ALBERT

Description: 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.

Description: 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.

Description: Well-developed detrital clay grain coats are observed in deep-marine sandstones of the Upper Cretaceous Springar Formation of the Vøring Basin in the Norwegian Sea. The detrital clay coats form thin and compact rims on individual sand grains and meniscus-shaped bridges between grains. These well-developed coats are found in high-density turbidites and proximal hybrid event beds with common to pervasive dewatering structures deposited in proximity to the base of a syndepositionally active basin high. Here, in one exploration well, detrital clay grain coats are common throughout a sandstone package 100 m thick. High-density turbidites and proximal and distal hybrid event beds drilled in mid- to distal-fan settings unaffected by seismically resolved seafloor topography show common dewatering features, but have only scattered detrital clay coats confined to individual dewatering pipes or dish structures. Hence, we propose that intense sediment dewatering has the potential to form detrital clay coats in deep-marine sandstones by a combination of elutriation and reorganization of clays during fluid escape from sediment bodies with pore fluid pressures significantly higher than the hydrostatic pressure. In submarine fan systems, deposition of sediment with coeval trapping of large volumes of interstitial pore fluid is most likely to occur where gravity flows undergo rapid deceleration in response to an abrupt decrease in confinement or gradient. Such environments include the channel–lobe transition and settings in proximity to seabed topography. The investigated sandstones are quartz arenites and subarkoses, with minor to moderate volumes of quartz cement (up to 6%). However, strongly to completely quartz-cemented intergranular pore space is observed where detrital clay coats or matrix does not cover quartz grains in the deepest part of the studied formation. Modeling of quartz cementation predicts that most intergranular macroporosity in the lower part of the Springar Formation would be quartz cemented if the sandstones were free of detrital clays. Based on our observations and modeling results we propose that intense sediment dewatering has the potential to form detrital clay coats, which can be important for retaining porosity in deeply buried sandstones and in basins with high present or past heat flow.

Description: 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.

Description: Borehole imaging (BHI) is a fast and precise method for collecting subsurface data. Rock calibration may reduce uncertainties inherent in interpretations of BHI logs. However, only few data sets are published that link borehole image facies to core and outcrop facies of deltaic successions. The objective of this paper is to compare and contrast sedimentologic features as seen in BHI, core, and outcrop, using a structured and hierarchical workflow. The research will provide a global framework for the interpretation of borehole images in similar environments. A shallow, behind outcrop, research well (“Mondot-1”) drilled in NW Spain, penetrated a 185.50 m (TVD) thick section of the deltaic Sobrarbe Formation. A Formation MicroImager (FMI) borehole image log and a comprehensive well log suite was acquired in the fully cored well. The Eocene Sobrarbe Formation consists mostly of siliciclastic and some carbonate facies. Rapid vertical and lateral facies changes over a few tens of meters are observed in outcrops of the Sobrarbe Formation. The cored part of the formation is composed of argillaceous sandstone and carbonate with few diagnostic sedimentary features that can be used to constrain a conceptual depositional model. To provide a sedimentologically sound interpretation of this FMI log, we focused on layers showing diagnostic sedimentary features. Subsequently, facies associations and stratigraphic sequences were interpreted. Each facies association contained sedimentologic tie points that anchored the interpretation with diagnostic features such as slumps. This paper suggests interpreting BHI false-color images of deltaic successions using conceptual geologic constraints such as 1) depositional tie points, 2) genetically related facies associations, and 3) a hierarchical stratigraphic framework, to establish meaningful conceptual depositional models.

Description: Borehole imaging (BHI) is a fast and precise method for collecting subsurface data. Rock calibration may reduce uncertainties inherent in interpretations of BHI logs. However, only few data sets are published that link borehole image facies to core and outcrop facies of deltaic successions. The objective of this paper is to compare and contrast sedimentologic features as seen in BHI, core, and outcrop, using a structured and hierarchical workflow. The research will provide a global framework for the interpretation of borehole images in similar environments. A shallow, behind outcrop, research well (“Mondot-1”) drilled in NW Spain, penetrated a 185.50 m (TVD) thick section of the deltaic Sobrarbe Formation. A Formation MicroImager (FMI) borehole image log and a comprehensive well log suite was acquired in the fully cored well. The Eocene Sobrarbe Formation consists mostly of siliciclastic and some carbonate facies. Rapid vertical and lateral facies changes over a few tens of meters are observed in outcrops of the Sobrarbe Formation. The cored part of the formation is composed of argillaceous sandstone and carbonate with few diagnostic sedimentary features that can be used to constrain a conceptual depositional model. To provide a sedimentologically sound interpretation of this FMI log, we focused on layers showing diagnostic sedimentary features. Subsequently, facies associations and stratigraphic sequences were interpreted. Each facies association contained sedimentologic tie points that anchored the interpretation with diagnostic features such as slumps. This paper suggests interpreting BHI false-color images of deltaic successions using conceptual geologic constraints such as 1) depositional tie points, 2) genetically related facies associations, and 3) a hierarchical stratigraphic framework, to establish meaningful conceptual depositional models.

Description: 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.

Description: 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.

Description: 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.

Description: The Campanian Loyd Sandstone Member of the Mancos Shale (Loyd) along the Rangely Anticline, Piceance Basin, Colorado, contains a series of multi-meter-thick, heterolithic, coarsening-upward successions (CUSs) with internal clinoforms comprising low-angle-dipping (〈 5°), parallel-laminated sandstone beds interbedded with bioturbated flaser-wavy-lenticular bedded sandstone and siltstone. Loyd clinoforms are delta foresets composed of prodelta and delta-front deposits, including mouthbars. Many CUSs exhibit scours filled with bioturbated sandstone, or interbedded bioturbated sandstone and siltstone or mudstone representing aggradational fill of subaqueous terminal distributary channels or the migration of mouthbars into channel scours. Mud drapes on sedimentary structures and mud rip-up clasts are extremely common. A high-abundance, high-diversity, trace-fossil assemblage includes vertical, 1–4-m-deep Ophiomorpha that may penetrate multiple bedsets of parallel-laminated sandstones and highly bioturbated finer-grained interbeds. Bioturbation increases sandstone content in finer-grained interbeds, and provides sandy conduits that increase connectivity between beds. Although parallel-laminated sandstones volumetrically dominate Loyd delta clinoforms, they likely represent relatively short-term freshwater and sediment input during river flooding that produced delta-front turbidity currents. Interbedded finer-grained beds, mud-draped sedimentary structures, and the high-abundance, high-diversity trace-fossil assemblages record longer amounts of time during reduced fluvial discharge, tidal reworking of sediments, and intense bioturbation under marine salinities. Controls on the internal characteristics of the Loyd delta deposits include: 1) a high sediment influx into a relatively shallow marine basin protected from wave action during normal regression; 2) relatively short-duration, episodic freshwater and sediment discharge from distributaries that reduced salinities, deposited sand as turbidity currents, and promoted delta-front channelization; and 3) longer-duration periods of reduced discharge with deposition of finer-grained sediment, tidal reworking, and bioturbation of sediments under higher salinities. These controls combined to produce the heterolithic, highly bioturbated, river-flood delivered, and tidally modified clinoforms of the Loyd that differ from deposits typically considered to be classic examples of fluvial-flood-dominated or extensively tidally modified deltas.