Copyright by Nysha Chaderton 2009 - The University of Texas at ...
Copyright by Nysha Chaderton 2009 - The University of Texas at ...
Copyright by Nysha Chaderton 2009 - The University of Texas at ...
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SUMMARY DEPOSITIONAL SETTING OF THE SCOTLAND FORMATION DEPOSITS<br />
<strong>The</strong> facies identified in the Scotland Form<strong>at</strong>ion outcrops range from<br />
conglomer<strong>at</strong>es, coarse-grained sands with gravel and pebbles to lamin<strong>at</strong>ed silty muds and<br />
fine grained sands. <strong>The</strong> facies and architectural components <strong>of</strong> the Scotland Form<strong>at</strong>ion<br />
fit into the mixed sand and mud submarine fan system <strong>of</strong> Reading (1991). <strong>The</strong> absence <strong>of</strong><br />
slump deposits in outcrops, and the sand content <strong>of</strong> the system suggests a mid-fan<br />
depositional loc<strong>at</strong>ion for the Scotland as opposed to either a proximal, slope loc<strong>at</strong>ion or a<br />
distal basin plain loc<strong>at</strong>ion.<br />
Trace fossils can be locally well developed in submarine fans, particularly in mid<br />
to outer fan settings. Thalassinoides and Planolites were observed <strong>at</strong> the Mount All<br />
loc<strong>at</strong>ion. <strong>The</strong>se trace fossils were locally abundant on the bases <strong>of</strong> mudstone beds. A<br />
similar assemblage <strong>of</strong> Thalassinoides, Scalarituba and Planolites were identified in the<br />
Nihoptupu and Tirikohua Form<strong>at</strong>ions <strong>of</strong> New Zealand th<strong>at</strong> are comprised <strong>of</strong> deep w<strong>at</strong>er<br />
turbidites deposited in an inter-arc basin <strong>of</strong> the Northland volcanic arc (MacEachern et<br />
al., 2007).<br />
Middle fan environments <strong>of</strong>ten contain trace fossils along the soles <strong>of</strong> sandy<br />
turbidites th<strong>at</strong> can suggest “shallow w<strong>at</strong>er” deposition (Crimes, 1977; Howell and<br />
Normark, 1982). Trace fossils, such as Diplocr<strong>at</strong>erion habichi, th<strong>at</strong> are rare in the<br />
Scotland Form<strong>at</strong>ion are generally shallow-w<strong>at</strong>er, high energy indic<strong>at</strong>ors ~ 200 m w<strong>at</strong>er<br />
depth (Pemberton and MacEachern, 1995). This anomalous trace fossil associ<strong>at</strong>ion is the<br />
result <strong>of</strong> the imit<strong>at</strong>ion <strong>of</strong> the high energy neritic environment in a mid fan setting. This<br />
occurs because fast flowing depositional currents result in short lived episodes <strong>of</strong> high<br />
oxygen<strong>at</strong>ion th<strong>at</strong>, coupled with the slow build-up <strong>of</strong> organic detritus in the middle fan<br />
leads to an imit<strong>at</strong>ion <strong>of</strong> high energy neritic environments (Howell and Normark, 1982).<br />
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