Francisco J. Rodríguez-Tovar

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).

Fe-oxide spherules infilling Thalassinoides burrows at the Cretaceous-Paleogene (K-P) boundary: Evidence of a near-contemporaneous macrobenthic colonization during the K-P event

A detailed ichnological analysis focused on Thalassinoides structures recorded just below the Cretaceous-Paleogene (K-P) boundary layer of the Agost section (southeast Spain) aimed to evaluate macrobenthic colonization during the K-P boundary event. Stereomicroscopy and field emission scanning electron microscopy analyses conducted on material filling in Thalassinoides trace fossils reveal the presence of dark infill material that includes spherule-like elements, similar to those previously differentiated in the K-P boundary layer. Energy-dispersive X-ray spectrometry indicates a ferruginous composition (goethite spherules). This represents the first record of spherules related to the K-P boundary event within trace-fossil infilling material. The passive filling of this material into the Thalassinoides bioturbation allows interpretation of the gravitational deposition just after Thalassinoides trace-maker colonization. The absence of erosive sedimentary structures or other material deposited between the Thalassinoides trace-maker colonization and the spherule deposition is interpreted as evidence of rapid colonization during the K-P boundary event, nearly contemporary with the spherule layer deposition.

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.

Trace fossils after the K–T boundary event from the Agost section, SE Spain

Palaeogene trace fossils penetrate the uppermost Cretaceous sediments in the Agost section, Betic Cordillera, SE Spain. Chondrites ? targionii , Zoophycos isp., Planolites isp. A, Planolites isp. B, ? Thalassinoides isp. A, Thalassinoides isp. B, Thalassinoides isp. C, Alcyonidiopsis longobardiae , and Diplocraterion ? parallelum have been identified. A well-developed endobenthic tiering pattern is interpreted. The uppermost tier (A) represents major benthic activity in the shallowest sediments at or just below the seafloor, recorded as bioturbated background (only discrete rare Planolites ). The next upper tier (B) displays the highest trace-fossil diversity, with Planolites in the shallow levels, and Thalassinoides and Alcyonidiopsis at slightly deeper ones. The intermediate tier (C) contains randomly distributed Thalassinoides and Alcyonidiopsis , cross-cut by Zoophycos and large and medium-sized Chondrites . The deepest tier (D) contains Zoophycos , cross-cut by medium- and mainly small-sized Chondrites . Two interpretations are proposed: (1) vertical partitioning of a singled multi-tiered community under steady-stable conditions in well-oxygenated water bottom, reflecting gradual changes deep into the sediment, with decreasing oxygen pore water and benthic food, and increasing substrate consistency, and (2) sequential colonization and community replacement, reflecting the work of two successive communities. The first community, mainly represented by Planolites , Alcyonidiopsis and Thalassinoides , was produced in a shallow, oxygenated soft substrate. Probably related to decreasing oxygen content and benthic food availability, this community was replaced by deeply burrowing organisms that produced Zoophycos and Chondrites . This sequential colonization can be determined by changes in environmental parameters related to the Cretaceous–Palaeogene (K–T) event, or may have resulted from normal ecological and early diagenetic processes.

The permutation test as a non-parametric method for testing the statistical significance of power spectrum estimation in cyclostratigraphic research

Abstract A computer-intensive significance test for estimated power spectra of cyclic sedimentary successions is presented. This simple method requires no more than a few minutes in computer time for a PC-486, and does not require distributional assumptions. It is suitable for all the spectral analysis approaches used in practice. Moreover, good performance is achieved with relatively short stratigraphical series. The method is similar to a permutation test that has been successfully applied to other statistical problems. In the proposed application of the permutation test to the spectral analysis of time series, the data of a stratigraphic sequence are ordered at random (random permutation) and the power spectrum is estimated by the given approach. The process is repeated many times (e.g. 1000 times) and thus it is possible to assess the statistical significance of the power spectrum of the original sequence for each frequency. Simulation results and the application to real data are shown in order to discuss the performance of the method.

Foraminiferal morphogroups in dysoxic shelf deposits from the Jurassic of Spitsbergen

Analysis of benthic foraminiferal assemblages was performed in Bathonian to Kimmeridgian deposits through a section covering the lower half of the Agardhfjellet Formation in central Spitsbergen. The section consists mainly of organic-rich shales, which contain low-diversity agglutinated assemblages. In this foraminiferal succession five morphogroups were differentiated according to shell architecture (general shape, mode of coiling and number of chambers), integrated with the supposed microhabitat (epifaunal, shallow infaunal and deep infaunal) and feeding strategy (suspension-feeder, herbivore, bacterivore, etc.). The environmental evolution of the analysed section is interpreted by using the stratigraphic distribution of morphogroups, combined with species diversities and sedimentary data, in a sequence stratigraphic framework. The section comprises two depositional sequences, which demonstrate that species diversity and relative frequency of morphogroups are correlative with transgressive–regressive trends controlling depth and oxygenation of the water column. In both sequences, the maximum flooding interval is characterized by increased organic carbon content, dominance of the epifaunal morphogroups and reduced species diversity: features reflecting the increased degree of stagnation separating the transgressive phase from the regressive phase.

ICHNOFABRIC EVIDENCE FOR THE LACK OF BOTTOM ANOXIA DURING THE LOWER TOARCIAN OCEANIC ANOXIC EVENT IN THE FUENTE DE LA VIDRIERA SECTION, BETIC CORDILLERA, SPAIN

Abstract The early Toarcian (Early Jurassic) global marine mass extinction is usually related to the development of organic-rich sediments preserved as black shales and interpreted as a global oceanic anoxic event—the Toarcian Oceanic Anoxic Event (T-OAE). In the Betic Cordillera, southern Spain, the deep-marine Fuente de la Vidriera section contains the T-OAE as recorded at the westernmost part of the European Tethys. Ichnological analysis of the section indicates a relatively abundant and moderately diverse trace-fossil assemblage composed of Alcyonidiopsis isp., Chondrites isp., Nereites isp., Palaeophycus heberti, Planolites isp., Teichichnus isp., Thalassinoides isp., and Trichichnus linearis. A well-developed endobenthic multi-tiered community is characterized by an upper tier represented by homogenized sediment—individual burrows difficult to discern, a middle tier with a relatively diverse trace-fossil assemblage of mainly vagile deposit feeders, and a lower tier with activities of semisessile deposit feeders. The ichnoassemblage indicates oxic or slightly dysoxic bottom waters that were relatively favorable for benthic organisms. The absence of anoxia is confirmed by previously published geochemical and isotopic data. The T-OAE did not induce extreme conditions for macrobenthic organisms inhabiting the seafloor in this area of the westernmost Tethys. Local factors probably limited the influence of the anoxic event in bottom waters but may have induced oxygen deficiency in upper water masses, producing unfavorable living conditions for pelagic biota and, consequently, a sudden decrease in ammonite abundance.

Carbon isotope evidence for the timing of the Cretaceous–Palaeogene macrobenthic colonisation at the Agost section (southeast Spain)

Abstract The Cretaceous–Palaeogene (K–T) boundary section of Agost (southeast Spain), one of the most complete sections existing, contains a well-developed trace-fossil assemblage, composed of dark- and light-filled trace fossils, registered in the uppermost Cretaceous (Maastrichtian, Plummerita hantkeninoides Biozone) sediments. The trace-fossil assemblage reveals that significant macrobenthic colonisation occurred around the K–T boundary interval. However, difficulties in recognising trace fossils affecting the K–T boundary layer, as well as in biostratigraphically characterising these trace fossils hindered a conclusive interpretation on the timing of this macrobenthic colonisation. With the aim of this characterisation, we determined the δ13C of the carbonate fraction of dark and light filling materials from the trace fossils, since the carbon isotope compositions of uppermost Cretaceous and lowermost Palaeogene materials are clearly different. The data compiled provide evidence for a significant distinction between light-filled trace fossils, with δ13C values higher than 1.6‰ PeeDee Belemnite (PDB), and dark-filled trace fossils, with δ13C values between 0.21 and 1.2‰ PDB, most of these being lower than 0.7‰ PDB. The comparison of these values with those from the uppermost Maastrichtian to the lowermost Danian sediments reveals that the macrobenthic colonisation occurred in different phases across the K–T boundary interval.

Sequence stratigraphy and bedding rhythms of an outer ramp limestone succession (Late Kimmeridgian, Northeast Spain)

Facies, stratal and spectral analyses of an outer ramp lime mudstone succession (Aguilon, north Iberian Ranges, Spain) are presented in this work. The studied succession is Late Kimmeridgian (eudoxus and beckeri zones) in age and comprises the transgressive and highstand deposits of a third-order depositional sequence. A number of higher-order sequences (bundles and sets of bundles) have been identified based on the comparative analysis of the bedding planes. The bundles and sets of bundles show a well-defined stratal pattern. Spectral analysis has provided further independent confirmation of the cyclical nature of the bundles and sets of bundles defined from field analysis. The bundles have variable thickness (from 1 to 2 m) and are formed by up to 10 micritic beds. They have been related to sea- level changes controlled by the orbital precession cycle, affecting the shallow productivity area. A significant amount of the lime mudstones accumulated in outer ramp settings were derived from resedimentation of the shallow carbonate production areas. Many of the bundles show a lower interval with a thinning and fining-up trend, indicating a progressive decrease of the carbonate production (and carbonate export) during periods of high-frequency sea-level rise. The late transgressive and highstand deposits show sets of bundles (groups of five bundles, from 5 to 8 m) probably related to sea-level changes controlled by the short eccentricity cycle. The overall thickness and the stacking pattern observed in the sets of bundles are controlled by the long-term sea-level variation. The sets of bundles located in the late transgressive deposits show thinner micritic beds in their lower or middle part. The sets of bundles found in the highstand deposits are thinner and show a thickening-up and thinning-up trend. On the studied carbonate ramp, during periods of long-term sea-level rise, the overall carbonate production (and carbonate export) is high, although the superposition of the high-frequency sea-level rises may result in episodic flooding and drowning of the shallow ramp areas. During periods of long-term, early highstand of sea level, the overall carbonate production (and carbonate export) is more reduced, but it has maximum peaks during the transgressive (and early highstand) intervals of the high-frequency sea-level cycles. Sedimentation during the long-term sea- level fall (late highstand) was scarce and discontinuous in the outer ramp area, and resulted in the overall thickness reduction of the sets of bundles. D 2003 Elsevier Science B.V. All rights reserved.