Luis Alberto Buatois

The paleoenvironmental and paleoecological significance of the lacustrine Mermia ichnofacies: An archetypical subaqueous nonmarine trace fossil assemblage

Although nonmarine environments commonly are considered as diverse and varied as marine settings, only a single recurrent and archetypical ichnofacies, the Scoyenia ichnofacies, has been formally defined. However, recent research proposed the terrestrial Termitichnus ichnofacies as a subset of the Scoyenia ichnofacies. The Mermia ichnofacies is formally defined herein to include nonmarine, fully aquatic trace fossil suites characterized by the dominance of horizontal to subhorizontal grazing and feeding traces produced by mobile deposit feeders, the subordinate occurrence of locomotion traces, overall high to moderate ichnodiversity and abundance, and low specialized grazing patterns. The Mermia ichnofacies typifies unconsolidated, fine‐grained, permanent subaqueous substrates, and well‐oxygenated, low‐energy lake bottoms, periodically punctuated by episodic sedimentation. In addition, it is suggested to include in the Scoyenia ichnofacies, floodplain and transitional fluvio‐lacustrine trace fossil assemb...

Insect Trace Fossil Associations in Paleosols: The Coprinisphaera Ichnofacies

Abstract Analysis of fifty-eight paleosol trace fossil assemblages, ranging from the Triassic to the Recent, allows refinement of continental ichnofacies models and the proposal of a Coprinisphaera ichnofacies. The Coprinisphaera ichnofacies consists of trace fossils of bees, wasps, ants, beetles, termites, and other unassigned insects. Meniscate burrows, mammal caves, and rhizoliths also may be present. This ichnofacies is named after the dung beetle nest Coprinisphaera, the most common component of this archetypal assemblage. In mature paleosols, the Coprinisphaera ichnofacies has moderate to relatively high trace fossil diversity and high abundance. Ethologically, this assemblage is dominated by nesting traces (calichnia) and exhibits a relatively complex tiering pattern, reflecting variable depths of emplacement of hymenopterous, termite, and dung beetle nests. Common components include the bee cells Celliforma, Uruguay, Ellipsoideichnus, Palmiraichnus, and Rosellichnus; the wasp nest Chubutolithes; the ant traces Attaichnus and Parowanichnus, and other beetle traces, such as Monesichnus, Fontanai, and Teisseirei. Termite nests may occur, but are less common components of the Coprinisphaera ichnofacies. The Coprinisphaera ichnofacies fulfills all the requirements to qualify as a Seilacherian or archetypal ichnofacies, namely recurrence in time and space, and distinct paleoenvironmental implications. Proposal of the Coprinisphaera ichnofacies is based on the analysis of twenty-eight cases, ranging from the? Late Cretaceous to the Recent. The Coprinisphaera chnofacies characterizes paleosols developed in paleoecosystems of herbaceous communities. These herbaceous communities range from dry-and-cold to humid-and-warm climates. More detailed paleoclimatological inferences can be obtained by evaluating the relative abundance of the various traces within the assemblage. A dominance of hymenopterous traces would indicate drier conditions, whereas the presence of termite nests would indicate more humid. The Coprinisphaera ichnofacies occurs in paleosols developed in various depositional systems subject to subaerial exposure, such as alluvial plains, desiccated floodplains, crevasse splays, levees, abandoned point bars, and vegetated eolian environments. This and other potential terrestrial ichnofacies are controlled by ecological parameters (e.g., vegetation, climate, and soil) rather than by depositional processes. The association of fossil insect nests indicates the extent of soil development and, consequently, such ichnofossils are one of the best indicators of paleosols. The previously proposed Termitichnus ichnofacies was defined to include all paleosol trace fossil assemblages. However, the available information indicates that terrestrial environments are far more complex. Therefore, it is suggested that the Termitichnus ichnofacies as presently defined be abandoned because it does not reflect the diversity of paleosol settings and fails to provide significant paleoecologic information. Formal definition of a Termitichnus ichnofacies in a more restricted sense, to include assemblages dominated by termite nests in paleosols of closed forest ecosystems, should await documentation of additional studies to prove recurrence. Other fossil insect-nest associations in paleosols (e.g., halictid nests in calcareous soils) do not have enough recurrence in time and space to be considered Seilacherian ichnofacies, but do represent potential ichnofacies. The model proposed in this paper includes the paleoecologically defined Coprinisphaera ichnofacies plus a definite number of associations, each one possessing its own paleoenvironmental implications, which do not show the necessary recurrence to be considered ichnofacies, at present. Climate and vegetation are considered key factors in the shaping of terrestrial ecosystems and should be taken into account for the definition of additional terrestrial ichnofacies.

Trace fossil analysis of lacustrine facies and basins

Abstract Two ichnofacies are typical of lacustrine depositional systems. The Scoyenia ichnofacies characterizes transitional terrestrial/nonmarine aquatic substrates, periodically inundated or desiccated, and therefore is commonly present in lake margin facies. The Mermia ichnofacies is associated with well oxygenated, permanent subaqueous, fine-grained substrates of hydrologically open, perennial lakes. Bathymetric zonations within the Mermia ichnofacies are complicated by the wide variability of lacustrine systems. Detected proximal–distal trends are useful within particular lake basins, but commonly difficult to extrapolate to other lakes. Other potential ichnofacies include the typically marine Skolithos ichnofacies for high-energy zones of lakes and substrate-controlled, still unnamed ichnofacies, associated to lake margin deposits. Trace fossils are useful for sedimentologic analysis of event beds. Lacustrine turbidites are characterized by low-diversity suites, reflecting colonization by opportunistic organisms after the turbidite event. Underflow current beds record animal activity contemporaneous with nearly continuous sedimentation. Ichnologic studies may also help to distinguish between marine and lacustrine turbidites. Deep-marine turbidites host the Nereites ichnofacies that consists of high diversity of ornate grazing traces and graphoglyptids, recording highly specialized feeding strategies developed to solve the problem of the scarcity of food in the deep sea. Deep lacustrine environments contain the Mermia ichnofacies, which is dominated by unspecialized grazing and feeding traces probably related to the abundance and accessibility of food in lacustrine systems. The lower diversity of lacustrine ichnofaunas in comparison with deep-sea assemblages more likely reflects lower species diversity as a consequence of less stable conditions. Increase of depth and extent of bioturbation through geologic time produced a clear signature in the ichnofabric record of lacustrine facies. Paleozoic lacustrine ichnofaunas are typically dominated by surface trails with little associated bioturbation. During the Mesozoic, bioturbation depth was higher in lake margin facies than in fully lacustrine deposits. While significant degrees of bioturbation were attained in lake margin facies during the Triassic, major biogenic disruption of primary bedding in subaqueous lacustrine deposits did not occur until the Cretaceous.

Early Colonization of the Deep Sea: Ichnologic Evidence of Deep-marine Benthic Ecology from the Early Cambrian of Northwest Argentina

Abstract Tiering and ichnoguild analysis provide valuable evidence on marine benthic paleoecology. This paper provides the first detailed study on the ecology of a Cambrian deep-marine ichnofauna by means of the analysis of its ichnoguilds and tiering structure. Endobenthic tiering in this Early Cambrian deep-sea community was moderately developed. Biogenic structures were emplaced mostly in the uppermost millimeters of the substrate, with the exception of post-depositional burrows preserved on the base of turbidite sandstones. Four ichnoguilds are defined. The Palaeophycus ichnoguild includes semi-permanent, shallow-tier, suspension feeder structures produced by vagile vermiform organisms. The Oldhamia ichnoguild consists of semi-permanent, very shallow-tier, undermat-miner structures produced by stationary vermiform organisms. The Helminthopsis ichnoguild comprises transitory, near-surface to very shallow-tier, mat-grazer structures produced by vagile vermiform animals. The Diplichnites ichnoguild consists of transitory, surface structures produced by vagile arthropods. Comparisons with coeval ichnofaunas indicate that these ichnoguilds are widespread in Vendian–Cambrian deep-marine biotas. This analysis suggests that Cambrian deep-water communities were remarkably different from younger examples and stresses the importance of microbial mats on the ecology of Neoproterozoic–Cambrian ecosystems. Feeding strategies associated with microbial mats persisted in the deep sea after the agronomic revolution that took place in shallow-water environments, suggesting a gradual closure of a taphonomic window during the Proterozoic–Cambrian transition. The presence of post-depositional burrows of the Palaeophycus ichnoguild at the base of turbidite sandstones indicates a higher burrowing depth than those envisaged by current models.

Sedimentary facies, depositional evolution of the Upper Cambrian–Lower Ordovician Santa Rosita formation in northwest Argentina

Abstract The Upper Cambrian–Tremadocian Santa Rosita Formation, the lowermost unit of the Santa Victoria Group in northwest Argentina, records part of the infill of a retroarc basin. Sedimentologic, ichnologic, and sequence stratigraphic evidence indicates that this unit represents a complex mosaic of siliciclastic facies that reflects the vertical passage of restricted fluvial and tide-dominated estuarine environments to open-marine settings affected by waves. Twelve facies grouped in two facies associations were recognized. The base of the Santa Rosita Formation represents a sequence boundary formed from a relative sea level fall responsible for the incision of fluvio-estuarine valleys in the underlying Meson Group, which most likely occurs close to the Middle–Late Cambrian transition. Valley filling, represented by the Tilcara Member, started with deposition of conglomerate and sandstone of the lowstand systems tract in braided fluvial systems restricted to the valley axis. The bulk of valley sedimentation, however, is recorded by estuarine deposits that accumulated during a subsequent transgression and were in turn replaced upward by transgressive marine facies (transgressive systems tract). The maximum flooding is represented by lower offshore, greenish gray shales of the Casa Colorada Member. These strata are overlain by upper offshore to offshore transition deposits that from progradational parasequence sets, which represent a highstand systems tract. Fine-grained deposits of the Casa Colorada Member are replaced upward by forced regressive shoreface sandstone of the Alfarcito Member. A major transgression, recorded at the base of the Rupasca Member, probably occurred during the Early Tremadocian and led to deposition of anoxic black shales in shelf areas. The Rupasca Member is characterized by a series of transgressive–regressive events during the Early Tremadocian and early Late Tremadocian. Deposition culminates in a regressive event recorded by the shoreface sandstone of the Humacha Member during the late Late Tremadocian.

Trace fossils from Jurassic lacustrine turbidites of the anyao formation (Central China) and their environmental and evolutionary significance

The Lower Jurassic Anyao Formation crops out near Jiyuan city, western Henan Province, central China. It is part of the infill of the nonmarine early Mesozoic Jiyuan‐Yima Basin. In the Jiyuan section, this unit is about 100 m thick and consists of laterally persistent, thin and thick‐bedded turbidite sandstones and mudstones displaying complete and base‐or top‐absent Bouma sequences, and thick‐bedded massive sandstones. The Anyao Formation records sedimentation within a lacustrine turbidite system developed in a pull‐apart basin. Processes involved include high and low density turbidity currents, sometimes affected by liquefaction or fluidization. Facies analysis suggests that this succession is formed by stacked aggradational turbidite lobes. The absence of thick mudstone packages indicates that background sedimentation was subordinate to high frequency turbidite deposition. The Anyao Formation hosts a moderately diverse ichnofauna preserved as hypichnial casts on the soles of thin‐bedded turbidite sands...

Lithofacies, biofacies, and ichnoassemblage evolution of a shallow submarine volcaniclastic fan-shelf depositional system (Upper Cretaceous, James Ross Island, Antarctica)

The Upper Cretaceous (Santonian-Campanian/lower Maastrichtian) Santa Marta Formation on James Ross Island, Antarctica, represents volcaniclastic shallow marine fan and shelf sedimentation adjacent to an active volcanic arc. A combined analysis of sedimentologic, paleoecologic, and ichnologic data allows for the recognition in this unit of six lithofacies associations, eight biofacies, and five trace fossils assemblages. Lithofacies are dominated by fine, massive, tuffaceous rocks; graded, turbidite-like tuffaceous sandstones; carbonaceous mudstones; resedimented conglomerates; coquinas; sandstones; silty sandstones; and minor stromatolite beds. Biofacies are defined by different composition and relative abundance of elements of the benthic fauna, mainly bivalves, gastropods, and serpulids, with minor elements represented by scaphopods, corals, brachiopods, and echinoids. Trace fossil assemblages include the most common elements of the Skolithos and Cruziana ichnofacies. A striking result of the analysis is that lithofacies, biofacies, and trace fossil assemblages form distinct, non-repetitive, vertically successive horizons, with their distribution boundaries roughly coincident. On this basis, seven major facies groups, showing a distinct combination of lithofacies, biofacies, and trace fossils, are distinguished in the Santa Marta Formation. These non-repetitive, vertically stacked facies groups reveal a one-way evolution of the depositional system during a transgressive-regressive cycle, with a new transgression at the top of the unit. The lower facies groups represent shallow marine settings with a very high rate of volcaniclastic sedimentation within subsiding basin. Shallow, volcaniclastic fan systems were probably formed at the base of delta slope and grew rapidly as a consequence of high sedimentary supply in equilibrium with basin subsidence. The upper facies groups probably represent sedimentation within the marine part of the envisaged deltaic system on a more stable shelf with diminished volcaniclastic sedimentary input.

Post glacial lacustrine event sedimentation in an ancient mountain setting: Carboniferous Lake Malanzán (Western Argentina)

Lacustrine deposits of the Malanzán Formation record sedimentation in a small and narrow mountain paleovalley. Lake Malanzán was one of several water bodies formed in the Paganzo Basin during the Late Carboniferous deglaciation. Five sedimentary facies have been recognized. Facies A (Dropstones-bearing laminated mudstones) records deposition from suspension fall-out and probably underflow currents coupled with ice-rafting processes in a basin lake setting. Facies B (Ripple cross-laminated sandstones and siltstones) was deposited from low density turbidity currents in a lobe fringe environment. Facies C (Massive or graded sandstones) is thought to represent sedimentation from high and low density turbidity currents in sand lobes. Facies D (Folded sandstones and siltstones) was formed from slumping in proximal lobe environments. Facies E (Wave-rippled sandstones) records wave reworking of sands supplied by turbidity currents above wave base level.The Lake Malanzán succession is formed by stacked turbidite sand lobe deposits. These lobes were probably formed in proximal lacustrine settings, most likely relatively high gradient slopes. Paleocurrents indicate a dominant direction from cratonic areas to the WSW. Although the overall sequence shows a regressive trend from basin fine-grained deposits to deltaic and braided fluvial facies, individual lobe packages lack of definite vertical trends in bed thickness and grain size. This fact suggests aggradation from multiple-point sources, rather than progradation from single-point sources. Sedimentologic and paleoecologic evidence indicate high depositional rate and sediment supply. Deposition within the lake was largely dominated by event sedimentation. Low diversity trace fossil assemblages of opportunistic invertebrates indicate recolonization of event beds under stressed conditions.Three stages of lake evolutionary history have been distinguished. The vertical replacement of braided fluvial deposits by basinal facies indicates high subsidence and a lacustrine transgressive episode. This flooding event was probably linked to a notable base level rise during postglacial times. The second evolutionary stage was typified by the formation of sand turbidite lobes from downslope mass-movements. Lake history culminates with the progradation of deltaic and braided fluvial systems

Vagorichnus, a new ichnogenus for feeding burrow systems and its occurrence as discrete and compound ichnotaxa in Jurassic lacustrine turbidites of Central China

A new ichnogenus, Vagorichnus, is figured and described from Jurassic lacustrine turbidites of the Anyao Formation, Henan Province, Central China. Vagorichnus consists of complex burrow systems composed of discontinuous curved to meandering segments in which irregular networks are formed. The ichnospecies V. anyao covers burrow systems characterized by constricted and irregularly annulated segments, and ridge‐like knobs. Although traces are preserved as hypichnial ridges on the sole of turbidite sandstones, several lines of evidence indicate that these ichnofossils record the activity of a post‐event infauna. Vagorichnus occurs as discrete and compound ichnotaxa. In the latter case, it grades into Gordia and Tuberculichnus. Vagorichnus is interpreted as invertebrate feeding structures (Fodinichnia).

Shallow marine event sedimentation in a volcanic arc-related setting: the Ordovician Suri Formation, Famatina Range, northwest Argentina

Abstract The Loma del Kilometro Member of the Lower Ordovician Suri Formation records arc-related shelf sedimentation in the Famatina Basin of northwest Argentina. Nine facies, grouped into three facies assemblages, are recognized. Facies assemblage 1 [massive and parallel-laminated mudstones (facies A) locally punctuated by normally graded or parallel-laminated silty sandstones (facies B] records deposition from suspension fall-out and episodic storm-induced turbidity currents in an outer shelf setting. Facies assemblage 2 [massive and parallel-laminated mudstones (facies A) interbedded with rippled-top very fine-grained sandstones (facies D)] is interpreted as the product of background sedimentation alternating with distal storm events in a middle shelf environment. Facies assemblage 3 [normally graded coarse to fine-grained sandstones (facies C); parallel-laminated to low angle cross-stratified sandstones (facies E); hummocky cross-stratified sandstones and siltstones (facies F); interstratified fine-grained sandstones and mudstones (facies G); massive muddy siltstones and sandstones (facies H); tuffaceous sandstones (facies 1); and interbedded thin units of massive and parallel-laminated mudstones (facies A)] is thought to represent volcaniclastic mass flow and storm deposition coupled with subordinated suspension fall-out in an inner-shelf to lower-shoreface setting. The Loma del Kilometro Member records regress ive-transgressive sedimentation in a storm- and mass flow-dominated high-gradient shelf. Volcano-tectonic activity was the important control on shelf morphology, while relative sea-level change influenced sedimentation. The lower part of the succession is attributed to mud blanketing during high stand and volcanic quiescence. Progradation of the inner shelf to lower shoreface facies assemblage in the middle part represents an abrupt basinward shoreline migration. An erosive-based, non-volcaniclastic, turbidite unit at the base of this package suggests a sea level fall. Pyroclastic detritus, andesites, and a non-volcanic terrain were eroded and their detritus was transported basinward and redeposited by sediment gravity flows during the low stand. The local coexistence of juvenile pyroclastic detritus and fossils suggests reworking of rare ash-falls. The upper part of the Loma del Kilometro Member records a transgression with no evidence of contemporaneous volcanism. Biostratinomic, paleoecologic, and ichnologic analyses support this paleoenvironmental interpretations and provide independent evidence for the dominance of episodic sedimentation in an arc-related shallow marine setting. Fossil concentrations were mainly formed by event processes, such as storms and volcaniclastic mass flows. High depositional rates inhibited formation of sediment-starved biogenic concentrations. Collectively, trace fossils belong to the Cruziana ichnofacies. Low diversity, scarcity, and presence of relatively simple forms indicate benthic activity under stressful conditions, most probably linked to high sedimentation rates. Contrasting sedimentary dynamics between ‘normal shelves’ and their volcaniclastic counterparts produce distinct and particular signatures in the stratigraphic record. Arc-related shelves are typified by event deposition with significant participation of sediment gravity flows, relatively high sedimentation rates, textural and mineralogical immaturity of sediments, scarcity and low diversity of trace fossils, and dominance of transported and reworked faunal assemblages genetically related to episodic processes.