Federico Olóriz

Jurassic magnetostratigraphy, 1. Kimmeridgian-Tithonian of Sierra Gorda and Carcabuey, southern Spain

Abstract Two coeval sections of red to white ammonite-rich pelagic limestones spanning the complete Kimmeridgian and most of the Tithonian were sampled in detail. All samples were treated by progressive thermal demagnetization to remove a present field overprint. Characteristic magnetization is carried primarily by magnetite. Polarity intervals are easily identified and correlate well between the two sections. The Tithonian polarity sequence can also be correlated to sections in northern Italy. The similarity between the polarity sequence and the M-sequence of marine magnetic anomalies, coupled with the precise biostratigraphic control, allows assignment of the following ages to the M-sequence: the Late/Early Tithonian boundary is correlated to the end of M-20, the Tithonian/Kimmeridgian boundary to the end of M-23, the Late/Early Kimmeridgian boundary to the latter part of M-24, and the Kimmeridgian/Oxfordian boundary within or slightly after M-25. The mean directions of characteristic magnetization have α 95 s less than 3° and demonstrate extensive differential block rotation within the Subbetic province. Paleolatitudes during the Kimmeridgian/Tithonian are in the range of 16–24°N.

A Late Jurassic Carbonate Ramp Colonized by Sponges and Benthic Microbial Communities (External Prebetic, Southern Spain)

Abstract During the Middle to Late Oxfordian (locally ranging into the earliest Kimmeridgian), the epicontinental shelf that persisted in the southeastern paleomargin of Iberia (Prebetic Zone) was largely colonized by siliceous sponges (Dictyida, Lychniskida, and Lithistida, in descending order of abundance). Spongiolithic lithofacies (sponge-rich deposits in which buildups are rare and small) represent a marine environment extensively colonized by sponges in the form of large sponge meadows showing associated epibenthic organisms (brachiopods, bivalves, and echinoderms). Marl-limestone rhythmites represent muddy bottoms colonized by scarce endobenthos (bivalves and irregular echinoids). However, the occurrence of patchy sponge bioherms provided a favorable substrate for epibionts and microbial lithoherms (microbialites). The record of meter-scale buildups showing sponge bioherm-microbial lithoherm in marl-limestone rhythmites resulted from the preferred colonization of sponge patches by benthic microbial communities, the growth of which on surrounding muddy bottoms was very limited or impossible. Sedimentation rate, substrate, bathymetry, light, nutrients, oxygenation, and environmental (water) energy determined the eco-sedimentary conditions responsible for the occurrence and composition of spongiolithic facies in the area studied. Throughout the Late Oxfordian and the earliest Kimmeridgian, the progressive increase in the rate of sedimentation, especially influx of siliciclastics, forced the disappearance of sponge bioherms-microbial lithoherms from the Prebetic shelf.

Foraminiferal Assemblages as Palaeoenvironmental Bioindicators in Late Jurassic Epicontinental Platforms: Relation with Trophic Conditions

Foraminiferal assemblages from the neritic environment reveal the palaeoecological impact of nutrient types in relation to shore distance and sedimentary setting. Comparatively proximal siliciclastic settings from the Boreal Domain (Brora section, Eastern Scotland) were dominated by inner-shelf primary production in the water column or in sea bottom, while in relatively seawards mixed carbonate-siliciclastic settings from the Western Tethys (Prebetic, Southern Spain), nutrients mainly derived from the inner-shelf source. In both settings, benthic foraminiferal assemblages increased in diversity and proportion of epifauna from eutrophic to oligotrophic conditions. The proximal setting example (Brora Brick Clay Mb.) corresponds to Callovian offshore shelf deposits with a high primary productivity, bottom accumulation of organic matter, and a reduced sedimentation rate for siliciclastics. Eutrophic conditions favoured some infaunal foraminifera. Lately, inner shelf to shoreface transition areas (Fascally Siltstone Mb.), show higher sedimentation rates and turbidity, reducing euphotic-zone range depths and primary production, and then deposits with a lower organic matter content (high-mesotrophic conditions). This determined less agglutinated infaunal foraminifera content and increasing calcitic and aragonitic epifauna, and calcitic opportunists (i.e., Lenticulina). The comparatively distal setting of the Oxfordian example (Prebetic) corresponds to: (i) outer-shelf areas with lower nutrient input (relative oligotrophy) and organic matter accumulation on comparatively firmer substrates (lumpy lithofacies group) showing dominance of calcitic epifaunal foraminifera, and (ii) mid-shelf areas with a higher sedimentation rate and nutrient influx (low-mesotrophic conditions) favouring potentially deep infaunal foraminifers in comparatively unconsolidated and nutrient-rich substrates controlled by instable redox boundary (marl-limestone rhythmite lithofacies).

Fossil assemblages, lithofacies, taphofacies and interpreting depositional dynamics in the epicontinental Oxfordian of the Prebetic Zone, Betic Cordillera, southern Spain

Abstract The study of six sections within the External Prebetic (Pozo Canada, Fuente Alamo, Chinchilla de Montearagon and Riogazas-Chorro II) and the Internal Prebetic (Navalperal and Rio Segura), comprises the first results of a taphonomic study to be incorporated into the ecostratigraphic interpretation of the Oxfordian in the Prebetic Zone, Betic Cordillera, southern Spain. A taphonomic analysis was made of 9350 specimens (including fragments) of macroinvertebrate fossils: ammonoids (64%), benthic organisms (26%), and belemnoids and nautiloids (10%). The taphonomic features analysed were: (a) state of preservation (ratio of moulds with/without shell and type of mould filling); (b) fossil size; (c) position within the bed; (d) corrasion (see [Brett, C.E., Baird, G.C., Palaios 1 (1986) 207–227]; (e) fragmentation; (f) epibionts and encrustment; (g) disarticulation; (h) uncoupling and (i) deformation. Analysis of the relative significance of these features, and their relation to the lithofacies, allows us to characterise and distinguish three major taphofacies: (a) taphofacies I, characterised by the greater average size of the specimens recorded, higher values of corrasion, encrustation and colonisation, and by the fact that a high proportion of the specimens are in a quasi-horizontal position; (b) taphofacies II, characterised by a higher proportion of smaller specimens and a greater variety of azimuthal orientation, although the quasi-horizontal position is always predominant and corrasion values are low; (c) taphofacies III, with predominantly small specimens, the highest proportion of quasi-horizontal orientation and fragmentation, and no evidence of corrasion. The taphofacies are stratigraphically and palaeogeographically distributed. In interpreting the taphofacies, the exposure time of skeletals is an essential parameter, and is related to the controlling effect of the sedimentation rate. This latter depends on factors such as the tectonic–eustatic dynamics, the relative distance from the shore, and the bottom physiography.

Flat-pebble conglomerates: a local marker for Early Jurassic seismicity related to syn-rift tectonics in the Sesimbra area (Lusitanian Basin, Portugal)

Flat-pebble conglomerates have been identified in the Lower Toarcian (Levisoni Zone) carbonates of the Sesimbra region (30 km south of Lisboa, Portugal) and related to submarine mass movements. Their origin is explained through a three-stage model based on the comparative analysis of potential generating mechanisms taking into account timing and type of geodynamic evolution in the Lusitanian Basin: (a) differential lithification of thin carbonate and non-bioturbated horizons embedded within a more argillaceous matrix; (b) disruption by seismic shocks related to active extensional faulting and block tilting; and (c) gravity sliding mixing material resulting from broken lithified horizons. This sequential process originated flat-pebble conglomerates during early Jurassic phases of syn-rift evolution in the southern Lusitanian Basin. q 2001 Elsevier Science B.V. All rights reserved.

First and Second Orders of Suture Complexity in Ammonites: A New Methodological Approach Using Fractal Analysis

The study of septal patterns in ammonoids has been centered on functional and/or constructional issues. Complexly fluted septa have been considered as complementary structures that reinforce the ammonite shell, their frilled sutures possibly manifesting the demand for strength. Ammonitic sutures display features that denote typical fractal behavior, since they can present very long perimeters relative to the contiguous shell areas, and most provide evidence of statistical self-similarity when observed at varying scales of magnification. However, there is a lower limit of scale measurements below which the fractal behavior of the curve no longer holds, and the perimeter length/step size relationship approaches an Euclidean geometry. This paper describes a new methodology that allows the accurate characterization of suture complexity in ammonoids using the technique of fractal analysis (step-line procedure). The proposed methodology helps to fix the position of this “cut-off point,” allowing for independent estimates of the fractal dimensions of the curve for both large and small measurement scales (i.e., first and second orders of suture complexity). This approach improves the resolution of fractals in the analysis of suture complexity, thus facilitating the potential interpretation of suture patterns in functional/constructional, evolutionary and paleoecological terms.

Diplocraterion: A Useful Marker for Sequence Stratigraphy and Correlation in the Kimmeridgian, Jurassic (Prebetic Zone, Betic Cordillera, southern Spain)

Abstract Diplocraterion parallelum with exclusively protrusive spreite are documented at particular horizons in fine-grained Lower Kimmeridgian (Upper Jurassic) deposits from the Prebetic Zone (Betic Cordillera, southern Spain). The occurrence of D. parallelum and the interpreted change from a Cruziana ichnofacies to a mixed Skolithos-Cruziana assemblage is related to increasing energy and more proximal and unstable substrates resulting from relative sea-level falls. These relative sea-level changes agree with a proposed Type-II sequence boundary inferred from sequence stratigraphic analysis. Bio-chronostratigraphic control shows the persistent occurrence of Diplocraterion close to the Platynota/Hypselocyclum Zone boundary (Lower Kimmeridgian); that is, these occurrences correlate between sections irrespective of slight deviations in the sedimentary package. Thus, Diplocraterion occurrence is proposed as a reference level for stratigraphy within epicontinental deposits of the northern margin of the westernmost Tethys. This work supports the usefulness of the trace fossil approach in basin analysis, either in sequence stratigraphic studies of deposits characterized by correlative conformities and/or stratigraphic correlation in basins wherein guide fossils are scarce.

Ecostratigraphic approaches, sequence stratigraphy proposals and block tectonics: examples from epioceanic swell areas in south and east Iberia

Abstract An ecostratigraphic approach is proposed here as a supplementary tool to sequence stratigraphic interpretations mainly based on lithology. As a case study, six sections were selected with condensed ammonitico-rosso facies of Early Tithonian age (Albertinum/Darwini Chron) within an epioceanic fringe. This fringe clearly differs in its ecologic, sedimentary, and tectonic frameworks from better documented epicontinental environments. In the studied sections, “short distance differences vs. long distance similarities” have been evaluated by comparing features of macro and microfacies in the ammonitico-rosso facies and by the analyses of 1239 megainvertebrates which were recorded bed-by-bed. Sixteen average faunal spectra containing anywhere from 50 to 150 specimens were analyzed. The ecostratigraphic interpretation is made by considering the ammonites/other megainvertebrates ratio, the assumed ecology and taphonomy for selected ammonite groups, the depositional dynamics, and proposed short-term sea-level changes and local tectonics. The trends observed in the composition of megainvertebrate faunal spectra are explained by ecospace changes caused by eustasy (shared trends in long-distance correlations) and by relative sea-level changes due to the combined action between tectonics and eustasy (counteractive trends in short-distance correlations).

Taphonomic tools to evaluate sedimentation rates and stratigraphic completeness in Rosso Ammonitico Facies (epioceanic Tethyan Jurassic).

A combined multidisciplinary approach has been applied to calculate minimum values of the stratigraphic completeness and, secondarily, sedimentation rates in 9.2 m thick Rosso Ammonitico facies from central Apennines (Italy) and 11 m thick deposits of the same facies in Southern Spain. Middle - Upper Toarcian expanded sedimentation in Valdorbia section (Umbria-Marche Apennines) and extremely condensed Oxfordian-Tithonian sedimentation at Puerto Escano section (External Subbetic) have been investigated using combined taphonomic, ichnologic and sedimentologic data and analyses. At Valdorbia, infaunal tiering is largely preserved and 27 horizons of infaunal-tiering truncation and casting reveal strong erosional activity forced by tempestite/turbidite events. Therefore, microstratigraphic gaps could be evaluated without biostratigraphic control. In this expanded section, 13 horizons of firm- and hardgrounds have been recorded showing simple or gradational tiering. Conversely, in the condensed Puerto Escano section, taphonomic analysis reveals 25 horizons of bioclasts truncation (mainly in ammonites), and 56 horizons of firm-hardgrounds intensively bioturbated. In Valdorbia rather than in Puerto Escano section, the evaluation of flattening in burrows and spherical bioclasts reveal a measurable mechanical compaction and dissolution. In addition, Rosso Ammonitico at Valdorbia section favoured the calculation of decompaction coefficients (nd) for each lithology easier than in Puerto Escano section. In condensed and essentially hiatal Rosso Ammonitico, mottled deposits due to intense bioturbation dominate and tiering cannot be recognizable. This fact is accentuated by usual overprinting of elementary depositional events, which in turn hampered the accurate calculation of missing deposits. Therefore, in condensed Rosso Ammonitico the latter was only available in terms of minimal missing-record trough the analysis of truncated bioclasts.

Recent Advances in Morphometric Approaches to Covariation of Shell Features and the Complexity of Suture Lines in Late Jurassic Ammonites, With Reference to the Major Environments Colonized

We report recent advances concerning a research programme focused on the characterization of suture complexity in ammonoids using the method of fractal analysis (stepline procedure), as well as the covariation between suture complexity, shell geometry and sculpture, paying attention to assumed major environments colonized by Late Jurassic ammonites. The application of the logarithmic spiral model and Fourier descriptors of whorl section have improved our previous characterization of shell morphology. In 507 specimens analysed, significant differences in fractal dimension (D f ) mean values were observed according to shell coiling, the shape of whorl section and flanks, the sculpture, and the ratio of outer surface to inner volume (S: V) of the chambers being especially determinant. Factor analysis shows a complex covariation between shell features and suture complexity, which determines a heterogeneous distribution of D f values within the ammonite morphospace. In addition, the results obtained indicate that suture complexity was not directly related to bathymetry, and/or that there were no major differences in habitat depths between epicontinental and epioceanic ammonites. Finally, we envisage the potential resolution of fractals in the analysis of suture complexity in ammonoids, as well as the potential interpretation of suture complexity in ecological terms, facing the future research in this field.