Transport and deposition of mud in deep‐water environments: Processes and stratigraphic implications

Deep-water mudstones are often considered as background sediments, deposited by vertical suspension fallout, and the range of transport and depositional processes are poorly understood compared to their shallow-marine counterparts. Here, we present a dataset from a 538.50 m-thick cored succession through the Permian muddy lower Ecca Group of the Tanqua depocentre (southwest Karoo Basin, South Africa). This study aims to characterize the range of mudstone facies, transport and depositional processes, and stacking patterns recorded in deep-water environments prior to deposition of the Tanqua Karoo sandy basin-floor fans. A combination of macroscopic and microscopic description techniques and ichnological analysis has defined nine sedimentary facies that stack in a repeated pattern to produce 2–26-m-thick depositional units. The lower part of each unit is characterized by bedded mudstone deposited by dilute, low-density turbidity currents with evidence for hyperpycnal-flow processes and sediment remobilization. The upper part of each unit is dominated by more organic-rich 27 bedded mudstone with common mudstone intraclasts, deposited by debris flows and transitional flows, with scarce indicators of suspension fallout. The intensity of bioturbation and burrow size increases upward through each depositional unit, consistent with a decrease in physicochemically stressed conditions, linked to a lower sediment accumulation rate. This vertical facies transition in the single well dataset can be interpreted to represent relative sea level variations, where the hyperpycnal stressed conditions in the lower part of the units were driven by sea level fall and the more bioturbated upper part of the unit represents backstepping, related to sea level rise. Alternatively, this facies transition may represent autogenic compensational stacking. The prevalence of sediment density flow deposits, even in positions distal or lateral to the sediment entry point, challenges the idea that deep-water mudstones are primarily the deposits of passive rainout along continental margins

The Earliest Evidence of Holometabolan Insect Pupation in Conifer Wood

Background: The pre-Jurassic record of terrestrial wood borings is poorly resolved, despite body fossil evidence of insect diversification among xylophilic clades starting in the late Paleozoic. Detailed analysis of borings in petrified wood provides direct evidence of wood utilization by invertebrate animals, which typically comprises feeding behaviors.\ud \ud Methodology/Principal Findings: We describe a U-shaped boring in petrified wood from the Late Triassic Chinle Formation of southern Utah that demonstrates a strong linkage between insect ontogeny and conifer wood resources. Xylokrypta durossi new ichnogenus and ichnospecies is a large excavation in wood that is backfilled with partially digested xylem, creating a secluded chamber. The tracemaker exited the chamber by way of a small vertical shaft. This sequence of behaviors is most consistent with the entrance of a larva followed by pupal quiescence and adult emergence — hallmarks of holometabolous insect ontogeny. Among the known body fossil record of Triassic insects, cupedid beetles (Coleoptera: Archostemata) are deemed the most plausible tracemakers of Xylokrypta, based on their body size and modern xylobiotic lifestyle.\ud \ud Conclusions/Significance: This oldest record of pupation in fossil wood provides an alternative interpretation to borings once regarded as evidence for Triassic bees. Instead Xylokrypta suggests that early archostematan beetles were leaders in exploiting wood substrates well before modern clades of xylophages arose in the late Mesozoic

Paleobiogeography: The relevance of fossils to biogeography

Paleobiogeography has advanced as a discipline owing to the increasing utilization of a phylogenetic approach to the study of biogeographic patterns. Coupled with this, there has been an increasing interdigitation of paleontology with molecular systematics because of the development of techniques to analyze ancient DNA and because of the use of sophisticated methods to utilize molecules to date evolutionary divergence events. One pervasive pattern emerging from several paleontological and molecular analyses of paleobiogeographic patterns is the recognition that repeated episodes of range expansion or geo-dispersal occur congruently in several different lineages, just as congruent patterns of vicariance also occur in independent lineages. The development of new analytical methods based on a modified version of Brooks Parsimony Analysis makes it possible to analyze both geo-dispersal and vicariance in a phylogenetic context, suggesting that biogeography as a discipline should focus on the analysis of a variety of congruent phenomena, not just vicariance. The important role that extinction plays in influencing apparent biogeographic patterns among modern and fossil groups suggests that this is another area ripe for new methodological developments

New Specimens of Nemegtomaia from the Baruungoyot and Nemegt Formations (Late Cretaceous) of Mongolia

Two new specimens of the oviraptorid theropod Nemegtomaia barsboldi from the Nemegt Basin of southern Mongolia are described. Specimen MPC-D 107/15 was collected from the upper beds of the Baruungoyot Formation (Campanian-Maastrichtian), and is a nest of eggs with the skeleton of the assumed parent of Nemegtomaia on top in brooding position. Much of the skeleton was damaged by colonies of dermestid coleopterans prior to its complete burial. However, diagnostic characters are recovered from the parts preserved, including the skull, partial forelimbs (including the left hand), legs, and distal portions of both feet. Nemegtomaia represents the fourth known genus of oviraptorid for which individuals have been found on nests of eggs. The second new specimen, MPC-D 107/16, was collected a few kilometers to the east in basal deposits of the Nemegt Formation, and includes both hands and femora of a smaller Nemegtomaia individual. The two formations and their diverse fossil assemblages have been considered to represent sequential time periods and different environments, but data presented here indicate partial overlap across the Baruungoyot-Nemegt transition. All other known oviraptorids from Mongolia and China are known exclusively from xeric or semi-arid environments. However, this study documents that Nemegtomaia is found in both arid/aeolian (Baruungoyot Formation) and more humid/fluvial (Nemegt Formation) facies

Mixed carbonate-siliciclastic tidal sedimentation in the Miocene to Pliocene Bouse Formation, palaeo-Gulf of California

Mixed carbonate–siliciclastic deposits provide unique insights into hydrodynamic processes that control sedimentation in tidal systems. This study presents sedimentological and ichnological data from the upper Miocene to lower Pliocene Bouse Formation, which accumulated during regional transgression at the margin of a tidal strait near the north end of the ancestral Gulf of California. The basal carbonate member of the Bouse Formation records deposition in a tide‐influenced, compositionally mixed carbonate–siliciclastic system dominated by salt marsh, tidal flat and channel environments. The basal carbonate member is an overall deepening up succession of facies associations comprising: Facies Association 1 – siliciclastic‐rich heterolithic facies, lime mudstone with desiccation cracks, and plant debris rich carbonate silt interpreted as siliciclastic‐rich tidal flats; Facies Association 2 – well‐sorted gravels, siliciclastic‐rich sandy strata, lime mudstone with desiccation cracks, and sandy microbial micrite interpreted as tidal‐channel deposits; Facies Association 3 – carbonate‐rich heterolithic lime mudstone to well‐sorted, cross‐bedded bioclastic grainstone interpreted as intertidal to shallow subtidal deposits; and Facies Association 4 – lime mudstone interpreted as shallow to deep subtidal low‐energy deposits that record the end of tidal conditions in the basin. Trace fossils include marine forms Gyrolithes, Teichichnus and Thalassinoides, and non‐diagnostic forms Arenicolites, Cochlichnus, Conichnus, Lockeia, Planolites, Skolithos and Treptichnus (known from marine, brackish and freshwater environments). The diminutive size of trace fossils reflects brackish conditions created by mixing of freshwater and seawater. This study provides evidence for a late Miocene to early Pliocene humid climate in south‐western North America, in stark contrast to the modern hyperarid climate. Factors that controlled the relative percentage of mixed carbonate and siliciclastic sediment include siliciclastic input from local rivers, in situ carbonate production, current energy, degree of tidal mixing and relative sea level. Pronounced facies variability at bedform, outcrop and basin scale documented in this study appears to be an important characteristic of mixed carbonate–siliciclastic deposits in tidal depositional systems