Sand grain detrital modes in CRP-1: provenance variations and influence of Miocene eruptions on the marine record in the McMurdo Sound region
Detrital modes for the sand-size fraction in 24 samples from the CRP- 1 drillcore arc described. Most samples are largely composcd of quart7.o-feldspathic detritus sourced
dominantly from Palaeozoic granitoids and quartzose sedimentary sequences. Minor contributions from basic lamprophyre dykes, felsic dykes and possibly Kirkpatrick basalts arc also identified as detrital components for the first time. The provenance also included a minor outcrop area of high-grade metamorphic rocks. Detritus derived from a Ferrar dolerite source is common throughout. It was possibly derived mainly from thick sills of the lower coastal ranges (intruding Palaeozoic and older "basement") rather than those sills intruding the stratigraphically higher Beacon sedimentary sequence, although this suggestion
is not strongly constrained. Tephra particles froin both magmatic and hydrovolcanic eruptions are well represented
and persistent at all levels in the core. although no primary tephra layers are present. The volcanic influence is minor in most of the Quaternary samples analysed (although these are few) and most Miocene samples. Conversely, the topmost part of the Miocene sequence (above 62 metres below sea floor (mbsf)) is strongly affected by volcanism. with two major basic-intermediate eruptions represented in the detrital record (at c. 61 and45 mbsf) and provisionally correlated with a volcano formerly situated near Mount Morning. A third eruption of evolved pumice is also recorded in the Miocene sequence at c. 116 mbsf.
Authors: Smellie, J.L.
1 January, 1998
Terra Antartica / 5