Progradational Sequence Research Articles

Storm response of a mixed sand gravel beach ridge plain under falling relative sea levels: A stratigraphic investigation using ground penetrating radar

AbstractBeach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore‐normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back‐barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post‐seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a palaeo‐storm initially created a washover fan into the back‐barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern‐day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern‐day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period. © 2019 John Wiley & Sons, Ltd.

Geochemistry of aggradational - Progradational sequence sets of the Upper Jurassic – Lower Cretaceous Vaca Muerta shales (Añelo area, Neuquén Basin, Argentina): Relation to changes in accommodation and marine anoxia

Unconventional shale plays have received marked attention over the last years because of their economic potential for hydrocarbon generation. The size and geology of the Neuquén Basin of western Argentina lends to large volumes of unconventional shale gas, particularly within the marine shales of the Upper Tithonian -- Valanginian Vaca Muerta Formation. This unit is characterized by a well-developed lithological transition from Tithonian monotonous organic-rich marly shales of several hundred metres thickness, to Lower Cretaceous increasingly carbonate-rich marls and marly limestones. Samples from four wells located in the central sector of the Neuquén Basin (Añelo area) were selected for petrographic, X-ray fluorescence and TOC analysis. Based on seismic interpretation of the strata geometry, these data were grouped according to their location in aggradational (AAS) and progradational accommodation sets (PAS). The AAS is composed of basinal black shale facies showing a planar stacking pattern, whereas the PAS is characterized by low-angle sigmoidal strata in which bottomset, foreset and topset deposits (and coeval basinal deposits) are recognized. Petrographic studies allowed to distinguish lithological variations between basinal (organic-rich, laminated unbioturbated shales and marly shales), bottomset (dark gray, diffuse laminated, slightly bioturbated shaly marls and marls), and foreset and topset deposits (gray, massive, bioturbated marls and calcareous marls with a wacky texture). Basinal deposits show a clear tendency towards compositions rich in silica. These distal deposits, together with the distalmost bottomset facies of the clinoforms, are relatively enriched in Al2O3. In turn, the content of CaO, MgO and P2O5 supplied by carbonate biogenic activity are higher in the shallower topset and foreset deposits. Distal (basinal and bottomset) deposits are significantly enriched in redox-sensitive elements (Mo, V, Co, S, Cr) and in organic productivity indicators (Zn, Ba, Cu and TOC).Basinal deposits accumulated under conditions of maximum sediment starvation, restricted circulation and low dissolved oxygen levels. These conditions partially persisted for the more distal progradational (bottomset) deposits, together with a progressive increase in carbonate intrabasinal productivity. Conversely, the foreset and topset deposits of the PAS formed under normal seawater oxygenation. These conditions favoured the increase of carbonate productivity associated with an ostensible decline of organic matter productivity and preservation. This approach to geochemical analysis in the sequence stratigraphic framework of the Vaca Muerta Formation suggests that redox conditions, biogenic carbonate productivity, detrital siliciclastic fluxes and carbon accumulation rates, were closely related to basin isolation, space available for sediment accumulation, and changes in water depth and marine water circulation.

Seaward growth of Antarctic continental shelves since establishment of a continent-wide ice sheet: Patterns and mechanisms

The location and setting of the continental shelf break along the Antarctic continental shelves influences the paleoceanographic circulation patterns as well as sedimentation and ice sheet dynamics. By evaluating the available multichannel seismic reflection data and drill core information, we mapped the base of progradational features associated with the first advances of grounded ice sheet to the outer shelf. The distance between the modern shelf edge and the pre-glacial shelf edge varies from >200 km (e.g. Ross Sea) to <6 km (e.g. Thurston Island, West Antarctica). We identified multiple processes and mechanisms which influence the amount of shelf progradation during the establishment of a grounded ice sheet on the outer Antarctic shelves. The tectonic structure of the shelves proves to be a key factor by establishing the width of the shelf as well as local tectonics such as horst/graben and fault systems, which guide the ice stream flow and therefore the resulting sedimentation. Unlike expected, the erosional potential of the hinterland seems to play a minor role in building progradational sequences, whereas fewer long-term grounding events on the shelf edge result in more continental shelf progradation than presumed from a more dynamic ice sheet. By using these observed relationships to extrapolate the former shelf edge to unmapped regions around the Antarctic continent, we estimate an overall seaward growth of the continental shelves by 7% in area and 1.28 ∗ 106 km3 of approximated sedimentary volume deposited along the shelf edge and upper slope.

The sedimentary and tectonic features of the Niger Delta

The Niger Delta, one of the largest delta in the world, is located on the eastern passive continental margin of the Atlantic Ocean. It was formed during the Niger River entering the Atlantic Ocean. The main part of the delta lies on the Atlantic oceanic crust, and the minor part on the African pre-Cambrian basement. The Central and West African Rift Systems indirectly control the formation of the Niger Delta through controlling the distribution and development of the Benue-Niger river system. It is a prograded delta with typical prograding sequence, i.e., regressive sequence. The prograding sequence is constituted with the marine shale (Akata Formation), paralic sand and shale (Agbada Formation) and continental alluvial sands (Benin Formation) from the bottom to the top. These three lithostratigraphic units are diachronous. All of them are younger seaward. There is a large scale gravity gliding tectonics. The main detachment fault lies in the Akata marine shale. The gravity tectonics can be divided into the front compressional deformation province and the trail extensional deformation province. The front compressional deformation formed a fold-thrust belt. The trail extensional deformation formed horst-graben structures. The detachment folds are well developed in the transitional zone between these two deformation provinces. Accompanied with the gravity-gliding tectonics, shale tectonics are widely developed in the Niger Delta. There is possibly some formation-relation between the gravity-gliding tectonics and the Cenozoic volcanic activities of the Cameroon volcanic line.

The Ichnological and Sedimentological Signature of a Late Paleozoic, Postglacial Marginal-Marine and Shallow-Marine, Tidally Influenced Setting: The Wudayhi Member of the Nuayyim Formation (Unayzah Group) in the Subsurface of Central and Eastern Saudi Arabia

Abstract Sedimentation in the Nuayyim Formation across subsurface central and eastern Saudi Arabia has been chiefly ascribed to continental sedimentary environments. However, a number of levels in this formation show evidence for marginal-marine and shallow-marine sedimentation. This paper documents trace-fossil faunas and sedimentological characteristics from these facies and presents a regional depositional model for the Wudayhi Member that confirms the presence of shallow-marine sedimentary environments. Marginal-marine and shallow-marine sedimentation in the Wudayhi Member includes estuarine deposits and upper-shoreface through lower-shoreface deposits. They are reflective of several transgressive–regressive (T-R) cycles in an overall shoaling-upwards, tidally influenced progradational succession that exhibit mixed-process (wave-, tide-, and fluvially-influenced) depositional environments. The succession displays an overall upward decrease in bioturbation intensity with elements of an impoverished proximal expression of the Cruziana Ichnofacies at the base in proximal- and distal- lower-shoreface deposits (Facies 5–6), passing into an impoverished expression of the Skolithos Ichnofacies in upper-shoreface deposits (Facies 4). Therein, Facies 5 records storm-influenced sedimentation and includes hummocky cross-stratification (HCS), combined-flow ripples, cross-lamination, and ichnofossils that alternate between storm-related and fair-weather assemblages. An overall reduction in both the diversity of ichnogenera and the intensity of burrowing across the shoreface profile, an apparent lack of middle-shoreface deposits, and the occurrence of storm-wave-generated structures interspersed with tidally generated structures in the center and southeast of the study area are interpreted as tidal modulation, suggesting macrotidal conditions at the time of sediment deposition. Estuarine sedimentation includes coal deposits (Facies 1), tidal flats (Facies 2), and fluvio-tidal deposits (Facies 3) that overlie the succession, and display a stressed, impoverished mixture of traces with facies-crossing elements of the Skolithos and Cruziana Ichnofacies in the north and northwest of the study area. Sedimentation took place on a broad and sandy, partially restricted shelf, chiefly influenced by tidal currents that was variably fluvially influenced. The interplay of the aforementioned processes results in a complex architecture that is traceable, based on the sedimentological and ichnological content. Colonization by bioturbating infauna exhibiting elements of an overall impoverished Skolithos and Cruziana Ichnofacies in the Wudayhi Member is interpreted to be related to sea-level rise, with regional transgression induced by the melting of glacier ice following the Late Carboniferous to Early Permian glaciation that affected southern Gondwana. Subsequently, as the Arabian Plate migrated northwards, isostatic rebound concomitant with increased tectonism associated with the Neotethys propagating into the Arabian Peninsula caused regional regression responsible for the progradational sequence presented herein in the Early to Middle Permian. Trace-fossil associations and ichnofacies presented in this paper are significant, because they provide evidence for marginal-marine and shallow-marine tide- and storm-influenced processes in the Unayzah Group during deposition of the Wudayhi Member of the Nuayyim Formation. Furthermore, it establishes a framework than can be linked to fully marine coeval deposits southeastern of the Arabian Peninsula into Oman.

Early Holocene sea level in the Canadian Beaufort Sea constrained by radiocarbon dates from a deep borehole in the Mackenzie Trough, Arctic Canada

Deglacial and Holocene relative sea level (RSL) in the Canadian Beaufort Sea was influenced by the timing and extent of glacial ice in the Mackenzie River corridor and adjacent coastal plains. Considerable evidence indicates extensive ice cover in this region of northwestern Canada during the Late Wisconsinan. However, no absolute ages exist to constrain maximum RSL lowering before the late Holocene (4.2–0 ka). In 1984, the Geological Survey of Canada drilled an 81.5‐m‐deep borehole in the western Mackenzie Trough at 45 m water depth (MTW01). The lower 52.5 m of the borehole was interpreted as a deltaic progradational sequence deposited during a period of rising sea level. The upper 29 m was described as foraminifer‐bearing marine sediments deposited after transgression of the site, when RSL rose above ~−74 m. Here, we present radiocarbon measurements from MTW01, acquired from benthic foraminifera, mollusc fragments and particulate organic carbon in the &gt;63 μm fraction (POC&gt;63 μm) in an attempt to constrain the chronology of sediments within this borehole and date the timing of transgression. The deepest carbonate macrofossil was acquired from 8 m above the transgressive surface (equivalent to 21 m b.s.l.), where mollusc fragments returned a date of 9400 +180–260 cal. a BP (2σ). This provides the oldest constraint on Holocene sea‐level lowering in the region, and implies that transgression at this site occurred prior to the early Holocene. Ages obtained from the lower 52.5 m of the borehole are limited to POC&gt;63 μm samples. These indicate that progradational sediments were deposited rapidly after 24 820 +390–380 cal. a BP (2σ). Due to the incorporation of older reworked organic matter, the actual age of progradation is likely to be younger, occurring after Late Wisconsinan glacial ice retreated from the coast.

Sedimentary facies analysis of the Mesozoic clastic rocks in Southern Peru (Tacna, 18°S): Towards a paleoenvironmental Redefinition and stratigraphic Reorganization

The Mesozoic rocks of southern Peru comprise a Middle Jurassic to Early Cretaceous sedimentary sequence deposited during a time interval of approximately 34 Myr. In Tacna, these rocks are detrital and constitute the Yura Group (Callovian to Tithonian) and the Hualhuani Formation (Berriasian). Basing on robust interpretation of facies and petrographic analysis, we reconstruct the depositional settings of such units and provide a refined stratigraphic framework. Accordingly, nine types of sedimentary facies and six architectural elements are defined. They preserve the record of a progradational fluvial system, in which two styless regulated the dispersion of sediments: (i) a high-to moderate-sinuosity meandering setting (Yura Group), and a later (ii) incipient braided setting (Hualhuani Formation).The Yura Group (Callovian-Tithonian) represents the onset of floodplain deposits and lateral accretion of point-bar deposits sited on a semi-flat topography. Nonetheless, the progradational sequence was affected by at least two rapid marine ingressions occurred during Middle Callovian and Tithonian times. Such marine ingressions reveal the proximity of a shallow marine setting and incipient carbonate deposition. In response to increase in topographic gradient, the Hualhuani Formation (Berriasian) deposited as extensive multistory sandy channels. The mineralogy of the Mesozoic sediments suggests sediment supplies and intense recycling from a craton interior (i.e. Amazon Craton and/or plutonic sources) located eastward of the study area.

The sedimentological changes caused by human impact at the artificial channel of Medjerda-River (Coastal zone of Medjerda, Tunisia)

Abstract. Recent sedimentary and morphological changes at the new mouth of Medjerda-River (Gulf of Tunis) are investigated using a multiproxy approach of sediment cores complited by 210Pbex and 137Cs method dating. The subject of the study is to focus on surveying the sedimentary evolution of Medjerda-Raoued Delta caused by the human intervention in the management of the main tributaries of the Medjerda-River (artificial channel of Henchir Tobias). Sediment cores (CEM-1 and CEM-3) were subjected to both multiproxy approaches (Grain size, geochemical analysis and dating radiometric 210Pbex and 137Cs). The sedimentological analysis of the new deltaic deposits shows a progradation sequence with the silt and clay deposits on the historic sandy substratum. The mean grain size evolution on the old beach profile shows a decreasing trend from backshore (CEM-3) to nearshore (CEM-1). The geochemical results show varying concentrations of chemical elements such as Fe, K, Rb, Nb, Cr, Ti, Ba, Ca, Sr, Zr, V, and potentially toxic metal trace elements such as Pb, Zn and the As. The Principal component Analysis (PCA) applied in the geochemical elements evolution confirms the marine origin of the sand deposits in the basic layers of the two cores. The chronological method (210Pbex and 137Cs) affirms that the first fluvial deposits were set up only after 1950. The sedimentological and geochemical result confirm the actual unless of coarser fluvial supplies under the human activities leading the negative coastal sediment balance and the shoreline retreat as well.

Silurian deltaic progradation, Tassili n’Ajjer plateau, south-eastern Algeria: Sedimentology, ichnology and sequence stratigraphy

The economic potential for unconventional shale oil and gas production in the Silurian of the Berkine – Ghadames and Illizi basins (BGI) in south-eastern Algeria has been recently confirmed through exploration drilling. The aim of the present paper attempts a better understanding of the Intra-Tassilian depression within the entire Silurian of the Tassili n’Ajjer plateau. The continuous deposits of the Silurian are exposed at the southern margin of the prolific BGI basins, in the Tassili n’Ajjer plateau, offering the chance to understand the sedimentology, ichnology, and to present a detailed sequence stratigraphy framework for the region.The 410 m-thick clastic Silurian sedimentary strata are subdivided into three formations in the context of sequence stratigraphy, namely: (i) the Oued Imihrou Fm. (Llandoverian) overlain by (ii) the Atafaïtafa Fm. (late Llandoverian to Wenlockian), and (iii) the Oued Tifernine Fm. (late Wenlockian to Pridolian). These can be also distinguished across the entire investigated area and laterally traceable over kilometers. Clear cyclic stacking patterns are identified within the four studied sections showing progressively a general trend of thickening- and coarsening-upward, over a complete 2nd-order megasequence (SIL-1 MS). This transgressive-regressive succession suggests deltaic progradation, shallowing and basin infilling as evidenced by numerous diagnostic sedimentary features and trace fossils, largely from eastern-to western-Tassili plateau. Indeed, the wealth of outcrop data in the Silurian siliciclastic succession enables us to distinct thirteen facies (facies A-M), ranging from shallow-to marginal-marine facies, and in turn, grouped into six facies associations (FA1-FA6). The lowermost part of the succession, which is the most prolific sources of hydrocarbons in North Africa, consists of thick organic-rich graptolite-yielding black ‘hot’ shales and ‘lean’ shales with sparse bioturbation with small Thalassinoides belonging to the distal Cruziana ichnofacies. In contrast, the uppermost part of the Silurian deposits becomes progressively coarser and fluvial in response to the progradation of the North African Akakus deltaic system, during regional sea level fall and uplifting of the region. These progradational deposits exhibit well-preserved trace fossils with moderate to high degree of bioturbation, such as Skolithos or the so-called “Tigillites” pipe-rock, Cruziana isp., Rusophycus isp., Monocraterion isp., and Syringomorpha.The SIL-1 MS is bounded by a post-glacial latest Hirnantian unconformity on the basal (SB1), as confirmed by the moderately diverse early Silurian graptolite faunas, and by the Caledonian unconformity on the top (SB7). Each of the three formations of SIL-1 MS reveals two major 3rd-order progradational sequences, commonly delineated by discontinuity surfaces (in ascending order, SB1 to SB7), and in turn, these six sequences (i.e. Si-1 to Si-6) are subdivided into at least ten shorter-term cycles. The regional extent of each unconformity is directly linked to significant facies changes and to inflection points on the global sea level curve.

Kinetic control of staurolite–Al2SiO5 mineral assemblages: Implications for Barrovian and Buchan metamorphism

AbstractThe distribution and textural features of staurolite–Al2SiO5 mineral assemblages do not agree with predictions of current equilibrium phase diagrams. In contrast to abundant examples of Barrovian staurolite–kyanite–sillimanite sequences and Buchan‐type staurolite–andalusite–sillimanite sequences, there are few examples of staurolite–sillimanite sequences with neither kyanite nor andalusite anywhere in the sequence, despite the wide (~2.5 kbar) pressure interval in which they are predicted. Textural features of staurolite–kyanite or staurolite–andalusite mineral assemblages commonly imply no reaction relationship between the two minerals, at odds with the predicted first development (in a prograde sense) of kyanite or andalusite at the expense of staurolite in current phase diagrams. In a number of prograde sequences, the incoming of staurolite and either kyanite, in Barrovian sequences, or andalusite, in Buchan‐type sequences, is coincident or nearly so, rather than kyanite or andalusite developing upgrade of a significant staurolite zone as predicted. The width of zones of coexisting staurolite and either kyanite, in Barrovian sequences, or andalusite, in Buchan‐type sequences, is much wider than predicted in equilibrium phase diagrams, and staurolite commonly persists upgrade until its demise in the sillimanite zone. We argue that disequilibrium processes provide the best explanation for these mismatches. We suggest that kyanite (or andalusite) may develop independently and approximately contemporaneously with staurolite by metastable chlorite‐consuming reactions that occur at lower P–T conditions than the thermodynamically predicted staurolite‐to‐kyanite/andalusite reaction, a process that involves only modest overstepping (&lt;15°C) of the stable chlorite‐to‐staurolite reaction and which is favoured, in the case of kyanite, by advantageous nucleation kinetics. If so, the pressure difference between Barrovian kyanite‐bearing sequences and Buchan andalusite‐bearing sequences could be ~1 kbar or less, in better agreement with the natural record. The unusual width of coexistence of staurolite and Al2SiO5 minerals, in particular kyanite and andalusite, can be accounted for by a combination of lack of thermodynamic driving force for conversion of staurolite to kyanite or andalusite, sluggish dissolution of staurolite, and possibly the absence of a fluid phase to catalyse reaction. This study represents an example of how kinetic controls on metamorphic mineral assemblage development have to be considered in regional as well as contact metamorphism.

High-resolution seismic reflection data acquisition and interpretation, Lake Neusiedl, Austria, northwest Pannonian Basin

A combined 400+ km of single- and multichannel seismic reflection data were acquired on Lake Neusiedl in northeast Austria in May 2013. This geophysical campaign was a multinational academic effort among the Universities of Vienna, Budapest, Bremen, and Southampton. Lake Neusiedl is an exceptionally shallow lake, with an average water depth of only approximately 1.4 m. Although high-resolution single-channel seismic reflection data have been collected before on this lake, the multichannel seismic acquisition, towing a 60 m cable and an air gun behind a retrofitted ferry boat, was a completely new approach in this area. The quality of the multichannel data turned out to be exceptionally good; i.e., the high-frequency data illuminated the subsurface of the lake for the first time, down to the pre-Cenozoic basement at approximately 600 m depth. The most prominent findings of the new data include (1) a consistent southeasterly dip of erosionally truncated Late Miocene (Pannonian) sediments beneath a very thin Holocene mud layer, (2) the presence of major throughgoing fault systems (including a positive flower structure), (3) at least one Pannonian progradational sequence defined by seismic clinoforms indicating a paleowater depth of approximately 40–80 m, (4) flat spots in several locations of the study area corresponding to possibly biogenic gas in a few hundred meters depth beneath the lake, (5) vertical data wipeouts, which are interpreted as gas chimneys reaching the lake bottom, and (6) definition of the pre-Cenozoic basement. Interestingly, the gas chimneys are interpreted to correspond to the well-known gas seeps (“Kochbrunnen”) in Lake Neusiedl, which were originally described as subaqueous water springs on the lake floor responsible for ice-free areas in the lake ice cover during winter.

Clinoform development and topset evolution in a mud‐rich delta – the Middle Triassic Kobbe Formation, Norwegian Barents Sea

AbstractClinoform surfaces are routinely used to mark transitions from shallow waters to deep basins. This concept represents a valuable tool for screening potential reservoir intervals in frontier basins where limited data are available. Variations in the character of clinoform geometries and shoreline and shelf‐edge trajectories are indicators of a range of different factors, such as palaeobathymetry, changes in relative sea‐level and sediment supply. Applications of conceptual and generalized models might, however, lead to erroneous assumptions about the supply of coarse‐grained material to the delta front and basin when superficial similarities between clinoform geometries are not treated holistically. The present study examines the mudstone‐dominated Middle Triassic Kobbe Formation – a potential hydrocarbon reservoir interval in the Barents Sea, where prodeltaic to deltaic deposits can be examined in cores, well logs and two‐dimensional and three‐dimensional seismic data. Despite pronounced acoustic impedance contrast to the surrounding shale, channel belt networks are not observed close to the platform edge in seismic datasets, even at maximum regressive stages. However, sub‐seismic prodeltaic deposits observed on the shallow platform indicate that prodeltaic deposits were sourced directly from the delta plain. Clinoform surfaces with different geometries and scale are observed basinward of the palaeoplatform edge of underlying progradational sequences, correlative to mudstone‐dominated prodeltaic core sections. Results indicate that platform‐edge deltas developed at discrete sites in the basin due to normal regression, but the positions of these deltas are not directly relatable to variations in clinoform geometries. Transitions from third‐order to fourth‐order clinoform geometries record discrete transgressive–regressive cycles but are not necessarily good indicators of sandstone deposition. Because of prolonged periods with high accommodation, channel avulsions were frequent and only very fine‐grained sandstone was deposited in heterolithic units at the delta front. Sandstones with good reservoir properties are predominantly found along basin margins.

Facies Analysis and Sequence Stratigraphy of Missole Outcrops: N’Kapa Formation of the South-Eastern Edge of Douala Sub-Basin (Cameroon)

Missole facies description and sequence stratigraphy analysis allow a new proposal of depositional environments of the Douala sub-basin eastern part. The sediments of Missole outcrops (N’kapa Formation) correspond to fluvial/tidal channel to shallow shelf deposits with in some place embayment deposits within a warm and semi-arid climate. Integrated sedimentologic, palynologic and mineralogical data document a comprehensive sequence stratigraphy of this part of the Douala sub-basin. Five facies associations occur: (1) facies association I is characterized by Floodplain deposits; (2) facies association II is Fluvial to mouth bar deposits; (3) facies association III characterise Shallow Shelf deposits; (4) facies association IV represents Distal bay or Lacustrine déposits; and (5) Facies association V is made of Fluvial channel deposits. Six depositional sequences were identified. These sequences are composed of four progradational sequences and two retrogradational sequences containing a fluvial channel portion represented by lag deposits at the base of retrogradational sequences. These deposits represent the outset of the relative sea level rise period. In the study area, the N’kapa Formation is composed of non-marine/coastal aggradational deposits representing the early stage of the regressive period. The occurrence of the estuarine/bay deposits with paleosols development is interpreted as evidence of climate change with significant relative base level fluctuation. The study of key minerals associated to sequence stratigraphy as well as palynology demonstrated that sequence architecture has been controlled mostly by climate evolution and outcrops are dated Paleocene – early Eocene.

Paleoenvironmental evolution of the southern Neuquèn basin (Argentina) during the Tithonian-Berriasian (Vaca Muerta and Picún Leufú Formations): a multi-proxy approach

The Tithonian-Berriasian interval in the southern part of the Neuquén Basin is represented by the Vaca Muerta and the Picún Leufú Formations. Facies analysis and correlation of the Vaca Muerta Formation and the lower part of the Picún Leufú Formation in the Picún Leufú Anticline allow us to characterize the evolution of successive facies belts representing siliciclastic shelf and mixed ramp environments. Shoreface and offshore facies are developed on the siliciclastic shelf in the western and southern parts of the Picún Leufú Anticline. The offshore transition domain is characterized by storm beds and slump features, whereas the offshore domain corresponds to black to grey shales and turbidites. The mixed siliciclastic-carbonate ramp is characterized by the development of a lagoon and high-energy shoal in the proximal part of the inner ramp, whereas the distal part comprises a tidal complex. The mid-ramp zone is characterized by storm influence and the outer ramp by fine-grained deposits. Two major transgressive-regressive sequences and five high-frequency transgressive-regressive sequences are recognized. The high-frequency transgressive-regressive sequences make up three progradational sequences, an aggradational-progradational sequence and an aggradational sequence. The geochemical characteristics and clay mineralogy of the Tithonian-Berriasian interval in the southern Neuquén Basin indicate that (1) climate played a key role in the evolution of the sedimentary environment, (2) a “normal marine” depositional environment with oxic sea water and sediment pore waters, rapidly changing to suboxic conditions at shallow depth below the seabed and (3) the occurrence of episodically restricted water-mass circulation at the onset of deposition of the Vaca Muerta Formation.

Sedimentary and structural evolution of a Pleistocene small-scale push moraine in eastern Poland: New insight into paleoenvironmental conditions at the margin of an advancing ice lobe

Abstract Recent studies of push moraines have focused on the interplay between the dynamics of ice margins and the environmental variables of the foreland into which they advance. These studies showed that the spatial distribution, geometry and style of the glaciotectonic deformation of push moraines are controlled by ice-induced stresses, the strain rate, the rheology of the deposits and hydraulic conductivity. In this work, we provide new insight into this interplay at a small spatio-temporal scale, specifically, the ancient glacial system of the Liwiec ice lobe within the younger Saalian ice sheet in eastern Poland. The paleoenvironmental variables that are analysed here refer to the dynamics of the hydrological processes that affected the patterns and sediment deposition rate on the terminoglacial fan and the resulting mechanical stratigraphy and hydraulic conductivity of the foreland. We document the progradational sequence of the fan deposits that developed as a result of the ice lobe thickening and the steepening of its stationary front. The sedimentary features of the fan, the lithology of its basement and the hydraulic conductivity of the foreland strongly influenced the geometry and kinematics of fold growth during the advance of the ice lobe. The predominance of flexural slip and the development of fractures, including fold-accommodation faults, were interpreted to be an effect of buckle folding due to horizontal shortening induced by ice advance. The partial overriding of the push moraine by the ice lobe and, thus, the submarginal conditions for deformation were inferred from the significant hinge migration and internal deformation of the strata under undrained conditions in one of the folds. The synfolding deposition pattern of the fan growth strata allowed us to suggest that the push moraine was probably formed by a sustained advance rather than surge.

Facies architecture of the K10 supersequence in the Browse Basin: when sequence stratigraphy meets lithostratigraphy

Regional seismic sequence stratigraphic mapping of the K10 supersequence (Berriasian–Valanginian) has brought into focus the relationship between sequence stratigraphic and lithostratigraphic units. In this extended abstract, the relationship between seismically-defined sandstone bodies and the Brewster Member, an important exploration target and reservoir in the Browse Basin, is investigated. Deposition of the K10 supersequence started at the onset of rifting between Greater India and the Northern Carnarvon Basin. Sediment sourced from uplifted areas resulted in deposition of the Barrow Delta in the Exmouth and Barrow sub-basins. In the Browse Basin, K10 is also a sand-rich progradational sequence, albeit diminutive compared to the Barrow Delta. Seismic mapping of K10 in the Caswell Sub-basin has resolved stratal geometries and, with the integration of well data, recognition gross depositional facies. Sandstone-prone siliciclastic platform facies (clinoform topsets) include the Brewster Member. The first reference to the Brewster Member in the Australian Stratigraphic Units Database applied the name to the upper part of the K10 sequence between 3,284 m and 3,405 m in Heywood–1. Usage of this name, however, has been inconsistently applied to sandstone-prone units within K10. Given the significance of the Brewster Member as an exploration target, and as a reservoir in the Ichthys-Prelude and Burnside gas fields, attention to integration of sequence stratigraphic and lithostratigraphic frameworks for this interval is timely.

Taphonomy of the middle Cambrian (Drumian) Ravens Throat River Lagerstätte, Rockslide Formation, Mackenzie Mountains, Northwest Territories, Canada

The Middle Cambrian (series 3, Drumian, Bolaspidella Biozone) Ravens Throat River Lagerstatte in the Rockslide Formation of the Mackenzie Mountains, northwestern Canada, contains a Burgess Shale-type biota of similar age to the Wheeler and Marjum formations of Utah. The Rockslide Formation is a unit of deep-water, mixed carbonate and siliciclastic facies deposited in a slope setting on the present-day northwestern margin of Laurentia. At the fossil-bearing locality, the unit is about 175 m thick and the lower part onlaps a fault scarp cutting lower Cambrian sandstones. It consists of a succession of shale, laminated to thin-bedded lime mudstone, debris-flow breccias, minor calcareous sandstone, greenish-coloured calcareous mudstone and dolomitic siltstone, overlain by shallow-water dolostones of the Broken Skull Formation, which indicates an overall progradational sequence. Two ~1-m-thick units of greenish calcareous mudstone in the upper part exhibit soft-bodied preservation, yielding a biota dominated by bivalved arthropods and macrophytic algae, along with hyoliths and trilobites. It represents a low-diversity in situ community. Most of the fossils occur in the lower unit, and only the more robust components are preserved. Branching burrows are present under the carapaces of some arthropods, and common millimetre-sized disruptions of laminae are interpreted as bioturbation. The fossiliferous planar-laminated calcareous mudstone consists of chlorite, illite, quartz silt, calcite and dolomite and is an anomalous facies in the succession. It was deposited via hemipelagic fallout of a mixture of platform-derived and terrestrial mud. Geochemical analysis and trace-element proxies indicate oxic bottom waters that only occasionally might have become dysoxic. Productivity in the water column was dominated by cyanobacteria. Fragments of microbial mats are common as carbonaceous seams. Complete decay of soft tissues was interrupted due to the specific sediment composition, providing support for the role of clay minerals, possibly chlorite, in the taphonomic process.

Soft-bodied biota from the middle Cambrian (Drumian) Rockslide Formation, Mackenzie Mountains, northwestern Canada

AbstractA new Burgess Shale-type Lagerstätte is described from the middle Cambrian (Series 3, Drumian) Rockslide Formation of the Mackenzie Mountains, Northwest Territories, Canada. The Rockslide Formation is a unit of deeper water ramp to slope, mixed carbonate, and siliciclastic facies deposited on the northwestern margin of Laurentia. At the fossil-bearing locality, the unit onlaps a fault scarp cutting lower Cambrian sandstones. There it consists of a succession of shale and thick-laminated to thin-bedded lime mudstone, calcareous sandstone, and greenish-colored calcareous mudstone, overlain by shallower water dolostones of the Avalanche Formation, which is indicative of an overall progradational sequence. The Rockslide Formation is of similar age to the Wheeler and Marjum formations of Utah, belonging to theBolaspidellaBiozone. Only two 1 m thick units of greenish mudstone exhibit soft-bodied preservation, with most specimens coming from the lower interval. However, the biota is common but not as diverse as that of other Lagerstätten such as the Burgess Shale in its type area. The shelly fauna is dominated by the hyolithHaplophrentis carinatusMatthew, 1899 along with sparse linguliformean brachiopods, agnostoid arthropods, and ptychoparioid trilobites. The nonmineralized biota includes the macrophytic algaMargaretia dorusWalcott, 1911, priapulid worms, and the carapaces of a number of arthropods. The arthropods belong toIsoxys mackenziensisn. sp.,Tuzoiacf.T. guntheriRobison and Richards, 1981;Branchiocaris? sp.,Perspicaris?dilatusRobison and Richards, 1981; and bradoriids, along with fragments of arthropods of indeterminate affinities. The style of preservation indicates that most soft parts underwent complete biodegradation, leaving just the more resistant materials such as chitinous arthropod cuticles. The range of preservation and similarity to the coeval biotas preserved in Utah suggests that the composition of this Lagerstätte is probably representative of the community living on the relatively deep-water ramp or slope during middle Cambrian time in Laurentia. This would argue that the extraordinary diversity of the Burgess Shale at Mount Field is anomalous.

The evolution of the slope breaks in Qiongdongnan Basin and their controlling factors

Qiongdongnan Basin (QB) experienced three main tectonic stages in the Cenozoic: rifting, thermal subsidence, and accelerated subsidence. Corresponding to these stages, the slope breaks also underwent three different evolutionary stages, which differed in space and time between the east and west of QB. Structural slope breaks developed during the rifting stage in the Paleocene. Transitional sedimentary strata without obvious slope break developed in the neritic environment during the thermal subsidence stage in the Neocene. Sedimentary slope breaks and gentle slope zone without slope break developed during the accelerated subsidence stage. The sedimentary slope breaks could be further classified into progradational and aggradational types, the starting points of which varied in space and time. Spatially, the progradational sequences in the Ledong and Lingshui sags started at the north of today’s deep central basin, distant from the basin edge. In the Songnan and Baodao sags, the aggradational sequences were close to the sag edge and essentially controlled by the underlying major boundary faults. Temporally, sedimentary slope breaks developed early in the east and late in the west and were initially partitioned and eventually unified. Fault activity controlled the types and ending time of structural slope breaks during the rifting stage, while tectonic subsidence controlled the time and places of progradational slope breaks during the accelerated subsidence stage. Sediment supply controlled the superposition patterns of the sedimentary sequences of the sedimentary slope breaks. It is suggested that the evolutionary history of the slope breaks has been primarily affected by the southward transition of the South China Sea ocean ridge, the westward collision of the Philippine Sea Plate, and the dextral strike-slipping of the Red River Fault.

Integrated high-resolution chemostratigraphy and facies-based stratigraphic architecture of the Lower Cretaceous (Aptian), Shu’aiba Formation, Saudi Arabia

High-resolution carbon isotope signatures were integrated with core descriptions and gamma-ray logs and used as a correlation tool for better age control to refine the sequence-stratigraphic framework of the Shu’aiba Formation in Saudi Arabia. The carbon isotope variations of the shallow carbonate Shu’aiba Formation correlate well with the Tethyan pelagic record and indicate an original marine signature for the Lower Cretaceous (Aptian) Shu’aiba Formation. Carbon isotope values of the Shu’aiba Formation range from 1.5‰ to 6‰ with minimal or no diagenetic effects. Oxygen isotope values range from −2.7‰ to −6.7‰ but were reset during diagenesis and cannot be applied for chemostratigraphic analysis. The Shu’aiba strontium isotope records range from 0.707356 to 0.707454 and differ slightly from the standard Aptian record because of diagenesis. The Shu’aiba Formation platform is a large-scale composite sequence (∼7 m.y.) composed of seven lower Aptian high-frequency sequences and two additional upper Aptian prograding sequences. Carbon isotope data were calibrated with core descriptions and gamma-ray logs to construct two detailed high-resolution stratigraphic cross sections. Carbon isotope data help refine the internal stratigraphic architecture of the Shu’aiba Formation especially on the slope and open-marine settings across the lower to upper Aptian boundary. The carbon isotope values of the Hawar “dense” unit in the base of the Shu’aiba Formation record major depletion corresponding to the global dissociation of methane hydrates, followed by major positive excursion associated with the deposition of Lithocodium and Bacinella facies coeval with the global oceanic anoxic event 1a. The rudist buildups on the platform have a value of approximately 4.5‰ at their base in most wells with a general uniform carbon isotope trend, followed by a gradual depletion to the top of the Shu’aiba Formation. Although some variations are observed in carbon isotope values associated with the lateral facies change from lagoon, margin, slope, open-marine, and basinal settings, carbon isotope trends are still similar and can be correlated fieldwide. Little evidence exists of meteoric diagenesis associated with the depletion of carbon isotope values. However, oxygen isotope records were possibly affected by meteoric diagenesis associated with subaerial exposure surfaces but did not get affected by the late Aptian hiatus, despite the massive karstification observed in cores. The good correlation between the original carbon isotope fluctuations and the third-order sequence framework of the Shu’aiba Formation fits well with the established carbon isotope curves that have been used as a proxy for global sea level changes during the Early Cretaceous. This study also shows that small-scale parasequences (fifth-order or higher) can be calibrated with carbon isotope curves, but they most likely represent relative sea level changes with local effects instead of global signatures. Application of high-resolution carbon isotope stratigraphy for the Shu’aiba Formation significantly constrain the stratigraphic framework and will lead to better geologic and simulation models for reservoir characterization and development.