Sea.

Comparing the Hydrological Response of Forested Headwaters (Unregulated and Regulated with Check Dams) under Mediterranean Semi-Arid Conditions

This study has evaluated the runoff and erosion rates in torrents of Southern Italy, two forested headwaters with very similar climatic, hydrological and geomorphological characteristics; in one headwater, 15 check dams were installed in the mid-1950s, while the other is not regulated with engineering works. To this aim, the hydrological variables have been modeled over 15 years after check dam installation using the HEC-HMS (Hydrologic Engineering Center-Hydrologic Modeling System) model coupled to the MUSLE (Modified Universal Soil Loss Equation) equation. The model simulations have shown that check dams have not played a significant role in reducing the surface runoff compared to the unregulated torrent; in both catchments, the well-developed forest cover determined very low runoff coefficients (lower than 0.3%) with a scarce runoff generation capacity. Additionally, the reduction in peak flow due to the check dams was not significant, on average −7.4% compared to the unregulated headwater. Check dams have retained sediments for about 8–10 years after their installation, reducing erosion by about 35%, although soil loss was much lower than the tolerance limit in both catchments. After the sediment retention capacity of the dam sediment wedge was depleted, the sediment yield in the regulated torrent was even higher (by about 20%) compared to the unregulated catchment. Overall, the study has shown that the use of check dams as a catchment management strategy of forested headwaters under semi-arid Mediterranean conditions should be considered with caution, since the structures could be ineffective to reduce water and sediment flows during floods or, in some cases, check dams may increase erosion rates.

Regional chronostratigraphy in the eastern Lesser Antilles quaternary fore-arc and accretionary wedge sediments: Relative paleointensity, oxygen isotopes and reversals

Paleomagnetism is a powerful tool for establishing an almost continuous chronostratigraphy for an entire region. When combined with other dating methods, absolute or relative, it can be used to develop a regional reference chronostratigraphic framework. During the summer of 2016, several piston cores were collected along the Atlantic side of the Lesser Antilles onboard the R/V Pourquoi pas? as part of the CASEIS Expedition. Core CAS16-24PC was devoted to chronostratigraphic analysis and allowed development of a quasi-continuous Quaternary record. In this study, after identifying and removing rapidly deposited layers such as turbidites and tephra layers, we reconstructed the relative paleointensity (RPI) variations by normalizing the natural remanent magnetization with the laboratory induced anhysteretic remanent magnetization. An age model was developed by comparing our RPI record with the PISO-1500 stack and paleomagnetic axial dipole moment model for the past 2 Myr (PADM-2M) and the planktic oxygen isotopic record (δ18O) for core CAS16-24PC with the LR04 benthic stack. By combining the δ18O stratigraphy with paleomagnetic analyses, we established an age model covering the Brunhes/Matuyama boundary and Jaramillo Subchron back to ~1.15 Ma with a mean sedimentation rate of 1.7 cm/kyr. This age model complements the paleomagnetic data from IODP campaigns and volcanic records, and offers almost complete inclination, declination and RPI records as a local reference.