Wangaloa and Abbotsford Formations : Measly Beach drillhole, South Otago, New Zealand

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SR_1995-012-pdf
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Lindqvist, J.K. 1995 Wangaloa and Abbotsford Formations : Measly Beach drillhole, South Otago, New Zealand . Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 95/12 44 p.

Abstract: A cored hole drilled near Measly Beach in Kaitangata Sub-basin has clarified the facies succession spanning the middle-upper Wangaloa and lower Abbotsford Formations. The drillsite was located 30 m from the cliff ridge above Measly Beach, 4.3 km south of Tokomairiro River Mouth, and 3.8 km north of Mitchells Point at grid reference H46/785365; elevation =35 m. The hole was fully cored (HQ gauge; 62 mm diameter core) and geophysically logged using combination gamma, 45 and 15 cm-spaced density, caliper; and spontaneous potential tools. Drilling was terminated at 102.95 m in Wangaloa Formation. The following succession was recorded: 0-5.65 m - Holocene. Topsoil (30 cm) overlying silty loess (to 3.83 m) and sandy quartzose pebble gravel. 5.65-38.9 m - Abbotsford Formation. In this Early Eocene (mid Waipawan) to Late Paleocene (uppermost Teurian) interval, five greensand beds overlying Thalassinoides-burrowed discontinuity surfaces grade up into burrow-mottled silty or fine sandy mudstone. A greensand unit at 6.34-8.65 m also contains goethite ooids and phosphate nodules. The burrowed discontinuity => greensand => mudstone sequences are interpreted as offshore transgression-regression cycles, representing sediment starvation due to abrupt sea-level rise, and subsequent progradation of fine grained shelf sediment during sea-level fall or stillstand. One sequence is capped by an unusual thin-bedded kaolinitic clay and mudstone interval (8.65-13.25 m), provisionally interpreted as a lowstand brackish basin of tidal-flat facies assemblage. 38.9-84.62 m -[upper] Wangaloa Formation. This succession of 37 sharp-based shellbed => sandstone cycles comparable to the Mitchells Point beds, is interpreted as a storm dominated lower shoreface unit deposited mostly above fair-weather wave base. Intervals of anomalously high gamma radiation correspond with fine to very-fine grained well sorted sandstone containing zircon and monazite-rich heavy mineral concentrations. Dominated by turritellid gastropods, mollusc assemblages are commonly preserved as shelly carbonate in calcitic concretions, and as decalcified and compacted moulds in uncemented sand. Individual decimetre-metre thick sands show multiple erosional truncations and variable dip directions typical of hummocky cross stratified beds. 84.62-92.0 m - Interpreted as a fluvial-estuarine channel fill sequence, this interval consists of small-scale fining-up cycles of quartz conglomerate, sandstone and carbonaceous mudstone, contains scattered shelly bivalves. Double-mud drapes in thin-bedded sandstone/mudstone suggest tidal influence. Dinoflagellate assemblages from mudstones indicate a Mid-Late Paleocene age (mid-late Teurian Palaeocystodinium golzowellse Zone). This unit is correlated with conglomerate exposed at the mouth of Washpool Creek, and its base represents a sequence boundary. 92.0-102.95 m - [middle] Wangaloa Formation. This well-sorted fine grained sandstone contains minor erosion surfaces and mould ic shell layers as in the 38.9-84.92 m interval and possibly correlates with the upper part of the uppermost well sorted shoreface sandstone exposed in low cliffs at Smiths Beach north of Wangaloa Domain.