Jordi M. de Gibert

Stratigraphy and sedimentology of the Middle Ordovician Hawaz Formation (Murzuq Basin, Libya)

The Middle Ordovician Hawaz Formation is a 200-m (660-ft)-thick succession made up of fine-grained quartzarenites displaying a variable degree of bioturbation. It records the deposition in a large-scale, low-gradient estuary, which was partially controlled by tectonic extension. The upper boundary of the formation is marked by two erosion surfaces (unconformities U1 and U2), related to the Late Ordovician glaciation. The U1 and U2 erosion surfaces generated a pronounced paleotopography that controlled the deposition of the Upper Ordovician sequences. Tectonism influenced the paleogeography, although faults were unimportant from the point of view of sedimentary thickness. Tectonic subsidence was moderate, and accumulation rates were low. Physiography favored tidal power, especially during transgressive episodes, when the coastal embayment was flooded. We defined 11 lithofacies, forming 6 facies associations. These associations are subtidal sandstones; storm-reworked, shoreface sandstones; shoreface-to-beach sandstones; channel-sandstone bodies; nearshore to inner-platform sandstones; and K-bentonites. Trace-fossil assemblages match Skolithos and Cruziana archetypal ichnofacies. On the basis of the dominant facies associations and ichnofacies, we divided the formation into three informal units, from base to top: HW.1, HW.2 and HW.3. Periodically, volcanic ash was supplied to the basin from distal eruptive centers and was preserved as thin beds of K-bentonite interstratified with the shoreface sandstones, but not with the tidal-dominated sandstones. We divided the Hawaz Formation into five third-order depositional sequences. Lowstand deposits were not identified. The lower boundaries of transgressive systems tracts are tidal ravinement surfaces or sequence boundaries, whereas the upper boundaries are flooding surfaces. The transgressive systems tracts are constituted by early transgressive tidal deposits separated by a wave ravinement surface from the late transgressive storm-dominated deposits. Highstand systems tracts consist of bioturbated shoreface-to-beach sandstones, which record seaward, shoreline progradation. Emilio obtained his Ph.D. in geology from the Universitat de Barcelona in 1988. Since then, he has been a lecturer in basin analysis and petroleum geology. He has been involved in several research projects on sedimentology and basin analysis in Spain, northern Africa, Antarctica and South America. His present-day research interests include three-dimensional modeling of sedimentary bodies and reservoirs. A professor of stratigraphy at the Universitat de Barcelona, M. Marzos research interest focuses on the application of clastic sedimentology, sequence stratigraphy, reservoir modeling, and basin analysis to the exploration and production of hydrocarbons. He has been involved in several research projects funded by oil companies in southern Europe, the North Sea, South America, and northern Africa. Jordi M. de Gibert received his Ph.D. from the Universitat de Barcelona in 1996. After a period at the University of Utah, he returned to Barcelona in 1999, where he currently holds a position as a tenure-track lecturer. His interests and areas of expertise include trace fossils, their paleobiological significance, and their implications for understanding ancient depositional environments. K. Tawengi received a B.Sc. degree in geology from Alfateh University, Libya, in 1984, and an M.Sc. degree in sedimentology and stratigraphy from Durham University, England, in 1996. He worked as an explorationist with Agip Oil Company in Libya from 1985 to 2000 and since then has worked as a senior exploration member with REPSOL Exploration in Murzuq S.A. His main fields of interest are sedimentology, stratigraphy, and subsurface geology. A. Khoja graduated in 1972 from the University of Libya. He received a diploma in petroleum geosciences from Oxford Polytechnic (1991) and an M.Sc. degree from Oxford Brookes University (1993). He joined the National Oil Corporation of Libya in 1972 and is presently the regional studies superintendent in the National Oil Exploration Department. Nestor obtained his degree in geology from Cordoba University (Argentina) in 1982 and his postgraduate in petroleum geology in the University of Cuyo, Argentina. He joined YPF in 1984 and worked in their exploratory department in Mendoza, Plaza Huincul, and Neuquen until the year 2000. Subsequently, he became Libya team leader for REPSOL- YPF in Madrid. He is currently director of exploration and production in Brazil.

Paleoethologic significance of bioglyphs: Fingerprints of the subterraneans

Abstract Bioglyphs are features in burrow or boring walls produced by such animal activity as scratching, drilling, plucking, gnawing, poking, and etching. Bioglyphs are important aspects to consider when making paleoethologic interpretations of trace fossils, because they can offer direct clues to understanding the mechanism of excavation of the trace fossil, the identity of the tracemaker, the purpose of the burrow or boring, and the character of the sediment in which the trace fossil has been produced.

Macroborings (Gastrochaenolites) in Lower Ordovician Hardgrounds of Utah: Sedimentologic, Paleoecologic, and Evolutionary Implications

Abstract New evidence of fossil macroborings in the Lower Ordovician (Ibexian) of western Utah demonstrates that the macroboring behavioral strategy was firmly established in the earliest stages of the great Ordovician diversification of the marine biosphere. In Utah, borings were excavated in hardgrounds that had developed on sponge-algal mounds and flat-pebble conglomerates in the Fillmore Formation (Ibexian). The most complete specimens possess a neck up to 1 cm in length that opens into a teardrop-shaped chamber with a maximum diameter of 1 cm. The chamber terminates at a depth of 3–4 cm below the hardground surface. These borings belong to the ichnogenus Gastrochaenolites. The organisms responsible for creating the borings are unknown. Sedimentologically, the effect of boring on hardgrounds was to break them into pebble- and cobble-sized clasts. The endolithic lifestyle represented by the borings may have evolved in response to ecologic pressures such as predation or competition for food resources. The macroborings from the Fillmore Formation represent an innovative strategy that may have resulted in the later development of new body plans and the early establishment of endolithic macroinvertebrates.

An ethological framework for animal bioerosion trace fossils upon mineral substrates with proposal of a new class, fixichnia

Animal bioerosion trace fossils upon mineral substrates are analyzed from the point of view of the Seilacherian ethological classification. Several of the currently accepted ethological classes: cubichnia, fugichnia, repichnia, fodinichnia, agrichnia, calichnia and aedificichnia are not represented in these substrates. This fact points out a lower behavioral diversity of hard substrate trace fossils when compared with soft sediment trace fossils. Bioerosion traces can be classified in just five classes: domichnia, pascichnia, equilibrichnia, praedichnia and fixichnia. Fixichnia is here erected to gather superficial etching scars resulting from the anchoring of fixation of sessile epiliths by means of a soft or skeletal body part. Praedichnia and fixichnia are exclusive of the bioerosion realm.

Cretaceous Ray Traces?: An Alternative Interpretation for the Alleged Dinosaur Tracks of La Posa, Isona, NE Spain

Abstract At the locality of La Posa, Isona, Spain, an extensive Upper Cretaceous bedding plane is exposed and exhibits thousands of ovate prints that had been interpreted as dinosaur tracks. Detailed study of these trace fossils allows the proposal of an alternative hypothesis that they were produced by the feeding activity of rays or other fish with similar behavior. Comparison with modern stingray pits from a tidal flat in Puerto Peñasco, Sonora, Mexico, reveals a great deal of similarity with the Cretaceous trace fossils in their distribution, morphology, environmental setting, and associated invertebrate bioturbation. Moreover, ray body fossils are known from neighboring contemporaneous deposits. The trace fossils here are attributed to the ichnogenus Piscichnnus.

Paleobiology of the Crustacean Trace Fossil Spongeliomorpha iberica in the Miocene of Southeastern Spain

The trace fossil Spongeliomorpha iberica locally occurs in the Tortonian (Upper Miocene) marine strata of the Fortuna basin in southeastern Spain, and its excellent preservation state allows a reliable reconstruction of its main morphologic features. The burrow systems are branched (but not anastomosing), and they include numerous, short, blind tunnels. The burrow walls are strongly ornamented with bioglyphs displaying a rhomboidal pattern, consisting mostly of individual “Y”-shaped scratches. Smaller, secondary bioglyphs consist of sets of less incised transverse scratches. These features allow us to assign the ichnospecies to a decapod crustacean, most likely an alpheid or thalassinidean shrimp. The burrow apparently served as a refuge for the inhabitant, which fed upon microorganisms growing on the walls of the burrow by means of scraping the interior surfaces with the maxillipeds or other mouth parts. It is also likely that the shrimp used the multiple blind tunnels to store organic material (probably plant detritus) to be used for later consumption. The crustaceans colonized mud firmgrounds, which were formed by erosion during a rapid sea-level fall. Thus, the burrows occur in direct association with erosional regressive surfaces and therefore are good stratigraphic indicators of abrupt paleoenvironmental change.

First trace-fossil evidence of bone-eating worms in whale carcasses

Abstract Whale corpses on the modern seafloor host particular communities that benefit from the large amounts of available labile organic matter. The study of these communities has revealed the presence of the siboglinid annelid Osedax that feeds on bone tissue by means of a symbiotic relationship with heterotrophic bacteria. Here we report the presence of tubular borings in a fragment of the neurocranium of a fossil baleen whale found in lower Pliocene rocks of southeastern Spain. They are formally described as Trypanites ionasi isp. n. The fossil borings can be assigned to annelid or sipunculid worms and may constitute the first evidence of an Osedax-like osteophagous behavior in the fossil record of cetaceans. Nevertheless, the definitive assignment to Osedax is not possible until we have more information on the morphology of modern siboglinid borings.

Diopatrichnus odlingi n.isp. (annelid tube) and associated ichnofabrics in the White Limestone (M. Jurassic) of Oxfordshire: sedimentological and palaeoecological significance

The shell-lined tubes ( Diopatrichnus odlingi n.isp.) frequently associated with Epithyris in the highly bioturbated shelly micrites of the White Limestone (Bathonian) at Kirtlington (Oxfordshire) represent the reworked caps of a tube-building polychaete similar to those of the modern onuphid Diopatra . The associated facies includes two distinct ichnofabrics. Ichnofabric 1 represents complex tiering in a relatively quiet subtidal environment with extensive bioturbation due mainly to deep tier crustacean burrows ( Thalassinoides ), with Diopatrichnus as an allochthonous component. Ichnofabric 2 has a more diverse suite of trace fossils associated with partial preservation of primary cross-stratification, and a lower bioturbation grade possibly formed on a channel bar or shoal.

Paleodepth and Paleoenvironment of Dactyloidites ottoi (Geinitz, 1849) from Lower Cretaceous Deltaic Deposits (Basque-Cantabrian Basin, West Pyrenees)

Abstract The rosetted trace fossil Dactyloidites ottoi (Geinitz) commonly has been associated with shallow-water, high-energy marine environments, although detailed sedimentological analyses of the host deposits are unfortunately few. The Aptian–Albian Otoio Formation (Basque-Cantabrian Basin) provides an excellent opportunity to test the paleobathymetric and paleoenvironmental controls on the restricted distribution of D. ottoi. The Otoio Formation records a great variety of shallow-water marine environments, but D. ottoi occurs only in intervals interpreted as fluvial-dominated deltas (Gilbert-type and mouth bar-type deltas). Moreover, detailed facies analysis and geometric relationships of the deltaic deposits suggest the following main controls on the distribution of D. ottoi: (1) paleodepth between 0 and 3 m, quantified from the foreset heights of Gilbert-type deltas; (2) siliciclastic and organic matter-rich sandy substrate; (3) high and discontinuous sedimentation rates; and (4) reduced salinity, responsible for the small size of the trace from the Otoio Formation. These observations are in agreement with published data from other localities.

Climatic control of trace fossil distribution in the marine realm

Abstract Modern coastal and shoreface faunas exhibit strong latitude (climate) controlled distributions. In contrast, most ichnotaxa are long-ranging, and ichnofacies are widely distributed geographically. This is readily explained by the dominantly warmer and more equable climates of much of the past, as well as the diversity of the producers of most ichnotaxa. Nevertheless, in the Pleistocene, and in the Eocene, cool-water ichnofabrics can be recognized. The latitudinal distributions of thalassinidean crustaceans and infaunal spatangoid echinoids are examined because of their propensity to form distinctive and often abundant trace fossils. Three climatic zones are tentatively recognized from modern shore and shoreface sediments, and which are considered to extend back to the Mesozoic: tropical and subtropical with pellet-lined burrows (Ophiomorpha), echinoid burrows and other traces; temperate with echinoid burrows and mud-lined or non-lined thalassinidean burrows (Thalassinoides), but without Ophiomorpha; and arctic (cold waters) with only a molluscan and annelid trace fossil association. Examples demonstrating this climatic trend are drawn from the Cenozoic and Pleistocene.