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Paleontology Journal
Volume 2013 (2013), Article ID 947839, 17 pages
http://dx.doi.org/10.1155/2013/947839
Research Article

Revision of the Messinian-Early Zanclean Sediments from ODP Hole 953C (Canary Island Archipelago, North-Eastern Atlantic): Biostratigraphy, Cyclostratigraphy, and Astronomical Tuning

Dipartimento di Scienze della Terra, Università di Siena, Via Laterina 8, 53100 Siena, Italy

Received 4 September 2012; Revised 22 January 2013; Accepted 23 January 2013

Academic Editor: Matías Reolid

Copyright © 2013 Federica Riforgiato. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

A quantitative study was performed on calcareous plankton of the Messinian-early Zanclean succession recovered at ODP Leg 157 Hole 953C (Canary Island Archipelago, North-Eastern Atlantic). This revision allowed to recognize some events typically recorded in the Mediterranean region, highlighting affinities between the Mediterranean and North Atlantic Ocean, in the considered time interval. The presence of such events in an open-ocean succession provides the possibility to substantially improve the biostratigraphic resolution and supplies useful correlation tools between the Mediterranean and oceanic areas. Moreover, to unravel cyclical patterns of deposition and given that the investigated succession shows no evident lithological pattern, cyclostratigraphic analyses have been based on abundance fluctuations of Globigerinoides-Orbulina group, neogloboquadrinids, and warm-water versus cool-water species ratio. As a result, forty-three precession-controlled cycles have been recognized spanning from 6.457 Ma to 4.799 Ma.

1. Introduction

The Messinian Salinity Crisis (MSC), affecting the Mediterranean area during the latest Miocene, has been the focus of numerous studies (e.g., [118]). It is considered as one of the catastrophic oceanographic events that occurred in the last 20 million years [5, 8, 19]. It was caused by the temporary isolation of the Mediterranean basin from the Atlantic Ocean, due to a combination of tectonic and climatic factors (e.g., [1921]). According to numerous authors, the onset of the MSC was synchronous over the entire Mediterranean basin and its end corresponded to the catastrophic flooding of marine waters from the Atlantic Ocean (e.g., [19, 20, 2234]). The sedimentary expression of this flooding is recorded everywhere, both in land sections and in the deep sea cores, showing that the transition from continental to marine environment across Miocene-Pliocene boundary was (i) typified by continuous sedimentation; (ii) geologically instantaneous; (iii) synchronous throughout the Mediterranean basin. However, the problem of the exact timing and origin of the Pliocene flooding of the Mediterranean is not yet completely understood, and the evidence is not irrefutable. Some authors support the early Pliocene flooding of the Mediterranean (e.g., [7, 8, 35]), while others support a late Messinian re-flooding (e.g., [6, 3641]). Indeed, during the salinity crisis, environmental conditions within the Mediterranean excluded most marine microfossil groups, which are traditionally used for biostratigraphic correlation.

To understand the cause(s) and consequences of the onset of the MSC in detail, an age control is needed for the part of the Atlantic immediately adjacent to the Mediterranean. In this connection, the ODP Leg 157 Hole 953C (Canary Island Archipelago, North-Eastern Atlantic) is considered favourable to the aims of the work for (i) the location; (ii) the excellent paleomagnetic data; (iii) micropaleontological records, despite intervals of no recovery.

Recently, an age control was obtained for the Messinian, both in the Mediterranean and in the low-latitude Atlantic Ocean, through integrated stratigraphic studies complemented by the astronomical tuning of sedimentary cycles or other cyclic variations in continuous marine successions (e.g., [3, 34, 4252]). Milankovitch cyclostratigraphy is nowadays considered one of the best tools to gain high-resolution chronostratigraphy in different depositional environments (continental, marginal marine, and deep sea). The presence of high-frequency cycles in deep-sea records and their tuning to the astronomical curve provide an accurate chronology for the stratigraphic events recognized through the studied sedimentary successions. Applications of cyclostratigraphy resulted in the construction of an accurate Astronomical Tuned Neogene Time Scale (ATNTS 2004) for the Quaternary, Pliocene, and late and middle Miocene [3, 4244, 5361]. The classic high frequency cyclicity recognized in most of the late Neogene Mediterranean sedimentary record is manifested by the alternation of homogeneous marl and sapropel (or sapropel equivalent) horizons, promoted by astronomical forcing [3]. In this paper, since the succession investigated does not show rhythmic lithological patterns, the proposed cyclostratigraphic reconstruction is mainly based on the quantitative distribution patterns of climate-sensitive planktonic foraminifera taxa (e.g., [6266]).

The aim of this paper is (i) to present an biostratigraphy for the Messinian-early Zanclean of the Hole 953C, based on quantitative data of planktonic foraminifera (previous studies by [67, 68] are to be considered inadequate for this research); (ii) to compare the bioevents recognized, with those occurring in other astronomically calibrated sections; (iii) to recognize other cyclic patterns for using as further control of the obtained astronomical calibration.

2. Material and Methods

2.1. Site Description

During Ocean Drilling Program Leg 157, four sites (Site 953 to 956; see [70]) were drilled in the volcaniclastic apron of Gran Canaria in the Canary Island Archipelago (North-Eastern Atlantic) (Figure 1). ODP Hole 953C is situated at 28°39′.012N, 15°08′.670W, 68 km northeast of Gran Canaria, 90 km west of Fuerteventura, and 98 km east of Tenerife, at water depth of 3577.8 m. It is the most distally located site on the flanks of Gran Canaria and thus seems to have been spared some of the major slumped intervals and unconformities present at Sites 954, 955, and 956. The recovered sedimentary succession spans the interval from the middle Miocene to Holocene, and the dominant nonvolcanic lithologies were divided into seven major units and three subunits (see [69]). The present study focuses on a 51.11 m thick succession from the Unit III, embracing cores 18R to 13R from 346.89 to 295.78 mbsf (Figure 1) and representing the Messinian-early Zanclean time interval. Core recovery was generally over 50%, and mainly consisting of gray to brownish-gray clayey nannofossil ooze, interbedded with minor graded nannofossil clay-silt, foraminifer lithic silt and sands, and foraminifer sands.

947839.fig.001
Figure 1: Location map of the ODP Leg 157 Sites 953–956 (Canary Islands) and simplified lithology of Site 953C based on the site description taken from Shipboard Scientific Party [69].
2.2. Sample Preparation and Micropaleontological Analysis
2.2.1. Foraminifera

Samples for foraminiferal analysis were disaggregated in normal water and washed through a 63 μm sieve. The residues were oven dried at 40°C. Qualitative and quantitative planktonic foraminiferal analyses were performed, using a stereoscopic microscope, on 170 samples (average spacing 20 cm). The samples were divided with a microsplitter to obtain unbiased aliquots with about 300 planktonic foraminifera. They were (1) picked, (2) mounted onto faunal slides, (3) determined at specific and supraspecific level, and (4) counted (200–300 specimens) from the larger than 125 μm fraction of the washed residue to collect quantitative faunal data. The assemblages are usually abundant and generally well preserved, although at times they are poor. Very few samples show a very scarce faunal content.

Raw data of microfossils were transformed into percentages over the total abundance, and percentage abundance curves were plotted. Species with phylogenetic affinities and similar environmental significance were also grouped to better interpret distribution patterns.

Furthermore, a semiquantitative analysis from the larger than 63 μm fraction was carried out on all samples in order to pinpoint the actual position of the bioevents.

Benthic foraminifera were also counted to determine plankton/benthos ratio, which is expressed as (e.g., [71]).

2.2.2. Calcareous Nannofossil

Standard smear-slides were prepared for the nannofossil analyses for the intervals encompassing the principal bioevents (from core 17R Section 3 to core 13R Section 5). Qualitative analyses on a total of 30 samples have been performed by Dr. Baldassini N (Siena University) to determine additional biohorizons and bioevents to improve the biostratigraphic resolution.

3. Micropaleontological Data

The analysis of the planktonic foraminiferal fauna allowed the identification of 45 taxa, which sometimes were grouped into categories on the basis of morphological, phyletic, or ecological affinities. The categories are (Table 1) Dentoglobigerina gr. (D. altispira altispira, D. altispira globosa), Globigerinita gr. (G. glutinata, G. uvula), Globigerinoides obliquus gr. (G. bollii, G. cf. elongatus, G. emeisi, G. extremus, G. obliquus), Globigerinoides quadrilobatus gr. (G. quadrilobatus, G. trilobus, G. sacculifer), Globoturborotalita decoraperta gr. (G. cf. apertura, G. decoraperta), Globorotalia menardii gr. (G. menardii, G. multicamerata), Neogloboquadrina gr. (N. acostaensis, N. pachyderma, N. dutertrei humerosa/N. dutertrei blowi), Orbulina gr. (O. bilobata, O. suturalis, O. universa), and Sphaeroidinellopsis seminulina gr. (S. seminulina paenedehiscens, S. seminulina seminulina). Most of the categories are self-explaining, but the labelling of some of them needs further explanation.

tab1
Table 1: ODP Hole 953C planktonic foraminiferal groups used for the quantitative analyses.

Figure 2 shows the quantitative distribution of those species (or categories) which generally display frequencies higher than 1.5%. The main components are Globoturborotalita nepenthes and Neogloboquadrina gr. which are continuously present throughout the investigated interval, reaching maxima frequencies of 90% and 80%, respectively.

947839.fig.002
Figure 2: ODP Hole 953C abundance curves of selected planktonic foraminiferal (as a percentage of the total planktonic foraminiferal fauna) and position of most significant biohorizons. Grey color in Globorotalia menardii gr., Neogloboquadrina acostaensis, and N. pachyderma distributions indicates the percentage of sinistral forms. The red dotted line designates the hiatus. The following acronyms indicate bioevents: LO (Last Occurrence), FO (First Occurrence), LRO (Last Regular Occurrence), and S/D (sinistral/dextral coiling change).

Neogloboquadrina gr. includes also small-sized specimens, sometimes under poor preservation conditions that were difficult to distinguish. Different coiling directions of the N. acostaensis (average value of 17%) have been counted separately as far as the study time interval coiling-change of this species has been proved to have potential biostratigraphic significance. Particularly, in the lower part of the studied interval, sinistrally coiled specimens prevail up to 344.57 mbsf, and after this level the dextrally coiled increases in abundance.

N. pachyderma comprises specimens with low trochospiral test, four to five and one-half chambers in the final whorl with the last chamber irregular often a kummerform, surface characterized by large euhedral calcite crystals, umbilicus from closed to open but always narrow, and aperture umbilical-extraumbilical with a thick apertural rim. This species is present from the base of the investigated interval showing abundances of about 30% with peaks of abundance in the range of 40%–60%. The coiling direction of N. pachyderma is prevalently sinistral.

N. dutertrei humerosa/N. dutertrei blowi (following the concept of [72]) comprises specimens showing low trochospiral test with five or more chambers in final whorl, surface uniformly moderately perforate with the characteristic rosette pattern formed by concentric arrangement of euhedral crystals on each chamber, umbilicus open and deep, aperture umbilical-extraumbilical, and a moderately high arch bordered by a distinct rim (in N. dutertrei humerosa). N. dutertrei humerosa/N. dutertrei blowi first occurs at 336.47 mbsf displaying low percentage value about 2.6%. The coiling direction of this phenotypic couple is prevalently sinistral.

G. decoraperta gr. and G. obliquus gr. show a continuous presence along the investigated interval with high abundance value of approximately 35.5% and 33%, respectively.

Dentoglobigerina gr. displays low frequencies (average value of 2.1%) intervals with isolated abundance peaks higher than 15%.

Sphaeroidinellopsis seminulina gr. shows a general trend very similar to that of Dentoglobigerina gr., displaying low values (approximately 2%) but a continuous distribution with peaks of abundance higher than 14%.

Keeled globorotalids are represented by Globorotalia miotumida, G. menardii gr., G. margaritae margaritae, and G. cibaoensis.

G. miotumida, which includes less inflated forms, is present from the bottom of the studied interval with low frequencies (average value of  7%) up to 344.35 mbsf where it disappears. From this depth three short influxes are recorded (average value of 0.5%). The coiling direction of G. miotumida is prevalently sinistral.

G. menardii gr. includes the species G. menardii and G. multicamerata. G. menardii shows low and scattered occurrence from the base of the investigated interval (average value of 1.3%). The coiling direction is prevalently dextral with short sinistral influxes. G. multicamerata, which includes the forms with seven to ten chambers in the final whorl, first occurs at 342.05 mbsf and displays a low a discontinuous distribution with a maximum of approximately 2%. Throughout the studied interval, it is exclusively dextral.

G. margaritae margaritae occurs firstly at 336.11 mbsf, displaying a continuous presence until the top of the studied interval with low percentage value (about 9%). The coiling direction of this species is prevalently sinistral.

G. cibaoensis first occurs at 325.25 mbsf, showing low (about 2%) and scattered distribution up to 297.28 mbsf where it disappears. Throughout the studied interval, it is prevalently sinistral.

Unkeeled globorotalids are represented by Globorotalia juanai, G. margaritae primitiva, and G. scitula. G. juanai is present from the base of the investigated interval, showing abundance of about 5% that decreases until its disappearance at 337.66 mbsf.

G. margaritae primitiva first occurs at 337.49 mbsf, displaying low but continuous distribution (about 9%) with isolated abundance peaks higher than 10%. Throughout the studied interval, it is exclusively sinistral.

G. scitula shows low (about 1.4%) and scattered occurrences from the base. The coiling direction of this species is exclusively dextral.

Additional and significant taxa such as Globigerina falconensis (about 16%), Globigerinita gr. (about 22%), G. quadrilobatus gr. (about 14%), Orbulina gr. (about 5%), and Sphaeroidinellopsis seminulina gr. (about 21%) are continuously present throughout the investigated interval.

4. Biostratigraphy

Calcareous plankton biostratigraphy of the Hole 953C is based on the stratigraphic distribution of several Late Miocene-early Pliocene marker species. Ten biostratigraphic events, which have previously been dated astronomically both in the Atlantic Ocean and in the Mediterranean Sea, are also recognized in this work.

In the following, distribution patterns of the main biostratigraphic marker species are discussed in detail and compared with other land or deep-sea successions both from the Mediterranean Sea and Atlantic Ocean. The first, last regular, and last occurrences (FO, LRO, and LO) are shown in Table 2.

tab2
Table 2: ODP Hole 953C calcareous plankton bioevents. The asterisk indicates that the bioevents occur within the hiatus, which is an age span about 6.436 to 6.252 Ma.
4.1. Planktonic Foraminifera
4.1.1. Neogloboquadrina acostaensis Coiling Change

The Neogloboquadrina acostaensis coiling change is defined by the first common occurrence of dextral forms after a long period of dominance of sinistrally coiled specimens. It has recorded in the preevaporite marls of many Mediterranean sections (e.g., [45, 52, 73, 7586]) and in the Atlantic Ocean successions (e.g., [48, 82, 87100]), slightly predating the onset of the latest Miocene glaciation [8, 45, 52, 94, 95, 101, 102]. This event always seems to be located within subchron C3An.1r [84, 97, 103]; it usually occurs prior to the disappearance of Globorotalia miotumida ([82] and reference therein), and it is astronomically dated at 6.358 Ma in the Mediterranean area and at 6.373 Ma in the Atlantic one [56]. At Hole 953C, a very prominent sinistral to dextral coiling change of N. acostaensis (Plate 1, Figures 5(1), 5(2a), 5(2b), and 5(2c)), is recognized at 344.57 mbsf (sample 157-953C-18R-3, 96.5–98.5 cm). Moreover, this event is followed by pronounced sinistral influxes of the group: twelve in Ain el Beida section [48], while Benson and Rakic-El Beid [98] only recognized five influxes, which are most likely related to a lower sample resolution: two sinistral influxes in Falconara section [52] and in Sorbas Basin [45]. All influxes are located within subchron C3An.1n. In the ODP Hole 953C, five sinistral influxes are recognized between 341.60 and 332.80 mbsf.

Above the last sinistral shift, the coiling of N. acostaensis remains dominantly dextral up to the late part of Chron C3r, where a sinistral coiling change of this taxon is recognized at 314.55 mbsf (sample 157-953C-15R-2, 95–97 cm). The presence of this event, referred as “first Pliocene N. acostaensis sinistral shifts,” is identified both in the Atlantic and in the Mediterranean succession (e.g., [25, 28, 29, 33, 34, 53, 66, 99]).

4.1.2. Last Regular Occurrence and Last Occurrence of Globorotalia miotumida

Globorotalia miotumida is a typical Late Miocene species, recorded in the Mediterranean area (e.g., [45, 52, 73, 78, 93, 105, 106]) and in the Atlantic Ocean successions (e.g., [48, 87, 89, 92, 96, 107, 108]) playing a key role in the correlations between the two areas. At Hole 953C, G. miotumida (Plate 2, Figures 6(10a), 6(10b), 6(12a), 6(12b), and 6(12c)) is represented by a rich population from the bottom, up to 344.57 mbsf (sample 157-953C-18R-3, 96.5–98.5 cm) where it realizes the LRO. In the overlying samples, G. miotumida becomes rare up to its LO. The last typical specimens were found at 344.35 mbsf (sample 18R-3, 75–77 cm).

According to the literature, these events directly postdate the sinistral to dextral coiling change of N. acostaensis. In the Atlantic Ocean, they have been recorded within subchron C3An.1r; the LRO in the Ain el Beida section was found in the range of 6.308–6.311 Ma [48]. In the Mediterranean area, these events occur in the upper part of subchron C3An.2n; at Falconara section the LO was found at 6.506 Ma [52] and at 6.51 Ma by Blanc-Valleron et al. [73], the LRO in the Sorbas Basin at 6.504 Ma [45].

The progressively restricted connection between the Atlantic and Mediterranean during the Messinian was probably responsible for the earlier disappearance of this species from the Mediterranean.

Based on the previously mentioned micropaleontological observations, (i) the change in coiling direction of N. acostaensis from left to right (6.37 Ma, [56]) and (ii) the LRO of G. miotumida (6.31 Ma, [48]) occurred in the same level. It follows that a hiatus is recorded in the Hole 953C at 344.57 mbsf with an age span about 6.436 Ma to 6.252 Ma. According to Brunner et al. [67], the top of Chron C3An.2n (6.436 Ma, [56]) and the base of Chron C3An.1n (6.252 Ma, [56]) were apparently removed by slumping.

4.1.3. First Occurrence of Globorotalia margaritae margaritae

The First Occurrence of Globorotalia margaritae margaritae has been more widely disputed, because of the taxonomical problems related to its identification near the evolutionary transition from its ancestor.

It has been commonly used as marker for the early Pliocene in the Mediterranean (e.g., [75, 76, 109113]), in the South Atlantic [114, 115] and in the South Pacific [116118]. Also, it was found in the uppermost Miocene of the Mediterranean [98]; North Atlantic [48, 82, 98, 119] and Eastern Atlantic [91, 92] within subchron C3An.1r (immediately above to disappearance of Globorotalia miotumida in the North Atlantic; [82]), while Benson et al. [97] reported the G. margaritae FO in the middle of C3An.2n in both Ain el Beida and Salè cores. Moreover, Saito et al. [120] recorded this event within subchron C3An.1n in the Western Atlantic off Florida, equatorial Pacific, and equatorial Indian Ocean.

This event is astronomically dated at 6.08 Ma [56]. At Hole 953C G. m. margaritae (Plate 2, Figures 6(7a), 6(7b), 6(8a), 6(8b), and 6(8c)) occurs firstly at 336.11 mbsf (sample 17R-4, 51–53 cm), but probably it is not the evolutive appearance of the taxon due to the underlying hiatus.

Additional bioevent has been also recognized in the Globorotalia juanai LO at 337.66 mbsf, which was recorded in the Ain el Beida section in AEB 29 cycle by Krijgsman et al. [48].

4.2. Calcareous Nannofossils
4.2.1. Last Occurrence of Nicklithus amplificus

The importance of the Last occurrence of Nicklithus amplificus as a biostratigraphic marker in the upper Miocene and its reliability for time stratigraphic correlation has been confirmed in studies of numerous deep-sea succession [8, 121123]; the LO was found at 5.978 Ma in the ODP Site 925 and 926 ([124] and reference therein), at 5.939 Ma in the eastern Mediterranean ([124] and reference therein) and in the age range of 5.972–5.975 Ma in the Ain el Beida section [48]. This event occurs very close to the C3An/C3r Chron boundary and marks the beginning of the Messinian Salinity Crisis [8] in the Mediterranean basins. In the Hole 953C, the LO of this species is recorded at 334.52 mbsf (sample 157-953C-17R-3, 42–44 cm).

4.2.2. Last Occurrence of Triquetrorhabdulus rugosus

The Last Occurrence of Triquetrorhabdulus rugosus is traditionally used for identifying the Miocene/Pliocene boundary in open ocean areas and is considered an additional event to recognize the CN10a/CN10b subzonal boundary [125]; it is astronomically dated at 5.279 Ma and at 5.255 Ma in the low-latitude Atlantic [124] and in the Loulja section [34], respectively. In the Mediterranean basin, the T. rugosus LO is not considered a useful biostratigraphic event, because it is too rare in the samples. Nevertheless, it was identified in several successions just below the base of the Thvera subchron, and this bioevent is astronomically dated at 5.279 Ma [25, 32, 124, 126129]. According to the paleomagnetic stratigraphy, T. rugosus LO has a closely comparable stratigraphic position in Atlantic and Mediterranean records, and it can be used to correlate the base of the Pliocene in its type area (Eraclea Minoa section—Sicily, [130]) to the oceanic record. At Hole 953C, the LO of this species occurred at 312.73 mbsf (samples 157-953C-15R-2, 63–65 cm).

Two additional bioevents have been also recognized: (i) the Helicosphaera stalis ovata LO at 325.78 mbsf (sample 157-953C-16R-3, 91–93 cm) that was recorded in the Ain el Beida section between AEB38 and AEB 39 cycles by Krijgsman et al. [48] and the (ii) Amaurolithus bizzarus FO at 304 mbsf (sample 157-953C-14R-2, 10–12 cm), astronomically dated at 5.033 in the Loulja section by van der Laan et al. [34].

5. Cyclostratigraphy and Astronomical Calibration

5.1. Calcareous Plankton as Proxy for Identifying Astronomical Cyclicity

According to Hilgen [54, 55] and Hilgen et al. [3, 43], the high frequency alternations of different lithologies, recognized throughout several Mediterranean land-based sedimentary sequences, have an origin related to the astronomical forcing. For example, the limestone-marl couplets which characterize the Lower Pliocene pelagic sediments (“Trubi Fm.” Auct., Sicily), reflect the periodicity of the Earth’s precession cycle (e.g., [5355, 127, 128]). The marls were considered as the “equivalent” of the sapropels characterizing higher stratigraphic levels (“M. Narbonne Fm.” Auct., Sicily). On this assumption, Hilgen [54, 55] proposed his astronomically calibrated time scale, where marl layers (sapropel equivalents) are correlated to insolation maxima/precession minima and limestones correspond to periods of higher productivity induced by minima of the insolation curve (precession maxima).

In the absence of an evident lithological rhythm, biotic proxies may be taken into account to highlight the astronomical cyclicity of a sedimentary succession. In this framework, cyclostratigraphy and astronomical tuning to the ATNTS [56] has been carried out by means of foraminifera-based proxies (e.g., [6266, 131, 132]). In particular, the abundances curves of Globigerinoides/Orbulina gr., neogloboquadrinids, and the ratio of warm-water versus cool-water species show Milankovitch periodicities. The relationship between selected climate-sensitive planktonic taxa and lithological cyclicity, correlated in turn to astronomical cycles, is well expressed in the lower Messinian deposits of Sicily, Spain, and Greece (Figure 3).

947839.fig.003
Figure 3: Relationship among astronomically forced lithological cycles, abundances of selected planktonic foraminifera, warm/cold ratio, and inferred insolation cycles in different Mediterranean successions (Sicily; Gavdos Basin—Greece; Sorbas Basin—Spain). (Modified after [73, 74].)
5.1.1. Globigerinoides

In agreement with their unanimously declared warm-climate affinity (e.g., [6264, 131]), the highest abundances of the Globigerinoides population seem to correspond to maxima of the insolation cycles. In the Sicilian “Tripoli Fm.” (Auct.), consisting of a repetition of the same lithological triplet (“sapropel type” brown laminate-diatomite-marl), high frequencies of Globigerinoides gr. concentrate within brown laminates and diatomitic layers, corresponding to insolation maxima [73, 133, 134], whereas lowest frequencies fall within the middle part of the marls. A similar situation is recorded in the coeval sediments of the Gavdos Island (Greece, [45, 46, 74, 135]) where the basic cycle is three-folded as well (sapropel-diatomite-marl). Here, the highest abundances of Globigerinoides spp. are recorded within the sapropel and in lower-middle part of the diatomites. In the Sorbas Basin (Southern Spain, [46]), the lower Messinian sediments of the upper Abad section display quadruplet-type lithological cycles (sapropel-marl-diatomite-marl). In this case, maxima abundances of Globigerinoides spp. + Orbulina spp. are recorded in the middle-upper part of the sapropels or at the transition between the sapropel layers and the first marly horizons (Figure 3).

5.1.2. Neogloboquadrina

Usually reported as cool taxa [136138], neogloboquadrinids show an evident preference for stratified waters within high-productivity zone associated with the deep chlorophyll maximum (DCM), at the base of the euphotic zone [139141].

The neogloboquadrinids show maxima frequencies in correspondence of the topmost part of the diatomite and marl layers in the Sicilian Tripoli [73, 134]; they generally reach the highest percentages at the base of the first marl layer in the upper Abad section [46, 142] and within the diatomites at Gavdos [74] (Figure 3), thus implying different parameters than temperature controlling theirs distribution.

5.1.3. Warm/Cold Ratio

The ratio of warm-water versus cool-water taxa using modern habitat characteristics described by Pujol and Grazzini [138], Lourens et al. [53], Pérez-Folgado et al. [74], and Sierro et al. [46] herein follows. Warm-water taxa include G. decoraperta gr., G. quadrilobatus gr., G. obliquus, and O. universa, while Neogloboquadrina gr., G. falconensis, and G. glutinata were taken as representative of cool condition.

G. decoraperta gr. (G. decoraperta and G. apertura) is not living today but its descendant, G. rubescens, is currently living in subtropical and tropical environments. This species usually grows in the surface nutrient-depleted waters of the mixed layer in oceanographic settings with a strong stratification in the water column [136, 143, 144].

In the Sorbas basin, this group is abundant in the upper part of the sapropels and the lower part of the diatomites on Gavdos [74].

O. universa behaves as G. rubescens in the Sorbas basin and on Gavdos [74].

G. falconensis is a species whose geographic, depth, and seasonal distribution patterns are poorly known, because in the literature it is grouped with G. bulloides. However, studies of planktonic foraminiferal assemblages from the western North Atlantic [145], surface sediment data from the South Atlantic [146], and southern Indian Ocean [147] indicate that this species prefers to live in the cool subtropical regions.

G. glutinata is a ubiquitous species living in subarctic to subantarctic waters, low in absolute amount but with a high percentage in waters with very low total foraminiferal concentrations [143]. This species is abundant in the homogeneous marl-sapropel transitions both in the western and eastern Messinian Mediterranean [46, 74].

Generally, planktonic taxa indicative of warm nutrient-poor superficial waters are abundant in sapropels or sapropelitic layers, whereas cold eutrophic deep-water forms characterize the homogeneous marls or the diatomites [46, 73, 102, 148150].

A close dependence between lithofacies and microfossil assemblages has been proved for sapropel-bearing successions, with by definition, and the same microfossil assemblages can be considered as sensitive to astronomical periodicity also in successions lacking sapropels. Consequently, the abundance variations of the after-mentioned taxa allowed the astronomically tuned with the insolation curve of Laskar et al. ([104], La041:1 solution).

Particularly, insolation maxima-precession minima correspond to (i) maxima in the distribution patterns of both Globigerinoides/Orbulina gr. and warm/cold ratio; (ii) minima in the distribution patterns of neogloboquadrinids (Figure 4).

947839.fig.004
Figure 4: Cartoon showing the tuning of the ODP Hole 953C with the insolation and eccentricity curves of La041:1 solution [104] and the correlation to Ain el Beida and Loulja sections ([34, 48], resp.). Grey dotted lines represent the tendency lines of selected taxa and warm/cold ratio curves. The numbers from 1 to 43 refer to the lithological cycles. Position of calcareous plankton bioevents: (a) Neogloboquadrina acostaensis coiling change and Globorotalia miotumida Last Regular Occurrence; (b) Nicklithus amplificus Last Occurrence; (c) Helicosphaera stalis ovata Last Occurrence; (d) N. acostaensis first influx sx; (e) Triquetrorhabdulus rugosus Last Occurrence; (f) Amaurolithus bizzarus First Occurrence.
947839.fig.005
Figure 5
947839.fig.006
Figure 6
5.2. Astronomical Tuning

The magnetic polarity reversal ([67, 70] and reference therein) and the bioevents recognized in the Hole 953C have been used to correlate the studied sedimentary records with Ain el Beida and Loulja sections (Morocco), astronomically calibrated by Krijgsman et al. [48] and van der Laan et al. [34], respectively. The sinistral/dextral N. acostaensis coiling change, the LO of N. amplificus, and the LO of T. rugosus are considered synchronous events, which were used as tie points to calibrate astronomically the Hole 953C sedimentary sequence. The S/D N. acostaensis and the LO of N. amplificus calibrated at 6.378 Ma and 5.975 Ma by Krijgsman et al. [48] and the LO of T. rugosus calibrated at 5.255 Ma in cycle LA 15R (and [34]) were used as the starting point for tuning the sedimentary cycles at the Hole 953C. In addition, the LO of Helicosphaera stalis ovata LO (recorded in the Ain el Beida section by [48]) and the first sinistral influx of N. acostaensis (recorded in Loulja section by [34]) are here considered.

Forty-three sedimentary cycles were recognized in the Hole 953C (Figure 4) and are informally and progressively numbered from the base to the top of the studied interval.

5.2.1. Chron C3An

According to the literature, the Chron C3An (6.733 Ma–6.033 Ma, [56]) comprises thirty-two sedimentary cycles and corresponds to 700 kyrs. At Hole 953C, only thirteen precession cycles (1–13) were recognized due to (i) the 1.92 m thick no-recovery interval in the core 17R, which covers a time interval of 0.088 Ma; (ii) the hiatus identified at 344.57 mbsf with an age span about 6.436 Ma to 6.252 Ma. The cycles are highlighted by positive fluctuations of Globigerinoides/Orbulina gr.-warm/cold ratio which are in opposite phase respect to the fluctuations of Neogloboquadrina gr. Cycles 6 to 8 fit excellently with the high-amplitude fluctuations of the eccentricity curve. According to Krijgsman et al. [48], maxima in eccentricity enhance climate fluctuations on a precessional scale, because the eccentricity modulates the precession amplitude favouring the formation of distinct cycles.

5.2.2. Chron C3r

The Chron C3r (5.235 Ma–6.033 Ma, [56]) comprises a total number of twenty-seven sedimentary cycles and corresponds to 798 kyrs in according to the ATNTS2004 [56]. Twenty precession cycles (14–33) are recognized, owing to the no-recovery interval in the cores 16 (4.86 m thick) and 15 (6.02 m thick) that covers a time interval of 0.1578 Ma and 0.208 Ma, respectively. The cycles are highlighted by the abundance peaks of Globigerinoides/Orbulina gr.-warm/cold ratio signal, which are in opposite phase with Neogloboquadrina gr. distribution (except the cycles 20 and 22). Moreover, cycles 14, 17, and 20 fit excellently with the high-amplitude fluctuations of the eccentricity curve. The increase in thickness of cycles 24 and 27 has been interpreted as a change in the sedimentation rate. Additionally, the cycle 27 is interpreted as “double cycle” due by the fluctuations of the faunal proxies, like cycle AEB 41 from Ain el Beida [48].

In this interval, the recorded bioevents are (i) the LO of N. amplificus in the cycle 17 at the astronomical age of 5.979 Ma; (ii) the LO of H. stalis ovata in the cycle 24 at the astronomical age of 5.681 Ma; (iii) the presence of Discoaster quinqueramus in the cycle 28, which corresponds to cycle AEB 42 of Ain el Beida section [48]; (iv) the first sinistral influx of N. acostaensis in the cycle 30 at the astronomical age of 5.297 Ma; (v) the LO of T. rugosus in the cycle 33 at the astronomical age of 5.244 Ma. The recognition of these last two bioevents and the base of the Thvera magnetic event are a useful guide to identify the Miocene/Pliocene boundary in the interval studied. Since, from a cyclostratigraphic perspective, the boundary falls within the insolation cycle 510, five precessional cycles below the Thvera magnetic event, and has an astrochronological age of 5.332 Ma [53].

5.2.3. Chron C3n.4n

The Chron C3n.4n (4.997 Ma–5.235 Ma, [56]) comprises a total number of ten sedimentary cycles, corresponding to 238 kyrs according to the ATNTS2004. In this interval, the relation between warm/cold ratio maxima versus neogloboquadrinids minima, allowed to identified only five precession cycles (35–39), because of no-recovery interval in the core 14 (6.97 m thick) that covers a time interval of 0.12 Ma. In particular, cycles 36-37 fit excellently with the high-amplitude fluctuations of the eccentricity curve. In this interval, the Globigerinoides/Orbulina gr. signal is not clear or completely absent. In the cycle 37, the FO of A. bizzarus is recognized, and it has an astronomical age of 5.038 Ma, corresponding to cycle LB 2R of Loulja section [34].

5.2.4. Chron C3n.3r

In the literature, the Chron C3n.3r (4.896 Ma–4.997 Ma, [56]) comprises a total number of 4.5 sedimentary cycles and corresponds to 101 Kyrs according to the ATNTS2004. Three precession cycles (39–41) are recognized owing to the 1.43 m thick no-recovery interval in the core 13 cover a time interval of 0.044 Ma. The cycles are highlighted by two negative fluctuations of Neogloboquadrina gr. that are in opposite phase with those of the warm/cold ratio Globigerinoides/Orbulina gr. signals. In the cycle 39, the presence of H. sellii suggests a correspondence to cycle LB 6 of Loulja section [34].

5.2.5. Chron C3n.3n

In the literature, the Chron C3n.3n (4.799 Ma–4.896 Ma, [56]) comprises a total number of 2.5 sedimentary cycles and corresponds to 97 kyrs according to the ATNTS2004. The cycles (42-43) are highlighted by two negative fluctuations of Neogloboquadrina gr., which are in opposite phase with those of the warm/cold ratio Globigerinoides/Orbulina gr. signals. Finally, the increase in thickness of the cycles has been interpreted as a change in the sedimentation rate.

6. Conclusion

This paper presents the results of qualitative and quantitative analyses of the calcareous plankton assemblages, carried out in tract of the Hole 953C succession encompassing the Messinian to early Zanclean. The study allowed to recognize ten important bioevents, well calibrated and widely used in the Mediterranean and Atlantic correlation. Moreover, a cyclostratigraphic approach has been attempted to obtain a detailed chronostratigraphic subdivision. Lacking any evident lithological cyclicity and the no-recovery intervals along the succession, the combination of climate sensitive records allowed to extract signals of the astronomical cyclicities. The fluctuations curves of Globigerinoides/Orbulina gr., neogloboquadrinids, and the ratio of warm-water versus cool-water species highlight a frequency indicative of the Earth’s precession periodicity. Particularly, the insolation curve is in phase with the Globigerinoides/Orbulina gr. and warm/cold ratio distribution and is in antiphase with the Neogloboquadrina gr. curve. As result, forty-three precession-controlled cycles have been recognized spanning from 6.457 Ma to 4.799 Ma.

Description of Plates 1 and 2

Plate 1 (see Figure 5).(1) Neogloboquadrina acostaensis (Blow): umbilical view, sample 953C-13R-3, 8–10 cm.(2) Neogloboquadrina acostaensis (Blow): (a) umbilical view, (b) spiral view, (c) ultrastructure, sample 953C-13R-3, 8–10 cm.(3)Neogloboquadrina pachyderma (Ehrenberg): (a) umbilical view, (b) spiral view, sample 953C-18R-2, 98–100 cm.(4)Neogloboquadrina pachyderma (Ehrenberg): (a) umbilical view, (b) spiral view, (c) ultrastructure, sample 953C-19R-1, 24.5–26.5 cm.(5)Neogloboquadrina pachyderma (Ehrenberg): (a) umbilical view, (b) spiral view, sample 953C-18R-2, 98–100 cm.(6)Neogloboquadrina pachyderma (Ehrenberg): umbilical view, sample 953C-17R-3, 57–59 cm.(7)Neogloboquadrina dutertrei humerosa (Takayanagi and Saito): umbilical view, sample 953C-13R-2, 140.5–142.5 cm.(8)Neogloboquadrina dutertrei humerosa (Takayanagi and Saito): (a) umbilical view, (b) spiral view, (c) ultrastructure, sample 953C-13R-3, 26–28 cm.(9)Neogloboquadrina dutertrei humerosa (Takayanagi and Saito): (a) umbilical view, (b) spiral view, sample 953C-12R-2, 41.5–43.5 cm.(10)Neogloboquadrina dutertrei blowi Rögl and Bolli: umbilical view, sample 953C-13R-3, 91–93 cm.(11)Neogloboquadrina dutertrei blowi Rögl and Bolli: (a) umbilical view, (b) spiral view, (c) ultrastructure, sample 953C-16R-1, 38–40 cm.

Plate 2 (see Figure 6).(1)Globorotalia scitula (Brady): (a) umbilical view, (b) side view, (c) spiral view, sample 953C-17R-2, 12–14 cm.(2)Globorotalia juanai Bermúdez and Bolli: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-18R-3, 75–77 cm.(3)Globorotalia scitula (Brady): (a) umbilical view, (b) side view, (c) spiral view, sample 953C-14R-2, 45–47 cm.(4)Globorotalia juanai Bermúdez and Bolli: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-17R-5, 108–110 cm.(5)Globorotalia margaritae primitiva Cita: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-17R-1, 80–82 cm.(6)Globorotalia margaritae primitiva Cita: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-17R-2, 138–140 cm.(7)Globorotalia margaritae margaritae Bolli and Bermúdez: (a) umbilical view, (b) side view, sample 953C-16R-3, 74.5–76.5 cm.(8)Globorotalia margaritae margaritae Bolli and Bermúdez: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-13R-4, 147–149.(9)Globorotalia cibaoensis Bermúdez: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-16R-1, 128–130 cm.(10)Globorotalia miotumida Jenkins: (a) umbilical view, (b) spiral view.(11)Globorotalia cibaoensis Bermúdez: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-15R-2, 46–48 cm.(12)Globorotalia miotumida Jenkins: (a) umbilical view, (b) side view, (c) spiral view.(13)Globorotalia menardii (Parker, Jones and Brady): (a) umbilical view, (b) side view, (c) spiral view, sample 953C-16R-2, 144.5–146.5 cm.(14)Globorotalia multicamerata Cushman and Jarvis: (a) umbilical view, (b) side view, (c) spiral view, sample 953C-13R-3, 41.5–43.5 cm.(15)Globorotalia menardii (Parker, Jones and Brady): (a) umbilical view, (b) side view, (c) spiral view, sample 953C-13R-3, 91–93 cm.

For quantitative data of ODP Hole 953C planktonic foraminifera, see Tables 1 and 2 of the Supplementary Material available online at  http://dx.doi.org/10.1155/2013/947839.

Acknowledgments

The author is particularly grateful to Gianfranco Salvatorini for discussing data, for his helpful comments, support, and encouragement. She thanks Niccolò Baldassini for calcareous nannoplankton analyses. She is grateful to Hugo Corbí and an anonymous reviewer for their critical reading of the paper. Samples for this study were obtained through the courtesy of the Integrated Ocean Drilling Program. This paper is dedicated to whom is no longer with us and to whom will come soon.

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