Benthic Foraminiferal Biofacies Research Articles

POST-GLACIAL PALEOCEANOGRAPHIC HISTORY OF SAANICH INLET, BRITISH COLUMBIA, BASED ON FORAMINIFERAL PROXY DATA

Five benthic foraminiferal biofacies characterize the late Pleistocene to Recent succession at ODP Sites 1033B and 1034B (Leg 169S) in Saanich Inlet, southern Vancouver Island, British Columbia. These faunas document three distinct paleoceanographic phases in the evolution of this inlet. From the latest Pleistocene, ~14,000 years BP, to the earliest Holocene, the distribution of benthic foraminifera ( Cribroelphidium excavatum [Biofacies 5]), Islandiella norcrossi [Biofacies 4], and Nonionella stella [Biofacies 3]) in Saanich Inlet was strongly controlled by the influence of cold, low-salinity waters associated with deglaciation. Early Holocene sediments are characterized by Stainforthia feylingi Biofacies 2. Despite a shallower sill depth at the entrance of Saanich than exists today sedimentological and foraminiferal evidence indicate that bottom waters were oxygenated. The foraminiferal fauna indicates that oxygen levels varied from a minimum low oxic (1.5–3 ml/l [67–133 μM]) level early on to suboxic (0.3–1.5 ml/l [13.3–67 μM]) conditions up section where sediments become progressively more laminated. During the early Holocene air temperatures in the region were up to 4°C warmer, and it was much drier than at present. The resultant reduced freshwater flow into the southern Strait of Georgia was conducive to the free exchange of Saanich Inlet bottom waters with those of well-oxygenated Haro Strait. After 7000 years BP the climate in the region cooled and, as the influence of freshwater from Strait of Georgia increased, oxygenation of Saanich bottom waters became a rare occurrence. Finely-laminated sediments characterized mid-Holocene to Recent sediments in the inlet reflecting the development of full anoxic conditions at depth. The Lobatula fletcheri–Buccella frigida Biofacies 1 characterizing this interval is allochthonous and derived by down-slope transport from shallower, more oxygenated regions of Saanich Inlet.

Two-Dimensional Paleoslope Modeling: A New Method for Estimating Water Depths of Benthic Foraminiferal Biofacies and Paleoshelf Margins

ABSTRACT A new method developed for estimating water depths of benthic foraminifers was implemented for Oligocene foraminiferal biofacies from the New Jersey Coastal Plain. We combined benthic foraminiferal biofacies and two-dimensional flexural backstripping to construct a two-dimensional paleoslope model. The original depositional geometry of New Jersey Oligocene strata was reconstructed by calculating the effects of sediment accumulation and flexural loading. Paleodepth estimates for benthic foraminiferal biofacies were calibrated to inner neritic facies along the resulting nonlinear profile (e.g., with clinoforms). Paleodepth estimates for ten foraminiferal biofacies ranged from 20 ± 10 m to 115 ± 30 m and were consistent with more qualitative estimates based on other methods (e.g., foraminiferal abundances and species diversity). Applying this method to the New Jersey coastal plain for the Oligocene showed clear distributional patterns of benthic foraminiferal biofacies. This enabled paleobathymetry to be determined for the reconstructed New Jersey margin as well as significant stratal surfaces within sequences (i.e., systems tracts and condensed sections). Paleodepth estimates ranged from nearshore (20 ± 10 m) up to 85 ± 25 m for deposits landward of the clinoform rollover of the underlying sequence boundary and from middle neritic to outer neritic (50 ± 20 m to over 100 ± 30 m) on the slopes of the clinoforms. During earliest transgressive systems tracts, paleodepths immediately seaward of the clinoform slope ranged from inner neritic ( 100 m) at downdip sites. During early highstands, paleobathymetry ranged from 45 ± 10 to 85 ± 25 m landward of the clinoform rollover to 85 ± 25 m to over 100 ± 30 m on the slope (seaward of the developing prograding sedimentary wedge), while during late HSTs, paleodepths shoaled to as shallow as 25 ± 10 m near the clinoform rollover. This method can be applied to other continental passive margins to reconstruct the stratal geometry of and estimate water depths on the shelf. Furthermore, by extending this process, relative sea level and eustatic timings and amplitudes could be evaluated.

Oligocene eustasy from two-dimensional sequence stratigraphic backstripping

Research Article| March 01, 2001 Oligocene eustasy from two-dimensional sequence stratigraphic backstripping Michelle A. Kominz; Michelle A. Kominz 1Department of Geosciences, Western Michigan University, 1187 Rood Hall, Kalamazoo, Michigan 49008-5150, USA Search for other works by this author on: GSW Google Scholar Stephen F. Pekar Stephen F. Pekar 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964-8000, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Michelle A. Kominz 1Department of Geosciences, Western Michigan University, 1187 Rood Hall, Kalamazoo, Michigan 49008-5150, USA Stephen F. Pekar 2Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964-8000, USA Publisher: Geological Society of America Received: 27 May 1999 Revision Received: 20 Dec 1999 Accepted: 28 Feb 2000 First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2001) 113 (3): 291–304. https://doi.org/10.1130/0016-7606(2001)113<0291:OEFTDS>2.0.CO;2 Article history Received: 27 May 1999 Revision Received: 20 Dec 1999 Accepted: 28 Feb 2000 First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michelle A. Kominz, Stephen F. Pekar; Oligocene eustasy from two-dimensional sequence stratigraphic backstripping. GSA Bulletin 2001;; 113 (3): 291–304. doi: https://doi.org/10.1130/0016-7606(2001)113<0291:OEFTDS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Estimates of the magnitudes of changes in third-order (0.5−2 m.y.) eustasy were obtained for Oligocene sequences defined by a suite of largely onshore boreholes of the New Jersey coastal plain. Benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study. The geometry of the margin through time was determined using two-dimensional backstripping. The depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries. Benthic foraminiferal biofacies were then used to determine the depths of the Oligocene margin profiles obtained from backstripping. The water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells. This internal consistency indicates that the data and the two-dimensional backstripping approach were robust. Where benthic biofacies require a vertical shift of the horizons generated by two-dimensional backstripping, eustatic changes were required and were readily calculated.Results indicate a major eustatic fall from the end of the Eocene to the first record of Oligocene deposition. Subsequent long-term shoaling of sea level through the Oligocene was ∼30 m in 10 m.y. Superimposed on this long-term trend were higher frequency (third-order) variations in eustasy with amplitudes of ∼40 m or less. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Abstract: Two-dimensional paleoslope modeling: a new method for estimating water depths for benthic foraminiferal biofacies, paleo shelf margins, and systems tracts

Abstract: Two-dimensional paleoslope modeling: a new method for estimating water depths for benthic foraminiferal biofacies, paleo shelf margins, and systems tracts

Foraminiferal evidence for Cenomanian sequence stratigraphy and palaeoceanography of the Boulonnais (Paris Basin, northern France)

A middle to upper Cenomanian chalk succession in the northwestern European Paris Basin (Escalles section) was investigated with respect to its sediment composition, biofacies, and foraminiferal content. Most planktic foraminifers exhibit a high-frequency cyclicity in their distribution pattern and show little relationship to the sequence stratigraphic subdivision. A few characteristic species of benthic foraminifers ( Tritaxia pyramidata, Ataxophragmium compactum, Dorothia levis, and Gavelinella cenomana) are related in their frequency distribution to certain systems tracts. Other benthic foraminiferal species are more evenly distributed through the systems tracts. Cluster analysis and factor analysis allow the separation of three benthic foraminiferal biofacies domains, which exhibit a characteristic frequency distribution pattern with respect to sequence stratigraphy. Biofacies 1 is dominant in the highstand systems tract (HST), and biofacies 3 is characteristic for the transgressive systems tract (TST). Biofacies 2 is most abundant around the maximum flooding–downlap surface (mfs) and less abundant around the sequence boundary. Factor analysis shows that most of the variance in the data set is explained by variables related to plankton productivity. Variables related to changes in water depth and changes in sea-level have minor influence on the variance of the whole data set, but have some influence on the variance of the benthic foraminiferal data set. The different reaction of benthic and planktic foraminifers to relative sea-level changes is also recorded in the total number of foraminifers per gram sediment (foraminiferal number) and in the ratio between planktic and benthic foraminifers (p/b-ratio). The foraminiferal number is highest at the mfs and lowest at the sequence boundaries of the investigated depositional sequences. The p/b-ratio has no correlation with the sequence stratigraphic subdivision, but shows a high-frequency cyclicity. The abundance pattern of planktic foraminifers is controlled by changes in the productivity of calcareous plankton. The regular variation in calcareous plankton productivity leads to marl (low productivity)–chalk (high productivity) cycles that form conspicuous couplets in the section. The productivity cycles are also recorded in gamma-ray logs in the environmental setting of the Escalles section. In contrast, the abundance patterns of benthic foraminifers are more influenced by relative sea-level changes, changes in water depth, and variations in substrate composition. The stacking of probably precession-controlled development of couplets lead to a distinct 100,000-year cyclicity that does not match very well with published sequence stratigraphic subdivisions.

Late Albian benthic foraminiferal biofacies and paleogeography of Northeast Germany

Late Albian benthic foraminiferal biofacies and paleogeography of Northeast Germany

Modern benthic foraminiferal biofacies across the Northern North Sea

Abstract Foraminiferal distributions along a transect across the northern North Sea have been investigated in II surface sediment samples. Based on benthic calcareous foraminifera, four biofacies are defined; the Cibicides lobatulus, the Bulimina marginata, the Elphidium excavatum and the Cassidulina laevigata biofacies. The Cibicides lobatulus biofacies is found in areas with coarse grained sediments and high energy regime. The Bulimina marginata biofacies is found in an area with shifting hydrography and the development ofa thermocline. All tests of Elphidium excavatum found in the Elphidium excavatum biofacies are considered reworked. The Cassidulina laevigata biofacies is located in connection with Atlantic water in the Norwegian Channel. The same distribution pattern is found for the agglutinated fauna. The distribution of planktonic specimens reflects the inflow of Atlantic water along the Norwegian Channel and on the Fladen Ground. A total number of14 7 benthic species were recognized in the samples.

Depositional and microfaunal response to Pliocene climate change and tectonics in the eastern Gulf of Alaska

The Yakataga Formation provides an excellent record of Pliocene paleoclimate in the Gulf of Alaska and northeastern Pacific Ocean. Evidence for glaciomarine influence and paleoclimatic change includes the distribution of ice-rafted debris and diamictite, planktic and benthic foraminiferal biofacies, and variable sediment accumulation rates. Three paleoclimatically defined intervals within the Pliocene Yakataga Formation are recognized in onshore and offshore sections. Interval P1 (5.35 to 4.2 Ma) contains the first evidence of Neogene glaciomarine deposition in the form of ice rafted debris and rare diamictite. Interval P2 (4.2 to 3.0–3.5 Ma) exhibits a reduction in glaciomarine influence and warming to cool temperate conditions. Interval P3 (3.0–3.5 to 1.8 Ma) contains massive amounts of glaciomarine diamictite and correlates with other evidence indicating the onset of major northern hemisphere glaciation. Sediment accumulation rate and foraminiferal based paleobathymetric curves show some correlation to the above paleoclimatic subdivision, but also significant independent relationships, indicating a strong tectonic influence on those parameters. Comparison of the Yakataga record to ODP sites in the North Pacific shows that there is good agreement in the ice-proximal (Yakataga) and deep-sea records of Pliocene paleoclimate change.

Expanded record of Quaternary oceanographic change: Amerasian Arctic Ocean

Four sediment cores collected from the Northwind and Mendeleyev ridges, Arctic Ocean, from 1089 m to 1909 m water depth, provide an oceanographic record extending back into the Matuyama reversed polarity chron. Benthic foraminiferal analyses show four prominent assemblage zones: Bolivina arctica , Cassidulina teretis , Bulimina aculeata , and Oridorsalis tener from the upper Matuyama reversed polarity chronozone through the Brunhes normal polarity chronozone. These assemblage zones represent depth-dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the Amerasian basin at ∼780 and 300 ka, and indicate oceanographic influence from the North Atlantic. Recognition of these benthic assemblage zones in Arctic cores from the Alpha Ridge indicates that the benthic foraminiferal zonations in intermediate to deep water (>1000 m) Arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the Quaternary paleoceanographic evolution of the Arctic Ocean.

Eocene-Oligocene Benthic Foraminiferal Biofacies and Depositional Sequences at the ACGS #4 Borehole, New Jersey Coastal Plain

Eocene-Oligocene Benthic Foraminiferal Biofacies and Depositional Sequences at the ACGS #4 Borehole, New Jersey Coastal Plain

Holocene Deepwater Benthic Foraminiferal Biofacies, Northwestern Gulf of Mexico: ABSTRACT

Holocene Deepwater Benthic Foraminiferal Biofacies, Northwestern Gulf of Mexico: ABSTRACT

Intertidal Benthic Foraminiferal Biofacies on the Central Gulf Coast of Texas: Modern Distribution and Application to Sea Level Reconstruction

Intertidal Benthic Foraminiferal Biofacies on the Central Gulf Coast of Texas: Modern Distribution and Application to Sea Level Reconstruction

Bathymetric Zonation and Relationship to Sea-Bed Environments of Modern Benthic Foraminiferal Biofacies, Northwestern Gulf of Mexico Slope: ABSTRACT

ABSTRACT The distribution of benthic foraminifera in surface sediments of the northwest Gulf of Mexico slope is studied in 51 piston core-top samples ranging in depth from 141 to 2,134 m (462 to 7,000 ft). Total faunas (living plus dead specimens) are documented as part of a larger study investigating the relationship of living benthic foraminiferal distributions, their relationship to surface sediment and infaunal environments, and taphonomic processes within these environments that produce fossil assemblages. A total of 161 taxa are recognized in the samples, only 23 of which have population abundances greater than 1%. Quantitative analyses of the data include cluster analysis of samples, principal components analysis (PCA), and detrended reciprocal averaging (DRA). Cluster analysis defines four major biotopes that occupy geographically distinct areas and are oriented parallel to depositional strike. Actual depth ranges of the biotopes overlap, pointing to the gradual nature of faunal change with depth on the slope, as recognized by previous studies in this area. Approximate faunal boundaries are present at 500 m (1,640 ft), 1,100 m (3,610 ft), and possibly 1,500 m (4,920 ft). PCA and DRA identify species relationships that characterize the biotopes. The shallowest biotope (141 to 500 m [462 to 1,640 ft]), within the limits of the weak oxygen minimum in this area (ca. 2.6 ml/l), is characterized by Uvigerina peregrina, Bolivina albatrossi, and Bulimina alazanensis. The next deeper biotope (ca. 500 to 1,600 m [1,640 to 5,250 ft]) is distinguished by Epistominella exigua, Pullenia subsphaerica, and Glomospira charoides. This biotope grades downslope (ca. 1,200 to 2,100 m [3,940 to 6,890 ft]) into one delineated by Eponides turgidus, Bulimina aculeata, Osangularia culteri, and Gyroidina orbicularis. The deepest biotope (ca. 1,500 to 2,134 m [4,920 to 7,000 ft]) is characterized by Alabamina decorata, Hoeglundina elegans, Reophax spp., and Hormosina sp. Downslope transport is evident in several samples.

Late Quaternary benthic foraminiferal biofacies and paleoceanography of Queen Charlotte Sound and southern Hecate Strait, British Columbia

Analysis of Late Quaternary benthic foraminifera in cores from Queen Charlotte Sound and Hecate Strait yields new information on the paleoceanographic history of the region. Q-mode cluster analysis grouped samples into seven associations reflecting benthic foraminiferal biofacies: the Gyroidina-Bolivina Biofacies and Gyroid­ ina-Seabrookia Biofacies are relict lower to middle bathyal faunas introduced to shallower depths when cooler water masses influenced the area; the Cribroel­ phidium Biofacies, I slandiella Biofacies, Epistominella Biofacies, and Bucella Biofacies are similar to each other in faunal makeup and characterize varying depositional conditions at neritic depths; the Lobatuln-Gavelinopsis Biofacies characterizes shallow, high energy, shelly banks. Repetition of many of these biofacies in the cores indicates an overall instability, or cyclic nature, of the water masses affecting the region through the Late Qua­ ternary. A gradual increase in the proportion of Buliminelln elegantissima, a foraminifer associated with terriginous plant debris suggests a gradual decrease in sea level dur­ ing deposition of the Bl lithologic unit (~= 12,000 years BP in the cores presented here) deposited at most sites. A population maximum of Buliminella elegantissima in diachronous lag deposits of the B2 lithologic unit (=11,600-10,000 years BP) indicates a maximum low­ stand. The almost complete absence of this species in superjacent B3 lithologic unit sediments indicates subse­ quent rapid subsidence and termination of terrestrial organic input, probably due to the collapse of the Fraser Glaciation forebulge. Deposition of the B3 unit had ter­ minated everywhere in the region by =9,000 years BP. A Cassidulina reniforme population maximum occurs in sediments dated between about 10,100 and 11,300 years B.P. The presence of high proportions of this species, associated with very cold water (glacial or near-glacial) regimes, indicates a brief interval of cooler conditions during deglaciation, isochronous with the Younger Dryas event of Europe and eastern North America. This suggests that this event is not restricted to the North Atlantic but represents a much more widespread phe­ nomenon.

Latest Oligocene to Earliest Pliocene Benthic Foraminiferal Biofacies of the Northeastern Gulf of Mexico

We examined uppermost Oligocene to lowermost Pliocene sections from four northeastern Gulf of Mexico boreholes for quantitative benthic foraminiferal faunal changes, stratigraphic ranges, paleobathymetry, organic carbon content, and planktonic foraminiferal relative abundances. The Eureka boreholes provide a depth transect in the De Soto Canyon area from the upper to lower bathyal zone: E68-136 (557m present depth, -600m paleodepth), E66-73 (857m present depth, 860-lOOOm paleodepth), E68-151A (1326m present depth, -1300m paleodepth), and E68-14 1A (1599m present depth, -1600m paleodepth). A number of taxa last appeared in the late Oligocene to early Miocene (Biochrons P22-N5) at E68-136; several of these disappearances constitute global last occurrences. A global benthic foraminiferal taxonomic turnover that began in the latest early Miocene in other parts of the ocean was restricted to the middle Miocene at E68-136 (Biochrons N9-N12), although faunal abundance changes began in late early Miocene Biochron N8. At middle bathyal borehole E66-73, ten taxa last occurred in Biochrons N8-N10, which is consistent with the timing of the taxonomic turnover in the Pacific and Atlantic. Depth-related faunal trends are examined and compared with previously published distributional data, resulting in revised paleobathymetric ranges of 12 taxa. Detailed age-paleodepth reconstructions reveal several stratigraphically and bathymetrically significant predominance biofacies in the northeast Gulf of Mexico: 1) Uvigerina pigmea dominated the middle-upper bathyal late Neogene; 2) Lenticulina spp. dominated the late Oligocenemiddle Miocene bathyal zone; 3) Oridorsalis spp., Gyroidinoides spp., and Globocassidulina subglobosa dominated the late Neogene lower bathyal zone; and 4) Uvigerina proboscidea was important in the late Neogene in the middle to upper bathyal zones. Four distinct bathymetric migrations are mapped, and 34 additional taxa are shown to have distinct paleobathymetric distributions. Planktonic foraminiferal biostratigraphic control allows us to evaluate the stratigraphic usefulness of benthic foraminiferal ranges. We revise the stratigraphic ranges of 12 bathyal benthic foraminiferal taxa, requiring re-correlation of the benthic foraminiferal zonal boundaries of Berggren and Miller (1989). INTRODUCTION Previous studies have shown that one of the largest benthic foraminiferal faunal changes of the Cenozoic occurred throughout the deep sea (>200m) in the late early to middle Miocene (Berggren 1972; Schnitker 1979, 1986; Woodruff and Douglas 1981; Boersma 1986; Thomas 1985, 1986a, 1886b, 1989, 1992; Woodruff 1985; Kurihara and Kennett 1986; Miller and Katz 1987; Thomas and Vincent 1987; Woodruff and Savin 1989; Miller et al. 1992; Thomas 1992; for an alternative view, see Boltovskoy and Boltovskoy 1988; Boltovskoy et al. 1992). These authors documented that major changes in taxonomic composition, percentages, and absolute abundances of benthic foraminifera began in the late early Miocene and culminated in the middle Miocene. Although this event has been well documented at open ocean locations, it remains poorly documented in marginal seas such as the Gulf of Mexico. The Eureka boreholes examined in this study (northeast Gulf of Mexico) yield faunal abundance changes and stratigraphic ranges that reflect this global middle Miocene benthic foraminiferal event. Benthic foraminiferal faunas have been recognized for their potential to assess paleobathymetry (e.g. Natland 1933; Bandy 1960). While Bandy (1960) promoted the concept that benthic foraminifera have distinct upper and lower depth limits, Streeter (1973) and Schnitker (1974) established that deep-water (>200m; bathyal-abyssal) benthic foraminifera are correlated to water mass properties that may vary independently of depth. Numerous subsequent studies have documented that deep-water benthic foraminiferal distributions are associated with physiochemical properties other than depth, and that depth alone does not control the vertical distribution of benthic foraminifera. For example, vertical distributions are correlated with water masses (e.g. Lohmann 1978; Corliss 1979; Schnitker 1979; Murray 1984; for Gulf of Mexico examples, see Pflum and 88? 86? 84? TEXT-FIGURE 1 Eureka bo ehole location map in the Gulf of Mexico. Contours are in meters. micropaleontology, vol. 39, no. 4, pp.367-403, plates 1-6, text-figures 1-32, tables 1-5, 1993 367 This content downloaded from 157.55.39.152 on Sat, 26 Nov 2016 04:11:28 UTC All use subject to http://about.jstor.org/terms M. E. Katz and K. G. Miller: Latest Oligocene to Earliest Pliocene benthicforaminiferal biofacies of the northeastern Gulf of Mexico TABLE 1 Age model parameters Datum Age (Ma) Depth (feet below sea level) E68-136 E66-73 E68-151 FO C. acutus & 5.

The Biostratigraphic Basis for Gulf Coast Miocene Sequence Stratigraphy

A chronostratigraphic framework was developed as a prelude to a regional sequence stratigraphic and associated systems tracts analysis of the offshore Louisiana and Texas Miocene. The integrated data base for this study included over 10,000 line mi of seismic data, 230 wireline logs, and detailed biostratigraphic analyses on 35 wells. The objective of the study was to map systems tracts and facies that may help delineate prospective areas. Because they are a fundamental stratigraphic unit within a sequence, this framework emphasizes condensed sections and their calibration by microfossil highest occurrence datums. Condensed sections have been delineated utilizing planktonic foraminiferal and calcareous nannofossil abundance and species diversity patterns, as well as detailed paleo-water depth determinations based on benthic foraminiferal biofacies. Pitfalls in the use of condensed sections may arise in shallow paleoshelf settings where datums may be unreliable, and in deeper environments where multiple abundance/diversity peaks may occur. However, an event stratigraphic scheme is generally the most satisfactory method for overcoming correlation problems inherent in the Gulf Coast unstable prograding shelf margin.

Neogene paleoceanographic events recorded in an active-margin setting: Humboldt basin, California

Recognition of North Pacific paleoceanographic events in the marginal Humboldt (Eel River) basin of northern California enables correlation of stratigraphic sections and development of a chronostratigraphy. Paleoclimatically related coiling shifts in Neogloboquadrina pachyderma (Ehrenberg) and benthic foraminiferal datums form the basis of the chronostratigraphy. Benthic foraminiferal datums are defined by the occurrence of selected benthic species and abundance maxima of benthic biofacies. The compiled chronostratigraphy is used to refine reconstructions of the depositional history of Humboldt basin. Paleoceanographic events, recognized by the distribution of benthic foraminiferal biofacies, are used to infer paleoceanographic history along the northeastern Pacific margin. The similarity in coiling curves of N. pachyderma from the marine sequence at DSDP Site 173 and the coastal Centerville Beach section of Humboldt basin and at other independently dated sites along the northeastern Pacific margin demonstrates that matching records of climatic oscillations is a reliable method of correlating marine sequences. Benthic fauna from the Centerville Beach section vary in phase with climatically related coiling shifts in N. pachyderma. In particular these data show an increase in displaced neritic fauna during inferred warm intervals and resurgence of deeper bathyal fauna during inferred cool events. Similar data are observed from the inland Eel River section, demonstrating that benthic foraminiferal trends recognized at Centerville Beach can be identified elsewhere in Humboldt basin. This in-phase benthic response to climatic fluctuations probably results from changes in vertical depth range of many benthic species in response to paleoclimatically related vertical changes in water-mass position. Depositional histories reconstructed for two key sites in southern Humboldt basin indicate low rates of sediment accumulation during early basin filling with hemipelagic sediments. Initiation of turbidite sedimentation in the early Pliocene resulted in a sharp increase in rate of sediment accumulation. This increase in rate of sediment accumulation is partially a response to tectonic uplift in the northern Coast Ranges and may be an effect of realignment of motion between the Pacific and North American plates at about this time. The inland site shoaled more rapidly during turbidite sedimentation as a result of a higher rate of sediment accumulation. The rate of sediment accumulation increased again at this site in the late Pliocene during deposition of shelf and nearshore facies. The Eel River region subsided concurrent with deposition of these shallow-water deposits.

An Evaluation of Paleogene Paleobathymetric Models: Benthic Foraminiferal Distributions in the Metrella Member of the Tejon Formation, Central California

Benthic foraminiferal biofacies provide a useful means for estimating paleobathymetry in Mesozoic and Cenozoic marine rocks. These estimates are made on the basis of biofacies models reflecting the distribution of benthic foraminifera in the modern ocean. Paleooceanographic evidence suggests that past oceans were probably much different from the modern ocean; therefore, benthic biofacies models need to be recalibrated for periods that differ significantly from the present. An analysis of benthic foraminifera from the middle Eocene Metrella Sandstone Member of the Tejon Formation provides an opportunity to test current paleobathymetric biofacies models for continental margin settings. Sedimentologic and stratigraphic evidence identified the Metrella strandline, shelf-edge, and slope. The distribution of three taxa thought to represent deep water (lower middle bathyal or deeper), Bathysiphon eocenica, Cyclammina spp., and Plectofrondicularia packardi s. l., indicates that they all are present or abundant in outer-shelf to shelf-edge environments. The much broader bathymetric range of these taxa may reflect a less density-stratified water column than in the modern ocean.

Middle Cenozoic Benthic Foraminiferal Biofacies, Stratigraphic Events, and Unconformity-Bounded Stratigraphic Units: Key to Stratigraphic Analysis of Active Margin Basins: ABSTRACT

An examination of the depositional history of two middle Cenozoic active margin basins in central California provides insights into the relative importance of tectonics and eustasy for controlling large-scale stratigraphic relationships. Both the Cuyama and southernmost San Joaquin basins were analyzed with respect to benthic foraminiferal biofacies, biostratigraphic and lithostratigraphic events, and the nature and extent of regionally important unconformities. The Cuyama basin exhibits two distinct cycles of basin subsidence and filling - one (late Oligocene to early Miocene) associated with the Vaqueros formation and the other (early to late Miocene) associated with the Monterey formation. The San Emigdio area of the southernmost San Joaquin basin exhibits only one major basin cycle (late Oligocene to late Miocene) associated with the Temblor and Monterey Formations. An analysis of the distribution of major unconformities, rapid bathymetric deepenings, periods of peak transgression, major shallow-marine progradational events, episodes of submarine fan development, and fluctuations in foraminiferal biofacies is used to compare basin history in the two areas. The timing of events is not always very well constrained but indicates that both eustasy and tectonics were important in shaping basin history. Several relationships suggest that tectonics is the relatively more important factor in these basins.more » Depositional history also is a key to understanding benthic foraminiferal biofacies distribution (particularly with respect to three-dimensional distribution of key marker species), which in turn provides insights into benthic foraminiferal biostratigraphy.« less

Paleobathymetric Maps of Tertiary La Honda Basin and Implications for Offset Along San Andreas Fault in Central California: ABSTRACT

Paleobathymetric maps of the La Honda basin of central California were constructed for ten intervals of geologic time from late Paleocene (Nezian) to middle Miocene (Luisian). The maps are based on analyses of benthic foraminiferal biofacies in more than 800 faunal lists compiled from the literature and from subsurface data provided by oil companies. The sequence of paleobathymetric maps shows the paleogeographic evolution of the La Honda basin. From the late Paleocene (Ynezian) to the early Oligocene (early Zemorrian), deep-sea sands and muds accumulated at water depths of 2000 m and more on a surface that sloped gently to the north and northeast. Striking changes in the configuration of the La Honda basin occurred during the late Oligocene and early Miocene (late Zemorrian). Much of the basin floor remained at water depths of 2000 m and greater, but submarine volcanic rocks locally built up to form seamounts, and movement along the Zayante-Vergeles fault led to shoaling and development of a narrow shelf and very steep slope along the southwestern margin of the basin. During the early and middle Miocene (Relizian and Luisian), the entire basin shoaled to depths of less than 1500 m. Comparison of paleobathymetric maps of the Lamore » Honda and San Joaquin basins lends support to the notion that the two basins were once contiguous but have been separated by about 320 to 330 km of right-lateral displacement along the San Andreas fault since the earliest Miocene (late Zemorrian and Saucesian).« less