﻿186 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  194 
  3 
  

  

  In 
  Iran, 
  the 
  Haft 
  Kel 
  field 
  is 
  situated 
  on 
  a 
  structural 
  high 
  on 
  a 
  long 
  

   anticline, 
  while 
  the 
  Masjid-i-Sulaiman 
  field 
  is 
  on 
  a 
  more 
  complicated 
  

   anticlinal 
  structure 
  (Lees, 
  1938) 
  . 
  In 
  the 
  Baku 
  district 
  of 
  the 
  U. 
  S. 
  S. 
  R. 
  

   such 
  structures 
  as 
  Bibi-Eibat 
  and 
  Surakhany 
  are 
  typical 
  domes, 
  while 
  

   most 
  of 
  the 
  other 
  fields 
  are 
  apparently 
  anticlinal 
  folds 
  (Hobson, 
  1938) 
  . 
  

  

  Faulting, 
  resulting 
  from 
  both 
  tensional 
  and 
  compressional 
  forces, 
  

   has 
  been 
  the 
  controlling 
  factor 
  in 
  the 
  formation 
  of 
  another 
  group 
  of 
  

   traps. 
  The 
  importance 
  of 
  faulting 
  in 
  oil 
  accumulation 
  did 
  not 
  receive 
  

   recognition 
  until 
  about 
  20 
  years 
  ago 
  when 
  the 
  discovery 
  of 
  the 
  Mexia 
  

   field 
  in 
  East 
  Texas, 
  followed 
  by 
  that 
  of 
  a 
  number 
  of 
  others 
  in 
  the 
  same 
  

   structural 
  province, 
  directed 
  attention 
  to 
  this 
  form 
  of 
  trap. 
  In 
  the 
  

   Mexia 
  district 
  the 
  regional 
  dip 
  of 
  the 
  sediments 
  is 
  eastward 
  ; 
  the 
  faults 
  

   nearly 
  parallel 
  the 
  strike 
  and 
  are 
  upthrown 
  to 
  the 
  east, 
  and 
  the 
  accumu- 
  

   lation 
  occurs 
  in 
  the 
  upthrown 
  block 
  against 
  the 
  fault 
  plane 
  (Lahee, 
  

   1929) 
  . 
  Some 
  20 
  fields 
  of 
  this 
  type 
  have 
  been 
  found 
  in 
  the 
  district, 
  but 
  

   elsewhere 
  in 
  the 
  United 
  States 
  such 
  fields 
  are 
  unusual. 
  Whittier 
  and 
  

   Round 
  Mountain 
  are 
  California 
  examples. 
  

  

  Overthrust 
  faulting, 
  while 
  not 
  the 
  major 
  factor 
  in 
  accumulation, 
  is 
  

   an 
  important 
  feature 
  of 
  such 
  fields 
  as 
  Turner 
  Valley, 
  Alberta 
  (Link 
  and 
  

   Moore, 
  1934), 
  and 
  McKittrick, 
  California. 
  Illing 
  (1938a) 
  states 
  that 
  

   the 
  Tabaquite 
  field, 
  Trinidad, 
  appears 
  to 
  have 
  accumulated 
  in 
  a 
  thrust 
  

   block. 
  At 
  Boryslaw, 
  Poland, 
  oil 
  is 
  believed 
  to 
  be 
  trapped 
  by 
  the 
  over- 
  

   turn 
  of 
  a 
  thrust 
  block 
  (Cizancourt, 
  1931). 
  

  

  The 
  penetration 
  or 
  deformation 
  of 
  sediments 
  by 
  intrusions, 
  either 
  

   saline 
  or 
  igneous, 
  forms 
  a 
  varied 
  group 
  of 
  traps 
  for 
  oil 
  and 
  gas. 
  Under 
  

   the 
  weight 
  of 
  the 
  overburden 
  deeply 
  covered 
  salt 
  masses 
  become 
  plastic 
  

   and, 
  at 
  points 
  of 
  weakness, 
  burst 
  through 
  the 
  strata 
  above 
  them 
  to 
  form 
  

   intrusive 
  plugs. 
  Depending 
  upon 
  the 
  pressure, 
  the 
  volume 
  of 
  salt 
  

   available, 
  and 
  the 
  character 
  of 
  the 
  overlying 
  sediments, 
  salt 
  plugs 
  show 
  

   great 
  variation 
  in 
  size, 
  form, 
  and 
  extent 
  of 
  movement. 
  Those 
  of 
  the 
  

   piercement 
  type 
  have, 
  in 
  many 
  cases, 
  penetrated 
  many 
  thousands 
  of 
  

   feet 
  of 
  overlying 
  deposits, 
  often 
  reaching 
  the 
  surface; 
  on 
  the 
  other 
  

   extreme 
  are 
  deep-seated 
  domes 
  which 
  may 
  have 
  penetrated 
  the 
  beds 
  

   above 
  them 
  for 
  only 
  a 
  comparatively 
  short 
  distance. 
  

  

  Piercement 
  domes 
  tend 
  to 
  drag 
  upward 
  the 
  edges 
  of 
  the 
  beds 
  pene- 
  

   trated, 
  and 
  the 
  porous 
  beds, 
  sealed 
  against 
  the 
  salt 
  mass, 
  form 
  annular 
  

   reservoirs. 
  If 
  the 
  salt 
  plug 
  does 
  not 
  reach 
  the 
  surface, 
  overlying 
  strata 
  

   may 
  be 
  arched 
  upward, 
  forming 
  circular 
  reservoirs 
  above 
  the 
  plug. 
  If 
  

   the 
  section 
  above 
  the 
  ascending 
  salt 
  mass 
  contains 
  beds 
  of 
  some 
  degree 
  

   of 
  competency, 
  faulting 
  may 
  result. 
  The 
  stretching 
  of 
  the 
  beds 
  over 
  

   the 
  plug 
  may 
  be 
  compensated 
  by 
  the 
  formation 
  of 
  a 
  central 
  graben. 
  

   Tangential 
  faults 
  along 
  the 
  margins 
  of 
  plugs 
  are 
  frequent. 
  In 
  some 
  

   regions, 
  such 
  as 
  Germany 
  and 
  Rumania, 
  the 
  salt 
  masses 
  have 
  been 
  

   highly 
  distorted 
  by 
  diastrophic 
  movements, 
  and 
  the 
  accompanying 
  

   reservoirs 
  have 
  been 
  intricately 
  folded. 
  

  

  