Ichnological Diversity Research Articles

Cenomanian/Turonian oceanic anoxic event 2 in October oil field, central Gulf of Suez, Egypt

Gulf of Suez is one of the world most prolific Cretaceous and Miocene oil provinces in Egypt. In this basin the Late Cenomanian/Early Turonian organic rich limestone and shale sediments are referred to oceanic anoxic event 2 (OAE2). Two oil-cored wells (GS 197-2 and OCT-A8) have encountered the Late Cenomanian/Early Turonian Abu Qada Formation in October Field, central part of Gulf of Suez. The aim of this work is to pick the global Cenomanian/Turonian anoxic boundary in the subsurface sediments within the Gulf of Suez basin. Consequently, the core samples of the studied wells have been investigated in order to recognize the lithofacies, biostratigraphy, geochemistry and isotope content of upper Raha, Abu Qada and lower Wata formations. The microfacies association of anoxic middle to outer shelf marine were recognized. In addition, remarkable turnover and significant change in biostratigraphy and ichnological diversity and abundance were confirmed the abrupt change in oxidation and nutrition the Cenomanian-Turonian boundary. The recorded positive δ13C excursion (1.8‰) matched with maximum TOC value encountered to mark OAE2 as well as source rock maturity and potentiality of Abu Qada Formation. The neighboring exposed section of Abu Qada Formation in Gabal Nezzazat show similar isotopic and biostratigraphic characteristics that recorded in the studied wells. This work define the Cenomanian-Turonian OAE2 as material based chronostratigraphic surface boundary in Nezzazat Group from surface to subsurface integrated data to improve sequence stratigraphic interpretation of the heterogeneous Upper Cretaceous shallow marine reservoirs in Gulf of Suez.

Using a modern analogue to interpret depositional position in ancient fluvial-tidal channels: Example from the McMurray Formation, Canada

The fluvial–tidal transition (FTT) is a complex depositional zone, where fluvial flow is modified by tides as rivers approach a receiving marine basin. Variations in the relative importance of tidal versus fluvial processes lead to a distinctive distribution of sediments that accumulate on channel bars. The FTT generally consists of three broad zones: (1) a freshwater-tidal zone; (2) a tidally influenced freshwater to brackish-water transition; and (3) a zone of relatively sustained brackish-water conditions with stronger tides. A very common type of deposit through the fluvial–tidal transition, especially on the margins of migrating channels, is inclined heterolithic stratification (IHS). At present, a detailed account of changes in the character of IHS across the FTT of a paleo-channel system has not been reported, although a number of modern examples have been documented. To fill this gap, we quantitatively assess the sedimentology and ichnology of IHS from seven cored intervals in three geographic areas situated within the youngest paleovalley (“A” Valley) in the Lower Cretaceous McMurray Formation of Alberta, Canada. We compare the data to trends defined along the FTT in the present-day Fraser River in British Columbia, Canada to interpret paleo-depositional position in the ancient fluvial–tidal channels.Analysis determined that the mean mudstone thickness is 8.2 cm in the southern study area (SA). Mean thickness increases to 11 cm in the central study area (CA), and decreases again to 4.4 cm in the northern study area (NA). The proportion of mudstone is 31% in SA, 44% in CA, and 27% in NA. Thickness-weighted mean bioturbation intensity in sands varied from 0.29 in SA and CA, to 0.28 in NA. On the other hand, thickness-weighted mean bioturbation intensity (BI) in mudstone increases from 1.46 in SA, to 1.77 in CA, and is 1.94 in NA. The ichnological diversity also increased from south to north.Sedimentological results show similar trends to those of the Fraser River, enabling the identification of a freshwater to brackish-water transition zone with tidal influence. The interpreted position of the transition is underpinned by the bioturbation intensity and trace-fossil diversity trends, indicating periodic brackish-water conditions throughout SA in the McMurray Formation during low river flow conditions. Together, these data suggest that a broad FTT existed in the “A” Valley, with fluvial-dominated channels to the south that experienced seasonal brackish-water inundation during base flow, and channels experiencing increasing brackish-water influence lying further north towards a turbidity maximum zone. The FTT zone appears to have extended for several hundred kilometers from south to north.Based on the sedimentological and ichnological data, as well as estimations of lateral accretion rates, we refute the commonly applied Mississippi River depositional analogue for McMurray Formation channels. Rather, we show that while not a perfect fit, the tidally influenced Fraser River shows much greater agreement with the depositional character recorded in McMurray Formation IHS. Future work on the McMurray system should focus on characterizing tide-dominated deltaic and estuarine systems, such as the Ganges-Brahmaputra, and on forward-modeling the evolution of tide-dominated and tide-influenced river systems.

A Dinosaur Ichnocoenosis from the Waterberg Plateau (Etjo Formation, Lower Jurassic), Namibia

ABSTRACTAbout a hundred dinosaur tracks, mostly preserved as isolated footprints, have been recorded at a single site within the borders of the Waterberg National Park, Otjozondjupa Region, north-central Namibia. They are found in an interdune setting within the Lower Jurassic Etjo Formation and represent medium-sized theropods with slender digits and high projection of digit three. From an ichnotaxonomic point of view, the Namibian tracks are intermediate in morphology between Grallator (which is known to occur at other localities within the same Etjo Formation) and Anchisauripus, being otherwise in a size range that is usually considered typical for the latter ichnotaxon or even for Eubrontes. The Waterberg tracks do not match the allometric growth model proposed by Olsen et al. (1998) for the Early Jurassic theropod track assemblage of the North American Connecticut Valley, and they highlight the difficulties of consistently discriminating between theropod ichnotaxa in the Grallator-Anchisauripus-Eubrontes plexus. The Waterberg ichnosite adds important data to our understanding of the ichnological diversity of the Etjo Formation, raising to three the dinosaur localities in Namibia with revised and updated ichnofaunas. The dinosaur ichnofauna from Namibia, of which the Waterberg tracksite is a basic component, shows high ichnotaxonomic similarity with coeval assemblages from the northern hemisphere. This points to an overall homogeneity of the global ichnofaunistic composition, even at lower latitudes.

Oregon Sea Stack: Ecological Diversity of a Modern Trypanites Ichnofacies

The paleoecology of rocky substrates in the rock record is commonly interpreted based on ichnology and is frequently associated with a bioeroding community (the Trypanites Ichnofacies) with low ichnological diversity. However, analyses of a modern, siliciclastic, intertidal hardground community at Lion Rock, located at Arcadia Beach State Park, Oregon, reveals a diverse community of boring, encrusting, and squatting/clinging organisms. Through observations and descriptions of organism distribution and abundance, more than 40 species of plants and animals are reported to reside within three littoral zones (upper, middle, and lower littoral zone) on the sea stack. A newly established erosional lower littoral zone is a subdivision of the lower littoral zone, where shifting foreshore sand influences colonization and biotic diversity. Borings are produced by four bivalves, Adula californiensis, Hiatella arctica, Penitella penita, and Zirfaea pilsbryi, and are identified as Gastrochaenolites traces. It is likely that ancient Trypanites Ichnofacies communities had considerably higher diversity and faunal abundance than their ichnological record indicates. It is also likely that Trypanites Ichnofacies are much more dynamic environments, with shifting sediment, wave energy and tidal energy influences. Comparisons with modern assemblages are thus crucial in assessing these environments in ancient successions.

Bioerosion of inorganic hard substrates in the Silurian of Estonia (Baltica)

Carbonate hardgrounds are unevenly distributed in the Silurian of Estonia, with only three bioeroded hardgrounds in the Telychian and one in the late Pridoli. There seem to be no trends in the bioerosion intensities and ichnotaxonomical diversity in the Silurian of Estonia. Only Trypanites occurs in the hardgrounds of the Silurian of Estonia and ichnological diversity of bioeroded organic hard substrates, containing Trypanites, Palaeosabella and Osprioneides is higher than inorganic substrates. The small number of bioeroded inorganic substrates could indicate that these substrates were probably less important than the organic hard substrates for the development of seafloor ecological niches in the Silurian of Estonia. The average bioerosion intensities of the hardgrounds are relatively high, but not unusual for the Silurian.

Ichnofabric characterization in cores: a method of digital image treatment

Ichnofabric analysis, as a relatively young ichnological approach, has witnessed rapid growth, showing its usefulness in basin analysis, with special attention to palaeoenvironmental interpretations. The ichnofabric approach has evolved from the description of trace composition and the intensity of bioturbation to integrate detailed information on numerous ichnofabric features, such as primary sedimentary structures, ichnological diversity, ichnological features, cross-cutting relation ships or tiering structures. This development has been associated with its application to the study of deep-sea sediments, especially in research on cores, which is not easy, owing to the particular features of cores. Here a method for improving ichnofabric characterization in modern marine cores is presented, on the basis of digital high-resolution image treatment, with special emphasis on the quantification of ichnofabric attributes. The proposed methodology is based on the modification of three image adjustments ( image adjustment ), the estimation of the percentage of the area occupied by bioturbation ( digital estimation ), the lateral and vertical quantification and comparison of pixel values for the infill of the trace fossils and the host sediment ( pixel counting ), and the integration of the information obtained in the visual representations of ichnofabrics (the ichnofabric representation ). The sequential application of these proposed steps allow, 1) better identification of trace fossils, together with cross-cutting relation ships and the characterization of trace-fossil assemblages, 2) estimation of the percent age of bioturbation associated to each ichnotaxon, the whole ichnocoenosis, or a complete ichnofabric, 3) differentiation between biodeformational structures and trace fossils, discrimination between ichnotaxa, distinction between passively and actively infilled structures, and 4) evaluation of the depth of penetration by particular tracemakers.

Patterns and Processes in the Ordovician Bioerosion Revolution

The Ordovician Bioerosion Revolution was a dramatic diversification of macroboring ichnotaxa during the Middle and Late Ordovician. This was also a time during which the intensity of carbonate substrate bioerosion greatly increased, reaching a peak in the Late Ordovician and Early Silurian that was not achieved again until the Jurassic. This burst of ichnological diversity was a function of the Ordovician Radiation of marine invertebrates, and it reflects the range and rate of niche differentiation on hard substrates at that time.

Analysis and application of ichnofabrics

Bioturbation at all scales, which tends to replace the primary fabric of a sediment by the ichnofabric (the overall fabric of a sediment that has been bioturbated), is now recognised as playing a major role in facies interpretation. The manner in which the substrate may be colonized, and the physical, chemical and ecological controls (grainsize, sedimentation rate, oxygenation, nutrition, salinity, ethology, community structure and succession), together with the several ways in which the substrate is tiered by bioturbators, are the factors and processes that determine the nature of the ichnofabric. Eleven main styles of substrate tiering are described, ranging from single, pioneer colonization to complex tiering under equilibria, their modification under environmental deterioration and amelioration, and diagenetic enhancement or obscuration. Ichnofabrics may be assessed by four attributes: primary sedimentary factors, Bioturbation Index (BI), burrow size and frequency, and ichnological diversity. Construction of tier and ichnofabric constituent diagrams aid visualization and comparison. The breaks or changes in colonization and style of tiering at key stratal surfaces accentuate the surfaces, and many reflect a major environmental shift of the trace-forming biota due to change in hydrodynamic regime (leading to non-deposition and/or erosion and/or lithification), change in salinity regime, or subaerial exposure. The succession of gradational or abrupt changes in ichnofabric through genetically related successions, together with changes in colonization and tiering across event beds, may also be interpreted in terms of changes in environmental parameters. It is not the ichnotaxa per se that are important in discriminating between ichnofabrics, but rather the environmental conditions that determine the overall style of colonization. Fabrics composed of different ichnotaxa (and different taphonomies) but similar tier structure and ichnoguild may form in similar environments of different age or different latitude. Appreciation of colonization and tiering styles places ancient ichnofabrics on a sound process-related basis for environmental interpretation.

Body Form and Trackway Pattern in Australian Desert Monitors (Squamata: Varanidae): Comparing Zoological and Ichnological Diversity

Other| June 01, 2000 Body Form and Trackway Pattern in Australian Desert Monitors (Squamata: Varanidae): Comparing Zoological and Ichnological Diversity JAMES O. FARLOW; JAMES O. FARLOW 1Department of Geosciences, Indiana-Purdue University at Fort Wayne, IN 46805 Search for other works by this author on: GSW Google Scholar ERIC R. PIANKA ERIC R. PIANKA 2Integrative Biology, C0930, University of Texas, Austin, TX 78712-1064 Search for other works by this author on: GSW Google Scholar PALAIOS (2000) 15 (3): 235–247. https://doi.org/10.1669/0883-1351(2000)015<0235:BFATPI>2.0.CO;2 Article history accepted: 07 Feb 2000 first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation JAMES O. FARLOW, ERIC R. PIANKA; Body Form and Trackway Pattern in Australian Desert Monitors (Squamata: Varanidae): Comparing Zoological and Ichnological Diversity. PALAIOS 2000;; 15 (3): 235–247. doi: https://doi.org/10.1669/0883-1351(2000)015<0235:BFATPI>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyPALAIOS Search Advanced Search Abstract To what extent does ichnological diversity (the number of distinctive trace fossil morphologies) serve as a proxy for zoological diversity (species richness of trackmakers in the living fauna) in footprint assemblages made by terrestrial lower vertebrates? This question was investigated in a study of body form and trackway features of monitor lizards (varanids) from the Western Australian desert. Body-shape parameters deemed likely to affect trackway pattern of seven varanid species were measured. These lizards differ in average adult size, but there is considerable size overlap between adults of small-bodied species and juveniles of large-bodied species. Although subtle species differences in body form were detected, these were largely swamped by intraspecific variability. Furthermore, the most distinctive features in which trails of monitor species differ reflect interspecific differences in foraging behavior rather than anatomical differences, and are features that would be difficult or impossible to recognize without actually capturing the trackmaker. These observations provide empirical support for the widely held belief that trace fossil diversity commonly under-represents zoological diversity. The degree to which this is so is likely to be influenced by trackmaker body size and metabolic physiology. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Body Form and Trackway Pattern in Australian Desert Monitors (Squamata: Varanidae): Comparing Zoological and Ichnological Diversity

Abstract To what extent does ichnological diversity (the number of distinctive trace fossil morphologies) serve as a proxy for zoological diversity (species richness of trackmakers in the living fauna) in footprint assemblages made by terrestrial lower vertebrates? This question was investigated in a study of body form and trackway features of monitor lizards (varanids) from the Western Australian desert. Body-shape parameters deemed likely to affect trackway pattern of seven varanid species were measured. These lizards differ in average adult size, but there is considerable size overlap between adults of small-bodied species and juveniles of large-bodied species. Although subtle species differences in body form were detected, these were largely swamped by intraspecific variability. Furthermore, the most distinctive features in which trails of monitor species differ reflect interspecific differences in foraging behavior rather than anatomical differences, and are features that would be difficult or imposs...

Ichnology of a glacially-influenced continental shelf and slope; the Late Cenozoic Gulf of Alaska (Yakataga Formation)

The study of trace fossils in glaciomarine strata is important because of the low preservation potential of fauna but glaciomarine settings have received little attention from ichnologists. Widespread biological activity is recorded by ichnofossil assemblages in glaciomarine strata of the Late Cenozoic (6 Ma to present) Yakataga Formation, Alaska. Glacial sedimentation began in the Gulf of Alaska in the Miocene along a deep water active margin basin dominated by turbidity currents and debris flows. Later strata record progradation of the continental slope by mass flow processes and the establishment of a broad shelf influenced by repeated glaciation, ice-rafting of coarse debris, changes in water depth and salinity, storms, earthquakes, and high sedimentation rates. Yakataga Formation strata show overall, a limited ichnological diversity and low degree of bioturbation in relation to comparable non-glacial settings although certain beds are highly bioturbated. Twenty-four ichnotaxa are identified and grouped into nine assemblages characteristic of different depositional settings and substrate types. Ichnogenera and body fossil evidence shows that polychaetes, arthropods, molluscs and echinoderms were the dominant infaunal benthic organisms with deposit feeding being the predominant feeding strategy; poorly consolidated muddy sediments excluded suspension feeders and limited the development of the Skolithos ichnofacies typical of non-glacial shelves characterized by clean, shifting sand substrates. Evidence of rapid sedimentation is given by escape structures (fugichnia), the presence of Diplocraterion, and by the mass mortality of bivalves. Firm-ground burrows, typical of the Glossifungites ichnofacies, are associated with erosional surfaces, boulder pavements and coquinas. Diminutive feeding traces may reflect salinities lowered by glacial meltwater inputs. The downslope transport of food by turbidity currents and mass flows may explain the development of a diverse Cruziana ichnofacies in water depths where in non-glacial settings the Nereites ichnofacies is found. An ichnological summary is presented for the Late Cenozoic Gulf of Alaska continental margin; similar ecological conditions obtain in the modern setting and provide valuable supportive data. Ichnofacies identified from the Yakataga Formation are probably widespread in Late Paleozoic and Late Cenozoic glacially-influenced marine strata.