We integrate legacy 2-D and high-resolution 3-D seismic data with Integrated Ocean Drilling Program Expedition 313 cores and logs to investigate downslope sediment transport on the Miocene New Jersey shelf (offshore eastern United States). Medium- to coarse-grained glauconite and glauconitic quartz sands were recovered at the bases of Lower to Middle Miocene intrashelf clinoforms despite the apparent absence of canyons, channels, or other organized sediment conduits before ca. 13.5−12.7 Ma. 3-D seismic imaging, however, reveals closely spaced U- and V-shaped erosional features at the base of sequence m5.47 (ca. 18 Ma) and within sequence m5.3 (ca. 16.6−16.1 Ma). These morphologies, interpreted as grooves and irregular depressions, record erosion by debris flows transporting sand-rich sediment downslope. Their lengths (≤700 m) and low length-to-width ratios (∼3) suggest incision by substrate blocks locally entrained and rapidly abraded during transport. We propose that basal erosion reflects patchy coupling between the debris flow and the substrate, involving bulk entrainment of loose sands, localized stick-pluck detachment of semi-cohesive blocks that form irregular depressions, and short-lived dragging that produces grooves. Grooved and scarred basal surfaces overlain by debrites are restricted to sequences m5.47 and m5.3. Sequence m5.47 shows deeper incision that disrupts clinoform geometry and partially truncates underlying sequences, whereas m5.3 preserves normal progradation. Both sequences record similar erosional processes with an oblique transport direction (∼50°) relative to clinoform progradation direction, which we attribute to a regional trough to the south. These results demonstrate that debris flows can occur on low-angle intrashelf clinoforms and that both frequent smaller-volume and rare, large-volume mass-wasting events are important in shaping intrashelf stratigraphy.
The Ellsworth Mountains form an isolated range in central West Antarctica. They comprise an almost continuous succession of Neoproterozoic−Permian sedimentary strata deformed during the latest Paleozoic to earliest Mesozoic Gondwanide orogeny. The resulting fold-and-thrust belt terminates abruptly at both the northern and southern ends of the range. Restoration of the Gondwanide fold belt within reconstructions of Gondwana places the Ellsworth Mountains on the ‘outboard’ Pacific (Panthalassic) side of the Coats Land crustal block of the East Antarctic craton, which has been identified as a likely former fragment of Laurentia, now ∼12,000 km to the north. The Precambrian basement of the crust containing the Ellsworth Mountains is almost indistinguishable from that of southwestern Texas (southern United States), and the overlying Neoproterozoic−Cambrian strata on both continents reflect contemporaneous two-stage continental rifting and ensuing late Cambrian drift and thermal subsidence. The detrital zircon record of the lower to middle Cambrian clastic strata shares a very high statistical similarity with that of contemporaneous sandstones in Texas, therefore suggesting a likely Laurentian provenance. We propose that a former “Ellsworth−Coats Land promontory” separated from Laurentia during the late Cambrian. This interpretation has significant global paleogeographic and paleoenvironmental implications. It implies that the hypothetical Pannotia supercontinent consisting of Laurentia plus the newly amalgamated Gondwana did fleetingly exist in Cambrian times, and that the early Paleozoic marine transgression and global cooling that accompanied the radiation of multicellular life may have been driven by the opening of a passage between Laurentia and Gondwana joining the Iapetus and paleo-Pacific ocean basins to initiate Panthalassa.
Digital instructional tools are an important component of undergraduate geoscience education, enhancing instructors’ ability to engage students with authentic geologic data, imagery, field environments, and interactive online learning experiences. However, increased availability does not ensure effective integration. Educators must not only learn new platforms but also align technology with disciplinary content and pedagogical goals. To address this need, the NASA-funded Infiniscope project developed browser-based authoring tools, Tour It and Simple Author, along with professional development programs designed to support educators in creating customizable digital instructional tools without requiring advanced technical expertise. Grounded in the Technological, Pedagogical, and Content Knowledge (TPACK) framework, this exploratory mixed-methods study examines how TPACK components manifest in educators’ final products and reflections following completion of Infiniscope trainings. Rather than comparing Tour It and Simple Author as competing tools, we use both contexts to investigate how educators demonstrate technological knowledge, technological content knowledge, technological pedagogical knowledge, and integrated TPACK. Educator-created products were analyzed using retrospectively aligned TPACK rubrics, and reflections were examined through pre- and post-training survey data and open-ended responses. Findings suggest authoring environments can serve as meaningful sites of professional learning, where educators iteratively develop and apply TPACK through design. Educators demonstrated uneven development across TPACK components depending on training structure and tool interface. These findings position TPACK as both a theoretical framework and a practical evaluative lens for understanding educator learning, underscoring the importance of professional development that intentionally supports the integration of all TPACK components.
Fluids devolatilized from subducted sediments flux the mantle wedge, resulting in arc magmatism and discharge from accretionary prisms near the trench. Less is known about the interaction of these fluids with forearc basement. Here, we investigate the remnants of exhumed mafic forearc basement exposed across southern California, USA, including the Willows Plutonic Complex, Catalina Gabbro, and the underlying subduction complex (Catalina Schist). We also investigate cobbles that represent forearc detritus preserved within the San Onofre Breccia. We performed petrographic, zircon U-Pb age, and trace element analyses of mafic forearc basement to determine the cause and timing of low-temperature metamorphism and metasomatism. Magmatic ages (174−163 Ma) overlap those of the Coast Range and Cedros ophiolites. Cratonal zircon inheritance and trace element signatures require that southern California forearc basement formed along the continental margin adjacent to the southwestern North American craton. Most importantly, we have documented extensive Cretaceous zircon recrystallization that accompanied alteration. Three age maxima are resolved: 105 Ma, 89 Ma, and 77 Ma. These overlap with accretional timing of the Mid-Cretaceous Catalina Schist and later accreted Late Cretaceous Pelona-Orocopia-Rand schists that are presumed to underlie the Catalina Schist at depth. Results from a mafic basement clast preserved in the Catalina blueschist facies metaconglomerate reproduce an equivalent recrystallization history with corresponding age maxima, linking metasomatism to subduction processes. Collectively, this evidence implies significant infiltration and metasomatism of mafic forearc basement by subduction-related fluids.
We describe geochemical and observational evidence for the mode and timing of speleogenesis in King Solomon's Cave and Morning Star Cave in southern Nevada (USA), which feature subaqueous calcite speleothems, including mammillary speleothems and a new speleothem we name scabbards, selenite swords, and evidence of vapor condensation-dissolution of massive gypsum crystals (i.e., selenite, CaSO4 & centerdot;2H2O). A U/Pb isochron age on a calcite scabbard of ca. 1.61 +/- 0.29 Ma is identical to an age of 1.63 +/- 0.26 Ma on a mammillary calcite at Morning Star Cave (10 km to south), placing both caves at or below the water table at that time. Stable oxygen isotopic data on a calcite mammillary and selenite sword suggest these subaqueous speleothems formed in warm geothermal waters with temperatures of similar to 40-57 degrees C, assuming near-modern source water delta 18O values. Following cave dewatering, venting of similar to 27 degrees C warm vapors and subsequent condensation released latent heat to maintain a modern temperature of similar to 23-24 degrees C at King Solomon's Cave, higher than the outside mean annual temperature of 20.4 degrees C. Because the selenite and calcite speleothems formed subaqueously, yet the caves are now on ridges >190 m above the nearby Muddy River, our data require some combination of mountain uplift and water table lowering since 1.6 Ma, as basin-fill deposits were eroded from the landscape to expose the modern bedrock and topography at Valley of Fire, with implications for river basin integration into the Colorado River drainage.
