Andy S. Gale

Orbital tuning of Cenomanian marly chalk successions: towards a Milankovitch time-scale for the Late Cretaceous

Outcrops of Cenomanian marly chalks in the Crimea (Ukraine) and SE England (UK), 2600 km apart, display conspicuous decimetre–scale rhythmicity and can be correlated by using 12 biostratigraphical events. Closely spaced samples from the two sections were used to generate long time–series of digitally captured grey–scale reflectance data. Spectral analysis of these data demonstrates that if the rhythmicity is assumed to be driven by precession (bedding cycles; mode at 20 ka), it is seen to be modulated by the short eccentricity cycle (100 ka bundles). The latter signal is expressed in the sediments by the occurrence of dark marls at precession minima occurring at eccentricity maxima. Although identified in the spectra, tilt (38 ka) and the long eccentricity cycle (400 ka) are not strongly expressed. Comparison of age modelled, unfiltered grey–scale data between the two sections reveals strikingly similar patterns, and enables the identification of a 80 ka hiatus in the UK chalks.

Cenomanian sequence stratigraphy and sea-level fluctuations in the Tarfaya Basin (SW Morocco)

We investigated the sequence architecture of two expanded Cenomanian successions along a depth transect in the Tarfaya Basin (SW Morocco) and correlated these successions to published records from northwest Europe and India. Changes in terrigenous material, carbonate and organic carbon content, carbonate microfacies and foraminiferal biofacies, as well as nondepositional and erosional surfaces were used to define depositional sequences and systems tracts. We identified two main transgressive cycles in the lower and middle-upper Cenomanian separated by a major regression at the early-middle Cenomanian transition (sequence boundary Ce 3). This regressive interval is characterized by lagoonal low-stand deposits indicating an overall sealevel fall of more than 30 m. Superimposed on the two main transgressive cycles, there are 11 third-order depositional sequences that correlate to globally recognized sealevel fluctuations and appear to be paced by long eccentricity variations (400 Ka period). Positive carbon isotope excursions in the middle Cenomanian (96.0 Ma) and latest Cenomanian (94.0 Ma) following sealevel lowstands together with planktonic foraminiferal and ammonite datums provide a robust framework for stratigraphic correlation. We suggest that the onset of these excursions was triggered by eccentricity minima during periods of low variability in obliquity (nodes), which probably coincided with glacioeustatic lowstands.

Ammonites and inoceramid bivalves from close to the middle-upper Albian boundary around Fort Worth, Texas

The Goodland/Comanche Peak Limestone, Kiamichi Formation and basal Duck Creek Limestones around Fort Worth Texas yield a limited number of cosmopolitan ammonite and inoceramid bivalve taxa that allow precise correlation with the sequence that has been used as a standard in northwest Europe. The upper part of the Goodland/Comanche Peak Limestones yields species of Dipoloceras that show the base of the Upper Albian substage, provisionally defined as the first appearance of D. cristatum (Brongniart, 1822), to lie within this unit. Brancoceras aff. cricki Spath, 1934, Mortoniceras (Deiradoceras) beloventer new species, and Actinoceramus cf. concentricus (Parkinson, 1819) parabolicus Crampton, 1996a, co-occurs with D. cristatum in the Comanche Peak Limestone. The Kiamichi Formation yields rare Mortoniceras (Mortoniceras) pricei (Spath, 1922), M. (Deiradoceras) prerostratum Spath, 1921, M. (D.) bipunctatum Spath, 1933, and Actinoceramus sulcatus (Parkinson, 1819) morphotypes that allow correlation with the European Hysteroceras orbignyi and Hysteroceras varicosum subzones of the Mortoniceras inflatum zone. The basal Duck Creek Limestone yields Mortoniceras (Deiradoceras) sp. and Hysteroceras cf. varicosum (J. de C. Sowerby, 1824), and can also be correlated with the varicosum subzone.

Ancient Origin of the Modern Deep-Sea Fauna

The origin and possible antiquity of the spectacularly diverse modern deep-sea fauna has been debated since the beginning of deep-sea research in the mid-nineteenth century. Recent hypotheses, based on biogeographic patterns and molecular clock estimates, support a latest Mesozoic or early Cenozoic date for the origin of key groups of the present deep-sea fauna (echinoids, octopods). This relatively young age is consistent with hypotheses that argue for extensive extinction during Jurassic and Cretaceous Oceanic Anoxic Events (OAEs) and the mid-Cenozoic cooling of deep-water masses, implying repeated re-colonization by immigration of taxa from shallow-water habitats. Here we report on a well-preserved echinoderm assemblage from deep-sea (1000–1500 m paleodepth) sediments of the NE-Atlantic of Early Cretaceous age (114 Ma). The assemblage is strikingly similar to that of extant bathyal echinoderm communities in composition, including families and genera found exclusively in modern deep-sea habitats. A number of taxa found in the assemblage have no fossil record at shelf depths postdating the assemblage, which precludes the possibility of deep-sea recolonization from shallow habitats following episodic extinction at least for those groups. Our discovery provides the first key fossil evidence that a significant part of the modern deep-sea fauna is considerably older than previously assumed. As a consequence, most major paleoceanographic events had far less impact on the diversity of deep-sea faunas than has been implied. It also suggests that deep-sea biota are more resilient to extinction events than shallow-water forms, and that the unusual deep-sea environment, indeed, provides evolutionary stability which is very rarely punctuated on macroevolutionary time scales.

GSSPs, global stratigraphy and correlation

Abstract Procedures used to define an international chronostratigraphic stage boundary and to locate and ratify a Global Boundary Stratotype Section and Point (GSSP) are outlined. A majority of current GSSPs use biostratigraphic data as primary markers with no reference to any physico-chemical markers, despite the International Subcommission on Stratigraphic Classification (ISSC) suggestion that such markers should be included if possible. It is argued that such definitions will not produce the high-precision Phanerozoic time scale necessary to understand such phenomena as pre-Pleistocene ice ages and global climate change. It is strongly recommended that all GSSPs should have physico-chemical markers as an integral part of their guiding criteria, and where such markers cannot be found, the GSSP should be relocated. The methods and approach embodied in oceanic stratigraphy – coring, logging, analysing and archiving of drill sites by numerous experts using a wide range of methods – could usefully serve as a scientific model for the analysis and archiving of GSSPs, all of which are on the present-day continents. The incorporation of many more stratigraphic sections into GSSP studies, the application of physico-chemical methods, and the replacement of old U–Pb dates by newer CA-TIMS U–Pb dates, together with the use of constrained optimization (CONOP) programs that produce a calendar of events from many sections, should lead to much more precise timescales for pre-Cenozoic time than are currently available.

Discussion on the Eocene–Oligocene boundary in the UK Journal , Vol. 163, 2006, pp. 401–415

Jerry Hooker, Margaret Collinson, Stephen Grimes, Nick Sille & David Mattey write: Recognition of the Eocene–Oligocene boundary in the Hampshire Basin, UK, has been debated since naming of the Oligocene Epoch in 1854. Previously, this was because the boundary itself had not been stabilized and because the strata concerned are largely non-marine. A Global Boundary Stratotype and Stratigraphic Point (GSSP) was established at Massignano, Italy, in 1993 in marine strata. Recognition of the boundary on extinction of the planktonic foraminiferan family Hantkeninidae made boundary identification difficult in the continental realm. Correlation to marginal marine and non-marine strata is nevertheless possible via magnetostratigraphic and sequence stratigraphic studies and, importantly, biostratigraphically via dinocyst zones at Massignano (Brinkhuis & Biffi 1993; Brinkhuis & Visscher 1995). Therefore, recent publication of the magnetostratigraphy, sequence stratigraphy and orbital cyclicity of much of the Hampshire Basin Solent Group (Gale et al . 2006) is welcomed and substantially increases the number of correlation tools available in this area. Such cyclical phenomena, however, rely on absolute dating or biostratigraphy for calibration. No radiometric dates exist for the Solent Group, so biostratigraphy remains the best means of dating the succession.nnThere are, however, problems with the way Gale et al . (2006) have interpreted biostratigraphic markers and therefore with their placement of the Eocene–Oligocene boundary and associated events. The organisms concerned are calcareous nannoplankton (NP zones) and mammals (MP reference levels). Thus, the record by Aubry (1985) of NP22 in the Argiles Vertes de Romainville, Paris Basin, was subsequently qualified by her (Aubry 1986, p. 307) as ‘zone NP22 (not younger; possibly older: NP21?)’. This dating was based solely on the presence of rare Isthmolithus recurvus , which ranges from NP19/20 to NP22 (Aubry 1992), this being the real level of dating for the Argiles Vertes de Romainville …

Astronomical calibration and global correlation of the Santonian (Cretaceous) based on the marine carbon isotope record

High-resolution records of bulk carbonate carbon isotopes have been generated for the Upper Coniacian to Lower Campanian interval of the sections at Seaford Head (southern England) and Bottaccione (central Italy). An unambiguous stratigraphic correlation is presented for the base and top of the Santonian between the Boreal and Tethyan realms. Orbital forcing of carbon and oxygen isotopes at Seaford Head points to the Boreal Santonian spanning five 405u2009kyr cycles (Sa1 to Sa5). Correlation of the Seaford Head time scale to that of the Niobrara Formation (Western Interior Basin) permits anchoring these records to the La2011 astronomical solution at the Santonian-Campanian (Sa/Ca) boundary, which has been recently dated to 84.19u2009±u20090.38u2009Ma. Among the five tuning options examined, option 2 places the Sa/Ca at the 84.2u2009Ma 405u2009kyr insolation minimum and appears as the most likely. This solution indicates that minima of the 405u2009kyr filtered output of the resistivity in the Niobrara Formation correlate to 405u2009kyr insolation minima in the astronomical solution and to maxima in the filtered δ13C of Seaford Head. We suggest that variance in δ13C is driven by climate forcing of the proportions of CaCO3 versus organic carbon burial on land and in oceanic basins. The astronomical calibration generates a 200u2009kyr mismatch of the Coniacian-Santonian boundary age between the Boreal Realm in Europe and the Western Interior, due either to diachronism of the lowest occurrence of the inoceramid Cladoceramus undulatoplicatus between the two regions or to remaining uncertainties of radiometric dating and cyclostratigraphic records.

First glimpse into Lower Jurassic deep-sea biodiversity: in situ diversification and resilience against extinction

Owing to the assumed lack of deep-sea macrofossils older than the Late Cretaceous, very little is known about the geological history of deep-sea communities, and most inference-based hypotheses argue for repeated recolonizations of the deep sea from shelf habitats following major palaeoceanographic perturbations. We present a fossil deep-sea assemblage of echinoderms, gastropods, brachiopods and ostracods, from the Early Jurassic of the Glasenbach Gorge, Austria, which includes the oldest known representatives of a number of extant deep-sea groups, and thus implies that in situ diversification, in contrast to immigration from shelf habitats, played a much greater role in shaping modern deep-sea biodiversity than previously thought. A comparison with coeval shelf assemblages reveals that, at least in some of the analysed groups, significantly more extant families/superfamilies have endured in the deep sea since the Early Jurassic than in the shelf seas, which suggests that deep-sea biota are more resilient against extinction than shallow-water ones. In addition, a number of extant deep-sea families/superfamilies found in the Glasenbach assemblage lack post-Jurassic shelf occurrences, implying that if there was a complete extinction of the deep-sea fauna followed by replacement from the shelf, it must have happened before the Late Jurassic.

Paleozoic echinoderm hangovers: Waking up in the Triassic

Echinoderms are among the marine invertebrates that underwent the most severe losses at the end-Permian extinction. The prevailing paradigm claims an extreme bottleneck with only very few, if not single, holdovers (“hangovers” herein) sparking the post-Paleozoic radiation. Here we identify previously overlooked Triassic echinoids, ophiuroids, and asteroids as unambiguous members of Paleozoic stem groups. These echinoderm hangovers occurred almost worldwide and had spread into a wide range of paleoenvironments by the Late Triassic. Our discovery challenges fundamentals of echinoderm evolution with respect to end-Permian survival and sheds new light on the early evolution of the modern clades, in particular on Triassic ghost lineages (i.e., inferred but undocumented fossil record) of the crown-group look-alikes of the Paleozoic hangovers.

Slope failure of chalk channel margins: implications of an Upper Cretaceous mass transport complex, southern England

The importance of mass transport and bottom currents is now widely recognized in the Upper Cretaceous Chalk Group of Northern Europe. The detailed dynamics and interaction of the two phenomena are difficult to study as most evidence is based on seismic data and drill core. Here, field observations provide evidence for recurring margin collapse of a long-lived Campanian channel. Compressionally deformed and thrust chalk hardgrounds are correlated to thicker, non-cemented chalk beds that form a broad, gentle anticline. These chalks represent a slump complex with a roll-over anticline of expanded, non-cemented chalk in the head region and a culmination of condensed hardgrounds in the toe region. Observations strongly suggest that the slumping represents collapse of a channel margin. Farther northwards, the contemporaneous succession shows evidence of small-scale penecontemporaneous normal faulting towards the south, here interpreted as gravitational settling of the chalk immediately adjacent to the channel margin. Detailed biostratigraphic studies and sedimentological observations provide evidence for at least two discrete collapse events and suggest the slumping to be the result of channel margin oversteepening rather than evidence for a regional tectonic phase. The described example thus serves as an analogue for processes commonly only inferred from subsurface data.