You don't really indicate what you are doing inside the case statement.  I
agree with Albert that you ought to move these criteria into a table.  
Structure might look like:

YearField   NValue    Marker  SomeValue    SomeEqn
2007             1            8.3
2007             1           12.7
2007             1           15.4
2007             2           14.7
2007             2           17.1

I would use a SomeValue field if the values of N and Marker should return a
single value.  You could use SomeEqn to store an equation that would be
evaluated in the given situation.

The challenge here is deciding what to do when you've found a criteria that
works.

I like Albert's idea of using SQL to identify your recordsets, but you have
to be careful of the order that you loop through the recordsets.  If the
values of N and Marker are in a data table, and you want to compare them to
these values in this new table, you will need to make sure you limit your
result set so that you don't perform the same action on the same record
multiple times.  One way to do this might be to create a recordset:

Dim rs as DAO.Recordset
Dim strSQL as string

strSQL = "SELECT NValue, Marker FROM yourTable " _
          & " WHERE [YearField] = 2007 " _
          & " ORDER BY NValue ASC, Marker DESC"
set rs = currentdb.OpenRecordset
Do While not rs.eof
   if x = nValue AND y > Marker Then
       'do something
       Exit Do
   endif
   rs.movenext
Loop

Without more information on what you are doing inside the Select Case
statements, or how this code is being used (is it in a forms event), I cannot
provide any more recommendations.

HTH
Dale