A Review of the Morphology, Physical Processes and Deposits of Modern Straits

This study reviews the morphology, hydrodynamics and sedimentology of 33 modern straits, including examples from diverse tectonic and climatic settings. Strait morphology ranges from short, simple straits to long, tortuous passages many 100s of kilometers long; depths range from 10 m to >1 km. The morphological building block of strait sedimentation is a constriction flanked by open basins; a single strait can contain one or several of these. Currents accelerate through the constrictions and decelerate in the basins, leading to a spatial alternation of high- and low-energy conditions. Currents in a strait can be classified as either ‘persistent’ (oceanic currents or density-driven circulation) or ‘intermittent’ (tidally or meteorologically generated currents). Constrictions tend to be bedload partings, with the development of transport paths that diverge outward. Deposition occurs where the flow decelerates, generating paired subaqueous ‘constriction-related deltas’ that can be of unequal size. Cross-bedding predominates in high-energy settings; muddy sediment waves and contourite drifts are present in some straits. In shallow straits that were exposed during the sea-level lowstand, strait deposits typically occur near or at the maximum flooding surface, and can overlie estuarine and fluvial deposits. The most energetic deposits need not occur at the time of maximum inundation.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5746061

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.

Sedimentology and ichnology of the mid-Cretaceous succession of Ouled Nail Mounts (Eastern Saharan Atlas, Algeria)

Shallow marine deposits characterize the upper Albian – lower Cenomanian deposits of Northern Algeria. In Djebel Azzeddine (Ouled Nail Mounts), the corresponding sediments have been subdivided into three distinctive units A to C. The first discovered ammonite fauna from the Bou Saada area allowed the attribution of a part of the mid-Cretaceous post-Continental Intercalaire deposits to the upper Albian. The ammonite-bearing level indicates a maximum flooding surface and could be correlated with similar levels from Northern Algeria. The studied succession is characterized by a low ichnodiversity containing eight ichnotaxa with abundant Thalassinoides, common Skolithos, and rare Gyrolithes, Oichnus, Planolites and cf. Tisoa. This ichnoassemblage is dominated by domichnion, fodinichnion and praedichnion trace fossils, and is attributed to the Skolithos and Glossifungites ichnofacies. These traces are produced mainly by decapod crustaceans, polychaetes and naticid gastropods. The sedimentological and ichnological data suggest shoreface to backshore environments with mixed tide/storm energy, and long subaerial exposures indicated by Lofer cyclothems in the lowermost part and dinosaur footprints in the upper part of the section.

Chronology of recent sedimentary infill of the Inner Río de la Plata Estuary, Argentina

The Inner Río de la Plata Estuary is a sedimentary depositional system that resulted from fluvial-deltaic activity. Gentle Pliocene–Pleistocene slopes make-up the northern side of the estuary whereas small cliffs of the same age constitute the southern side. A long coastal estuarine barrier developed at about 6000 years BP when the maximum flooding surface occurred. Attached to this barrier, and at a lower elevation, is a large strandplain (covering an area of about 2400 km2) which displays more than 220 beach ridges. In different areas, the dating indicates a periodicity of 13.4–13.7 years for the development of each beach ridge. These data are like the periodicity of the ENSO effects, which could be associated with the variability of Sunspots. These ridges were formed shortly after the maximum flooding surface, which was followed by a gradual fall in sea-level that contributed significantly to the Inner Río de la Plata Estuary sedimentary infill. In addition, ENSO activities were probably instrumental in the distribution of the main geoforms in the Inner Rio de la Plata Estuary. Small deltas, which were generated by other rivers and creeks such as the Nogoyá Arroyo and the Gualeguay River, developed coevally with the coastal estuarine barrier. The Ibicuy Delta grew in the middle of the inner Río de la Plata Estuary when the former Paraná River flowed northwards during the sea-level fall. The upper part of the delta front was reworked, giving rise to a large dunefield. Thereafter, a chenier plain developed along with tidal flats. The current Paraná Delta continues to prograde at a rate of about 56–64 m/year (m year−1). The sedimentary infill of the Inner Río de la Plata Estuary occurred along the Holocene.

Biostratigraphy and sequence stratigraphy of the Toarcian Ludwigskanal section (Franconian Alb, Southern Germany)

Extensive construction work at the canal cutting of the Ludwigskanal near Dörlbach, Franconian Alb, provided the opportunity to re-investigate a scientific-historical and biostratigraphically important reference section of the South-German Toarcian. The 16 m thick section, described bed by bed with respect to lithology and macrofossils, starts within the Upper Pliensbachian Amaltheenton Formation, covers the Toarcian Posidonienschiefer and Jurensismergel Formation, and ends in basal parts of the Opalinuston Formation. Carbonate contents are high in the Posidonienschiefer and successively decline within the Jurensismergel to basal parts of the Opalinuston. The high carbonate contents in the Posidonienschiefer are associated with comparatively low organic carbon contents. However, organic carbon contents normalized to the silicate fraction are similarily high if compared to other regions in Germany. Only the persistence of high organic carbon levels into middle parts of the Upper Toarcian differs from those of most regions in central Europe. Ammonite biostratigraphy indicates a thickness of >9 m for the Upper Pliensbachian, 1.15–1.20 m for the Lower Toarcian, 5.04 m for the Upper Toarcian, and >0.5 m for the Lower Aalenian. Despite the low sediment thickness, all Toarcian ammonite zones and almost all subzones are present, except for major parts of the Tenuicostatum Zone and the Fallaciosum Subzone. On the basis of discontinuities, condensed beds, and correlations with neighbouring sections in Southern Germany, a sequence stratigraphic interpretation is proposed for the Toarcian of this region: (i) The Posidonienschiefer Formation corresponds to one 3rd order T-R sequence, from the top of the Hawskerense Subzone to a fucoid bed at the top of the Variabilis Subzone, with a maximum flooding surface at the top of the Falciferum Zone. (ii) The Jurensismergel Formation exhibits two 3rd order T-R sequences: The first ranges from the basis of the Illustris Subzone (i.e., the Intra-Variabilis-Discontinuity) to the top of the Thouarsense Zone, with a maximum flooding surface within the Thouarsense Zone. The “belemnite battlefield” reflects a transgressive “ravinement surface” within the first Jurensismergel Sequence, not a maximum regression surface at its basis. The second sequence extents from the erosive basis of the Dispansum Zone to the top of the Aalensis Subzone, with a maximum flooding surface at the Pseudoradiosa-Aalensis Zone boundary. Finally, the Opalinuston starts with a new sequence at the basis of the Torulosum Subzone. Transgressive system tracts of these 3rd order T-R sequences are commonly phosphoritic, while some regressive system tracts show pyrite preservation of ammonites. The maximum regression surfaces at the basis of the Toarcian and within the Variabilis Zone reflect a significant submarine erosion and relief formation by seawater currents, while this effect is less pronounced at the basis of the Dispansum Zone and basis of the Torulosum Subzone (i.e., the boundary Jurensismergel-Opalinuston Formation).

Mississippian Meramec Lithologies and Petrophysical Property Variability,STACK Trend, Anadarko Basin, Oklahoma

Mississippian Meramec reservoirs of the STACK (Sooner Trend in the Anadarko [Basin] in Canadian and Kingfisher counties) play are comprised of silty limestones, calcareous siltstones, argillaceous-calcareous siltstones, argillaceous siltstones and mudstones. We found that core-defined reservoir lithologies are related to petrophysics-based rock types derived from porosity-permeability relationships using a flow-zone indicator approach. We classified lithologies and rock types in non-cored wells using an Artificial Neural Network (ANN) with overall accuracies of 93% and 70%, respectively. We observed that mudstone-rich rock type 1 exhibits high clay and low calcite while calcareous-rich rock type 3 has high calcite and low clay content with rock type 2 falling in between rock types 1 and 3. Results of the ANN were applied to a suite of well logs in non-cored wells in which we generated lithology and rock-type logs. We identified that the Meramec consists of seven stratigraphic units characterized as strike-elongate, shoaling-upward parasequences; each parasequence is capped by a marine-flooding surface. The lower three parasequences (lower Meramec) form a retrogradational parasequence set that back-steps to the northwest and is capped by a maximum flooding surface. The upper Meramec is characterized by parasequences that form an aggradational to progradational stacking pattern followed again by a retrogradational trend. We predict that the parasequence stacking, associated lithology distribution, and diagenetic cements appear to control the spatial distribution of petrophysical properties (porosity, permeability, water saturation), pore volume, and hydrocarbon pore volume (HCPV). Calcareous-rich lithologies exhibit lower porosity, permeability, and HCPV and higher water saturation. Argillaceous-rich lithologies that occur near the maximum flooding surface are the most favorable reservoir intervals as they exhibit relatively higher porosity, permeability, HCPV, and lower water saturation. Productivity could not be directly correlated to rock types as operational and completion factors along with overpressure and oil phase play important roles on production.

Benthic foraminiferal assemblages from maximum flooding surface J30, Middle Jurassic Dhruma Formation, Central Saudi Arabia

ABSTRACT: The benthic foraminiferal have been studied from mudstone-wackestones of the D5 Unit of the Dhruma Formation that represent the Middle Jurassic J30 maximum flooding surface of Sharland et al. (2001). The benthic assemblage consists of a mixture of smaller agglutinated species, Haplophragmoides, Kutsevella, Sculptobaculites, Trochammina), and calcareous species (Nautiloculina, nodosariids, ophthalmidiids, polymorphinids, and spirillinids) without any larger foraminifera. The assemblage is indicative of open-marine midshelf conditions, and contains a number of cosmopolitan taxa that are known from the Middle Jurassic in other areas of the Tethys. The recovery of open-marine and cosmopolitan smaller benthic foraminifera in the D5 Unit of the Dhruma Formation provides a new tool for identifying the J30 maximum flooding surface and correlating the interval with other regions of the Tethys.

Sequence stratigraphy of the late Carboniferous Clifton Formation, New Brunswick

The Maritimes Basin of Atlantic Canada contains a rich record of Pennsylvanian cyclothems. Previous studies have focused on rapidly subsiding depocenters in the central part of the basin where Carboniferous successions feature cyclic alternations between terrestrial and marginal marine strata. In contrast, the Pennsylvanian Clifton Formation was deposited on the relatively stable New Brunswick platform and contains almost entirely terrestrial strata. Although early studies of the Clifton Formation noted a cyclic architecture, particularly within Member B, this unit has remained understudied. We provide a sedimentological and sequence stratigraphic framework for the lower 85 m of Member B and interpret our results relative to a broader regional framework. Near the base of the study interval, the highstand systems tract is composed of red floodplain mudrocks; overlying sequence boundaries are composed of calcretes and (or) channels. The transgressive systems tract and maximum flooding surface are represented by coals and aquatic bivalve-bearing mudrocks. Moving upward through the section, the architecture of the highstand systems tract remains largely unchanged while sequence-bounding paleosols become less well developed, the transgressive systems tract becomes thinner and eventually not preserved, and the maximum flooding surface is only occasionally preserved, possibly represented by carbonaceous shales. These changes in cyclic architecture may be attributed to changes in the magnitude of glacioeustatic fluctuations, climate, and (or) the accommodation/sediment supply ratio. The results of this study show that the Clifton Formation represents the terrestrial/proximal endmember for cyclicity in the Maritimes Basin and provide new insight into paleotopography as a possible control on cyclothem architecture.

Sequence Stratigraphy Analysis Based on Wireline Log, Mudlog, and 2D Seismic of GHC Field, Baong Formation, Aru Sub Basin, North Sumatra Basin

The Baong Formation is one of the formations that has hydrocarbon potential in the Aru Sub Basin, North Sumatra Basin (Figure 1). However, geological information in that area is still far less than is available in others. Analysis of sequence stratigraphy needs to be done to enrich geological information of the study area, maximize the results of exploration before exploitation, and make it easier to find the distribution of potential layers of oil and gas. Methods that are used in this research are electrofacies analysis to show the appearance of rock grain size and geological processes that affect its formation, Well Seismic Tie and interpretation of the horizon along with structures to produce a Time Structure Map, and correlate the sequences in log wells and 2D seismic cross section to know the same area of each sequence. Based on third-order sequence, the Baong Formation was divided into two types of system tract, such as Lowstand System Tract (LST) and Transgressive System Tract (TST). Maximum Flooding Surface (MFS) as the lower boundary of LST, Transgressive Surface (TS) as the boundary between LST and TST, and Maximum Flooding Surface as the upper boundary of TST. Based on fourth-order sequence, each of the system tracts was divided into seven parasequences with Flooding Surface as the boundary. The research area can also be interpreted into a conceptual model of a hydrocarbon system.