Maastrichtian Time Research Articles

The Maastrichtian transgression onto the northwestern flank of the Proto-Oman Mountains: sequences of rudist-bearing beach to open shelf facies

Abstract The Maastrichtian Qahlah and Simsima Formations, the first autochthonous deposits on the obducted Oman ophiolite complex, crop out in a gridle of jebels around the Oman Mountains. Those around the NW flank, between Al Dhayd (Sharjah) and Al Ayn-Buraymi (Dubai-Oman) are documented to illustrate: (1) an exposed regional reference section for the widespread Simsima Formation, at Jebel Faiyah (Sharjah); (2) the marked transgressive nature of the sequence onto the obducted complex; and (3) the rich rudist faunas there, associated with various beach to shelf facies, and their palaeoecological and palaeobiogeographical implications. ‘Basement’ (serpentinites in the north and sedimentary nappes in the south) is overlain by locally developed laterites and the dominantly siliciclastic, marginal continental to marine deposits of the Qahlah Formation, followed, with local erosion and overlap, by the carbonate-dominated Simsima Formation. The latter continues the deepening trend, passing from basal rudist-rich inshore facies to open shelf foraminiferal packstones to wackestones. The whole sequence onlaps eastwards onto the obducted complex. Its truncated top is overlain by Palaeogene slope deposits. In the north (Jebel Faiyah area) the Maastrichtian sequence has an open, relatively high energy aspect. A shelf margin of Simsima Formation rudist limestones briefly developed in the early Maastrichtian around Qarn Murrah. Further transgression to the southeast drowned this and, by ‘mid’-Maastrichtian times, a bouldery beach conglomerate of the Qahlah Formation, with in situ Durania , was forming at Jebel Faiyah itself, along a cliff-backed shoreline with sandy embayments. Over this came tidally influenced rudist-rich facies and foraminiferal limestones of the Simsima Formation. In the south (Jebel Huwayyah area), in contrast, marginal fan-delta gravels and sandstones, of early Maastrichtian age, were followed by more restricted shallow marine silty marls and limestones with Loftusia , rudists and corals, of early to mid-Maastrichian age. These Qahlah deposits were overlapped by a relatively rudist-poor Simsima Formation sequence. The obducted complex was thus strongly emergent at the start of the Maastrichtian, and the Aruma Sea transgressed onto its western flank, as the ophiolite subsided through that stage, forming a relatively open shelf in the north, becoming broader and more restricted further south. The rudist assemblages found on this shelf are similar to those of other open Tethyan shelves in the eastern and central Mediterranean and Middle East.

Late Cretaceous deep-water agglutinated foraminiferal assemblages from the North Atlantic and its marginal seas

The stratigraphic and biogeographic distribution of more than 170 species of deep-water agglutinated benthic foraminifers (DWAF) from the North Atlantic and adjacent marginal seas has been compared with paleoenvironmental data (e.g. paleobathymetry, oxygenation of the bottom waters, amount of terrigenous input and substrate disturbance). Six general types of assemblages, in which deep water agglutinated taxa occur, are defined from the Turonian to Maastrichtian times: 1. High latitude slope assemblages 2. Low to mid latitude slope assemblages 3. Flysch-type assemblages 4. Deep water limestone assemblages (»Scaglia«-type) 5. Abyssal mixed calcareous-agglutinated assemblages 6. Abyssal purely agglutinated assemblages Latitudinal differences in faunal composition are observed, the most important of which is the lack or extreme paucity of calcareous forms in high latitude assemblages. East-to-west differences appear to be of comparatively minor importance. Most DWAF species occur in all studied regions and are thus considered as cosmopolitan. Biostratigraphic turnovers in the taxonomic content of assemblages are observed in the lowermost Turonian, mid- Campanian and in the upper Maastrichtian to lowermost Paleocene. These datum levels correspond to inter-regional and time-constant paleooceanographic events, which probably also affected the deep-water benthic biota. This allows us to use deep-water agglutinated foraminifers for biostratigraphy in the North Atlantic sequences deposited below CCD and to geographically extend the currently used zonal schemes which have been established in the Carpathian and Alpine areas.

Changes in floral diversities, floral turnover rates, and climates in Campanian and Maastrichtian time, North Slope of Alaska

One-hundred-and-ten angiosperm pollen taxa have been found in upper Campanian to Masstrichtian rocks of the Colville River region, North Slope of Alaska. These are the highest paleolatitude Campanian and Maastrichtian floras known from North America. Total angiosperm pollen diversity rose during the Campanian and declined toward the end of the Maastrichtian. However, anemophilous porate pollen of the Betulaceae-Myricaceae-Ulmaceae complex increased gradually in diversity during the late Campanian and Maastrichtian and into the Paleocene. Turnover of angiosperm taxa was active throughout most of late Campanian and Maastrichtian time; rapid turnover affected mainly the taxa of zoophilous herbs, representing an bundant but ecologically subordinate element of the vegetation. Last appearances of pollen taxa during the late Campanian and Maastrichtian probably represented mainly extinctions rather than emigrations; end- Cretaceous angiosperm extinctions in the North American Arctic began well before the Cretaceous-Tertiary boundary event. The last appearances in the late Maastrichtian took place in bursts; they appear to represent stepwise rather than gradual events, which may indicate the existence of pulses of climatic change particularly in late Maastrichtian time.

Background Extinction and Mass Extinction of the Brachiopods from the Chalk of Northwest Europe

The white monotonous chalk from the Upper Cretaceouslowermost Tertiary ofNorthwest Europe spans at least 24 million years and contains a rich, well-preserved fauna of minute brachiopods. Based on taxonomical range charts and timespecific diversities, this fauna is studied in terms of mean species longevity, rate of species origination, and rate of extinction. The brachiopodfauna initially appears to have colonized the chalk sea in mid-Coniacian times. From there on a slow buildup of species diversity reflects a gradual niche diversification of the chalk. Adjustment and evolutionary stability reaches a climax in Late Maastrichtian time. During the Coniacian-Maastrichtian interval, mean rate of extinction is low (0.07 My-1) and mean rate of origination equally low (0.09 My-1). A sudden mass extinction at the Maastrichtian-Danian boundary, however, eliminated more than 70% of the species. The most specialized species, in particular the secondarily free-lying species, apparently became extinct at the boundary. Only six species are known to cross the Maastrichtian-Danian boundary. These are all relatively featureless, non-specialized forms and, together with possible survivors in basin margin areas, gave rise to a rapidly formed, highly diverse Early Danian fauna through adaptive radiation. The Early Danian fauna differs in taxonomic composition from the Maastrichtian fauna both on species as well as on higher taxonomic levels. A dichotomous classification of extinction seems real for the brachiopods from the chalk as their mass extinction at the Maastrichtian-Danian boundaty both quantitatively and qualitatively differ from their Late Cretaceous background extinction.

Upper cretaceous to paleocene depositional sequences and sandstone petrography of southwestern Patagonia (Argentina and Chile)

Upper Cretaceous to Paleocene strata exposed along the Andean margin of Patagonia south of 50°S were deposited in a foreland basin and comprise a complex transition from continental to marine facies. Three unconformity-bounded sequences are observed within the sedimentary succession studied. Sequence 1 (upper Campanian) displays a rapid north-to-south transition from upper delta plain mudstones (Cerro Fortaleza Formation) through lower delta plain and subaqueous delta plain sandstones (La Anita Formation) to delta-slope and basinal turbidites (Alta Vista and Tres Pasos Formations). Sequence 2 (Maastrichtian-Paleocene) was initiated with braided river sediments (La Irene Formation), deposited over a Type II unconformity ( sensu Vail et al., 1984). These rocks are overlain by meandering fluvial sandstones and mudstones (Chorrillo Formation) that interfinger to the south with fossiliferous shallow marine sandstones (upper Cerro Cazador Formation). Sequence 3 (Paleocene) is composed of shallow marine conglomerates and crossbedded sandstones (Calafate and Cerro Dorotea Formations). These rocks are separated by an angular unconformity from subjacent units. Sandstone petrographic analysis indicates the presence of two main petrofacies within the rocks studied. A quartz-rich petrofacies, present to the north of the basin during late Campanian to early Maastrichtian time, was derived from continental crustal block and recycled orogen sources that were possibly exposed to the northwest of the basin. The second petrofacies (volcanic-rich petrofacies) was restricted to the south of the basin during the late Campanian to early Maastrichtian, but covered the entire area during the late Maastrichtian and Paleocene. These sediments were derived from a dissected magmatic arc located to the west of the study area. The presence of abundant tuffaceous intercalations, as well as fresh andesitic fragments, indicates contemporaneous volcanism near the Cretaceous/Tertiary boundary. The marked contrast in observed petrofacies may be a reflection of the major Andean segmentation at 49°S, at the present intersection of the Chile Rise with the South American coast.

The trans-Pacific spread of equatorial shallow-marine benthos in the Cretaceous

Abstract From Aptian to Maastrichtian times, the development of broad tracts of anomalously shallow ocean floor in the Pacific, studded with reef-rimmed seamounts and islands, allowed some Caribbean benthos to spread westwards by larval drift between staging posts in Tethyan/Atlantic waters debouching between the Americas. There is as yet no compelling evidence that the Pacific was completely traversed in this manner during the first and major phase of intra-plate volcanothermal activity in the Aptian-Albian: evidently there still existed a sufficiently wide region of Pacific abyss to the west to serve as a barrier to larval dispersal. However, clear evidence for the ‘landfall’ of Caribbean-derived species on eastern Tethyan shores in Campanian to Maastrichtian times is provided by several examples of disjunct endemics from the two regions. Such taxa include rudist bivalves, gastropods, larger foraminifera, and calcareous algae. This episode coincides with a second, smaller phase of mid-plate volcanothermal activity in the Pacific, which, in conjunction with the relict topography from the earlier phase, evidently furnished a temporarily continuous chain of staging posts for the trans-Pacific spread of the shallow-marine benthos.

The tectonic evolution of the North Celtic Sea and Cardigan Bay basins with special reference to basin inversion

The morphology and structural evolution of the North Celtic Sea Basin (NCSB) and Cardigan Bay Basin (CBB) are, in large part, controlled by reactivation of basement features of Caledonian and possibly Variscan origin. From earliest Triassic until Maastrichtian times sedimentation was almost continuous, initially in a rapidly subsiding rift system and finally in a progressive passive sag phase. At the onset of the Alpine orogeny, both basins experienced spectacular inversion along readily identifiable axes. The inversion takes the form of a compressive reactivation and reversal of the pre-existing growth faults and a broad regional upwarping of the Cretaceous depocentre. The amount of inversion varies depending on the location within the basin but values in excess of 1000 m are possible. By utilising regional seismic data the timing of inversion can be estimated as occurring between Maastrichtian and Eocene times which correlates with the so called Laramide pulse of the Alpine orogeny.

Antarctic marine temperatures: Late Campanian through Early Paleocene

An oxygen isotope paleotemperature study of benthic foraminifera from the upper Campanian through lower Paleocene section at Seymour Island, near the coast of Antarctica, was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation. The isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that Campanian through Paleocene high‐latitude shelf waters near Antarctica had temperatures between approximately 4.5° and 10.5°C. Temperatures during early and middle Maastrichtian time were slightly higher than those of either the late Campanian or late Maastrichtian. The inference of temperate climatic conditions in Antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera, as well as with published conclusions based upon paleobotanical evidence. The Maastrichtian and Campanian water temperatures at Seymour Island are similar to those inferred from published isotope ratios of Pacific Late Cretaceous benthic foraminifera from low latitudes, indicating that Campanian through early Paleocene deep ocean waters, at least in the Pacific and perhaps elsewhere as well, could have formed by sinking of surface waters in polar regions.

The sediments of Wadi Qena (Eastern Desert, Egypt)

The first deposition of near-shore sandstones on basement rock in the northern Wadi Qena area occurred during Lower Carboniferous times. Paleozoic deposits are overlain by similar sandstones of Cretaceous age with a large but inconspicuous hiatus between them representing erosion and non-deposition. A Cenomanian transgression inundated sandstones in the north as well as basement rock in the south. The Cenomanian and Turonian sea deposited marine and near-shore material in the Wadi Qena area, and only to the south of it were fluviatile beds laid down. The extant Red Sea Hills, at that time, represented a high and formed a peninsula extending in northerly direction into the shelf sea of the Tethys ocean. The sea withdrew in or after Coniacian times and the following erosion removed almost all Coniacian marine deposits. During Campanian times, the sea returned and also flooded the Red Sea Hill peninsula. Phosphoritic marls, at times of unrest, were redeposited as phosphorite sands in the south. Carbonate deposition followed, ending in Maastrichtian times. An erosional phase during the Cretaceous-Tertiary transition removed most of these chalks and limestones from the Wadi Qena area, and Paleocene and Eocene seas deposited limestone and mmarly chalk before a final regression marked the closure of the Tethys ocean.

Late Maastrichtian paleoenvironments and dinosaur biogeography in the western interior of North America

During Late Maastrichtian time, three major sedimentary depositional provinces existed in continental environments of the western interior region of North America. The sediments accumulated within these provinces are herein termed the piedmont, alluvial plain, and coastal lowland lithosomes. These sedimentary lithosomes correspond to broad paleoenvironmental and paleophysiographic provinces that resulted from the westward shift of the Pacific coast, the bisection and retreat of the interior epeiric sea, and the development of an intermontane basin system during Maastrichtian time. These dramatic physiographic changes created environments markedly different from those that had prevailed during most of the Late Cretaceous, when western North America consisted of a narrow peninsula flanked on the east by a remarkably stable and monotonous coastal plain. In conjunction with these physiographic and environmental changes, three diverse dinosaur-dominated continental vertebrate faunas arose, herein termed the Leptoceratops, Triceratops, and Alamosaurus faunas. Each was peculiar to a sedimentary/environmental province and among them there was little interchange. The separation of these faunas indicates that the dinosaur-dominated communities had adapted to changing or “deteriorating” environmental conditions at the close of Cretaceous time. The Alamosaurus fauna characterized markedly seasonal, semi-arid, environments of the intermontane basins south of about 35°N latitude. The Triceratops fauna inhabited humid coastal floodplains and swamps bordering the retreating northern embayment of the epeiric sea, north of latitude 35°N. The Leptoceratops fauna inhabited cool piedmont environments flanking the mountainous Cordilleran Overthrust Belt north of 35°N latitude. Recognition of this biogeographic zonation indicates that the Triceratops biozone is only of local utility, and that the biostratigraphy of Upper Cretaceous continental deposits in North America must reflect the provincialism now recognized. Moreover, the evident adaptability of dinosaur faunas to varied and changing environmental conditions suggests that climatic change alone may not have been responsible for their demise.

The transition from a passive margin to an Upper Cretaceous foreland basin related to ophiolite emplacement in the Oman Mountains

The Upper Cretaceous Muti Formation in the Oman Mountains exemplifies the transition from a passive continental margin to a foreland basin related to thrusting and ophiolite emplacement. Field data largely substantiate theoretical models that depict a flexural forebulge moving continentward of an advancing thrust-load, followed by flexural downwarping and collapse as nappes override a continental margin. Five units of the Upper Cretaceous (? late Cenomanian–late Campanian) Muti Formation depositionally, or structurally, overlie Mesozoic passive-margin paleoenvironments ranging from abyssal plain to continental rise, slope, and carbonate platform. The Arabian continental margin and Tethys ocean rifted in Permian and Triassic time, giving rise to a mature passive margin in the Jurassic and Lower Cretaceous. At the end of Lower Cretaceous time, northeastward subduction apparently began, and the Semail ophiolite formed, probably in a marginal basin setting. As subduction continued, the trench migrated toward the Arabian continent preceded by a flexural fore-bulge that soon reached the adjacent Arabian continent (Cenomanian-Turonian; ca. 90−88.5 Ma), halting deposition regionally (“Wasia-Aruma break”). Flexural uplift was greatest near the shelf edge, with removal of as much as 600 m of the platform edge succession, and redeposition onto the base of slope as slump sheets, debris flows, and lithoclastic turbidites. As the advancing thrust-load impinged on the edge of the Tethys ocean, the crust was downflexed (late Coniacian–Campanian time; 88.5−73 Ma), creating a foredeep that partly filled with terrigenous clastics, olistostromes, detached blocks of rift-related carbonate build-ups, seamount volcanics and continental basement rocks. The basin depocenter migrated inboard with time, collapsing, in turn, Mesozoic abyssal plain, base of slope, and slope settings to establish a foreland basin on the foundered shelf. Terrigenous sediments accumulated in deep water below the carbonate compensation depth (CCD), together with lithoclastic limestones and detached blocks shed from submarine fault scarps. Successive foreland basins were overridden by the advancing nappes. During the later stages of thrusting onto the continent, Mesozoic sediment decollement nappes were bulldozed ahead of the Semail nappe, ploughing into the existing foreland basin. In conjunction with the final emplacement of the Semail ophiolite, the foreland basin migrated to its most continentward location and filled with clastics derived by subaerial erosion of the Semail nappe and other units. The nappes were submerged again in late Maastrichtian time, possibly in response to flexural relaxation, followed by re-establishment of a carbonate platform. Further compression and thrusting in the Paleocene-Eocene gave rise to a successor foreland basin adjacent to the northern Oman Mountains front.

Cretaceous paleogeography of southern South America

During Berriasian-Hauterivian times the Andean regions north of 38°S and south of 42°S were occupied by two magmatic island arcs and two back-arc marine basins, the Andean and Austral Basins. At the same time the Chubut Basin of central Patagonia was being filled with continental sediments. In northern Argentina and Bolivia, the Aimara Basin began to develop with deposition of continental sediments intercalated with basaltic rocks. In northeastern Argentina, Paraguay, Uruguay and southern Brazil, a series of basins formed in Precambrian-Paleozoic basement were the site of continental sedimentation and eruption of basic flows. In Barremian-Cenomanian times the uplift of the Cordillera Principal of Argentina and Chile began and a general regression occurred in the Andean and Austral Basins. Continental sedimentation prevailed in the Chubut Basin of central Patagonia, as well as in all other basins of central-northern, and eastern Argentina and southern Brazil. In Bolivia a shallow marine transgression occurred during Cenomanian time. And in the Santos Basin of southern Brazil a proto-oceanic stage is represented by Aptian evaporites. In (Turonian-Coniacian) Santonian-Campanian times most of the Andean area was uplifted and thick volcanic and volcanoclastic sequences were accumulated in a series of restricted continental basins along the Andes of central and northern Chile. In the easternmost areas, south of 33°S, red continental sediments were deposited. In the Austral Basin marine sedimentation was restricted to the southern part. Most of the Parana Basin was emergent, although in the northern areas continental sedimentation continued. In northern Argentina and Bolivia continental sediments with interbedded basalts and shallow marine deposits were accumulated. The Atlantic basins of southern Brazil were characterized by marine sedimentation, and the Salado Basin was the site of continental deposition. In Maastrichtian time sedimentation was discontinued in the continental basins of west-central Argentina and central and northern Chile, although volcanism was still active. The marine area of the Austral Basin became more restricted. A large region of northern Patagonia, northeastern Argentina and Bolivia were covered by a shallow sea, and some restricted marine basins were developed on the coast of central Chile. Marine sedimentation was also continuous in the Atlantic basins of southern Brazil and central Argentina. Continental deposition was restricted to central Patagonia and the intracratonic Parana Basin of southern Brazil. There was a correlation between diastrophism, magmatic activity and global cycles of sea level changes. Contemporary regression existed in areas, such as the Andean Basin, where tectonic vertical movements were greater than eustatic changes of sea level. The Cretaceous flora is mostly known from Patagonia. Lower Cretaceous invertebrates are mostly known from west-central Argentina, whereas Upper Cretaceous invertebrates are almost exclusively known from southern Patagonia. Vertebrates are better known from continental Upper Cretaceous strata of central-northern Patagonia and southern Brazil. The Cretaceous climate north of 43°S was characterized by warm and extremely arid conditions. South of this arid belt was an area with temperate and humid climate.

Les faunes de Rudistes du crétacé supérieur charentais du chantier de l'autoroute “l'Aquitaine”

Along the Aquitaine motorway of Charente, while the strata of Cenomanian and Turonian age are typified by Rudist faunas, the Senonian fauna is, on the whole, poorly represented. Sediments of Coniacian and Santonian age have yielded no rudists while the uppermost part of the succession (Late Campanian to Maastrichtian times?) has supplied a non-diagnostic fauna.

Evaporite diapirs in the La Popa basin, Nuevo León, Mexico

Reconnaissance mapping and stratigraphic work in the La Popa basin of Nuevo Leon, northern Mexico, has revealed two large structural features with cores of gypsum and anhydrite at the surface. These features are interpreted to be the surface expression of evaporite diapirs. They are exposed in folded sedimentary rocks belonging to the Potrerillos Formation of the Difunta Group of Maastrichtian age (Late Cretaceous). Sandstone units within the Potrerillos Formation pinch out toward the piercement features. Carbonate lentils composed of rudistid reefs and associated carbonate clastics flank the features and pinch out away from the features into marine shale members of the Potrerillos Formation. Most carbonate lentils occur in the immediate vicinity of the evaporite features and are interpreted to be genetically related to the diapirs. Syndiapiric sedimentary-facies patterns can be documented over 4,000 vertical feet (1,200 m) of section within the Potrerillos Formation. The large vertical extent of facies peculiarities near the piercement features indicates that the features were active for an extended period corresponding to at least two regressive-transgressive cycles during Maastrichtian time. A radial drainage pattern away from the northern feature indicates that the features are probably active today. A limestone inclusion from within one of the features has been dated as Kimmeridgian in age (Zuloaga or Smackover equivalent) and suggests that the evaporites are probably derived from the Jurassic Minas Viejas Formation. It is not known at present whether salt underlies the surface crust of gypsum and anhydrite. At the time that the first syndiapiric sediments of the Potrerillos Formation were deposited, the Minas Viejas Formation was buried at an estimated depth of 17,000 ft (5,200 m). The thick pre-Laramide cover, the pre-Laramide age of at least some of the syndiapiric sedimentary features, and the location of stocks away from major anticlines indicate that the emplacement of the diapirs is not related to Laramide compression. Geostatic loading is considered to be the most important mechanism for emplacement of the domes.

The unusual cenomanian oyster Pycnodonte biauriculatum

From Albian to Maastrichtian times oysters belonging to the genus Pycnodonte were a major component of the bivalve fauna. In marly and sandy Cenomanian facies several oysters occurred in banks; one of them is Pycnodonte (P.) biauriculatum which is distributed from the Iberian Peninsula to Central Asia. In western France, from Maine to North Aquitaine it formed oysterbanks' as monospecific communities. The species was particularly well adapted to live on a soft, probably waterlogged, substrate. Three ontogenetical stages were recognised: they were induced by the morphological adaptations required to keep the commissure of the shell above the oozy substrate and hence maintain the normal biological functions. Despite an exceptionally successful development P. (P.) biauriculatum is a very short-lived species: between 44,000 and 125,000 years. This extraordinary but brief success can be explained by the important Late Cenomanian transgressions.

The Sistan suture zone of eastern Iran

A deformed accretionary prism and a flanking forearc basin extending from Birjand southeast to Zahedan, Iran, record the destruction of an arm of the Neo-Tethys during Senonian-Paleocene time and consequent collision of the Afghan and Lut eratonic blocks. The accretionary prism at 32 °N is subdivided into two northwest-trending en echelon belts termed the “Ratuk” and “Neh” complexes, respectively. On the east, the Ratuk complex is characterized by ophiolitic block-against-block or serpentinite-matrix melange and large fault slivers of epidote blueschist tectonite. The Ratuk complex was built prior to Maastrichtian time. The Neh complex to the southwest is Senonian to Eocene in age and includes, in addition to ophiolitic melange, weakly metamorphosed marine sedimentary rock exposed in extensive belts bounded by steeply dipping faults. The Sefidabeh forearc basin deposits onlap both the Neh and Ratuk complexes and the southwest margin of the Afghan block. They make up as much as 8 km of Cenomanian to Eocene terrigenous elastics and carbonates that display a complex but coherent stratigraphy. Facies relations demonstrate the uplift and subaerial exposure of the Ratuk structural high, followed by its subsidence contemporaneous with construction of the Neh complex and calc-alkalic volcanism on the northeast (inner) side of the basin. The accretionary prism-forearc basin polarity, the structural vergence and general younging of the accretionary prism to the southwest, as well as the position of the (relatively) high P T metamorphic rock on the inner side of the prism are consistent with northeast-dipping subduction. Widespread emergence of the entire belt and the initiation of folding of the Sefidabeh basin deposits during middle Eocene are interpreted to be consequences of the entry of the Lut block into the subduction zone. Continued convergence of the continental blocks is expressed by a regional system of folds and transcurrent faults corresponding to east-northeast compression. These structures are buried by mildly deformed Miocene volcanic rocks. Extensive post-Miocene right-slip faulting is inferred to be an effect of Miocene “terminal” collision of Arabia and Eurasia.

Late cretaceous history of eolian deposition in the mid-pacific mountains, central North Pacific Ocean

Eolian dust preserved in deep-sea sediment can provide a direct historical record of global atmospheric circulation. Data from a reasonably complete Upper Cretaceous section of pelagic sediments recovered at DSDP Site 463 in the central North Pacific provides a good record of eolian activity during the time period between about 112 and 66 m.y. ago. We have isolated the eolian component from these sediments, determined its mass accumulation rate and combined these data with the mineralogy of the inorganic fraction determined by others to construct a record of eolian deposition. Volcanic input is significant during Aptian-Albian and Maastrichtian times, otherwise continentally derived minerals dominate. Mass accumulation rates of the continental eolian component range from over 500 mg/cm 2/10 3yr during the late Albian to a low of 5 mg/cm 2/10 3yr during Coniacian time. (For comparison, the upper Miocene to Pleistocene rate averages about 20 mg/cm 2/10 3yr.) The temporal pattern of Late Cretaceous eolian accumulation of Site 463 generally matches known changes in sea level, suggesting that source availability is the dominant control of eolian sedimentation during that time.

Biogeography of the Saharan Gretaceous and Paleocene epicontinental transgressions

The first trans-Saharan epicontinental transgression began in the Late Cenomanian and peaked in the Early Turonian. The sea entered through rifts (Nigeria) and subsiding areas (north Africa) and, at maximum extent, spilled out onto stable craton. The central Sahara was land in late Early Turonian time; the sea seems to have remained in the central part of the Benue rift, to sally forth again during the minor Coniacian transgressive pulse. The Coniacian transgression went no further than eastern and central Niger Republic. For a short time during the Cenomanian-Turonian link-up between the Tethys and the South Atlantic, some organisms (mainly ammonites and pelecypods) passed across the Sahara. The Coniacian marine deposits of eastern Niger contain several elements typical of the Mungo River Formation of Cameroun, and coastal Nigeria. These faunistic indications imply that the topographical obstacle formed by the Zambuk ridge of northeastern Nigeria was swamped at maximum transgression. A third, very extensive epicontinental transgression began in latest Campanian time and reached its acme in the Early Maastrichtian. In the central Sahara, at least, there was a retreat of the sea in later Maastrichtian times. A final transgression peaked during the Paleocene, after which the sea withdrew permanently from the northwest African hinterland. The same marine ostracod associations occur in the Paleocene of coastal Nigeria, the Sokoto embayment, Mali and Libya, thus providing strong evidence of a marine connexion, albeit brief, between the South Atlantic and the Tethys, despite the lack of outcrop evidence in the crucial Niger valley region.

Oxygen isotopic evidence for the depth stratification of tertiary and cretaceous planktic foraminifera

Oxygen isotope analyses of Tertiary and Cretaceous planktic foraminifera indicate that species have been stratified with respect to depth in the water column at least since Albian time. There is a relationship between morphology and depth habitat. Species with globigerine morphology have consistently occupied shallower depths than have species with globorotalid morphology. Biserially arranged species occupied both shallow and deep levels in the water column. On the average, it appears that ancient species with shallow habitats have been more susceptible to dissolution and have been preserved less well than species dwelling in deeper habitats. This relationship is similar to that observed for Recent planktic foraminifera. Comparison of carbon isotope ratios of adult and juvenile forms indicates that either the source of the carbon found in the shell or the carbon isotopic fractionations which occur during calcite secretion change during the development of individual foraminifera. The carbon isotopic ratios do not provide a reliable means for reconstructing the depth habitats of ancient species. Temperature-depth profiles for tropical Tertiary oceans have been reconstructed from the isotopic temperatures of planktic and benthic foraminifera. The vertical thermal structure of Oligocene oceans resembled that of modern oceans most closely. Those of Paleocene and Maastrichtian times differed most from that of modern oceans.

Eustacy during the Cretaceous: Its implications and importance

Evidence for eustatic fluctuations in mean sea level during the Cretaceous is provided, with the dating of thirteen transgressive episodes between late Valanginian and early Maastrichtian time, separated by intervals of eustatic regression. The assumption of a direct genetic link between mean sea level and volumetric changes in the mid-oceanic ridge systems would, in turn, imply that plate motion was strongly episodic, with individual movements probably having a time span of the order of one to two million years, and being separated by several million years of subdued plate motion. The concept of marine cycles of strongly diachronous transgression is rejected and episodes of eustatic transgression are considered to be short-lived, rarely extending beyond two million years duration and, in general, probably much less. The relationship between the major Cretaceous transgressions and regressions and contemporary magnetic polarity reversals, orogeny and continental volcanism are discussed. An interpretation is also presented of the effects of eustatic fluctuations on Cretaceous oceanic sedimentation and the input of nutrients into the marine environment, as well as on palaeoclimate and such biological phenomena as species diversification, population “explosions”, mass faunal extinctions and evolutionary theory.