ALBERT

Description: A detailed magnetostratigraphic investigation of the Pignola-Abriola section of Norian to Rhaetian age permits the identification of 22 magnetic polarity reversals grouped in 10 magnetozones. We correlate the magnetostratigraphy of the Pignola-Abriola section with the Newark astrochronological polarity time scale (APTS). In total, 19 correlation options were tested, and only one (option 7) yielded a statistically significant correlation that was consistent with the available information on the stratigraphic age of the Newark APTS. After some adjustments to minimize erratic variations in sediment accumulation rates, a final correlation (option 7.1) was used to generate an age model of sedimentation for the Pignola-Abriola section. The Pignola-Abriola section has been correlated with Rhaetian sections from the literature, notably the current global boundary stratotype section and point candidate for the base of the Rhaetian at Steinbergkogel, Austria, where the Norian-Rhaetian boundary is proposed to be placed at a stratigraphic level containing the first appearance datum (FAD) of conodont Misikella posthernsteini , traced on the Newark APTS to ca. 209–210 Ma. Issues regarding the taxonomy of M. posthernsteini , a species characterized by transitional forms with its ancestor Misikella hernsteini , lead us to propose the alternative option of placing the Norian-Rhaetian boundary at a prominent negative 13 C org spike observed in the Pignola-Abriola section at meter 44.5, 50 cm below the level containing the FAD of M. posthernsteini sensu stricto and close to the base of radiolarian Proparvicingula moniliformis zone. This level has been magnetostratigraphically correlated to Newark magnetozone E20r.2r at ca. 205.7 Ma. Assuming an age of ca. 201.3 Ma for the Triassic-Jurassic boundary, the Rhaetian Stage would have a duration of ~4.4 m.y.

Description: The Pramollo Basin (Italy-Austria) is one of the richest body and trace fossil sites of the Alps, and exhibits a well-preserved Permian–Carboniferous fluvio-deltaic to marginal-marine sedimentary succession. Despite the exceptionally abundant and well-preserved ichnological heritage, the trace fossils of the Pramollo Basin are not well studied, particularly those of Permian units. This study focuses on the ichnofauna of the Val Dolce Formation (Permian; partly Asselian to partly Sakmarian), with the goal of documenting its ichnological heritage and reconstructing its paleoenvironment. These research questions are addressed by applying network theory, an emerging field of complexity science that focuses on web-like systems made of interconnected entities. An ichnological system can be seen as a set of interlinked ichnotaxa, the topology of which depends on the organism-environment interactions. In addition, traditional paleontological and sedimentological observations are used to reconstruct the paleoenvironment. The following ichnotaxa are documented from the Val Dolce Formation: Archaeonassa isp., Curvolithus simplex , Cylindrichnus isp., Helminthoidichnites tenuis , Nereites missouriensis , Planolites isp., Phymatoderma isp., Pramollichnus pastae , Psammichnites plummeri , Taenidium isp., and Zoophycos isp. Network analysis indicates that the Val Dolce ichnological system is structured, with ichnotaxa organized in environment-driven ichnoassociations: Cylindrichnus - Planolites (proximal delta front), Phymatoderma - Zoophycos (prodelta with dysoxic porewaters), Cylindrichnus - Helminthoidichnites - Curvolithus - Zoophycos (distal delta front–proximal prodelta), and Helminthoidichnites - Taenidium - Curvolithus - Nereites - Zoophycos (prodelta). Furthermore, the delta front–prodelta gradient is accompanied by increasing bioturbation intensity and diversity, reflecting the decreasing intensity of major environmental stressors (hydrodynamics, freshwater input, turbidity). Centrality measures of network analysis allow the topological position of traces to be discerned within the studied system, detecting the paleoenvironmental resolution of individual ichnotaxa. As intersections of sets can be described by networks, the studied ichnoassociations can be considered as occupying intersecting behavioral niches. In analogy with the concept of a Hutchinsonian niche, an ichnotaxon’s niche exists in a multidimensional abstract space defined by environmental parameters, which are expressed as spatial variables in the paleolandscape. Consequently, ichnoassociations are not just association patterns, but represent spatial, environmental, and topological entities. This approach allows the reconstitution of spatial relationships between the geographical ranges of ichnotaxa and ichnoassociations, providing information on the physical arrangement of different subenvironments, that is, the structure of the paleoenvironment.

Description: The Mead Stream section (South Island, New Zealand) consists of a 650-m-thick series of continuous, well-exposed strata deposited on a South Pacific continental slope from the Late Cretaceous to the middle Eocene. We examined the uppermost Paleocene–middle Eocene part of the section, which consists of ~360 m of limestone and marl, for detailed magnetic polarity stratigraphy and calcareous nannofossil and foraminifera biostratigraphy. Magneto-biostratigraphic data indicate that the section straddles magnetic polarity chrons from C24r to C18n, calcareous nannofossil zones from NP9a to NP17 (CNP11–CNE15, following a recently revised Paleogene zonation), and from the Waipawan to the Bortonian New Zealand stages (i.e., from the base of the Ypresian to the Bartonian international stages). The Mead Stream section thus encompasses 17 m.y. (56–39 Ma) of southwest Pacific Ocean history. The ages of calcareous nannofossil biohorizons are consistent with low- to midlatitude data from the literature, indicating that during the early–middle Eocene, the low- to midlatitude calcareous nannofossil domain extended at least to ~50°S–55°S in the South Pacific. Correlation of the magnetic polarity stratigraphy from the Mead Stream section with the geomagnetic polarity time scale allows us to derive sediment accumulation rates (SAR), which range between 8 and 44 m/m.y. Comparing the SAR with paleotemperature proxy records, we found that two intervals of increased SAR occurred during the early Eocene climatic optimum (52–50 Ma) and during the transient warming event peaking with the middle Eocene climatic optimum (40.5 Ma). This correlation indicates that, at Mead Stream, the climate evolution of the early–middle Eocene is recorded in a sedimentation pattern whereby, on a million-year time scale, warmer climate promoted continental weathering, transportation, and accumulation of terrigenous sediments.

Description: A bstract : Mudstone-dominated marine successions are common in the geological record, yet a full understanding of their depositional processes is often hampered by a lack of generally accepted diagnostic criteria to distinguish between hemipelagic settling and deposition from a flowing medium. The Marnoso Arenacea Formation, a turbidite unit of Miocene age cropping out in the northern Apennines of Italy, offers the possibility to address some of these uncertainties. A relatively small (~ 10%) but distinctive portion of the Marnoso Arenacea Formation is composed of white marlstone beds (WM beds) that have frequently been interpreted as due to hemipelagic settling of fine-grained particles (hemipelagites). The analysis of the anisotropy of magnetic susceptibility (AMS) revealed the presence in the WM beds of maximum susceptibility axes clustered within the depositional plane along the average paleoflow direction inferred from flute casts at the bases of the nearest turbidite beds, whereas the minimum susceptibility axes are oriented perpendicular to the bedding plane. This fabric is interpreted as largely sedimentary in origin (albeit a contribution from tectonic shortening cannot be excluded) and due to the alignment within the bedding plane of paramagnetic grains (e.g., muscovite) and possibly also ferromagnetic grains (magnetite) under low-velocity currents. The trend of the maximum susceptibility axes, and hence of the paleoflow direction, is approximately oriented NNW–SSE after correction for Apennines thrust-sheet rotation since the Miocene. These results suggest that the WM beds cannot be entirely due to hemipelagic settling, as often stated in the literature. A discussion of alternative depositional mechanisms leads us to conclude that the WM beds may have been deposited under the influence of contour currents and should therefore be referred to as muddy contourites.

Description: Modern generations of apparent polar wander paths (APWPs) show the occurrence in North American and African coordinates of a major and rapid shift in pole position (plate shift) during the Middle to Late Jurassic (175–145 Ma) that alternative curves from the literature tend to underestimate. This Jurassic massive polar shift (JMPS), of vast and as-yet unexplored paleogeographic implications, is also predicted for Eurasia from the North Atlantic plate circuit, but Jurassic data from this continent are scanty and problematic. Here we present paleomagnetic data from the Kimmeridgian–Tithonian (upper Jurassic) Garedu Formation of Iran, which was part of Eurasia since the Triassic. Paleomagnetic component directions of primary (pre-folding) age indicate a paleolatitude of deposition that is in excellent agreement with the latitude drop predicted for Iran from APWPs incorporating the JMPS. Moreover, we show that paleolatitudes calculated from these APWPs, used in conjunction with simple zonal climate belts, better explain the overall stratigraphic evolution of Iran during the Mesozoic. As Iran drifted from the tropical arid belt to the mid-latitude humid belt in the Late Triassic, carbonate platform productivity stopped while widespread coal-bearing sedimentation started, whereas as Iran returned to arid tropical latitudes during the JMPS, carbonate platform productivity and evaporitic sedimentation resumed. These results illustrate (1) the potent, but often neglected, control that plate motion (continental drift and/or true polar wander) across zonal climate belts exerts on the genesis of sedimentary facies; and (2) the importance of precisely controlled paleogeographic reconstructions for tectonic interpretations, especially during times of fast plate motion like the Jurassic. As a suggestion for future research, we predict that the adoption of Eurasian reference paleopoles incorporating the JMPS may lead to a reconciliation (or reinterpretation) of existing geologic and paleomagnetic data regarding the deformation history of central Asia.

Description: Jurassic paleomagnetic data from North America have long been contentious, generating ambiguities in the shape of the global-composite apparent polar wander path. Here we show from a restudy of two subdivisions of the Late Jurassic Morrison Formation at the classic locality at Norwood on the Colorado Plateau that the derived paleopoles reflect variable overprinting probably in the Cretaceous and are of limited value for apparent polar wander determination. We instead assembled an updated set of Jurassic paleopoles from parauthocthonous Adria, the African promontory, using primary paleomagnetic component directions derived from stratigraphically superposed intervals and corrected for sedimentary inclination error. These paleopoles are found to be in superb agreement with independent igneous paleopoles from the literature across the so-called Jurassic monster polar shift, which in North American coordinates is a jump of ~30° arc distance from the 190- to 160-Ma stillstand pole at 79.5°N 104.8°E to a 148 ± 3.5-Ma pole at 60.8°N 200.6°E defined by four Adria sedimentary paleopoles and the published Ithaca, Hinlopenstretet, and Swartsruggens-Bumbeni igneous paleopoles. The implied high rate of polar motion of ~2.5°/Myr across the monster shift is compatible with maximum theoretical estimates for true polar wander. We include a critique of published Jurassic paleomagnetic data that have been variably used in reference APWPs but that as a result of their low quality muted the real magnitude of the Jurassic monster shift. Finally, we provide paleocontinental reconstructions to describe examples of the bold signature that the monster polar shift left in the distribution of climate-sensitive sedimentary facies worldwide.