Marine Shelf Deposits Research Articles

Early-Middle Jurassic lithological and depositional facies of the Da Lat back-arc basin

The Da Lat back-arc basin formed on a deformed lithosphere caused by subduction of the Paleo-Pacific plate under Eurasia in the Mesozoic.
 Lithology and sedimentary structure analysis from field works and UAV imaging show that the Early-Middle Jurassic deposits in this area can be divided into 7 types of litho-depositional facies: (i) coastal conglomerate; (ii) channel/shallow lake sandstone; (iii) shoreface sandstone; (iv) estuarine siltstone and mudstone; (v) deep marine shale; (vi) mass transport deposits; and (vii) turbidite.
 These facies’ spatio-temporal distributions are closely related to their grain size. In the basin margin, Early Jurassic coarse-grained deposits are exposed, marking the opening of the basin, grading upward into shallow marine-shelf deposits. In the Middle Jurassic, the basin margin was uplifted corresponding to continental depositional environment, while the basin centre was filled by outer shelf deposits, reflecting a deepening process. Interbedding with these deposits are near shore and estuarine deposits.

MIDDLE-LATE PERMIAN AND EARLY TRIASSIC FORAMINIFERAL ASSEMBLAGES IN THE WESTERN SALT RANGE, PAKISTAN

A newly obtained foraminiferal assemblage from the Guadalupian−Lopingian, and Induan of the Western Salt Range (Pakistan) comprises 47 species (including 7 species of fusulinoideans) of 24 genera and 71 species (including 9 species of fusulinoideans) of 41 genera, in Nammal and Zaluch sections, respectively. Our results show that only 4 species went extinct during the Guadalupian−Lopingian mass extinction (GLME), suggesting the GLME was minor for smaller foraminifers in the Salt Range. Most species went extinct during the Permian-Triassic mass extinction (PTME), except the two survivor genera, Nodosinelloides and Planiinvoluta. During the end-Permian mass extinction, majorities of the species became extinct in lower part of Chhidru Formation, beacuse they are not tolerant to the terigenious-clastic input in the upper part of Chhidru Formation. The extinction process of foraminifers in the Nammal and Zaluch sections has been documented for the first time. Five foraminiferal assemblages are established in the shallow marine shelf deposits of Western Salt Range, i.e., Wordian Geinitzina araxensis assemblage in tide-influenced subaqueous delta to middle shelf environment, Capitanian Baisalina pulchra assemblage and Wuchiapingian Codonofusiella schubertellinoides assemblage in inner-outer shelf carbonate deposits, Changhsingian Colaniella pseudolepida assemblage and Induan Nodosinelloides-Planiinvoluta assemblage in mixed siliciclastic–carbonate shelf setting. The Baisalina pulchra and Codonofusiella schubertellinoides assemblages have wide geographic distribution and have been found in Transcaucasus, China, Turkey, Crimea and Oman. The other three assemblages (i.e., Geinitzina araxensis, Colaniella pseudolepida, and Nodosinelloides-Planiinvoluta assemblages) found in this study are likely local/regional assemblages. The foraminifers were observed with the standard microscopic system Leica-DM500. A total of 681 specimens of foraminifers are reported in the Zaluch Group and Mianwali Formation of Nammal and Zaluch sections. Five hundred ninety-nine smaller foraminifers specimens were recovered. Among the smaller foraminifera, Nodosinelloides, Pachyphloia, Geinitzina, Colaniella, Hemigordius, Tuberitina, and Langella are the most dominant genera. Larger foraminifera genera include Nankinella, Codonofusiella, Reichelina, Necdetina and Pisolina, represented by 82 specimens. A total of 3 classes (e.g., Nodosariata, Fusulinata, and Tubothalamea) and seven orders (i.e., Miliolida, Spirillinida, Lagenida, Parathuramminida, Endothyrida, Fusulinida, and Earlandiida) are identified in the current study. Among them, Lagenida becomes the most dominant by diversity and abundance. Shannon diversity and other indices rise progressively from Wordian to Changhsingian in the shallow marine sediments before dropping to zero in the Early Triassic mixed siliciclastic–carbonate shelf deposits.

Firmground crustacean burrow systems (Glossifungites ichnofacies) in marine shelf deposits, Paleocene Clayton Formation, Alabama, USA

The Paleocene (Danian) Clayton Formation of western Alabama, USA, includes multiple marine shelf parasequences, each comprising a relatively thick marl, capped by a thin limestone, the latter variably reflecting marine flooding episodes. The marls host relatively large firmground burrow systems that penetrate 50–60 cm beneath, and are cast by, superjacent limestones. Excavation of two partially exposed burrow systems – one beneath a highstand parasequence-bounding flooding surface and the other beneath an overlying coplanar sequence boundary/transgressive surface (SB/TS) – reveals complex, primarily horizontal, irregularly branching networks. The former, allied with Thalassinoides paradoxicus, lacks wall bioglyphs, whereas the latter, allied with Spongeliomorpha iberica, is characterized by pervasive, mainly rhombohedral wall bioglyphs that reflect a relatively more firm substrate. Contrasts between these burrow systems are consistent with sequence stratigraphical context and inferred differences in the mechanism and magnitude of depositional hiatuses responsible for firmground development. Both excavated burrow systems likely represent cumulative structures produced by multiple organisms over extended periods of time. The cumulative nature and potential taphonomic biases associated with these and comparable burrow systems in the stratigraphical record preclude confident interpretation of tracemakers and their behaviours. The Clayton burrow systems likely were produced by one or more species of decapod crustacean that engaged in suspension-feeding, surface detritus feeding, gardening or some combination thereof.

Gems and Placers—A Genetic Relationship Par Excellence

Gemstones form in metamorphic, magmatic, and sedimentary rocks. In sedimentary units, these minerals were emplaced by organic and inorganic chemical processes and also found in clastic deposits as a result of weathering, erosion, transport, and deposition leading to what is called the formation of placer deposits. Of the approximately 150 gemstones, roughly 40 can be recovered from placer deposits for a profit after having passed through the “natural processing plant” encompassing the aforementioned stages in an aquatic and aeolian regime. It is mainly the group of heavy minerals that plays the major part among the placer-type gemstones (almandine, apatite, (chrome) diopside, (chrome) tourmaline, chrysoberyl, demantoid, diamond, enstatite, hessonite, hiddenite, kornerupine, kunzite, kyanite, peridote, pyrope, rhodolite, spessartine, (chrome) titanite, spinel, ruby, sapphire, padparaja, tanzanite, zoisite, topaz, tsavorite, and zircon). Silica and beryl, both light minerals by definition (minerals with a density less than 2.8–2.9 g/cm3, minerals with a density greater than this are called heavy minerals, also sometimes abbreviated to “heavies”. This technical term has no connotation as to the presence or absence of heavy metals), can also appear in some placers and won for a profit (agate, amethyst, citrine, emerald, quartz, rose quartz, smoky quartz, morganite, and aquamarine, beryl). This is also true for the fossilized tree resin, which has a density similar to the light minerals. Going downhill from the source area to the basin means in effect separating the wheat from the chaff, showcase from the jeweler quality, because only the flawless and strongest contenders among the gemstones survive it all. On the other way round, gem minerals can also be used as pathfinder minerals for primary or secondary gemstone deposits of their own together with a series of other non-gemmy material that is genetically linked to these gemstones in magmatic and metamorphic gem deposits. All placer types known to be relevant for the accumulation of non-gemmy material are also found as trap-site of gemstones (residual, eluvial, colluvial, alluvial, deltaic, aeolian, and marine shelf deposits). Running water and wind can separate minerals according to their physical-chemical features, whereas glaciers can only transport minerals and rocks but do not sort and separate placer-type minerals. Nevertheless till (unconsolidated mineral matter transported by the ice without re-deposition of fluvio-glacial processes) exploration is a technique successfully used to delineate ore bodies of, for example, diamonds. The general parameters that matter during accumulation of gemstones in placers are their intrinsic value controlled by the size and hardness and the extrinsic factors controlling the evolution of the landscape through time such as weathering, erosion, and vertical movements and fertility of the hinterland as to the minerals targeted upon. Morphoclimatic processes take particular effect in the humid tropical and mid humid mid-latitude zones (chemical weathering) and in the periglacial/glacial and the high-altitude/mountain zones, where mechanical weathering and the paleogradients are high. Some tectono-geographic elements such as unconformities, hiatuses, and sequence boundaries (often with incised valley fills and karstic landforms) are also known as planar architectural elements in sequence stratigraphy and applied to marine and correlative continental environments where they play a significant role in forward modeling of gemstone accumulation. The present study on gems and gemstone placers is a reference example of fine-tuning the “Chessboard classification scheme of mineral deposits” (Dill 2010) and a sedimentary supplement to the digital maps that form the core of the overview “Gemstones and geosciences in space and time” (Dill and Weber 2013).

Shuram–Wonoka carbon isotope excursion: Ediacaran revolution in the world ocean's meridional overturning circulation

The late Ediacaran Shuram–Wonoka excursion, with δ13Ccarb values as low as –12‰ (PDB) in marine-shelf deposits and spanning up to 10 Myr, is the deepest and most protracted δ13Ccarb negative anomaly recognised in Earth history. The excursion formed on at least four continents in low (≤32°) palaeolatitudes, and in China is associated with a major phosphogenic event. Global and intrabasinal correlation, magnetostratigraphy, isotope conglomerate tests and further geochemical data are consistent with a primary or syn-depositional origin for the excursion. Continental-margin phosphorites are generated by oceanic upwelling driven by surface winds, and δ13Ccarb negative anomalies are explicable by oceanic upwelling of 13C-depleted deep oceanic waters, arguing that a feature common to these exceptional Ediacaran events was unprecedented perturbation of the world ocean. These events occurred during the transition from an alien Proterozoic world marked by low-palaeolatitude glaciation near sea level and strong seasonality to the familiar Phanerozoic Earth with circum-polar glaciation and temperate climate, suggesting that the Shuram–Wonoka excursion is related to this profound change in Earth's climate system. Of various hypotheses for Proterozoic low-palaeolatitude glaciation, only the high obliquity (>54°) hypothesis, which posits secular decrease in obliquity to near the present-day value (23.5°) during the Ediacaran, predicts an unparalleled revolution in the Ediacaran world ocean. The obliquity controls the sense of the world ocean's meridional overturning circulation, which today is driven by the sinking of cold, dense water at the poles and upwelling driven by zonal surface winds. When the decreasing obliquity passed the critical value of 54° during the Ediacaran the meridional temperature gradient reversed, with the equator becoming warmer than the poles and Hadley low-latitude (<30°–35°) atmospheric zonal circulation reversing. This reversal of the temperature gradient is unique to the Ediacaran Period and caused reversal of the oceanic meridional overturning circulation, with upwelling of anoxic, 13C-depleted deep oceanic waters producing a deeply negative and protracted δ13Ccarb signature on late Ediacaran marine-shelf deposits.

Cambrian–Ordovician orogenesis in Himalayan equatorial Gondwana

An early Paleozoic tectonic event, the Kurgiakh orogeny, has long been known from the western Tethyan Himalaya, and it is conspicuously recorded by an angular unconformity between Cambrian marine shelf deposits and coarse Ordovician conglomerate, as well as widespread granitic plutons. Although the lateral extent of this event is poorly known, two regions in the central and eastern Himalaya, the Kumaon of India and klippen of Bhutan, contain conglomerate units that may be correlative with this event. In the Kumaon, the Ralam Formation, which contains a basal polymictic conglomerate unit with detrital zircon grains as young as ca. 512 Ma, is overlain by sandstone containing the arthropod walking trace Diplichnites gouldi , an ichnospecies known from Ordovician and younger strata. The late early Cambrian trilobite Redlichia sp., recovered from the underlying Martoli Group, indicates that the conglomerate is post−early Cambrian and, based on stratigraphic analysis, also likely records the Kurgiakh orogeny. In central Bhutan, the lower Paleozoic succession contains conglomerate units with monomictic quartz sandstone clasts and less mature sandstone matrix. These units have also been assigned to a variety of ages, but rocks that apparently underlie these strata contain the Furongian (late Cambrian) zonal trilobite Kaolishania granulosa . Here, we show that detrital zircon ages of a conglomerate clast (no grains younger than = ca. 781 Ma) are distinctly older than those of the matrix, which contains a large peak at 490−500 Ma. Thus, these conglomerate units are also potential lateral correlatives of the Ordovician conglomerate deposits of the western Himalaya. Our paleontological and geochronologic data suggest that the Kumaon and Bhutan conglomerate units, and possible equivalents in Tibet, correlate with those of the western Himalaya. This increases their known along-strike extent by over 1000 km, bringing the total extent to ∼1200 km. Thus, the Kurgiakh orogeny spanned much of the Himalayan orogen along the northern Gondwanan margin and reflected a widespread tectonic reorganization of the peri-Gondwanan realm to Andean-type margins. Recent work indicates that it also likely extended into the Lhasa block and both the North and South China blocks. This event was associated with widespread ca. 500 Ma arc-related plutonism recorded in the Himalaya, and with abundant detrital zircon grains of that age in younger Himalaya strata. Based on current fossil data, the duration of the hiatus associated with the Cambrian-Ordovician boundary, which separates pre- and postdeformational strata, ranges from 22 to 36 m.y. Available geochronological data do not provide greater constraint. If the event was close in age to the depositional age of the Ordovician molasse, then the main phase of tectonic uplift, erosion, and deposition may have been much later than the presumed Cambrian-Ordovician boundary interval age of ca. 485 Ma.

Geomorphology control on the development of reservoir depositional systems, Devonian Donghetang Formation in the Tabei Uplift of the Tarim Basin, China

The Devonian Donghetang Formation is one of the important extensive marine sandstone units for oil/gas exploration on Tabei Uplift of the Tarim Basin, particularly in the Hade and Halahatang oilfields. However, not all of this sandstone is good quality reservoir, and so the sedimentary facies are critical to prediction of reservoir in the area. Based on an analysis of logs, core, outcrop and seismic data, a new hypothesis is proposed for the Donghetang Formation as a 2nd or 3rd order stratigraphic sequence (SQ_Ddh), formed between unconformities Tg22 (top) and Tg3 (bottom), consisting of local transgressive (braided delta deposits) and extensive high-stand (foreshore and shoreface deposits) system tracts. Through networked seismic data, integrated with erosion and decompaction correction, the palaeogeomorphology during development of SQ_Ddh has been reconstructed and several geomorphological units can be distinguished. The sedimentary facies and distribution of SQ_Ddh were related closely to the depositional geomorphology. Between the margin of the northern paleo-uplift zone and the northwestern and northeastern depressions there developed braided deltas during the period of the early TST, and wave-dominated shorelines during the HST period when extensive shorefaces developed across the central low-uplift zone. Beyond the southeastern shoreline, there developed offshore and marine-shelf deposits. The foreshore and delta-front mouth bar sandstones constitute the most favorable reservoir, surrounding the paleo-uplift and the marginal uplift zones.

Sequence Stratigraphy of Miocene Tide-Influenced Sandstones In the Minas Field, Sumatra, Indonesia

Abstract The Miocene Sihapas Group in the Minas field, Indonesia, is composed of a succession of tens-of-meters-thick, erosionally based, tide-influenced sandstone intervals interbedded with marine shale-dominated intervals. Despite more than 1600 wells drilled into this 12-km-wide by 30-km-long mature super-giant field, complex internal tidal facies architecture within these sandstone intervals makes predicting local connectivity within the reservoirs challenging. Past interpretations of Minas field suggested that reservoir sandstone intervals are incised-valley deposits, based on assumptions that abrupt coarsening at the base of reservoirs reflects river incision into the shelf and tidal reservoir facies formed in coastal embayments during transgression. In this paper a new interpretation is proposed that suggests that shorelines remained strongly tide-influenced throughout regressive–transgressive depositional episodes. Pronounced discontinuity surfaces in these deposits are interpreted to have formed by a variety of mechanisms: (1) tidal erosion of the sea floor in front of regressing shorelines; (2) lowstand fluvial valley incision; and (3) the reworking of deposits during transgression of the shelf. Consideration of a wider variety of regressive and transgressive tidal depositional settings and erosional processes allowed revision of Minas field stratigraphy to better explain the observed complex facies variations that control reservoir production behavior. Minas field is divided into five major reservoir intervals that overlie low-grade metamorphic basement. The older deposits, comprising the S and D reservoir intervals, contain multiple upward-coarsening tide-influenced regressive shoreline successions, locally cut out by tide-influenced channel sandstone bodies, and capped by thin beds of marine shelf transgressive sandstone and overlying marine shale. Seismic images indicate that these deposits filled erosional basement topography during a period of long-term relative sea level rise. The upper three reservoir intervals (B, A2, and A1) are each interpreted to be fourth-order regressive shoreline deposits that were variably reworked by tidal currents during transgression. Successive intervals record progressively lower average rate of accommodation development, more rapid falling-stage regression, deeper lowstand incision, and greater reworking during intervening transgressions. Together, these three intervals comprise a third-order, flooding-surface-defined, forward-stepping sequence set deposited on a low-gradient continental shelf. Paradoxically, because intervals deposited during more rapid progradation tend to be thinner, in most wells more regressive sandstone intervals contain proportionally more open marine shelf deposits. This reflects that valley incision is localized, and regressive deposits that formed in lower long-term accommodation growth rate settings tend to be more completely reworked by tidal currents during subsequent transgression.

First Triassic lungfish from the Arabian Peninsula

Triassic lungfish (Dipnoi) have been extensively documented from the Gondwanan continental and marine shelf deposits of Africa and Madagascar (Teixeira, 1949; Lehman et al., 1959; Beltan, 1968; Martin, 1979, 1981; Kemp 1996), Australia (Kemp, 1993, 1994, 1997a, 1998), India (Jain et al, 1964; Jain, 1968), and Antarctica (Dziewa, 1980). Numerous records also exist from Laurasian landmasses including Europe (Agassiz, 1838; Schultze, 1981), North America (Case, 1921) and central and eastern Asia (Liu and Yeh, 1957; Vorobyeva, 1967; Martin and Ingavat, 1982). By comparison, nothing is known of contemporary lungfish fossils from the Middle East. Thus, the recent recovery of a single tooth plate representing a new geographic occurrence of the genusCeratodusAgassiz, 1838 from paralic marine deposits of the Jilh Formation, a latest Anisian to lower Carnian unit that crops out along the eastern margin of the Proterozoic Arabian Shield in central Saudi Arabia (Fig. 1), is significant because it provides the stratigraphically oldest record of dipnoans from the Arabian Peninsula.

Chemical composition of the graphitic black carbon fraction in riverine and marine sediments at sub-micron scales using carbon X-ray spectromicroscopy

The chemical composition of the graphitic black carbon (GBC) fraction of marine organic matter was explored in several marine and freshwater sedimentary environments along the west coast of North America and the Pacific Ocean. Analysis by carbon X-ray absorption near-edge structure spectroscopy and scanning transmission X-ray microscopy shows the GBC fraction of Stillaguamish River surface sediments to be dominated by more highly ordered and impure forms of graphite, together forming about 80% of the GBC, with a smaller percent of an aliphatic carbon component. Eel River Margin surface sediments had very little highly ordered graphite, and were instead dominated by amorphous carbon and to a lesser extent, impure graphite. However, the GBC of surface sediments from the Washington State Slope and the Mexico Margin was composed almost solely of amorphous carbon. Pre-anthropogenic, highly oxidized deep-sea sediments from the open Equatorial Pacific Ocean contained over half their GBC in different forms of graphite as well as highly aliphatic carbon, low aromatic/highly acidic aliphatic carbon, low aromatic/highly aliphatic carbon, and amorphous forms of carbon. Our results clearly show the impact of graphite and amorphous C phases in the BC fraction in modern riverine sediments and nearby marine shelf deposits. The pre-anthropogenic Equatorial Pacific GBC fraction is remarkable in the existence of highly ordered graphite.

Transgressive changes from tidal estuarine to marine embayment depositional systems: The Lower Cretaceous Woburn Sands of southern England and comparison with Holocene analogs

The Lower Cretaceous Woburn Sands (Lower Greensand Group) in southern England constitutes one of the most intensively studied tidal sandstone outcrops for sedimentological and reservoir analog studies. Most recent workers have interpreted the whole 30–60-m (100–200-ft)-thick succession around Leighton Buzzard as representing an ancient tide-dominated estuary. However, unequivocal estuary characteristics are limited to the lowermost part (about 15–20 m [50–66 ft]). We suggest that a significant portion of the Woburn Sands, and most of the middle part, was formed in a tide-dominated marine embayment. Hence, the vertical facies change from the lower to middle part of the Woburn Sands is interpreted as a change from (1) a narrow estuary to (2) a broad marine embayment. The Wash embayment in eastern England is a striking modern analog; it receives most of its sediments and waters from marine sources and is largely filled with nondiluted seawater. Moreover, the Holocene transgressive history of The Wash is remarkably similar to the transgressive evolution of the Woburn Sands. Early estuarine sequence models predict landward translation of facies zones along the valley thalweg during transgression, but eventual facies translation in the strike direction has not been fully documented or discussed. An embayment facies that is not commonly confined in the early incised valley can occur vertically between the estuarine valley fill and marine shelf deposits and is probably underrepresented in current models. However, this segment of the transgression, comprising along-strike bay expansion and the development of a broad marine embayment, may be more important than previously thought.

Geochemical study of some Cretaceous rocks from Kuwait: comparison with oils from Cretaceous and Jurassic reservoirs

A set of 18 Cretaceous rock samples from wells drilled in the Raudhatain and Minagish Oil Fields and 10 oil samples from Cretaceous reservoirs (Raudhatain, Bahra, Burgan and Minagish Oil Fields) were characterized using geochemical methods including compound-specific carbon isotope analyses of n-alkanes and isoprenoids. In addition, one oil (Miqua) from the Jurassic (Marat Formation) of the Great Burgan Oil Field was included in the study. Despite having high organic carbon content in some samples, the Burgan and Zubair formations and the Ratawi Shale Member, of Albian to Valanginian age, are not source rocks for the oils for several reasons, but primarily due to lack of correlation of molecular and isotope chemistry as well as a humic organic matter type. These results are consistent with the corresponding depositional conditions for these rocks, which are deltaic/estuarine in the Burgan Formation and littoral/deltaic in the Zubair Formation. The Minagish and Sulaiy Formations of Late Jurassic to Cretaceous age appear to be potential source rock candidates based on their molecular and bulk isotope geochemistry. Detailed isotopic analysis using individual normal and isoprenoid C15+ alkanes did not provide a good correlation between these possible source rocks and the oils. However, one sample from the Sulaiy Formation was found to be comparable to the oils. The oils belong to the same genetic family and were expelled from a source rock with a dominant carbonate lithology (e.g. the Sulaiy-Minagish Formations). These formations contain sulphur-rich, amorphous kerogen as observed in recent, shallow marine shelf deposits. The Miqua oil, which accumulated in the Jurassic Marat Formation reservoir, does not differ from the other oils in terms of genetic characteristics. This oil is the deepest and most mature of the set. Maturity assessment has not been possible using well-known parameters based on steranes, terpanes or methylphenanthrenes. However, sulphur-bearing aromatics, comprised of alkylated BT and DBT, show important variations. Parameters based on alkylated BT and DBT have been applied successfully as tools to evaluate maturity changes. Oil maturity was determined to be middle oil window, but has been found not to be related directly to the present depth of the reservoir. However, it has been established that within the same oil field, oil maturity increases with reservoir depth. Evaluation of these maturity characteristics may be related to major chronological events, especially major tectonic movements that have enabled oil to fill different reservoirs successively. The reconstruction of the most important phases, i.e. genesis and migration through active faults, will provide guidelines to understand the present-day maturity pattern of these oils.

FÁCIES, ANÁLISE ESTRATIGRÁFICA E EVOLUÇÃO PÓS-GLACIAL DO MEMBRO TRIUNFO/FORMAÇÃO RIO BONITO, NA FAIXA SUBAFLORANTE DO NORTE CATARINENSE

The Triunfo Member, the unit of Rio Bonito Formation, is the post-glacial deltaic system of the glaciomarine and marine sedimentation of the Rio do Sul Formation (Itarare Group). The wells drilled by CPRM in the eastern margin of Parana Basin are continuously and constitute an important documentation of the Rio Bonito Formation. The sequential analysis of seven wells in northern Santa Catarina State allows the characterization of the following facies successions/associations: glaciomarine, deglaciation, fluvial, deltaic, and marine offshore to shoreface. A stratigraphic section through the studied wells reveals the lateral distribution of the facies associations and the mapping of erosional regressive (corresponding to sequence boundaries) and transgressive surfaces. The investigated area is compartmentalized into three sedimentation domains: the northern one, PP9 to PP 11 wells, where six depositional sequences (four in the Rio do Sul-Triunfo transition and two in the Triunfo Member) overlie the marine substrate of the Rio do Sul Formation. Each sequence is formed by fluvial, deltaic and deglaciation associations (lower part of the sequence), and by glaciomarine and marine associations (upper part). Despite little sampling in the Rio do Sul Formation, the central domain reveals distinctive characteristics (PP6 to PP8 wells): thick glaciomarine deposits in the Rio do Sul substrate, thin transition zone and the predominance of fluvial associations in the Triunfo Member. The southern domain, PP4 and PP5 wells, has thick marine shelf deposits in the underlying Rio do Sul Formation, which partially corresponds to the Rio do Sul-Triunfo transition from the northern domain. Five depositional sequences are identified in the southern domain, and they are correlated with the central and northern domains. In addition, the marine shelf association of the southern domain changes laterally to deltaic deposits toward south (the basal Triunfo delta of the Rio do Sul area).

FÁCIES, ANÁLISE ESTRATIGRÁFICA E EVOLUÇÃO PÓS-GLACIAL DO MEMBRO TRIUNFO/FORMAÇÃO RIO BONITO, NA FAIXA SUBAFLORANTE DO NORTE CATARINENSE

The Triunfo Member, the basal unit of Rio Bonito Formation, is the post-glacial deltaic system of the glaciomarine and marine sedimentation of the Rio do Sul Formation (Itararé Group). The wells drilled by CPRM in the eastern margin of Paraná Basin are continuously and constitute an important documentation of the Rio Bonito Formation. The sequential analysis of seven wells in northern Santa Catarina State allows the characterization of the following fácies successions/associations: glaciomarine, deglaciation, fluvial, deltaic, and marine offshore to shoreface. A stratigraphic section through the studied wells reveals the lateral distribution of the fácies associations and the mapping of erosional regressive (corresponding to sequence boundaries) and transgressive surfaces. The investigated area is compartmentalized into three sedimentation domains: the northern one, PP9 to PP 11 wells, where six depositional sequences (four in the Rio do Sul-Triunfo "transition" and two in the Triunfo Member) overlie the marine substrate of the Rio do Sul Formation. Each sequence is formed by fluvial, deltaic and deglaciation associations (lower part of the sequence), and by glaciomarine and marine associations (upper part). Despite little sampling in the Rio do Sul Formation, the central domain reveals distinctive characteristics (PP6 to PP8 wells): thick glaciomarine deposits in the Rio do Sul substrate, thin "transition" zone and the predominance of fluvial associations in the Triunfo Member. The southern domain, PP4 and PP5 wells, has thick marine shelf deposits in the underlying Rio do Sul Formation, which partially corresponds to the Rio do Sul-Triunfo "transition" from the northern domain. Five depositional sequences are identified in the southern domain, and they are correlated with the central and northern domains. In addition, the marine shelf association of the southern domain changes laterally to deltaic deposits toward south (the "basal Triunfo delta" of the Rio do Sul área).

Lithostratigraphy and geological setting of Upper Proterozoic shoreline-shelf deposits, Hagen Fjord Group, eastern North Greenland

During the Late Proterozoic a more than 1000 m thick succession of sediments was deposited on the shelf fringing the north-eastern corner of the Greenland craton. These sediments were classified together with an underlying turbidite sequence in the Hagen Fjord Group (Haller, 1961), which is here redefined to contain only Upper Proterozoic, mainly shallow marine shelf deposits outcropping between Independence Fjord and Kronprins Christian Land in eastern North Greenland. Both siliciclastic and carbonate sedimentation occurred during the Late Proterozoic, and the changing tectonic environment along the northern and eastern shelf-margin of Greenland at that time is well recorded within the sediment sequence. Correlation of the Hagen Fjord Group with similar shelf deposits elsewhere along the eastern and northern margin of the Canadian-Greenlandian Shield is discussed.

Teredolites, wood substrates, and sea-level dynamics

Allochthonous logs and/or Teredolites , clavate borings produced within xylic (wood) substrates, occur in extraordinary abundance as sedimentary components in transgressive marine shelf deposits of the lower Paleocene Clayton Formation in western Alabama. It is pro-posed herein that the abundance and preservational state of these components were controlled by (1) an influx pulse of xylic substrates into marine and marginal-marine environments, (2) hydraulic concentration of substrates during ravinement, and (3) condensation associated with sediment starvation, all three of which are induced by sea-level rise. The proposed relations among fossil wood, ichnofossils produced therein, and sea-level dynamics may be of use in the discrimination of sequence stratigraphic packages and their bounding surfaces; these relations also have implications for paleobotanical prospecting and the biological evolution and stratigraphic distribution of marine organisms that inhabit xylic substrates.

Trace fossils from the Lower Cambrian Bastion Formation of North-East Greenland

New trace fossil collections are described from Lower Cambrian siliciclastic shallow marine shelf deposits of the Bastion Formation of North-East Greenland, together with a taxonomic re-assessment of previously reported material. The entire assemblage comprises 19 ichnogenera, 25 ichnospecies, as well as two vernacular ichnotaxa. Although no new ichnotaxa are present the material reveals new information on the 3-dimensional structure of two of the contained ichnogenera, namely Plagiogmus Roedel and Psammichnites TorelI. The stratigraphic range of a single ichnospecies, Rusophycus latus Webby, is formally extended from the Lower Ordovician to the Lower Cambrian. The assemblage compares favourably with Lower Cambrian ichnocoenoses described from other continents, particularly at the ichnogeneric level. Comparison with similar sequences suggests that the sub-trilobitic Lower Bastion Formation is late Tommotian to early Atdabanian in age, possibly entirely Atdabanian.

Glacially- and tidally-influenced shallow marine sedimentation of the late Precambrian Port Askaig Formation, Scotland

The late Precambrian Port Askaig Formation forms part of the thick succession of metasediments and volcanics of the Dalradian Supergroup of northwest Britain. The glacianegnic Port Askaig Formation is well exposed on the Garvellach Islands in western Scotland and consists of a series of thick and regionally extensive diamictites interbedded with sandstones, siltstones, dolomites and minor conglomerates. Diamictite facies are similar to glaciomarine diamicts described from the Late Cenozoic Yakataga Formation in the Gulf of Alaska, formed by settling of fine-grained suspended sediment and ice-rafting in relatively shallow water (< 250 m) . Two particularly distinctive diamictite units, the Great Breccia and the Disrupted Beds are interpreted as the product of downslope resedimentation events; it is significant that the Port Askaig Formation was deposited during a period of increasing tectonic activity in the Dalradian Basin. Thick and extensive sand sequences interbedded with the diamictite facies are interpreted as tidally influenced shallow marine shelf deposits; sands may have been derived from deltaic sources on the basin margin and transported into the basin during storms. The entire Port Askaig Formation appears to represent an overall shallowing upwards sequence punctuated by smaller scale transgressive (diamictite) and regressive (sandstone) events. Interpretation of the Port Askaig Formation as a succession of glacially and tidally-influenced shelf sediments has significant implications for the reconstruction of palaeoclimatic histories and regional palaeogeographies during late Precambrian time.

Mineralogy and Diagenesis of Miocene and Pleistocene Sediments, Northeastern Gulf of Mexico: ABSTRACT

Cored Miocene and Pleistocene sediments from the northeastern Gulf of Mexico (ranging in depth from 1,400 to 2,000 m) consist of interbedded sands, silts, and muds with varying degrees of consolidation. Samples selected from these sediments were studied for their mineralogy and diagenesis. The Miocene sediments represent various subenvironments of the ancestral Mississippi River delta complex; Pleistocene sediments are marine shelf deposits. Sands from both Miocene and Pleistocene cores are fine to very fine-grained feldspathic litharenites with abundant (approx. = 25%) matrix fines and minor (<7%) carbonate clasts and shell fragments. Carbonate diagenesis is a continuing process in these sediments. Clayey sands contain disseminated siderite crystallites formed during organic matter fermentation. In clean sands, scattered thin (<15 cm) bands of poikilotopic carbonate-cemented sand are present in the middle of thicker unconsolidated intervals. Cemented bands are thicker in the Miocene section, having grown during burial through dissolution of shell fragments and reprecipitation at the margin of cemented zones. Diagenetic events evident in the Miocene core illustrate processes that could occur in the Pleistocene sediments with continued burial. These are: (1) dolomitization of some calcite cements, (2) precipitation of Fe-carbonate as crystallites, rims on dolomite cements, and overgrowths on siderite crystallites, andmore » (3) zeolite formation on amorphous silica substrates. Amorphous silica is associated with limited dissolution of feldspars or lithic fragments.« less

Submarine Canyon, Slope, and Shelf Sedimentation in an Upper Eocene-Oligocene Progradational System (Limnos Island, North Aegean Sea, Greece): ABSTRACT

The only well-exposed outcrops of a post-Alpine late Eocene-Oligocene basin in the north Aegean Sea are at Limnos Island. These mostly consist of typical slope deposits overlain by remnants of shallow marine shelf and continental (braided-river) deposits. Three main slope lithofacies are distinguished. Canyon deposits consist of thick-bedded, massive, and pebbly sandstones (facies B), conglomerates (facies A), pebbly mudstone where the matrix shows flow (facies F), rock falls (nummulitic limestones), and zones of slump folds in sandstones (facies F). Channelized facies of massive sandstones, classical turbidites, and thin interbeds of sandstone and mudstone (facies E - probably overbank or levee deposits) are associated with canyon deposits. Pelagic and hemipelagic slope deposits consist of mudstone (facies G) and thin-bedded sandstone (facies D) with occasional small to medium-scale slump folds. These mud-rich slope deposits are incised by several channels filled with conglomerates, thick massive sandstones with well-developed dish structures, and turbidites interbedded with thin layers of mudstone (facies C). This unit composes a typical thinning and fining-upward sequence.