Javier Elorza

Taphonomy of the Late Cretaceous dinosaur-bearing beds of the Laño Quarry (Iberian Peninsula)

Abstract The Lano quarry, located in the northern part of the Iberian Peninsula (Basque–Cantabrian Region), has yielded a diverse continental vertebrate assemblage from the Late Cretaceous (late Campanian to early Maastrichtian). The fossil assemblage consists of almost 40 species, including bony fish, amphibians, lizards, snakes, turtles, crocodilians, dinosaurs, pterosaurs and mammals. Lano is the most productive European vertebrate locality hitherto known from the Late Cretaceous. The sedimentology of the Lano section shows that the three associated fossiliferous beds (known as L1A, L1B and L2) were deposited in an alluvial system composed primarily of fluvial sands and silts. The sedimentary structures are consistent with channel areas within an extensive braided river. The L1A level was excavated in detail and mapped following a square-metre grid system. The main features of the multispecies vertebrate assemblage are as follows: wide range of body size (including microfossils); large proportion of adult individuals; rare articulated skeletal parts; size-sorting and dominance of small elements; high spatial density; long bones showing some preferential orientation; variable dip; variable degree of breakage and large proportion of splintering; wide range of weathering and abrasion; no evidence of predatory activity or chemical alteration. On the basis of these features, we suggest that the Lano association lies between the taphonomic modes for attritional vertebrate assemblages in fluvial channels, though it tends more toward the channel-fill than the channel lag mode. The L1A sample of Lano is a heterogeneous assemblage of elements ranging from isolated bones and teeth to articulated skeletons with allochthonous and para-autochthonous characteristics. It consists of a mixture of vertebrates from different palaeocommunities, and includes aquatic (or semi-aquatic) elements and remains transported from a variety of habitats on the alluvial plain. The dinosaur bones are commonly broken and show a greater degree of abrasion than those of freshwater vertebrates, indicating that they may be allochthonous. However, actinopterygians, amphibians, pleurodiran turtles and eusuchian crocodilians are interpreted as being para-autochthonous. Palaeobatrachid frogs, bothremydid turtles and alligatoroid crocodilians are the most relatively abundant vertebrates of the Lano fossil assemblage. The occurrence of pelomedusid turtles and crocodilians is indicative of an intertropical, warm climate.

Environmental stress and diagenetic modifications in inoceramids and belemnites from the Upper Cretaceous James Ross Basin, Antarctica

SummaryNew petrographic and isotopic data from inoceramid bivalve shells and belemnite rostra from the lower Campanian and belemnite rostra from the mid-upper Maastrichtian of the Marambio Group, James Ross Basin, Antarctica are presented. Most of the inoceramid data were processed from shell fragments of the large formAntarcticeramus rabotensis (Crame and Luther) at the stratigraphic level marking the extinction of the inoceramids in the James Ross Basin (uppermost early Campanian-basal late Campanian). Standard transmitted light microscopy and cathodoluminescence (CL) studies in thin sections ofA. rabotensis show clear evidence of environmental stress, which is reflected as marked growth breaks in the shell banding of this large inoceramid bivalve. At Redonda Point, CL and the mean oxygen isotopic value (δ18O=-3.11‰ 3 (PDB); n=11; t°=25.4°C) indicate a varied degree of diagenetic modification, but without any evidence of neomorphism along the prismatic microstructures. Early Campanian belemnite rostra are much less diagenetically modified (at the Brandy Bay section; and the Santa Marta section; δ18O=-0.50‰ (PDB); n=5; t°=14.0°C and 3 δ18O=-0.94‰ (PDB); n=21; t°=15.8°C) and are non luminescent 3 except for localized, organic-rich bands. The mean oxygen isotopic value for mid-late Maastrichtian belemnite rostra (at the Seymour Island section; δ18O=-0.11‰ 3 (PDB); n=5; t°=12.5°C) indicates a substantial drop in the sea-water paleotemperature, suggesting a causal relationship between the early extinction of the inoceramid bivalves in high latitudes of the Southern Hemisphere and the falling sea-water temperature.

New petrographic and geochemical insights on diagenesis and palaeoenvironmental stress in Late Cretaceous inoceramid shells from the James Ross Basin, Antarctica

New petrographic and geochemical insights from inoceramid bivalve shells of lower Campanian (Marambio Group, James Ross Basin, Antarctica) show that they suffered significant palaeoenvironmental stress just before their disappearance in the southern high latitudes. Inoceramid data have mainly been derived from shell fragments of the large form Antarcticeramus rabotensis Crame & Luther, collected at stratigraphical levels marking the early disappearance of inoceramids in the James Ross Basin (10 m.y. before the Cretaceous/Tertiary boundary in Antarctica). Cathodoluminescence studies and minor and trace element intra-shell variations in A. rabotensis shells, along with their whole shell geochemistry (major, minor, and trace elements, including REE), have revealed evidence of only weak diagenesis but significant palaeoenvironmental stress. The most relevant evidence of such adverse palaeoenvironmental conditions in A. rabotensis shells is reflected by marked growth interruptions in the normal shell layering, including the occurrence of a previously undetected inner aragonitic nacreous layer formed of alternating aragonitic and calcitic sublayers. The weak diagenesis produced characteristic geochemical intra-shell variations, which have subsequently been detected in the inoceramid shell microstructure, especially in the inner aragonitic nacreous layer.

Strain determinations using inoceramid shells as strain markers: a comparison of the calcite strain gauge technique and the Fry method

Abstract To test the accuracy and reliability of the strain gauge technique for calcite e-twin analysis, calcite e-twin strain and finite strain were determined using a new tectonic marker, inoceramid shells (macrofossils composed of aggregates of pseudo-hexagonal calcite prisms with a honeycomb microstructure). Although the calcite prisms in the inoceramid shells were not randomly distributed and showed strong crystallographical orientation, the strain gauge technique yields principal strain orientations that correlate precisely with those found by the Fry method. Thus, this technique can also be used to establish the ellipsoid strain orientation in rocks where calcite grains show strong crystallographical orientation.

TAPHONOMY OF VERTEBRATE FOSSIL ASSEMBLAGES FROM SWAMPY CIRCUM-LAKE ENVIRONMENTS: AN EXAMPLE FROM THE LATE EOCENE OF ZAMBRANA (IBERIAN PENINSULA)

Abstract Biostratinomic and bone-diagenesis parameters are used to evaluate the effects of abiotic and biotic processes on the final composition of two late Eocene vertebrate assemblages preserved in a swampy circum-lake environment from the Zambrana site (Basque-Cantabrian Region, northern Iberian Peninsula). No significant transport or bone sorting by fluvial action is observed, and complete and fragmentary bones in the assemblages (Z4 and Z6 beds) show the same biostratinomic features. The attritional bone accumulation in both excavated beds was caused mostly by biotic factors related to routine ecological deaths of population members, probably with some input from predators on the most vulnerable ungulate individuals (autochthonous), although a weak input of small remains by superficial water currents from nearby areas (parautochthonous) cannot be rejected. The vegetation and wet conditions of the swampy environment, together with possible predator and scavenger activity, could have caused the disarticulation and dispersion of some vertebrate remains, mainly those of ungulates. The bones were buried relatively quickly in the phreatic zone under reducing conditions and suffered considerable crushing and fragmentation because of lithostratigraphic compaction. Mineralogic similarities between sedimentary fillings in the fossils and the host sediment, as well as the homogeneous rare earth element (REE) trends of the fossils, are indicative of a uniform and unique diagenetic history and the absence of reworked elements. The fossil bone mineral is well-crystallized francolite (carbonate fluorapatite). The REE enrichment of bones and their calcite and pyrite crusts and fillings were formed during early diagenetic phases. The black coloration of the bones may be explained by their high hydrocarbon (n-alkane components) contents.

Sponges and corals from the Middle Eocene (Bartonian) marly formations of the Pamplona Basin (Navarre, western Pyrenees): taphonomy, taxonomy, and paleoenvironments

Sponges and corals from the Bartonian marly formations of the Pamplona Basin (South Pyrenean area, Navarre) are described for the first time. The fossiliferous levels correspond respectively to flood-influenced delta-front (Ardanatz Sandstone) and restricted outer-platform (Ilundain Marls Fm.) environments. The fossil sponges exhibit diagenetic fragmentation, but they are often complete specimens. The skeleton appears partially or totally replaced by calcite and/or in some cases large crystals of celestite. Celestite forms relatively early during diagenesis in a dysoxic environment. Neomorphic fibrous quartzine-lutecine spherulites are also present. Hexactinellids and lithistids occur, but the former predominate. The associations include the species Laocoetis samueli, Guettardiscyphia thiolati and/or Pleuroguettardia iberica, cf. Rhizocheton robustus, and two lithistids indet. Corals are present only in the Ardanatz Sandstone. The fossil skeletons are composed of large neomorphic sparry calcite crystals. The assigned species are Stylocoenia taurinensis, Astrocoenia octopartita, Ceratotrochus bodellei, Placosmiliopsis bilobatus, and Desmophyllum castellolense. The sponge and coral taxa are similar to those previously described from other contemporaneous geological formations of the Pyrenean realm. The Pamplona Basin assemblages appear less diverse than those of the Bartonian of the eastern South Pyrenean area, more similar to that of the Eocene of Biarritz (Aquitanian Basin). This lower diversity is not due to a lower-resolution sampling but to taphonomic bias and/or paleoecological differences. The dominance of hexactinellids, erect morphologies, and sedimentological and micropaleontological data show that the sponge communities lived in deep shelfal waters. The corals, mainly associated with levels with high terrigenous content, seem reworked from shallower and more proximal environments.

Gastropods and bivalves from the Eocene marly formations of the Pamplona Basin and surrounding areas (Navarre, western Pyrenees)

ABSTRACT Gastropods and bivalve associations from the middle and ?upper Eocene (Bartonian and ?Priabonian) sedimentary succession of the Pamplona Basin are described. This succession was accumulated in the western part of the South Pyrenean peripheral foreland basin and extends from deep marine turbiditic (Ezkaba Sandstone Formation) to deltaic (Pamplona Marl, Ardanatz Sandstone and Ilundain Marl formations) and marginal marine deposits (Gendulain Formation). Fossils are generally fragmentary and many correspond to remains that have undergone taphonomic reworking. Significant effects of diagenesis are also detected, with evidence of compression or deformation, dissolution, aragonite-calcite neomorfism and cementation by celestite. Bioerosion traces and fossil encrusters are common. Fossils of 37 taxa, 25 gastropods and 12 bivalves, have been identified confidently. The number of species is probably considerably higher, as the study of some fossils, mainly the most small-sized species, is pending. One new species, Athleta (Volutospina) delvallei Astibia, Merle & Pacaud, n. sp. (Gastropoda, Volutidae), is described herein. Fossil assemblages are comparable to those from the Eocene of the Basque Coast (North Pyrenean area) and Aragon and Catalonia (west-central and eastern part of South Pyrenean area). Most of the mollusc taxa seem to be endemic to the Pyrenean area, but several Tethyan and Northern elements have also been recorded. These results enlarge the database for a better understanding of the evolution of global marine biodiversity throughout the Eocene.

Extending Back the Palaeogene Astronomical Time Scale: An Integrated Analysis of the Upper Maastrichtian Strata in the Basque Basin

We present a comprehensive, integrated, cyclo–magnetostratigraphic analysis and study of the calcareous nannofossils of the upper Maastrichtian hemipelagic succession in three sections of the Basque Basin (Zumaia, Sopelana, and Hendaia). The sections were correlated at a bed-by-bed scale through careful analysis of the lithological stacking pattern and significant sedimentary features. For spectral analysis, we used an available carbonate proxy record spanning 64 m of section below the K–Pg (Cretaceous–Palaeogene) boundary at Zumaia containing 72 precession-related limestone–marl couplets. The continuous wavelet spectrum helped to determine and visualize the orbital forcing at both the short (~100 kyr) and long (405 kyr) eccentricity bands. We applied bandpass Gaussian filters to the carbonate record to extract the relevant periodicities and provide a cycle-numbering scheme starting at the K–Pg boundary. The full hierarchy of precession cycles and eccentricity-related bundles was then extended towards the base of the Zumaia section, which contains 33 short eccentricity-related bundles, thus spanning more than 3 Myr. The C31r–C31n chron boundary (estimated to occur at ~3.08 Myr prior to the K–Pg boundary) in the lower part of the succession was determined unambiguously in all three sections studied, although the C30n–C29r reversal could not be determined due to a pervasive reverse magnetization acting on the purplish lithologies in the upper part of the succession. Relevant calcareous plankton bioevents were able to be accurately placed on the cyclo–magnetostratigraphic template. The cyclostratigraphic framework also allowed us to estimate the duration of previously defined sea-level-related, third-order depositional sequences in the basin, which appear to be strongly paced by the long-term 1.2 Myr obliquity amplitude modulating cycle.