High-resolution intra- and interbasinal correlation of the Danian-Selandian transition (Early Paleocene): The Bjala section (Bulgaria) and the Selandian GSSP at Zumaia (Spain)

The Danian-Selandian (D-S) boundary has been identified for the first time in the Black Sea coast at Bjala (Bulgaria) based on a new integrated bio-, magneto- and cyclostratigraphic study. Several correlation criteria as established for the basal Selandian GSSP from Zumaia (Basque Basin) are evaluated. Noteworthy, is the almost complete lack of calcareous nannoplankton species Braarudosphaera bigelowi in the Bulgarian sections, a sharp decrease of which was indicated as suitable criteria for defining the D-S boundary as it occurred both at Zumaia and in the classical locations of the North Sea basin. Conversely, the second evolutionary radiation of the calcareous nannofossil genus Fasciculithus together with the occurrence of Fasciculithus tympaniformis that define the NP4/NP5 zonal boundary seem to be reliable criteria to approximate the D-S boundary. In detail, however, the best approach is to integrate biostratigraphic data within a magnetostratigraphic and/or cyclostratigraphic framework. Refinements on the placement of chron C27n at Zumaia and robust bed-by-bed correlation between several Basque sections and Bjala indicates that the D-S boundary is located 30 precession cycles (~ 630 ky) above C27n. In addition to the precession-related marl-limestone couplets and 100-ky eccentricity bundles recognized in the studied sections, expression of the stable 405-ky long eccentricity allows direct tuning to the astronomical solutions. A correlation of the land-based sections with previously tuned data from ODP Site1262 from the Southern Atlantic is challenged. Our choice is consistent with original tuning at Zumaia but shifts one 100-ky cycle older previous tuning from Site 1262 along the interval above C27n. Under the preferred tuning scheme the D-S boundary can be given an age of 61.641 ±0.040 Ma on the La04 orbital solution.     

Proposed GSSP for the base of Cambrian Stage 7, coinciding with the first appearance of Lejopyge laevigata, Hunan, China

The Luoyixi section, exposed in a roadcut along the Youshui River (Fengtan Reservoir), Guzhang County, Hunan Province, China, is proposed as the stratotype for the base of an unnamed stage boundary (base of the Cambrian stage provisionally termed Stage 7). The proposed position of the GSSP is 121.3 m above the base of the Huaqiao Formation, at a horizon coinciding with the first appearance of the cosmopolitan agnostoid trilobite Lejopyge laevigata. The section fulfills all the requirements for a GSSP, and the horizon can be constrained not only with the primary stratigraphic marker (L. laevigata) but also with secondary biostratigraphic, sequence-stratigraphic, and chemostratigraphic correlation tools. The first appearance of L. laevigata is one of the most readily recognizable levels in the Cambrian, and can be correlated with precision to all paleocontinents.     

Effects of diagenesis on the astrochronological approach of defining stratigraphic boundaries in calcareous rhythmites: The Tortonian GSSP

Since the establishment of astrochronology, calcareous rhythmites are frequently used as the basis of high‐resolution chronostratigraphy. In particular for the Neogene, calcareous rhythmites serve as stratotypes and for absolute dating of stratigraphic boundaries (Global Stratotype Sections and Points – GSSPs). However, the exact mechanisms responsible for the formation of the rhythmic intercalation of lithologies in such successions are complex and not easily reconstructed. To a large extent this is the effect of diagenetic modifications of the original sediment. Here, two examples of Neogene calcareous rhythmites are studied; the Monte dei Corvi section and the Monte Gibliscemi section. The first is the GSSP location of the Serravallian–Tortonian boundary, whereas the second is an auxiliary stratotype for the same boundary. During the past years, astrochronological approaches were applied to these successions to considerably increase time resolution compared to the elaborated biostratigraphic database. The present study focuses on micropetrographic, trace element and clay mineralogical methods in order to gain a better understanding of the genesis of the rhythmites. In the Monte Gibliscemi section, sediment parameters that are robust against diagenetic change clearly reflect primary differences, i.e. cyclical environmental changes. In contrast, no clear primary signal is determined for the Monte dei Corvi section on a couplet scale, leaving the origin of the rhythm ambiguous. This impedes the interpretation of the latter and the comparability between the two successions, and also compromises any bed‐by‐bed correlation between the two. The unclear origin of the rhythmites of Monte dei Corvi introduces uncertainty into the applicability of astrochronology to this succession.     

Global Standard Stratotype-section and Point (GSSP) of the Furongian Series and Paibian Stage (Cambrian)

The Global Standard Stratotype-section and Point (GSSP) of the Furongian Series (uppermost series of the Cambrian System) and the Paibian Stage (lowermost stage of the Furongian Series), has been recently defined and ratified by the International Union of Geological Sciences (IUGS). The boundary stratotype is 369 metres above the base of the Huaqiao Formation in the Paibi section, northwestern Hunan Province, China. This point coincides with the first appearance of the cosmopolitan agnostoid trilobite Glyptagnostus reticulatus, and occurs near the base of a large positive carbon isotopic excursion (SPICE excursion).     

Characterization and astronomically calibrated age of the first occurrence of Turborotalia frontosa in the Gorrondatxe section, a prospective Lutetian GSSP: implications for the Eocene time scale

The Gorrondatxe section, a prospective Lutetian Global Stratotype Section and Point (GSSP), has recently been used as the master reference section to reassess the correlation between Eocene magnetostratigraphic and calcareous planktonic biostratigraphic scales. However, the exact calibration of some events remained ill defined, as they were thought to be missing in Gorrondatxe due to a fault. The most important missing events were the first occurrence of the planktonic foraminifera Turborotalia frontosa and the C22n/C21r chron boundary. Either might be a reliable correlation criterion for the Ypresian/Lutetian boundary, as both approach the age of the original Lutetian Stratotype. New studies allowed the identification of the former event 9 m above the Gorrondatxe fault, within magnetic polarity Chron C21r and calcareous nannofossil Zone CP12a. Distinctive test features that characterize the most primitive morphotype of T. frontosa are described. Despite the high turbidite content, recurrent pelagic limestone–marl couplets and bundles occur, whose formation was driven by precession and eccentricity astronomical cycles. The first occurrence of T. frontosa was found 27 couplets and 5.5 bundles (60 m) below the first occurrence of the calcareous nannofossil Blackites inflatus , which is dated at 48 Ma. Hence, the age of the first occurrence of T. frontosa is estimated at 48.55 Ma, confirming that it is the most suitable planktonic foraminiferal correlation criterion for the Ypresian/Lutetian boundary. These results show that the stratigraphic interval missing due to the Gorrondatxe fault cannot be greater than a few metres and reinforce the value of this section as a prospective Lutetian GSSP.     

Seawater strontium isotope curve at the Silurian/Devonian boundary: a study of the global Silurian/Devonian boundary stratotype

Present application of ⁸⁷Sr/⁸⁶Sr chemostratigraphy to detailed stratigraphical tasks is limited by inaccurate calibration of the general seawater strontium curve to absolute as well as to relative time scales. For this reason, refinement of the general seawater strontium curve has been suggested, using mainly clearly defined global boundary stratotype sections. This study reports the first ⁸⁷Sr/⁸⁶Sr data from the global Silurian/Devonian boundary stratotype section and fills an existing 1-Ma gap in available data. Generally, the data from the stratotype fit the range interpolated from published ⁸⁷Sr/⁸⁶Sr data of the general curve, but the slight differences may suggest an existence of a high-order oscillation near the Silurian/Devonian boundary. Higher ⁸⁷Sr/⁸⁶Sr values in the Devonian part of boundary bed 20 (20-beta) may indicate an exotic material influx of recycled sediment.     

Heat and chill requirements of Fraxinus flowering in Galicia (NW Spain)

Fraxinus pollen data from eight Galician localities (1999-2003), recorded using 7-day Lanzoni VPPS pollen traps, were studied to determine their temporal and spatial distribution. The determination of the chill and heat required to trigger flowering and the start cumulative date were calculated using ten years of pollen data from Ourense. The sum of maximum temperatures from the 55 days before the peak date showed the lowest standard deviation coefficient and the mean quantity of accumulated heat was 741. Temperatures below 0°C and/or rainfall at the beginning of flowering caused a longer period before the peak date was registered. Temperatures recorded in November were very important for chill accumulation and determine the heat requirement needed to trigger Fraxinus flowering in Galicia.     

Correlating the global Cambrian–Ordovician boundary: Precise comparison of the Xiaoyangqiao section,Dayangcha, North China with the Green Point GSSP section,Newfoundland, Canada

The Cambrian–Ordovician boundary interval exposed at the Xiaoyangqiao section, North China is presented. The distribution of stratigraphically important fossils in the Xiaoyangqiao section revealed several nearly coeval graptolite, conodont, trilobite, and acritarch bioevents in the uppermost Cambrian–lowermost Ordovician carbonate-siliciclastic sedimentary sequence. The precise correlation to the Green Point GSSP section, western Newfoundland, Canada allows for the identification of the corresponding GSSP level in the Xiaoyangqiao section. The combined data from the Xiaoyangqiao section and the Green Point GSSP section provide a series of events that all can be applied as proxies for identification of the Cambrian–Ordovician boundary horizon outside the GSSP. Based on this, the Xiaoyangqiao section, Dayangcha, is here strongly recommended as a candidate for an Auxiliary Boundary Stratigraphic Section and Point section (ASSP) for the base of the Ordovician System, because it provides one of the best and most complete Cambrian–Ordovician transitions in the world and because the first planktic graptolites are from the Xiaoyangqiao section.     

Potential Global Standard Stratotype-section and Point (GSSP) for a Cambrian stage boundary defined by the first appearance of the trilobite Ptychagnostus atavus, Drum Mountains, Utah, USA

The base of the Ptychagnostus (or Acidusus) atavus Zone is one of the most clearly recognizable horizons on an intercontinental scale in the Cambrian System, and would serve as an excellent position for the base of a new stage-level chronostratigraphic subdivision. Among well-exposed, readily accessible sections in Laurentia, the “Stratotype Ridge” section, Drum Mountains, western Utah, USA, is perhaps the most suitable for a Global Standard Stratotype-section and Point (GSSP) defined by the first appearance datum (FAD) of the cosmopolitan agnostoid trilobite P. atavus. In the “Stratotype Ridge” section, the FAD of P. atavus occurs near the base of a calcisiltite bed 62 m above the base of the Wheeler Formation. A position corresponding closely to this horizon can be recognized with precision in Gondwana, Siberia, Kazakhstan, and Baltica using a combination of stratigraphic tools, the most useful of which are trilobite biostratigraphy, conodont biostratigraphy, and sequence stratigraphy. Brachiopod biostratigraphy and chemostratigraphy provide general constraints on the position of the horizon intercontinentally.     

Advances in Cambrian stratigraphy and paleontology: Integrating correlation techniques, paleobiology, taphonomy and paleoenvironmental reconstruction

Papers resulting from the Fourth International Symposium on the Cambrian System, held in Nanjing, China, in 2005 cover three major aspects of geology and paleontology: (1) the developing global standard for Cambrian chronostratigraphy or regional correlation schemes; (2) regional lithostratigraphy, sedimentology and paleoenvironments; (3) organismal paleobiology, phylogenetic affinities and taphonomy.A generalized curve of carbon isotopes (δ¹³C) through the Cambrian suggests a relationship between major biotic events, sea level history and the development of deposits of exceptional preservation (Lagerstätten). Recognition of this relationship increases the importance of the δ¹³C profile as a tool for intercontinental and intracontinental correlation. Significant δ¹³C excursions in the Cambrian are: BACE (negative excursion at the base of the Cambrian System); ZHUCE (positive excursion in the lower part of Stage 2); SHICE (negative excursion in the middle part of Stage 2); CARE (positive excursion near the base of Stage 3); MICE (positive excursion in the lower part of Stage 4); AECE (negative excursion in the middle part of Stage 4); ROECE (negative excursion near the base of Stage 5); DICE (negative excursion beginning near the base of the Drumian Stage); SPICE (positive excursion beginning at the base of the Paibian Stage); TOCE (negative excursion near the top of Stage 10). All acronyms other than SPICE are newly proposed.