The marl-limestone rhythmites from the Lower Kimmeridgian (Platynota Zone) of the central Prebetic and their relationship with variations in orbital parameters

Earth and Planetary Science Letters, 111 (1992) 407-424

407

Elsevier Science Publishers B.V., Amsterdam [DT]

The marl-limestone rhythmites from the Lower Kimmeridgian (Platynota Zone) of the central Prebetic and their relationship with variations in orbital parameters Federico O16riz a, Francisco J. Rodrlguez-Tovar b, Mario Chica-Olmo c and Eulogio Pardo c a Departamento de Estratigraffa y Paleontolog{a, Facultad de Ciencias, Universidad de Granada e lnstituto Andaluz de Geolog(a Mediterrdnea (CSIC-UG), Granada 18002, Spain b Instituto Andaluz de Geolog(a Mediterrdnea (CSIC-UG) y Departamento de Estratigraf(a y Paleontolog[a, Facultad de Ciencias, Universidad de Granada, Granada 18002, Spain c Departamento de Geodindmica, Universidad de Granada, IAGM-CSIC, Granada, 18002, Spain Received August 18, 1991; revision accepted April 21, 1992

ABSTRACT The origin of the rhythmic marl-limestone bedding recognized in Lower Kimmeridgian (Platynota Zone) succesions of the central Prebetic (Southern Spain) is interpreted. A detailed analysis was carried out on the basis of field observations and mathematical procedures of two sections characterized by the variable alternation of marly and limestone horizons. The study primarily reveals signs of a possible secondary imprint in the stratification. However, we conclude that this imprint cannot have been sufficiently important to cause the recorded stratification or significantly alter the existing primary bedding. The mathematical procedure applied to the thicknesses of the beds reveals the existence of different orders of cyclicity that are not recognizable in the field. We were able to date these cycles by detailed biostratigraphy and the application of Fourier/spectral analysis. The close relationship between the timing calculated for the marl-limestone rhythms recognized in the Lower Kimmeridgian (Platynota Zone) successions and the periodicity assumed for Milankovitch cycles has been shown for the first time in the Prebetic Zone and leads us to accept the influence of orbital variations on sedimentation in the sector that was studied. We have also been able to recognize the influence of local factors which determined differences in the depositional organization in the sections studied.

1. Introduction and geological setting The South Iberian paleomargin is a region with a relatively complicated geological history which must be considered in the context of the relative movements between Iberia and Africa. Autochthonous-parautochthonous (Prebetic, Algarve) and allochthonous (Subbetic and lateral equivalents) units belonged, respectively, to proximal and distal areas of the margin, the latter

Correspondence to: F. Ol6riz, Departimento de Estratigrafla y Paleontologia, Facultad de Ciencias, Universidad de Granada e Instituto Andaluz de Geologla Meditemlnea (CSIC-UG), Granada 18002, Spain.

having been mainly structured by thrust tectonism during the Alpine orogeny. Recent proposals, in which there are only minor differences in the timing of events, have invoked three major episodes in the explanation of the evolution of the South Iberian margin during the Mesozoic [1]: transform (180-140 m.y. BP, approximately Carixian-Kimmeridgian), transform-transtensional (140-120 m.y. BP, approximately Kimmeridgian-Berriasian), and extensional (120-80 m.y. BP, approximately Berriasian-Coniacian). There are also other proposals (e.e., the Atlantic model s.l.) that admit a passive margin situation [2,3], which may or may not include the first appearance of oceanic crust at different times during the Mesozoic.

0012-821X/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved

408

F. O L ~ R I Z

The basic differentiation of the South Iberian margin was already apparent in the Late Jurassic when epicontinental platforms and distal pelagic swell areas formed (Fig. 1). A comprehensive interpretation of the South Iberian margin during the Late Jurassic was presented up by Ol6riz et al. [4], who took into account both the ecological-depositional dynamics and the tectonic instability of the distal compared to the epicontinental areas. The studied area belongs to the epicontinental realm of the External Zone of the Betic Cordillera. In this realm, limestone-marl successions were deposited in low areas [5]. Platformtype A m m o n i t i c o rosso and associated facies were frequent during the Oxfordian and today they are found dominantly in the central and eastern parts of the margin [5]. Siliciclastic intercalations were episodic and unevenly developed, but they became significant around the Oxfordian-Kimmeridgian boundary. The siliciclastics had a northern source (central and eastern Prebetics), but cases are also known in which material from

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a southern source is present (eastern Algarve [6]). Changes in facies and thicknesses reveal topographical differences in the platforms, even in relatively small areas (central Prebetics). Deep active faults led to greater regional differences. In general, the epicontinental areas were potentially favourable for recording interactions between tectonism and eustasy [4,5]. With the exception of those areas with persistent carbonate platform deposition, the shelf topography favoured the development of sponge and coral buildups in the eastern Algarve [7] and of mainly sponge buildups in the central Prebetics [8] on highs, whereas associations of cephalopods accompanied by bivalves a n d / o r brachiopods occupied the surrounding low areas. In general, the epicontinental environment covered a comparatively small area and diversification was uneven, although greater diversification was achieved during the Oxfordian. In the Kimmeridgian there was a trend towards uniformity, a trend which became more accentuated during the middle Kimmeridgian (lower upper

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M A R L - L I M E S T O N E RHYTHMITES O F THE PREBETIC AND ORBITAL PARAMETERS

Kimmeridgian sensu gallico) with the more general carbonate platform conditions. The shallow proximal facies indicative of the shallowing of the platform system--a shallowing that eventually resuited in the emergence of a large sector of the Prebetics during the Berriasian [9]--was already frequent in the Tithonian and early-middle Berriasian. 2. The sections studied

The study was carried out in two sections (Puerto l_x)rente and Segura de la Sierra; see Fig. 2) selected from the central Prebetic (southern Spain). These sections can be considered representative of the uppermost Oxfordian-lower Kimmeridgian succesions in the Cazorla and Segura de la Sierra sectors respectively. Both are characterized by terrigenous-carbonate lower Kimmeridgian sedimentary rocks. Although carbonate sedimentation, which corresponds to the shallow platform areas of the Late Jurassic western Tethys, was predominant, frequent intercalations of siliciclastic deposits are also found. Occasionally, these 'intercalations' reach 4 m in thickness. The lithology in both sections is characterized by the alternation of marls, marly limestones and limestones. Detailed biostratigraphical analysis of lower Kimmeridgian material in the Puerto Lorente and Segura de la Sierra sections allowed the recognition of all the standard zones of the lower Kimmeridgian of Sub-Mediterranean Europe [10]. 2.1 The Puerto Lorente section

This outcrop belongs to the Sierra de Cazorla sector of the External Prebetic [11], which is the most proximal part of the Prebetic realm. The significant characteristics of the External Prebetic are the moderate thickness of a Mesozoic cover of basically Jurassic material and the limited development, or absence, of the uppermost Jurassic, Neocomian and Paleogene. The Sierra de Cazorla has been structured into a series of nappes running NNE-SSW and dipping towards the east [12]. The outcrop from which this section was taken can be found on the topographical sheet for

409

Cazorla (No. 21-37, 928) and is situated between km 18 and 19 of the road running from Cazorla, through El Chorro, to the source of the Guadalquivir river (2°59'25 ", 37°50'15"). The outcrop (Fig. 2) may also be reached by the road that runs from the town of Quesada to the source of the Guadalquivir. The succession is 50 m thick and basically made up of alternating marls, marly limestones and limestones. The lower boundary of the Kimmeridgian rhythmite is an upper Oxfordian ferruginized surface that has previously been referred to by several authors (it was called a hardground in Foucault [12] and Acosta et al. [8]) and is characterized by a high concentration of fossil remains. The upper boundary of the Platynota Zone was identified within a 20 cm thick marly intercalation [10]. The following is a summary of the lithological characteristics of the succession: (1) Dark green marls of 150 cm in thickness in which no macroinvertebrate fossils were found. These lie directly on the 'hardground'. A 20 cm thick calcareous layer in which the first Kimmeridgian fossil remains are recognizable is prominent in these marls. The state of preservation of these fossils is poor, however. (2) A further alternation of calcareous and marly calcareous intervals ranging in thickness between 15 and 30 cm appears on the top of this marly intercalation. These more calcareous layers are interrupted by yet another intercalation of marls of approximately 5 m in thicknes. This intercalation enables us to clearly distinguish the overlying layers, which are basically characterised by the large increase in thickness of the calcareous intervals, and also by the increase in average individual thickness of the limestone beds, which sometimes even reach 1 m in thickness. Marly intercalations are present. In contrast to the lower boundary of the Platynota Zone, precise identification of the Platynota-Hypselocyclum boundary can only be made from biostratigraphy [10]. Unlike the Segura de la Sierra section, no synsedimentary sliding is recognized in the Puerto Lorente outcrop. Study of the microfacies reveals that the lithoclasts are mainly small, with no sign of either preferential orientation or predominant morphological characteristics. Quartz is the most abundant lithoclast, although mica fragments have

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M A R L - L I M E S T O N E RHYTHM1TES OF THE PREBETIC AND ORBITAL PARAMETERS

been recognized too. Scattered carbonaceous remains are also frequent, as too, occasionally, are oncoids. The bioclasts are mainly represented by filaments and radiolaria, and, too a lesser extent, by brachiopods, pelecypods, belemnites, echinoid spicules, ostracods, red algae and foraminifers (mainly Epistominidae): Gasteropods, aptychi, bryozoa, corals and sponge spicules were also observed. Traces of bioturbation and serpulids are abundant at some horizons. Textural analysis reveals a greater abundance of mudstones compared to wackstones or packstones, the latter being found mainly in the higher parts of the section.

2.2 The Segura de la Sierra section The outcrop belongs to the Segura de la Sierra Sector within the Internal Prebetic [11] which is associated with the most distal part of the Prebetic realm. In comparison with the External Prebetic, the distinctive stratigraphic characteristics are the presence of Portlandian and Neocomian material, and the greater thickness of the stratigraphic successions, which are, moreover, more complete and occur predominantly as Cretaceous rather than Jurassic outcrops. The dominant structural geological feature is mainly gentle folding facing the Meseta. The Segura de la Sierra section (Fig. 2) was taken from an outcrop situated less than 1 km from the village of Segura de la Sierra on the road to Los Arroyos (2°38'25 ", 38018'05 ") (see the Orcera topographical sheet, No. 22-35, 887). The succession, which is approximately 70 m thick, is mainly made up of alternating marls, marly limestones and limestones. An upper Oxfordian condensed horizon is found at the base. At the top this succession gradually gives way to a thick dolomitized succession that is considered to be middle Kimmeridgian in age (lower dolomitic interval, J1 in Garcla-Hern~indez [13]). The marly intervals are most highly developed in the basal and upper parts of the succession. In the basal part they alternate with marly limestone layers, attaining a total thickness of approximately 17 m. In the upper part of the section dark marly intercalations of 4 m in thickness develop with a few intercalations of limestone beds. Between the two marly intervals at bottom and top of the succes-

411

sion, a basically carbonate and generally more calcareous interval of about 50 m is found. This interval is made up of sets of limestone beds separated by thin marly intercalations. The average individual thickness of each limestone level is around 20 cm. Most of the section is affected by generally slight slumping. The synsedimentary structures tend to concentrate in the basal part of the lower limestone interval and in the upper part of the limestone intervals which develop at the top of the Platynota Zone. An exact definition of the lower boundary of the dolomitized interval, on the basis of the study of the microfacies components, was not possible, and the location of this boundary was therefore rather variable. The lithoclasts are mainly made up of quartz grains, although micas (biotite and glauconite) are also found. The grain size is on the whole small and no preferential orientation is observed. Clasts were found in a framework parallel to the bedding in only a few cases, and a microripple-like structure was observed occasionally. Carbonaceous remains and oncoids are frequent throughout the section. Filaments, and to a lesser extent, radiolaria are the most abundant bioclasts. The other bioclasts are not particularly significant, with Epistominidae as the most abundant foraminifera. Bioturbation is normally slight. The analysis of microfacies shows a greater abundance of mudstones, while wackstones, and in some cases packstones, are normally much less frequent and are concentrated in the higher parts of the succession. Dolomite rhombohedra have been observed.

3. Chronology Examination of ammonite faunas provided a particularly good timing for the Platynota Zone and allows a tentative delimitation of the Hypselocyclum Zone. The Divisum Zone and the basal middle Kimmeridgian were also recognized for the first time within the upper Jurassic of this region [10]. The discovery of Sumeria platynota (Reinecke) throughout practically all of the Segura de la Sierra section has permitted the biostratigraphic characterization of the Platynota Zone. This zone

412

is recognized by the recorded distribution of Sutneria platynota (Reinecke) a n d / o r those forms which normally accompany it. The Desmoides and Guilherandense subzones were recognized. The Orthosphinctes Subzone is proposed here for the basal levels with reservations, as neither uppermost Oxfordian guide-ammonites nor typical species from the Desmoides Subzone of the Platynota Zone were found. Precise identification of the boundaries at subzone level was frequently impossible. In the general context of the Platynota Zone, our attention is drawn to the occurrence of the record of the maxima of Ataxioceratinae in the Desmoides subzone, corresponding to the proliferation of Orthosphinctes (Ardescia). The upper boundary of the Platynota Zone correlates well with the top of the diverse record of this subgenus, which, moreover, contributed to another increase in Ataxioceratinae in the directly underlying levels. The most significant ammonites found in the Platynota Zone are: Taramelliceras (Metahaploceras) sp. gr. litocerum (Oppel); T. (M.) sp. gr. kobyi wegelei Schairer; Glochiceras (Lingulaticeras) sp. gr. nudatum (Oppel); Nebrodites (Nebrodites) sp.1. gr. hospes hospes (Neumayr); Sutneria platynota (Reinecke); Orthosphinctes (Ardescia) sp. gr. desmoides debelmasi Atrops; O. (A.) sp. gr. desmoides desmoides (Wegele); O. (A.) sp.gr, thieuloyi Atrops; O. (A.) sp. gr. proinconditus Atrops; O. (Lithacosphinctes) sp. gr. evolutus (Quenstedt); O. sp.; Ataxioceras (Schneidia) sp. gr. fontannesi Atrops; and A. (S.) sp. gr. guilherandense Atrops. The dating obtained in the lower Kimmeridgian of the central Prebetic in the Cazorla and Segura de la Sierra sectors not only increases our knowledge of the region in strictly paleontological terms but also helps in our understanding of the dynamics of the eco-sedimentary evolution in the epicontinental basins of the central part of the South Iberian paleomargin [4]. The following descriptions only refer to the Platynota Zone, which is the only time interval within the lower Kimmeridgian that is useful in our study. The time calibration of the cyclicity obtained has been made in accord with proposals on chronology in recent papers and global stratigraphic charts. We therefore take the interval

F. OL~RIZ ET AL.

between 4 m.y. [14] and 5 m.y. [15,16,17] as the Kimmeridgian stage. Because the Kimmeridgian is subdivided into six bio-chronozones in both the epicontinental and the epioceanic realms [18,19], we shall work with a mean duration of between 700 and 800 ka per bio-chronozone.

4. Rhythmic bedding case study The study of the origins and periodicity of rhythmic stratification has been the subject of much discussion in recent years, and interest was increased considerably as a result of the compilations by Einsele and Seilacher [20] and Berger et al. [21]. It is at present accepted that rhythmic stratification can be caused by processes of (a) primary or (b) secondary origin. (a) The primary origin of rhythmic stratification has been postulated by several authors. Although the autocyclic origin of some of these sequences cannot be dismissed (turbiditic and storm processes, etc.), allocyclic processes have been suggested as the main causes of rhythmicity in sediments. In most cases reference is made to changes in the insolation rate (Milankovitch cycles) forced by variations in the earth's orbital parameters (obliquity, eccentricity and precession). The most commonly advanced argument supporting the Milankovitch modulation is that the calculated average 'period' in a sequence of sedimentary cycles coincides roughly with one of the four major orbital periods: the 21 ka precession cycle, the 41 ka obliquity cycle and the 100 ka or 413 ka eccentricity cycles. The relationship between changing climates and sedimentary cyclicities during the Pleistocene ice ages is well known [e.g. 22-25]. Similar relationships have been proposed for pre-Pleistocene deposits [e.g. 26-31], and as a consequence Milankovitch cycles are now being frequently referred to in the interpretation of rhythmic variations in the sedimentary record. Other processes, however, such as tectonism, can sporadically induce widespread deviations in the sedimentary pattern which mask the record of the Milankovitch-related periodicity. (b) In considering the appearance of rhythmic bedding in outcrop, several authors refer to the significance of the secondary reinforcement

MARL-LIMESTONE RHYTHMITES OF THE PREBETIC AND ORBITAL PARAMETERS

(carbonate redistribution during burial, diagenesis and differential weathering) of minor fluctuations in the original or primary distribution of the components in the sediments [32-38]. It is generally accepted that at least a slight variation in primary composition should exist in a rhythmic succession. Consequently an important first step in the study of these alternations is the acquisition of reliable information on the probability and intensity of secondary processes. This problem has been considered in several papers [34,35,38-40]. The two sections analyzed by us are made up of rhythmically alternating levels of marls, limestones and marly limestones. The total thickness of the interval (Platynota Zone) varies between 50 m in the Puerto Lorente section and 70 m in the Segura de la Sierra section. At Puerto Lorente the sucession is characterized by thick marly inputs at the base and in the middle; at Segura de la Sierra it is the top of the succession that bears most of the marly input. The absence of sedimentary structures and significant clastic accumulations allows us to discount the existence of events such as storms and turbidity currents--events which could have either caused the rhythmicity or superposed a pattern on it. Our consideration of the possible existence of an imprint of secondary processes (diagenesis and weathering) took into account the following characteristics:

(A) For the existence of a secondary imprint: (1) There are no differences in the macroinvertebrate fossil content between the levels of different lithological characteristics (limestone/marl). (2) The same type of trace fossils (Chondrites) are found in consecutive levels with different lithological characteristics. (3) There are cases in which trace fossils possibly belonging to the same ichnocenosis cross the stratification surfaces without exhibiting any changes. (4) Deformed fossils are abundant, mainly as a result of crushing. (5) There are preferential directions of deformation in the recognized trace fossils. (6) In some limestone levels calcite infills (geodes) are normally found in the ammonoid nuclei. (7) Stylolitic surfaces have been recognized. (8) Some beds were found to have laterally variable morphology.

413

(B) Against the existence of a secondary origin: (1) The absence of clear mineralogical differences between the marly and marly limestone levels [41]. (2) The mineralogical composition of the clay component indicates the absence of intense diagenesis [41]. (3) The absence of any increase in crystallinity of the illite from top to bottom in the sections [411. (4) Fossils fractured by secondary deformation are not often found. (5) In some cases trace fossils are cut along the stratification plane separating adjoining horizons of different lithological characteristics. (6) No evidence was found of either flaser structures or pressure shadows. Analysis and consideration of the features listed above reveals the probable existence of a secondary imprint. However, we do consider that everything points to a weak or soft secondary imprint, which means that it would not seem to have been the principal cause of the rhythmic bedding recognized in the sections. This fact conditions the methodology that we employed and must be taken into account in calculation of the periodicities.

4.1 Calculation of the periodicity It is not easy to characterize the relationship between the rhythmic bedding recognized in the sections studied and the allocyclic depositional processes influenced by the orbital fluctuations proposed by Milankovitch and applied by some authors to other upper Jurassic sediments [30,39,40,42,43]. Our analysis of periodicity basically followed Einsele's [44] recommendations. However, we paid special attention to both the paleogeographic context and the transtensional character of the margin during the interval under examination. The following characteristics are therefore significant: (1) A very high mean sedimentation rate for the Platynota Zone. (2) The fact that sedimentation took place in a relatively shallow and unstable basin. (3) The existence of relatively thick marly or clayey intercalations.

414

F. OL6RIZ ET AL.

4.1.1 Remarks on the method There are several ways to calculate cycles within rhythmically bedded successions: (1) The average duration per cycle is determined by dividing the absolute age of the stratigraphic succession by the number of cycles [30,31,39,40,43]. (2) Alternatively, cycle average durations can be estimated by Fourier/spectral analysis of the recorded mineralogical, geochemical, paleontological or stratigraphic features in the Pleistocene [22,24,25] and pre-Pleistocene [43,45-48] sediments. In the spectral analysis of the pre-Pleistocene sediments restrictions should be taken into account concerning (i) uncertainties in time scales induced by different proposals on absolute ages, and (ii) the fact that the sedimentation rate must be considered constant. (In the context of (ii), however, note that Kominz and Bond [49] proposed a new method of testing periodicities in cyclic sedimentation, by estimating ages within cyclic strata by considering the time/thickness ratio of the facies within individual cycles.) Fourier/spectral analysis is the only reliable method, however, of revealing periodicities, and it is also very objective in the identification of two or more periodicities and the calculation of their temporal ratios. The method applied in this paper is that of Schwarzacher and Fischer [48], with adjustments made for the peculiarities of the sections that we have examined. We did carry out a thickness analysis because, according to Foucault and Renard [40], there are positive correlations between bed thickness and climatic variations in the

Mesozoic marl-limestone sediments of southern Spain. A b e d - b y - b e d study of the successions was carried out, with attention to the bedding planes, their distance from a reference horizon, their lateral continuity ('range'), and the types of sediments meeting each other at the bedding planes [48]. Among the bedding plane ranges distinguished by Schwarzacher and Fischer [48], that of order 2 was applied to "a very weak bedding plane, discontinuous at outcrop scale", while that of order 3 refers to "a strong bedding plane, continuous through outcrop, [with perhaps] a visible thin film of clay". We recognize, in addition, a new bedding plane of order 2.5 for contacts of secondary origin (due to diagenesis a n d / o r weathering) between both limestones or marly limestones and 'laminar limestones' or 'laminar marly limestones'. In this definition, we take into account the distinctiveness of the surface and the thicknesses of the layers in contact. The 2.5 plane is therefore significant because it allows us to distinguish the record of the true marly inputs. Master bedding planes (MBP) were located at the base of distinct marly intercalations. 4.1.2 Data analysis Before application of the mathematical model used by Schwarzacher and Fischer [48], it is necessary to identify the geologically imposed differences in the cases studied here. The treatment applied to the thickness of the marly packets is very important, as it conditions the results and their interpretation. Unlike the marly beds studied by Schwarzacher and Fischer [48], which were never more than a few centimetres thick and

TABLE 1 Quantitative characterization of the studied sections. E = Total thickness of the section; e = thickness of the section without marls; N= total number of beds. The following refers to the thicknesses of analyzed beds: x = mean; M= mode; m = average; V = variance; Cv = coefficient of variance SECTION SEGURA DE SIERRA PUERTO LORENTE

LA

E

e

N

x

M

m

V

Cv

62.4 m

43.2 m

226

19.1 cm

15 cm

17 cm

125

59%

53 m

40.1 m

175

22.9 cm

i0 cm

2O

199

62%

cm

415

M A R L - L I M E S T O N E RHYTHMITES OF THE PREBETIC AND ORBITAL PARAMETERS

pearance ('laminar marly limestones') but was of secondary origin (2): (1) When dealing with an authentic marly interval, its thickness was ignored, which means that there were cases when intervals of several metres in thickness were ignored. Our treatment implies that the marly inputs sensu stricto were very short-period events. We assumed these short periods to be below the mean value of the sedimentation rate of the succession. The inclusion of the thickness of the marly inputs sensu stricto,

indeed were in most cases only a few millimetres thick, our marly levels are at times several metres in thickness. Schwarzacher and Fischer proposed two alternatives for dealing with the marly levels, (a) to ignore the marly intervals or (b) to deal with the sections as a sequence of marly limestone couplets. The treatment that we have applied to the marly intervals varied according to whether we were dealing with an authentic marly interval (1), or whether the interval simply had a marly ap-

FREQUENCY

16 14 12

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60

80

THICKNESS •

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100

120

(cm)

Lorente

FREQUENCY 30 25 20 15 10 5 0 0

20

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60 THICI~NEsS

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S e g u r a d e ia S i e r r a

Fig. 3. Frequency distributions of bedding thicknesses in the studied sections.

120

416

F. OL~RIZ ET AL.

therefore, would clearly have resulted in a bias in the results of our study. Some of these marly levels can be clearly related to increases in erosion connected with tectonic activity, and therefore, by ignoring them we partially isolate the punctuating effect of tectonism on the deposition. (2) Sedimentary bodies considered to be of secondary origin were added to the adjacent calcareous or marly calcareous strata for the calculation of thicknesses. In this case the levels were several centimetres thick.

The characterization of the successions was carried out on the basis of the calculation of the mode, mean, average, variance and coefficient of variance of the thicknesses (Table 1). From comparison of the results obtained in the two sections, we can conclude that the Segura de la Sierra section (as compared to the Puerto Lorente) is characterized by: (a) a greater number of beds (226 vs. 175), (b) a smaller average bed thickness (19.1 vs. 22.9 cm), and (c) a larger mode (15 vs. 10). Moreover, although the vari-

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Fig. 4. Sequential variation in thickness of beds: Segura de ia Sierra section (A) and Puerto Lorente section (B).

MARL-LIMESTONE RHYTHMITES OF THE PREBETIC AND ORBITAL PARAMETERS

417

enveloping lines towards greater and smaller thicknesses, in the Puerto Lorente section there are significant peaks (e.g. at 20 and 25 cm) which accompany the mode (at 10 cm), especially towards greater thicknesses. One of the main problems to be taken into account in the calculation of the periodocity is temporal calibration. In the majority of studies carried out, and in our case too, the time content represented by each layer is generally unknown and not necessarily constant. This can be a problem seeing as most of the methods of mathemati-

ance in the two sections is different, the coefficient of variance is very similar (59% vs. 62%). The diagrams of frequency distributions of bedding thicknesses for both sections are shown in Fig. 3. We must point out the similarity in the distribution of thicknesses and the concentration of the majority of thicknesses in the 5-40 cm range: One of the characteristics that distinguishes the two successions is the difference in the relative distribution of thickness frequencies: Whereas in the Segura de la Sierra section there is a well-expressed mode at 15 cm, with regular

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418

F.

cal analysis of temporal series require data obtained at constant sampling intervals. In our case, we chose a control interval that was greater than the most frequent thickness interval (mode) and smaller than the mean value obtained for the thicknesses in each of the successions. Thus, for the Segura de la Sierra section a 17 cm interval was chosen, between the mode (15 cm) and the mean (19.1 cm) of the thicknesses, and for the Puerto Lorente section we chose a 15 cm interval, again between the mode (10 cm) and the mean (22.9 cm) of the thicknesses. A series of conditions must be taken into account in collecting the data: (a) The thickness of the marly levels s e n s u s t r i c t o must be ignored. (b) The thickness of the intercalations of 'laminate material' is added to that of the layer located immediately above and the resulting thickness is treated as that of a single layer. (c) When the sampling interval, or unit of measure, is contained more than once in a single layer, the thickness of this layer is recorded as many times as the sampling interval included in it.

OL6RIZ

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(d) When, in the process of measuring a bed, the record of the sampling interval exceeds the upper limit of the bed being measured, and is shared between two consecutive beds, this sampling interval is only considered in the representation of the bed including the larger part of the interval. (e) When the sampling interval belongs to more than two layers, and one of these provides more than half of the interval's thickness, the thickness of this layer is recorded. (f) When the sampling intervals belong to more than two beds, and neither of these provides more than half the interval's sampling, the thickness recorded is the mean of the thickness of the layers in which the sampling interval is contained. When measurement following this procedure is completed the data must be represented graphically (Figs. 4 and 5). As can be seen in Fig. 4A and B, the individual thickness of the beds (vertical axis) is shown in relation to the total number of sampling intervals considered (horizontal axis). This representation can be made directly with the data collected (Fig. 4A and B), or after the data have been smoothed by means of a running aver-

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M A R L - L I M E S T O N E R H Y T H M I T E S O F T H E P R E B E T I C AND O R B I T A L P A R A M E T E R S

age of 3 with the weight 1,1,1 (Fig. 5A and B). It can clearly be seen that the greatest thicknesses are found in the middle parts. For a general characterization of the successions, in which the behaviour of each section can be seen, it is useful to carry out a geostatistical analysis of the thicknesses obtained by the procedure described above. In the application of geostatistical methods to solve problems of estimation and simulation of spatial variables, the basic tool employed was the 'variogram' [50] of the data obtained in the two successions. This analysis is based on the variability, or correlation existing between the different data, when the distance between the points analyzed increases. We can thus obtain information on the structure of a phenomenon through a first qualitative, or even quantitative, impression of the structure of the successions being analyzed. In Fig. 6 we plot on the horizontal axis the constant sampling interval (CSI) previously selected for each section and, on the vertical axis, the mean value of the square of the difference between the values of the variable picked according to the CSI.

y ( h ) = ½ E [ f ( x + h ) - f ( x ) ] 2 dx where h = CSI, E = average expectation and x = sampling points By the application of mathematical analysis to this basic procedure, periodicity structures (Fig. 6A and B) were revealed which were not macroscopically recognizable in the outcrops. These structures were more easily recognized in the variograms obtained in the Segura de la Sierra section. One of the most delicate parts of the study is the temporal calibration of the cycles obtained by Fourier/spectral analysis. For this reason, and in an attempt to obtain the most reliable timing possible, we used ammonite biozones, the corresponding chronozones and the metre-scale thicknesses in order to adapt the methodology to the type of information treated. Thus, repetitions of less than 1 m are not recorded in any of the graphic representations, whether they be of smoothed or unsmoothed data. The application of power spectra analysis was therefore carried out with 700-800 ka as the duration of the Platynota chronozone. As can be seen below, a variation of 12-14% in the temporal interval un-

419

der consideration does not greatly affect the cyclicity values obtained. On the basis of the above, 1 m of succession in the Segura de la Sierra section represents between 16 and 19 ka, while in the Puerto Lorente section 1 m represents between 17 and 20 ka. Because the graphic representation is obtained from the previously calculated thickness data, many peaks appear (Fig. 7A and B). In order to obtain a simpler, more significant image, we smoothed the results using the Hanning filter, which brings out the frequency of appearance of the most representative peaks (Fig. 8A and B). 5. Interpretation of the results

The cyclic character recognized in the two sections does not appear in the same fashion in both successions. Thus, the diagrams of frequency distributions of bedding thickness (Fig. 3A and B) show a greater number of variations in the Puerto Lorente section, which could suggest a greater irregularity in depositional conditions. Similarly, as shown in the variograms (Fig. 6A and B), the cyclicity is much better recognized in the Segura de la Sierra section than in that of Puerto Lorente. This may be related to the existence of topographical differences in the platform and the presence of local effects which distorted sedimentation. L6pez-Galindo et al. [41] have interpreted the topographical differences in the area (low areas represented by the Segura de la Sierra section and high areas by the Puerto Lorente section) as having influenced the existence of hydrodynamic differentation, which resuited in exclusively quantitative variation in the composition of clay mineral associations. The results obtained on the basis of the interpretation of the graphs in Figs. 7 and 8 (power spectrum analysis) are summarized in Tables 2 and 3.

5.1 The Segura de la Sierra section Figure 7A shows the Fourier/spectral analysis of unsmoothed data for the Segura de la Sierra section. Of the total number of peaks obtained, eleven were selected with a repetition scale of more than 1 m in the succession studied. The periodicities of these peaks are shown in Table

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422

2A. On the basis of the relationship between the peaks (Fig. 7A) and the periodicities calculated for each peak, the latter can either be bundled together or kept separate. Thus, peak 1 is isolated, with a corresponding periodicity of 718 + 48 ka. (This peak is rejected because it dissapears on smoothing.) Peaks 2 and 3 could be bundled with an interval of periodicities of 143 + 10 ka-104 + 7 ka; peaks 4 and 5 bundle around 73 ___5 ka-56 + 4 ka; peaks 6 - 7 - 8 - 9 bundle around 34 + 2 ka-25 + 2 ka; and peaks 10-11 bundle around 22 + 1 ka-20 + 1 ka. If we now analyze the peaks corresponding to the spectral analysis of the smoothed data, only the most outstanding peaks are recognized. In the Segura de la Sierra section, seven peaks were recognized (Fig. 7B), and selective bundling allows us to distinguish periodicities of approximately 359 ___24 ka, 104 + 7 ka, 56 + 4 ka, 34 + 2 ka-25 ± 2 ka and 22 ± 1 ka-20 + 1 ka, corresponding to peaks 1, 2, 3, 4-5 and 6-7 respectively. 5.2 The Puerto Lorente section

Figure 8A shows the spectral analysis of unsmoothed data for the Puerto Lorente section. Of the peaks obtained, nine were selected with a repetition scale of more than 1 m in the succession studied. The periodicities of these peaks are shown in Table 3A. In this case, the possible groupings are as follows: Peaks 1, 2 (this peak is rejected because it disappears on smoothing), and 3 could be kept separate with periodicities of approximately 378 + 25 ka, 189 + 13 ka and 127 + 8 ka respectively. Peaks 4-5, 6, and 7-8-9 can be bundled around 68 + 5 ka-60 + 3 ka, 29 + 2 ka and 24 ___2 ka-18 + 1 ka respectively. The spectral analysis of the smoothed data is shown in Fig. 8B. In the Puerto Lorente section, eight peaks were recognized which, by means of the same treatment as above, permit the deduction of periodicities of approximately 378 + 25 ka, 127 + 8 ka and 68 + 5 ka-60 + 3 ka for peaks 1, 2 and 3-4, and 29 + 2 ka and 24 + 2 ka-18 -t- 1 ka for peaks 5 and 6-7-8. As can be seen, the periodicities of the different cycles is similar to the timing estimated for some of the orbital parameters causing the rhythmic climatic variations suggested by Milankovitch.

F. OL~RIZ ET AL.

But there is no exact correspondence between the periodicities obtained by us and those accepted for astronomic cycles, and this is to be expected in the geological context described above. A whole series of factors must be taken into account which could have in some way distorted the record of the primary cyclicity. As mentioned above, the most significant of these factors are: (a) phenomena of secondary superimposition, (b) the effect that tectonic pulses and variations in sea level had on the sedimentary dynamics [4,5], and (c) the errors inherent in the application of the methodology in the conditions imposed by the outcrops. This leads us to consider orbital perturbations (mainly precession and eccentricity cycles) as mechanisms responsible for the genesis of some of the cycles recognized (cycles of around 24-18 ka, 127-104 ka and 378359 ka). 6. Conclusions

Detailed study of the rhythmic bedding recognized in two sections representative of sedimentation during the early Kimmeridgian (Platynota Zone) of the central Prebetic (Southern Spain) leads us to consider the possible existence of a secondary imprint (diagenesis, weathering) which affected the distribution of carbonates and their macroscopic expressions in the outcrops. However, we consider that this imprint was not sufficiently important to significantly distort the primary rhythmicity, and certainly not enough to superimpose a secondary rhythmicity distorting the original. On the basis of the analyses carried out on the rhythmicity, we deduce the existence of a pattern of cyclic stratification in which, at different scales, marly, marly limestone and limestone levels alternate in the successions studied. Spectral analysis allows us to recognize different orders of cyclicity corresponding approximately to the following periodicities: 22-20 ka, 104 ka and 359 ka in the Segura de la Sierra section, and 24-18 ka, 127 ka and 378 ka in the Puerto Lorente section. It is clear that the periodicities of around 115 ka could correspond to the eccentricity cycle, those of around 21 ka to the precession cycle, and those close to 370 ka to the wide-range eccentricity cycle located at ap-

MARL-LIMESTONE RHYTHMITES OF THE PREBETIC AND ORBITAL PARAMETERS

proximately 400 ka. It is an open question as to whether the periodicity in the ranges 68-56 ka and 34-25 ka could be related to interactions between local factors and orbital variations (obliquity cycle). While admitting a certain margin of error owing to the geological context that we have described, we believe that in future adjustments can be made to the cycles obtained on the basis of the analysis of variations in the mineralogical, isotopic and paleontological characteristics of these and other successions. In addition, it has been shown that the cyclic character recognized in the two sections does not appear in the same fashion in both successions. The reason for this should be considered to have some relation to the existence of topographical differences in the platform and the presence of local effects related to these differences, which distorted the sedimentation.

Acknowledgements This paper was made possible thanks to the financial support of PB 0271 (CSIC) and both the EMMI and Geoestadfstica-Teledeteccidn groups

(Junta de Andaluc[a ). References 1 M.C. Comas, V. Garcla-Duefias and J.C. Balanya, El dominio sudib6rico como margen continental mesozoico, in: Symp. Geology of the Pyrenees and Betics, Abstr., pp. 11, 1988. 2 E. Puga, Sur l'existence dans le complexe de la Sierra Nevada (Cordili~res B6tiques, Espagne de Sud) d'6clogites et sur leur origine probable h partir d'une croute oc6anique m6sozo'ique, C.R. Acad. Sci. Paris 285, 16, 1379-1382, 1977. 3 J.A. Vera, Correlaci6n entre las Cordilleras B&icas y otras Cordilleras Alpinas durante el Mesozoico, in: Curso Conf. PICG, pp. 129-160, Acad. Cien. Exac. Fis. Nat., Madrid, 1981. 4 F. Ol6riz, B. Marques and F.J. Rodrlguez-Tovar, Eustatism and faunal associations. Examples from the South Iberian margin during the upper Jurassic (OxfordianKimmeridgian), Eclogae Geol. Helv. 84(1), 83-106, 1991. 5 B. Marques, F. Ol6riz and F.J. Rodrlguez-Tovar, Interactions between tectonics and eustasy during the upper Jurassic and lowermost Cretaceous. Examples from the South of Iberia, Bull. Soc. Geol. Fr. 162(6), 1109-1124, 1991. 6 B. Marques and F. OI6riz, La plate-forme de L'Algarve au Jurassique superieur: Les grandes discontinuites stratigraphiques, Cuad. Geol. Iber. 13, 237-249, 1989.

423

7 S. Rosendahl, Die oberjurassiche Korallenfazies von AIgarve (Siidportugal), Arb. Inst. Geol. Pal~iontol. Univ. Stuttgart 82, 1-125, 1985. 8 P. Acosta, M. Garcla-Hermlndez and A. Checa, Biohermos de esponjas y estromatolitos en la secuencia transgresiva oxfordiense de la Sierra de Cazorla, Geogaceta 5, 39-41, 1988. 9 M. Garcla-Hermlndez and A.C. L6pez-Garrido, The Prebetic Platform during the Jurassic: A sedimentary evolution upon a distensive margin, in: 2nd Int. Symp. Jurassic Stratigraphy (Lisbon), II, pp. 1017-1030, 1987. 10 F. Ol6riz and F.J. Rodrfguez-Tovar, Lower Kimmeridgian biostratigraphy in the central Prebetic (Southern Spain, Cazorla and Segura de la Sierra sectors), Neues Jahrb. Geol. Palhontol. Abh., in press. 11 L. J6rez-Mir, Geologla de la Zona Preb6tica, en la transversal de Elche de la Sierra y sectores adyacentes (provincias de Albacete y Murcia), Thesis, Univ. Granada, 1973. 12 A. Foucault, Etude g6ologique des sources du Guadalquivir (Provinces de Ja6n et de Grenade, Espagne m6ridionale), Thesis, Univ. Paris VI, 1971. 13 M. Garcla-Hernfindez, E1 Jurfisico terminal y el Crethcico inferior en las Sierras de Cazorla y del Segura (Zona Preb6tica), Thesis, Univ. Granada, 1978. 14 G. Westermann, Gauging the duration of stages: A new approach for the Jurassic, Episodes 7(2), 26-28, 1984. 15 B.U. Haq, J. Hardenbol and P.R. Vail, Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change, in: Sea-Level Changes--An Integrated Approach, SEPM Spec. Publ. 42, 71-108, 1988. 16 lUGS, Global Stratigraphic Chart, Episodes 12(2), 1989 (Suppl.). 17 G.S. Odin and Ch. Odin, Echelle num6rique des temps g6ologiques, G6ochronique 35, 1990 (Suppl.). 18 R. Enay, H. Tintant and M. Rioult, Kimm6ridgien, in: Les zones du Jurassique en France, C.R. Acad. Sci. Paris 6, 22-27, 1971. 19 F. O16riz, Kimmeridgense-Tith6nico inferior en el sector central de las Cordilleras B6ticas (Zona Subb6tica). Paleontologla. Bioestratigrafla, Thesis, Univ. Granada, 1978. 20 G. Einsele and A. Seilacher, eds., Cyclic and Event Stratification, Springer, New York, 1982. 21 A. Berger, J. Imbrie, J. Hays, G. Kukla and B. Saltzman, eds., Milankovitch and Climate, Reidel, Boston, 1984. 22 J.D. Hays, J. Imbrie and N.J. Shackleton, Variations in the Earth's orbit: pacemaker of the Ice Ages, Science 194, 1121-1132, 1976. 23 A.L. Berger, Long-term variations of caloric insolation resulting from the Earth's orbital elements, Quat. Res. 9, 139-167, 1978. 24 J. Imbrie and J.Z. Imbrie, Modeling the climatic response to orbital variations, Science 207, 943-953, 1980. 25 J. Imbrie, A theorical framework for the Pleistocene Ice Ages, J. Geol. Soc. London 142, 417-432, 1985. 26 C. Darmedru, P. Cotillon and M. Rio, Rythmes climatiques et biologiques en milieu marin p61agique. Leurs relations dans les d6p6ts cr6tac6s alternants du bassin voeontien (Sud-Est de la France), Bull. Soc. G6ol. Fr. 7, XXIV(3), 627-640, 1982.

424 27 E.J. Barron, M.A. Arthur and E.G. Kauffman, Cretaceous rhythmic bedding sequences: a plausible link between orbital variations and climate, Earth Planet. Sci. Lett. 72, 327-340, 1985. 28 A.G. Fischer, Climatic rhythms recorded in strata, Annu. Rev. Earth Planet. Sci. 14, 351-376, 1986. 29 T.J. Algeo and B.H. Wilkinson, Periodicity of mesoscale Phanerozoic sedimentary cycles and the role of Milankovitch orbital modulation, J. Geol. 96, 313-322, 1988. 30 G. Dromart, Deposition of Upper Jurassic fine-grained limestones in the westhern subalpine basin, France, Palaeogeogr., Palaeoclimatol., Palaeoecol., 69, 23-43, 1989. 31 M.T. Burchell, M. Stefani and D. Masetti, Cyclic sedimentation in the Southern Alpine Rhaetic: the importance of climate and eustasy in controlling platform-basin interactions, Sedimentology 37, 795-815, 1990. 32 H.S. Campos and A. Hailam, Diagenesis of English Lower Jurassic limestones as inferred from oxygen and carbon isotope analysis, Earth Planet. Sci. Lett. 45, 23-31, 1979. 33 W. Eder, Diagenetic redistribution of carbonate, a process in forming limestone-marl alternations (Devonian and Carboniferous, Rheinisches Schiefergebirge, W. Germany), in: Cyclic and Event Stratification, G. Einsele and A. Seilacher, eds., pp. 98-112, Springer, New York, 1982. 34 W. Ricken, Epicontinental marl-limestone alternations: event deposition and diagenetic bedding (Upper Jurassic, southwest Germany), in: Sedimentary and Evolutionary Cycles (Lecture Notes in Earth Sciences) 1, U. Bayer and A. Seilacher, eds., pp.127-162, Springer, 1985. 35 W. Ricken, Diagenetic Bedding. A Model for MarlLimestone Alternations, Springer, New York, 1986. 36 W. Ricken, The carbonate compaction law: a new tool, Sedimentology 34, 571-584, 1987. 37 M. Valenzuela, J.C. Garcla-Ramos and C. Su~rez de Centi, La sedimentaci6n en una rampa carbonatada dominada por tempestades, ensayos de correlaci6n de ciclos y eventos en la ritmita margo-calcfirea del Jurfisico de Asturias, Cuad. Geol. Ib6r. 13, 217-235, 1989. 38 A. Hallam, Origin of minor limestone-shale cycles: climatically induced or diagenetic?, Geology 14, 609-612, 1986. 39 G. Einsele, Limestone-marl cycles (periodites): diagnosis, significance, causes--a review, in: Cyclic and Event Stratification, G. Einsele and A. Seilacher, eds., pp. 8-53, Springer, New York, 1982.

F. OLORIZ ET AL. 40 A. Foucault and M. Renard, Contr61e climatique de la s6dimentation marno-calcaire dans le M6sozo'ique d'Espagne (Sierra de Fontcalent, province d'Alicante): arguments isotopiques, C.R. Acad. Sci. Paris 305(II), 517521, 1987. 41 A. L6pez-Galindo, F. Ol6riz and F.J. Rodrlguez-Tovar, Mineralogical analysis in marly intercalations and integrated approaches to paleoenviromental interpretation. An example from the South Iberian margin during the upper Jurassic, in: Proceedings of the 7th Euroclay Conference, 2, pp. 707-712, Dresden, 1991. 42 S. Ferry and J.L. Rubino, La modulation eustatique du signal orbital dans les s6diments p61agiques, C.R. Acad. Sci. Paris 305(II), 477-482, 1987. 43 A. Foucault and T. Clerc-Renaud, Etude stratonomique des alternances marne-calcaire du Kimm6ridgien au Valanginien, in: Stratigraphie Int~gr~e du Sillon Citrab6tique (Sierra de Fontcalent, Province d'Alicante, Espagne), Geobios 20(3), 337-387, 1987. 44 G. Einsele, General remarks about the nature, occurrence and recognition of cyclic sequences (periodites), in: Cyclic and Event Stratification, G. Einsele and A. Seilacher, eds., pp. 3-7, Springer, New York, 1982. 45 W. Schwarzacher, An application of statistical time-series analysis of a limestone-shale sequence, J. Geol. 72, 195213, 1964. 46 W. Schwarzacher, Sedimentation models and Quantitative Stratigraphy (Developments in Sedimentology, 19), Elsevier, 1975. 47 W. Schwarzacher, Principles of quantitative lithostratigraphy--the treatment of single sections, in: Quantitative Stratigraphy, F.M. Gradstein, ed., pp. 361-386, Unesco, 1985. 48 W. Schwarzacher and A.G. Fischer, Limestone-shale bedding and perturbations of the earth's orbit, in: Cyclic and Event Stratification, G. Einsele and A. Seilacher, eds., pp. 72-95, Springer, New York, 1982. 49 M.A. Kominz and G.C. Bond, A new method of testing periodicity in cyclic sediments: application to the Newark Supergroup, Earth Planet. Sci. Lett. 98, 233-244, 1990. 50 M. Chica-Olmo, An~ilisis geoestadlstico en el estudio de la explotaci6n de los recursos minerales, Thesis, Univ. Granada, 1988.