Disruption of the Hellenic arc: Late Miocene extensional detachment faults and steep Pliocene‐Quaternary normal faults—Or what happened at Corinth?

The Yorktown Formation of Virginia and North Carolina is divided into three ostracode assemblage zones based on the occurrence of 230 species in 43 samples. The samples were compared in Q-mode using the Dice binary similarity coefficient and cluster analysis. From oldest to youngest, the three zones are the Pterygocythereis inexpectata, Orionina vaughani, and Puriana mesacostalis Zones. The first two are late Miocene in age and the last, which is poorly represented in Virginia, is considered to be early Pliocene in age. The level of association (R-mode study using the Dice coefficient) between 80 of the more commonly occurring species is shown by means of a dendrogram; values for the biostratigraphic fidelity and constancy of each of these species for each of the zones are given. A general trend through time from late Miocene to early Pliocene for the Yorktown transgression and regression is suggested, based on the occurrence of brackish-water ostracodes and bivalves, particularly Cyprideis and Corbicula. It is suggested that rapid transgression of the sea occurred during early Yorktown time to a maximum during the time represented by the middle Orionina vaughani Zone. A more or less steady regression of the sea followed during the remainder of Yorktown time. INTRODUCTION The Yorktown Formation (upper Tertiary) of North Carolina and Virginia is a very fossiliferous, lithologically heterogeneous unit with an exposed thickness (natural exposures or open-pit mines) of about 70-120 feet. The sandy clays and clayey sands assigned to the Yorktown crop out discontinuously in a 16,800-squaremile area between the Rappahannock River in Virginia and the Neuse River in North Carolina (fig. 1). South of the Neuse River, deposits of the same general age as the Yorktown are usually mapped as Duplin Marl. No microfossil zonation exists for the Yorktown. This report presents the results of a reconnaissance collecting program in conjunction with examination of existing museum collections, the object being to provide a regional ostracode zonation. Localities (fig. 1; p. 10) were chosen on the basis of geographic and stratigraphic spread. More detailed collecting will be done in locally complex areas such as the York-James peninsula where the distribution of numerous lithofacies within the Yorktown is being studied (Johnson, 1969; Coch, 1968; Bick and Coch, 1969). 78 0 25 50 75 100 KILOMETERS i i i i 11 i I I FIGURE 1. Location of collections; numbers correspond to those in locality list (p. 10). Dashed line encloses area in which Yorktown Formation crops out in natural exposures.

The paleomagnetic stratigraphy, biostratigraphy, and paleoclimatology have been studied in two marine sections of late Miocene to early Pliocene age in New Zealand. A total of over 850 separately oriented cores were collected from 270 sites. The Blind River section (41°43′ S.) is now adjacent to the southernmost subtropical (temperate) water mass, but planktonic foraminifera indicate that the area was covered by subantarctic water during much of late Miocene and early Pliocene time. The Mangapoike River section (38°55′ S.) records temperature oscillations mainly within the subtropical water mass during late Miocene–early Pliocene age, with perhaps one subantarctic interval during latest Miocene time. The Miocene-Pliocene boundary in New Zealand has consistently been placed at the first evolutionary appearance of Globorotalia puncticulata at the boundary between the late Miocene Kapitean Stage and the early Pliocene Opoitian Stage. This boundary lies within sediments deposited during the Gilbert Reversed Epoch between the Nunivak Event (base at 4.14 m.y. B.P.) and the Gilbert C Event (top at 4.33 m.y. B.P.) in both sections. Thus, the Miocene-Pliocene boundary, as recognized in New Zealand, is dated as 4.3 ± 0.1 m.y., which appears to be slightly younger than the type (International) Miocene-Pliocene boundary in Italy (4.9 to 5.1 m.y.). Biostratigraphic ranges of planktonic foraminifera between New Zealand and the Mediterranean differ in detail, perhaps due to different paleo-oceanographic histories. A major cooling episode during the early Gilbert Reversed Epoch is recorded at Blind River and Mangapoike River. This cooling is more pronounced in the southern section examined, where it is represented by the occurrence of a central subantarctic planktonic foraminiferal assemblage. In the northern section, cooling was also pronounced, although of shorter duration, represented by a probably northern subantarctic assemblage. The Miocene-Pliocene boundary in Europe has still only been dated indirectly by means of non-Mediterranean sections. Interpretation of late Cenozoic paleomagnetic data from Mediterranean deep-sea cores collected from Glomar Challenger is rejected.

Studies of Late Miocene – Pliocene continental shelf and slopes sediments on the south-eastern continental margin, Niger Delta (a broad region from the shelf – slope break extending to the ultra-deep waters: > 1500m), have revealed markedly different responses to sea level fluctuations. Significant features of the stratigraphy include siliciclastic-dominated facies consisting principally of one or more of the following genetic types: deltaic distributary mouth bars, channel and shoreface sands, barrier beach, shelf and offshore turbidites. These sands are Late Miocene – Early Pliocene in age and were deposited in deep water settings on the slope of the ‘Y’ field by a range of depositional processes that include slumps, debris flows and turbidity currents. Most of these sands could be interpreted to relate to periods of base level fall, if not Global Eustatic lowstands. Working within a sequence stratigraphic framework, eight (8) sequences have been delineated on the basis of reflection termination patterns. The major sequences were related to sea level fall during which the shelf was exposed to erosion. A cross section of the stratigraphic correlation drawn showed that the horizons are laterally continuous. However, pinch-out channel sands and lenticular sandbodies are evident. The recognition of depositional surfaces on the stratigraphic cross-sections allows subdivision of the stratigraphy into systems tracts: HST, FSST, TST and LST. On the seismic package, three (3) main seismic surfaces with distinct chronostratigraphic expressions are evident. They include non-marine, marine and fault plane surfaces. In addition, clinoform strata in the basin-margin setting of this field have relatively flat topsets and sloping clinoforms. On the shelf settings, a composite surface exists consisting of the merged sequence boundary, otherwise marked and interpreted as 4.2 Ma sequence boundary, transgressive surface (TS) and maximum flooding surface (MFS), unless separated by an incised valley fill (IVF). In the ‘Y’ field, failure, slumping and re-sedimentation processes that cause base-of-slope thickening in response to gravity and geotropic flows modify the slope. Furthermore, within the same basinal setting, affected by the same sea level rise, the facies boundaries are diachronous. Keywords: Seismic stratigraphy, Petrophysics, Sea level change, South-eastern, Miocene – Pliocene Sedimentation, Offshore Niger Delta DOI: 10.7176/JNSR/11-14-04 Publication date: July 31 st 2020

The westernmost Mediterranean basins formed in a supra-subduction system during the Miocene. We have found that since the late Miocene, the previously extending region has been deformed by contractional and strike slip fault systems due to the Iberia – Africa tectonic plates convergence, producing the reorganization of the main tectonic structures. The westernmost Mediterranean realm is seismically active because it hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which plate convergence is absorbed by minor to moderate-size tectonic structures, each absorbing a comparatively small part of the deformation. However, the understanding of the crustal configuration and the evolution of this basin was limited due to the limited penetration and resolution of the images of the subsurface.We collected and processed >3.000 km of a modern seismic dataset to characterized for the first time 1) the deep structure and the crustal domains of the Alboran Basin, 2) the sedimentary infill and as a consequence, the basin evolution, and 3) the main active faults of the basin. Based on these results, we were able to identify the main fault systems and quantify the total slip accommodated by those prominent tectonic structures of the area, late Miocene - early Pliocene in age. Our results show that the estimated total slip accommodated by the main fault systems is similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on those faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin. These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. We performed a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed.

<p>The Alboran Basin is located in the westernmost Mediterranean Sea. This basin was formed during the Miocene, and since the late Miocene, has been deformed due to the Iberia – Africa tectonic plates convergence, producing the contractive reorganization of some structures at the basin. Thus, the Alboran Basin is a seismically active area, which hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which several small faults are accommodating the deformation.</p><p>Based on a modern set of active seismic data, we were able for the first time to quantify the total slip accommodated by the most prominent tectonic structures of the area, late Miocene - early Pliocene in age. Our results show that the estimated total slip accommodated by the main fault systems may be similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on that faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin.</p><p>These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. Using the most complete dataset until the date, we performed a revision of the geometry and characteristics of the main fault systems offshore. Based on this data, we perform a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed.</p>

Tectono-sedimentary analysis of a complex, extensional, Neogene basin formed on thrust-faulted, Northern Apennines hinterland: Radicofani Basin, Italy

A new monachine phocid pinniped assemblage from the north–central coast of Chile is described. The material was recovered from a marine bonebed of the Bahía Inglesa Formation which, based on macro– and microfossil evidence, is probably Late Miocene–Early Pliocene in age. At least two genera, Acrophoca and Piscophoca (both originally described from the Pisco Formation of Peru), are present. The Chilean material is significantly different from that of the two described species from the Pisco Formation and probably represents new species, though these are not named pending description of new material reported from Peru. The postcrania are morphologically intermediate between the northern Phocini and southern Lobodontini. The Bahía Inglesa Formation pinniped assemblage represents the first occurrence of fossil seals in Chile, and provides valuable information regarding the late Neogene radiation of monachines in the Southern Hemisphere. The occurrence of Acrophoca sp. in beds underlying a condensed Mio–Pliocene bonebed suggests that these strata are no older than Late Miocene.

After several years of intense fieldwork in the area of Huayquerías del Este, northern Mendoza (Argentina), the results account for more than 1,000 specimens and 67 taxa of vertebrates documented from the Huayquerías and Tunuyán formations. In this contribution, we present the first record of an indeterminate Typotheria Interatheriinae coming from a fossil-bearing level in the lower section of the Tunuyán Formation, 10–15 m above the contact with the underlying Huayquerías Formation (5.84 ± 0.41 Ma, late Miocene; Messinian), which implies an interval age between the latest Miocene (upper Messinian) and early Pliocene (Zanclean) age for the lower levels of the Tunuyán Formation where the interathere remain comes from. The specimen (IANIGLA-PV 450) is a fragment of mandible with a broken right p3?, whose small size and features (shortening of the trigonid, a low trigonid-talonid length ratio <1, and a circular-outlined talonid) distinguish it from late Miocene species of Protypotherium (P. antiquum, P. distinctum, and P. minutum), but also from early and middle Miocene interatheres (e.g., Miocochilius, Interatherium, Caenophilus). We recognize it as an Interatheriinae indet., and based on the peculiar features of this specimen it could be a new taxon, but its fragmentary and isolated condition prevent us from providing an accurate diagnosis. IANIGLA-PV 450 is the first mention of an Interatheriinae for the Tunuyán Formation and the central-west region of Argentina, but also the Last Appearance Datum (LAD), latest Miocene–early Pliocene, for the group.

ABSTRACTA revised stratigraphy is presented for the late Miocene–early Pliocene sedimentary rocks of the northern Aorangi Range, Wairarapa. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially coeval, while the overlying Makara Greensand is shown to be a diachronous unit that ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke groups, and provides new insights into regional geological history. Previous seismic imaging studies have identified an episode of accelerated crustal shortening and deformation in the Wairarapa region near the Miocene–Pliocene boundary. The Clay Creek Limestone has proven to be a useful marker horizon for constraining the timing and style of this deformational episode, which is interpreted to have occurred prior to 7.2 Ma.

The Cenozoic Niger Delta displays a complex gravity collapse system underpinned by overpressured shale that forms a d&amp;#233;collement for normal faults, detachment folds and imbricate-fold-thrust structures in a linked extensional-contractional system. To better understand the timing and dynamics of gravity-driven deformation in the eastern Niger Delta (END) and western Niger Delta (WND) since the late Cretaceous, we performed 2D forward kinematic structural restoration and backstripping of regional 2-D seismic sections using KronosFlow software. The restored cross-section, in the END, extends from the present-day onshore (the Oligocene-Tortonian extensional zone) to the abyssal plain, while that of the WND extends from the present-day continental shelf to the abyssal plain. A comparison of restored cross sections shows that the modern continental shelves of the END and WND are dominated by counter-regional and regional normal faults, respectively. Between the late Eocene (ca. 34 Ma) and the late Miocene (9.3 Ma), the END displays gravity-driven deformation, localised in the Oligocene-Tortonian extensional zone with relatively low deformation on the slope and the deep basin. However, a correlation of restored cross sections over the late Eocene-late Miocene, suggests that gravity-driven deformation in the WND was localised within the Oligocene-Tortonian extensional zone with little or no deformation on the slope and the deep basin. Between the late Miocene (ca. 9.3 Ma) and the early Pliocene (ca. 5.7-4.9 Ma), the Oligocene-Tortonian extensional zone prograded to the present-day continental shelf resulting in a coupling of extensional deformation to contractional deformation in the END at least since the late Miocene. In the WND, the Oligocene-Tortonian extensional zone prograded to the present-day continental shelf during the late Miocene (ca. 9.5 Ma) but there was no coupling between extension and contraction until the early Pliocene (ca. 4.9 Ma). While there is a general reduction in gravity-driven deformation in the END over the Pleistocene, there is an overall increase in gravity collapse of sedimentary wedge in the WND. The unique structural configuration of the present-day continental shelf in the END and WND exerted distinct control on the gravity collapse of the regions throughout the Neogene. The dominance of counter-regional normal faults on the END continental shelf facilitated a large-scale increase (x2) in regional subsidence and sediment storage on the shelf over the late Eocene-late Miocene. However, the dominance of regional normal faults on the WND continental shelf facilitates an overall progradation and sediment transfer to the deep basin since the late Miocene/early Pliocene. This study documents the long history of gravity-driven deformation of the eastern and western Niger Delta and could be applied in the reconstruction of other shale tectonic basins.

Neotectonic intersection of the Aegean and Cyprus tectonic arcs: extensional and strike-slip faulting in the Isparta Angle, SW Turkey

Quantifying geomorphic evolution of earthquake-triggered landslides and their relation to active normal faults. An example from the Gulf of Corinth, Greece

Three named stratigraphic units that are wholly or in part of Pliocene age form discontinuous outcrops around the southeast margin of the Los Angeles basin: the Fernando Formation (lower and upper Pliocene), the Capistrano Formation (upper Miocene and lower Pliocene), and the Niguel Formation (upper Pliocene). The Fernando Formation is exposed in the Puente Hills, in the Northwestern Santa Ana Mountains, and at Upper Newport Bay; it consists of two stratigraphic units that typically are separated by an unconformity. The thickness of the formation ranges from nearly 6,000 ft in the western Puente Hills to about 1,300 ft at Newport. The common lithologic types in the upper unit are siltstone, sandstone, and conglomerate; the lower unit is predominantly siltstone. Gaps in the faunal record preclude accurate zonation, but much of the provincial Pliocene is represented by a composite section. Using a twofold chronology, the lower unit at most localities is early Pliocene in age, and the upper unit, late Pliocene, although a precise time boundary is difficult to define on the basis of mollusks. M gafaunas from the northeast part of the basin characteristically indicate inner sublittoral environments, whereas those nearer the present coast, which contain large displaced assemblages, suggest deposition in outer sublittoral to upper bathyal depths. Basinward, the Fernando Formation grades into subsurface strata that commonly are called Repetto and Pico Formations. The Capistrano Formation is exposed at Newport Bay and in the Capistrano syncline. Most of the formation at Newport is composed of mudstone, but near Dana Point it consists of a radiolarian mudstone facies; a deep-sea, fan-valley, coarse-grained facies; and a foraminiferal mudstone facies. In the vicinity of San Juan Capistrano, the type area, the formation is about 2,100 ft thick and is composed chiefly of mudstone. Between El Toro and Arroyo Trabuco, the Oso Member, a large lenticular sandstone unit as much as 1,400 ft thick, constitutes most of the formation. The lower part of the Capistrano Formation and the Oso Member are assigned a late Miocene age; the upper part in the San Juan Capistrano-Dana Point area is early Pliocene and locally separated from the lower part by an unconfo mity. At Newport Bay the upper part is eroded, and the formation is entirely late Miocene in age. Small assemblages of mollusks from the upper part of the formation near Dana Point are displaced, and their species content suggests deposition in the upper bathyal zone. The lower part (Miocene) of the Capistrano Formation probably correlates with the Malaga Mudstone Member of the Monterey Shale and with the upper part of the Puente Formation; the upper part (Pliocene), with the lower unit of the Fernando Formation at Newport Bay and in the Puente Hills. The Niguel Formation caps most of the low hills between El Toro and San Juan Capistrano. Much of the formation at the northernmost and westernmost outcrops may be nonmarine, and the uppermost beds in the type area 5 mi north of San Juan Capistrano may be nonmarine. The chief constituents of the formation are sandstone, conglomerate, and siltstone. Conglomeratic beds at the base are deeply channeled into older rocks. A thickness of 350 ft is estimated for the formation in the type area. Mollusk assemblages contain many species diagnostic of a Pliocene age, and the composite fauna is provisionally assigned to the latter half of the epoch. Mixed depth assemblages are common, but the localities in the inland area contain an abundance of shallow, warm-water species, whereas those nearer th coast contain some extant species that range into upper bathyal depths. The composite megafauna is strikingly similar to those from the San Diego Formation at Pacific Beach and from the upper member of the Fernando Formation in the eastern Puente Hills; it closely resembles those from the upper part of the Pico Formation in the eastern Ventura basin and from the Careaga Sandstone in the Santa Maria district. End_of_Article - Last_Page 438------------

The vegetation and climate of a Neogene petrified wood forest of Mizoram, India

Analysis of Antarctic glaciations by seismic reflection and refraction tomography