Abstract The evolution of the global oceanic and atmospheric circulation systems has been affected by several forcing processes, with orbital variations being dominant on shorter geological time scales. Over longer periods of time (>10 Ma) the tectonic evolution of the solid Earth has been recognized as the major control on the development of the global climate system. Tectonic activity acts in one of two different ways to influence regional and global climate. The earliest solid Earth-climatic interaction recognized was the effect that the opening and closure of oceanic gateways had on the circulation patterns in the global ocean. Major effects on regional and sometimes global climate have been attributed to such changes, e.g. closure of the Isthmus of Panama ( Driscoll & Haug 1998 ). Since the late 1980s a second form of climate-tectonic interaction has been recognized, involving the growth and erosion of oro-genic belts. In this second category the Arabian Sea region must be considered the global type example.

Abstract We present a multi-proxy study of sediment Core 905 from the Arabian Sea offshore Somalia to assess the validity of a number of proxies for productivity, temperature and wind strength, to reconstruct the monsoon history in the western Arabian Sea. The present-day seasonal variation in productivity in the modern Arabian Sea off Somalia reflects the change from the high-productivity SW monsoon to the low-productivity NE monsoon seasons. Annual productivity is therefore largely controlled by SW monsoon driven upwelling. The geochemical records of Core 905 document millennial-scale variations, for example, in Ba/Al and C org content. The Younger Dryas and the time equivalent period to Heinrich event 1 show low annual productivity whereas the early Holocene and Bølling-Allerød periods are characterized by high productivity. The upwelling-productivity peaked during Early Holocene time and was followed by a decrease toward the modern values. The total flux of planktic foraminifera and the concentration of the planktic foraminifera G. bulloides are not always controlled by the total productivity. Variations in calcite dissolution, the advection of expatriate fauna or a seasonal decoupling of primary and secondary production appear to hamper straightforward interpretations of those foraminifera records. We conclude that at significantly changed climatic boundary conditions compared with the present day, bulk-sediment-related proxies of productivity more consistently record the local upwelling history than foraminifer-based productivity proxies.

Abstract Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a suite of ‘critical’ events in the Earth’s history. The main events include the late Eocene radiolarian extinction, the late Palaeocene benthic foraminiferal extinction associated with the Late Palaeocene Thermal Maximum (LPTM), the Cretaceous-Palaeogene (K-P) extinction, the mid-Maastrichtian event, and several episodes of sapropel deposition documenting the late Cenomanian, late Albian and early Albian warm periods. A compilation of stable isotope results for foraminifera from Leg 171B sites and previously published records shows a series of large-scale cycles in temperature and δ 13 C trends from Albian to late Eocene time. Evolution of δ 18 O gradients between planktic and benthic foraminifera suggests that the North Atlantic evolved from a circulation system similar to the modern Mediterranean during early Albian time to a more open ocean circulation by late Albian-early Cenomanian time. Sea surface temperatures peaked during the mid-Cretaceous climatic optimum from the Albian-Cenomanian boundary to Coniacian time and then show a tendency to fall off toward the cool climates of the mid-Maastrichtian. The Albian-Coniacian period is characterized by light benthic oxygen isotope values showing generally warm deep waters. Lightest benthic oxygen isotopes occurred around the Cenomanian-Turonian boundary, and suggest middle bathyal waters with temperatures up to 20 °C in the North Atlantic. The disappearance of widespread sapropel deposition in Turonian time suggests that sills separating the North Atlantic from the rest of the global ocean were finally breached to sufficient depth to permit ventilation by deep waters flowing in from elsewhere. The Maastrichtian and Palaeogene records show two intervals of large-scale carbon burial and exhumation in the late Maastrichtian-Danian and late Palaeocene-early Eocene. Carbon burial peaked in early Danian time, perhaps in response to the withdrawal of large epicontinental seas from Europe and North America. Much of the succeeding Danian period was spent unroofing previously deposited carbon and repairing the damage to carbon export systems in the deep ocean caused by the K-P mass extinction. The youngest episode of carbon exhumation coincided with the onset of the early Eocene Warm Period and the LPTM, and has been attributed to the tectonic closure of the eastern Tethys and initiation of the Himalayan Orogeny.

Abstract A series of widespread Maastrichtian and Palaeogene reflectors in the western North Atlantic have been interpreted to record episodes of vigorous bottom-water circulation produced by periodic flooding of the deep North Atlantic basins with southern source waters. In general, the ages of these reflectors have been poorly known with estimated ages spanning several million years. New seismic and core data from Ocean Drilling Program Leg 171B tightly constrain the ages of several of the most prominent reflectors and demonstrate that several of them are associated with geologically short-lived events associated with major palaeoclimatic, palaeoceanographic and evolutionary transitions. On Blake Nose in the western North Atlantic, Reflector A c formed shortly after the close of the early Eocene warm period between 48 and 49 Ma. The reflector corresponds to an abrupt inception of vigorous deep-water circulation that winnowed foraminiferal sands at 2000–2500 m water depth and caused mass wasting into the deep basins of the Bermuda Rise. Reflector A c is correlative with a sequence of unconformities present in nearly every part of the global ocean from the shallow shelf to the deep sea, suggesting that this time interval is associated with global change in ocean circulation, including a major sea-level lowstand. The reflector and unconformities are roughly equivalent in age to glacial tillites on the Antarctic Peninsula, suggesting a link to an early phase of southern hemisphere glaciation. Another widespread reflector, A b , has a late Palaeocene to earliest Eocene age on the Bermuda Rise. On Blake Nose, the equivalents of Reflector A b consist of a stack of three closely spaced hiatuses ranging from early late Palaeocene (58.5–60.5 Ma) to latest Palaeocene ( c . 55.5 Ma) age. The youngest of these hiatuses is associated with the carbon isotope excursion at the Late Palaeocene Thermal Maximum (LPTM), when there was a major reorganization of deepwater circulation and dramatic, transient warming of high latitudes. Bottom currents appear to have prevented the widespread deposition of sediments at water depths shallower than c . 2200 m from the LPTM until early mid-Eocene time. Erosion on Blake Nose was produced by a strengthened, southward-flowing deep western boundary current at the same time that a southern source watermass produced extensive erosion on the Bermuda Rise. We suggest that the increased flow of the deep western boundary current reflects a stronger outflow of warm intermediate waters shallower than 2000 m from Tethys. The combination of warmer intermediate waters and erosion along the margin may have helped to trigger slope failure of gas hydrate reservoirs around the North Atlantic margin and set the LPTM—greenhouse feedback system in motion. Reflector A* is correlative with highly deformed Maastrichtian sediments on Blake Nose and Maastrichtian chalk interbedded with red claystone on Bermuda Rise. Seismic and coring evidence from Blake Nose shows that the K–P boundary slumping was associated with the magnitude c . 11–13 Richter Scale earthquake generated by the Chicxulub impact event. The chalk sequence on the Bermuda Rise appears to represent the distal turbidites produced by slumping of the margin. Correlation of the chalk beds with Reflector A* shows that the mass wasting deposits are found over nearly the entire western North Atlantic basin. Apparently, much of the eastern seaboard of North America must have catastrophically failed during the K–P impact event, creating one of the largest submarine landslides on the face of the Earth.

Abstract A transect of three holes drilled across the Blake Nose, western North Atlantic Ocean, retrieved cores of black shale facies related to the Albian Oceanic Anoxic Events (OAE) 1b and 1d. Sedimentary organic matter (SOM) recovered from Ocean Drilling Program Hole 1049A from the eastern end of the transect showed that before black shale facies deposition organic matter preservation was a Type III–IV SOM. Petrography reveals that this SOM is composed mostly of degraded algal debris, amorphous SOM and a minor component of Type III–IV terrestrial SOM, mostly detroinertinite. When black shale facies deposition commenced, the geochemical character of the SOM changed from a relatively oxygen-rich Type III–IV to relatively hydrogen-rich Type II. Petrography, biomarker and organic carbon isotopic data indicate marine and terrestrial SOM sources that do not appear to change during the transition from light-grey calcareous ooze to the black shale facies. Black shale subfacies layers alternate from laminated to homogeneous. Some of the laminated and the poorly laminated to homogeneous layers are organic carbon and hydrogen rich as well, suggesting that at least two SOM depositional processes are influencing the black shale facies. The laminated beds reflect deposition in a low sedimentation rate (6m Ma −1 ) environment with SOM derived mostly from gravity settling from the overlying water into sometimes dysoxic bottom water. The source of this high hydrogen content SOM is problematic because before black shale deposition, the marine SOM supplied to the site is geochemically a Type III–IV. A clue to the source of the H-rich SOM may be the interlayering of relatively homogeneous ooze layers that have a widely variable SOM content and quality. These relatively thick, sometimes subtly graded, sediment layers are thought to be deposited from a Type II SOM-enriched sediment suspension generated by turbidites or direct turbidite deposition.

Abstract Outstandingly well-preserved benthic foraminiferal successions from upper Aptian-lower Albian sediments at Site 1049 (Leg 171, Blake Nose escarpment, western North Atlantic) provide a detailed record of the faunal turnover across Oceanic Anoxic Event lb (OAE lb). Changes in abundance, diversity and species composition reflect strong fluctuations in carbon flux and bottom-water oxygenation. Before the onset of black shale sedimentation, the originally diverse assemblages are replaced by low-diversity associations, dominated by species inferred to be opportunistic phytodetritus feeders and thriving on an enhanced carbon flux to the sea floor. The 46 cm thick laminated black shale horizon corresponding to OAE lb is virtually devoid of benthic foraminifers or contains highly impoverished assemblages, suggesting that intense eutrophication and/or strong stratification triggered near anoxia at the sea floor during black shale deposition. Above the black shale, reoccurrence of the pre-black shale fauna points to relatively rapid bottom-water reoxygenation. The benthic foraminiferal record of Leg 171 provides clear evidence that no major extinctions occurred across OAE lb, as most of the species occurring below the black shale reappear above it. In contrast to other Cretaceous anoxic events, OAE lb may have been more limited in duration or in geographical and water-depth extent, allowing recolonization from adjacent, more hospitable areas, once local conditions improved at the sea floor. Prolific radiation within the suborder Rotaliina and diversification of Textulariina with calcareous cement appear to have started in the Aptian time before OAE lb, and continued into early AIbian time to give rise to many of the modern lineages.

Abstract Detailed biostratigraphic analyses of nine cores from the Atlantic Coastal Plain and two cores from the Blake Nose, western Atlantic Ocean, provide the basis for subdivision and correlation of upper Maastrichtian sediments along a shallow- to deep-water transect. The calcareous nannofossil record from these sites shows distinct differences between the middle to outer neritic Coastal Plain sediments and the lower to upper bathyal Blake Nose sediments. Micula murus , a reliable marker species for low- to mid-latitude sites, is shown herein to respond to differing palaeoenvironmental conditions of nearshore v. open-ocean sites. Its usefulness as a biostratigraphic marker for neritic sediments is called into question. The last appearance datum of Ceratolithoides kamptneri is documented as a reliable biozone marker for latest Maastrichtian time (within CC26b) in this region. The evolutionary radiation and resulting biostratigraphic utility of species of Ceratolithoides, Lithraphidites and Micula is discussed in detail, and their first and last occurrences are tied to magneto-stratigraphic chrons where possible. Ceratolithoides amplector, Ceratolithoides indiensis and Ceratolithoides pricei are shown to be useful, biostratigraphically, in sediments deposited under bathyal conditions. Several species of Lithraphidites ( Lithraphidites? charactozorro, Lithraphidites kennethii and Lithraphidites grossopectinatus ) can be used to further subdivide upper Maastrichtian sediments at both neritic and bathyal localities. The first and last occurrence of Micula praemurus in Zones CC25a and CC26a, respectively, are shown to be useful biostratigraphic datum points.

Abstract Widespread biological, geochemical and sedimentological shifts within the Maastrichtian are well documented, but data are limited for the low-latitude Atlantic. New observations from Ocean Drilling Program (ODP) sites located on Blake Nose in the subtropical western North Atlantic increase information concerning the Maastrichtian history of this critical region. Planktonic δ 18 O results suggest up to 6 °C of local surface water warming (or 4‰ decrease in salinity) at the same time as most of the globe was cooling. Benthic δ 13 O and δ 13 C values of both planktonic and benthic taxa show little if any directional trend or excursions on long time scales; however, planktonic and benthic taxa exhibit strong δ 13 C and δ 18 O cycles (up to 0.8 and 0.6‰, respectively) across a short interval of high-resolution sampling. Other portions of the cores have not yet been studied at high resolution. The last occurrence of inoceramid shell fragments on Blake Nose matches previously documented global patterns, i. e. a mid-Maastrichtian extinction event that occurred later in low latitudes than in high southern latitudes. Models for Maastrichtian change seem to be converging on variation in intermediate to deep water ocean circulation as a unifying process. Blake Nose data are consistent with this conclusion, but demonstrate new regional patterns and emphasize the importance of precise and accurate chronostratigraphic correlation in understanding Maastrichtian change.

Abstract The Cretaceous-Tertiary (K-T) boundary at Blake Nose, in the NW Atlantic, is recorded by a coarse, poorly graded and poorly cemented layer mostly consisting of green spherules that are mainly composed of smectite. Geochemical patterns across the boundary are governed by the source material of the spherule bed and postdepositional processes. The chemical composition and the nature of this bed indicate that it derived from melted target rocks from the Chicxulub impact structure. Ir and other typical extraterrestrial elements do not present significant enrichments, which suggests that the spherule bed material derived from crustal rocks. Ir instead reaches its highest concentration in the burrow-mottled calcareous ooze above the spherule bed, suggesting that it is associated to the finest fraction deposited after the target-rock-derived material. Only the Ni and Co content show slight enrichments within the upper part of the spherule layer, although most of the trace element profiles resulted from diagenetic alteration. During the alteration of glass to smectite, the concentrations of certain trace elements, such as the rare earth elements, were severely changed. In addition, oxygen-poor conditions also led to the remobilization of redox-sensitive elements, which show enhanced concentration at the top or above the spherule bed. Diagenetic remobilization may have also affected the Ir concentration.