A stratigraphic framework for eastern Labrador Sea cores has been developed for the interval 0–90 000 years BP through analysis of oxygen isotopes, volcanic ash, benthonic foraminifera, and the radiolarian Diplocyclas davisiana. Benthonic and planktonic foraminiferal isotope stratigraphy and the time scale of Shackleton and Opdyke provide a basis for the approximate dating of a series of marker events which include ash zones at ca. 59 000 and ≤ 21 000 years BP; benthonic foraminiferal abundance maxima at ca. 83 000, 75 000, 60 000, 19 000, and 3000 years BP; and D. davisiana percentage maxima at ca. 90 000, 73 000, 64 000, 54 000, 45 000 – 32 000, and 10 000 years BP. Incursions of subpolar planktonic foraminifera into the area during parts of isotopic stage 2 (between about 13 000 and 25 000 years BP but probably excluding the 15 000–18 000 years BP glacial maximum interval) and during the isotopic stage 4/5a transition (around 75 000 years BP) suggest that the eastern Labrador Sea was free of sea ice, at least in summer during periods of rapid continental ice sheet growth which lead to the isotopic stage 4 and stage 2 glacial maxima. A larger than normal stage 1/stage 2 difference in the isotopic composition of benthonic foraminifera (1.8‰) implies that this open water and attendant surface cooling was a potential source for colder than modern deep water. In contrast the Norwegian Sea was a reservoir of warmer than modern deep water during the last glacial.
During the last fourth-order glacial-interglacial cycle (e.g. post oxygen isotope stage 5) the Lagniappe Delta system located in the northeast Gulf of Mexico, prograded several tens of miles seaward along two main NE-SW and N-S trending fairways. The delta complex is underlain by a well-developed calcareous shale-rich condensed section that was deposited during isotope stage 5. The delta complex comprises many progradational lobes that were deposited during fifth-order sea-level falls and during the fourth-order maximum lowstand and early rise of sea level associated with isotope stages 4 to 2. Each significant fifth-order sea level fall developed a sequence boundary with an unconformity updip and a correlative conformity downdip on which a delta lobe was deposited. Autocyclic processes also lead to deposition of numerous lobes through lobe switching. During the maximum sea-level lowstand, deep erosion related to the development of an extensive incised valley system occurred across the top of the prograding wedges that were deposited during relative sea-level fall (the falling stage systems tract) and modified all of the previous updip unconformities. The base of the incised valley system, and its correlative downdip conformity, form the main fourth-order sequence boundary. It is on this surface that the last part of the delta complex was deposited during the maximum lowstand and early rise of sea-level. Thus, during the last fourth-order cycle, several fifth-order 'initial' sequence boundaries and one fourth-order 'final' sequence boundary were formed. Infilling of the incised valley system occurred mainly during the early and late rise of sea-level (isotope stages 2 and younger), prior to a major landward shift of deltaic sedimentation in response to the rapid eustatic rise in sea level during isotope stage 1.
Cover images: from top left clockwise: (a) Outcrop photograph of the thinning-upward sheet sandstones, Lower Pennsylvanian Jackfork Group, Baumgartner Quarry, Arkansas. (b and c) Core photograph and image log are from the Upper Cretaceous Dad Sandstone, Lewis Shale, Wyoming. Images are from the CSM Strat Text #61 core (Chapters 6, 7, 12). (d) Seismic profile across the Marlim Field, Campos Basin (Chapter 15). Figure courtesy of Carlos Bruhn and AAPG. (e) 3-D image of the reservoir interval at the Thunder Horse and Thunder Horse North Fields, northern deep Gulf of Mexico. Surface dipping to lower right shows the top reservoir interval. Allochthonous salt body and the three well paths are shown. Figure is courtesy of Cindy Yeilding and BP. (f) Schematic 3-D block diagram of a migrating channel levee-system (Chapter 7). Figure is courtesy of Mike Roberts (g) Wireline log from offshore Angola (Chapters 6-9). Figure is courtesy of Gulf Coast Section SEPM Foundation.
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