Biostratigraphy and carbon isotope stratigraphy of ...

Journal of the Royal Society of New Zealand

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Biostratigraphy and carbon isotope stratigraphy of uppermost Cretaceous‐lower Cenozoic Muzzle Group in middle Clarence valley, New Zealand C. J. Hollis , B. D. Field , C. M. Jones , C. P. Strong , G. J. Wilson & G. R. Dickens To cite this article: C. J. Hollis , B. D. Field , C. M. Jones , C. P. Strong , G. J. Wilson & G. R. Dickens (2005) Biostratigraphy and carbon isotope stratigraphy of uppermost Cretaceous‐lower Cenozoic Muzzle Group in middle Clarence valley, New Zealand, Journal of the Royal Society of New Zealand, 35:3, 345-383, DOI: 10.1080/03014223.2005.9517789 To link to this article: http://dx.doi.org/10.1080/03014223.2005.9517789

Published online: 30 Mar 2010.

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Date: 29 January 2016, At: 14:50

345 Journal of the Royal Society of New Zealand Volume 35, Number 3, September, 2005, pp 345-383

Biostratigraphy and carbon isotope stratigraphy of uppermost Cretaceous-lower Cenozoic Muzzle Group in middle Clarence valley, New Zealand

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C. J. Hollis1, B. D. Field1, C. M. Jones1, C. P. Strong1, G. J. Wilson1, and G. R. Dickens2 Abstract Muzzle Group strata exposed along southeast-flowing tributaries of the Clarence River valley, Marlborough, record hemipelagic-pelagic sedimentation across a high latitude (c. 55°S), terrigenous sediment-starved, continental margin from latest Cretaceous to middle Eocene times. Studies of dinoflagellates, foraminifera, calcareous 13 nannofossils, and radiolarians have been integrated with bulk carbonate δ C profiles to establish the chronostratigraphy for two stratigraphic sections along Bluff and Muzzle Streams, middle Clarence valley. The two sections comprise similar successions. Uppermost Cretaceous (upper Haumurian) micritic limestone of Mead Hill Formation is overlain unconformably by Teredo Limestone, a c. 0.25 m thick bed of highly glauconitic, calcareous sandstone. This unit, the basal member of Amuri Limestone, is overlain conformably by c. 15 m thick Lower Limestone, micritic limestone that is glauconitic at base and progressively more marl-rich in its upper part. Lower Limestone grades up into Lower Marl, a poorly exposed, 40-70 m thick unit of alternating marl and micritic limestone beds. Biostratigraphy indicates that the base of Amuri Limestone is younger at Bluff Stream (earliest Eocene, early Waipawan) than at Muzzle Stream (late Paleocene, late Teurian). In the condensed (12 m) upper Paleocene-lower Eocene Amuri Limestone sequence at Muzzle Stream, a trend in δ 13 C from high ( 2.4‰) to low ( 1‰) values is consistent with global records across three major climate or carbon cycle perturbations: the late Paleocene carbon isotope maximum (PCIM, 59-56 Ma), the initial Eocene thermal maximum (IETM, 55.5 Ma), and the early Eocene climatic optimum (EECO, 53-50 Ma). Probably only the upper PCIM is preserved in the 4 m thick siliceous limestone interval overlying Teredo Limestone. The IETM is well-defined by a 1‰ negative δ 13 C excursion at the base of a 0.8 m thick marl-rich unit (Dee Marl), 5 m above the base of Lower Limestone at Muzzle Stream, and the abrupt appearances of Eocene-restricted species or distinctly warm-water elements within dinoflagellate, foraminiferal, calcareous nannofossil, and radiolarian assemblages. The lithological expression of the IETM as a recessive marly unit has now been identified in three Clarence valley sections (Muzzle, Dee, and Mead Streams), representing a 20 km continental margin transect. Sedimentation rate trends across this margin indicate that the local effects of extreme global warming were increased supply of terrigenous mud, probably due to enhanced precipitation, weathering and erosion, and a decrease in pelagic sedimentation, reflecting a decrease in oceanic productivity. Bluff section lacks an IETM record but contains an expanded (20 m) early Eocene succession that records the onset of the EECO as a progressive

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Institute of Geological and Nuclear Sciences Ltd, P.O. Box 30 368, Lower Hutt, New Zealand. [email protected] Department of Earth Sciences, Rice University, Houston, TX 77005, USA. R04011; Received 26 July 2004; accepted 4 April 2005; Online publication date 21 September 2005 2

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Fig. 1 Location of continental margin or ocean platform transects with high-resolution early Cenozoic sedimentary records on a global paleogeographic map for the early Eocene (55 Ma; map produced by ATLAS, Cambridge Paleomap services, Cambridge, UK). Transects: BN, Blake Nose (Kroon et al. 2001 ); DR, Demerara Rise (Erbacher et al. 2004); EG, Egypt (Speijer et al. 2000); ET, Equatorial Transect (Lyle et al. 2002); MR, Maude Rise (Barker et al. 1988); NJ, New Jersey (Gibson et al. 2000); NZ, New Zealand (this study); SP, Spain (Schmitz & Pujalte 2003); SR, Shatsky Rise (Bralower et al. 2002); TR, Tasman Rise (Exon et al. 2001); WR, Walvis Ridge (Zachos et al. 2004).

increase in marl-rich units associated with consistently low δ 13 C (0.02 m thick marly beds are common in the upper 4 m. The base of Lower Marl is placed at the level at which marl and marly limestone beds first become almost as thick as intervening micritic limestone beds. Only the lowermost 6 m of Lower Marl was sampled as the overlying interval is poorly exposed. Previous studies (Morris 1987) indicate that the unit is c. 70 m thick and it is overlain by 55 m of younger Amuri Limestone units, including Upper Limestone, Upper Marl, and Fells Greensand. BIOSTRATIGRAPHY The aims of biostratigraphic study of these sections were to establish the age of the basal Amuri Limestone unconformity in Muzzle and Bluff sections and to refine the age control of the Teredo Limestone-Lower Limestone-basal Lower Marl succession. Both sections are correlated to local and international stages using dinoflagellate, foraminiferal, calcareous nannofossil and radiolarian biostratigraphy (Fig. 8, 9). Carbon isotopes are used to correlate the sections with global stable isotope events (Fig. 10). The biostratigraphy and carbon isotope stratigraphy are then integrated to establish age relationships between rock units in Bluff, Muzzle and Mead Stream sections (Fig. 11). We adopt a two-fold subdivision for the


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Hollis et al.—Clarence valley Paleogene stratigraphy

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Fig. 7 BluffStream section. MHF, Mead Hill Formation; TL, Teredo Limestone; LL, Lower Limestone; LM, Lower Marl. (Photo: C. Hollis.)

Teurian stage (Morgans et al. 1996) in which the base of the late Teurian is defined by the first occurrence (FO) of Fasciculithus tympaniformis. This event defines the base of calcareous nannofossil zone NP5 at 59.7 Ma (Berggren et al. 1995). We introduce a two-fold subdivision for the Waipawan stage in which the base of the late Waipawan is defined by the FO of Tribrachiatus orthostylus. This event occurs close to the base of nannofossil zone NP11 at 53.6 Ma (Perch-Nielsen 1985; Berggren et al. 1995). In the absence of this event, the base of late Waipawan may also be recognised by the FOs of the dinoflagellate species Dracodinium waipawaense and Schematophora obscura (mid-NP11; Wilson 1988), the FO of the planktic foraminiferal species Morozovella lensiformis (mid-NP 11 ; Hollis et al. 2005) and the LO (last occurrence) of the following radiolarian species: Amphisphaera goruna, Bury ella granulata, and Lychnocanium auxilla (lower NP11; Hollis et al. 2005). Dinoflagellates Although dinoflagellates occur somewhat sporadically in Muzzle Group rocks (Strong et al. 1995; Hollis et al. 2005), when present they often provide critical biostratigraphic constraints. Of the 78 samples processed from Muzzle and Bluff sections, 31 samples yielded age-diagnostic dinoflagellate assemblages (Appendices 1,2A,B). Recovery was poor in Lower Limestone at Muzzle Stream, but relatively good in other units. Recovery was poor in all units at Bluff Stream. The scarcity of dinoflagellates may be due to highly oxic depositional conditions or significant post-depositional degradation. The scarcity of other plant matter, including spores and pollen, indicates remoteness from vegetated land areas. Assemblages are correlated to New Zealand dinoflagellate zones (Wilson 1984,1988) and age assignments are based on the revised New Zealand time scale (Morgans et al. 2004). Four dinoflagellate assemblages (O30/f445-f448) from uppermost Mead Hill Formation at Muzzle Stream (Fig. 8, Appendix 2A) are correlated to the Manumiella druggii zone, which indicates a late Haumurian (Maastrichtian) age. Two assemblages from Teredo Limestone and basal Lower Limestone (O30/f443-f444) are inferred to be Teurian (Paleocene) based on the absence of Manumiella druggii and the presence of Cerodinium cf. striatum. Seven assemblages from overlying Lower Limestone and lower Dee Marl (O30/f424-f427, f440-f442) lack key


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