The single specimen of Giraliaster sp. A (D.8228.

264, Figs 1, 2) was collected from a sequence of olive-green to rusty-brown siltstones and 6ne sand- stones located within the uppermost levels of the Hidden Lake Formation (the uppermost formation within the Gustav Group). It is associated with a sparse ammoxllte fauna 1D which a small pachydls- cid, provisionally assigned to Menuites patagonicus {PAvLczz), predominates {M.R.A. Thomson, pers. comm. 1997). The benthos is dominated by inocera- mid bivalves assigned to the Mytiloides' africa~us Hzmz group, and there are strong Santonian age affinities (Ineson et al. 1986).

Specimens D.8615.55 (Huttonechinus antarctica), D.8617.59 and RF 10/12 {Micraster aff. regularis) were collected from approx~mately the lowermost 230 m of the Lachman Crags Member, Santa. Msrta Formation (the lowermost lithostratigraphical unit within the Marambio Group) (Figs 1, 2). The litho- logies at this level are typically fine-grained, tuffa- ceous silty sandstones, together with subordinate mudstones and, pebbly sandstones (Pirrie 1989; Scasso et al. 1991). The benthonic fauna is slightly more proli6c than in the underlying levels and inoceramids occur together with nuculid, pinnid and trigoniid bivalves, and naticid gastropods. A distinctive ammonite assemblage includes a range of small scaphitids, baculitids, nostoceratids and diplomoceratids. Together with belemnites such as Dimitolebus (Dimitolebus) cf. ongleyi STEvENs and D. (Dimibocamax) cf. seymouriensis DovLz, they lndlcate a Late SantoIllan-Early Campanlan age- range (Olivero 1988; Doyle 1990).

Structural repetition, by a major NE-SW trending reverse fault (or faults) has led to extensive expo-