New Zealand Journal of Geology and Geophysics abstracts
Cretaceous-Tertiary foraminiferal succession at Flaxbourne River,
Marlborough, New Zealand
C. P. STRONG
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract The stratigraphically and biostratigraphically most
complete Cretaceous-Tertiary (K-T) boundary succession yet identified in New
Zealand occurs in bathyal limestones of the Mead Hill Formation at Flaxbourne
River, coastal Marlborough. It is one of three New Zealand K-T sections with a
well-delineated "fireball" layer, containing anomalous iridium, soot particles,
and fullerenes, and it contains a highly fossiliferous latest Cretaceous marl
unit, not seen in other sections, immediately underlying the K-T boundary clay.
The c. 50 m thick Flaxbourne section is the only New Zealand locality
known with an essentially complete sequence of earliest Paleocene foraminiferal
zones. These include (K-T boundary is zero datum): Guembelitria cretacea
Zone (P0), 0.0-0.07 m; Parvularugoglobigerina eugubina Zone (P?),
0.07-0.24 m; P. eugubina-Subbotina triloculinoides Subzone (P1a),
0.24-0.40 m; S. triloculinoides-Globanomalina compressa/Praemurica
inconstans Subzone (P1b), 0.40-0.50 m; and Globanomalina
compressa/Praemurica inconstans-Praemurica uncinata Subzone (P1c),
0.50-11.5 m. Strata from 11.5 m to the highest exposed beds at
c. 38 m are classified as undifferentiated Paleocene. Cretaceous
planktic "survivor taxa" occur up to 0.40 m but are replaced rapidly above
Zone P0 by Paleocene taxa.
Latest Cretaceous strata are dominated by
Heterohelix/Globigerinelloides planktic foraminiferal assemblages,
associated with sparse (typically <5%), mainly epifaunal benthic taxa and
rare radiolarians. Commencing abruptly at the base of the boundary clay,
maximum size of planktic and benthic specimens decreases sharply, while
abundance of both radiolarian and benthic foraminifera increase about tenfold
relative to planktics, features which typify the basal 0.4 m of Paleocene
strata. Heterohelix/Hedbergella associations characterise planktic
assemblages initially, but give way to Eoglobigerina /Chiloguembelina
planktic assemblages. Epifaunal taxa dominate benthic faunas, but infaunal
forms show minor abundance peaks. Benthic abundance remains near 45% up through
c. 0.3 m but then declines sharply to c. 25% at 0.40 m
(highest detailed sample).
Stratigraphically higher samples were studied in less detail. From 0.5 to
11.5 m they contain poor foraminiferal assemblages similar to those
described above, but these are then replaced by planktic-poor (<5%
planktics) assemblages with normal-sized benthic taxa, including Gavelinella
beccariiformis and Nuttallides cretatruempyi, which occur to
the top of the exposed section.
Keywords Cretaceous-Tertiary boundary; Marlborough;
foraminifera; Maastrichtian; Danian; Haumurian; Teurian
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43: 1-20
0028-8306/00/4301-0001 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (5426K); (scanned from paper original: notes about this process)
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