Abstract The Rioni Basin is an underexplored petroliferous basin located at the Georgian margin of the Black Sea flanked by two folded belts (the Greater Caucasus and the Achara–Trialet Belt). Whereas the stratigraphy of the northern onshore Rioni Basin has elements which are common with that of the offshore Shatsky Ridge, the southern onshore Rioni Basin segment is both stratigraphically and structurally akin to the offshore Gurian folded belt in the eastern Black Sea. In the northern basin segment, the existing oil fields (East and West Chaladidi) and an undeveloped oil discovery (Okumi) are related to either post-salt or pre-salt antiformal traps in detachment folds or in poorly understood stratigraphic pinchouts beneath a regional Upper Jurassic evaporite sequence. In the southern Rioni Basin, the oil in existing fields has either anticlinal four-way closures (Supsa) or a subthrust trap (Shromisubani) related to the leading edge of the north-vergent Achara–Trialet folded belt. Despite the long history of petroleum exploration in the Rioni Basin, these proven plays are not fully understood and systematically explored using modern technology. The existence of an Upper Jurassic regional evaporite seal highlights the possibility of pre-salt plays in the northern part of the basin.

The Paleocene–early Eocene interval is punctuated by a series of transient warming events known as hyperthermals that have been associated with changes in the carbon isotope composition of the ocean-atmosphere system. Here we present and discuss a detailed record of calcareous nannofossil and foraminiferal assemblages coupled with high-resolution geochemical, isotopic, and environmental magnetic records across the middle Ypresian at the Contessa Road section (Gubbio, Italy). This allows characterization of the Eocene Thermal Maximum 3 (ETM3, K or X) and recognition of four minor (I1, I2, J, L) hyperthermals. At the Contessa Road section, the ETM3 is marked by short-lived negative excursions in both δ 13 C and δ 18 O, pronounced changes in rock magnetic properties, and calcium carbonate reduction. These changes coupled with the moderate to low state of preservation of calcareous nannofossils and planktonic foraminifera, higher FI and agglutinated foraminifera values, along with a lower P/(P + B) ratio (P—planktonic; B—benthic) and coarse fractions provide evidence of enhanced carbonate dissolution during the ETM3. A marked shift toward warmer and more oligotrophic conditions has been inferred that suggests unstable and perturbed environmental conditions both in the photic zone and at the seafloor.

The Shatsky Rise is an oceanic plateau consisting of three main massifs that were constructed in the Pacific Ocean by intense volcanism during the Late Jurassic to Early Cretaceous. In order to explore the sources of this oceanic plateau, we present noble gas compositions from fresh quenched glasses cored by ocean drilling at Integrated Ocean Drilling Program Site U1347 on the Tamu Massif and Site U1350 on the Ori Massif. The studied glasses are normal-type basalts, the most abundant of four types of basalts defined by trace element compositions. Possible disturbances of noble gas compositions by posteruption radiogenic ingrowth in aged glasses are assessed by extraction of gases from glass vesicles by stepwise crushing. The 3 He/ 4 He ratios in glasses from Site U1347 are lower than atmospheric 3 He/ 4 He, presumably owing to magma degassing coupled with radiogenic ingrowth of 4 He. In contrast, glasses from Site U1350 exhibit a limited range of 3 He/ 4 He (5.5–5.9 Ra). Uniform 3 He/ 4 He cannot be achieved if gases in glass vesicles have been affected by secondary contamination or posteruption radiogenic ingrowth. Therefore, the uniform 3 He/ 4 He in the normal-type basalts from Site U1350 is ascribed to their source characteristics. Relatively low 3 He/ 4 He among oceanic basalts suggests the involvement of recycled slab material in the source of the normal-type basalts. However, the depleted radiogenic isotope signatures are inconsistent with recycled slab being a distinct melting component. Instead, we propose that the normal-type basalts of the Shatsky Rise were sourced from a domain where subducted fertile material is dispersed in the mantle.

Oceanic plateaus are formed by a large volume of basaltic rocks on top of the oceanic lithosphere. Alteration of these basalt lava piles leads to significant chemical element exchanges between mantle and oceans that can strongly influence chemical budget. Here we report boron (B), chlorine (Cl), and other element concentrations in basalt samples from the Shatsky Rise to define alteration processes and to estimate the significance of oceanic plateaus in storing these elements. Sampling includes 121 basaltic lavas and 92 fresh glasses collected at various depths from Holes U1346A, U1347A, U1349A, and U1350A during Integrated Ocean Drilling Program Expedition 324. Loss on ignition (LOI) results indicate that alteration affected basalts from the summit sites (U1346 and U1349) more deeply than those from the flank sites (U1347 and U1350). The positive correlations between B, K, and LOI observed in the basalts indicate that low-temperature seawater-derived alteration was the predominant process affecting Shatsky Rise basalts. This is confirmed by the elevated B/K and modest Cl/K ratios of these altered basalts relative to the fresh glasses. In addition, B concentrations in the summit basalts (~132 ppm) are significantly higher than those in normal altered oceanic crust and are likely related to the presence of illite. This suggests that the Shatsky Rise oceanic plateau may be an important sink for B in the Pacific oceanic crust.

It has been suggested that the Shatsky Rise oceanic plateau formation began simultaneously with a reorganization of spreading at a triple junction bordering the northern Pacific plate, and this coincidence has led to speculation about the connections between the two events. We present new marine geophysical data that constrain the seafloor spreading history of the Pacific-Izanagi-Farallon triple junction just before the birth of the Shatsky Rise. Bathymetric data reveal en echelon, abandoned spreading centers trending northwest-southeast located adjacent to the southwest flank of the Shatsky Rise. Magnetic anomalies and bathymetry are interpreted to indicate that segments of the Pacific-Farallon Ridge near the triple junction propagated northwest from chron M23 (153 Ma) to chron M22 (151 Ma) during a spreading ridge reorganization at the edge of a likely microplate. Our detailed examination of bathymetric and magnetic anomaly lineations also shows that the strike of the Pacific-Izanagi Ridge changed gradually on the west side of the triple junction around chron M22. Our observations indicate that the plate boundary reorganization began several million years before the formation of the Shatsky Rise, implying that the eruption of the plateau did not cause the reorganization.

The Shatsky Rise is one of the largest oceanic plateaus, a class of volcanic features whose formation is poorly understood. It is also a plateau that was formed near spreading ridges, but the connection between the two features is unclear. The geologic structure of the Shatsky Rise can help us understand its formation. Deeply penetrating two-dimensional (2-D) multichannel seismic (MCS) reflection profiles were acquired over the southern half of the Shatsky Rise, and these data allow us to image its upper crustal structure with unprecedented detail. Synthetic seismograms constructed from core and log data from scientific drilling sites crossed by the MCS lines establish the seismic response to the geology. High-amplitude basement reflections result from the transition between sediment and underlying igneous rock. Intrabasement reflections are caused by alternations of lava flow packages with differing properties and by thick interflow sediment layers. MCS profiles show that two of the volcanic massifs within the Shatsky Rise are immense central volcanoes. The Tamu Massif, the largest (~450 km × 650 km) and oldest (ca. 145 Ma) volcano, is a single central volcano with a rounded shape and shallow flank slopes (<0.5°–1.5°), characterized by lava flows emanating from the volcano center and extending hundreds of kilometers down smooth, shallow flanks to the surrounding seafloor. The Ori Massif is a large volcano that is similar to, but smaller than, the Tamu Massif. The morphology of the massifs implies formation by extensive and far-ranging lava flows emplaced at small slope angles. The relatively smooth flanks of the massifs imply that the volcanoes were not greatly affected by rifting due to spreading ridge tectonics. Deep intrabasement reflectors parallel to the upper basement surface imply long-term isostasy with the balanced addition of material to the surface and subsurface. No evidence of subaerial erosion is found at the summits of the massifs, suggesting that they were never highly emergent.

The Shatsky Rise, located in the northwest Pacific Ocean, is one of the largest oceanic plateaus. The origin and evolution of the oceanic plateaus are unclear because these features are remote and poorly imaged with geophysical data. Marine multi-channel seismic (MCS) data were collected over the Shatsky Rise to image its upper crustal structure. These data have the potential to improve understanding of the processes of basaltic volcanism and the formation and evolution of oceanic plateaus by providing direct insights into the geometry and distribution of igneous eruptions. In contrast to sedimentary settings, it is often difficult to interpret deeper layers within basaltic crust because of rugged layering and scattering. Reflections in igneous crust are characterized by poor lateral continuity compared with marine sediments and often by weak impedance contrasts, resulting in a lower signal-to-noise ratio and a more challenging interpretation. In this paper we apply the two-dimensional (2-D) anisotropic continuous wavelet transform (CWT) method to improve interpretations of MCS data from the Shatsky Rise oceanic plateau. Applying the transform to the time domain MCS profiles with appropriate values of wavelength and period produces new images with enhanced continuity of reflectors and reduced amplitudes of incoherent noise at different periods. The analysis of the results obtained by using 2-D CWT on the MCS data over the Tamu massif part of the Shatsky Rise also helps reveal features such as dome-like bulges possibly associated with lava intrusion and faults in the deeper part of the crust associated with volcanic rock. These were not readily seen in the original seismic images, but the suppression of random noise and other signals with low coherence makes their interpretation possible. These and similar results provide new insights into the complexity of the igneous processes forming the Tamu massif.

The eruptive history of the Shatsky Rise, a large oceanic plateau in the northwestern Pacific Ocean, is poorly understood. Although it has been concluded that the Shatsky Rise volcanic edifices erupted rapidly, there are few solid chronological data to support this conclusion. Similarly, the Shatsky Rise is thought to have formed near the equator, but paleolatitude data from the plateau are few, making it difficult to assess its plate tectonic drift with time. To understand the formation history of this oceanic plateau, paleomagnetic measurements were conducted on a total of 362 basaltic lava samples cored from the Shatsky Rise at 4 sites (U1346, U1347, U1349, and U1350) during Integrated Ocean Drilling Program Expedition 324. Examining changes in paleomagnetic inclinations, we gain a better understanding of eruptive rates by comparison of observed shifts in inclination with expected paleosecular variation. At three sites (U1346, U1347, and U1349) little change in paleomagnetic directions was observed, implying that the cored sections were mostly erupted rapidly over periods of <~100–200 yr. Only Site U1350 displayed directional changes consistent with significant paleosecular variation, implying emplacement over a period of ~1000 yr. The paleomagnetic data are consistent with the idea that the Shatsky Rise igneous sections were mostly emplaced rapidly, but there were some time gaps and some fl ank locations built up more slowly. Because paleosecular variation was inadequately sampled at all the Shatsky Rise sites, paleolatitudes have large uncertainties, and because of the equatorial location, magnetic polarity is also uncertain. All sites yield low paleolatitudes and indicate that the Shatsky Rise stayed near the equator during its formation. Given that the locus of magmatism moved northward relative to the Pacific plate while staying near the equator, the Pacific plate must have drifted southward relative to the spin axis during the emplacement of the plateau.

Fresh basalts from the Ontong Java Plateau (OJP) and the Shatsky Rise show lithium enrichments comparable to those of mid-oceanic ridge basalts (MORBs) and ocean island basalts (OIBs), with Li contents being significantly higher at a given MgO content. The Li isotopic compositions of the Shatsky Rise basalts (δ 7 Li = +6‰ to +7‰) are at the higher end of the range exhibited by OIBs, whereas OJP basalts (δ 7 Li = +3‰ to +5‰) have Li isotopic compositions similar to MORBs. Among all the basalts from the two oceanic large igneous provinces (LIPs), one sample from the Shatsky Rise is isotopically enriched (e.g., low 143 Nd/ 144 Nd and 176 Hf/ 177 Hf) and has higher K/Ti and lower La/Nb than the other samples. Relationships between δ 7 Li and K/Ti, La/Nb, and Rb/Nb of this sample indicate that it may have been affected by mantle that was metasomatized by slab-derived fluids. Apart from this isotopically enriched sample, δ 7 Li values of basalts from the two oceanic LIPs are positively correlated with K/Ti and Rb/Nb. Obvious linear relationships exist between δ 7 Li and Yb/Li, Y/Li, and Dy/Li for samples from the Shatsky Rise. These geochemical relationships can be explained by magmatic assimilation of hydrothermally influenced crust. The high δ 7 Li values of the Shatsky Rise basalts imply that the degree of assimilation is high because shallow magma chambers allow greater assimilation of hydrothermally influenced crust. In contrast, the low δ 7 Li values of the OJP samples may indicate they have undergone little assimilation as compared with the Shatsky Rise basalts.