Download (.pdf) Oxygen availability effects on early diagenetic calcite dissolution in the Arabian Sea as inferred from calcareous dinoflagellate cysts
by Ines Wendler
Wendler, I., Zonneveld, K.A.F., Willems, H., 2002. Global and Planetary Change, 34, 219-239.
In oceanic regions with high primary production, such as the Arabian Sea, the primary signals of proxies are often... more
In oceanic regions with high primary production, such as the Arabian Sea, the primary signals of proxies are often altered by diagenetic processes. The present study aims at assessing the effects of early diagenesis on calcareous dinoflagellate cysts, which represent a relatively new tool for reconstructing the paleoenvironmental conditions within the photic zone. For this purpose, surface sediment samples from within and below the oxygen minimum zone (OMZ) of the northeastern and southwestern Arabian Sea have been analysed quantitatively for their calcareous dinoflagellate cyst content. The calculated cyst accumulation rates (ARs), the relative abundances and cyst fragmentation values were compared to bottom water oxygen (BWO) content and ARs of organic carbon at the sample positions. Different patterns were found in the northeastern and southwestern part of the Arabian Sea. In the SW, no relationship between cyst ARs and BWO is distinguishable, and the distribution of cyst ARs is thought to largely reflect primary cyst production. In the NE, much higher ARs of all species are found in samples from within the OMZ in comparison to samples from below it. This is interpreted to result from better calcite preservation within the OMZ, presumably due to reduced oxic degradation of organic matter. The differential drop of cyst ARs of the individual species at the lower boundary of the OMZ in the NE Arabian Sea, as well as the species-specific change in relative abundance and fragmentation, indicate different sensitivity to calcite dissolution of the different species. These results show that early diagenetic calcite dissolution can change both relative and absolute abundances of calcareous dinoflagellate cysts, which has to be considered if using them for paleoenvironmental reconstructions. Furthermore, it is shown that considerable calcite dissolution can occur above the carbonate saturation horizon in high productive areas. However, calcite preservation can be substantially increased, as soon as oxygen concentrations are too low for oxic degradation of OM. Under low oxic conditions (within and near the OMZ), the main factor controlling organic matter (OM) preservation appears to be BWO concentrations. Under higher oxygen levels (below f1500 m depth in the NE Arabian Sea) there seems to be an increasing influence of bioturbation and sedimentation rate on the preservation of OM by controlling its oxygen exposure time. This study presents an example of a highly productive basin in which differences in early diagenetic processes can lead to the preservation of a signal that is either dominated by primary production (off Somalia) or by secondary alteration (off Pakistan), although in both areas, an oxygen depleted zone is present. For estimating the effects of early diagenetic calcite dissolution in a sediment by metabolic CO2 (and
probably by H2S oxidation), not only the content of organic carbon but also other geochemical proxies for paleoredoxconditions
have to be included for paleoenvironmental reconstructions.
Cretaceous oceanic red beds (CORBS) in the Austrian Eastern Alps: Passive-margine vs. active-margin depositional settings
by Ines Wendler
Wagreich, M., Neuhuber, S., Egger, H., Wendler, I., Scott, R., Malata, E., Sanders, D., 2009. Cretaceous Oceanic Red Beds: Stratigraphy, Composition, Origins, and Paleoceanographic and Paleoclimatic Significance
SEPM Special Publication, 91, 73-88.
CORBs are described from a north–south transect from the passive European margin with the Helvetic–Ultrahelvetic shelf... more CORBs are described from a north–south transect from the passive European margin with the Helvetic–Ultrahelvetic shelf and continental slope through the Alpine Tethys, including the Rhenodanubian Flysch Zone into the southern, tectonically active margin of the Austro-Alpine microplate, including the Northern Calcareous Alps. In the Helvetic (shelf) and Ultrahelvetic (slope) part of the European margin, the proportion of CORBs in the Upper Cretaceous successions increases significantly with increasing water depth and increasing pelagic character. In the Ultrahelvetic units of Upper Austria (Rehkogelgraben, Buchberg), CORBs define a continuous red interval from the Lower Turonian to the Lower Campanian. The onset of CORB deposition in the Ultrahelvetic Zone corresponds to a major change in paleoceanographic conditions from anoxic during the Late Cenomanian OAE 2 to highly oxic during the Early to Middle Turonian. In the Rhenodanubian Flysch, hemipelagic red and green shales alternate with turbiditic siltstones and minor sandstones in the Upper Aptian–Lower Cenomanian Lower Varicolored Marls, the Coniacian–Lower Campanian Seisenburg Formation, and the uppermost Campanian Perneck Formation. CORBs in the Rhenodanubian Flysch are controlled mainly by tectonic events and sea-level changes, and occur during times of transgressions, low clastic input, and low turbidite frequencies. In the Austro-Alpine Northern Calcareous Alps, CORBs occur from the Santonian onwards in the upper parts of transgressive sequences of the Gosau Group, e.g., in the Tiefenbach and the Dalsenalm sections. In areas where clastic input was low, CORB deposition continued up into the Maastrichtian. Based on these data a peak of oceanic red beds is inferred for the middle Santonian–Early Campanian time interval. Prerequisites for CORB sedimentation are low clastic input, low sedimentation rates, and increasing paleo–water depth. CORBs can be classified as a variation of three end members: clayey CORBs, consisting mainly of terrigenous clay minerals; calcareous CORBs, mainly pelagic limestones; and siliceous CORBs, consisting mainly of biogenic SiO2.
Early Turonian shallow marine red beds on the Levant carbonate platform (Jordan), Southern Tethys
by Ines Wendler
Wendler, J., Wendler, I., Kuss, J., 2009. Cretaceous Oceanic Red Beds: Stratigraphy, Origins, Paleoceanographic and Paleoclimatic Significance, SEPM Special Publication, 91, 171-179.
A one-meter-thick marine red bed (Cretaceous oceanic red beds, CORBs) is reported from Early Turonian sediments... more
A one-meter-thick marine red bed (Cretaceous oceanic red beds, CORBs) is reported from Early Turonian sediments associated with the Levant carbonate platform in central Jordan. These CORBs are of regional significance, in that deposits similar in facies and age are present in various sections of the Levant carbonate platform farther southwest in the Sinai. The red bed represents a rare shallow marine counterpart to the widely known deeper marine CORBs. The onset of sedimentation of these brick-red marls in a shallow sea (shallow subtidal) of the southern Tethys margin is shown to be synchronous with the Tethys-wide onset of marine red beds in oceanic settings in the latest Early Turonian. The transition into red marls marks a significant change in sedimentation from marly, gypsum-rich clay, representing lowstand deposits below, into a sequence including massive platform limestone beds forming a transgressive systems tract above the red bed. The sedimentary conditions on the Levant platform during red-bed deposition show some similarities to its deeper marine counterparts on the Northern Tethys margin: they are related to strongly fluctuating sedimentation rates, and they follow periods of high marine productivity, which occurred in the aftermath of AE2. It is obvious that both strong synsedimentary fluctuations in water depth and accumulation rate and significant early and late evaporite diagenesis influenced the investigated section, so the cause of the red coloring is likely to be not solely a synsedimentary feature. The time-equivalent onset of shallow marine red beds and deep marine red beds
in the Early Turonian indicates that both share common global prerequisites regardless of the paleobathymetry.
Large chambered sponge borings on a Late Cretaceous abrasion platform at Cracow, Poland
A new ichnospecies of the bioeroding sponge ichnogenus Entobia, i.e., E. cracoviensis isp. n., is distinguished by... more A new ichnospecies of the bioeroding sponge ichnogenus Entobia, i.e., E. cracoviensis isp. n., is distinguished by having a single, large, isolated chamber and radiating canals. It occurs in a rockground surface on a Turonian or Santonian abrasion platform that is cut into Oxfordian limestones as exposed at Bonarka, Cracow. The morphology of the new ichnospecies is compared with fossil and modern sponge boring morphologies. In every case, the borings lack their upper parts and are roofless. Three models are constructed for the depositional history of the rockground and its colonization by the E. cracoviensis tracemaker: (1) that the roof has been removed by physical erosion, causing, or subsequent to, the death of the sponge; (2) that the lack of the roof is primary (biological), the roof having been removed by the sponge itself; and (3) that the boring sponge was psammobiontic, initiating its boring beneath a thin sand deposit, where there was no need to maintain a roof to the boring. The third model, based on living species of Aka, fits the details of preservation best, and is considered to represent the most likely scenario.
Diopatrichnus odlingi n.isp. (annelid tube) and associated ichnofabrics in the White Limestone (M. Jurassic) of Oxfordshire: sedimentological and palaeoecological significance
Gibert, J.M. de 1996. Proceedings of the Geologists ' Association. 107, 189-198.
The shell-lined tubes (Diopatrichnus odlingi n.isp.) frequently associated with Epithyris in the highly bioturbated... more 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 modem onuphid Diopatra. The associated facies includes two distinct ichnofabrics. Ichnofabric I 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.
Ichnology of a restricted epicontinental sea, Arapien Shale, Middle Jurassic, Utah, USA
Gibert, J.M. de; Ekdale, A.A. 2002. Palaeogeography, Palaeoclimatology, Palaeoecology 183(3-4): 275-286.
Three trace fossil assemblages associated with different lithofacies have been recognized in the Arapien Shale (Middle... more Three trace fossil assemblages associated with different lithofacies have been recognized in the Arapien Shale (Middle Jurassic) near Nephi, UT, USA. The Planolites montanus assemblage occurs in thinly laminated micrites, and it is characterized by low ichnotaxonomic diversity, shallow burrow penetration depth, small size of the traces, and low intensity of bioturbation. The Lockeia siliquaria assemblage is restricted to few-millimeters-thick grainstone layers, and it exhibits low ichnodiversity, small size and shallow burrow penetration of the traces as well. The Gyrochorte comosa assemblage is associated with 1–5-cm-thick grainstone storm beds, and it shows higher ichnodiversity and higher intensity of bioturbation. The trace fossil assemblages suggest unfavorable environmental conditions for benthic life during fair-weather periods, which partly improved after storm disturbances. The possible stress factors are related to the paleogeographic restriction and arid paleoclimate of the epicontinental sea where the Arapien Shale was deposited. In this particular setting, salinities would have reached values above normal marine producing thermohaline stratification of the body of water and, consequently, low oxygen levels in the bottom. Hence, hypersalinity and poor bottom oxygenation are proposed here as the main controls on the trace fossil assemblages of the Arapien Shale.
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Macroborings (Gastrochaenolites) In Lower Ordovician Hardgrounds of Utah: Sedimentologic, Paleoecologic, and Evolutionary Implications
Benner, J.S; Ekdale, A.A.; Gibert, J.M. de 2004. Palaios 19: 543–550.
New evidence of fossil macroborings in the Lower Ordovician (Ibexian) of western Utah demonstrates that the... more 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). Themost 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.
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An ichnofabric approach to the depositional interpretation of the intensely burrowed Bateig Limestone, Miocene, SE Spain
Gibert, J.M. de; Goldring, R. 2007. Sedimentary Geology 194(1-2), 1-16.
The foraminiferal-rich pelagic Bateig Limestone forms several varieties of the important building stones quarried at... more The foraminiferal-rich pelagic Bateig Limestone forms several varieties of the important building stones quarried at Bateig Hill in southeastern Spain. Three principal ichnofabrics (Bichordites, mottled-Palaeophycus and mottled-Ophiomorpha) are recognized, which are present in at least two (possibly up to four) repeated successions (cycles). Each succession begins with an erosional event. The Bichordites ichnofabric represents a new type of facies, formed as thin turbidity/grain flow, stratiform units derived from sediment slips off a fault into deep water. Each slipped unit became almost completely bioturbated by infaunal echinoids, colonizing by lateral migration. Because of the thinness of the units, successive colonizations tended to truncate the underlying burrows giving rise to a pseudo-stratification. As the Bichordites ichnofabric accumulated on the fault apron, thus reducing the effective height of the fault scarp, the substrate gradually came under the influence of currents traversing the shelf. This led to a change in hydraulic regime, and to the mottled-Palaeophycus and mottled-Ophiomorpha ichnofabrics in sediment deposited under bed load transport, and associated with laminar and cross-stratified beds and local muddy intervals. Reactivation of the fault triggered erosion and channeling and a return to grain flow sedimentation, and to the Bichordites ichnofabric of the succeeding cycle. The highest unit of the Bateig Limestone is formed entirely of cross-stratified calcarenites with occasional Ophiomorpha (Ophiomorpha-primary lamination ichnofabric) and is similar to many shallow marine facies but they still bear a significant content of pelagic foraminifera. The sedimentary setting bears resemblance with that described for the Pleistocene Monte Torre Paleostrait and the modern Strait of Messina (Italy), where the narrow morphology of the depositional area enhanced tidal currents and allowed for high-energy sandy deposition in relatively deep areas. More data on the Miocene paleogeography of the Bateig area should provide further testing for this hypothesis. The ichnofacies and stacking of the Bateig Limestone differ from the classic Seilacherian model in that they reflect changes in hydraulic process and are associated with faulting and subsidence and changes in sediment supply. Recognition of the unusual ichnofabrics and their relationships provides a clear indication of the overall dynamic setting.
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Isotopic evidence for massive oxidation of organic matter following the Great Oxidation Event
by Alex Brasier
Kump, Junium, Arthur, Brasier, Fallick et al. 2011 Science paper on the Shunga-Francevillian d13C excursion. Now available on the Science Express website.
Now available on Sciencemag.org Now available on Sciencemag.org
Update of the carbon and oxygen isotopic records of the Early–Late Pliensbachian (Early Jurassic, ~187 Ma): Insights from the organic-rich hemipelagic series of the Lusitanian Basin (Portugal)
Silva, R.L., Duarte, L.V., Comas-Rengifo, M.J., Mendonça Filho, J.G., Azerêdo, A.C., 2011.
Chemical Geology, 283, 177–184.
Juan Diego Rodríguez-Blanco, Samuel Shaw and Liane G. Benning (2011) The kinetics and mechanisms of Amorphous Calcium Carbonate (ACC) crystallization to calcite, via vaterite Nanoscale 3: 265-271 doi: 0.1039/C0NR00589D
The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via... more The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5–25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73 ± 10 and 66 ± 2 kJ mol−1, respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5–40 °C) is also presented.
The Role of Episodic Starvation in the formation of Shell beds of the Cincinnatian Ordovician: an Alternative to the Storm-Winnowing Proximality Model.
by Ben Dattilo
2008 Benjamin F. Dattilo, Carleton E. Brett, Cameron J. Tsujita, and Robert Fairhurst
Shell bed development can be a product of complex sedimentological and biological factors. The Upper Ordovician... more Shell bed development can be a product of complex sedimentological and biological factors. The Upper Ordovician sediments near Cincinnati, Ohio constitute a succession of thinly interbedded shelly carbonates and mudrocks. Despite years of study, the development of Cincinnatian shell beds and metre-scale cycles has, until recently, been attributed solely to storm reworking. This “storm-winnowing model” treats shells as passive sedimentary clasts, ignoring other factors of shell-bed development. A recently proposed alternative is Brett and Algeo’s idea that these shell beds grew during long periods of normally low sedimentation, while most mud accumulated during brief periods of high sedimentation. Under this “episodic starvation model”, any storms would winnow pre-existing muds and shell beds alike. We tested both models in the Edenian-Maysvillian (early to mid Katian) strata of the Cincinnati region by compiling observations on their petrologic, taphonomic, and paleoecological characteristics. The storm-winnowing does not explain several observed features that the episodic starvation model does, including: (i) storm-related sedimentary structures in mudrocks and limestones; (ii) lack of a sufficiently fossiliferous precursor deposit to winnow; (iii) deep-water faunas in grainstones; (iv) mixed taphonomic conditions of shell bed fossils; (v) ubiquitous discontinuity surfaces; (vi) carbonate concretion horizons; (vii) unwinnowed shell beds; and (viii) micrite in packstones. Episodic starvation is a superior explanation because it explains all of these features and allows for the complex interplay of other environmental and biological factors that contribute to shell bed growth. It may also be applicable to other deposits, previously interpreted as tempestites.
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Rodriguez-Blanco, J. D., Shaw, S. and Benning L. G. (2008) How to make ‘stable’ ACC: protocol and structural characterization.Mineralogical Magazine 72/1 p. 283-286 doi: 10.1180/minmag.2008.072.1.283
The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via... more The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to calcite, via vaterite, were studied at a range of environmentally relevant temperatures (7.5–25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to calcite via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of calcite. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of calcite nucleation and crystallization are 73 ± 10 and 66 ± 2 kJ mol−1, respectively. A model to calculate the degree of calcite crystallization from ACC at environmentally relevant temperatures (7.5–40 °C) is also presented.
Facies architecture of an isolated carbonate platform: tracing the cycles of the Latemàr (Middle Triassic, northern Italy)
The 720-m-thick succession of the Middle Triassic Latemàr Massif (Dolomites, Italy) was used to reconstruct the... more The 720-m-thick succession of the Middle Triassic Latemàr Massif (Dolomites, Italy) was used to reconstruct the lagoonal facies architecture of a small atoll-like carbonate platform. Facies analysis of the lagoonal sediments yields a bathymetric interpretation of the lateral facies variations, which reflect a syndepositional palaeorelief. Based on tracing of lagoonal flooding surfaces, the metre-scale shallowing-upward cycles are interpreted to be of allocyclic origin. Short-term sea-level changes led to subaerial exposure of wide parts of the marginal zone, resulting in the development of a tepee belt of varying width. Occasional emergence of the entire lagoon produced lagoon-wide decimetre-thick red exposure horizons. The supratidal tepee belt in the backreef area represented the zone of maximum elevation, which circumscribed the sub- to peritidal lagoonal interior during most of the platform’s development. This tepee rim, the subtidal reef and a sub- to peritidal transition zone in between stabilized the platform margin. The asymmetric width of facies belts within individual metre-scale cycles was caused by redistribution processes that reflect palaeowinds and storm paths from the present-day south and west. The overall succession shows stratigraphic changes on a scale of tens of metres from a basal subtidal unit, overlain by three tepee-rich intervals, separated by tepee-poor units composed of subtidal to peritidal facies. This stacking pattern reflects two third-order sequences during the late Anisian to early middle Ladinian.
Insight into depositional conditions of carbonate-dominated palustrine sedimentation around the K/T-boundary (Faciès Rognacien, northeastern Pyrenean foreland, southwestern France)
by Daniel Marty
Marty, D. & Meyer, C.A. 2006: Insight into depositional conditions of carbonate-dominated palustrine sedimentation around the K/T-boundary (Faciès Rognacien, northeastern Pyrenean foreland, southwestern France). Geological Society of America Special Paper 416, 169–187.
The Faciès Rognacien is a sequence of highly bioturbated and pedogenically
modifi ed palustrine carbonates that... more
The Faciès Rognacien is a sequence of highly bioturbated and pedogenically
modifi ed palustrine carbonates that were deposited under oxic conditions around the
Cretaceous-Tertiary (K-T) boundary in the northeastern Pyrenean foreland basin
(SW France). The sedimentary structures and early diagenetic features identifi ed
(mottling, nodule formation, brecciation, pseudomicrokarst, cracking, charophytes,
Microcodium) suggest deposition in a palustrine environment between the subarid
and intermediate climate type. Sedimentological and paleoecological analysis enables
us to distinguish two facies associations, the lacustrine pond facies and the freshwater
marsh facies associations. The majority of the carbonates are attributed to the
freshwater marsh facies. The lacustrine pond facies occurs only in isolated paleolows,
and is identifi ed on the basis of its paleobiological content (charophytes, ostracodes).
This suggests that the palustrine carbonates of the Faciès Rognacien were deposited
in a seasonal wetland (carbonate-producing freshwater marsh), rather than in the
marginal zone of a large, shallow lake. In this wetland paleoenvironment, all carbonates
underwent widespread pedogenesis, and small, ephemeral ponds are of limited
distribution, most likely recording deposition in paleolows.
Sedimentology, taphonomy, and ichnology of Late Jurassic dinosaur tracks from the Jura carbonate platform (Chevenez—Combe Ronde tracksite, NW Switzerland): insights into the tidal-flat palaeoenvironment and dinosaur diversity, locomotion, and palaeoecology
by Daniel Marty
Marty, D. 2008: Sedimentology, taphonomy, and ichnology of Late Jurassic dinosaur tracks from the Jura carbonate platform (Chevenez—Combe Ronde tracksite, NW Switzerland): insights into the tidal-flat palaeoenvironment and dinosaur diversity, locomotion, and palaeoecology. PhD Thesis University of Fribourg, GeoFocus 21, 278 pp.
--> Award of the Science Faculty of the University of Fribourg for the best doctoral thesis of the year in the area of experimental sciences.
Dinosaur tracks are biogenic, sedimentary structures and not body fossils or biological objects in the common sense.... more
Dinosaur tracks are biogenic, sedimentary structures and not body fossils or biological objects in the common sense. They result from the complex interaction of the kinematics of the trackmaker, its foot anatomy, and the substrate properties, and from taphonomic processes acting prior to the incorporation of the tracks into the sedimentary record. The objective of this work is an interdisciplinary study of a large sample of dinosaur tracks and trackways linking sedimentology with vertebrate ichnology, palaeontology, and palaeoecology.
Excellent conditions are provided by the Late Jurassic (Kimmeridgian) Chevenez—Combe Ronde tracksite, which is one of several tracksites located on the future course of the Transjurane highway near Porrentruy (Canton Jura, NW Switzerland). Here, eight superimposed dinosaur track-bearing surfaces were systematically excavated level-by-level within a 0,65 m thick laminite interval, unearthing almost 1400 dinosaur tracks. The main track level, located at the base of the interval, is the most diverse ichnoassemblage composed of 14 trackways of tiny (Pes Length < 25 cm) and small (25 cm < PL < 50 cm) sauropods and 43 trackways of minute (PL < 10 cm), small (10 cm < PL < 20 cm), and medium-sized
(20 cm < PL < 30 cm) bipedal, tridactyl dinosaurs.
The main issues are: (1) identification of true tracks, undertracks, and overtracks, and their relationships with substrate properties, their link with the exposure index, and their utility in the reconstruction of the palaeoenvironment; (2) implications of the main track level ichnoassemblage for dinosaur behaviour, the terrestrial palaeoecosystem, and vertebrate ichnofacies; (3) relationships between variability in trackway patterns and configurations with locomotion speed, behaviour, and substrate properties as well as implications for locomotion capabilities; (4) Quantification and relevance of sauropod trackway gauge; and (5) interpretation of manus-dominated and pes-only sauropod trackways.
The approach is first actualistic by studying human footprints and processes acting during their formation and preservation on modern tidal-flats. In these highly structured environments, microbial mats are ubiquitous, strongly facies-specific, and occupy a key position during and after footprint formation. Undertracks readily form in biolaminated sediment, whilst underprints and deep tracks are common in unlaminated, water-saturated sediment. Most consolidated vertebrate tracks are affected by taphonomic processes, including renewed and/or repeated growth of microbial mats leading to the formation of modified true tracks, internal overtracks (track fills), and overtracks.
The sauropod tracks and the encasing laminite interval of the Combe Ronde site are then subject of detailed sedimentological and taphonomical analyses. This discloses the sediment properties at the time of track formation and reveals the processes modifying the tracks during subaerial exposure and integrating them into the sedimentary record. Track morphology, associated track features, and sedimentary features can be linked with the exposure index, identifying the palaeoenvironment as a supratidal flat not located in close proximity to a coastline. These flats were susceptible for track recording only during short periods after wetting due to a rainy period or due to occasional storms. Longer periods of subaerial exposure prior to burial are indicated by the presence of internal overtracks and/or overtracks, and rapid covering up is indicated by the lack of overtracks on top of tracks with large displacement rims. Cross-sections of sauropod tracks provide insight into the consolidation history of the substrate prior to track formation and into the walking dynamics of dinosaurs, confirming that sauropods put their hindfeet in a pronounced plantigrade way on the ground.
The level-by-level superimposition of the studied surfaces enables to identify true tracks, undertracks, and overtracks. The best-defined true tracks (anatomical morphotypes) of the main track level are then used for ichnotaxonomy and trackmaker identification, and the detailed analyses of trackway parameters, including trackway gauge, provide insight into the locomotion capabilities of dinosaurs.
The best-defined minute and small tridactyl tracks can be assigned to the ichnogenus Carmelopodus, extending it from the Middle Jurassic into the Late Jurassic. These tracks were likely left by a small theropod dinosaur similar in size to Compsognathus or Juravenator. The medium-sized tridactyl tracks of morphotype II exhibit some of the typical features of the ichnogenus Therangospodus (attributed to large and robust theropods) but also some of ornithopod ichnotaxa.
The sauropod trackways show a wide range of patterns and configurations but are all medium- to wide-gauge. Therefore, they are assigned tentatively to the ichnogenus Brontopodus attributed to derived “brachiosaurid” or “titanosaurid” dinosaurs. The variability of the trackways reflects the general locomotion capabilities of the trackmakers and is an expression of individual walking style and behaviour, which may be related to substrate properties. Trackway patterns (the degree of manus overprinting by the pes) and different trackway configurations including trackway gauge are not only related to locomotion speed, and they provide no evidence of a relationship with ontogeny.
The gauge of sauropod trackways can be quantified with the pes trackway ratio and the here defined [WAP/PL]-ratio (Width of the pes Angulation Pattern / Pes Length). Gauge is possibly related to the substrate and the behaviour of the trackmaker adapting to it, but this does not change the overall medium-gauge to wide-gauge appearance of the trackways. The manus-dominated and pes-only sauropod trackways of the Combe Ronde site are explained by trackmakers exerting more pressure on the manus than the pes, and by overprinting of the manus by the pes, respectively.
The alignment of trackways on the main track level shows no evidence of a nearby shoreline and of interactions between the different groups of dinosaurs. It indicates gregarious behaviour amongst tiny and small sauropods, and suggests that minute and small bipedal dinosaurs were frequent visitors on the supratidal flats.
The ichnoassemblage of the main track level is the first one found in the Jura Mountains displaying abundant minute and small tridactyl tracks. This is also typical for the other Ajoie ichnoassemblages, which further exhibit tracks of tiny to large (up to 1,1 m PL) sauropods, and tracks of medium-sized to large (up to 0,8 m PL) bipedal dinosaurs. Sauropod trackways include narrow-gauge and wide-gauge trackways indicating the presence of “basal” and derived sauropods. This suggests that dwarfed insular animals can be excluded as trackmakers of the tiny and small sauropod trackways of the Ajoie ichnoassemblages and the Combe Ronde tracksite and that the Jura carbonate platform was connected with the landmasses of the London-Brabant Massif and the Massif Central during periods of emersion. Dinosaurs used the Jura carbonate platform for the establishment of in situ, predominantly saurischian dinosaur populations, but also as a migration corridor between the massifs.
Because the Ajoie ichnoassemblages are dominated by small tridactyl tracks, they differ from other Jurassic tetrapod ichnofacies in carbonate settings, notably from the Brontopodus ichnofacies. In the case of those ichnoassemblages commonly attributed to the Brontopodus ichnofacies, the lack or rareness of small tridactyl tracks may indicate the absence of small trackmakers in those palaeoenvironments or unsuitable conditions for the formation and preservation of small tracks.
This study highlights the benefits of systematic and interdisciplinary analyses of dinosaur tracks, which disclose variations related to behaviour and to differences in substrate. This allows recognizing anatomical morphotypes and trackway configurations representative of typical trackmaker behaviour. The latter can then also be used in ichnotaxonomical classification. Similar approaches should be in the focus of future work and performed on the other tracksites and ichnoassemblages of the Ajoie. Together with the evidence from other tracksites of the Jura Mountains, this will contribute towards a better understanding of the terrestrial palaeoenvironments and palaeogeography, and of dinosaur palaeoecology and palaeobiogeography on the Jura carbonate platform.
