Natural values of the Solitary Islands Marine Park - Marine Parks ...

8 Natural values of the Solitary Islands Marine ParkFigure 9.Resistant layers of rockstrata in a fossilisedsequence of induratedsandstone.Figure 10.A swim-through and gutterformation on a shallowrocky reef.Throughout the Coffs Harbour area, hard metamorphosed slates jut out over muchof the seabed from Sawtell to Brooms Head. These slates form numerous submergedreefs, washes and emergent islands, islets and rocks, including the five main islands inthe Solitary Islands group and at least 10 smaller islets and rocks (e.g. North-west Rock).These outcrops are a seaward extension of the adjacent coastal range, which has astrong influence on the coastline of the marine park.Variations in sea level have also influenced the geomorphology of the marine park,with the sea level being considerably lower during the last glacial period around20,000–15,000 years ago. Different erosionaland depositional forces acted on the rocks andsediments of this area during that time. A linear reef,paralleling the coastline in places, occurs at a depthof about 60 metres, and this may be a previouscoastline (paleocoastline).The coastal streams and rivers immediately adjacentto the marine park are very short due to theproximity of the coastal range, and this shortnessinfluences sediment rates and inputs.Shelf sediments in the area consist mainly ofmaterial from rivers and streams, relic quartzose(i.e. material resembling or containing quartz) andcarbonate rich sands (Zann 2000a). The structureof the ocean beaches is strongly influenced bywave exposure, resulting in sand bars, troughsand gutters, and rip channels that are frequentlychanging (Short 2003) (Figure 12). While the seabedmorphological zones can be defined by differencesin slope, relief and distance from the shore, apartfrom the bedrock areas they are dominated by sand.The wide distribution of sand throughout the innercontinental shelf reflects the absence of coastalsediments finer than sand; high-energy, strong tidalcurrents; and oceanic swells (Boyd et al 2004).