middle east geologic time scale 2013

GeoArabia, 2013, v. 18, no. 3, p. 103-130 Gulf PetroLink, Bahrain

MIDDLE EAST GEOLOGIC TIME SCALE 2013 Chrono- and sequence-stratigraphy of the Mid-Permian to Early Triassic Khuff sequences of the Arabian Plate Moujahed I. Al-Husseini and Bastian Koehrer ABSTRACT The Middle Permian (Guadalupian), Upper Permian (Lopingian) and Lower Triassic Khuff and correlative formations in the Arabian Plate consist of six “third-order” sequences, from oldest to youngest KS6 to KS1, and at least 45 “fourth-order” sequences. They are here dated using biostratigraphic constraints and correlated to two independent sequence-stratigraphic time scales: (1) global sequences calibrated in the Geological Time Scale GTS 2012; and (2) orbitalforcing glacio-eustatic sequences that track the 0.405 million year (Myr) orbital eccentricity signal in the M&H-2010 scale (Matthews and Al-Husseini, 2010). The chronostratigraphic calibration of the Khuff sequences provides a reference section and common nomenclature that can be used for regional and global correlations. It permits positioning the hydrocarbon reservoirs of the Khuff and equivalent formations in a sequence-stratigraphic framework that can be used in exploration and reservoir characterization. The lower sequence boundary of the Khuff Formation (Khuff SB) is correlated to global Wordian SB Wor1 near the Roadian/Wordian Boundary at 268.8 ± 0.5 Ma, and correlative SB 19C at 268.9 Ma in the M&H-2010 scale. The upper sequence boundary of the Khuff Formation with the overlying Sudair Formation (Sudair SB) is correlated to Olenekian SB Ole1 near the Induan/Olenekian Boundary at 250.0 ± 0.5 Ma, and correlative SB 17 at 249.5 Ma in the M&H-2010 scale. These calibrations imply the Khuff was deposited in about 19.4 Myr, and consists of 48 “stratons”; i.e. transgressive-regressive (T-R) depositional subsequences with an average duration of 0.405 Myr corresponding to long-eccentricity orbital cycles 664 to 617. The 48 stratons are predicted to form four “dozons” (19C, 18A, 18B and 18C), each consisting of 12 stratons. Individual dozons lasted 4.86 Myr and are separated by regional sequence boundaries (SB 19C to SB 17A). In Oman, Khuff Sequence KS6 on the Saiq Plateau is correlated to the subsurface Lower Khuff Member, and both are interpreted to consist of 12 subsequences that are correlated to stratons 664–653 forming Dozon 19C between 268.9– 264.0 Ma. KS6 is correlated to the four global sequences Wordian Wor1 to Capitanian Cap1 dated between 268.8–264.0 Ma in GTS 2012. Khuff Sequence KS5 corresponds to the Middle Khuff Member up to the top of Middle Khuff Anhydrite in subsurface Oman. On the Saiq Plateau, KS5 potentially consists of 12 cycle sets (Koehrer et al., 2010) that are correlated to stratons 652–641 of Dozon 18A, between 264.0–259.2 Ma. It is correlated to global sequences Capitanian Cap2 and Cap3 dated between 264.0–259.8 Ma in GTS 2012. Khuff Sequence KS4 consists of 11 cycle sets on the Saiq Plateau and other localities in Al Jabal al-Akhdar in Oman (Koehrer et al., 2010, 2012). It is assumed that one cycle set remains unidentified in KS4, completing its correlation to stratons 640–629 of Dozon 18B between 259.2–254.3 Ma. KS4 correlates to the global sequences Wuchiapingian Wuc1 and Wuc2 dated between 259.8–254.2 in GTS 2012. Khuff sequences KS3, KS2 and KS1 combined consist of 10 cycle sets in Al Jabal al-Akhdar (Koehrer et al., 2010, 2012), and two are presumed

103

Al-Husseini and Koehrer

unidentified so as to correlate to the 12 stratons 628–617 of Dozon 18C between 254.3–249.5 Ma. Sequence KS3 correlates to Changhsingian global sequences Cha1 and Cha2 dated between 254.2–252.5, and KS2 and KS1 to latest Permian– Early Triassic global sequences Cha 3 and Induan–Olenekian Ind1 dated between 252.5–249.9 Ma in GTS 2012. The Permian/Triassic Boundary (PTB), dated at 252.2 ± 0.5 Ma in GTS 2012, occurs in lowermost Khuff Sequence KS2, in cycle set KCS 2.3, and based on the orbital calibration of the Upper Permian (Lopingian) Series in South China, it occurs in Straton 623 between 252.3 and 251.9 Ma.

INTRODUCTION The Middle Permian–Lower Triassic Khuff and correlative formations in the Arabian Plate consist mainly of carbonates and evaporites that attain a thickness of more than 1,000 m (Al-Jallal, 1995; Sharland et al., 2001). The formations overlie terrestrial clastics typified by the Gharif Formation of Oman, and their lower boundaries represent the start of the regional transgression of the “Fusulinid Sea” over many parts of the Arabian Plate (Montenat et al., 1976; Le Métour, 1987; Baud et al., 2001a, b; Osterloff et al., 2004; Richoz et al., 2005; Baud and Bernecker, 2010, see references therein, Figure 1). The formations are overlain by the basal shales of the Lower Triassic Sudair Formation in Saudi Arabia (Manivit et al., 1983) and Oman (Osterloff et al., 2004; Forbes et al., 2010), and correlative rock units elsewhere in the Arabian Plate (Figure 2). The Khuff Formation has been interpreted in several regions as one “second-order” super-sequence consisting of six “third-order”, transgressive-regressive (T-R) sequences (Figures 1 and 2; Insalaco et al., 2006; Maurer et al., 2009; Koehrer et al., 2010, 2012): LATE PERMIAN (CHANGHSINGIAN) KHUFF PALEOGEOGRAPHY 45°E

30°N 0

N

250

gr

KUWAIT Kuh-i-Mand

Qibah

Khursaniyah Berri Abqaiq

Abu Sa'fah

BAHRAIN

Ghawar Khurais

Al Fayda Ad Dawadimi

Darma

Wadi Ar Rayn

Arabian Shield

20°

Riyadh SHD-1 Well

Awali

os

Te t

30°

hy

Su

Iran Terranes in Cimmeria

sR

tu

re

ift

Middle and outer shelf carbonates

Kuh-e-Surmeh Kangan IRAN South Fars Figures 7 and 9 South Pars

Ras alAbu Al Khaimah Bukhoosh North Nasr Field Zakum QATAR

Harmaliyah Arzanah

Wadi Al Mulayh

Marginal-marine/ deltaic deposits

Dalan

North Pars Karan

SAUDI ARABIA

Buraydah

o-

Za

Quadrangles with Khuff Outcrops

25°

Ne

Kuh-e-Dena

IRAQ

km

Baq’a’

Inner shelf 55° carbonates

50°

Hail Umm UAE Shaif Wadi Maqam Lekhwair-70 Well

Musandam 25°

Gulf of Oman

Al Jabal al-Akhdar Figure 1b

Yibal

Saiq Plateau Figure 6 and 8

OMAN

Sulayyimah

Al Huqf Hasirah-1 Figure 4

Wadi Tathlith

45°

50°

20°

55°

Sayyala-29 Figure 5

Figure 1a: Late Permian paleogeography showing localities mentioned in the paper, and key oil (green) and gas (red) fields in the Khuff and equivalent formations (compiled by Maurer et al., 2009). The Khuff crops out in several quadrangles in Saudi Arabia and is discussed by Vaslet et al. (2005). 104

Arabian Plate Khuff Sequences

• • • •

Mid-Permian Khuff sequences KS6 and KS5, Late Permian Khuff sequences KS4 and KS3, latest Permian–Early Triassic Khuff Sequence KS2, and Early Triassic Khuff Sequence KS1.

The reservoirs in sequences KS4 to KS1 contain some of the world’s greatest reserves of nonassociated gas in fields in Bahrain, Iran, Saudi Arabia, United Arab Emirates and Qatar, as well as oil in the Yibal Field in Oman (Figure 1a). The age calibration and correlation of these and other T-R sequences across the Arabian Plate is a work-in-progress launched in 2008 as the Middle East Geological Time Scale (Al-Husseini, 2008). This paper presents a revision to the age calibrations of the Khuff T-R sequences that was attempted in 2010 (Al-Husseini and Matthews, 2010). It starts by predicting the ages of the regional sequences of the Mid-Permian to Early Triassic based on a model of orbital-forcing glacio-eustasy, referred to as the M&H-2010 scale (after Matthews and Al-Husseini, 2010; Figure 2, Tables 1 and 2). Next the OUTCROP MAP, OMAN MOUNTAINS 57°E

57°30'

58°

58°30'

59°

Gulf of Oman Q

Jabal Bawshar

Semail Ophiolite

23°30'N

S PTr

Jabal Tayin

Wadi Hedek

J P

JK

Al Jabal al-Akhdar

23°30'

Hulw Wadi Mayh PTr Jabal Abu Da’vd

Pc CO

Wadi Mijlas Tt

CO Ja

ba

Figure 8

Saiq Plateau

25

km

Wadi Aday

Semail Ophiolite

Pc

23°

Muscat

Tt

J

N

0

l AJ by a

Ja

ba

d

lA

J

sw

ad

23°

JK

Semail Ophiolite

Tt Tt

Hamrat ad Duru Range

Ja

S

ba

57°

lH

am

m

ah

57°30'

(Q) Quaternary

Q

Jabal Safra

58°

Kawr Group (Triassic–Cretaceous)

(Tt) Tertiary

Al Aridh Group (Triassic–Late Cretaceous)

(J) Sahtan Group (Jurassic)

Umar Group (Triassic–Cretaceous)

(JK) Kahmah Group (end Jurassic–mid-Cretaceous) Baid Formation (Late Permian–Jurassic) (PTr) Akhdar Group (Late Permian–Triassic (CO) Haima Group (Cambrian–Ordovician) (P) upper Huqf Group (Precambrian–Cambrian)

Hamrat Duru Group (Late Permian–Late Cretaceous)

(Pc) lower Huqf Group (Precambrian)

S

Hawasina Nappes

Wasia Group (mid-Cretaceous)

(S) Semail Ophiolite (mid-Late Cretaceous) Metamorphic sole (mid-Late Cretaceous)

54°

BAHRAIN

Abu Dhabi UAE

N

26°

Gulf of Oman

Location Muscat

OMAN

22°

0

59° 58°

QATAR

22°

SAUDI ARABIA 200

km

Muti Formation (mid-Late Cretaceous) Aruma Group (end Cretaceous)

Q

58°30'

Arabian Sea 18° YEMEN

18° 54°

58°

Figure 1b: Localities of sections of the Permian–Triassic (PTr) formations in Al Jabal al-Akhdar that are discussed in the paper (Koehrer et al., 2010, 2012; Bendias et al., 2013; Walz et al., 2013).

105


Table 1 Calibration of Khuff Sequence Stratigraphy (Million Years Before Present Ma) Stage Olenekian Olenekian Induan/Olenekian Olenekian Induan Induan Induan Induan Chang/Induan Changhsingian Changhsingian Changhsingian Changhsingian Changhsingian Wuch/Chang Changhsingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Wuchiapingian Capitan/Wuchiaping Capitanian? Capitanian? Capitanian? Capitanian Capitanian Capitanian Capitanian Capitanian Capitanian Capitanian Capitanian Capitanian Capitanian Capitanian Capitanian Word/Capitanian Capitanian Wordian Wordian Wordian Wordian Wordian Wordian Wordian Wordian Roadian/Wordian

Global Sequence Boundary (SB)

J. Ogg & Orbital Orbital 405 C. Huang Surface Clock Cycle GTS-12 SB

SB Ole1

249.9

Boundary

250.0

SB In1

250.6

PTB

252.2

SB Cha3

252.5

SB Cha2

253.1

Boundary

254.2

SB Cha1

254.2

SB Wuc2

255.8

SB Wuc1

259.8

Boundary

259.8

SB Cap3

SB Cap2

262.4

264.0

SB Cap1

265.1

Boundary

265.1

SB Wor3

SB Wor2

266.4

267.5

SB Wor1

268.8

Boundary

268.8

Al Jabal al-Akhdar Oman

Iran South Fars

Zhuzang South China

1

2

249.5

616

SB 17

Sudair

Aghar Mbr

3

249.9

617

18C-12

?

KS1c

250.3

618

18C-11

KCS 1.0

KS1b

250.7

619

18C-10

KCS 1.1

KS1a

251.1

620

18C-9

SB KS1

KS2d

251.5

621

18C-8

KCS 2.1

KS2c

251.9

622

18C-7

KCS 2.2

KS2b

252.3

623

18C-6

SB KS2

KS2a

252.7

624

18C-5

?

KS3b

Sequence 16

253.1

625

18C-4

KCS 3.1

KS3a4

Sequence 15

253.5

626

18C-3

KCS 3.2

KS3a3

Sequence 14

253.9

627

18C-2

KCS 3.3

KS3a2

Sequence 13

254.3

628

SB 18C

SB KS3

KS3a1

Sequence 12

254.7

629

18B-12

?

KS4c4

Sequence 11

255.1

630

18B-11

KCS 4.1

KS4c3

Sequence 11

255.5

631

18B-10

KCS 4.2

KS4c2

Sequence 10

255.9

632

18B-9

KCS 4.3

KS4c1

Sequence 9

256.3

633

18B-8

KCS 4.4

KS4b3

Sequence 8

256.7

634

18B-7

KCS 4.5

KS4b2

Sequence 7

257.1

635

18B-6

KCS 4.6

KS4b1

Sequence 6

257.5

636

18B-5

KCS 4.7

KS4a5

Sequence 5

258.0

637

18B-4

KCS 4.8

KS4a4

Sequence 4

258.4

638

18B-3

KCS 4.9

KS4a3

Sequence 3

258.8

639

18B-2

KCS 4.10

KS4a2

Sequence 2

259.2

640

SB 18B

SB KS4

KS4a1

Zhuzang 1

259.6

641

18A-12

KCS 5.1

Nar Mbr

Emeishan

260.0

642

18A-11

KCS 5.2

260.4

643

18A-10

KCS 5.3

260.8

644

18A-9

KCS 5.4

261.2

645

18A-8

KCS 5.5

261.6

646

18A-7

KCS 5.6

262.0

647

18A-6

KCS 5.7

262.4

648

18A-5

KCS 5.8

262.8

649

18A-4

KCS 5.9

263.2

650

18A-3

KCS 5.10

263.6

651

18A-2

KCS 5.11

264.0

652

SB 18

SB KS5

Base Middle Khuff

264.4

653

19C-12

KCS 6.1

Lower Khuff 12

264.8

654

19C-11

KCS 6.2

Lower Khuff 11

265.2

655

19C-10

KCS 6.3

Lower Khuff 10

265.6

656

19C-9

KCS 6.4

Lower Khuff 9

266.1

657

19C-8

KCS 6.5

Lower Khuff 8

266.5

658

19C-7

KCS 6.6

Lower Khuff 7

266.9

659

19C-6

KCS 6.7

Lower Khuff 6

267.3

660

19C-5

KCS 6.8

Lower Khuff 5

267.7

661

19C-4

KCS 6.9

Lower Khuff 4

268.1

662

19C-3

KCS 6.10

Lower Khuff 3

268.5

663

19C-2

KCS 6.11

Lower Khuff 2

268.9

664

SB 19C

Khuff SB

Khuff SB

PTB

GLB Basalt

Oman Sayyala-29 4

1. Koehrer et al. (2010, 2012); 2. Insalaco et al. (2006); 3. Wang et al. (2011) and 4. Matthews and Al-Husseini (2010)

106


Table 2 Calibration of Global and Arabian Sequence Stratigraphic Surfaces (Million Years Before Present Ma) Stage Olenekian/Anisian Olenekian Olenekian Olenekian Olenekian Induan/Olenekian Induan Induan Induan Permian/Triassic Changhsingian Changhsingian Changhsingian Changhsingian Wuchiaping/Chang Wuchiapingian Wuchiapingian Wuchiapingian Capitan/Wuchiaping Capitanian Capitanian Capitanian Wordian/Capitanian Wordian Wordian Wordian Wordian Roadian/Wordian Roadian Roadian Kungurian/Roadian

Global Surface

GTS-04 GTS-12 Age Linear

J. Ogg & C. Huang

Error

Orbital Clock

405 Cycle

Dozon Boundary

Arabian Plate

249.5

SB 616

SB 17

Sudair SB

250.9

mid-620

MFS Tr20

251.7

mid-622

MFS Tr10

252.3

SB 623

Boundary

247.1

247.1

247.1

SB Ole4

246.6

247.7

247.9

SB Ole3

247.6

248.5

248.3

SB Ole2 SB Ole1

247.9 249.3

248.7 249.8

248.5 249.9

Boundary

249.5

250.0

250.0

SB In1 MFS Cha3

249.9

250.5

250.6 251.3

Boundary

251.0

252.2

252.2

SB Cha3

251.5

252.6

252.5

SB Cha2

252.5

253.3

253.1 253.5

253.3

mid-626

SB Cha1

253.8

254.2

254.2

254.3

SB628

Boundary

253.8

254.2

254.2

SB Wuc2

256.0

256.1

255.8 257.0

256.1

mid-633

SB Wuc1

260.4

259.8

259.8

259.2

SB 640

SB 18B

SB KS4

Boundary

260.4

259.8

259.8

SB Cap3

262.0

261.4

262.4

SB Cap2

263.0

262.4

264.0

264.0

SB 652

SB 18

SB KS5

SB Cap1

265.8

265.1

265.1

Boundary

265.8

265.1

265.1

265.2

655

268.9

SB 664

MFS Ind1

0.50

250.2

MFS Cha1

MFS Wuc1

MFS Wor3

0.50

266.5

266.9

266.4

SB Wor2

267.0

267.5

267.5

SB Wor1

267.5

268.2

268.8

Boundary

268.0

268.8

268.8

SB Roa2

268.4

269.3

269.3

SB Roa1

270.6

272.3

272.3

Boundary

270.6

272.3

272.3

SB KS3

0.30 MFS P30

0.40

0.50

265.8

SB Wor3

MFS P40 SB 18C

MFS P20

SB 19C

Khuff SB

0.50

0.50

model sequences are correlated to the empirical global sequences compiled by Snedden and Liu (2011) from the charts of Hardenbol et al. (1998) and Haq and Schutter (2008) as calibrated in the Geological Time Scale GTS 2012 (Gradstein et al., 2012; Henderson et al., 2012; Ogg, 2012; see www. stratigraphy.org; C. Huang and J. Ogg, written communications, 2012, 2013). The model and global scales are shown to share five Mid-Permian–Early Triassic sequence boundaries that are used to date the six Khuff sequences. The paper also compares the dating of the Upper Permian in South China using radiometric data and the M&H-2010 scale. The results are encouraging, and support using orbital periods to tune empirical scales to as far back as the Mid-Permian.

SEQUENCE-STRATIGRAPHIC TIME SCALES M&H-2010 Orbital Time Scale The dominant periods of the Fourier representation of the eccentricity of the Earth’s orbit around the Sun are ca. 0.1, 0.405 and 2.4 Myr (Laskar et al., 2004, 2011). These periods are predicted by the glacio-eustatic model of Matthews and Frohlich (2002) to be manifested as T-R sequences that have average durations of 0.1, 0.405, and 2.0, 2.4 and 2.8 Myr. They recommended using the term “fourthorder” for the 0.405 Myr sequence, and “third-order” for the 2.0, 2.4 and 2.8 Myr sequences. The application of these recommendations proved impractical because they conflict with the existing definitions of “orders” used in empirical sequence stratigraphy (e.g. Emery and Myers, 1996; Tinker, 1998; Table 3).

107


Table 3 Comparison of Nomenclature for Sequence Stratigraphy Cycle Order Reference

Second Order

Third Order

3.0–50 Myr

0.5–3.0 Myr Depositional Sequence

Fourth Order

Fifth Order

0.1–0.5 Myr Emery and Myers (1996)

Parasequence Set

Parasequence

0.1–1.0 Myr Tinker (1998)

10–100 Myr Supersequence

1.0–10 Myr Composite Sequence

M&H-2010 scale and Matthews and Frohlich (2002)

14.58 Myr Orbiton (36 Stratons)

4.86 Myr Dozon (12 Stratons)

High-frequency Sequence HFS)

Cycle Set

0.405 Myr Straton (Long Eccentricity)

0.01–0.10 Myr Cycle

0.1 Myr (Short Eccentricity)

Note: Throughout this paper sequence-stratigraphic terms, such as “third-order”, “parasequence”, “cycle”, etc. (Table 3) are shown in quotation marks as used by the original authors. To circumvent confusion regarding the usage of sequence-stratigraphic terms, Matthews and Al-Husseini (2010) introduced the term “straton” to mean the T-R sequence that has an average duration of 0.405 Myr (Laskar et al., 2004, 2011). In the M&H-2010 scale, stratons are identified by integer numbers with Straton 1 starting at ca. 372,000 years ago (0.372 Ma) and continuing today. The age for the start of any straton (e.g. Straton M) is: Age for start of Straton M = (M-1) x 0.405 + 0.372 Ma For example, Straton 623 (M = 623) is important because it may contain the Permian/Triassic Boundary (PTB) dated in GTS 2012 as 252.2 Ma (Table 1), and between 252.28 ± 0.08 and 252.10 ± 0.06 Ma (Shen et al., 2011). The age for the start of Straton 623 is estimated as: (623-1) x 0.405 + 0.372 = 252.281 = ca. 252.3 Ma The M&H-2010 scale predicts that the Middle Permian to Lower Triassic contains five regional sequence boundaries (SB) that are separated by intervals of 4.86 Myr (12 x 0.405 Myr) and that bound groups of 12 stratons. From youngest to oldest the five regional boundaries are named SB 17A, SB 18C, SB 18B, SB 18A and SB 19C (Figure 2; Tables 1 and 2). The 36 stratons that occur between sequence boundaries denoted by the letter “A” form an “orbiton” (e.g. Orbiton 18 between SB 18A and SB 17A, Figure 2). The sequence boundaries denoted by the letter “A” may, in some cases, be more prominent and the age of their lower sequence boundary (SB without an “A”) is calculated as follows: Age of SB N = 1.586 + N x 14.58 Ma For example, for N = 17, the age of SB 17 (Sudair SB in Figure 2; Tables 1 and 2) is: Age of SB 17 = 1.586 + 17 x 14.58 = 249.446 = ca. 249.5 Ma.

Global Sequence Boundaries in GTS 2012 Table 2 shows the age estimates for the stage boundaries of the Mid-Permian (Guadalupian), Late Permian (Lopingian) and Early Triassic epochs in GTS 2004 (Ogg, 2004; Wardlaw et al., 2004; Gradstein et al., 2004) and their revisions in GTS 2012 (Ogg, 2012; Henderson et al., 2012; Gradstein 108


Ole4

250.0 ± 0.5

Changhsingian

Tr20

251.3

252.2 ± 0.5

Tr10

252.5

Cha2

MFS P40

253.1 253.5

Cha1 254.2 ± 0.3

Age (Ma)

Sudair Formation

249.9 250.2 250.6

Ind1

Sequence

-100

Ole1

Cha3

Lopingian (Late)

0

247.9 248.3 248.4

Ole3 Ole2

Induan

255

100

MFS

254.2

Dozon

Dozon 17A

Sudair SB

249.5

Khuff Sequences KS2 + KS1

250.9 251.7

SB KS2

252.3

Khuff Sequence KS3

253.3

SB KS3

254.3

Orbiton

1.0

Landward 0.5 0.0

Sea Level (m)

Orbiton 17

Olenekian Early

TRIASSIC

250

Coastal Onlap

Stage/Age (Ma) 247.1 ± 0.5

M&H-2010 Orbital Scale

SB 17

Dozon 18C

SB 18C

Wuc2 255.8

Wuchiapingian

MFS P30

257.0

256.1

Khuff Sequence KS4

Dozon 18B

Orbiton 18

Epoch

Age (Ma)

Period

GTS 2012

Wuc1

SB KS4 259.8 ± 0.4

PERMIAN

?

262.4

MFS P25

Cap2

Guadalupian (Middle)

264.0 265

SB 18B

Khuff Middle Anhydrite

Cap3

Capitanian

259.2

Dozon 18A

Khuff Sequence KS5

262.4

SB KS5

264.0

SB 18

Cap1 265.1 ± 0.5 Wor3

265.8 266.4

Wordian

MFS P20

265.1

Wor2

Presentday sea level

265.2

Khuff Sequence KS6

Dozon 19C

267.5 Wor1 268.8 ± 0.5

Roa2

268.8

Longterm trend

270

Roadian

272.3 ± 0.5

Khuff SB

269.3

Roa1

Gharif Formation

268.9

SB 19C

Orbiton 19

260

259.8

Dozon 19B

272.3

Figure 2: Correlation of the six Khuff sequences KS6 to KS1 to the global T-R sequences compiled by Snedden and Liu (2011) for Triassic (Hardenbol et al., 1998) and Permian (Haq and Schutter, 2008) in the Geological Time Scale GTS 2012 (Henderson et al., 2012; Ogg, 2012; C. Huang and J. Ogg, written communication, 2012, 2013; see also Tables 1 and 2). The global and Khuff sequences are also correlated to the model M&H-2010 orbital scale (Matthews and Al-Husseini, 2010) constructed by dozons (4.86 Myr) and orbitons (14.58 Myr). 109


et al., 2012). The stage boundaries in GTS 2012 carry an estimated uncertainty of between ± 0.3 and ± 0.5 Myr) (Figure 2). The global sequences in Figure 2 are compiled in Snedden and Liu (2011) from Hardenbol et al. (1998) for the Cenozoic–Mesozoic (Early Triassic in Figure 2), and Haq and Schutter (2008) for the Paleozoic (Middle and Late Permian in Figure 2). The sequences are named after the first three letters of the stage in which their lower sequence boundary (SB) occurs, followed by an integer. For example, Capitanian Sequence Cap2 occurs between SB Cap2 at 264.0 Ma and base Wuchiapingian SB Wuc1 at 259.8 Ma (Figure 2). Three age estimates for each sequence boundary are given in Table 2. The first is from GTS 2004 (Sneddon and Liu, 2011), and the second is its recalibration in GTS 2012 by linear interpolation between stage boundaries. The third estimate was made by C. Huang and J. Ogg (written communications, 2012, 2013), and differs in some cases from the linear interpolation. For example, the linear interpolation from GTS 2004 to GTS 2012 implies an age of 268.2 Ma for Wordian SB Wor1. In contrast, C. Huang and J. Ogg correlate SB Wor1 to base Wordian at 268.8 + 0.5 Ma. A significant difference occurs for the age of Capitanian SB Cap2 with an age of 262.4 Ma by linear interpolation versus 264.0 Ma taken at the base of Jinogondolella altudaensis Zone in GTS 2012 by C. Huang and J. Ogg (written communications, 2012, 2013). The chronostratigraphic constraints for the global sequences (Hardenbol et al., 1998; Haq and Schutter, 2008), as well as those for Saudi Arabia (Haq and Al-Qahtani, 2005), have not been documented in the public domain. It is therefore not possible to assess their accuracy except possibly where they are shown to correlate to stage boundaries as in the case of the Middle and Upper Permian. As discussed below three stage boundaries are correlated to Khuff sequence boundaries (Figure 2). In contrast to the Permian stage boundaries, the Triassic stage boundaries and the Permian/Triassic Boundary (PTB) are not correlated to global sequence boundaries.

Correlation of Five Key Sequence Boundaries in the GTS 2012 and M&H-2010 Scales The five Middle Permian–Lower Triassic sequence boundaries that separate dozons in the M&H2010 scale can be correlated by numerical age to within + 0.6 Myr to five global sequence boundaries (Figure 2; Tables 1 and 2) as calibrated by C. Huang and J. Ogg (written communications, 2012, 2013): • • •

• •

Orbital SB 17 at 249.5 Ma is about 0.4 Myr younger than SB Ole1 at 249.9 Ma, and is within the + 0.5 Myr uncertainty for estimates in the Early Triassic. Orbital SB 18C at 254.3 Ma correlates to SB Cha1 at 254.2 Ma. Orbital SB 18B at 259.2 Ma is about 0.6 Myr younger than SB Wuc1 corresponding to the Middle/Lower Permian Boundary (Guadalupian/Lopingian Boundary, GLB) at 259.8 + 0.4 Ma. The correlation is adopted because the alternative global correlatives, SB Cap3 or SB Wuc2, result in greater mis-ties. The age of the Middle/Lower Permian Boundary is not well constrained. It was revised from 260.4 + 0.7 in GTS 2004 to 259.8 + 0.4 Ma in GTS 2012 (Table 2), and other estimates range between 262.3 Ma (Menning et al., 2008) and 259.0 Ma (Shen et al., 2010). As discussed on pages 112–113 and in Figure 3, astronomical tuning of the Upper Permian Series in South China, suggests the age of the boundary is close to the orbitally predicted 259.2 Ma. Orbital SB 18 correlates to early Capitanian SB Cap2 at 264.0 Ma. Orbital SB 19C at 268.9 Ma correlates to SB Wor1 and the Roadian/Wordian Boundary dated at 268.8 ± 0.5 Ma.

KHUFF SEQUENCES KS6 TO KS1 This section reviews the sequence and biostratigraphic constraints of the six Khuff sequences KS6 to KS1, mainly in subsurface Oman (Figures 4 and 5, Osterloff et al., 2004), the outcrops in Al Jabal al-Akhdar in Oman (Enclosure, Figures 6 and 8, Koehrer et al., 2010, 2012), as well as

110


Khuff Sequences KS4 to KS1 in the South Fars region in subsurface Iran (Figures 7 and 9, Insalaco et al., 2006). It starts with the lower boundary of the oldest Khuff Sequence KS6, the Khuff Sequence Boundary (Khuff SB), proceeds upwards through the six Khuff sequences KS6 to KS1, ending with the upper boundary of Khuff Sequence KS1, the Sudair Sequence Boundary (Sudair SB).

Khuff Sequence Boundary (Khuff SB): 268.9 Ma The Khuff SB or correlative Sub-Khuff Unconformity in subsurface Oman separates the terrestrial clastics of the Gharif Formation from the overlying carbonates or mixed clastics-carbonates in the lower part of the Khuff Formation (Figures 4 and 5, Osterloff et al., 2004). On the Saiq Plateau, Permian terrestrial clastics, about 15 m thick, unconformably overlie lower Paleozoic or Proterozoic formations (Enclosure and Figure 6; Koehrer et al., 2010; Bendias et al., 2013). The unconformity is sometimes referred to as “Hercynian unconformity”, “midCarboniferous unconformity” or “pre-Khuff unconformity” (e.g. Sharland et al., 2001). It is here referred to as the “Sub-Permian Unconformity”. The terrestrial clastics are known as the “lower Saiq member”, “Saiq unit A1”, “basal Saiq clastics”, or “basal Khuff clastics”. The latter term is believed to be misleading because by stratigraphic position, lithology and fluvial-estuarine depositional setting the terrestrial clastics correlate to the subsurface Gharif Formation (Figures 4 and 5; Al-Husseini and Matthews, 2010). The Khuff SB on the Saiq Plateau is picked at the boundary between the “lower Saiq member” and the overlying mixed clastics and carbonates of the Khuff-equivalent part of the Saiq Formation (Enclosure and Figure 6). Over paleohighs in Al Jabal al-Akhdar, the terrestrial clastics are absent and the Sub-Khuff Unconformity (Khuff SB) merges with the Sub-Permian Unconformity. The Khuff SB can be traced from the Arabian Peninsula into the Zagros Mountains where it separates the carbonates and evaporites of the Dalan Formation from the underlying terrestrial clastics of the Faraghan Formation or older rocks (Szabo and Kheradpir, 1978; Al-Jallal, 1995; Insalaco et al., 2006). In the Alborz Mountains in North Iran it passes to the base of the Wordian– Capitanian Ruteh Limestone Formation, which overlies the terrestrial clastics of Shah Zeid Formation or Dorud ironstone (Gaetani et al., 2009; Crippa and Angiolini, 2012). Age: The lowermost part of the Khuff Formation is assigned to the Neoschwagerina schuberti Zone implying the start of the transgression that deposited the Khuff Formation and equivalents is mid-Murghabian (Montenat et al., 1976; Rabu et al., 1986). However, the relationship between the Murgabian Stage of the Pamirs Realm and the North American Roadian and Wordian stages in GTS 2012 is not precisely established (Henderson et al., 2012; Davydov and Arefifard, 2013). Most biostratigraphic studies assign the Khuff SB to the Wordian Stage. In the Al Huqf outcrops in Oman (Figure 1), brachiopod fauna found in Khuff Member 3, which occurs about 15 m above the Khuff SB, indicate a Wordian age (Angiolini et al., 1998, 2003, 2004). Palynological studies of the Gharif and Khuff formations in subsurface Oman and Saudi Arabia indicate the Khuff SB occurs at the base of Oman-Saudi Arabia Palynological Zone OSPZ6 in the Wordian (Stephenson et al., 2003; Stephenson, 2006). Baud and Bernecker (2010) confirmed the Wordian age for the basal part of the Khuff-equivalent Maqam Formation in Wadi Maqam (Figure 1) by citing the finding of conodonts Hindeodus excavatus and Hindeodus wordensis by C. Henderson and A. Nicora in 2009. Based on the foraminiferal assemblage found in Al Jabal al-Akhdar (Presumatrina and primitive Afghanella species), H. Forke (written communication, 2012) considered the onset of carbonate deposition to occur between the base of the Murgabian (late Roadian?–Wordian) to the lower part of middle Murgabian (Wordian). Dating of the Khuff Formation using strontium-isotope measurements has been attempted but was inconclusive. Stephenson et al. (2012) measured 87Sr/86Sr ratios from several brachiopods taken from Khuff Member 3 in Al Huqf. They obtained a mean value of 0.7027, which implies a Roadian or even Kungurian age (see their figure 4, and figure 24.9 in GTS 2012; Henderson et al., 2012). They considered the global strontium-isotope dataset to be insufficiently sampled in the Wordian– Roadian interval and retained a Wordian age for the Khuff SB. (Continued on p. 114) 111


Limestone, silicalite, muddy algal siltstone, muddy.

K2

Bioclastic micrite, cherty limestone.

Lagoon

Siltstone, fine sandstone, algal limestone and sandy mudstone.

Tidal flat and mire Lagoon Subtidal Mire Tidal flat and tidal channel Lagoon

K3-1 C5

254.2 Ma

K4 C7

250

K5-1 K5-2

Calcarenaceous and lithic sandstone and siltstone.

K6 C14

Muddy fine sandstone and siltstone.

200

C16 C17

Longtan Formation

C18

Wuchiapingian

UPPER PERMIAN (LOPINGIAN)

C11 C12

C19 C20

Mire Distributary channel Interdistributary bay Tidal channel Distal bar Mire Tidal channel Interdistributary bay Mire

Siltstone, sandstone.

Distal bar

Fine sandstone, siltstone and sandy mudstone.

Tidal flat

Calcareous fine sandstone with interbeds of (muddy) siltstone. Muddy siltstone and fine sandstone.

K11 C32 K12

Muddy siltstone, limestone.

259.8 Ma

GTS 2012

Fine sandstone, (muddy) siltstone, with interlayers of mudstone and limestone.

Emeishan Basalt (259-260 Ma)

Figure 3: See facing page for caption and legend. 112

SS

Straton

13

627

12

628

629

630

LSS 10

631

9

632

8

633

7

634

6

635

5

636

4

637

3

638

TSS

2

639

LSS

1

640

HSS

Tidal flat Mire Lagoon

CSII

Mire TSS

Mire Tidal channel Mire Tidal flat Mire Tidal flat Mire Lagoon Mire

C34-1

C34-2 K13 C35

626

11

Tidal flat and mire

C29

14

Distributary channel

K9 C27 C28

625

TSS

Mire

Calcareous siltstone, fine sandstone, mudstone.

K8

15

CSIII

Tidal flat and mire

C23

50

HSS

Lagoon Tidal flat Tidal channel Mouth bar

Muddy siltstone and muddy limestone.

K7-2

100

Mire Lagoon Mire

Muddy siltstone with layers of ferrous limestone.

K7-1

624

Tidal flat

Siltstone, sandy mudstone and bioclastic micrite. Calcarenaceous siltstone, muddy siltstone. Siltstone, fine sandstone, sandy mudstone.

16

Mire

Siltstone, mudstone and algal limestone.

C8 C9

4th order Sequence

Tidal flat and mire

Siltstone, sandy mudstone and algal limestone.

K3-2 C6-1 C6-2

150

Sedimentary Facies

K1 C1

C2

300

Lithological Association

CS

Sedimentary Features

Tidal flat and lagoon

Lithology

Lower deltaic plain

252.2 Ma

Changxing Formation

Changhsingian

EARLY TRIASSIC

Depth (m) Age

Tidal flat and mire Subtidal bar Lagoon Mire and paleosol

LSS

Tidal flat-lagoon

Stratigraphy

MB (K) Coal (C)

ZHUZANG SECTION, GUIZHOU PROVINCE, SOUTH CHINA

HSS CSI

SB 18C (259.2 Ma)


UPPER PERMIAN (LOPINGIAN) SERIES IN SOUTH CHINA The chronostratigraphy and sequence stratigraphy of the Upper Permian Series in South China provide a good dataset for testing the accuracy of the M&H-2010 scale. Several sections that represent this series in South China contain radiometrically dated volcanic rocks at various stratigraphic levels, as well as the three Global Boundary Stratotype and Section Points (GSSP, Golden Spike) of the Upper Permian: (1) PTB: Permian/Triassic Boundary (Yin et al., 2001) dated 252.3 Ma (Shen et al., 2010) and 252.2 ± 0.5 Ma in GTS 2012; (2) WCB: Wuchiapingian/Changsinghian Boundary (Jin et al., 2006b) dated at 254.0 Ma (Shen et al., 2010) and 254.2 ± 0.3 Ma in GTS 2012; (3) GLB: Guadalupian/Lopingian Boundary (Jin et al., 2006a) corresponding to the Capitanian/ Wuchiapingian Boundary and Middle/Upper Permian Boundary, dated at 259.8 ± 0.4 Ma in GTS 2012 (Henderson et al., 2012). In many localities in South China the Upper Permian Series immediately overlies the Emeishan Basalt dated 259.0 ± 3.0 Ma (Shen et al., 2010), and which also correlates to global Wuchiapingian SB Wuc1 (Figures 2 and 3). One section that is particularly appropriate for testing the M&H-2010 scale is located at Zhuzang in the Zhijin coalfield, western Guizhou Province of South China (Figure 3 and Table 1; Wang et al., 2011). In this section the Upper Permian Series overlies the Emeishan Basalt, consists of 16 “fourth-order” sequences without evidence of significant hiatuses, and is capped by the Permian/Triassic Boundary at the top of Sequence 16 (Wang et al., 2011). With the exception of Sequence 11, the thickness of the sequences ranges between 10 and 30 m and is 21 m on average (Figure 3). Sequence 11 is exceptionally thicker at 55 m and has a mire (bog) sedimentary facies near its interpreted maximum flooding surface, which in several other sequences is interpreted as a sequence boundary. It is therefore likely that Sequence 11 contains two stratons (2 cycles of 0.405 Myr) and that the Upper Permian in Zhuzang consists of the 17 stratons 640 to 624 in Figure 3. Converting the 17 stratons to time at 0.405 Myr/straton gives 6.9 Myr, and subtracting this interval from the age of model SB 18B at 259.2 Ma (Figure 2), implies the PTB at the top of Sequence 16 has an age of 252.3 Ma, just 0.1 Myr older than the estimate in GTS 2012.

SB

Decrease A/S mfs Increase A/S

Sandstone

Chert

Horizontal bedding

Siltstone

Fossils

Wavy bedding

Muddy siltstone

Plant leaves

Bidirectional bedding

Silty mudstone

Rootlets

Siderite

Mudstone

Lenticular bedding

TSS : Transgressive Sequence Set

Basalt

Tabular bedding

HSS : Highstand Sequence Set

Limestone

Small cross bedding

CS : Composite Sequence

Coal

Flaser bedding

MB : Marine band (K)

SB

SS : Sequence Set LSS : Lowstand Sequence Set

Figure 3 (continued): Zhuzang Section from Zhijin coalfield, western Guizhou Province, South China (Wang et al., 2011). The section represents the Upper Permian (Lopingian) starting immediately above the Emishan Basalt and ending at the top of fourth-order Sequence 16 at the Permian/Triassic Boundary (PTB). The section is interpreted in terms of 16 fourth-order sequences by Wang et al. (2011) and 17 stratons (0.405 Myr) in this paper.

113

Al-Husseini and Koehrer (Continued from p. 111) Global and Orbital Correlations: A Wordian age for the Khuff SB implies it is younger than early Wordian SB Wor1 with an estimated age of 268.2 Ma by linear interpolation or 268.8 Ma as estimated by C. Huang and J. Ogg (written communications, 2012, 2013). It may be as young as mid-Wordian SB Wor2 at 267.5 Ma, or late Wordian SB Wor3 at 266.4 Ma. In the M&H-2010 scale the Khuff SB is correlated to SB 18C at 268.9 Ma, close to the Roadian/Wordian Boundary (268.8 ± 0.5 Ma in GTS 2012) and SB Wor1 (Figure 2).

Khuff Sequence KS6: 268.9–264.0 Ma The Lower Khuff Member in subsurface Oman overlies the Gharif Formation and is overlain by the massive carbonates of the Middle Khuff Member (Figures 4 and 5). The thickness of the Lower Khuff Member varies from about 30 m in South Oman to a maximum of 330 m in the Lekhwair-70 Well (Figure 1a, Osterloff et al., 2004). A. Al-Harthy (2000, PDO unpublished report in Osterloff et al., 2004) interpreted the Lower Khuff Member in terms of three regional sequences, denoted P17, P18 and P19, the latter containing the regionally correlative “Khuff Marker Limestone” (KML, Figures 4 and 5), here interpreted to correspond to Wordian MFS P20 (Sharland et al., 2001, 2004). Al-Husseini and Matthews (2010) correlated the Lower Khuff Member to Khuff Sequence KS6 on the basis of stratigraphic position in the lowermost part of the formation. In the Sayyala-29 Well the Lower Khuff Member is 144 m thick, and based on the motif of the density log and carbonateshale cyclicity they interpreted it as 12 subsequences, denoted LK1 to LK12 (LK for Lower Khuff) in ascending order (Figure 5 and Table 2). On the Saiq Plateau in the Oman Mountains, Koehrer et al. (2010) interpreted Khuff Sequence KS6 (167 m thick) between the top of the “lower Saiq member” (possibly Gharif Formation below the Khuff SB) and Microbial Marker 1 (SB KS5) (Enclosure and Figure 6). They divided the sequence into 12 “cycles”, 5–30 m thick, and considered them as “fifth-order”. Bendias et al. (2013) interpreted the same Saiq Plateau KS6 section in terms of 14 “fourth-order” cycle sets of which two occur in the “lower Saiq member”. They interpreted 43 “fifth-order” cycles in Khuff Sequence KS6 (Enclosure). It is here suggested that the 12 “cycles” of Koehrer et al. (2010) are “cycle sets” and may correlate, onefor-one, to the 12 subsequences LK1 to LK12 in the Sayyala-29 Well (Enclosure, Figures 5 and 6). Age: By stratigraphic position above the Khuff SB, the age of the lower part of KS6 is Wordian. The age of its upper part is not constrained, and may be Wordian or early Capitanian (Koehrer et al., 2010, 2012; Forke et al., 2012). Wordian Maximum Flooding Surface MFS P20: Wordian MFS P20 of Sharland et al. (2001, 2004) is here interpreted to correspond to the MFS of Khuff Sequence KS6 (Figures 4 and 5). In Al Jabal al-Akhdar, Koehrer et al. (2010) interpreted one MFS in Sequence KS6 in a 15 m-thick unit named the “Muddy Marker” in cycle set KCS 6.4 (Enclosure). It contains thick stacks of massive dark-blue, bioturbated mudstone. They considered it the lowest energy zone, mainly characterized by suspension setting, starvation and background sedimentation below storm wave base. They suggested its dark blue color may be due to less oxygenated waters in a deeper-water setting. The “Muddy Marker” may correlate to the Khuff Marker Limestone (KML), which is a regionally correlative pure carbonate unit in subsurface Oman (Osterloff et al., 2004; compare Figures 4 to 6, Enclosure). A possible position for MFS P20 may be in Straton 655 (ca. 265.2 Ma) and the late Wordian MFS Wor3 at 265.8 Ma in global Sequence Wor3 (Figure 2). Global and Orbital Correlations: If Sequence KS6 consists of 12 stratons and the Khuff SB occurs near the base Wordian, then KS6 would correlate to Dozon 19C between 268.9–264.0 Ma, and SB KS5 would correlate to SB 18 at 264.0 Ma (Figure 2). In this scenario, Sequence KS6 would correlate to the four global sequences Wor1 to Wor 3 and Cap1 between 268.8–264.0 Ma (Figure 2).

Khuff Sequence KS5: 264.0–259.2 Ma Osterloff et al. (2004) interpreted three sequences, denoted P20, P23 and P27, between the top of the Lower Khuff Member (Sequence KS6) and the top of the “Khuff Middle Anhydrite” (Figure 4). The top of the Khuff Middle Anhydrite is a regional sequence boundary that is readily recognized in

114


Gamma-Ray (API)

0.0

Sonic

150.0

(μsec/m) 500.0

Compensated Neutron Log

Lithology

Depth (meter)

Sequence

Member

Formation Sudair

45.0

Density

KS1

1.95

UPPER PERMIAN

?

Khuff Formation

1,760

Dominated by limestones and dolomites with thin interbeds of shale and occasional anhydrites.

Tr20

1,800

Limestone-mudstone/ wackestone, variable argillaceous, generally light gray.

1,860 1,880

Tr10

PTB GR Signature

1,900

Key identifying elements:

1,920

(1) The upper boundary is here conformable and picked at the contact of continuous carbonates with the red or gray-green shales of the basal Sudair and marked by a decrease in gamma.

P40

1,940 1,960

P35

2,000

KS4

P30

(2) The lower boundary is conformable marked by a sharp change from carbonates to clastics of the Gharif and an increase in gamma and sonic and a sharp break on the neutron-density.

P27

(3) Occurrence of anhydrite in the Middle Khuff. Uppermost section below the Sudair may be slightly anhydritic.

2,020 2,040

Middle

2,060

Middle Anhydrite

2,080

Khuff Sequence KS5

2,100 2,120 2,140 2,160

P23

2,180 2,200

P20

2,220 2,240

? KML P19

2,260

Khuff Sequence KS6

Lower

2,280

Gharif

Dolomite, anhydritic, often with relict textures. Shale, variable calcareous, varicolored red, green-gray, gray.

1,980

Khuff

2.95

1,840

KS3

Descriptive Lithology

1,740

1,820

KS2

MIDDLE PERMIAN

-15.0

(gm/cc)

100.0

1,780

Upper

LOWER TRIASSIC

Series

HASIRAH-1, KHUFF FORMATION, AKHDAR GROUP, OMAN

2,300 2,320

P18

2,340 2,360

(4) Top of the Middle Khuff coincides with the top occurrence of Permian fauna (benthonic forams, algae) and is always placed at the base of a distinct shale unit (red or gray-green cf. Sudair shales). (5) The boundary between the Middle and Lower Khuff is quite distinctly marked by the change to a sequence of continental mottled red, green and gray shales and marine limestones. To the south the continental deposits predominate. Marked by a sharp increase in gamma and sonic and a sharp break on the neutron-density. (6) A "Marker Limestone" bed is identified in the Lower Khuff of South and Central Oman. It loses its character northwards to Lekhwair.

2,380

P17

2,400 2,420

Khuff SB

2,440

Gharif Formation

Figure 4: Hasirah-1 Well showing positions of Khuff depositional sequences P17 to Tr20 of Osterloff et al. (2004). Note Wordian MFS P20 should be repositioned in the Khuff Marker Limestone (KML). 115


KHUFF SEQUENCE KS6, SAYYALA-29, CENTRAL OMAN Density

(API)

150

Sonic

40

Arabian Plate Sequence

2.95

Porosity (%)

0.45

-0.15

Straton

(msec/ft)

(gm/cc)

1.95

Subsequence

Middle Khuff Member

140

Lithology

LK12

653

LK11

654

LK10

655

LK9

656

LK8

657

LK7

658

LK6

659

LK5

660

1,200

LK4

661

1,210

LK3

662

LK2

663

LK1

664

1,070

1,080

Dozon 18A

0

KS5

Gamma-Ray Local Stratigraphy

1,090

1,100

1,110

KML

SB KS5 (ca. 264.0 Ma)

MFS P20

1,160

MFI P18

1,180

1,190

1,220

1,230

Upper Member

Haushi Group

Gharif Formation

Roadian

1,240

Dozon 19C

1,150

Khuff Sequence KS6

1,140

Lower Khuff Member

Khuff Formation

Akhdar Group

Middle

PERMIAN

Wordian−Capitanian

1,130

MFI P17

Khuff Sequence Boundary (ca. 268.9 Ma)

1,250

1,260

Fine clastics Carbonates

1,270 m

Figure 5: Type section of Khuff Sequence KS6 in subsurface Oman is taken in Sayyala-29 Well. A. Al-Harthy (2000, PDO unpublished report in Osterloff et al., 2004) divided the Lower Khuff Member into three transgressive-regressive cycles with maximum flooding intervals (MFI) P17, P18 and P19 (Khuff Marker Limestone, KML). Based on the character of the density log and shale/carbonate lithology, the Lower Khuff Member is interpreted in terms of 12 subsequences (LK for Lower Khuff) and correlated to stratons 664 to 653. Wordian MFS P20 of Sharland et al. (2001, 2004) is here repositioned in the Khuff Marker Limestone (KML). 116


many regions of the Middle East: top “Khuff Median Anhydrite” in the United Arab Emirates and Qatar, top “Khuff-D Anhydrite” in Saudi Arabia, top Nar Member of Dalan Formation in Iran, and top Satina Member in Iraq (Al-Jallal, 1995; Sharland et al., 2001). Al-Husseini and Matthews (2010) correlated Sequence KS5 to sequences P20, P23 and P27 (Figure 4). Koehrer et al. (2010) interpreted Khuff Sequence KS5, 214 m thick, on the Saiq Plateau between “Microbial Marker 1” (SB KS5) and “Microbial Marker 2” (SB KS4), and divided it into the 12 “cycle sets” KCS 5.1 to KCS 5.12 in descending order (Enclosure and Figure 6). In contrast, Walz et al. (2013) interpreted four “high-frequency” sequences (HFS KS 5-I to HFS KS 5-IV) and 19 “cycle sets” in the same section. The difference between 12 and 19 “cycle sets” in the same Saiq Plateau KS5 section indicates that more rigorous criteria and additional (chrono-) stratigraphic calibration data are required to interpret sequences in terms of sequence hierarchy and order. In the Wadi Hedek Section (272 m thick, Figure 1b), Walz et al. (2013) interpreted 21 medium-scale, “fourth-order” cycle sets and 66 small-scale “fifth-order” cycles. Age: The age of Sequence KS5 is Capitanian based on the presence of Sphairionia sikuoides (Forke et al., 2012). In the uppermost part of the sequence the occurrence of miliolid foraminifer Shanita amosi and several other genera (e.g. Paraglobivalvulina, Rectostipulina) indicate a latest Capitanian age (Insalaco et al., 2006; Forbes et al., 2010; Koehrer et al., 2010, 2012; Forke et al., 2012). These genera occur immediately below the Middle Khuff Anhydrite in the subsurface (Insalaco et al., 2006; Forbes et al., 2010; Koehrer et al., 2010, 2012; Forke et al., 2012). Capitanian Maximum Flooding Surface MFS P25 (?): Sharland et al. (2001, 2004) positioned Wordian MFS P20 in the lower part of the subsurface Middle Khuff Member, which is here interpreted as Capitanian (Figures 4 and 5). It is recommended to re-position MFS P20 into the Lower Khuff Member and use Capitanian MFS P25 (?) instead, corresponding to the “Chert Marker” in outcrops of the Al Jabal al-Akhdar (Koehrer et al., 2010; Walz et al., 2013). Global and Orbital Correlations: As noted above biostratigraphic evidence indicates the upper part of Sequence KS5 is latest Capitanian implying SB KS4 correlates in the global scheme to basal Wuchiapingian SB Wuc1 at 259.8 Ma in GTS 2012 (i.e. Capitanian/Wuchiapingian Boundary, Guadalupian/Lopingian Boundary, GLB, Middle/Upper Permian Boundary) (Figure 2). In the orbital model Sequence KS5 is correlated to Dozon 18A between 264.0 and 259.2 Ma, and the 12 cycle sets KCS 5.1 to KCS 5.12 on the Saiq Plateau to stratons 652–641 (Figure 6). Based on the proposed orbital correlation, Sequence KS5 might correlate to two global Capitanian sequences Cap2 and Cap3 between 264.0–259.8 Ma (Figure 2).

Khuff Sequence KS4: 259.2–254.3 Ma In subsurface Oman (Figure 4), Sequence KS4 corresponds to sequences P30 and P35 and possibly the lower part of P40 of Osterloff et al. (2004). Koehrer et al. (2010, 2012) interpreted Khuff Sequence KS4 on the Saiq Plateau (Enclosure and Figure 6) and correlated it across the outcrops in Al Jabal al-Akhdar in Oman (Figure 1b), where it ranges in thickness from 152 m to 171 m. They considered it a “third-order” sequence and divided it into two “high-frequency” sequences (HFS), HFS KS4b and HFS KS4a (here renamed as HFS KS4-I and HFS KS4-II to avoid confusion with terms used in South Fars by Insalaco et al., 2006; Enclosure), 11 “fourth-order” cycle sets (KCS 4.1–KCS 4.11, in descending order), and 66 “fifth-order” cycles. Insalaco et al. (2006) interpreted Khuff Sequence KS4 above the Nar Member of the Dalan Formation in Iran (Figures 1a and 7). It is ca. 159 m thick in subsurface South Fars, 114 m in Kuh-e Surmeh and 117 m in Kuh-e Dena. They considered it a “third-order” composite sequence, and divided it into three “fourth-order” T-R sequences (KS4a, KS4b, KS4c in ascending order) and 12 “parasequence sets” (KS4a1 to KS4a5, KS4b1 to KS4b3, KS4c1 to KS4c4). Age: Khuff Sequence KS4 is interpreted in both Iran and Al Jabal al-Akhdar as representing the Wuchiapingian Stage (Insalaco et al., 2006; Koehrer et al., 2010, 2012).

117


720

4.1

630

4.2

631

4.3

220

280

662

300

663 664

SB 19C ?Roadian–Wordian Khuff SB (268.9 Ma) Gharif Fm Sub-Permian Unconformity

Figure 6: (a) Koehrer et al. (2010) interpreted Khuff Sequence KS6 on the Saiq Plateau above the Basal Saiq Clastics (probably the Gharif Formation) to consist of 12 cycles that are here correlated to stratons 664 to 653 of Dozon 19C between 268.9 (SB 19C, Khuff SB) and 264.0 Ma (SB 18). (b) Koehrer et al. (2010, 2012) interpreted Khuff sequences KS5 and KS4 in terms of 12 and 11 cycle sets, respectively. The 23 cycle sets are here correlated to stratons 652 to 629 of dozons 18A and 18B. Note in Dozon 18B one straton is assumed to be unidentified and arbitrarily shown as Straton 634 in Khuff Cycle Set KCS4.6. (See Figure 1 for location, Figure 2 and Enclosure, Tables 1 and 2 for overview of Khuff sequence stratigraphy).

633

634?

320

340

SB 18B SB KS4

259.2 Ma 360

380

400

420

440

460

480

500

4.4

4.5

MFS P30 635

4.6

636

4.7

637

4.8

638

4.9

639

4.10

640

4.11

641

5.1

642

5.2

643

5.3

644

5.4

645

5.5

646

5.6

647

5.7

MFS 648 P25

5.8

649

5.9

650

5.10

651

5.11

652

5.12

520

540

SB 18 SB KS5 (264.0 Ma)

560

118

3rd KS KS3

Straton 629

632

661 700

Stage

200

260

KCS 4th

Khuff Sequence KS4 (170 m)

660

Chan. 254.3 Ma

240

5th


659

40

Cyclicity

628

Khuff Formation

658

(API)

10

Wuchiapingian (Dozon 18B)

657

GammaRay

SB 18C SB KS3

180

654

MFS 656 P20

(meter)

3rd KS

Capitanian (Dozon 18A)

680

4th


660

160

655

Khuff Formation

640

40

264.0 Ma

Wordian–Capitanian (Dozon 19C)

620

(API)

Cyclicity

SB KS5 653

580

600

10

Straton

Formation

Stage

(meter)

Depth

560

Total GammaRay

Depth

(b)

(a)

Formation

KHUFF SEQUENCES KS6, KS5 AND KS4, SAIQ PLATEAU, OMAN


KHUFF SEQUENCE KS4, SOUTH FARS, IRAN

South KS4c4 629

Restricted facies, internal sands and lagoons Main reservoir intervals

Sequence KS4c (58 m)

Major exposure surface and breccia unit

KS4c1 thin (~1 m) dolomitic reservoir level

KS4c3 630

Maximum Accommodation Zone (MAZ)

Zone of mouldic bioclastic and oolitic transgressive sandwave complexes

KS4c2 631

SB 18C (254.3 Ma)

North

"Muddy" maximum flooding zone mudstone layer with "open" bioclast elements followed by azoic muds chemical oceanographic event poor oxygenation

MFS P30

Small subtidal oolitic and bioclastic shoals with local lagoons. Deepening-up bioclastic grain-capped cycles.

KS4b3 633

Good mouldic porosity in late aggradational/ retrogradational sands

Mainly limestone intervals

Excellent poroperm dolomitized shoal and lagoon facies

Dominated by shallow-water restricted facies and shallow-water oolitic tidal shoals

Mainly dolomitic intervals

KS4b2 634

KS4b1 635

Dozon 18B

Main reservoir interval

Sequence KS4b (53 m)

Upper Dalan Member

KS4a4 637 Aggradation of grain-supported facies - small shallowwater oolitic tidal shoals. Mud-capped cycles.

KS4a Maximum Accommodation Zone (MAZ)

KS4a3 638

KS4a2 639

Dominated by shallow-water restricted facies (lagoons and sabkhas)

Parasequence set cycles

Capitanian Nar Member, Dalan Formation

KS4a1 640

Major exposure surface and breccia unit

Straton

Figure 7: Khuff Sequence KS4 in subsurface South Fars, Iran (after Insalaco et al., 2006).

119

SB 18B (259.2 Ma)

Minor reservoir intervals

KS4a5 636

Sequence KS4a (48 m)

UPPER PERMIAN (Wuchiapingian)

KS4c1 632


Wuchiapingian Maximum Flooding Surface MFS P30: In Al Jabal al-Akhdar, Koehrer et al. (2012) interpreted the main MFS in Sequence KS4 in cycle set KCS 4.6 (Figure 6 and Enclosure) at the maximum thickness of grainstones interbedded with muddy foreshoal textures, indicating the most open-marine conditions. Insalaco et al. (2006) interpreted three MFSs in Sequence KS4 in South Fars and considered the one in KS4c to be the dominant one (Figure 7). Both papers correlated their MFSs to Wuchiapingian MFS P30 of Sharland et al. (2001, 2004). Global and Orbital Correlations: Khuff Sequence KS4 correlates to global Wuchiapingian sequences Wuc1 and Wuc2 between 259.8–254.2 Ma, which in turn may correlate to HFS KS4-I and HFS KS4-II (HFS4a and HFS KS4b of Koehrer et al., 2012). In the M&H-2010 scale KS4 correlates to Dozon 18B between 259.2–254.3 Ma (Figure 2). The 12 “parasequence sets” in Iran and 11 “cycle sets” in Oman (with one presumed unidentified) are correlated to stratons 640–629 and to “fourthorder” sequences 1 to 11 in the Zhuzang Section of South China (Table 1). In the orbital model Straton 633 contains the MFS of HFS KS4-II (KS4a of Koehrer et al., 2012) and the MFS of KS4b of Insalaco et al. (2006) (Figures 6 and 7). In the Zhuzang Section of South China the base of Straton 633 correlates to the surface separating the transgressive and regressive sequence sets (TSS and HSS) corresponding to the MFS of “composite sequence” CSII (Wang et al., 2011). These correlations imply Straton 633 contains the MFS of global sequence Wuc1 and correlative MFS P30 of the Arabian Plate, with an age of ca. 256.1 Ma.

Khuff Sequence KS3: 254.3–252.3 Ma In Al Jabal al-Akhdar in Oman, Khuff Sequence KS3 varies in thickness between 62 to 69 m, and consists of the four “cycle sets” KCS 3.4 to KCS 3.1 (Figures 1b and 8, Enclosure; Koehrer et al., 2010, 2012). It corresponds in part or completely to Late Permian sequence P40 of Osterloff et al. (2004). Insalaco et al. (2006) reported that Khuff Sequence KS3 is ca. 115 m thick in subsurface South Fars (Figures 1a and 9), or about twice as thick as in Kuh-e Surmeh (47 m) and Kuh-e Dena (60 m). They divided it into lower “third-order” Sequence KS3a, which consists of the four “parasequence sets” KS3a1 to KS3a4, and overlying “fourth-order” Sequence KS3b, which consists of the five “depositional units” KS3b0 to KS3b4. Age: On biostratigraphic evidence the lower boundary of Sequence KS3, SB KS3, is correlated to the Wuchiapingian/Changhsingian Boundary (WCB) and its upper boundary, SB KS2, occurs below the Permian/Triassic Boundary (PTB) (Figure 2; Insalaco et al., 2006; Maurer et al., 2009; Koehrer et al., 2010, 2012). In subsurface Oman, the PTB occurs in the transition between the Middle and Upper Khuff members (Figure 4; Osterloff et al., 2004; Vachard and Forbes, 2009; Forke, 2009, unpublished PDO report in Forbes et al., 2010), implying the uppermost Permian SB KS2 occurs near the top of the Middle Khuff Member, possibly the top of P40 of Osterloff et al. (2004). Changhsingian Maximum Flooding Surface MFS P40: In Al Jabal al-Akhdar, Koehrer et al. (2010, 2012) interpreted the MFS of Sequence KS3 in cycle set KCS 3.2 (Figure 8 and Enclosure). It occurs in a distinctive one meter-thick coral-rich floatstone bed informally named the “Coral Marker”. Insalaco et al. (2006) interpreted the MFS of Sequence KS3 in South Fars in KS3a3 (Figure 9). Both studies correlate their MFSs to Late Permian MFS P40 of Sharland et al. (2001, 2004), and both occur in Straton 626 with an orbital age of ca. 253.3 Ma (Figure 2). These correlations imply Changsinghian MFS P40 correlates to the MFS Cha1 of global sequence Cha1, which has an age of ca. 253.5 Ma in GTS 2012. In the Zhuzang Section of South China the MFS of “composite sequence” CSIII is older if it is correlated to the base of Straton 627 at 253.9 Ma. Global and Orbital Correlations: The lower boundary of Khuff Sequence KS3 is correlated to the Wuchiapingian/Changhsingian Boundary (WCB) and therefore to SB Cha1 at 254.2 Ma in GTS 2012 (Figure 2). The upper boundary of KS3 occurs below the Permian/Triassic Boundary and would therefore correlate to SB Cha3 at 252.5 Ma in GTS 2012 (Figure 2). Sequence KS3 is correlated to the five stratons 628–624 in the lower part of Dozon 18C (Figure 2 and Table 1). The five stratons 628– 624 may correspond to the KS3a1 to KS3a4 “parasequence sets” and the “fourth-order” sequence KS3b in South Fars (Figure 9), to “fourth-order” sequences 12–16 in the Zhuzang Section (Figure 3),

120


Khuff Formation

621

KCS 2.2

623

KCS 2.3

Changhsingian SB 18C SB KS3

254.3 Ma

KCS 1.1

619

KCS 1.2

620

KCS 2.1

621

KCS 2.2

622

KCS 2.3

623

100

KCS 3.1

MFS 626 P40

KCS 3.2

627

KCS 3.3

628

KCS 3.4

629

KCS 4.1

HFS

(meter)

60

249.5 Ma

Khuff Sequence KS1

618

120

140

625

160

180

Depth

?

120

PERMIAN

KCS 2.1

MFS 622 Tr10

SB KS2

KCS 1.0

80

SB KS1

60

140

KCS 1.2

KS

160

Khuff Sequence KS2

620

40

5th 4th

624?

180

KCS 3.1

625

KCS 3.2

626

KCS 3.3

627

KCS 3.4

628

200 KS4

220

Khuff Sequence KS3

Induan

MFS Tr20

KCS 1.1

Cyclicity

Sudair SB SB 17 617?

Khuff Sequence KS1

TRIASSIC

20

100

50

Sudair SB 619

80

0

(API)

10

20

249.5 Ma

40

KS

Gamma-Ray

Straton

4th

HFS

Straton

40

5th

KCS

10

Cyclicity

Khuff Sequence KS2

?

Total GammaRay (API)

Khuff Sequence KS3

0

Sudair Formation Formation

Stage Olenekian

System

(meter)

Depth

KHUFF SEQUENCES KS3, KS2 AND KS1, AL-JABAL AL-AKHDAR, OMAN Saiq Plateau Wadi Hedek

Figure 8: Khuff sequences KS3, KS2 and KS1 in Saiq Plateau and Wadi Hedek, Al Jabal al-Akhdar, Oman (after Koehrer et al., 2010, 2012). Wadi Hedek Cycle Set KCS1.0 is absent in the Saiq Plateau. The orbital time scale M&H-2010 predicts that two stratons remain to be identified, probably 624 and 617. (See Figure 1 for location, Figure 2 and Enclosure, Tables 1 and 2 for overview of Khuff sequence stratigraphy).

121


Main reservoir intervals

Sequence KS1 (ca. 107 m)

MFS Tr20

617

KS1b2

618

KS1b1 KS1a4

Peritidal and evaporitic supratidal flats with tidal channels, shallow shoals, local microbial facies, and green shales

Transgressive pulses which generate accommodation which is filled by grainstone shoal facies. Capped by lagoon and mudflat facies.


KS1c1 KS1b3

Microbial-influenced depositional systems - lagoons, tidal flats and poorly-oxygenated embayments K1 microbial event

KS1a3 KS1a2 619 KS1a1

Anhydritised tidal flats

Sequence KS2 (ca. 57 m)

KS1c2

MFS Tr10

Grainy facies in MFZ

KS2d 620

KS2c 621

Thrombolites

KS2b 622 KS2a 623

Platform flooding surface

Epikarst

Increasing frequency of grainy beds and reappearance of oolites

KS3b3 Appearance of intercalated foram-rich sands

KS3b2

Stacked burrowed rooted lagoonal and tidal flats

KS3b1

Straton 624

Sequence KS3b (ca. 60 m)

Highly aggradation KS3b

KS3b0


KS3a4 625 Sequence KS3a (ca. 55 m)

Upper Dalan Member

UPPER PERMIAN (Changhsingian)

KS3b4

MFS P40

Maximum Accommodation Zone (MAZ) (thick muddy embayment unit)

Local peloidal and bioclastic tidal shoals

Double anhydrite bands KS4c4 major exposure surface

Restrictive coastal lagoons and shallow-water poorly oxygenated muddy embayments and small grainstone/ packstone levels

KS3a3 626

Local erosion of anhydrite bands

KS3a2 627

KS3a1 628 Flooding surface

Figure 9: Khuff sequences KS3, KS2 and KS1 in subsurface South Fars, Iran (after Insalaco et al., 2006). 122

SB 18C (254.3 Ma)

Kangan Formation

LOWER TRIASSIC (Induan)

Base Aghar Peritidal and evaporitic supratidal flats with tidal Erosively-based oolitic channels, green shales and and peloidal grainstone local microbial facies channels and shallow shoals

South SB 17 (249.5 Ma)

KHUFF SEQUENCES KS3, KS2 AND KS1, SOUTH FARS, IRAN

Dozon 18C

North


and to “cycle sets” KCS 3.4 to KCS 3.1 with one remaining unidentified in the Oman Mountains (Figure 8 and Table 1). E. Insalaco (written communication, 2013) noted that the correlation of KS3b in South Fars to Straton 624 implies it consists of the five “depositional units” KS3b0 to KS3b4, and is much thicker than other stratons. He speculated that this anomaly might be related to the higher aggradation and possibly better preservation associated with this depositional package, but that this interpretation requires further clarification.

Khuff Sequences KS2 and KS1: 252.3–249.5 Ma In Al Jabal al-Akhdar in Oman, Khuff Sequence KS2 ranges in thickness from 55 to 61 m and consists of the three “cycle sets” KCS 2.3 to KCS 2.1 (Koehrer et al., 2010, 2012, Figure 8 and Enclosure). Sequence KS1 attains a maximum thickness of 84 m in Wadi Hedek, where it consists of three “cycle sets” KCS 1.2 to KCS 1.0. Sequences KS2 and KS1, together, correspond to Triassic sequences Tr10 and Tr20 of Osterloff et al. (2004, Figure 4). Insalaco et al. (2006) reported that Sequence KS2 ranges in thickness from 50 m at Kuh-e Dena to 57 m in subsurface South Fars, and interpreted it as a “fourth-order” sequence, which consists of four “parasequence sets” KS2a to KS2d, Figure 9). Khuff Sequence KS1 is ca. 100 m thick in South Fars and reaches 129 m in Kuh-e Dena. It is interpreted as a “third-order” sequence and divided into three “fourth-order” sequences KS1a, KS1b and KS1c, and 10 “depositional units” (KS1a1 to KS1a4, KS1b1 to KS1b3, and KS1c1 to KS1c3, Figure 9). Age: Sequence KS2 straddles the Changsinghian and Induan stages with the Permian/Triassic Boundary picked in cycle set KCS 2.3 on the Saiq Plateau in Oman and KS2b in Iran (Enclosure, Figures 8 and 9; Table 1). Khuff Sequence KS1 is interpreted as Induan–?early Olenekian by stratigraphic position above the PTB and below the Sudair SB, which occurs near the Induan/ Olenekian Boundary (see below). Induan Maximum Flooding Surfaces MFS Tr10 and Tr20: Sharland et al. (2001) interpreted two maximum flooding surfaces, MFS Tr10 and MFS Tr20, in the Early Triassic (Scythian) and positioned them in the uppermost part of the Khuff Formation. In their revised study, Sharland et al. (2004) interpreted MFS Tr10 as Induan but did not discuss the age or position of MFS Tr20. The youngest two MFSs of the Khuff Formation occur in cycle sets KCS 2.2 and KCS 1.2 on the Saiq Plateau (Koehrer et al., 2010), and they are correlated to stratons 622 and 620, respectively, in the Induan. So it is proposed that MFS Tr10 (ca. 251.7 Ma) and MFS Tr20 (250.9 Ma) be taken as the flooding surfaces of KS2 and KS1, respectively, in global sequences Cha3 and Ind1 (Figure 2 and Table 1). Global and Orbital Correlations: Sequences KS2 and KS1 correlate to global sequences Cha3 and probably Ind1 between SB Cha3 at 252.5 Ma and SB Ole1 at 249.9 Ma (Figure 2). They correlate to the seven stratons 623–617 in the upper part of Dozon 18C (Figure 2 and Table 1). In Oman “cycle sets” KCS 2.3, 2.2 and 2.1 are tentatively correlated to stratons 623, 622 and 621, and KCS 1.2, KCS 1.1 and KCS 1.0 to stratons 620, 619 and 618, with Straton 617 missing, possibly due to erosion and postdepositional tectonics during the Late Cretaceous (Koehrer et al., 2012). “Cycle set” KCS 2.3 contains the Permian/Triassic Boundary (252.2 ± 0.5 Ma) as consistent with the age of Straton 623 between 252.3 and 251.9 Ma. In South Fars the four stratons 623 to 620 may correlate to the four “parasequence sets” KS2a, KS2b, KS2c and KS2d, and the three stratons 619 to 617 to the three “fourth-order” sequences KS1a, KS1b and KS1c (Figure 9 and Table 1).

Sudair Sequence Boundary In the Arabian Peninsula, the Khuff Formation is overlain by the Sudair Formation and equivalent rock units, and the intervening boundary is referred to as the Sudair Sequence Boundary (Sudair SB, Figures 4 and 8, Enclosure). In South Fars in Iran, the Sudair SB passes to the boundary between

123


the Kangan Formation and overlying Aghar Shale Member of the Dashtak Formation (Figure 9, Insalaco et al., 2006). In Al Jabal al-Akhdar, Rabu et al. (1986) described the lowermost part of the Sudair-equivalent as: “commonly includes decimeter-thick beds of dolomite with quartz and intra-formational breccia with a sandstone-dolomite cement (Wadi Mu’aydin), beds of maroon siltstone (Wadi Misin), and a close succession of hardgrounds separating the dolomite beds and reflecting periodic emergence.” The Sudair SB represents a regional regression that was dated in the Oman Mountains by chemostratigraphy as late Induan (between the top of the Griesbachian to middle Dienerian) (Richoz, 2006; Baud and Richoz, 2013). Forbes et al. (2010) characterized the Triassic Upper Khuff Member and Sudair Formation in subsurface Oman by Palynozone 2351 of Petroleum Development Oman (PDO) (Densoisporites nejburgii with Endosporites papillatus). They reported that in the lower shale of the Sudair Formation small marine acritarchs, characterized by Veryhachium spp., define PDO Palyno-subzone 1095. They added that the Veryhachium-Micrhystridium acritarch bloom, together with the associated miospores, appears to be an Induan–early Olenekian worldwide event. Palynological analysis of samples taken from the basal shale of the Sudair Formation in the SHD-1 Well in Central Saudi Arabia (Figure 1a) also contain abundant Veryhachium spp. of Early Triassic age (Manivit et al., 1983). Forbes et al. (2010) also reported that a single specimen of Hemigordiellina tenuifistula, noted by Vachard (2007), suggests an Olenekian age at the base of the Sudair Formation outcrop-equivalent, and that Vachard (2007) recognized an Induan biozone (sporadic Hemigordiellina sinensis) in uppermost Khuff-equivalent outcrops in Al Jabal al-Akhdar. In the Musandam Peninsula outcrops (Figure 1), Maurer et al. (2009) reported that a succession that is most likely equivalent to the Sudair Formation yields an association of Hoyenella sinensis and Meandrospira pusilla. They added that morphotypes and association of these foraminifera indicates a late Induan–Olenekian age. They considered the age of the youngest Khuff Sequence KS1 to be Induan. In the Al Jabal al-Akhdar outcrops, Oman (Figure 1), Koehrer et al. (2010) reported that foraminiferal fauna with sporadic occurrences of Hoyenella sinensis and H. tenuifistula occur in the lower part of the Sudair Formation outcrop equivalent on the Saiq Plateau (“Middle Mahil Member”). They considered the Sudair Formation as Olenekian, and Khuff Sequence KS1 as Induan. Pöppelreiter et al. (2011) reported that in the Al Jabal al-Akhdar outcrops Cornuspira mahajeri occurs with shell fragments in the “Claraia beds” in the lowermost Sudair Formation outcrop equivalent. They took the occurrence of this Lower Triassic “disaster fauna” together with a prominent positive δ13CCarb isotope shift to indicate a late Induan–early Olenekian (late Dienerian–early Smithian) age for the lower part of the Sudair Formation. They positioned Olenekian MFS Tr30 in the Sudair Formation, corresponding to the Aghar Shale Member of the Dashtak Formation in South Fars (Insalaco et al., 2006). The above-cited biostratigraphic studies place the Sudair SB near the Induan/Olenekian Boundary dated at 250.0 ± 0.5 Ma in GTS 2012, implying it correlates to either latest Induan SB Ind1 at 250.6 Ma, or earliest Olenekian SB Ole1 at 249.9 Ma (Figure 2 and Table 2). In the M&H-2010 scale the Sudair SB correlates to orbital SB 17 at 249.5 Ma (base Straton 616).

DISCUSSION Putting Sequences in Order The terms used in this paper to categorize sequences are quoted from the original papers. Most authors adopt the term “order” to categorize sequences; for example, a “third-order” sequence consists of several “fourth-order” sequences, which in turn are composed by “fifth-order” sequences (Table 3). The “fifth-order” sequence is generally synonymous with “cycle” and “parasequence”, and the “fourth-order” sequence with “parasequence set” and “cycle set”. Some

124


Table 4 Proposed new Khuff Sequence Stratigraphic subdivision based on Dozons and Stratons Age M&H-2010 Orbital Scale

Khuff Composite Sequence (CS)

Dozon (4.86 Myr)

High-frequency Sequence (HFS) (GTS 2012)

Straton (0.405 Myr)

254.3–249.5 Ma

Composite Sequence KS1-KS3

Dozon 18C

4 HFS: Cha1 to Ind1

12 stratons: 628–617

259.2–254.3 Ma

Composite Sequence KS4

Dozon 18B

2 HFS: Wuc1 and Wuc2


264.0–259.2 Ma


Dozon 18A

2 HFS: Cap2 and Cap3


268.9–264.0 Ma


Dozon 19C

4 HFS: Wor1 to Cap1


12 HFS

48 stratons

Complete Khuff

19.4 Myr

4 Composite Sequences

4 dozons

authors use additional terms to subdivide “fourth-order” sequences into longer “high-frequency” sequences (HFS) and shorter “cycle sets” or “parasequence sets” (Tinker, 1998). The calibrations that are made in this paper imply that Khuff sequences KS6, KS5 and KS4 have durations of ca. 5.0 Myr, while the briefest KS1 lasted only ca. 1.2 Myr. The durations of the 12 global sequences that span the same time interval in GTS 2012 vary from about 4.0 Myr for Wuc1 to 0.6 Myr for Cha2 (Figure 2). Thus the durations attributed to empirical “third-order” sequences range from 0.6–5.0 Myr, and do not match the prediction by the model of Matthews and Frohlich (2002) that “third-order” sequences lasted 2.0, 2.4 or 2.8 Myr. Here, the four dozons 19C, 18A, 18B and 18A are interpreted to correspond to the four “composite” sequences KS6, KS5, KS4 and KS3–KS1 (Table 4). The global sequences used in the GTS 2012 (Wor1 to Ind1) are interpreted to represent “high-frequency” sequences rather than classical “third-order” composite sequences (Tables 3 and 4). To avoid confusion regarding the sequence-stratigraphic hierarchy of the Khuff Formation across the Arabian Plate, we recommend using the M&H-2010 orbital scale to subdivide the Khuff Formation into 48 “stratons” and 4 “dozons” (Table 4). The four “dozons” 19C to 18C correspond to the four “composite” sequences KS6, KS5, KS4 and combined KS3 to KS1.

Converting Stratons to Time The “cycle sets” of Koehrer et al. (2010, 2012) and “parasequence sets” of Insalaco et al. (2006) are good candidates for “stratons”. Several pitfalls, however, can occur when converting these sets or “fourth-order” sequences to time. The most common is assuming that the section is without hiatuses. On the Saiq Plateau, this pitfall is evident at the Sudair SB because cycle set KSC1.0, seen in Wadi Hedek, is missing on the Saiq Plateau (Figure 8). Two more stratons are predicted to be missing in Al Jabal al-Akhdar if the count of 12 is to be completed for Dozon 18C in combined “composite” sequence KS3 to KS1 (Table 4). A strategy for recognizing significant hiatuses is to correlate sequence boundaries, maximum flooding surfaces and stratons between several localities. In this paper KS4 to KS1 are shown in Al Jabal al-Akhdar and South Fars, located about 500 km apart and each encompassing a study area of

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more than 100 square km (Figures 1, 6 to 9). A total of 24 stratons are predicted in these sequences, which appears to be the case in South Fars, but not so in Al Jabal al-Akhdar where only 22 are recognized. In the Ghawar Field of Saudi Arabia (Figure 1), 20 “high-frequency” sequences (HFS) have been recognized in KS4 to KS1 (Al-Eid and Tawil, 2011; Al-Dukhayyil et al., 2012; A. Al-Tawil, personal communication, 2012). It is possible that these HFS are rather “stratons” with four stratons missing over this structure that was located in a more proximal setting than South Fars. Another pitfall is suspected to occur in the Zhuzang Section in South China (Figure 3; Wang et al., 2011), where “fourth-order” Sequence 11 may consist of two stratons implying it represents ca. 0.8 Myr. The opposite pitfall is suspected in South Fars where the five “depositional units” in Sequence KS3b may be “fifth-order” sequences with durations of about 0.1 Myr rather than 0.405 Myr (Figure 9). Some of these pitfalls may be avoided by collecting additional stratigraphic data to better constrain the ages of sequence boundaries and maximum flooding surfaces/intervals in terms of stratons. F. Maurer (written communication, 2013) emphasized that the lack of detailed biostratigraphy in many Khuff sections makes a detailed correlation of sequences difficult. He suggested that the use of other proxies, such as carbon isotopes, may provide an alternative tool for correlations. Clarkson et al. (2012, their figure 4) show a correlation of the Triassic part of the Khuff Formation between Musandam and Wadi Sahtan in Al Jabal al-Akhdar. It illustrates that the Musandam Section has a much higher sedimentation rate, implying that in Al Jabal al-Akhdar region not all stratons might be recorded. He thinks it might be beneficial to use the carbonate-isotope signature for a section with high-resolution sequences, such as the Zhuzang Section, and compare it with the Arabian Plate for a better fine-tuning of the straton-to-straton correlation.

Regional, Global and Orbital Isochronous Surfaces Three major sequence boundaries are recognized in Al Jabal al-Akhdar (Koehrer et al., 2010, 2012): (1) Khuff SB marking the start of the marine transgression, (2) SB KS4 at the top of the Middle Anhydrite or its equivalent, and (3) Sudair SB at the breccia level at the top of the Khuff Formation. In the global scheme only two Mid-Permian–Early Triassic sequence boundaries, SB Ole2 and SB Wuc1, are interpreted as “major” in the compilation of Snedden and Liu (2011). Therefore only one sequence boundary is recognized as “major” in both the Arabian and global frameworks: correlative SB KS4 and SB Wuc1. In the orbital M&H-2010 scale, five sequence boundaries are predicted to be regional and these are recognized in both the Arabian and global schemes (Figure 2). Of the five, SB 17A (Sudair SB) and SB 18A (SB KS5) are predicted to be more prominent than the other three (Figure 2). This prediction is true for SB 17A corresponding to the major regression at the Sudair SB, characterized by the influx of terrestrial clastics and exposure above carbonates and evaporites. It is less clear whether SB 18A is a more prominent sequence boundary in comparison to SB KS4 (top Middle Anhydrite) or the Khuff SB. The significance of SB 18A may be that its correlative SB KS5, at the base of Sequence KS5, represents the start of a second transgression of much greater regional extent than KS6. This scenario is suggested by regional correlations from Iran and Oman (Tethys-side) to Saudi Arabia (Al-Jallal, 1995), and the interpretation that the Khuff transgression first reached as far as the Arabian Shield during the Capitanian (Vaslet et al., 2005). This scenario implies that the extent of coastal onlap onto the Arabian Plate of Capitanian Sequence KS5 was far greater than that of Wordian–?early Capitanian KS6, or opposite to that depicted in the global onlap curve (Figure 2).

CONCLUSIONS This study uses biostratigraphic and sequence-stratigraphic constraints to position the Khuff Formation between global Wordian sequence boundary SB Wor1 at ca. 268.8 ± 0.5 Ma and Olenekian sequence boundary SB Ole1 at ca. 249.9 ± 0.5 Ma as calibrated in GTS 2012 (Figure

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2; Tables 1 and 2). These two boundaries correlate by numerical age to two model-predicted, regional sequence boundaries at 268.9 and 249.5 Ma in the M&H-2010 orbital scale. The model scale predicts that the Khuff Formation contains 48 T-R sequences with an average duration of 0.405 Myr, corresponding to the long-eccentricity orbital cycle and referred to as “stratons”. Moreover the 48 stratons are predicted to group into four “dozons” each lasting 4.86 Myr (Table 4). The chronostratigraphic framework presented in this paper is believed to have an accuracy of less than one million years, and perhaps approaching 0.405 Myr – the duration of a straton. The Khuff Formation on the Saiq Plateau in Al Jabal al-Akhdar provides a comprehensively documented, reference section at outcrop for the Mid-Permian (Wordian) to Early Triassic (Induan– ?early Olenekian) sequence stratigraphy (Enclosure). A total of 45 transgressive-regressive (T-R) “fourth-order” cycle sets are considered good candidates to represent all but three of the 48 stratons, with three remaining to be identified or absent due to faulting (Enclosure, Figures 6 and 8; Table 1). In the Al Jabal al Akhdar outcrops in Oman, the four dozons correlate closely to composite Khuff sequences KS6, KS5, KS4 and combined KS3 to KS1 (Figure 2; Tables 1, 2 and 4). The M&H-2010 scale was also used to calibrate the Upper Permian (Lopingian) Zhuzang Section in South China (Figure 3 and Table 1). The section is bounded below by the Emeishan Basalt dated at 259.0 ± 3.0 Ma and corresponding to global basal Wuchiapingian sequence boundary SB Wuc1 dated at 259.8 Ma in GTS 2012. It is bounded above by the Permian/Triassic Boundary dated at 252.2 ± 0.5 Ma. The application of the M&H-2010 scale dates the Zhuzang Section between 259.2 and 252.3 Ma. The results from Oman and South China are believed to support the prediction by Laskar et al. (2004, 2011) that the 0.405-Myr clock is stable as far back as the Permian/Triassic Boundary, and that the M&H-2010 scale can be used to estimate the ages of Mid-Permian–Early Triassic T-R sequences. Geoscientists working on the Khuff reservoir in the Middle East are encouraged to use the M&H2010 orbital scale as a sequence-stratigraphic template, instead of empirical cycle definitions and orders. In the M&H-2010 orbital scale, Khuff reservoir zones can be better positioned in a regional chrono- and sequence-stratigraphic framework using time-calibrated “stratons” (0.405 Myr cycles) and “dozons” (4.86 Myr cycles). This may allow correlating the Khuff and its correlative formations in a consistent way from field to field across the Arabian Plate.

ACKNOWLEDGEMENTS The authors thank Jim Ogg and Chunju Huang for sharing their estimates for the ages of the global sequences calibrated in the Geologic Time Scale GTS 2012. Enzo Insalaco, Chunju Huang, Florian Maurer, Mike Stephenson and Daniel Bendias are thanked for their comments and suggestions that have improved the manuscript. Bastian Koehrer would especially like to thank Tom Aigner, Michael Pöppelreiter and his former colleagues of the Sedimentary Geology working group of the University of Tübingen. GeoArabia’s Assistant Editor Kathy Breining is thanked for proofreading the manuscript, and GeoArabia’s Production Co-manager, Arnold Egdane, for designing the paper for press.

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ABOUT THE AUTHORS Moujahed I. Al-Husseini founded Gulf PetroLink in 1993 in Manama, Bahrain. Gulf PetroLink is a consultancy aimed at promoting technology in the Middle East petroleum industry. Moujahed received his BSc in Engineering Science from King Fahd University of Petroleum and Minerals in Dhahran (1971), MSc in Operations Research from Stanford University, California (1972), PhD in Earth Sciences from Brown University, Rhode Island (1975) and Program for Management Development from Harvard University, Boston (1987). Moujahed joined Saudi Aramco in 1976 and was the Exploration Manager from 1989 to 1992. In 1996, Gulf PetroLink launched the journal of Middle East Petroleum Geosciences, GeoArabia, for which Moujahed is Editor-in-Chief. Moujahed also represented the GEO Conference Secretariat, Gulf PetroLink-GeoArabia in Bahrain from 1999–2004. [email protected] Bastian Koehrer is a Development Geologist in Wintershall’s German business unit, working on mature oil field and tight gas sands development in the German North Sea and Lower Saxony. He has more than five years of E&P project experience in Germany, Oman, Qatar and the UAE with a professional track record in both carbonate and clastic reservoirs. Bastian obtained a PhD degree (2011) in Carbonate Sedimentology (Khuff Formation, Oman) from the University of Tübingen (Germany) in research collaboration with Shell (Qatar) and Petroleum Development Oman. Bastian is a member of the EAGE, AAPG and DGMK and has published several papers on carbonate sequence stratigraphy and reservoir outcrop analogs. His work interests include integration of rock, log and test data to improve reservoir characterization and 3-D reservoir modeling during the development and production stages of the field life cycle. [email protected]

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