Biostratigraphic Dataset Research Articles

Magnetostratigraphy and stable isotope stratigraphy of the middle-Eocene succession of the Ainsa basin (Spain): New age constraints and implications for sediment delivery to the deep waters

Stratigraphic cycles preserved in sedimentary successions are controlled by the interaction of tectonics, climate, sediment supply and sea-level variations. Understanding the influence of these drivers on sedimentary systems dynamics is crucial to understand and extract information from sedimentary archives. In the deep marine deposits of the Ainsa foreland basin (lower to middle Eocene, southern central Pyrenees, Spain), the origin of well-preserved cyclicity between channelized sandy submarine fans and hemipelagic deposits remains subject to debate because of the absence of chronostratigraphic constraints on high resolution geochemical proxies. Here, we contrast a combination of newly acquired and legacy geochemical datasets (carbon and oxygen stable isotopes, organic matter content, major and trace elements and the mineralogical composition of bulk hemipelagic sediments) tuned by a new age model to global “target” curves to discuss the possible drivers of the stratigraphic cycles found in the deep marine sediment gravity flow deposits of the Hecho Group. Our new age model is based on magnetostratigraphic and biostratigraphic datasets acquired on a composite section going from the Banaston system to the distal deposits of the Sobrarbe deltaic complex. Four major polarity zones are identified in the studied succession covering the time span from C21n (lower members of the Banaston system) to C19r (Sobrarbe deltaic complex). Our age model is corroborated by the identification of the nannoplankton zone NP16 in the Guaso system (C20n).Comparison between global carbon isotope curve and local isotope dataset shows some differences, suggesting the preservation of a local isotope signal modulated by eustatism, changes in the environment of deposition and/or restriction in water circulation in the Ainsa basin. Yet, comparison of the stratigraphic record with global sea-level curves highlights that sands are mainly delivered to the basin during lowstands, pointing to the important role of eustasy even in an active foreland tectonic context. The exception to the rule is the Banaston member II, whose deposition during a sea-level highstand seems to be controlled by the growth of tectonic structures.

A Cretaceous carbonate escarpment from Western Sicily (Italy): biostratigraphy and tectono-sedimentary evolution

The presence of a huge carbonate slope of Cretaceous age is recorded in some imbricated thrust sheets from the Maghrebian fold-and-thrust belt cropping out in northwesternmost Sicily (southern Italy). The sedimentological features of this escarpment, named as the Western Sicily Cretaceous Escarpment (WSCE), have been recently described. The present paper aims to provide a detailed bio-chronostratigraphic characterization of the different facies types that occur in the four lithostratigraphic units spanning the whole slope depositional system. The detailed biostratigraphic analysis and correlation of a number of well-exposed sections allowed to differentiate eight informal biozones and to place the different studied sections, either from a single tectonic unit or from different ones, in a reliable chronostratigraphic frame. The integration of sedimentological and biostratigraphic data allowed in turn to time-constrain the main tectono-sedimentary events along the WSCE. In particular: i) the abrupt transformation from a carbonate ramp to a tectonically-controlled escarpment during the Berriasian-Valanginian; ii) the peak of tectonic instability leading to the emplacement of thick megabreccia bodies and repeated submarine volcanic emissions during the Aptian- Cenomanian; iii) the almost coeval increase in the skeletal supply in response to highstand shedding occurred during the Albian-Cenomanian; iv) the tectonic backstepping of the carbonate depositional system during the Senonian ending with the definitive shutdown of the carbonate factory in the late Maastrichtian. The acquired biostratigraphic dataset is in large part new for the Cretaceous of Sicily and provides information on the associations that populated a southwestern Tethyan carbonate platform during the Cretaceous.

Depositional history of the western Nile Delta, Egypt: Late Rupelian to Pleistocene

The availability of onshore and offshore three-dimensional seismic surveys facilitated detailed seismic sequence-stratigraphic interpretation of a large swath of the western Nile Delta evolution since the late Oligocene. The resulting sequence-stratigraphic framework is calibrated against more than 60 wells. The interpretation of repetitive sequence boundaries, that is, unconformities, on seismic sections was constrained by high-resolution abundance and diversity within biostratigraphic data sets and lithofacies-stacking patterns interpreted from well logs. Our series of depositional facies maps reflect environments of undifferentiated lowstand and transgressive systems tracts, that is, depositional elements interpreted between the lower bounding unconformity surface (sequence boundary) and maximum flooding surface above. These typically constitute terrestrial distributary channels and floodplains landward of strike-aligned lowstand deltas and marine shoreline deposits at and over the relict shelf break area of the underlying sequence boundary. Basinward deep-marine shales, slope channels, splays, fans, and terminal channel lobes define the remainder of the deposition over the rather extensive deep-marine slope apron region of the western Nile Delta. Incised valleys, canyons, and broad slope channels often confine any of the above-mentioned depositional facies at the lower bounding unconformity of each sequence.

Correlation and high-resolution timing for Paleo-tethys Permian-Triassic boundary exposures in Vietnam and Slovenia using geochemical, geophysical and biostratigraphic data sets

Correlation and high-resolution timing for Paleo-tethys Permian-Triassic boundary exposures in Vietnam and Slovenia using geochemical, geophysical and biostratigraphic data sets

Wilkes Land Late Pleistocene diatom age model: From bio-events to quantitative biostratigraphy

A new method merges conventional and quantitative biostratigraphic approaches, supported by magnetic polarity data, to develop a chronological framework for sediment core MD03-2595 retrieved on the continental rise off Wilkes Land, East Antarctica before proceeding to paleoceanographic and paleoclimatic analysis. This combined method helped to identify climatic cycles, highlight stratigraphic discontinuities and reworking, and assess regional sedimentological and diatom biostratigraphic evolution. Core MD03-2595 spans the last 0.8Ma, from the Mid Pleistocene Transition (MPT) to the Early Holocene. A hiatus includingMarine Isotope Stages (MIS) 19, 18 and 17 was identified, and a decreasing trend in sediment accumulation rates from MIS 16 to the Holocene was observed. This quantitative diatom biostratigraphic dataset, placed in its own sedimentological and paleomagnetic context, provides new information regarding the paleobiogeographic distribution and ecological responses of biostratigraphically significant diatom species, such as Thalassiosira elliptipora and T. fasciculata, for the Matuyama–Brunhes (M–B) transition, and Actinocyclus ingens, Hemidiscus karstenii and Rouxia spp. for the middle and late Pleistocene diatom biozonation.

REASSESSMENT OF THE EARLY-MIDDLE EOCENE PLANKTIC FORAMINIFERAL BIOMAGNETOCHRONOLOGY: NEW EVIDENCE FROM THE TETHYAN POSSAGNO SECTION (NE ITALY) AND WESTERN NORTH ATLANTIC OCEAN ODP SITE 1051

We examined a planktic foraminiferal biostratigraphic record from the Tethyan Possagno section (Venetian Prealps of northeastern Italy) spanning the lower–middle Eocene transition, from Chron C24r to the base of Chron C20r and from Zones E1 to lower E8. Our results provide an updated magnetochronological calibration from the Tethyan realm of the lowest and highest occurrences of the zonal markers. All the foraminiferal biostratigraphic events utilized in the most recent and widely used zonal schemes have been recognized. Most of them are in reasonable agreement with the known magnetochronological calibration, such as those at the Paleocene/Eocene boundary and lowermost Eocene. However, a number of events, specifically the bases of Morozovella aragonensis, Acarinina cuneicamerata, and Guembelitrioides nuttalli, occur at a significantly lower position at Possagno than in the most recent zonal schemes. A comparable magnetostratigraphic position has been recorded for the first two bioevents in the western North Atlantic Ocean ODP Site 1051 (Blake Nose, Atlantic Ocean). Furthermore, the base of A. cuneicamerata and the top of Morozovella subbotinae occur in reverse order with respect to previous schemes, thus negating the effectiveness of Zone E6 as now used. We propose an alternative definition of the Zone E6/E7a boundary by substituting the base of Astrorotalia palmerae for that of A. cuneicamerata . This proposal avoids combining E6 and E7a into a single zone. Additionally, we recorded a significantly different magnetostratigraphic position for the base of Turborotalia frontosa , a critical event for the Ypresian-Lutetian boundary placement. Our biostratigraphic dataset is unique in the integration of deep-benthic foraminiferal events with magnetostratigraphy and calcareous plankton data. Because biostratigraphic data of planktic foraminifera from the Possagno section derive from the same sample set analyzed for calcareous nannofossils, we were able to outline an integrated, updated, calcareous plankton stratigraphy of the lower–basal middle Eocene from a Tethyan location.

Paleomagnetism and biostratigraphy of sediments from Southern Ocean ODP Site 744 (southern Kerguelen Plateau): Implications for early-to-middle Miocene climate in Antarctica

New paleomagnetic results from lower-to-middle Miocene samples from Ocean Drilling Program (ODP) Holes 744A and 744B, cored during ODP Leg 119 on the southern Kerguelen Plateau (Indian Ocean sector; Southern Ocean), provide a chronostratigraphic framework for an existing and under-utilized paleoclimate archive during a key period of Antarctic climate and ice sheet evolution. Site 744 is strategically positioned for high-latitude paleoceanographic and paleoclimatic studies because it lies within the southern domain of the Antarctic Circumpolar Current (ACC) and in proximity to the large and active Lambert Glacier-Amery Ice Shelf drainage system of the East Antarctic Ice Sheet. Magnetostratigraphic results were reported previously for this site, but technical difficulties and limited sampling prevented confident correlation of the magnetic polarity record with the geomagnetic polarity timescale. Our results, which are constrained by new semi-quantitative analyses of diatom assemblages and radiolarian first and last appearance events that are evaluated within a regional Southern Ocean biostratigraphic dataset through Constrained Optimization (CONOP) model runs, permit significant refinement of previous age models for the lower-to-middle Miocene sequence recovered at Site 744 (spanning the interval from ~21 to 13.7Ma). An extended record of sediment accumulation, with average sedimentation rates of ~0.7–0.9cm/kyr, is interrupted by a series of hiatuses in the middle Miocene. These disruptions in sediment supply, or erosional events, could mark a local response of north–south fluctuations in the location and/or strength of the Antarctic Circumpolar Current during transient glacial events within the Mid-Miocene Climate Optimum (MMCO; ~17 to 14.45Ma). With the enhanced age control provided by this study, combined with a refined chronostratigraphy for the underlying upper Eocene to Oligocene strata, Site 744 becomes a good candidate for future high-resolution stable isotope and microfossil paleoecological work, which will further elucidate the late Paleogene and early Neogene paleoenvironmental history of the Southern Ocean.

INTEGRATED STRATIGRAPHY OF MIDDLE-LATE MIOCENE SYNOROGENIC DEPOSITS OF THE EASTERN SOUTHERN APENNINE CHAIN: THE SAN BARTOLOMEO FLYSCH

The present paper deals with the stratigraphic and biostratigraphic study of the middle-late Miocene thrust-top basin deposits of the San Bartolomeo Flysch, exposed north of Matese mountains and analysed during the geological survey of the sheet N° 405 Campobasso of the new Geological Map of Italy, 1:50.000 scale. The integrated study of calcareous nannofossils and planktonic foraminifera, based on the semi-quantitative distribution range of index species, revealed the presence of age-diagnostic assemblages which are comparable with those of different middle-late Miocene deep-marine sedimentary settings of the Mediterranean Basin. The biostratigraphic dataset suggests an early Serravallian – early middle Tortonian age. In terms of calcareous nannofossil biostratigraphy, the studied succession falls between the Last Occurrences of Sphenolithus heteromorphus and the First Occurrence of Discoaster bellus gr., corresponding to the MNN6 – MNN8 zone interval. In terms of planktonic foraminiferal biostratigraphy the studied sediments fall between the Last Occurrence of Globorotalia peripheroronda and the First Regular Occurrence of Neogloboquadrina acostaensis , corresponding to the MM6 p.p. - MMi10 p.p. zone interval. This study documents the applicability of the recent Mediterranean middle –late Miocene biozonations for the biostratigraphic study of siliciclastic synorogenic sediments, and challenges the most recent studies that dated the San Bartolomeo Flysch to the late Tortonian- early Messinian.

Precise timing of the Upper Taghanic Biocrisis, Geneseo Bioevent, in the Middle–Upper Givetian (Middle Devonian) boundary in Northern Spain using biostratigraphic and magnetic susceptibility data sets

The ability to correlate with high precision among geological successions is critical in evaluating the global coincidence and therefore magnitude and duration of geological events. This is a difficult problem given resolution uncertainties and ambiguities in biostratigraphic data sets. The magnetostratigraphy susceptibility (MSS) method, based on low-field bulk magnetic susceptibility (MS) measurements of closely spaced samples, provides a well-established, abiotic, high-resolution correlation tool in stratigraphy, that when combined with bio-, chemostratigraphic, and other geophysical techniques, offers ways to resolve correlation problems. In addition, such data sets lend themselves to time-series analysis, where developing high-resolution timing of events becomes possible. This paper examines the final episode (equivalent to the Geneseo Bioevent in the Appalachian Basin) of the important Taghanic Biocrisis known from globally distributed Middle Devonian geological sections. The Geneseo Bioevent is important because the extinction of some major fossil groups occurred during this time, while other groups declined significantly, including many benthonic groups. However, the maxima of extinctions does not appear to have occurred everywhere simultaneously. To help resolve timing of this bioevent, results are reported for two Middle Devonian successions from Northern Spain, the S. Huergas de Gordón and Punta Boletos sections, both showing the final Taghanic Biocrisis, Geneseo interval, and correlate these successions to the same interval within an independent, global database. Time-series analyses of the MSS data sets from the Spanish sections was performed using Multi-Taper (MTM) and Fourier Transform (FT) methods, and have extracted well-defined Milankovitch bands from the primary MS data from each section. Using FT and MTM values for eccentricity at ~ 400 kyr and ~ 100 kyr, a floating-point time scale was developed for the two Spanish sections that provides age resolution to ~ 50 kyr for these successions. The results show that the Geneseo Bioevent in Northern Spain occurred within a narrow time window estimated to have lasted for ~ 70 kyr. This time window fall s within the Polygnathus ansatus (uppermost part)– Ozarkodina semialternans conodont zones, just at the Middle–Upper Givetian boundary of the Middle Devonian in what appears to be the upper, regressive phase of T–R cycle IIa.

HYDROCARBON SOURCE ROCK ASSESSMENT AND REVISED BIOSTRATIGRAPHY OF DSDP SITE 369A, OFFSHORE NORTHWEST AFRICAN MARGIN

Deep Sea Drilling Project (DSDP) Site 369A, drilled off Cape Bajador, NW Africa, provided an opportunity to examine the source rock potential and biostratigraphy of the offshore Aaiun‐Tarfaya Basin. Within the Albian‐Campanian interval, total organic carbon (TOC) contents were found to be highly variable and cyclic, ranging from less than 0.5% to nearly 12%. Variations in hydrocarbon generation potential (S1 + S2) versus depth in general paralleled variations in TOC. Organic matter was generally marine in origin and oil‐prone.The newly generated data reported in this paper expand the range of TOC values which have been reported from the study region. However, they also illustrate the kinds of problems which can be introduced as a result of sampling bias. Sampling for this study tended to focus on darker‐coloured, more organic‐rich lithologic core intervals, contrasting with previous shipboard analyses which appeared to have focused on lighter‐coloured intervals. Based on the abundance of calcareous nannofossils, the elevated TOC contents appear to have been, at least partly, driven by elevated surface productivity which in turn increased biological oxygen demand within the sediment.New biostratigraphic data was used to identify an unconformity between the late Albianl early Cenomanian and the early Campanian successions, consistent with previous interpretations. Integration of the geochemical and biostratigraphic datasets indicates that these organic‐rich sediments are in general equivalent to Cretaceous Oceanic Anoxic Events 1B, 1D and 3. Considering the apparent net thickness of these oil‐prone sediments and the possibility that they may be widely distributed throughout the basin, they may have the potential to generate commercially significant volumes of oil where buried sufficiently deeply.