Richard E. Casey

Distribution of living polycystine radiolarians in the Gulf of Mexico and Caribbean Sea, and comparison with the sedimentary record

Abstract Plankton tows and bottom samples from the Gulf of Mexico and Caribbean Sea were examined to study the distribution, ecology, and preservation of modern radiolarians. Abundances of radiolarians from this region, an area of low primary productivity, are low. Diversities are variable in the surface waters; diversity indices decrease with increasing water depth, indicating that fewer niches are occupied by radiolarians in deep water. Living radiolarians are confined to specific water masses, some species ranging between two masses, and can be used as indicators of these water masses in ecologic or paleo-oceanographic studies. The record of radiolarian tests present in the sediment is dissimilar to the record of living radiolarians in the water column, but is similar to the record of empty tests falling through the water column. This indicates that a considerable length of time is involved in the settling of radiolarian tests. It also confirms the validity of ecologic interpretations based on a study of sediments only.

Reflector Horizons and Paleobathymetric History, Eastern Panama

Basement rocks of eastern Panama, exposed around the Golfo de San Miguel, include dense well-preserved pillow basalt and diabase which are overlain by deformed chert and thin-bedded siliceous radiolarian-rich abyssal oceanic sedimentary rocks of Late Cretaceous (in part, early Campanian) age. This basalt-chert relation of the Late Cretaceous is approximately correlative with the lower reflector horizon of the deep oceans. A second abyssal volcanic phase with radiolarian-rich sediments occurs in the lower and middle parts of the Morti Tuffs, early to middle Eocene in age, which represents the equivalent of the upper reflector horizon in the deep oceans. A third abyssal volcanic phase associated with radiolarian-rich tuffaceous sediments, with some chert and agglomerate, occurs in the middle Oligocene to lower Miocene formations; this sequence has not been identified as a specific reflector in deep-sea sections. A deep-marine erosional or nondepositional interval occurs between the Late Cretaceous basement rocks and the Eocene Morti Tuffs; a second hiatus separates the Morti Tuffs from the overlying middle Oligocene to lower Miocene Pacific Tuffs and Clarita Limestone. In eastern Panama, the development of a Panamanian ridge or block is shown by the progressively shallower water facies during the middle and later Neogene, leading to paralic and nonmarine facies of the Pliocene-Pleistocene. Cessation of interoceanic communication occurred gradually during this phase, terminating finally in the Pliocene-Pleistocene. This paleobathymetric development is likely similar to that for nearby northwestern Colombia; it is in distinct contrast to the developmental history of the Canal Zone region where deep-ocean sedimentation was terminated in the middle Eocene. These middle Eocene shallower water facies of the Canal Zone may have been the source for displaced shallower water facies that are intermixed in some cases with deep-water Eocene facies of eastern Panama.

Polycystine Radiolarian Distribution and Enhancements Related to Oceanographic Conditions in a Hypothetical Ocean: ABSTRACT

ABSTRACT Radiolarian data from Holocene sediments of the world oceans were fitted to a hypothetical ocean exhibiting characteristics of all oceans. Warm water sphere radiolarians exhibit major poleward boundaries to their distributions at subtropical and polar convergences. Warm water forms exhibit poleward extensions in the western boundary currents. Collosphaerids are enhanced in sediments under the anticyclonic gyres and eastern tropical regions. The Dictyocoryne profunda-truncatum group appears to be indicative of warm water sphere mesotrophic conditions. Cold water sphere radiolarians dominate sediments poleward of the polar convergences and occur in significant percentages under the eastern boundary currents and equatorial divergences. Intermediate and deep water radiolarians appear to be enhanced under the polar cyclonic gyres, eastern boundary currents, and the oceanic divergences and convergences. These radiolarian indices of present oceanographic conditions (currents, divergences, convergences, and oligotrophic to eutrophic conditions) should aid in deciphering similar paleoceanographic conditions.

Radiolarian responses to recent and neogene California El Niño and anti-El Niño events

Abstract Plankton tows from 1983 and 1964 California El Ninos suggest that high standing crops of both warm and cold radiolarian faunas are characteristic of these conditions over the southern California continental borderland. High standing crops of both warm and cold radiolarians are suggested to occur during California El Ninos because the California Current diminishes in intesity allowing warm faunas to invade from the west (central-gyre waters) and south (gyre and eastern tropical Pacific waters); and, a strongly developed California Countercurrent aids in creating a geostrophic dome that allows cold faunas to invade from the north. These same radiolarian faunas characteristic of California El Ninos are found in the Holocene varved sediments of the Santa Barbara Basin and can be correlated to the known California El Nino events of 1957–1958 and 1964. El Nino like events determined via the same radiolarian criteria are found at 6 and 8 Ma in Monterey laminated (presumably varved) sedimentary rocks. It is suggested that warm and cold periods in Monterey may be related to the frequency and magnitude of El Nino like events. It is also suggested that during Neogene warm periods (such as at 8 and 10 Ma) the paleo-California Current was narrower, closer to the coast, and did not extend as far south as during anti-El Nino periods (such as at 5 Ma).

Radiolarian Species Composition, Density, and Diversity as Indicators of Water Structure and Circulation on South Texas Shelf: ABSTRACT

ABSTRACT Radiolarian species composition, density, and diversity can be used to define the structure of the water column and circulation patterns of waters overlying the south Texas shelf. Radiolarian species that occur in the western North Atlantic, Caribbean and Gulf of Mexico are also found in the south Texas shelf waters. The radiolarian assemblage from the western North Atlantic has the greatest density and diversity. Radiolarian densities and diversities are lower in the Caribbean and Gulf of Mexico, and are lowest in the waters over the shelf. Radiolarian densities and diversities on the shelf reflect incursions of open ocean waters at varying depths. Certain radiolarian assemblages and their position on the shelf, as well as radiolarian density and diversity can be used to identify winter, spring and fall physical oceanographic conditions on the south Texas shelf. Radiolarians can also be used as indicators of physical oceanographic conditions in studies of ancient shelves.

Cenozoic Radiolarians of the Atlantic Basin and Margins

Abstract Living radiolarians in the Atlantic are indicative of specific water masses. Radiolarian skeletons occur only in the upper few centimeters of late Neogene sediments over most of the mid and lower latitudes of the Atlantic. This is in contrast to common occurrences of radiolarians in the sediments of these latitudes during much of the Paleogene and early Neogene. Paleogene to early Neogene radiolarian biostratigraphies are cosmopolitan due to the pan-tropical oceanic connection. Isolation of the Atlantic starting in Mid-Miocene resulted in changes in siliceous sedimentation and the development of provincial radiolarian faunas. The development of a lew cosmopolitan radiolarian zonation based on tropical submergent forms may aid in interoceanic warm water correlations.

Brizalina lowmani, a Meroplanktonic Foraminifera Useful as Indicator of Shelfal Circulation and Eutrophication (with Comments on Biostratigraphy and Evolution): ABSTRACT

ABSTRACT Brizalina lowmani was found to be the most abundant living foraminiferan of the south Texas outer continental shelf, both in the sediment and in the water column. Brizalina lowmani, considered a nearshore benthonic foraminifer evidently possesses a meroplanktonic stage which allows it to take advantage of the pelagic and benthonic environments. Our study indicates that standing crops of B. lowmani in the water column can be used to determine provenance and direction of shallow and deep shelf currents. Standing crops of B. lowmani in the sediment can be used as indicators of bottom shelf current and direction, depth and area of winter water column mixing, and degree of eutrophism of bottom and overlying waters. The meroplanktonic nature of B. lowmani allows a wide dispersal of the form, suggesting why similar forms can be utilized as biostratigraphically useful index fossils. The form, B. lowmani, may be reminiscent of the early evolution of planktonic foraminiferans.

Neogene Deep-Living Radiolarian Zonation and Its Uses: ABSTRACT

A Neogene radiolarian zonation using deep-living radiolarians has been developed. This zonation consists of 6 radiolarian zones with the nominant taxa of each zone first occurring at the base of its zone, and that nominant taxa running throughout its zone. These zones are the Eucyrtidium cienkowskii (22.5-19 Ma), Siphocampe arachnea (19-14 Ma), Oroscena with digitate spines (14-11 Ma), Botryostrobus bramlettei (11-6 Ma), Clathrocyclas bicornis (6-2.5 Ma), and Cycladophora davisiana davisiana (2.5-0 Ma) Zones. These zones were developed by using Antarctic, equatorial, and North Pacific Deep Sea Drilling Project holes, and are believed to be cosmopolitan zones due to their being based on deep-living radiolarians. These zones are dated by correlating the first occurrences of the nominant taxa with warm-water radiolarian datums that have been paleomagnetically dated. These zones are not designed for routine use, but rather for tying together other more provincial zonations, and for comparing oceanographic phenomena on global datum planes. To date, this zonation has been used to correlate Antarctic zonations intra- and inter-regionally and to study the evolution of radiolarian lineages. End_of_Article - Last_Page 243------------

Effects On and Recovery of Microplankton and Microbenthon to Gulf of Mexico Oil Spills Impacting Outer and Mid Shelfal, Inner Shelfal, and Estuarine Environments

During 1979, 1980, and 1981 3 major and different environments of human interest and economic well-being were impacted by 3 different and major Gulf of Mexico oil spills. All the studied spills had pre-spill data. This study revealed 3 conclusions useful in the monitoring of spill recovery. (1) Immediately or continually impacted areas exhibited a mass mortality for microplankton in pelagic systems, and an abnormally high concentration (collection) of nematodes in nearshore sands. (2) Impacted benthonic areas exhibited increases in nematode standing corps followed by increases in benthonic forminiferal standing crops. (3) Recovery to pre-spill conditions may be indicated by termination of red tide condition or mortality of susceptible microplankton; return to pre-spill standing crops, taxonomic character, and diversity of microbenthon or microplankton; and return to pre-spill seasonal fluctuation of peaks and lows in microbenthon and microplankton.

Radiolarian Distribution and Enhanced Preservation in Modern Sediments: Indicators of Oceanographic Environments: ABSTRACT

Analysis of the geographic distribution of radiolarians shows that they are preserved in restricted zones and/or enhanced under particular oceanographic environments. Surface, warm-water-dwelling radiolarians are preserved in the equatorial region. However, intermediate and deep, cold upwelling radiolarians exhibit cosmopolitan distributions in the sediments with enhancement under oceanographic convergences and divergences. Specifically artostrobids and plectopyramids appear to be enhanced in the sediments under oceanographic convergence and divergences; the Dictyocoryne profunda-truncatum group is enhanced under high productivity regions; and actinommids in general and collosphaerids in particular are enhanced under the oligotrophic gyre regions. The enhancement under co vergences and divergences may be due to (1) mass mortality of deep and/or cold forms brought into warm surface waters via upwelling at a divergence or laterally at a convergence, (2) an increase in standing crop of deep forms under high productivity regions or higher productivity at the convergences nutricline, or (3) a stripping of the metallic protective coating of shallow forms by bacteria at the nutricline. Collosphaerids may be enhanced in oligotrophic gyres owing to the acquisition of detrital aluminum on their surfaces which might deplete the deeper waters and inhibit deeper water radiolarian preservation. Collosphaerids are also enhanced along the Mid-Atlantic Ridge which may be due to metal abundance in the sediments, low sedimentation rates, and/or high silica concentration of interstitial and bottom waters. End_of_Article - Last_Page 946------------