von Rad, U., Haq, B. U., et al., 1992Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 12223. FIRST RESULTS OF LATE TRIASSIC PALYNOLOGY OF THE WOMBAT PLATEAU,NORTHWESTERN AUSTRALIA1Wolfram Brenner2ABSTRACTCores from Leg 122, Sites 759, 760, 761, and 764, were sampled at intervals of one sample per 1.5-m section inthe Upper Triassic sequences. Spores, pollen, acritarchs, freshwater algae, and dinoflagellate cysts were studied toestablish a palynostratigraphic framework for the Late Triassic.The palynological sequence is interpreted in terms of Australian spore-pollen zones: the Carman Samaropolle-nites speciosus Zone, the Norian Minutosaccus crenulatus Zone, and the Rhaetian Ashmoripollis reducta Zone. TheSamaropollenites speciosus Zone-Minutosaccus crenulatus Zone boundary is marked by the change of pollenabundance and has a gradual character. Therefore, a transitional uppermost Carnian to Norian Samaropollenitesspeciosus/Minutosaccus crenulatus Zone is used. Age-determining dinoflagellate cysts are present in the Norian andRhaetian sediments.INTRODUCTIONDuring Leg 122 of the Ocean Drilling Program (ODP), nineholes were drilled at four sites (Site 759, 760, 761, and 764) in anorth-south transect on the Wombat Plateau, a small sub-plateauof the northern Exmouth Plateau (Fig. 1). The oldest sedimentsdrilled on the Wombat Plateau are late Carnian in age. They arealso the oldest marine sediments drilled during the 20-yearhistory of Deep Sea Drilling Project (DSDP) and ODP drilling.The sediment succession begins with late Carnian prodeltaclaystone and siltstone followed by deltaic, marginal-marine,and fluvial nonmarine sediments in the uppermost Carnian and inthe Norian (Sites 759 and 760). Uppermost Norian sedimentswere recovered at Site 761 and Rhaetian sediments at Sites 761and 764. The uppermost Norian consists of a carbonaceousclaystone with coal seams. The overlying Rhaetian sequence atSite 761 is comprised of crinoid limestone and laminated clay-stone facies. Site 764, which is located farther basinward, nearthe shelf edge, consists of a reef complex overlain by a shelflimestone. Jurassic sediments are completely missing on theWombat Plateau.The Upper Triassic sequence is unconformably overlain byLower Cretaceous sediments in the central part of the plateau(Site 761), which pinch out toward the south (Site 760).Toward the north (Site 764), the Cretaceous is further thinned,and only a condensed Upper Cretaceous section is present.The purposes of this paper is to provide a palynostrati-graphic zonation and a palynofacies framework of the UpperTriassic sediments. Except for a short comment on unde-scribed species, taxonomic discussion and description of thedinoflagellate cyst, acritarch, freshwater algae, and spore/pollen assemblages will be given elsewhere.METHODSDuring Leg 122, shipboard palynological studies weremade from about 120 samples of the Triassic sediments.Onboard laboratory processing facilities precluded routine useof hydrofluoric acid (HF). The preparation technique used onthe ship (Haq, von Rad, O'Connell, et al., 1990) yields only a1 von Rad, U., Haq, B. U., et al., 1992. Proc. ODP, Sci. Results, 122:College Station, TX (Ocean Drilling Program).2 GEOMAR, Wischhofstr. 1-3, 2300 Kiel 14, Federal Republic of Germany.partial assemblage of the entire palynomorph content of thesediment and is not usable for quantitative stratigraphic andpalynofacies examinations. Therefore, the shipboard sampleswere not used for shore-based studies.About 250 samples were taken from the Upper Triassicsediments of the Wombat Plateau. All the samples were giventhe following standard palynological processing treatment:after cleaning and drying, 20 g of the sample were boiled with35% hydrochloric acid (HC1) and then washed over a 10-/xmsieve. The residue was processed with HF and washed againover a 10-µm sieve. A small quantity of residue was removedfor fluorescence and SEM studies. The remainder was treatedwith 60% nitric acid (HNO3) to remove pyrite and amorphousorganic debris. Slides were mounted with Entellan.PALYNOFACIESPalynofacies definition can be based primarily on totalkerogen component or on palynomorph assemblages (Batten,1982; Bint and Helby, 1988; Hart, 1986). The latter definitionis used in this study.The different components of a organic microfossil assem-blage have different origin, either aquatic or terrestrial.Aquatic elements are freshwater algae, marine algae (di-noflagellate cysts and acritarchs), animal parts, such as scole-codonts (teeth of annelids), or the inner organic layer offoraminifers, also called foram-liners. Terrestrial elements arewood fragments, cuticle, spores, and pollen.The terminology used here for palynofacies nomenclaturerefers more to the composition of palynomorph assemblagesthan to an absolute environment interpretation. For example, ahigh terrestrial palynomorph input can overprint the marineassemblages; therefore, environments within the shallow-marinerealm (e.g., estuarine or lagoonal) could be interpreted as re-stricted marine or even nonmarine. A detailed study of thepalynofacies, incorporated with well-log data and sedimentolog-ical interpretations, will be the subject of future work.PALYNOSTRATIGRAPHYZonation Used For Leg 122The spore-pollen zonation of the western Australian Trias-sic is based on the biostratigraphic units of Dolby and Balme(1976), modified by Helby et al. (1987) (Fig. 2). These zones413W. BRENNERFigure 1. Bathymetric map (in meters) of the Australian NorthwestShelf region showing location of ODP sites on the Wombat Plateau.are defined in the sense of the International Guide to Strati-graphic Classification (Hedberg, 1976) as assemblage zones byDolby and Balme (1976) and as Oppel zones by Helby et al.(1987). The only published dinoflagellate zonation of thewestern Australian Triassic is by Helby et al. (1987). Theshorter ranges of the dinoflagellate cysts in contrast to thespores and pollen make it possible to define the zones asinterval zones in the sense of Hedberg (1976).The boundary between the Samaropollenites speciosusZone and the Minutosaccus crenulatus Zone is defined by amarked decline in prominence of Enzonalasporites vigens,Samaropollenites speciosus, and an uphole increase in Falcis-porites australis (Helby et al., 1987). Therefore, this boundaryhas a more gradual character. In addition, the uppermostCarnian and Norian sediments of the Wombat Plateau weredeposited in various