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Earth’s largest biotic crisis occurred during the Permo–Triassic Transition (PTT). On land, this event witnessed a turnover from synapsid- to archosauromorph-dominated assemblages and a restructuring of terrestrial ecosystems. However, understanding extinction patterns has been limited by a lack of high-precision fossil occurrence data to resolve events on submillion-year timescales. We analyzed a unique database of 588 fossil tetrapod specimens from South Africa’s Karoo Basin, spanning ∼4 My, and 13 stratigraphic bin intervals averaging 300,000 y each. Using samplestandardized methods, we characterized faunal assemblage dynamics during the PTT. High regional extinction rates occurred through a protracted interval of ∼1 Ma, initially co-occurring with low origination rates. This resulted in declining diversity up to the acme of extinction near the Daptocephalus–Lystrosaurus declivis Assemblage Zone boundary. Regional origination rates increased abruptly above this boundary, co-occurring with high extinction rates to drive rapid turnover and an assemblage of short-lived species symptomatic of ecosystem instability. The “disaster taxon” Lystrosaurus shows a long-term trend of increasing abundance initiated in the latest Permian. Lystrosaurus comprised 54% of all specimens by the onset of mass extinction and 70% in the extinction aftermath. This early Lystrosaurus abundance suggests its expansion was facilitated by environmental changes rather than by ecological opportunity following the extinctions of other species as commonly assumed for disaster taxa. Our findings conservatively place the Karoo extinction interval closer in time, but not coeval with, the more rapid marine event and reveal key differences between the PTT extinctions on land and in the oceans.

The rock record from the late Early Jurassic in southern Africa encompasses the history of voluminous continental flood basalt outpourings associated with the magmatic events in the Karoo–Ferrar Large Igneous Province (LIP) in southern and eastern Gondwana. This multiphase magmatism produced one of Earth’s largest continental flood basalt successions volumetrically and is assumed to have been a main driving mechanism in late Early Jurassic global environmental perturbations, including mass extinctions and changes in climate. In southern Africa, these Lower Jurassic flood basalts are interbedded with fossiliferous sedimentary rocks, which in turn host the last signs of ‘Karoo life’ in the form of fossil plants, invertebrates and vertebrates, including the trackways of hopping mammals and the ultimate Karoo dinosaurs. The sedimentology and palaeontology of the interbeds archived depositional and biotic processes in running water as well as in and around shallow, up to ∼10 m deep freshwater lakes and ponds in the late Early Jurassic. This study explains how a complex freshwater palaeo-habitat prevailed – albeit temporarily – in this extremely stressful environment, which was unlike any modern volcanic system. The evidence collectively points to seasonally wet, warm temperate climatic conditions during the early phases of Karoo volcanism. Moreover, the evidence in the rocks also suggests that the dynamic volcanic conditions resulted in shifting habitats that likely facilitated the migration of the ultimate Karoo biota towards the north and west, away from the main Karoo land of fire, just before Gondwana started to disassemble. This refinement of the environmental dynamics in southern Gondwana presented herein lays the groundwork for future high-resolution volcanological, geochronological and chemostratigraphical studies aimed at the nuanced understanding of the global environmental effect of the Karoo–Ferrar LIP.

Magmatic sheet intrusions contribute significantly to the upper crustal magma transport network. The emplacement mechanism of the magmatic sheets controls the final geometry of the intrusions and the characteristics of host rock deformation. Previous observations have highlighted the preponderance of brittle structures, associated with shallow-level sheet intrusions. However, recent studies have suggested that non-brittle host rock behaviour also occurs, particularly related to the formation of magma fingers during shallow-level sill intrusion. Here, we examine both brittle and non-brittle intrusion mechanisms and expand upon them with field observations from a series of widespread and variable magmatic systems. Non-brittle emplacement appears primarily associated with viscous flow of the host rock during intrusion and is therefore intimately linked to the contemporaneous host rock rheology as well as magma dynamics. Purely brittle and non-brittle emplacement processes are found to be end members with many intrusions containing evidence of both behaviours. Deriving the host rock characteristics is therefore important for discerning potential diagnostic intrusion indicators and intrusion geometries both within the field and in modelling. Incorporation of variable host material behaviours in numerical and analogue modelling, tuned using direct field observations, may consequently further our understanding of the controls on shallow-level intrusion.

A widely misused criterion to interpret lobe deposits in submarine fan systems at outcrop, and in core and well logs, is a thickening and/or coarsening upward profile. Lobe deposits from the Laingsburg depocentre, SW Karoo Basin, demonstrate that a full range of bed thickness patterns exists within lobes. When lobes are defined by their laterally extensive bounding surfaces that are marked by abrupt facies changes, five types of bed stacking patterns are identified: thickening upward, thinning upward, thickening then thinning upward, thinning then thickening upward, and constant. The abrupt bounding surfaces are interpreted to record avulsion of feeder distributive channels. The stratigraphic bed thickness pattern preserved in a lobe reflects the internal organization of smaller-scale lobe elements, rather than lobe-wide initiation and progradation as implied by a thickening-upward only pattern. The full range of bed thickness patterns in lobes can be used to understand the stacking of lobe elements, the evolution of sediment deposition through time and space, and the relative movement of depocentres.

The body size of fossil organisms has been an important area of research for paleobiologists for well over a century, because body size can tell us much about widespread trends in the evolution of major groups of living things. However, paleobiologists often study body size by focusing only on size-related information collected from fossils. Without information about a fossil organism's biology and geologic history beyond its size, we cannot understand what is driving body-size change over evolutionary time in a meaningful way. Luckily, the ways evolutionary biologists already think about growth and development (ontogeny) and evolutionary relationships among taxa (phylogeny) can help us resolve this issue. In particular, by looking at how a species' body size, age, and other observable traits (phenotype) change over its growth and development, we can track how a species' body-size changes over the course of its time on Earth. Furthermore, we can compare these patterns between closely related species, and identify the sources of body-size change in deep time. To show how these ideas are a practical solution to problems in the fossil record, we applied them to a common pattern called the “Lilliput effect.” Named after the island of Lilliput and its tiny inhabitants in Gulliver's Travels, this pattern describes a sharp decrease in organism body size during extinctions in Earth history. Despite the Lilliput effect being very common, we understand little about how it occurs. Along with providing a stronger definition for the Lilliput effect, we use our framework to note some likely processes for the Lilliput effect (such as changes to development), and some famous cases where we could easily test these ideas. Body size has a long history of study in paleobiology and underlies many important phenomena in macroevolution. Body-size patterns in the fossil record are often examined by utilizing size data alone, which hinders our ability to describe the biological meaning behind size change on macroevolutionary timescales. Without data reflecting the biological and geologic factors that drive size change, we cannot assess its mechanistic underpinnings. Existing frameworks for studying ontogeny and phylogeny can remedy this problem, par ticularly the classic age–size–“shape” space originally developed for studies of heterochrony When evaluated based on metrics for age, size, and phenotype in populations, propose mechanisms for size change can be outlined theoretically and tested empirically in the record Using this framework, we can compare ontogenetic trajectories within and between specie and determine how changes in size emerge. Here, we outline ontogenetic mechanisms for evo lutionary size change, such as heterochrony, as well as how geologic factors can drive appar ent non-biolo ical size chan e (e ta honomic size sortin) To demonstrate the utility of this framework in actual paleobiological problems, we apply it to the Lilliput effect, a compelling and widely documented pattern of size decrease during extinction events. However, little is known about the mechanisms underlying this pattern. We provide a brief history of the Lilliput effect and refine its definition in a framework that can be mechanistically tested. Processes that likely produce Lilliput effects include allometric and sequence repatterning (including heterochrony) and evolutionary size-selective sorting. We describe these mechanisms and highlight relevant examples of the Lilliput effect for which feasible empirical tests are possible.

Diagenesis is one of the most important factors that affects reservoir rock property. Despite the fact that published data gives a vast amount of information on the geology, sedimentology, and lithostratigraphy of the Ecca Group in the Karoo Basin of South Africa, little is known about the diagenesis of the potentially feasible or economically viable sandstones and mudrocks of the Ecca Group. This study aims to provide an account of the diagenesis of sandstones and mudstones from the Ecca Group. Twenty-five diagenetic textures and structures were identified and grouped into three stages that include early diagenesis, burial diagenesis and uplift-related diagenesis. Clay minerals are the most common cementing materials in the sandstones. Smectite, kaolinite, and illite are the major clay minerals that act as pore lining rims and pore-filling materials. A part of the clay minerals and detrital grains was strongly replaced by calcite. Calcite precipitates locally in the pore spaces and partially or completely replaced clay matrix, feldspar, and quartz grains at or around their margins. Precipitation of cements and formation of pyrite and authigenic minerals occurred during the early diagenetic stage. This process was followed by lithification and compaction which brought about an increase in tightness of grain packing, loss of pore spaces, and thinning of bedding thickness due to overloading of sediments and selective dissolution of the framework grains. Mineral overgrowths, mineral replacement, clay-mineral transformation, dissolution, deformation, and pressure solution occurred during burial diagenetic stage. After rocks were uplifted, weathered and unroofed by erosion, this resulted in decementation and oxidation of iron-rich minerals. The rocks of the Ecca Group were subjected to moderate-intense mechanical and chemical compaction during their progressive burial. Intergranular pores, secondary dissolution, and fractured pores are well developed in the sediments of the Ecca Group. The presence of fractured and dissolution pores tend to enhance reservoir quality. However, the isolated nature of the pore linkage makes them unfavorable producers of hydrocarbons, which at best would require stimulation. The understanding of the space and time distribution of diagenetic processes in these rocks will allow the development of predictive models of their reservoir quality, which may contribute to the reduction of risks involved in hydrocarbon (oil and gas) exploration.

Deep‐water mudstones overlying basin‐floor and slope sandstone‐prone deposits are often interpreted as hemipelagic drapes deposited during sand starvation periods. However, mud transport and depositional processes, and resulting facies and architecture of mudstones in deep‐water environments, remain poorly understood. This study documents the sedimentology and stratigraphy of basin‐floor and slope mudstones intercalated with sandstone‐prone deposits of the Laingsburg depocentre (Karoo Basin, South Africa). Sedimentologic and stratigraphic criteria are presented here to distinguish between slope and basin‐floor mudstones, which provide a tool to refine palaeogeographical reconstructions of other deep‐water successions. Several mudstone units were mapped at outcrop for 2500 km2 and investigated using macroscopic and microscopic core descriptions from two research boreholes. Basin‐floor mudstones exhibit a repeated and predictable alternation of bedsets dominated by low‐density turbidites, and massive packages dominated by debrites, with evidence of turbulent‐to‐laminar flow transformations. Slope mudstones exhibit a similar facies assemblage, but the proportion of low‐density turbidites is higher, and no repeated or predictable facies organisation is recognised. The well‐ordered and predictable facies organisation of basin‐floor mudstones suggest local point sources from active slope conduits, responsible for deposition of compensationally stacked muddy lobes. The lack of predictable facies organisation in slope mudstones suggests deposition took place in a more variable range of sub‐environments (i.e. ponded accommodation, minor gully/channel‐fills, levees). However, regional mapping of three mudstone units evidence basinward tapering and similar thicknesses across depositional strike. This geometry is consistent with the distal part of basin margin clinothems, and suggests laterally extensive mud delivery across the shelf edge combined with along‐margin transport processes. Therefore, the sedimentology and geometry of mudstones suggests that mud can be delivered to deep‐water dominantly by sediment gravity flows through point source and distributed regionally, during periods of up‐dip sand storage. These findings challenge the common attribution of deep‐water mudstones to periods of basin‐floor sediment starvation. This multi‐scale study documents the sedimentology and stratigraphy of basin‐floor and slope mudstones intercalated with sandstone‐prone deposits of the Laingsburg depocentre (Karoo Basin, South Africa). For the first time, we present a set of criteria to distinguish between submarine slope and basin‐floor mudstones. The results highlight that deep‐water mud can be dominantly delivered by sediment gravity flows by a combination of laterally extensive supply and point‐source delivery systems during periods of up‐dip sand storage, challenging the model of deep‐water sediment starvation.

Turbidity currents commonly bypass sediment in submarine channels on the continental slope, and deposit sediment lobes farther down-dip on the flat and unconfined abyssal plain. Seafloor and outcrop data have shown that the transition from bypass to deposition usually occurs over complex zones referred to as channel–lobe transition zones (CLTZs). Recognition of these zones in cores and outcrop remains challenging due to a lack of characteristic sedimentary facies and structures. This paper focuses on Unit E of the Permian Fort Brown Formation in the Karoo Basin, South Africa, in the Slagtersfontein outcrop complex, which has previously been interpreted as a CLTZ. This study integrates thin-section micrographs, sedimentary facies, bed-set and stratigraphic architecture, and palaeoflow directions to achieve a multiscale analysis of CLTZ features. A novel process-based facies scheme is developed to evaluate deposits in terms of the depositional or erosional tendencies of the flows that formed them. This scheme allows bypass to be distinguished from depositional zones by the spatial distribution of certain sediment facies. Areas of net sediment bypass were predominantly marked by erosive sediment facies and a larger variability in palaeoflow direction while depositional areas showed a lower variability in palaeoflow directions. Metre-scale structures in the bypass-dominated area reveal seafloor erosion and scour formation. Field relations suggest the presence of a ∼500 m long mega-scour in the CLTZ. The characteristic structures documented here are applicable for identifying CLTZs in sparse datasets such as outcrops with limited palaeogeographical context and sediment cores obtained from subsurface systems.

Two seismic-scale submarine channel-levee systems exposed in the Karoo Basin, South Africa provide insights into slope conduit evolution. Component channel fills in a levee-confined channel system (Unit C) and an entrenched channel system (Unit D) follow common stacking patterns; initial horizontal stacking (lateral migration) is followed by vertical stacking (aggradation). This architecture is a response to an equilibrium profile shift from low accommodation (slope degradation, composite erosion surface formation, external levee development, sediment bypass) through at-grade conditions (horizontal stacking and widening) to high accommodation (slope aggradation, vertical stacking, internal levee development). This architecture is likely common to other channel-levee systems. A detailed correlation panel (presented schematically in Figure 2) is available at www.geolsoc.org.uk/SUP18456.

Vertebrate paleontologists have proposed a model for the terrestrial end-Permian event in the Karoo Basin, South Africa. The scenario envisions vegetational collapse that resulted in a phased extinction of vertebrate taxa in the uppermost Daptocephalus Assemblage Zone and overlying Lystrosaurus Assemblage Zone. These biodiversity patterns are placed into composite stratigraphic sections at key localities, several of which are in close spatial proximity. We present a stratigraphic framework at two of these localities, Old Lootsberg Pass and Tweefontein, physically correlated over ∼ 2 km distance into which new and previously reported fossils are placed. Glossopterid-dominated megafloras occur in both the Daptocephalus and Lystrosaurus biozones, along with palynological assemblages. Katbergia, a burrow used by others as an indicator of the transition and post-transition interval, occurs in paleosols much lower in the upper Daptocephalus Assemblage Zone, along with various subhorizontal cylindrical structures interpreted as vertebrate burrows. New vertebrate specimens include: (1) a large skull of either Daptocephalus leoniceps or Dicynodon sp.; (2) a partial skull with large canine assignable to either Dicynodon, Daptocephalus, or Lystrosaurus mccaigi; (3) a Lystrosaurus canine in grayish-red siltstone; (4) a skull of Lystrosaurus murrayi; and (5) a non-diagnostic post-cranial skeleton of lystrosaurid affinity. These fossils are combined with the published Karoo-vertebrate dataset to test the stratigraphic position of the Daptocephalus and Lystrosaurus Assemblage Zone boundary. We conclude that: (1) glossopterids in the Lystrosaurus Assemblage Zone indicate persistence of the clade past what is considered to be an extinction event; (2) the presence of palynomorphs known from recovery clades above the proposed vertebrate-biozone boundary indicate that these groups were present in the basin, but outside of the megafloral taphonomic window; (3) the position of the proposed vertebrate assemblage-zone boundary is stratigraphically inconsistent and varies in its reported stratigraphic position at a minimum of 25 m, and up to 70 m, across a distance of only ∼ 2 km; and (4) terrestrial ecosystem dynamics only can be assessed when a high resolution stratigraphic framework is developed into which biostratigraphic data are placed and, thereafter, patterns can be evaluated.