Hi,
I’m trying to setup a continental extension model with sedimentary filling. I was following this file to debug fastscape parameters. fault_analysis_study/prmfiles/symmetric-1e-5.prm at master · Djneu/fault_analysis_study · GitHub . i looked at this post Problem with sedimentary filling process - #4 by Djneu and it seems sediment age should be passive filed. somehow when i try to run my parameter file it complains about sediment_age field being a chemical composition. 
Here is my setup,
subsection Mesh deformation
set Mesh deformation boundary indicators = top : fastscape
set Additional tangential mesh velocity boundary indicators = left, right
subsection Fastscape
set Vertical exaggeration = 1
set Maximum timestep length = 1500
set Number of fastscape timesteps per aspect timestep = 1
set Maximum surface refinement level = 3
set Surface refinement difference = 1
set Additional fastscape refinement = 1
set Use marine component = true
set Use ghost nodes = false
set Y extent in 2d = 100e3
set Sediment rain rates = 0.1e-3,0.05e-3 # m/yr
set Sediment rain time intervals = 1e6
subsection Boundary conditions
set Right = 1
set Left = 1
end
subsection Erosional parameters
set Drainage area exponent = 0.4 #m
set Slope exponent = 1 #n
set Multi-direction slope exponent = -1 #p
set Bedrock diffusivity = 5e-3 #kd
set Bedrock river incision rate = 1e-5 #kf
set Bedrock deposition coefficient = 1 #G
set Sediment diffusivity = -1
set Sediment river incision rate = -1
set Sediment deposition coefficient = 1 #G
end
subsection Marine parameters
set Sea level = -500
set Sand porosity = 0
set Silt porosity = 0
set Sand e-folding depth = 0
set Silt e-folding depth = 0
set Sand-silt ratio = 1
set Depth averaging thickness = 1e2
set Sand transport coefficient = 200
set Silt transport coefficient = 200
end
end
end
subsection Compositional fields
set Number of fields = 10
set Names of fields = sediment_age,plastic_strain, noninitial_plastic_strain,sediment, uc_plastic, uc_no_plastic,lc_plastic, lc_noplastic,L_mantle,A_mantle
end
i add a initial composition for sediment_age (empty column)
subsection Initial composition model
set List of model names = ascii data
subsection Ascii data model
set Data directory =
set Data file name = composition-with-sediments1.txt
end
end
subsection Boundary composition model
set Fixed composition boundary indicators = top
set Allow fixed composition on outflow boundaries = true
set List of model names = initial composition,function
subsection Function
set Coordinate system = cartesian
set Variable names = x,y,t
set Function expression =if(y>390e3, t/1e6, 0); \ sediment age
0; plastic strain
0; \ non-initial plastic strain
if(y>390e3 && t>0, 1, 0); \ sediment1
if(y>390e3 && x>=400e3 && x<= 600e3, t==0, 1,0); \ uc_1
if(y>390e3 && x<=400e3 && x>= 600e3, t==0, 1,0); \ uc_2
0; \ lc_1
0; \ lc_2
0; \ L_mantle
0; \ A_mantle
end
end
The error message is,
Exception ‘ExcMessage("There is a field sediment_age that is of type chemical composition. " “Please change it to type generic so that it does not affect material properties.”)’ on rank 48 on processing:
An error occurred in line <235> of file </home/chameera/buildaspect/aspect/source/mesh_deformation/fastscape.cc> in function
void aspect::MeshDeformation::FastScape::initialize() [with int dim = 2]
The violated condition was:
it == chemical_field_names.end()
Additional information:
There is a field sediment_age that is of type chemical composition.
Please change it to type generic so that it does not affect material
properties.
is there a way to solve this error ? 
Best,
Chameera
(seems like