Eustasy Recording Potential of an Isolated Devonian to Pennsylvanian

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					     Eustasy Recording Potential of an Isolated Devonian to Pennsylvanian Carbonate Platform in a Foreland
                            Basin Setting (Tengiz, Pricaspian Basin, Kazakhstan)*
                                                                     By
                                                                       1
                                                    Jeroen Kenter and P.M. (Mitch) Harris2

                                                    Search and Discovery Article #20047 (2008)
                                                                     Posted May 19, 2008

*Abstract prepared for AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008

1
    ETC, chevron, Voorburg, Netherlands (jeroenkenter@chevron.com)
2
    ETC, chevron, San Ramon, CA, USA. (MitchHarris@chevron.com)

                                                                           Abstract

Research drilling of continental margins over the last decade has validated a significant number, as well as the timing, of EPR sea-
level events for the past 100 My. However, for the older geological record diverging sea level estimates (EPR curve, continental
flooding records, planktic evolutionary records) still exist and the extraction of reliable eustatic records remains problematic.

Tengiz field is an isolated carbonate buildup in the southeastern Pricaspian Basin, containing a complete Late Famennian to Early
Bashkirian platform succession that was deposited in a relatively stable but rapidly subsiding foreland basin setting facing a thrust belt
to the south. Since the Famennian, the platform aggraded and periodically back-stepped, resulting in approximately 1400 m (4480 ft)
of relief above the Famennian platform, followed by up to 2 km (1.2 miles) of Serpukhovian progradation. Vertical trends in relative
shoaling and deepening, recorded exposure and/or erosional events, and biostratigraphy provide a relative sea level record of
punctuated sea level falls and rises that is made up of 2nd and 3rd order sequences which are superimposed by higher (4-5th order)
frequency platform cycles.

Though several of the observed sea level lowstands correspond to 3rd order eustatic sequences on the EPR curve, the influence of
rapid changes in the paleobathymetry of the foreland basin, which caused significant thickening of sequences and drowning in the
Late Devonian elsewhere in the basin, appears to have a strong influence on the regional sequence stratigraphic framework. This
article addresses the interplay between subsidence and recorded sequences in such foreland basin settings.
   Paleozoic Carbonates in Foreland Basin Settings:
Northern Pricaspian Basin (Kazakhstan) and Cantabrian
                     Zone (Spain)
                         Jeroen Kenter1, P.M. (Mitch) Harris3
  1   Chevron Energy Technology Company, Voorburg, Netherlands, 2Chevron Energy
                 Technology Company, San Ramon, California, U.S.A.

                              CENTRAL                   OUTER
      SLOPE                                           PLATFORM        SLOPE
                             PLATFORM

                                                    Bash.


                                                            Serpu-
                                    Visean                  khovian
                                  Tournaisian
                                        Famennian




                With contributions by Oscar Merino-Tomé, Juan Bahamonde,
                      Juan Colmenero, Tom Heidrick, Kairat Jazbayev
Outline

  Rationale

  Carbonate systems in foreland basin
  settings

  Tectonic setting Pricaspian Basin

  Tengiz Field accommodation history

  Outcrop analog from northern Spain:
  platforms and thrust-top buildups in a
  foreland basin setting

  Conclusions

                                           2
Rationale

  Sedimentation in tectonically active settings controlled
  by 1) structural grain, 2) timing and rate of
  deformation, and 3) eustacy

  Many carbonate hydrocarbon reservoir systems
  formed in foreland basin settings

  Generally difficult to extract geometry and timing from
  outcrop BUT

  Outcrop analog from northern Spain shows variation
  of depositional style in time and space

  May assist understanding/interpretation of carbonate
  system evolution in such tectonic regimes and in
  Pricaspian in particular
                                                         3
General tectonic settings of carbonate
buildups




                                                                                                                  Bosence 2005
                Reprinted from Sedimentary Geology, V.175, 1-4, Bosence, A genetic classification of carbonate platforms based on
                basinal and tectonic settings in the Cenozoic, p.49-72, with permission from Elsevier ( http://www.sciencedirect.com/).
                                                                                                                                          4
Foreland basin and thrust-top buildups
    Foreland margin buildups                                                                      Thrust-top buildups




                                                                                                                                                            Bosence 2005
Reprinted from Sedimentary Geology, V.175, 1-4, Bosence, A genetic classification of carbonate platforms based on basinal and tectonic settings in the Cenozoic, p.49-72, with
permission from Elsevier (http://www.sciencedirect.com/).
                                                                                                                                                                                 5
North Caspian Basin – Background

Produces oil from subsalt Devonian-
Carboniferous carbonate platforms

Pricaspian Basin holds 46 BBOE (56% gas)

Four supergiant carbonate fields: Tengiz,
Karachaganak, Astrakhan and Kashagan

Complex tectonic history of
                                                 4 km
 •   Thermal subsidence and rifting until late      Tengiz production
     Carboniferous                                      bubbles


 •   Collision and thrusting starting in
     Permian

 •   Separation from Tethys Ocean and
     formation of salt basin in Kungurian

                                                                        6
Top Devonian (sketch) structure map

                 Terrain
                                                                           Terrain
                                                                             rch
                                                                     rskaya a
                                                               Primo
                                                                                 Kairan
                                                         Kashagan g es
                                                                 in at
                                 B                                 as r
                              thr uzac                          cre nce
                                 us hi         Fo             In ide
                                   tb                            s
            Caspian                   elt        re          sub                   Tengiz
                                                      de
              Sea                                       ep

                      North Usturt
                       “Platform”


                                                               Terrain

Thick isolated                 Dev-Carb isolated platforms                   Southwards
and thrust-top                                                            thickening (2.5 to
                               Drowned Devonian? buildups                  4.0 km) isolated
 platforms?
                                                                               platform
                                                                             archipelago
                                                                                               7
Generalized Paleozoic stratigraphy and
geohistory
     STYLE                           TECTONICS
                                  Isolation from Tethys
                                 Ocean and evaporite fill
Platforms in front
  and on top of                  Buzachi compressional
    thrustbelt                     phase (Hercynian)




  Platforms with
                                  Primorskaya rift
variable thickness
                                 phase with variable
   and internal
                                   and increasing
   geometries;
                                  subsidence rates
   drowning in
                                   towards south
     foredeep


                                                        8
Tengiz sequence stratigraphy framework
and accommodation history
 Age    Epoch       Stage       Age
 (Ma)                           (Ma)                       Fall          Rise
                                                                  0
                                270.0
                  Kungurian
 375                            275.6
 380              Artinskian
 385                            284.4
                                                             3rd Order
 390              Sakmarian
 395                            294.6
                   Asselian
 300                            299.0
                   Gzhelian
                                303.9
 305              Kasimovian    306.5
 310
                  Moscovian
                                311.7
 315
                  Bashkirian    318.1 12.6
                                               Bash_SSB
                                               Serp_SSB
                                                                                        Aggradation
 320             Serpukhovian           4.4     HST                      1st Order      Predominantly progradation
 325                            328.3          Lvis2_MFS
 330                                    43.5
                                                                                        Rapid aggradation and
                                               Lvis_SSB

 335                Visean              43.5   Lvis1_MFS

                                        43.5                                            backstepping
 340
                                               Evis_SSB
                                345.3          Tour_MFS
 345                                                                                    Moderate aggradation and
                                                TST
 350              Tournaisian           15.8                                            backstepping
 355                            359.2          Fame_SSB


 360
                                                                                        Mostly aggradation and
 365              Famennian                                                             minor backstepping
 370    Late
 375
                                374.5
 380               Frasnian                                                             3rd order sequences with
 385                            385.3                                                 duration ~1 ma; 4/5th order
                   Givetian
 390
        Middle                  391.8                                                parasequences with duration of
 395                Eifelian
                                397.5                                                          ~0.2-0.4 ma

                                                                                                                      9
Northern Spain: “intact” and thrust-top
systems in a foreland basin setting




 Vertical rotation
 provides seismic-scale
 access to depositional
 style
                                          10
Cantabrian Zone: Marine foreland basin
  Complex arc-shaped collision/deformation system
  Nucleation of Serpukhovian to Moscovian isolated
  platforms in foreland basin
  Highly variable subsidence rates caused by advancing
  thrust belt
  As a result, local drowning of buildups and variable
  depositional styles and internal geometries across basin
  Development of local basins at – and on top of frontal part
  of thrust belt
  Filled by (Moscovian-Ghzelian) alternating clastics and
  carbonate ramps and low relief platforms
  Angular unconformities and thickness variations reflect
  tectonic deformation rates but 3rd order (and higher)
  eustatic SL signal preserved

                            Merino-Tomé, Bahamonde, Fernandez and Colmenero, in press
                                                                                  11
Internal (proximal) vs External (distal) zones




                             Internal zone




             External zone




                                                 12
Bashkirian


             Internal Zone:
             Evolution low- to high
             angle and high relief
             progradation (>10 km); no
             basinal input - starved




             External Zone:
             Low relief platforms and
             ramps




                                        13
Bashkirian-Moscovian transition


                                  Internal Zone:
                                  Clastics partially fill
                                  starved basin modifying
                                  progradation from
                                  horizontal [ ] to
                                  climbing [ ]




                                  External Zone:
                                  Clastics draping low
                                  relief ramp [ ]




                                                         14
Moscovian



            Internal Zone:
            General
            aggradational growth
            style [ ] with minor
            progradational pulses
            [ ]




            External Zone:
            Formation of
            buildups; high rates
            (> 2 km/Ma) of
            platform progradation
            [ ]

                                    15
         Late Moscovian - Early Kasimovian

            Internal Zone:
                •   Migration of thrust front towards the foreland incorporates
                    carbonate platforms
                •   Rapidly subsiding basins develop in front and on top of the
                    thrust wedge (thrust-top platforms)

            External zone
                •   Carbonate sedimentation continuous
SW                                                                                         NE
 FRONTAL UNIT                    CENTRAL UNIT        GAMONEDO-CABRALES UNIT   CUERA UNIT




            10 km




                                                                                           16
  Frontal basins and thrust-top platforms

                  Mid-late Myachkovskian (late Moscovian)
                                                                     Internal Zone:
External Zone:                                                       deformation and
active platform        Basins developed at the frontal part of the   uplifting of the
growth                               thrust wedge                    carbonate shelf




                    Early Krevyakian (early Kasimovian)

                                                                     Internal Zone:
External Zone:        Flexural warping generated subsiding basins    Continued
active platform        developed on top of the frontal part of the   thrusting
growth                               thrust wedge




                                                                                        17
Summary and Conclusions

  Northern Pricaspian has 46 BBOE and 4 supergiant
  isolated platforms in Paleozoic foreland basin
  settings

  Highly complex and variable system

  Both un- and deformed isolated buildups and thrust-
  top platforms have reservoir potential

  Cantabrian Zone (Spain) provides well-studied
  outcrop analogs of arc-shaped system

  Spain provides mosaic of carbonate buildup styles in
  space and time and as a result of tectonic
  deformation and eustatic sea level


                                                         18