Lluís Cabrera

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.

Late Neogene lacustrine record and palaeogeography in the Quillagua–Llamara basin, Central Andean fore-arc (northern Chile)

Abstract The Cenozoic Quillagua–Llamara basin (northern Chile, Central Andes) is an asymmetrical, intramassif fore-arc basin with a relatively wide northern sector separated from a narrower southward extension by a basement threshold. The northern sector was characterised by a noticeable Oligocene?–late Neogene alluvial-fan and lacustrine dominated deposition which resulted in sequences up to 900 m thick, whereas the southern sector was often a bypass zone with thinner fluvial and lacustrine sediment accumulation. The basin infill includes two third-order alluvial–lacustrine unconformity-bounded units which include other higher-frequency (4th to 5th order) sequences. The evolution of the Late Miocene–Pliocene lacustrine episodes in the Quillagua–Llamara basin was not only controlled by the regional variations from arid to hyperarid palaeoclimate conditions, due to the combined influence of the Pacific high pressure cell, the rain shadow effect exerted by the rising Andes and the northward flowing cold oceanic currents, but also by: (a) the extensional tectonics and evolution and uplift of the fore-arc region which defined the location and size of the depocentres; (b) the resulting basement palaeorelief which affected sediment thickness and facies distribution during the late basin-infill episodes; and (c) the tectonic modifications of watersheds, water divides and drainage networks in the Precordillera which caused considerable changes of water income in the lacustrine systems. Understanding of this regional tectonosedimentary evolution is a necessary first step before analysing of the low- to high-order lacustrine sequence changes in the region. Lacustrine water supply was very sensitive to tectonics; even gentle tectonic tilting and uplifting in critical water-divide zones could result in changes in water balance in the lacustrine basins and trigger variations in the depositional record. The very conspicuous, lacustrine regime changes recorded in the Quillagua–Llamara basin infill cannot be considered in themselves conclusive proof of an exclusive climatic forcing, since they took place close to either major regional drainage changes or to gentle but noticeable tectonic reactivation in the fore-arc region.

First partial face and upper dentition of the Middle Miocene hominoid Dryopithecus fontani from Abocador de Can Mata (Vallès‐Penedès Basin, Catalonia, NE Spain): Taxonomic and phylogenetic implications

A well-preserved 11.8-million-years-old lower face attributed to the seminal taxon Dryopithecus fontani (Primates, Hominidae) from the Catalan site ACM/C3-Ae of the Hostalets de Pierola area (Vallès-Penedès Basin, Catalonia, NE Spain) is described. The new data indicate that D. fontani is distinct at the genus level from Late Miocene European taxa previously attributed to Dryopithecus, which are here reassigned to Hispanopithecus. The new facial specimen also suggests that D. fontani and the Middle Miocene Pierolapithecus catalaunicus are not synonymous. Anatomical and morphometric analyses further indicate that the new specimen shows a combination of lower facial features-hitherto unknown in Miocene hominoids-that resembles the facial pattern of Gorilla, thus providing the first nondental evidence of gorilla-like lower facial morphology in the fossil record. Considering the current evidence, the gorilla-like facial pattern of D. fontani is inferred to be derived relative to previously known stem hominids, and might indicate that this taxon is either an early member of the Homininae or, alternatively, a stem hominid convergent with the lower facial pattern of Gorilla. The biogeographic implications of both alternatives are discussed. This new finding in the Hostalets de Pierola section reinforces the importance of this area for understanding the elusive question of the Middle Miocene origin and early radiation of great apes.

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.

Old World first appearance datum of “Hipparion” horses: Late Miocene large-mammal dispersal and global events

The magnetobiochronological dating of the late Miocene hipparionine horses ( “Hipparion” ) in the western Mediterranean places its first appearance datum (FAD) in the circum-Mediterranean region at the Chron C5r, at a minimum age of 11.1 Ma. This date challenges some of the widely accepted datings of this bioevent in western Eurasia and is relevant to the discussion of the mode and tempo of “Hipparion” dispersal. The migration of the “Hipparion” North American ancestor is related to the glacioeustatic sea-level lowstand of the supercycle TB3.1 (early Tortonian) and to the concurrent deep-sea hiatus NH4 and oceanic δ 18 O isotopic event Mi5. The “Hipparion” dispersal was a conspicuous, worldwide, on-land bioevent that was coeval with major late Miocene oceanic and high-latitude paleoclimatic global changes.

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.

Statistical grid-based facies reconstruction and modelling for sedimentary bodies. Alluvial-palustrine and turbiditic examples

The geological community is increasingly aware of the importance of geological heterogeneity for managing subsurface activities. In sedimentary bodies, facies distribution is an important factor constraining geological heterogeneity. Statistical grid-based sedimentary facies reconstruction and modelling methods (FRM methods) can be used to provide accurate representations (reconstructions or models) of facies distribution at a variety of scales, which can be conditioned to hard and soft data. These representations enable geological heterogeneity to be quantified; and therefore, serve as important inputs to manage projects involving subsurface activities. FRM methods are part of a general workflow comprising the construction of a surface-based framework, which is used to build the modelling grid in which these methods operate. This paper describes this workflow and provides an overview, classification, description and illustration of the most widely used FRM methods (deterministic and stochastic). Among others, two selected datasets comprising alluvial-palustrine and turbiditic deposits are used for illustration purposes. This exercise enables critical issues when using FRM methods to be highlighted and also provides some recommendations on their capabilities. For deterministic facies reconstruction, the main choice of the method to be used is between that employing a continuous or a categorical method. For stochastic facies modelling, choosing between the different techniques must be based on the scale of the problem, the type and density of available data, the objective of the model, and the conceptual depositional model to be reproduced. Realistic representations of facies distribution can be obtained if the available methods are applied appropriately.

Coal deposition in carbonate rich shallow Lacustrine systems: The Calaf and Mequinenza sequences (Oligocene, eastern Ebro Basin, NE Spain)

Two main coal-bearing sequences developed during the Oligocene in the Tertiary Ebro Basin, the Calaf (early Oligocene) and Mequinenza (late Oligocene) coal basins. Coal deposition took place in shallow marsh-swamp-lake complexes which sometimes became closed and evolved under warm climatic conditions with fluctuating humidity. These shallow lacustrine systems are closely interrelated with the terminal parts of the distributive fluvial systems which spread from the tectonically active Ebro basin margins. Laterally extensive lignite-bearing sequences, including rather thin, lenticular autochthonous and/or hypautochthonous coal seams with high ash and sulphur contents, characterized coal deposition in the shallow lacustrine systems. Coal seam geometry, which makes them nearly subeconomic, resulted from the tectonic instability during basin margin evolution and the sometimes closed, arid conditions under which the lacustrine systems evolved. High ash and sulphur contents resulted from the inadequate isolation of peat forming environments from clastic influx and from the very low acidity and sometimes high sulphate contents of the lacustrine waters. Coal exploration in shallow lacustrine sequences similar to those described here must take into account that the spread of coal-forming environments and maxima of coal deposition are usually coincident with lake expansions and retraction or shifting of the terminal fluvial zones interrelated with the lacustrine areas.