| 1. |
- Fredin, Ola, et al.
(författare)
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Relict lateral moraines in northern Sweden : evidence for an early mountain centered ice sheet
- 2002
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Ingår i: Sedimentary Geology. - 0037-0738 .- 1879-0968. ; 149:1-3, s. 145-156
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Tidskriftsartikel (refereegranskat)abstract
- Glacial geomorphology along the eastern rim of the Scandinavian mountain range includes glacial landforms from the last deglaciation as well as from earlier glacial stages. One of the most prominent landform groups from earlier glacial stages, and the most diagnostic for ice sheet reconstruction, is a set of lateral moraines. In this paper, we describe these lateral moraines within a key area around Kvikkjokk, northern Sweden. Position of these lateral moraines in relation to the last deglaciation patterns indicates that they were formed before the last glacial maximum (LGM). The location and morphology of moraines show that they were deposited by a mountain centred ice sheet with outlet glaciers along major valleys, emanating from the highlands west of the Kvikkjokk area. This ice sheet was likely less than 170-km wide and no more than 600-m thick. Climatologically and glaciologically, we expect the relict lateral moraines to have been deposited before 75 ka BP (marine oxygen isotope stage 4). Their preservation is a consequence of subsequent overriding of nonerosive cold-based ice. Ice-marginal landforms and deposits from mountain centred ice sheet configurations in Fennoscandia are scarce. Therefore, the relict lateral moraines are important tools for reconstructing these elusive early glacial stages, possibly correlated to the ice sheet inception.
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| 2. |
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| 3. |
- Egenhoff, Sven, et al.
(författare)
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Sedimentology and sequence stratigraphy of a pronounced Early Ordovician sea-level fall on Baltica - The Bjorkasholmen Formation in Norway and Sweden
- 2010
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 224:1-4, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- The Bjorkasholmen Formation consists of interbedded carbonates, shales, and glauconitic beds and is characterized by heavy bioturbation and few preserved sedimentary structures. The unit shows five facies shale, glauconitic packstone, and three predominantly mud-dominated carbonate facies. Carbonates and shales are arranged in small-scale deepening-upward cycles. A minimum of fourteen of these small-scale cycles are recognized in the Bjorkasholmen Formation. They are arranged in stacks of 3 to 5, forming a total of four medium-scale cycles separated by decimeter-thick shale units. Based on the predominance of mud-rich facies the succession is interpreted to have been deposited in an overall tranquil setting during one mayor sea-level fall and subsequent initial rise of third order. Time-estimates suggest that the 14 small-scale cycles fall into the Milankovitch band of precessional forcing, and the overriding medium-scale cycles likely represent short eccentricity. The sequence stratigraphic interpretation shows that the Bjorkasholmen Formation is characterized by failing stage, lowstand and initial transgressive systems tracts. Consequently, the contact between the Bjorkasholmen and the underlying Alum Shale Formation represents the basal surface of forced regression. The maximum regressive surface is defined by a hiatus in the Oland sections and by shallow-marine packstones within mud-rich distal ramp carbonates in Norway. The top of the Bjorkasholmen Formation represents a flooding surface at the base of the transgressive systems tract. A comparison of time-equivalent successions worldwide suggests that the Bjorkasholmen Formation represents a tectonically-enhanced lowstand with two overriding short-term Milankovitch eustatic signals. Although deposition of the Bjorkasholmen Formation coincides with the initiation of a foreland basin in the Caledonides of Norway it remains unclear how these tectonic movements may have lead to the widespread Bjorkasholmen lowstand during the Early Ordovician. It is Suggested in this Study that a combination of compressional forces from Avalonia and the Caledonian margin may have acted in concert to produce an uplift of larger parts of the Baltica plate for a time-span of approximately 0.5 Myr.
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| 4. |
- El-ghali, Mohamed Ali Kalefa, et al.
(författare)
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Distribution of diagenetic alterations in fluvial and paralic deposits within sequence stratigraphic framework : Evidence from the Petrohan Terrigenous Group and the Svidol Formation, Lower Triassic, NW Bulgaria
- 2006
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 190:1-4, s. 299-321
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Tidskriftsartikel (refereegranskat)abstract
- Elucidation of diagenetic alterations in the Petrohan Terrigenous Group (fluvial; highstand systems tract HST) sandstones and Svidol Formation (tide-dominated deltaic and tidal flat, transgressive systems tract TST and highstand systems tract HST, respectively) sandstones and calcarenite, Lower Triassic, NW Bulgaria was constrained within a sequence stratigraphic framework. Eogenetic alterations in the fluvial HST sandstones include (i) formation of grain-coating infiltrated clays as a result of percolation of mud-rich surface waters into underlying coarse-grained and permeable channel-fills and crevasse splay sandstones; (ii) formation of pseudomatrix by mechanical compaction of mud intraclasts that were incorporated into the coarse-grained channel sandstones during their lateral avulsion; and (iii) cementation by calcite (delta O-18(VPDB)=-6.5 parts per thousand to -3 parts per thousand; delta C-13(VPDB) =-5.1 parts per thousand to +0.6 parts per thousand) and dolomite (delta O-18(VPDB)=-6.1 parts per thousand to -0.3 parts per thousand 0; 81 3 CVPDB=-7.2 parts per thousand to -5.8 parts per thousand) in the crevasse splay and floodplain sediments. Mesogenetic alterations that are encountered in the fluvial HST sandstones include (i) illitization of grain-coating clays, mud intraclasts, and mica, possibly because of simultaneous albitization of feldspars; (ii) cementation by calcite (delta O-18(VPDB) = - 14.5 parts per thousand to - 8.4 parts per thousand; delta C-13(VPDB)=-7.7 parts per thousand to +0.6 parts per thousand) and dolomite (delta O-18(VPDB)=- 15.8 parts per thousand to -5 parts per thousand; delta C-13(VPDB)= - 7.9 parts per thousand to + 1.5 parts per thousand); and (iii) limited amounts of quartz overgrowths in the channel sandstones owing to occurrence of thick grain-coating clays. Conversely, the tide-dominated deltaic TST sandstones and the tidal flat HST calcarenite were pervasively cemented by calcite (delta O-18(VPDB)=-6.6 parts per thousand to -3.1 parts per thousand; delta C-13(VPDB)=-5.1 parts per thousand to +0.6 parts per thousand) and siderite (delta O-18(VPDB)=-7.2 parts per thousand to -5.7 parts per thousand; delta C-13(VPDB) =+0.3 parts per thousand to +0.9 parts per thousand) particularly below marine and maximum flooding surfaces, due to the presence of abundant bioclasts and prolonged residence time of the sediments under certain geochemical conditions along these surfaces. The remaining open pores were cemented during mesodiagenesis by calcite (delta O-18(VPDB)=-6.6 parts per thousand to -3.1 parts per thousand and delta C-13(VPDB)=-5.1 parts per thousand to +0.6 parts per thousand) and dolomite (delta O-18(VPDB))13=-6.6 parts per thousand to -3.1 parts per thousand. and delta C-13(VPCB)=-5.1 parts per thousand to +0.6 parts per thousand). This study shows that constructing a conceptual model for the distribution of diagenetic alterations is possible by integration of diagenesis with sequence stratigraphy. The model shows that tide-dominated deltaic TST sandstones and tidal flat HST calcarenite were pervasively cemented by carbonates during near-surface codiagenesis, owing to the presence of abundant bioclasts. Conversely, fluvial LST sandstones remained poorly cemented during near-surface eodiagenesis due to the lack of bioclasts, but were cemented by mesogenetic calcite, dolomite and quartz overgrowths instead.
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| 5. |
- El-ghali, Mohamed Ali Kalefa, et al.
(författare)
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Distribution of diagenetic alterations in glaciogenic sandstones within a depositional facies and sequence stratigraphic framework : Evidence from the Upper Ordovician of the Murzuq Basin, SW Libya
- 2006
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 190:1-4, s. 323-351
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Tidskriftsartikel (refereegranskat)abstract
- The spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the Upper Ordovician glaciogenic quartzarenite sandstones in the Murzuq Basin, SW Libya, which were deposited during the Haritanian glaciation when the basin was laying along the continental margin of Gondwana. Eogenetic alterations encountered include: (i) replacement of detrital silicates, mud matrix and pseudomatrix by kaolinite in paraglacial, tidedominated deltaic, in foreshore to shoreface (highstand systems tract; HST) and in post-glacial, Gilbert-type deltaic (lowstand systems tract; LST) sandstones, particularly below the sequence boundaries (SB). Kaolinite fort-nation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline. (ii) Cementation by calcite (61 80VPD,3 = - 3.1 parts per thousand to + 1.1 parts per thousand and delta C-13(VPDB)=+ 1.7 parts per thousand to +3.5 parts per thousand) and Mg-rich siderite in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, in the glacial, tide-dominated estuarine (transgressive systems tract; TST) sandstones and in the postglacial, shoreface TST sandstones is interpreted to have occurred from marine pore-waters. (iii) Cementation by Mg-poor siderite, which occurs in the post-glacial, Gilbert-type deltaic LST sandstones and in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline. (iv) Pervasive cementation by iron oxides has occurred in the glacial, shoreface-offshore TST sandstones and postglacial, shoreface TST sandstones immediately below the maximum flooding surfaces (NUS), which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor. (v) Formation of grain-coating infiltrated clays mainly in the glacial, fluvial incised-valley LST sandstones and in the post-glacial, Gilbert-type deltaic LST sandstones as well as, less commonly, in the paraglacial, foreshore to shoreface HST sandstones and in the tide-dominated deltaic HST sandstones below the SBs.Mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial, fluvial incised-valley LST sandstones, post-glacial, Gilbert-type deltaic LST sandstones and glacial, shoreface TST sandstones, in which early carbonate cements are lacking. Illite, chlorite and albitized feldspars, which occur in small amounts, are most common in the glacial, tidedominated estuarine TST sandstones and paraglacial, shoreface HST sandstones. This study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir-quality evolution in glacial, paraglacial and post-glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework.
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| 6. |
- Gong, Yin, et al.
(författare)
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Insights into evolution of a rift basin : Provenance of the middle Eocene-lower Oligocene strata of the Beibuwan Basin, South China Sea from detrital zircon
- 2021
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 419
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Tidskriftsartikel (refereegranskat)abstract
- Investigating rift basins and their provenance is difficult because their tectonic framework is continuously evolving. The Beibuwan Basin in the South China Sea is a typical rift basin that shares many characteristics of major rift basins worldwide. We present new detrital zircon UPb ages from the Beibuwan basin and, by combining with published data from surrounding drainages, are able to define its potential sources and to investigate its provenance evolution from the middle Eocene-lower Oligocene. Detrital zircon age spectra from distinct structural units and formations of the rift basin reveal spatial-temporal differences in provenance. In the middle-upper Eocene, a similar age pattern with major peaks at 263–253 Ma and 450–416 Ma is preserved across the basin and suggests that sediment was uniformly derived from the Yunkai Massif and Hainan Island. In contrast, during the lower Oligocene the basin displays markedly diverse ages with peaks at 250–243, 416, 756, 967–945, 1096–1084 Ma. The increase of Neoproterozoic zircons in the lower Oligocene stratum suggests that a major change in provenance occurred, most likely associated with the reorganization of the paleo-Pearl River along its central reaches due to a topography reversal associated with the uplift of Tibet and the onset of seafloor spreading in the South China Sea. Our spatial analysis of ages indicates that during the lower Oligocene, the detrital input varied across the basin. Rifting processes in the Beibuwan Basin generated multiple isolated depocenters separated by intra-basinal highs. The basin's architecture greatly affected sediment routing, with structural highs serving as barriers to sediment transport. Sediment provenance in the Beibuwan Basin is primarily controlled by drainage evolution and isolated depocenters associated with an evolving topography, processes which are relevant to the evolution of rift basins globally.
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| 7. |
- Greenwood, Sarah L., et al.
(författare)
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The sensitivity of subglacial bedform size and distribution to substrate lithological control.
- 2010
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 232, s. 130-144
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Tidskriftsartikel (refereegranskat)abstract
- The varied nature of a glacial substrate has often been invoked to account for the varied distribution, arrangement and morphological expression of subglacial bedforms. The ease and rate of sediment production from the bedrock substrate, and the rheological, mechanical and hydraulic properties of the resultant subglacial sediment layer have been argued, in certain samples or settings, to account for the local-to-regional distribution of bedforms and bedform types, and varying morphological expression such as size, shape, elongation, or spatial arrangement. From locally coherent observations and relationships it is tempting to extrapolate such patterns to express a more fundamental lithological control on subglacial bedform properties and formation. Here we use a large, systematically compiled dataset (> 30,000 subglacial bedforms inscribed by the Irish Ice Sheet) to explore potential lithological controls upon subglacial bedform distribution and morphological expression. We expect any lithological control upon form, size or distribution to be expressed through a spatial correlation between bedform properties and those of the bed lithology; we extract bedform morphometric and distribution statistics and underlying lithology data from datasets held in a geographic information system for comparative analyses. At ice sheet scale, i.e. considering our whole bedform population, we find no apparent relationship between the lithology of either bedrock or till substrate and bedform occurrence, density of arrangement, or size. Regional to local examples do, in contrast, exhibit some coincident changes in substrate and bedform expression. These are typically manifest as an abrupt shortening or lengthening of drumlins at a lithological boundary, superimposed upon more gradual, regional trends. However, not all local variability observed in the bedform population can be attributed to a lithological driver and, where it can be inferred, lithological control is often in tandem with, or subordinate to, other drivers such as topographic setting or ice dynamics. We propose a hierarchy of controls upon bedform form and distribution, strongly coupled to spatial scale: lithological differences can modulate local scale form and expression but bedform incidence and properties are primarily governed by ice sheet scale glaciological patterns and drivers. Only under certain (unknown) conditions at a local scale is the bedforming process sensitive to the lithological properties of the bed.
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| 8. |
- Hu, Yazhou, et al.
(författare)
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Distinguishing borings and burrows in intraclasts : Evidence from the Cambrian (Furongian) of North China
- 2023
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Ingår i: Sedimentary Geology. - : Elsevier. - 0037-0738 .- 1879-0968. ; 443
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Tidskriftsartikel (refereegranskat)abstract
- Hardgrounds represent synsedimentary cemented stratigraphic beds that form at or near the seafloor. Borings represent a key line of evidence for investigations of hardground development and record the evolution of bioerosion and boring organisms. The unequivocal identification of borings is done through identification of the crosscutting relationship between the proposed boring and a hard substrate, such as lithoclasts and/or shells, with morphological criteria able to be used when dealing with a homogeneous substrate, such as micritic hardgrounds. Bioeroded hardgrounds and burrows with a micrite halo/lining are subject to fracturing and reworking, resulting in accumulations of intraclasts in flat-pebble conglomerates (FPC). The recognition of borings and broken burrows with a halo can be challenging in FPC. Using trace fossils preserved in situ and in FPC from late Cambrian carbonates of North China, we establish a set of criteria for distinguishing borings from burrows with a halo in FPC. Features such as the relative volume of burrows and borings versus the host pebble and the number of traces per pebble, the cross-cutting relationship with different colored laminae, and the presence of pyrite or glauconite encrustations can all be invoked to aid recognition of borings. Examination of the cross-cutting relationship and encrustation of trace fossils are not sufficient on their own. Our results suggest caution is necessary in defining borings in FPC, particularly as synsedimentary deformation of burrows with a halo in late Cambrian FPC can create structures that resemble borings.
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| 9. |
- Khalifa, Muftah Ahmid, et al.
(författare)
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Impact of depositional facies on the distribution of diagenetic alterations in the Devonian shoreface sandstone reservoirs, Southern Ghadamis Basin, Libya
- 2015
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 329, s. 62-80
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Tidskriftsartikel (refereegranskat)abstract
- The middle Devonian, shoreface quartz arenites (present-day burial depths 2833-2786 m) are important oil and gas reservoirs in the Ghadamis Basin, western Libya. This integrated petrographic and geochemical study aims to unravel the impact of depositional fades on distribution of diagenetic alterations and, consequently, related reservoir quality and heterogeneity of the sandstones. Eogenetic alterations include the formation of kaolinite, pseudomatrix, and pyrite. The mesogenetic alterations include cementation by quartz overgrowths, Fedolomite/ankerite, and illite, transformation of kaolinite to dickite, illitization of smectite, intergranular quartz dissolution, and stylolitization, and albitization of feldspar. The higher energy of deposition of the coarser-grained upper shoreface sandstones combined with less extensive chemical compaction and smaller amounts of quartz overgrowths account for their better primary reservoir quality compared to the finer-grained, middle-lower shoreface sandstones. The formation of kaolin in the upper and middle shoreface sandstones is attributed to a greater flux of meteoric water. More abundant quartz overgrowths in the middle and lower shoreface is attributed to a greater extent of stylolitization, which was promoted by more abundant illitic clays. This study demonstrated that linking the distribution of diagenetic alterations to depositional facies of shoreface sandstones leads to a better understanding of the impact of these alterations on the spatial and temporal variation in quality and heterogeneity of the reservoirs.
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| 10. |
- Mansurbeg, Howri, et al.
(författare)
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Hydrothermal dolomitization of the Bekhme formation (Upper Cretaceous), Zagros Basin, Kurdistan Region of Iraq : Record of oil migration and degradation
- 2016
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Ingår i: Sedimentary Geology. - : Elsevier BV. - 0037-0738 .- 1879-0968. ; 341, s. 147-162
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Tidskriftsartikel (refereegranskat)abstract
- The common presence of oil seepages in dolostones is widespread in Cretaceous carbonate successions of the Kurdistan Region of Iraq. This integrated field, petrographic, chemical, stable C, O and Sr isotopes, and fluid inclusion study aims to link dolomitization to the origin and geochemical evolution of fluids and oil migration in the Upper Cretaceous Bekhme carbonates. Flux of hot basinal (hydrothermal) brines, which is suggested to have occurred during the Zagros Orogeny, resulted in dolomitization and cementation of vugs and fractures by coarse crystalline saddle dolomite, equant calcite and anhydrite. The saddle dolomite and host dolostones have similar stable isotopic composition and formed prior to oil migration from hot (81-115 degrees C) basinal NaCl-MgCl2-H2O brines with salinities of 18-22 wt.% NaCl eq. The equant calcite cement, which surrounds and hence postdates saddle dolomite, has precipitated during oil migration from cooler (60-110 degrees C) NaCl-CaCl2-H2O brines (14-18 wt.% NaCl eq). The yellowish fluorescence color of oil inclusions in the equant calcite indicates that the oil had API gravity of 15-25 degrees composition, which is lighter than present-day oil in the reservoirs (API of 10-17 degrees). This difference in oil composition is attributed to oil degradation by the flux of meteoric water, which is evidenced by the low delta C-13 values (-8.5 parts per thousand to -3.9 parts per thousand VPDB) as well as by nil salinity and low temperature in fluid inclusions of late columnar calcite cement. This study demonstrates that linking fluid flux history and related diagenesis to the tectonic evolution of the basin provides important clues to the timing of oil migration, degradation and reservoir evolution.
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