Ichnofabric Analysis Research Articles

Trace fossil evidences of an Early Miocene paleoseismic event and depositional regime change from the Kutch (Kachchh) Basin

Unconsolidated siliciclastic sediments can undergo post-burial deformation, which leads to the formation of distinctive sedimentary structures, known as soft-sediment deformation structures (SSDS). The presence of a series of sand volcanoes confined to a particular lithostratigraphic horizon can represent a paleoseismic activity and, thereby, exemplifies the concept of “seismite”. The Kutch Basin has been a tectonically active region since the initiation of eastern Gondwana rifting followed by a tectonic inversion during the Cenozoic due to the collision of the Indian and Eurasian plates. A stratum-bound series of sand volcanoes belonging to the Khari Nadi Formation (KNF) is exposed along the banks of Khari River. They separate the shallow marine deposits below and non-marine deposits above with their characteristic marine and paleosol trace fossil suites, respectively. Although a seismogenic origin has been much debated for the SSDS, the ichnofabric analysis of the sand-volcano-bearing stratum unequivocally points toward such an origin under a shallow seafloor condition. In addition to the sedimentary regime change from an open shallow-marine setting to a continental depositional environment concomitant with basinal uplift, the behavior of the burrowing crustaceans testifies to a syn-depositional development of a fault network associated with the fluidization, sand volcanism, and the resilience of the trace-producers in surviving those processes until the sedimentary regime change in the overlying strata. Although the ichno-sedimentological evidence apparently differs from the previous works that proposed a continuous base-level rise from the beginning of deposition of the Khari Nadi Formation up to the middle part of the overlying Chhasra Formation, the paleoseismic activity, its ichnologic signature, and the depositional regime change refer to a higher-resolution (i.e., lower-order) sequence-stratigraphic change causing a short-duration regression within a longer-duration cycle of base-level rise.

Burdigalian ichnofabric from the Guri Member, Dezful Embayment, southwestern Iran

The carbonate strata of the Burdigalian Guri Member are located in the Dezful Embayment along the northern Persian Gulf shore. Ichnofabric analysis and paleoecology of the Guri Member in the Dezful Embayment are described by investigating three outcrop sections. The facies features of the Guri Member show a very shallow marine environment with high oxidation content. The Guri Member contains remarkably well-preserved specimens of Thalassinoides suevicus. It is mainly recorded as Y and T forms in the shallow water facies. Two ichnofabrics were recognized in the dominantly carbonate sedimentary succession. Ichnofabrics A, and B are interpreted as representing the tidal flat and lagoon environments respectively. Ichnofabric interpretation of the Miankuh section might be simply indicating more time to colonization in relation to the Parsi section. Keywords: ichnofabric, Miocene, Dezful Embayment, Guri Member.

UNLOCKING THE ARCHITECTURE OF THE COLONIZATION WINDOW: ICHNOFABRICS FROM UPPER CRETACEOUS TIDE-INFLUENCED MEANDER-LOOP DEPOSITS

ABSTRACT Studies dealing with the colonization window typically emphasize two major features: duration (short term vs. long term) and frequency of colonization (episodic vs. continuous). However, our understanding of tide-influenced meander loops requires consideration of an additional feature, the architecture of the colonization window, which comprises not only the spatial dimension and geometry of the colonization surface, but also its evolution through time. Tide-influenced meander-loop systems show a heterogeneous trace-fossil distribution that reflects the variety of processes operating along the point-bar and overbank colonization surfaces. Ichnofabric analysis of tide-influenced meander-loop deposits from the Upper Cretaceous Tremp Formation (Pyrenees, Spain) provides valuable insights into the sedimentary and ichnological dynamics of these marginal-marine systems and allows the importance of stratal geometry controlling the colonization window to be evaluated. Six ichnofabrics are identified in point bars and associated overbank deposits. These ichnofabrics differ in bioturbation index (e.g., higher in the upper part than the lower-middle parts of point bars), preservation of primary sedimentary fabric (typically preserved in the lower-middle parts of point bars), inferred behavior and trophic types (e.g., dominance of dwelling or feeding structures in the lower-middle and upper parts of point bars, respectively), and other features such as depth of penetration, ichnotaxonomic composition, presence or absence of root trace fossils and/or mottling, or number of superimposed suites. The key environmental factor controlling the nature and distribution of ichnofabrics is the morphology of the point-bar lateral-accretion surfaces and their evolution through time. The architecture of the colonization window is here linked to the helicoidal flow and discharge changes in meandering channels, and the successive development of lateral accretion units with time.

Stratigraphical, microfacies, and ichnological characteristics and depositional environments of the Permo‒Carboniferous Aheimer Formation, western side of the Gulf of Suez, Egypt

The palaeoenvironments of the upper Palaeozoic succession in the eastern foot slopes of the Northern Galala Plateau, west of the Gulf of Suez, Egypt, are interpreted based on a detailed study of the sequence-stratigraphic framework, sedimentary facies and trace fossils. The upper Carboniferous–lower Permian Aheimer Formation has been studied in its type section exposed in Wadi Aheimer. Three unconformities bound four 3rd-order depositional sequences, including the upper Carboniferous DS NG 1, and the lower Permian DS NG 2‒4. These sequences are correlated with their counterparts on the North African and Arabian plates. The sedimentary facies characteristics indicate palaeoenvironments ranging from fluvial, estuarine, intertidal, shallow subtidal, shoreface to offshore transitional settings. The abundant and diverse ichno-assemblages are composed of horizontal, vertical and sub-vertical traces. At least 26 ichnotaxa have been identified, representing suites of the Glossifungites, proximal Cruziana, and proximal-archetypal Cruziana ichnofacies. Ichnofabric analysis revealed three distinct ichnofabrics: Tisoa, Schaubcylindrichnus and Zoophycos ichnofabrics. The trace and body fossil distribution and trophic structure of some of the recorded faunal assemblages confirm relatively stable and low-stress shallow-marine environments. In contrast, the trophic structure of some other assemblages indicates the influence of particular environmental parameters, including substrate consistency, bathymetry, water energy, productivity, rate of sedimentation, salinity and oxygen availability. The integrated results indicate that the sequences were formed during an interval dominated by different perturbations that resulted in a wide spectrum of depositional features. Moreover, evidence for Carboniferous–Permian glaciation is tentatively established in North Egypt but require further investigations.

The ichnology of shallow-marine and transitional environments

Abstract The ichnology between marine and non-marine environments is a key field of work concerning the understanding of the variation of environmental parameters in inland-to-offshore transitional environments. In order to understand the geological and palaeobiological processes at these locations, this Special Publication attempts to discuss records in shallow-marine and transitional environments throughout the Phanerozoic, including topics such as ichnotaxonomy, ichnofacies analysis, ichnofabric analysis for records from both shallow-marine and transitional environments, and neoichnological aspects. The volume includes 14 papers in total: one focused on aspects of neoichnology in rock iguanas in coastal settings, nine concerning various shallow-marine palaeoenvironment topics and four addressing issues about dinosaur tracks in transitional environments.

Thalassinoides Ichnofabrics of Lower Cambrian Longwangmiao Formation (Stage 4, Toyonian) on the Yangtze Platform, South China: Improving Paleoenvironmental Interpretations

AbstractAn analysis of Thalassinoides ichnofabrics in the Cambrian Stage 4 Longwangmiao Formation from six sections near Chonqing in the Middle and Upper Yangtze Block of South China was conducted to promote the understanding of the paleoenvironment of this period. Thalassinoides ichnofabrics are divided into three types according to their morphology, bioturbation index, abundance and related parameters: banded, mottled and grid. The completeness of the ichnofabrics gradually increases from banded to grid, the scale of the burrows expands, and the structure transitions from two‐dimensional to three‐dimensional. Malacostracans, phyllocarids and enteropneusts are the most likely burrowers. The findings reveal that frequent changes in paleoenvironmental conditions are the dominant factors for generating the various Thalassinoides ichnofabrics. The changes in depositional rate, substrate properties and nutrient levels affect the behavior and building patterns of the burrowers, thus leading to the diversity of Thalassinoides ichnofabrics. In the lower Longwangmiao Formation beds, many incomplete Thalassinoides burrow systems were built in the substrates with terrigenous detrital minerals, revealing significant environmental pressure on the burrowers. Later, the Thalassinoides burrows went into complete three‐dimensional boxworks. At the end of the stage, bioturbation almost disappeared, which indicates that burrowers were finding it difficult to survive in the harsh environment.

Ichnofabric analysis of shallow to deep marine Carboniferous sediments, from the southern Paleotethys margin, Alborz Basin (northern Iran): approaching autogenic and allogenic environmental controls

ABSTRACT This study integrates ichnological and sedimentological data to interpret depositional environments in the carbonate sediments of the Mobarak Fm. (Lower Carboniferous) in the Alborz Mountains of northern Iran. Seven ichnofabrics including Thalassinoides (Th), Zoophycos‒Phycosiphon (Zo-Ph), Skolithos‒Thalassinoides (Sk-Th), Zoophycos‒Diplocraterion (Zo-Di), Thalassinoides‒Rhizocorallium (Th-Rh), Zoophycos‒Arenicolites (Zo-Ar) and Chondrites‒Phycosiphon (Ch-Ph) have been identified in the studied succession. Th ichnofabric is characterised by the dominance of the deposit-feeding trace fossils, revealing low sedimentation rate and activity of the organisms in a loose substrate. Vertical succession of the Zo-Ph, Sk-Th and Zo-Di ichnofabrics indicates change in the firmness of the substrate. Th-Rh and Zo-Ar ichnofabrics reveal two different energy phases including a lower energy condition with the activity of deposit-feeders and a higher energy phase identified by the activity of suspension-feeders. Ch-Ph ichnofabric is characterised by low diversity and low abundance of trace fossils that were identified in black, limy shale, displaying a long lasting outer ramp setting with low energy, low sedimentation rate, and dysoxic-anoxic conditions of the substrate. Ichnological features of the Mobarak Fm. are controlled by subsidence-inducing changes in the accommodation space of the depositional system dictating variations in paleoenvironmental conditions such as oxygen levels and hydrodynamic energy.

Ichnofabric analysis as a tool for characterization and differentiation between calcareous contourites and calciturbidites

ABSTRACTThe Eocene–Miocene Cyprus paleoslope system records complex deep-marine sedimentation comprising background vertical settling of autochthonous pelagic–hemipelagic particles (chalks) which were punctuated by calcareous bottom currents (contourites) and gravity flows (calciturbidites). The Eocene Lefkara Formation at the Petra Tou Romiou beach section (Cyprus) shows the incidence of deep-marine bottom currents and distal turbiditic episodes in a context of pelagic–hemipelagic sedimentation. Trace-fossil analysis of this section, using an ichnofabric approach (i.e., ichnodiversity, Bioturbation Index, Bedding Plane Horizontal Index and crosscutting relationships), was conducted to precisely describe the paleoenvironmental conditions of this complex setting. Ichnofabric analysis allow the characterization and differentiation of sporadic turbiditic events that disrupted both pelagic–hemipelagic and contourite deposition. Calciturbidite intervals show ichnofabrics consisting of postdepositional U-shaped traces (i.e., Arenicolites isp., ?Diplocraterion isp.,) and vertical borings typical of consolidated substrates. High-energy sandy contourite deposits are dominated by horizontal deposit-feeder traces and the development of ichnofabrics with Planolites isp., and Thalassinoides isp. The record of ichnofabrics with slightly deformed Planolites in the interbeds of sandy contourites or in the transition between the facies reveals variations in sedimentation in the bi-gradational contourite succession, and can potentially act as an indicator of depositional hiatus.

Ichnofabric analysis of bathyal chalks: the Miocene Inglis Formation of the Andaman and Nicobar Islands, India

In the Bay of Bengal, the Andaman and Nicobar Islands represent part of the Burma–Sunda–Java subduction complex. The Islands are composed of sediments ranging in age from Jurassic to Recent, represented by ophiolites, flysch sediments, along with deep marine sediments scraped off from the subducting plate. The stratigraphic succession that overlies meta-sedimentary and ophiolite suites consists of turbidite and non-turbidite sequences, along with thick-bedded nannofossil chalks. The present study describes ichnofabrics of chalks from the Inglis Formation (Early to Middle Miocene). These chalks are highly to moderately bioturbated and comprise several levels of ferruginised layers as weak discontinuity surfaces. The studied section shows the recurring occurrence of ichnotaxa belonging to Asterosoma, Chondrites, Cladichnus, Ophiomorpha, Palaeophycus, Planolites, Taenidium, Thalassinoides, and Zoophycus. Sediments are represented by Bioturbation indices varying between BI-2 to BI-5, represented by (a) light coloured trace fossils in dark sediment (LID ichnofabric) and (b) dark coloured trace fossils in light sediment (DIL ichnofabric). Ichnofabric analysis suggests multiple colonization, complex tiering, and multilayer tiering. The LID ichnofabric exposed at Kalapathar reveals three tiers, a diverse shallow tier and a moderately low diverse middle and deep tiers. At the Lacam Point Section, in contrast, the LID ichnofabric is represented by condensation of the tiers and the absence of shallow tiers. The DIL ichnofabric at the Kalapathar Section seems to be more expanded and is represented by four tiers with extensive bioturbation. Ichnofabric analysis supports deposition of the chalk sediments in a lower bathyal paleoenvironment and suggests that organic matter, pore water, and bottom-water oxygenation were the main controlling factors. Thus, the ichnofabric analysis of the Early-Middle Miocene Inglis Formation gives first-hand information regarding the poorly known chalk facies of the Andaman and Nicobar Islands pre-Bengal fan stage of the Indian plate.

New ichnofabrics of the Cenomanian–Danian Chalk Group

ABSTRACT The Cenomanian–Danian Chalk Group of NW Europe is characterized by distinct trace-fossil assemblages dominated by Thalassinoides isp., Planolites isp., Zoophycos isp., and Chondrites isp., whereas ichnogenera such as Taenidium and Phycosiphon are rare. The trace fossils form a complex tiering arrangement, which reflects burrowing activities of diverse benthic associations that operate at different levels in the sediment column, dynamic sedimentation rates, and changes in substrate hardness during progressive burial, forming intricate ichnofabrics. In the Danish Basin, studies of chalk ichnofabrics have focused mainly on the Maastrichtian. Studies of the shallower, grain-rich Danian chalk have revealed similar trace-fossil assemblages, whereas the ichnology of the fine-grained, deeper-water Danian deposits is poorly known. Based on detailed facies and ichnofabric analysis of a mid-Danian silica-rich, pelagic chalk located in the central, deeper shelf area of the Danish Basin, four facies types, eight ichnotaxa, and two ichnofabrics are recognized. Most conspicuous and abundant are randomly distributed, variously sized meniscate burrows attributed to Bichordites isp. and Taenidium isp., whereas other common chalk trace fossils are rare or absent. This trace-fossil assemblage outlines two new ichnofabrics in the NW European chalk, which are dominated principally by upper-tier traces. The producer of the abundant Bichordites isp. and Taenidium isp. burrows is identified as a sea urchin on the basis of an exceptionally preserved Bichordites isp. trace aligned with an irregular echinoid body fossil. The identified ichnofabrics controlled early silicification and produced a more complex distribution of silica concretions compared with chalk successions elsewhere. This results in volumetrically thick silica concretion-rich units rather than distinctive silica bands as seen in other Upper Cretaceous and Danian chalk units.

Applied ichnology in sedimentary geology: Python scripts as a method to automatize ichnofabric analysis in marine core images

Image analysis has been succesfully applied in core research, especially in studies from modern deposits, to enhance the visibility of ichnological features and characterize ichnoassemblages and ichnofabrics. Its application to ichnological research provides useful information for marine core studies, hence sedimentary geology, but also for hydrocarbon exploration. Here we develop a new methodology, using Python programming language, which significantly improve the ichnological analysis. The method automatizes the process of obtaining continuous ichnological information, in this case about the percentage of bioturbation as a key aspect of the ichnofabric approach. The method affords the possibility of automatically generating continuous percentage and other index records using pixel counts in previously treated images. The resulting data sets are easy to correlate with the information usually obtained from cores (e.g., geochemical and mineralogical data). Such an integration of different proxies for to the field of sedimentary geology especially in the use of ichnological analysis, making it easier for the researcher, less time consuming, and more likely to be undertaken. The coding and sharing of open software tools allow for great flexibility, giving researchers in ichnology or related fields the option to implement new features, develop more complex tools to improve the package, and share findings with the scientific community.

Burrowed matrix powering dual porosity systems – A case study from the Maastrichtian chalk of the Gullfaks Field, Norwegian North Sea

Abstract Chalk reservoirs are commonly modelled as dual-porosity systems, in which a very porous but low permeable matrix is intersected by highly permeable vugs and fractures from which oil and gas can be produced. The Gullfaks Field in the Norwegian North Sea contains such a reservoir, which is producing from Maastrichtian chalk in addition to the conventional Triassic and Jurassic siliciclastic reservoirs. However, in comparison to the prolific chalk fields in the southern North Sea (e.g. Ekofisk, Valhall), chalk reservoirs in the northern part (e.g. Oseberg and Gullfaks fields) experience challenged production due to reservoir presence and quality related to depositional facies and structural conditions. Analyses of cores from three wells in the Maastrichtian Shetland Group of the Gullfaks Field reveal that this interval is completely bioturbated during several stages, e.g. mottling with diffuse bioturbated texture in an early softground stage that became subsequently overprinted by more discrete burrows with active and passive fill and different rock properties during the stiffground and firmground stages of the ooze. A rich and moderately diverse trace-fossil assemblage consists of abundant Zoophycos, common Chondrites, Taenidium, Thalassinoides and Virgaichnus, and rare Nereites, Planolites, Spirophyton and Teichichnus. Ichnological features allow the differentiation of five recurrent ichnofabrics (Thalassinoides, Zoophycos, Chondrites, Nereites and Zoophycos-Taenidium ichnofabrics) with variable influence on porosity and permeability. The Thalassinoides ichnofabric in chalk has the highest impact on improving reservoir quality, whereas Zoophycos and partly Chondrites ichnofabrics, in marly chalk and chalky marlstone respectively, contribute to creating potential reservoir zones if burrow density is high enough. Thin-section analysis of the different ichnofabrics illustrates the negative or positive effect of burrows on porosity distribution, whereas micro-CT imaging reveals an intriguing system of partly open micro-burrows (e.g. Virgaichnus) within the matrix, which serves as source for porosity. This burrow porosity provides a connection in the matrix that hosts open vugs and fractures, thus improving oil production.

Ichnofabric logs for the characterization of the organic content in carbonates

Abstract This study proposes an approach to visualize ichnological data from cores that allows direct comparison with downhole logs. It provides preliminary but accurate environmental information, especially on the oxygenation and/or the organic matter content at the sea floor. The method comprises three steps: Step 1) ichnological analysis of the sediments including quantification of bioturbation intensity, identification of the main ichnotaxa and sizes of the burrows, depth of burrowing or tiering, and documentation of cross-cutting relationships; Step 2) ichnofabric definition following a series of criteria including the bioturbation index, the ichnoassemblage, and the sediment type; and Step 3) the organization of the ichnofabrics from low bioturbation indices and deep tiers to completely bioturbated. The resulting ichnofabrics are plotted against depth and can directly be compared to spectral natural gamma ray logs, which in the discussed example are dominated by variations of the uranium content reflecting the organic matter content in the sediment. The ichnofabric analysis of carbonate sediment cores of the Maldives, recovered during IODP Expedition 359, demonstrates a good correlation between synthetic ichnofabric logs and downhole gamma radiation logs. The combined study of these logs provides information on the main changes in the organic matter content of the sediment. The graphical representation of ichnofabrics together with gamma ray logs presented here is a very useful implement for sedimentologists working on cores.

Lateral variability of ichnofabrics in marine cores: Improving sedimentary basin analysis using Computed Tomography images and high-resolution digital treatment

Major ichnofabric attributes may be related to a number of limiting marine parameters for tracemakers with paleoenvironmental significance, including ocean/atmosphere dynamics. This is why ichnofabric analysis has proven to be a very useful tool in sedimentary basin analysis — as well as in other Earth Science disciplines — although it is a comparatively recent approach in ichnological research. Ichnofabric characterization is usually based on 2D visual observations of a single view in both outcrops and cores. Yet ichnofabric features can vary vertically and laterally within a very short-distance, which may lead to misinterpretations. Here, a new methodological approach is presented, allowing for a more objective evaluation of ichnofabric features, based on the high-resolution digital treatment of Computed Tomography images on marine sediments cores. The method evaluates variations in ichnoassemblages, cross-cutting relationships, and the degree of bioturbation structures in nearby selected images pertaining to several sections of the same interval of a core. Average values of the obtained data imply a significant improvement of the resolution than 2D observations, and therefore a more precise and objective characterization of ichnofabrics. The usefulness of the method and its differences with respect to traditional ichnofabric analysis are exemplified by a study of the gravity core FSG09-10 (Galicia Bank domain, NW Iberian Peninsula), showing as a very significant tool to interpret paleoenvironmental changes (i.e., sedimentation rate, nutrient availability, and bottom water oxygenation) from the Last Glacial Maximum (LGM) to Heinrich Event 1 (HE1). This example reveals the importance of proposed methods in order to characterize the ichnofabrics, including their lateral variability, with clear implications for future research on basin analysis.

Outcrop and core integrative ichnofabric analysis of Miocene sediments from Lepe, Huelva (SW Spain): Improving depositional and paleoenvironmental interpretations

Ichnofabric analysis was conducted in Miocene sediments from Lepe (Huelva, SW Spain) based on integrative outcrop and core research, to improve interpretations of depositional and paleoenvironmental conditions, with special attention to sequence stratigraphy. Seven intervals were differentiated in outcrops based on stratigraphic and ichnological features, consisting of two ichnofabrics: Ophiomorpha-Thalassinoides-Spongeliomorpha ichnofabric characterizes intervals 1, 2, 6, 7 and 8, while Palaeophycus-Planolites-Phycosiphon ichnofabric characterizes intervals 3, 4 and 5. Fourteen ichnofabrics were differentiated in the core, mainly in view of lithological features, including ferruginous material, grain size, mottled background, ichnotaxa, and Bioturbation Index. A comparison between outcrop and core ichnofabrics through the upper 13.5m, corresponding to the uppermost Tortonian-lowermost Messinian interval, revealed certain similarities as well as some differences. A continuous and relatively slow siliciclastic deposition with punctual variations in the sedimentation rate can be interpreted that, associated with favorable paleoenvironmental parameters such as aerobic conditions and nutrient availability, evidence that a well-developed and diverse macroinvertebrate trace maker community existed at that time. Softgrounds are dominant, but occasionally loosegrounds and even firmgrounds could develop. The ichnofabric distribution shows long-range patterns in outcrop and core, and short-range patterns exclusively in core. Long-range patterns reflect the last phases of a transgressive system tract, with a “maximum flooding zone” at the end, and then a highstand normal regression. High-frequency, short-range, repetitive patterns in ichnofabrics from core, mainly between ichnofabrics 6/8 to 9 from lower to upper part of the pattern, can be linked to “local flooding surfaces”, subdividing the “maximum flooding zone” into parasequences. Our results reveals the usefulness of the integrative ichnofabric analysis, including outcrop and core materials, in sedimentary basin analysis, assessing paleoenvironmental conditions and improving sequence stratigraphy characterization.

Stratigraphic variation in ichnofabrics at the “Shackleton Site” (IODP Site U1385) on the Iberian Margin: Paleoenvironmental implications

Ichnofabric analysis was conducted on cores from Site U1385 (IODP Expedition 339) to interpret paleoenvironmental conditions at the southwest margin of the Iberian Peninsula during the Pleistocene. Site U1385 provides an important record for the study of orbital and suborbital-scale climate variability, changes related to ocean/atmosphere dynamics, and affected environmental parameters. A detailed study of the ichnofabric characterization is presented, focusing on the types of ichnofabrics, relative abundance, amount of bioturbation, grouping, ichnofabric succession/transitions and vertical distribution. Seven ichnofabrics were differentiated; green mottled ichnofabric, Planolites ichnofabric, Taenidium &Planolites ichnofabric, Thalassinoides-like &Palaeophycus ichnofabric, Planolites &Thalassinoides/Thalassinoides-like ichnofabric, Zoophycos ichnofabric, and Chondrites ichnofabric. They exhibit significant differences in terms of ichnofabric features as well as in their stratigraphic distribution. The most abundant ichnofabrics are Planolites &Thalassinoides/Thalassinoides-like ichnofabric and green mottled ichnofabrics, with a dominance of the middle tier ichnofabrics. The degree of bioturbation is moderate, with a mean BI around 3, but showing a clear bimodal distribution: one group of intervals is characterized by high bioturbation (BI=6), while another displays low-moderate BI values (BI=1–2). In general, ichnofabric features confirm generally good environmental conditions (oxic environment and high food availability) for the macrobenthic tracemaker community, especially favorable in the uppermost part of the sediment. A complete ichnofabric succession, from deep to shallow tier ichnofabrics, is commonly registered (i.e., Zoophycos ichnofabric or Chondrites ichnofabric to Planolites &Thalassinoides/Thalassinoides-like ichnofabric, and then either to green mottled ichnofabric, or to Planolites ichnofabric and then green mottled ichnofabric). However, there are some intervals where an incomplete succession between deep and shallow ichnofabrics is observed (i.e., Chondrites ichnofabric to green mottled ichnofabric or Zoophycos ichnofabric to green mottled ichnofabric), indicating relevant modifications of environmental parameters such as oxygen or food supply. Types of ichnofabrics and the Bioturbation Index show significant short-term changes through the studied core. Such variations are probably correlated to millennial-scale climatic perturbations, such as glacial terminations and related phenomena (Heinrich events, ice-rafting events, etc.), or long-term cyclic patterns related to orbital climate variability. The patterns could be tied to a significant change in the climate system, such as the one associated with the middle Pleistocene transition.

Integrated litho-ichnofacies and ichnofabric analysis of the lowermost part of the Kunzum La Formation along the Khemangar khad and the Parahio Valley sections, Spiti Region (Zanskar-Spiti-Kinnaur Basin), Northwest Himalaya, India)

The Cambrian sequence, designated as the Kunzam La Formation, is exposed along the cLassical Parahio Valley section and also on left bank of the Khemangar khad in the Parahio Valley (Spiti), the Latter constitutes the lowermost exposed part of the Kunzum La Formation. The lower part of the Parahio Valley section and outcrop near the left bank of the Khemangar khad were studied for integrated litho-ichnofacies and ichnofabric analysis. The study establishes a genetic reLationship of the strata of these two localities. Five lithofacies are recognised in both the examined sections. The lithofacies indicate a wave-dominated shallow marine environment of deposition for these Cambrian rocks. The overall calcuLated ichnofabric indices in 74 m exposed strata at the Khemangar khad locality range from ii1=80.% (represented by 25.8 m), ii2= 17% (represented by 5.4 m) and ii4=2.5 % (represented by 0.8 m). The 42 m rocks examined in the main Parahio Valley section indicate ichnofabric indices ranging from ii1=37% (represented by 17.8 m), ii2=21% (represented by 8.0 m), ii3=40% (represented by 15.2 m) and ii4=2.0% (represented by 1.0 m). The presence of archetypal Cruziana ichnofacies, parallel and wavy Laminations, hummocky cross stratification (HCS) and trough cross stratification (TCS) supports a wave-dominated shallow water environment from upper shoreface to middlelower shoreface setup for the deposition of the lowermost part of the Kunzum La Formation in the Parahio Valley.

Substrate adaptations of sessile benthic metazoans during the Cambrian radiation

AbstractMany marine benthic metazoans must stabilize themselves upon the seafloor for survival, and as a result their morphologies are controlled in part by local substrate conditions. The Agronomic Revolution (AR), spurred by increasing vertical bioturbation during the Ediacaran–Cambrian transition, permanently altered the nature of shallow marine substrate conditions and led to a major shift in adaptive strategies among benthic metazoans. These ecological and evolutionary changes, known as the Cambrian Substrate Revolution (CSR), are generally understood from observations of benthic metazoan fossils across the Ediacaran/Cambrian boundary, but the timing and geographic extent of this transition are less well known. This analysis attempts to constrain the temporal and spatial pattern of the AR and CSR by performing a global-scale paleoecological analysis of the adaptive strategies of benthic fauna living during the Cambrian. This analysis focused on Burgess Shale-type (BST) faunas because of their exceptional preservation, and was conducted through direct observation of fossil specimens, analysis of data compiled from the Paleobiology Database, and literature review. From these analyses, faunal groups are assigned a metric, the Substrate Adaptability Index (SAI), that relates the overall affinity the fauna demonstrates toward either Proterozoic-style (SAI=0) or Phanerozoic-style (SAI=1) substrate conditions. The results of this analysis demonstrate that most early and middle Cambrian faunas were mixtures of Phanerozoic- and Proterozoic-style adaptive strategists, suggesting that Proterozoic-style substrates were still influential in controlling adaptive strategies in marine environments until at least that time. This is further supported by ichnofabric analysis of many of these localities, where overall bioturbation levels are exceedingly low, indicating a lack of mixed-layer development and the prevalence of firm Proterozoic-style substrates well into the Cambrian.

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.

Ichnofabric analysis of the Tithonian shallow marine sediments (Bhadasar Formation) Jaisalmer Basin, India

The shallow marine sedimentary sequence of the Jaisalmer Basin exhibits one of the important and well-developed Tithonian sedimentary outcrops for western India. The ichnology and ichnofabric of the lower part of Bhadasar Formation (i.e., Kolar Dongar Member) belonging to Tithonian age are presented and discussed. The Kolar Dongar Member represents a shallow marine succession that contains 16 ichnotaxa: Ancorichnus ancorichnus, Conichnus conicus, Gyrochorte comosa, cf. Jamesonichnites heinbergi, Imponoglyphus kevadiensis, Laevicyclus mongraensis, Monocraterion tentaculatum, Ophiomorpha nodosa, Palaeophycus tubularis, P. bolbiterminus, Phycodes palmatus, Planolites beverleyensis, Rhizocorallium isp., Rosselia rotatus, R. socialis, and Teichichnus rectus. The ichnofabric analysis divulges five distinct ichnofabrics, each typifying distinct depositional environment within shallow marine conditions. The ichnofabric Ophiomorpha 1 with syn-sedimentary faulting exemplifies high energy conditions typical of lower shoreface environment, whereas the Ophiomorpha 2 ichnofabric typifies upper shoreface environment. The Ancorichnus ichnofabric reflects lower offshore condition of deposition. The high ichnodiversity Ancorichnus–Rosselia ichnofabric is indicative of inner shelf conditions, while low ichno-diversity Teichichnus ichnofabric indicates prevalence of low energy brackish bay environment. Thus, Tithonian Kolar Dongar Member indicates depositional environment ranging from shoreface to offshore to inner shelf and finally to brackish bay environment.