Transgressive Phase Research Articles

Middle Triassic carbonates of Eastern Iberia (Western Tethyan Realm): A shallow platform model

Much of the eastern sector of the Mesozoic Iberian basin belongs to the ‘Mediterranean type’ Triassic. This type is characterized by a Middle Triassic stratigraphic record comprised of two carbonate Muschelkalk units (lower and upper) separated by a detrital-evaporite middle Muschelkalk unit. In the present study areas, the two first marine flooding episodes of the Middle Triassic led to the deposition of extensive shallow-water carbonates on a block-controlled epicontinental platform in the lower and upper Muschelkalk units. These carbonates were part of third-order transgressive–regressive sequences. The two carbonate sequences display similar vertical facies and stratigraphic sub-unit arrangements. The base of the two sequences is marked by a (lower) carbonate-marl alternation, which was deposited in mixed tidal flat-to-lagoon settings. In the middle of the sequences, the carbonate character is predominant and facies associations mainly suggest shallow waters and high environmental variability. The change from a transgressive to regressive trend occurs in the middle of the sequences, although the position of the maximum flooding zone can vary from one to another stratigraphic section. The tops of the sequences show two different lithological assemblages, which are coeval and grade laterally to each other. One assemblage is a ‘carbonate terminal complex’ formed by tidal flat and sabkha deposits, which is predominant in the lower Muschelkalk unit. The other assemblage is a lagoon-peritidal (upper) carbonate-marl alternation, predominant in the upper unit. Together, the two sequences suggest a complex platform morphology with a mosaic facies distribution, which evolved from a not very high energy ramp-like profile (transgressive phases, TST) to a lower energy rimmed shelf, ending with tidal/lagoon environments (regressive phases, HST). Facies associations, however, suggest somewhat deeper depositional settings for the upper than lower Muschelkalk unit. Here we compare the two carbonate units in the study areas with those described in the literature from other Triassic basins of Eastern Iberia and the SW Germanic Basin, all forming part of the Peri-Tethys area of the Tethyan Realm.

Environmental changes related to the Holocene sea-level transgression and successive highstand (7–5.5 Kyr) at the NE coastal plain of Buenos Aires (Argentina)

We present a high resolution multi-proxy study about environmental changes that occurred during the Holocene sea-level transgression and successive highstand (7–5.5 Kyr) in the central zone of Bahía Samborombón (∼35.6° S), Argentina. This study, one of the first in the area that integrates geomorphological and paleontological proxy data (pollen, non-pollen palynomorphs, foraminifera and mollusk shells), and focusing on a short time interval, offers the advantage of recognizing environmental and vegetation changes in a more comprehensive way. The aim of this work is to reconstruct the salt marsh vegetation history and paleoenvironmental changes; and to develop a model of the geomorphological evolution during the mid-Holocene sea-level transgressive phase. Between 6700 cal yr BP and 6500 cal yr BP, several rapid environmental changes took place. Those changes affected vegetation and microfauna, as well as the geomorphological features. During this period, middle to high salt marsh vegetation developed in an extensive and open tidal plain, where wide and long paleo tidal channels were flowing. Between 6500 and 6220 cal yr BP, the salt marsh transitioned into low salt marsh one as a response to a continued rise in sea level, resulting in the landward transgression of the coastline. The relative sea level reached the highstand between 6220 and 5500 cal yr BP and, consequently, extensive inundation of the coastal plain took place, except for the elevated areas such lunettes and ridges. After 5500 cal yr BP, seaward prograding beach and sand ridges formed in response to the onset of a regressive phase. Since then, the ancient tidal plain, extending ∼10 km from the present coastline, has been subjected to aeolian and pedogenetic processes.

Depositional dynamics of the Devonian rocks and their influence on the distribution patterns of liptinite in the Sifa-1X well, Western Desert, Egypt: Implications for hydrocarbon generation

Samples from the Devonian succession in the Sifa-1X well located mid-way between the Egyptian Faghur Basin and the Libyan Cyrenaica Platform were examined in this study. The distribution of liptinite group macerals was investigated under reflected and transmitted light microscopy. Diverse and abundant liptinites of terrigenous and marine origin were identified. The palynological investigations included analysis of the miospores assemblages and palynofacies categories by multiple statistical approaches in addition to calculation of the sedimentation rates. These analyses signified four miospores biotopes and three palynofacies biotopes that were used to assess the ramps of paleoclimatological and paleoenvironmental changes during sedimentation. These biotopes were used to define a model of liptinite maceral distribution throughout the Devonian in the study area. The model suggested two different phases of basinal dynamics in terms of climate, sea level, and sedimentation rates, namely an Early-Middle Devonian transgressive phase and a Late Devonian regressive phase. Conditions during the Early-Middle Devonian transgressive phase were oxic to dysoxic with low sedimentation rates and oxic during the Late Devonian regressive phase. Oxygen depletion was under the threshold required to induce significant preservation of the quantity and quality of organic matter, including liptinite macerals. The redox conditions were confirmed by trace element analysis. The high oxygen level affected both the quantity and quality of the liptinite macerals and greatly reduced the preservation of the amorphous organic matter. The quality of the organic matter varied from kerogen type I, II, mixed types II/III and type III. The mixture of these kerogen types was assessed by organic elemental and pyrolysis gas chromatography analyses. In addition, the entire Devonian succession in the Sifa-1X well is in the oil window, as also indicated by miospore coloration. This indicates that the organic matter in the Devonian strata have the potential to generate oil and gas.

Stratigraphy of the Gorstian and Ludfordian (upper Silurian) Hemse Group reefs on Gotland, Sweden

ABSTRACT The Hemse Group is one of the least understood stratigraphic units of the Silurian sequence of Gotland, Sweden. New results from airborne transient electromagnetic (ATEM) measurements in combination with previously published data from field studies and geophysical investigations shed new light on carbonate platform development during the early- to mid-Ludlow Hemse Group. ATEM reveals a transgressive phase that began near the Wenlock-Ludlow boundary, which resulted in deposition of marls and corresponds roughly to the Hemse limestone units a-c and the Hemse Marl NW. In this phase little or no reef development occurs. The end of the transgressive phase coincides with the weak Linde Event. The following highstand favoured extensive reef growth forming a reef barrier system of both fringing reefs and more rampiform settings with stromatoporoid biostromes and occasional biohermal buildups. The Kuppen-Snabben Unconformity Complex marks an erosional (karstic) sequence boundary and rocky shoreline and the transition from a rampiform setting with reef biostromes towards a more rimmed setting with patch reefs.

Maastrichtian–Paleocene sequences at Dakhla-Abu Minqar District, Western Desert, Egypt: stratigraphical and paleoenvironmental framework

Integrated lithostratigraphic and biostratigraphic data of two well-exposed Maastrichtian–Paleocene successions, namely, the Owina and the Abu Minqar sections (Dakhla Oasis, Western Desert, Egypt), led to enhance the age resolution and shed lights on the paleoenvironmental conditions throughout the deposition of the investigated sequences. The integrated biostratigraphic data provide eight calcareous planktonic zones (five planktonic foraminifera, and three calcareous nannofossil zones) cover the studied interval. The paleoenvironmental setting of the Maastrichtian interval which represented by the lower Kharga Shale unit (Micula murus and Gansserina gansseri calcareous plankton zones) reveals shallow marine environmental conditions of inner neritic probably of marginal setting with high organic matter influx and low-oxygen level interrupted by some transgressive phases. While, shallower marine conditions associated with a sea-level drop mark the Cretaceous/Paleogene (K/Pg) boundary. The lowermost part of the Paleocene interval (NP3, NP4, P1b, P1c, and P2 calcareous plankton zones) which covered the lower part of the upper Kharga Shale unit is marked by middle-outer neritic depositional setting, well-oxygenated seawater, as well as a low organic matter influx coupled with relative sea-level rise. Above this level until reach the base of the Tarawan Formation, a major drop in the sea-level is observed. This interval is marked by absence of the calcareous planktonic taxa. Only agglutinated foraminiferal taxa are recorded during this interval. While the Tarawan Formation (P4b planktonic foraminiferal Zone) is marked by outer neritic depositional setting that represents a sea-level transgressive phase. According to the field observations and the presence/absence of the calcareous planktonic zonal marker species; two tectonic events are detected. The tectonic event I took place at the K/Pg boundary and resulted in a significant hiatus at the studied area. Tectonic event II is observed at the contact between the Dakhla and the Tarawan formations across the Danian–Selandian transition. It is evidenced by the existence of an erosive (irregular) surface at the basal part of the Tarawan Formation. These events could be attributed to the echo of the Syrian Arc tectonism which interrupted the global sea-level curve throughout the Maastrichtian–Paleocene time.

The turnaround from transgression to regression of Holocene barrier systems in south‐eastern Australia: Geomorphology, geological framework and geochronology

AbstractHolocene regressive strandplains that preserve a series of former shorelines are extensive on coasts that were remote from major Pleistocene ice sheets (for example, Australia and Brazil), whereas transgressive barrier islands are typical in glacial forebulge regions (for example, North America and Europe). In strandplains, the regressive phase of strandline development was preceded by a transgressive phase during the final stages of postglacial sea‐level rise. This study examines the turnaround from transgression to regression through chronostratigraphic description of three barrier systems in south‐eastern Australia: Seven Mile Beach, Bengello Beach and Pedro Beach. The authors reconstruct geomorphic and depositional histories using ground‐penetrating radar and vibracores along transects across the landwardmost ridges, and optically‐stimulated luminescence and radiocarbon dating. At the Seven Mile Beach barrier system, extensive washover deposits are preserved that include distinctive, landward‐directed, flame‐shaped washover fans along the bayside shoreline of the landwardmost ridge. Landward‐dipping ground‐penetrating radar reflections in radargrams provide evidence of the culmination of the transgressive phase and transition into the regressive phase dominated by progradation, evidenced by the change to seaward‐dipping reflections. A similar progradational plain formed at the Bengello Beach barrier system, but transgressive deposits are largely absent at the site investigated, where an eroded headland created limited accommodation space until sand supply was sufficient for progradation. The Pedro Beach barrier system depositional history is more complex. There, a smaller embayment filled rapidly during the mid‐Holocene, and transgressive sands were deposited as sea level reached its present level and impounded a wetland. Accommodation space in the embayment was filled by ca 4000 years ago. Overall, results indicate that the Holocene turnaround transition occurred between 8400 and 7000 years ago, and was preserved at the landward margin of these three strandplains. Holocene morphostratigraphy differs among sites primarily as a function of sea level, sediment supply and antecedent topography.

Lithological attributes of hd-001 well, shallow offshore, Niger delta basin, Nigeria

Lithological analysis was carried out on 96 ditch cuttings samples from HD-001 well located within the shallow offshore Niger delta basin, Nigeria. Three lithofacies sequences were delineated by the integration of wireline logs textural/lithologic attritudes and the distribution of index accessory minerals. They are transitional paralic, paralic and marine paralic sequences. The lithologic, textural and wireline log data indicate that the entire interval studied in the HD-001 well belongs to the Agbada Formation. The Formation is made up of alternating sand and shale units which suggests rapid shoreline progradation. The grain size increases from essentially fine to medium-grained at the basal part of the well to dominantly coarser grain at the upper part. The index accessories recognize shallow marine to coastal deltaic settings environment of deposition. Sand bodies which represent sub-environments within those settings are deposited in sequences. Each sequence begins with a transgressive phase followed by significant regressions.  Â

Holocene progradation and retrogradation of the Central Texas Coast regulated by alongshore and cross‐shore sediment flux variability

AbstractFifteen transects of sediment cores located off the central Texas coast between Matagorda Peninsula and North Padre Island were investigated to examine the offshore record of Holocene evolution of the central Texas coast. The transects extend from near the modern shoreline to beyond the toe of the shoreface. Lithology, grain size and fossil content were used to identify upper shoreface, lower shoreface, ebb‐tidal delta and marine mud lithofacies. Interpretations of these core transects show a general stratigraphic pattern across the study area that indicates three major episodes of shoreface displacement. First, there was an episode of shoreface progradation that extended up to 5 km seaward. Second, an episode of landward shoreline displacement is indicated by 3–4 km of marine mud onlap. Third, the marine muds are overlain by shoreface sands, which indicates another episode of shoreface progradation of up to 5 km seaward. Radiocarbon ages constrain the onset of the first episode of progradation to ca 6.5 ka, ending at ca 5.0 ka when the rate of sea‐level rise slowed from an average rate of 1.6–0.5 mm/yr. Results from sediment budget calculations and sediment transport modelling based on reasonable estimates of an ancient shoreline shape and wave climate indicate that the first progradation was a result of sand supplied from erosion of the offshore Colorado and Rio Grande deltas. The transgressive phase occurred between ca 4.9 ka and ca 1.6 ka and coincided with a major expansion of the Texas Mud Blanket, which resulted in burial of offshore sand sources and the shoreface being inundated with mud. The second, more recent episode of shoreface progradation began ca 500 years ago with a maximum rate of ca 6 m/yr. This most recent change signals a healing phase of coastal evolution from the late Holocene transgressive event. Currently, the shoreline along the central Texas coast is retreating landward at an average rate of 0.30 m/yr, indicating that the second progradation event has ended.

Sedimentology and Palaeoenvironmental Reconstruction of the Early Cambrian Kussak Formation, Salt Range, Pakistan

Comprehensive sedimentological and sequence stratigraphic analyses of the Kussak Formation were carried out at the Nilawahan Gorge, the Karuli Section and the Khewra Gorge, Pakistan. The studied Kussak Formation has been grouped into: (1) bioturbated mudstone, (2) interbedded sandstone/shale, (3) sandy dolomite, (4) glauconitic sandstone and (5) laminated sandstone and siltstone. Hard to friable sandstone is present with condensed neobolus beds in the mud at the top. Bioturbation and glauconite are in middle parts, while a few beds of sandy dolomite are also present in the upper and middle parts of the Kussak Formation. These five depositional sequences had developed during the phase of transgression. Mineralogically, the average modal composition classifies it as quartz arenite. Rock fragments belong to the igneous origin, and feldspar grains most likely indicate an igneous and metamorphic source. The field and petrographic study indicate that the source area belongs to arid and semi-arid environments. Presence of wavy and flaser bedding indicates tidal flat deposition. Burrows, mud cracks, and synaeresis cracks indicate supra-tidal environment. Subsurface data show the finning upward sequence that confirms the deposition during transgression. In summary, the environment of deposition is subtidal, intertidal to supra-tidal environment. Palaeogeographic setting shows that the Kussak Formation source belongs to Aravalli and Malani ranges.

Late Quaternary landscape evolution of the buried incised valley of Concordia Sagittaria (Tagliamento River, NE Italy): A reconstruction of incision and transgression

While recent landscape changes can be usually easily read through accessible morphological features, relatively ancient processes can be difficult to detect as the associated morphologies and deposits are often buried below younger sediments. With the aim of understanding the evolution of the distal Venetian-Friulian Plain (NE Italy) after the Last Glacial Maximum (LGM), this work presents the analysis performed on a dataset of ca. 2300 mechanical and hand-made cores, which allowed a detailed reconstruction of the formation and evolution of an incised valley, now almost completely filled and with little to absent morphologic expression. Such valley, up to 1.2 km wide, with a depth of 20 m below the LGM alluvial plain and traced for a length of 25 km, is the result of the complex interplay between minor spring-fed rivers and the Tagliamento River. The detailed characterization of the infilling allowed to identify two main phases in the valley evolution. The first one is related to the activity of the paleo Tagliamento River and led to the deposition of a 10 m thick gravelly unit (ca. 19–9.5 ka cal BP). The second phase, which followed a disconnection of the Tagliamento, is linked to the Holocene marine transgression and led to the formation of a lagoon environment within the valley and to the deposition of a ca. 15 m thick unit of lagoon muds (ca. 8 ka cal BP - historic time). This latter unit lays on top of gyttja deposits, indicating for the first time in this area the presence of widespread lacustrine environments in the Early Holocene. This work presents an in-depth analysis on the evolution of a distal plain incised valley, from its formation to its final filling, providing at the same time the means to describe the development of the entire alluvial plain landscape, spanning from the end of the LGM to the middle Holocene. We present new data on the paleoenvironmental and morphologic evolution of the Venetian-Friulian Plain area as a consequence of the interplay between autogenic forces and sea-level rise. Our study allowed to understand the importance of both Alpine rivers and groundwater-fed streams in the formation of large incised valleys in the coastal sector of the whole Venetian-Friulian Plain. Finally, as during the transgressive phase the upstream sediment input in the valley was almost absent, this study provides insights into facies and architecture of a rare example of downstream-controlled filling of an incised valley.

Depositional Environments in the Eastern Paratethys during the Final Middle Miocene Transgression (Kura Basin, Eastern Georgia)

The mineral composition and depositional environments of the Konkian in eastern Georgia (Kura trough, eastern Paratethys) corresponding to the Kosovian (13.65–12.829 Ma) in the Central Paratethys and the final Middle Miocene marine transgression in Paratethys are considered. Jurassic and Cretaceous volcanic rocks of the Lesser Caucasus (Adzhar–Trialet and Artvin–Bolnisi zones) were identified as the main provenances for the terrigenous material. Eight lithofacies types distinguished for the studied rocks characterize depositional environments with significant wave or submarine-fluvial influence. The change of depositional environment was controlled by the phases of transgression, as well as by the progradation and lateral migration of the prodelta. The development of depositional environment corresponds to the Konkian stratigraphic beds and reflects the main stages of the final Middle Miocene transgression in the Eastern Paratethys.

Paleoredox and Environmental Conditions of Southern Neo-Tethys Deposits in South Iraq (Yamama Formation) by Geochemical Indicators

A geochemical and environmental study was carried out for the sediments of the Southern Neo-Tethys Ocean, represented by the Yamama Formation (Berriasian-Valaganian) in southern Iraq. The formation has a particular reservoir importance. The typical WQ-220 and WQ-280 wells were selected from the West Qurna field. Data of Gamma-ray logs were used for 30 depths of the typical well. Ten core samples were analyzed by X-Ray Fluoresces and total organic matter from both wells. The results showed that shaliness was relatively low, with an average of 16.5%, leading to a decrease in the presence of clay minerals and trace elements because the environment of the Yamama Formation is relatively far away from the coast. Qualitative evaluation of clay minerals was carried out by thorium/potassium ratio, which showed the dominance of illite and smectite. This may be due to an increase in the salinity of the ocean at that time or because potassium bonds are strong enough to resist the diagenesis processes. The origin of shale in the Yamama Formation was studied using the relationship TiO2-MgO+Fe2O3; the sources were passive margin group, oceanic island arc and active continental margin. The redox potential of paleoenvironment was determined by the thorium/uranium ratio, which showed that the beginning of depositional environment was slightly oxidized, but with the increase of sedimentation, it turned into a reduced environment, which indicates a transgression phase of sea level. The results of euxinic affinity, based on the relationship between molybdenum and Total Organic Carbon (TOC), reflect dyoxic facies which is deposited in extremely low but non-zero oxygen content, while the upper was approaching anoxic facies zone. The paleoenvironment of the Yamama Formation was of restricted deep marine water (outer shelf - upper part of the benthic zone) which contained a marine transgression phase because of the opening of Southern Neo-Tethys Ocean in the Valanginian age.

Reconhecimento e mapeamento sísmico de paleocanais ao largo da Plataforma Continental Interna da ilha de Santa Catarina

As características do fundo e da sub-superfície rasa da plataforma continental interna adjacente à ilha de Santa Catarina foi mapeada a partir da interpretação de 27 perfis sísmicos os quais evidenciaram 8 estruturas sedimentares correlacionadas a antigos sistemas fluviais, logo, considerados como paleocanais. Os refletores acústicos identificados, que representam contatos entre estratos sedimentares, denominados de R1, R2 e R3, delimitam antigos cenários deposicionais e representam sistemas pretéritos de drenagem. Os paleocanais identificados mostraram-se fortemente associados às flutuações do nível do mar desde a fase transgressiva que teve início após o Último Máximo Glacial através do afogamento de desembocaduras fluviais e da planície costeira pretérita, até o posterior recobrimento por um lençol de areias transgressivas que conformou a atual plataforma continental adjacente à ilha de Santa Catarina.

Differentiation of subglacial conditions on soft and hard bed settings and implications for ice sheet dynamics: a case study from north-central Poland

We reconstruct patterns of subglacial processes on a hard bedrock and a soft bed under the southern sector of Scandinavian Ice Sheet (SIS) occurring in the basal till of the Late Saalian Glaciation at the Wapienno, Barcin and Młodocin sites (north-central Poland). Based on detailed sedimentological studies, two phases of SIS transgression were recognised. In the initial phase of the transgression, the SIS advanced onto a frozen substrate (continuous permafrost). The low permeability of the substratum led to a high subglacial water pressure (SWP) and increased basal sliding. The local increase of SWP led to the development of different types of structures and sediments. On a hard bedrock, with low SWP, abrasion predominated and linear structures were developing, while in the case of high SWP, the ice was decoupled from the hard substrate, pressurised liquefied sediment flowed, and structures of the p-form and s-form type developed. On a soft bed, the ice-bed contact was of a mosaic type and the ice movement had an ice-stream character. The ice-stream developed towards the east in the marginal zone of the SIS and used a W-E oriented valley filled by the Wapienno Formation fluvial complex. During a later phase, the ice movement was slower and did not have a stream character. Its direction changed to SE. The deposition of the main part of the diamicton occurred mainly as a result of the lodgement process.

Early Marine Isotope Stage 5 sea levels, coastal dune palaeoenvironments, and human occupation on the southeast coast of South Africa

Quaternary-age human and animal footprints have been reported from coastal deposits along the South African coast. These footprints and their sedimentary contexts can inform on Quaternary palaeoenvironments and processes stratigraphically associated with the palaeoanthropological record of past human occupation in the coastal zone, and exploitation of its resources. This study examines the palaeoenvironmental context and sedimentology of Marine Isotope Stage 5 aeolianite at Nahoon Point, southeastern coast of South Africa, where preserved human footprints have been previously recorded. This study identifies seven sedimentary facies from 20 logged profiles through the coastal aeolianite in order to develop a landscape-scale stratigraphic framework for coastal palaeoenvironmental reconstruction during the period of the MIS 5 highstand. Two phases of aeolianite deposition are identified, which bracket a single stepped sea-level transgression phase up to +7.82 ± 0.82 m asl, evidenced by intraformational beachrock facies and marine benches. This correlates with the second known global MIS 5e highstand; no evidence for the first highstand reported from the literature was found in the study area. Aeolianite bed geometries and sedimentary structures indicate that wind regimes and rainfall seasonality were similar to present. Newly discovered faunal tracks in aeolianites of the first depositional phase suggest the presence of unidentified bovids of varying sizes. Evidence for human activity is preserved in all three recorded depositional phases, suggesting people were present throughout the early MIS 5 sequence despite changing environmental conditions. This evidence suggests that human occupation of coastal areas, and the exploitation of marine food resources was more widespread than generally thought in southern Africa during early MIS 5.

Incised Valley Depositional System of the Cretaceous Yolde Formation of the Gongola Sub-basin Northern Benue Trough N.E. Nigeria

This research was carried out in the Gongola Sub-basin of the Northern Benue Trough aimed at deciphering of the paleo-depositional environment of the Yolde Formation based on facies on facies analysis. Six lithofacies were identified to include trough crossbedded sandstone facies (St), massive bedded sandstone facies (Sm), planar crossbedded sandstone facies (Sp), ripple laminated sandstone facies (Sr), parallel sandstone facies (Sl) and mudstone facies (Fm). These build into two facies association of fluvial channel and tidally influenced fluvial channel facies associations. The fluvial successions typical characterizes the lower stratigraphic horizons and their contained dominances of trough crossbedded sandstone facies with high channel to overbank facies and contained mud-clast reflecting deep, high energy braided river system. The submergences of these channels by surging sea level rise generated the tidally influenced fluvial facies association and this package characteristically defines the upper interval stratigraphic architecture of this formation, displaying occasional bi-directional current system and abundant marine ichnogenera. This architectural symmetry is reflective of an incised valley fills, developing as a consequence of Cenomanian transgressive phase induced by the mid-Cretaceous global marine transgression.

Incised Valley Depositional System of the Cretaceous Yolde Formation of the Gongola Sub-basin Northern Benue Trough N.E. Nigeria

This research was carried out in the Gongola Sub-basin of the Northern Benue Trough aimed at deciphering of the paleo-depositional environment of the Yolde Formation based on facies on facies analysis. Six lithofacies were identified to include trough crossbedded sandstone facies (St), massive bedded sandstone facies (Sm), planar crossbedded sandstone facies (Sp), ripple laminated sandstone facies (Sr), parallel sandstone facies (Sl) and mudstone facies (Fm). These build into two facies association of fluvial channel and tidally influenced fluvial channel facies associations. The fluvial successions typical characterizes the lower stratigraphic horizons and their contained dominances of trough crossbedded sandstone facies with high channel to overbank facies and contained mud-clast reflecting deep, high energy braided river system. The submergences of these channels by surging sea level rise generated the tidally influenced fluvial facies association and this package characteristically defines the upper interval stratigraphic architecture of this formation, displaying occasional bi-directional current system and abundant marine ichnogenera. This architectural symmetry is reflective of an incised valley fills, developing as a consequence of Cenomanian transgressive phase induced by the mid-Cretaceous global marine transgression.

“Seismic attributes and reservoir simulation’ application to image the shallow-marine reservoirs of Middle-Eocene carbonates, SW Pakistan”

Carbonates form brilliant stratigraphic traps. The execution of traditional seismic data interpretation using time and depth mapping generates ambiguities in the discrimination of porous and non-porous reservoir beds. In these stratigraphic circumstances, placement of development wells within the unproven prospects is a trial for exploration geophysicist. The 3D post-stack seismic attributes and quantitative seismo-petrophysical simulation (QSPS) are applied on Habib Rahi Limestone (HRL) Member from a gas field, SW Pakistan. 45 Hz spectral magnitude delineates the lithology, fractures, and geomorphology of gas-bearing shoal reservoir facies than full-spectrum seismic tools. 45 Hz predicts a north-east oriented gas-bearing stratigraphic lead, which covers an area of 105 km2. The QSPS reveals a very low-density (2–2.1 g/c.c.) and low-velocity (~2500–3000 m/s) of shoal reservoir. The high-quality shoal limestone reservoirs of HRL with ~30% porosity are deposited during the regression phase of sea-level fall in the east. The low-quality fine-grained seal facies with <9% porosity are deposited during the substantial transgression phase of sea-level rise in the west. The cross plots of seismic-based porosity (%) versus inverted velocity (m/s), inverted density (g/c.c), and reservoir thickness (m) show correlation coefficients of (R)2>0.92, (R)2>0.97, and (R)2>0.89. The coarse-grained gas-bearing reservoirs experience 31.8 m thickness and least density (2–2.1 g/c.c.) are deposited during sea-level fall. The 31.3 m thick and high-density (2.2–2.3 g/c.c.) fine-grained seal facies are deposited during sea-level rise. This workflow can serve as an analogue for the development of carbonate fairways within Asia and similar world basins.

Multi-Proxy Characterisation of the Storegga Tsunami and Its Impact on the Early Holocene Landscapes of the Southern North Sea

Doggerland was a landmass occupying an area currently covered by the North Sea until marine inundation took place during the mid-Holocene, ultimately separating the British landmass from the rest of Europe. The Storegga Event, which triggered a tsunami reflected in sediment deposits in the northern North Sea, northeast coastlines of the British Isles and across the North Atlantic, was a major event during this transgressive phase. The spatial extent of the Storegga tsunami however remains unconfirmed as, to date, no direct evidence for the event has been recovered from the southern North Sea. We present evidence of a tsunami deposit in the southern North Sea at the head of a palaeo-river system that has been identified using seismic survey. The evidence, based on lithostratigraphy, geochemical signatures, macro and microfossils and sedimentary ancient DNA (sedaDNA), supported by optical stimulated luminescence (OSL) and radiocarbon dating, suggests that these deposits were a result of the tsunami. Seismic identification of this stratum and analysis of adjacent cores showed diminished traces of the tsunami which was largely removed by subsequent erosional processes. Our results confirm previous modelling of the impact of the tsunami within this area of the southern North Sea, and also indicate that these effects were temporary, localized, and mitigated by the dense woodland and topography of the area. We conclude that clear physical remnants of the wave in these areas are likely to be restricted to now buried, palaeo-inland basins and incised river valley systems.

Paleogeographic, paleoclimatic and sea-level implications of glauconite deposits in Egypt: A review

Glauconite deposits are confined to the Western Desert in Egypt of four different sequences and ages from older to younger include, 1) Lower Cenomanian Bahariya Formation, 2) Lower-Middle Campanian Qusseir Formation, 3) Upper Campanian Duwi Formation, and 4) Lutetian-Bartonian Hamra Formation.Lower Cenomanian, Upper Campanian and Lutetian-Bartonian glauconites occur as pellets, while the Lower-Middle Campanian glauconite occurs as fine-grained particles of non-pelletal texture. Based on K2O contents, the Lower Cenomanian and Upper Campanian glauconites are classified as slightly evolved, while the Lower-Middle Campanian and Lutetian-Bartonian glauconite are categorized as evolved. Positive correlations between K2O and Fe2O3 in the Bahariya Formation, Qusseir Formation and Hamra Formation deposits suggest a layer lattice glauconitization mechanism for these deposits. On the other hand, the lack of correlation between Fe2O3 and K2O declines the layer lattice formational mechanism for the Duwi Formation glauconite. A neo-formation mechanism was suggested for this glauconite. Rare earth elements patterns are the same in the four deposits and resemble the shallow sweater pattern.The four glauconite deposits formed in shallow marine environments and might correspond to major eustatic transgressive and global warming events. Glauconite of the Bahariya Formation corresponds to the Early Cenomanian Tethys major transgression in Egypt and can be correlated to the Albian/Cenomanian global cycle boundary as well as the early Cenomanian “hot greenhouse”. The sequence boundary near the topmost part of the Qusseir Formation matches the global warming of the Middle Campanian Event (MCE). The upper Campanian glauconite of the Duwi Formation occurs as lowstand wedge and may correlate to the late Campanian climatic warm optimum. The stratigraphic position of the Hamra glauconite above the unconformity surface refers to transgressive phase that may match with latest Lutetian major sequence boundary (Lu4) and global warming event of the Middle Eocene Climatic Optimum (MECO).Paleogeographic maps show that the Western Desert of Egypt during Cenomanian and Lower Campanian covered by shallow marine setting, which match with the proposed setting for the glauconites in these ages. However, paleogeographic maps for the Upper Campanian and Middle Eocene were modified to fit with the suggested setting of glauconites of these epochs. The prevalence of shallow marine setting during these four ages interprets the restricted occurrences of glauconites at the Western Desert of Egypt during these epochs.