The enigma of intricately fitted beach boulders near Raglan, New Zealand

<p>An intertidal rocky platform tucked in behind a rocky headland on open-ocean Gibson Beach, near Raglan, supports an agglomeration of cobble- to large-boulder-sized clasts of Cenozoic sandstone and limestone. Rather than exhibiting just point contacts, many larger clasts are tightly interlocked and fitted with their neighbours and/or the underlying platform bedrock. Clast interface geometry relates to the strength contrast between adjacent rock types, linked to their calcite (cement) content. The end-product is an armoured, highly stable framework of boulder clasts resembling a giant three-dimensional jigsaw puzzle. While the direct impact of breaking waves likely plays a role in in situ jostling of boulders, we speculate that mechanical abrasion and fitting between larger clasts may also be promoted and maintained by in situ microvibration of the boulders as a consequence of wave-induced microseismic shaking within the cliff-backed rocky platform and headland, especially during major storm wave assault from the southwest.</p

Paleogeography of Late Eocene to earliest Miocene Te Kuiti Group, central-western North Island, New Zealand

<div><p>We present a series of 13 paleogeographic maps representing development of the Waikato–King Country Basin through the Late Eocene to Early Miocene in central-western North Island when the New Zealand platform was undergoing widespread marine inundation. The maps are the end-point of a basin analysis of the Te Kuiti Group, which has included development of a revised lithostratigraphy, biostratigraphy, chronostratigraphy and the application of facies analysis. The new stratigraphic framework has identified six major unconformity-bound sequences within the Te Kuiti Group and the paleogeographic maps are drawn for time-slices through unconformities and systems tracts. A major unconformity between the Whaingaroa Formation and the Aotea Formation dated c. 29 Ma marks the start of reverse faulting on the Taranaki Fault. At c. 27 Ma, reverse displacement on the Manganui Fault started. Several phases of displacement on the Manganui Fault ensured that land persisted over part of the Herangi High throughout the Duntroonian (Ld) and Waitakian (Lw) Stages spanning the Late Oligocene and earliest Miocene.</p></div