Maximum Regressive Surface Research Articles

Constraining the duration of the southern Gondwana Irati-Whitehill Sea through cyclostratigraphy and its relation with deep-time astronomical solutions

The search for orbital cycles preserved in the sedimentary record is at the forefront of the refinement of the Geologic Time Scale. Semi-enclosed to restricted environments and epicontinental seas are suited for this type of analysis because they are very responsive to the climate conditions around the basin depocenter. This study presents the first astronomical time scale for the late Paleozoic Irati-Whitehill Sea (southern Gondwana – Paraná basin) using downhole logging of HV-44-RS. Applying orbital tuning and statistical null hypothesis techniques over the natural gamma-ray, we built two floating astronomical time scales for the same record and anchored them on a new UPb (bentonite) numerical age of 280.8 ± 1.4 Ma. Our results place the Irati Formation between 283.68 and 280.50 ± 2.98 (orbital tuning) and 284.27–280.47 ± 1.41 Ma (null hypothesis), giving the vast epicontinental Irati-Whitehill Sea its most precise minimum duration so far of 3.16 ± 1.02–3.80 ± 0.1 Myr during the late Cisuralian. Spectral analysis suggests a depositional pattern strongly modulated by long (405-kyr) and short (∼ 100-kyr) eccentricity cycles. As an exercise, we compare one of the produced astronomical age models and recently calculated eccentricity solutions that reach the late Paleozoic interval (ZB20d). Such comparison shows a remarkable correlation in variability and amplitude with this eccentricity solution. Astronomical forcing is also related to black shale accumulation with periods of high organic carbon lasting ∼405 kyr and occurring every two long eccentricity cycles after maximum regressive surface, demonstrating a predictive pattern behind these late Cisuralian regional anoxia. Our approach indicates that the Irati Formation and other correlative southern Gondwana basins are a hotspot for cyclostratigraphy still underexplored. Furthermore, we contribute to verifying astronomical solutions in deep geological time.

Sequence stratigraphy and the Ubarana-Upper Cretaceous exploratory play within the lower Albian – middle Eocene section of the Mundaú sub-basin, Ceará Basin

The Ceará Basin is located at the east portion of the Brazilian Equatorial Margin, and it is subdivided from west to east into four sub-basins: Piauí-Camocim, Acaraú, Icaraí and Mundaú, the latter being the focus of this study. The lower Albian to middle Eocene section of the Mundaú sub-basin is characterized by the Ubarana-Upper Cretaceous exploratory play, with turbidite reservoirs. That same chronostratigraphic interval shows important discoveries on the African Margin, such as the Jubilee field, and on the Equatorial Margin in offshore fields in Guyana and Suriname. For this study, it was used data from eight exploratory wells and ten 2D seismic lines, located on the shelf-edge portion, in shallow waters, to the deep-water region. In this study, six low resolution Transgressive-Regressive sequences were identified. These T-R sequences are bounded at the top and bottom by maximum regressive surfaces (MRS), that were recognized in the well data, and posteriorly in the seismic data, through seismic stratigraphy methods. In addition to the MRS, maximum flooding surfaces (MFS) are recognized in the exploratory wells, through low and high frequency T-R cycles. In addition, this work allowed the identification of turbidite plays in deep waters regions The genesis of those turbidites, defined as the low-density type, is associated with a base-level rise at the shoreline, when the normal regression phase occurs. Thus, this study contributes with stratigraphic description of the lower Albian-middle Eocene section, and identification of turbidite reservoirs within that interval, which are important to the exploration and discovery of hydrocarbons in context in the Brazilian Equatorial Margin.

Stratigraphic Modelling of the Lower/Middle Oxfordian (Upper Jurassic) Outer Ramp Deposits from the NE Paris Basin (France)

We investigate herein the lateral and vertical lithological heterogeneities of the Lower/Middle Oxfordian deposits (“Terrain à Chailles” and “Marnes des Eparges” formations) in the north-eastern Paris Basin. This new detailed stratigraphic framework documents the evolution at high resolution of an outer ramp based on regional correlations in order to constrain the evolution of petrological properties between the clayey “Argiles de la Woëvre” Formation and the more calcareous “Marnes et Calcaires à Coraux de Foug Formation. The “Argiles de la Woëvre” Formation is targeted for the deep storage of nuclear waste in north-eastern France. Nine wells are correlated over the “Zone of Interest for Further Research” (ZIRA), defined by the French agency for radioactive waste management (Andra), with a resolution of 0.5–1.0 m. The architecture and the age control of these formations have been refined, revealing that the “Terrain à Chailles” Formation is characterised by a regular slightly inclined sedimentation gently deeping in the SW direction and shows a lithological evolution from silty claystones to an increased occurrence of its calcareous content towards the top (Lower Oxfordian, uppermost mariae and cordatum ammonite zones). The above “Marnes des Eparges” Formation, characterised by claystone limestone alternations, is assigned to the Middle Oxfordian (plicatilis ammonite zone), deposited during a slightly enhanced subsidence phase in the SE part of the basin and documented and associated with onlaps geometries on the more proximal areas. However, this change in geometry does not affect petrological properties over ZIRA, as this is not accompanied by lithological changes. The environmental factors controlling petrological heterogeneities over ZIRA are also discussed. The stepwise increase in the carbonate content and the decrease in the detrital content towards the Lower to Middle Oxfordian deposits was likely triggered by a climate change towards drier conditions, modulated by sea level changes on a ramp morphology. A major condensation phase encompassing most of the Lower Oxfordian cordatum ammonite zone is also highlighted. The occurrence of a maximum regressive surface associated with gentle slope topography is a probable trigger for condensation. Changes in geometries are, however, associated with the activity of the Metz Fault, which potentially had an influence on the subsidence rates of the basin at that time.

First-Order Stratigraphic Boundaries of the Late Cretaceous–Paleogene Retroarc Foreland Basin in Colombia

The present-day Magdalena Valley, Eastern Cordillera, and Llanos Basin were part of a regional multiphase basin that started as an extensional basin in the Jurassic. Then, it was transformed into a retroarc foreland basin in the Late Cretaceous and subsequently separated into a hinterland and a foreland basin during the late Eocene. We incorporated new data from the Llanos Basin and Eastern Cordillera and chronostratigraphically correlated it with the adjacent basins. Their correlation contributed to establishing the stratigraphic boundaries formed during the first-order changes that marked the beginning and the end of the lifespan of the retroarc foreland basin. In the initial stage, the lateral extent along the dip of the significant depocenter that extended from the Magdalena Valley to the westernmost Llanos Basin was approximately 300–470 km. At the same time, the western flank of the Eastern Cordillera and most of the Llanos Basin were uplifting. The contact between the retrograding marine facies of the Upper Lidita, Buscavidas, Umir, Guadalupe, and Palmichal units marks a late Campanian maximum regressive surface formed during the initial exhumation of the orogen, the Central Cordillera. Therefore, it represents a first-order stratigraphic surface. This surface does not extend across the whole basin. In the uplifting areas, subaerial unconformities truncate the middle Campanian rocks. Their combination represents the lower first-order boundary of the sequence, and their diachroneity is the product of the northward migration of the orogen. The Teruel, Hoyon, Bogota, Cacho, Socha, Barco, and Cuervos formations are truncated by a regional subaerial unconformity. It was formed during orogenic unloading that marks the termination of the foreland basin in the Eocene. As it marks another first-order change, it is the upper boundary of the first-order sequence.

Resolving stratigraphic architecture and constraining ages of paralic strata in a low‐accommodation setting, Firebag Tributary, McMurray Formation, Canada

AbstractThe McMurray Formation in McMurray Depocentre, Canada, is typically subdivided into stratigraphic units based on regionally mappable marine mudstones, the bases of which define flooding surfaces (bottom to top: Lower McMurray, C2, C1, B2, B1, A2, A1 depositional unit). However, the McMurray Formation comprises a variety of palaeoenvironments, with the north‐eastern Firebag Tributary hosting significant delta‐plain deposits in the Lower McMurray and B1 depositional units. Facies analysis of 60 cores and 4763 wireline logs was used to resolve the palaeoshoreline trajectory and stratigraphic architecture in Firebag Tributary. Of 14 identified facies, three delta‐plain facies reveal: (1) eluviated palaeosols, interpreted as shrublands and woodlands formed during base‐level fall; (2) gleyed palaeosols, interpreted as tidal marshes; and (3) coals formed in coastal mires, the two latter facies are interpreted to accumulate during base‐level rise. Eluviated palaeosols occur below the Lower McMurray coal seam, implying valley incision and a maximum regressive surface. Gleyed palaeosols underlying the coal seam atop the B1 depositional unit do not record base‐level fall. Wetting‐upward coals overlying either palaeosol facies indicate base‐level rise (i.e. major flooding surface). B1 depositional unit coals and gleyed palaeosols are overlain by shallow‐marine facies or are eroded by wave ravinement during transgression. Consequently, the tops of coals or gleyed palaeosols correlate to the bases of regional marine mudstones elsewhere in McMurray Depocentre. Stratigraphic cross sections showcase palaeoshoreline regression and transgression. During the Lower McMurray and B1 depositional units, widespread coals and palaeosols indicate the palaeoshoreline resided near the western edge of Firebag Tributary. Regression during C2 through B2 depositional units and A2 and A1 depositional units resulted in palaeoshorelines near the Alberta–Saskatchewan border. To complement a previously dated Lower McMurray ash (121.39 ± 0.2 Ma), a new high‐confidence maximum depositional age from ash in the B1 coal seam (115.09 ± 0.16 Ma) allows an estimate to be made of depositional duration, indicating depositional units represent ca 0.16 Myr.

K-means clustering using principal component analysis to automate label organization in multi-attribute seismic facies analysis

The use of unsupervised machine learning methods such as K-means, Hierarchical Agglomerative Clustering, and Self-organizing maps is constantly increasing in seismic interpretation. Regarding unsupervised methods, the K-means technique is one of the simplest ways to cluster seismic facies, although it presents neither a structure between the generated labels nor a measure of similarity when considering their order. To solve this drawback, we propose two automated label organization techniques that use principal component analysis (PCA) to organize those obtained from the algorithm, preserving some degree of similarity. To demonstrate the effectiveness of these methods, we interpreted two stratigraphic surfaces known as Maximum Transgressive Surface (MTS) and Maximum Regressive Surface (MRS), then extracted some attributes to run clustering experiments. Furthermore, we performed the principal component analysis and selected the first three components to be clustered. Subsequently, these components were used to organize the labels obtained with K-means through the two proposed techniques. Finally, we interpreted the outstanding results obtained from the methodologies proposed, allowing us to understand better seismic facies and the depositional environments over stratigraphic surfaces.

Palaeosols in an Upper Pliocene fluvial to shallow marine succession (Valdelsa Basin, Central Italy): A sequence-stratigraphic perspective

The present study provides an example of how palaeopedology and facies analysis may be integrated for the interpretation of a cyclothemic succession in the Upper Pliocene (Piacenzian) of the Valdelsa Basin (central Italy). The stacking of facies and intervening bounding surfaces, including palaeosols, outline a hierarchy of elementary (EDS) and composite (CDS) depositional sequences within the unconformity-bounded stratigraphic units (S4-S6 synthems) which compose the succession. The focus of the study is on synthem S4 and the transition to synthem S5. Synthem S4 records the development of a distal alluvial plain dominated by floodbasin mudstone with subordinated channelized sandstone (S4 1 ), followed by the incision of a fluvial valley aggraded by the cyclical stacking of braided and low sinuosity channelized conglomerate and sandstone (S4 2 ). Synthem S5 includes lower shoreface sandstone and inner shelf mudstone related to a major transgression which affected the study area during the late Piacenzian. Evidence of soil-forming processes is well preserved within sub-unit S4 1 where five palaeosols (PS4a-e) are stacked within the facies architecture of EDS1 c-d , both being defined as transgressive to high stand tracts. Increasing palaeosol development was observed within both EDSs, while palaeosols were generally thicker and more closely stacked within EDS1 d . Palaeosols were interpreted as marking minor cycles of accommodation space creation within EDS1 c , while marking a better defined high stand tract in EDS1 d . Increasing upward soil development was observed within each EDS, with generally better developed soils in EDS S41d. The unconformable transition from S4 to S5 is marked by a thin veneer of slope deposits, bearing pedogenic carbonates reworked from a missing PS4f palaeosol, formed during the shaping of the erosional surface separating sub-units S4 1 and S4 2 . The results of this study indicate that: 1) the sedimentary and pedogenic processes recorded in the channelized facies and palaeosols in the floodbasin facies of sub-unit S4 1 , are coherent with a palaeoenvironmental setting dominated by seasonal climate; 2) the facies-palaeosol architecture of S4 synthem corresponds to those described in sequence-stratigraphic models applied to continental successions. The pedo-sedimentary signature of the major sea-level fluctuation recorded in the transition between S4 and S5 synthem differs from these models. In this case a well-developed and drained palaeosol, expected to record the maximum regressive surface shaped during the falling stage of sea level, is missing. This difference is related to a rapid fall and subsequent rise of relative sea level which marked the transition between S4 and S5 synthems. • Palaeosol and facies analysis coherently restore a Piacenzian fluvial system. • A seasonal climate controlled sediment dispersal and weathering. • Palaeosols are key-surfaces in the cyclical fluvial facies architecture. • Cyclothemic stack of palaeosols partially fits sequence-stratigraphic models. • Major sequence boundary lacks a well developed palaeosol.

Chemostratigraphy as a tool for sequence stratigraphy in the Devonian Hare Indian Formation in the Mackenzie Mountains and Central Mackenzie Valley, Northwest Territories, Canada

The Hare Indian Formation (HIF) is a late Eifelian to Givetian organic-rich mudstone constituting the lower portion of the Horn River Group (HRG), which has been minimally scrutinized in the literature. This paper proposes depositional environments and a sequence stratigraphic framework for the HIF. Using composition data collected via energy-dispersive X-ray fluorescence, geochemical proxies inform detrital input, silica source, and paleoredox conditions. Cross-plots and chemostratigraphic profiles of detritally sourced Al, Ti, and K and redox-sensitive Mo and V inform depositional and stratigraphic constraints. Silica proportions vary, indicating that sediment was derived from detrital and biogenic sources. Al, Ti, and K distributions increase upwards, showing increased continentally sourced minerals. Redox-sensitive metals are highest in the Bluefish Member (BM), suggesting intermittent euxinia. Based on the presence of continental and pelagic sediments, the sedimentary environment is interpreted as proximal- to mid-shelf. These proxies guide systems tract interpretations. Si and redox-sensitive metal concentrations peak higher in the BM, accompanied by lowered concentrations of Al, Ti, and K, suggesting a maximum flooding surface. At the top of the Prohibition and Bell Creek members, redox-sensitive enrichments are lower with higher concentrations of Al, Ti, and K, suggesting a maximum regressive surface. Transgression occurred during the initial deposition of the BM, followed by regression for the remainder of the HIF. The sedimentology of the HIF can be difficult to decipher; the use of chemostratigraphy supports its geological history (including sedimentation trends and a local record of relative sea level) using methods that may be applied to other fine-grained successions.

Insight to the geological character of the Early Triassic strata in the Western Salt Range, Pakistan: A comparative study

The sedimentary strata along the Permian–Triassic Boundary in the Western Salt Range of the sub‐Himalayas were analysed to gain an insight of its geological character regarding palaeoenvironments, palaeoclimate, and sequence stratigraphic attributes. The Early Triassic Mianwali Formation is dominated by shallow marine facies with transgressive phases, differentiation in facial character, and palaeowater depth among different sections. The study suggests that compared to the siliciclastic‐dominated Nammal Gorge Section, the Zaluch Nala Section is more carbonate‐dominated, representing algal‐laminated limestones, dolomitic marls, and siliciclastics – mainly restricted to the Mittiwali Member. There is a general decrease in ammonoids and increase in thickness from east to west, that is believed to be due to algal‐induced rapid sedimentation in the shallow marine environments as compared to deeper marine in the east. The Mianwali Formation has been deposited in two transgressive systems tracts, two highstand systems tracts, and one falling‐stage regressive systems tract. Two flooding surfaces, one each in the Mittiwali and Narmia members, have been recognized. The maximum regressive surfaces at the bottom (with the Chhidru Formation) and top (with the Tredian Formation) mark second‐order eustatic falls. The study also advocates for existence of a low‐energy platform in the temperate waters of the Palaeo‐Tethys. The sediments have similarities with various sections of Gondwanaland having the same trend of shallow marine facies and presence of algal‐laminated deposits. In the Middle Triassic, the gradual loss of sediment binding organisms shifted the low‐energy meandering patterns to high‐energy braided systems.

Depositional controls on lacustrine coquinas from an early cretaceous rift lake: Morro do Chaves Formation, Northeast Brazil

The Morro do Chaves Formation is a hybrid sedimentary succession composed of shell beds interbedded with mudstones and sandstones deposited during the rifting process of the Gondwana in a complex lake rift system, forming one of the thickest coquina deposits around the world. Despite being deeply investigated over the last decades in outcrops, the entire stratigraphic organization is not well understood yet, mainly because of the absence of continuous well core data, in addition to challenging geometries and facies distribution of the shell beds. This study focus on the characterization of facies and facies associations, and the development of a conceptual depositional model for the Morro do Chaves Formation, based on the analysis of four continuous well cores and the stratigraphic correlation among them. The described carbonate and carbonate-hybrid rocks are composed mainly of bivalves that form flat shell banks developed during dry periods with low tectonic activity. The siliciclastic rocks (mudstones, sandstones and hybrid rocks) occur interbedded with the carbonate rocks and indicates periods of active tectonic and/or climatic wet periods. The deposits are arranged in a hierarchical organization of 6 m-scale T-R cycles showing aggradation and progradation patterns. The system is controlled mainly by allocyclic (e.g., tectonics and climate) and the autocyclic (e.g., waves and currents) processes. The maximum regressive surface record an important change in the environment with a gradual increase of terrigenous input into the basin until the fast creation of accommodation space for the deposit of extensive shales that drowned and mark the end of the shell bank system. This study on facies, geometries and stratigraphic surfaces adds new and useful knowledge for helping in the understanding of complex coquina reservoirs and is applicable in the exploration of new areas with correlate lacustrine systems.

Seismic stratigraphy of late Neogene - Quaternary units and evolutionary model in the inner sector of Bahia Blanca estuary (Argentina)

The Quaternary sedimentary deposit of the inner sector of Bahía Blanca estuary (BBE), Argentina, was studied using high-resolution seismic profiles, core samples and correlation with continental – marine units outcropping in the continent. We interpreted four prominent seismic reflection surfaces and the acoustic basement which together defined five seismic stratigraphic units (S0, S1, S2, S3, S4) and four related systems tracts. Studying those units, we proposed a fourth Stage deposition evolutionary model that took place in a relative sea-level fluctuation context after the Miocene in the BBE area. The first stage contained the deposition of the regressive seismic units S0 and S1. The S0 was determined as an acoustic basement. The top of the S0 erosional surface (SU) was determined and it was formed by subaerial processes during the Late Pleistocene fall in sea-level and the following marine reworking during transgression. The unit was correlated with the oldest continental Miocene loess deposit and was associated with an Early Lowstand Systems Tract (ELST). Unit S1 was associated with a Late Lowstand Systems Tract (LLST). An irregular stratigraphic surface was observed above it. It was inferred as a Maximum Regressive Surface and the Ravinement Surface (RS/MRS) which are related to a maximum regression and subsequent transgression. The S1 unit was correlated with Pliocene-Pleistocene continental deposits. The Miocene - Pleistocene coastline movement in this sector would be associated with both Neogene Andean dynamics and the Last Maximum Glacial. After that, during the second Stage in the Late Pleistocene - middle Holocene the sea-level on the Bahia Blanca coast rose and unit S2 was formed. We interpreted unit S2 as a Transgressive System Tract which developed until the maximum sea-level of the Mid-Holocene. The coastline extension on the continent conformed the Maximum Flooding Surface. After a stabilization period to the mid Holocene, the sea-level started falling, offering conditions for the deposition of the High Stand System Tract (S3 – S4). Following stabilization, the third Stage took place and a progradation unit S3 was deposited overlying the MFS and a minor stratigraphic surface Bedset Boundary (BsB) separated this unit from S4. During the fourth phase, the sea-level continued to fall until the present level and the last HST (S4) was interpreted, which is interpreted as an aggradational – progradational deposit formed in the Middle Holocene to the present day by a change in the rate of sediment supply or energy flux.

Synchrony evolution of two contradictory prograding Gilbert-type deltas at the margins of the foreland basin (case study from the Neogene Western Carpathian Foredeep)

The study concerns about two Miocene deltas located along the opposite margins of the Western Carpathian Foredeep (peripheral foreland basin), their architecture and evolution. Three synchrony phases of development of the Gilbert-type deltas were recognized based on 3D and 2D seismic data, well logs and cores. Individual phases are separated by seismic stratigraphy surfaces. The base of the deltas is formed by the erosional discontinuity (seismic stratigraphy surface 1), which is the sequence boundary of the 3rd order cycle. During the first phase, the sediment supply exceeds accommodation space creation and progradation of deltas and the normal regression regime dominates. The first phase is terminated by the maximum regressive surface/transgressive surface (seismic stratigraphy surface 2) and interpreted as the lowstand systems tract. In the second phase, the aggradation and retrogradation regime of deltas reveals the acceleration of the accommodation space creation and the deposits are interpreted as the transgressive systems tract. The third phase is bounded by the maximum flooding surface (seismic stratigraphy surface 3) and shows progradation of the delta in the normal regression regime, then the sediment supply exceeds the accommodation space. The maximum regressive surface (seismic stratigraphy surface 4) terminates this phase and allows to interpret it as the highstand systems tract. The synchrony evolution of deltas is explained by the tectonic activity along the fault system oriented perpendicular to the basin axis. Position of the deltas is also responsible for continuous sediment supply and its variations. The tectonic activity of the transverse fault system across the entire basin hidden the signals of the reciprocal activity of the opposite basin margins directed by flexural tectonics. • Two Gilbert-type deltas prograding contradictory at margins of foreland basin. • Ruling factors of synchronous Gilbert-type delta evolution – eustasy vs. tectonics. • Role of fault activity in reciprocal stratigraphy of foreland basin depozones. • Phases of the delta evolution in the concept of sequence stratigraphy.

Late Pleistocene-Holocene history of a tectonically active segment of the continental margin (Nekor basin, Western Mediterranean, Morocco)

In active basins, tectonics can segment the continental shelf and control its stratigraphic architecture and physiography. Segmentation can explain the local evolution and morphology of the continental shelf because of sea-level variations, local tectonic segmentation and hydrodynamic processes. Here we investigate the tectonically active Morocco continental margin (southern Alboran Sea) using high-resolution seismic profiles and multibeam bathymetric data. The active faults bounding the transtensive Nekor basin triggered the segmentation of the shelf into three sectors showing different subsidence rates: a western sector corresponding to an extensive fault relay, a central sector corresponding to the subsiding Al-Hoceima Bay and an eastern sector corresponding to the footwall of the Trougout senestral normal fault. Results show that the staircase morphology of the shelf corresponds to successive submarine terraces at the shelf edge (ST1), mid-shelf (ST2) and inner-shelf (ST3) around −110 m,-80 m, and −40 to −20 m deep, respectively. The terraces correspond to the top of prograding wedges seaward and are erosive landward. They are correlated with stillstand from the Last Glacial Maximum to the Holocene highstand. Above the terraces, sub-aqueous dune fields are interpreted as degraded and deposited during the post-glacial transgression. In the central sector, typical delta front seafloor undulations on the shelf and crescent shaped bedforms at the head of marine incisions on the upper slope denote a fluvial influence during the Holocene. Seismic stratigraphy analysis revealed the preservation of six seismic units bounded by polygenic regional unconformities (S1, S2, S3, S4 and S5). Based on comparison with other Mediterranean margins, S1 to S5 are attributed to 4th order maximum regressive surface. We discuss the local preservation of the system tracts as a function of the vertical motion and the physiography of this tectonically active domain. This study provides useful clues for future local paleo-seismic analysis and to advance our understanding of sedimentary processes in active areas. • We present new data of the morphology of the Mediterranean Moroccan shelf. • Marine terraces are present and correlated to local sea level variations. • The active tectonic locally segments the shelf and control the stacking pattern. • The relation between the stacking pattern and the morphology is investigated. • We propose a depositional model correlating the morphology and the stratigraphy of the shelf.

Interplay of tectonism and eustasy during the Early Permian icehouse: Southern Sydney Basin, southeast Australia

This investigation presents an outcrop‐based integrated study of sedimentological analysis and sequence stratigraphy applied to the Lower Permian sedimentary succession in the southern Sydney Basin, Australia. This succession accumulated in several depositional environments and sub‐environments that range from non‐marine (fluvial) to marine (outer shelf), representing the fill of a sedimentary basin that resembles a fault‐bounded, rift basin. The stratigraphic analysis indicates a deepening‐upward trend, and the sequence stratigraphic approach has established that these sediments can be attributed to the lowstand, transgressive, and highstand systems tracts. Lowstand sediments can be defined by fluvial facies that are located between the subaerial unconformity and the maximum regressive surface. Transgressive facies correspond to estuarine, upper and lower shoreface, and inner and outer shelf depositional environments and are located between the maximum regressive and the maximum flooding surfaces. Highstand bottomset sediments are accumulated above the maximum flooding surface and are represented by outer shelf facies. The stratigraphic architecture indicates the development of an almost complete depositional sequence, mainly developed under the control of tectonically induced subsidence, but also influenced by the high sedimentation rates and the high gradient of the inherited topography. Eustatic sea‐level fluctuations were of minor importance during the deposition of the examined sediments.

Sequence stratigraphy, basin morphology and sea-level history for the Permian Kapp Starostin Formation of Svalbard, Norway

AbstractBased on seven measured sections from Svalbard, the marine strata of the Permian Kapp Starostin Formation are arranged into seven transgressive–regressive sequences (TR1–TR7) ofc. 4–5 Ma average duration, each bound by a maximum regressive surface. Facies, including heterozoan-dominated limestones, spiculitic cherts, sandstones, siltstones and shales, record deposition within inner, middle and outer shelf areas. The lowermost sequence, TR1, comprises most of the basal Vøringen Member, which records a transgression across the Gipshuken Formation following a hiatus of unknown duration. Temperate to cold, storm-dominated facies established in inner to middle shelf areas between the latest Artinskian and Kungurian. Prolonged deepening during sequences TR2 and TR3 was succeeded by a long-term shallowing-upward trend that lasted until the latest Permian (TR4–TR7). A major depocentre existed in central and western Spitsbergen while to the north, Dickson Land remained a shallow platform, leading to a shallow homoclinal ramp in NE Spitsbergen and Nordaustlandet. The Middle Permian extinction (late Capitanian) is recorded near the base of TR6 in deeper parts of the basin only; elsewhere this sequence is not recorded. Likewise the youngest sequence, TR7, extending to the upper formational contact of latest Permian age, is found only in the basin depocentre. Comparison with age-equivalent strata in the Sverdrup Basin of Canada reveals a remarkably similar depositional history, with, for example, two (third-order) sea-level cycles recorded in the Late Permian of both regions, in keeping with the global record. Sequence stratigraphy may therefore be a powerful correlative tool for onshore and offshore Permian deposits across NW Pangaea.

The Co-Occurence ofTrypanitesandGlossifungitesSubstrate-Controlled Trace-Fossil Assemblages In A Triassic Mixed Siliciclastic–Carbonate Depositional System: Baldonnel Formation, Williston Lake, B.C., Canada

Abstract Detailed outcrop analysis of an Upper Triassic, shallow marine, mixed siliciclastic–carbonate ramp succession in northwestern Canada reveals numerous disconformities that are characterized by substrate-controlled trace-fossil assemblages. Although Glossifungites assemblages, and to a lesser extent, Trypanites assemblages, are common in the Upper Carnian Baldonnel Formation, in several horizons, a pattern of paired Trypanites–Glossifungites-demarcated discontinuity surfaces occurs. These paired surfaces occur in the same overall environmental setting and are interpreted to have the same general stratigraphic implications in each case. The Trypanites surfaces invariably occur lower in the section. They penetrate into sandy bioclastic limestone and are infilled and overlain by a coarse-grained detrital lag. Their development indicates early cementation in a coastal setting. The Trypanites surfaces form coplanar maximum regressive surfaces and transgressive surfaces of erosion and are correlatable on a regional scale. The lags are overlain, in turn, by laminated calcareous siltstone (denoting offshore deposition) and bioclastic sandstone (a return to shoreface depositional conditions). The siltstone–sandstone contacts are characterized by low-diversity Glossifungites assemblages, which are interpreted as an amalgamated succession of storm-induced wave ravinement surfaces emplaced in front of a rapidly prograding shoreface. Paired Trypanites–Glossifungites surfaces in the Baldonnel Formation reflect fluctuations in relative sea level and sediment input in an overall low accommodation mixed siliciclastic–carbonate ramp setting.

Comment on Non‐unique stratal geometries: implications for sequence stratigraphic interpretations, by: P.M. Burgess and G.D. Prince,Basin Research(2015) 27, 351–365

AbstractThe non‐unique variability highlighted by Burgess & Prince (Basin Res. 2015,27, 351) (i.e. the origin and timing of maximum flooding surfaces, maximum regressive surfaces and subaerial unconformities; the process of topset aggradation in relation with the various types of shoreline trajectory; and the multiple controls that may affect the progradation and retrogradation of a shoreline) is irrelevant to the workflow of sequence stratigraphy. What is relevant is the observation of the unique stratal geometries that are diagnostic to the definition of all units and surfaces of sequence stratigraphy. In downstream‐controlled settings, these unique stratal stacking patterns relate to the forced regressive, normal regressive and transgressive shoreline trajectories. Multiple controls interplay during the formation of each type of stacking pattern, including accommodation, sediment supply and the energy of the sediment‐transport agents. This interplay explains the non‐unique variability, but does not change the unique criteria that afford a consistent application of sequence stratigraphy. Failure to rationalize the non‐unique variability within the context of unique stratal geometries is counterproductive, and obscures the simple workflow of sequence stratigraphy.

Time-Transgressive Confinement On the Slope and the Progradation of Basin-Floor Fans: Implications For the Sequence Stratigraphy of Deep-Water Deposits

Abstract Observations from outcrop and subsurface datasets indicate that key stratigraphic surfaces in ancient submarine slope successions are diachronous and form during periods of seascape degradation and sediment bypass. Evidence for time transgressive confinement of submarine channel–levee systems includes composite basal erosion surfaces, cut-off bends and hanging valleys, and external levees overlying lobe deposits. After the onset of a sediment supply cycle, progressive confinement will develop on the submarine slope, through a combination of incision and external levee construction, such that successive sediment gravity flows will maintain their downslope energy farther into the basin. This way, frontal lobe deposits are incised by channel systems and overlain by external levee deposits as the channel–levee system becomes more entrenched and propagates farther into the basin. The stratigraphic response on the related basin floor is fan growth and net progradation until a maximum basinward extent is reached, which corresponds to the time of maximum through-channel sediment transfer (bypass). At this time a maximum regressive surface forms, although in reality this is challenging to identify in the rock record. Conceptually, this basin-floor process response to progressive slope confinement at a point could be autocyclic, but would be amplified with an allogenically driven waxing-then-waning sediment supply cycle. The coupled progressive confinement of the submarine channel–levee system and basin-floor fan growth will result in a diachronous lithological basal surface to the system. This challenges the idea of the deep-water sequence boundary being isochronous and passing into a single correlative conformity at the base of the basin floor fan, or that there is temporal distinction between deposition by high- and low-density turbidity currents.

Architecture and facies model in a non-marine to shallow-marine setting with continuous base-level rise: An example from the Cretaceous Denglouku Formation in the Changling Depression, Songliao Basin, China

The analysis of 2D and 3D seismic data, drilled cores and well log data has resulted in a sequence stratigraphic framework of the Cretaceous Denglouku Formation in the Changling Depression in the underfilled Songliao Basin. The Cretaceous Denglouku Formation can be divided into four third-order sequences. Each sequence consists of two systems tracts: a transgressive systems tract and a highstand systems tract. A braided river delta is the main sedimentary facies in the study interval. These sequences were deposited in a back-arc rift basin during a transitional period from fault-dominant subsidence to downwarp subsidence. A sequence stratigraphic model is discussed based on the above interpretations. Typical unconformities are absent due to the absence of base level fall. Instead, maximum regressive surfaces, which are generally reworked by transgressive ravinement, act as the sequence boundaries. Each sequence bounded by these surfaces can be divided into two depositional units: a transgressive unit (TST) and normal regressive unit (HST). On land, a TST is characterized by a decreasing channel/floodplain ratio, and an HST is characterized by an increasing channel/floodplain ratio. Lakes are analogs to marine settings in which the shoreline moves forwards and backwards, and their strata show alternating retrogradation and progradation patterns. The results of this study may encourage the application of similar approaches to the correlation of successions within and beyond the Songliao Basin.

Genetically Related Incised Valleys and Deltas: Sequence and Modern Analogue Modeling From the Nonmarine Santa Barbara Coalfield, Late Pliocene, Italy

Abstract The morphodynamics of coeval incised valleys and deltas are relatively well understood in marine-paralic environments, but not in the nonmarine, lacustrine counterparts. Here, we analyze the morphology and depositional and sequence architecture of a small-scale valley to deltaic complex preserved in a late Pliocene intermontane coalfield in the Northern Apennines, Italy. Outcrop exposures are integrated with 160+ well logs in an area of less than 1.5 km2. The main goal of this study is to demonstrate that spatially restricted yet fully preserved nonmarine systems are well suited for depositional, sequence, and modern analogue modelling, and deserve more attention in the literature. In this study, outcrop and borehole data are merged into isopach maps, highlighting the sedimentary response to a discrete cycle of lake-level retreat and re-expansion. Falling-stage and lowstand phases were characterized by incision of a meandering valley onto a previous highstand shelf, and by the avulsive progradation of an attached, shelf-edge delta. The supply-dominated character of the depositional system along with the limited wave fetch favored in this phase the preservation of the maximum regressive surface across the entire incised-valley to deltaic transect. The following lake-level re-expansion involved estuarine valley back-filling, and the transition from river-dominated to wave-dominated deltaic deposition. Enhanced wave ravinement and associated shoreline-independent prodelta forestepping promoted the development of a transgressive shelf-break bypass. These results are compared with reference sequence and accommodation models, as well as with two modern Ethiopian lakes undergoing acute forced regression. The similar scale and morphology of modern stranded highstand shelves and shelf-edge deltas provide a parallel for assessing the original topographic gradients and depositional dynamics of the late Pliocene case study. Modern and ancient analogues also shed light on the amplification of climate records in endorheic lakes, on the potentially strong avulsive character of falling-stage deltas, and on the sedimentary response to short-lived lacustrine fluctuations in rapidly subsiding basins.