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On August 6, 2021, the chief researcher of the IO RAS, Doctor of Geological and Mineralogical Sciences, Professor Ivar Oskarovich Murdmaa turned 90 years old. The main focus of I.O. Murdmaa is the study of bottom sediments of seas and oceans, their lithology, mineralogy, deposition processes, facies and formations, the theory of oceanic sedimentogenesis. He first distinguished marine volcanoterrigenous sediments and described the facies variability of modern sediments of island arcs. Ivar Murdmaa is known for his studies in mineralogy of oceanic sediments, processes of pelagic sedimentogenesis and associated iron-manganese nodules formation. Studying sediment formation in rift zones of mid-ocean ridges, he identified a new genetic type of sediments named edaphogeonus sediments, elaborated mineralogical criteria for their recognition and formation processes. In recent years I.O. Murdmaa is actively developing the theoretical concept of "sedimentosphere", paying special attention to a new direction – the study of the erosion-accumulative activity of bottom currents and the formation of contourites.

Lithological and micropaleontological (planktonic and benthic foraminifers, diatoms) studies in four sediment cores revealed major patterns of lithostratigraphy and biostratigraphy of contourites and gravitites in the uppermost sediment layer within the depth range 3500–4300 m of the northern sector of the Patagonian continental slope contourite system. It is ascertained that in conditions of low terrigenous material supply from the land and high, although variable bottom contour current velocities of waters of Antarctic origin, hemipelagic calcareous nanno-foraminiferal ooze deposited in the Holocene over middleupper Pleistocene contourites in the southern part of the study area (cores AI–2609, AI–2610). The Holocene calcareous surface layer is absent in the northern part of the study area (cores AI–2611, AI–2612). Middle-Upper contourites and gravitites are unevenly enriched in diatoms and radiolarians here, up to formation of slightly siliceous-terrigenous diatomaceous mud. Reworked Neogene foraminifers and diatoms evidence for erosion of Neogene deposits bottom currents and gravity flows.

Several features probably formed by contour bottom currents were recognized on the Rio Grande Rise by high-resolution seismic survey in the transatlantic profiles of the #32 and #52 cruises of R/V Akademik Ioffe carried out by the Shirshov Institute of Oceanology, Russian Academy of Sciences. The deposits of mixed turbidite–contourite sedimentary systems near the base of its southern and northern slopes seem to be formed as a result of the interaction of downslope gravity flows and the along-slope deep-water Lower Circumpolar Water + Weddell Sea Deep Water current. Sediment waves and disputable small plaster contourite drifts are probably formed by circulation of the Antarctic Intermediate Water in the Cruzeiro-do-Sultrough at the top of the rise.

The Ioffe Drift located in the Antarctic Bottom Water pathway from the Vema Channel to the Brazil Basin provides a suitable site to study past variations in bottom contour currents and their contribution to erosion and accumulation of deep-sea sediments. Our previous study of the reference core AI-2436 from the drift summit (Ivanova et al., 2016a) documented the stratigraphic sequence of the uppermost part of the sedimentary cover ranging from the recent through upper Pliocene, the reduced thickness and/or absence of biostratigraphic zones, and the occurrence of several hiatuses. Here, we provide the multi-proxy biostratigraphic, magnetic susceptibility (MS), color reflectance and X-ray fluorescence (XRF) data in the sediment cores AI-3318 from the summit and AI-3316 from the NE slope of the Ioffe Drift. The new data report numerous long- and short-term stratigraphic gaps over the last ~3 Ma. An interval of specific high-amplitude peaks representing abrupt changes in volume MS and XRF variability is identified from 2.51/2.59 to ~1.9 Ma which can likely serve as a regional stratigraphic benchmark in the future studies of deep-sea contourites. The correlation of three sediment records from the drift suggests that the most pronounced series of hiatuses, associated with enhanced AABW flow intensity occurred from 1.6 to ~0.81 Ma (i.e. roughly, during the Mid-Pleistocene Transition), and from 2.51/2.59 to ~1.9 Ma (i.e. covers the onset of the modern-type deep-water circulation in the South Atlantic (Turnau and Ledbetter (1989)). Comparison of the studied sediment records with DSDP Site 516 reveals reduced thickness of all recovered biostratigraphic zones and more often occurrence of hiatuses in the Ioffe Drift than on the Rio Grande Rise suggesting more vigorous contour currents in the former area.

Herein we provide information on the sedimentological and paleoceanographic research on the Argentine Patagonian continental slope during cruise 79 of the R/V Akademik Mstislav Keldysh in March 2020. The preliminary scientific results are discussed.

The paper presents information on geochemical and mineralogical investigations of sedimentary rocks carried out in April 2019 in the Northern Morocco. A set of data on mineral and chemical composition of the Late Miocene deposits was obtained in the region of the contourite paleo-channel. The obtained results improved lithological description of the studied outcrops and confirmed the significant role of bottom currents in formation of the Late Miocene deposits of the southern Rifian corridor.

Series of two papers are dedicated to study of erosional and depositional processes in the northern part of the previously distinguished contourite system on the Patagonian continental slope between 46-42° at a water depth range of 2100-5200 m. The first paper is focused on interpretation of high-resolution seiscmoacoustic data collected using the parametric echo-sounder SES 2000 deep with acoustic penetration of 60 mbsf. Analysis of seismic data revealed seismic facies of contourites and gravitites as well as erosional features formed under the influence of gravity flows (gravity-driven processes) moving downslope through the canyon system. It was demonstrated that gravitites deposited by gravity flows represent a source of sediment material for contourite drift formation. Domination of erosion over deposition in the study area might be explained by the intense dynamics of bottom waters, including contour currnets, internal waves, benthic storms and gravity flows.

The study of six sediments cores from the Ioffe Drift area documented the reduced thickness and/or absence of biostratigraphic zones and the occurrence of several hiatuses. The multi-proxy biostratigraphic, magnetic susceptibility (MS), color reflectance and X-ray fluorescence (XRF) data from five of the six cores reported numerous long- and short-term stratigraphic gaps over the last ~3–4 Ma. The correlation of sediment records from the drift suggests that the most pronounced series of hiatuses, associated with enhanced Lower Circumpolar Deep Water (LCDW) flow intensity, occurred from 2.51/2.59 to ~1.9 Ma (i.e., the onset of the modern-type deep-water circulation in the South Atlantic). This interval of specific high-amplitude peaks representing abrupt changes in volume MS and chemical composition variation may well serve as a regional stratigraphic benchmark in future studies of deep-sea contourites. A temporary intensification of the LCDW flow, probably due to its increased production in the Antarctic, led to deep erosion, ultimately resulting in long-term hiatuses and hence contributing to the enormously compressed Upper Pliocene–Middle Pleistocene section of the drift. The interval from 1.47/1.6 to 0.81 Ma, embracing the Mid-Pleistocene Transition, contains the longest stratigraphic gaps, up to ~1 Ma in some cores. Comparison of the studied sediment records to DSDP Site 516 reveals the reduced thickness of all the recovered biostratigraphic zones and evidence of more frequent hiatuses in the Ioffe Drift than on the neighboring Rio Grande Rise, suggesting more vigorous contour currents in the former.

The study of geomorphology and seismic structure of the Ioffe Drift area was undertaken on the basis of high-resolution sub-bottom profiling data, an old low-resolution single-channel seismic profile, and single-beam and multibeam bathymetric data. The drift occupies the central part of a tectonic ridge related to the Florianopolis (Rio Grande) Fracture Zone. The drift’s morphology and orientation, which are significantly controled by the basement relief, were also strongly affected by bottom currents. The acoustic penetration of 60–80 m allowed detailed investigation of only the upper part of the drift deposits. Four seismic units were identified in the acoustic structure of the drift. Changes in the seismic characteristics of the units represent changes in bottom conditions during the drift’s formation from tranquil to highly dynamic. Evidence of drastic erosion permeates the entire structure of the drift. The major unconformities separating the units correspond to the most prominent erosional events in the drift’s history. The absence of data does not allow the age of these unconformities to be identified. The correlation between seismic records collected from the drift and from the Rio Grande Rise demonstrates the lower impact of bottom currents on sedimentation across the rise.

The comprehensive analysis of a large dataset of seismic, lithological, geochemical and micropaleontological data has shed light on the Ioffe Drift’s origin and evolution. Although the drift’s prehistory still has blank spots, it is suggested that oceanographic processes may have affected the formation of this depositional body since its earliest stage. The drift’s formation probably began over the volcanic ridge in the Florianopolis Fracture Zone just after the ridge’s formation approximately 95–80 Ma ago. Variations in bottom-current intensity in response to regional and global paleoceanographic and paleoclimatic changes are most clearly imprinted in the seismic structure of the upper 80 m of drift deposits and in sediment records recovered by cores (down to 7 m below sea floor (mbsf)). The drift’s contourite formation underwent alternating phases of erosion caused by the intensification of bottom currents, probably followed by prevailing pelagic settling upon weakening of the bottom currents. The most thoroughly studied history of the Ioffe contourite drift, the Late Pliocene to Recent, was interrupted by multiple erosional hiatuses resulting from the activity of the Lower Circumpolar Deep Water (LCDW) bottom current during the intervals from 2.51/2.59 to 1.9 Ma and from 1.47/1.6 to 0.81 Ma. The numerous hiatuses that detached layers of calcareous contourites are an essential characteristic of the Ioffe Drift deposits, as well as layered sedimentary structures expressing effects of different bottom-currents velocities on the contourite deposition.

Herein we provide information on the integrated geological, geophysical, sedimentological, paleoceanographic, hydrophysical and biological investigations in the Central Atlantic during the cruise 45 of the R/V “Akademik Nikolaj Strakhov” in October-November 2019. The preliminary scientific results are discussed.

A high resolution seismic survey carried out by the Shirshov Institute of Oceanology, Russian Academy of Sciences in 2004–2012 near the foot of the continental slopes of the Derbent Basin (Middle Caspian) revealed evidence for active accumulation of contourites in the Pliocene–Holocene. The discovery of these forms and deposits in the Middle Caspian is of great importance for understanding the sedimentation and formation of the bottom topography of the Caspian Sea.

Facts confirming the hypothesis of contourite sediment infill of the Equatorial Mid-Ocean Canyon (EMOC) are presented. We examined two cores recovered in Cruises 37 and 43 of the R/V Akademik Ioffe (2012, 2013). The cores recovered upper Quaternary miopelagic clays on the EMOC floor (AI-3149) and the adjacent abyssal plain (AI-2620). The study of these cores unraveled significant differences in their composition. In contrast to the lithologically homogeneous Core AI-2620, Core AI-3149 includes interlayers enriched in the biogenic CaCO3, terrigenous silt, and authigenic ferromanganese micronodules. These peculiarities are attributed to activity of the Antarctic Bottom Water (AABW) contour currents along the EMOC.

The geological and geophysical expedition duringcruise 52 of the R/V Akademik Ioffe was organized bythe Shirshov Institute of Oceanology, Russian Academyof Sciences, according to the expeditionary programof FASO Russia; it was combined with transit ofthe vessel after the end of the Arctic tourist season,from September 29 to November 8, 2016 (port of exit:Gdansk, Poland; port of entry: Ushuaia, Argentina).The objectives of the expedition were formulatedby scientific supervisor I.O. Murdmaa. The scientificparty included 12 persons. The expedition was led byE.V. Ivanova and her deputy D.G. Borisov. The tasksof the expedition were carried out by the geologicalteam (head E.A. Ovsepyan) and seismic profiling andmeteorology team (head N.V. Libina).The expedition was aimed at high-resolution seismicprofiling along the ship?s track and in the centralpart of the Ioffe Drift, with collection of sedimentcores and grab samples in order to investigate theimpact of bottom circulation on sedimentation.Geological works included sediment sampling tostudy contourites (sediments formed by contour currents)and other lateral sedimentation products (turbidites,gravitites). The studies were carried out intransform valleys of the Mid-Atlantic Ridge (MAR),on the Ioffe contourite drift in the southern BrazilBasin, and on contourite terraces of the southernArgentine continental slope. The stations of sedimentsampling by gravity corers (127 mm in diameter) andan Okean 0.25 grab sampler were selected on seismicprofiles with a high-resolution SES-2000 deep subbottomecho sounder (4?7 kHz). Positioning of thevessel at the scheduled sites was assisted by GPS. Themethods of preliminary onboard analyses during theexpedition, including 5487 NM of seismic profiling,were performed along the vessel track starting from theexit to the Atlantic, except for the economic zones ofEuropean countries and Argentina, and including194 miles in a survey area in the central Ioffe Drift.Twenty-seven geological sampling stations were made(Fig. 1) with the collection of 3 sediment cores and17 grab samples or minicores. Fil: Ivanova, E. V.. Russian Academy Of Sciences; Rusia Fil: Murdmaa, I. O.. Russian Academy Of Sciences; Rusia Fil: Borisov, D. G.. Russian Academy Of Sciences; Rusia Fil: Simagin, N. V.. Russian Academy Of Sciences; Rusia. Lomonosov Moscow State University; Rusia Fil: Ovsepyan, E. A.. Russian Academy Of Sciences; Rusia Fil: Libina, N. V.. Russian Academy Of Sciences; Rusia Fil: Isola, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Bulycheva, E. V.. Russian Academy Of Sciences; Rusia Fil: Shulga, N. A.. Russian Academy Of Sciences; Rusia Fil: Krek, A. V.. Russian Academy Of Sciences; Rusia Fil: Lobus, N. V.. Russian Academy Of Sciences; Rusia Fil: Lapidus, L. V.. Russian Academy Of Sciences; Rusia

The high-resolution SES-2000 deep seismic profiles performed by R/V Akademik Ioffe (2010) recorded a calcareous contourite drift over the Florianopolis fracture zone ridge, South Atlantic, named the Ioffe Drift. Core AI-2436 retrieved from the drift summit recovered calcareous nannofossil–foraminiferal ooze contourites with small amounts of fine-grained terrigenous siliciclastic material. The calcareous ooze is intercalated with foraminiferal sand and more clayey ooze layers in the Upper Pleistocene section. According to planktonic foraminiferal and nannofossil biostratigraphy, the age of the uppermost section of the drift ranges from the Late Pliocene to the Late Pleistocene. It includes several stratigraphic hiatuses due to erosion, especially at the end of Pliocene–Early Pleistocene and in the intervals 1.51–0.81 and 0.44–0.27 Ma. The Ioffe Drift accumulated under the influence of the eastern branch of the Antarctic Bottom Water (AABW) outflow from the Vema Channel. Temporary intensification of the AABW flow, likely due to its increased production in the Weddell Sea, led to deep erosion ultimately resulting in long-term hiatuses and hence contributing to the enormously compressed Upper Pliocene–Middle Pleistocene section of the drift.

High-resolution seismoacoustic and multibeam data revealed a large field of sediment waves covering the Santa Catarina Plateau on the Brazilian Southern Margin. Within the field several zones were determined: a zone of large sediment waves (up to 70 m in height), a zone of smaller sediment waves (15–30 m in height) and a zone of buried sediment waves. The correlation of the seismoacoustic and multibeam data with the results of numerical modeling of bottom current velocities showed a strong influence of bottom currents on the formation of sediment waves. The process of wave burial in the northern part of the field can be caused by the interplay between gravity flows from the continental slope and bottom currents.

This study is based on the seismoacoustic data (3.5 kHz) collected during cruise 9209 of the RV Maurice Ewing (1992), organized within the framework of preparation for ODP drilling – leg 154. The analysis of the acquired data helped distinguish major acoustic facies and their spatial distribution in the study area. It was found out that almost the entire northern segment of the Ceara Rise is covered by a vast field of contourite sediment waves. The distribution of sediment wave heights is suggested to be controlled by geostrophic currents of AABW and NADW as well as by processes on the boundaries between water masses. Contourite erosional features are not widespread and generally resulted from the interaction of the bottom current with prominent topographic obstacles like western scarp of the Ceara Rise or basement outcrops.

Several high-resolution “SES 2000 deep” seismic profiles and a core of bottom sediments were obtained in cruises 33, 35, and 37 of the R/V Akademik Ioffe in the area of the Columbia channel (continental rise of Brazil, South America). The analysis of seismic facies and direct correlation of acoustic and lithological data indicates that sedimentation in this area is mostly controlled by the contour current of the Antarctic Bottom Water (AABW). The gravity flows from seamounts and continental slope only episodically contributed coarser material to the deposition of the muddy contourites. The mixed gravitite-contourite systems consisting of accumulative bodies (drifts) and erosion channels are the results of interaction of these sedimentation processes.

Acoustically stratified seismic images are widely used in studies of sedimentation mechanisms producing thick sedimentary aprons on continental rises. However, insuffcient vertical resolution of seismic records commonly restricts a more detailed interpretation of individual reflectors within accumulations to reconstruct specifc short-term sedimentological events. (Reflectors correspond to boundaries between sedimentary layers with different acoustic properties and are imaged in seismic records as continuous lines.) Very high resolution (VHR) seismic profiling conducted during Cruise 33 of the Russian research vessel Akademik Ioffe (2011) provided correlation of acoustic reflectors, distanced from one another by less than 50 centimeters, with thin sedimentary layers recovered by gravity cores.