The composite California Coast Range ophiolite consists of remnants of Middle Jurassic oceanic lithosphere, a Late Jurassic deep-sea volcanopelagic sediment cover, and Late Jurassic intrusive sheets that invade the ophiolite and volcano-pelagic succession. The dismembered Middle Jurassic Coast Range ophiolite remnants (161–168 Ma) were parts of the axial sequence of an oceanic spreading center that consisted of basaltic submarine lava, subvolcanic intrusive sheets, and gabbro, and coeval but off-axis upper lava, dunite-wehrlite mantle transition zone, peridotite restite, and dikes rooted in the mantle transition zone that fed the upper lava. Hydrothermal metamorphism overprints the lavas, subvolcanic sheets, and part of the gabbro. The nearly complete magmatic pseudostratigraphy with minimal syngenetic internal deformation accords with a “hot” thermal structure and robust magma budget, indicative of fast spreading. Upper Jurassic volcanopelagic strata composed of tuffaceous radiolarian mud-stone and chert (volcanopelagic distal facies) overlie the ophiolite lava disconformably and grade up locally into arc-derived deep-marine volcaniclastics (volcanopelagic proximal facies). An ophiolitic breccia unit at northern Coast Range ophiolite localities caps shallow to deep levels of fault-disrupted Middle Jurassic oceanic crust. The Late Jurassic igneous rocks (ca. 152–144 Ma) are mafic to felsic subvolcanic intrusive sheets that invade the Middle Jurassic ophiolite, its Late Jurassic volcanopelagic cover, and locally the ophiolitic breccia unit. Hydrothermal metamorphism of volcanopelagic beds and underlying ophiolite meta-igneous rocks accompanied the Late Jurassic deep-sea magmatic events. The Middle Jurassic ophiolite formed at a spreading ocean ridge (inferred from its Jurassic plate stratigraphy). Intralava sediment and thin volcanopelagic strata atop the Coast Range ophiolite lava record an 11–16 m.y. progression from an open-ocean setting to the distant submarine apron of an active volcanic arc, i.e., the sediments accumulated upon oceanic lithosphere being drawn progressively closer to a subduction zone in front of an ocean-facing arc. Trace-element signatures of Coast Range ophiolite lavas that purportedly link ocean-crust formation to a suprasubduction-zone setting were influenced also by processes controlled by upper-mantle dynamics, especially the mode and depth of melt extraction. The polygenetic geochemical evidence does not decisively determine tectonic setting. Paleomagnetic and biostratigraphic evidence constrains the paleolatitudes of Coast Range ophiolite magmatism and volcanopelagic sedimentation. Primary remanent magnetism in ophiolite lavas at Point Sal and Llanada Coast Range ophiolite remnants records eruption within a few degrees of the Middle Jurassic paleoequator. The volcanopelagic succession at Coast Range ophiolite remnants consistently shows upward progression from Central Tethyan to Southern Boreal radiolarian assemblages, recording Late Jurassic northward plate motion from the warm-water paleo-equatorial realm. Northward seafloor spreading was interrupted by local Late Jurassic rift propagation through the Middle Jurassic oceanic lithosphere. Coast Range ophiolite crust with volcanopelagic soft-sediment cover that lay in the path of propagating rifts hosted rifting-related magmatic intrusions and hydrothermal metamorphism. The advancing broad deformation zone between propagating and failing rifts left paths of pervasive crustal deformation marked now by fault-disrupted ophiolite covered by depression-filling ophiolitic breccias, found at northern Coast Range ophiolite remnants. Coast Range ophiolite lithosphere that lay outside the propagating and failed rift zones lacks those features. The rift-related magmatism and crustal deformation took place at ephemeral spreading-center offsets along a transform fault. Late Jurassic seafloor spreading carried Middle Jurassic oceanic lithosphere northeastward toward a subduction zone in front of the Middle to Late Jurassic arc that fringed southwestern North America. Termination of oblique subduction during the late Kimmeridgian, replaced by dextral transform faulting, left a Coast Range ophiolite plate segment stranded in front (west) of the trench. The trench was then filled and locally bridged by the arc’s submarine sediment apron by the latest Jurassic, allowing coarse volcaniclastic (proximal volcanopelagic) deposits to lap onto earlier, plate-transported tuffaceous radiolarian chert (distal volcanopelagic) deposits. Deep-marine terrigenous muds and sands from southwestern Cordilleran sources then buried the stranded Coast Range ophiolite–volcanopelagic–ophiolitic breccia unit oceanic crust during latest Jurassic northward dextral displacement, which proceeded offshore. Those basal Great Valley Group strata record lower continental-slope and basin-plain marine sedimentation on Jurassic oceanic basement, i.e., the Coast Range ophiolite and adjacent Franciscan oceanic lithosphere (Coast Range serpentinite belt). Forearc basin deposition did not begin until the mid–Early Cretaceous, when the inception of outboard Franciscan subduction lifted and tilted the Coast Range ophiolite–volcanopelagic–ophiolitic breccia unit–basal Great Valley Group succession and Coast Range serpentinite belt to form a basin-bounding forearc ridge. Thereafter, Cretaceous Franciscan subduction and accretionary wedge growth operated in front (west) of the submerged ridge, and Great Valley Group forearc basin terrigenous sediments accumulated behind it.

La Désirade Island in the Cenozoic Lesser Antilles forearc region exposes a pre-Tertiary complex of oceanic volcanic, plutonic, and dike rocks. Previous work has established the stratigraphy and structure of the La Désirade igneous complex and also its late Mesozoic age. Dredge hauls from the nearby submerged Désirade fault scarp consist of similar volcanic and dike rocks plus greenstone, diabase, and gabbro. The composite section from island and submarine escarpment resembles upper oceanic crust but of controversial origin, original tectonic setting, and geodynamic significance. More precise ages for the La Désirade igneous complex and its individual members provide important constraints on proposed tectonic models. We reanalyzed Radio-laria from intralava sediments in basaltic pillow lava and zircon from trondhjemite to pinpoint their age. The radiolarian assemblage correlates with those of formations in east-central and west-central Mexico. The Mexican radiolarian faunas are chronostratigraphically calibrated by co-occurring ammonites and Buchia. Abundant Mexican biostratigraphic and chronostratigraphic data (ammonites, Radiolaria, and Buchia) constrain the composite radiolarian assemblage from six localities on La Désirade to zone 4, upper subzone 4β (mid-upper Tithonian). Using the new chemical abrasion (CA) thermal ionization mass spectrometry zircon method of Mattinson, the results from three zircon fractions from trondhjemite provide a 143.74 ± 0.33 Ma U-Pb age for the La Désirade igneous complex. Combined biostratigraphic, chronostratigraphic, and geochronometric data put the geochronologic age for the mid-late Tithonian near 143.74 Ma, a maximum for the latest Jurassic.

New data from an Upper Triassic to Lower Cretaceous deep marine succession—the herein reinstated and restricted Gemuk Group—provide a vital piece of the puzzle for unraveling southwestern Alaska's tectonic history. First defined by Cady et al. in 1955 , the Gemuk Group soon became a regional catchall unit that ended up as part of at least four different terranes. In this paper we provide the first new data in nearly half a century from the Gemuk Group in the original type area in Taylor Mountains quadrangle and from contiguous rocks to the north in Sleetmute quadrangle. Discontinuous exposure, hints of complex structure, the reconnaissance level of our mapping, and spotty age constraints together permit definition of only a rough stratigraphy. The restricted Gemuk Group is at least 2250 m thick, and could easily be at least twice as thick. The age range of the restricted Gemuk Group is tightened on the basis of ten radiolarian ages, two new bivalve ages, one conodont age, two U-Pb zircon ages on tuff, and U-Pb ages of 110 detrital zircons from two sandstones. The Triassic part of the restricted Gemuk Group, which consists of intermediate pillow lavas interbedded with siltstone, chert, and rare limestone, produced radiolarians, bivalves, and conodonts of Carnian and Norian ages. The Jurassic part appears to be mostly siltstone and chert, and yielded radiolarians of Hettangian-Sinemurian, Pliensbachian-Toarcian, and Oxfordian ages. Two tuffs near the Jurassic-Cretaceous boundary record nearby arc volcanism: one at 146 Ma is interbedded with red and green siltstone, and a second at ca. 137 Ma is interbedded with graywacke turbidites. Graywacke appears to be the dominant rock type in the Lower Cretaceous part of the restricted Gemuk Group. Detrital zircon analyses were performed on two sandstone samples using SHRIMP. One sandstone yielded a dominant age cluster of 133–180 Ma; the oldest grain is only 316 Ma. The second sample is dominated by zircons of 130–154 Ma; the oldest grain is 292 Ma. The youngest zircons are probably not much older than the sandstone itself. Point counts of restricted Gemuk Group sandstones yield average ratios of 24/29/47 for Q/F/L, 15/83/2 for Ls/Lv/Lm, and 41/48/11 for Qm/P/K. In the field, sandstones of the restricted Gemuk Group are not easily distinguished from sandstones of the overlying Upper Cretaceous turbidite-dominated Kuskokwim Group. Petrographically, however, the restricted Gemuk Group has modal K-feldspar, whereas the Kuskokwim Group generally does not (average Qm/P/K of 64/36/0). Some K-feldspar-bearing graywacke that was previously mapped as Kuskokwim Group ( Cady et al., 1955 ) is here reassigned to the restricted Gemuk Group. Major- and trace-element geochemistry of shales from the restricted Gemuk Group and the Kuskokwim Group show distinct differences. The chemical index of alteration (CIA) is distinctly higherforshales of the Kuskokwim Group than forthose of the restricted Gemuk Group, suggesting more intense weathering during deposition of the Kuskokwim Group. The restricted Gemuk Group represents an estimated 90–100 m.y. of deep-water sedimentation, first accompanied by submarine volcanism and later by nearby explosive arc activity. Two hypotheses are presented for the tectonic setting. One model that needs additional testing is that the restricted Gemuk Group consists of imbricated oceanic plate stratigraphy. Based on available information, our preferred model is that it was deposited in a back-arc, intra-arc, or forearc basin that was subsequently deformed. The terrane affinity of the restricted Gemuk Group is uncertain. The rocks of this area were formerly assigned to the Hagemeister subterrane of the Togiak terrane—a Late Triassic to Early Cretaceous arc—but our data show this to be a poor match. None of the other possibilities (e.g., Nukluk and Tikchik subterranes of the Goodnews terrane) is viable; hence, the terrane subdivision and distribution in southwestern Alaska may need to be revisited. The geologic history revealed by our study of the restricted Gemuk Group gives us a solid toehold in unraveling the Mesozoic paleogeography of this part of the northern Cordillera.

Irwin's (1972) terrane concept fathered tectonostratigraphy and has done much to decipher complex geology throughout the Circum-Pacific region, Caribbean, and elsewhere in the world. The present chapter analyzes the tectonostratigraphy of seemingly unrelated Jurassic terranes utilizing an accurate chronostratigraphic framework. Faunal paleolatitudinal data, paleomagnetic data (where available), and microfacies analysis have been utilized in the tectonostratigraphic interpretations. Four terranes/subterranes are analyzed herein: (1) the Izee terrane (Blue Mountains, northeastern Oregon), (2) the Rogue Valley subterrane (southwestern Oregon), (3) the Smith River subterrane (northwestern California), and (4) the San Pedro del Gallo terrane (east-central and central Mexico, western Cuba). Paleolatitudinal data indicate that all of these terranes/subterranes have undergone tectonic transport. The Izee terrane originated at low paleolatitudes (Central Tethyan province) during the Late Triassic and migrated to higher paleolatitudes (Southern Boreal province: 30° N) by the late Bathonian (Middle Jurassic). Northward movement is postulated to have occurred along a megashear analogous to the present-day San Andreas fault system. The Rogue Valley and Smith River subterranes both originated at low paleolatitudes (Central Tethyan province) during the Callovian and were transported to higher paleolatitudes (Southern Boreal province) by the the middle Oxfordian (early Late Jurassic). The Huayacocotla remnant of the San Pedro del Gallo terrane originated at high Southern Boreal paleolatitudes (30–40° N) during the late Bathonian or early Callovian and, subsequently was transported from northwest to southeast along the west side of the Walper megashear. By the latest Tithonian (Late Jurassic), the Huayacocotla remnant had been transported to low paleolatitudes (Central Tethyan province). Unconformities in the Bathonian to Callovian interval in the Izee terrane(?) and in the Huayacocotla remnant of the San Pedro del Gallo terrane are believed to reflect the breakup of Pangea. As demonstrated by the author in previous reports, each remnant of the San Pedro del Gallo terrane shows the same paleobathymetric fingerprint: (1) marine deposition at inner neritic depths during the Callovian to early Oxfordian (Middle to early Late Jurassic), (2) marine deposition at outer neritic depths during the late Oxfordian (Late Jurassic), and (3) sudden deepening to upper abyssal depths from the early Kimmeridgian (Late Jurassic) until the end of the Cretaceous. The sudden deepening event (outer neritic to upper abyssal) during the early Kimmeridgian is associated with a disconformity and hiatus in all San Pedro del Gallo remnants (early Kimmeridgian strata overlie middle Oxfordian strata). This event reflects the opening of the Gulf of Mexico. Combined faunal and floral data indicate that the San Pedro del Gallo terrane was in a back-arc position at approximately the same latitude as the Foothills terrane of the Sierra Nevada during the middle Oxfordian. Given the faunal data as well as some paleomagnetic data, it is probable that these San Pedro del Gallo remnants might represent some of the missing Upper Jurassic back-arc deposits from farther north (i.e., western Nevada?). In the Smith River subterrane, the disconformable contact between the volcanopelagic facies and Galice Formation sensu lato reflects a sudden influx of siliciclastic turbidite from a Jurassic volcanoplutonic arc source area and from older rocks of the accreted continental margin that lay inboard of the Nevadan island-arc complex. The same event is represented by the deposition of the siliciclastic turbidite of the Monte del Oro and Mariposa Formations (Foothills terrane, western Sierra Nevada) and by that of the Galice Formation sensu stricto (Rogue Valley subterrane).

Abstract Tectonostratigraphic data derived from ongoing biostratigraphic, chronostratigraphic, paleobathymetric, paleobiogeographic, and lithostratigraphic investigations in west-central and east-central Mexico suggest that the Gulf of Mexico formed in two phases: Phase 1: Rifting and subsequent sea-floor spreading during the Late Jurassic (middle Oxfordian). All but the southwestern portion of the Gulf of Mexico formed during Phase 1. Phase 2: Northwest-to-southeast tectonic transport of allochthonous San Pedro del Gallo terrane remnants along the west side of Walper Megashear during the Middle Jurassic to Early Cretaceous. Where the stratigraphic successions are complete, megafossil data indicates that the San Pedro del Gallo terrane was situated at Southern Boreal paleolatitudes (>30° N) in the Nevadan back arc domain during the Middle Jurassic (late Bathonian to early Callovian) and was subsequently carried to lower paleolatitudes during the Late Jurassic and Early Cretaceous. For example, in the Huayacocotla remnant, the Boreal ammonite Kepplerites was recovered in the subsurface from the Palo Blanco Formation by Cantú-Chapa. In North America, Kepplerites is known from the Izee terrane (east-central Oregon), Western Interior (Montana and Saskatchewan), and northward to southern Alaska. Radiolarian, calpionellid, ammonite, and bivalve faunal data indicate that the Huayacocotla remnant had been transported to Northern Tethyan paleolatitudes (23° N to 29° N) during the Kimmeridgian and Tithonian and to Central Tethyan paleolatitudes (<23° N) by the beginning of the Early Cretaceous.

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We correlate seismic map units identified on industry seismic lines in the Gulf of Chiriquí, southwestern Panama, with onland igneous rocks and sedimentary formations described in this chapter. We propose six principal stages in the stratigraphic development of southwestern Panama based on our results and the results of previous workers in Costa Rica, westernmost Panama, and the western Colombian basin. The first stage in southwestern Panama is represented by basaltic basement rocks of Jurassic?-Late Cretaceous age interbedded with Upper Cretaceous pelagic sedimentary rocks. Following previous workers and data presented here, we suggest that these rocks formed in an intraoceanic, oceanic plateau setting. A second stage is represented by a major stratigraphic hiatus inferred to represent an erosional event that affected the basaltic basement of Panama in Paleocene time. A third stage is represented by a widespread basal transgressive section of coarse clastic rocks and reefal carbonate rocks of early to middle Eocene age. This section records initiation of clastic sedimentation over much of southern Central America. A fourth stage is represented by a thick section of mainly marine turbidites that appears to represent continued erosion of the land areas in southern Central America and upward deepening of adjacent marine environments. A fifth stage is represented by a stratigraphic hiatus in middle Miocene to late Miocene time that may represent the “breakup” unconformity associated with initiation of strike-slip faulting and rifting in the Gulf of Chiriquí. A sixth stage is represented by early Pliocene to Pleistocene rifting and syn-rift sedimentation in the Gulf of Chiriqu&iacute. Thick sedimentary fill of rift basins may reflect accelerated uplift of southern Central America and increased activity of the Middle America arc. The regional extent of the stratigraphic record of several of these stages across large areas of southern Central America and the western Colombian basin supports the previously proposed hypothesis that the crust of southern Central America represents the western upturned edge of a Late Cretaceous Caribbean oceanic plateau known from deep-sea drilling and seismic stratigraphic studies in the Colombian and Venezuelan basins of the Caribbean Sea.

ABSTRACT Radiolaria offer a valuable new means of interpreting the stratigraphy and in turn the structure of complex orogenic belts such as the California Coast Ranges. This is the third in a series of studies which have utilized Radiolaria to interpret the Mesozoic stratigraphy of the California Coast Ranges; it focuses on Lower Cretaceous biostratigraphy of the Great Valley sequence and Franciscan Complex. A detailed system of radiolarian zonation (four zones and three subzones) has been developed for the Lower Cretaceous (Berriasian to Albian) portion of the Great Valley sequence. This zonal system has been integrated as closely as possible with biostratigraphic data offered by megafossils and planktonic foraminifera. With the completion of this third and final study on the radiolarian biostratigraphy of the California Coast Ranges a detailed system of zonation now exists for the Mesozoic succession of the California Coast Ranges and encompasses strata ranging in age from Late Jurassic (Kimmeridgian) to Late Cretaceous (Maestrichtian). To facilitate communication with the geologic community the formal zonal names have been equated with a numerical code. Five new families, 11 new genera, and 40 new species are described and figured herein.

ABSTRACT This report deals with the biostratigraphy, lithostratigraphy, and micropaleontology of the Corsicana Formation of North Central Texas. A comparison of strata at the type locality of the Corsicana Formation with the type area of the Kemp Formation clearly demonstrates that these units are lithostratigraphic equivalents and can be encompassed by one formational name. Since the Corsicana Formation has a well-defined type locality and contains by far the best exposures of these units in their respective type areas, it is suggested that the term Kemp be abandoned and the term Corsicana be retained. The definition of the Corsicana Formation is emended, therefore, to include the calcareous clays, mudstones, and marls that overlie the Nacatoch Formation and underlie the Paleocene Kincaid Formation (Midway Group). The present investigation indicates that the Corsicana Formation is middle Maestrichtian in age and is assignable to the Globotruncana contusa-stuartiformis Assemblage Zone, G. gansseri Subzone. Through a detailed analysis of the planktonic foraminiferal assemblage, it has become possible to subdivide the Globotruncana gansseri Subzone into two new zonules: a lower Globotruncana aegyptiaca Zonule and an upper Racemiguembelina fructicosa Zonule. The Corsicana Formation includes a rich, well preserved planktonic foraminiferal assemblage consisting of fortynine species (four of which are new) assigned to thirteen genera. The scanning electron microscope has been utilized extensively in this study to describe and illustrate these taxa. The genus Racemiguembelina Gallitelli (1957) is emended and a new term ponticulus is proposed for the unique umbilical cover plates that characterize this genus.

It is postulated that worldwide transgressions (pulsations) and regressions (interpulsations) throughout the course of geologic time are related to the elevation and subsidence of oceanic ridge systems and to sea-floor spreading. During the Mesozoic-Cenozoic interval, for example, the Cretaceous represents a period of worldwide transgression of the seas over the continents. Such a transgression may have been caused by the elevation of the old Mid-Pacific Ridge system, which in turn displaced a considerable amount of sea water from the ocean basins to the continents. Two multiple working hypotheses are proposed to explain major transgressions and regressions and the elevation and subsidence of oceanic ridge systems. One hypothesis interrelates the sea-floor spreading hypothesis to the hypothesis of sub-Mohorovičić serpentinization. The second hypothesis relates the sea-floor spreading hypothesis to a hypothesis involving thermal expansion and contraction.

The Upper Cretaceous strata of the Gulf Coast region of México, Texas, and southwestern Arkansas contain rich, abundant, well-preserved, and, hitherto, poorly studied assemblages of planktonic foraminifera. The rapid evolution and cosmopolitan nature of these planktonic microfossils make them an ideal biostratigraphic tool for the development of detailed, long-distance systems of zonation. In the present report, the planktonic foraminifera have been utilized to subdivide the Upper Cretaceous of the western Gulf Coast region into the following biostratigraphic units: (1) The Rotalipora s.s. Assemblage Zone: Rotalipora evoluta Subzone to Rotalipora cushmani - greenhornensis Subzone. Late Washitian to early Eagle-fordian (early to late Cenomanian). (2) The Marginotruncana helvetica Assemblage Zone: Marginotruncana sigali Subzone to Whiteinella archaeocretacea Subzone. Middle to late Eagle-fordian (early to late Turonian). (3) The Marginotruncana renzi Assemblage Zone: Early Austinian (Coniacian). (4) The Globotruncana bulloides Assemblage Zone: Marginotruncana concavata Subzone to Globotruncana fornicata Subzone. Middle to late Austinian (early to late Santonian). (5) The Globotruncana fornicata—stuartiformis Assemblage Zone: Archaeoglobigerina blowi Subzone (Dictyomitra multicostata Zonule to Planoglobulina glabrata Zonule); Globotruncana elevata Subzone (Pseudotextularia elegans Zonule to Globotruncana calcarata Zonule); and Rugotruncana subcircumnodifer Subzone ( Globotruncana lapparenti s.s. Zonule to Rugotruncana subpennyi Zonule). Archaeoglobigerina blowi Subzone = early Taylorian (early Campanian); Globotruncana elevata Subzone = late Taylorian (late Campanian); and Rugotruncana subcircumnodifer Subzone = early Navarroan (early Maestrichtian). (6) The Globotruncana contusa — stuartiformis Assemblage Zone: Globotruncana gansseri Subzone to Abathomphalus mayaroensis Subzone. Middle to late Navarroan (middle to late Maestrichtian). This system of zonation is based (1) on the association of diagnostic taxa at given stratigraphic horizons; (2) the range zones and concurrent range zones of the various taxa; (3) the relative abundance of important taxa at various stratigraphic horizons; and (4) the phylogeny and evolution of Upper Cretaceous planktonic foraminifera. It has become established through the analysis of more than 1000 fossiliferous samples from the surface and sub-surface in both the western part of the Gulf Coast region and in the Caribbean region. Where possible, samples were collected within the framework of measured sections of the lithic units under study. Samples for planktonic foraminifera were collected as far south in the western Gulf Coast region as the approximate latitude of Tampico, México (22° north latitude) and as far north as Brownstown, Sevier County, Arkansas (34° north latitude). At a given stratigraphic horizon, such as the Globotruncana elevata Subzone, there are few species of planktonic foraminifera that do not occur in both the Tethyan faunal province and southern part of the Boreal faunal province. In most cases planktonic species that do not occur in both areas are new species, whose stratigraphic and geographic distribution are yet unknown. The present study indicates that the above-mentioned system of zonation is applicable at the zonule level at least as far north as the latitude of Brownstown, Arkansas. Furthermore, Olsson’s (1964) work in New Jersey and investigations in progress in California by the writer, Douglas, and others suggest that the system of zonation introduced here can be applied at the subzone level as far as 40° north latitude in eastern North America and as far as 34° north latitude in western North America. One of the chief by-products of this study is the creation of a regional correlation chart for the Upper Cretaceous of the western Gulf Coast region that is based on planktonic-foraminiferal zonation. Accurate biostratigraphic dating of lithic units in eastern México utilizing planktonic foraminifera indicates that a number of formational units are time transgressive from north to south. Units like the San Felipe Formation and Agua Nueva Formation are considerably older in northern México near Monterrey than they are in southern México near Tampico. The present study has yielded few radical changes in the dating of lithic units in Texas and Arkansas previously established on the basis of megafossils (Stephenson and others, 1942). Notable among these changes are Navarroan ages for the Upson Clay and San Miguel Formation of the Rio Grande area of Texas (approximate latitude of Eagle Pass) and all, but perhaps, the lowermost part of the Marlbrook Marl of Arkansas. Correlation with the type-European Upper Cretaceous stages is rendered difficult (1) by the imprecise and often obsolete definition of the stages in their type areas and (2) by a lack of accurate data concerning the stratigraphic distribution of planktonic foraminifera in the type sections of the stages. The first of these problems affects all Upper Cretaceous biostratigraphy irregardless of the group of organisms used for correlation. It can perhaps only be solved by an international stratigraphic commission chosen to modernize the definition of the European stages. The second problem can be solved by detailed sampling of strata included in the type sections of each European stage for planktonic foraminifera. Until a detailed reanalysis of the majority of the type-European stages is made, the writer prefers to use North American stage names — particularly those of the standard Gulf Coast section. European stage names are used in this report only in a tentative way. The Eaglefordian Stage of the standard Gulf Coast Upper Cretaceous section has been subdivided into 3 new substages: (1) the Lozierian; (2) the Bocian; and (3) the Sycamorian. The Boquillas Formation in Val Verde and Terrell Counties, Texas, has been subdivided into a lower unit termed the Rock Pens Member and an upper unit termed the Langtry Member. The terms Ateo Chalk and Bruceville Chalk Marl , first used informally by Durham (1957), have been formally introduced here.