Yes this is possible.
I wouldn't call this a contour plot, it's really more like a bubble plot.
You can't make triangles with geobubble, but you can with geoscatter. geoscatter provides lots of the same functionality as geobubble, but you have to scale the markers yourself and you don't get a size legend (not sure what that might look like for triangles).
x=randi([20 50],50,1);
y=-randi([70 130],50,1);
s=rand(50,1)*300;
c=randi(8,50,1);
figure
geoscatter(x,y,s,c,'filled')
colormap(jet(8))
colorbar('location','southoutside','Ticks',linspace(1,8,9))
figure
geoscatter(x,y,s,c,'^','filled')
colormap(jet(8))
colorbar('location','southoutside','Ticks',linspace(1,8,9))
