John-Paul Zonneveld

Trace fossil assemblages in a Middle Triassic mixed siliciclastic- carbonate marginal marine depositional system, British Columbia

Abstract A diverse ichnofossil assemblage characterizes the mixed siliciclastic-carbonate marginal marine succession of the upper Liard Formation (Middle Triassic), Williston Lake, northeastern British Columbia. Sedimentary facies within this succession consist of five recurring facies associations: FA1 (upper shoreface/foreshore); FA2 (washover fan/lagoon); FA3 (intertidal flat); FA4 (supratidal sabkha) and FA5 (aeolian dune). Shoreface/foreshore sediments (FA1) accumulated on a storm-dominated, prograding barrier island coast and are characterized by a low-diversity Skolithos assemblage (Diplocraterion, Ophiomorpha, Palaeophycus, Planolites, Skolithos and Thalassinoides). Washover fan/lagoonal sediments (FA2) are dominated by trophic generalists. (Cylindrichnus, Gyrochorte, Palaeophycus, Planolites, Skolithos, Trichichnus and an unusual type of bivalve resting trace), consistent with deposition in a setting subject to periodic salinity and oxygenation stresses. Intertidal flat deposits (FA3) are characterized by a diverse mixture of dwelling, feeding, and crawling forms (Arenicolites, Cylindrichnus, Diplocraterion, Laevicyclus, Lingulichnus, Lockeia, Palaeophycus, Planolites, Rhizocorallium, Siphonichnus, Skolithos, Teichichnus, Taenidium, and Thalassinoides, reflecting the presence of adequate food resources in both the substrate and in the water column. Vertical burrow-dominated trace fossil assemblages within thin, sharp-based sand beds are interpreted as intertidal tempestites and reflect post-event colonization of the intertidal zone by shoreface organisms. Supratidal sabkha deposits (FA4) are characterized by an exceptionally low-diversity trace fossil assemblage (Cylindrichnus, Monocraterion and rare diminutive Ophiomorpha). Solution collapse breccia and root traces overprint many primary physical and biogenic sedimentary structures, reflecting numerous cycles of desiccation and flooding. Aeolian dune deposits (FA5) consist of unfossiliferous, exceptionally well-sorted sandstone beds.

DIVERSE ICHNOFOSSIL ASSEMBLAGES FOLLOWING THE P-T MASS EXTINCTION, LOWER TRIASSIC, ALBERTA AND BRITISH COLUMBIA, CANADA: EVIDENCE FOR SHALLOW MARINE REFUGIA ON THE NORTHWESTERN COAST OF PANGAEA

Abstract Diverse and locally abundant Lowermost Triassic (lower Induan, Griesbachian) trace-fossil assemblages are described and their significance for the location and characteristics of western Pangean environmental refugia are assessed. Trace fossils within the Montney Formation in northwestern Alberta and northeastern British Columbia record the activities of a wide variety of marine invertebrates. Many forms represent the dwelling and feeding traces of allochthonous storm-transported colonizers. Anachronistic forms—more typical of Paleozoic than Mesozoic successions—including Cruziana, Diplichnites, Monomorphichnus, and Trichophycus, are common. Notably these Paleozoic holdovers, as well as Rhizocorallium, Thalassinoides, and Spongeliomorpha, were likely constructed by marine arthropods. Trace fossils are rare in both shallow water (upper shoreface and foreshore) and offshore depositional settings, but are abundant in offshore transition to distal lower shoreface depositional settings. Low diversity and low ichnofabric indices characterize autochthonous infauna in Montney offshore transition settings, whereas high diversity, low ichnofabric indices distinguish allochthonous infauna in the same settings. High diversity and high ichnofabric indices typify distal lower shoreface successions. Several lines of evidence, including diminutive trace fossils and low diversity of resident infauna in proximal-offshore settings, support the hypothesis of shallow marine anoxic to dysoxic conditions in the study area during the Griesbachian. This trace-fossil distribution, and the abundance of allochthonous faunas in the study interval, reflect an infauna whose distribution was limited by both wave-stressed proximal settings and oxygen-stressed distal settings, resulting in colonization of a very narrow habitable zone. High diversity of trace-fossil assemblages in the study interval suggests the presence of shallow marine refugia wherein organisms survived the extinction interval and weathered the adverse conditions that dominated the worlds oceans during the lowermost Mesozoic. Mid- to high paleolatitude refugia, such as the Pedigree-Ring-Kahntah area, played a crucial role in both extinction survival as well as post-event recolonization of the worlds oceans.

Chapter 4 – The Ichnofacies Paradigm

The ichnofacies paradigm has evolved over a six-decade period since its original inception by Dolf Seilacher. It is a multidimensional framework underpinned by recurring, facies-controlled groupings of biogenic structures that reflect animal responses to paleoenvironmental conditions. These constitute spatially and temporally extensive associations commonly regarded as “Seilacherian Ichnofacies.” The marine realm hosts five recurring softground ichnofacies (Psilonichnus, Skolithos, Cruziana, Zoophycos, and Nereites), generally distributed in a proximal–distal trend reflecting a passive response to increasing water depth (i.e., controlled by depositional factors that progressively change with bathymetry). There are three substrate-controlled ichnofacies (Trypanites, Teredolites, and Glossifungites), recording organism occupation of palimpsest substrates. Finally, there are six continental ichnofacies (Scoyenia, Mermia, Coprinisphaera, Termitichnus, Celliforma, and Octopodichnus–Entradichnus), mainly recording organism responses to temperature and the availability of moisture (i.e., climate-driven associations) in terrestrial settings or oxygenation, depositional energy, and substrate consistency in subaqueous settings. The Seilacherian ichnofacies operate as facies models, built through the distillation of ichnological characteristics derived from numerous modern and ancient case studies. Like lithofacies models, they serve as a norm for comparison, a framework for observations, a predictor in new situations, an integrated basis for interpretation, and a basis for teaching and communication.

Magnetostratigraphy Across the Wasatchian/Bridgerian Nalma Boundary (Early to Middle Eocene) in the Western Green River Basin, Wyoming

New paleomagnetic and biostratigraphic data from the western Green River Basin of Wyoming provide a magnetobiostratigraphic framework to correlate the late Wasatchian through early Bridgerian North American Land Mammal Ages (NALMA) to the Geomagnetic Polarity Time Scale (GPTS). Three‐hundred and twelve paleomagnetic samples were collected from 73 sites within a 350‐m continuously exposed flat‐lying section. The section is characterized by alternating packages of well‐developed paleosol mudstone horizons (Wasatch Formation) and lacustrine shale/limestone horizons (Green River Formation). Fossil mammal assemblages are known from various levels within the section and constrain the location of the Wasatchian/Bridgerian NALMA boundary to lie between 60 and 120 m. Paleomagnetic results of paleosol horizons are generally characterized by two components, a present‐day field component with low unblocking temperatures up to 400°C, and a characteristic component with unblocking temperatures up to 680°C. Characteristic magnetizations have either N‐NW and steeply down directions or antipodal S‐SE and up directions. The characteristic component is interpreted as primary based on antipodal polarity directions and congruence with the expected Eocene direction for western Wyoming. Results indicate that the first 30 m of section are characterized by normal polarity, the next 230 m by dominantly reversed polarity, followed by a 70 m interval of alternating polarity. Given radiometric ages for the late Wasatchian (early Lostcabinian “subage”) and middle Bridgerian, as well as previous Wasatchian and Bridgerian magnetostratigraphic results, two potential correlations to the GPTS are possible. Correlation 1 places the Wasatchian/Bridgerian NALMA boundary within Chron C23r at about 52 Ma. Correlation 2 places the boundary within Chron C22r at about 50.5 Ma. Correlation 2 is tentatively preferred as it agrees most closely with previous estimates for the age of the boundary and assumes more uniform sediment accumulation rates.

SEDILICHNUS, OICHNUS, FOSSICHNUS, AND TREMICHNUS: 'SMALL ROUND HOLES IN SHELLS' REVISITED

Abstract Small round pits and holes in fossil skeletal material are found in a wide variety of invertebrate substrates from diverse environmental settings. They are associated with parasitism, predation and commensal attachment. Four ichnogenera have been proposed for these trace fossils: Sedilichnus Müller, Oichnus Bromley, Tremichnus Brett and Fossichnus Nielsen, Nielsen and Bromley. Previous authors have established that Tremichnus is a junior synonym of Oichnus. Herein we show that Oichnus and Fossichnus are junior synonyms of Sedilichnus. Sedilichnus, as defined herein, includes 10 ichnospecies. Sedilichnus spongiophilus, S. simplex, S. paraboloides, S. ovalis, S. coronatus, S. gradatus, S. halo, S. asperus, S. excavatus and S. solus. Consistent with previous work Sedilichnus ichnospecies are defined solely by morphological criteria and not by a priori assumptions regarding depositional environment or tracemaker. Thus, this ichnotaxon is recognized in both marine and continental settings on a wide variety of invertebrate skeletal tests. As is true with many ichnotaxa, Sedilichnus ichnospecies represent end-members in morphological spectra, however each ichnospecies is clearly differentiable from the others. Sedilichnus spongiophilus are circular, non-penetrative pits in shells. Sedilichnus paraboloides are penetrative holes with spherical paraboloid forms and typically have larger external openings and smaller internal openings. Sedilichnus simplex are simple cylindrical borings that have both penetrative and non-penetrative forms. Sedilichnus coronatus differ from other forms by the presence of an etched or granular halo surrounding the boring. Sedilichnus gradatus have two concentric parts, an outer boring and an inner shelf of smaller diameter. Sedilichnus ovalis and S. asperus are both oval in outline differing in the presence of tapering paraboloid margins in S. ovalis and margins perpendicular to the substrate in S. asperus. Sedilichnus excavatus and S. solus are primarily non-penetrative and differ from other Sedilichnus by the presence of central, raised bosses or platforms. These two ichnospecies differ in the shapes of their external walls and the proportional thickness of the bounding groove.

A subseafloor carbonate factory across the Triassic-Jurassic transition

Triassic-Jurassic (T-J) boundary successions record a paucity of carbonate in association with the mass extinction. Here we demonstrate that three globally disparate T-J sections contain volumetrically important early diagenetic carbonate, i.e., carbonate formed soon after deposition of the sediment but commonly ignored as secondary, that contains information about the extinction and may constitute a previously unrecognized pathway in the carbon cycle. Petrographic analyses of unusual carbonate fans from three sites reveal that they grew just below the sediment-water interface, nearly concomitant with primary sediment deposition. Thus, the shallow subseafloor can be a carbonate sink of unknown size, and may be a predictable consequence of ocean acidification where carbonate precipitation first returns within the sediment before recovering in the water column.

The Ichnotaxonomy of Vertically Oriented, Bivalve-Generated Equilibrichnia

Abstract Bivalves have pursued an infaunal lifestyle since early in their history. Trace fossils that have been attributed to the infaunal activity of bivalves include Hillichnus, Lockeia (=Pelecypodichnus), Lophoctenium, Protovirgularia, Ptychoplasma, Siphonichnus and Scalichnus. Re-evaluation of the ichnogenera Siphonichnus and Scalichnus supports consolidation into a single ichnogenus, Siphonichnus, which has taxonomic precedence. Siphonichnus, as redefined herein, presently includes four ichnospecies. Siphonichnus eccaensis Stanistreet et al. is an unlined vertical tube characterized by concave downward laminae penetrated by a single central shaft and is interpreted to reflect downward burrowing in response to net erosion during the life span of the animal. Siphonichnus phiale (Hanken et al., 2001) is characterized by concave upwards laminae and reflects equilibrichnial behavior by the tracemaker. Siphonichnus lepusaures n. isp. is characterized by concave upwards laminae with a pair of vertically ori...

Chapter 19 – Shorefaces

The shoreface is a seaward sloping, sandstone depositional wedge, and can be subdivided into a lower, middle, and upper shoreface. The sediment wedge grades basinward into offshore sandy and silty shales and landward into foreshore sandstones and/or conglomerates. The lower shoreface lies within fair-weather wave base. The trace-fossil assemblages typically reflect a diverse and abundant Cruziana Ichnofacies. The middle shoreface contains swaley and lesser hummocky cross-stratified sandstones with a trace-fossil assemblage dominated by the Skolithos Ichnofacies. The upper shoreface is dominated by multidirectional trough cross-bedding. Trace fossils are rarely abundant and consist of deeply penetrating structures of the Skolithos Ichnofacies. Under exceedingly high-energy conditions, Macaronichnus may be developed near the transition with the foreshore. Shoreface successions display a wide range of variability, largely restricted to the lower and middle shoreface intervals. This variability appears to be controlled by relative storm dominance and the episodic nature of associated storm-bed deposition.

Chapter 27 – Porosity and Permeability in Bioturbated Sediments

Owing to the textural contrast that commonly exists between matrix and trace fossils, biogenic flow media are common in the rock record. Broadly speaking, the permeability contrast between the matrix and the trace-fossil-affected zones constitutes the most important parameter for characterizing biogenically influenced flow media. Biogenic permeability is separated into two categories: (1) highly contrasting permeability fields (dual-permeability networks) and (2) comparably diffuse and lowly contrasting permeability fields (dual-porosity networks). Dual-permeability flow media normally display poor reservoir characteristics in that only the permeable conduits (i.e., trace fossils) effectively transmit fluids, and resources may be absent in the tighter matrix. Also, a large number of tortuous, tubular flow paths constitute the flow medium. Dual porosity may also reduce the resource quality of a sedimentary rock by introducing nearly unpredictable heterogeneities and often presenting a gradient of permeability fields between the burrowed and matrix end-members. The assessment of bulk permeability, which in practical terms is the upscaled permeability from trace-fossil versus matrix-scale to bed- and bedset scales, is in need of research and refinement. At the present, a few studies have shown that the bulk permeability of strata containing isolated burrows dominantly follows the harmonic mean of burrow/matrix permeabilities. As burrow connectivity increases, the geometric and the arithmetic means of permeability can be applied. A gradation exists between the three methods that we are not yet able to characterize. Recent research has shown that the geometric and harmonic means can be applied to media that are > 20% bioturbated. Factors other than connectivity influence bulk permeability, including burrow diameter and burrow architecture. The influence of these parameters is not yet quantified.

Chapter 16 – Estuaries

Estuaries are characterized by the mixing of fluvial and marine waters and the presence of energy gradients associated with wave, tide, and river processes. This chapter explores the influence that the juxtaposition of unsteady through reduced salinities and variable energy distributions has on the distribution and composition of trace fossils in estuary settings. Due to the wide physiographic range of estuary occurrences, a simple summary model for the identification of estuaries is not presented. However, some common ichnological and sedimentological elements of estuaries are explored: (1) the presence of brackish-water bioturbation, (2) the observance of bioturbated intertidal flat deposits, (3) the presence of burrowed inclined heterolithic stratification, and (4) the identification of Glossifungites-demarcated omission surfaces, which may be associated with transgressive erosion in marginal-marine settings. More generally, the distribution of food resources and brackish water—a result of tidal mixing and energy distributions—dictates the longitudinal distributions of tracemaking organisms and their biogenic structures. Considering the above ichnological characteristics, the identification of estuaries from ichnological datasets very much depends on a large number of observations from a spatially significant dataset.