15. calcareous nannofossils, deep sea drilling …
TRANSCRIPT
15. CALCAREOUS NANNOFOSSILS, DEEP SEA DRILLING PROJECTHOLES 417D, 418A, AND 418B
S. Gartner, Department of Oceanography, Texas A&M University, College Station, Texas
Fossiliferous Mid-Cretaceous calcareous sediments wererecovered from Holes 417D (Leg 5IB), 418A (Leg 52), and418B (Leg 53). Core recovery in this section was incom-plete at all three holes. Nevertheless, a detailed biostrati-graphic study was undertaken in order to glean whateveruseful information might be obtained about the mid-Cretaceous history of the North Atlantic. Checklists of cal-careous nannofossils for the three holes are given in Figures1 to 3 with certain species illustrated on Plate 1. On thebasis of the first appearance in the stratigraphic record ofLithastrinus floralis, a distinctive nannofossil species, theoldest sediment above basement in each hole is the sameage. According to Thierstein (1973), this species first ap-pears near mid-Aptian and is common to abundant in upperAptian and younger sediments. No similar predecessorspecies is known. In all three of the above holes Lithastrinus
floralis appears a short distance above the sediment-basement contact. Following the time scale of van Hinte(1976), the age of basement in this area is estimated to benot less than 112 m.y.
In the holes only one fossiliferous interval was encoun-tered below the lowest occurrence of Lithastrinus floralisand in two of them, Samples 417D-2-3, 111-112 cm and418A-15-1, 7-9 cm, common specimens of Corollithionacutum were recorded. Although Roth and Thierstein(1972) reported this species to range from Aptian to Cam-panian, in this study it was not encountered in any sampleother than the above two. At Hole 418B, Corollithionacutum was not found but the only fossiliferous samplefrom below the lowest occurrence of Lithastrinus floralis(Sample 418B-34-1, 3-4 cm), yielded a poorly preservedresidual assemblage, and the absence of Corollithionacutum may be the result of dissolution.
Aside from the same age in the lowest part of the sec-tions, the nannofossil succession at the two sites is different;how much of this is attributable to incomplete core recoveryis not at all clear. In Hole 417D an early Albian to lateAptian age is represented in Cores 20 and 21. The middleAlbian, characterized by the partial range of Predisco-sphaera cretacea below the lowest occurrence of Eiffel-lithus turriseiffeli, is represented by a barren interval. Thefossiliferous interval above this is in Section 17-1, whichcontains abundant Eiffellithus turriseiffeli and, therefore,represents an age not older than late Albian, although it maybe as young as Cenomanian.
In Hole 418A, the entire fossiliferous interval, exceptingthe lowermost sample (15-1, 7-9 cm), is early Albian to lateAptian in age. The interval in question extends from the topof Sample 10-1, 52-54 cm to Sample 14, CC, 4-6 cm, and isbracketed between the lowest occurrence of Predisco-sphaera cretacea (early Albian) which datum was not en-countered, and the lowest occurrence of Lithastrinus floralis
(middle Aptian) which was recorded. No part of the approx-imately 100 cm of Cenomanian to upper Albian sedimentrepresented in Section 17-1 at Hole 417D was recovered atHole 418A. This may be the result of poor core recovery,but it is equally possible that a thin fossiliferous upperAlbian-Cenomanian section was penetrated within the un-cored 22.5 meters between Cores 9 and 10.
The most complete mid-Cretaceous section was recov-ered in Hole 418B. The mid-Cretaceous biostratigraphy ofManivit et al. (1977) is quite useful in dating this section.The upper Aptian to lower Albian is represented by Cores29 through 33, bracketed by the lowest occurrence ofLithastrinus floralis in Sample 33-1, 134-135 cm and thelowest occurrence of Prediscosphaera cretacea in Sample28-3, 50-51 cm. Middle Albian is represented by Section28-2, and is bracketed at the base by the lowest occurrenceof Prediscosphaera cretacea and at the top by the lowestoccurrence of Eiffellithus turriseiffeli in Sample 28-2, 13-14cm. Upper Albian is represented in Sections 28-1 and 28-2having, at the base, the lowest occurrence of Eiffellithusturriseiffeli and, at the top, the lowest occurrence of Lith-raphidites alatus in Sample 28-1, 21-22 cm. The latterdatum is not always totally reliable but is well developed inthis section. The Cenomanian is represented in Cores 26,27, and 28, marked at the base by Lithraphidites alatus andat the top by transition to an unfossiliferous interval. Thetop of the fossiliferous interval, Sample 26-1, 35-36 cm, islate Cenomanian in age, based on the highest occurrence ofCruciellipsis chiastia immediately below it in Sample 26-1,50-51 cm.
The close proximity of the sites to one another, and thenearly identical depth to basement, leads to the expectationthat their early history was similar, yet their paleontologicalrecord is similar only in that the oldest sediments abovebasement have the same age. Although the imperfect corerecovery reduces interpretation to the level of speculation,the marked discrepancy in the degree of development ofcalcareous sediments of post early Aptian age is puzzling. Ifthe sites did indeed have histories of sedimentation as dif-ferent as might be inferred from the paleontological recordof the calcareous nannofossils, then the history of euxinicsediments in the North Atlantic may be more complex thanheretofore suspected.
REFERENCESManivit, H., Perch-Nielsen, K., Prins, B., and Verbeek, J.W.,
1977. Mid Cretaceous calcareous nannofossil biostratigraphy,Ron. Nederl. Akad. Weten., ser. B, v. 80, p. 169-181.
Roth, P.H. and Thierstein, H., 1972. Calcareous nannoplankton:Leg 14 of the Deep Sea Drilling Project. In Hayes, D.E.,Pimm, A.C., et al., Initial Reports of the Deep Sea DrillingProject, v. 14: Washington (U.S. Government Printing Of-fice), p. 421-485.
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0 0
AGE
CENOMANIANTO
LATE ALBIAN
EARLY ALBIANTO
LATE APTIAN
EARLY APTIAN
LEG 51BHOLE417D
Core, SectionDepth (cm)
17-1, 16-18
17-1,69-70
17-1, 103-104
17-1,110-111
BARREN INTERVAL
20-1,23-25
20-2, 19-20
21-2,56-57
21-3,7-8
21-3,20-21
21-3, 111-112
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IMPORTANTNANNOFOSSILDATUMLEVELS
L.O. Eiffeiiithusturriseiffeli
L.O. Lithastrinus floralis
Corollothion acutum
Figure 1. Nannofossil species checklist and abundance estimates for Hole 417D. a = abundant, c - common; f=few; r = rare.
AGE
EARLY ALBIANTO
LATE APTIAN
EARLY APTIAN
LEG 52HOLE418A
Core, SectionDepth (cm)
10-1,52-54
BARREN INTERVAL
12-1,51-53
12-1,97-99
12-1, 146-148
12-2,20-23
12-2, 25-27
12-2,31-33
13-1,39-41
BARREN INTERVAL
13, CC, 12-14
14, CC, 4-6
15-1,7-9
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IMPORTANTNANNOFOSSILDATUMLEVELS
L.O. Lithastrinus floralis
Corollithion acutum
Figure 2. Nαnnofossil species checklist and abundance estimates for Hole 418A. a = abundant, c = common; f-few; r = rare.
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106
AGE
CENOMANIAN
LATE ALBIAN
MIDDLE ALBIAN
EARLY ALBIANTO
LATE APTIAN
EARLY APTIAN
LEG 53HOLE 418B
Core, SectionDepth (cm)
26-1,35-36
26-1,50-51
26-1,88-89
26-1, 121-122
27-1,51
28-1, 11-12
28-1,21-22
28-1,92-93
28-1,133
28-2, 13-14
28-2,81-82
28-2, 109-110
28-2, 129-130
28-3, 50-51
29-1,31-32
31, CC
32-1,5-6
32-1,73-74
32-1,125-126
33-1,39-40
33-1, 104-105
33-1, 134-135
34-1,3-4
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IMPORTANTNANNOFOSSILDATUMLEVELS
H.O. Cruciellipsis chiastia
L.O. Lithraphidites alatus
H.O. Hayesites albiensis
L.O. Eiffellithus
L.O. Prediscosphaera
L.O. Lithastrinus fioraiis
•after van Hinte, 1976
Figure 3. Nannofossil species checklist and abundance estimates for Hole 418B. a = abundant; c = common; f=few; r = rare.
CALCAREOUS NANNOFOSSILS
Thierstein, H.R., 1973. Lower Cretaceous calcareous nanno- van Hinte, J.E., 1976. A Cretaceous time scale, Am. Assoc. Pet-plankton biostratigraphy, Abh. Geol. Bundesanst., Wien, v. rol. Geol. Bull., v. 60, p. 498-516.29, p. 1-52.
819
S. GARTNER
PLATE 1All Photographs ×2500
Figures la, b Broinsonia enormis (Shumenko). Sample 53-418B-26-1, 121-122 cm.la. Phase contrast, plain polarized light,lb. Cross-polarized light.
Figures 2a, b Corollithion acutum Thierstein. Sample 51B-417D-21-3, 111-112 cm.2a. Interference contrast.2b. Cross-polarized light.
Figures 3a, b Tetrapodorhabdus decorus (Deflandre).Sample 53-418B-27-1, 51 cm.3a. Phase contrast.3b. Cross-polarized light.
Figures 4a, b Vekshinella sp. Sample 53-418B-26-1, 88-89 cm.4a. Interference contrast.4b. Cross-polarized light.
Figures 5a, b Cretarhabdus coronadventis (Reinhardt) n. comb.Sample 53-418B-27, 51 cm.5a. Phase contrast.5b. Cross-polarized light.
Figures 6a, b Podorhabdus albianus (Black). Sample 53-418B-26-1, 88-89 cm.6a. Interference contrast.6b. Cross-polarized light.
Figures 7a, b Hayesites albianus Manivit. Sample 53-418B-28-1.108-109 cm.7a. Interference contrast.7b. Cross-polarized light.
Figures 8a, b Rucinolithus irregularis Thierstein.8a. Interference contrast.8b. Cross-polarized light.
Figures 9a, b Lithraphidites alatus Thierstein. Sample 53-418B-26-1, 35-36 cm.9a. Interference contrast.9b. Cross-polarized light.
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PLATE 1
CALCAREOUS NANNOFOSSILS
2b
4b
5b
7b
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