Sedimentological Aspects Research Articles

Faunal specificity, endemism and paleobiogeography: the post-glacial (Hirnantian-early Rhuddanian) graptolite fauna of the North-African border of Gondwana: a case study

Abstract Several types of stratigraphic successions are found at the top of the glacial to periglacial “Complexe terminal” forming the uppermost Ordovician of the North-African border of Gondwana. Locally, there may be a progressive transition from microconglomeratic clays (diamictites) with dropstones to more normal marine clays accompanied by the almost immediate reappearance of graptolites. Study of the graptolites has revealed a distinctive composition at the specific level, differing from contemporaneous faunal associations in adjacent regions, which consist of such classical species as “Glyptograptus” persculptus, Akidograptus ascensus, Parakidograptus acuminatus, etc. The faunal composition has long posed a chronostratigraphic problem, which has now been largely resolved, the fauna being interpreted as Hirnantian to early Rhuddanian in age. On the other hand, the clear evidence of faunal specificity poses a number of problems in the post-glacial context, namely: the disappearance of graptolites in the mid-Caradoc from these regions poses a problem as to the origin of the new specific fauna. Three hypotheses are considered, none of which is satisfactory. Most available data point to an eastern communication, although it is possible that the rejuvenation of the Mauritanides to the west “erased” all prior evidence, giving a wrong idea as to the communications which existed in the area under consideration; what mechanisms caused and maintained this isolation? The hypothesis of a wide, east-west trending depression produced by the overloading of the frontal ice sheet and its progressive disappearance concomitant with the glacial rebound is being considered; what were the effects of isolation on the morphology of graptolites and their population? The virgella and the virgula in several species are remarkably long and this could be attributed to a reduction in water density. The size of monospecific populations also attests to an adaptation to a restricted regime with sandy deposition; how can one explain why some species like N. pseudovenustus, N. inazzaouae, N. normalis brenansi and Ps. kiliani, occur also in other parts of the world? If these species occur where the classical species are absent, the opposite is even more difficult to explain, leading one to postulate the presence of a selective “filter”; how did this faunal specificity disappear progressively? The extent of the sea with Nd. africanus and Nd. fezzanensis put an end to isolation, although it respected the east-west trend. However, there was an opening to the adjacent regions corresponding to present-day Libya. To conclude, if pelagic faunas are considered to be poor paleogeographic tools, faunal specificity rather than endemism should be regarded as the starting point for further reflection. However, all faunal specificity must be fully documented and the results integrated in a framework that includes all aspects of sedimentology, tectonics and climatology. Seven new species are briefly described: Normalograptus nseirati sp. nov., Normalograptus gelidus sp. nov., Normalograptus arrikini sp. nov., Normalograptus pretilokensis sp. nov., Neodiplograptus inezzani sp. nov., Neodiplograptus incommodus sp. nov. and “Glyptograptus” saharensis sp. nov.

三次元サイスミック地形学 (seismic geomorphology) 手法による貯留層のイメージングと分布解析

This paper attempts to review the historical background, petroleum geological significance, major contributions and basic methodology of “seismic geomorphology”, which has recently been developed as an integration of 3D seismic technology/3D visualization technique and sedimentology/sequence stratigraphy. Seismic geomorphology may be defined as the study of sediment body morphology and properties using 3D seismic data, and is expected to be indispensable for future sedimentology and hydrocarbon exploration/development, since seismic geomorphology provides detailed information on the sediment morphology, distributions and depositional processes. From the sedimentological aspect, seismic geomorphology clarifies detailed internal structures of depositional elements, and improves general depositional models of various depositional systems. From the petroleum geological aspect, seismic geomorphology plays an important role to bridge over sedimentology, geophysics and reservoir engineering in an integrated reservoir characterization workflow.In a seismic geomorphological analysis procedure, basic sequence stratigraphic framework should be constructed, first, and reconnaissance survey over 3D seismic data should be conducted, next. Subsequently, targeted reservoir rock bodies are displayed in detail by slicing, horizon surface displaying, volume attribute analysis and trace shape (seismic facies) analysis on the 3D seismic data. Finally, sedimentological interpretation is conducted for the displayed sediment body to determine depositional elements, processes and facies distributions. It is regarded that proper pattern recognition and blend of spatial seismic geomorphology and temporal seismic stratigraphy are the keys to obtain effective solutions in the seismic geomorphological analysis.

Reply to comment on 'Tectono‐sedimentary evolution of lower to middle Miocene half‐graben basins related to an extensional detachment fault (western Crete, Greece)'

In their comment, van Hinsbergen et al. (2008) question the validity of the tectono-sedimentary model proposed by Seidel et al. (2007) for the Topolia type breccia deposits in western Crete. Apart from various sedimentological aspects that could probably be sorted out in the field, they argue that the proposed time brackets of c. 20–15 Ma for the formation of the Topolia breccia do not reflect the onset of extensional deformation in the overriding plate of the Hellenic subduction zone after collision. Instead, they propose that the onset of extensional deformation is reflected by the formation of a late Miocene (c. 12–11 Ma) sedimentary basin unconformably overlying the Topolia type breccia deposits. Notwithstanding the fact that the age of the breccia is otherwise not well constrained apart from being deposited prior to the exposure of the highpressure metamorphic units in western Crete, we do not concur with this view. Whatever van Hinsbergen et al. (2008) mean with terms syn-orogenic and post-orogenic in the present context, they claim that the onset of crustal scale, post-orogenic N–S extension is dated by the oldest Cretan supradetachment basin. They also state that this basin formed well after the deposition of the oldest Neogene sedimentary unit in western Crete – the Topolia breccia . First, it should be noted that Crete represents a narrow horst structure developed in the forearc of the active Hellenic subduction zone since the Pliocene. When dealing with crustal scale processes, the highly incomplete Neogene sedimentary record on the island is just one limited source of information. Moreover, the buoyant escape model proposed by Thomson et al. (1998, 1999) should not be misunderstood to invoke extrusion from a subduction channel , as quoted by van Hinsbergen et al. (2008), which may rather be a potential cause of the marked uplift of Crete since the Pliocene (Meier et al., 2007). In the buoyant escape model, the partly subducted microcontinent is proposed to return towards the Earth surface by filling the space created by continuous roll back as a more or less coherent slice, becoming exhumed beneath an extensional detachment fault (e.g. Fassoulas et al., 1994; Kilias et al., 1994; Jolivet et al., 1996). This process probably causes extensional deformation in the hangingwall to the detachment, which is represented by the unmetamorphic upper units on Crete; extensional deformation continues because of roll back into the present. Any record of normal faulting in the upper plate to the extensional detachment does not allow an unequivocal distinction to be made between the buoyant escape stage (Thomson et al., 1999) and a subsequent stage of more coaxial crustal extension (Thomson et al., 1999; Rahl et al., 2005), stages possibly referred to as syn-orogenic and post-orogenic by van Hinsbergen et al. (2008). The structural record of the high-pressure metamorphic Phyllite–Quartzite Unit shows an episode of intense extensional deformation in the brittle field (e.g. Seidel et al., 2005), which took place between c. 20 and 15 Ma, according to fission track thermochronometry (Thomson et al., 1998, 1999) and at a depth of less than about 10 km (Kuster and Stockhert, 1997). This extensional deformation therefore happened after the major part of rapid exhumation from more than 30 km depth, when the high-pressure metamorphic Phyllite–Quartzite Unit already resided in the upper crust. We suspect that this marked extensional deformation of the Phyllite–Quartzite Unit should have had dramatic effects also in the higher levels of the upper crust and consequently at the surface. We therefore envisage that the formation of fault scarps, which are required to produce the fault-bound proximal breccia deposits with a minimum thickness of several hundred meters, preserved in western Crete, could be contemporaneous with the buoyant escape stage as well as with this later stage of extensional deformation. The breccia deposits, as all other units of the upper plate to the extensional detachment, were juxtaposed with the high-pressure metamorphic Phyllite–Quartzite Unit along normal faults during ongoing extension. In our simple structural model (Seidel et al., 2007), we propose that the normal fault presently bounding the Topolia breccia towards the south could have evolved by progressive deformation (or by repeated reactivation) from the fault along which the breccia was deposited on the hangingwall block, the rocks of the Phyllite– Quartzite unit forming the footwall block being juxtaposed with the breccia at a late stage of deformation. The proposed half-graben geometry corresponds to that observed in other extensional tectonic settings (e.g. Davis and Coney, 1979; Wernicke, 1981; Davis et al., 1986) with a more complete structural record and is motivated by the clast size and roundness trends observed in the Topolia area. We feel that the interpretation in terms of a major half-graben bounding fault with progressive exhumation of the footwall block is consistent with Correspondence: Dr Markus Seidel, Am Lindbruch 29, D-41470 Neuss, Germany. E-mail: markus.seidel@gmx.net

Leaves in turbidite sands: The main source of oil and gas in the deep-water Kutei Basin, Indonesia: Discussion

Saller et al. (2006) have concluded that leaves in the upper Miocene turbidite sands were the main source of oil and gas in the deep-water Kutei Basin, East Kalimantan (Borneo), Indonesia. They have reported that oils from the Kutei Basin have high (4–7) pristane/phytane ratios, suggesting a coaly organic source. This is consistent with other observations made on oils from the Gippsland Basin in Australia, showing high pristane/phytane ratios (5–6) that were attributed to coniferous rain forests and related land-plant organic matter (Shanmugam, 1985). Saller et al. (2006) have also concluded that leaf fragments were carried into deep water along with sand by turbidity currents during lowstands of sea level. This conclusion deserves close scientific scrutiny. Although Saller et al. (2006) have discussed both geochemical and sedimentological aspects, I confine this discussion to sedimentological details. I also take this opportunity to introduce more clarity into our understanding of deep-water deposition through discussing conceptual, observational, and interpretational problems. First, Saller et al. (2006, p. 1588) stated that “Specific well names and depths are not included in this manuscript for confidentiality reasons.” The strength of any scientific article is its transparency of data, which provides other researchers an opportunity to verify the conclusions of an article without constraints. Saller et al. used cuttings samples from 50 wells and conventional core samples from 16 wells, but because they did not provide a map showing well locations, it is impossible to evaluate the relative position of a sample with respect to the paleoshelf edge. This is critical to the central theme of this article, which is the source of land-plant organic matter (i.e., highstand delta versus lowstand shelf-edge delta). Saller et al. could have included a location map of wells, but could have changed the original well names. Second, the basic tenet of …

Facies analysis, palaeoenvironmental reconstruction, and biostratigraphy of the “Pesciara di Bolca” (Verona, northern Italy): An early Eocene Fossil-Lagerstätte

The world-famous “Pesciara di Bolca” Fossil-Lagerstätte has been examined in its palaeontological and sedimentological aspects. A re-examination of the co-occurring age-diagnostic larger foraminifers ( Alveolina and Nummulites) indicates a SBZ 11 (late Ypresian) age. Sedimentological characters allowed us to distinguish between autochthonous micritic limestones and allochthonous biocalcarenites–biocalcirudites; the latter are the product of penecontemporaneous transport from nearby areas. The depositional model here proposed involves a basin with restricted circulation and a prevailing micrite sedimentation. This basin was affected by relative sea-level oscillations and coarser grained storm-induced deposition. The palaeoenvironmental reconstruction suggests neighbouring emerged land and very shallow sea bottoms inhabited by large foraminifers such as Alveolina and Nummulites. As yet, it is unclear whether a true coral reef was present nearby. The bottom on which the Pesciara deposits accumulated is interpreted as poorly oxygenated, possibly with stromatolite-like bacterial mats, thus allowing the exceptional preservation of the fish and plants.

Petrographical, Palynological, and Sedimentological Aspects Regarding the Genesis of Palaeogene Lignites Near Alexandroupolis, Thrace, Greece

Several minor lignite deposits of Palaeogene (Eocene to Oligocene) age occur in the vicinity of Alexandroupolis, Thrace, northern Greece. A few rather thin seams were mined in the past by small private operations for local use. Coal samples have been collected from old mine dumps and outcrops around abandoned mine posts to be studied by means of maceral analysis at high magnification. The groundwater and vegetation index are calculated from the maceral composition and used to draw conclusions concerning the environment of deposition. In addition, block samples of coal cut perpendicular to bedding were studied at intermediate magnification and under fluorescence thus revealing some interesting bedding features as well as well-preserved plant organisms. The coals are characteristically finely laminated and highly gelified. Palynological preparations have thus far yielded only poorly preserved palynomorph assemblages rather low in diversity and dominated by fern spores. This fern dominance is rather unusual; however, it is compatible with the occurrence of fertile fern fronds observed in petrographic coal sections. Accompanying clastic sediments exhibit cyclic fining-upward sequences at a scale averaging about 1 m in vertical extent. Grain sizes range from small gravel to clay and silt. In some cases, siltstones in the roof of coal seams include abundant plant fragments showing parallel venation. The evidence presented from various sources suggests a rather unstable fluvial environment and a generally high water table on the flood plain for the formation of these lignites.

Morphological Features and Sedimentological Aspects of Wadi Al-Kura, North of Jeddah, Western Coast of Saudi Arabia

Morphological Features and Sedimentological Aspects of Wadi Al-Kura, North of Jeddah, Western Coast of Saudi Arabia

A Winter Field-based Course on Limnology and Paleolimnology

The Union College (New York) course Lakes and Environmental Change balances the practical constraints of offering a field-based limnology / paleolimnology course during a winter term without the availability of a large lake or research vessel. Reliable ice conditions and an abundance of nearby small lakes assure a variety of candidate lake systems. Beginning with drainage basin analysis and progressing through water-column measurements, analysis of spatial distribution of surface sediment characteristics, and culminating with collection and analysis of sediment cores, this inherently interdisciplinary course ties together aspects of geochemistry, ecology, sedimentology, and physics. We compare two lake systems each year and in most cases the field and laboratory work represents some of the first limnologic work done on the lakes. Through this systematic framework for investigating each year's lakes, the course resembles an authentic research project, rather than a series of unrelated lab exercises. Classroom activities consist of lectures and literature discussions divided about equally between limnology and paleolimnology. Lab exercises take place in the field, where students learn to use a variety of field gear, and in the laboratory, where students master techniques for sampling and analyzing sediment cores.

Coal facies studies in the eastern United States

Coals in the eastern United States (east of the Mississippi River) have been the subject of a number of coal facies studies, going back to the 19th century. Such studies would not necessarily fall within a strict modern classification of coal facies studies, but if a study encompassed some aspects of paleobotany, palynology, petrology, geochemistry, or sedimentology, we assumed that some data and interpretations may be of use in evaluations of the facies. References are presented, as a guide for further research, with annotation in the tables.

CARRACEDO, J. C. & DAY, S. 2002. Canary Islands. Classic Geology in Europe Series Volume 4. viii + 294 pp. Harpenden: Terra Publishing. Price £14.95 (paperback). ISBN 1 903544 07 6

The Canary Islands in the Northeast Atlantic are a wonderful place to study volcanic, structural and sedimentological aspects of ocean island volcanoes. Their geology is varied and superbly exposed, with over fourteen million years of submarine and subaerial, effusive and explosive volcanic activity, intrusion, caldera collapse, landslides, and erosion recorded. Visitors should not be put off by the recent over-sensationalist TV documentaries predicting future landslides and the inundation of Florida and New York by tsunami! The presence of voluminous felsic explosive products, sediments and uplifted submarine successions, make the Canaries more varied than the Hawaiian islands with which they are often compared. With low-cost flights, accommodation and car-hire, they have become particularly accessible to northern Europeans. To my knowledge Canary Islands is the only field guidebook that attempts to cover the geology of all seven main islands in the Canary archipelago. This is an ambitious remit, and the authors …

Physical, chemical and sedimentological aspects of the Mediterranean outflow off Iberia

A multidisciplinary study of the Mediterranean outflow in the region west of the Strait of Gibraltar and off the southern and southwestern coasts of the Iberian Peninsula was developed in the frame of the Canary Islands Azores Gibraltar Observations Project. Two high-resolution CTD surveys, which included water sampling for chemical (nutrients and dissolved oxygen) and sedimentological analyses, took place in September 1997 (summer cruise) and January 1998 (winter cruise) in the study region. The correspondence between the high-salinity Mediterranean Water (MW) layer and the low-nutrient content and relatively high abundance of particles was a general result. Further details of the thermohaline analysis and of the geostrophic computations, especially for the layer of MW, are compared with the results obtained for the chemical properties and the sedimentological characteristics.

Sedimentological and Petrographical Aspects of Upper Miocene Evaporites in the Beypazari and Çankiri-Çorum Basins, Central Anatolia, Turkey

Upper Miocene evaporites in the Beypazari and Cankiri-Corum basins were deposited in an inter-montane playa–lake complex environment and are intercalated with gypsiferous mudstones and clay-stones. In the Beypazari basin, these evaporites are part of the Kirmir Formation, and in the Çankiri-Çorum basin they occur in the Bozkir Formation. In these two basins, the evaporite minerals comprise mainly Ca-sulfate (gypsum and anhydrite) and Na-sulfate minerals (glauberite and thenardite). The Kirmir Formation consists of a cyclic alternation of gypsiferous claystone, carbonate mud-stone, gypsum-cemented sandstone, alabastrine gypsum rosettes after glauberite, and laminated-banded pseudomorphic alabastrine secondary gypsum after Na-sulfate minerals; at the top, a thick-bedded porphyroblastic secondary gypsum lithofacies is present. The Na-sulfate lithofacies in the Kirmir Formation is dominated by lens-shaped idiomorphic glauberite crystals, which are cemented and/or replaced by thenardite. In the weathering zone of the Na-sulfate deposit, glauberite minerals are transformed to the secondary gypsum that shows a very typical crystalline texture. The main crystalline textures of this secondary gypsum are reticulate, acicular, spindle-shaped acicular, and zigzag textures with acicular crystalline fabric in alabastrine and porphyroblastic secondary gypsum matrix. The Bozkir Formation in the Cankiri-Corum basin comprises, in ascending order, claystone, gypsum-cemented sandstone, laminated to thin-bedded limestone and claystone alternations, nodular alabastrine and porphyroblastic secondary gypsum after anhydrite, laminated secondary gypsum (after gypsarenite?), and thick-bedded alabastrine secondary gypsum after glauberite (at some localities) and claystone alternations, alabastrine micro-nodular secondary gypsum after anhydrite and claystone with displacively grown discoidal gypsum crystal alternation, partly primary and partly secondary gypsum with claystone, and, at the top, selenitic gypsum, a lithofacies of the gypsarenite-gypsiferous claystone alternation. The evaporite sequences of the Bozkir Formation can be divided simply into two parts—a lower part represented by predominantly secondary gypsum and an upper part consisting of mainly primary gypsum (selenites and gypsarenites). Geochemical study of the secondary gypsum after glauberite shows that this type of gypsum has less than 1% Na2O, which is attributed to weathering of the outcrop. Thus, typical secondary gypsum textures after glauberite may be used as a guide in Na sulfate exploration.

Invited Review: Contribution of the Scottish Offshore to the advancement of geology

Synopsis Since the late 1960s, the search for hydrocarbons in the seas around Scotland has led to an enormous increase in geological knowledge. In addition to new data related directly to the origins and entrapment of hydrocarbons, the geology of Scotland can now be linked to that of Scandinavia and other parts of adjacent Western Europe via rock sequences in the Central and Northern North Sea which, especially for the Mesozoic and Tertiary, are mostly not represented on the Scottish land surface. Part of the ‘missing’ history of Scotland during that time span can now be deduced from the surrounding offshore geology. Apart from the valuable stratigraphical input, important new information has been gained on aspects of sedimentology (e.g. the distribution of Late Permian evaporites and Early Tertiary turbidites) and structural geology. The previously unknown Central-Viking Graben, trending roughly N-S, began to form in the mid-Permian along the ‘median line’ between Britain and the continent, and was subsequently infilled with Permian sediments, now locally at depths in excess of 10 km. High quality, closely constrained seismic data have shown up previously unknown patterns of extensional and transtensional faults in three dimensions.

Sulfate Minerals in Evaporite Deposits

Evaporite deposits preserve a wealth of information on Earth’s past surface conditions. The deposits are sensitive indicators of depositional environment and climate, recorded in a wide variety of mechanically and chemically produced sedimentary structures and fabrics. Unique to evaporite deposits is the record they carry of the hydrochemistry of surface waters, including seawater. Sulfate minerals are important components in understanding the hydrochemistry of ancient surface waters. Sedimentological aspects of evaporite deposits were compiled by Melvin (1991). In the compilation, sedimentology specific to Ca-bearing sulfates was described by Warren (1991); Lowenstein and Hardie (1985), Handford (1991), and Smoot and Lowenstein (1991) discussed the sedimentology of evaporites in general. These general principles can be applied specifically to the sulfate minerals in evaporite deposits. Sedimentological aspects of sulfate minerals in evaporite deposits are not discussed here. For this information, the reader is referred to the above references. Hardie et al. (1985) and Spencer and Lowenstein (1988) discussed the petrography of evaporites and the interpretation of fabrics of evaporite minerals. Examples of petrographic aspects of sulfate minerals in evaporites are presented here along with references specific to the sulfate minerals. For a more complete understanding of these aspects the reader is referred to the above references. The major focus of this chapter is on the chemical aspects of the common sulfate minerals that occur in evaporite deposits. The discussion begins with an explanation of the concept of chemical divides and the determination of evaporation paths, and the evolution of brines in accordance with mineral solubility and the composition of dilute inflow waters. Determination of the precipitation pathways of the more soluble salts is more complex. Examples of sulfate-mineral assemblages in evaporation systems, calculated via thermochemical modelling, are given for both marine and non-marine systems. The mineralogy of evaporite deposits is …

ABSTRACT: Shale Microfacies-Eagle Ford Group (Cenomanian-Turonian) North-Central Texas Outcrops and Subsurface Equivalents

Abstract The Eagle Ford Group is a mixed siliciclastic/carbonate unit that records a Late Cretaceous (Cenomanian to Turonian) transgression. A major condensed interval (cycle 2.5 of the UZA-2 supercycle) occurs within the Eagle Ford Shale. Eagle Ford strata are overlain disconformably by the Austin Chalk. The Austin/Eagle Ford contact represents the Turonian/Coniacian boundary (89 MA). The Cenomanian/Turonian (92 MA) boundary occurs within the Eagle Ford Group. Regionally, Eagle Ford strata consist of two major depositional units: a lower (transgressive) unit dominated by dark well-laminated shales (exhibiting only minor evidence of bioturbation); and an upper (regressive) unit consisting of thinly interstratified (high-frequency cycles) shales, limestones, and carbonaceous quartzose siltstones. Petrographic characterization of shales from Eagle Ford outcrops near Austin, Waco and Dallas, Texas and subsurface equivalents in a core (Getty #1 J. T. Wilson) from LaSalle County, Texas reveals six microfacies: 1) pyritic shales; 2) phosphatic shales; 3) bentonitic shales; 4) fossiliferous shales; 5) silty (quartzose) shales; and 6) bituminous claystone and shales. Transgressive Eagle Ford shales consist mainly of microfacies 1, 4, and 6. The Eagle Ford condensed interval consists of microfacies 1, 2 and 3, and highstand Eagle Ford shales are comprised of microfacies 4 and 5. Eagle Ford microfacies exhibit distinctive sedimentological aspects and have source rock characteristics that vary systematically within a sequence stratigraphic framework. Transgressive Eagle Ford shales (occurring below the condensed interval) have optimum oil-prone source potential, whereas overlying regressive shales are gas-prone. Transgressive and condensed Eagle Ford strata represent poorly oxygenated low-energy, (below storm wave base) marine paleoenvironments of deposition. In contrast, overlying regressive Eagle Ford lithofacies accumulated in higher energy (above storm wave base), well-oxygenated, shallow marine paleoenvironments.

Sedimentological aspects and preservation of Lower Cretaceous (Aptian) bentonites (fuller's earth) in southern England

Sedimentological aspects and preservation of Lower Cretaceous (Aptian) bentonites (fuller's earth) in southern England

Sedimentological Aspects and Environmental Conditions Recognized from the Bottom Sediments of Al-Kharrar Lagoon, Eastern Red Sea Coastal Plain, Saudi Arabia

Sedimentological Aspects and Environmental Conditions Recognized from the Bottom Sediments of Al-Kharrar Lagoon, Eastern Red Sea Coastal Plain, Saudi Arabia

Paleocurrent and fabric analyses of fluvial conglomerates of the Paleogene Noda Group, northeast Japan

Clast-supported fluvial conglomerates of the Paleogene Noda Group, northeast Japan, consist of two contrasting formations; the lower Minato Formation comprising dominantly acidic volcanic gravels, and the conformably overlying Kuki Formation of Mesozoic basement gravels. Crudely horizontally stratified or massive sheets of conglomerates, facies Gm, comprise most of the sediments of both the formations, and show no abrupt lateral changes of facies. Debris flow deposits are absent from the sediments of the group. Paleocurrent analysis from gravel imbrication of facies Gm suggests that sediments of the Minato Formation were deposited by eastward paleoflow and had multiple sources in the western volcanic range. Such characteristics of the formation seem to show contrasting sedimentological aspects when compared with a typical alluvial fan or a fan delta. Sediments of the lower part of the group were formed as a coalescing braid delta. Elsewhere, denudation of Lower Mesozoic basement rocks in the northern source area provided sources for the uppermost part of the group (Kuki Formation). Fabric and structure of the deposits give some clues to understand the complexities of small-scale fluvial topographies. Symmetrical or asymmetrical concave-up gravel alignments of the conglomerate (facies Gt) suggest a small-scale channel dissecting obliquely into a broad longitudinal bar of facies Gm. Elsewhere, dip orientations of imbricated gravels of facies Gm coincide well with the maximum dip direction of cross-bedding within the overlying sand bar (facies Sp). However, the facies change from Gm to Sp is remarkable. Features of gravel imbrication provide useful information to understand bounding surface problems.

Sedimentological aspects of the Humber Group (Upper Jurassic) of the South Central Graben, UK North Sea

ABSTRACTComplex structure, poorly understood sedimentology and poor biostratigraphic control make the Upper Jurassic Humber Group of the South Central Graben one of the least understood and most complex hydrocarbon reservoirs of the North Sea. Detailed logging of available core from 19 exploration wells has been combined with an improved understanding of the relevance of trace fossils and a recognition of important base‐level variations to provide a greatly enhanced understanding of the depositional system active within the area at that time. A new sedimentological model, based upon the distribution of facies and facies associations, illustrates that Upper Jurassic structure and consequent basin geometry were the principal controls upon the distribution of depositional environments. Rifting and second‐order transgression controlled the back‐stepping onlap patterns observed and higher frequency base‐level fluctuations controlled the internal architecture of individual sandbodies. The model presented accounts for features of these deposits that were previously considered anomalous, such as the thickness of bioturbated sandstones, paucity of foreshore deposits and complex age relationships of sands.

Stratigarphy and Sedimentology of the Kuşçular Formation (Lower Paleocene), the West of Elazığ, Turkey

Stratigraphic and sedimentological aspects of Kuşçular Formation has been firstly recognized in this study which represent in the west of Elazığ. The sediments of this formation consist of seven lithofacies. they are; 1- Massive conglomerates, 2-Stratified conglomerates, 3-Massive sandstones, 4-Horizantel bedded sandstones, 5-Red mudstones, 6-Nodular gypsum, 7-Stratified gypsums. Fine-grained facies are dominant at the lower levels of sequences represent in the prograding alluvial fan envirenments. These successions represent a depositional basin which rapidly filled. Ions necessary for gypsium occurances in the playa deposits are thought to come from the sulfide minerals of Elazığ Complex, crystalline limestone of Keban Metamorphics and Harami Formation.