Shallow marine palynofacies from K/P boundary, Marambio (Seymour) Island, Antarctic Penninsula.

RODRÍGUEZ BRIZUELA, R.; BARREDA, V.; SANTILLANA, S.; MARENSSI, S.

Fukuoka, Japan

Congreso; 17 International Sedimentological Congress; 2006

A palynofacial analysis of sedimentary rocks from the K/P transition within the López de Bertodano Formation, Marambio (Seymour) Island, Antarctic Peninsula, is presented in this contribution. In this section, the boundary is well known by stratigraphical / sedimentological [1] and paleontological / biostratigraphical [2, 3] studies. Palynofacies concept has been successfully applied to distinguish landward from basinward shifts in depositional settings [4] in response to sea level variations. The purpose of this first approach is to analyze palynofacies through this high-latitude K / P section, looking forward relate palynofacies to recognized sedimentary settings [1]. This preliminary study consisted mainly of a quantitative analysis of the three basic types of palynological sedimentary organic matter. Following Batten [5], these are: palynomorphs, structured organic matter (STOM) and amorphous organic matter (AOM). Nine samples, stratigraphically separated by fifteen centimeter intervals trough the K/P boundary were analyzed. Standard laboratory maceration procedures (HCL and HF chemical digestion) were used to prepare the samples. The residues were not sieved to avoid removing much of the AOM. Transmitted light microscopy was used to examine the slides and at least 300 particles were point counted per slide. RESULTS Dispersed organic particles assemblages are dominated by AOM in frequencies higher than 80 %. STOM and palynomorphs represents around 10% - 20% of the association with predominance of black debris (60 % - 80%) and, in lower frequencies, spores, pollen and others phytoclasts (40% - 20%). This palynofacies evidences sedimentation in a shallow marine inner shelf paleoenvironment. Characteristically the facies is dominated by higher frequencies of AOM with a subordinate participation of continental and marine STOM and palynomorphs [6]. All samples correspond to the same palynofacies, except the K/P boundary one. A significant palynofacial change occurs in this interval, where the sedimentary organic matter is composed practically by 100 % of AOM, with traces of black debris and sterile in palynomorphs. This palynofacies analysis is consistent with earlier sedimentological interpretations of inner shelf sedimentation trough the K/P interval on Marambio (Seymour) Island. The glauconitic level at the K/P boundary represents a condensed interval and the maximum flooding of the subcycle II, in a general regressive trend [1]. The low sedimentation rate in this horizon may be related to the palynofacial change in the K/P boundary.