Late Miocene—Early Pliocene Paleomagnetic Stratigraphy, Paleoclimatology, and Biostratigraphy in New Zealand

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.

Palaeoclimatic and palaeoenvironmental interpretations of the Late Oligocene, Late Miocene–Early Pliocene in the Çankırı-Çorum Basin

Sedimentary rocks exposed along the periphery of the San Fernando Valley indicate the area was a separate marine basin during Miocene and Pliocene time. Although the surrounding geology is well known, the basin is virtually unrecognized as a major Tertiary basin of Southern California. Structure, stratigraphy, and sedimentology indicate the basin’s history is similar to that of other Continental Borderland basins. Localized subsidence in the Late Middle Miocene formed the basin as a discrete unit. Basin filling took place during Pliocene and Pleistocene time. Benthonic Foraminifera indicate that the San Fernando basin was separate from the adjacent and deeper Ventura basin but remained an integral part of the east-west Ventura embayment. Over 900 meters of Late Miocene and Pliocene sediments are well exposed on the south side of the basin. Shales and diatomites typify the Miocene sequence whereas silts and sands are characteristic of the Pliocene. Laminated diatomite was probably deposited in a subsill oxygen-deficient environment analogous to the existing Santa Barbara basin. Coarse, arkosic continental sands interfinger with Pliocene marine sediments at the eastern end of the basin. Benthonic Foraminifera and Radiolaria show that subsidence to middle bathyal depths occurred during Late Miocene (Delmontian) and Early Pliocene (Repettian) time. Rapid shoaling during the Pliocene is evidenced by the systematic appearance of slope, shelf, and neritic foraminiferal faunas. Abundant Pliocene macrofossils also characterize shelf-depth deposits. Shallow-water micro and macrofaunas within deep water sediments are interpreted as displaced by turbidity currents or slumping. Planktonic Foraminifera and an increase in radiolarian (Spumellina) diameter suggest cool surface temperatures during the Late Miocene and increasingly warmer temperatures in the Early Pliocene.

Late neogene biostratigraphy and stable isotope stratigraphy of a drilled core from the Gulf of Mexico

Extensional faults exposed in the Peloponnesus and mainland Greece, most of which are described here for the first time, record a transition from regional extension of the Aegean domain to the modern tectonic system. The East Peloponnesus Detachment System trends north‐northwest from the southern Peloponnesus to ∼30 km north of the Gulf of Corinth, dips gently northeast, and is late Miocene–early Pliocene in age. It has a minimum displacement of 25–30 km and appears to be the youngest of the regional‐scale extensional systems with significant displacement that formed parallel to the Hellenic arc. The partially coeval East Sterea Extensional System, which extends from the Gulf of Corinth to the Aegean Sea, contains low‐angle normal faults that both crosscut and trend parallel to older structures of the Hellenic arc. Late Miocene to early Pliocene displacement within this zone disrupted the arc‐parallel structures of the Hellenides. Upper Pliocene‐Quaternary normal faults, which trend approximately east‐west and generally dip steeply at the surface, continue the disruption of the Hellenic arc. Much of the subsidence within the Gulf of Corinth appears to be unrelated to the younger faults and is instead related to the motion on the East Peloponnesus Detachment, which crosscuts the modern graben.

Late Miocene paleoclimatology: Subantarctic water mass, Southwest Pacific

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.

<p>The late Miocene-early Pliocene geology of the Makara and Ruakokoputuna Valleys in the northern Aorangi Range, south-east Wairarapa, is described in detail. In this area, a succession of Neogene sedimentary units laps onto basement rocks of Cretaceous age, and late Miocene-early Pliocene stratigraphy varies markedly, from bathyal mudstone to high energy coastal environments, over distances of only a few kilometres. Sections were measured at four key locations, which provided reference sites for stratigraphic changes across the study area. Additional detailed field mapping was carried out around Te Ahitaitai Ridge. Depositional environments were interpreted using grain size analysis, macrofossil and foraminiferal assemblages, and palynology. Foraminiferal biostratigraphy was used to constrain the ages of samples. Data obtained by these methods were combined with previous authors’ work to produce a synthesis map, unit correlations, and geological cross-sections of the Makara and Ruakokoputuna Valleys. Late Miocene-early Pliocene geological history is interpreted, and a depositional model is proposed to explain the presence of giant cross-beds in the Clay Creek Limestone. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially laterally equivalent, while the overlying Makara Greensand is shown to be a diachronous unit which ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) in age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke Groups, and provides new insights into regional geological history. The late Miocene-early Pliocene stratigraphy records a history of regional subsidence, punctuated by episodes of deformation which caused localised uplift and erosion. Previous seismic imaging studies identified one such 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 deformation, which is interpreted to have occurred prior to 7.2 Ma. Major differences in stratigraphy between the upthrown and downthrown sides of the Mangaopari Fault indicate that the fault was active during this deformational episode. Lithostratigraphic units from the study area have been correlated with units in other parts of the Wairarapa, and these correlations suggest that late Miocene deformation in the region may have propagated from south to north.</p>

<p>The late Miocene-early Pliocene geology of the Makara and Ruakokoputuna Valleys in the northern Aorangi Range, south-east Wairarapa, is described in detail. In this area, a succession of Neogene sedimentary units laps onto basement rocks of Cretaceous age, and late Miocene-early Pliocene stratigraphy varies markedly, from bathyal mudstone to high energy coastal environments, over distances of only a few kilometres. Sections were measured at four key locations, which provided reference sites for stratigraphic changes across the study area. Additional detailed field mapping was carried out around Te Ahitaitai Ridge. Depositional environments were interpreted using grain size analysis, macrofossil and foraminiferal assemblages, and palynology. Foraminiferal biostratigraphy was used to constrain the ages of samples. Data obtained by these methods were combined with previous authors’ work to produce a synthesis map, unit correlations, and geological cross-sections of the Makara and Ruakokoputuna Valleys. Late Miocene-early Pliocene geological history is interpreted, and a depositional model is proposed to explain the presence of giant cross-beds in the Clay Creek Limestone. Despite major differences in lithology, the Clay Creek Limestone and Bells Creek Mudstone are shown to be partially laterally equivalent, while the overlying Makara Greensand is shown to be a diachronous unit which ranges from late Miocene (Kapitean) to early Pliocene (Opoitian) in age. This revised stratigraphy raises questions about the current classification of the Palliser and Onoke Groups, and provides new insights into regional geological history. The late Miocene-early Pliocene stratigraphy records a history of regional subsidence, punctuated by episodes of deformation which caused localised uplift and erosion. Previous seismic imaging studies identified one such 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 deformation, which is interpreted to have occurred prior to 7.2 Ma. Major differences in stratigraphy between the upthrown and downthrown sides of the Mangaopari Fault indicate that the fault was active during this deformational episode. Lithostratigraphic units from the study area have been correlated with units in other parts of the Wairarapa, and these correlations suggest that late Miocene deformation in the region may have propagated from south to north.</p>

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>

Microzooplankton grazing in different water masses associated with the subtropical convergence round the south island, New Zealand

A distinct (0.5 per mil) carbon-13/carbon-12 isotopic shift in the light direction has been identified in a shallow marine sedimentary sequence of Late Miocene age at Blind River, New Zealand, and correlated with a similar shift in Late Miocene Deep Sea Drilling Project sequences throughout the Indo-Pacific. A dated piston core provides an age for the shift of 6.2 +/- 0.1 million years. Correlations based on the carbon isotopic change require a revision of the previously established magnetostratigraphy at Blind River. The carbon shift at Blind River occurs between 6.2 and 6.3 +/- 0.1 million years before present. A new chronology provides an age for the evolutionary first appearance datum of Globorotalia conomiozea at 6.1 +/- 0.1 million years, the beginning of a distinct latest Miocene cooling event associated with the Kapitean stage at 6.2 +/- 0.1 million years, and the beginning of a distinct shallowing of water depths at 6.1 +/- 0.1 million years. The Miocene-Pliocene boundary as recognized in New Zealand is now dated at 5.3 +/- 0.1 million years. Extension of carbon isotope stratigraphy to other shallow Late Miocene sequences should provide an important datum for international correlation of Late Miocene shallow and deep marine sequences.

Miocene, Pliocene, and Pleistocene strata were deposited in two embayments in the central Atlantic Coastal Plain, the Salisbury to the north and Albermarle to the south. Both embayments underwent local tectonics, and no single area within either has a continuous section. Deposition in both embayments began in early Miocene time. In the Salisbury embayment, the early deposits were largely biogenic (Fairhaven Member of the Calvert Formation), and the center of deposition was located in Maryland. Relatively continuous clastic deposition commenced in the late early Miocene and continued through the middle Miocene (Plum Point Marl Member of the Calvert Formation and the Choptank and St. Marys formations). Deltaic deposition began in the northern part of the embayment, as seen in the Calvert and Kirkwood formations and influenced environments west of the delta lobe. The center of deposition in the Salisbury embayment shifted southward into Virginia during late Miocene time (“Virginia St. Marys” beds) and continued there through the early and middle(?) Pliocene (Yorktown Formation); only the southeastern part of the embayment received sediments in the late Pliocene and early Pleistocene (uppermost part of the “Yorktown” Formation). Environments throughout this time were largely inner shelf (less than 60-m depths), and some marginal-marine to nonmarine intervals. The Albemarle embayment in North Carolina received largely biogenic and biochemical deposition during the early and early middle Miocene (Pungo River Formation). This was followed by uplift in the late middle and late Miocene. Clastic sedimentation started near the Miocene-Pliocene boundary and continued with minor hiatuses throughout much of the Pliocene and into early Pleistocene (Yorktown, uppermost part of the “Yorktown,” Duplin, Croatan, and Waccamaw formations). Some Pungo River strata formed in middle-shelf environments as deep as 100 m; most younger strata were deposited in inner-shelf environments (less than 60-m depth), but some in marginal-marine intervals.