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Abstract The closure of the Mozambique Ocean defines the final assembly of the megacontinent Gondwana and is associated with a vast region of crustal growth in the Arabian-Nubian Shield. Despite this central paleogeographic position, there are few constraints on the position of terranes within and bounding the Mozambique Ocean. We report paleomagnetic data from ca. 726 Ma dikes exposed in southern Oman. Well-resolved magnetite magnetization is constrained to be primary by a conglomerate test on mafic clasts within overlying Cryogenian diamictite. The resulting paleomagnetic pole indicates that Oman was at a paleolatitude of 37 ± 2.5°N and was rotated ~80° counterclockwise from its present-day orientation. This position is consistent with Oman forming a contiguous plate with the India and South China cratons on the northern margin of the Mozambique Ocean in a distinct tectonic domain from Arabian-Nubian arcs to the south. This position reveals an ~5500-km-wide oceanic realm prior to subsequent closure that resulted in a major zone of Neoproterozoic crustal growth. 

A long-term cooling trend through the Ordovician Period, from 487 to 443 Ma, is recorded by oxygen isotope data. Tropical ocean basins in the Early Ordovician were hot, which led to low oxygen concentrations in the surface ocean due to the temperature dependence of oxygen solubility. Elevated temperatures also increased metabolic demands such that hot shallow water environments had limited animal diversity as recorded by microbially dominated carbonates. As the oceans cooled through the Ordovician, animal biodiversity increased, leading to the Great Ordovician Biodiversification Event. The protracted nature of the cooling suggests that it was the product of progressive changes in tectonic boundary conditions. Low-latitude arc-continent collisions through this period may have increased global weatherability and decreased atmospheric CO₂levels. Additionally, decreasing continental arc magmatism could have lowered CO₂outgassing fluxes. The Ordovician long-term cooling trend culminated with the development of a large south polar ice sheet on Gondwana. The timescale of major ice growth and decay over the final 2 Myr of the Ordovician is consistent with Pleistocene-like glacial cycles driven by orbital forcing. The short duration of large-scale glaciation indicates a high sensitivity of ice volume to temperature with a strongly nonlinear response, providing a valuable analog for Neogene and future climate change.▪Oxygen isotope data record progressive and protracted cooling through the Ordovician leading up to the onset of Hirnantian glaciation.▪The gradual cooling trend is mirrored by an Ordovician radiation in biological diversity, consistent with temperature-dependent oxygen solubility and metabolism as a primary control.▪Long-term cooling occurred in concert with low-latitude arc-continent collisions and an increase in global weatherability. Although CO₂outgassing may have also decreased with an Ordovician decrease in continental arc length, in the modern, CO₂outgassing is variable along both continental and island arcs, leaving the relationship between continental arc length and climate uncertain.▪Evidence for significant ice growth is limited to less than 2 Myr of the Hirnantian Stage, suggesting a high sensitivity of ice growth topCO₂and temperature.▪Independent estimates for ice volume, area, and sea level change during the Hirnantian glacial maximum are internally consistent and comparable to those of the Last Glacial Maximum. 

Abstract The North American craton interior preserves a >1 Ga history of near surface processes that inform ongoing debates regarding timing and drivers of continental‐scale deformation and erosion associated with far‐field orogenesis. We tested various models of structural inversion on a major segment of the Midcontinent Rift along the Douglas Fault in northern Wisconsin, which accommodated ≳10 km of total vertical displacement. U‐Pb detrital zircon and vein calcite Δ₄₇/U‐Pb thermochronometry from the hanging wall constrain the majority of uplift (≳8.5 km) and deformation to 1052–1036 Ma during the Ottawan phase of the Grenvillian orogeny. Combined U‐Pb zircon dates, Δ₄₇/U‐Pb calcite thermochronometry, and field data that document syn‐ to early post‐depositional deformation in the footwall constrain a second stage of uplift (1–1.5 km) ca. 995–980 Ma during the Rigolet phase of the Grenvillian orogeny. A minor phase of Appalachian far‐field orogenesis is associated with minimal thrust reactivation. Our combined analyses identified the 995–980 Ma Bayfield Group as a Grenvillian foreland basin with an original thickness 0.5–2 km greater than currently preserved. By quantifying flexural loading and other subsidence mechanisms along the Douglas Fault, we identify dynamic subsidence as a mechanism that could be consistent with the development of late‐Grenvillian transcontinental fluvial systems. Minimal post‐Grenvillian erosion (0.5–2 km) in this part of the craton interior has preserved the Bayfield Group and equivalent successions, limiting the magnitude of regional erosion that can be attributed to Neoproterozoic glaciation. 

Miocene strata of the Claremont, Orinda, and Moraga formations of the Berkeley Hills (California Coast Ranges, USA) record sedimentation and volcanism during the passage of the Mendocino triple junction and early evolution of the San Andreas fault system. Detrital zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) age spectra indicate a change in sedimentary provenance between the marine Claremont formation (Monterey Group) and the terrestrial Orinda and Moraga Formations associated with uplift of Franciscan Complex lithologies. A sandstone from the Claremont formation produced a detrital zircon chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) maximum depositional age of 13.298 ± 0.046 Ma, indicating younger Claremont deposition than previously interpreted. A trachydacite tuff clast within the uppermost Orinda Formation yielded a CA-ID-TIMS U-Pb zircon date of 10.094 ± 0.018 Ma, and a dacitic tuff within the Moraga Formation produced a CA-ID-TIMS U-Pb zircon date of 9.974 ± 0.014 Ma. These results indicate rapid progression from subsidence in which deep-water siliceous sediments of the Claremont formation were deposited to uplift that was followed by subsidence during deposition of terrestrial sediments of the Orinda Formation and subsequent eruption of the Moraga Formation volcanics. We associate the Orinda tuff clast and Moraga volcanics with slab-gap volcanism that followed the passage of the Mendocino triple junction. Given the necessary time lag between triple junction passage and the removal of the slab that led to this volcanism, subsidence associated with ca. 13 Ma Claremont sedimentation and subsequent Orinda to Moraga deposition can be attributed to basin formation along the newly arrived transform boundary. 

Large igneous provinces (LIPs) can potentially cause cooling on tens- to thousand-year timescales via injection of sulfur aerosols to the tropo-sphere, and on million-year timescales due to the increase of global weatherability. The ca. 719-Ma Franklin LIP preceded onset of the Sturtian Snowball Earth glaciation by less than two million years, consistent with CO2 drawdown due to weathering of Ca- and Mg-rich LIP basalts, which may have contributed to cooling past a critical runaway ice-albedo threshold. A relatively cool background climate state and Franklin LIP emplacement near a continental margin in the warm wet tropics may have been critical factors for pushing the Earth’s climate past the threshold of runaway glaciation. 

Paleomagnetic, rock magnetic, or geomagnetic data found in the MagIC data repository from a paper titled: Tracking Rodinia Into the Neoproterozoic: New Paleomagnetic Constraints From the Jacobsville Formation 

Abstract. The warmer early Pliocene climate featured changes to global sea surface temperature (SST) patterns, namely a reduction in the Equator–pole gradient and the east–west SST gradient in the tropical Pacific, the so-called “permanent El Niño”. Here we investigate the consequences of the SST changes to silicate weathering and thus to atmospheric CO2 on geological timescales. Different SST patterns than today imply regional modifications of the hydrological cycle that directly affect continental silicate weathering in particular over tropical “hotspots” of weathering, such as the Maritime Continent, thus leading to a “weatherability pattern effect”. We explore the impact of Pliocene-like SST changes on weathering using climate model and silicate weathering model simulations, and we deduce CO2 and temperature at carbon cycle equilibrium between solid Earth degassing and silicate weathering. In general, we find large regional increases and decreases in weathering fluxes, and the net effect depends on the extent to which they cancel. Permanent El Niño conditions lead to a small amplification of warming relative to the present day by 0.4 ∘C, suggesting that the demise of the permanent El Niño could have had a small amplifying effect on cooling from the early Pliocene into the Pleistocene. For the reducedEquator–pole gradient, the weathering increases and decreases largely cancel, leading to no detectable difference in global temperature at carbon cycle equilibrium. A robust SST reconstruction of the Pliocene is needed for a quantitative evaluation of the weatherability pattern effect. 

A striated surface is present at an erosional unconformity between foliated Paleoproterozoic Michigamme Formation and fluvial conglomerate and sandstone of the Neoproterozoic Jacobsville Formation exposed at L’Anse Bay (Michigan, USA). These striations have been interpreted to be the result of ice flow in either the Proterozoic, the Pleistocene, or the modern. Recently, the glacial origin interpretation for this striated surface has been used to argue that it may be related to ca. 717–635 Ma Cryogenian snowball Earth glaciation. This interpretation would make the surface a rare example of a Neoproterozoic glacial pavement, with major chronostratigraphic implications that in turn impose constraints on the timing of intracratonic erosion related to the formation of the Great Unconformity. In this contribution, we present new observations showing that the surface is a tectonic slickenside caused by largely unconformity-parallel slip along the erosional unconformity. We document structural repetition of the Michigamme-Jacobsville contact with associated small-scale folding. The unconformity-parallel slip transitions into thrust faults that ramp up into the overlying Jacobsville Formation. We interpret that the surface records contractional deformation rather than ancient glaciation, recent ice movement, or recent mass wasting. The faulting likely occurred during the Rigolet phase of the Grenvillian orogeny, which also folded the Jacobsville Formation in the footwall of the Keweenaw fault. 

Paleomagnetic, rock magnetic, or geomagnetic data found in the MagIC data repository from a paper titled: Paleomagnetic Records From Pulsed Magmatism in the Southwestern Laurentia Large Igneous Province and Cardenas Basalt Support Rapid Late Mesoproterozoic Plate Motion 

The Nonesuch Formation microbiota provide a window into ca. 1075 Ma life within the interior of ancient North America. The Nonesuch water body formed following the cessation of widespread volcanism within the Midcontinent Rift as the basin continued to subside. In northern Michigan and Wisconsin, USA, the Copper Harbor Conglomerate records terrestrial alluvial fan and fluvial plain environments that transitioned into subaqueous lacustrine deposition of the Nonesuch Formation. These units thin toward a paleotopographic high associated with the Brownstone Falls angular unconformity. Due to these “Brownstone Highlands,” we were able to explore the paleoenvironment laterally at different depths in contemporaneous deposits. Rock magnetic data constrain that when the lake was shallow, it was oxygenated as evidenced by an oxidized mineral assemblage. Oxygen levels were lower at greater depth—in the deepest portions of the water body, anoxic conditions are recorded. An intermediate facies in depth and redox between these endmembers preserves detrital magnetite and hematite, which can be present in high abundance due to the proximal volcanic highlands. This magnetic facies enabled the development of a paleomagnetic pole based on both detrital magnetite and hematite that constrains the paleolatitude of the lake to 7.1 ± 2.8°N. Sediments of the intermediate facies preserve exquisite organic-walled microfossils, with microfossils being less diverse to absent in the anoxic facies where amorphous organic matter is more likely to be preserved. The assemblage of cyanobacteria and eukaryotes (both photoautotrophs and heterotrophs) lived within the oxygenated waters of this tropical Mesoproterozoic water body.