ALBERT

Beschreibung: Ooimmuration is here defined as a taphonomic process by which fossils are preserved within ooids. It is a form of lithoimmuration, although depending on the role of microbes in the formation of the ooid cortex, ooimmuration can also be considered a type of bioimmuration. Fossils enclosed within ooids are protected from bioerosion as well as the abrasion common in energetic depositional environments such as ooid shoals. Many taxa in some fossil assemblages may be known only because they were ooimmured. We describe as examples of ooimmuration fossils preserved in an oolite from the Middle Jurassic (Bajocian) Carmel Formation in southwestern Utah.

Beschreibung: A category of wrinkle structures, often termed Kinneyia structure or Runzel marks, comprises bedding plane features consisting typically of anastomosing, low-relief, flat-topped ridges with intervening depressions. Topographic relief is usually less than a millimeter. They are locally common on the upper surfaces of fine- to medium-grained sandstone beds interbedded with mudstone deposited in offshore settings, especially in Precambrian and lower Paleozoic strata but as young as Cretaceous. For more than the last two decades these wrinkle structures have been widely regarded as due to microbial mats, and have been taken as evidence for dominance in the Proterozoic of microbially stabilized sediment and, in the Phanerozoic, a matground marine benthic ecology which gradually gave way to a mixground ecology. The detailed morphology and cross-cutting relationships demonstrated by a range of specimens of Proterozoic, Cambrian, and Silurian age, however, cast this interpretation into doubt. The relationship between the wrinkled surface and bioclasts such as shells and both prior- and later-formed scour surfaces, and horizontal and vertical burrows show that these wrinkles did not develop due to the surface topography of microbial mats or compaction of microbial mats during burial, but instead formed at the top of a sand bed at the interface with an overlying layer of mud. Deformation is ascribed to vibration from low-magnitude earthquakes. The presence in some units of small-scale sedimentary dikelets and crack arrays that formed later after some stiffening, along with locally associated seismites and other evidence for nearby faulting, show that syndepositional tectonic activity was not unexpected and support the interpretation that this category of wrinkle structures is a type of seismite.

Beschreibung: Detrital-zircon U-Pb geochronology documents a regional- to continental-scale drainage reorganization along the eastern Gulf Coastal Plain (USA) from the Late Cretaceous (Cenomanian) to the Paleocene–Eocene. We present detrital-zircon U-Pb ages and Th/U values from the Maastrichtian Ripley Formation to determine the sedimentary provenance and to provide spatiotemporal resolution of drainage reorganization. The Ripley Formation contains a 12.7% overall average abundance of detrital zircons with low (〈 0.1) Th/U values relative to the underlying Cenomanian Tuscaloosa Group (3.6%), the overlying Paleocene–Eocene Wilcox Group (2.8%), an Appalachian foreland composite (2.1%), and the laterally equivalent McNairy Sandstone in the northern Mississippi Embayment (3.8%). Multidimensional scaling of detrital-zircon U-Pb spectra shows that the Ripley Formation is dissimilar from underlying and overlying Gulf Coastal Plain units, the McNairy Sandstone, and an Appalachian foreland composite sample because of differences in proportions of Appalachian (490–270 Ma) and Grenville (1250–900 Ma) zircons. We interpret the southern Appalachian Piedmont province as the principal sediment source region for the Ripley Formation to account for the elevated abundance of grains with low (〈 0.1) Th/U values and unique detrital-zircon U-Pb age spectra. Results suggest a regional-scale (105 km2) drainage network, which delivered sediment to the Maastrichtian coast followed by northwestward littoral transport and eventual mixing with Appalachian foreland-derived sediment in the northern Mississippi Embayment. This study further brackets drainage reorganization along the eastern Gulf Coastal Plain and demonstrates how simple chemical–age relationships, such as zircon Th/U values coupled with U-Pb ages, can be used to evaluate sediment provenance.

Beschreibung: Although carbonate ramps are ubiquitous in the geologic record, the impacts of oceanographic processes on their facies patterns are less well constrained than with other carbonate geomorphic forms such as isolated carbonate platforms. To better understand the role of physical and chemical oceanographic forces on geomorphic and sedimentologic variability of ramps, this study examines in-situ field measurements, remote-sensing data, and hydrodynamic modeling of the nearshore inner ramp of the modern northeastern Yucatán Shelf, Mexico. The results reveal how sediment production and accumulation are influenced by the complex interactions of the physical, chemical, and biological processes on the ramp. Upwelled, cool, nutrient-rich waters are transported westward across the ramp and concentrated along the shoreline by cold fronts (Nortes), westerly regional currents, and longshore currents. This influx supports a mix of both heterozoan and photozoan fauna and flora in the nearshore realm. Geomorphically, the nearshore parts of this ramp system in the study area include lagoon, barrier island, and shoreface environments, influenced by the mixed-energy (wave and tidal) setting. Persistent trade winds, episodic tropical depressions, and winter storms generate waves that propagate onto the shoreface. Extensive shore-parallel sand bodies (beach ridges and subaqueous dune fields) of the high-energy, wave-dominated upper shoreface and foreshore are composed of fine to coarse skeletal sand, lack mud, and include highly abraded, broken and bored grains. The large shallow lagoon is mixed-energy: wave-dominated near the inlet, it transitions to tide-dominated in the more protected central and eastern regions. Lagoon sediment consists of Halimeda-rich muddy gravel and sand. Hydrodynamic forces are especially strong where bathymetry focuses water flow, as occurs along a promontory and at the lagoon inlet, and can form subaqueous dunes. Explicit comparison among numerical models of conceptual shorefaces in which variables are altered and isolated systematically demonstrates the influences of the winds, waves, tides, and currents on hydrodynamics across a broad spectrum of settings (e.g., increased tidal range, differing wind and wave conditions). Results quantify how sediment transport patterns are determined by wave height and direction relative to the shoreface, but tidal forces locally control geomorphic and sedimentologic character. Similarly, the physical oceanographic processes acting throughout the year (e.g., daily tides, episodic winter Nortes, and persistent easterly winds and waves) have more impact on geomorphology and sedimentology of comparable nearshore systems than intense, but infrequent, hurricanes. Overall, this study provides perspectives on how upwelling, nutrient levels, and hydrodynamics influence the varied sedimentologic and geomorphic character of the nearshore areas of this high-energy carbonate ramp system. These results also provide for more accurate and realistic conceptual models of the depositional variability for a spectrum of modern and ancient ramp systems.

Beschreibung: Dolomitized fault–fracture structures in the Trenton and Black River formations (TBR) are the type example for “hydrothermal” petroleum reservoirs world-wide. However, fluid histories of these structures are only partially understood. Trenton and Black River reservoirs in the southern Michigan Basin are composed of fault-associated, vertical dolomite bodies that are highly fractured and brecciated. Open spaces are partially to completely filled by saddle dolomite and less frequently by calcite cement. Cathodoluminescence microstratigraphies of void-filling carbonate cements are not correlatable between oil fields. Fluid inclusion homogenization temperatures (Th) measured in carbonate cements indicate two fluid endmembers: a warm fluid (∼ 80° to 180° C) and a hot fluid (180° to ∼ 260° C). Increasing Th proximal to the underlying Proterozoic Mid-Michigan Rift (MMR) suggest that the hot fluids emanated from the rift area. Included fluids are saline (16.1–49.4 wt. % NaCl equivalent), and salinity likely is sourced from overlying Silurian Salina Group evaporites. First melting temperatures (Tfm), interpreted as eutectic temperatures (Te), of fluids range from –112° C to –50° C, indicating a complex Na–Ca–KCl brine; the expected composition of dissolved Salina salts. Lower Te proximal to the MMR suggest the rift as a source of additional complexing ions. C and O isotope values for carbonate cements are depleted with respect to δ18O (–6.59 to –12.46‰ VPDB) relative to Ordovician seawaters, and somewhat depleted with respect to δ13C (–1.22 to +1.18‰ VPDB). Equilibrium calculations from δ18O and Th values indicate that cement precipitating waters were highly evolved (+1.3 to +14.4‰ δ18O‰ VSMOW) compared to Ordovician and Silurian seawaters (–5.5‰ δ18O‰ VSMOW). Strontium isotope values indicate two fluid sources: Proterozoic basement and Late Silurian evaporites. Values of 87Sr/86Sr for cements in the Freedom, Napoleon, Reading, and Scipio fields (0.7086–0.7088) are influenced by warm water sourced from Silurian strata, and values for cements in the Albion, Branch County, and Northville fields (0.7091–0.7110) record continental basement signatures. Cement precipitating fluids in TBR oil fields likely have similar sources and timing. However, water–rock interactions along fault pathways modified source waters, giving each oil field a unique petrographic and geochemical signature. Fluid movement in TBR oil fields likely were initiated by reactivation of basement faulting during Silurian–Devonian tectonism.

Beschreibung: Gastropod drillholes on prey shells provide an opportunity to test the importance of predation in an evolutionary context. Although records of drilling predation are widespread across the Phanerozoic, the temporal distribution and relative importance of this mode of predation is still controversial. Further, some studies indicate a decline of drilling predation in the Mesozoic but other studies do not. In this study, we present a new dataset of gastropod drilling predation on Kimmeridgian and Tithonian bivalves of Kutch, India. Our study suggests that drilling was one of the prevailing modes of predation in the Upper Jurassic of Kutch with strongly variable intensities, ranging from 2% in the Kimmeridgian Seebachia to 26% in the Tithonian Pinna. A significant, albeit small, increase in drilling intensity from the Kimmeridgian to the Tithonian assemblages is associated with a change in relative sea-level and depositional environment. The morphology of drillholes and recent discovery of body fossils from the same stratigraphic units suggest naticid gastropods as the most likely drillers. A literature survey, along with previously collected specimen from the Jurassic of Kutch, reveals a more complex history of drilling predation than previously assumed.

Beschreibung: The terrestrial feeding trace Edaphichnium lumbricatum is known from the Triassic to the Pleistocene and is characterized by tubular burrows with ellipsoidal fecal pellets, indicating substrate feeding by earthworms or other invertebrates. We describe 11 specimens attributable to Edaphichnium isp. from Egg Mountain, a terrestrial locality with a diverse fossil assemblage from the Upper Cretaceous Two Medicine Formation in Montana, USA, and assess their paleoenvironmental and paleoecological implications. These ichnofossils were recovered from a 1.5 meter stratigraphic succession comprised of calcareous siltstones and limestones with abundant fossil insect pupal cases, representing well-drained paleosols. Although burrows are not always present, three recurring arrangements of Edaphichnium isp. fecal pellets are identified: linearly arranged pellets, horizon-confined pellets, and pellets in clusters dispersed vertically and horizontally throughout the matrix. Two color patterns (light and dark pellets) are also distinguished. Pellets are fine-grained and have a consistently ellipsoidal shape (length:diameter of 1.57), with maximum lengths ranging from 1.9–6.7 mm (mean 4.1 mm) and maximum diameters ranging from 1.0–4.1 mm (mean 2.6 mm). Geochemical analyses indicate pellets are comprised of varying proportions of calcite, plagioclase, and quartz, and are enriched in phosphorus relative to the sedimentary host matrix. Possible trace makers include chafer or other coleopteran larvae, millipedes, and earthworms, suggesting a range of capable trace makers of Edaphichnium-like fecal pellets. Edaphichnium isp. at specific stratigraphic horizons suggests increased organic content in the subsurface, potentially connected to depositional hiatuses. Edaphichnium isp. adds a secondary component to the Celliforma ichnofacies known from Egg Mountain and surrounding strata, and to the array of nesting, feeding, and dwelling traces of wasps, beetles, other invertebrates, mammals, and dinosaurs from the locality.

Beschreibung: The Pennsylvanian stratigraphy of the western Cumberland Basin has been influenced by salt tectonics, specifically the formation of the Minudie Anticline, a salt wall. South of the Minudie Anticline, along the shoreline of the Joggins Fossil Cliffs UNESCO World Heritage Site, the post–Boss Point Formation succession comprises an ∼ 3 km succession of strata assigned to the Little River, Joggins, Springhill Mines, and Ragged Reef formations. North of the Minudie anticline, the Grande Anse Formation lies in angular unconformity on the Boss Point and basal Little River formations. Biostratigraphic studies have not been able to discern whether the Grande Anse Formation is equivalent to all, or just one, of the Joggins to Ragged Reef units south of the salt wall (the Minudie Anticline). To further investigate the relationship of the Grande Anse Formation with the units along the Joggins shoreline, forty sandstone samples from the post–Boss Point Fm strata were selected for a chemostratigraphic study, using inductively coupled plasma mass spectrometry (ICP-MS) to determine major-element compositions. Transformed ICP-MS data, subjected to a Kruskal-Wallis test and post-hoc tests, show that there is no significant difference between Grande Anse and Ragged Reef formations in the mean values of almost all analyzed elements. In contrast, there are significant differences when comparing these two units and the older Little River, Joggins, and Springhill Mines formations in the case of elements usually encountered in detrital mineral phases (Si, Al, Ti, Na, and Fe). Sandstones of the Grande Anse and Ragged Reef formations show greater compositional maturity than the Little River, Joggins, and Springhill Mines formations. This trend is explained by a gradual overall change in paleoclimate from semiarid conditions during deposition of the Little River Formation to humid conditions during deposition of the Grande Anse and Ragged Reef formations, causing greater chemical weathering of the sediment. These findings indicate that 〉 2 km of sediment (Little River, Joggins, and Springhill Mines formations) accumulated south of the salt wall during the major episode of salt diapirism, followed by erosion of any topographic high associated with the salt wall, and accumulation of a further 〉 500 m of sediment (the laterally equivalent Ragged Reef and Grand Anse formations), all within a timespan of only ∼ 2 Myr.

Beschreibung: Quantitative analysis of quartz microtextures by means of scanning electron microscopy (SEM) can reveal the transport histories of modern and ancient sediments. However, because workers identify and count microtextures differently, it is difficult to directly compare quantitative microtextural data analyzed by different workers. As a result, the defining microtextures of certain transport modes and their probabilities of occurrence are not well constrained. We used principal-component analysis (PCA) to directly compare modern and ancient aeolian, fluvial, and glacial samples from the literature with nine new samples from active aeolian and glacial environments. Our results demonstrate that PCA can group microtextural samples by transport mode and differentiate between aeolian transport and fluvial and glacial transport across studies. The PCA ordination indicates that aeolian samples are distinct from fluvial and glacial samples, which are in turn difficult to disambiguate from each other. Ancient and modern sediments are also shown to have quantitatively similar microtextural relationships. Therefore, PCA may be a useful tool to constrain the ambiguous transport histories of some ancient sediment grains. As a case study, we analyzed two samples with ambiguous transport histories from the Cryogenian Bråvika Member (Svalbard). Integrating PCA with field observations, we find evidence that the Bråvika Member facies investigated here includes aeolian deposition and may be analogous to syn-glacial Marinoan aeolian units including the Bakoye Formation in Mali and the Whyalla Sandstone in South Australia.

Beschreibung: Paleocene sandstones in the Kupe Field of Taranaki Basin, New Zealand, are subdivided into two diagenetic zones, an upper kaolinite–siderite (K-S) zone and a lower chlorite–smectite (Ch-Sm) zone. Petrographic observations show that the K-S zone has formed from diagenetic alteration of earlier-formed Ch-Sm sandstones, whereby biotite and chlorite–smectite have been altered to form kaolinite and siderite, and plagioclase has reacted to form kaolinite and quartz. These diagenetic zones can be difficult to discriminate from downhole bulk-rock geochemistry, which is largely due to a change in element-mineral affinities without a wholesale change in element abundance. However, some elements have proven useful for delimiting the diagenetic zones, particularly Ca and Na, where much lower abundances in the K-S zone are interpreted to represent removal of labile elements during diagenesis. Multivariate analysis has also proven an effective method of distinguishing the diagenetic zones by highlighting elemental affinities that are interpreted to represent the principal diagenetic phases. These include Fe-Mg-Mn (siderite) in the K-S zone, and Ca-Mn (calcite) and Fe-Mg-Ti-Y-Sc-V (biotite and chlorite–smectite) in the Ch-Sm zone. Results from this study demonstrate that the base of the K-S zone approximately corresponds to the base of the current hydrocarbon column. An assessment with 1D basin models and published stable-isotope data show that K-S diagenesis is likely to have occurred during deep-burial diagenesis in the last 4 Myr. Modeling predicts that CO2-rich fluids were generating from thermal decarboxylation of intraformational Paleocene coals at this time, and accumulation of high partial pressures of intraformational CO2 in the hydrocarbon column is considered a viable catalyst for the diagenetic reactions. Variable CO2 concentrations and residence times are interpreted to be the reason for different levels of K-S diagenesis, which is supported by a clear relationship between the presence or absence of a well-developed K-S zone and the present-day reservoir-corrected CO2 content.