No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Global sedimentation and distribution of deep-sea hiatuses: late Eocene - Oligocene
Abstract
Global distribution of deep-sea hiatuses is determined based on multiple microfossil stratigraphies and sediment accumulation rates are calculated to determined synchroneity of oceanographic events and changes in biologic productivity. Five largely synchronous hiatus intervals are observed at the following ages and planktonic foraminiferal zones: PHa (PH=Paleogene hiatus) at 24.5-26.0 O Ma (N4/P22), PHb at 30-32 Ma (P21/P20), PHc at 34-36.5 Ma (P18/P17), PHd at 37.5-38.5 Ma (P17/P16), and PHe at 39.0-41.0 Ma (P14/P15). These relatively short hiatuses are mainly found in high productivity regions. In contrast, large erosional unconformities spanning 5-50 m.y. appear restricted to low productivity regions and where deposition occurred below the CCD. There is general agreement between the five synchronous hiatuses and the sea level on lap curve of Vail and Hardenbol (1979). Global cooling events coincide with these hiatuses suggesting that climatic cooling and the resultant current intensification are the main driving force of deep-sea hiatus formation. Sedimentation rates of pelagic sequences averaged over 2 m.y. indicate major productivity changes. Late Eocene sedimentation rates are about 8-10m/m.y. in the Pacific and Atlantic, but are only 4-5m/m.y. in the Indian Ocean. A 2 to 3 fold increase in the sedimentation rate is apparent during the early Oligocene in the Atlantic and Pacific, but not in the Indian Ocean. Productivity decreases again during the late Oligocene. The maximum sedimentation rates in the early Oligocene appear to reflect increased upwelling during global cooling.
... Questions concerning the identity of the environmental agent(s) responsible for this evolutionary change, and the rate at which this change took place are logically independent from the morphological identification of progenesis itself. However, it is known that the interval from the Middle through Late Eocene was a time of widespread oceanographic change including a permanent drop in bottom water temperature (Shackleton and Kennett, 1975; Douglas and Savin, 1978; Keigwin, 1980), global deepening of the CCD (Berger, 1972; Van Andel et al., 1975), lowering of sea level (Vail and Hardenbol, 1979; Haq et al., 1987; Keller et al., 1987 ), development of the psychrosphere (Benson, 1975), intensified bottom water circulation (Keller et al., 1985; Miller et al., 1985 ), fluctuations in the thermal structure of surface waters (Keller, 1983) and the incidence of multiple impacts of extraterrestrial objects (Keller et al., 1983; Keller et al., 1987; Hazel, in press). While most of these environmental changes occurred more or less continuously throughout the interval from the Middle Eocene through the Oligocene, it is noteworthy that multiple layers of impact ejecta are confined to those planktic foraminiferal biozones in which substantial shifts in relative abundance patterns as well as morphological changes are taking place in a number of planktic foraminiferal lineages (Keller et al., 1987 ). ...
It has been argued that the successive appearance of a distinct set of test morphologies by planktic foraminifera represents evidence for the multiple evolution of mechanical optima (Steineck and Fleisher, 1978). However, morphometric, isotopic and biostratigraphic analyses of the globigerine species Subbotina linaperta from Middle-Late Eocene Atlantic Ocean deep sea cores suggests that changes in developmental pathways may also play an important role in planktic foraminiferal evolution. During a period of prolonged and global change in the Middle-Late Eocene marine environment, at least one western Atlantic population of S. linaperta was characterized by a marked decrease in mean test size that persisted throughout the remainder of this species' teilzone. In addition, this Late Eocene population exhibited anomalous relative abundances and a pronounced change in depth habitat when compared to conspecific populations in the Gulf of Mexico and South Atlantic. Quantitative morphometric analyses indicate the observed size reduction to be a secondary result of selection for the ontogenetically accelerated attainment of sexual maturity; a mode of developmentally mediated evolution termed progenesis. The temporal persistence of this progenetically dwarfed population throughout the remainder of the Late Eocene at this locality serves to illustrate the potential of this evolutionary mechanism to produce sustained morphological and ecological changes within populations of marine plankton as well as implying that this population was at least partially isolated from the general circulation of the Gulf Stream during this time interval. In addition, similarities between the nature of phenotypic change in this population and the common anecdotal observation of test size reduction in a number of planktic foraminiferal lineages at the Cretaceous-Tertiary boundary and during the Paleogene-Neogene faunal transition suggest that selection for different developmental patterns may provide an alternative explanation for the reappearance of simple globigerine morphotypes after major planktic foraminiferal extinction events. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/28329/1/0000088.pdf
Species ranges and relative abundances of dominant planktonic foraminifers of eight late Eocene to early Oligocene deep-sea sections are discussed to determine the nature and magnitude of extinctions and to investigate a possible cause-effect relationship between impact events and mass extinctions.Late Eocene extinctions are neither catastrophic nor mass extinctions, but occur stepwise over a period of about 1–2 million years. Four stepwise extinctions are identified at the middle/late Eocene boundary, the upperGlobigerapsis semiinvoluta zone, theG. semiinvoluta/Globorotalia cerroazulensis zone boundary and at the Eocene/Oligocene boundary. Each stepwise extinction event represents a time of accelerated faunal turnover characterized by generally less than 15% species extinct and in itself is not a significant extinction event. Relative species abundance changes at each stepwise extinction event, however, indicate a turnover involving > 60% of the population implying major environmental changes.There microtektite horizons are present in late Eocene sediments; one in the upperG. semiinvoluta zone (38.2 Ma) and two closely spaced layers only a few thousand years apart in the lower part of theGloborotalia cerroazulensis zone (37.2 Ma). Each of the three impact events appears to have had some effect on microplankton communities. However, the overriding factor that led to the stepwise mass extinctions may have been the result of multiple causes as there is no evidence of impacts associated with the step preceding, or the step following the deposition of the presently known microtektite horizons.
ResearchGate has not been able to resolve any references for this publication.