Fast simple object serialization

I am looking for fastest serialization method tiles in 2D world. Lets say the world is big and because computer can't handle that much blocks loaded at the same time, so I splitted the world to chunks. BinaryFormatter seems to be slow. Is there any faster method, how to serialize the chunk object?

WChunk object structure

public class WChunk
{
    public int ChunkX;
    public int ChunkY;
    public SortedDictionary<WPoint, WTile> Tiles;
}

WTile object structure

public class WTile
{
    WPoint Location;
    int Data;
}