Late Santonian Research Articles

Archamamelis, hamamelidalean flowers from the Upper Cretaceous of Sweden

Lignite fossil flowers (including pollen) and isolated stamens of probable hamamelidalean (possible hamamelidaceous) affinities from the upper Cretaceous (Late Santonian or Early Campanian) of Sweden are described. The flowers are 6–7-merous with probably a double perianth, one whorl of stamens and (2-?)3 carpels. The stamens are disporangiate; each theca opens by a valve towards the centre of the flower. Pollen is tricolpate, tectate-columellate and reticulate; the endexine is lamellated in the apertural region. The gynoecium has free styles and a syncarpous ovary. In the one flower that was serially sectioned the ovary is either non-functional or development of the few (2?) ovules is retarded.

The evolution of the Oman Mountains Foreland Basin

Abstract The Late Cretaceous fill of the Oman Mountains foredeep is subdivided into four sub-sequences using seismic stratigraphic principles based on seismic, well and outcrop data. Sub-sequence FD-a (Late Coniacian to Early Santonian) was overriden by the Hawasina allochthon on the sea bed of the foredeep. FD-b (Early to Late Santonian) was deposited during thrusting and slices of foredeep sediment were tectonically accreted onto the allochthon during the final stages of thrusting. FD-c and FD-d (Late Santonian to Late Coniacian) were deposited after the emplacement of the allochthon into the foredeep. Subsidence curves for the foredeep area show that an emergent peripheral bulge bounded the cratonic side of the foredeep throughout the Late Cretaceous. There is no evidence that the forebulge migrated with time ahead of the advancing Hawasina thrust sheets. Instead the bulge remained in situ while the basin narrowed during thrusting. During the Maastrichtian, after infill of the foredeep, the Oman Mountains area subsided beneath sea level. Clastic supply from the drowned hinterland ceased and carbonate deposition followed. The main Oman Mountain building episode was during the Late Miocene when continent-continent collision occurred in the Zagros Mountains.

Facies Stratigraphy and Relative Sea-Level History--Upper Cretaceous Eutaw Formation, Central and Eastern Alabama: ABSTRACT

ABSTRACT The Eutaw Formation (130 to 400 ft thick) rests disconformably on incised valleys (a type 1 unconformity) occuring at the top of the underlying non-marine Tuscaloosa Formation (Cenomanian-early Turonian). The Eutaw is topped by an erosional discontinuity which has slight relief and a discontinuous conglomeratic lag. In the outcrop and shallow subsurface, the Eutaw Formation has four main paralic and nearshore facies which are arranged in two discontinuity-bounded genetic packages of facies (or parasequences) both of which developed in a single eustatic cycle. The Eutaw facies are: carbonaceous and ostried-rich clayey silts (back barrier); planar, trough, and low-angle cross-bedded medium-fine sands (barrier island); fossiliferous bioturbated fine sands (lower shoreface); and calcareous clays, silts, and sands (inner shelf). The intraformational facies discontinuity is likely a parasequence boundary developed at maximum eustatic high stand in latest Santonian.

Influence of tectonics and palaeoenvironment on late cretaceous clay sedimentation in the upper benue trough, Nigeria

AbstractThe Late Cretaceous sedimentary sequence in the Upper Benue Trough consists of seven formations. Outcrop samples from the type localities of these units were analysed by X‐ray diffraction for their day mineral content. The composition and distribution of the clay minerals are influenced by tectonics, relief and water depth. Three main depositional phases are recognizable on the basis of clay mineral assemblages, two of which are associated with tectonic movements. The first phase, characterized by the presence of chlorite, illite, kaolinite and mixed‐layer clays is common to Albian‐Cenomanian sediments. This phase is succeeded by mixed‐layer clays and smectite‐rich, Turonian‐Early Santonian sediments.The re‐occurrence of chlorite and illite in association with kaolinite and mixed‐layer clays in the Post‐Santonian sediments constitutes the third depositional phase.These clay mineral assemblages are indicative of two periods of tectonism (Albian and Late Santonian) and an intervening Turonian‐Early Santonian period of quiescence in the Upper Benue Trough.

Upper cretaceous (Santonian-Campanian) ammonite and inoceramid biostratigraphy of the Chico Formation, California

Outcrops of the Upper Cretaceous (Coniacian-Campanian) Chico Formation, exposed along the east flank of California's northern Great Valley, have yielded a highly diverse, well-preserved molluscan fauna. Previously uncollected deposits, as well as classic localities, have been stratigraphically collected to determine the Santonian-Campanian succession of important ammonites and inoceramid bivalves. Five megafossil zones are readily identifed in outcrops of the Chico Formation. These are, in ascending stratigraphic order, the zones of Hyphantoceras venustum, Baculites capensis, Bostrychoceras elongatum, Inoceramus schmidti and Baculites chicoensis. Two of the zones, Bostrychoceras elongatum and I. schmidti, are missing at the type locality of the Chico Formation because of a stratigraphic disconformity. As a result, previous conceptions about the ranges of some important ammonites and inoceramids in California are in error. Lowest exposures of the H. venustum Zone in the Chico Formation are probably latestConiacian in age. Recent palaeomagnetic sampling of Cretaceous strata of the Great Valley (Ward et al., 1983) has confirmed that the Baculites chicoensis Zone is indicative of the lowest Campanian. The age of the I. schmidti Zone in California is therefore latest Santonian. This molluscan sequence enables precise correlation of Chico strata with other Upper Cretaceous outcrop in the Great Valley; in addition, lowermost deposits of the Upper Cretaceous Nanaimo Group of British Columbia can now be firmly correlated with California strata.

The Austin Chalk-Taylor Clay succession in Texas and the Santonian-Campanian boundary

Re-evaluation of samples from several Texas localities over the Austin Chalk-Taylor Clay boundary for planktic Foraminifera, and comparison with recent work on European and North African successions confirms the general correlation of the Texan formations with the European Stage succession. The sedimentary hiatus indicated by Pessagno (1967) does not appear to be present: the Late Santonian-Early Campanian zonal marker Globigerinita elevata (Brotzen) occurs in the Lower Taylor Clay associated with late representatives of Marginotruncana. The Lower Taylor Clay may belong to the Late Santonian in some localities.

Relation of Unconformities, Tectonics, and Sea Level Changes, Cretaceous of Western Interior, United States and Canada: ABSTRACT

Intrabasin tectonics have influenced patterns of deposition and geographic distribution of major unconformities within the Cretaceous of the Western Interior. Eight major regional to subregional unconformities have been identified. Five of these have been related by previous workers to sea level changes and to well-documented regressive-transgressive cycles. New studies of recurrent movement on basement-controlled fault blocks suggest a synchronous relation among fault block movement, sea level changes, and unconformities. Which fault blocks moved on the basin floor, and when, can be explained by stress fields generated by direction and rates of plate motion. Unconformities associated with north-northwest fault trends are caused by more westerly movement, and those associated with east-northeast trends by more northerly plate motion. Expansion of the Gulf of Mexico, the Atlantic Ocean, or the Arctic Ocean during these plate motions may account for associated sea level changes. The 81 to 82 m.y. unconformity and shoreline regression in the Western Interior and synchronous volcanic events on the northern margin of the Gulf of Mexico illustr te the relations. Uncertainty exists in dating many of the unconformities. However, by use of the time scale of Obradovich and Cobban, the approximate dates for unconformities are estimated as follows: (1) late Neocomian to early Aptain, >100 m.y.; (2) late Aptian-early Albian, 100 m.y. ±; (3) Albian, 96 to 97 m.y.; (4) early Cenomanian, 93 m.y. ±; (5) Turonian to early Coniacian, 87 to 88 m.y.; (6) late Coniacian-early Santonian, 81 to 82 m.y.; (7) late Campanian 71 to 74 m.y.; and (8) late Maestrichtian, 64 to 69 m.y. Several billion barrels of oil have been found in sandstones associated with unconformities in the Cretaceous. Future stratigraphic trap exploration will be guided by a knowledge of tectonic influence on sedimentation during sea level changes and how these factors controlled distribution of source rock, migration patterns, reservoir rock, and seal. End_of_Article - Last_Page 1006------------

Sedimentation cycles in the cretaceous and cenozoic of Western Australia

There have been eight major marine transgressions on the western margin of Australia since the Late Santonian. These are equated with sea-level highs which are believed to be worldwide. Of the several mechanisms for sea-level control which have been proposed, the one favoured here is that of variation in the rate of sea-floor spreading. Such variation does not need to be world wide itself to have a worldwide effect. The sediments formed during the sedimentation cycles resulting from the transgressions are unconformity-bounded stratigraphie units, the units of seismic stratigraphy. The concept of worldwide sea-level highs may be of considerable value in interregional correlation and has important consequences for the evolution of shallow water marine organisms and those immediately above sea level.

Ophiolite and island-arc volcanism in Costa Rica

The Pacific margin of Costa Rica is a very deformed basement terrane of ophiolite composed of pillowed and massive basalt, mafic and ultramafic plutonic rocks, volcanic breccia, hyaloclastite, radiolarian chert, and limestone. The ophiolite underwent changes through burial metamorphism after subduction of the Cocos plate under the southwestern margin of the Caribbean plate. In some areas the ophiolite is a melange. While the age of the emplacement of the ophiolite in northwestern Costa Rica is late Santonian to early Campanian, the period of accumulation of the ophiolite seems to be very long, possibly extending from middle Tithonian to late Santonian. New age determinations based on foraminifera and radiolaria support the previous dating. A relative scarcity of turbidite in the ophiolite of Costa Rica, compared to other similar terranes of the Pacific margin, has been associated with the intra-oceanic origin of the southern Central American arc. The island-arc suite clastic rocks first unconformably covered the ophiolite in Costa Rica in early Campanian time. Their origin is closely related to the intrusive and volcanic activity of a plutonic-volcanic arc located between South and North America since early Campanian time. The clastic rocks of the island-arc suite are low-porosity volcanogenic types. Limestone has accumulated from Cretaceous time to the present, in some areas forming porous biohermal bodies. Vertical tectonics originated marginal- and intra-arc sedimentary basins intermittently throughout the evolution of the arc. A fourfold geotectonic division of Costa Rica is proposed.

Sea-floor spreading and the early opening of the North Atlantic

We have examined available magnetic and gravity data bearing on the initiation of sea-floor spreading in the North Atlantic between Ireland and Newfoundland. The change in character of the magnetic field on the continental margin on either side of the Atlantic from a landward magnetic quiet zone to a seaward “noisy”, magnetic signature is postulated to be related to a change from continental to oceanic crust. Sea-floor spreading between Ireland and Newfoundland was initiated during the long normal geomagnetic polarity interval in the Late Cretaceous. Rockall Trough may have opened at this time. At the end of the normal polarity interval (Late Santonian) the ridge axis jumped westward to bypass Rockall Trough and the related offset initiated the Charlie Gibbs fracture zone. A reconstruction is presented for the relative position between North America and Europe prior to the initiation of sea-floor spreading in the Late Cretaceous.