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The breakup of Pangea fundamentally shaped modern continents and controlled the climatic distribution and biodiversity on Earth. Although our knowledge on the processes that control the assembly and breakup of supercontinents has significantly improved, the timing of supercontinent assembly and breakup initiation remains in some cases controversial. According to the available data, the assembly of Pangea was completed in middle Permian time, resulting in the formation of major orogenic belts and transform faults like the N–S‐trending, dextral, Caltepec fault in Mexico. Pangea breakup initiation is bracketed to early Middle Triassic time. In this work, we present new sedimentological, structural and U‐Pb geochronological data from a fluvial unit, the Matzitzi Formation of southern Mexico, the age and tectonic setting of which have remained an enigma for the past century. Our data document that the Matzitzi Formation is the stratigraphic record of a late Permian, anastomosing fluvial system that flowed in a—NNE‐trending extensional trough developed on top of the Caltepense belt, a transpressive belt formed along the Caltepec fault. We propose and discuss three possible scenarios for the tectonic setting of the Matzitzi Formation. In the first scenario, the unit is the stratigraphic record of the Caltepec fault late activity, which caused local NW–SE extension along the western margin of Pangea during its final assembly. In the second scenario, the Matzitzi Formation was deposited in an extensional basin formed by slab rollback along the western equatorial Pangea margin. In the third scenario, the extensional basin of the Matzitzi Formation was formed in the framework of the Pangea breakup. In this case, our data would suggest that Pangea breakup initiation must be dated back to late Permian time, which is ca. 15 m.y. older than the Middle Triassic age documented by the previous work. Considering that evidence of Permian extension has also been reported along the Appalachian belt, we suggest that the Matzitzi Formation was deposited during regional‐scale extension of western equatorial Pangea; therefore, we preliminarily support the third scenario. The distribution of Permian extension along suture belts developed during Pangea assembly highlights the fundamental role played by pre‐existent zones of weakness in the breakup of a supercontinent. [ABSTRACT FROM AUTHOR]

Abstract: Shale of the Upper Cretaceous Slater River Formation extends across the Mackenzie Plain of the Canadian Northwest Territories and has potential as a regional source rock because of the high organic content and presence of both oil‐ and gas‐prone kerogen. An understanding of the thermal history experienced by the shale is required to predict any potential petroleum systems. Our study integrates multi‐kinetic apatite fission track (AFT) and apatite (U‐Th)/He (AHe) thermochronometers from a basal bentonite unit to understand the timing and magnitude of Late Cretaceous burial experienced by the Slater River Formation along the Imperial River. We use LA‐ICP‐MS and EPMA methods to assess the chemistry of apatite, and use these values to derive the AFT kinetic parameter rmr0. Our AFT dates and track lengths, respectively, range from 201.5 ± 36.9 Ma to 47.1 ± 12.3 Ma, and 16.8 to 10.2 μm, and single crystal AHe dates are between 57.9 ± 3.5 and 42.0 ± 2.5 Ma with effective uranium concentrations from 17 ppm to 36 ppm. The fission track data show no relationship with the kinetic parameter Dpar and fail the χ2‐test indicating that the data do not comprise a single statistically significant population. However, when plotted against their rmr0 value, the data are separated into two statistically significant kinetic populations with distinct track length distributions. Inverse thermal history modelling of both the multi‐kinetic AFT and AHe datasets, reveal that the Slater River Formation reached maximum burial temperatures of ~65–90 °C between the Turonian and Paleocene, indicating that the source rock matured to the early stages of hydrocarbon generation, at best. Ultimately, our data highlight the importance of kinetic parameter choice for AFT and AHe thermochronology, as slight variations in apatite chemistry may have significant implications on fission track and radiation damage annealing in apatite with protracted thermal histories through the uppermost crust. [ABSTRACT FROM AUTHOR]

Abstract: Floodplains, paleosols, and antecedent landforms near the apex of the Brahmaputra fan delta in north‐central Bangladesh preserve cycles of fluvial sediment deposition, erosion and weathering. Together these landforms and their associated deposits comprise morphostratigraphic units that define the river's history and have influenced its channel position and avulsion behaviour through the Late Quaternary. Previously, temporal differentiation within these units has not been sufficient to decipher their sequence of deposition, an important step in understanding the spatial pattern of migration of the Brahmaputra River. Holocene units in this region are fairly well established by radiocarbon dating of in situ organic material, but pre‐Holocene units are considered Pleistocene‐aged if organic material is dated >48 000 year BP (the limit of radiocarbon dating) or the sediments are positioned beneath a prominent paleosol, interpreted as a buried soil horizon that developed during a previous sea level lowstand. In such cases, these morphostratigraphic units have been broadly interpreted as Pleistocene without knowing their absolute depositional ages or relative evolutionary chronology. Here we use detailed sediment analysis to better differentiate morphostratigraphic units at the Brahmaputra's avulsion node, establishing the sequence of deposition and subsequent weathering of these bodies. We then test this relative chronology by luminescence dating of the sands beneath these landform surfaces. This work provides the first absolute depositional age constraints of terrace sediments for the Middle to Late Pleistocene Brahmaputra River and upper Bengal basin. The luminescence ages are complemented by detailed compositional trends in the terrace deposits, including clay mineralogy and the degree of weathering. Together, these newly dated and carefully described morphostratigraphic units reflect eustasy‐driven cycles of terrace development by way of highstand floodplain deposition and subsequent lowstand exposure and weathering, along with active tectonic deformation. Defining this Late Quaternary history of terrace development and position of the Brahmaputra River is a first step toward an integrated understanding of basin and delta evolution over multiple glacioeustatic cycles and tectonically relevant timescales. [ABSTRACT FROM AUTHOR]

Abstract: The Lobo Formation of southwestern New Mexico consists of spatially variable continental successions attributed to the Laramide orogeny (80–40 Myr), although its age and provenance are virtually undocumented. This study combines sedimentological, magnetostratigraphical and geochronological data to infer the timing and origin of the Lobo Formation. Measured sections of Lobo strata at two locations, Capitol Dome in the Florida Mountains and in the Victorio Mountains, indicate significant differences in depositional environments and sediment provenance. At Capitol Dome, where Lobo strata were deposited above a syncline developed in Palaeozoic strata, deposition took place in fluvial, palustrine and marginal lacustrine settings, with alluvial‐fan deposits only at the top of the formation. Combined magnetostratigraphy and a young U–Pb detrital zircon age suggest deposition of the section at Capitol Dome from ~60 to 52 Ma. The Lobo Formation in the Victorio Mountains was deposited in alluvial‐fan and fluvial settings; the age of deposition is poorly bracketed between 66 ± 2 Ma, the weighted‐mean age of two young zircons, and middle Eocene (~40 Ma), the approximate age of overlying volcanic rocks. U–Pb zircon ages from sandstones at the Victorio and Capitol Dome localities indicate that different source rocks provided sediment to the Lobo Formation. Local Proterozoic basement (~1.47–1.45 Ga) dominated the source of the Lobo Formation in the Victorio Mountains, consistent with abundant granitic clasts that are present in the proximal facies there; a diverse range of grain ages suggest that recycled Lower Cretaceous strata provided the dominant source for Lobo Formation sediment at the Capitol Dome locality. The U–Pb data suggest that the depositional systems at the two sites were not connected. Contrasts in depositional setting and detrital zircon provenance indicate that the Palaeogene Lobo Formation in southwest New Mexico was deposited in an assemblage of local depositional settings, possibly in separate structural basins, as a consequence of Laramide tectonics in the region. [ABSTRACT FROM AUTHOR]

Abstract: The Chatham Rise is located offshore of New Zealand's South Island. Vast areas of the Chatham Rise are covered in circular to elliptical seafloor depressions that appear to be forming through a bathymetrically controlled mechanism, as seafloor depressions 2–5 km in diameter are found in water depths of 800–1100 m. High‐resolution P‐Cable 3D seismic data were acquired in 2013 across one of these depressions. The seafloor depression is interpreted as a mounded contourite. Our data reveal several smaller buried depressions (<20–650 m diameter) beneath the mounded contourite that we interpret as paleo‐pockmarks. These pockmarks are underlain by a complex polygonal fault system that deforms the strata and an unusual conical feature results. We interpret the conical feature as a sediment remobilization structure based on the presence of stratified reflections within the feature, RMS amplitude values and lack of velocity anomaly that would indicate a nonsedimentary origin. The sediment remobilization structure, polygonal faults and paleo‐depressions are the indicators of the past subsurface fluid flow. We hypothesize that the pockmarks provided the necessary topographic roughness for the formation of the mounded contourites thus linking fluid expulsion and the deposition of contouritic drifts. [ABSTRACT FROM AUTHOR]

Pervasive fracture networks are common in many reservoir-scale carbonate bodies even in the absence of large deformation and exert a major impact on their mechanical and flow behaviour. The Upper Cretaceous Jandaíra Formation is a few hundred meters thick succession of shallow water carbonates deposited during the early post-rift stage of the Potiguar rift ( NE Brazil). The Jandaíra Formation in the present onshore domain experienced <1.5 km thermal subsidence and, following Tertiary exhumation, forms outcrops over an area of >1000 km2. The carbonates have a gentle, <5⁰, dip to the NE and are affected by few regional, low displacement faults or folds. Despite their simple tectonic history, carbonates display ubiquitous open fractures, sub-vertical veins, and sub-vertical as well as sub-horizontal stylolites. Combining structural analysis, drone imaging, isotope studies and mathematical modelling, we reconstruct the fracturing history of the Jandaíra Formation during and following subsidence and analyse the impact fractures had on coeval fluid flow. We find that Jandaíra carbonates, fully cemented after early diagenesis, experienced negligible deformation during the first few hundreds of meters of subsidence but were pervasively fractured when they reached depths >400-500 m. Deformation was accommodated by a dense network of sub-vertical mode I and hybrid fractures associated with sub-vertical stylolites developed in a stress field characterised by a sub-horizontal σ1 and sub-vertical σ2. The development of a network of hybrid fractures, rarely reported in the literature, activated the circulation of waters charged in the mountainous region, flowing along the porous Açu sandstone underlying the Jandaíra carbonates and rising to the surface through the fractured carbonates. With persisting subsidence, carbonates reached depths of 800-900 m entering a depth interval characterised by a sub-vertical σ1. At this stage, sub-horizontal stylolites developed liberating calcite which sealed the sub-vertical open fractures transforming them in veins and preventing further flow. During Tertiary exhumation, several of the pre-existing veins and stylolites opened and became longer, and new fractures were created typically with the same directions of the older features. The simplicity of our model suggests that most rocks in passive margin settings might have followed a similar evolution and thus display similar structures. [ABSTRACT FROM AUTHOR]

The Salar de Atacama Basin holds important information regarding the tectonic activity, sedimentary environments and their variations in northern Chile during Cretaceous times. About 4000 m of high-resolution stratigraphic columns of the Tonel, Purilactis and Barros Arana Formations reveal braided fluvial and alluvial facies, typical of arid to semi-arid environments, interrupted by scarce intervals with evaporitic, aeolian and lacustrine sedimentation, displaying an overall coarsening-upward trend. Clast-count and point-count data evidence the progressive erosion from Mesozoic volcanic rocks to Palaeozoic basement granitoids and deposits located around the Cordillera de Domeyko area, which is indicative of an unroofing process. The palaeocurrent data show that the source area was located to the west. The U/Pb detrital zircon geochronological data give maximum depositional ages of 149 Ma for the base of the Tonel Formation (Agua Salada Member), and 107 Ma for its middle member (La Escalera Member); 79 Ma for the lower Purilactis Formation (Limón Verde Member), and 73 Ma for the Barros Arana Formation. The sources of these zircons were located mainly to the west, and comprised from the Coastal Cordillera to the Precordillera. The ages and pulses record the tectonic activity during the Peruvian Phase, which can be split into two large events; an early phase, around 107 Ma, showing uplift of the Coastal Cordillera area, and a late phase around 79 Ma indicating an eastward jump of the deformation front to the Cordillera de Domeyko area. The lack of internal deformation and the thicknesses measured suggest that deposition of the units occurred in the foredeep zone of an eastward-verging basin. This sedimentation would have ended with the K-T phase, recognized in most of northern Chile. [ABSTRACT FROM AUTHOR]

The Tombador Formation exhibits depositional sequence boundaries placed at the base of extensive amalgamated fluvial sand sheets or at the base of alluvial fan conglomeratic successions that indicate basinward shifts of facies. The hierarchy system that applies to the Tombador Formation includes sequences of different orders, which are defined as follows: sequences associated with a particular tectonic setting are designated as 'first order' and are separated by first-order sequence boundaries where changes in the tectonic setting are recorded; second-order sequences represent the major subdivisions of a first-order sequence and reflect cycles of change in stratal stacking pattern observed at 102 m scales (i.e., 200-300 m); changes in stratal stacking pattern at 101 m scales indicate third-order sequences (i.e., 40-70 m); and changes in stratal stacking pattern at 100 m scales are assigned to the fourth order (i.e., 8-12 m). Changes in palaeogeography due to relative sea level changes are recorded at all hierarchical levels, with a magnitude that increases with the hierarchical rank. Thus, the Tombador Formation corresponds to one-first-order sequence, representing a distinct intracratonic sag basin fill in the polycyclic history of the Espinhaço Supergroup in Chapada Diamantina Basin. An angular unconformity separates fluvial-estuarine to alluvial fan deposits and marks the second-order boundary. Below the angular unconformity the third-order sequences record fluvial to estuarine deposition. In contrast, above the angular unconformity these sequences exhibit continental alluvial successions composed conglomerates overlain by fluvial and eolian strata. Fourth-order sequences are recognized within third-order transgressive systems tract, and they exhibit distinct facies associations depending on their occurrence at estuarine or fluvial domains. At the estuarine domain, they are composed of tidal channel, tidal bar and overlying shoreface heterolithic strata. At the fluvial domain the sequences are formed of fluvial deposits bounded by fine-grained or tidal influenced intervals. Fine grained intervals are the most reliable to map in fourth-order sequences because of their broad laterally extensive sheet-like external geometry. Therefore, they constitute fourth-order sequence boundaries that, at the reservoir approach, constitute the most important horizontal heterogeneity and, hence, the preferable boundaries of production zones. The criteria applied to assign sequence hierarchies in the Tombador Formation are based on rock attributes, are easy to apply, and can be used as a baseline for the study of sequence stratigraphy in Precambrian and Phanerozoic basins placed in similar tectonic settings. [ABSTRACT FROM AUTHOR]

Laser ablation-multi collector-inductively coupled mass spectrometry U- Pb geochronology, detailed field mapping and stratigraphic data offer improved insights into the timing and style of Laramide deformation and basin development in the Little Hatchet Mountains, southwestern New Mexico, USA, a key locality in the 'southern Laramide province.' The Laramide synorogenic section in the northern Little Hatchet Mountains comprises upper Campanian to Maastrichtian strata consisting of the Ringbone and Skunk Ranch formations, with a preserved maximum thickness of >2400 m, and the correlative Hidalgo Formation with a total thickness >1700 m. The Ringbone Formation and superjacent Skunk Ranch Formation are each generally composed of (1) a basal conglomerate member; (2) a middle member consisting of lacustrine shale, limestone, sandstone, and interbedded ash-fall tuffs; and (3) an upper sandstone and conglomerate member. Basaltic andesite flows are intercalated with the upper member of the Ringbone Formation and the middle member of the Skunk Ranch Formation. The Hidalgo Formation, which crops out in the northern part of the range, is dominantly composed of basaltic andesite breccias and flows equivalent to those of the Ringbone and Skunk Ranch formations. The Laramide section was deposited in an intermontane basin partitioned across intrabasinal thrust structures, which controlled growth-stratal development. U- Pb zircon ages from five tuffs indicate that the age range of the Laramide sedimentary succession is ca. 75-70 Ma. U- Pb detrital-zircon age data ( n = 356 analyses) from the Ringbone Formation and a Lower Cretaceous unit indicate sediment contribution from uplifted Lower and Upper Cretaceous rocks adjacent to the basin and the contemporary Tarahumara magmatic arc in nearby northern Sonora, Mexico. The new ages, combined with published data, indicate that uplift, basin development, and magmatism in the region proceeded diachronously northeastwards as the subducting Farallon slab flattened under northern Mexico and southern New Mexico from Campanian to Palaeogene time. [ABSTRACT FROM AUTHOR]