Cor G. Langereis

Late Neogene chronology: New perspectives in high-resolution stratigraphy

We present an integrated geochronology for late Neogene time (Pliocene, Pleistocene, and Holocene Epochs) based on an analysis of data from stable isotopes, magnetostratigraphy, radiochronology, and calcareous plankton biostratigraphy. Discrepancies between recently formulated astronomical chronologies and magnetochronologies for the past 6 m.y. have been resolved on the basis of new, high-precision Ar/Ar ages in the younger part of this interval, the so-called Brunhes, Matuyama, and Gauss Epochs (5 Chrons C1n‐C2An; 0‐3.58 Ma), and revised analysis of sea floor anomalies in the Pacific Ocean in the older part, the so-called Gilbert Epoch (5 Chron C2Ar‐C3r; 3.58‐5.89 Ma). The magneto- and astrochronologies are now concordant back to the Chron C3r/C3An boundary at 5.89 Ma. TheNeogene(Miocene,Pliocene,Pleistocene, and Holocene) and Paleogene are treated here as period/system subdivisions oftheCenozoicEra/Erathem,replacements for the antiquated terms Tertiary and Quaternary.TheboundarybetweentheMiocene and Pliocene Series (Messinian/Zanclean Stages),whoseglobalstratotypesectionand point (GSSP) is currently proposed to be in Sicily,islocatedwithinthereversedinterval just below the Thvera (C3n.4n) Magnetic Polarity Subchronozone with an estimated age of 5.32 Ma. The Pliocene/Pleistocene boundary, whose GSSP is located at Vrica (Calabria,Italy),islocatednearthetopof the Olduvai (C2n) Magnetic Polarity Subchronozone with an estimated age of 1.81 Ma. The 13 calcareous nannoplankton and 48 planktonic foraminiferal datum events for the Pliocene, and 12 calcareous nannoplankton and 10 planktonic foraminiferal datum events for the Pleistocene, are calibrated to the newly revised late Neogeneastronomical/geomagneticpolarity time scale.

Extending the astronomical ( polarity) time scale into the Miocene

An astronomical time scale is presented for the late Miocene based on the correlation of characteristic sedimentary cycle patterns in marine sections in the Mediterranean to the 65”N summer insolation curve of La90 [ 1,2] with present-day values for the dynamical ellipticity of the Earth and tidd dissipation by the moon. This correlation yields ages for all sedimentary cycles and hence also for the recorded polarity reversals, and planktonic foraminiferal and dinoflagellate events. The Tortonian/Messinian (T/M) boundary placed at the first regular occurrence of the Globorofuliu conomiozea group in the Mediterranean is dated at 7.24 Ma. The duration of the Messinian is estimated at 1.91 Myr because the Miocene/Pliocene boundary has been dated previously at 5.33 Ma [3]. The new time scale is confirmed by “OAr/ 3gAr ages of volcanic beds and by the number of sedimentary cycles in the younger part of the Mediterranean Messinian.

Tibetan plateau aridification linked to global cooling at the Eocene-Oligocene transition

Continental aridification and the intensification of the monsoons in Asia are generally attributed to uplift of the Tibetan plateau and to the land–sea redistributions associated with the continental collision of India and Asia, whereas some studies suggest that past changes in Asian environments are mainly governed by global climate. The most dramatic climate event since the onset of the collision of India and Asia is the Eocene–Oligocene transition, an abrupt cooling step associated with the onset of glaciation in Antarctica 34 million years ago. However, the influence of this global event on Asian environments is poorly understood. Here we use magnetostratigraphy and cyclostratigraphy to show that aridification, which is indicated by the disappearance of playa lake deposits in the northeastern Tibetan plateau, occurred precisely at the time of the Eocene–Oligocene transition. Our findings suggest that this global transition is linked to significant aridification and cooling in continental Asia recorded by palaeontological and palaeoenvironmental changes, and thus support the idea that global cooling is associated with the Eocene–Oligocene transition. We show that, with sufficient age control on the sedimentary records, global climate can be distinguished from tectonism and recognized as a major contributor to continental Asian environments.

Late Neogene evolution of the Taza-Guercif Basin (Rifian Corridor, Morocco) and implications for the Messinian salinity crisis

Abstract Magnetostratigraphic and biostratigraphic results are presented from Neogene deposits in the Taza–Guercif Basin, located at the southern margin of the Rifian Corridor in Morocco. This corridor was the main marine passageway which connected the Mediterranean with the Atlantic during Messinian times. Correlation of the biostratigraphy and polarity sequence of the Taza–Guercif composite section to the astronomical time scale, allows an accurate dating of three subsequent events in the Rifian Corridor. (1) The oldest marine sediments marking the opening of the Rifian Corridor were deposited at 8 Ma. At this age, a deep (600 m) marine basin developed in the Taza–Guercif area, marked by deposition of precession-controlled turbidite–marl cycles. (2) Paleodepth reconstructions indicate that a rapid (5 m/ka) shallowing of the marine corridor took place at the Tortonian/Messinian boundary, at an age of 7.2 Ma. This shallowing phase is primarily related to active tectonics, although a small glacio-eustatic sea level lowering also took place. (3) The Taza–Guercif Basin was emergent at an age of 6.0 Ma and, subsequently, continental sedimentation continued well into the Early Pliocene. We suggest that shallowing and restricting the marine passageway through the Rifian Corridor actually initiated the Messinian salinity crisis, well before the deposition of the Messinian evaporites in the Mediterranean.

A new astronomical timescale for the loess deposits of Northern China

Here, we present a refined timescale for the entire sequence of Quaternary Chinese loess, which relies upon the correlation of detailed monsoon records to the astronomical solution of Laskar (1990) and the oceanic ODP677 δ18O record of Shackleton et al. (1990). The chronological scheme considers in detail the relative structures of the palaeoclimatic and palaeomagnetic records to produce an accurate timescale that is consistent with the current understanding of loess depositional and post-depositional processes. Analysis of this chronological framework demonstrates downward displacement of the palaeomagnetic horizons with respect to the climatic record.

Late Miocene magnetostratigraphy, biostratigraphy and cyclostratigraphy in the Mediterranean

A new chronology for the late Miocene of the Mediterranean is presented by combining magnetostratigraphic, biostratigraphic (planktonic foraminifera and dinoflagellates) and cyclo-stratigraphic data. Long and continuous upper Miocene sections on Gavdos (Metochia section) and Sicily (Gibliscemi section) display cyclic alternations of homogeneous marls and sapropels and can be correlated on the basis of their distinct cyclic patterns. The Metochia section yields a good paleomagnetic signal and the position of 17 polarity reversals can be determined. The resulting polarity sequence allows an unambiguous correlation to the geomagnetic polarity time scale (GPTS). The paleomagnetic signal in the Gibliscemi section is too weak to determine a reliable polarity sequence, except for the lowermost part of the section. Detailed biostratigraphic analysis results in the identification of 13 planktonic foraminiferal and 9 dinoflagellate bioevents, which can all be accurately dated. The Tortonian/Messinian boundary, defined by the First Regular Occurrence (FRO) of the G. conomiozea group, is determined in chron C3Br.1r with an age of 7.12 Ma, according to the GPTS (CK95) of Cande and Kent [1].

A new chronology for the middle to late Miocene continental record in Spain

Abstract The first detailed chronology for the middle to late Miocene continental record in Spain is presented, based on high-resolution magnetostratigraphic data of mammal-bearing sections which were studied in several basins (Calatayud-Daroca, Teruel, Valles-Penedes, Duero and Jucar-Cabriel). Our results indicate that these sections compose an almost complete magnetostratigraphic succession from the lower Aragonian (MN4) to the middle Turolian (MN12). Seven successive Mammal Neogene (MN) zone boundaries are directly dated in these sections, which often contain faunas of two successive zones in superposition. The three oldest boundaries are dated in the Aragonian type area (Calatayud-Daroca Basin). The MN4/MN5 boundary (Vargas section) occurs in chron C5Cr(o) with a corresponding age of 17.26 ± 0.01 Ma, the MN5/MN6 boundary (Aragon section) in chron C5ACn(0.8), with an age of 13.75 ± 0.03 Ma, and the MN6/MN7–8 boundary (Aragon section) in the interval C5Ar.1n–C5Ar.3r with an age of 12.75 ± 0.25 Ma. The MN7–8/MN9 (Aragonian/Vallesian) boundary, occurring in chron C5r.1n at 11.1 Ma, and the MN9/MN10 boundary, in chron C4Ar.3r at 9.7 ± 0.1 Ma, are recorded in the Valles-Penedes Basin (Vallesian type area) and are supported by the results from the Duero Basin (Torremormojon section). In the Turolian type area (Teruel Basin), the MN10/MN11 (Vallesian/Turolian) boundary (La Gloria section) occurs in chron C4An(y) at 8.7 ± 0.1 Ma. Taking into account the pre-existing data from the Jucar-Cabriel Basin, the MN11/MN12 boundary (Cabriel Valley section) is recalibrated to C4n.1n, at an age of 7.5 ± 0.1 Ma.

The Rossello composite: a Mediterranean and global reference section for the Early to early Late Pliocene

A high-resolution magnetostratigraphy (planktonic foraminiferal) biostratigraphy and cyclostratigraphy is presented for the Pliocene Trubi marls in the Punta di Maiata section on Sicily. The integrated stratigraphy of the Rossello composite section of Hilgen ([1], Newslett. Stratigr., 17, 1987) is thereby completed. This composite section provides an unprecedented high-quality reference section for the Early to early Late Pliocene, containing a continuous sequence ranging from below the Thvera Subchron into the Matuyama Chron (4.86-2.45 Ma). The Punta di Maiata section extends from the Sidufjall Subchron of the Gilbert into the Gauss Chron (4.50-3.30 Ma). Linear interpolation between paleomagnetic datum planes in this section yields first-order age estimates of 3.72 (±0.01) and 3.59 (±0.01) Ma for the last common occurrence (LCO) and the actual last occurrence (LO) of Globorotalia margaritae. In addition, this age of 3.59 Ma provides an accurate age for the Zanclean-Piacenzian (Z/P) boundary, provided the LO of G. margaritae is maintained as a criterion to define this boundary in the Mediterranean. Irrespective, however, of the criterion used, the Punta di Maiata and Punta Piccola subsections of the Rossello composite are at present the most suitable sections to be designated as stratotypes for the Z/P boundary. The global significance of the Rossello composite is further strongly enhanced by the establishment of an astronomically calibrated geomagnetic polarity time scale based on the correlation of the Trubi sedimentary cycles with the astronomical record.

Integrated magnetostratigraphy and biostratigraphy of the upper Pliocene-lower Pleistocene from the Monte Singa and Crotone areas in Calabria, Italy

The results of a detailed magnetostratigraphic and biostratigraphic study of late Pliocene to early Pleistocene marine marl sequences from the Monte Singa and Crotone areas in Calabria, Italy are presented. The magnetostratigraphy from the Monte Singa sequence ranges from below the Gauss/Matuyama boundary up to and including the lower Olduvai boundary. Normal polarities at a level corresponding to isotope stage 81 most probably represent the R~union subchron. From the lower Olduvai boundary upward, a reliable magnetostratigraphy could not be established due to increased weathering of the marls, resulting in mainly secondary magnetizations. The magnetostratigraphy from the composite sequence of the Crotone area belongs to a large part of the Matuyama Chron and includes the Olduvai subchron. The position of the lower and upper boundaries of the Olduvai subzone could be established more precisely than from earlier results. Moreover, the upper boundary of the Olduvai subzone poses an ambiguity: a relatively long normal polarity interval representing the main Olduvai subchron and corresponding to a duration of 115 ka is followed by a short (30 ka) reversed subchron and the short (15 ka) normal Vrica subchron. Another option, and more in accordance with the duration of the Olduvai subchron in literature, would be to consider the complete N-R-N polarity succession with a total duration of 160 ka as representing the Olduvai subchron, implying that this Olduvai subchron has a short reversed interval in its upper part. Linear interpolation and extrapolation yield ages for the most important late Pliocene-early Pleistocene biostratigraphic datum levels. An age of 1.69 Ma is found for the Pliocene-Pleistocene boundary, using the conventional polarity time scale dated with radiometric results. However Hilgen [1], in correlating the sapropel groups and patterns to the precession curve of the Earths orbit, obtained significantly different ages for the polarity transitions of the present study. According to this astronomically calibrated polarity time scale, the age of the Pliocene-Pleistocene boundary is 1.81 Ma.

Neogene evolution of the Aegean arc: paleomagnetic and geodetic evidence for a rapid and young rotation phase

New paleomagnetic data of the entire Aegean outer-arc are presented. The results indicate a young Pleistocene and rapid clockwise rotation phase in the western Aegean arc, covering at least Zakynthos and the Peloponessos. The eastern Aegean arc, incorporating Kassos, Karpathos and Rhodos, also experienced Pleistocene anticlockwise rotations. The anisotropies of the magnetic susceptibility (AMS) data are in agreement with arc-parallel extension in the south and south-eastern Aegean arc and arc-normal compression in the north-west, in agreement with structural and geodetic observations. We compare the paleomagnetic results with the present-day pattern of rotation as computed from geodetic data, and we find good agreement. The onset of the Pleistocene rotations coincides with the beginning of uplift and a change in the stress pattern of extension. We compare our findings with existing models for the Aegean area. fl 2000 Elsevier Science B.V. All rights reserved.