Sedimentary Gap Research Articles

Clay mineralogy of the Tertiary sediments in the Internal Subbetic of Málaga Province, S Spain: implications for geodynamic evolution

AbstractThe clay mineralogy of a set of Tertiary marine sediments from the Internal Subbetic of the Betic External Zone was examined. Two types of sedimentary environment were distinguished: a platform environment consisting of limestones, marls, organogenic limestones, conglomerates and silexites distributed heterogeneously in time and space; and deep environments, where the sedimentation consisted of marls, marly limestones, marly clays and silexites, with no sedimentary gap. A third group of sediments studied belongs to the Águila Complex, with mineralogical and stratigraphic characteristics very similar to the platform sediments. This third type of sediment is found in the sediments of the Campo de Gibraltar Complex as large, disperse blocks resulting from tectonic activity. A very similar mineral association was observed in all three domains, consisting of smectite, illite, mixed-layer I-S, kaolinite and lesser amounts of palygorskite and chlorite. Materials mainly derive from the erosion of Mesozoic sediments, and sedimentation was controlled by the compressive tectonics of the region.

Paléophytogéographie de la formation de Scarborough : nouvelles données et implications

Palynological study of the upper part of the Don Formation, in the Toronto area, confirms the progressive change from a mixed forest with numerous thermophilous trees (Quercus, Ulmus, Carya) to a cold balsam fir forest (Abies balsamea, Picea mariana, Pinus banksiana) towards the end of the Sangamonian climatic optimum. The Scarborough Formation pollen content indicates a forest-tundra or treed tundra environment similar to modern subarctic conditions. Macrofossil content also points to harsh climatic conditions. Mean annual temperature could then have been 10°C lower than the present in the Toronto area. Our data refute the reconstruction of a climatic cycle (cold-warmer-cold) within the Scarborough Formation. To explain the simultaneous presence of floristic elements typical of presently contrasted climatic regions (cold boreal, warm temperate), we propose that Lake Scarborough acted as a climatic buffer for riverine plants: thermophilous species survived in an englaciation context in remote regions. The upper part of the Don Formation corresponds with the end of the Sangamonian climatic optimum (end of isotopic substage 5e). After a sedimentary gap of unknown duration, the Scarborough Formation is apparently correlative to the Lévrard Till in the Middle St. Lawrence River Valley (isotopic stage 5b).

Mise en évidence d'un magmatisme alcalin d'intraplaque post-Calédonien dans le bassin silurien des Ouled Abbou (Meseta côtière, Maroc)

The Silurian of Ouled Abbou (coastal Meseta) consists of volcano-sedimentary deposits overlaying a silicoclastic formation which is characterised by sedimentary gap at Ashgill. The volcanism, of alkaline nature, is associated with unstable platform deposits involving a distensive sit up subsequent to a crustal uplift. This intumescence at the origin of the Ashgillian gap is generated by a mantellic advection inducing an epizonal metamorphism dated to 447 ±12 My.

Âges et environnements des Couches rouges d'Anoual (Jurassique moyen et Crétacé inférieur, Haut-Atlas oriental, Maroc)

Lithology, sedimentology and palaeoenvironments allow a lithostratigraphic subdivision of the Red beds into five formations. A marine episode identified near the top of the first formation is Early Bathonian in age. An erosional unconformity overlies this marine level just below the Lower Cretaceous deposits. It could be related to a large sedimentary gap between the Lower Bathonian and the Lower Cretaceous series.

Hiatuses on Vøring Plateau: sedimentary gaps or preservation artifacts?

The sediments recovered on ODP Leg 104 have been reported to be characterized by hiatuses. The hiatuses were defined by biostratigraphy and were believed to be caused by erosion related to temporary changes of bottom current composition and velocity. They have been associated with major paleoenvironmental changes, reorganization of global deep water production, and increased bottom water flows. Because of the importance of hiatuses for ongoing research, we decided to closely investigate the sedimentation history for the most significant Pliocene and Miocene biostratigraphic hiatuses by sedimentologic and geochemical means. The sedimentologic studies include clay mineral distributions, grain size data, and organic carbon concentrations. The geochemical studies include determination of 87 86 Sr ratios, 10Be and Ir concentrations. The results of the sedimentologic studies suggest either that paleoenvironmental changes associated with hiatuses are not represented in the preserved sediments, or that the hiatuses are an artifact of interpretation of the biostratigraphic data. Strontium isotopes indicate continuous sedimentation for the interval investigated at Site 642, an interpretation confirmed by the steady decline in 10Be. 87 86 Sr ratios in the interval from above and below proposed hiatuses H 2.2 2.3 and H2.1 2.2 at Site 643 display stronger changes with depth than expected by steady sedimentation. Ir data for this same interval indicate reduced sedimentation rates. Combining both, sedimentologic and geochemical evidence, the proposed hiatuses could not be confirmed and may represent preservation artifacts.

Tectonique syn-sédimentaire en Tunisie centrale (région du Jebel Mrhila) pendant l’Aptien-Albien

The important sedimentary gaps, the variations of thicknesses and fades which characterize the Aptian-Albian series in the J. Mrhila area, are linked, at least partly, to the action of two tectonic features. 1. The Mrhila-Cherichira fault, with a NNE-SSW direction, is responsible for the collapse of the area located north of this major accident; the southwards tilt of this area made the accumulation of very thick marine sediments possible, during Clansayesian toLateAlbian time, at Koudiat El Beida (KEB) and in Bled El Gouna 1 (BEG. 1) wells. These sediments do not occur in the uplifted area, south of the fault. 2. The second feature, corresponding to the Sbiba fault, with a N140 direction, had, as effect, the reduction of the Albian series within the Tiouacha 1 (Ti. 1) boring. This variation is significant, even if it is, by far, less important than that occurring on both sides of the major NNE-SSW fault. It seems that this Sbiba fault played a role in Clansaysian to Upper Albian sedimentation, which resulted in the formation of a losangic basin.

Late Pliocene continental magnetochronology in the Guadix-Baza Basin (Betic Ranges, Spain)

The late Pliocene shallow lacustrine sequences in the Guadix-Baza basin (Betic Ranges, southeast Spain) are a suitable setting for mammal chronology because of the abundance of rich, mammal-bearing sites. Stratigraphic superposition of late Ruscinian and Villanyian vertebrate fossils makes the Galera Section very appropriate for magnetostratigraphic dating. Sediments are characterized by a weak but measurable magnetization predominantly carried by magnetite. Other remanence carriers, such as iron sulphides and hematite, may be significant only in some particular lithologies, such as dark palustrine organic silts and red alluvial beds, respectively. Direct correlation of the Galera Section to the geomagnetic polarity time scale provides a reliable dating of the late Ruscinian and Villanyian mammal units. The Ruscinian/Villanyian boundary (MN15/MN16) is found to occur in the lower Gauss chron, and approximately correlates to the 3.3 Ma cooling event observed in stable-isotope and planktonic foraminifera deep sea records. The earliest occurrence of late Villanyian assemblages (MN17) in the lower part of the Matuyama chron allows dating of the early/late Villanyian boundary (MN6/MN17) to approximately 2.4–2.6 Ma. Based on the presence of late Villanyian assemblages underlying the base of the Olduvai chron, a maximum age of 1.95 Ma (top of C2r) is attributed to the Villanyian/Biharian (MN17/MmQ) boundary. A 300 kyr sedimentary gap in the Galera Section is suggested to correlate with a probable early Villanyian hiatus, an hypothesis that agrees with the absence of fossils of this age elsewherein the Baza Formation.

Global and regional factors controlling changes of coastlines in Southern Iberia (Spain) during the holocene

The interaction between global (glacio-eustatic sea-level rise) and regional factors (oceanographic and tectonic) has controlled the evolution of coastline during the Holocene in Southern Iberia. At ca. 10,000 14C years BP a deceleration of relative sea-level rise took place both in the Atlantic and Mediterranean littorals, with a maximum transgression at 6450 14C years BP. In subsiding areas (present tidal flats) estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit-bar systems developed. Two phases of major progradation are distinguished in these systems: the first one between 6450 and 3000 14C years BP, with a sedimentary gap at ca. 4000 14C years BP; and the second one from 2750 14C years BP up to present, with an intervening gap between 1200 and 1050 14C years BP. These progradation phases develop during stillstands followed by relative sea-level fall, while the sedimentary gaps represent relative high sea level. In the Mediterranean areas, with a higher uplift rate, marine terraces almost coeval to those gaps occur. The most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14C years BP represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes. At ca. 1000 14C years BP the estuaries record a greater fluvial than marine influence, and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones. The European Medieval Warm period is characterized, at least during its initial phase, by low pressure climate conditions, while during the Little Ice Age anticyclonic conditions gave rise to a strong coastal progradation.

Sedimentary record in french karstic infillings during the last climatic cycle [ Enregistrement sédimentaire dans les remplissages karstiques français au cours du dernier cycle climatique.

Comparison of the sedimentary records in karstic infilhngs (cave entrances and rock-shelters) from three French regions (northern Alps, Franche-Comté, Périgord) is proposed for the last climatic cycle. There are displays large regional discrepancies, both in the periods recorded periods and in the extent and timing of the sedimentary gaps. These discrepancies are related to the respective geographical position of these three areas relatively to the glacial fronts during the last climatic cycle.

Missing Records and Depositional Breaks in French Late Pleistocene Cave Sediments

Cave entrance and rock shelter infillings are positioned within the Pleistocene chronology for three areas of France (northern Alps, Franche-Comté, and Périgord). Despite minor local variations, it is possible to identify regional types with a consistent depositional record over long intervals of time. The interregional variability relates to the frequency and position of the gaps within the infillings. Sites in the northern Alps have not yielded any artifacts older than the Upper Paleolithic (Magdalenı́an), and dated sedimentary sequences do not go back beyond the Older Dryas. More complete sequences in Franche-Comté contain Mousterian industries. Two major gaps occur here, one lasting about 50,000 yr during the Lower Glacial and Lower Pleniglacial periods, and the other lasting some 10,000 yr during the Upper Pleniglacial. The sequences are more complete in the Périgord, where all major climatic phases have been identified with no significant sedimentary gaps. Differences in sedimentary records can be explained by variations in regional conditions during the last interglacial-glacial cycle and especially by the distance from the maximum advance of ice daring glaciation.

Magnetostratigraphy of the Late Triassic Bolücektası Tepe section (southwestern Turkey): implications for changes in magnetic reversal frequency

A magnetostratigraphic study of light-pink to white pelagic limestones from the Bolücektası Tepe section (southwestern Turkey) provides a magnetic polarity sequence well calibrated with the conodont zonation for the Lower Carnian and uppermost Carnian-Middle Norian (Late Triassic). Thermal (between 400 and 550°C) and alternating field (30–60 mT) demagnetizations isolate the characteristic remanent components. Rock magnetic experiments suggest that magnetite is the dominant magnetic carrier, but a small hematite fraction also exists in the Lower Carnian light-pink limestones. A major sedimentary gap (Middle-Upper Carnian) divides the section in two submembers which reveal two statistically different mean directions, differing in declination by about 30°. A sequence of 39 polarity intervals is obtained, 18 in the Carnian (ten in the Lower Carnian and eight in the uppermost Carnian) and 21 in the Lower-Middle Norian. The magnetic reversal frequencies which can be derived from these results, together with the available magnetostratigraphic data for the Middle-Early Jurassic, Triassic and Late Permian, show a pattern which is in rough agreement with the suggested 150–200 million year time constant in the reversal process since the Kiaman superchron. However, significant short-period fluctuations in reversal frequency cannot be excluded.

REE geochemical evolution and its significance of early precambrian metamorphic terrain, Wuyang, Henan

The supracrustal rocks of the Wuyang metamorphic terrain are divided into the Zhao ’anzhuang, Tieshanmiao and Yangshuwan Formations. These three Formations were dated at 3000–2550 Ma, 2550–2300 Ma and 2300–2200 Ma, respectively. ΣREE and La/Yb)n of the Zhao ’anzhuang Formation volcanic rocks are obviously higher than those of the Tieshanmiao Formation equivalents, suggesting a sedimentary gap (2550 Ma boundary) between these two formations. The Zhao ’anzhuang Formation is older than the Tieshanmiao Formation. The sediments of these two Formations show no obvious differences in REE and are generally characterized by low ΣREE and positive Eu anomalies. On the contrary, the sediments of the Yangshuwan Formation are characterized by high ΣREE and negative Eu anomalies. Detailed discussions demonstrate that the Yangshuwan Formation was deposited in an oxidizing environment whereas the other two formations were formed in a reducing environment. At the end of the evolution of the Tieshanmiao Formation about 2300 Ma ago, the sedimentary environment was transformed from reducing to oxidizing. On the basis of the SHAB (soft/hard acid and base) theory, an oxidation-reduction model for sedimentary REE evolution has been established. It is proposed that the mantle tends to become gradually depleted in REE, especially in LREE, and the indices ΣREE and La/Yb)n of mantle-derived volcanic rocks also tend to become lower and lower.

Le Berriasien d'Angles (Alpes-de-haute-provence, France)

Upper Tithonian to Berriasian pelagic limestones underlying the hypostratotypic Valanginian section at Angleshave been biostratigraphically studied through calpionellids, in order to complete the study of a Lower Cretaceous reference section that also comprises the Barremian stratotype. The few thin slump deposits in the studied intervall does not allow to anticipate how strong are the sedimentary gaps we evidenced, especially in the upper Tithonian, and the upper lower to middle Berriasian that is entirely missing. The first hiatus is not even underlined by any slump; the erosional surface is sealed by pelagic mudstones and can be only evidenced by a gap in the vertical repartition of calpionellids.

Interprétation de la déglaciation rhodanienne au Würm, des moraines « internes » à la cuvette lémanique

Between the "inner moraines" and the upperside of the Leman Lake, we observe the following elements : — two generations of "inner moraines" of as yet undetermined age, the oldest being over 241 10 ±900 B.P.; — a series of over-deepened basins now either wholly filled up with lacustrine deposits (Malville, Le Bouchage) or not (Le Bourget, Annecy, Léman), with thicknesses of several hundred meters; — a series of paraglacial or glacio-lacustrine supra-morainic deposits directly related to the déglaciation, which are disposed "en echelon" from the downstream side to the upstream side; — on single till cover to the downstream side of the Geneva basin, directly superposed to the substratum or to a wurmian ante-morainic complex; — a thick complex of superposed morainic, lacustrine and marshy deposits in which several interstadials were dated from 34550 to 23500 B.P. in the Leman basin only (Chablais, Vaud). Present chrono-stratigraphic conclusions, notably concerning the age of the maximum glacial advance, differ between the frontal area (early Wùrm) and the upstream side of the Leman basin (late Wùrm). Now, we note that : — undoubted, dated interstadial deposits only occur in the Leman basin, far upstream from the "inner moraines"; — between the "inner moraines" and the Leman basin, there is only one single till cover as well as déglaciation deposits, without any evidence of interstadial formations or of true glacial stops. Therefore, in all likelihood, the morainic deposit of the Plateau Savoyard represents one single glacial phase, predating the oldest Leman interstadials (34600 ± 2700 B. P.). One indétermination still subsists, regarding its age, in relation with both the sedimentary gaps in the glacial-interstadial series and the duration of the sedimentation process of the déglaciation and of later lacustrine deposits.

Pridolian graptolites and their use in correlation

The use of graptolites to subdivide the youngest (Pridoli) stratotype of the Silurian System in the Barran­dian poses difficulties for correlation with other regions. The proposed zonal subdivision is the same as that established earlier by Pfibyl in 1940. Since that time, however, various graptolites of the same age have been recognized in several sections all over the world. This abundance of new data makes detailed zonal correlation with the Barrandian area much more difficult because the Barrandian graptolites are probably not fully documented. The absence of some taxa may be due to condensed carbonate sedimenta­tion in which sedimentary gaps are to be expected. It can not be excluded, however, that undiscovered graptolites still exist in the Pridoli Series of the type area. The graptolites aside, other fauna! groups in the Pridoli Series are unfortunately strongly endemic and thus their correlation value is weak.

Micropaleontological assemblages, paleoenvironments and sedimentary evolution of Cretaceous deposits in the Algarve (Southern Portugal)

The Cretaceous of the Algarve comprises some lithostratigraphic units (carbonatic in shallow-water environments, siliciclastic in estuarine or fluviatile areas) which are essentially dated by their micropaleontological assemblages which contain calpionellids, lituolids, orbitolinids, involutinids, dasycladacean algae, charophytes. The formations are interpreted in the following terms: one regressive-transgressive cycle (late Oxfordian-basal Valanginian), two regressive sequences (Hauterivian-Barremian, Bedoulian) and one transgressive sequence (Gargasian-middle Cretaceous), separated by three major discontinuities at the base of the Valanginian, lower Bedoulian and upper Bedoulian. The sedimentary evolution and the geometry of deposits are controlled by various geodynamic factors the influence of which is analyzed: the relative changes of sea level are the main factor which determines the repartition of the formations in the different isotopic zones; the rate of subsidence on this passive continental margin (well marked during the Aptian and Albian) and sedimentary influxes increasing during the Hauterivian-Barremian contribute to the vertical regressive or transgressive evolutions. Orogenic movements occur only in the Neocomian, near a diapiric area. These factors record, on the south portuguese continental shelf, different stages of the history of the Northern Atlantic: the Neocimmerian and the Bedoulian riftings induces major discontinuities and sedimentary gaps. The beginning of the expansion of the Northern Atlantic determines the increasing of subsidence during the Aptian and Albian.

Calcareous plankton biostratigraphy and biochronology of the Pliocene-Lower Pleistocene succession of the Capo Rossello area, Sicily

In the first part of this paper we present the calcareous nannofossil biostratigraphy of the Capo Rossello section (Sicily), which suggests that a sedimentary gap exists at the contact between the “Trubi” and the overlying Monte Narbone Formation, close to the top of the proposed Zanclean stratotype. This suggestion is supported by the planktonic foraminiferal results and field observations. In contrast, the transition from the “Trubi” to the Monte Narbone Formation is well exposed, gradational and biostratigraphically continuous in the nearby section of Punta Piccola. A composite of the Capo Rossello and Punta Piccola sections serves as a good biostratigraphic reference for the Pliocene of the Mediterranean. In a second part of this paper, we have attempted to update the Mediterranean Pliocene time framework by integrating all of the available biostratigraphic, biochronologic, chronostratigraphic, paleomagnetic and radiometric data.

Facies and sediment dynamics in Charlie-Gibbs fracture zone during the Late Quaternary

Analysis of five cores from the Charlie-Gibbs fracture zone enables us to define the sedimentary characteristics in four different types of environments: a sill disrupting the southern valley, open channels in the northern and southern valleys, a flanking plateau of the northern side wall in the northern valley, and an enclosed depression in the northern valley. Five lithofacies have been recognized: clayey-silty mud (40%), clayey-silty calcareous mud (25%), calcareous sands (20%), sedimentary breccia (10%) and silty-sandy calcareous mud (5%). The predominance of terrigenous clayey material is evidence for a mainly continental origin of the fracture-zone sediments. Yet another striking feature is the abundance of foraminiferal sands rich in pelagic calcareous and siliceous components associated with coarser ice-rafted elements. Despite the pelagic origin of components, a uniform draping of sediments — which kind of sedimentation we call “ubiquiste” (Faugères et al., 1979) — has not been noted in the survey area, due to the reworking processes of already deposited materials by bottom geostrophic currents or gravity flows. The influence of the bottom-current processes on sedimentation is confirmed by the following characteristics: (1) the presence of sharp or erosional contacts between two facies; (2) low clay fraction in certain levels, caused by winnowing of sedimentary materials; (3) high clay fraction in other levels, considered to be the result of dilution of pelagic material by clay particles transported in the nepheloid layer and trapped in a depression downstream of a sill; and (4) Icelandic smectites transported by Iceland—Scotland Overflow Water (I.S.O.W.). The influence of gravity flow dynamic processes is indicated by sandy or silty-sandy centimetric turbidites, very thick mega-sequences (8 m) transported by a single mass flow, and important sedimentary gaps, whence gravity flows originated.

PERMIAN AND TRIASSIC STRATIGRAPHY, ZAGROS BASIN, SOUTH‐WEST IRAN

The Permian and Triassic beds deposited in the Zagros Basin form a massive carbonate and evaporite sequence in excess of 2000m. These strata were divided into clearly recognizable and mappable lithostratigraphic units and major lithofacies types using surface exposures, subsurface log information and sample cuttings. Formation and member designations are given to distinct and widespread lithostratigraphic units and where possible, the boundaries of these units are selected to coincide with sedimentary gaps or boundaries of sedimentary cycles. A well type‐section and a surface reference section are established to illustrate the distribution of these units both vertically and horizontally. Major unconformities were observed and documented at the base of the Permian and at the top of the Triassic, a smaller break was noted between the Triassic and Permian sediments. Revision of the Jurassic‐Triassic boundary is made, based on this new stratigraphic evidence.

Jurassic-Cretaceous Boundary in Iran

As a result of late Kimmerian movements, discontinuous sedimentation and a sedimentary gap through the Tithonian and Neocomian characterize many parts of Iran. In other places (eastern Koppeh Dagh, east-central Iran, and coastal southwest Iran) mainly red continental sediments or evaporites were deposited during this time interval. Continuous marine sedimentation took place in the western Koppeh Dagh, North Alborz, and the interior of the Zagros Mountains.