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Puddingstone, also known as eitherpudding stone orplum-pudding stone, is a popular name applied to a type ofconglomerate that consists of distinctly rounded pebbles whose colours contrast sharply with the colour of the finer-grained, often sandy, matrix or cement surrounding them. The rounded pebbles and the sharp contrast in colour gives this type of conglomerate the appearance of a raisin orChristmas pudding.[1][2] There are different types of puddingstone, with different composition, origin, and geographical distribution. Examples of different types of puddingstones include the Hertfordshire, Schunemunk, Roxbury, and St. Joseph Island (Drummond Island) puddingstones.
Hertfordshire puddingstone is asilica-cementedconglomerate composed of roundedflintpebbles andcobbles with matrix of finesand and silica cement. The Hertfordshire Puddingstone is characterized by silica-cemented flint gravel that is brown to deep red in colour and often exhibits black exteriors and thin rinds on cut or polished surfaces. It typically occurs scattered across the land surface as isolatedconcretion-like masses in the areas ofHertfordshire andPlumstead Common,England. Large masses of Hertfordshire Puddingstone often occur within localPleistocene glacialtills. More than a dozen large blocks of this puddingstone were recovered fromPaleogene sediments during construction of the A10 bypass from Thundridge to Puckeridge in 2004. This indicates that the loose blocks of Hertfordshire Puddingstone were probably eroded out of these sediments. Although it is hypothesized that it is groundwatersilcrete, its origin remains unresolved.[3][4]
The Schunemunk puddingstone is a conglomerate inNew York andNew Jersey that is part of a 3,000 feet (910 m) thickgeologic formation formally known as theSkunnemunk Conglomerate. It is exposed extensively onBearfort Mountain, inBoonton andRockaway Township in New Jersey and onSchunemunk Mountain in New York. This puddingstone is a distinctive, LateDevonian, grayish-purple to grayish-red, thin to very thick-bedded,cross–bedded, conglomerate. Within the Skunnemunk Conglomerate, it is interbedded with grayish-purple to grayish-redsandstone, thin-bedded, medium-gray sandstone, and greenish-gray and grayish-redshale withmudcracks. This conglomerate consists of pebbles and cobbles of white veinquartz, red and greenquartzite, sandstone, red and graychert, and red shale. The grayish-purple to grayish-red conglomerate and sandstone is cemented largely byhematite and microcrystalline quartz. The cobbles that it contains range in size from 2.5 in (6.4 cm) to 6.5 in (17 cm).[5][6] Pieces of Skunnemunk Conglomerate are easy to recognize and have been found in glacial deposits throughout the lower Hudson Valley region.[7]
The Roxbury puddingstone is a massive,Ediacaran, clast-supported pebble and cobble conglomerate that occurs within the Brookline Member of theRoxbury Conglomerate that is exposed aroundBoston,Massachusetts region. This conglomerate is composed of a grey feldspathic sand matrix and well-rounded pebbles and cobbles of quartzite,granite,felsite, andquartz monzonite. The beds of ‘puddingstone’ are complexly interbedded with layers of massivediamictite and laminated and gradedargillite and sandstone. It likely accumulated asturbidites and submarine slumps within asubmarine fan or outer slope environment within a deep rift basin submerged by marine waters.[8][9]
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Jasper conglomerate, which is also denominated "pebble jasper conglomerate", "Saint Joseph Island puddingstone", "Drummond Island puddingstone", or "Michigan(ian) puddingstone", occurs inSaint Joseph Island and the vicinity of theSaint Mary's River, north and northwest of theBruce Mines ofNorthern Ontario,Canada, circa 65 kilometres (40 mi) east ofSault Sainte Marie, Ontario. In these locales, it occurs as thick beds ofPaleoproterozoic pebble conglomerate within the medial part of ageologic formation that is named the Lorrain Formation of the Cobalt Group. The jasper conglomerate consists of subrounded pebbles of red jasper, black chert, white quartzite, hematite, and semi-transparent quartz in a matrix of coarsely grained quartzite. It contains circa 30% to 90% of pebbles. Within the deposits of Lorrain Formation, the jasper conglomerates occur principally as the sedimentary fills of erosional troughs and channels of what are interpreted to be eitheralluvial fans or deposits ofbraided river.[10][11] These deposits are inferred to be nonglacial in origin and immediately postdate the PaleoproterozoicMakganyene glaciation.[12]
Elsewhere, e. g. inDrummond Island,Michigan,United States, jasper conglomerate, there denominated "Drummond Island puddingstone", occurs as loose gravel withinPleistoceneglacial drift. These fragments of jasper conglomerate areglacial erratics that continentalice sheets from Northern Ontario eroded and then spread throughout Michigan, including in Drummond Island, and as far south asOhio andKentucky during repeated glacial advances and retreats.[13]