Abstract: We have examined the Neogene stratigraphic successions recovered from six wells located along a present-day middle neritic (current depositional depth 92 m) to upper bathyal depth (current depositional depth 482 m) transect oblique to the shelf/slope margin in the northern Gulf of Mexico (GOM) using calcareous plankton biostratigraphy. The latter were used to conduct stratigraphic interpretation of the sections and to determine their completeness. We establish that all sections vary considerably in thickness and completeness, depending on depth of deposition, as estimated from benthic foraminiferal analysis, which shows that depositional depth at the six sites changed little through the Neogene. The shallowest section (~90-m estimated depositional depth through the Neogene) is the thinnest with the most complete Upper Miocene–Pleistocene record, whereas the deepest section (~600– 800-m estimated depositional depth) is the thickest but also contains the least complete Pliocene–Pleistocene record. The Upper Miocene to Pleistocene sediments deposited between ~200- and 500-m estimated depositional depth exhibit a characteristic allostratigraphic architecture, with sedimentary units bounded by unconformities associated with 1- to 2-Myr hiatuses that vary little along the transect. We integrate the stratigraphic architecture along our local transect in the regional Cenozoic depositional framework in the GOM of Galloway and coauthors and establish that the allostratigraphic units (AUs) correspond well with several of the genetic and seismic sequences delineated. We interpret the depth-related increase in thickness of the Upper Miocene–Pleistocene AUs in light of the sedimentary processes discussed by these authors. However, our interpretation differs considerably from theirs based on our documentation of temporally incomplete sections in the wells. The sedimentary pattern in Well-3 (~200-m estimated depositional depth) is quite different from that at nearby Well-1 (~100–600-m estimated depositional depth), although very similar to the wells further west, even though the distance between Well-3 and Well-6 is about four times that between Well-3 and Well-1. We note also that the stratigraphic pattern in Well-1 changed ~8 Ma, from highly discontinuous before to remarkably continuous after. We have found no clear evidence that glacio-eustasy shaped the Neogene stratigraphic record in the study area. Therefore, we question whether glacio-eustasy was the primary forcing mechanism on stratigraphic architecture in the GOM beyond the shallow part of shelves and propose that salt tectonics may have been a more prominent factor in controlling accommodation. An allostratigraphic architecture was described earlier from the De Soto Canyon northeast of the GOM transect, where the AUs and their boundaries were shown to match, respectively, the seismic sequences and surfaces on the nearby Florida margin. We therefore consider the AUs along the GOM transect as corresponding as well to seismic sequences and therefore to parts of depositional sequences. Based on this, we review notable difficulties in characterizing seismic features (sequences and surfaces) in concrete stratigraphic records and recommend a greater awareness of the temporal significance of unconformities, many of which are associated with multimillion-year hiatuses.

ABSTRACT We review past and recent advances in Oligocene chronostratigraphy (and its internal subdivisions) and geochronology, the so-called “missing” Oligocene debate of the 1960s, and planktonic foraminiferal biostratigraphies of (sub)tropical and austral biogeographies. The Oligocene spans the interval from Chron C13r.0.14 to Subchron C6Cn.2n (0) , corresponding to astronomical cycles 84 01-C13n to 58 01-C6Cn . It is currently subdivided into two (Rupelian and Chattian) ages/stages. The planktonic foraminiferal biostratigraphy is characterized by a 7-fold (sub) tropical and 4-fold austral zonation, respectively.

ABSTRACT The work of Bé (1968) and Bé and others (1969) on the shell porosity of modern planktonic foraminifera provides additional criteria for categorizing the taxonomy of Oligocene genera and even species according to their test pore size and concentration. Use of these criteria in addition to the type of wall texture provides further information for the separation of groups of normal perforate Oligocene planktonic foraminifera for phylogeny and classification. In addition to wall textures recognized in the Eocene (Hemleben and Olsson, 2006) two types of wall texture are recognized in Oligocene spinose planktonic foraminifera: a Neogloboquadrina -type which occurs in the new genus Ciperoella and a conglobatus -type which occurs in two species of Dentoglobigerina.

ABSTRACT The taxonomy, biostratigraphy, and phylogeny of Oligocene Catapsydrax, Globorotaloides, and Protentelloides is reviewed. Catapsydrax and Globorotaloides are long-ranging genera with robust and dissolution-resistant tests. Both genera appeared in the early Eocene. Catapsydrax disappeared in the late Miocene while Globorotaloides has living representatives. Catapsydrax is ubiquitous in its distribution and highly variable in test size. Oligocene species of Globorotaloides are typically small (<250 μm) and usually rare in the tropics but may be common in high latitude and upwelling regions. After little evolutionary change in the Eocene and early Oligocene, Globorotaloides and Catapsydrax diversified at low latitudes in the mid- to late Oligocene resulting in the appearance of several new species and the quasi-clavate genus Protentelloides in the late Oligocene. So far Protentelloides spp. have only been found in the equatorial Atlantic Ocean. The following species are recognized as valid: Catapsydrax dissimilis (Cushman and Bermúdez), Catapsydrax indianus Spezzaferri and Pearson, Catapsydrax unicavus Bolli, Loeblich, and Tappan, Globorotaloides atlanticus Spezzaferri and Coxall n. sp., Globorotaloides eovariabilis Huber and Pearson, Globorotaloides hexagonus (Natland), Globorotaloides quadrocameratus Olsson, Pearson and Huber, Globorotaloides stainforthi (Bolli, Loeblich, and Tappan), Globorotaloides suteri Bolli, Globorotaloides testarugosus (Jenkins), Globorotaloides variabilis Bolli, Protentelloides dalhousiei Zhang and Scott, and Protentelloides primitivus Zhang and Scott.

ABSTRACT The taxonomy, phylogeny, and biostratigraphy of Oligocene and early Miocene Paragloborotalia and Parasubbotina are reviewed. The two genera are closely related; Paragloborotalia was derived from Parasubbotina in the early Eocene. Parasubbotina was more diverse during the middle Eocene, while Paragloborotalia experienced considerable diversification during the mid-Oligocene and in the latest Oligocene-earliest Miocene. A significant finding has been the synonymization of Globorotalia ( Tuborotalia ) mendacis Blow, and Turborotalia primitiva Brönnimann and Resig with Globorotalia birnageae Blow. The following species from the time interval of interest are regarded as valid: Paragloborotalia acrostoma (Wezel), Paragloborotalia birnageae (Blow), Paragloborotalia continuosa (Blow), Paragloborotalia incognita (Walters) Paragloborotalia kugleri (Bolli), Paragloborotalia mayeri (Cushman and Ellisor), Paragloborotalia nana (Bolli), Paragloborotalia opima (Bolli), Paragloborotalia pseudocontinuosa (Jenkins), Paragloborotalia pseudokugleri (Blow), Paragloborotalia semivera (Hornibrook), Paragloborotalia siakensis (LeRoy), Parasubbotina hagni (Gohrbandt), and Parasubbotina varianta (Subbotina). Paragloborotalia is a long-lived group of planktonic foraminifera that spanned the early Eocene to late Miocene and provided the root stock for the evolution of multiple smooth, nonspinose, and keeled globorotaliid lineages during the Neogene. The early Oligocene forms of Paragloborotalia (nana, opima, siakensis, pseudocontinuosa ) have 4 or 5 globular chambers in the final whorl with radial spiral sutures and a broadly rounded periphery. A trend from radial to curved spiral sutures is observed in late Oligocene and earliest Miocene lineages. Most species of Paragloborotalia had wide distributions, but some were more common in tropical to warm subtropical waters (e.g., siakensis, kugleri ) and were especially dominant in the equatorial Pacific divergence zone (e.g., nana, opima, and pseudocontinuosa ) analogous to modern tropical upwelling Neogloboquadrina. Other species thrived in cool subtropical and temperate waters (e.g., acrostoma, incognita ).

ABSTRACT The taxonomy, phylogeny and biostratigraphy of Oligocene Globigerina, Globigerinella and the new genus Quiltyella is reviewed. Globigerina and Globigerinella are long-ranging genera that extend into the modern. Globigerina appeared in the middle Eocene and diversified in the early Oligocene to give rise to several geographically wide-ranging and cosmopolitan species. Globigerinella originated and diversified in the early Oligocene and includes both common cosmopolitan species together with rare clavate and digitate species that were previously referred to the genus Protentella Lipps. Based on new wall textural studies we describe a third related genus, Quiltyella Coxall and Spezzaferri n. gen., which is always rare and highly geographically restricted. This is distinguished from Globigerina and Globigerinella by the higher pore concentration and extreme digitate chamber morphology. The following species are considered as valid: Globigerina archaeobulloides Hemleben and Olsson n. sp., Globigerina bulloides d’Orbigny, Globigerina officinalis Subbotina, Globigerinella clavaticamerata (Jenkins), Globigerinella megaperta Rögl, Globigerinella molinae (Popescu and Brotea), Globigerinella navazuelensis (Molina), Globigerinella obesa (Bolli), Globigerinella praesiphonifera (Blow), Globigerinella roeglina Spezzaferri and Coxall n. sp., and Globigerinella wagneri (Rögl), Quiltyella clavacella (Rögl), and Quiltyella nazcaensis (Quilty).

ABSTRACT Ciperoella Olsson and Hemleben n. gen. is erected for Oligocene spinose species that have a neogloboquadrinid-type wall texture and 4½-5 similarly sized chambers in the final whorl. Four species are recognized as distinct, namely Ciperoella anguliofficinalis (Blow), Ciperoella angulisuturalis (Bolli), Ciperoella ciperoensis (Bolli), and Ciperoella fariasi (Bermúdez). Their taxonomy, phylogeny, and biostratigraphy is discussed.

ABSTRACT The taxonomy, phylogeny and biostratigraphy of Oligocene and lower Miocene Globoturborotalita is reviewed. Globoturborotalita is a long-ranging genus appearing in the basal Eocene and still present in modern oceans with one living representative G. rubescens. Species attributed to this genus are generally common and cosmopolitan. The following species are recognized as valid: Globoturborotalita barbula Pearson and Wade, Globoturborotalita bassriverensis Olsson and Hemleben, Globoturborotalita brazieri (Jenkins), Globoturborotalita cancellata (Pessagno), Globoturborotalita connecta (Jenkins), Globoturborotalita eolabiacrassata Spezzaferri and Coxall n. sp., Globoturborotalita euapertura (Jenkins), Globoturborotalita gnaucki (Blow and Banner), Globoturborotalita labiacrassata (Jenkins), Globoturborotalita martini (Blow and Banner), Globoturborotalita occlusa (Blow and Banner), Globoturborotalita ouachitaensis (Howe and Wallace), Globoturborotalita paracancellata Olsson and Hemleben n. sp., Globoturborotalita pseudopraebulloides Olsson and Hemleben n. sp., and Globoturborotalita woodi (Jenkins).

ABSTRACT The taxonomy, phylogeny and biostratigraphy of late Oligocene and early Miocene Globigerinoides and Trilobatus is reviewed. Trilobatus and Globigerinoides are two long-ranging genera appearing in the late Oligocene and early Miocene, respectively. They diversified within the range interval of Paragloborotalia kugleri and are still present in modern oceans as some of the most abundant mixed-layer dwelling groups. The distinctive characteristic of the genera is the presence of one to several supplementary apertures on the spiral side. Globigerinoides species possess a ruber/sacculifer -type wall, Trilobatus possesses a sacculifer-type wall texture. The ruber -type wall texture probably appeared in the late Miocene with the appearance of G. ruber s.s. The following species of Globigerinoides are recognized as valid: G. altiaperturus Bolli, G. bollii Blow, G. italicus Mosna and Vercesi, G. joli Spezzaferri n. sp., G. neoparawoodi Spezzaferri n. sp., G. obliquas Bolli, and G. subquadratus Brönnimann. The following species of Trilobatus are recognized as valid: T. altospiralis Spezzaferri n. sp., T. immaturus (LeRoy), T. praeimmaturus (Brönnimann and Resig), T. primordius (Blow and Banner), T. quadrilobatus (d’Orbigny), T. subsacculifer (Cita, Premoli Silva, and Rossi) and T. trilobus (Reuss).

ABSTRACT The taxonomy, biostratigraphy, and phylogeny of Oligocene Subbotina is discussed and reviewed. We include forms that have teeth extending into the umbilicus. A total of nine species are accepted as distinct, namely Subbotina angiporoides (Hornibrook), Subbotina corpulenta (Subbotina), Subbotina eocaena (Gümbel), Subbotina gortanii (Borsetti), Subbotina linaperta (Finlay), Subbotina minima (Jenkins), Subbotina projecta Olsson, Pearson, and Wade n. sp., Subbotina tecta Pearson and Wade, and Subbotina utilisindex (Jenkins and Orr).

ABSTRACT The taxonomy, phylogeny, and biostratigraphy of Oligocene and lower Miocene Dentoglobigerina and Globoquadrina are reviewed. Because of the discovery of spine holes in various species assigned to these genera, the entire group is now considered to have been fully or sparsely spinose in life and hence part of Family Globigerinidae. One new species, Dentoglobigerina eotripartita Pearson, Wade, and Olsson n. sp., is named. Dentoglobigerina includes forms with and without umbilical teeth and species for which the presence or absence of a tooth is a variable feature. A significant finding has been the triple synonymy of Globigerina tripartita Koch, Globigerina rohri Bolli, and Globoquadrina dehiscens praedehiscens Blow, which greatly simplifies part of the taxonomy. The genus Globoquadrina is restricted to its type species, Globigerina dehiscens Chapman and others. The following species from the time interval of interest are regarded as valid: Dentoglobigerina altispira (Cushman and Jarvis), Dentoglobigerina haroemoenensis (LeRoy), Dentoglobigerina binaiensis (Koch), Dentoglobigerina eotripartita Pearson, Wade, and Olsson n. sp., Dentoglobigerina galavisi (Bermúdez), Dentoglobigerina globosa (Bolli), Dentoglobigerina globularis (Bermúdez), Dentoglobigerina juxtabinaiensis Fox and Wade, Dentoglobigerina larmeui (Akers), Dentoglobigerina prasaepis (Blow), Dentoglobigerina pseudovenezuelana (Blow and Banner), Dentoglobigerina sellii (Borsetti), Dentoglobigerina taci Pearson and Wade, Dentoglobigerina tapuriensis (Blow and Banner), Dentoglobigerina tripartita (Koch), Dentoglobigerina venezuelana (Hedberg), and Globoquadrina dehiscens (Chapman, Parr, and Collins). The genus Dentoglobigerina also comprises other Neogene/Quaternary species not listed, including the living species Dentoglobigerina cf. conglomerata (Schwager).

ABSTRACT The taxonomy, phylogeny, and biostratigraphy of Oligocene Turborotalita is reviewed. We recognize two species in the Oligocene, Turborotalita praequinqueloba Hemleben and Olsson and Turborotalita quinqueloba (Natland). The two species are distinguished primarily by the number of chambers in the final whorl (typically 4-4½ versus 4½-5½ respectively). We extend the stratigraphic range of T. quinqueloba down through the Oligocene and into the upper Eocene, making it the longest-lived of all the extant morphospecies. Combined with recently published research on the earliest Paleocene, it appears likely that Turborotalita represents a distinct clade that persisted for the entire Cenozoic, having first appeared in the immediate aftermath of the Cretaceous / Paleogene mass extinction.

ABSTRACT The taxonomy, phylogeny and biostratigraphic ranges of three Oligocene species of Acarinina are discussed together with their synonymies. Acarinina diversified in the Paleocene and Eocene and only a few species remain in the OligoceneThe following taxa are recognized as valid species: Acarinina collactea (Finlay), Acarinina echinata (Bolli), and Acarinina medizzai (Toumarkine and Bolli).

ABSTRACT The taxonomy, phylogeny and biostratigraphy of the Oligocene Globanomalinidae (comprising the genera Pseudohastigerina and Turborotalia ) is reviewed. Members of the Family have a macroperforate, nonspinose, smooth to weakly cancellate wall. Extinctions in the late Eocene left the Family restricted to just a few surviving forms which themselves became extinct in the early Oligocene. The group is very useful for biostratigraphy, with the extinctions of Pseudohastigerina naguewichiensis and Turborotalia ampliapertura providing the lowest two biozone boundaries of the Oligocene. The following species are recognized as valid: Pseudohastigerina micra (Cole), Pseudohastigerina naguewichiensis (Myatliuk), Turborotalia ampliapertura (Bolli), and Turborotalia increbescens (Bandy).

ABSTRACT New microstructural observations on the tests of microperforate and medioperforate planktonic foraminifera from the Oligocene are presented and comparisons are made with some Holocene specimens. Two types and two subtypes of wall texture are distinguished: the glutinata -type (in Globigerinita and Tenuitella ; with the danvillensis -subtype in Dipsidripella ), and the ototara -type (in most Chiloguembelina ), with the chipolensis -subtype (in Cassigerinella and some Chiloguembelina ). Given also the gross morphological differences between the two major groups (trochospiral versus biserial or enrolled-biserial), these wall textures likely indicate separate evolutionary radiations from different groups of benthic foraminifera and so help define the higher taxonomy of the planktonic foraminifera. Accordingly, the following superfamilies are recognized in the chapters of this work: Globigerinitoidea and Guembelitriodea. Their placement relative to other superfamilies of foraminifera is not yet known.

ABSTRACT The taxonomy, biostratigraphy, and phylogeny of the Oligocene Globigerinitidae (comprising the genera Dipsidripella , Globigerinita and Tenuitella ) is reviewed. This family is here included in the Superfamily Globigerinitoidea based on the distinctive wall texture. The group is united by possessing a ‘radially crystalline’ wall texture (the glutinata -type wall) which typically bears pyramidal pustules and in most species is microperforate (pores <1 μm in diameter). The genus Dipsidripella is included in the family here for the first time. In Dipsidripella the wall is often medioperforate (pores 1-2 μm in diameter; danvillensis -subtype). The following species are recognized as valid and occurring in the Oligocene: Dipsidripella danvillensis (Howe and Wallace), Dipsidripella liqianyui Huber and Pearson, Globigerinita glutinata (Egger), Globigerinita uvula (Ehrenberg), Tenuitella angustiumbilicata (Bolti), Tenuitella gemma (Jenkins), Tenuitella munda (Jenkins), and Tenuitella praegemma (Li).

ABSTRACT The taxonomy, phylogeny, and biostratigraphic ranges of six Oligocene species of Chiloguembelina and Jenkinsina are discussed together with their synonymies. The following species are recognized in this chapter: Chiloguembelina adriatica n. sp., Chiloguembelina andreae n. sp., Chiloguembelina cubensis (Palmer), Chiloguembelina ototara (Finlay), Jenkinsina columbiana (Howe), and Jenkinsitia triseriata (Terquem).