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High resolution oxygen isotopes profiles of well-preserved uppermost Jurassic oyster shells and vertebrate (ichthyosaur and fish) teeth from Central Poland were obtained using a microdrill and an ion microprobe (SHRIMP IIe/MC). Internal variability of δ18O values of oyster shells (-1.7 to 1.3% VPDB) collected from the offshore interval of the studied section is greater than that determined previously from bulk oysters. Relatively high δ18O values of the studied oysters may be linked to a slight increase in the salinity of the mid-Polish basin. Low δ18O values of co-occurring ichthyosaur tooth enamel substantiate endothermy of these reptiles. An observed ontogenetic increase in the ichthyosaur enamel δ18O values (from ∼ 19.4 to ∼ 21.6% VSMOW) may be a result of long distance migrations although the effect of metabolic factors at rising body mass cannot be completely excluded. It is postulated that δ18O values of the latest portion of the ichthyosaur tooth enamel can be used for the calculation of ancient water oxygen isotope composition and verification of oxygen isotope temperatures. High δ18O values of the enameloid of Caturus lungfishes (23.6 to 26.5% VSMOW) collected from an upper part of the studied section, which was deposited in a restricted lagoonal environment after a marine regression, are probably a result of a high evaporation rate. The fishes could have breathed atmospheric air and withstood episodes of water hypoxia. Internal oxygen isotope records of the shells and teeth are promising proxies for studies of the paleoenvironment and activity of animals.
Fossilized reefs can preserve critical information about changes in marine environments over a relatively short period of time. The interpretation of these changes is often hindered by the complexity of reef growth with respect to architecture, biotic zonation, and time. High-resolution mapping and data collection incorporating both sequence stratigraphical and paleoecological principles are needed to document the architectural complexity of reef development. To demonstrate this, we present a case study in which both principles are integrated to build a new stratigraphic framework for an Albian-aged rudist-coral patch reef outcrop (Paul Spur, Bisbee, AZ, USA). The dataset reveals that the outcrop preserves five stages of development: (1) initial shoal deposition; (2) pioneer reef growth; (3) reef diversification; (4) reef hiatus; and (5) rudist shoal development. These stages represent periods of deposition and reef growth within high-frequency transgressive-regressive sequences. Interpretations of sedimentological and paleoecological data are then used to demonstrate the variable influence of different environmental controls on reef growth. Prevailing wind and current direction act as higher order controls on overall reef architecture by influencing windward-leeward asymmetry. Fluctuations in relative water depth as well as sedimentation rate, source, and type is an important influence on reef community and growth habit. Though corals and rudists cohabited during much of the reef's history, corals dominated when water depth was greater and external sediment influx lesser, whereas rudists dominated in shallow water depths and during periods of high external sediment influx. This work demonstrates that detailed evaluation of stratigraphy and paleoecology, as well as careful consideration of timelines and heterogeneity, is essential for building an accurate stratigraphic framework that allows a more thorough understanding of processes driving reef growth.
Bioerosion by microorganisms is termed microbioerosion. In aquatic systems, microbioerosion affects various substrates, most commonly relatively soluble ones such as sulfates, phosphates, and carbonates. However, the record of microbioerosion in fossil calcareous organisms in lake environments is limited. In northern Mendoza Province, at the locality Paramillos de Uspallata, Triassic sedimentary rocks outcrop, including the Agua de la Zorra Formation, which was deposited in a deltaic and lacustrine system. This study assesses possible bioerosion by microorganisms on spinicaudata shells from the lacustrine sequence and discusses their preservation potential in lacustrine environments. Spinicaudatans from the Agua de la Zorra Formation were analyzed under a binocular microscope and via scanning electron microscopy. Traces, the product of microbioerosion, preserved as molds, were assigned as Type 1 and 2 and were then compared with those generated by cyanobacteria, bacteria, chlorophyte, and fungi that inhabit fresh and brackish water environments. Microbioerosion occurs post-mortem and enhances dissolution of the spinicaudata shells. This, together with bias in extraction methodologies and sampling, is considered the reason for the rarity of spinicaudatans with traces of bioerosion in the lacustrine record.
Silicification is a diagenetic process that can affect the fidelity of trace fossil preservation. The combination of compaction and oversilicification associated with chert precipitation can alter the original fabric created by the trace producers. Sedimentary structures and trace fossils in mixed chert-carbonate systems are especially prone to these processes, leading to the preservation of a limited or biased ichno-assemblage and the omission of important paleoecologic detail. We summarize useful criteria for identifying chert-associated trace fossils and present a formal naming scheme. Using this nomenclature, we identified silicified trace fossils in the chert-rich Permian strata from northwestern Utah. An assemblage of burrows is present in outcrops of the Trapper Creek Formation, consisting of nodule-like growths of microcrystalline quartz in close association with bioturbated horizons. Thin section micro-textures of burrow fill lend additional support to the bioturbated origin of chert nodules. Silicified Thalassinoides fossils are present, as are chert nodules with a Rhizocorallium-like morphology.
Coprolites are a useful tool to obtain information related to the life history of the producer, trophic interactions, biodiversity, paleoenvironments, and paleoclimate, among other issues. We analyze here a sample of 111 coprolites recovered from levels of the Santa Cruz Formation (lower–middle Miocene, Burdigalian–early Langhian), outcropping in different localities of the Santa Cruz Province, Patagonian Argentina. Based on size and shape, two morphotypes were identified: coprolites assigned to morphotype I vary from ovoid to subspherical in shape, while coprolites assigned to morphotype II are cylindrical in shape. Several coprolites have bone and teeth inclusions belonging to small mammals (i.e., Octodontoidea and/or Chinchilloidea rodents). Morphometry, composition, and taphonomy of the bone remains suggest that the coprolites were produced by carnivorous mammals. According to the features of the guild of carnivorous mammals from the Santa Cruz Formation, we interpret that hathliacynids and/or small borhyaenoids (Sparassodonta) are the most probable producers. Different traces recorded in the coprolites, such as borings and putative eggs, suggest that the feces were exploited by coprophagous insects, probably dung beetles, for different purposes such as feeding and possible oviposition.
Marine organisms are uncommonly preserved in amber. Recently, they were reported to be associated with Burmese amber. However, most of specimens from previous reports were preserved on the amber surface or within the sediment surrounding the amber. Based on X-ray tomography and thin-section optical microscopy of Burmese amber, we report here the first genuine and unambiguous evidence of inclusion of crinoid ossicles preserved in the fossil resin. Preservation of this exclusively marine group in amber gives insights into the paleoenvironment of the crinoid-amber association and provides additional evidence to support previous observations of shallow-water stalked crinoids from the mid-Cretaceous, when many stalked crinoids started to shift offshore due to increased predation pressure during the Mesozoic Marine Revolution. Crinoid remains, represented by disarticulated stem and arm ossicles assignable to Isocrinus cf. legeri (Repelin), point to a mid-Cretaceous age for the Burmese amber and support some previous hypotheses suggesting a close proximity between the resin-producing trees and seawater.