Pliocene Age Research Articles

Chronostratigraphy of Upper Miocene-Quaternary volcanism in northern Costa Rica

The Santa Rosa ignimbritic plateau (Bagaces Formation) of Upper Miocene to Late Pliocene age (between 8 to 1.6 m.y. ago), the north of Costa Rica, consists of a pile of pyroclastic flow deposits with minor interbedded lava flows and terrigenous sediments overlain by several pumice flow deposits (volume ca. 50 km3 DRE): Rio Liberia pumice-flow deposit Formation (ca. 1.6 m.y. ago), Guayabo Pyroclastic Formation (between 1.5-0.6 m.y. ago), and Canas pumice-flow deposit (<1 m.y.), and topped by the recent volcanic centers of the Guanacaste chain (< 600 000 years ago). This succession has been sampled for K-Ar dating. Aditional rocks were collected from the region between the Arenal volcano (active since 1968) and the Monteverde andesitic plateau in the north (2-1 m.y. ago). There are also more examples of relatively recent volcanism in this region, for example the San Miguel dome (<0.7 m.y. ago) in the fore arc, and Los Perdidos complex (caldera and domes) of Upper Quaternary age (ca. 0.1 Ma), which is overlaped by the dormant Chato volcano (38-3.5 x 103 years old) near the actual volcanic front. The total volume of volcanic rocks erupted during the Quaternary is equivalent to about 900 +/- 150 km3 of dense rock. The volume of basaltic andesitic magma is several times larger than the volume of silicic magma erupted during the same period. The age of silicic volcanism precedes and overlaps with the age ofthe Quaternary andesitic volcanic front, which is largely younger than 600 000 years. This study demonstrates that in the geodynamical evolutin of the Southern Central America Orogen Volcanism is one of alternating periods of huge volcanic activity separated by periods of relative reposal.

Late Miocene lacustrine sedimentation in the Mytilinii Basin, Samos Island, Greece

The Mytilinii Basin, eastern Samos Island, Greece, is one of many basins that developed in southeastern Europe during the Upper Neogene. The oldest lacustrine portion is of Late Miocene age, and besides tuffs, includes bituminous limestones, marlstones, dolostones and porcelanites of the Pythagorion Formation, and the limestones and diatomites of the overlying Hora Beds. Younger sedimentary rocks of Turolian through Pliocene age partially covered the Pythagorion Formation and Hora Beds (PFHB). Diatom floras range from well preserved to highly corroded and from sparse to abundant. The main taxa include Cyclotella aegaea, C. aegaea var. pythagoria, an unidentified Cyclotella and Nitzschia frustulum, and less common Epithemia turgida, E. reichelti, Synedra ulna, Tryblionella granulata, Encyonema silesiaca, Diploneis ovalis and Cocconeis placentula. Chrysophyte cysts, Hydrobia molluscs and trace fossils occur sporadically. The environmental evolution of the PFHB can be divided into three major stages. Fluctuating shallow to deeper waters in a saline lake characterized Stage A. Saline lake and playa environments with evidence for frequent earthquake events in the form of convolute bedding, drape folds and brecciated sediments characterized Stage B. During Stage C, the lake may have partially or completely split into two separate lakes. In the southeast, a saline playa passed laterally into a deeper-water lake. Locally, fresher-water ponds occurred. Subsequently, a deeper, possibly oligotrophic lake developed. In contrast, a saline lake with abundant diatoms formed in the northwest of the basin, in which diatom blooms led to whiting events and deposition of carbonate laminae. Cyclotella dominated the early floras in this water body, with later assemblages being co-dominated by Cyclotella and Nitzschia frustulum, possibly reflecting seasonal changes. Sedimentation was terminated by uplift and (or) increasing aridity associated with the Messinian Salinity Crisis.

Latest Pacific Basin record of a bony-toothed bird (aves, Pelagornithidae) from the Pliocene Purisima Formation of California, U.S.A.

ABSTRACT Fossils of pelagornithids (bony-toothed birds) have been reported from strata of Paleocene to Pliocene age, and from every continent. The extreme fragility of pelagornithid bones has no doubt contributed to their geographically and temporally sporadic record, and thus it has been difficult to appreciate any long-term phylogenetic trends through geologic time for this group. We report a well-preserved partial humerus of the gigantic bird Pelagornis from the late Neogene Purisima Formation of central California. Due to its incompleteness, we refrain from naming a new species. This fossil is fortuitously bracketed by two ash beds, which have been correlated with volcanic rocks at 3.35 ± 0.05 Ma and 2.5 ± 0.2 Ma, indicating a middle to late Pliocene age for this fossil. This fossil extends the record of the pelagornithids in the Northeast Pacific, previously only known up until the early late Miocene (10–12 Ma). This fossil is the latest record of a pelagornithid for the Pacific Basin, and additionally represents the latest reliably dated pelagornithid record worldwide. This record suggests that the pelagornithids survived until the end of the Pliocene, and became extinct during the ocean restructuring and climatic upheavals that caused the demise of many other groups of marine vertebrates at that time.

A paleomagnetic and paleointensity study on Pleistocene and Pliocene basaltic flows from the Djavakheti Highland (Southern Georgia, Caucasus)

New paleomagnetic, rock-magnetic and paleointensity results obtained on samples from 23 basaltic lava flows belonging to four different flow sequences (Mashavera, Kvemo Orozmani, Zemo Karabulaki and Diliska) of Pleistocene and Pliocene age from the eastern Djavakheti Highland, in southern Georgia, are presented. Radiometric dating of these sequences yields ages between 1.8 and 2.18 Ma for Mashavera, 2.07 and 2.58 Ma for Zemo-Karabulakhi and 2.12 and 3.27 for Diliska. No radiometric ages are available for the Kvemo Orozmani sequence, which is considered to be coeval to the Mashavera sequence. Rock-magnetic experiments including measurement of thermomagnetic, hysteresis and IRM-acquisition curves suggest low-Ti titanomagnetite as main carrier of remanence, although a lower Curie-temperature component was also observed in several cases. Reversible and non-reversible curves were recorded in thermomagnetic experiments. Paleomagnetic analysis generally indicated the presence of a single component (mainly in the Mashavera sequence), but also two more or less superimposed components in some other cases. In 21 sites a characteristic component could be determined and all except one were characterised by normal-polarity directions. Flows from the Mashavera sequence had a rather steep inclination (73.1°). Nevertheless, a mean paleomagnetic direction of all four sequences is obtained ( D = 8.5°, I = 60.8°, N = 4, α 95 = 11.7°, k = 62.7) which agrees with the Plio-Quaternary directions obtained in previous studies in Georgia. The paleomagnetic pole obtained (latitude ϕ = 82.1°, longitude λ = 118.2°, A 95 = 8.0°, k = 240.7) agrees with the pole values of both the 0 Ma and the 5 Ma windows of the synthetic Eurasian polar wander path from Besse and Courtillot (2002). In order to analyse the behaviour of secular variation, the scatter of paleosecular variation of virtual geomagnetic poles of both the Mashavera flow and all 18 studied flows of Pleistocene age was calculated. It could be observed that both data-sets seem to fit well the expected scatter at latitude 41°N. Paleointensity experiments were carried out with the Coe modification of the Thellier method. Twenty-five out of 84 samples (30%) provided reliable paleointensity results. These successful results were mainly obtained in the Mashavera sequence. Most flows yielded paleointensity results in the 30–45 μT range, in accordance with expected Pliocene to present day intensities. Two flows, however, located near the top of the Mashavera sequence yield high paleointensity values around 60 μT. Anomalous paleointensity results in the upper-lying Mashavera flows together with the steep inclinations observed in that sequence, could perhaps signal the near onset of the Olduvai-Matuyama reversal.

A sequence stratigraphic framework for a narrow, current-swept continental shelf: The Durban Bight, central KwaZulu-Natal, South Africa

High resolution seismic lines from the inner and mid-shelf of the Durban Bight reveal an unprecedented view of the seismic stratigraphy of the central KwaZulu-Natal uppermost continental margin. Seven units are recognised from the shelf on the basis of their stratal architecture and bounding unconformities. These comprise four incompletely preserved sequences consisting of deposits of the highstand systems tract (Unit B), falling stage systems tracts (Unit C), the transgressive systems tract (Units A, D and G) and lowstand systems tracts (early fill of the incised valleys and strike diachronous prograding reflectors of Unit A). Seismic facies recognised as incised valley fills correspond to the lowstand and transgressive systems tracts. When integrated with published accounts of onshore and offshore lithostratigraphy and local sea level curves, we recognise an Early Santonian transgression (Unit A to Unit B), superimposed by uplift-induced pulses of forced regression. A Late Campanian relative sea level fall (Unit C) followed. Sediments of the Tertiary period are not evident on the Durban Bight shelf except for isolated incised valley fills of Unit D lying within incised valleys of Late Pliocene age. Overlying these are two stages of Pleistocene shoreline deposits of indeterminate age. Erosion concurrent with relative sea level fall towards the last glacial maximum shoreline carved a third set of incised valleys within which sediments of the Late Pleistocene/Holocene have infilled.

Pre-glacial and interglacial pollen records over the last 3 Ma from northwest Canada: Why do Holocene forests differ from those of previous interglaciations?

We synthesize pollen spectra from eleven dated stratigraphic sections from central and northern Yukon. Palaeomagnetic and tephra dating indicates the earliest assemblages, representing closed canopy Pinus and Picea forest, are middle-late Pliocene age. More open forest conditions, indicated by increased Poaceae and with evidence of permafrost, are dated at ca 3 Ma. While Pinus pollen is abundant at 3 Ma, it is reduced in records after 2.6 Ma, and subsequent Pleistocene interglacial forest records are repeatedly dominated by Picea, along with Alnus and small but significant amounts of Abies. Surface sample comparisons indicate that Abies was more widespread and abundant in past interglaciations than at present and that Middle-Pleistocene Picea– Abies forest grew in the northern Yukon Porcupine Basin, 500 km beyond modern Abies limits. In contrast, Pinus, which occurs today in southern and central Yukon, was not a significant component of these Pleistocene interglacial forests. Late-Holocene pollen assemblages with rare Abies and high Pinus are the most distinct in the past 2.6 Ma. Possible factors driving Holocene difference are paleoclimate, paludification, changes in megafaunal herbivory and an unusual fire regime. Anthropogenic burning is a factor unique to the Holocene, and if it is shown to be important in this case, it would challenge our notion of what constitutes boreal wilderness.

Pliocene–Pleistocene stratigraphy and macrofauna of the Farasan Islands, South East Red Sea, Saudi Arabia

The stratigraphy of the Farasan Islands (Pliocene–Pleistocene deposits) is established on the basis of a detailed study of six stratigraphic sections described and sampled in the field. Detailed examinations involve the microfacies analyses and identification of macrofossils makes it possible to determine two new informal formations, namely, from the base to the top: Esbah formation of Pliocene age and Farasan formation of Pleistocene age. The detected microfacies types of the studied samples are only carbonate facies and include five major types: mudstone, wackestone, packstone, floatstone and boundstone. No grains of quartz sand or igneous mineral were found in the islands. The nomenclature of the biostratigraphic units established in the present work is not intended to define world-wide zonal standards. It is only used to subdivide the sequence into biostratigraphic zones according to 137 macrofaunal species (78 bivalves, 56 gastropods and three echinoids). These biozones, namely: Lithophaga teres zone (Early Pliocene), Clypeaster reticulates–Laganum depressum zone and Chesapecten madisonius–Noetia limula interval zone are assigned to the Late Pliocene; meanwhile, Noetia limuli–Anadara ovalis interval zone and A. ovalis range zone are assigned to the Pleistocene age. The affinity of the Pliocene–Pleistocene fauna recorded from the Farasan Islands increase with time towards the Indo-Pacific realm. The identified bivalves and gastropods are dominated by the Indo-Pacific forms suggesting the connection of the Red Sea rift with the open Indian Ocean via the Gulf of Aden and Bab El Mandab in the latest Miocene and Early Pliocene.

Cenozoic post-breakup compressional deformation and exhumation of the southern Australian margin

We present results from a margin-wide analysis of the history of post-breakup Cenozoic compressional deformation and related exhumation along the passive southern margin of Australia, based on a regional synthesis of seismic, stratigraphic and thermochronological data. The Cenozoic sedimentary record of the southern margin contains regional unconformities of intra-Lutetian and late Miocene–Pliocene age, which coincide with reconfigurations of the boundaries of the Indo-Australian Plate. Seismic data show that post-breakup compressional deformation and sedimentary basin inversion—characterised by reactivation of syn-rift faults and folding of post-rift sediments—is pervasive from the Gulf St Vincent to Gippsland basins, and occurred almost continually since the early- to mid-Eocene. Inversion structures are absent from the Bight Basin, which we interpret to be the result of both the unsuitable orientation of faults for reactivation with respect to post-breakup stress fields, and the colder, stronger lithosphere that underlies that part of the margin. Compressional deformation along the southeastern margin has mainly been accommodated by reactivation of syn-rift faults, resulting in folds with varying ages and amplitudes in the post-rift Cenozoic succession. Many hydrocarbon fields in the Otway and Gippsland basins are located in these folds, the largest of which are often associated with substantial localised exhumation. Our results emphasise the importance of constraining the timing of Cenozoic compression and exhumation in defining hydrocarbon prospectivity of the southern margin.

Late Neogene volcanics and interbedded palaeosols near Mount Kenya

Abstract Two lava flows with interbedded palaeosols outcrop c. 40 km SW of Mount Kenya, near the Amboni River north of Mweiga, Kenya along the Nyeri/Thompson Falls Road, at 0°18′S; 37°48′E. These flows, overlain by loess, are principally trachyandesite and form the base of the Mount Kenya Volcanic Series which, in the early literature, is described as being of probable Miocene/Pliocene age. Here we report 39 Ar/ 40 Ar dates ( c. 5.2–5.5 Ma) and reversed magnetizations which establish a Latest Miocene to Earliest Pliocene age for these flows. Weathering characteristics of palaeosols interbedded with the lavas indicate generally dry climatic conditions during the Late Miocene, punctuated with humid events during the Pliocene and Quaternary. These Late Miocene–Quaternary palaeosols depict a relatively long and complex weathering history, followed by loess deposition. The palaeosols appear to have been episodically deflated, initially in phase with the deposition of lavas when surfaces were devoid of vegetation and later during periods of climatic deterioration when wind systems intensified. Such weathering histories within palaeosol profiles are also documented on nearby Mount Kenya, where well-weathered lower palaeosol horizons developed on Matuyama-age tills are overlain by much younger less-weathered horizons developed on Brunhes-age loess. The geochronology of Late Miocene lavas reported here provides maximum ages for weathering histories of palaeosols formed in a xeric tropical highland climate.

Spatial variability of recent sedimentation in Lake Ohrid (Albania/Macedonia)

Abstract. Lake Ohrid is likely of Pliocene age and thus commonly referred to as the oldest existing lake in Europe. In this study spatial variability of recent sediment composition is assessed using &gt;50 basin wide distributed surface sediment samples. Analysis of biogeochemical bulk parameters, selected metals, pigment concentrations as well as grain size distributions revealed a significant spatial heterogeneity in surface sediment composition. It implies that sedimentation in Lake Ohrid is controlled by an interaction of multiple natural and anthropogenic factors and processes. Major factors controlling surface sediment composition are related to differences in geological catchment characteristics, anthropogenic land use, and a counterclockwise rotating surface water current. In some instances processes controlling sediment composition also seem to impact distribution patterns of biodiversity, which suggests a common interaction of processes responsible for both patterns.

Fossilisation of a silica diagenesis reaction front on the mid-Norwegian margin

The diagenetic transformation of biogenic silica from opal-A to opal-CT was recognised on seismic reflection data over an area of 78 × 10 3 km 2 on the mid-Norwegian margin. The opal-A/CT diagenetic boundary appears as a positive, high amplitude reflection that generally cross-cuts the hosting stratigraphy. We demonstrate that it is not a sea bottom simulating reflection (BSR) and also that is not in thermal equilibrium with the present day isotherms. We present arguments that three styles of deformation associated with the opal-A/CT reflection – polygonal faulting, regional anticlines and synclines and differential compaction folding – indicate that the silica diagenesis reaction front is fossilised at a regional scale. Isochore maps demonstrate the degree of conformity between the opal-A/CT reflection and three seismic horizons of Late Miocene to Early Pliocene age that potentially represent the paleo-seabed when ‘fossilisation’ of the reaction front took place. The seismic interpretational criteria for recognition of a fossilised diagenetic front are evaluated and the results of our study are integrated with previous studies from other basins of the NE Atlantic in order to determine if the arrest of silica diagenesis was diachronous along this continental margin.

A GEOARCHAEOLOGICAL STUDY OF THE ANCIENT QUARRIES OF SIDI GHEDAMSY ISLAND (MONASTIR, TUNISIA)

Amongst a large number of ancient quarries scattered along the North African coast, those at Sidi Ghedamsy (Monastir, Tunisia) have supplied building stones of Pliocene age. Two lithofacies have been distinguished in the quarry faces: (i) fine sandy limestone, which has been used in the construction of Roman and Arabic monuments; and (ii) porous and coarse limy sandstone, which is of bad quality for construction. Laboratory analysis results confirm that the exploitation of stone in antiquity was well focused on the levels containing the first type. This is confirmed by geotechnical tests, which show that the fine sandy limestone is harder and less porous than the coarse limy sandstone. Extraction of these stones began in the Roman period. The Romans exploited the quarries using steel tools that permitted the extraction of blocks from several levels. In the eighth century, Arabic quarry workers continued the stone extraction using the same technique, but they produced blocks of small and medium size. Statistical measurements have been done on the quarry faces and on the walls of the Ribat in order to understand the degree of conformity between the dimensions of the extracted blocks and those used for building, and ultimately to attempt to date the quarries and the construction of the Ribat.

The Tropics as Reservoir of Otherwise Extinct Mammals: The Case of Rodents from a New Pliocene Faunal Assemblage from Northern Venezuela

We report a new vertebrate assemblage from the Pliocene Vergel Member of the San Gregorio Formation in northwestern Venezuela, which includes Crocodylia and Testudines indet., toxodonts, at least four species of xenarthrans of the Dasypodidae, Pampatheriidae, Glyptodontidae and Megatheriidae, and rodents. The last are Cardiatherium, cf. Caviodon (Hydrochoeridae), Neoepiblema (Neoepiblemidae), and what is here described as a new genus of a low-crowned octodontoid. cf. Caviodon is the first cardiomyine for northern South America. The rodent assemblage resembles in its ecological composition those of the late Miocene (Huayquerian) from the “Mesopotamian” of Argentina and the Acre region in Brazil, with partially overlapping systematic composition. The stratigraphic position of the San Gregorio Formation and mammals other than caviomorphs suggest a late Pliocene age for these sediments, implying the endurance of rodent taxa beyond their biochron in southern South America.

CLAY MINERALOGY AND LA-ICP-MS DATING OF SUPERGENE U-Cu NONTRONITE-BEARING MINERALIZATION AT NABBURG-WOLSENDORF, SOUTHEASTERN GERMANY

Nontronite has been reported from a wide range of mineral deposits on the continent and in marine environments, commonly associated with basic igneous rocks, base-metal sulfides, Fe sulfides, Fe–Mn oxide–hydroxides and gold. This smectite-type phyllosilicate forms during the low-temperature alteration of sulfide-bearing parent material. In contrast, nontronite from vein-type fluorite mineralization at Nabburg–Wolsendorf, in southeastern Germany, developed in a sulfur-deficient environment under supergene conditions associated only with uranyl phosphates, mainly uranocircite. It was investigated by XRD, IR spectrometry, XRF, CEC analysis and SEM–EDX. Phyllosilicates and uranium mica are coeval and of Pliocene age. A U–Pb age of 4.0 ± 0.1 Ma was determined using Laser-Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA–ICP–MS). Some younger ages cluster, possibly indicating a multiphase history of crystallization. Both minerals came into existence at temperatures around 30°C when the region underwent pervasive chemical weathering under humid tropical climatic conditions. Uranium was derived from the decomposition of uraninite and coffinite in the veins and from the weathering of U-bearing accessory minerals in the granite, whereas the major elements and barium in uranocircite originated from the alteration of the granitic country-rocks. The vein minerals, e.g. , fluorite acted solely as bedrock, but were not involved in this supergene mineralization. Nontronite–uranocircite mineralization can develop in almost all granitic terranes under supergene conditions like those described. The log Al3+/H+ 3 and log Ca2+/H+ 2 values are decisive as to whether nontronite, kaolinite or green opal (nontronite plus opal) comes into existence. Both types of supergene alteration minerals, kaolinite and green opal, developed side-by-side with the nontronite–uranocircite mineralization during the Neogene in this area. Uranium–lead dating using the LA–ICP–MS technique serves to constrain the age of this mineralization.

Structural controls on Quaternary deepwater sedimentation, mud diapirism, and hydrocarbon distribution within the actively evolving Columbus foreland basin, eastern offshore Trinidad

Eastward migration of the Caribbean plate relative to the South American plate has caused lithospheric loading along the northern margin of South America, which is recorded by an 1100-km-long foreland basin which is oldest in the west (Maracaibo basin, 65–55 Ma) and youngest in the east (Columbus basin, eastern offshore Trinidad, 15–0 Ma). The Orinoco River has been the primary source of sediment for the basin since early Miocene. We have integrated approximately 775 km of deep-penetration 2D seismic lines acquired in the area of eastern offshore Trinidad as part of the 2004 “Broadband Ocean-Land Investigations of Venezuela and the Antilles arc Region” (BOLIVAR) project, 8000 km 2 of shallow industry 3D seismic data, and published industry well data from offshore eastern Trinidad. Active mud diapirism in the Columbus basin is widespread and is related to overthrusting and tectono-sedimentary loading of upper Miocene-lower Pliocene age mud. Analysis of the shallow 3D seismic data reveals the presence of extensive gravity-flow depositional elements on the Columbus basin slope and the deepwater area. These stacked gravity-flow deposits are characterized by mass-transport deposits at the base, turbidite frontal-splay deposits, leveed-channel deposits, and capped by fine-grained condensed-section deposits. Exploration targets in the deepwater area are located towards the center of the Columbus basin, where northeast-trending fault-propagation folds are important Plio-Pleistocene trap-forming elements. Deep basin wells drilled in recent years have proven that turbidites were transported into the deepwater Columbus basin during the Plio-Pleistocene. Analysis of these well results suggests that a deeper oil charge is present within the deepwater Columbus basin area. The primary uncertainty for this variable hydrocarbon system is whether fault or diapiric pathways connect or divert the petroleum charge at depth with shallower reservoir rocks.

The extinct baleen whale fauna from the Miocene-Pliocene of Belgium and the diagnostic cetacean ear bones

Significant advances of our understanding of the evolutionary history of baleen whales have been gained by the recent focus on the extinct baleen bearing groups. However, a historically important collection from the middle Miocene to Pliocene of Antwerp, Belgium, comprising a third of all described species of early baleen-bearing mysticetes, has proven difficult to include in modern studies. These species are surrounded by taxonomic confusion because they were based on non-comparable composite material. The Belgian species are revised here with a designation of comparable lectotypes. The best-represented comparable element is the periotic bone that surrounds the inner ear. The periotic is shown to have significant diagnostic value, like that of teeth in many extinct mammals. Of the Belgian mysticetes, the genera Amphicetus and Herpetocetus are retained. Plesiocetus is retained and referred to Balaenopteridae, while Idiocetus is tentatively referred to Balaenidae. Burtinopsis, Heterocetus, Isocetus and Mesocetus are considered nomen dubia. Interestingly, all the major extinct mysticete groups known from the west-North Atlantic are represented in the Belgian fauna, although with different relative diversities, while no species seem to fall outside of these families. Diorocetidae, Aglaocetidae and Pelocetidae were thus well established with an east-west North Atlantic distribution by the Middle Miocene, indicating that these families originated in the Oligocene to Early Miocene. Cetotheriidae (sensu stricto) is represented by only one species that is probably Pliocene in age, suggesting a later dispersal to the east-North Atlantic region.

A paleoclimate record with tephrochronological age control for the last glacial-interglacial cycle from Lake Ohrid, Albania and Macedonia

Lake Ohrid is probably of Pliocene age, and the oldest extant lake in Europe. In this study climatic and environmental changes during the last glacial-interglacial cycle are reconstructed using lithological, sedimentological, geochemical and physical proxy analysis of a 15-m-long sediment succession from Lake Ohrid. A chronological framework is derived from tephrochronology and radiocarbon dating, which yields a basal age of ca. 136 ka. The succession is not continuous, however, with a hiatus between ca. 97.6 and 81.7 ka. Sediment accumulation in course of the last climatic cycle is controlled by the complex interaction of a variety of climate-controlled parameters and their impact on catchment dynamics, limnology, and hydrology of the lake. Warm interglacial and cold glacial climate conditions can be clearly distinguished from organic matter, calcite, clastic detritus and lithostratigraphic data. During interglacial periods, short-term fluctuations are recorded by abrupt variations in organic matter and calcite content, indicating climatically-induced changes in lake productivity and hydrology. During glacial periods, high variability in the contents of coarse silt to fine sand sized clastic matter is probably a function of climatically-induced changes in catchment dynamics and wind activity. In some instances tephra layers provide potential stratigraphic markers for short-lived climate perturbations. Given their widespread distribution in sites across the region, tephra analysis has the potential to provide insight into variation in the impact of climate and environmental change across the Mediterranean.

Diatom-based correlation of early to mid-Pliocene drillcores from the southwestern Ross Sea, Antarctica

The ANDRILL AND-1B drillcore in southern Victoria Land Basin, Antarctica recovered an upper Miocene to early Pleistocene continental shelf stratigraphic section, including a spectacular Pliocene and Pleistocene sequence of alternating diamictite and diatom-rich sediments. This punctuated sequence reflects variation between glacial sediments deposited by ice advance over the site and open-marine diatom productivity and sedimentation. An early Pliocene age for the base of diatom-rich sediment is constrained through integrated diatom biostratigraphy and magnetostratigraphy. The presence of marine diatom Shionodiscus tetraoestrupii from the top of the core to 583.64mbsf indicates the lowest diatom-bearing sediments are younger than 5Ma. This drillcore provides important new chronostratigraphic control for paleoenvironmental changes also recorded in three drillcores from the western coast of the McMurdo Sound area, DVDP-10 and -11 in Taylor Valley and CIROS-2 from the seaward edge of Ferrar Fjord. The refined continental shelf biostratigraphy developed from AND-1B provides a framework for regional correlation to understand better the timing and character of large paleoenvironmental changes in the western Ross Sea that involve the history of the West Antarctic Ice Sheet (WAIS). Multivariate analysis, along with traditional biostratigraphic approaches, enables the correlation and comparison of coeval intervals in these drillcores. A composite stratigraphic sequence from these four cores suggests the early and mid-Pliocene Ross Sea experienced extended intervals of open-marine conditions with minimal sea-ice cover and high diatom production and sedimentation. This new information provides important constraints on Antarctic paleoclimate and ice sheet history during an important interval when global climate was warmer than today. The history preserved in these four drillcores will be an important tool to guide and test future ice sheet and climate models.

Integrated stratigraphy of the Middle to Late Pliocene upper Miyazaki Group, southern Kyushu, Southwest Japan

Neogene sedimentary deposits are present in the Miyazaki region, southern Kyushu, on the Pacific side of southwestern Japan. The upper part of the Miyazaki Group, exposed in the Tsuma–Takanabe region of northern Miyazaki, is divided into the Tsuma, Sadowara, and Takanabe formations, in ascending order, and contains a planktic foraminiferal and calcareous nannofossil record of Pliocene events of the mid-latitude northwestern Pacific. The geological age of these units is based on magneto- and biostratigraphy. Five calcareous nannofossil datum horizons are recognized: the last occurrence (LO) of Reticulofenestra pseudoumbilicus, the termination of acme zone II of Reticulofenestra minutula var. C, the LO of R. minutula var. B, calcareous nannofossil datum plane A, and the termination of acme zone I of R. minutula var. C. Six planktic foraminiferal bioevents are also recognized: a coiling direction change, from sinistral to dextral, in the genus Pulleniatina; the first occurrence (FO) of Globorotalia crassaformis; the LOs of Globorotalia margaritae, Sphaeroidinellopsis seminulina, and Dentoglobigerina altispira; and the FO of Neogloboquadrina asanoi. The presence of two calcareous nannofossil bioevents, Datum A and the termination of acme zone I of R. minitula var. C, suggests that the normal and reversed polarity intervals of the upper part of the Takanabe Formation correspond to Chron C2An.1n (latest Gauss Normal Epoch) and Chron C2r.2r (earliest Matuyama Reversed Epoch), respectively. Based on combined floral and faunal data and magnetostratigraphic chron boundaries from the ATNTS2004, the upper part of the Miyazaki Group is Middle to Late Pliocene in age.

Variation in fluid contacts in the Azeri field, Azerbaijan: sealing faults or hydrodynamic aquifer?

Abstract The Azeri field in the South Caspian Sea, offshore Azerbaijan, is a periclinal anticline 20 km in length containing multiple stacked reservoirs of Pliocene age. Appraisal wells that were drilled at the eastern end of the structure identified multiple oil–water contacts and fluid pressure gradients in both of the principal reservoirs, the Pereriv B and D. At the time, these data were interpreted to indicate the presence of compartments at the eastern end of the field as a result of sealing faults within the aquifer. This local compartmentalization seemed to be in marked difference to the majority of the field where pressure connectivity had been observed. A new analysis of the pressure data for the Pereriv B shows that aquifer pressures at sea‐level datum define a simple water potential gradient. As a result of this, the oil–water contact in this reservoir is gently inclined towards the NNE. The precise inclination and orientation of the oil–water contact has been determined geometrically using the depths and coordinates of free-water levels and oil–water contacts from around the field. The best-fit inclined oil–water contact for the Pereriv B also provides a good fit to the contact observed from seismic amplitudes. The new analysis provides a more optimistic view of reservoir connectivity, and the conceptual geological model for the eastern end of the field is now consistent with observations made in the rest of the Azeri field.