Jorge Agustí

A calibrated mammal scale for the Neogene of Western Europe. State of the art

Abstract A magnetobiostratigraphically calibrated mammal scale for the Neogene of Western Europe is presented in this paper. The Mammal Neogene (MN) units originally proposed by Mein [Report on activity RCMNS-Working groups (1975)] have been re-defined here on the basis of first appearances of selected small and large mammal taxa. The chronology of the lower boundaries of each unit had been established mostly after the significant magnetobiostratigraphic framework developed in the last decade in a number of Spanish basins: Ebro, Calatayud–Daroca, Valles–Penedes, Teruel, Fortuna, Cabriel and Guadix–Baza. In the case of the early and middle Miocene (particularly, MN 1, MN 2 and MN 3), the authors have also taken into account the magnetobiostratigraphic framework developed in the North Alpine Foreland Basin. Some alternative correlations of the magnetostratigraphic data from this last basin are proposed in order to achieve a higher degree of consistence with the data from the Iberian basins. A quite well established magnetostratigraphic calibration of the MN boundaries can be proposed for most of the Neogene, from Middle Miocene to Late Pliocene. On the other hand, the chronological boundaries of the Early Miocene MN units are still poorly constrained due to: (1) scarcity of well-studied, continuous, thick magnetostratigraphic sections; (2) the difficulty in defining the boundaries of the MN zones for this time-span due to the relative homogeneity and persistence of the fossil rodent faunas and the absence of significant large mammal dispersal events. Some of the troubles which arise with the application of the MN units strengthen the need to take into account the palaeobiogeographical meaning of these units and their real suitability to date and correlate through extensive geographic areas.

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.

Chronology of the late Turolian deposits of the Fortuna basin (SE Spain): implications for the Messinian evolution of the eastern Betics

The magnetostratigraphy of the mammal-bearing alluvial fan‐fan delta sequences of the Fortuna basin (SE Spain) has yielded an accurate chronology for the late Turolian (Messinian) basin infill. From early to late Messinian (at least between 6.8 and 5.7 Ma), the Fortuna basin records the sedimentation of alluvial‐palustrine deposits over a confined shallow basin. Changing environmental conditions in the latest Messinian are illustrated by the retreat of palustrine facies. A rapid progradation of the marginal clastic wedges and the initiation of an efficient basin drainage at5.8 Ma (lower part of chron C3r) most likely represents the onshore response to the drastic drop of base level taking place during the Messinian salinity crisis. This study further provides improved age estimates for the late Turolian land mammal events in southern Spain. The oldest MN 13 locality in the studied sections is correlated to chron C3Ar at an age of 6.8 Ma. The entry of camels and the murid Paraethomys in southern Spain occurs in chron C3An.1n at 6.1 Ma, and gives further support for land mammal exchange between Africa and the Iberian peninsula prior to the salinity crisis, in good agreement with

The 'Tortonian salinity crisis' of the eastern Betics (Spain)

The late Miocene depositional history of the Lorca and Fortuna basins, both occupying an internal position in the eastern Betics of Spain, is marked by a regressive sequence from open marine marls, via diatomites and evaporites, to continental sediments. Based on facies similarities, these evaporites have often been correlated to the well-known Mediterranean evaporites of the Messinian salinity crisis, although this correlation was never substantiated by reliable chronological data. In this paper, we present an integrated stratigraphy of this regressive sequence which shows that the evaporites of the Lorca and Fortuna basins are entirely of late Tortonian age and as such have no relation with the Messinian salinity crisis. The main phase of basin restriction, resulting in deposition of diatomites and evaporites, took place at 7.8 Ma, while the last marine deposits (massive evaporites of the Lorca basin) are dated at 7.6 Ma. Consequently, this ‘Tortonian salinity crisis’ of the eastern Betics had a duration of approximately 200 kyr, while continental deposition prevailed throughout the entire Messinian as also revealed by the fossil mammal record. The ‘Tortonian salinity crisis’ of the eastern Betics is obviously related to a local phase of basin restriction caused by uplift of the metamorphic complexes at the basin margins, probably in concert with strike-slip activity along SW^NE trending fault systems. The development of a submarine sill is of crucial importance for the increase in salinity because it allows marine waters to continuously enter the basin at the surface while it restricts or prevents the outflow of dense saline waters at depth. Furthermore, we show that evaporite and diatomite cyclicity in these restricted basins is predominantly related to precession controlled circum-Mediterranean climate changes and that glacio-eustatic sea level changes only play a minor role. It is remarkable that the lithological sequence of the Tortonian salinity crisis mimics in many aspects that of the Messinian salinity crisis. This suggests that the diatomaceous facies is an essential part of the lithological sequence associated with basin restriction. fl 2000 Elsevier Science B.V. All rights reserved.

Explaining the end of the hominoid experiment in Europe.

The Vallesian Crisis involved the extinction of most of the hominoids that settled successfully in Europe during the middle and early Late Miocene, including Dryopithecus, Ankarapithecus and Graecopithecus. This event has been dated at 9.6 Ma, predating by more than one million years the spread of the C4 grasses and the retreat of forests over large parts of the globe at 7-8 Ma. The finding of macrofloral remains in the Terrassa section (Vallès-Penedès Basin) sheds new light on the nature of vegetational change associated with the hominoid extinction. This section presents an abundant late Vallesian vertebrate fauna and has been accurately dated at 9.2 - 9 Ma by paleomagnetism. Therefore, it provides the best indication of the kind of vegetation that occupied the area after the Vallesian Crisis. It is suggested that the extinction of the late Miocene Western European hominoids was not related to the spread of grasses, but to a significant increase of a floral association dominated by deciduous trees.

The Vallesian mammal succession in the Vallès-Penedès basin (northeast Spain): Paleomagnetic calibration and correlation with global events

Abstract The integrated lithostratigraphic, biostratigraphic and magnetostratigraphic study of new and classical alluvial fan sequences in the Valles-Penedes Basin (northeast Spain, Western Mediterranean) enabled a considerable refinement of the Vallesian mammalian succession in this basin and its correlation with the Magnetic Polarity Time Scale. Up to 12 new sections were logged and sampled in a search of mammal remains and a paleomagnetic analysis was carried out. The correlation among these sections was based on the small mammal content and the succession of magnetozones, enabling the establishment of four main composite sections (Les Fonts, Montagut, Terrassa and Viladecavalls). As a result, the Vallesian in the Valles-Penedes Basin appears punctuated by four main mammalian events, which coincide with the appearance of the genera Hipparion, Cricetulodon, Progonomys and Rotundomys. The Hipparion event did not coincide with any further change in the associations of small and large mammals. The dispersal of the cricetid Cricetulodon, in its turn, involved the first set of extinctions in the Vallesian, affecting the rodent and carnivore and artiodactyl associations. The main break during the Vallesian coincided with the dispersal of the murids of the genus Progonomys and implied a sudden drop in the diversity of the rodent and artiodactyl species of warm wet-forested affinities. This phase is characterized by the association of the murid Progonomys and the cricetid Cricetulodon and includes the last record of hominoids in the basin. The replacement of Cricetulodon by the sigmodont cricetid Rotundomys was associated with the entry of some typical early Turolian species. According to the correlation established, it is concluded that the FAD of Hipparion in the Valles-Penedes Basin is dated at 11.1 Ma, at the base of Chron C5r.1n. This data is congruent with other datings in Northern Africa and Eastern Europe, suggesting the isochrony of this event in the Mediterranean regions. The Cricetulodon FAD is dated to 10.4 Ma, in Chron C5n. The Progonomys dispersal, coincident with the late Vallesian Crisis, is dated at 9.7 Ma, in Chron C4Ar.3r. The Rotundomys FAD is dated at 9.2–9.3 Ma, in the upper part of Chron C4Ar.1n. The Vallesian mammal bioevents affected the peri-Mediterranean zones, including Northern Africa, and other regions in Northern and Western Eurasia. These paleofaunistic changes were caused by temperature descent from subtropical to warm-temperate conditions as well as by changes in the aridity balance and seasonality. This climatic evolution was the result of the interplay of diverse global events (cooling of the high latitude regions, growing of the Antarctica ice sheet, and enhancement of the thermohaline oceanic circulation) and of large-scale tectonic and paleogeographic processes (surface uplift of the Himalayas, the Tibetan Plateau and other tectonic reliefs, closing of gateways between the Mediterranean marine regions and the World Ocean). The magnetobiochronology resulting from the study of the Western Valles sequences suggests a close chronological correlation between some of these global and regional processes and the Vallesian bioevents recorded.

Magnetostratigraphy of the Vallesian (late Miocene) in the Vallès-Penedès Basin (northeast Spain)

The magnetostratigraphic analysis of the late Miocene continental deposits from the Valles-Penedes Basin, combined with its well-documented fossil mammal record, has provided a well-resolved chronology for the upper basin infill. The study is based on the biostratigraphic and magnetostratigraphic cross-correlation of 12 sections throughout the alluvial sequences in the western Valles area. The biostratigraphic framework consists of 21 mammal localities corresponding to the Mammal Neogene MN9 and MN10 units. The composite magnetic polarity sequence is based on 400 paleomagnetic sites. Correlation with the Geomagnetic Polarity Time Scale (GPTS) has led to an absolute dating of the faunal events and a precise chronostratigraphy of the Vallesian mammal stage in its type area. The Hipparion First Appearance Datum (FAD), at the MN8MN9 boundary, is dated at 11.1 Ma in the Valles-Penedes Basin. This age, compared to other radiometrically dated localities in Europe, North Africa and Turkey, is consistent with an isochronous dispersal of this equid through the Mediterranean region. A possible isochrony at a larger geographical scale (Old World, Mesogea) must await more reliable ages of the Hipparion FAD in Asia and Africa. The Cricetulodon FAD (MN9aMN9b boundary) is dated to 10.4 Ma, in chron C5n. The Progonomys FAD (MN9MN10 boundary), corresponding to the intra-Vallesian faunal crisis, is dated at 9.7 Ma (C4Ar.3r). The Vallesian spans 2.4 Myr, from 11.1 Ma (C5r.1n) to 8.7 Ma (C4An) and correlates to the early Tortonian.

A complete terrestrial Oligocene magnetobiostratigraphy from the Ebro Basin, Spain

Abstract The integrated litho-, bio- and magnetostratigraphic cross-correlation of 11 continuous and correlatable sections in the southeastern Ebro Basin (NE Spain) produced a complete Oligocene magnetic polarity stratigraphy ranging from latest Eocene to earliest Miocene. The magnetic polarity zonation of the different alluvial and shallow lacustrine sections has been correlated to the GPTS using fossil mammals and the distinct sequence and pattern of polarity reversals. The composite magnetic polarity sequence defines a continuous sequence from Chron C15n to Chron 6Cn.2n, from 34.8 to 23.7 Ma (late Eocene–early Miocene). In addition, a few short normal and reverse polarity events that correlate to cryptochrons in the GPTS are found (i.e. in C11n.1r and C8n.1r). The resulting regional magneto–biostratigraphic framework based on fossil mammals is proposed to refine the dating of the European Oligocene biochronological mammal Paleogene units and correlate them with the standard Oligocene marine stages and the North American land mammal ages. The magnetochronology now established enables more precise dating of the late Eocene and Oligocene paleofloristic and paleofaunistic changes in southwestern Europe, which were coeval to ongoing global paleoclimatic and paleoceanographic changes on Earth caused by high latitude cooling and ice sheet development in eastern Antarctica.

Calibration of the late Pliocene-early Pleistocene transition in the continental beds of the Guadix-Baza basin (southeastern Spain)

In this paper a survey of the correlation between magnetic polarity and the mammalian succession in the Plio-Pleistocene sequence of the Guadix-Baza basin is presented. In this basin a complete continental sequence from the early Pliocene to the Middle Pleistocene is present, allowing the correlation of mammalian biozones with the geomagnetic polarity scale. Two sections of the Baza sector of the basin have been analyzed in order to calibrate the Pliocene-Pleistocene transition: the Galera (middle Pliocene to early Pleistocene) and the Orce (late Pliocene to early Pleistocene). It is concluded that the boundary between the MN 15 (late Ruscinian) and the MN 16 (early Villanyian) is placed between the 2An. 3n chron and the 2An. In subchron. The late Villanyian (MN 17) extends up to the upper part of chron 2r. 1r. The entry of the Pleistocene marker Allophaiomys pliocaenicus can be placed within subchron 2n (Olduvai).

LATE PLIOCENE CONTINENTAL MAGNETOCHRONOLOGY IN THE GUADIX-BAZA BASIN (BETIC RANGES, SPAIN)

Abstract The late Pliocene shallow lacustrine sequences in the Guadix-Baza basin (Betic Ranges, southeast Spain) are a suitable setting for mammal chronology because of the abundance of rich, mammal-bearing sites. Stratigraphic superposition of late Ruscinian and Villanyian vertebrate fossils makes the Galera Section very appropriate for magnetostratigraphic dating. Sediments are characterized by a weak but measurable magnetization predominantly carried by magnetite. Other remanence carriers, such as iron sulphides and hematite, may be significant only in some particular lithologies, such as dark palustrine organic silts and red alluvial beds, respectively. Direct correlation of the Galera Section to the geomagnetic polarity time scale provides a reliable dating of the late Ruscinian and Villanyian mammal units. The Ruscinian/Villanyian boundary (MN15/MN16) is found to occur in the lower Gauss chron, and approximately correlates to the 3.3 Ma cooling event observed in stable-isotope and planktonic foraminifera deep sea records. The earliest occurrence of late Villanyian assemblages (MN17) in the lower part of the Matuyama chron allows dating of the early/late Villanyian boundary (MN6/MN17) to approximately 2.4–2.6 Ma. Based on the presence of late Villanyian assemblages underlying the base of the Olduvai chron, a maximum age of 1.95 Ma (top of C2r) is attributed to the Villanyian/Biharian (MN17/MmQ) boundary. A 300 kyr sedimentary gap in the Galera Section is suggested to correlate with a probable early Villanyian hiatus, an hypothesis that agrees with the absence of fossils of this age elsewherein the Baza Formation.