ARTICLE REVIEW

BREARD, CALLENDAR, NAULT 493 PALEOECOLOGIC AND BIOSTRAIGRAPHIC MODELS FOR PLEISTOCENE THROUGH MIOCENE FORAMINIFERAL ASSEM­ BLAGES OF THE GULF COAST BASIN Sylvester Q. Breard, Arden D. Callender, Michael J. Nault APPLIED BIOSTRATIGRAPHIX CO. 1572 WEST GRAY #368 HOUSTON, TEXAS 77019 ABSTRACT Operationally oriented paleoecologic models for Pleistocene through Miocene foraminifera uti­ lized in hydrocarbon exploration of the Gulf Coast Basin are developed, along with an updated, refined biostratigraphic chart. Estimated paleoecologic tolerances for major benthic and planktic foraminiferal markers are also presented. A number of rules and problems encountered in oil industry paleoenvironmental reconstruction are discussed.

Key benthic paleoenvironmental markers for particular depth zones of the Plio-Pleistocene and Miocene are graphically presented. Improvements over previous models include greater utilization of calcareous and arenaceous foraminiferal species not used, recognized, or reported in earlier studies.

Einer subdivisions of bathyal paleoenvironments are recognized and are of particular signifi­ cance due to current Gulf of Mexico deep water exploration. Operationally, the abyssal environ­ ment is difficult to recognize due to the lack of abyssal zone markers and a reliance on faunal abundance to delineate abvssal from bathval.

A number of genera and species are identified as having changed habitat preference through time. Some forms have moved progressively into deeper water (Ceratolmliiniua, Cyclammina cancel­ lated, and Nonion pompilioidcs). Conversely, the movement of species into progressively shallower occurrences through time (Pidlciua bidloides) appears to be less common.

The widespread occurrence of known Gulf of Mexico foraminiferal species from countries such as Mexico, Venezuela, Ecuador, Jamaica, Trinidad, Haiti, the Dominican Republic, and Cuba sug­ gests that these models have direct application to Neogene and Pleistocene studies in Central and South America, and the Caribbean, as well as the US Gulf Coast.

A variety of deep water benthic marker foraminifera are introduced, many for the first time.

These taxa help fill in gaps for deeper water sections where standard benthic marker foraminifera do not occur. This will help debunk the popular myth that benthic foraminifera are useless as markers in the exploration of deep water sections. INTRODUCTION Over the years, numerous foraminiferal paleoeco­ logic models have been proposed for the late Tertiary and Pleistocene strata in the Gulf Coast (Crouch, 1965; Albers et al., 1966; Poag and Valentine, 1976; Skinner, 1966; Smith, 1991). Drawing on these sources, plus the combined experience gained from various oil and gas exploration companies with which the writers have been employed (Amoco, Arco, BPX, Chevron, Sohio, Tenneco and Texaco), we present an updated model for foraminiferal ecology and biostratigraphy. Charts illus­ trating key paleoenvironmental marker species for Miocene, Pliocene, and Pleistocene strata are presented, as well as paleoenvironmental range charts for key biostratigraphic marker species. The Neogene and Pleistocene biochronostratigraphy is also updated for deep water zones.

Our objective is to provide operationally oriented models for determining environments from well cut­ tings. The models are based on a combination of litera­ ture (Phleger, 1960; Walton, 1964; Loep, 1965; Pflum and Frerichs, 1976; Lamb, 1981; Poag, 1981) plus thou­ sands of (unpublished) observations from many hun­ dreds of wells examined by the writers in the Gulf Coast Basin.

Improvements over previous models include greater utilization of arenaceous taxa, addition of more recently recognized deep water calcareous taxa, and finer subdivisions of the bathyal realm. Many of these improvements are drawn from recent experience with deep water biostratigraphy and paleoecology of the Flexure Trend and deeper areas of the Gulf of Mexico.

The charts provided should prove useful to future gen­ erations of micropaleontologists,stratigraphers and geologists in domestic exploration and may also prove beneficial to international explorationists. FORAMINIFERAL PALEOECOLOGY The literature of foraminiferal paleoecologic studies is vast, much of that published being based on the modern Gulf of Mexico. A basic assumption to be addressed in a later section is that many of the ecologi­ cally relevant taxa have maintained that preference of environment through time. Although recognizing the fossil ecologic analogs of modern foraminifera can be a problem, it is diminished when dealing with species no older than the Miocene, when benthic and planktic communities began to modernize (Poag, 1977). 494 GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES SELECTED FORAMINIFERAL PALEOENVIRONMENTAL INDICATORS - PLIO/PLEISTOCENE - GULF OF MEXICO 100' 300' 600' 1500' 3000' 6000'T i NON-I MARINE I MARGINAL | MARINE 1 INNER | NERITIC MIDDLE NERITIC I OUTER NERITIC UPPER BATHYAL MIDDLE BATHYAL LOWER BATHYAL ABYSSAL | CiarODnytes . freshwater os;racoas | wood/lignite | AmmoDacuiites spc. Ammonia beccari. j ElDhidium sop. Milianmina sop. I "rotir'ammma spp. ! ostracods oyster frags Complies by. S.Q Breara A D Caiienaer M.j. Nault (October. 1993! Anphisteojna lessoni Argulogenna B Asterigcnna carinata Bulimnela 1 Citiiodes cccoi-incus Cibicides stratton Discoro s flondana Discorois D Eponides hannai Epoxides 'epandus Lenticuima 1 Nonio" spp Reusella miac erica HoDulusspp i smooth} Tentula ria ccnica Textulanarrayari Tnmosi na A Uvigerina peregrriai'smalii DEEP INNER D-gene^a irregularis Rooulus 6J RcDulus spp. (beacec) 3olivira soinata Buumina marrj nata Bulin.naovata Cancris sagra Dental raspp. Eoorudes antil-afj.T! .Varginulina Dlana:us S'phorina D^'Chra •Jvige'ir-a peroynna {COTlTiOn:

DEEP MIDDLE 3onv ra oaroata Bohvina subaenariensis me^cana C bi&des neof orrdanuS (rarei Liebusel.asoldanii Nodosana albatrossi ^seudociavulTia moxcara Pjlienia DUIcices tsmal 1) Saracenana H Siononma sradyara Sphaeroidma bu/loiGesisrralh TextulaneHa barren: Arguocjerir.a •riagna Doiiv:na imDcrcata Cassiduli na :;ubg:ooosa C bicid'es corouientus Cioicdes natanzasensis Cibicides neoflondanus •:tornmon-larg^) Cicic aes >.imoona".us Gaudryina allontica Gyroidina altiformis Hoeglundma elegans Hyaimeabalihica Ler.ticj:ina rjereg.-ira MargiriLlira nmoata Marginu!ma suoaculesta Noaosana longiscata Norion arfi"is Planulina fovGOlara S'phogene'sna •ame lata Tcx:u!a.na crass'seota Uvigerina oyrdi Uvigerina t'linin DEK? OUTER Buumina ai'in s 3uNmi*ia mexicana Cancrisnuttall Planmna ar ir •r.sis Pseudog'andulma coma'.uia S gmoi i.na scniumberger Stilostomelia anM'.ea Teniulana ber.iudezi Textulana mexicana TeAtularia tatumi irare) Uvigenna aubenana ismaili Ammodiscus tenu-s Aiomaiins {hn;ii Anomalma globulosa Ceraiobul.mina pacifica Irare) Cibicides cicatricosus Ci&cioes grosseoer'o'atus Cibic:aes kulier.bergi Cibicides rugosa Eggerella brady: i'large; GaLdryina 'lintn Gyroidma .neosoldanii HaD.orjrragmoides suDglocosun Karrenella novanghae Or'.dorsal is jmbonstus f'arge) Recurvoidusspp. Saccanmha ailanuca Trochammma globiger.r.iformss Uvigenna charlto.'iae Uvigenna rjstica icommor.) Bu.imina rostrata CeratoDUii. rnina pacifica (fewi Latjcarmma pauoeraia Nonior pompilioides (PLEISTOCENE ONLY! NurraMides decorata Ondorsalis iener Osang'j.anacuiter Pleurostomel'a spp. Vulvunna ser.na'.u:a Sane ta ^na as L.OWE3 3ATHVAL usoaily w.h abundance increases Planw.c and arenaceous SDC-cies often coM'nale the ;issemDlago Figure 1. - Selected foraminiferal paleoenvironmental indicators for the Pliocene and Pleistocene of the Gulf Coast Basin.

Poag (1981) has shown that temperature and salinity- are major factors in the distribution of living foraminifera. Other factors include substrate, food sup­ ply, and pressure to name a few. While most of these factors are difficult to measure, especially in more ancient sediments, the relative depth relationship of faunal assemblages and species are more easily deter­ mined. Crouch (1955) states that no exact depth rela­ tion is implied by his Miocene zonation. In other words, the assigned depth zones are relative - Zone B is deeper than Zone A. Consequently, an outer shelf zone in the lower Miocene may differ in exact depth limita­ tions from an outer shelf zone in the Pleistocene.

Changes through time in temperature, currents, sedi­ ment type, water mass, rates of deposition, and basin configuration all affect the microfaunal assemblages. KEY ENVIRONMENTAL MARKERS VERSUS ASSEMBLAGES Few foraminiferal species are limited to a single envi­ ronment (Walton, 1964; Murray, 1974). Among the most valuable taxa are those with either very limited ecologi­ cal tolerances (very rare, excepting some brackish water species), or those with known upper depth limits (Pflum and Frerichs, 1976). The enclosed environmen­ tal charts (Figs. 1 and 2) list Miocene and Plio- Pleistocene species identified either in the literature or by the writers as characteristic of particular zones.

Zonations which rely on genera only (Culver, 1988; Smith, 1991) are less accurate from an operational van­ tage due to two factors: time limits for evaluation (short) and occurrence of genera with wide bathymet- ric ranges (most). For example, the benthic genus Uvigerina ranges from abyssal depths up into the inner shelf. Species within this genus have more specific ranges. For example, Uvigerina rustica ranges from abyssal to upper bathyal; Uvigerina flintii ranges from upper bathyal to outer neritic; and Uvigerina Iwwei is typical only of the neritic zones.

Assemblages are very useful, probably being more accurate than key zonal, markers, because of the mixed nature of well cuttings. A good example of microfaunal assemblages is provided by Puri (1953). Examining Figure 7 of that paper, it is possible for an experienced paleontologist to determine relative bathymetry (shal­ low vs. deep) by the figured species. By knowing gen­ eral diversity and abundance trends of various species and assemblages (Walton, 1964), we are also able to estimate ranges for either new or unpublished taxa. BREARD, CALLENDAR, NAULT 495 SELECTED FORAMINIFERAL PALEOENVIRONMENTAL INDICATORS - MIOCENE - GULF OF MEXICO 0' 100' 300' 600' 1500' 3000' 6000'~ NON-MARINE MARGINAL MARINE INNER NERITIC MIDDLE NERITIC OUTER NERITIC UPPER BATHYAL Charoohytes | freshwater osiracoas j wooa/liynite Ammooacu:ites spp. Ammonia beccam E'phidium scp. Mi.iamrnicaapp. ostracons oysier trags Trocharrirnina teasi Compiled by S.Q. Breard A.D. Callender M.J. Nault (October.' 993) Arr.DMstegina lesson AmahisteginaB Bigenerna A B^generina B Bigonema2 Biger.enna -BsgenenriahuTiaei C:biciaes ccncenincus Discoros "2 Discorb s 24 D.scorbisd ssona Eponides rrwisJfploi mi'.ioiids Nonion spo. Non:onelia sop. Reusella miocorrca Robulus arrericanus Sipnonir-.a t:avisi (rarei Sorites spp. 'extularia sop.

DEEP INNER B.'arina vicksburgenais Ecomaes antilla rum Rorxnusspc:. ; beadedj Sichonina advena irarej Jvigeri na nowei peregrma (few) Bolivina rr.arginata Bolivina nu:ticostaia Bulimmaovata Bu'imina ouooides BLtiixineliacuna Cancris sagra Cibicides ir.oreyi Cioioaes amencanus CiDiuues carstensi Cibicides looaiulus Discords 3 Gyro.dina K Gyoidina miocenica Nodosara vertecraliii Nonion pizzarense Siononma aavena S.phonina davisi Uvigerina iuvicu:ata Uv;genna peregr na (common) DEEP MIDDLE Bolivina llorcara Boiivma thalrr.anni Cibicides flondan'js Cibiciaes38 Gvro'dma scalata (few: L.eDjsolla Dyarnensis Saracerana ser.ni Uvigerna 'irenensis MIDDLE BATHYAL LOWER BATHYAL ABYSSAL Allomorp^ina ~~~~~~~^_^^ trigo-.a ^^~~^~~^ Anorralira ~~~~~~. alazanensis Ammodiscus Cibicides bradyi tenuis Cibicices wa ii Anomalma CvciP.mm.na globuiosa cancellaia Arcmalina icomrron) semicnbratjs Eggereila b'advi Cbiciaes carnorti (small! C bicides Goesella acaincosus miocenica Cibicides Gyroidina Tundulus orbicularis CiD:cices Gvroidma soldan:i Sncherasens s Haplophragmoides C bicidus carmaturn wjellorstorfi HaclCDh'agrr.cides Cyciammina- emaciatum Egqerella braay Hapiopnragmoices (large) Drobiscidiform s Gvroama Haplophragnioides neosotdami wilsoni HaDiocnragmoides Karrenela Dradyi subglcbosurn LIODU seila Karrer.ella pozonenss novangliae NOP ion Matanzia pomrj'loides bemuoezi Planulina Nomon harargensis Dompilioides ^seudogiarcul na flarger- comaiu a commonl P-jllerna ouiloides Ondorsalis Schenci-.iella urnoona^us ticcidentahs ?!a"iLhna rerr: TextuiaratatLrri Saccammina icomrionj atlantica Uviaenna Uvgenna Decca 1-'! ade!e'*sis Uvqenna rustica Uvigerina r js:ica (iarge-^orrrron) (rare! Bulimira rosrata Karerella SLbcynnd'ica Laticanmra pajpe ra:a Oridorsans ter.er Osangulanacu.ter Osanguiana rrexicana PleurcstomeNa spp Tniaxilina atlartica Jvigerina serticosa Vuivulma nex.caaa Same fauna as LOWER BATHYAL. uajally w :th ncreases in aoonaance iBanay.'96-; Bergyren ana Miller. 1989) Figure 2. - Selected foraminiferal paleoenvironmental indicators for the Miocene of the Gulf Coast Basin ABYSSAL PALEOENVIRONMENTS In general, abyssal paleoenvironments are poorly known in the Gulf of Mexico (COM) fossil record and rarely described from literature of the Gulf Coast Basin.

Previously published abyssal zonations (Albers et al., 1966; Tipsword et al., 1966) list species with occurrence ranges into the bathyal, such as Nonion potnpilioides, Osangularia citlter, Cibicides wuellerstorfi, and Uvigerina scnticosa. Earlier zonations (Crouch, 1955;-Loep, 1965) did not separate abyssal from bathyal.

Pflum and Frerichs (1976) list nine sample stations in their COM study below 6000 feet. All taxa listed have upper depth limits in the bathyal realm. Two species, Uvigerina scnticosa and Nonion pompilioides, are listed as characteristic of the abyssal zone. While accurate for the modern GOM, we have observed Uvigerina scnti­ cosa in the lower bathyal and small Nonion pompilioides as shallow as upper bathyal in Miocene sections.

Bandy .(1964) states that lower bathyal zone foraminiferal assemblages are generally about the same as the abyssal zone faunas. Berggren and Miller (1989) note that abyssal biofacies are distinguished from bathyal primarily upon abundances. As a matter of fact, AB12, the youngest abyssal zone of Berggren and Miller (1989), ranges from the base of N12-N23, which covers the entire Plio-Pleistocene and over a third of the Miocene, and lists no abyssal extinction markers for that lengthy zone (over 11 million years).

Although benthic foraminifera have been recorded from the hadal zone (16,000 feet or deeper) by Bandy (1967) and Haynes (1981), we lack knowledge of defini­ tive abyssal-only marker species. From an operational viewpoint, we therefore submit that the abyssal zone in the Gulf Coast Neogene and Pleistocene section is too poorly known or defined to be recognized with confi­ dence. It is probable that reliable markers for the abyssal zone will eventually be found among the are­ naceous foraminifera (see Hemleben, et al., 1990).

GENERAL RULES FOR INDUSTRY PALE­ OENVIRONMENTAL DETERMINATION A few general rules are applicable for accurate deter­ mination of paleoenvironments with well cuttings:

1. The more abundant or diverse the fauna, the greater the potential accuracy of the environment picked.

2. Generally, one should emphasize the deepest dwelling species of an assemblage.

3. Reworking of shallow water species into deeper set­ tings is common, considering the nature and origin of turbidites (Bandy and Arnal, 1960). For example, it is 496 GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES not unusual to find the brackish species Ammonia bccca- rii and lignite in bathyal faunal assemblages due to downslope transport.

4. It is common to encounter samples from sandy tur- bidite, storm or slump deposits within bathyal settings with scarce to near-absent microfauna (eg., diluted fauna of Trenchard, 1968).

5. It is felt that planktic/benthic ratios (or planktic abundance curves) are relative, but not precise, pale- oenvironmental indicators (Grimsdale and van Morkhoven, 1955; Ventress, 1991). Although planktic floods have been considered to be slope and deeper (Smith, 1991), we have observed floods of Globigerina and Globigcrinoides spp. on the shelf. However, floods of Orbulina do occur most commonly in the bathyal range.

6. Increases in relative abundance of foraminifera in sediments reflect not only deepening, but slower rates of sedimentation (Moore, 1955). These abundance increases often occur in association with maximum flood surfaces.

7. Sudden paleocnvironmental changes (for example, from middle to deep outer neritic) without expected intermediate environments are suggestive of faults, unconformities, or possible gouge (Glaessner, 1955; Poag, 1977; Ventress, 1991).

PROBLEMS IN INDUSTRY PALEOENVI- RONMENTAL STUDIES A number of factors, many involving drilling and sample quality, can inhibit accuracy in paleocnviron­ mental interpretation:

1. Drilling Mud Additives - A great variety of addi­ tives, including mica, barite, calcite, gypsum, bentonite, glass, lignite, silica beads, nutplug, sand, and gilsonite are found in well cuttings. Abundant additive influxes reduce or obscure the microfauna within a sample.

2. Casing Cement - Cement usually obscures micro- fauna 30 to several hundred feet beyond casing point.

3. Bypass - On occasion, well cuttings bypass the shale shaker; hence no sample and no environment (see Poag, 1977).

4. Downhole Contamination - As drilling mud circu­ lates through the wellbore, it carries previously drilled and washed out formation fragments uphole, contami­ nating the well with younger sediments and micro- fauna. Failure to recognize "caving" can cause paleoe- cological calls to be inaccurate (Poag, 1977).

5. Environmental Mixing - Various physical processes (storms, turbidites, slumps, etc.) can mix species of dif­ ferent (shallower and deeper) assemblages together.

With experience, biostratigraphers will usually recog­ nize mixing. Jones (1956) lists several methods for recognition of ecologically or stratigraphically mixed faunas. HABITAT CHANGE THROUGH TIME Through millions of years of evolution and adapta­ tion, various marine taxa have changed or readjusted to new habitats. Dunlap (1981) observes that, in spite of the study by Boltovsky (1980) indicating middle bathyal similarities of Oligocene and Quaternary fau­ nas, a few exceptions do exist. Berggren and Miller (1989) state that a number of benthic foraminiferal species have changed depth distribution, migrating into deeper water niches over time. For example the Eocene Claiborne species Mclonis planatum was found by Gaskell (1989) to be characteristic of and abundant in transitional zones between normal and brackish facies of the Wheelock Member, Cook Mountain Formation in Houston County, Texas. The closely related Notion (Melonis) affinis of the Neogene is a char­ acteristic outer shelf to bathyal species (Poag, 1981).

Robinson (1970) describes the bathymetric fluctua­ tions of the arenaceous genus Cyclammina, observing that it extends into the neritic zone in Miocene sections, and becomes progressively rarer and deeper in Pliocene to younger faunas. Akers (1954) notes that recent Cyclammina cancellata occurs no shallower than 1,500 ft, considerably deeper than Miocene occurrences.

Documentation of the bathymetric travels of the cal­ careous benthic genus Ceratobulimitm is revealing. Early species, such as C. crctacen, C. pcrplcxa and C. cxiniia of the Late Cretaceous to middle Eocene, are limited to inner and middle shelf environs (Bandy, 1949; Tipsword, 1962; Sliter and Baker, 1972). Ccratobulimina alazanensis, which appears in the late Eocene, moves into outer shelf and possibly upper bathyal by middle Oligocene (Hackberry facies; Garrett, 1938). We have observed C. alazanensis (rarely) in middle shelf faunas of the lower Miocene. Whittaker (1988) documents C.

alazanensis from Ecuador (N7-N12), but gives no pale­ ocnvironmental data. By late Miocene, most occur­ rences of Ceratobulimina are limited to the bathyal. The species Ccratobulimina pacifica is restricted to middle and lower bathyal by Pliocene and early Pleistocene in the Gulf of Mexico, and is bathyal only in modern oceans (Barker, 1960).

Although Nonion pompilioides is typically considered a lower slope to abyssal species (Albers et al., 1966; Tipsword et al., 1966), we have documented Miocene occurrences of N. pompilioides in an upper bathyal realm, and small forms within outer shelf faunas hav­ ing no other bathyal species. Berggren (1987) docu­ ments the fluctuations of N. pompilioides, ranging from outer neritic to upper bathyal (mid to late Oligocene), but as deep as lower bathyal to abyssal only since the middle Miocene. Late Pleistocene well sample occur­ rences of this species are usually lower bathyal, but in the recent Gulf of Mexico fauna, N. pompilioides is lim­ ited to the abyssal zone (Pflum and Frerichs, 1976).

An example of the reverse trend is provided by Pullenia bulloides. This species, which ranges into deep middle neritic in the Pleistocene, is more typical of upper bathyal to deep outer neritic in the Miocene (shallowest occurrences).

Berggren and Miller (1989) document the migration of several foraminiferal genera into the bathyal zone, including species of Uvigerina, Melonis, Siphottina, and Planulina in the Eocene, and Sphaeroidina in the Oligocene. To this list we can add Ccratobulimina in the late Miocene. While it is apparent that selected genera have migrated to new habitats through time, this does not diminish their value in paleobathymetric models. BREARD, CALLENDAR, NAULT 497 As long as micropaleontologists carefully document the faunas, the overall assemblage should dictate the accu­ racy of the paleoenvironment in which these species occur. APPLICATION BEYOND THE GULF OF MEXICO One of the great values of the paleoecologic models presented here is its potential usage in areas outside the immediate Gulf Coast Basin. One clue to this potential is a perusal of the foraminiferal literature of Central and South America and the Caribbean region.

Several recent publications on Mexico (Sansores and Flores-Covarrubias, 1972; Kohl, 1985) list numerous Neogene species found in U.S. Gulf Coast sections.

Literature on Venezuela (Hedberg, 1937; Franklin, 1944; Renz, 1948) list many species used in our models.

Galloway and Morey (1929) and Whittaker (1988) are valuable references for microfaunal studies of Ecuador, listing many species common to both regions.

The various Caribbean islands have had many deep water faunas described. Countries with listings of many species common to both regions include Cuba (Hadley, 1934; Palmer and Bermudez, 1936), Jamaica (Cushman and Jarvis, 1930; Cushman and Todd, 1945), Haiti (Coryell and Rivero, 1940), the Dominican Republic (Bermudez, 1949), and Trinidad (Cushman and Stainforth, 1945; Bolli, 1957). These references have been especially useful for workers in the deep water sections of the US Gulf of Mexico, as few deep water faunas, excepting Leroy and Levison (1974) and Leroy and Hodgkinson (1975), have been described. The list of references presented here is by no means compre­ hensive. Kohl (1985) and Whittaker (1988) should be referred to for complete bibliographies.

Recent studies of bathyal foraminiferal fauna (van Morkhoven et al., 1986; Berggren and Miller, 1989) sug­ gest widespread, if not global uniformity in deep water fauna. Therefore, our paleoecologic models would appear to have value in microfaunal studies of Central and South America and the Caribbean region, and the bathyal portion of the models may have a worldwide application. MIOCENE THROUGH PLEISTOCENE MICROFAUNAL BIOSTRATIGRAPHY Although a complete evaluation and description of foraminiferal biostratigraphy is beyond the scope of this paper, it is necessary to update previously described zonations and to introduce several deep water markers to fill in biostratigraphic gaps left by use of commonly known shelf-dwelling "tops". The combi­ nation of standard benthic markers, planktic foraminifera and nannoplankton extinctions with these bathyal horizons achieves greater resolution than pre­ viously possible. Recently published charts with which this zonation can be compared include Skinner (1972), Poag and Valentine (1976), Poag (1977), Stude (1984), Dunlap (1988), and Ventress (1991).

The basic zonation presented here (Figs. 3 and 4) dif­ fers little from above noted schemes other than inte­ grating new markers, selected locals, and less fre­ quently used planktic species. It is placed within a nan- nofossil framework similar to that of Dunlap (1988) and Ventress (1991). This zonation is by no means com­ prehensive. Many other local markers, acmes, and increases are known within the industry. Poag (1977) states that perhaps thousands of additional local zones are extensively used for correlation in the Gulf Coast Basin.

A relatively new marker, Ehrenbergina fauna, based on the local occurrence of Ehrenbergina trigona with other associated fauna, denotes the upper Pleistocene Sangamon interval in the bathyal zone. A faunal increase lacking £. trigona is characteristic for the same interval in the neritic zone. Another calcareous species, Stilostoniclla antillea, has been used as downdip equiva­ lent (approximate) to Trimosina A, a neritic species. In bathyal sections, S. antillea occurs without Trimosina A.

In sections where both species can be expected to occur, S. antillea will typically be found just below the LAD (Last Appearance Datum) or extinction of Trimosina A.

A local increase (acme) of Giomospira chawidcs, a bathyal arenaceous species, is noted in a number of downdip well, stratigraphicallv below the LAD of Hyalinea balthica in the Gulf of Mexico. This acme is absent on the shelf. Another bathyal species, Uvigerina hispida, occurs within a deepening of the Aftonian. It is a good bathyal equivalent for Angulogerina B, a neritic species, and often occurs with a planktic foraminiferal flood, especially Sphacroidinella dehiscens. The deep water morphotype of Tcxtularia sica is very diagnostic of upper to middle bathyal deposits younger than the LAD of Globorotalia miocenka. The geographically widespread T. ska has been noted from East Breaks eastward to Mississippi Canyon in the Gulf of Mexico.

Two foraminifera, Ceratobulimina pacifica and Haplophragmoides emaciation, are useful markers of expanded lower Pleistocene bathyal intervals.

Ceratobulimina pacifica typically appears within a mid­ dle to lower bathyal deepening, as part of a significant faunal influx. Conversely, Haplophragmoides emaciatum usually appears within lower diversity, sand-rich expanded sections below the C. pacifica horizon.

Arenaceous extinctions and local acmes have not been published as extensively in the Gulf Coast Basin. A recent exception is the paper by Rosen and Hill (1990), which employs arenaceous assemblages to define Pliocene sequences in the GOM.

Another bathyal species, Uvigerina rustica, helps delineate the Globigeriria druri/i - Globigerina nepenthes section of the Pliocene. Best developed in middle to lower bathyal waters, U. rustica becomes extinct with or just above the LAD of G. nepenthes. Floods of Orbulina universa may be locally correlative in lower to middle bathyal settings in the Pliocene and Miocene (Poag, 1977).

The GOM Miocene-Pliocene boundary is possibly the most contentious of any time-stratigraphic boundary worldwide. The two uppermost Miocene benthic mark­ ers in most industry schemes are Robulus E and Bigenerina A, both neritic species. In a slope setting, various planktic taxa, both foraminifera and nannn- 498 GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES PLIOCENE PLEISTOCENE !EPOCHS 1— "I-0> en O N> 1 __ z Si rn > S3 ~ z i !>:i Hill b o G.O.M. PROVINCIAL AGE / STAGE 1— "I-0> en O N> rjl -fc> (ON) O O O CD NJ C N> o CO JS. - 1 CJi AGE IN M.Y. 7 T 2 a s f | Hill I i £ * ST 11 * i fills 1 ! I : ' ' - £• E '• : : : s s a !•!••• 5 j j j | : 1 1 i : i ! | f | ' i • i : ? ? , •f ! ; f'V * .- i i'"N, ii \!i I ' ' ' f " f " !. . - • r • - •: - "> • ' II. BENTHIC/PLANKTIC FORAMINIFERA Major Forarn Markers Local Foram Markers i i INNER 1 m DEEP INNER 1 m MIDDLE m: 5 i DEEP MIDDLE o DO o s i l OUTER DO o s ! DEEP OUTER I 5 - - 1 UPPER ? I 5 - - i MIDDLE 1 II LOWER > 1— 1 It f fSfl C*J ro O CD IP |S 1° 3J fn AGE IN M.Y. Figure 3. - Microfaunal biostratigraphy and paleoenvironmental ranges of marker foraminifera of Pliocene and Pleistocene strata of the Gulf Coast Basin plankton, have been utilized. Rainwater (1964) con­ tends that no valid criteria exist for determination of the Miocene-Pliocene boundary in the Gulf Coast. However, several lower bathyal benthic foraminifera occur near or just below the top of the Miocene, includ­ ing Planulina renzi, and the somewhat older Tritaxilina atlantica. Another bathyal event, a local acme of Nonion pompilioides, appears to be a near equivalent to the ner- itic marker Cristellaria K. A number of bathyal benthic foraminifera became extinct in the Miocene (van Morkhoven et al., 1986; Berggren and Miller, 1989), and should provide biostratigraphers with future topics of study, as their relationships within established zona- tions are discovered, hopefully through continued deep water exploration.

PALEOENVIRONMENTAL RANGES OF MARKER SPECIES Despite the extensive literature on foraminifera, no single published source exists for paleoenvironmental tolerance data of marker species of the Gulf Coast Basin. Tipsword et al. (1966) state that the best marker species are those with the greatest tolerance for many different environments, but poor as paleoecologic indi­ cators. Tipsword (1962) describes key faunal compo­ nents of marker faunas, but gives scant data on pale- oenvironments. Dunlap (1988) notes that traditional benthic markers progressively disappear downdip, and must be replaced by planktic zonal indicators. Because it is vital for all geologists and geophysicists to understand that marker species have environmental constraints, we have included in Figures 3 and 4, the usable paleoenvironmental range of each marker listed. The ranges presented are primarily based on many thousands of observations by the authors during the nearly 50 years cumulative experience with various oil companies and as consulting micropaleontologists/ biostratigraphers. No such chart could claim complete accuracy, but as information documented here is based on a wealth of data from wells spanning the Gulf Coast Basin, both onshore and offshore, we feel it will be a valuable interpretive tool for exploration and produc­ tion geoscientists in their search for the increasingly elusive hydrocarbon reservoir. BREARD, CALLENDAR, NAULT 499 MIOCENE ! EARLY MIDDLE -ATE | FLEMING GROUP 1 1 ro i\3 r\3 -* -* _. _* 1 _. _. — — -. -* ^ l\3 -* O

.••:'•..•••::•'.• ,'.• ii ?.-*;•-••'•::••••••',••' /•••; • noiG o "> i m ft: jo o "»o s3 II' 11 !•§, 13 1 i ffji«l3!|i| i : i i F | i i § i i T 1 i 1 1 ! i i i | i j , INNER ! M 1 DEEP INNER % > r-m O m z < 23 O lllllll 1 MIDDLE % > r-m O m z < 23 O ! III Illinium III II llllllllllfl 1 1 DEEP MIDDLE o > r-m O m z < 23 O ri n i jTT ff F J OUTER 2 m III It DEEP OUTER II i UPPER CD 5 1 1 | MIDDLE I I O -< m 1 LOWER > r-"' iin HI IIII ~r^—r is ? > is CO 03 CO CD AGE IN M.Y. Figure 4. - Microfaunal biostratigraphy and paleoenvironmental ranges of marker foraminifera of Miocene strata of the Gulf Coast Basin SUMMARY 1. Paleoecologic models for Plio-Pleistocene and Miocene foraminifera are presented. The widespread occurrences of Gulf Basin foraminifera 1 species sug­ gests possible application to Central and South America and the Caribbean. Bathyal zonations may have cosmopolitan value.

2. The abyssal environment is judged to be too poorly defined to be recognize due to the lack of abyssal zone markers and a reliance on faunal abundances only. Arenaceous taxa may prove useful for splitting out this zone.

3. Through time, a number of foraminiferal genera and species have changed habitat preference, with several migrating into deeper water since the Miocene {Cyclammina cancellata, Nonion pompilioides, Ceratobulimina spp.). Migration into shallower water (Pullenicr bulloides) is less common. 4. The Miocene through Pleistocene biostratigraphic zonation is updated, introducing a number of bathyal and local benthic markers. These tops fill in strati- graphic gaps and end the misconception that only planktic species are useful for downdip correlations. 5. Paleoenvironmental ranges are presented for all listed marker foraminifera. Because no such chart has been published previously, this represents a valuable new tool for geoscientists who should and must use foraminiferal marker zones in their work. ACKNOWLEDGMENTS The authors wish to thank their numerous colleagues at the various companies with which they been employed. We also want to acknowledge past and cur­ rent researchers in our rapidly shrinking field of micropaleontology and biostratigraphy. Special thanks to two anonymous reviewers for their comments and suggestions. This paper is dedicated to the memory of two late great microscope-using data collectors and true biostratigraphers with whom the authors have had the privilege of working: A,J. Gaudin of Tenneco and Henry D. Linder of Amoco. REFERENCES CITED Akers, W.H., 1954, Ecological aspects and stratigraphic significance of the foraminifera Cyclammina cancellata 500 GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES Brady: Jour. Paleo., v. 28, no. 2, p. 132-152. Albers, C.C., et al., 1966, Foraminiferal ecological zones of the Gulf Coast: GCAGS Trans., v. 16, p. 345-348. Bandy, O.L., 1949, Eocene and Oligocene foraminifera from Little Stave Creek, Clarke County, Alabama:

Bull. Amer. Paleo., v. 32, no. 131, 210 p. Bandy, O.L., 1964, General correlation of foraminiferal structure with environment; in J. Imbrie and N.D. Newell, eds., Approaches to Paleoecology, John Wiley & Sons, Inc., New York, p. 75-90. Bandy, O.L., 1967, Foraminiferal indices in paleoecol­ ogy. EPR67-ER20, unpublished manuscript, 77 p. Bandy, O.L. and R.E. Arnal, 1960, Concepts of foraminiferal paleoecology: AAPG Bull., v. 44, no. 12, p. 1921-1932. Barker, R.W., 1960, Taxonomic Notes on the Species Figured by H.B. Brady in His Report on the Foraminifera Dredged by H.M.S. Challenger During the Years 1873-1876: SEPM Spec. Pub. No. 9, 238 p. Berggren, W.A., 1987, Bathyal benthics: back to basics; in Innovative Biostratigraphic Approaches to Sequence Analysis: New Exploration Opportunities: GCSSEPM 8th Ann. Research Conf., Papers and Abstracts, p. 24-33. Berggren, W.A. and K.G. Miller, 1989, Cenozoic bathyal and abyssal calcareous benthic foraminiferal zona­ tion: Micropaleontology, v. 35, no. 4, p. 308-320. Bermudez, P.J., 1949, Tertiary smaller foraminifera of the Dominican Republic: Cushman Lab. Foram. Research, Spec. Pub. No. 25,322 p. Bolli, H.M., 1959, Planktonic foraminifera as index fos­ sils in Trinidad, West Indies and their value for worldwide stratigraphic correlation: Eclog. Geol.

Helv., v. 57, no. 2, p. 627-637. Boltovskoy, E., 1980, On the benthonic bathyal-zone foraminifera as stratigraphic guide fossils: Jour. Foram. Research, v. 10, no. 3, p. 163-172. Coryell, H.N. and F.C. Rivero, 1940, A Miocene micro- fauna of Haiti: Jour. Paleo., v. 14, no. 4, p. 324-344. Crouch, R.W., 1955, A practical application of paleoe­ cology in exploration: GCAGS Trans, v. 5, p. 89-96. Culver, S.J., 1988, New foraminiferal depth zonation of northwestern Gulf of Mexico: Palaios, v. 3, no. 1, p. 69-85. Cushman, J.A. and P.W. Jarvis, 1930, Miocene foraminifera from Buff Bav, Jamaica: Jour. Paleo., v. 4, p. 353-368. Cushman, J.A. and R.M. Stainforth, 1945, The foraminifera of the Cipero Marl Formation of Trinidad, British West Indies: Cushman Lab. Foram. Research, Spec. Pub. No. 14, 75 p., 16 pis. Cushman, J.A. and R. Todd, 1945, Miocene foraminifera from Buff Bay, Jamaica: Cushman Lab. Foram. Research, Spec. Pub. No. 15, 73 p., 12 pis. Dunlap, J.B., 1981, Paleoecology - fact or fiction; in Recognition of Shallow-Water Versus Deep-Water Sedimentary Facies in Growth-Structure Affected Formations of the Gulf Coast Basin: GCSSEPM 2nd Ann. Research Conf., Program and Abstracts, p. 31- 33. Dunlap. J.B., 1988, Biostratigraphy of the Gulf of Mexico in Offshore Louisiana Oil and Gas Fields, Volume 2: New Orleans Geol. Soc, p. 81-83. Franklin, E.S., 1944, Microfauna from the Carapita Formation of Venezuela: Jour. Paleo., v. 18, no. 4, p. 301-319. Galloway, J.J. and M. Morey, 1929, A lower Tertiary foraminiferal fauna from Manta, Ecuador: Bull.

Amer. Paleo., v. 15, no. 55, p. 7-56, 6 pis. Garrett, J.B., 1938, The Hackberry Assemblage - an interesting foraminiferal fauna of post-Vicksburg age: Jour. Paleo., v. 12, no. 4, p. 309-317. Gaskell, B.A., 1989, Paleoecology of the Eocene Wheelock Member of the Cook Mountain Formation in western Houston County, Texas: GCAGS Trans., v. 39, p. 365-374. Glaessner, M.F., 1955, Taxonomic, stratigraphic and ecologic studies of foraminifera and their interpreta­ tions: Micropaleontology, v. 1, no. 1. p. 3-8. Grimsdale, T.F. and F.P.C.M. van Morkhoven, 1955, The ratio between pelagic and benthonic foraminifera as a means of estimating depth of deposition of sedi­ mentary rocks: Proc. 4th World Petrol. Congress, sec. 1/d, paper 4, p. 473-491. Hadley, W.H., 1934, Some Tertiary foraminifera from the north coast of Cuba: Bull. Amer. Paleo., v. 20, no. 70A, p. 1-41. Haynes, J.R., 1981, Foraminifera: John Wiley & Sons, New York, 433 p. Hedberg, H.D., 1937, Foraminifera of the middle Tertiary Carapita Formation of northwestern Venezuela: Jour. Paleo., v. 11, no. 8, p. 661-697. Hemleben, C, M.A. Kaminski, W. Kuhnt and D.B. Scott, eds., 1990, Paleoecology, Biostratigraphy, Paleoceanography and Taxonomy of Agglutinated BREARD, CALLENDAR, NAULT 501 Foraminifera: NATO ASI Series C, v. 327, Kluwer Academic Publishers, Boston, 1017 p. Jones, D.J., 1956, Introduction to Microfossils: Harper & Brothers Publishers, New York, 406 p. Kohl, B., 1985, Early Pliocene benthic foraminifera from the Salina Basin, southeastern Mexico: Bull. Amer.

Paleo., v. 88, no. 322,173 p. Lamb, J.L., 1981, Marine environmental terminology and depth- related environments: GCAGS Trans., v. 31, p. 329-337. Leroy, D.O. and K.A. Hodgkinson, 1975, Benthonic foraminifera and pteropods from a deep-water dredge sample, northern Gulf of Mexico: Micropaleontology, v. 21, no. 4, p. 420-447. Leroy, D.O. and S.A. Levinson, 1974, A deep-water Pleistocene microfossil assemblage from a well in the northern Gulf of Mexico: Micropaleontology, v. 20, no. 1, p. 1-37. Loep, K.J., 1965, A study of ecology and distribution of recent foraminifera in the northwest Gulf of Mexico: GCAGS Trans., v. 15, p. 167-177. Moore, D.G., 1955, Rates of deposition shown by rela­ tive abundance of foraminifera: AAPG Bull., v. 39, no. 8, p. 1594-1600. Murray, J.W., 1974, Distribution and Ecology of Living Benthic Foraminiferids: Crane, Russak & Co., New York, 274 p. Palmer, D.K. and P.J. Bermudez, 1936, Late Tertiary foraminifera from the Matanzas Bay region, Cuba: Sociedad Cubana de Historia Natural, Memoirs, v. 9, no. 4, p. 237-258. Pflum, C.E. and W.E. Frerichs, 1976, Gulf of Mexico deep- water foraminifers: Cushman Foundation Foram. Research, Spec. Pub. No. 14,125 p. Phleger, F.B., 1960, Ecology and Distribution of Recent Foraminifera: Johns Hopkins Univ. Press, Baltimore, 297 p. Poag, C.W., 1977, Biostratigraphy in Gulf Coast Tertiary exploration: in E.G. Kauffman and J.E. Hazel, eds., Concepts and Methods of Biostratigraphy: Dowden, Hutchinson and Ross, Inc., p. 213-233. Poag, C.W., 1981, Ecological Atlas of Benthic Foraminifera of the Gulf of Mexico: Hutchinson Ross Publishing Co., 174 p. Poag, C.W. and PC. Valentine, 1976, Biostratigraphy and ecostratigraphy of the Pleistocene basin, Texas- Louisiana continental shelf: GCAGS Trans., v, 26, p. 185-256. Puri, H.S., 1953, Contributions to the study of Miocene of the Florida Panhandle: Florida Geol. Survey Bull., no. 35, 345 p. Rainwater, E.H., 1964, Regional stratigraphy of the Gulf Coast Miocene: GCAGS Trans., v. 14, p. 81-124. Renz, H.H., 1948, Stratigraphy and fauna of the Agua Salada Group, State of Falcon, Venezuela: GSA Memoir no. 132, 219 p. Robinson, G.S., 1970, Change of the bathymetric distri­ bution of the genus Cyclammiw. GCAGS Trans., v. 20, p. 201-209. Rosen, R.N. and W.A. Hill, 1990, Biostratigraphic appli­ cation to Pliocene-Miocene sequence stratigraphy of the western and central Gulf of Mexico and its inte­ gration to lithostratigraphy: GCAGS Trans., v. 40, p. 737-743. Sansores, J.C. and C. Flores-Covarrubias, 1972, Foraminiferos bentonicos del Terciario superior de la Cuenca Salina del Istmos de Tehuantepes, Mexico: Instituto Mexicano de Petroleo, vols. 1 and 2, 535 p. Skinner, H.C., 1966, Modern paleoecological tech­ niques: an evaluation of the role of paleoecology in Gulf Coast exploration: GCAGS Trans., v. 16, p. 59- 79. Skinner, H.C., ed., 1972, Gulf Coast Stratigraphic Correlation Methods with an Atlas and Catalogue of Principal Index Foraminiferida: Louisiana Heritage Press, New Orleans, 213 p. Sliter, W.V. and R.A. Baker, 1972, Cretaceous bathymet­ ric distribution of benthic foraminifers: Jour. Foram. Research, v. 2, no. 4, p. 167-183. Smith, C.C., 1991, Foraminiferal biostratigraphic framework, paleoenvironments, rates of sedimenta­ tion, and geologic history of the subsurface Miocene of southern Alabama and adjacent state and federal waters: Geol. Survey of Alabama, Bull. 138, 223 p. Stude, G.R., 1984, Neogene and Pleistocene biostrati­ graphic zonation of the Gulf of Mexico Basin; in Characteristics of Gulf Basin Deep-Water Sediments and Their Exploration Potential: GCSSEPM 5th Ann. Research Conf., Program and Abstracts, p. 92-101. Tipsword, H.L., 1962, Tertiary foraminifera in Gulf Coast petroleum exploration and development; in E.H. Rainwater and R.P. Zingula, eds., Geology of the Gulf Coast and Central Texas: Houston Geol. Soc. Guidebook, p. 16-57. Tipsword, H.L., F.M. Setzer and F.L. Smith, 1966, Interpretation of depositional environment in Gulf Coast petroleum exploration from paleoecology and related stratigraphy: GCAGS Trans., v. 16, p. 119-130. 502 GULF COAST ASSOCIATION OF GEOLOGICAL SOCIETIES Trenchard, W.H., 1968, Sedimentation and the distribu­ tion of marine biofacies: GCAGS Trans., v. 18, p. 205- 207. Van Morkhoven, F.P.C.M., W.A. Berggren and A.S. Edwards, 1986, Cenozoic Cosmopolitan Bathyal Benthic Foraminifera: Bull. Centres Rech. Explor.- Prod. Elf-Aquitane, Pau, Memoir 11,421 p., 126 pis. Ventress, W.P.S., 1991, Paleontology and its application in south Louisiana hydrocarbon exploration; in D.

Goldthwaite, ed., An Introduction to Central Gulf Coast Geology: New Orleans Geol. Soc, p. 85-98. Walton, W.R., 1964, Recent foraminiferal ecology and paleoecology; in J. Imbrie and N.D. Newell, eds., Approaches to Paleoecology: John Wiley & Sons, New York, p. 151-237. Whittaker, J.E., 1988, Benthic Cenozoic Foraminifera from Ecuador: British Museum of Natural History, London, 194 p.