Hiatuses in the late Pliocene–Pleistocene stratigraphy of the Ioffe calcareous contourite drift, western South Atlantic

Marine and Petroleum Geology 111 (2020) 624–637

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Research paper

Hiatuses in the late Pliocene–Pleistocene stratigraphy of the Ioffe calcareous contourite drift, western South Atlantic

T

Elena Ivanova∗, Dmitrii Borisov, Olga Dmitrenko, Ivar Murdmaa Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovskii prospekt, 36, Moscow, 117997, Russian Federation

A R T I C LE I N FO

A B S T R A C T

Keywords: Hiatuses Biostratigraphy MS XRF scanning Color reflectance Contourites Calcareous drift

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.

1. Introduction Stratigraphic investigation and correlation of contourite sections in the South Atlantic represent a complicated task because of a wide distribution of hiatuses disturbing the continuity of the geological record. Meanwhile, identification of temporal gaps in the contourite records is of special importance for the interpretation of stratigraphically rapid (103–106 years) changes in sedimentation, microfossil assemblages, climate and deep water paleocirculation (e.g. Meyers and Sageman, 2004; Viana and Rebesco, 2007). Several contourite and mixed contourite-turbidite depositional systems including the Vema contourite fan, Columbia channel mixed system, and Sao Tome Seamount mixed system (e.g., Mézerais et al., 1993; Massé et al., 1994; Lima et al., 2009; Borisov et al., 2013) were previously discovered on the pathway of the Antarctic Bottom Water (AABW) flow in the Brazil Basin. However, the Ioffe Drift provides an unique opportunity to apply a multi-proxy approach, including classical micropaleontology and modern magnetic susceptibility (MS), color reflectance and XRF scanning techniques to

∗

identify the age of stratigraphic units and hiatuses in its body. The modern contourite paradigm assumes a possibility to apply present contourite drifts at the present ocean floor as facies models for comparative studies of their potentially oil and gas bearing fossil analogues (e.g. Viana, 2007; Rebesco et al., 2014). The calcareous Ioffe Drift formed in typical pelagic realm, characterized by very slow average sedimentation rates (due to numerous hiatuses), and by low marine organic matter content, hardly can serve as a model of potential hydrocarbons collector. However, its example would help to elucidate wider problems of calcareous (foraminiferal dominated) contourites accumulation which may well occur in a geological setting more appropriate for hydrocarbon deposits generation. The calcareous Ioffe Drift was discovered by high-resolution seismic profiling during cruise 32 of the RV Akademik Ioffe (2010) (Murdmaa et al., 2014). The drift overlies bedrocks of the Florianopolis Fracture Zone ridge (FFZR), located to the north of the Rio Grande Rise, Western South Atlantic (Fig. 1A and B). The reference core AI-2436 from the drift summit recovered the Late Pliocene to Late Pleistocene sediments

Corresponding author. E-mail address: [email protected] (E. Ivanova).

https://doi.org/10.1016/j.marpetgeo.2019.08.031 Received 8 May 2019; Received in revised form 16 August 2019; Accepted 18 August 2019 Available online 22 August 2019 0264-8172/ © 2019 Elsevier Ltd. All rights reserved.

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Fig. 1. A) Regional bathymetric map of the Rio Grande Rise – Ioffe Drift area with Florianopolis Fracture Zone (FFZ). Major directions of Antarctic Bottom Water currents are shown by the dotted blue line. The location of DSDP site 516 is marked by a triangle. The inset shows the location of the study area in the SW Atlantic. (B) A detailed map of the study area with bathymetric profiles and core sites indicated. (E) bathymetric profiles crossing the drift, red arrows indicate core site location. (C) modeled current velocities and directions at water depth of 3900 m (according to Frey et al., 2017). (D) Meridional transect of potential temperature from (Morozov et al., 2010). Water masses: NADW – North Atlantic Deep Water, LCPW – Lower Circumpolar Water, WSDW – Weddell Sea Deep Water. (E) bathymetric profiles crossing the drift, red arrows indicate core site location. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

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from the South American continent (Fig. 1A). The central part of the drift is about 60 km long with the water depth above the summit of about 3750 m (Fig. 1B and C); the northern slope is steeper than others. The Ioffe Drift is located in the Antarctic Bottom Water (AABW) pathway from the Argentine Basin to the Brazil Basin through the Vema Channel (Fig. 1A). According to the CTD-data from the supplementary materials in Morozov et al. (2010), the boundary between NADW and the upper layer of AABW, lies at a depth of 3420–3520 m, i.e. above the drift summit. In turn, the AABW is represented by Lower Circumpolar Water (LCPW) with potential temperatures ranging from 0.2 °C to 2 °C (Fig. 1D). The boundary between LCPW and the lower AABW, also called Weddell Sea Deep Water (WSDW) with potential temperatures of < 0.2 °C, is traced at a depth of 4160–4390 m in the study area (Fig. 1D; Reid et al., 1977; Morozov et al., 2010). Unfortunately, lack of sufficient data coverage does not allow a detailed reconstruction of the present-day bottom current circulation in the study area. Bottom current velocities exceeding 20 cm/s were measured at water depth range of 4600–4750 m in the transform valley north of the drift using the Lowered Acoustic Doppler Current Profiler (LADCP, Morozov and Tarakanov, 2014). LADCP sites are located 30 km to the north and north-west of the core AI-2436 from the drift summit. Foraminiferal lysocline and calcite compensation depth in the region of the Rio Grande Rise and Vema Channel correspond to water depths of approximately 4050 and 4500 m, respectively (Melguen and Thiede, 1974). Hence, the study area (Fig. 1; Table 1) presently lies above the foraminiferal lysocline. According to modeling results (Frey et al., 2017, Fig. 1C) it is influenced by a gyre of LCPW moving clockwise around the Ioffe Drift.

Table 1 Coordinates, water depth, core length and physiographic environment of sediment cores. For location see Fig. 1B,C,E. Core

Latitude

Longitude

Depth, m

Length, m

Location

AI-3316 AI-3318

26°49.33′S 26°50.98′S

33°57.46′W 34°00.41′W

3900 3785

4.89 3.46

AI-2436a

26°51.60′S

34°01.40′W

3800

7.14b

NE drift slope small hillock near the drift summit drift summit

a b

From Ivanova et al. (2016a), corrected. The upper part of the core is stretched during processing.

and provided the first evidence of several long-term hiatuses and of the contourite origin of the drift body (Ivanova et al., 2016a). However, the uppermost sediment cover of the drift is not yet investigated. Meanwhile, the later high-resolution seismic profiling and bathymetric survey demonstrated rather variable geometry and acoustic structure of its summit and slopes shaped since the onset of contourite accumulation, likely in the Miocene. MS, color reflectance and XRF scanning techniques are commonly used for core correlations in high-resolution paleoceanographic studies as rather time-efficient and non-destructive methods. MS reflects the relative proportion of terrigenous clastic material in the sediment (e.g. Kissel et al., 1999; Bozzano et al., 2011). Besides, the anisotropy of magnetic susceptibility was used by some authors as a signature of bottom current erosion (e.g. de Menocal et al., 1988). In the South Atlantic, only a few MS records are available covering the last 1.5–3.5 Ma (e.g. von Dobeneck and Schmieder, 1999; Schmieder, 2004: Lacasse et al., 2017). The longest of these records (Lacasse et al., 2017) characterizes the intermediate-depth (about 1000 m) sites from the Rio Grande Rise, which is under the influence of' the North Atlantic Deep Water (NADW). Yet, MS pattern is not investigated for the deep sites bathed by AABW. Color reflectance is commonly considered as a proxy for an express evaluation relative biogenic material content in mixed terrigenous/ calcareous sediments. Optical lightness L* is shown rather closely following CaCO3 content of the Late Pleistocene sediments, however, the relationship between these parameters is less defined for longer periods in mixed terrigenous/calcareous sediments (e.g. Schneider et al., 1995; Balsam et al., 1999). XRF scanning provides semi-quantitative estimates of a wide spectrum of chemical elements, notably Ca, Fe, Si, Al, Ti. These elements and especially their ratios are extensively used as tracers in paleoenvironmental reconstructions (e.g. Arz et al., 2001, 2003; Vidal et al., 2002; Gruetzner, 2003; Calvert and Pedersen, 2007; Van Rooij et al., 2007; Romero et al., 2008; Bahr et al., 2014). For example, Ca/ Fe, Ca/Ti and Ca/Al represent biogenic/lithogenic ratios reflecting changes in terrigenous sediment contribution (e.g. Rothwell et al., 2006; Ingram et al., 2010; Rothwell and Croudace, 2015). Here, we present multi-proxy data on gravity cores AI-3316 and AI3318 obtained during cruise 46 of the RV Akademik Ioffe (2014) from the NE slope and summit of Ioffe Drift at water depths of 3900 and 3785 m, respectively, in order to refine the stratigraphy of the upper sediment cover and the duration of stratigraphic gaps. We also aimed to investigate the potential of MS, XRF, and color reflectance L* records for identification of hiatuses at different time scales and for regional correlations of contourite sediment sections.

3. Material and methods Seismic profiles (central frequency 4–7 kHz) obtained by means of the parametric sub-bottom echo-sounder SES 2000 deep during cruises 32 and 52 of the R/V Akademik Ioffe (2010, 2016, respectively) crossed the summit and northern slope of the Ioffe Drift (Fig. 1B,E). The gravity cores AI-3316 and AI-3318 (Table 1) were collected during cruise 46 of the same vessel on aforementioned profiles using an 8 m-long gravity corer with the outer diameter of 127 mm (Ivanova et al., 2016b, Fig. 1B). Core AI-3318 was retrieved from the drift summit in order to obtain a more appropriate record of the uppermost sediment cover than the reference core AI-2436 where the upper part was stretched (Ivanova et al., 2016a, Fig. 1B and C). Core AI-3316 is taken from the NE slope, on the AABW pathway to the east along the drift (Fig. 1B–D). Thus, the core locations allow comparing the processes on the summit and the upper slope. The cores were opened, visually described and continuously sampled onboard (Ivanova et al., 2016b). During and after the cruise, 1–cm thick samples and archive halves were stored at 4 °C. Onshore, the wet samples were sieved through the 63 and 100 μm meshes. In both cores, planktic foraminifers (PF) were studied from the dry grain size fraction > 100 μm in 10 cm intervals throughout the core sections with the emphasis on species with well-established levels of the first (FO) and/or last (LO) occurrence. In total, PF were analyzed from 50 samples in core AI-3316 and from 34 samples in core AI-3318. At several of the same downcore levels, nannofossils (N) were studied from 23 samples in core AI-3316 and from 24 samples in core AI-3318. The method details are described in Ivanova et al. (2016a). The color reflectance measurements were performed on split cores with 1 cm resolution using the spectrophotometer Konica Minolta CM2300d (SCE mode, D65/2°, color space L*a*b*) and following the IODP protocol (www.iodp.edu PP Handbook, 1997). Split cores were covered with the Hostaphan foil RN 15/15 μm. White calibration was carried out before measurements and at the end of each core section. Zero calibration was performed before starting the measurement. Volume magnetic susceptibility was measured on warmed to room temperature archive halves of split cores (AI-3316 and AI-3318) at

2. Physiographic and oceanographic setting The study area is located in the central part of the Ioffe Drift (Fig. 1A and B). This contourite drift, included into the Global contourite distribution database (Flanders Marine Institute, Ghent University, 2018), embraces a 700 m high linear SW–NE elongated ridge related to the asymmetric Florianopolis Fracture Zone ridge (FFZR, Meisling et al., 2001) in the Southern Brazil Basin, between 26° and 28°S, 900 km away 626

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diagenesis of the pelagic type (Munsell Color Company, 1995, Figs. 2 and 3). Sediment colors and occurrence of rare ferromanganese nodules suggest a pelagic realm of sedimentation (strongly oxic early diagenesis) for both cores. According to results of the smear-slide description relative proportions of foraminifers (including their test fragments) and nannofossils slightly changes along the cores. Sediments enriched with nannofossils (nanno-foraminiferal ooze) are lighter; their color is close to 10YR8/2. Deposits enriched with foraminifers (foraminiferal ooze) are a bit darker and look more orange, so their color is closer to 10YR7/4. Both recovered sections are characterized by the downcore transition from foraminiferal ooze to nanno-foraminiferal ooze. A number of 2-6- cmthick dark yellowish orange layers slightly enriched with terrigenous clay and fine-grained siliciclastic were found throughout the cores. In most cases these layers have gradual contact at the top and sharp or uneven erosional contact at the bottom (Figs. 2C and 3 B, C), likely marking hiatus (stratigraphic discontinuity) surfaces. The dark layers mainly overlie layers of light nanno-foraminiferal ooze. Despite these slight variations in sediment color and composition the calcium carbonate content does not show significant changes (90.8–100% in core AI-3318 and 81–100% in core AI-3316, Suppl. material). Spheroidal Fe-Mn nodules with a diameter from 1 to 3 cm were found at 226–228, 247–248 and 274–276 cm in core AI-3318 as well as at 0–3 and 436–437 cm in core AI-3316.

0.5 cm intervals using the Bartington MS3 meter and Bartington MS2E surface sensor (Bartington Instruments, 2011). The results are provided in SI. Dried sediment samples for CaCO3 determination are taken from both cores with sampling intervals of 10–20 cm CaCO3 and total organic carbon contents were determined with the express carbon analyzer AN7529 on 33 and 45 samples from cores AI-3318 and AI-3316, respectively. The XRF measurements were performed on split cores with 2–3 cm resolution using the Olympus Vanta C hand held analyzer. The studied core sections were covered with a 6 μm-thick Mylar film to avoid contamination of the instrument. The analyzer was operated in the GeoChem mode (measurements at 40 kV for 30 s per sample, measurements at 8 kV for 60 s per sample) according to (Fisher et al., 2014). The element ratios (Ca/Ti and Ca/Al) were further used in this study. As concentration of trace elements like Zr and Rb is extremely low (never exceeding 11 ppm) in the high-calcareous sediments, we did not apply their ratios. Accelerator mass spectrometer (AMS)–14C dates are measured on PF in the Poznan Radiocarbon Laboratory from two samples from core AI3318. 4. Results 4.1. Lithology Both core sections are very similar. The recovered sediments are represented by bioturbated calcareous ooze mainly consisting of planktic foraminiferal tests and calcareous nannofossils with variable proportion of the major biogenic constituents and fine-grained terrigenous material admixture (Ivanova et al., 2016b). Dark yellowish orange (10YR6/6), light grayish orange (10YR7/4) and very pale orange (10YR8/2) sediment colors dominate throughout suggesting oxic early

4.2. Biostratigraphy Cores AI-3318 and AI-3316 recovered the sediments from the late Pliocene to Recent with the Pliocene/Pleistocene boundary dated by 2.59 Ma according to (Cohen et al., 2013 updated in 2018). The downcore microfossil preservation generally varies from perfect to

Fig. 2. A. Lithology of core AI-3318, CaCO3 content (%), color reflectance (L* and a*), Fe concentration and volume magnetic susceptibiity (MS) plotted versus depth. B and C show the fragments of core with major stratigraphic boundaries in higher resolution (sediment color on photos is artificial, high-contrast filter was applied). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 627

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Fig. 3. A. Lithology of core AI-3316, CaCO3 content, color reflectance (L* and a*), Fe concentration and volume magnetic susceptibiity (MS) plotted versus depth. B and C show the fragments of core with major stratigraphic boundaries in higher resolution (sediment color on photos is artificial, high-contrast filter was applied). For an explanation and legend see Fig. 2. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Fig. 4. Stratigraphy of core AI-3318: ranges of indicative species, planktonic foraminiferal and nannofossil zones, volume magnetic susceptibiity (MS), color reflectance (L*), Ca/Al and Ca/Ti ratios plotted versus depth. Suggested hiatuses are shown on the right. Foraminiferal and nannofossil zones are defined according to zonations suggested in previous studies (Barash et al., 1983; Gartner, 1977; Dmitrenko, 1987; Berggren et al., 1983a, 1995). Samples studied for planktonic foraminifera (PF) and nannofossils (N) are marked by dots in corresponding columns. Arrows indicate the last (presumably in situ) occurrence of species. Insert represents the interval with the sharp MS peaks. See Sections 4.2 and 4.3 in the text for details. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

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ascertained by two AMS-14C dates (Table 2). Scarce tests of G. ruber are found at 192 cm, 326 cm and in the core-catcher (CC) which is likely the result of core processing or downcore contamination. Other index species of the regional Quaternary frame are continuously present within the following intervals: Globigerinella calida calida (0–120 cm), Globorotalia crassaformis hessi (70–346 cm), Globorotalia truncatulinoides (0–190 cm) and Globorotalia crassaformis viola (120–260 cm) with a random downcore occurrence of rare specimens of the latter two species (Fig. 4). Based on the downcore distribution of the aforementioned four species, zone Globigerinella calida calida (0.28–0.81 Ma) is tentatively identified between 40 and 120 cm while the zone Globorotalia crassaformis hessi (0.81–1.47 Ma) is most likely washed out suggesting a hiatus at 120 cm where both FO of G. calida calida and LO of G. viola are reported at the same level (Ivanova et al., 2016a). The base of underlying zone Globorotalia crassaformis viola (1.47–1.9 Ma) is defined by the persistent occurrence of G. truncatulinoides above 190 cm. The lowermost Quaternary zone Globorotalia tosaensis (1.9–2.39 Ma) roughly corresponding to zone PL6 (Berggren et al., 1995; Wade et al., 2011) and the upper part of zone N21 (Blow, 1969) embraces the interval 190–220 cm bounded below by LO Globorotalia miocenica. Meanwhile, some other extinct Pliocene species, notably G. exilis and Globigerinoides obliquus extremus, disappear at about the same time and also persistently occur in the overlying zone G. tosaensis as well as randomly occurring Globorotalia pertenuis, G. margaritae, Globigerinoides obliquus obliquus and others. The lowermost part of section (220–340 cm) is referred to as the Upper Pliocene zone Globorotalia miocenica (2.39–3.13 Ma), meaning zone PL5 (Berggren et al., 1983a, 1995; Wade et al., 2011) or the lower part of zone N21 (Blow, 1969). Zone Globorotalia miocenica seems not to be completely recovered as follows from the absence of LO Dentoglobigerina altispira (3.13 Ma according to Wade et al., 2011). In zone Globorotalia miocenica, foraminiferal fauna contains the aforementioned Pliocene species along with G. multicamerata whereas the Lower Pliocene species are not found. The same and some older extinct taxa are found in core AI-3316 from the NE slope of the drift which penetrated stratigraphically deeper than the core AI-3318 (Figs. 4 and 5). In the upper part of the core section, the Quaternary zones are defined as follows: Globigerinoides

moderate in both cores; however, several levels are affected by dissolution. Nevertheless, in both cores AI-3316 and AI-3318, we identified planktic foraminiferal and nannofossil zones previously established in the reference core AI-2436 (Ivanova et al., 2016a) from the Ioffe Drift summit and partially from the Rio Grande Rise (Barash et al., 1983; Dmitrenko, 1987). The Pleistocene section of the recent tropical-subtropical foraminiferal zonation by Wade et al. (2011) is hardly applicable to the study area as the indicative species Globorotalia tosaensis and Globigerinoides fistulosus extremely rarely occur in our core material. Besides, Wade et al. (2011) scheme does not consider the valuable regional species datum levels within the Pleistocene section mentioned below. However, we applied Wade et al. (2011) zonation for the Pliocene sections of our cores. In turn, biostratigraphic zones in the reference core AI-2436 (Ivanova et al., 2016a) were defined based on previous research on the species datum levels (first and/or last occurrences, FO and/or LO, respectively) and stratigraphic frames mostly from the Central and South Atlantic but also from other locations. In particular, we used publications on planktic foraminifers (Bolli and Premoli Silva, 1973; Berggren et al., 1983a,b; 1995; Kennett and Srinivasan, 1983; Pujol, 1983; Bolli and Saunders, 1985) and nannofossils (Gartner, 1977; Berggren et al., 1983a, 1995; Okada, 2000; Bylinskaya and Golovina, 2004). As the new core AI-3316 from the NE drift slope penetrated stratigraphically deeper than the reference core AI-2436, the available foraminiferal and nannofossil zonations and datum levels for Pliocene from Wade et al. (2011) and Bergen et al. (2015) were also applied as described next.

4.2.1. Planktic foraminiferal zones The warm-water (subtropical to tropical) assemblages occur throughout both sections AI-3318 and AI-3316 with the species diversity commonly ranging within 20–30 taxa per sample. The extant species dominate the assemblages from both cores whereas extinct Neogene species are found in their lower parts (Figs. 4 and 5, Appendix 1). In core AI-3318 from the drift summit, pink specimens of Globigerinoides ruber continuously occur in the upper 40 cm defining the self-titled uppermost foraminiferal zone (Fig. 4). The absence of Holocene sediments and the Late Pleistocene age of the upper 20 cm is

Fig. 5. Stratigraphy of core AI-3316: ranges of indicative species, planktonic foraminiferal and nannofossil zones, volume magnetic susceptibiity (MS), color reflectance (L*), Ca/Al and Ca/Ti ratios plotted versus depth. Suggested hiatuses are shown on the right. For an explanation and legend see Figs. 2 and 4. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 629

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Table 2 Accelerator mass-spectrometry (AMS) radiocarbon dates from the core AI-3318 measured in Poznan Radiocarbon Laboratory. Laboratory code

Depth in core, cm

Dated material

AMS-14C date, years

Poz-71478 Poz-71479

10–11 20–21

mixed planktic foraminifers mixed planktic foraminifers

33140 ± 580 > 46000

ruber (pink) from 0 to 37 cm, Globigerinella calida calida from 37 to 117 cm, Globorotalia crassaformis viola from 117 to 167 cm and Globorotalia tosaensis from 167 to 227 cm (Fig. 5). In this core, as well as in core AI-3318, zone Globorotalia crassaformis hessi is not preserved and a hiatus is assumed at 117 cm. Rare tests of some Quaternary index species randomly occur below the established persistent occurrence whereas reworked specimens of several Neogene species are reported in the upper parts of the core section, above the LO levels (Fig. 5). The uppermost Pliocene zone Globorotalia miocenica (or PL5) is documented between LO levels of the same species and Dentoglobigerina altispira at 227 and 407 cm, respectively. The lowermost zone Dentoglobigerina altispira corresponding to the Late Pliocene zone PL4 (3.13–~3.16 Ma after Wade et al., 2011) contains common specimens of Neogene species, notably Dentoglobigerina altispira, Globorotalia limbata, Globoquadrina venezuelana and Sphaeroidinellopsis kochi. According to Kennett and Srinivasan (1983), the latter two species are typical of the tropical early Pliocene zone N19 of Blow (1969). They were most likely either reworked upward, or the core has penetrated into the older zone PL3.

and Calcidiscus macintyrei at 97 cm. The disappearance of Discoasters determines the boundary of zones Calcidiscus macintyrei and Discoaster brouweri at 137 cm. Although both D. brouweri and D. pentaradiatus occur downcore below this level, the boundary between the same named zones (2.29 Ma after Bergen et al., 2015) could be identified by an upward increase in the latter species abundance up to 227 cm (Fig. 5). On the contrary, only combined zone Discoaster surculus/Discoaster tamalis (> 2.51 Ma after Bergen et al., 2015) could be defined in the lower part of the section, from 287 to 489 cm based on the species distribution, within the intervals 297–448 and 297–489 cm, respectively. Nevertheless, the rather persistent occurrence of D. tamalis in the latter interval as well as the absence of D. surculus in the lowermost part suggest that the core recovered > 2.73 or 2.9 Ma according to available publications on the datum levels of these species (Bergen et al., 2015, Rahman and Roth, 1989).

4.2.2. Nannofossil zones In both cores, nannofossils are abundant and represented by ~40 taxa. In core AI-3318, Emiliania huxleyi occurs in the upper 55 cm and its upward increasing abundance defines the lower boundary of the selftitled uppermost zone (0.27 Ma after Gartner, 1977) presumably at 25 cm (Fig. 4). Another index-species, Gephyrocapsa oceanica and Pseudoemiliania lacunosa, (0.27–0.44 Ma) are documented from the intervals 0–180 and 25–340 cm, respectively. The boundary between the same named zones at 0.44 Ma is tentatively located at 70 cm based on the increasing abundance of G. oceanica and decreasing one of P. lacunosa. The lower boundary of zone Pseudoemiliania lacunosa (0.92 Ma) is tentatively placed at 180 cm as three zones of Gartner's scheme (1977, with the dates from Bergen et al., 2015), notably the zone of small Gephyrocapsa (0.92–1.25 Ma), Helicosphaera sellii (1.25–1.6 Ma) and Calcidiscus macintyrei (1.6–1.9 Ma) are most likely washed out thereby suggesting a hiatus between zones Pseudoemiliania lacunosa and Discoaster brouweri (Fig. 4). Different Discoasters persistently occur downcore, below 180 cm, while specimens of D. pentaradiatus seem to be contaminated upwards to 140 cm. Existing resolution allows no more exact refinement than the Discoaster brouweri/Discoaster pentaradiatus zone within the 180–240 cm interval. LO D. surculus defines the boundary at 240 cm with the underlying combined zone Discoaster surculus/Discoaster tamalis which contains both index species with the latter one found only in one sample from 320 cm. In core AI-3316, the presence of Emiliania huxleyi assigns the sample from 7 cm to the lower boundary of the reduced same named zone (Fig. 5). Similarly, all Quaternary zones are strongly reduced as follows from the downcore distribution of index species. Gephyrocapsa oceanica and Pseudoemiliania lacunosa are reported from 7 to 177 cm and from 27 to 489 cm, respectively. The boundary between the same named zones (0.44 Ma) is defined by the end of the persistent occurrence of the latter species at 37 cm. As the zone of small Gephyrocapsa (0.92–1.25 Ma) is washed out the hiatus is suggested between zones Pseudoemiliania lacunosa (0.44–0.92 Ma) and Helicosphaera sellii (1.25–1.6 Ma) at 77 cm. A 20-cm interval below is marked by the presence of H. sellii and corresponds to the self-titled zone. Although the index species of the underlying zone Calcidiscus macintyrei (1.6–1.9 Ma) occurs up to 37 cm, the large coccoliths of the taxa are documented within the interval 97–488 cm thereby assigning the boundary of zones Helicosphaera sellii

The value of volume MS varies from 2·10-6 to 37 ·10−5 (SI), whereas the median values in both cores are almost similar, 11.36·10−5 SI in AI3316 and 11.43 ·10−5 SI in AI-3318 (Figs. 2–6, Suppl. material). MS records demonstrate the same rather high-variability patterns with the most pronounced changes within the intervals 165–250 cm in core AI3316 and 178–254 cm in core AI-3318, roughly corresponding to the lowermost Pleistocene interval 2.59–1.9 Ma as follows from the biostratigraphy (Figs. 2–6). These intervals are characterized by a set of 7 closely spaced high-amplitude peaks (with a 7–18 cm step in between). Most of the peaks show well-defined asymmetry with an abrupt change at the bottom followed by a gradual upward change (especially at 203, 211.5, 224.5, 248 cm in core AI-3316) thus suggesting hiatuses (Figs. 2 and 3). In the lower part of core AI-3316, a series of high-amplitude peaks is documented with a spacing interval of 16–38 cm. Some peaks (304, 327.5 cm in core AI-3316 and 322, 334 cm in core AI-3318) demonstrate an aforementioned type of asymmetry (Fig. 6). The asymmetric peaks correspond to the dark layers enriched with clay and siliciclastic material. As mentioned above most of these layers have sharp or erosional bottom contact and gradual top contact. The downcore records of L*-parameter show a sufficiently robust positive correlation to %CaCO3 record from core AI-3316 except of a few peaks at 170 cm and within the interval 330–400 cm which might result from the difference in sampling resolution (Fig. 2, Suppl. material). In core AI-3318, a positive correlation of L* and %CaCO3 records is less obvious likely because of the extremely high carbonate content as well as the aforementioned difference in sampling resolution (Fig. 3, Suppl. material). Significant changes in the L*-value mark visible changes in sediment composition and color within the core sections as well as the lower and upper boundaries of the intervals with abrupt MS changes in both cores (Figs. 4 and 5). Rather abrupt changes in the L*parameter are also documented at nannofossil zone boundaries in both cores, notably in the uppermost part of core AI-3316 (Fig. 5). The downcore increase of the L*-value in the upper parts of the cores correlates with slight decrease in foraminiferal abundance and marks the transition between foraminiferal ooze and nanno-foraminiferal ooze. In both cores, the distribution of a-parameter is quite similar to the MS records and do not provide any additional information (Figs. 2 and 3). In the b-parameter, no distinguishable patterns are found either. In both cores, high-amplitude variability patterns with abrupt

4.3. Magnetic susceptibility, color reflectance, and XRF measurements

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Fig. 6. Correlation of XRF data in cores AI-3316 (right) and AI03318 (left). Suggested hiatuses are shown on the right.

5. Discussion

changes and numerous high amplitude peaks are also demonstrated by XRF geochemistry records (Figs. 4–6, Suppl. material) of Ca/Al and Ca/ Ti, reflecting the ratio of biogenic to terrigenous material. These XRF records generally show in-phase variability with L* records (Fig. 6). However, expected correspondence with CaCO3 is rather unclear, likely because of much lower sampling resolution of the latter. On the other hand, Fe records nicely mirror MS records in both cores demonstrating the same abrupt changes, especially pronounced within the Early Pleistocene interval, from ~2.51/2.59 to 1.9 Ma (Figs. 2 and 3).

Hiatus is concerned here as an ascertained or assumed geological phenomenon expressed by disappearance of a stratigraphic interval from sediment (in this case mainly contourite) section irrespective of its physical origin, which might vary depending on sediment composition and paleoceanographic environments. Understanding of sedimentological and hydro-mechanical mechanisms of the hiatuses formation needs further investigation by joint efforts of corresponding specialists. Anyway, the authors follow traditional approaches and believe that

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1995; Bylinskaya and Golovina, 2004; Ivanova et al., 2016a). Regardless of the hiatus, the 1.9 Ma level seems to be robust and well-documented by biostratigraphic and MS records (Figs. 4 and 5). The Pliocene/Pleistocene boundary is reported at ~243 cm by nannofossils whereas the abrupt changes in lithology/sediment color, L*, MS and XRF data collectively suggest a hiatus at about this level (Figs. 2, 4 and 6). Several short-term erosional events might be inferred from abrupt changes in MS and XRF records within the interval 1.9–2.51/ 2.59 Ma, as well as above, in the Pleistocene, and below, in the Late Pliocene. The age of two lowermost hiatuses can barely be identified. As the core did not penetrate the underlying PF zone Dentoglobigerina altispira, we are confident that these hiatuses are younger than 3.13 Ma, i.e. occurred within the 2.59–3.13 Ma interval. In core AI-3316 from the drift slope, the correlation of PF and N zones is also quite good although hiatuses seem to be more numerous (Fig. 5). The abrupt changes in the L* and MS records associated with some boundaries between nannofossil zones, notably the two uppermost ones, suggest hiatuses as well. This can explain a significant reduction of nannofossil zones thickness in the upper part of the section. Two hiatuses reflect missing nannofossil and foraminiferal zones at 77 and 117 cm, respectively. The levels of 1.9 and 2.51/2.59 Ma are reported by both microfossil groups with a reasonable difference in downcore depth. In this core, the abrupt high-amplitude peaks in color reflectance L*, MS and XRF records most likely indicate the occurrence of several erosional hiatuses in the Pleistocene, notably between 1.9 and 2.51/2.59 Ma. Similarly, the upper Pliocene section also seems to contain four to six hiatuses inferred from the abrupt changes in MS and XRF values. Previous studies demonstrated the link between location of nodules in sediment cores, hiatuses and bottom current activity (e.g. Pautot and Melguen, 1975; von Stackelberg, 1979; Nishimura, 1992). The revealed nodules might reflect significant decrease in sedimentation rate and mark hiatuses as their growth is possible only when sedimentation rate is low. Some of the nodules were found in the interval related to abrupt changes in MS value and stratigraphic hiatuses (at 226–228, 247–248 cm in AI-3318) thus independently confirming the hiatus occurrences.

bottom currents activity serves as the major dynamic factor for both erosional and non-depositional hiatuses development. The terms duration or timing of a hiatus means a simplified expression for the disappeared stratigraphic time interval, but not duration of erosion (nondeposition) itself that might be much shorter, even geologically instantaneous. Geological correlation of long-term hiatuses between the studied cores by more reliable, but low resolution zonal biostratigraphy and of more short-term ones inferred from high-resolution MS, color reflectance, and XRF records permits to refine stratigraphy of the uppermost acoustically stratified sediment cover overlaying the central Ioffe Drift area. On the other hand, inter-correlation of several independent proxy records serves for the future elaboration of theoretical approaches explaining AABW circulation patterns which led to the revealed extensive hiatus formation characteristic of the Ioffe Drift. 5.1. Multi-proxy evidence of erosional hiatuses on the Ioffe Drift In both cores AI-3318 and AI-3316, a rather good correlation is ascertained between foraminiferal and nannofossil zones (Figs. 4 and 5) regardless of the upward and downward contamination of PF and N in both sections which is typical of the region (Berggren et al., 1983b; Barash et al., 1983; Ivanova et al., 2016a). As mentioned in Section 4.1 and 4.2, lithological and micropaleontological data document several hiatuses in both sediment cores. We also suggest that the high-amplitude peaks in MS and XRF element ratios demonstrating abrupt changes reflect the hiatuses (Fig. 6). The abrupt MS and Fe increase after a hiatus (erosion event) likely means the deposition of terrigenous material relatively enriched in Fe-minerals under conditions of still high bottom currents velocity (Figs. 2 and 3). The gradual upward decrease in both parameters seems to reflect a slowing down of the currents responsible for both the erosion and input of terrigenous material. This assumption is supported by a simultaneous increase in Ca/Ti and Ca/Al ratios (Figs. 4–6). However, enrichment of sediments with Fe and especially with Mn at MS peaks might also be related to their concentration during oxic early diagenesis in a non-depositional environment. Linkages between lithological, MS and XRF data are especially evident in the interval 170–247 cm from core AI-3316 and at 243 cm in core AI-3318 (Figs. 2 and 3). In some cases, the anti-phase abrupt changes are synchronous in MS and L* records, notably, at around the Pliocene/Pleistocene boundary at 2.59 Ma (Cohen et al., 2013 updated in 2018), close to the lower boundary of nannofossil zone Discoaster brouweri (2.51 Ma according to Bergen et al., 2015) in both cores (at 243 cm in AI-3318 and ~247 cm in AI-3316, Figs. 2 and 3). Coinciding of biostratigraphic boundaries with MS and L* peaks in all provided records allows identification of more or less reliable hiatuses. The most robust hiatuses (or series of hiatuses as in the Early Pleistocene) are nicely represented by abrupt changes in MS and XRF records. Absence of stratigraphic zones as well as sharp lithological and/or color boundaries (including L*-parameter) also point to hiatuses (Figs. 2–6). In core AI-3318 from the drift summit, hiatuses at 120 and 180 cm correspond to the absence of foraminiferal and nannofossil zones, respectively (Fig. 4). The hiatus at 120 cm in foraminiferal zonation points to a significant gap in the Quaternary section, from 1.47/1.51 to 0.81 Ma or even more roughly corresponding to the Mid-Pleistocene Transition (MPT) and the intensification of bottom currents in the Vema Channel (Ivanova et al., 2016a). Moreover, the underlying hiatus at 180 cm suggests a gap of about 1 Ma due to erosion and/or long-term non-deposition, from 1.9 to 0.92 Ma, in the nannofossil zonation (nondeposition during a million years seems unlikely). The discrepancy between gaps inferred from PF and N zonations might be caused by differences in reworking of sand-size PF tests as compared to tiny and light coccoliths by bottom currents, as well as in PF and N resistance to selective dissolution which is found in DSDP/ODP sites and sediment cores from the nearby and remote locations (e.g. Berggren et al., 1983a,

5.2. Potential of MS, color reflectance and XRF records for identification of regional stratigraphic hiatuses Due to the strongly reduced thickness of biostratigraphic zones and the occurrence of multiple long-term hiatuses, our MS records cannot be directly correlated to either the SUSAS stack (von Dobeneck and Schmieder, 1999), or to the available MS records from the subtropical South Atlantic (Schmieder, 2004) and the shallow part of the Rio Grande Rise (Lacasse et al., 2018) covering approximately 1.5, 2.1 and 3.5 Ma, respectively. This is not surprising as Lacasse et al. (2017) documented a rather variable number of MS peaks in the individual records from three sediment core studied indicating that some individual peaks cannot be identified and dated. However, MS records from both cores AI-3318 and AI-3316 demonstrate a clearly distinct interval of high-amplitude peaks in the Early Pleistocene, between ~1.9 and ~2.51/2.59 Ma according to the ages of zonal boundaries (Figs. 2 and 3). The upper peak at 1.9 Ma can be correlated to peak 9 (1.85 ± 0.1 Ma) from intermediate-depth MS records on Rio-Grande Rise (Lacasse et al., 2017) keeping in mind the age uncertainties in our cores. The lower MS peak at 2.5/2.59 Ma seems to be coeval to the unnamed strong peak at 2.5 ± 0.1 Ma between peaks 6 and 5 identified by Lacasse et al. (2017) in core MD11-L2P1. In previous studies, optical lightness L* was commonly used as a proxy for relative changes in carbonate content of marine sediment, at least for the Late Pleistocene-Holocene (Balsam et al., 1999). Our downcore records of L*-parameter show a reasonably good correlation to CaCO3 records in both cores keeping in mind the difference in 632

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Fig. 7. Correlation of biostratigraphic zones in cores AI-2436 (Ivanova et al., 2016a), AI-3318, AI-3316 (this study), and DSDP Hole 516. The zonations of Barash et al. (1983) on PF and Dmitrenko (1987) on N are used for the upper ~10 m, while the zonation of Berggren et al. (1983a) is applied below (using the zonal boundary ages from Wade et al., 2011; Bergen et al., 2015). PF zones mean planktonic foraminiferal zones. Assumed boundaries between zones and hiatuses are marked by dashed lines and undulated horizontal lines, respectively. See the text for details on age boundaries and location of hiatuses.

We argue that the occurrence of numerous hiatuses explains the aforementioned reduction in the thickness of biostratigraphic zones. A significant impact of selective dissolution on foraminiferal fauna and thickness of zones from the Ioffe Drift cores seems to be unlikely as foraminiferal tests commonly show good, rather good or even perfect preservation although our sites are much deeper (3750–3900 m) than the ODP site 516 (1313 m). A weak dissolution influence fits well with the established modern 4050 m-depth of foraminiferal lysocline in the area (Melguen and Thiede, 1974) and likely indicates that LCPW boundary with more corrosive WSDW was generally below 3750 m during the Late Pliocene-Quaternary. The only exception could be some relatively short-term intervals like during MIS 3-2 as shown in (Ovsepyan and Ivanova, 2019) for the Vema Channel area. No significant increase in thickness of the biostratigraphic zones or in number of hiauses is found on the drift slope (core AI-3316) compared to the summit area (cores AI-2436 and AI-3318, Figs. 4 and 5). If the identified hiatuses are of erosion origin, it means that surface bioproductivity and pelagic sedimentation in the Ioffe Drift area was not necessarily slower than at the similar depths in the subtropical South Atlantic where the thickness of Late Pliocene-Quaternary sections are commonly somewhat higher than in our cores (Fig. 7). Rather the sediments were washed out by post-depositional erosion.

sampling intervals (Figs. 2 and 3). Besides, the record of L*-parameter strikingly mirrors Ca/Ti and Ca/Al records especially in core AI-3316 where almost all peaks are synchronous in the three records throughout the Late Pliocene - Pleistocene section and show general anti-phasing with MS record. The correlation (in-phase or anti-phase) between MS, XRF and L* records and especially with the aforementioned gaps in biostratigraphic zonations strongly supports a potential of those proxies for identification of hiatuses.

5.3. Correlation of biostratigraphic zones on the Ioffe Drift and Rio Grande Rise Although the contourite drifts are commonly characterized by high sedimentation rates (e.g. Robinson and McCave, 1994; Rebesco et al., 2014; Stow et al., 2013), our previous (Ivanova et al., 2016a) and present studies demonstrate rather reduced thickness of all recovered Quaternary biostratigraphic zones in the sediment sections from the Ioffe Drift. This is especially evident from a comparison to the nearby DSDP Site 516 from the Rio Grande Rise (Fig. 7) where the pelagic sedimentation seems to prevail over the lateral advection and other mechanisms (Barker et al., 1983) and most likely valid for the Late Pliocene zones as well. The only exception represented by the enhanced thickness of the uppermost zones G. ruber pink and E. huxleyi in the reference core AI-2436, results from the artificial stretching during the core processing (Ivanova et al., 2016a). If the stretching is subtracted from the length of core AI-2436, the thickness of each recovered biostratigraphic zone appears to be rather similar in the three cores from the Ioffe Drift.

5.4. Paleoceanographic implications of the most prominent hiatuses Our data demonstrate numerous hiatuses on the Ioffe Drift since ~3 Ma, i.e. the onset of the Pleistocene type climatic and paleoceanographic fluctuations (Shackleton and Opdyke, 1976; Vincent and Berger, 1982) resulted from the closure of the Panamian seaway (e.g. 633

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continuous MS and XRF scanning data for identification of even short-lived hiatuses while color reflectance L* is proved to be useful for inferring of invisible lithological changes in PlioPleistocene calcareous sediments. (3). Integration of biostratigraphic data with MS, color reflectance L* and XRF records permits a rather confident identification of hiatuses notably within the intervals from 1.6 to 0.81 Ma (including the Mid-Pleistocene Transition), and 2.51/2.59–1.9 Ma (reorganization of deep-water circulation since the Pliocene/ Pleistocene boundary) in both core records. The occurrence of the same hiatuses in the previously studied core AI-2436 from the drift summit suggests their regional character which needs further investigation. Some (likely short-lived) younger and older hiatuses are also tentatively identified, notably in core AI-3316 from the NE slope of the drift. (4). The occurrence of several hiatuses and the reduced thickness of all biostratigraphic zones in the Ioffe Drift sections when compared to those at DSDP sites from the nearby Rio Grande Rise supports our previous suggestion about the vigor of AABW contourite currents coming from the Vema Channel and strongly affecting the sedimentation (accumulation and erosion) in the drift area. It particularly concerns the intervals of pronounced changes in the global climate and ocean circulation during the Middle (MPT) and Early Pleistocene.

Keigwin, 1982; Schmittner et al., 2004). The Pliocene/Pleistocene boundary at 2.51/2.59 Ma in our cores roughly corresponds to the onset of “modern” deep water stratification in the South Atlantic (Turnau and Ledbetter, 1989) after a major step in intensification of Northern Hemisphere glaciation at 2.7 Ma ago (Haug and Tiedemann, 1998; Lisiecki and Raymo, 2005), overall AMOC strengthening (3–2.5 Ma, Karas et al., 2017) and changes in deep water mass properties due to Antarctic sea ice advance (Hill1 et al., 2017). We speculate that reorganization of circulation and reintroduction of large AABW volumes into the Rio Grande Rise area (Turnau and Ledbetter, 1989) might trigger a stronger erosion of foraminiferal and nannoforaminiferal ooze due to increased bottom current activity and/or nondeposition in the study area, notably during the early Pliocene, from 2.51/2.59 to 1.9 Ma. The earlier hiatuses on the Ioffe Drift cannot be dated precisely but one can assume that some of them correspond to the increased paleospeed events in the Rio Grande area at 3.15–3.10, 2.85 and 2.7 Ma inferred by Turnau and Ledbetter (1989). Less prominent interval, from 1.47/1.6 to ~0.81 Ma, with several hiatuses and gaps in biostratigraphic zones (Figs. 2–6) most likely reflects long-term erosion which terminated by the end of MPT, defined at 0.95–0.8 Ma (e.g. Schmieder et al., 2000; de Garidel-Thoron et al., 2005; Kleiven et al., 2011). Previously, Ledbetter and Ciesielski (1986) suggested the reduction in frequency and extent of deep hiatuses in the South Atlantic and southeast Indian Ocean by ~ 1Ma. Strong erosion prior to 1–0.81 Ma seems to be associated with increased AABW, notably CDW, production and higher flow speeds of the deep western boundary currents suggested for glacials (Hall et al., 2001; McCave and Hall, 2006; Ivanova et al., 2016a).

Acknowledgments The authors are grateful to scientific party, master and crew of R/V Akademik Ioffe cruise 46 for their professional support in the material collection for this study. N. Nemchenko, N. Simagin, I. Klementieva, L. Demina and M. Kornilova are thanked for technical assistance with MS, color reflectance and CaCO3, measurements. We appreciate fruitful discussions with E. Morozov, G. Kazarina, B. Galbrun and E. Moreno. The authors are thankful to D. Yuferov, CEO of LLC Geoelement for professional support in XRF measurements. Appreciation is extended to an anonymous reviewer for the valuable comments which allowed to improve the manuscript. The study was supported by the Russian Science Foundation (grant 18-17-00227). The English editing was provided by XpertEditor Editing Services. The results of nannofossils analyses were obtained in the framework of the Shirshov Institute state assignment (theme No. 0149-2019-0007).

6. Conclusions (1). Biostratigraphic study of cores AI-3316 and AI-3318 from the NE slope and summit area of the Ioffe Drift allowed for the identification of foraminiferal and nannofossil zones previously described in the reference core AI-2436 (Ivanova et al., 2016a). In addition, core AI-3316 from the drift NE slope spanning the last ~3.15 Ma (i.e. penetrated into older sediments than the other two cores). (2). The interval from 2.51/2.59 to ~1.9 Ma shows a characteristic pattern in MS and XRF records of both cores (supported by less pronounced changes in color reflectance L*) and could possibly be used in the future contourite studies as a regional stratigraphic bench mark. Thus our study demonstrates the potential of

Appendix 1. General characteristic of main foraminiferal species occurrences within stratigraphic zones

zone

Globigerinoides ruber pink

Globigerina calida calida

Gr. crassaformis viola

Globototalia tosaensis

Globorotalia miocenica

Dentoglobigerina altispira

Interval in core AI-3318, cm Interval in core AI-3316, cm Species Dentigloborotalia anfracta Globorotalia crassaformis crassaformis Globorotalia crassaformis hessi Globorotalia crassaformis viola Globorotalia crassaformis ronda Globorotalia hirsuta Globorotalia inflata Globorotalia triangula Globorotalia menardii Globorotalia scitula Globorotalia truncatulinoides Globorotalia tosaensis Globorotalia ungulata Neogloboquadrina dutertrei Neogloboquadrina incompta Neogloboquadrina pachyderma Pulleniatina obliquiloculata

0–40 0–37

40–120 37–117

120–190 117–167

190–220 167–227

220–346 227–407

407–488

C C

R C

R C

C

vR C

R

R

R C C

C C C

R R C

R R C

R–C

R–C С vR vR

R–C

C R

R C

C R

R R

R R

R R R vR

vR R R vR

vR R vR vR

vR vR

R

634

vR vR vR R

vR

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E. Ivanova, et al. Globigerina bulloides Globigerina falconensis Globigerinoides conglobatus Globigerinoides elongatus Globigerinoides ruber Globigerinoides ruber pink Globigerinoides sacculifer Orbulina universa Beella digitata Globigerinella siphonifera Globigerinella calida calida Turborotalita quinqueloba Turborotalita humilis Globoturborotalita rubescens Globoturborotalita rubescens pink Globoturborotalita tenella Sphaeroidinella dehiscens Candeina nitida Globigerinita glutinata Globorotalia multicamerata Globorotalia miocenica Globorotalia pertenuis Globorotalia margaritae Globorotalia exilis Globorotalia limbata Globorotalia miulticamerata Globigerinoides fistulosus Globigerinoides extremus Dentoglobigerina altispira Globoquadrina venezuelana Sphaeroidinellopsis kochi

R R R C C C C R R C C vR R C C C R C

R R R C C

R–C R–C vR R C

R–C

R vR C C C vR C C vR vR

vR R C

R–C C

C R

C R–C

C

C

C R–C

R R R–C C C vR C R–C

R–C

R

C C C vR C C R C

vR C R C R R

vR

C vR vR C vR

C vR C vR C R–C C R

R C

R R vR vR

R R vR vR

vR

vR

vR

R vR R

vR vR

R C C R

Note: upward and downward contaminated occurrences are given in italics. Occurrences: C = common, R = rare, vR = very rare. Distribution of indicative species and the sampling levels are shown in Figs. 4–5.

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.marpetgeo.2019.08.031.

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