Search

Fluvial point bar deposits are described from the ca. 1 Ga Diabaig Formation, representing some of the most compelling architectural evidence of planform sinuosity recognized in pre-vegetation sedimentary strata to date. The stratigraphic architecture of the deposits indicates different planform transformations in response to meander-bend expansion and downstream migration. Point bar architectural motifs are locally abundant in the unit and this is attributed to elevated amounts of mud-calibre cohesive sediment. Mud afforded landscape stability that, together with limited stream power, was sufficient to corral sediment into single-thread, sinuous channels. Significant volumes of fine-grained sediment were encouraged to accumulate by the local basin setting of several topographically confined endorheic depressions. These conditions ceased once the hydrologically closed valleys were filled, with the overlying sandstone-dominated Applecross Formation subsequently deposited by low-sinuosity, braided rivers that bypassed fine-grained sediment oceanward. Other endorheic basins conducive to the formation of depositional meanders should be expected to have been relatively widespread on pre-vegetation Earth, though many individually limited in size, confined by their inherited topographies. Depositional architectures representative of sinuous channel planforms remain scarce within more extensive, externally drained basins.

The sedimentary-stratigraphic record is regularly considered only in the context of regional climate, tectonic configuration, and sea-level. In this study we provide examples of how biotically influenced autogenic processes may come to be overprinted on these extrinsic, allogenic controls. A sedimentological analysis is given for the Mississippian (Visean) siliciclastic strata which crop out in counties Donegal and Mayo in NW Ireland. Eleven sedimentary facies record deposition of dominantly clastic and humic organic sediments which accumulated in alluvial, fluvial, estuarine, and fully marine environments. The preserved architecture of the sedimentary deposits is shown to be dependent on local autogenic dynamics, processes that were in turn modified or entirely controlled by biota (“biosphere signatures”). Sedimentological criteria, specifically the type and distribution of preserved biosphere signatures, suggests deposition occurred in a dominantly wet, humid environment in keeping with Laurussia's proposed equatorial position but potentially at odds with previous suggestions of seasonal aridity. The humid climate and resultant perennially active water conduits facilitated the widespread preservation of inclined heterolithic stratification (IHS). Allogenic and autogenic processes are ultimately linked, with external factors such as sea-level, tectonics, and climate all impacting the spatial distribution, abundance and prevailing forms of biota. The flooding of the Laurussian continent is accompanied by a shift from plant-induced to animal-induced biosphere signatures basinwards of the estuary funnel. In this way, the interplay between allogenic and autogenic processes is recorded at sedimentary outcrop through the capacity of extrinsic forcings to influence the rates and locations of intrinsic life-sediment interactions.

This thematic set is the second of a pair of volumes delving into the co-evolution of life and sedimentary environments in deep time. Whilst the full gamut of life-sediment interactions is far too vast to cover in its entirety, across both volumes this set provides examples of how different organisms have interacted with sedimentary environments across the entirety of the Phanerozoic. The first thematic set of this pair focussed on plant-sediment interactions from the Carboniferous to the Pliocene (Davies et al., 2022; PALAIOS Volume 37, Issue 6), whereas this second set has a loose running theme of ‘animals’; documenting examples of interactions between metazoans and the environments that they occupied.

The evolution of land plants during the Palaeozoic Era transformed Earth’s biosphere 1. Because the Earth's surface and interior are linked by tectonic processes, the linked evolution of the biosphere and sedimentary rocks should be recorded as a near-contemporary shift in the composition of the continental crust. To test this hypothesis, we assessed the isotopic signatures of zircon formed at subduction zones where marine sediments are transported into the mantle 2,3, thereby recording interactions between surface environments and the deep Earth. Using oxygen and lutetium-hafnium isotopes of magmatic zircon that respectively track surface weathering (time-independent) 4 and radiogenic decay (time-dependent) 5, we find a correlation in the composition of continental crust after 430 Myr ago, which is coeval with the onset of enhanced complexity and stability in sedimentary systems related to the evolution of vascular plants. The expansion of terrestrial vegetation brought channelled sand-bed and meandering rivers, muddy floodplains, and thicker soils, lengthening the duration of weathering before final marine deposition 6,7. Collectively, our results suggest that the evolution of vascular plants coupled the degree of weathering and timescales of sediment routing to depositional basins where they were subsequently subducted and melted. The late Palaeozoic isotopic shift of zircon indicates that the greening of the continents was recorded in the deep Earth.

The amount of mudrock preserved globally in alluvium increased in stratigraphic synchrony with the Paleozoic evolution of land plants. This observation has been explained by vegetation promoting both the retention of mud through baffling, stabilization, and flocculation, and the production of mud through chemical weathering. However, the latter explanation has been challenged on the basis that it is perceived to require imbalance in the long-term global carbon cycle. We present a compendium of empirical evidence that is supportive of increased global fine sediment supply, and thus the contention that land plants did, in fact, promote the production of mud on the continents. We refine previous broad-brush analyses of Paleozoic mudrock content by specifically tracking shifts in the mudrock content of regions of alluvial and tidal landscapes that remained locally unvegetated even after the greening of the continents, namely inclined heterolithic stratification (IHS) that records submerged in-channel bars. We show that the Paleozoic mudrock increase was pronounced even within these areas, away from any biomechanical binding and baffling effects of plants. Precambrian and Cambrian IHS are composed almost exclusively of sandstone, whereas Silurian through to Carboniferous examples show a steady increase in total mudrock content. This progressive rise in the mudrock component of channel bars cannot alone be explained by physical retention of mud by vegetation and requires heightened fine sediment concentrations from the hinterland, which suggests that plants increased the volume of mud available at source. The muddying of Earth’s preserved IHS serves as a proxy that suggests evolving Paleozoic land plants triggered a global increase in the production and supply of fine-grained sediment.

Amongst all the disciplines in Earth Sciences, paleontology and sedimentary geology share a particularly striking and complicated frontier. On the one hand, some of the topics that they encompass are apparently separated by huge gulfs in methods and expertise: multiple degrees of separation need to be counted to get from, say, molecular phylogeny to sediment diagenesis, or paleophysiology to sequence stratigraphy. Yet there are arguably further areas where the boundary between the subjects is far more porous, consisting of sub-disciplines that refuse to be pigeon-holed and instead demand consensus between paleontologists and sedimentary geologists. This hazy border zone is the natural territory of PALAIOS, the remit of which is to emphasize “the impact of life on Earth's history as recorded in the paleontological and sedimentological records”, and which has previously published seminal advances in topics such as ichnology, taphonomy, and carbonate sedimentology. Recognizing this, this first of two thematic sets in the journal, which seek to explore how the sedimentary rock record has chronicled ancient life and sediment interactions, might seem unnecessary. Yet what makes these collected papers distinct is that they defy classification within any particular sub-discipline: rather these are either ‘paleontological’ papers that pay additional attention to sedimentological context or ‘sedimentological’ papers that emphasise the importance of life in sedimentary environments. In each instance they demonstrate the potential to understand much more about ancient Earth when the procedures of the two disciplines are undertaken in unison, and hopefully showcase avenues of exploration to inspire further research in this vein.

In modern rivers, vegetation affects hydrological, geomorphological and sedimentological functioning, so extant fluvial systems can provide only partial analogues for those rivers that operated before the evolution of land plants. However, pre-vegetation rivers were the norm for the first 90% of Earth9s history and so a better understanding of their sedimentary product can provide insights into both the fundamental underlying mechanisms of river behaviour and the ways in which fluvial processes operated on ancient Earth. In addition to a short review of the history of research into pre-vegetation alluvium, this paper presents a fieldwork-based case study of the later Proterozoic Torridon Group, which contains some of the most extensive and easily accessible exposures of pre-vegetation alluvium worldwide. Three alluvial architectural deposits have been recognized: (1) channel-bedform deposits (c. 80%); (2) barform deposits (c. 20%); and (3) out-of-channel deposits (≪1%). Channel-bedform deposits have erosional bases and most frequently stack vertically to form thick multistorey channel-bedform sequences. The preferential preservation of these deposits, which record the deepest parts of river channels, suggests that channel migration had a dominant control on preservation in the Torridon Group. Less frequently, channel-bedform deposits pass upwards into a genetically related barform deposit. Barform preservation in these instances is interpreted to be due to channel avulsion, which protected the barforms from reworking. Channel-bar thickness, measured from the basal erosional surface of a channel-bedform deposit to the top of its associated barform deposit, indicates minimum water depths of 1.7 to 8.0 m. Downstream-accreting barform deposits are most frequent, but lateral and upstream modes of accretion are also well represented. Dominant southeastward-palaeoflow directions imply that the Torridonian rivers were sourced from the Grenvillian Mountain Belt. The preserved architectural deposits and narrow dispersal of palaeocurrent data are explained by interpreting the Torridon Group as the alluvium of dominantly low-sinuosity rivers, with signatures recording autogenic fluvial adjustments. In the few rare instances where out-of-channel deposits are preserved, they contain fossil evidence for microbial mats, which prove that not all Proterozoic river systems were wholly abiotic. The overall characteristics of the Torridon alluvium, in terms of its ubiquitous highly tabular beds of sand-grade or coarser material, make it an archetypal example of pre-vegetation alluvium as known globally. Thematic collection: This article is part of the SJG Collection on Early-Career Research available at: https://www.lyellcollection.org/cc/SJG-early-career-research

It is widely understood that Earth9s stratigraphic record is an incomplete record of time, but the implications that this has for interpreting sedimentary outcrop have received little attention. Here we consider how time is preserved at outcrop using the Neogene–Quaternary Red Crag Formation, England. The Red Crag Formation hosts sedimentological and ichnological proxies that can be used to assess the time taken to accumulate outcrop expressions of strata, as ancient depositional environments fluctuated between states of deposition, erosion and stasis. We use these to estimate how much time is preserved at outcrop scale and find that every outcrop provides only a vanishingly small window onto unanchored weeks to months within the 600–800 kyr of ‘Crag-time’. Much of the apparently missing time may be accounted for by the parts of the formation at subcrop, rather than outcrop: stratigraphic time has not been lost, but is hidden. The time-completeness of the Red Crag Formation at outcrop appears analogous to that recorded in much older rock units, implying that direct comparison between strata of all ages is valid and that perceived stratigraphic incompleteness is an inconsequential barrier to viewing the outcrop sedimentary-stratigraphic record as a truthful chronicle of Earth history. Supplementary material: Further details of the regional geology and specific information on outcrops are available at https://doi.org/10.6084/m9.figshare.c.4561001

This is a short comment on “The impacts of land plant evolution on Earth's climate and oxygenation state – An interdisciplinary review” by Tais W. Dahl and Susanne K.M. Arens, Chem. Geol. 547 (2020) Article 119665. We discuss what the sedimentary-stratigraphic record (SSR) can reveal about the influence of ancient land plants on erosion, and demonstrate that the intensive properties of the SSR are supportive of hypotheses that the evolution of vegetation slowed global erosion rates.

MURFI was financially supported in part by the UK Space Agency, and by the following grants: Balme: UK SA grants ST/L00643X/1 and ST/R001413/1; Bridges: UK SA grant ST/R00143X/1; Butcher and Wright: STFC studentship grant ST/N50421X/1; Coates and Griffiths: UK SA grant ST/R002223/1; Cousins: Royal Society of Edinburgh Research Fellowship and UK SA grant ST/P001297/1; Davis: UK STFC grant ST/K502388/1; Grindrod: UK SA and STFC grants ST/J005215/1, ST/L006456/1, ST/N000528/1; Gunn: UK SA grants ST/P001408/1, ST/P001394/1, ST/N006410/1; Muller: UK SA grant ST/P002145/1; Preston: UK SA grant ST/P001254/1; Stabbins: UK SA studentship grant ST/N002377/1. We thank the UK Harwell Campus Satellite Applications Catapult for providing access to the control room that became the MOC, and the STFC Rutherford Appleton Laboratory for other ROC support. The 2016 Mars Utah Rover Field Investigation (MURFI) was a Mars rover field trial run by the UK Space Agency in association with the Canadian Space Agency's 2015/2016 Mars Sample Return Analogue Deployment mission. MURFI had over 50 participants from 15 different institutions around the UK and abroad. The objectives of MURFI were to develop experience and leadership within the UK in running future rover field trials; to prepare the UK planetary community for involvement in the European Space Agency/Roscosmos ExoMars 2020 rover mission; and to assess how ExoMars operations may differ from previous rover missions. Hence, the wider MURFI trial included a ten-day (or ten-‘sol’) ExoMars rover-like simulation. This comprised an operations team and control centre in the UK, and a rover platform in Utah, equipped with instruments to emulate the ExoMars rovers remote sensing and analytical suite. The operations team operated in ‘blind mode’, where the only available data came from the rover instruments, and daily tactical planning was performed under strict time constraints to simulate real communications windows. The designated science goal of the MURFI ExoMars rover-like simulation was to locate in-situ bedrock, at a site suitable for sub-surface core-sampling, in order to detect signs of ancient life. Prior to “landing”, the only information available to the operations team was Mars-equivalent satellite remote sensing data, which were used for both geologic and hazard (e.g., slopes, loose soil) characterisation of the area. During each sol of the mission, the operations team sent driving instructions and imaging/analysis targeting commands, which were then enacted by the field team and rover-controllers in Utah. During the ten-sol mission, the rover drove over 100 m and obtained hundreds of images and supporting observations, allowing the operations team to build up geologic hypotheses for the local area and select possible drilling locations. On sol 9, the team obtained a subsurface core sample that was then analyzed by the Raman spectrometer. Following the conclusion of the ExoMars-like component of MURFI, the operations and field team came together to evaluate the successes and failures of the mission, and discuss lessons learnt for ExoMars rover and future field trials. Key outcomes relevant to ExoMars rover included a key recognition of the importance of field trials for (i) understanding how to operate the ExoMars rover instruments as a suite, (ii) building an operations planning team that can work well together under strict time-limited pressure, (iii) developing new processes and workflows relevant to the ExoMars rover, (iv) understanding the limits and benefits of satellite mapping and (v) practicing efficient geological interpretation of outcrops and landscapes from rover-based data, by comparing the outcomes of the simulated mission with post-trial, in-situ field observations. In addition, MURFI was perceived by all who participated as a vital learning experience, especially for early and mid-career members of the team, and also demonstrated the UK capability of implementing a large rover field trial. The lessons learnt from MURFI are therefore relevant both to ExoMars rover, and to future rover field trials. Postprint

A survey was administered to 183 Ugandan farmers in August 2014 to assess the factors that influence their willingness to become members of a proposed new agricultural cooperative. In particular, we were interested in a better understanding of how farmers viewed the social benefits associated with cooperation. These social benefits have the potential to become valuable sources of social capital. Four valid and reliable measures of social benefits were identified. Social benefits that farmers may use to get by (bonding networks) had two dimensions: emotional support and social support. Social benefits that farmers may use to get ahead (bridging networks) also had two dimensions: tangible and intangible resource sharing. The desire to gain these social benefits from cooperation (except for emotional support) emerged as strong predictors of farmers’ willingness to cooperate in a proposed new agricultural cooperative. Surprisingly, the expected economic benefits of cooperation did not have a significant effect on willingness to cooperate. Implications and suggestions for future research and cooperative development and management are also discussed.

The Mesoproterozoic-Neoproterozoic Torridonian Sandstone of NW Scotland has renewed sedimentological significance following recent advances in the understanding of pre-vegetation alluvium, as it is one of the most extensive and easily-accessible successions of such strata worldwide. This paper presents the first modern sedimentological analysis of the unit’s constituent Meall Dearg Formation (late Mesoproterozoic), recognizing a dominance of alluvial facies, with subordinate aeolian facies. Alluvial strata within the Meall Dearg Formation contain direct evidence for event deposition by high-energy floods, including: (1) widespread upper- and transitional-upper flow regime elements; (2) frequent stacking of successively-lower flow-regime elements; (3) common subcritical subaqueous dune fields with superimposed ripple marks; (4) occasional thin, desiccated mudstones; and (5) evidence that microbial mats colonized substrates during intervals of sedimentary stasis. Together these strands of primary sedimentary geological evidence indicate that the alluvial deposition of the Meall Dearg Formation was typified by supercritical flows during high-energy floods, punctuated by prolonged intervals of sedimentary stasis. The preservation potential of all of the features was boosted by highly aggradational sedimentary conditions. These primary observations have implications for the ‘norm’ in pre-vegetation alluvium and confirm that, despite increasing recognition of diversity within Precambrian fluvial systems, classical pre-vegetation motifs of high-energy alluvial flood deposits preserved as “sheet-braided” alluvium are still an archetypal sedimentary signature in some instances. Using supportive evidence from the Meall Dearg Formation, we recommend that the term “sheet-braided” be used in inverted commas in future studies; this emphasises the polygenetic depositional nature of the 20:1 width:thickness fluvial style, while maintaining the value of the term in the isolation of a key characteristic of pre-vegetation sedimentary architecture., Supported by Shell International Exploration and Production B.V under Research Framework agreement PT38181. Two anonymous reviewers and editor Adrian Hartley are thanked for comments which improved the manuscript.

The first-order importance of tectonic and environmental controlsfor terrigenous sediment supply has rarely been questioned, but the role of vegetation in the modification of ancient alluvial signa ...

A wide variety of sub-ripple-scale sedimentary surface textures are known from bedding planes in the sedimentary rock record. Many of these textures were traditionally ascribed an abiotic origin (e.g., due to rain drop impact, adhesion, etc.), but in recent decades the role of microbial mats and biofilms in sculpting and mediating some forms has become increasingly recognized. Microbial sedimentary textures are now well-described and understood from modern tidal environments and biological soil crusts, but descriptions from fluvial settings are less common, despite their known occurrence in ancient alluvium. This paper reports a suite of primary sedimentary surface textures which were observed forming in discrete bodies of standing water in the lower reaches of the ephemeral Murchison River, Western Australia. Microbial sedimentary signatures included bubble impressions (burst and intact) and roll-ups, in addition to reduced horizons. Many of these features exhibited rapid temporal evolution of their morphology in the dry days following an interval of heavy rain. Significantly, these microbial features were witnessed in close spatial proximity to other abiotic and biotic sedimentary surface textures including raindrop impressions, adhesion marks, desiccation cracks, and vertebrate and invertebrate traces. Such proximity of abiotic and microbial sedimentary surface textures is rarely reported from bedding planes in the rock record, but these modern observations emphasize the fact that, particularly in non-marine environments, such structures should not be expected to be mutually exclusive. An appreciation of the fact that primary sedimentary surface textures such as these develop during intervals of stasis in a sedimentation system is crucial to our understanding of their significance and diversity in the rock record.

Model-based decision making is commonly used in performance assessments to assure water resource protection for both human health and the environment for hundreds of years into the future. To make decisions regarding aquifer protection against potential contamination, a conceptual site model (CSM) describing the hydrodynamic behavior needs to account for subsurface heterogeneities in sufficient detail. When site-specific data are sparse, larger-scale geologic descriptions are adopted with the consequence of losing small-scale features (at the cm scale) that can control contaminant transport. In this study, a multiple lines of evidence approach is used to construct vadose zone CSMs based on an evaluation of several types of data, including geologic logs, borehole moisture content and concentration data, geophysical spectral gamma logging data, and groundwater concentration data for a tank farm at the Hanford Site in southeastern Washington State. The resulting CSMs of the unsaturated zone represent a synthesis of what is known about flow and transport processes at the site-scale and maintain consistency with knowledge that has been accumulated at the regional scale. Through a process of extensive data analyses, a systematic approach is described to create an evidence base that supports the evaluation and development of CSMs. Numerical models are then used to evaluate the impact that smaller-scale heterogeneities have on contaminant transport through the vadose zone for a performance assessment on waste tank closure. Together, the field data and the numerical experiments suggest that although small-scale features close to source releases can have an impact on horizontal spreading, overall there is a relatively minor impact on transport for the site under study as evaluated by differences in peak fluxes and arrival times for historical leak events, and for potential releases resulting from waste tank closure. Use of alternative CSMs, developed through careful examination of available characterization and monitoring data, provides confidence that geologic heterogeneities do not impact contaminant transport behavior significantly enough to alter the assessment of risk for closure at this site.

The landscapes and seascapes of Earth’s surface provide the theatre for life, but to what extent did the actors build the stage? The role of life in the long-term shaping of the planetary surface needs to be understood to ascertain whether Earth is singular among known rocky planets, and to frame predictions of future changes to the biosphere. Modern geomorphic observations and modelling have made strides in this respect, but an under-utilized lens through which to interrogate these questions resides in the most complete tangible record of our planetary history: the sedimentary-stratigraphic record (SSR). The characteristics of the SSR have been frequently explained with reference to changes in boundary conditions such as relative sea level, climate, and tectonics. Yet despite the fact that the long-term accrual of the SSR was contemporaneous with the evolution of almost all domains of life on Earth, causal explanations related to biological activity have often been overlooked, particularly within siliciclastic strata. This paper explores evidence for the ways in which organisms have influenced the SSR throughout Earth history and emphasizes that further investigation can help lead towards a mechanistic understanding of how the planetary surface has co-evolved with life. The practicality of discerning life signatures in the SSR is discussed by: 1) distinguishing biologically-dependent versus biologically-influenced sedimentary signatures; 2) emphasizing the importance of determining relative time-length scales of processes and demonstrating how different focal lengths of observation (individual geological outcrops and the complete SSR) can reveal different insights; and 3) promoting an awareness of issues of equifinality and underdetermination that may hinder the recognition of life signatures. Multiple instances of life signatures and their historic range within the SSR are reviewed, with examples covering siliciclastic, biogenic and chemogenic strata, and trigger organisms from across the spectrum of Earth’s extant and ancient life. With this novel perspective, the SSR is recognised as a dynamic archive that expands and complements the fossil and geochemical records that it hosts, rather than simply being a passive repository for them. The SSR is shown to be both the record and the result of long-term evolutionary synchrony between life and planetary surface processes.

Mudrocks get a vegetative assist Mudrocks such as slate and shale are rarely found in stratigraphy older than about 500 million years. McMahon and Davies compiled a large database of mudrock occurrence over the past 3.5 billion years to help assess the origin of this ubiquitous rock type (see the Perspective by Fischer). Mudrocks appeared at the same time as did deep-rooted land plants. The interplay between plants and sedimentary rocks suggests that a change in erosion rate and the chemistry of sediments delivered to the oceans occurred around 500 million years ago. Science, this issue p. 1022 ; see also p. 994

Vadose zone hydrology plays a key role on moisture flow and contaminant migration through the vadose zone to the underlying aquifer. In particular, vadose zone residence times are significantly impacted by the geologic media heterogeneities, physical and hydraulic properties of sediments, and the moisture content of sediments. This is especially true for the relatively low moisture contents (e.g., less than 10% volumetric) that are typical of dry semi-arid conditions such as those existing for Hanford sediments in southeastern Washington, USA. The objectives of this article are to present a detailed assessment and an evaluation of the technical basis for selection of the vadose zone conceptual model for a waste disposal facility at the DOE Hanford Site. Specifically, we provide a detailed description and an assessment of the vadose zone modeling used in Environmental Restoration Disposal Facility (ERDF). The ERDF is a shallow near-surface disposal facility that is situated in the Central Plateau portion of the Hanford Site. The current disposal area is approximately 1000 m long, 400 m wide, with a depth of 22 m. As of middle of year 2015, approximately 14 million metric tons of waste had been disposed at ERDF, which occupies approximately 6.5 million m3 of volume.

The focus of this study was to define the shape and extent of tritium groundwater contamination emanating from a legacy burial ground and to identify vadose zone sources of tritium using helium isotopes ( 3 He and 4 He) in soil gas. Helium isotopes were measured in soil-gas samples collected from 70 sampling points around the perimeter and downgradient of a burial ground that contains buried radioactive solid waste. The soil-gas samples were analyzed for helium isotopes using rare gas mass spectrometry. 3 He/ 4 He ratios, reported as normalized to the air ratio (R A ), were used to locate the tritium groundwater plume emanating from the burial ground. The 3 He (excess) suggested that the general location of the tritium source is within the burial ground. This study clearly demonstrated the efficacy of the 3 He method for application to similar sites elsewhere within the DOE weapons complex.

PSYCHOLOGY AND RELIGION: Three Joint Symposia from the ACPA-APA Meetings of 1957, 1958, 1959. American Catholic Psychological Association, Fordham University, New York Selected Papers from the ACPA Meetings of 1957, 1958, 1959. New York: American Catholic Psychological Association TO LIVE IS CHRIST: Robert W. Gleason, S. J. Sheed and Ward THE INFORMATION SERVICE IN GUIDANCE: Willa Norris, Franklin R. Zeran, Raymond N. Hatch, Rand McNally WORKING WITH SUPERIOR STUDENTS: THEORIES AND PRACTICES: Bruce Shertzer, Ed. VOCATIONAL MATURITY OF NINTH-GRADE BOYS: Donald E. Super, Phoebe L. Over-street, et. al., Monograph 2.

The pre-Silurian alluvial rock record is dominated by accumulations of laterally-extensive, sheet-like sandstone strata with minimal mudrock; a depositional style frequently explained as representing fluvial processes particular to “pre-vegetation” Earth. While the sedimentological and geomorphological influence of Palaeozoic embryophytes and other higher vegetation has been commonly inferred, the influence of the non-marine microbial matgrounds that preceded them has been less well studied. The ?Ediacaran-Cambrian Series Rouge of northern France and the Channel Islands is a rare example of a predominantly alluvial succession which exhibits both pre-vegetation sedimentary motifs and evidence for the existence of terrestrial microbial mats. The latter include likely microbial sedimentary surface textures, the enigmatic matground “pseudofossils” Aristophycus and Arumberia, and probable mat fragments and mat-related microtextures preserved in argillaceous sediment. The sedimentological characteristics of the Series Rouge are described and analysed in order to assess the role of microbial influences on pre-vegetation alluvial systems. Near ubiquitously trough-cross bedded sheet-braided facies, with rarely preserved channel-forms, indicate that alluvial sedimentation was dominated by in-channel dune migration, and depositional-strike exposures reveal the periodic downstream migration of complex bar-forms. Lateral accretion elements and minor discontinuous lenses of more argillaceous material are locally present. Thus, despite the evidence for matgrounds, sedimentary architecture was essentially ‘abiotic’. Using this evidence from the Series Rouge, we argue that the surficial cohesion provided by matgrounds did not exceed thresholds for reworking by hydrodynamic processes thus having little or no effect on their preserved sedimentary architecture.

Outcrop photographs which show two-dimensional representations of three-dimensionally dipping surfaces (e.g., bedding planes, cross-bed foresets) are commonly utilized in the description of sedimentary strata. In many instances, accurate depiction of the dip direction of such features is paramount for understanding their interpretation, and for visualizing the true form of three-dimensional bodies (e.g., conceptualizing the form of an architectural element in a cliff-face, preserved as a vertical slice that has been cut oblique to paleocurrent direction). However, as an outcrop photograph often presents information on a vertical plane and directional data refers to a horizontal plane, the accurate co-depiction of both sets of information may be challenging. There is presently no universal method for illustrating such measurements on outcrop photographs: techniques in common usage are often imprecise, and the lack of uniformity hinders comparison between different images. Here we present a method for accurately depicting horizontal direction data on vertical outcrop photographs which permits instant visualization of dip relative to the illustrated outcrop geometry. The method is simple to apply, does not compromise primary data, and is unobtrusive to other visual information within images; thus having utility across a broad spectrum of geological investigations.

Examines the principles of vacuum fusion, the necessary apparatus, and its use in performing gas analysis.