Publication Date:
2023-07-10
Description:
Upper Berriasian to lower Aptian calcareous nannofossil assemblages have been studied from a siliciclastic deep-sea fan complex and a subjacent limestone sequence drilled beneath the lower continental rise in the western North American Basin, 270 miles (435 km) off Cape Hatteras, North Carolina (USA). Sharp lithologic facies changes and reworking by turbidites complicate the biostratigraphic interpretation, but provide an excellent opportunity to better distinguish "nearshore" from open-ocean nannofossil species, and to investigate the introduction of neritic taxa into the deep-see environment, a phenomenon that appears to have been widespread within the circum-North Atlantic during Neocomian times. Well-preserved assemblages in dark, carbonaceous claystones were probably displaced from the oxygen minimum zone along the upper slope or outer shelf. Neritic, continental margin species prevalent in this facies include the holococcolith Zebrashapka vanhintei n. gen., n. sp., Lithraphidites alatus magnus n. spp., Pickelhaube furtiva n. gen., and a host of nannoconids and micrantholiths.
A qualitative evaluation of widely used guide fossils suggests that the triad of proposed markers for the base of Roth's Zone NC3 make their first appearances in the following (ascending) order: Diadorhombus rectus, TUbodiscus verenae, Calcicalathina oblongata. Of these, we chose the nominative species for the zone, T. verenae, to mark its base and to approximate the Berriasian/Valangian boundary. Cyclagelosphaera deflandrei is strongly affected by diagenesis and is therefore not a reliable index species for the base of Zone NC4 near the Valanginian/Hauterivian boundary (the last occurrence of T. verenae is also not suitable there). In addition, Lithraphidites bollii, a form apparently confined to the low latitudes of the Tethyan region, was absent at the more temperate Site 603 and not available as a subzonal marker for the upper Hautervian-lower Barremian (mid-NC4 and mid-NC5, respectively). Cruciellipsis cuvillieri, however, provides a reliable datum just below the Hauterivian/Barremian boundary (base of NC5), despite the potential for reworking in this section. Nannoconids tend to be reworked in this section, and do not provide trustworthy forms to mark the Barremian/Aptian boundary (base of NC6). Hayesites irregularis n. comb, probably does provide a useful first appearance datum within the lower Aptian, if it is not confused with a more birefringent and globular form, Rucinolithus terebrodentarius n. sp. Rhagodiscus angustus is mimicked by a similar form (Zeughrabdotusl pseudoangustus n. sp.), which apparently ranges down to the Hauterivian, thus Lithastrinus floralis provides a more useful first appearance datum for the base of the middle-upper Aptian Rhagodiscus angustus Zone (NC7).
Aside from the new taxa mentioned above, the following are also described: Cretarhabdusl delicatus n. sp. and Cyclagelosphaera jiangii n. sp.
Keywords:
93-603B; Assipetra infracretacea; Axopodorhabdus dietzmannii; Biscutum sp.; Braarudosphaera discula; Braarudosphaera regularis; Calcicalathina oblongata; Chiastozygus litterarius; Chiastozygus striatus; Chiastozygus tenuis; Conusphaera mexicana; Corollithion achylosum; Corollithion acutum; Corollithion conicus; Corollithion ellipticum; Cretarhabdus crenulatus; Cretarhabdus sp.; Cruciellipsis cuvillieri; Cruciplacolithus hayi; Cyclagelosphaera deflandrei; Cyclagelosphaera margerelii; Deep Sea Drilling Project; DEPTH, sediment/rock; Diadorhombus rectus; Diazomatolithus lehmanii; Diloma placinum; Diloma primitivum; Discorhabdus biradiatus; Discorhabdus ignotus; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; Eiffellithus sp.; Ethmorhabdus hauterivianus; Glaukolithus diplogrammus; Glomar Challenger; Grantarhabdus coronadventis; Grantarhabdus meddii; Haqius circumradiatus; Hayesites irregularis; Leg93; Lithologic unit/sequence; Lithology/composition/facies; Lithraphidites alatus ssp. magnus; Lithraphidites carniolensis; Manivitella pemmatoidea; Manivitella sp.; Micrantholithus hoschulzii; Micrantholithus obtusus; Micrantholithus sp.; Microstaurus chiastius; Microstaurus conus; Nannoconus colomii; Nannoconus dolomiticus; Nannoconus globulus; Nannoconus grandis; Nannoconus sp.; Nannoconus spp.; Nannoconus steinmannii; Nannofossil abundance; Nannofossils preservation; Nannofossil zone; Octopodorhabdus plethotretus; Percivalia fenestrata; Pickelhaube furtiva; Reinhardtites sp.; Rhabdolekiskus parallelus; Rhagodiscus asper; Rhagodiscus infinitus; Rhagodiscus swinnertonii; Rucinolithus wisei; Sample code/label; Smear slide analysis; Speetonia colligata; Stage; Stephanolithion laffittei; Tegumentum stradneri; Tetrapodorhabdus coptensis; Tubodiscus sp.; Tubodiscus verenae; Vekshinella stradneri; Visual description; Watznaueria barnesae; Watznaueria biporta; Watznaueria britannica; Zebrashapka vanhintei; Zeugrhabdotus embergeri; Zeugrhabdotus erectus; Zeugrhabdotus pseudoangustus
Type:
Dataset
Format:
text/tab-separated-values, 5040 data points
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