Porphyrin geochemistry of DSDP Hole 71-511

Late Jurassic-early Cretaceous black shales and an overlying sequence of Albian-Campanian zeolitic claystones from the Falkland Plateau (DSDP/IPOD Leg 71, Site 511) were analyzed for tetrapyrrole pigment type and abundance. The "black shale" sequence was found to be rich in DPEP-series dominated free-base, nickel (Ni) and, to a lesser extent, vanadyl (V = 0) porphyrins. A low level of organic maturity (i.e. precatagenesis) is indicated for these strata as nickel chelation by free-base porphyrins is only 50-75% complete, proceeding down-hole to 627 meters sub-bottom. Electronic and mass spectral data reveal that the proposed benzo-DPEP (BD) and tetrahydrobenzo-DPEP (THBD) series are present in the free-base and Ni species, as well as the more usual occurrence in V = 0 porphyrin arrays. Highly reducing conditions are suggested by an abundance of the PAH perylene, substantial amounts of the THBD/BD series and a redox equilibrium between free-base DPEP and 7,8-dihydro-DPEP series, which exist in a 7:1 molar ratio. The Albian-Campanian claystone strata were found to be tetrapyrrolepoor, and those pigments present were typed as Cu/Ni highly dealkylated (C26 max.) etioporphyrins, thought to be derived via redeposition and oxidation of terrestrial organic matter (OM). Results from the present study are correlated to our past analyses of Jurassic-Cretaceous sediments from Atlantic margins in an effort to relate tetrapyrrole quality and quantity to basin evolution and OM sources in the proto-Atlantic.

Calcareous nannofossils of ODP Leg 101 holes

Leg 101 of the Ocean Drilling Program drilled 19 holes at 11 sites to investigate the geology of the Straits of Florida and the northern Bahamas. Drilling at Site 626 indicated that the Gulf Stream has had significant flow through the Straits of Florida for at least the last 24 million years. Winnowed, foraminiferal grainstones and packstones with sparse nannofossil assemblages and the reworking of older nannofossils suggest strong bottom-current activity throughout this interval. Drilling north of Little Bahama Bank and in Exuma Sound documents the growth of platform slopes during the late Cenozoic. Nannofossil biostratigraphy of the upper Cenozoic sediments from the Little Bahama Bank and Exuma Sound slope transects indicates relatively continuous deposition, with only short breaks in the periplatform ooze and/or calciturbidite accumulation during the late Pliocene. These unconformities may be linked to sea-level lowstands. Nannofossil assemblages are generally poorly preserved owing to accelerated diagenesis caused by high aragonite and high magnesium calcite contents of bank-derived material. High rates of influx of bank-derived materials appear to coincide with highstands of sea level. Periplatform sediments are largely limited to the upper Cenozoic at Little Bahama Bank. Pelagic and/or hemipelagic conditions existed during the Late Cretaceous and Paleogene. A relatively complete, continuous section of Oligocene is present in the Little Bahama Bank area, although the rest of the Paleogene is thin. Paleogene material is also present in Northeast Providence Channel, although its thickness is uncertain. A thick upper Campanian chalk sequence with abundant, moderately to well-preserved nannofossils occurs in the Little Bahama Bank area. Hemipelagic nannofossil marls and marly chalks at Little Bahama Bank contain an excellent nannofossil record, which indicates a continuous lowermost to middle Cenomanian sequence overlying the upper Albian drowned platform. These hemipelagic sediments are significantly younger than the organic-rich, middle Albian limestones in Northeast Providence Channel. The latter indicate that a deep-water channel was already well established by the middle Albian.

Age determination of ODP Leg 120 samples

Conventional K-Ar and 40Ar/39Ar analyses on whole-rock samples are reported for basaltic samples retrieved on the Central and Southern Kerguelen plateaus during Ocean Drilling Program Leg 120. Sites 747, 749, and 750 recovered basalts from the plateau basement, whereas Site 748 drilled a lava flow interbedded with sediments of probable Albian age. The freshest core basalts from the basement yielded dates falling in the 110-100 m.y. interval. Sample 120-749C-15R-3 (26-31 cm) gave conventional K-Ar, total fusion, and plateau 40Ar/39Ar ages that are closely concordant: 111.5 ± 3.2 m.y., 109.9 ± 1.2 m.y., and 109.6 ± 0.7 m.y., respectively. Sample 120-750B-15R-5 (54-60 cm), when taking into account the analytical uncertainties, yields conventional K-Ar and 40Ar/39Ar plateau ages that can be considered similar: 101.2 ± 7.5 and 118.2 ± 5 m.y., respectively. Inspection of the 39Ar/40Ar vs. 36Ar/40Ar diagram does not reveal the occurrence of an initial argon component of radiogenic composition in the two samples. Accordingly, our results suggest that the formation of the basement of the Central Kerguelen Plateau was closed at 110 m.y.. Furthermore, these results are in agreement with a K-Ar age of 114 ± 1 m.y. mentioned in the literature for a basalt dredged in the 77°E Graben. The still scant amount of data indicates that the outpourings of the Central Kerguelen Plateau correspond rather well with widespread continental magmatism in Gondwanaland that is believed to mark the incipient opening of the eastern Indian Ocean. This implies a huge head for the mantle plume at the source of these liquids. Nevertheless, on land and at sea the exact duration of magmatism remains unknown. Therefore, a catastrophic pattern similar to that currently invoked for the Deccan Traps at the end of the Cretaceous, though possible, is not yet required by present geochronologic data.

Minerals of bulk samples and clay fraction at DSDP Leg 80 Holes

At the request of the Leg 80 scientific party, selected samples of Cretaceous age were processed by X-ray diffraction at the mineralogy laboratories at the Ecole des Mines (Albian to Late Cretaceous samples) and at the Institut de Géologie at Dijon (Barremian samples). The results were used in developing the lithostratigraphy and sedimentology discussed in this volume by Rat et al. 1985 (doi:10.2973/dsdp.proc.80.140.1985) in their study of Barremian-Albian paleoenvironment, by Graciansky and Gillot in their study of Albian and Cenomanian limestones, and by Graciansky and Bourbon in their paleoenvironmental reconstructions for the Late Cretaceous chalks.

Early Cretaceous palynomorphes from ODP Hole 113-692B

Detailed descriptions of in situ ?Valanginian to Albian Antarctic palynofloras are presented from Weddell Sea claystones with high percentages of organic matter ("black shales") and intercalated volcanic ash layers. The claystones were recovered from two sites (ODP Leg 113, Sites 692 and 693) on the continental margin of Dronning Maud Land. Palynological investigations of these Cretaceous sediments revealed a ?Valanginian-Hauterivian age for the Site 692 sediments and an Aptian-Albian age for Site 693. This paper is focused on the palynomorphs of Site 692. Miospores, dinoflagellate cysts, and acritarchs are listed and compared with early Cretaceous microfloras from the Antarctic Peninsula, Australia, and South America. The dinocyst assemblage of Site 692 seems to be very similar in composition to an assemblage from the South Shetlands (?Valanginian-Hauterivian-Barremian). It also agrees well with associations described from early Early Cretaceous sequences from the Perth Basin, southwestern Australia. According to the Australian miospore zonation schemes, the sporomorph flora from Site 692 belongs to the South Australian Foraminisporis wonthaggiensis Zone (early Valanginian to Hauterivian) or the lower part of the dinocyst Muderongia Superzone (Valanginian to Hauterivian).

Mineralogy, lithology and stable isotope composition of diagenetic siliceous rocks from ODP Leg 129 sites

Ocean Drilling Program Leg 129 recovered chert, porcellanite, and radiolarite from Middle Jurassic to lower Miocene strata from the western Pacific that formed by different processes and within distinct host rocks. These cherts and porcellanites formed by (1) replacement of chalk or limestone, (2) silicification and in-situ silica phase-transformation of bedded clay-bearing biosiliceous deposits, (3) high-temperature silicification adjacent to volcanic flows or sills, and (4) silica phase-transformation of mixed biosiliceous-volcaniclastic sediments. Petrologic and O-isotopic studies highlight the key importance of permeability and time in controlling the formation of dense cherts and porcellanites. The formation of dense, vitreous cherts apparently requires the local addition and concentration of silica. The influence of permeability is shown by two examples, in which: (1) fragments of originally identical radiolarite that were differentially isolated from pore-water circulation by cement-filled fractures were silicified to different degrees, and (2) by the development of secondary porosity during the opal-CT to quartz inversion within conditions of negligible permeability. The importance of time is shown by the presence of quartz chert below, but not above, a Paleogene hiatus at Site 802, indicating that between 30 and 52 m.y. was required for the formation of quartz chert within calcareous-siliceous sediments. The oxygen-isotopic composition for all Leg 129 carbonate- and Fe/Mn-oxide-free whole-rock samples of chert and porcellanite range widely from d18O = 27.8 per mil to 39.8 per mil vs. V-SMOW. Opal-CT samples are consistently richer in 18O (34.1 per mil to 39.3 per mil) than quartz subsamples (27.8 per mil to 35.7 per mil). Using the O-isotopic fractionation expression for quartz-water of Knauth and Epstein (1976) and assuming d18Opore water = -1.0 per mil, model temperatures of formation are 7°-26°C for carbonate-replacement quartz cherts, 22°-25°C for bedded quartz cherts, and 32°-34°C for thermal quartz cherts. Large variations in O-isotopic composition exist at the same burial depth between co-existing silica phases in the same sample and within the same phase in adjacent lithologies. For example, quartz has a wide range of isotopic compositions within a single breccia sample; d18O = 33.4 per mil and 28.0 per mil for early and late stages of fracture-filling cementation, and 31.6 per mil and 30.2 per mil for microcrystalline quartz precipitation within enclosed chert and radiolarite fragments. Similarly, opal-CT d101 spacing varies across lithologic or diagenetic boundaries within single samples. Co-occurring opal-CT and chalcedonic quartz in shallowly buried chert and porcellanite from Sites 800 and 801 have an 8.7 per mil difference in d18O, suggesting that pore waters in the Pigafetta Basin underwent a Tertiary shift to strongly 18O-depleted values due to alteration of underlying Aptian to Albian-Cenomanian volcaniclastic deposits after opal-CT precipitation, but prior to precipitation of microfossil-filling chalcedony.

Geochemistry and kinetic models od Cretaceous samples

The source rock potential of Cretaceous organic rich whole rock samples from deep sea drilling project (DSDP) wells offshore southwestern Africa was investigated using bulk and quantitative pyrolysis techniques. The sample material was taken from organic rich intervals of Aptian, Albian and Turonian aged core samples from DSDP site 364 offshore Angola, DSDP well 530A north of the Walvis Ridge offshore Namibia, and DSDP well 361 offshore South Africa. The analytical program included TOC, Rock-Eval, pyrolysis GC, bulk kinetics and micro-scale sealed vessel pyrolysis (MSSV) experiments. The results were used to determine differences in the source rock petroleum type organofacies, petroleum composition, gas/oil ratio (GOR) and pressure-volume-temperature (PVT) behavior of hydrocarbons generated from these black shales for petroleum system modeling purposes. The investigated Aptian and Albian organic rich shales proved to contain excellent quality marine kerogens. The highest source rock potential was identified in sapropelic shales in DSDP well 364, containing very homogeneous Type II and organic sulfur rich Type IIS kerogen. They generate P-N-A low wax oils and low GOR sulfur rich oils, whereas Type III kerogen rich silty sandstones of DSDP well 361 show a potential for gas/condensate generation. Bulk kinetic experiments on these samples indicate that the organic sulfur contents influence kerogen transformation rates, Type IIS kerogen being the least stable. South of the Walvis Ridge, the Turonian contains predominantly a Type III kerogen. North of the Walvis Ridge, the Turonian black shales contain Type II kerogen and have the potential to generate P-N-A low and high wax oils, the latter with a high GOR at high maturity. Our results provide the first compositional kinetic description of Cretaceous organic rich black shales, and demonstrate the excellent source rock potential, especially of the Aptian-aged source rock, that has been recognized in a number of the South Atlantic offshore basins.

Dinoflagellate cysts of ODP Leg 101 holes

The Albian-Cenomanian sediments in Holes 627B and 635B contain diverse dinoflagellate-cyst assemblages, which show affinities with coeval assemblages from offshore Morocco and northwest Europe. A total of 34 samples were analyzed from the shallow-water platform sediments and neritic marly chalk of Hole 627B and from the argillaceous chalk and limestone of Hole 635B. Dinoflagellate cysts indicate that the top of the shallow-water platform drilled at Hole 627B must be attributed to the late Albian. Dinocysts also date the drowning of the carbonate platform of the Blake Plateau. This drowning started in the latest Albian (Vraconian) and continued into the Cenomanian. The site area changed from an inner to intermediate or outer(?) neritic environment. The area around Hole 635B from the late Albian appears to have been situated in a deeper environment than the area around Hole 627B during the same period. The new dinoflagellate-cyst species Compositosphaeridiuml bahamaensis n. sp., Maghrebinia breviornata n. sp., and Subtilisphaeral habibi n. sp. are described, and Pervosphaeridium truncatum is emended. Additional taxonomic remarks about other species are included.

(Table 3) Stable isotope record of Cretaceous foraminifera from DSDP Hole 44-392A

Mid-Cretaceous (Barremian-Turonian) plankton preserved in deep-sea marl, organic-rich shale, and pelagic carbonate hold an important record of how the marine biosphere responded to short- and long-term changes in the ocean-climate system. Oceanic anoxic events (OAEs) were short-lived episodes of organic carbon burial that are distinguished by their widespread distribution as discrete beds of black shale and/or pronounced carbon isotopic excursions. OAE1a in the early Aptian (~120.5 Ma) and OAE2 at the Cenomanian/Turonian boundary (~93.5 Ma) were global in their distribution and associated with heightened marine productivity. OAE1b spans the Aptian/Albian boundary (~113-109 Ma) and represents a protracted interval of dysoxia with multiple discrete black shales across parts of Tethys (including Mexico), while OAE1d developed across eastern and western Tethys and in other locales during the latest Albian (~99.5 Ma). Mineralized plankton experienced accelerated rates of speciation and extinction at or near the major Cretaceous OAEs, and strontium isotopic evidence suggests a possible link to times of rapid oceanic plateau formation and/or increased rates of ridge crest volcanism. Elevated levels of trace metals in OAE1a and OAE2 strata suggest that marine productivity may have been facilitated by increased availability of dissolved iron. The association of plankton turnover and carbon isotopic excursions with each of the major OAEs, despite the variable geographic distribution of black shale accumulation, points to widespread changes in the ocean-climate system. Ocean crust production and hydrothermal activity increased in the late Aptian. Faster spreading rates [and/or increased ridge length] drove a long-term (Albian-early Turonian) rise in sea level and CO2-induced global warming. Changes in ocean circulation, water column stratification, and nutrient partitioning lead to a reorganization of plankton community structure and widespread carbonate (chalk) deposition during the Late Cretaceous. We conclude that there were important linkages between submarine volcanism, plankton evolution, and the cycling of carbon through the marine biosphere.

Benthic foraminifers in Mesozoic and Cenozoic sediments of the southwestern Atlantic

Benthic foraminiferal assemblages in Mesozoic and Cenozoic sediments were studied at Sites 511, 512, 513, and 514 drilled during Leg 71 in the southwestern Atlantic on the Maurice Ewing Bank and in the Argentine Basin. Benthic foraminifers in almost all stratigraphic subdivisions of Sites 511 and 512 reflect the gradual subsidence of the Falkland Plateau from shelf depths in the Barremian-Albian, when a semiclosed basin with restricted circulation of water masses and anaerobic conditions existed, to lower bathyal depths in the Late Cretaceous and Cenozoic, with an abrupt acceleration at the boundary of Lower and Upper Cretaceous. The composition, distribution, and preservation of Late Cretaceous assemblages of benthic foraminifers suggest considerable fluctuations of the foraminiferal lysocline and the CCD. This is evidenced by dissolution facies and foraminiferal assemblages in which agglutinated and resistant calcareous forms predominated during high stands of the CCD and by calcareous facies in which rich assemblages of calcareous species predominated during low stands. The highest position of the CCD on the Plateau (less than 1500-2000 m) was in the late Cenomanian, Turonian, and Coniacian. In the Santonian and Campanian the CCD was at depths below 1500-2000 meters. At the end of the Campanian the CCD shifted again to depths comparable with those of Cenomanian and Turonian time. In the latest Campanian and the Maestrichtian the CCD was low and nanno-foraminiferal oozes with a rich assemblage of benthic foraminifers accumulated. Foraminiferal assemblages at Sites 513 and 514 in the Argentine Basin also testify to oceanic subsidence from lower bathyal depths in the Oligocene to abyssal ones at present. This process was complicated by the influence of geographical migrations of the Polar Front caused by extensions of the ice sheet in the Antarctic after the opening of the Drake Passage during the Oligocene. In Mesozoic and Cenozoic deposits of the Falkland Plateau and the Argentine Basin seven assemblages of benthic foraminifers were distinguished by age: early-middle Albian, middle-late Albian, Late Cretaceous (including four groups), middle Eocene, late Eocene-early Miocene, middle-late Miocene, and Pliocene-Quaternary. The Albian assemblages contain many species common to the foraminiferal fauna of the Austral Biogeographical Province. The Late Cretaceous assemblage contains, along with Austral species, species common to foraminifers of North America, Western Europe, the Russian platform, and the south of the U.S.S.R. Deep-sea cosmopolitan species prevail in Cenozoic assemblages.

Geochemistry, lithology and maceral analysis at DSDP Hole 71-511

The quantity, type, and maturity of the organic matter in Recent through Upper Jurassic sediments from the Falkland Plateau, DSDP Site 511, have been determined. Sediments were investigated for their hydrocarbon potential by organic carbon and Rock-Eval pyrolysis. Kerogen concentrates were prepared and analyzed in reflected and transmitted light to determine vitrinite reflectance and maceral content. Total extractable organic compounds were analyzed for their elemental composition, and the fraction of the nonaromatic hydrocarbons was determined by capillary column gas chromatography and combined gas chromatography/mass spectrometry. Three main classes of organic matter can be determined at DSDP Site 511 by a qualitative and quantitative evaluation of microscopic and geochemical results. The Upper Jurassic to lower Albian black shales contain high amounts of organic matter of dominantly marine origin. The content of terrigenous organic matter increases at the base of the black shales, whereas the shallowest black shales near the Aptian/Albian boundary are transitional in composition, with increasing amounts of inert, partly oxidized organic matter which is the dominant component in all Albian through Tertiary sediments investigated. The organic matter in the black shales has a low level of maturity and has not yet reached the onset of thermal hydrocarbon generation. This is demonstrated by the low amounts of total extractable organic compounds, low percentages of hydrocarbons, and the pattern and composition of nonaromatic hydrocarbons. The observed reflectance of huminite and vitrinite particles (between 0.4% and 0.5% Ro at bottom-hole depth of 632 m) is consistent with this interpretation. Several geochemical parameters indicate, however, a rapid increase in the maturation of organic matter with depth of burial. This appears to result from the relatively high heat flow observed at Site 511. If we relate the level of maturation of the black shales at the bottom of Hole 511 to their present shallow depth of burial, they appear rather mature. On the basis of comparisons with other sedimentary basins of a known geothermal history, a somewhat higher paleotemperature gradient and/or additional overburden are required to give the observed maturity at shallow depth. A comparison with contemporaneous sediments of DSDP Site 361, Cape Basin, which was the basin adjacent and to the north of the Falkland Plateau during the early stages of the South Atlantic Ocean, demonstrates differences in sedimentological features and in the nature of sedimentary organic matter. We interpret these differences to be the result of the different geological settings for Sites 361 and 511.

Mineralogy and geochemistry of altered ash, pelagic clay, and a clay vein in basalt from DSDP Leg 62 Holes

Volcanic ash was recovered from lower Aptian to Albian deposits from DSDP Sites 463, 465, and 466; pelagic clay of the upper Pleistocene to Upper Cretaceous was recovered mainly from Site 464, with minor amounts at Sites 465 and 466. We present X-ray-mineralogy data on pelagic clay and altered volcanic ash recovered from the four Leg 62 sites. In addition, two ash samples from Sites 463 and 465, a pelagic clay from Site 464, and a clay vein from the basaltic basement at Site 464 each were analyzed for major, minor, and trace elements. Our purpose is to describe the mineralogy and chemistry of altered ash and pelagic clays, to determine the sources of their parent material, and to delineate the diagenetic history of these clay-rich deposits. Correlation of chemistry and mineralogy of ash and pelagic clay with volcanic rocks suspected to be their parent material is not always straightforward, because weathering and diagenetic alteration caused depletion or enrichment of many elements.

Organic geochemistry and sedimentology of lower to mid-Cretaceous at DSDP Leg 77 Holes

Analyses of 40 carbonate core samples - 27 from Site 535, 12 from Site 540, and 1 from Site 538A - have confirmed many of the findings of the Shipboard Scientific Party. The samples, all but one Early to mid-Cretaceous in age (Berriasian to Cenomanian), reflect sequences of cyclically anoxic and oxic depositional environments. They are moderately to very dark colored, dominantly planar-parallel, laminated lime mudstones. Most show the effects of intense mechanical compaction. Visual kerogen characteristics and conventional Rock-Eval parameters indicate that these deep basinal carbonates contain varying mixtures of thermally immature kerogen derived from both marine and terrigenous precursors. However, variations in kerogen chemistry are evident upon analysis of the pyrolysis mass spectral data in conjunction with the other geochemical analyses. Particularly diagnostic is the reduction index, Rl, a measure of H2S produced during pyrolysis. Total organic carbon, TOC, ranges from 0.6 to 6.6%, with an overall average of 2.4%. Average TOCs for these fine-grained mudstones are: late Eocene 2.5% (1 sample), Cenomanian 2.2% (6), Albian 2.0% (10), Aptian 1.3% (1), Barremian-Hauterivian 2.8% (11), late Valanginian 4.8% (3), Berriasian-early Valanginian 1.6% (7). Most of the carbonates have source-potential ratings of fair to very good of predominantly oil-prone to mixed kerogen, with only a few gas-prone samples. The ratings correlate well with the inferred depositional environments, i.e., whether oxic or anoxic. Several new organic-geochemical parameters, especially Rl, based on pyrolysis mass spectrometry of powdered whole-rock samples, support this view. Tar from fractures in laminated to bioturbated limestones of Unit IV (late Valanginian) at 535-58-4, 19-20 cm (530 m sub-bottom) appears to be mature, biodegraded, and of migrated rather than on site indigenous origin.

Major, trace and rare earth element concentration of ODP Site 210-1277 basalts, Newfoundland margin

Drilling of the distal Newfoundland margin at Ocean Drilling Program Site 1277 recovered part of the transition between exhumed sub-continental mantle lithosphere and normal mid-ocean-ridge basalt (N-MORB) volcanism perhaps related to the initiation of seafloor spreading, which may have occurred near the Aptian/Albian boundary, coincident with the final separation of subcontinental mantle lithosphere. Subcontinental mantle lithosphere was recovered near the crest of a basement high, the Mauzy Ridge. This ridge lies near magnetic Anomaly M1 and is inferred to be of Barremian age. The recovered section is dominated by serpentinized spinel harzburgite, with subordinate dunite and minor gabbroic intrusives, and it includes inferred high-temperature ductile shear zones. The serpentinite is capped by foliated gabbro cataclasite that is interpreted as the product of a major seafloor extensional detachment. The serpentinized harzburgite beneath is highly depleted subcontinental mantle lithosphere that was exhumed to create new seafloor within the ocean-continent transition zone. After inferred removal of overlying brittle crust, the detachment was eroded, producing multiple mass flows that were dominated by clasts of serpentinite and gabbro in a lithoclastic and calcareous matrix. Basaltic lavas were erupted spasmodically, mainly as sheet flows, with subordinate lava breccia, hyaloclastite, and possible pillow lava. The sedimentary-volcanic succession and the exhumed mantle lithosphere experienced later high-angle extensional fracturing and probably faulting. Extensional fissures opened incrementally and were filled with silt-sized carbonate, basalt-derived clastic sediment, and hyaloclastite, forming neptunian dykes and geopetal structures. Chemical analysis of representative basalts for major elements and trace elements were made using a high-precision, high-accuracy X-ray fluorescence method (utilizing increased count times) and by whole-rock inductively coupled plasma-mass spectrometry that yielded additional evidence for rare earth elements. The analyses indicate N-MORB to slightly enriched compositions. The MORB was produced by relatively high degree melting of a fertile mantle source that differed strongly from the cored serpentinized peridotites. The basalts exhibit a distinct negative Nb anomaly on MORB-normalized plots that can be explained by prior extraction of melt from upper mantle that had previously been affected by subduction, possibly during closure of the Iapetus or Rheic oceans. In the proposed interpretation, mantle lithosphere was exhumed to the seafloor and experienced mass wasting to form serpentinite-rich mass flows. The interbedded MORB records the beginning of a transition to "normal" seafloor spreading. This interpretation takes into account drilling results from the Iberia-Galicia margin and the Jurassic Alps-Apennines.