Ophiomorpha Burrows Research Articles

Geological and biostratigraphical factors in hydrocarbon recovery optimization using integrated seismic, petrophysical, and core data, Niger Delta

The study of geologic heterogeneities (the quality of reservoir rock according to its spatial variation in properties such as grain size, mineralogy, organic content, fossil content, and natural fracture) and their impact on recovery factors, optimization, and performance of injection fluids in concurrent development (production of both oil and gas at the same time) of oil rim reservoirs (reservoirs with a thin oil column that is overlain with a large gas cap) has become necessary to explore the role of geological and biostratigraphical heterogeneity in optimizing hydrocarbon recovery from oil rim reservoirs in the Niger Delta using integrated seismic, petrophysical, and core data. This is to achieve optimum hydrocarbon recovery instead of relying only on development strategies, which is usually the practice and thus fails. Petrel and Eclipse software were used to simulate the static and dynamic models, respectively, for three oil rim reservoirs, using data (seismic, petrophysical, core, and reservoir data) from a green field in the Niger Delta, Nigeria, for concurrent development under the natural depletion (base case), surfactant enhanced-water-alternating-gas (SeWAG), and water-alternating-gas (WAG) injection options. In each option, two scenarios of injection well positions were simulated: gas-oil contact (GOC) and oil-water contact (OWC). Geological studies showed that Reservoir 1 is a heterolith facies of lower-shoreface deposits with traces of Ophiomorpha burrows, Reservoir 2 is a channel facies of lower shoreface deposits with Ophiomorpha burrows, and Reservoir 3 is a heterolith facies of upper shoreface without vertical burrows. When SeWAG of ratio 1:4:2 was injected at OWC, the highest oil recovery factor was observed compared to other options, and injection at GOC gave the highest gas recovery factor. Permeability anisotropy (Kv/Kh) for reservoirs 1 and 2, with Ophiomorpha burrows being considered, was 0.32 and 0.34, respectively. High recovery factors for both oil and gas were recorded. However, the model of the same reservoir without Ophiomorpha burrows gave reduced values of Kv/Kh of 0.12 and 0.15, respectively, with reduced recovery factors. Reservoir 3, which doesn't have burrows in the initial model, has a Kv/Kh value of 0.11 with low recovery factors in various development cases. However, when Ophiomorpha burrows were integrated into the model, Kv/Kh was 0.31, and the recovery factors increased significantly. The study has shown that geological and biostratigraphical interactions induce Kv/Kh. It has a significant optimization impact on recovery factors in concurrent development and enhances vertical sweep efficiency in EOR (Enhanced Oil Recovery). The study further shows that Ophiomorpha burrows improve the geologic heterogeneity quality of a reservoir (permeability anisotropy) by enhancing the injection fluid to get into micro- and macropore spaces for efficient sweeping of oil and gas into the development well.

Non-avian theropod phalanges from the marine Fox Hills Formation (Maastrichtian), western South Dakota, USA.

We report here the first dinosaur skeletal material described from the marine Fox Hills Formation (Maastrichtian) of western South Dakota. The find consists of two theropod pedal phalanges: one recovered from the middle part of the Fairpoint Member in Meade County, South Dakota; and the other from the Iron Lightning Member in Ziebach County, South Dakota. Comparison with pedal phalanges of other theropods suggests strongly that the Fairpoint specimen is a right pedal phalanx, possibly III-2, from a large ornithomimid. The Iron Lightning specimen we cautiously identify as an ornithomimid left pedal phalanx II-2. The Fairpoint bone comes from thinly bedded and cross-bedded marine sandstones containing large hematitic concretions and concretionary horizons. Associated fossils include osteichthyan teeth, fin spines and otoliths, and abundant teeth of common Cretaceous nearshore and pelagic chondrichthyans. Leaf impressions and other plant debris, blocks of fossilized wood, and Ophiomorpha burrows are also common. The Iron Lightning bone comes from a channel deposit composed of fine to coarse sandstone beds, some of which contain bivalves, and a disseminated assemblage of mammal teeth, chondrichthyan teeth, and fragmentary dinosaur teeth and claws. We interpret the depositional environment of the two specimens as marginal marine. The Fairpoint bone derives from a nearshore foreset setting, above wave base subject to tidal flux and storm activity. The Iron Lightning specimen comes from a topset channel infill probably related to deposition on a tidal flat or associated coastal setting. The taphonomic history and ages of the two bones differ. Orthogonal cracks in the cortical bone of the Fairpoint specimen suggest post-mortem desiccation in a dryland coastal setting prior to transport and preservation in the nearby nearshore setting described above. The pristine surface of the Iron Lightning specimen indicates little transport before incorporation into the channel deposit in which it was found. The Fairpoint bone bed most probably lies within the Hoploscaphites nicolletii Ammonite Zone of the early late Maastrichtian, and would therefore have an approximate age of 69 Ma. The Iron Lightning bone is from the overlying H. nebrascensis Ammonite Zone, and is thus about one million years younger.

CHARACTERIZATION OF INCHNOGENERA TRACE FOSSILS IN SEDIMENTARY FACIES; A CASE STUDY OF TOMAYODE FIELD, NIGER DELTA NIGERIA

To provide a comprehensive explanation of the properties and relevance of trace fossils ichnogenera in the Niger Delta sedimentary facies necessitate this study. The provided core photographs containing identified trace fossils were qualitatively analysed and described using ichnofacies characteristics, appearance, lithology, grain size, structures, and depositional environments. Teichichnus and Ophiomorpha burrows have been identified as ichnogenera. They were found in heterolithic fine-grained sandstone with interbedded mudstone that exhibits hummocky and swaley cross – stratifications, as well as ripples cross – laminations, which are frequently encountered in marine shoreface environments. Ophiomorpha and Teichichnus are believed to have been produced by soft-bodied organisms such as crustaceans. They are deposit-feeding organisms with documented evidence of coexistence. The stratigraphic records left by these trace fossils are of particular interest to geologists and other scientists because they aid in palaeo-environmental evaluation, which is a precursor to hydrocarbon generation and accumulation, and subsequent exploration and exploitation.

A review of last interglacial sea-level proxies in the western Atlantic and southwestern Caribbean, from Brazil to Honduras

Abstract. We use a standardized template for Pleistocene sea-level data to review last interglacial (Marine Isotope Stage 5 – MIS 5) sea-level indicators along the coasts of the western Atlantic and southwestern Caribbean, on a transect spanning from Brazil to Honduras and including the islands of Aruba, Bonaire, and Curaçao. We identified six main types of sea-level indicators (beach deposits, coral reef terraces, lagoonal deposits, marine terraces, Ophiomorpha burrows, and tidal notches) and produced 55 standardized data points, each constrained by one or more geochronological methods. Sea-level indicators are well preserved along the Brazilian coasts, providing an almost continuous north-to-south transect. However, this continuity disappears north of the Rio Grande do Norte Brazilian state. According to the sea-level index points (discrete past position of relative sea level in space and time) the paleo sea-level values range from ∼ 5.6 to 20 m above sea level (a.s.l.) in the continental sector and from ∼ 2 to 10 m a.s.l. in the Caribbean islands. In this paper, we address the uncertainties surrounding these values. From our review, we identify that the coasts of northern Brazil, French Guiana, Suriname, Guyana, and Venezuela would benefit from a renewed study of Pleistocene sea-level indicators, as it was not possible to identify sea-level index points for the last interglacial coastal outcrops of these countries. Future research must also be directed at improving the chronological control at several locations, and several sites would benefit from the re-measurement of sea-level index points using more accurate elevation measurement techniques. The database compiled in this study is available in spreadsheet format at the following link: https://doi.org/10.5281/zenodo.5516444 (Version 1.02; Rubio-Sandoval et al., 2021).

Palaeoenvironmental reconstruction and oolitic ironstone mapping of the Agbaja Ironstone Formation in the Nupe Basin, North-central Nigeria: Insights from sedimentological and aeromagnetic analyses

This study focusses on the sedimentological and aeromagnetic characteristics within the Agbaja Ironstone Formation to establish the sedimentary depositional history and map oolitic ironstone zones in the Lokoja district of the Nupe Basin. Forty sandstone samples were collected for granulometric, sedimentary facies and petrographic analyses to reconstruct depositional processes of the Agbaja Ironstone Formation. Aeromagnetic data analysis was engaged to map the oolitic ironstone rich zones. The iron-rich sandstones in the Agbaja Ironstone Formation occur as oolitic ironstone, ironstone concretion and laterites. The bivariate grain size plots and multivariate discriminant analyses suggest that 92% of the sandstone in the formation were deposited in beach and coastal dunes under fluvial-river actions, while 8% are of the marine environment deposited under wave actions. The quartz-feldspar lithic (QFL) ternary diagram and palaeocurrent analyses of the samples revealed that the matured, sub-arkosic sandstones originated from the cratonic interior (Abakaliki uplifts). The bioturbation and reactivation by Ophiomorpha burrows and herringbone on the fine-medium grained sandstones in the formation contributed to the observed high magnetic intensity values. High magnetic signatures (−94.784 to 1.191 nT), analytic signal peaks and depth levels from the 2-D source parameter images are the basis for the produced oolitic ironstones prospectivity map in this study.

Pleistocene Ophiomorpha nodosa from Buenos Aires, Argentina: Paleoenvironmental implications for ghost shrimp trace fossils along South America

Ophiomorpha nodosa Lundgren1891 is described from Puente de Pascua Formation Late Pleistocene of northeastern Buenos Aires province. The pelletal morphology and the base of ramifications of O. nodosa burrows are compared with mid-Holocene, Late Pleistocene Pehuen-Có locality and southern Brazil records. The preservation between sites differs in the degree of erosion and weathering, in situ or ex situ provenance, fragmentary shafts with or without branching and degree of cementation. These comparisons between sites suggest that different environmental conditions have generated the accumulation of trace fossils in transgressive and highstand depositional environments from foreshore through offshore. Neoichnological observations ascribe the burrowing of Ophiomorpha to ghost shrimps. For South American records Audacallichirus (formerly Sergio) mirim Rodrigues and Hödl, 1990 has been suggested as the producer, due to the similarity in morphology between modern and fossil burrows, and geographic distribution of ghost-shrimps. Finding of a widespread ichnotaxon possibly produced by the same taxon in different environmental conditions in the southwestern Atlantic suggests behavioral plasticity. The paleoenvironment of Puente de Pascua Formation in the level with Ophiomorpha burrows is interpreted a tidal flat in intertidal to subtidal depositional environments and relatively calm waters.

Facies Architecture Analysis for Paleo-environment Evaluation in “Tom” Oil Field, Eastern Niger Delta, Nigeria

The cored section of reservoir C, well 4 of the drilled five wells that penetrated three reservoirs A, B and C in “TOM” oil field, Eastern Niger Delta was analysed and described on the basis of lithofacies, sedimentary structures and trace fossil records by using core data and wireline log motifs, with the aim of carrying out thorough geological core analysis to interpret the depositional environment of the oil field. The lithofacies are sandstones with interbedded mudstones and siltstones, the dominant sedimentary structures are parallel to ripple cross laminations, hummocky and swaley cross stratifications, sandy hetherolitics, planar to low angle cross bedding with traces of Teichichnus and Ophiomorpha burrows. The gamma-ray log motifs were noted and used to further constrain the character of the sedimentary facies and depositional environment of the field. A tidal incised – fluvial dominated shallow marine (lower, middle, upper shoreface) comprises of tidal channel sands and tidal flat of the coastal shelf depositional setting in the marginal marine mega depositional environment had been inferred for the “TOM” field.
 Keywords: Shoreface, Reservoir, Lithofacies, Structures

Macroinvertebrate fauna and depositional environment of the lower Upper Cenomanian Oberhäslich Formation in the Saxonian Cretaceous Basin (Germany)

In Saxony (southeast Germany), the global early Late Cretaceous transgression is reflected by the onlap of shallow-marine siliciclastics of the lower Upper Cenomanian Oberhäslich Formation (Calycoceras naviculare Zone) onto the eastern Erzgebirge, the central part of the emergent Mid-European Island. Based on detailed logging of sections south of Dresden and the study of extensive collection material, the depositional environment and macroinvertebrate assemblages of the Oberhäslich Formation have been reconstructed. This unit, with a mean thickness of 10–15m, usually shows a fining-upward trend that may become reversed towards the top, was laid down in a single 3rd-order sea-level cycle and is capped by an unconformity at the base of the overlying upper Upper Cenomanian Dölzschen Formation (sequence boundary Cenomanian 5; junction of the Calycoceras naviculare and Metoicoceras geslinianum zones). The macroinvertebrate assemblage of the Oberhäslich Formation, collected mainly from bioturbated, fine- or rarely medium-grained, quartz-rich sandstones, is fairly diverse, comprising nearly 50 taxa, predominantly bivalves (94.3%). Most conspicuous and abundant are relatively large forms such as Rhynchostreon (R.) suborbiculatum (25%) and Inoceramus pictus spp. (21%), eponymous taxa of the Rhynchostreon suborbiculatum/Inoceramus pictus assemblage. Non-bivalve benthic invertebrates are rare and represented by rather poorly preserved irregular and regular echinoids, siliceous sponges, a few gastropods, crustacean remains and a single starfish. Common Thalassinoides and Ophiomorpha burrows indicate that crustaceans were an important part of the infauna. Pervasive bioturbation resulted in a post-depositional homogenization of the sediments while all body fossils are preserved as (composite) internal moulds. The guild structure of the Rhynchostreon suborbiculatum/Inoceramus pictus assemblage shows a predominance of epifaunal and semi-infaunal suspension feeders (95.3%), suggesting eutrophic and unstable “green-water conditions” of an inner-shelf setting. Deposit-feeding biota are rare. The common occurrence of articulated bivalves and storm-induced shell beds indicate episodic rapid burial, most probably by tempestites. A current-influenced, well-oxygenated and nutrient-rich environment slightly below fair-weather base is inferred for the fine-grained sandy, fossiliferous sediments of the Oberhäslich Formation.

Sedimentary and petrofacies analyses of the Amasiri Sandstone, southern Benue Trough, Nigeria: Implications for depositional environment and tectonic provenance

This study was undertaken to determine the depositional environment, provenance and tectonic setting for the Turonian Amasiri Sandstone, southern Benue Trough, Nigeria, using lithofacies analysis and re-appraisal of petrography of the sandstones. Local stratigraphy and field relationships show a thick succession of shales alternating with elongate/parallel sandstone ridges extending eastwards from Akpoha to Amasiri through Itigidi and Ugep to Apiapum areas. Lithofacies analysis reveals 9 lithofacies suggestive of storm (mass flow) and tidal shelf processes. These include dark grey to black laminated shale/silty mudstones, bioturbated mudstones, coquinoid limestones, very fine-grained bioturbated sandstones with shell hash/debris in places and limestone rip-up clasts, massive and chaotic sandy conglomerate with rip – up clasts, fine to medium-grained, parallel laminated sandstone, hummocky cross-stratified, massive, medium to coarse-grained sandstones, medium to very coarse-grained, planar cross-bedded sandstone, with clay-draped foresets and Ophiomorpha burrows, and coarse-grained trough cross-bedded sandstone. Petrofacies analysis identifies the sandstones as feldspathic and arkosic arenites. Ternary plot of framework mineralogy indicates derivation from an uplifted continental block related to the nearby Oban Massif and Cameroon Basement Complex.

Environmental significance of Ophiomorpha in a transgressive–regressive sequence of the Spitsbergen Paleocene

The study focuses on occurrences of Ophiomorpha burrows in a transgressive–regressive succession composing the Early Paleocene Firkanten Formation deposited in paralic, prodelta to delta front conditions in the Central Basin of Spitsbergen. The burrows colonize sandstones of the Todalen Member at four sites and belong to two ichnospecies: Ophiomorpha cf. nodosa , forming dominantly vertical shafts; and O. cf. irregulaire , consisting of horizontal sinuous tunnels ending in subconical shafts. Both species are observed in shoreface sandstones deposited as a barrier bar. Lithological features and stratigraphic positions suggest that the trace-makers preferentially colonized high-energy sand environments. Foraminiferal faunas occurring below and above the barrier sandstones indicate brackish water conditions for the Ophiomorpha levels, which accordingly are of restricted, monospecific nature. It is inferred that the trace-makers had a dominantly suspension feeding habit as a modern analogue Calianassa major . Portrayed in a sequence stratigraphic framework, the Ophiomorpha -bearing sandstones in middle reaches of the Central Basin were deposited in the final stage of the transgressive systems tract, which drowned the underlying coal-bearing paralic facies. Moreover, in the northern, coal-rich parts of the basin, occurrence of Ophiomorpha signals marine ingression into the paralic system. Keywords: Trace fossils; Paleocene; shoreface sandstones; brackish water; transgression signal. (Published: 6 April 2016) Citation: Polar Research 2016, 35 , 24192, http://dx.doi.org/10.3402/polar.v35.24192

Petrophysical Characterization of Bioturbated Sandstone Reservoir Facies In the Upper Jurassic Ula Formation, Norwegian North Sea, Europe

Abstract A petrophysical study of bioturbated shoreface sandstone rocks was completed by mapping local variations in air permeability measured in core samples acquired from the Upper Jurassic Ula Formation of the Norwegian Central Graben. Analysis of the shoreface fabrics resulting from bioturbation was studied using arithmetic, harmonic, and geometric numerical modeling and analytical techniques. The arithmetic mean best illustrates samples dominated by high volumes of horizontal or subvertical burrows (50–80%). The distal Skolithos to proximal Cruziana ichnofacies is an example of a rock fabric that can be characterized using the arithmetic mean. The harmonic mean best exemplifies samples dominated by low volumes of vertically oriented burrows (10–50%). The archetypal Skolithos ichnofacies is an example of a rock fabric that can be characterized using the harmonic mean. At extreme volumes of bioturbation (90–100%), isotropic flow units begin developing irrespective of burrow orientation. Numerical models of Ophiomorpha in two different sedimentary bedding features (laminated sandstone and massive sandstone) show that single-phase fluid flow is influenced by parameters such as burrow permeability, burrow connectivity, and bioturbation volume. Spot-permeametry measurements show that the Ophiomorpha burrows have higher permeability values than the host matrix. In the laminated-sandstone models, horizontal shale laminae and low bioturbation intensities promote lamination-parallel fluid flow. At higher volumes of bioturbation, fluid flow becomes increasingly isotropic due to greater amounts of burrow interpenetrations across mud laminae. In the massive-sandstone model, no flow barriers exist. As such, low volumes of bioturbation result in only minor influences on fluid flow. At higher volumes of bioturbation, greater burrow interconnectivity occurs and results in an enhancement of vertical and horizontal burrow permeabilities. Based on the results outlined above, this paper emphasizes the impact bioturbation plays in helping improve reservoir quality in the Ula Formation. Perhaps more importantly, the effectiveness of the numerical models presented to characterize fluid flow in different bioturbated fabrics (e.g., archetypal Skolithos ichnofacies) highlights the fact that the fluid-flow results outlined in this paper can also be applied more broadly to different shoreface successions using ichnofacies knowledge alone.

Sedimentological evidence for the Late Holocene sea level change at the Enjefa Beach exposures of Kuwait, NW Arabian Gulf

The mid-late Holocene drop in relative sea level has resulted in the deposition and progradation of coastal facies along the Enjefa Beach in Kuwait, NW Arabian Gulf. These coastal facies display various depositional subenvironments, including landward foreshore beach, tidal channel, shallow tidal channel, and coastal sand flat. The foreshore beach facies consist of dominantly planar laminated beds. Main tidal channel subenvironments are interpreted for the trough cross-bedded facies. The shallow tidal channel deposits are composed of variable oriented planar wedge-shaped and ripple cross-bedded facies. The coastal sand flat deposits consist of extensively burrowed beds with a large network of Ophiomorpha burrows. These exposures are overlain by the recent continental deposits of rubbles and artificial infill. The mere exposed occurrence of these rocks as well as the above facies stacking pattern reflects progradation as a result of relative drop in sea level. Based on the carbon dating of these sediments, the last phase of the relative sea level drop likely occurred around 1,800 years ago. Neotectonics of local structuring, due to the regional northeastward movement of the Arabian Plate under the Zagros Fold Belt, might have a role in this sea receding

Sedimentological Characteristics and Geochemistry of Ajali Sandstone Exposed at Ofe-Jiji and Environs, Northern Anambra Basin, Nigeria

Textural, mineralogical and structural studies as well as outcrop mapping of sandstone in Ofe-Jiji and environs were carried out in order to interpret depositional environment of Ajali sandstone exposed at Ofe-Jiji and environs of the northern Anambra Basin. The sandstone is false bedded, medium-coarse grained (average of 1.13 mm in diameter), poorly sorted and strongly coarsely skewed with an average skewness value of -0.72. Chemical analysis indicates that the sandstone exhibits average SiO₂ contents ranging from 59.12 to 60.20% with an average value of 59.80% while alumina (Al₂O₃) content range between 2.51 and 2.75% with an average of 2.63%. The mineralogical composition shows on the average 56.98 quartz, 6.30 feldspar, 31.78% rock fragment and 4.93% matrix and cement. The major framework composition is Q₅₆ F₃₆ L₂ which classifies the sandstone as lithic arenite. The sub angular texture and the geochemical assay of 22.74 ratios (SiO₂/Al₂O₃) and 3.36 ratios (Na₂O/K₂O) indicate low chemically stable minerals in the sandstone and depict mineralogical immaturity. Also, the average ZTR% index of 52.36% with Tourmaline as the least abundant of ultra-stable minerals indicates sub-mature to immature mineralogy of the sandstone. The sandstone may be described as Fe-Sandstone based on Herron Classification Scheme. The dominance of Fe₂O₃ (26.57%) in the sandstone renders it ferruginous and reflects oxidizing environment. Ophiomorpha burrow in the upper unit of the beds strongly suggests fluvial origin.

Architectural complexity of marine crustacean burrows: unusual helical trace fossils from the Miocene of Mallorca, Spain

Gibert, J.M. de, Mas, G. & Ekdale, A.A. 2012: Architectural complexity of marine crustacean burrows: unusual helical trace fossils from the Miocene of Mallorca, Spain. Lethaia, Vol. 45, pp. 574–585. Unusual helical trace fossils occur in Tortonian shelfal calcarenites in the island of Mallorca. Their morphology may be either simple (ichnogenus Gyrolithes) or, more commonly, consist of two concentric helical burrows (ichnogenus Lapispira). They bear a very characteristic pelleted lining and are associated and probably connected to Thalassinoides and Ophiomorpha burrow systems very abundant in the same unit. These features allow the interpretation that the tracemaker was a thalassinidean shrimp. The complex and compound nature of these trace fossils is comparable to that seen in other modern and fossil crustacean burrow systems, and it reflects the behavioural plasticity of the architects. □Trace fossils, ichnology, ichnofabrics, crustacean burrows, Miocene, shallow marine, Lapispira.

RESPONSE OF TRACEMAKERS TO TEMPORARY PLATFORM DROWNING: LOWER CENOMANIAN OF SOUTHERN ISTRIA (WESTERN CROATIA)

The Early–Late Cretaceous transition marked the beginning of the final disintegration of the Adriatic Carbonate Platform, which eventually resulted in the formation of the Dinarides mountain belt in the Paleogene, Neogene, and Quaternary. In southern Istria (Croatia) a continuous succession crops out that shows deepening from shallow subtidal to carbonate ramp in the latest Albian followed by gradual shallowing in the early Cenomanian, including well-preserved Ophiomorpha and Thalassinoides burrow systems in sections from Cintinera Cove and Vinkuran quarry. Burrow systems that overlie hummocky cross-stratified deposits are good indicators of specific environmental conditions during deposition. During transgression, favorable conditions for suspension- and deposit-feeding crustaceans were established which resulted in complex networks of Ophiomorpha and Thalassinoides. The increase in bioturbation up-section is recorded by a gradual increase in the bioturbation index as well as the size of burrow systems during transgressive events; a completely bioturbated interval in Vinkuran quarry indicates the maximum flooding surface. Formation of burrow systems was interrupted by subsequent clinoform progradation interpreted as a highstand shedding of shallow-marine bioclasts caused by high carbonate production and intense bioerosion of rudist and chondrodont shells, causing the relatively rapid infilling of the basin and re-establishment of the shallow-marine peritidal deposition in the entire northwestern part of the Adriatic Carbonate Platform.

Manganese nodules in the Miocene Bahía Inglesa Formation, north-central Chile: Petrography, geochemistry, genesis and palaeoceanographic significance

Manganese nodules recovered from two stratigraphic horizons of Tortonian–Messinian (late Miocene) age in the Bahía Inglesa Formation of north-central Chile were studied using XRD, SEM and geochemical analysis. The dominant mineral in the nodules is todorokite, which suggests a diagenetic, marine environment. This is supported by field observations of nodules replacing Ophiomorpha burrows. Preliminary, traditional statistical analysis of the nodule geochemistry, including single element, binary and ternary ratios, suggests that the nodules are of the supergene, deep marine type, as also indicated by the presence of foraminifers typical of the upper continental slope, as well as debris flow and turbidity current deposits in an associated submarine palaeocanyon. However, abnormally low Cu concentrations seem to contradict this interpretation, so that additional analyses were carried out. This included multiple discriminant analysis (MDA), as well as a new technique applied for the first time to manganese nodules, namely artificial neural network analysis (ANN). In both methods central log-ratio (CLR) normalization was applied to the raw data. The results, in particular those of the ANN analysis, suggest that the Bahia Inglesa nodules present a chemical signature distinct from that of nodules described to date. A new class is therefore proposed, namely supergene intermediate marine (partially restricted basin).

Sedimentary facies and stratigraphy of a last interglacial coastal barrier in south Brazil

Shoreline sedimentation during the last interglacial highstand on the Rio Grande do Sul Coastal Plain, southern Brazil, is represented by a sandy barrier that extends almost uninterrupted for hundreds of kilometers along the coast. Facies analyses of high quality exposures in several sandpits situated in the northern part of the coastal plain provided an opportunity to examine the stratigraphic nature of these deposits. Based on distinct assemblages of physical and biogenic sedimentary structures, the vertical sequence of facies reveals a regressive (prograded) barrier with vegetated coastal dune sands overlying beach and shallow marine sediments. Progradation was probably promoted by abundant supplies of nearshore sand during the highstand and early fall of sea level (forced regression) associated with the last interglacial period, around 125 ka. As indicated by elevations of Ophiomorpha burrows, the maximum level reached by the sea was around 7 m above the present sea level. Paleocurrent data suggest that, in the studied area, shoreline orientation, hydrodynamics and sediment transport during the last interglacial highstand were similar to present-day conditions.

A late Pleistocene progradational clastic shoreface succession in Jamaica: Implications for the preservation potential of the echinoid Leodia

A section in the Late Pleistocene Port Morant Formation of Jamaica shows a progradational deltaic succession passing from offshore muddy sands, through shoreface to foreshore deposits. The transition zone/lower shoreface has abundant Ophiomorpha burrows and contains common examples of the echinoid Leodia cf. sexiesperforata (Leske). Modern Leodia occur in shallow marine carbonate sands, and the Port Morant occurrence is the first record of abundant Leodia in the geological record. Despite their strong test construction that should give Leodia a high preservation potential, these echinoids have a poor fossil record because the environments in which they lived are rarely preserved. Consequently, the fossil record is biased towards species that occur in environments with high preservation potential.

Decapod Crustaceans from the Maastrichtian Fox Hills Formation

Examination of all known specimens of decapod crustaceans from the Fox Hills Formation has resulted in recognition of five species and three distinctly different forms of pereiopods that cannot be assigned to a recognized taxon with certainty. Callichirus waagei n. sp. is proposed for a callianassid claw preserved within an Ophiomorpha burrow. Hoploparia sp. and Raninella oaheensis Bishop, 1978, are reported from the formation for the first time, and the cheliped of the latter species is noted, also for the first time. Latheticocarcinus shapiroi Bishop, 1988, the most common species of decapod in the formation, is re-described; the lateral flanks of this homolid crab are recognized for the first time, and the carapace is reconstructed. Necrocarcinus siouxensis Feldmann, Awotua and Welshenbaugh, 1976, is noted, but no new specimens were studied. All the decapods were preserved within concretions and all but one specimen of Hoploparia were disarticulated elements, suggesting that they may have been molted remains. Cuticle was well preserved and thin section examination of the lamellar structure of Hoploparia cuticle confirmed that, although thoroughly altered chemically, details of lamellar structure are retained.

Anomuran Microcoprolites from the Lowermost Navesink Formation (Maastrichtian), Monmouth County, New Jersey

Anomuran microcoprolites are preserved in the Late Cretaceous lowermost Navesink Formation in Monmouth County, New Jersey. These microcoprolites occur within lens-to cigar-shaped phosphatic clay masses that occasionally include fragments of anomuran appendages. Individual microcoprolites are pellet-or rod-shaped and morphologically similar in longitudinal and cross-section to fecal material excreted from the ventro-dorsal hindgut of modern anomurans. The association of these anomuran microcoprolites in situ with Ophiomorpha burrows and the decapod crustacean Protocallianassa provides a compelling association for the identity of their producer.