function DateQuarterStart(const D: TDateTime): TDateTime;
var
  Year, Month, Day, Quarter: Word;
begin
  SysUtils.DecodeDate(D, Year, Month, Day);
  Quarter := 4 - ((12 - Month) div 3);
  Month := 0;
  SysUtils.IncAMonth(Year, Month, Day, (Quarter * 3) - 2);
  Result := SysUtils.EncodeDate(Year, Month, 1);
end;
//delphi/2164