Firth, John V; Wise, Sherwood W (1992): Chiasmolithus species in middle Eocene and Oligocene sediments of ODP Holes 105-647A and 120-748B [dataset publication series]. PANGAEA, https://doi.org/10.1594/PANGAEA.758691, Supplement to: Firth, JV; Wise, SW (1992): A preliminary study of the evolution of Chiasmolithus in the middle Eocene to Oligocene of Sites 647 and 748. In: Wise, SW; Schlich, R; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 120, 493-508, https://doi.org/10.2973/odp.proc.sr.120.157.1992
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Abstract:
In this preliminary biometric study of the calcareous nannofossil species Chiasmolithus expansus, Chiasmolithus oamaruensis, and Chiasmolithus altus from the upper middle Eocene to lower Oligocene of Sites 647 and 748, we document a complete gradation of forms among all three species. Chiasmolithus oamaruensis has significantly higher morphologic variance than the other species. The Chiasmolithus population at each site changes from C. expansus to C. oamaruensis and then to C. altus. This may not reflect a true evolutionary sequence because a major reversal in shape change of the central cross-bar structure accompanies this sequence, and because C. altus is morphologically closer to C. expansus than it is to C. oamaruensis. The change in the width of the cross-bar structure is primarily a result of changes in the alignment of the central connecting bar, rather than of changes in the cross-bar angle. At Site 748, two fluctuations in morphology produce sample populations intermediate between all three species. In addition, reported stratigraphic and paleogeographic occurrences of C. oamaruensis and C. altus show different latitudinal distributions. These morphological and distributional patterns may be explained by a continuous morphologic gradient between C. oamaruensis and C. altus, with C. oamaruensis occurring more commonly in cool-water paleoenvironments, and C. altus occurring more commonly in cold-water paleoenvironments. Thus, paleoenvironmental fluctuations at Site 748 may be the cause of the morphologic fluctuations in Chiasmolithus. This hypothesis can be tested against previously proposed evolutionary models by more detailed sampling of sections along a latitudinal transect.
Project(s):
Ocean Drilling Program (ODP)
Coverage:
Median Latitude: 25.388225 * Median Longitude: -14.196975 * South-bound Latitude: -58.441000 * West-bound Longitude: -45.262000 * North-bound Latitude: 53.331300 * East-bound Longitude: 78.998100
Date/Time Start: 1985-10-15T04:10:00 * Date/Time End: 1988-03-15T11:00:00
Event(s):
105-647A * Latitude: 53.331300 * Longitude: -45.262000 * Date/Time Start: 1985-10-15T04:10:00 * Date/Time End: 1985-10-23T18:15:00 * Elevation: -3869.0 m * Penetration: 736 m * Recovery: 444.6 m * Location: South Atlantic Ocean * Campaign: Leg105 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 75 cores; 716.6 m cored; 0 m drilled; 62 % recovery
120-748B * Latitude: -58.441000 * Longitude: 78.998100 * Date/Time Start: 1988-03-14T07:30:00 * Date/Time End: 1988-03-15T11:00:00 * Elevation: -1301.0 m * Penetration: 225.1 m * Recovery: 190.15 m * Location: South Indian Ridge, South Indian Ocean * Campaign: Leg120 * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 25 cores; 225.1 m cored; 0 m drilled; 84.5 % recovery
License:
Creative Commons Attribution 3.0 Unported (CC-BY-3.0)
Size:
2 datasets
Download Data
Datasets listed in this publication series
- Firth, JV; Wise, SW (1992): (Table 1) Chiasmolithus species and intermediate forms of ODP Holes 105-647A and 120-748B. https://doi.org/10.1594/PANGAEA.758689
- Firth, JV; Wise, SW (1992): (Table 2) List of biostratigraphica and paleomagnetic datums for ODP Hole 105-647A. https://doi.org/10.1594/PANGAEA.758690