Transgressive Surface Of Erosion Research Articles

Unraveling stratigraphic complexities of transgressive surfaces with trace fossil omission suites and juxtaposed softground suites

Recognizing stratigraphically important bounding surfaces relies on assessing the facies that juxtapose these surfaces as well as the trace fossil omission suite associated with the surface. The ability to differentiate between purely transgressive surfaces and those that conceal earlier stratigraphic surfaces that allude to a more complex history of development regarding the identification of allogenic surfaces of sequence stratigraphic significance that might have otherwise been overlooked. This study analyzes four examples of transgressive surfaces of erosion from Cretaceous-aged strata, with three of the examples representing a TSE/SB (amalgamated transgressive surface of erosion with a sequence boundary) that mask earlier base level falls. Consideration of variable omission suites along depositional strike and dip highlights the influence of substrate rheology on the nature of omission suites. In this study we demonstrate marked changes in the omission suite along bounding surfaces along proximal to distal trends that arise due to changes in underlying rheology. Finally, detailed core analysis is shown to be an imperative asset to subsurface investigation to address the limitations of using wireline well data alone in identifying stratigraphically important surfaces for more accurate regional mapping and characterization of transgressive surfaces. This study highlights that many stratigraphically important surfaces such as those that correspond to a TSE/SB may go unnoticed if utilizing wireline data alone. Overall, this study provides a comprehensive approach to further understanding and identifying transgressive surfaces in the rock record, especially those that demarcate a more complex history other than simple transgressive ravinement.

High-resolution geophysical and geochronological analysis of a relict shoreface deposit offshore central California: Implications for slip rate along the Hosgri fault

Abstract The Cross-Hosgri slope is a bathymetric lineament that crosses the main strand of the Hosgri fault offshore Point Estero, central California. Recently collected chirp seismic reflection profiles and sediment cores provide the basis for a reassessment of Cross-Hosgri slope origin and the lateral slip rate of the Hosgri fault based on offset of the lower slope break of the Cross-Hosgri slope. The Cross-Hosgri slope is comprised of two distinct stratigraphic units. The lower unit (unit 1) overlies the post–Last Glacial Maximum transgressive erosion surface and is interpreted as a Younger Dryas (ca. 12.85–11.65 ka) shoreface deposit based on radiocarbon and optically stimulated luminescence (OSL) ages, Bayesian age modeling, seismic facies, sediment texture, sediment infauna, and heavy mineral component. The shoreface was abandoned and partly eroded during rapid sea-level rise from ca. 11.5 to 7 ka. Unit 2 consists of fine sand and silt deposited in a midshelf environment when the rate of sea-level rise slowed between ca. 7 ka and the present. Although unit 2 provides a thin, relatively uniform cover over the lower slope break of the older shoreface, this feature still represents a valuable piercing point, providing a Hosgri fault slip rate of 2.6 ± 0.8 mm/yr. Full-waveform processing of chirp data resulted in significantly higher resolution in coarser-grained strata, which are typically difficult to interpret with more traditional envelope processing. Our novel combination of offshore radiocarbon and OSL dating is the first application to offshore paleoseismic studies, and our results indicate the utility of this approach for future marine neotectonic investigations.

Quaternary Lowstand Prograding Wedges of the Salento Continental Shelf (Southern Adriatic Sea, Italy): Architectural Stacking Patterns and the Control of Glacio-Eustatic Sea Level Fluctuations and Foreland Tectonic Uplift

The performance of both the tectonic uplift and of the 4th-order glacial eustatic sea level fluctuations in controlling the stratigraphic architecture of Quaternary lowstand prograding wedges of the Salento continental shelf (Southern Adriatic sea, Italy) during a time interval spanning from the Middle Pleistocene to the Holocene has been pointed out through the interpretation of high-resolution seismic reflection profiles and their correlation to the curves of the isotopic stratigraphy. Three main transgressive surfaces of erosion (RS1, RS2 and RS3) punctuate the stratigraphic architecture of the Salento continental shelf, separating Quaternary lowstand prograding wedges between them. All along the Middle Pleistocene, increasing the tectonic uplift of the Puglia offshore, combining with 4th-order glacio-eustatic variations, have dealt with the pattern of a broad forced regression prograding wedge, favoring a platform progradation of approximately 15 km. The architectural stacking patterns of the overlying Late Pleistocene and Holocene prograding wedges are controlled by 4th-order glacio-eustatic sea level changes, allowing for the formation of incomplete depositional sequences. In this period, the eustatic signature overcomes the tectonic mark, implying a decline in the uplift of the Apulian foreland in the course of the final 250 ky.

Tectonic and eustatic control on channel formation, erosion, and deposition along a strike-slip margin, San Diego, California, USA

Active margins are characterized by small mountainous streams, which contribute significantly to global sediment transport from land to sea. The response of active margin streams to base-level change due to eustatic sea-level cycles is less well understood than passive margin streams, which form the basis of most sequence stratigraphic models. The southern California margin offers an opportunity to investigate the evolution of small mountainous streams along a strike-slip margin over a sea-level cycle. High-resolution Chirp subbottom data were examined from the Silver Strand littoral cell in San Diego, California, which is located in a region of localized transtension associated with a step in the Newport Inglewood-Rose Canyon fault zone. Chirp data reveal active faulting on multiple fault strands, a subaerial surface likely formed from MIS 4 to MIS 2, fluvial incision associated with MIS 2, and the transgressive surface of erosion formed during sea-level rise from MIS 2 to MIS 1. Interpreted acoustic units observed in the data include the Cretaceous outcropping Rosario Group, Miocene to Pliocene prograding clinoforms, subaerial deposits associated with MIS 4 to MIS 3, channel fill and transgressive lag deposits formed during the most recent sea-level transgression, and Holocene marine sediment. The Chirp data examined in this study build upon findings from other seismic studies, sediment cores, trenching, and outcrops that have been examined on- and offshore San Diego. Combined, these data suggest that the fault-controlled pull-apart basin formed in this region influences sediment transport and deposition throughout the last glacial cycle. During highstand, the fault-controlled wide shelf, subsiding basin, and circulation patterns result in trapping of sediment in San Diego Bay and nearshore, cutting off sediment delivery to the deep-sea. During lowstand, the fault-controlled morphology creates a drainage divide that deflects streams to the south which lengthens and reduces slope of the drainage pathways. These findings are in contrast to observations in other fault controlled littoral cells along the southern California margin where sediment delivery to the deep-sea remains active during highstands, highlighting the variability of stream response to base-level change along active strike-slip dominated margins.

Episodes of seabed rise and rapid drowning controlling the development of regressive and transgressive rhodolithic limestones in a tectonically-active subduction setting (Early Miocene, Wairarapa region, New Zealand)

ABSTRACT Early Miocene limestones from the Wairarapa region of New Zealand were deposited on thrust-bounded margins of trench-slope basins, and consist of two superposed stratal units, namely units A and B, interpreted as forced regressive and forced transgressive foralgal and rhodolith-bearing deposits, respectively. Unit A is floored by a regressive surface of marine erosion cut into shelfal to bathyal siliciclastic successions, and is overlain across a transgressive surface of erosion by Unit B. A drowning surface abruptly places the latter deposits in contact with deeper hemipelagites and turbidites. The succession is explainable within a tectono-eustatic based framework as follows: (1) Structurally controlled rapid relative sea-level fall, (i.e. sea-bed rise), from upper bathyal to shelfal depths promoted development of regressive (‘lowstand’) mixed carbonate–siliciclastic deposits. Continuation of seabed rise resulted in deposition of pure carbonate sediments, which are represented by channel-fill rhodolithic rudstones; (2) early stage of relative sea-level rise (i.e. seabed drowning) caused emplacement of transgressive glauconitic limestones, consisting of either foralgal deposits, or incised rhodolithic limestones; (3) continued relative sea-level rise terminated carbonate production. The present study documents carbonate production and termination in a tectonically active and confined intra-slope setting, reflected in the development and distribution of unusual forced regressive, and transgressive rhodolithic-heterozoan carbonates.

Acceleration in the rate of the Boreal Sea transgression recorded in the Lower Cretaceous McMurray Formation, Canada

Depositional environments are typified as low-to high-accommodation space settings based on the sediment accumulation rate. In low-accommodation settings, persistent top truncation of regressive units renders it challenging to accurately determine the rate of accommodation space creation. Herein, we analyze a nearly continuous succession of the Lower Cretaceous McMurray Formation, which was deposited during the foreland development of the Western Canada Sedimentary Basin in northeast Alberta, Canada (the McMurray Depocenter). Across the study area, the McMurray Formation consists of a vertical succession of 6 discrete regressive depositional units (DU) bounded by flooding surfaces and/or transgressive surfaces of erosion. The sedimentology, architecture and stratigraphy of these DUs are investigated and statistical analysis is used to quantitatively assess variations in DU thickness. Additional statistical analysis is used to quantitatively assess the vertical distribution of transgressive mudstone subfacies in the McMurray Formation.The mean thickness of each DU is 10.4 m, and each DU represents approximately 1.7 million years of deposition. This indicates that the McMurray Formation preserves deposition in a low-accommodation space setting, and that creation of accommodation space was primarily controlled by transgression of the Boreal Sea. An abrupt decrease in DU thicknesses is interpreted to result from concomitant increased erosional truncation of DUs via wave action during transgression and changes in basin morphology. DU thickness variations correlate to a change in the marine expression of the transgressive mudstone underlying each DU. Together, these data suggest an acceleration in the rate of the Boreal Sea transgression, and we hypothesize that the duration of still-stands during which DUs accumulated diminished in the latter stages of McMurray Fm deposition. This study demonstrates that detailed sedimentologic and stratigraphic research tied to statistical analysis can be used to quantify changes in the rate of transgression, especially in low-accommodation space settings.

Late Pleistocene-Holocene sedimentary evolution in the coastal zone of the Red River Delta

The Red River Delta is considered one of the largest megadelta systems in Asia. The formation of this delta has been controlled by the continent-ocean interaction and sea-level fluctuation during the Cenozoic. In this study, we present a new sequence stratigraphic framework of the Red River Delta based on borehole lithofacies analysis and high resolution seismic data. The Late Pleistocene–Holocene sediments in the coastal zone of the Red River Delta were subdivided into three systems tracts: (1) the lowstand systems tract (LST) is characterized by a Late Pleistocene alluvial silty sand facies complex (arLSTQ13b); (2) the transgressive systems tract (TST) is illustrated by the coastal marsh facies complex and the lagoonal greenish-gray clay facies of Early-Middle Holocene (amt, mtTSTQ21−2); and (3) the highstand systems tract (HST) is composed of the Middle-Late Holocene deltaic clayish silt facies complex (amhHSTQ22−3). The boundaries between these three systems tracts are not isochronous, namely: (1) The LST-HST boundary has been associated with the Würm 2 Glaciation, which occurred at ~40-18 Ka.; (2) The TST-LST boundary is identified by a transgressive erosion surface, whose age ranges from ~12-5 Ka.; and (3) the HST-TST boundary is an unconformity between the submarine deltaic facies complex and the Middle Holocene marine flooding plain.

Sedimentology and basin-fill history of the Cenozoic succession of the Sylhet Trough, Bengal Basin, Bangladesh

The Sylhet Trough, a petroleum province of the Bengal Basin, accommodates a huge thickness of Eocene to Recent sedimentary successions. However, the basin-fill history of the trough is poorly understood; specifically, constrains on timing of deposition of the individual units are yet to be established. Therefore, we aimed at establishing sedimentation and basin-fill history of the Sylhet Trough based on detailed lithofacies analysis of the outcropping Cenozoic succession. We have divided the entire Cenozoic succession into three megasequences which can be further sub-divided into nine lithostratigraphic units based on bounding discontinuities, such as transgressive erosion surface, regressive erosion surface, transgressive surface, marine flooding surface, and incised valley floor. The oldest is the Megasequence 1, comprised of shallow marine shelfal deposits overlain by shallow marine to nearshore deposits. In the middle, the Megasequence 2 is representing tide-dominated marine to coastal (deltaic) depositional systems with evidence of cyclic marine regression and transgression. Repetitive occurrence of incised channel, tidal inlet, tidal ridge/shoal, tidal flat and other tidal deposits are separated by shelfal deposits. The top of the Megasequence 2 is marked by a pronounced erosion surface interpreted as an incised valley floor indicating the final phase of marine regression followed by the gradual establishment of the overlying continental-fluvial depositional systems (i.e., the Megasequence 3). This youngest megasequence is characterized by stacked braided river sand bars that pass up-sequence into meandering river deposits. Based on the Cenozoic eustatic sea level curve, we suggest that the upper boundaries of the Megasequence 1 and Megasequence 2 are approximately at 39.5 Ma and 5.0 Ma, respectively.

The stratigraphy of the Cretaceous (Albian stage) Gault and Upper Greensand formations: Dorset to Buckinghamshire and the western Weald, UK

The present account is a review of the successions in the Albian Gault and Upper Greensand formations, their lithology and their ammonite biostratigraphy, proved at outcrop between Dorset and Buckinghamshire, in the western Weald and that recorded in boreholes in the intervening area. It is concluded that the Wessex and Weald regions formed a single sedimentary basin during the Albian Stage. The lithostratigraphy and biostratigraphy are described area by area and are combined with recent accounts of the Albian sediments of the adjacent regions to describe lateral and stratigraphical variations in the depositional environments and sources of sediment. We conclude that although the steady overall rise in sea level in the Albian had an important effect on the local depositional environments and in the distribution of Albian sediments in England and adjacent areas, the influence of intermittent tectonic phases on the development of transgressive erosion surfaces was such that individual pulses in global eustatic sea-level rise cannot be correlated with confidence with most of the transgressions in the Albian.

Systems tracts and their bounding surfaces in the low- accommodation Upper Mannville group, Saskatchewan, Canada

Abstract Sequence stratigraphic interpretations of paralic successions can be challenging, because such settings are commonly controlled by a combination of allogenic controls and autogenic processes, leading to complex depositional architectures. In low-accommodation systems where parasequences are less than 15 m thick, the challenges in recognizing discrete stratigraphic surfaces are exacerbated by limited vertical separation between surfaces or their outright erosional amalgamation, requiring high-resolution facies analysis to resolve their geometries. Herein, we present criteria derived from core data and well logs to differentiate between allogenic and autogenic surfaces in a low-accommodation paralic setting, using the Lower Cretaceous Mannville Group of west-central Saskatchewan, Canada as a case study. The upper part of the Mannville Group (Sparky, Waseca and McLaren formations) displays complex stratigraphic relationships related to base-level changes. Marine flooding surfaces (MFS) and transgressive surfaces of erosion (TSE) of 3rd and 4th order record allogenic changes ( e.g., basin subsidence and/or eustatic changes in sea level), and are used to define parasequence boundaries of strandplain-shoreface successions. Deltaic deposits not only possess these allogenic transgressive surfaces, but autogenic 5th-order flooding surfaces, which are broadly similar in appearance, as well. These autogenic surfaces record responses to channel avulsion or lobe abandonment, separate discrete delta lobes, and display limited lateral extents. Shoreface-related flooding surfaces, by contrast, bound true allogenic parasequences and, therefore, have regional correlatability. The Waseca Formation also possesses surfaces related to base-level fall. To the north, a subtle regressive surface of marine erosion (RSME) marks the base of the falling stage systems tract. Elsewhere, a widespread subaerial unconformity (SU) separates the Waseca into lower and upper members. In most areas, the SU is amalgamated with surfaces generated by later base-level rise. Upper Mannville strata in the study area, therefore, can be separated into parts of two depositional sequences. The main deposits of the lower sequence comprise a highstand systems tracts (HST) in the Sparky Formation. The base of the Lower Waseca Member marks the onset of a transgressive systems tract (TST), associated with widespread shoreline retreat. A 3rd-order maximum flooding surface (MxFS) marks the end of transgression and resumption of normal progradational regression in a highstand systems tract associated with the Lower Waseca Member. Following highstand normal regression, a major base-level fall initiated a subaerial unconformity that marks the base of the upper sequence. Fluvial valley incision led to sediment bypass and deposition of forced regressive and lowstand shoreface and delta complexes of the falling stage systems tract (FSST) and lowstand systems tract (LST), respectively, in the northern part of the study area. Pedogenic modification of subaerially exposed sediment occurred in interfluve areas. Ensuing TST accumulation was initially confined to the tidal-fluvial estuarine infill of the incised valleys and transgressive bay deposits of the Upper Waseca Member. The Upper Waseca is capped by a 3rd-order maximum flooding surface (MxFS), which separates it from the overlying McLaren Formation. This marks the return to regional shoreline progradational regression and corresponds to the highstand systems tract (HST) of the upper sequence.

Sequence stratigraphic and sedimentologic significance of the trace fossil Rhizocorallium in the Upper Triassic Nayband Formation, Tabas Block, Central Iran

This study analyzes in detail the beds bearing Rhizocorallium in the Upper Triassic Nayband Formation (Tabas Block, Central Iran) and shows their potential in interpreting depositional settings, ecological features and sequence stratigraphy. An integrated approach combining ichnological, sedimentological and stratigraphic methods has significantly enhanced our understanding of the changes in the spatial distribution style and morphological differences among the same ichnospecies of Rhizocorallium. The Upper Triassic Rhizocorallium assemblages from the Nayband Formation reveal significant spatial variations in the orientation and dimensions (i.e., length, width, limb diameter), the tiering pattern, and the colonization style throughout systems tracts and at erosional discontinuities or omission surfaces. Based on the wide variety of forms and orientation, numerous morphotypes of Rhizocorallium are grouped into two main types, i.e., those that are mostly facies controlled and those that appear abundantly in a confined stratigraphic interval and are facies independent. In this respect, three paleoichnocoenoses or habitats for the rhizocorallid producers could be differentiated according to the burrow morphology and the nature and consistency of the substrate: (1) stable habitat, represented by soft substrates including horizontal, long, straight or slightly sinuous, spreite-bearing, U-shaped protrusive burrows of Rhizocorallium irregulare (=R. commune var. irregulare). This habitat resulted from processes operating in settings that are characterized by soft substrates, reduced sedimentation rates, and abundant food supply, typical of low- to moderate-energy, fully marine conditions; (2) unstable, physically-controlled habitat, represented by a suite of shifting substrates with low- to high-energy settings, including short, U-shaped protrusive spreiten-burrows of R. jenense (Type 1). In this habitat alternating and contrasting energy conditions did exist due to repeated storm events that were the main controlling factor in the distribution and preservation of Rhizocorallium; (3) substrate-controlled habitat represented by a suite of stiff-to-firm substrates including oblique to vertical protrusive or retrusive spreiten U-shaped burrows of R. jenense (Type 2). The erosional discontinuities or omission surfaces related to this habitat include parasequence-bounding transgressive surfaces of erosion (TSE) and parasequence-bounding flooding surfaces (FS) and are mainly associated with the Rhizocorallium-dominated Glossifungites ichnofacies. Complementary ichnological information indicates that the shift in the orientation and the morphological features of rhizocorallid burrows point to broad changes of environmental parameters, which are, in turn, controlled by the rate of sea-level changes.

Prevention of infectious complications in predicted severe acute pancreatitis (SAP) – a single center randomized controlled trial

Venezuela has the largest hydrocarbon reserves in the world and most of these are within the Orinoco Oil Belt. The Oficina Formation of the Orinoco Oil Belt and the Oritupano Field comprises a wide range of environments formed under variable salinity conditions. These include freshwater fluvial and fluvio-tidal transition zones, brackish-water estuarine and delta-plain segments, alternating brackish-water and near-normal marine delta-front and prodelta settings, and normal-marine wave-dominated shoreface and offshore-shelf environments. The Oficina Formation thus provides an ideal opportunity to evaluate trace-fossil distribution and ichnofacies gradients along a depositional profile and to calibrate salinity-related trace-fossil models. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). Fluvial deposits in freshwater portions of tide-influenced, estuarine channels and distributary channels of tide-dominated deltas are locally intensely bioturbated, displaying low-diversity occurrences of the Scoyenia Ichnofacies. Brackish-water delta-plain and estuarine deposits display lower degrees of bioturbation and low ichnodiversity, as revealed by depauperate Cruziana Ichnofacies and the Skolithos Ichnofacies. Wave-dominated deltaic deposits display the Skolithos and the depauperate Cruziana Ichnofacies, but the presence of some ichnotaxa (e.g., Chondrites) suggests periods of lower salinity stress, probably during times of reduced freshwater discharge. Open-marine deposits are characterized by intense bioturbation and very high diversity, as shown by the archetypal Cruziana Ichnofacies in low-energy distal settings, whereas high-energy proximal settings are characterized by the Skolithos Ichnofacies. Faunal distribution is strongly controlled by salinity, which makes trace-fossil evidence particularly useful for paleoenvironmental characterization of marginal-marine systems. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of marginal-marine deposits, outlining transgressive surfaces of erosion. The Oficina Formation shows remarkable similarities in sedimentary facies and both trace-fossil and micropaleontological content with the Cretaceous McMurray Formation of western Canada.

From freshwater to fully marine: Exploring animal-substrate interactions along a salinity gradient (Miocene Oficina Formation of Venezuela)

Venezuela has the largest hydrocarbon reserves in the world and most of these are within the Orinoco Oil Belt. The Oficina Formation of the Orinoco Oil Belt and the Oritupano Field comprises a wide range of environments formed under variable salinity conditions. These include freshwater fluvial and fluvio-tidal transition zones, brackish-water estuarine and delta-plain segments, alternating brackish-water and near-normal marine delta-front and prodelta settings, and normal-marine wave-dominated shoreface and offshore-shelf environments. The Oficina Formation thus provides an ideal opportunity to evaluate trace-fossil distribution and ichnofacies gradients along a depositional profile and to calibrate salinity-related trace-fossil models. The Oficina Formation contains four softground ichnofacies (Scoyenia, depauperate Cruziana, Skolithos, and archetypal Cruziana) and two substrate-controlled ichnofacies (Teredolites and Glossifungites). Fluvial deposits in freshwater portions of tide-influenced, estuarine channels and distributary channels of tide-dominated deltas are locally intensely bioturbated, displaying low-diversity occurrences of the Scoyenia Ichnofacies. Brackish-water delta-plain and estuarine deposits display lower degrees of bioturbation and low ichnodiversity, as revealed by depauperate Cruziana Ichnofacies and the Skolithos Ichnofacies. Wave-dominated deltaic deposits display the Skolithos and the depauperate Cruziana Ichnofacies, but the presence of some ichnotaxa (e.g., Chondrites) suggests periods of lower salinity stress, probably during times of reduced freshwater discharge. Open-marine deposits are characterized by intense bioturbation and very high diversity, as shown by the archetypal Cruziana Ichnofacies in low-energy distal settings, whereas high-energy proximal settings are characterized by the Skolithos Ichnofacies. Faunal distribution is strongly controlled by salinity, which makes trace-fossil evidence particularly useful for paleoenvironmental characterization of marginal-marine systems. In addition, the Glossifungites and Teredolites Ichnofacies indicate erosional exhumation of marginal-marine deposits, outlining transgressive surfaces of erosion. The Oficina Formation shows remarkable similarities in sedimentary facies and both trace-fossil and micropaleontological content with the Cretaceous McMurray Formation of western Canada.

Depositional facies and ichnology of a tidally influenced coastal plain deposit: the Ogwashi Formation, Niger Delta Basin

The Ogwashi Formation is re-interpreted as tidally influenced coastal plain deposit based on the detailed outcrop description of exposures and facies analysis. Facies associations comprise strata interpreted to be the deposits of the following environments: fluvio-estuarine channels, tidal channels, tidal flats, coastal plain channels and coastal floodplain/mire. The fluvio-estuarine channels deposits are characterised by high-energy conglomerate and coarse-grained sandstone that are strongly to weakly bioturbated with trace fossils belonging to the Skolithos and the depauperate Cruziana ichnofacies. The tidal channel deposit contains mud chips and mud lenses (at the base) and includes mud draped planar and trough cross-beds. The tidal flat deposit comprises sandy heterolithic sediments that are intensely burrowed. The coastal plain channel deposits are mud-filled channels, with sand sheets interpreted as splay deposits and variegated sandy claystone which has undergone pedogenic alteration. The floodplain and mire deposits are light grey mudstone and dark grey carbonaceous mudstone with plant remains and lignite. These depositional successions show a change from marine to non-marine conditions, interpreted to be a result of relative sea level changes. The architectural elements of the coastal plain succession are grouped into channelised, sandy cross-stratified and floodplain deposits. The channelised elements occur either as isolated or as multistorey channel deposits. Sequence stratigraphic interpretation reveals one depositional sequence with a sequence boundary and an erosive transgressive surface of erosion identified by the occurrence of the Glossifungites ichnofacies with sharp, erosive contacts.

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.

Tubular tempestites from Jurassic mudstones of southern Poland

This paper presents tubular tempestites from southern Poland and their application for environmental and sequence stratigraphy interpretation. Tubular tempestites are present in muddy successions of the Lower Jurassic Ciechocinek Formation and in the Middle Jurassic Częstochowa Ore-Bearing Clay Formation in the Silesian-Kraków region. They occur as sand-filled tubes of Spongeliomorpha and Thalassinoides entrenched in the mudstone, which form two characteristic horizons. Tubes were emplaced in semi-consolidated substrate and filled with sand brought by storm-generated bottom currents. The trace fossils reveal features typical of Glossifungites ichnofacies associated firmgrounds, which record discontinuities in the stratigraphical record, linked with a depositional hiatus or condensation and erosion of the sea-floor. The coincidence of these horizons with early phases of regional transgressions suggests that they represent transgressive surfaces of erosion. Their limited spatial extent probably resulted from varying intensity of erosion, which locally scoured deeply down to already consolidated substrate, whereas in other places erosion was weaker or even absent, and thus it is not marked in the sedimentary record there.

Lithostratigraphy and depositional history of Upper Ordovician and lowermost Silurian sediments recovered from the Qusaiba-1 shallow core hole, Qasim region, central Saudi Arabia

Lithostratigraphy and depositional history of Upper Ordovician and lowermost Silurian sediments recovered from the Qusaiba-1 shallow core hole, Qasim region, central Saudi Arabia

Lithofacies and sequence stratigraphic framework of the Kockatea Shale, Dandaragan Trough, Perth Basin

Initial studies affirm large-scale shale-gas potential for the Permo-Triassic intervals of the Perth Basin. The Dandaragan Trough, as a major depocentre in the basin and with the highest number of wells intersecting these intervals, has possibly the greatest shale-gas potential in the area. The primary self-contained shale-gas system proposed for the Dandaragan Trough is in the basal Kockatea Shale (Hovea Member), which was deposited during the Late Permian-Early Triassic. Seven lithofacies have been identified in a continuous 35 m core from the Hovea Member of the Kockatea Shale at Redback–2. Among recognised lithofacies, besides siliceous mudstone, which contains clastic particles, most are representative of deposition in a shallow marine environment with different energy levels. Bioturbated lithofacies reveal deposition in a higher-energy environment compared with the other lithofacies. The sequence stratigraphic framework of the Hovea Member is established based on diagnosis of the lithofacies, cyclical stacking patterns, transgressive surfaces of erosion (TSE), and condensed sections (CSs). The framework supports deposition mainly in an aqueous environment with rare regressions. Periodic tectonic activity can be revealed in high-frequency relative sea-level changes during Hovea Member deposition. Gamma ray (GR) log analysis indicates that the highest GR peak is related to black-shale lithofacies with 1.75% TOC content. The greatest amounts of TOC, however, exist in the fossiliferous mudstone and pyritic mudstone lithofacies. A north–south GR correlation of the Hovea Member shows nearly the same lithological distribution throughout the trough despite its thinning in various areas.

Dispersal Patterns of the Late Cretaceous to Early-Tertiary Sediments in the Southern Anambra Basin, Southeastern Nigeria

The dispersal patterns of the Late Cretaceous to Early Tertiary sediments in southern Anambra Basin were studied to delineate spatial facies distributions for improved mapping and hydrocarbon prospectivity. Seven lithofacies distinguished from eleven outcrop sections aided the interpretation of depositional environments for the different depositional units. Interpreted paleoenvironments ranged from estuarine/lagoonal to tidal delta and shallow marine depositional environments. Sequence stratigraphic interpretation of the deposits using vertical relationships between the delineated facies and foraminiferal and palynofacies assemblages and the interpreted environmental setting identified two complete sequences (SEQ-1 and -2) and two incomplete sequences (SEQ-3 and -4) in the study area. The sequiences are enveloped by three Type-1 Sequence Boundaries (SB), two Transgressive Surfaces of Erosion (TSE) and four Maximum Flooding Surfaces (MFS). The identified surfaces were used to delineate formation boundaries and as such would assist in the improved mapping of the Anambra Basin and adjoining depocenters. The massive sand units of the Highstand and Transgressive Systems Tracts constitute good (potential) reservoirs, while the transgressive shales would constitute seals for potential traps in the study area. The delineation of these petroleum system elements, especially those associated with the Transgressive and Highstand Systems Tracts has conferred great hydrocarbon prospectivity potential on the sedimentary sequences in the Basin. The absence of deep marine and slope complexes of the Lowstand Systems Tract (LST) in the interpreted sequences is indicative that the study area is the up-dip section of the Anambra Basin.

Integrated Ichnology, Sedimentology and Stratigraphy of the Lower Cretaceous Sparky Alloformation (Mannville Group), Lloydminster Area, west-central Saskatchewan, Canada

Abstract The Lower Cretaceous Sparky Alloformation in the Lloydminster area of Saskatchewan, Canada consists of a complex succession of deltaic and marginal-marine deposits reflecting progradation towards the north and northwest (N-NW). The bounding discontinuities used to delineate the Sparky Allomember correspond to marine flooding surfaces (FS). Based on the integration of ichnological and sedimentological characteristics of succession, ten discrete facies have been identified. These are combined into five recurring facies associations. Facies Association 1 (FA1) comprises sediments deposited below fairweather wave base but above storm wave base. Facies associations 2 and 3 (FA2 and FA3) coarsen upward and represent the progradation of wave- and storm-dominated shorefaces as well as mixed river- and wave-influenced deltas, respectively. Facies Association 4 (FA4) typically cuts through FA3, and displays a fining-upward trend, and is interpreted as distributary channel deposits. Complete cycles of FA2 and FA3, wherein the tops of the cycles have not been removed by downcutting channels, are capped by coastal plain/delta plain deposits of Facies Association 5 (FA5). The Sparky Alloformation terminates at an upper contact marked by renewed marine transgression and the formation of a regionally extensive transgressive surface of erosion (TSE). Three coarsening-upward cycles are identified within the Sparky Alloformation, each bounded by allogenically produced flooding surfaces. These units, termed Lower, Middle and Upper allomembers, are characterized by wave- and storm-dominated shorefaces and associated mixed river-and wave-influenced deltaic successions reflecting progradation towards the N-NW. The Sparky Alloformation consists of sediments deposited during periods of pronounced progradation and corresponds to a highstand systems tract.