Stratigraphy and Climatic Phases

The sedimentary filling of Bolomor Cave is formed, mainly, by the external material from the hillsides and the gorge. Over the strong stalagmite basal levels which occupy the entire cavity from zenith dripping are laid those inputs with a maximum density of 10 m.

Representacion longitudinal norte-sur de la estratigrafia general de Cova del Bolomor

Longitudinal representation north-south of the general stratigraphy of Bolomor Cave

Vista este-oeste de la estratigrafia del Sector Septentrional, niveles VI a XVIII.

East-west view of the stratigraphy of the Northen Sector, levels VI to XVII

Identificación de los niveles en la estratigrafía del Sector Septentrional y niveles de la estratigrafía del Sector Occidental.

Identification of the stratigraphic levels in the northern sector. Stratigraphic levels of the western sector

Vista sur-norte de la estratigrafia del Sector Occidental, niveles I a XVIII.

South-north view of the western sector’s stratigraphy, levels I to XVIII

SEDIMENTOLOGY AND CLIMATIC PHASES

The karst deposit of Bolomor Cave presents some paleoclimatic implications which come from data elaborated principally from sedimentology, macrofauna and microfauna. These values are traduced in a sequence which is resumed from the base to the ceiling, in four paleoclimatic phases and, afterwards, they have elaborated a proposal to adjust the discontinuous terrestrial stratigraphic sequence of Bolomor with the oceanic continual sequence.

Bolomor I Phase (archaeological levels XVII to XV, between 250.000 – 350.000 years ago).  Basal ensemble which corresponds to a fresh climatic cycle with some humidity, at least seasonal, during which there is an accumulation of materials from external zones and there is a breccia of the sediment.  We find ourselves in the base with the incorporation of materials which were weathered in zones with some distance in respect to the point of their final deposition. The environment seems fresh and humid, at least seasonally, what allows the dissolution-concretion of carbonates of the habitat. Chronologically it has to be inscribed in the isotopic stage 8 and 9.

Bolomor II Phase (archaeological levels XIV and XIII, between 185.000 – 240.000 years ago). Climatic cycle with warm-temperate interstadial features, and seasonally very humid, which have allowed the periodic flooding of the cave.  A gradual but strong change of the climatic conditions is marked with the level XIV. The climatic parameters change notably, giving place to the presence of soft water flows which introduce materials with a determined selection. The clean contact with the following level XIII, seems to indicate the decapitation of the sedimentary ceiling of the anterior ensemble, in a first moment soft, XIII c and b, warm-temperate phase, and seasonally very humid. Chronologically it inscribes inside the isotopic stage 7.

Bolomor III Phase (archaeological levels XII to VIII, between 130.000 – 180.000 years ago). Climatic cycle with a fresh and humid oscillation, which slowly evolves to a more arid situation (level XII). Later, it stops, little by little and finally there’s a temperate and very humid climate (level VIII). There is a start of a new climatic episode, initially soft (XIIIa) which will degrade progressively till arriving to the layer XII, and stopping progressively in XI-X-IX-VIII. In a fresh and humid environment at its start, it gradually enters an arid stage in the sequence which can be seen in level XII. These conditions stop slowly till finishing the cycle in level VIII, moment in which we have installed a new temperate and a very humid climate. Isotopic stadium 6.

Bolomor IV Phase (archaeological levels VII to I, between 128.000 – 90.000 years ago).

It represents the Upper part of the sequence with temperate and humid oscillations for the last interglacial. A globally soft period, with little marked fresh lapses (levels VII to III) which provoke the accumulation of small rocks, result of the weathering of the cavity’s dome by the action of the ice. The elevated humidity has also provoked the partial flooding of the cave and the development of the breccias. The environmental indicators of coldness, especially in relation with those characterized by previous periods, are notably attenuated. On the other hand, it seems that there is a generalization of a climatic regime which has cyclic conditions, there are still fresh lapses (levels VII-VI, V-IV-III) during the which there is an accumulation of detritic material of small size, and are interrupted giving place to a water circulation of continuous flows, very carbonated which create a crust on the ceiling of levels VI, III and Ic.  We are in a globally soft period, with little marked degradation during which we have a high and oscillating humidity. This phase is related with the isotopic 5 stadium.

estratigrafia_02+03

Stratigraphic outline of Bolomor Cave. Proposal of relationship with the oceanic sequence

MAGNETIC AND CLIMATIC SUSCEPTIBILITY

The magnetic susceptibility (MS) relates the magnetic properties conserved in the Bolomor sediments with the estimation of the paleoclimate and the correlation with other sites. Using the MS and the ciclostratigraphy (EC) it presents a paleoclimatic structure based in this method (MSEC) by means of a graphic correlation. This building is related with the isotopic record of the marine oxygen (OIS). Brooks B. Ellwood of the Paleomagnetism Laboratory at Lousiana State University proposes that the MSEC can be used as an independent methodology, together to other conventional methods as are sedimentology and palinology, to look for changes in the paleoclimate.

estratigrafia_09

Magnetic susceptibility curve according to B. Ellwood

RADIOMETRIC DATES

The chronometric information expressed in numerical digits and with an undetermined stripe of the same associated, has the expositive consideration of “absolute age” although this doesn’t mean that the context related to the piece considered was formed in that same moment or date. Its main value for the study resides in a quantifiable reference, a “chronometrical location” in which to situate the contextualization to study. This dating, this method and its results must be accompanied of others which contrast the considered chronometrical values. Reductionism in this field also takes us to positions of demonstrative weakness and our methodological shortage can’t be hidden in a relative quantified “absolute” value. In Bolomor we have developed diverse actions aimed to the obtaining of dating by radioactive methods.

Samples of clays of the correspondent levels for the application of the thermoluminescence method (TL) by Wanda Stanska-Prószzynska and Hanna Prószzynska-Bordas (Sedimentology Laboratory of the Geography and Regional Sciences. Varsovia University, Poland):

Level II: 121.000±18.000 BP

Level XIIIa: 152.000±23.000 BP

Level XIVb: 233.000±35.000 BP

Level XIVa: 225.000±34.000 BP

This dates, by its coherence and adequacy with other methods has been considered, without objection, as valid.

The osseous samples of levels IV, V, XII, XIII, XV and XVII where taken by G. Belluomini (Dipartimento di Scienze della Terra de la Universidad “La Sapienza” in Rome):

Level IV-V: 390.000±100.000 BP

Level XVII: 525.000±125.000 BP

This date has been obtained of numerous bones of herbivores (level IV-V) and from level XVII from dental enamel, by AAR. The laboratory considers more adequate this second material. The interval between the measurement of the superior levels (IV-V) and the inferior (XVII) present an interval of 0,14±0,1 and the kinetic constant for the site is 3,57 x 10-7 yrs -1. The obtained values are considered high. Equally the indetermination is excessively high. Despite this the 525.000 value, taking off the negative frame of age, situates the date near to the considered values for the depositional moment of the OIS 9 in which it locates and, therefore, we have proceeded to its inclusion in the publications but some appropriate reserves.

The carbonated samples for the radioactive method of Th-U were recovered and elaborated by R. Julia (Geology Institute Jaime Almera, Barcelona) and exceeded the limits of the method (verbal communication):

Level XV: >350.000 BP

This date is adjusted at the characteristics of the depositional moment OIS 8 in which it is located, although it doesn’t present a determined value.

In the year 1996 we proceeded to the recovering of a wide series of lithic pieces of burnt flint for its dating after the calibration by radioactivity of the correspondent sedimentary levels. The study, carried out by N.C. Debenham (Quaternary TL Survey of Nottingham) presented the following values:

Level I: 320.000±33.000 BP

Level II: 324.000±31.000 BP

Level II: 435.000±48.000 BP

Level IV: 398.000±48.000 BP

Level IV: 235.000±21.000 BP

Level IV: 268.000±27.000 BP

     These six dates according to the laboratory, present a low reliance rate (68%). Also, the chronometry isn’t consistent within the figures or within the stratigraphical order and the indetermination is excessively high, as the same Laboratory admits. The high variability is incomprehensible in respect to inferior levels with a more recent chronology than the upper ones. Also, high temporality lapses in a same level are not adequate. The location of all these values in the OIS 5 doesn’t correspond to the same and are very alienated. Therefore, this data can only be the result of a methodological problem of the analysis by thermoluminescence and is rejected as not valid.

In 2005 we carried out an AAR dating on gastropods in the XIII strata, layer 11 (OIS 7) which gave a date of 229 ± 53 ka. Correspondent to the strata XII and over an equine molar, the number was <180 ka (Trinidad Torres, Molecular Stratigraphy Laboratory, Madrid). All of them concordant with other modes previously used and its location in the stratigraphy.

PALEOCLIMATIC IMPLICATIONS FROM A MACRO- AND MICRO- FAUNA PERSPECTIVE

The study of the bone remains recovered till now have allowed the identification of numerous faunal species whose distribution all along the sequence and relative frequency indicate the development of environmental changes in the surroundings of the site:

Bolomor I Phase (levels XV to XVII), we can observe, in a general way, the predominance of the horse which has its highest values of the sequence, along with the deer. Together with them the presence of the steppe rhinoceros is also on its highest levels and the megaceros would indicate the presence of fresh and a little humid climates, in this part of the sequence, being these species linked to the same. Micro mammals, on their side, reflect the development of different ecological niches: Allocricetus bursae occupied open and dry spaces, and the Talpa europaea humid meadows, corroborating a fresh and less humid climate.

Bolomor II Phase (levels XIII to XIV), the previous fresh and less humid conditions would transform into some characteristics of a higher humidity and warmth with a strong presence of red deer and an important decrease of the horse with the emergence of the first turtles.  The conditions of high humidity and flooding of the cave gave difficulties for its habitability.

Bolomor III Phase (levels VIII to XII), the previous conditions of warm and humid climates tended more towards a drier climate, as it is indicated by the disappearance of the megaceros and the importance which the horses acquired.

Bolomor IV Phase (levels I to VII), characterized by the emergence of species with a marked temperate character: elephant, hippopotamus, boar, aurochs, and the ass, whose presence would indicate, together with an increase of the temperatures and humidity, the expansion of forest zones in the surroundings of the site. The presence of the hippopotamus is linked to the existence of lake zones, areas which are also frequented by aurochs. Equus hydruntinus is an equid of temperate and humid climates, with interstadial or interglacial characterists, like the boar, and are exclusive of this phase.

Dibujo de molares de Cricetulus (Allocricetus) bursae. Hamster migrador.

Dibuix de molars de Cricetulus (Allocricetus) bursae. Hàmster migrador

OTHER BIOTIC REMAINS

The study of small shells of marine bivalves contributes to the evaluation of possible changes in the coastal line and its relation with climatic oscillations. This provenance might possibly come from the deposition, in pellet form of marine birds (cormorants, shearwaters, storm petrels and seagulls, within others) which eat fish and mollusks. These small mollusks have been documented in levels V, VII, XIII, XIV and XV of the sequence, with characteristics which indicate moments of a mild climate and possibly a major proximity to the sea. To this documentation we also incorporate dental and vertebral remains of fish (level I). Other continental mollusks (snails and conchs) as Rumina and Melanopsis, indicate a humid habitat in their correspondent levels (Ia, Ib, Ic, IV, VIIb and XIIIc).

The anthracological remains found, in front of the absence of palinological data, in form of fossilized seed has allowed us to document the presence of two vegetal species: Celtis australis (honeyberry) and Prunus spinosa (blackthorn), which colonized different places. The honeyberry needs more humid floors and is associated to elms which would circle the riverside of the Vaca River in the climatic phases Bolomor II and IV. The blackthorn is frequently in woods of oak trees which could extend all over the depression of the Valldigna and occupy the shadowy sides of the mountains, at least during the fresh moments of the stage isotopic 5 (Phase Bolomor IV).

Gasteropodos continentales  

Small shells of marine bivalves documented in levels V, VII, XIII, XIV and XV of the sequence

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Small shells of marine bivalves documented in levels V, VII, XIII, XIV and XV of the sequence

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