Abstract The Ribblesdale fold belt, representing the Variscan inversion of the Bowland Basin, is a well-known geological feature of northern England. It represents a crustal strain discontinuity between the granite-underpinned basement highs of the northern Pennines and Lake District in the north, and the Central Lancashire High/southern Pennines, in the south. Recent seismic interpretation and mapping have demonstrated that the Ribblesdale fold belt continues offshore towards Anglesey via the Deemster Platform, beneath the Permo-Triassic sedimentary cover of the southern part of the East Irish Sea Basin. The Môn–Deemster fold–thrust belt (FTB) affects strata of Mississippian to late Pennsylvanian age. Variscan thrusts extend down into the pre-Carboniferous basement but apparently terminate at a low-angle detachment deeper in the crust, here correlated with the strongly sheared Penmynydd Zone exposed in the adjacent onshore. Up to 15% shortening is observed on seismic sections across the FTB offshore, but is greater in the strongly inverted onshore segment. Pre-Carboniferous thrusting post-dates formation of the Penmynydd Zone, and is probably of Acadian age, when basement structures such as the southward-vergent Carmel Head Thrust formed. Extensional reactivation of the Acadian structures in early Mississippian time defined the northern edge of the offshore Bowland Basin. The relatively late brittle structures of the Menai Strait fault system locally exhume the Penmynydd Zone and define the southern edge of the basin. The longer seismic records from the offshore provide insights to the tectonic evolution of the more poorly imaged FTB onshore.

Abstract The Appalachian–Caledonian Orogen preserves a complex record of piecemeal trans-oceanic terrane transfer and accretion during the early Paleozoic collision between West Gondwana and Laurentia, whilst the intervening Iapetus oceanic tracts were largely destroyed. The now preserved terranes include arc fragments of Laurentian and Gondwanan affinity, oceanic fragments incorporated into the Gondwanan continental margin, and remnants of the Gondwanan continental slope apron and adjacent platform (both Ganderia and Megumia). A new tectonostratigraphic synthesis for the island of Anglesey (and adjacent NW Wales) reveals a comprehensive record of the Appalachian orogenic cycle in the UK segment of the orogen of the peri-Gondwanan margin prior to amalgamation into the Laurentian margin. We identify elements of Late Neoproterozoic accretion forming the pre-Appalachian basement; Cambrian extension, deposition and continental margin growth; Early Ordovician accretion and renewed extension; and, finally, terminal Caledonian collision and continental foreland-basin development.

Abstract A dip histogram for intracontinental M >5.5 reverse-slip ruptures reveals a trimodal distribution with a dominant Andersonian peak (fault dip, δ =30±5°) flanked by subsidiary clusters at δ =10±5° and 50±5°, and no dips greater than 60°. For a simple compressional regime ( σ v = σ 3 ), the dominant peak is in accord with the reshear of optimally oriented faults with a friction coefficient of μ s =0.6±0.2, implying frictional lock-up at δ =60±10° consistent with the observed upper dip bound. The low-dip cluster ( δ =10±5°) is dominated by thrusting in the frontal Himalaya and may incorporate staircase thrust systems in cover sequences with deflections along bedding anisotropy. The cluster of moderate-to-steep reverse fault ruptures ( δ =50±5°) is likely dominated by compressional inversion of inherited normal faults. In both circumstances, however, there appears to be competition between Andersonian thrusts in various stages of development and non-optimal failure planes dipping at either high or low angles. A delicate balance between levels of differential stress and fluid-pressure determines whether or not a poorly oriented thrust or reverse fault reactivates in preference to the development of new, favourably oriented Andersonian thrusts.

ABSTRACT The Ascension-Monterey Canyon system, one of the largest submarine canyon systems in the world, is located offshore central California. The system is composed of two parts which contain a total of six canyons: 1) the Ascension part to the north, which includes Ascension, Año Nuevo and Cabrillo Canyons, and 2) the Monterey part to the south, which includes Monterey Canyon and its distributaries, Soquel and Carmel Canyons. These six canyons have a combined total of 16 heads: one head each for Ascension, Soquel and Monterey Canyons, two heads for Año Nuevo Canyon, three heads for Carmel Canyon, and eight heads for Cabrillo Canyon. Ascension, Año Nuevo and Cabrillo Canyons coalesce in 2,300 m of water to form the Ascension Fan-Valley. Soquel and Carmel Canyons join Monterey Canyon at depths of 915 m and 1,900 m, respectively, to form Monterey Fan-Valley (the main channel of the system). Ascension Fan-Valley joins Monterey Fan-Valley on the proximal part of Monterey Fan in 3,290 m of water. The Ascension-Monterey Canyon system has a long and varied history. The ancestral Monterey Canyon originated in early Miocene time, cutting east-west into the crystalline basement of the Salinian block (possibly subaerially), somewhere near the present location of the Transverse Range of California. Since that time (~ 21 Ma), the Salinian block, riding on the Pacific Plate, moved northward along the San Andreas fault zone. During this period of transport the Monterey Bay region was subjected to several episodes of submergence (sedimentation) and emergence (erosion) that alternately caused sedimentary infilling and exhumation of Monterey Canyon. The present configuration of the Ascension-Monterey Canyon System is the result of tectonic displacement of a long-lived submarine canyon (Monterey Canyon), with associated canyons representing the faulted offsets of past Monterey Canyon channels. Slivering of the Salinian block along several fault zones trending parallel or sub-parallel to the San Andreas fault zone (the Ascension fault and the Palo Colorado-San Gregorio fault zone, in particular) displaced to the north the westerly parts of Monterey Canyon. In this manner Monterey Canyon “fathered” Cabrillo Canyon, Año Nuevo Canyon, Ascension Canyon and Pioneer Canyon, along with an unnamed canyon located between Ascension and Pioneer Canyons. Tectonics continue to dictate the morphology and processes active in the system today. The Palo Colorado-San Gregorio fault zone marks the continental shelf boundary in the Monterey Bay region and divides the canyon system into two parts, the Ascension and Monterey parts. The Monterey Canyon part has a youthful, V-shaped profile while the Ascension part, except for the heads that notch the shelf, and both fan-valleys exhibit more mature, U-shaped profiles. Earthquakes stimulate mass-wasting on the continental slope; most of the Ascension part of the system now receives its sediment from this source. The Monterey part, however, intercepts sediments carried by longshore transport and is the main regional conduit for terrestrial sediment transport to the abyssal plain.