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The Joggins Fossil Cliffs site was selected as a UNESCO World Heritage site because of its unparalleled preservation of Pennsylvanian terrestrial organisms in their environmental context. Despite an abundance of research over the past 150 years, significant questions remain regarding the Joggins paleoenvironment, including the degree of marine influence and whether the gymnospermous Cordaites trees may represent the earliest mangroves. Sedimentologic and paleontologic data from interbedded limestone beds indicate open marine conditions in the oldest part of the section, with a waning marine influence up section. Limestone beds, which occur primarily at the base of cycles interbedded with coal and floodplain deposits, are 15–100 cm thick and contain ostracodes, bivalves, and echinoderm fragments. Independent lines of evidence to support a diminishing marine influence in fluvial and coastal deposits with time include: (1) the presence of punctate brachiopods, echinoderm fragments, and ostracodes infilled with framboidal pyrite in older limestone beds; (2) antithetic abundances between ostracodes and freshwater bivalves; and (3) an overall coarsening upward in the sequence. These results indicate that Joggins was, at least in the oldest portion of the formation, closer to the open ocean than previously surmised.
Geophysical methods can be used to identify the frequency and spatial distribution of plant debris, as well as for the study of the development of such accumulations in recent depositional settings. Side-scan sonar and a sub-bottom profiler were used to generate acoustic images of plant macroremains along a 16.9 km stretch of the meandering course of the Preto River in the municipality of Itanhaém, São Paulo, Brazil. Numerous inclined heterolithic stratification (IHS) deposits with plant debris constitute point bars, while sand dunes mark the migration of the channel along the straighter portions of the river. A large concentration of methane gas was found associated with older organic sediments in the river. The acoustically generated results were confirmed by the analysis of cores with all data integrated into the geographic information system (GIS) environment. The present study is one of the first to apply the methods of geotechnology to taphonomic research.
Stratal geometries, cyclical stacking patterns, and taphonomic analysis of the Aaron Scott Quarry in the Jurassic Morrison Formation indicate that sediments accumulated within a prograding fluvio-deltaic lacustrine system. Sediments were deposited during the progressive fill of a large lake. Stratal geometries and stacking patterns display relationships similar to larger-scale deltaic sequences caused by fluctuations in base level. Stratigraphic, paleontologic, and sedimentologic analysis indicates that water-volume-driven, base-level changes were responsible for the accumulation and preservation of the assemblage. The assemblage accumulated during a lowering of base level during the late stages of an overall fall caused by drought and was buried by a rapid rise at the end of the drought. Fluvio-deltaic lake fill consists of numerous off-lapping beds of sparsely bioturbated, coarsening-upward mudstone capped by thin, bioturbated silty mudstones. Erosional surfaces dip to the west and cut older mudstone parasequences. Retrogradation, aggradation, and progradation of strata typify stratigraphic trends above the erosion surface. Coarse braided stream sands cap off successive sequences as accommodation is filled prior to the next lowstand and sequence boundary incisement. The quarry is a large, taxonomically diverse deposit formed by the concentration of animals at the margins of a lake during a drought. Animals congregated near the banks as smaller watering holes dried. Bone locations and orientations indicate reworking by fluvial and wave currents. Vertical preservational trends indicate accumulation over a period of years. Trace fossil, lake invertebrate distributions, and sedimentological evidence indicate that periodic establishment of oxygen stratification within lake waters may have contributed to conditions favorable for bone preservation.
Drilling predation is among the most studied biotic interactions in the fossil record, and its overall patterns are well established on Cenozoic mollusks from North America. Few studies have examined such predation in Europe, which experienced a different geologic history. This study aims to evaluate taxonomic and environmental effects on molluscan drilling intensities from the Miocene of the Central Paratethys using drill frequency (DF) and prey effectiveness (PE), a measure of prey's ability to survive predatory attacks. 166 bulk samples from Austria and Slovakia that included 39,234 whole shells from the Karpatian (upper Burdigalian) and Badenian (Langhian and lower Serravallian) showed that at the level of stages, environments and localities, DF and PE were always below 10% and were slightly higher in bivalves than gastropods. Predation intensities from the Central Paratethys are therefore distinctly lower than those of other Miocene seas and it is hypothesized that this is explained by the rarity of naticid and muricid gastropods in the study area. The underlying factors controlling abundances of these drilling predators in the Central Paratethys could be related to the complex paleogeographic history of this inland sea. Intertidal DFs and PEs increased temporally, but differences in sublittoral DFs were not significant and PE values decreased significantly. Temporal patterns in DF and PE are influenced by disparities in sampled environments between the lower and middle Miocene. In general, comparisons of DFs across environments within the Karpatian and Badenian yielded similar results using higher and lower taxa. In contrast, such comparisons of PE were dependent upon taxonomic resolution.
The Cenomanian–Turonian (C–T) boundary interval is marked by one of the most prominent perturbations of the Mesozoic carbon cycle, Oceanic Anoxic Event 2 (OAE2). Increased fertilization of surface waters caused by greater fluvial input of nutrients may have caused the widespread deposition of organic-rich black shales during the OAE2 (productivity model). Alternatively, sluggish oceanic circulation may have enhanced stratification of the water column favoring the preservation of organic matter due to anoxic bottom-water conditions (preservation model). In order to gather evidence for the driving mechanism behind the deposition of the OAE2 black shales, calcareous nannofossils from the midlatitudinal Holywell section (Eastbourne, southeastern England) were studied. Ten bioevents, including last occurrences of six species and first occurrences of four, were recognized throughout the 11-m-thick interval. Preservation of calcareous nannofossils was moderate to good in all studied samples. The C–T interval here contains an abundant (mean 2.4 × 109 specimens/g sediment) and highly diverse (mean 58 spp./sample) calcareous nannoflora, with Watznaueria, Zeugrhabdotus, Biscutum, and Prediscosphaera the most common taxa. The most remarkable change in assemblage composition through the OAE2 is the decrease of Biscutum spp. Low abundances of Biscutum, combined with elevated numbers of Watznaueria spp. and/or Polycyclolithaceae, indicate reduced surface-water fertility during the OAE2 in midlatitudinal European shelf areas. A reduction of primary productivity seems to be quite common in midlatitudinal sections, whereas calcareous nannofossils and geochemistry indicate an increase in primary productivity in low-latitudinal sections. It is therefore likely that the origin of the OAE2 in mid latitudes was caused by sluggish ocean circulation, which intensified stratification. Reduced rates of mixing prevented the oxygenation of bottom waters in these regions, causing black shale deposition.
Exposures of the middle Cambrian Potsdam Group of northern New York, including the type section, represent a suite of interfingering eolian dune and aquatic deposits that record the activities of early land-going arthropods. Quartz arenites at these exposures are dominantly fine to medium grained, well sorted, and have hematite-coated well-rounded, high-sphericity quartz grains characterized by secondary optically continuous quartz cement overgrowths. Eolian beds are laminated and dominated by m- to dm-scale foresets characterized by large-scale, laterally extensive cross-beds that dip >∼15°–34° and contain reverse-graded lamination, en-echelon microfaulted slumps, adhesion structures, and very high ripple-index asymmetric ripples that lie on the foresets with crests that trend downdip. Lower parts of foresets are interpreted as toesets, and contain unusual Diplichnites and Protichnites trackways, which record the uphill, downhill, crest-parallel, and switchback-style movement of arthropods in dry or damp sand. Trackways that ascend dune faces do not possess a medial tail drag, whereas trackways that descend do, and turns of trackways often have deep continuous medial impressions; these features suggest arthropods leaned into the slope when turning downhill in dry sand. More shallowly dipping (∼4°–15°) cross-beds are interpreted as bottomsets. Like nearby intertidal Potsdam deposits, these beds contain Protichnites trackways and Arenicolites burrows. Paleocurrent analyses imply a coastline in which offshore and mixed-direction winds moved dunes seaward. Considered together, these strata record migration of coastal dunes into aquatic environments and flooding and reworking of distal dune bottomsets. In this setting, the same suite of epifaunal arthropods inhabited dry, damp, and aquatic marine environments.