Abstract The superposition of structures produced by different tectonic phases is common in sedimentary basins. Yet the earlier structures often remain overlooked with potentially negative exploration consequences. In the Maiella anticline, Pliocene compression has folded carbonate sequences containing Cretaceous extensional structures. The geometry and evolution of the Apulian carbonate platform margin outcropping on the Maiella Mountain are described by two opposing groups of models. One proposes a structurally controlled platform margins cut by syn-sedimentary Cretaceous faults; the other assumes a passive Cretaceous palaeo-escarpments progressively filled by Cretaceous to Tertiary sediments later deformed by the Pliocene compression. Assuming models in line with either one of these two groups has significant implications for exploration plays on both platforms and adjacent basins of analogous subsurface systems. These include: hypothesized margin geometries; sediment transport mechanisms (directions and distribution); size of sequences; type and size of traps and associated exploration targets, risks and uncertainties. We demonstrate that during the Late Cretaceous the platform margin was cut by normal faults which controlled the palaeogeography of the platform and the sediment input into the adjacent basin in which thick, resedimented, carbonate megabreccia and turbidites were deposited. These carbonates represent exploration targets in similar settings worldwide.

ABSTRACT The early Miocene Markagunt (MGS) and late Oligocene Sevier (SGS) gravity slides in southwestern Utah, USA, exhibit the full range of structural features commonly seen in modern landslides, but on a gigantic scale—they are among Earth’s largest terrestrial landslides. The MGS, discovered in 2013, consists of four distinct structural segments: (1) a high-angle breakaway segment, (2) a bedding-plane segment, (3) a ramp segment where the slide cut up-section and the basal fault “daylighted,” and (4) a former land-surface segment where the upper plate moved at least 35 km over the Miocene landscape. The MGS remained undiscovered for so long precisely because of its gigantic size (>5000 km 2 , >95 km long, estimated volume 3000 km 3 ) and initially confusing mix of extensional, translational, and compressional structures overprinted by post-MGS basin-range tectonism. Preliminary mapping of the SGS, discovered in 2016, shows it to be smaller (>2000 km 2 ) and slightly older than the MGS. Both gravity slides are large contiguous sheets of andesitic lava flows, volcaniclastic rocks, source intrusions, and regional ash-flow tuffs that record southward, gravitationally induced catastrophic failure of the southern flank of the Oligocene to Miocene Marysvale volcanic field. Failure was preceded by slow gravitational spreading accommodated by the Paunsaugunt thrust fault system, which is rooted in Middle Jurassic evaporite-bearing strata at a depth of ~2 km; this thrust system deformed Middle Jurassic through lower Oligocene strata. MGS emplacement is presently constrained between ca. 23 and 21 Ma; SGS emplacement is presently constrained between ca. 25 and 23 Ma. The presence of basal and lateral cataclastic layers, injectites (clastic dikes), pseudotachylyte (frictionite), deformed clasts, and a variety of kinematic indicators suggests that each gravity slide represents a single catastrophic emplacement event from the north to the south; possibly the MGS comprises two gravity slides. The principal zone of failure was in mechanically weak, clay-rich sedimentary strata at the base of the volcanic section. The MGS and SGS are significant because they provide examples of lithified landslide structures so large that they may be mistaken for tectonic features. However, these gravity slides lie at right angles to regional compressional tectonic structures and are cut longitudinally by modern basin-range normal faults, and thus offer compelling case studies for how to differentiate features resulting from surficial verses tectonic processes. Here we offer a history of MGS and SGS discovery, our current understanding of the gravity slides as of late 2018 (which are the focus of ongoing research), and a guide to locations of particularly instructive exposures where we document our conclusions about size, distinctive structural features, emplacement ages, and interpreted emplacement mechanisms.

Abstract In northwest Arizona, the relatively unextended Colorado Plateau gives way abruptly to the highly extended Colorado River extensional corridor within the Basin and Range province along a system of major west-dipping normal faults, including the Grand Wash fault zone and South Virgin–White Hills detachment fault. Large growth-fault basins developed in the hanging walls of these faults. Lowering of base level in the corridor facilitated development of the Colorado River and Grand Canyon. This trip explores stratigraphic constraints on the timing of deformation and paleogeographic evolution of the region. Highlights include growth-fault relations that constrain the timing of structural demarcation between the Colorado Plateau and Basin and Range, major fault zones, synextensional megabreccia deposits, nonmarine carbonate and halite deposits that immediately predate arrival of the Colorado River, and a basalt flow interbedded with Colorado River sediments. Structural and stratigraphic relations indicate that the current physiography of the Colorado Plateau–Basin and Range boundary in northwest Arizona began developing ca. 16 Ma, was essentially established by 13 Ma, and has changed little since ca. 8 Ma. The antiquity and abruptness of this boundary, as well as the stratigraphic record, suggest significant headward erosion into the high-standing plateau in middle Miocene time. Thick late Miocene evaporite and lacustrine deposits indicate that a long period of internal drainage followed the onset of extension. The widespread distribution of such deposits may signify, however, a large influx of surface waters and/or groundwater from the Colorado Plateau possibly from a precursor to the Colorado River. Stratigraphic relations bracket arrival of a through-flowing Colorado River between 5.6 and 4.4 Ma.

Abstract Devonian limestone and dolostone formations are superbly exposed in numerous mountain ranges of southeastern Nevada. The Devonian is as thick as 1500 m there and reveals continuous exposures of a classic, long-lived, shallow-water carbonate platform. This field guide provides excursions to Devonian outcrops easily reached from the settlement of Alamo, Nevada, ~100 mi (~160 km) north of Las Vegas. Emphasis is on carbonate-platform lithostratigraphy, but includes overviews of the conodont biochronology that is crucial for regional and global correlations. Field stops include traverses in several local ranges to study these formations and some of their equivalents, in ascending order: Lower Devonian Sevy Dolostone and cherty argillaceous unit, Lower and Middle Devonian Oxyoke Canyon Sandstone, Middle Devonian Simonson Dolostone and Fox Mountain Formation, Middle and Upper Devonian Guilmette Formation, and Upper Devonian West Range Limestone. Together, these formations are mainly composed of hundreds of partial to complete shallowing-upward Milankovitch-scale cycles and are grouped into sequences bounded by regionally significant surfaces. Dolomitization in the Sevy and Simonson appears to be linked to exposure surfaces and related underlying karst intervals. The less-altered Guilmette exhibits characteristic shallowing-upward limestone-to-dolostone cycles that contain typical carbonate-platform fossil- and ichnofossil-assemblages, displays stacked biostromes and bioherms of flourishing stromatoporoids and sparse corals, and is punctuated by channeled quartzose sandstones. The Guilmette also contains a completely exposed ~50-m-thick buildup that is constructed mainly of stromatoporoids, with an exposed and karstified crest. This buildup exemplifies such Devonian structures known from surface and hydrocarbon-bearing subsurface locations worldwide. Of special interest is the stratigraphically anomalous Alamo Breccia that represents the middle member of the Guilmette. This spectacular cataclysmic megabreccia, produced by the Alamo Impact Event, is as thick as 100 m and may be the best exposed proven bolide impact breccia on Earth. It contains widespread intervals generated by the seismic shock, ejecta curtain, tsunami surge, and runoff generated by a major marine impact. Newly interpreted crater-rim impact stratigraphy at Tempiute Mountain contains an even thicker stack of impact breccias that are interpreted as parautochthonous, injected, fallback, partial melt, resurge, and possibly post-Event crater fill.

Abstract The Neogene stratigraphic section in the Split Mountain area exposes megabreccia deposits up to 12 km long with volumes up to 3 × 10 8 m 3 . Shattered-rock domains still portray the bedrock distribution of lithologies. Jigsaw-puzzle fabric occurs on a variety of scales from microscopic to outcrop. Broken and stretched pegmatites tend to rise upward as step-ups in the inferred down-flow directions. Upper Miocene subaerial megabreccias about 65 m thick disturbed the underlying strata to depths less than a meter during their emplacement. This includes producing grooved and decapitated stones both in the substrate and below shear surfaces especially within the basal few meters of the megabreccia deposits. The lower portions of a megabreccia are rich in step-ups, ramps, and crushed-rock streamers that rise upward in the down-flow direction. After flooding of the basin by the ancestral Gulf of California, a lower Pliocene megabreccia moved across the sea floor deforming underlying sedimentary layers by injections and sunken megabreccia lobes that locally caused tightly folded bottom-sediment packages >35 m thick to rise as diapirs. Near the leading edge, on the southwest corner of the deposit, there is a small volume of more traditional sandy conglomerate deposited as the mass rapidly slowed and stopped. Both subaerial and subaqueous megabreccias contain lithologic domains that preserve the distribution of bedrock lithologies, jigsaw-puzzle fabric, step-ups and crushed-rock streamers; these features all require non-turbulent flow. These huge volumes of shattered bedrock moved 10–12 km distance in late Miocene as dry subaerial masses, and again across the floor of an early Pliocene inland sea. All the observed features strongly indicate flow as sturzstroms.