Ancient Depositional Environments Research Articles

Geochemical Characteristics and Geological Significance of Black Shale at the Bottom of the Mufushan Formation in the Lower Cambrian, Lower Yangtze Platform, South China

Black shale, as an important unconventional energy resource, has attracted significant attention in recent years. By studying its sedimentary and geochemical characteristics, it is possible to reconstruct ancient depositional environments and paleoclimatic conditions. The Lower Cambrian black shale is widely distributed in the Lower Yangtze region, but its tectonic background and provenance have been subject to debate. In this study, we conducted geochemical testing and analysis on samples collected from the basal black shale of the Mufushan Formation in the Mufushan section, Nanjing. The Th/Sc-Zr/Sc diagram indicates that the black shale of the Mufushan Formation has not undergone sedimentary recycling. Analysis of major element ratios, rare earth element (REE) distribution patterns, δEu, (La/Yb)N, and the La/Th-Hf and La/Yb-∑REE discrimination diagrams suggest that the source rocks of the black shale mainly consist of granites and sedimentary rocks rich in ferromagnesian minerals, representing felsic rocks derived from the upper crust, with some involvement of mafic rocks. Considering the provenance attributes, geological age relationships, and tectonic evolution of the South China continent, the granite component in the source rocks is inferred to have formed during Neoproterozoic magmatic activity, and the source area corresponds to the Jiangnan Orogenic Belt. Analysis of K2O + Na2O-SiO2, K2O/Na2O-SiO2/Al2O3, La-Th-Sc, Th-Co-Zr/10, and Th-Sc-Zr/10 diagrams suggests that the source area of the Mufushan Formation black shale was a passive continental margin.

Lithofacies analysis and Depositional Environment of Eocene – Paleocene Sediments of Ewekoro Quarry SW, Nigeria

The genetic relationship between depositional processes and rock properties (like lithofacies) provide a potentially powerful tool for interpreting ancient depositional environments. The study aims at a more detailed lithologic and Petrographic description of the sediments of this formation in other to acertain the chemical characteristics of the limestone so as to better delineate its uses both industrially, agriculturally and other applications. Seven samples were collected from Ewekoro quarry on the Latitude of 60481N- 60531N and Longitude of 30351E-30401E south western part of Nigeria. The sediments were subjected to lithologic description and petrographic analysis. The lithologic description was carried out with the aid of binoculars microscope, this shows the following lithologies are present sandy shale, shale, marl, limestone, and sandstone. Petrographic analysis shows that the limestone consists of 90-99% calcite, 0-2% quartz as its constituent minerals, sample NSA2 is mainly Sparitic limestone and sample SSA1 is mainly Micritic limestone. The sandstone composition are 50- 65% quartz, 0-5% feldspar and the calcite serve as the cement and it is about 10-32% of the rock volume. Microfossils account for 10-18%. The sediments were deposited in shallow environment based on the presence of ichnofossils (burrows), micro gastropod shells and other broken shells. From the mineralogy, the calcite crystals are suggests a fresh water vadoze environment while the Sparry calcite shows evidences of diagenesis within the formation. The relative age of foraminifera present indicate a Palaeocene/Eocene boundary to Lower Eocene and a lagoonal to inner neritic environment with little influence of marine transgression. Ewekoro limestone is well suited as a raw material for fertilizer besides its general usuage for cement manufacturing.

Depositional Environments and Stratigraphy of Quaternary Paleochannel Systems Offshore of the Georgia Bight, Southeastern U.S.A.

Long, J.H.; Hanebuth, T.J.J.; Alexander, C.R., and Wehmiller, J.F., 2021. Depositional environments and stratigraphy of Quaternary paleochannel systems offshore of the Georgia Bight, southeastern U.S.A. Journal of Coastal Research, 37(5), 883–905. Coconut Creek (Florida), ISSN 0749-0208. Paleochannels are common subsurface geological features beneath inner continental shelves and coastal plains and are important archives of ancient depositional environments. This study, focusing on a 450-km portion of the inner continental shelf of the SE United States, adds to understanding of the timing of paleochannel development, the paleoenvironments in which they formed, and the mechanisms that drove their formation. Integrated analysis of 1089 km of high-resolution seismic reflection data and 12 sediment cores reveals that (1) most paleochannels documented here formed in backbarrier environments (estuarine or lagoonal) and were subsequently filled during transgression or following avulsion, preserving mud-rich, tidally influenced deposits; (2) the preservation of nonmarine deposits is rare; (3) paleochannels are either solitary or amalgamated, forming paleochannel complexes within which they are arranged in multistory (vertically stacked) or multilateral (horizontally offset) configurations, a product of local hydrodynamic conditions, antecedent geology, glacioeustatic cycles, and regional isostatic adjustments; and (4) a general southerly increase in the overall degree of channelization is observed across the Georgia Bight, a function of long-term accommodation, interaction with underlying stratigraphy, and dominant coastal processes. The composition and spatiotemporal distribution of paleochannel systems has implications for understanding the long-term evolution and preservation of complex coastal systems and informing regional Quaternary sea-level reconstructions.

Modern and Holocene microbial mats and associated microbially induced sedimentary structures (MISS) on the southeastern coast of Tunisia (Mediterranean Sea)

AbstractOn the southeastern Tunisian coastline, very diverse living microbial mats colonize the lower supratidal and intertidal zones, and locally may extend into the upper infratidal zone. The interaction between the benthic cyanobacteria and their siliciclastic substratum leads to the development of several types of microbially induced sedimentary structures (MISS). The mapping of the microbial mats has allowed the identification of the types of MISS that characterize the different segments of the coastal environment. The modern microbial mats have been compared with those recorded at the top of the Holocene deposits, which are composed of biodegraded microbial black mats alternating with white laminae made of clastic and evaporitic sediments, indicative of very high frequency cycles of flood and drought. A hypothetic profile showing their occurrences along the different areas bordering the coastline is proposed as a guide for the reconstruction of the ancient depositional environment. The roles of tidal dynamics, storms, and climate in controlling their genesis and spatial distribution, are discussed and highlighted. The modern MISS of southeastern Tunisia are compared with their equivalents that are well documented through the different geological eras.

PALEOENVIRONMENTAL AND MATURITY INDICATOR OF CEPU BLOCK OIL, WONOCOLO FORMATION, EAST JAVA-INDONESIA

Biomarkers identification of aromatic hydrocarbon fraction of Cepu oil samples was carried out to determine the ancient depositional environment, the source of origin and indicators of the maturity of the old well of the Cepu Block oil, Wonocolo Formation, East Java Indonesia. Biomarkers was identified through the Gas Chromatography-Mass Spectroscopy (GC-MS) method. The distribution of aromatic hydrocarbon biomarkers indicates the presence of naphthalene compounds and their derivatives, sesquiterpenoids, diterpenoids and heterocyclic aromatic groups. The presence of identified biomarkers indicates the source of the oil organic compound coming from higher plants Angiosperms. The presence of methyl phenanthrene and aromatic heterocyclic biomarkers such as dibenzothiophene and dibenzofuran , as well as fluorene shows that Cepu Block oil was deposited not only in the terrestrial environment, but also lacustrine and marin under oxidic precipitation conditions. The presence of methyl phenanthrene with MPI value of 0.86 and isocadalene abundance higher than cadalene indicates moderate to high maturity of the Cepu Block oil analyzed. Keywords: Cepu Block oil, aromatic hydrocarbon, biomarker, paleoenvironment, GC-MS analysis.

Early diagenesis of iron and sulfur in Bornholm Basin sediments: The role of near-surface pyrite formation

Pyrite formation in marine sedimentary environments plays a key role in the global biogeochemical cycles of carbon, sulfur and iron, regulating Earth’s surface redox balance over geological time scales. The sulfur isotopic composition of pyrite is one of the major geochemical tools for investigating early diagenetic processes in modern marine sediments and substantive changes to the Earth’s surface environment in ancient sedimentary rocks. We studied sulfur–iron diagenesis and the sulfur isotopic evolution in sediments of the Bornholm Basin, southwestern Baltic Sea, to track the formation of pyrite in the near-surface sediments. Pyrite accumulation is observed with depth over the uppermost 100 cm before the extent of pyritization of the highly reactive iron pool (Fepy/FeHR) stays constant at ca. 0.9, suggesting that the use of a single iron-speciation parameter as a proxy for anoxic and sulfidic conditions needs to be supported by other independent indicators in sedimentary records. Stable sulfur isotopic analysis demonstrates that the bulk pools of elemental sulfur and iron monosulfide do not exchange isotopes completely with aqueous sulfide. We suggest that the reactions with polysulfide and aqueous sulfide are probably restricted to the surface of the solid-phase sulfur and iron-sulfur aggregates. Although pyrite is growing throughout the uppermost sediment column, the pyrite at depth has a sulfur isotopic composition similar to that of pyrite formed near the sediment surface. To understand the isotopic discrepancy between pyrite and aqueous sulfide in the deeper sediments, we developed a simple diagenetic model, which reproduces the observed sulfur isotopic composition of pyrite well. Our results suggest that much of the pyrite is rapidly formed near the sediment–water interface, and its δ34S is not as influenced by the 34S-enriched pool of aqueous sulfide in the deeper part of the sediment, allowing 32S-enriched pyrite to be preserved in deeper sediments. This near-surface diagenesis and the associated isotopic pattern are possibly of relevance for many marine sediments with high organic matter content, and high aqueous sulfide but low reactive iron availability. Moreover, our sulfur isotopic data demonstrate that extremely slow pyritization is ongoing in the deep lacustrine clay sediments. These results have implications for the interpretation of sulfur–iron geochemical data in both modern and ancient settings as well as for improving reconstructions of ancient depositional environments and a better understanding of the marine sulfur cycle throughout Earth’s history.

ECOLOGICAL AND TAPHONOMIC FIDELITY IN FOSSIL CRINOID ACCUMULATIONS

ABSTRACTAmong fossiliferous marine facies, deposits rich in stalked echinoderms, particularly encrinites, have long been suspected to be susceptible to taphonomic biases because intact calyxes are under-represented or masked by disarticulated skeletal debris. In the middle Mississippian Fort Payne Formation of south-central Kentucky, penecontemporaneous crinoid-rich facies are exposed in close proximity along the shores of Lake Cumberland. Crinoidal packstone buildups preserve a broad preservational spectrum, with articulated crinoid calyxes with arms and columns attached, intact calyxes, holdfasts, and long articulated columns, in a matrix of entirely disarticulated crinoidal fragments. Along a 250 m transect across the flanks and crest of this buildup, identification of 563 specimens of crinoids and blastoids revealed a symmetrical distribution of taxa in which the crest was dominated by disparid and camerate crinoids and the flanks were dominated by camerates. Taphonomic analysis of the same transect showed that intact crinoid calyxes with or without attached arms and column occurred across the entire buildup, but nearly complete specimens with attached arms and column were most common on the western flank and less common on the crest and eastern flank. Taxonomic and taphonomic distributions demonstrate a primary ecologic zonation across the buildup with only localized post-mortem dispersal of crinoids. This is the first demonstration of primary ecologic zonation of a crinoid community preserved within a single lithofacies. Depending on depositional and taphonomic circumstances, crinoids are preserved intact close to their living site; understanding these physical and biological processes provides a significant feedback in reconstructing these ancient depositional environments.

Where does the time go? Assessing the chronostratigraphic fidelity of sedimentary geological outcrops in the Pliocene–Pleistocene Red Crag Formation, eastern England

It is widely understood that Earth's stratigraphic record is an incomplete record of time, but the implications that this has for interpreting sedimentary outcrop have received little attention. Here we consider how time is preserved at outcrop using the Neogene–Quaternary Red Crag Formation, England. The Red Crag Formation hosts sedimentological and ichnological proxies that can be used to assess the time taken to accumulate outcrop expressions of strata, as ancient depositional environments fluctuated between states of deposition, erosion and stasis. We use these to estimate how much time is preserved at outcrop scale and find that every outcrop provides only a vanishingly small window onto unanchored weeks to months within the 600–800 kyr of ‘Crag-time’. Much of the apparently missing time may be accounted for by the parts of the formation at subcrop, rather than outcrop: stratigraphic time has not been lost, but is hidden. The time-completeness of the Red Crag Formation at outcrop appears analogous to that recorded in much older rock units, implying that direct comparison between strata of all ages is valid and that perceived stratigraphic incompleteness is an inconsequential barrier to viewing the outcrop sedimentary-stratigraphic record as a truthful chronicle of Earth history. Supplementary material: Further details of the regional geology and specific information on outcrops are available at https://doi.org/10.6084/m9.figshare.c.4561001

The method of distinguishing sedimentary environment of sandstone reservoirs by XRF

Although XRF elemental analysis is one of the major methods of depositional environment research in shale, it has not formed a unified standard in sandstone. With XRF portable analysis technology developing recently, the advantages of its portability, economy, high efficiency and the protection of the original sample make it more widely used. This study area has only few wells in the northern part of Xihu Sag with the problem of unclear sedimentary facies and sedimentary environment definition. In this case, the work attempts to determine the ancient depositional environment and typical sedimentary microfacies by using XRF core dense sampling method. According to the test accuracy of the hand-held X fluorescence spectrometer, the environmental discrimination elements of Sr, Mn, Ti, Mg, Ca and Fe were selected. The data of the cementing development layer were excluded by the casting and scanning electron microscopy. This paper normalized the relevant elements by GR curve, and the content of related elements in the fine sediment of one unit is obtained, which eliminates possible misjudgement caused by the content of fine sediment in determination of sedimentary environment in the sandstone reservoir. Then this study uses the standardized elemental and elemental ratio of the study area to determine the ancient depositional environment. Finally, according to the relationship between sedimentary microfacies and elements in the study area, two types of reference plate are selected to determine the sedimentary microfacies, providing the basis for fine grading of sedimentary microfacies.

A new model for the formation of microbial polygons in a coastal sabkha setting

AbstractThe stratigraphic record of microbially induced sedimentary structures spans most of the depositional record. Today, microbes continue to generate, bind and modify sediments in a vast range of depositional environments. One of the most cited of these settings is the coastal microbial mat system of the Persian/Arabian Gulf. In this setting, an extensive zone of microbial mat polygons has previously been interpreted as resulting from desiccation‐related contraction during episodic drying. This study employs 15 years of field‐based monitoring of the interaction between environmental factors and the development and evolution of polygon morphologies to test the desiccation model in this setting. On the basis of these observations, a new model is proposed that accounts for the genesis and development of microbial polygons without the need for desiccation‐induced shrinkage. Conversely, the formation, development and erosion of microbial polygons is a direct result of the production of large amounts of organic matter in a healthy, yet spatially limited, microbial community. The recognition of microbial polygons has previously been applied as a diagnostic tool for the reconstruction of ancient depositional environments. The present study calls these interpretations into doubt. It is inferred that preservation of the microbial polygons as a recognizable form would be rare. Biological degradation and compaction will reduce polygons to produce the ‘wispy’ laminae that are a common feature of ancient sabkha lithofacies.

Geobody architecture of continental carbonates: “Gazda” travertine quarry (Süttő, Gerecse Hills, Hungary)

Abstract The Gazda quarry is one of the largest outcrops of the present-day Suttő travertine complex that is situated close to the town of Suttő (Hungary), in the Pannonian Basin. Sedimentological and petrographical analyses show that the Gazda travertine body is built out of phytohermal, wavy laminated, massive and flat laminated travertine lithofacies representing reed mound, slope, lacustrine and palustrine depositional environments, respectively. Based on petrographic analyses, the following three main textural features were recognized that allow to describe the most common microscopic features: (1) micrite textures; (2) micritic coatings and crusts; and (3) different types of clasts. Each major lithofacies is characterized by a particular association of these textural types. The geometry of the travertine beds follows the antecedent land-surface, a NE-SW striking pre-Pleistocene valley. It is proposed that in this valley travertine precipitation took place along a gently sloping terrain. The Gazda travertine system was fed by at least two groundwater-springs. One of them was located NE of the quarry from which waters were flowing along the axis of the valley. The other source was located to the East of the Gazda quarry and waters joined the main water-course along the valley. Closest to the confluence, a phytohermal mound developed with lateral slope and eventual pond depositional systems. Onlapping and interfingering with the flat laminated lithofacies indicate alternating activity of the two springs. Fractures observed in the quarry are mainly related to postdepositional gravitational sliding, however, neotectonic forces resulting in NW-SE tension also played a role in the formation of the fractures. Stable oxygen and carbon isotope analyses show that water temperature was approximately 25 °C. Petrographic studies indicate that only syn-diagenetic processes affected the precipitates. Therefore the original stable oxygen isotope signatures, characteristic of the depositional environment, were preserved. Detailed sedimentological and geochemical study of the Gazda travertine complex allowed small-scale facies characterization providing information about the ancient depositional environment and the heterogeneous nature of these carbonates.

Dolomite formation in the shallow seas of the Alpine Triassic

AbstractThe Alpine Triassic units of Switzerland, Northern Italy and Western Austria offer an extensive geological archive, in which the enigmatic process of dolomite formation can be studied in a palaeoenvironmental context. Recent studies clearly demonstrate that large amounts of the Alpine Triassic dolomites are late diagenetic or hydrothermal. Nevertheless, as part of multiple generations of diagenetic overprint, some generations of fine‐crystalline, Ca‐rich dolomite appear strictly confined to their depositional facies and show signs of very early formation at surface temperatures in specific ancient depositional environments. In this review, three cases of Alpine Triassic dolomites are discussed, where dolomite rocks may have formed during or soon after sedimentation. The sedimentary facies indicate contrasting palaeoenvironmental conditions and, hence, document three different possible processes of dolomite formation: (i) In the Dolomite Mountains (Northern Italy), dolomite beds of the partly isolated Middle Triassic (Anisian/Ladinian) Latemar Platform are confined to the very top of shallowing‐upward lagoonal facies cycles. (ii) Dolomite beds of the San Giorgio Basin (Southern Switzerland), an intra‐platform basin that opened during the Anisian/Ladinian transition, are associated with organic carbon‐rich shales, which were deposited in a deeper water environment under anoxic conditions. (iii) In the entirely dolomitized platform facies of the Dolomia Principale (Hauptdolomit Formation), a very early generation of fine‐crystalline dolomite occurs in the shallowest part of evaporative peritidal cycles. This platform extended over thousands of square kilometres along the Tethys margin during the Late Triassic (Carnian and Norian) and large amounts of carbonate were deposited under hypersaline sabkha‐like conditions. Representing three distinct depositional environments, these three different Triassic systems show features in common with several dolomitization models developed from the study of modern dolomite‐forming environments; for example, the sabkha model, the evaporative lagoon/lake model, the organogenic model and the microbial model. Although these actualistic models may be applicable to reconstruct the palaeoenvironmental conditions during dolomite formation, dolomite‐forming processes during the Triassic were apparently quite different from the modern world in terms of distribution and scale. Recent developments in stable‐isotope geochemistry and high‐resolution geochemical probing offer the possibility to make better reconstructions of Triassic palaeoceanographic conditions and suggest a non‐actualistic approach to better understand dolomite formation during the Triassic.

Greigite from carbonate concretions of the Ediacaran Doushantuo Formation in South China and its environmental implications

Greigite (Fe3S4) is a ferrimagnetic iron sulfide that commonly forms as a precursor of pyrite in anoxic environments where the supply of reactive Fe outpaces that of sulfide (H2S and HS−). Because of its metastability and sensitivity to redox changes during burial, greigite has been rarely documented in rocks older than the Cretaceous. Here we report well-preserved greigite in carbonate concretions of the upper Doushantuo Formation (ca. 551Ma) in the Yangtze Gorge area, South China. Greigite in the carbonate concretions coexists with anhedral and framboidal pyrite, and is distributed in clay-rich carbonates with card-house microtextures and dolomitic spherical structures indicative of early diagenetic formation during shallow burial. Preservation of greigite in carbonate concretions of the upper Doushantuo Formation implies that these concretions maintained a closed micro-system since their formation and that they provide information about the ancient depositional and early diagenetic environments.

Fluvial seismic geomorphology: a view from the surface

Abstract Three-dimensional seismic data enable geoscientists to image the stratigraphic record along selected stratal or time slices. These slices provide detailed images of the planform geometry of ancient depositional systems and environments. In this presentation we attempt to provide a partial answer to the question: what kind of information do nonmarine channel and valley patterns and parameters convey regarding sediment load, channel stability, structural or climatic history of the area, and palaeochannel and reservoir architecture? Geomorphologists have long recognized four basic channel patterns: straight, meandering, braided and anastomosing. They have also developed a classification based on aerial pattern and sediment load. This relationship seems straightforward; however the patterns form a continuum with a great deal of complexity related to degree and character of sinuosity, braiding and anabranching. For example an equal- width sinuous pattern suggests moderate to high lateral stability, and low bed load to suspended load deposits. A wide bend sinuous pattern suggests low to moderate lateral stability, and higher bed load to suspended load deposits. Because of convergence and divergence, interpretation of controls on palaeochannel patterns is difficult. Nevertheless, a better understanding of the various controls on modem river morphology and dynamics can produce useful information regarding palaeo-systems. For example, river type (straight, braided, meandering and anastomosing) depends upon upstream controls such as geologic history (glaciated v. non-glaciated systems), tectonics (relief), lithology (sediment type) and climate (hydrology and vegetation), and downstream controls such as base-level (up and down) and length (avulsion). In addition, factors such as bedrock, active tectonics, floods and vegetation cause considerable pattern variability. Only by taking into account the effect of these controls and by using all available data can there be more predictive and interpretive explanations of seismic data.

Identification and preservation of landforms diagnostic of past ice-sheet activity on continental shelves from three-dimensional seismic evidence

Ice ages have occurred a number of times in Earth9s history, and are important in understanding changes in long-term climate. However, it is difficult to demonstrate the presence of ice sheets in the ancient record because their sedimentary products can resemble those from nonglacial processes (e.g., debris flows). Diagnostic large-scale glacial landforms, produced beneath ice sheets and preserved on continental shelves after deglaciation, can establish a glacial origin. Three-dimensional seismic evidence from the 2.7 Ma Naust Formation, Norwegian margin, illustrates several glacial landforms that are also commonly occurring features on modern high-latitude shelves: (1) streamlined mega-scale lineations produced by fast-flowing ice streams; (2) ploughmarks formed by iceberg keels; and (3) regularly spaced transverse ridges or push moraines formed during ice retreat. We have found, for example, buried ice-keel ploughmarks on a paleoshelf dating to ca. 2 Ma. Norwegian margin seismic stratigraphy data show that ice advanced and retreated many times, and some paleoshelf surfaces were preserved. Such paleosurfaces must survive ocean basin destruction for glacial landforms to be useful in identification of ancient depositional environments.

Stratigraphy and sedimentology of the Middle Ordovician Hawaz Formation (Murzuq Basin, Libya)

The Middle Ordovician Hawaz Formation is a 200-m (660-ft)-thick succession made up of fine-grained quartzarenites displaying a variable degree of bioturbation. It records the deposition in a large-scale, low-gradient estuary, which was partially controlled by tectonic extension. The upper boundary of the formation is marked by two erosion surfaces (unconformities U1 and U2), related to the Late Ordovician glaciation. The U1 and U2 erosion surfaces generated a pronounced paleotopography that controlled the deposition of the Upper Ordovician sequences. Tectonism influenced the paleogeography, although faults were unimportant from the point of view of sedimentary thickness. Tectonic subsidence was moderate, and accumulation rates were low. Physiography favored tidal power, especially during transgressive episodes, when the coastal embayment was flooded. We defined 11 lithofacies, forming 6 facies associations. These associations are subtidal sandstones; storm-reworked, shoreface sandstones; shoreface-to-beach sandstones; channel-sandstone bodies; nearshore to inner-platform sandstones; and K-bentonites. Trace-fossil assemblages match Skolithos and Cruziana archetypal ichnofacies. On the basis of the dominant facies associations and ichnofacies, we divided the formation into three informal units, from base to top: HW.1, HW.2 and HW.3. Periodically, volcanic ash was supplied to the basin from distal eruptive centers and was preserved as thin beds of K-bentonite interstratified with the shoreface sandstones, but not with the tidal-dominated sandstones. We divided the Hawaz Formation into five third-order depositional sequences. Lowstand deposits were not identified. The lower boundaries of transgressive systems tracts are tidal ravinement surfaces or sequence boundaries, whereas the upper boundaries are flooding surfaces. The transgressive systems tracts are constituted by early transgressive tidal deposits separated by a wave ravinement surface from the late transgressive storm-dominated deposits. Highstand systems tracts consist of bioturbated shoreface-to-beach sandstones, which record seaward, shoreline progradation. Emilio obtained his Ph.D. in geology from the Universitat de Barcelona in 1988. Since then, he has been a lecturer in basin analysis and petroleum geology. He has been involved in several research projects on sedimentology and basin analysis in Spain, northern Africa, Antarctica and South America. His present-day research interests include three-dimensional modeling of sedimentary bodies and reservoirs. A professor of stratigraphy at the Universitat de Barcelona, M. Marzo's research interest focuses on the application of clastic sedimentology, sequence stratigraphy, reservoir modeling, and basin analysis to the exploration and production of hydrocarbons. He has been involved in several research projects funded by oil companies in southern Europe, the North Sea, South America, and northern Africa. Jordi M. de Gibert received his Ph.D. from the Universitat de Barcelona in 1996. After a period at the University of Utah, he returned to Barcelona in 1999, where he currently holds a position as a tenure-track lecturer. His interests and areas of expertise include trace fossils, their paleobiological significance, and their implications for understanding ancient depositional environments. K. Tawengi received a B.Sc. degree in geology from Alfateh University, Libya, in 1984, and an M.Sc. degree in sedimentology and stratigraphy from Durham University, England, in 1996. He worked as an explorationist with Agip Oil Company in Libya from 1985 to 2000 and since then has worked as a senior exploration member with REPSOL Exploration in Murzuq S.A. His main fields of interest are sedimentology, stratigraphy, and subsurface geology. A. Khoja graduated in 1972 from the University of Libya. He received a diploma in petroleum geosciences from Oxford Polytechnic (1991) and an M.Sc. degree from Oxford Brookes University (1993). He joined the National Oil Corporation of Libya in 1972 and is presently the regional studies superintendent in the National Oil Exploration Department. Nestor obtained his degree in geology from Cordoba University (Argentina) in 1982 and his postgraduate in petroleum geology in the University of Cuyo, Argentina. He joined YPF in 1984 and worked in their exploratory department in Mendoza, Plaza Huincul, and Neuquen until the year 2000. Subsequently, he became Libya team leader for REPSOL- YPF in Madrid. He is currently director of exploration and production in Brazil.

Types of internal structure and external morphology of submarine dunes under the influence of tide- and wind-driven processes (Dover Strait, northern France)

The expression of tide- and wind-driven processes in the internal architecture and external morphology of very large submarine dunes is investigated at a dune field located in the central part of the Dover Strait (Southern North Sea). Current measurements and sediment transport calculations enable quantification of the dominant tide- and wind-driven processes, and very high resolution seismic recordings are used to analyse internal structure and external morphology of dunes. In the study area, moderate to storm winds induce temporary currents that can lead to the reversal of sediment transport direction and induced erosive processes on the seabed. Dune master-bedding consists of extended erosive surfaces with 9–11° slopes that bound storm-generated sets of cross-beds, 1.5–4.85 m thick (2.65 m on average). Three types of architectures are observed within the dune field, and occasionally within single dunes. These types, which display a strong linkage between internal structure and external morphology, consist of: (1) asymmetric dunes with cosets, which dip in the direction of the marked external asymmetry of the dunes; (2) dunes with a complex external morphology composed of mega-herringbone structures, each displaying an opposing progradation direction; and (3) dunes with a symmetric megaripple bedding unit at their summit. The diversity of the internal architecture and external morphology results from the variable combinations of tide- and wind-driven processes occurring in the study area. The asymmetry of tidal peak current velocity and the relative strength of wind-driven currents are the parameters that have the most important influence on dune architecture. Asymmetric dunes with cosets result from a strong asymmetry in tidal peak current velocity, which is reversed only slightly during storms. Dunes with mega-herringbone structures and dunes with symmetric megaripple units at their summit are observed in areas where the asymmetry of the tidal peak current velocity is negligible, allowing reversal of the sediment transport and dune migration directions each time moderate winds blow. The latter architectural type is specific to sand-rich areas. The different dune architecture types display strong geometrical similarities to structures observed in dunes from other shelf environments where driving processes are different. This implies that a study based only on a geometric description of internal structures will not enable the reconstitution of ancient depositional environments. A better discriminant criteria seems to be the thickness of the second-order sets of cross-beds which is correlated with specific hydro-sedimentary processes. Dune height also probably has an important influence on the thickness of second-order sets of cross-beds, as dune height and set thickness display a clear relationship in the present study.

About this title

It has been increasingly realized by sedimentologist in the petroleum industry and academia that integration of ichonological information into sedimentological models, and vice versa, is one of the main means by which we can improve our understanding of ancient depositional environments. This volume aims to provide an analytical review of yhe ichnology of all major depositional environments and the use ichnology in biostratigraphic and sequence stratigraphic analysis, as well as highly refined palaeeoenvironmental studies. The remit of the book is achieved through a combination of review articles and novel research papers that outline methodologies and protocols for improving our understanding of ancient palaeoenvironments. Trace fossils from microscopic borings to dinosaur footprints are considered. The comprehensive coverage of ancient depositional environments meanc that the book will be of use as a course text for undergraduates as well as an invaluable reference text for all students of ichnologist, sedimentologists or petroleum geologists by trade.

THEMIS characterization of the MER Gusev crater landing site

Gusev crater, previously interpreted as the depocenter for the Gusev‐Ma'adim Vallis fluvio‐lacustrine system, is a proposed landing site for one of the Mars Exploration Rovers (MER). Here we use new remote‐sensing data from the Thermal Emission Imaging System (THEMIS) supplemented by data from the Thermal Emission Spectrometer (TES), Mars Orbiter Camera (MOC), and Mars Orbiter Laser Altimeter (MOLA) to characterize the geology of Gusev crater. Thermal infrared data from THEMIS and TES were used to map thermophysical units on the basis of relative albedos and diurnal temperature variations. THEMIS and MOC visible images were used to map unit morphologies and to estimate crater density ages. MOLA data were used to identify unit contacts and stratigraphic relationships. Various data were then combined to construct a new surface unit map and stratigraphy for units on the floor of Gusev. Seven surface units were identified in Gusev, mostly Hesperian in age, but with two showing evidence of later modification and redistribution. Five or more surface units and layering are present within the MER‐A landing ellipse, attesting to the geologic diversity of this site. Surface units show features that could be consistent with fluvio‐lacustrine, aeolian, and/or volcanoclastic deposition, but the spatial resolution of visible/infrared data does not allow for the identification of unambiguous volcanic or fluvio‐lacustrine textures. However, a MER landing in Gusev may provide the opportunity to analyze multiple units, distinguish rock types, examine stratigraphic relationships, and shed light on the ancient depositional environment.

Pterosaur swim tracks and other ichnological evidence of behaviour and ecology

Abstract New finds of pterosaur tracks (cf. Pteraichnus ) from the Summerville and Sundance formations (Late Jurassic) of western North America associated with elongate scrape marks and small circular paired depressions indicate that pterosaurs could swim, or at least float in water, and that they may have fed on small animals living at the sediment surface in shallow water. In this respect their behaviour resembled certain seabirds. The ichnological evidence for pterosaur ‘swim’ and ‘feeding’ traces consists of scrape marks interpreted as traces left when the paddling limb of a pterosaur registered on the substrate, and small circular paired depressions as traces left when the beak of a pterosaur was probing for food. Such traces resulting from aquatic activity are consistent with the nearshore environments in which pterosaur bones and trackways have been found. There is growing evidence for an extensive and complex Pteraichnus ichnofacies in the Late Jurassic of western North America; over 80 specimens have been collected with many more remaining in the field. In particular we draw attention to the large quantitative data base that is available for morphometric, size-frequency studies and the potential for behavioural studies of individual locomotion and flocking. In addition the sites hold considerable promise for understanding what appears to be the world’s largest pterosaur ichnofacies in the context of ancient depositional environments and regional sequence stratigraphy.