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ABSTRACT

A diversified assemblage of cryptospores and trilete miospores are reported from the Nuayyim-2 borehole, Saudi Arabia. Four new genera and six new species are described: Chelinohilates maculatus sp. nov., Complectitetras alhajrii gen. and sp. nov., Imperfectotriletes patinatus gen. and sp. nov., Laevolancis chibrikovae sp. nov., Sphaerasaccus glabellus gen. and sp. nov., and Vestitusdyadus qalibahinus gen. and sp. nov. Independent biostratigraphical control using chitinozoans and graptolites indicates that all the studied samples are Llandovery (Rhuddanian) in age. A new biostratigraphic scheme for strata near the Ashgill-Llandovery boundary is proposed: one assemblage biozone is divided into two interval biozones that are both further subdivided into two sub-biozones. The criteria used to create these biozones are the first occurrences of taxa (including the earliest trilete spores) and the relative abundance of envelope-enclosed cryptospores. The palaeogeographically widespread distribution of similar spore assemblages during the Late Ordovician-Early Silurian suggested that the parent plants were cosmopolitan and thrived in a variety of climatic conditions. Therefore, they were little affected by climatic changes associated with the Hirnantian glaciation. This might provide an explanation for the apparent lack of significant impoverishment in spore biodiversity during this glaciation.

INTRODUCTION

This study reports on spore assemblages (cryptospores and trilete miospores) from the Nuayyim-2 (NYYM-2) borehole (Figure 1) drilled through Palaeozoic and Precambrian strata of central Saudi Arabia. The late Precambrian to Permian strata of Saudi Arabia are subdivided into six major depositional packages that are informally referred to as Super Groups (I-VI) (Stump et al., 1995). All of the samples analysed in this study derive from cores 8-10 that were obtained from the Qusaiba Member. The Qusaiba Member and overlying Sharawra Member belong to the Qalibah Formation and are placed in the lower part of the Super Group IV. These members are interpreted as offshore clays (Qusaiba Member) and pro-deltaic sands (Sharawra Member) of a vast deltaic system (Stump et al., 1995).

Figure 1:

Palaeozoic outcrops on the Arabian Peninsula, and the Nuayyim-2 well discussed in this study.

Figure 1:

Palaeozoic outcrops on the Arabian Peninsula, and the Nuayyim-2 well discussed in this study.

Acritarchs (Le Hérissé et al., 1995) and chitinozoans (Paris et al., 1995) have been examined using the same samples utilised in this study, and were reported in a special publication discussing the Palaeozoic palynostratigraphy of Saudi Arabia (Owens et al., 1995). Chitinozoans from cores 9 and 10 belong to the L. nuayyimensis Biozone, while those from core 8 belong to the A. qusaibaensis Biozone. These local biozones are tentatively correlated with the British graptolite zones: the L. nuayyimensis Biozone is correlated with the late atavus and the lower part of the acinaces graptolite Zones, and the A. qusaibaensis Biozone is correlated with the late acinaces and lower cyphus graptolite Zones. These strata are thus interpreted as late Rhuddanian in age.

Acritarchs from cores 9 and 10 belong to Biozone 2, while those from core 8 belong to Biozone 3. It is also worth noting that assemblages from both biozones contain some acritarchs not previously reported below the Aeronian. When considering the age based on chitinozoans and graptolites (Legrand in Le Hérissé et al., 1995), Le Hérissé suggested that discrepancies exist for the appearance of certain acritarch taxa in the Nuayyim-2 assemblages.

Cryptospores are relatively abundant and assemblages are very similar in all of the examined samples. The observed cryptospores consist of monads, dyads and tetrads, and include both naked and envelope-enclosed forms. Rare trilete miospores, belonging to the genus Ambitisporites, occur only in the oldest examined level. The organic matter is well-preserved, yellow to brown in colour, indicating low thermal maturity.

IDENTIFICATION OF A TRUE TRILETE MARK

One of the major difficulties encountered during this study was the identification of a true trilete mark. Many specimens, here referred to as Imperfectotriletes vavrdovae gen. and comb. nov. and Imperfectotriletes patinatus gen. and sp. nov., have an imperfectly developed trilete structure present on a thin proximal face that is frequently ruptured. These specimens are clearly physically broken out of permanent tetrads. The pseudo-trilete mark appears to form as a consequence of damage resulting from the physical separation from the three other spores of the tetrad. We do not consider such spores to be true trilete spores and consider them as cryptospores. They are identified using the following criteria: (1) specimens with a pseudo-trilete structure and/or torn proximal face; (2) specimens having parts of the tetrad still adhering; and (3) specimens in which all three rays of the trilete structure are not apparent. Based on these restrictions, only two specimens, from the same level (11,978.5 ft), can be accepted as true trilete spores. Both belong to the genus Ambitisporites and are included in the Ambitisporites avitus-dilutus morphon.

The oldest reported true trilete spores are from the Bedinan Formation, southeastern Turkey, dated as Ashgill in age using acritarchs, chitinozoans and trilobites (Steemans et al., 1996). Upper Caradoc to lower Llandovery strata from the Brabant Massif, Belgium, yield rare specimens described as Leiotriletes sp. I that may represent true trilete miospores (Martin, 1973). However, true trilete miospores become abundant only much later. In southern Britain they are relatively common from the Aeronian (Burgess, 1991; Richardson, 1988).

SYSTEMATICS

Cryptospores

Genus Abditusdyadus Wellman and Richardson, 1996

Type species: Abditusdyadus histosus Wellman and Richardson, 1996

Abditusdyadus laevigatus Wellman and Richardson, 1996 (Plate 1: a, b, c, d)

Dimensions: 25 (32) 45 by 25 (40) 59 μm measured on 18 specimens.

Genus Chelinohilates Richardson, 1996

Type species: Chelinohilates erraticus Richardson, 1996

Chelinohilates maculatus sp. nov. (Plate 1: e, f, g, h)

Derivation of name: Latin macula, mesh.

Holotype and type locality: Nuayyim-2, Qusaiba Member, Qalibah Formation, 11,978.5 ft, slide 32708, England finder co-ordinates N46/3.

Diagnosis: A Chelinohilates ornamented outside of the contact area with muri which form an irregular to regular subpolygonal to rounded reticulum. The hilum is laevigate. The margin of the hilum is formed by a subequatorial crassitude that is sometimes bordered by a thin zona.

Description: Amb subcircular to circular. Subequatorial crassitude 1-3 μm wide delimits a more or less circular laevigate hilum. The crassitude is sometimes extended by a thin zona up to 3 μm wide. Distal surface thicker than the proximal one, ornamented by an irregular to regular rounded to subpolygonal reticulum. Muri 1.5-3 μm wide, lumina 2-6 μm in maximum diameter.

Dimensions: 36 (39) 41 μm measured on 7 specimens.

Comparison: Chelinohilates lornensis Wellman and Richardson, 1996 is ornamented by a more regular and polygonal reticulum formed by thinner muri.

Genus Complectitetras gen. nov.

Type species: Complectitetras alhajrii gen. and sp. nov.

Derivation of name: Latin complecti, to enclose.

Diagnosis: Permanent cryptospore tetrads composed of tightly-adherent laevigate sub-triangular to subcircular spores with low and rounded, more-or-less fused, equatorial crassitudes. Tetrads enclosed by two outer envelopes: the inner envelope is ornamented and thick; the outer envelope is laevigate and thin. This outer envelope is not always visible, either because it has been destroyed or because it is tightly appressed to the inner envelope. Sculpture consist of muri that form a reticulum.

Comparison: Velatiteras Burgess, 1991 comprises laevigate tetrads enclosed in a solitary ornamented or laevigate envelope.

Remarks: The generic variability cannot be ascertained because only one species is observed. The absence of a break in ornamentation at the junction between the spores of the tetrads suggest that there is a continuous ornamented inner envelope which encloses the tetrad. The outer envelope is often clearly distinguishable. These observations are the basis for the suggestion that two envelopes exist.

Complectitetras alhajrii gen. and sp. nov. (Plate 1: i, j, k)

Derivation of name: in recognition of Al-Hajri’s considerable contribution to studies of the Palaeozoic palynostratigraphy of Saudi Arabia.

Holotype and type locality: Nuayyim-2, Qusaiba Member, Qalibah Formation, 11,977.5 ft, slide 32707, England Finder Co-ordinates L39/-.

Diagnosis: A Complectitetras ornamented by a perfect reticulum characterised by small lumina.

Description: Permanent tetrad enclosed within two envelopes. Tetrads composed of four laevigate spores with unfused equatorial crassitudes 2-4 μm wide. The thick inner envelope is closely appressed to the enclosed tetrad, and is sculptured by muri 0.5-1 μm wide and high, which form a regular rounded to subpolygonal reticulum 0.5-1 μm wide. There is no break in ornament at the junction between adjacent spores. The thin outer laevigate envelope is variably appressed to the inner envelope and is sometimes difficult to observe.

Dimensions: 36 (49) 56 μm measured on 10 specimens.

Comparison: C. alhajrii is distinguishable from V. retimembrana (Miller and Eames) Wellman and Richardson, 1996 by the regular rounded to subpolygonal reticulum and by the smaller size of the lumina. V. cristata Burgess and Richardson, 1995 has an equatorially projecting reticulum that is poorly defined. Ornamentation is located on the envelope in both of these taxa. The published illustrations of Nodospora rugosa in Richardson (1988) (mainly Plate 19: 2-4) clearly show an outer laevigate envelope and an inner layer ornamented by convolute murinate elements. However, it is not possible to ascertain the presence of an inner envelope.

Remarks: The dense ornamentation and presence of two envelopes mask the structure of the enclosed polyad and it is not always possible to verify the number of constituent units. This observation was also noted by Wellman (1996) concerning Segestrespora? sp. A, which is possibly a synonym of Vestitusdyadus qalibahinus gen. and sp. nov. V. qalibahinus has the same general structure except that it is a dyad.

Plate 1:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-d) Abditusdyadus laevigatus Wellman and Richardson 1996.

  • (a) slide 32592, 11,965.0 ft, S38/3, FM 1554;

  • (b) slide 32592, 11,965.0 ft, M40/4, FM 1555;

  • (c) slide 32708, 11978.5 ft, V44/1, FM 1556;

  • (d) slide 32708, 11,978.5 ft, K54/2-4, FM 1557.

  • (e-h) Chelinohilates maculatus sp. nov.

  • (e) Holotype slide 32708, 11,978.5 ft, N46/3, FM 1558;

  • (f) slide 32593, 11,965.0 ft, W46/2, FM 1559;

  • (g) slide 32587, 11,911.6 ft, S41/0, FM 1560;

  • (h) slide 32592, 11,965.0 ft, M33/3, FM 1561.

  • (i-k) Complectitetras alhajrii gen. and sp. nov.

  • (i) slide 32708, 11,978.5 ft, P55/2, FM 1562;

  • (j) Holotype slide 32707, 11,977.5 ft, L39/0, FM 1563;

  • (k) slide 32707, 11,977.5 ft, J45/3, FM 1564.

  • (l) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensu Steemans, Le Hérissé and Bozdogan, 1996. Slide 32708, 11,978.5 ft, T41/0, FM 1565.

Plate 1:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-d) Abditusdyadus laevigatus Wellman and Richardson 1996.

  • (a) slide 32592, 11,965.0 ft, S38/3, FM 1554;

  • (b) slide 32592, 11,965.0 ft, M40/4, FM 1555;

  • (c) slide 32708, 11978.5 ft, V44/1, FM 1556;

  • (d) slide 32708, 11,978.5 ft, K54/2-4, FM 1557.

  • (e-h) Chelinohilates maculatus sp. nov.

  • (e) Holotype slide 32708, 11,978.5 ft, N46/3, FM 1558;

  • (f) slide 32593, 11,965.0 ft, W46/2, FM 1559;

  • (g) slide 32587, 11,911.6 ft, S41/0, FM 1560;

  • (h) slide 32592, 11,965.0 ft, M33/3, FM 1561.

  • (i-k) Complectitetras alhajrii gen. and sp. nov.

  • (i) slide 32708, 11,978.5 ft, P55/2, FM 1562;

  • (j) Holotype slide 32707, 11,977.5 ft, L39/0, FM 1563;

  • (k) slide 32707, 11,977.5 ft, J45/3, FM 1564.

  • (l) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensu Steemans, Le Hérissé and Bozdogan, 1996. Slide 32708, 11,978.5 ft, T41/0, FM 1565.

Plate 2:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensus Steemans, Le Hérissé and Bozdogan, 1996.

  • (a) slide 32708, 11,978.5 ft, U41/0, FM 1566;

  • (b) slide 32707, 11,977.5 ft, O42/0, FM 1567.

  • (c) Hispanaedicus ?sp. 2. Wellman, Higgs and Steemans, 2000. Slide 32592, 11,965 ft, L38/3, FM 1568.

  • (d) Hispanaediscus sp. B. slide 32708, 11,978.5 ft, O56/0, FM 1569.

  • (e-h) Imperfectotriletes patinatus gen. and sp. nov.

  • (e) slide 32708, 11,978.5 ft, G45/3, FM 1570;

  • (f) slide 32708, 11,978.5 ft, X46/1, FM 1571;

  • (g) slide 32708, 11,978.5 ft, T39/4, FM 1572;

  • (h) Holotype slide 32707, 11,977.5 ft, L45/0, FM 1573.

  • (i-m) Imperfectotriletes vavrdovae (Richardson, 1988) gen. and comb. nov.

  • (i) slide 32708, 11,978.5 ft, O44/1, FM 1574;

  • (j) slide 32592, 11,965.0 ft, M47/4, FM 1575;

  • (k) slide 32707, 11,977.5 ft, G39/0, FM 1576;

  • (l) slide 32708, 11,978.5 ft, G45/3, FM 1577;

  • (m) slide 32592, 11,965.0 ft, U41/0, FM 1578.

  • (n-o) Laevolancis chibrikovae sp. nov.

  • (n) slide 32707, 11,977.5 ft, Q43/3, FM 1579;

  • (o) Holotype slide 32592, 11,965 ft, U45/4, FM 1580.

Plate 2:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensus Steemans, Le Hérissé and Bozdogan, 1996.

  • (a) slide 32708, 11,978.5 ft, U41/0, FM 1566;

  • (b) slide 32707, 11,977.5 ft, O42/0, FM 1567.

  • (c) Hispanaedicus ?sp. 2. Wellman, Higgs and Steemans, 2000. Slide 32592, 11,965 ft, L38/3, FM 1568.

  • (d) Hispanaediscus sp. B. slide 32708, 11,978.5 ft, O56/0, FM 1569.

  • (e-h) Imperfectotriletes patinatus gen. and sp. nov.

  • (e) slide 32708, 11,978.5 ft, G45/3, FM 1570;

  • (f) slide 32708, 11,978.5 ft, X46/1, FM 1571;

  • (g) slide 32708, 11,978.5 ft, T39/4, FM 1572;

  • (h) Holotype slide 32707, 11,977.5 ft, L45/0, FM 1573.

  • (i-m) Imperfectotriletes vavrdovae (Richardson, 1988) gen. and comb. nov.

  • (i) slide 32708, 11,978.5 ft, O44/1, FM 1574;

  • (j) slide 32592, 11,965.0 ft, M47/4, FM 1575;

  • (k) slide 32707, 11,977.5 ft, G39/0, FM 1576;

  • (l) slide 32708, 11,978.5 ft, G45/3, FM 1577;

  • (m) slide 32592, 11,965.0 ft, U41/0, FM 1578.

  • (n-o) Laevolancis chibrikovae sp. nov.

  • (n) slide 32707, 11,977.5 ft, Q43/3, FM 1579;

  • (o) Holotype slide 32592, 11,965 ft, U45/4, FM 1580.

Genus Dyadospora Strother and Traverse, 1979

Type species: Dyadospora murusattenuata Strother and Traverse, 1979

Morphon Dyadospora murusattenuata Strother and Traverse, 1979 sensu Steemans, Le Hérissé and

Bozdogan, 1996 (Plate 1: l; Plate 2: a, b)

Dimensions: 21 (32.5) 45 by 24 (38) 56 μm measured on 45 specimens.

Genus Hispanaediscus Cramer emended Burgess and Richardson, 1991

Type species: Hispanaediscus verrucatus Cramer emended Burgess and Richardson, 1991

Hispanaediscus? sp. 2 Wellman, Higgs and Steemans, 2000 (Plate 2: c)

Description: Amb triangular. Equatorial crassitude 2.0 μm wide. No trilete mark visible. Distal surface ornamented with muri, rugulae and verrucae with a highly irregular shape and size in polar view. The elements appear to have a coarse radial alignment near the equator. Muri and rugulae meander and occasionally bifurcate. They are up to 4 μm in length and 1-2 μm in width.

Dimensions: 39 μm

Comments: This taxon is also reported and described from the Hawiyah-151 borehole in Saudi Arabia (Wellman et al., this volume).

Hispanaediscus sp. B (Plate 2: d)

Description: Hilate ornamented cryptospore with a subcircular amb. Hilum entirely laevigate and bordered by a crassitude 2 μm wide. Ornamented outside of the contact area by irregular to polygonal verrucae, 1-1.5 μm wide, less than 1 μm high and 0.5-1 μm apart.

Dimensions: 43 μm

Comparison: Hispanaediscus wenlockensis Burgess and Richardson, 1991 has proximal radial muri and larger verrucae.

Genus Imperfectotriletes gen. nov.

Type species: Imperfectotriletes patinatus gen. nov. and sp. nov.

Derivation of name: Latin imperfectus, imperfect.

Diagnosis: A subcircular to subtriangular monad with a thin disrupted proximal exine which shows irregular trilete cracks.

Comparison: Similar to Ambitisporites or Archaeozonotriletes but lacking a true trilete mark. The proximal face or equatorial border are frequently torn, and remnants of the other members of the tetrad frequently remain attached.

Remark: This genus contains monads with an equatorial crassitude that are close to Ambitisporites, and patinate forms that are close to Archaeozonotriletes. Rather than creating two new genera characterised by the thickness of the equatorial-distal exine, as is the case for the trilete spores, we prefer to use only one genus because both species are artefacts essentially formed in the same manner.

Imperfectotriletes patinatus gen. and sp. nov. (Plate 2: e, f, g, h)

1982 Single spore, broken out of tetrahedral tetrad in Gray, Massa and Boucot, Figure 5.

1985 Single spore physically broken from a tetrahedral tetrad, in Gray, Plate 1: 1.

1985 Trilete spores broken away from tetrads in Johnson, Plate X: 9-12.

partim 1988 ?Ambitisporites vavrdovii Richardson, p. 93, 97, Plate 20: 1-3; non-Figures 4-6.

?1988 ? Ambitisporites imperfectus Richardson, in Vavrdova, Plate I: 3.

?1988 single spore with Y-mark rupture in Vavrdova, Plate III: 3.

partim 1996 Ambitisporites? vavrdovii Richardson, in Steemans, Le Hérissé and Bozdogan, p. 66, Plate VI: 5; non-Figure 6.

Derivation of name: Latin patinatus, patinate.

Holotype and type locality: Nuayyim-2, Qusaiba Member, Qalibah Formation, 11,978.5 ft, slide 32707, England Finder Co-ordinates L45/0.

Diagnosis: A patinate Imperfectotriletes.

Description: Laevigate monads with a subcircular to subtriangular amb. Distally patinate. The thickness of the exine is 1 (2) 3 μm wide at the equator, sometimes slightly narrower at the radial apices than interadially. Proximal face thin, frequently torn, showing irregular trilete cracks. Remains of the tetrads frequently still attached to the monads.

Dimensions: 21 (49) 51 (8 specimens measured).

Comparison: Similar to I. vavrdovae but with a patinate structure. It is not always easy to differentiate patinatus from vavrdovae. They could represent end members of a same continuous morphological variation. The difference is similar to that between Ambitisporites avitus-dilutus and Archaeozonotriletes chulus.

Imperfectotriletes vavrdovae (Richardson, 1988) gen. and comb. nov. (Plate 2: i, j, k, l, m)

1985 Ambitisporites? in Johnson, Plate X: 6.

1985 Trilete spore with curvaturae in Johnson, Plate X: 7.

?1985 Trilete spore possibly broken away from a tetrad in Johnson, Plate X: 8.

Basionym partim 1988 ?Ambitisporites vavrdovii Richardson, p. 93, 97, Plate 20: 4-6, non-Figures 1-3. 1991 Ambitisporites? vavrdovii Richardson, in Burgess, p. 594, Plate 2, Figures 16-18. partim 1996 Ambitisporites? vavrdovii Richardson, in Steemans, Le Hérissé and Bozdogan, p. 66, Plate VI: 6, non-Figure 5.

Description: Identical to the original description but here we exclude patinate specimens.

Dimensions: 28 (37) 42 μm (14 specimens measured).

Genus Laevolancis Burgess and Richardson, 1991

Type species: Laevolancis divellomedium (Chibrikova) Burgess and Richardson, 1991 Laevolancis chibrikovae sp. nov. (Plate 2: n, o; Plate 3: a)

1996 Laevolancis divellomedia (Chibrikova) Burgess and Richardson, in Wellman, p. 112, Plate 1: 21-24; Plate 2: 17-19.

1997 Laevolancis cf. divellomedium (Chibrikova) Burgess and Richardson, in Wang, Li and Wang p. 69-70, Plate II: 12-13.

Derivation of name: The specific epithet is in recognition of Dr. Chibrikova who described Archaeozonotriletes divellomedium for the first time (Chibrikova, 1959).

Holotype and type locality: Nuayyim-2, Qusaiba Member, Qalibah Formation, slide 32592, 11,965.0 ft, England Finder Co-ordinates U45/4.

Diagnosis: A L. divellomedium with the proximal surface torn and/or with remnants of the other spore in the dyad adhering, indicating that it formed by the physical dissociation of a dyad.

Description: Amb circular to sub-circular. Equatorial and subequatorial crassitude 1 (2) 4 μm wide delimits a circular hilum. Hilum laevigate. Hilum thinner than the distal exine, and generally collapsed, torn, or missing. The border of the hilum can be partially torn. Remains of the dyads sometimes still attached to the physically separated monads.

Dimensions: 23 (33.5) 42 μm measured on 15 specimens.

Comparison: Similar to L. divellomedium except in that the hilum is usually torn or missing, indicating that it represents monads that are physically separated from permanent dyads. I. vavrdovae and I. patinatus have irregular trilete cracks on the proximal surface.

Laevolancis divellomedia (Chibrikova 1959) Burgess and Richardson, 1991 (Plate 3: b, c, d, e)

Dimensions: 28 (30) 37 μm measured on 16 specimens.

Genus Pachytetras Hagström, 1997

Type species: Pachytetras rugosa Hagström, 1997 Pachytetras rugosa Hagström, 1997 (Plate 3: f)

?1988 Nodospora sp. C in Richardson, p. 94, Plate 19: 9-10.

1991 Murornate tetrads in Burgess and Richardson, p. 619-620, Figure 3M-O.

1993 Murornate tetrads Burgess and Richardson, in Wellman, p. 58, Plate 4: 4-6.

1996 Murornate tetrads Burgess and Richardson, in Steemans, Le Hérissé and Bozdogan, p. 67, Plate VI: 11-12.

1997 Pachytetras rugosa Hagström, p. 306, Figures 6F-G.

1997 Pachytetras? rugosa? Hagström, p. 307, Figures 6J-K.

Dimension: 37 μm, one specimen.

Remarks: Nodospora sp. C in Richardson is close to the P. rugosa but the quality of the figures do not permit visual comparison. Steemans (unpublished) has examined material from Gotland (Hagström, 1997) and considers that P. rugosa and P? rugosa? are end-members representing intraspecific variability among the same taxon.

Genus Pseudodyadospora Johnson, 1985

Type species: Pseudodyadospora laevigata Johnson, 1985 Pseudodyadospora laevigata Johnson, 1985 (Plate 3: g)

Dimensions: 21 (29) 38 by 28 (35) 45 μm measured on 9 specimens.

Pseudodyadospora petasus Wellman and Richardson, 1993 (Plate 3: h, i) Dimensions: 19 (29) 38 μm measured on 18 specimens.

Genus Rimosotetras Burgess, 1991

Type species: Rimosotetras problematica Burgess, 1991 Rimosotetras problematica Burgess, 1991 (Plate 3: j, k)

Dimensions: 24 (42) 58 μm measured on 14 specimens.

Genus Rugosphaera Strother and Traverse, 1979

Type species: Rugosphaera cerebra Miller and Eames, 1979 Rugosphaera tuscarorensis Strother and Traverse, 1979 (Plate 3: l, m)

Dimensions: 20 (27) 31 μm measured on 10 specimens.

Remarks: Frequently occurs in monospecific clusters comprising up to 20 specimens.

Genus Segestrespora Burgess, 1991

Type species: Segestrespora membranifera (Johnson) Burgess, 1991 Segestrespora laevigata Burgess, 1991 (Plate 3: n)

Dimensions: 24 (41) 60 by 23 (34) 45 μm measured on 16 specimens.

Segestrespora (Dyadospora) membranifera (Johnson, 1985) Burgess, 1991 (Plate 3: o, p)

Dimensions: 22 (28) 38 by 28 (35) 44 μm measured on 14 specimens.

Segestrespora (Pseudodyadospora) rugosa (Johnson, 1985) Burgess, 1991 (Plate 3: q)

Dimensions: 37 by 22 μm and 51 by 33 μm, two specimens measured.

Genus Sphaerasaccus gen. nov.

Type species: Sphaerasaccus glabellus gen. and sp. nov.

Derivation of name: Latin sphaera, sphere, and saccus, sac.

Diagnosis: A subcircular to subtriangular laevigate monad enclosed within a laevigate envelope. Comparison: Rugosphaera is enclosed within a rugulate envelope.

Sphaerasaccus glabellus gen. and sp. nov. (Plate 4: a, b)

1996 Laevigate monads enclosed within a laevigate envelope in Wellman, p. 118, Plate 3: 18-20.

Derivation of name: Latin glaber, smooth.

Holotype and type locality: Nuayyim-2, Qusaiba Member, Qalibah Formation, slide 32592, 11,965.0 ft, England Finder Co-ordinates K39/-.

Diagnosis: A Sphaerasaccus enclosed within a thin laevigate envelope.

Plate 3:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a) Laevolancis chibrikovae sp. nov. slide 32708, 11,978.5 ft, F45/3, FM 1581.

  • (b-e) Laevolancis divellomedia (Chibrikova 1959) Burgess and Richardson, 1991.

  • (b) slide 32707, 11,977.5 ft, G44/4, FM 1582;

  • (c) slide 32707, 11,977.5 ft, Q37/1-2, FM 1583;

  • (d) slide 32708, 11,978.5 ft, L46/2-4, FM 1584;

  • (e) slide 32707, 11,977.5 ft, R42/3, FM 1585.

  • (f) Pachytetras rugosa Hagström 1997. Slide 32708, 11,978.5 ft, F40/3, FM 1586.

  • (g) Pseudodyadospora laevigata Johnson 1985. Slide 32708, 11,978.5 ft, J47/0, FM 1587.

  • (h-i) Pseudodyadospora petasus Wellman and Richardson, 1993.

  • (h) slide 32708, 11,978.5 ft, O39/1, FM 1588;

  • (i) slide 32708, 11,978.5 ft, P55/0, FM 1589.

  • (j-k) Rimosotetras problematica Burgess, 1991.

  • (j) slide 32583, 11,908.0 ft, J36/2, FM 1590;

  • (k) slide 32707, 11,977.5 ft, W42/4, FM 1591.

  • (l-m) Rugosphaera tuscarorensis Strother and Traverse, 1979.

  • (l) slide 32707, 11,977.5 ft, Q41/2, FM 1592;

  • (m) slide 32587, 11,911.6 ft, S38/1, FM 1593.

  • (n) Segestrepora laevigata Burgess 1991. Slide 32708, 11,978.5 ft, Q46/3, FM 1594.

  • (o-p) Segestrespora membranifera (Johnson, 1985) Burgess, 1991.

  • (o) slide 32592, 11,965.0 ft, G45/3, FM 1595;

  • (p) slide 32708, 11,978.5 ft, Z45/2, FM 1596.

  • (q) Segestrespora rugosa (Johnson, 1985) Burgess, 1991. Slide 32592, 11,965.0 ft, U46/2, FM 1597.

Plate 3:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a) Laevolancis chibrikovae sp. nov. slide 32708, 11,978.5 ft, F45/3, FM 1581.

  • (b-e) Laevolancis divellomedia (Chibrikova 1959) Burgess and Richardson, 1991.

  • (b) slide 32707, 11,977.5 ft, G44/4, FM 1582;

  • (c) slide 32707, 11,977.5 ft, Q37/1-2, FM 1583;

  • (d) slide 32708, 11,978.5 ft, L46/2-4, FM 1584;

  • (e) slide 32707, 11,977.5 ft, R42/3, FM 1585.

  • (f) Pachytetras rugosa Hagström 1997. Slide 32708, 11,978.5 ft, F40/3, FM 1586.

  • (g) Pseudodyadospora laevigata Johnson 1985. Slide 32708, 11,978.5 ft, J47/0, FM 1587.

  • (h-i) Pseudodyadospora petasus Wellman and Richardson, 1993.

  • (h) slide 32708, 11,978.5 ft, O39/1, FM 1588;

  • (i) slide 32708, 11,978.5 ft, P55/0, FM 1589.

  • (j-k) Rimosotetras problematica Burgess, 1991.

  • (j) slide 32583, 11,908.0 ft, J36/2, FM 1590;

  • (k) slide 32707, 11,977.5 ft, W42/4, FM 1591.

  • (l-m) Rugosphaera tuscarorensis Strother and Traverse, 1979.

  • (l) slide 32707, 11,977.5 ft, Q41/2, FM 1592;

  • (m) slide 32587, 11,911.6 ft, S38/1, FM 1593.

  • (n) Segestrepora laevigata Burgess 1991. Slide 32708, 11,978.5 ft, Q46/3, FM 1594.

  • (o-p) Segestrespora membranifera (Johnson, 1985) Burgess, 1991.

  • (o) slide 32592, 11,965.0 ft, G45/3, FM 1595;

  • (p) slide 32708, 11,978.5 ft, Z45/2, FM 1596.

  • (q) Segestrespora rugosa (Johnson, 1985) Burgess, 1991. Slide 32592, 11,965.0 ft, U46/2, FM 1597.

Plate 4:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Spahaerasaccus glabellus gen. and sp. nov.

  • (a) Holotype slide 32592, 11,965.0 ft, K39/0, FM 1598;

  • (b) slide 32707, 11,977.5 ft, G40/1, FM 1599.

  • (c-d) Tetrahedraletes medinensis Strother and Traverse emend. Wellman and Richardson, 1993.

  • (c) slide 32587, 11,911.6 ft, K39/2-4, FM 1600;

  • (d) slide 32587, 11,911.6 ft, M39/2-4, FM 1601.

  • (e-f) Velatitetras laevigata Burgess, 1991.

  • (e) slide 32587, 11,911.6 ft, L35/3-4, FM 1602;

  • (f) slide 32587, 11,911.6 ft, D43/1-3, FM 1603.

  • (g-h) Velatitetras retimembrana (Miller and Eames, 1982) Wellman and Richardson, 1996.

  • (g) slide 32593, 11,969.0 ft, W47/0, FM 1604;

  • (h) slide 32587, 11,911.6 ft, P38/3-4, FM 1605.

  • (i-j) Velatitetras rugosa (Strother and Traverse, 1979) Steemans, Le Hérissé and Bozdogan, 1996.

  • (i) slide 32583, 11,908.0 ft, S39/4, FM 1606.

  • (j) Velatitetras sp. slide 32708, 11,978.5 ft, X46/1-3, FM 1607.

  • (k-l) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (k) slide 32583, 11,908.0 ft, M39/0, FM 1608;

  • (l) Holotype slide 32707, 11,977.5 ft, P38/1, FM 1609.

Plate 4:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Spahaerasaccus glabellus gen. and sp. nov.

  • (a) Holotype slide 32592, 11,965.0 ft, K39/0, FM 1598;

  • (b) slide 32707, 11,977.5 ft, G40/1, FM 1599.

  • (c-d) Tetrahedraletes medinensis Strother and Traverse emend. Wellman and Richardson, 1993.

  • (c) slide 32587, 11,911.6 ft, K39/2-4, FM 1600;

  • (d) slide 32587, 11,911.6 ft, M39/2-4, FM 1601.

  • (e-f) Velatitetras laevigata Burgess, 1991.

  • (e) slide 32587, 11,911.6 ft, L35/3-4, FM 1602;

  • (f) slide 32587, 11,911.6 ft, D43/1-3, FM 1603.

  • (g-h) Velatitetras retimembrana (Miller and Eames, 1982) Wellman and Richardson, 1996.

  • (g) slide 32593, 11,969.0 ft, W47/0, FM 1604;

  • (h) slide 32587, 11,911.6 ft, P38/3-4, FM 1605.

  • (i-j) Velatitetras rugosa (Strother and Traverse, 1979) Steemans, Le Hérissé and Bozdogan, 1996.

  • (i) slide 32583, 11,908.0 ft, S39/4, FM 1606.

  • (j) Velatitetras sp. slide 32708, 11,978.5 ft, X46/1-3, FM 1607.

  • (k-l) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (k) slide 32583, 11,908.0 ft, M39/0, FM 1608;

  • (l) Holotype slide 32707, 11,977.5 ft, P38/1, FM 1609.

Description: Circular to subcircular monads with a thick laevigate wall. Enclosed within a thin, tight or loosely adherent, envelope. The envelope is abundantly folded. No contact features are present. Dimensions: 25 (32) 41 μm measured on 7 specimens.

Genus Tetrahedraletes Strother and Traverse, 1979 emended Wellman and Richardson, 1993

Type species: Tetrahedraletes medinensis Strother and Traverse, 1979

Tetrahedraletes medinensis Strother and Traverse, 1979 emended Wellman and Richardson, 1993 (Plate 4: c, d)

Dimensions: 27 (41) 56 μm measured on 77 specimens.

Genus Velatitetras Burgess, 1991

Type species: Velatitetras laevigata Burgess, 1991

Velatiteras anatoliensis Steemans, Le Hérissé and Bozdogan, 1996

Dimension: 49 (52) 58 μm measured on 3 specimens.

Remark: All specimens are too badly preserved to be photographed.

Velatitetras laevigata Burgess, 1991 (Plate 4: e, f)

Dimensions: 34 (46) 65 μm measured on 19 specimens.

Velatitetras (Nodospora) retimembrana (Miller and Eames, 1982) Wellman and Richardson, 1996 (Plate 4: g, h)

Dimensions: 36 (41.5) 66 μm measured on 8 specimens.

Velatitetras (Nodospora) rugosa (Strother and Traverse, 1979) Steemans, Le Hérissé and Bozdogan, 1996 (Plate 4: i)

Dimensions: 39 (43) 46 μm measured on 4 specimens.

Velatiteras sp. (Plate 4: j)

Description: Laevigate permanent tetrad enclosed within a verrucate envelope. Tetrad comprises subcircular to subtriangular, laevigate, spores with low equatorial crassitudes 2-3 μm wide.

Envelope firmly adherent to the tetrad, ornamented with low rounded verrucae 1-1.5 wide, 0.5-1 μm high, with a rounded top.

Dimensions: 45 μm, one specimen.

Comparison: V anatoliensis is ornamented by small grana.

Plate 5:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (a) slide 32590, 11,944.5 ft, L43/3, FM 1610;

  • (b) slide 32708, 11,978.5 ft, J55/2, FM 1611.

  • (c-d) Morphon Ambitisporites avitus Hoffmeister, 1959 sensu Steemans, Le Hérissé and Bozdogan, 1996.

  • (c) slide 32708, 11,978.5 ft, O44/2, FM 1612;

  • (d) slide 32708, 11,978.5 ft, F42/0, FM 1613.

  • (e-f) Crowned monad.

  • (e) slide 32707, 11,977.5 ft, R46/3, FM 1614;

  • (f) slide 32592, 11,965.0 ft, H45/0, FM 1615.

  • (g-h) Genus A sp. A.

  • (g) slide 32707, 11,977.5 ft, S41/1, FM 1616;

  • (h) slide 32708, 11,978.5 ft, Y56/1, FM 1617.

  • (i) Micrornamented dyads in cluster. Slide 32593, 11,969 ft, J35/4, FM 1618.

  • (j-k) Micrornamented monad.

  • (j) slide 32707, 11,977.5 ft, T45/3, FM 1619;

  • (k) slide 32587, 11,911.6 ft, K40/2-4, FM 1620.

  • (l) Micrornamented tetrad. Slide 32707, 11,977.5 ft, L40/3, FM 1621.

  • (m) Tetrad sp. Slide 32592, 11,965.0 ft, E49/1, FM 1622.

  • (n) Monad type. Slide 32707, 11,977.5 ft, U43/4, FM 1623.

Plate 5:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (a) slide 32590, 11,944.5 ft, L43/3, FM 1610;

  • (b) slide 32708, 11,978.5 ft, J55/2, FM 1611.

  • (c-d) Morphon Ambitisporites avitus Hoffmeister, 1959 sensu Steemans, Le Hérissé and Bozdogan, 1996.

  • (c) slide 32708, 11,978.5 ft, O44/2, FM 1612;

  • (d) slide 32708, 11,978.5 ft, F42/0, FM 1613.

  • (e-f) Crowned monad.

  • (e) slide 32707, 11,977.5 ft, R46/3, FM 1614;

  • (f) slide 32592, 11,965.0 ft, H45/0, FM 1615.

  • (g-h) Genus A sp. A.

  • (g) slide 32707, 11,977.5 ft, S41/1, FM 1616;

  • (h) slide 32708, 11,978.5 ft, Y56/1, FM 1617.

  • (i) Micrornamented dyads in cluster. Slide 32593, 11,969 ft, J35/4, FM 1618.

  • (j-k) Micrornamented monad.

  • (j) slide 32707, 11,977.5 ft, T45/3, FM 1619;

  • (k) slide 32587, 11,911.6 ft, K40/2-4, FM 1620.

  • (l) Micrornamented tetrad. Slide 32707, 11,977.5 ft, L40/3, FM 1621.

  • (m) Tetrad sp. Slide 32592, 11,965.0 ft, E49/1, FM 1622.

  • (n) Monad type. Slide 32707, 11,977.5 ft, U43/4, FM 1623.

Genus Vestitusdyadus gen. nov.

Type species: Vestitusdyadus qalibahinus gen. and sp. nov.

Derivation of name: Latin vestitus, to dress.

Diagnosis: Permanent cryptospore dyads composed of tightly-adherent, laevigate, sub-circular spores, with low and rounded, more or less fused, equatorial crassitudes. Dyads enclosed by two envelopes. The inner envelope is ornamented and the outer envelope is laevigate. Sculpture consist of muri forming a reticulum.

Comparison: Segestrespora Burgess, 1991 is enclosed within a solitary, ornamented or laevigate, envelope.

Remarks: The absence of a break in ornamentation at the junction between the two spores suggests that the dyad is enclosed within a continuous, ornamented, envelope. The generic variability cannot be appreciated because only one species is observed.

Vestitusdyadus qalibahinus gen. and sp. nov. (Plate 4: k, l; Plate 5: a, b)

?1996 Segestrespora? sp. A in Wellman, p. 120, Plate 3: 11-12.

Derivation of name: qalibahinus, Qalibah Formation.

Holotype and type locality: Nuayyim-2, Qusaiba Member, Qalibah Formation, 11,977.5 ft, slide 32707, England Finder Co-ordinates J45/3.

Diagnosis: A Vestitusdyadus ornamented by a perfect recticulum characterised by small lumina.

Description: Dyads with a sub-circular to circular amb enclosed within two envelopes. The thick inner envelope is closely appressed and sculptured by muri 0.5-1.5 μm wide and high, which form a regular rounded to subpolygonal reticulum 0.5-1.5 μm wide. There is no break in ornamentation at the junction between the two spores. The thin outer laevigate exoexine is variably appressed to the inner envelope and sometimes difficult to observe.

Dimensions: 30 (35) 42 by 42 (48) 58 μm measured on 8 specimens.

Comparisons: Wellman (1996) noted the presence of only one thick, ornamented, envelope in the taxon he called Segestrespora? sp. A. However, one must bear in mind that the thin outer envelope is often very difficult to discern, and it is possible that this taxon is synonymous with V. qalibahinus.

Remarks: In one case, an identical ornamentation is found on a specimen which seems to be a monad (11,965.0 ft, slide 32592, England Finder Co-ordinate L34/-).

Trilete miospore

Genus Ambitisporites Hoffmeister, 1959

Type species: Ambitisporites avitus Hoffmeister, 1959.

Morphon Ambitisporites avitus Hoffmeister sensu Steemans, Le Hérissé and Bozdogan, 1996 (Plate 5: c, d)

Dimensions: 35 and 47 μm measured on 2 specimens.

Incertae sedis

Crowned monad (Plate 5: e, f)

Description: Amb circular to subcircular in polar compression. Equatorial to subequatorial crassitude 1-3 μm wide delimits a circular to subcircular hilum. Hilum entirely laevigate. Exine over the distal surface is thicker than that over the proximal surface. A thin membrane, 5 μm wide, occurs equatorially-distally, commencing just below the crassitude. The top of this membrane is jagged with small coni less than 0.5 μm wide, high and apart.

Dimensions: 26 and 31 μm.

Genus A

Diagnosis: Ornamented and permanently fused pseudodyads, divided by a single more or less central thickened encircling band, and totally enclosed within a closely adherent to completely separated laevigate envelope.

Comparison: Segestrespora Burgess, 1991 comprises a laevigate dyad enclosed within a laevigate or ornamented envelope.

Genus A. sp. A (Plate 5: g, h)

partim 1988 Pseudodyadospora sp. B in Richardson, p. 95, Plate 16: 6-7.

?partim 1988 Pseudodyadospora sp. B in Richardson, p. 95, Plate 16: 3-5.

Description: Pseudodyad elliptical to sub-circular in lateral view and totally enclosed within an envelope. A single darkened encircling band, 2-3 μm wide, occurs at the junction between the spores. The dyads are ornamented by irregularly distributed verrucae, that are of irregular shape, 1-2 μm wide, less than 1 μm high and less than 1-1.5 μm apart.

Dimensions: 33 x 35 and 41 x 44 μm.

Remarks: Specimens described by Richardson (1988) Plate 16: 3-5 have a sculpture comprising smaller grana.

New combination with this genus based on published material not present in the Nuayyim-2 borehole:

Genus A sp. B

1988 Pseudodyadospora rugosa Johnson, in Richardson, p. 95, Plate 16: 1; Plate 17: 1-2.

Remarks: The ornamentation is on the dyads and not on the enclosing envelope.

Micrornamented dyads (Plate 5: i)

Description: Dyads circular in polar view, sometimes distally invaginated. The junction between the two spores is sometimes strongly detached. The spores possess an equatorial crassitude developed to varying degrees (very slight-pronounced). The dyads are generally isomorphic and are often preserved in more or less polar compression. The exine has a micrornamentation of pointed coni or grana less than 0.5 μm high, wide and apart.

Dimensions: 23 (27.5) 31 by 26 (34) 40 μm measured on 7 specimens.

Remarks: Micrornamented monads, dyads and tetrads are all similar except for the number of constituent spores. It is unclear if the micrornamentation represents true ornament or is an artefact. Could be preserved in cluster.

Micrornamented monads (Plate 5: j, k)

Description: Monads oval to subcircular in polar view. The exine has a micrornament of pointed coni or grana less than 0.5 μm high, wide and apart.

Dimensions: 28 (33) 41 μm measured on 10 specimens.

Comparisons: The naked laevigate monads described by Wellman (1996) are very similar but are described as laevigate. However, the microgranulation is so indistinct that it is easily missed.

Micronamented tetrads (Plate 5: l)

Description: Unfused permanent tetrads comprising subcircular to subtriangular spores. Individual spores with a rounded crassitude, which is 3-6 μm wide, and an invaginated distal surface. Distinct lines of attachment are discernible on the surface of the tetrad between the crassitudes of adjacent spores. The exine has a micrornament of pointed coni or grana less than 0.5 μm high, wide and apart.

Dimensions: 36 (39) 41 μm measured on 5 specimens.

Monads type 1 (Plate 5: m)

Description: Ornamented subcircular monad. Ornament consists of irregularly shaped verrucae, 1-5 μm wide and 0.5-1 μm high, with tops rounded to pointed, that are irregularly spaced (>0.5 to 1 μm apart).

Dimensions: 32 and 29 μm measured on two specimens.

Tetrad sp. (Plate 5: n)

Description: Tetrads of sub-circular spores joined by unfused equatorial crassitudes 2-3 μm wide. The tetrad is ornamented by irregular, subcircular-anastomosing-convoluted, verrucae 2 by 2 to 3 by 6 μm wide/long, 1-2 μm apart, 1 μm high.

Dimensions: 36 μm

BIOSTRATIGRAPHY

Spore assemblages from the Caradoc to the mid Llandovery are very similar with only minor differences reported (Gray, 1985; Richardson, 1996b; Wellman, 1996; Steemans, 1999). These assemblages are largely dominated by cryptospores: monads, dyads and tetrads. The cryptospores are either naked or enclosed within an envelope that is either laevigate or ornamented. Identical ornament occurs on all three morphotypes (i.e. monads, dyads and tetrads). The relative proportion of envelope-enclosed cryptospores decreases throughout the Llandovery and they become very rare in younger sediments. Generally, the spores comprising the polyads (dyads and tetrads) are tightly appressed and do not dissociate, as they often do in younger Silurian sediments. In this study, the only observed monads, excepting Rugosphaera, are those that have been physically broken out of polyads (e.g. I. vavdovae, I. patinatus or L.chibrikovae).

The Ordovician-Silurian boundary is included in the Nodospora sp. A-murusdensa (Richardson, 1988) or murusdensa-murusattenuata (Richardson and Edwards, 1989) Assemblage Biozones, which range from the Ashgill to the Rhuddanian (Figure 2). They are succeeded by the avitus-dilutus Biozone (Richardson and McGregor, 1986; Richardson, 1988; Burgess, 1991), which ranges from the ?late Rhuddanian to early Telychian, and by the chulus-nanus Biozone (Burgess and Richardson, 1991; Richardson, 1996b; Richardson and McGregor, 1986), which ranges from the late Telychian to the Homerian. The latter two biozones are characterised by the incoming of the genera Ambitisporites and Archaeozonotriletes respectively, and the absence of envelope-enclosed cryptospores.

Figure 2:

Intercalibrated correlations between the biostratigraphic scale I established in Libya and UK, the biostratigraphic scale II established in Turkey, the chitinozoans biostratigraphic scale (Paris et al., 1995), and the biostratigraphic scale III established in Saudi Arabia and on the basis of the literature.

Figure 2:

Intercalibrated correlations between the biostratigraphic scale I established in Libya and UK, the biostratigraphic scale II established in Turkey, the chitinozoans biostratigraphic scale (Paris et al., 1995), and the biostratigraphic scale III established in Saudi Arabia and on the basis of the literature.

Recently, rare true trilete spores (Ambitisporites avitus-dilutus) were reported from the Ashgill of Turkey (Steemans et al., 1996), where they are associated with abundant envelope-enclosed cryptospores. These new findings suggested that current spore biozonation schemes require modification. Furthermore, there have been several other recent reports of post-mid Llandovery envelope-enclosed cryptospores suggesting that such spores persist until at least the Lochkovian (Burgess and Richardson, 1995; Richardson, 1996a; Wellman and Richardson, 1996; Wellman et al., 1998). However, except for Turkey and the material from Saudi Arabia described herein, the post-mid Llandovery envelope-enclosed cryptospores represent rare occurrences and they do not constitute major elements of the total spore assemblage.

In refining the spore biozonation scheme for the Ordovician-Early Silurian we have considered a number of important events (Figure 2). The first is the incoming of A. avitus-dilutus in the Hirnantian. The second is the first appearance of true L. divellomedia. Regarding the latter, there is currently no continuous section where the incoming of L. divellomedia is reported. This taxon is not known from the Ordovician, but there are no observations from the top of the Ashgill. In the present study true L. divellomedia is shown to occur in the Rhuddanian. We therefore suggest that L. divellomedium first occurs in the interval between the latest Hirnantian-earliest Rhuddanian. It is not easy to precisely locate the first appearance of I. vavrdovae and I. patinatus as both species were previously grouped in the same taxon (A? vavrdovae). To solve this problem a comprehensive revision of the published material is needed. The oldest Imperfectotriletes are reported from the Ashgill of Libya (Richardson, 1988) and Turkey (Steemans et al., 1996), prior to the first appearance of A. avitus-dilutus. A potentially earlier report of Imperfectotriletes patinatus is from the Melez Chograne Formation of Libya that is interpreted as Caradoc in age (Gray et al., 1982), although the evidence used in age determination has been questioned (Richardson and McGregor, 1986).

Based on our findings from Saudi Arabia and a review of published data, we propose the following biostratigraphic subdivisions. It should be noted that these biozones are erected based on limited data, with gaps in both our temporal and spatial understanding, and thus require testing. However, we anticipate that as knowledge improves the scheme can be further modified. It should also be noted that we currently have no outcrop in which the base of these biozones could be defined.

Imperfectotriletes spp.- Laevolancis divellomedia Assemblage Biozone.

Age: Ashgill to Telychian.

Occurrence: Ashgill, Turkey (Steemans et al., 1996); Rhuddanian, Saudi Arabia (this work and Wellman et al., this volume); Llandovery, Pennsylvania (Strother and Traverse, 1979); Llandovery, Virginia (Pratt et al., 1978); Ashgill to Telychian, Libya (Richardson, 1988; Steemans et al., 1996); Ashgill and Llandovery, southwest Wales (Burgess, 1991).

Description: Cryptospores and trilete spores present, in addition to pseudo-trilete monads derived from physically dissociated cryptospores. The assemblage consists of cryptospore monads, dyads and tetrads, that are either naked or envelope-enclosed. Envelopes are either laevigate or ornamented: reticulate, rugulate, murinate and granulate. Trilete spores are generally rare, but there abundance progressively increases in younger strata. The abundance of envelope-enclosed cryptospores progressively decreases in younger strata.

Subdivisions:

Imperfectotriletes spp. Interval Biozone.

Age: Ashgill and Rhuddanian.

Occurrence: Ashgillian, Turkey (Steemans et al., 1996); Ashgillian, Libya (Richardson, 1988).

Description: Incoming of Imperfectotriletes. spp. Sub-biozone α is characterised by the absence of true trilete spores (Ambitisporites spp.). Sub-biozone β is defined by the first occurrence of true trilete spores, but such spores are rare throughout this sub-biozone.

Laevolancis divellomedia Interval Biozone.

Age: Rhuddanian to Aeronian.

Occurrence: Rhuddanian, Saudi Arabia (this work and Wellman et al., this issue); Llandovery, Brazil and Paraguay (Melo, 1997; Melo and Steemans, 1997, unpublished data).

Description: Incoming of L. divellomedium. Sub-biozone α is characterised by abundant envelope-enclosed cryptospores, and rare true trilete spores (Ambitisporites spp.). Sub-biozone β is characterised by rare envelope-enclosed cryptospores, but true trilete spores become more abundant. The transition between the sub-biozones is progressive.

The spore assemblages described herein are very similar in all of the analysed samples. All the samples belong to the Imperfectotriletes spp.-L. divellomedia Assemblage Biozone, and more precisely to the L. divellomedia Interval Biozone. The rarity of true trilete spores and the abundance of envelope-enclosed cryptospores in samples from cores 10 and the lower part of core 9 suggest correlation with sub-biozone α (Figure 3). The upper part of core 9 and core 8 contain only rare envelope-enclosed cryptospores, but true trilete spores remain rare too, thus suggesting correlation with the upper part of sub-biozone α.

Figure 3:

Stratigraphic distribution of the cryptospores/spores from the Nuayyim-2 borehole. Chitinozoan biozones (Paris et al., 1995). (A) Downwards or upwards known extension of the naked cryptospores; (B) range of the naked cryptospores in the Nuayyim-2 borehole; (C) downwards or upwards known extension of the cryptospores enclosed within an envelope; (D) range of the cryptospores enclosed within an envelope in the Nuayyim-2 borehole; (E) downwards or upwards known extension of the trilete spores; and (F) range of the trilete spores in the Nuayyim-2 borehole.

Figure 3:

Stratigraphic distribution of the cryptospores/spores from the Nuayyim-2 borehole. Chitinozoan biozones (Paris et al., 1995). (A) Downwards or upwards known extension of the naked cryptospores; (B) range of the naked cryptospores in the Nuayyim-2 borehole; (C) downwards or upwards known extension of the cryptospores enclosed within an envelope; (D) range of the cryptospores enclosed within an envelope in the Nuayyim-2 borehole; (E) downwards or upwards known extension of the trilete spores; and (F) range of the trilete spores in the Nuayyim-2 borehole.

The Genus Hispanaediscus has previously not been recovered below the Homerian (Burgess and Richardson, 1991; Dufka, 1995; Wellman, 1993). Therefore, the oldest occurrence of this genus is now found in the Rhuddanian of Saudi Arabia. However, this genus is more diversified and progressively more abundant in the Homerian.

PALAEOGEOGRAPHY

Hitherto described Ordovician to early Llandovery spore assemblages are all very similar in composition with very little variation reported (Gray, 1985; Richardson 1996; Wellman, 1996; Steemans, 1999). As shown in Figure 4, similar spore assemblages are described from palaeogeographically widespread localities ranging from the palaeoequator, e.g. China (Wang et al., 1997), to regions close to the southern pole, e.g. Brazil or Paraguay (Melo, 1997; Melo and Steemans, 1997). These findings suggest that the parent plants of these spores were cosmopolitan and were able to survive under varied climatic conditions. This is a possible explanation of the reason why there is no impoverishment in spore biodiversity during the Hirnantian glaciation: the parent plants would be tolerant of climatic changes associated with glaciation.

Figure 4:

Palaeogeographical map at the Llandovery (Scotese and McKerrow, 1990). Localities where cryptsopores/trilete spores are described. (1) Ashgill, Kentucky, USA (Gray, 1985; Gray, 1988); Ashgill, Illinois, USA (Strother, 1991); Llandovery, Pennsylvania, USA (Johnson, 1985; Strother and Traverse, 1979); Llandovery, New York, USA (Miller and Eames, 1982); Llandovery, Virginia, USA (Pratt et al., 1978); (2) Llandovery, Ontario, Canada (Eley and Legault, 1988); (3) Llandovery, Anticosti Island, Quebec, Canada (Duffield, 1985); (4) Caradoc, Southern Britain, UK (Wellman, 1996); Ashgill and Llandovery, Wales, UK (Burgess, 1991); (5) Llandovery, Norway (Smelror, 1987); (6) Ashgill or Llandovery, Belgium (Steemans, unpublished); (7) Bohêmia, Czeckia (Vavrdova, 1984; Vavrdova, 1988, 1989); (8) Llandovery, Libya (Gray et al., 1982); Ashgill-Llandovery, Libya (Richardson, 1988); (9) Ashgill, Bulgaria (Lakova et al., 1992); (10) Ashgill, Tarim, China (Wang et al., 1997); (11) Ashgill, Turkey (Steemans et al., 1996); (12) Llandovery, Saudi Arabia (the present study; Wellman et al., this volume); (13) Llandovery, Brazil (Melo, 1997; Melo and Steemans, 1997; and Steemans unpublished); (14) Llandovery, Paraguay (Gray et al., 1992); Llandovery, Paraguay (Pereira and Steemans, unpublished data); (15) latest Ordovician-earliest Llandovery, South Africa (Gray et al., 1986); and (16) latest Ordovician-earliest Llandovery, Australia (Foster and Williams, 1991).

Figure 4:

Palaeogeographical map at the Llandovery (Scotese and McKerrow, 1990). Localities where cryptsopores/trilete spores are described. (1) Ashgill, Kentucky, USA (Gray, 1985; Gray, 1988); Ashgill, Illinois, USA (Strother, 1991); Llandovery, Pennsylvania, USA (Johnson, 1985; Strother and Traverse, 1979); Llandovery, New York, USA (Miller and Eames, 1982); Llandovery, Virginia, USA (Pratt et al., 1978); (2) Llandovery, Ontario, Canada (Eley and Legault, 1988); (3) Llandovery, Anticosti Island, Quebec, Canada (Duffield, 1985); (4) Caradoc, Southern Britain, UK (Wellman, 1996); Ashgill and Llandovery, Wales, UK (Burgess, 1991); (5) Llandovery, Norway (Smelror, 1987); (6) Ashgill or Llandovery, Belgium (Steemans, unpublished); (7) Bohêmia, Czeckia (Vavrdova, 1984; Vavrdova, 1988, 1989); (8) Llandovery, Libya (Gray et al., 1982); Ashgill-Llandovery, Libya (Richardson, 1988); (9) Ashgill, Bulgaria (Lakova et al., 1992); (10) Ashgill, Tarim, China (Wang et al., 1997); (11) Ashgill, Turkey (Steemans et al., 1996); (12) Llandovery, Saudi Arabia (the present study; Wellman et al., this volume); (13) Llandovery, Brazil (Melo, 1997; Melo and Steemans, 1997; and Steemans unpublished); (14) Llandovery, Paraguay (Gray et al., 1992); Llandovery, Paraguay (Pereira and Steemans, unpublished data); (15) latest Ordovician-earliest Llandovery, South Africa (Gray et al., 1986); and (16) latest Ordovician-earliest Llandovery, Australia (Foster and Williams, 1991).

CONCLUSIONS

The study of the Llandovery samples from the Nuayyim-2 borehole has allowed the description of six new species and four new genera of cryptospores and has consequently increased considerably our knowledge of the miospore diversity from this poorly known inteval. The improved precision in the definition of what is considered to be a true trilete mark now allows a clearer boundary to be drawn between cryptospores and true trilete spores. Therefore, the previously named species ?Ambitisporites vavrdovae is now transferred to the synonymy of the new genus Imperfectotriletes. The presence of rare true trilete spores in the assemblages examined, indicates that these miospores appeared earlier in eastern Gondwana (Turkey and Saudi Arabia) than elsewhere. A biostratigraphic scale is proposed for the Ashgill to late Llandovery interval. The one new Assemblage Biozone created, is divided into two Interval Biozones, both being further subdivided into two sub-biozones. It is accepted that the stratigraphic data on which these biozones are established still lack precision, particularly if they are used for long range correlations between palaeogeographically distant areas. Nevertheless, these biozones appear useful for local correlations.

APPENDIX

List of cited cryptospores and trilete spores taxa.

Abditusdyadus laevigatus Wellman and Richardson, 1996

Ambitisporites avitus Hoffmeister 1959 sensu Steemans, Le Hérissé and Bozdogan, 1996

Ambitisporites? vavrdovae Richardson, 1988

Archaeozonotriletes chulus (Cramer, 1966) Richardson and Lister, 1969

Chelinohilates maculatus sp. nov.

Chelinohilates lornensis Wellman and Richardson, 1996

Complectitetras alhajrii gen. and sp. nov.

Dyadospora murusattenuata Strother and Traverse, 1979 sensu Steemans, Le Hérissé and Bozdogan,

1996 Hispanaediscus? sp. 2 Wellman, Higgs and

Steemans, 2000 (this volume) Hispanaediscus sp. Steemans, Higgs and Wellman,

2000 (this volume) Hispanaediscus wenlockensis Burgess and

Richardson, 1991 Imperfectotriletes patinatus gen. and sp. nov.

Imperfectotrilets vavrdovae gen. and sp. nov.

Laevolancis chibrikovae sp. nov.

Laevolancis divellomedia (Chibrikova, 1959) Burgess and Richardson, 1991

Leiotriletes sp. I Martin, 1973

Pachytetras rugosa Hagström, 1997

Pseudodyadospora laevigata Johnson, 1985

Pseudodyadospora petasus Wellman and Richardson, 1993

Pseudodyadospora rugosa Johnson 1985, in Richardson, 1988

Pseudodyadospora sp. B Richardson, 1988

Rimosotetras problematica Burgess, 1991

Rugosphaera tuscarorensis Strother and Traverse, 1979

Segestrespora membranifera (Johnson, 1985) Burgess, 1991

Segestrespora rugosa (Johnson, 1985) Burgess, 1991

Segestrespora laevigata Burgess, 1991

Sphaerasaccus glabellus gen. and sp. nov.

Tetrahedraletes medinensis Strother and Traverse, emended Wellman and Richardson, 1993 Velatiteras anatoliensis Steemans, Le Hérissé and Bozdogan, 1996 Velatitetras sp. Steemans, Higgs and Wellman, 2000 (this volume)

Velatitetras retimembrana (Miller and Eames, 1982) Wellman and Richardson, 1996

Velatitetras rugosa Steemans, Le Hérissé and Bozdogan, 1996

Velatitetras cristata Burgess and Richardson, 1995

Velatitetras laevigata Burgess, 1991

Vestitusdyadus qalibahinus gen. et sp. nov.

ACKNOWLEDGEMENT

The authors acknowledge with gratitude the Saudi Arabian Ministry of Petroleum and Mineral Resources and the Saudi Arabian Oil Company for permission to publish this study.

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ABOUT THE AUTHORS

Philippe Steemans received his PhD degree in Geology from Liège University, Belgium, in 1986. He worked for two years in limestone quarries with the Carmeuse Society. Since 1990 he has been employed by the National Fund for Scientific Research in Belgium as a Research Associate. He is specialised in the palynology (miospores and cryptospores) of the Ordovician, Silurian and Devonian.

Ken T. Higgs is a Senior Lecturer in Geology at University College Cork, Ireland. He received his BSc in 1971 and his PhD in 1975 from the University of Sheffield. He then joined the Geological Survey of Ireland in 1975 as a Palynologist and Stratigrapher. In 1986 he was appointed as Lecturer in palaeontology and stratigraphy in the Department of Geology at University College Cork, where he has established a research laboratory in Palaeozoic and Mesozoic palynology.

Charles H. Wellman was awarded a BSc (Hons) degree in Geology from the University of Southampton in 1987 and a PhD from Cardiff University in 1991. His PhD research was conducted jointly between the Natural History Museum (London) and Cardiff University and involved a study of spore assemblages from the Silurian-Devonian Old Red Sandstone deposits of Scotland. Charles subsequently worked on a number of post-doctoral research projects studying various aspects of Ordovician-Devonian terrestrial palynology and palaeobotany, as well as spending time in industry as a Petroleum Geologist and Environmental Geoscientist. In 1997 Charles was appointed “Lecturer in Palynology” in the Centre for Palynology of the University of Sheffield, where he teaches and continues his research.

Figures & Tables

Figure 1:

Palaeozoic outcrops on the Arabian Peninsula, and the Nuayyim-2 well discussed in this study.

Figure 1:

Palaeozoic outcrops on the Arabian Peninsula, and the Nuayyim-2 well discussed in this study.

Plate 1:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-d) Abditusdyadus laevigatus Wellman and Richardson 1996.

  • (a) slide 32592, 11,965.0 ft, S38/3, FM 1554;

  • (b) slide 32592, 11,965.0 ft, M40/4, FM 1555;

  • (c) slide 32708, 11978.5 ft, V44/1, FM 1556;

  • (d) slide 32708, 11,978.5 ft, K54/2-4, FM 1557.

  • (e-h) Chelinohilates maculatus sp. nov.

  • (e) Holotype slide 32708, 11,978.5 ft, N46/3, FM 1558;

  • (f) slide 32593, 11,965.0 ft, W46/2, FM 1559;

  • (g) slide 32587, 11,911.6 ft, S41/0, FM 1560;

  • (h) slide 32592, 11,965.0 ft, M33/3, FM 1561.

  • (i-k) Complectitetras alhajrii gen. and sp. nov.

  • (i) slide 32708, 11,978.5 ft, P55/2, FM 1562;

  • (j) Holotype slide 32707, 11,977.5 ft, L39/0, FM 1563;

  • (k) slide 32707, 11,977.5 ft, J45/3, FM 1564.

  • (l) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensu Steemans, Le Hérissé and Bozdogan, 1996. Slide 32708, 11,978.5 ft, T41/0, FM 1565.

Plate 1:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-d) Abditusdyadus laevigatus Wellman and Richardson 1996.

  • (a) slide 32592, 11,965.0 ft, S38/3, FM 1554;

  • (b) slide 32592, 11,965.0 ft, M40/4, FM 1555;

  • (c) slide 32708, 11978.5 ft, V44/1, FM 1556;

  • (d) slide 32708, 11,978.5 ft, K54/2-4, FM 1557.

  • (e-h) Chelinohilates maculatus sp. nov.

  • (e) Holotype slide 32708, 11,978.5 ft, N46/3, FM 1558;

  • (f) slide 32593, 11,965.0 ft, W46/2, FM 1559;

  • (g) slide 32587, 11,911.6 ft, S41/0, FM 1560;

  • (h) slide 32592, 11,965.0 ft, M33/3, FM 1561.

  • (i-k) Complectitetras alhajrii gen. and sp. nov.

  • (i) slide 32708, 11,978.5 ft, P55/2, FM 1562;

  • (j) Holotype slide 32707, 11,977.5 ft, L39/0, FM 1563;

  • (k) slide 32707, 11,977.5 ft, J45/3, FM 1564.

  • (l) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensu Steemans, Le Hérissé and Bozdogan, 1996. Slide 32708, 11,978.5 ft, T41/0, FM 1565.

Plate 2:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensus Steemans, Le Hérissé and Bozdogan, 1996.

  • (a) slide 32708, 11,978.5 ft, U41/0, FM 1566;

  • (b) slide 32707, 11,977.5 ft, O42/0, FM 1567.

  • (c) Hispanaedicus ?sp. 2. Wellman, Higgs and Steemans, 2000. Slide 32592, 11,965 ft, L38/3, FM 1568.

  • (d) Hispanaediscus sp. B. slide 32708, 11,978.5 ft, O56/0, FM 1569.

  • (e-h) Imperfectotriletes patinatus gen. and sp. nov.

  • (e) slide 32708, 11,978.5 ft, G45/3, FM 1570;

  • (f) slide 32708, 11,978.5 ft, X46/1, FM 1571;

  • (g) slide 32708, 11,978.5 ft, T39/4, FM 1572;

  • (h) Holotype slide 32707, 11,977.5 ft, L45/0, FM 1573.

  • (i-m) Imperfectotriletes vavrdovae (Richardson, 1988) gen. and comb. nov.

  • (i) slide 32708, 11,978.5 ft, O44/1, FM 1574;

  • (j) slide 32592, 11,965.0 ft, M47/4, FM 1575;

  • (k) slide 32707, 11,977.5 ft, G39/0, FM 1576;

  • (l) slide 32708, 11,978.5 ft, G45/3, FM 1577;

  • (m) slide 32592, 11,965.0 ft, U41/0, FM 1578.

  • (n-o) Laevolancis chibrikovae sp. nov.

  • (n) slide 32707, 11,977.5 ft, Q43/3, FM 1579;

  • (o) Holotype slide 32592, 11,965 ft, U45/4, FM 1580.

Plate 2:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Morphon Dyadaspora murusattenuata Strother and Traverse, 1979 sensus Steemans, Le Hérissé and Bozdogan, 1996.

  • (a) slide 32708, 11,978.5 ft, U41/0, FM 1566;

  • (b) slide 32707, 11,977.5 ft, O42/0, FM 1567.

  • (c) Hispanaedicus ?sp. 2. Wellman, Higgs and Steemans, 2000. Slide 32592, 11,965 ft, L38/3, FM 1568.

  • (d) Hispanaediscus sp. B. slide 32708, 11,978.5 ft, O56/0, FM 1569.

  • (e-h) Imperfectotriletes patinatus gen. and sp. nov.

  • (e) slide 32708, 11,978.5 ft, G45/3, FM 1570;

  • (f) slide 32708, 11,978.5 ft, X46/1, FM 1571;

  • (g) slide 32708, 11,978.5 ft, T39/4, FM 1572;

  • (h) Holotype slide 32707, 11,977.5 ft, L45/0, FM 1573.

  • (i-m) Imperfectotriletes vavrdovae (Richardson, 1988) gen. and comb. nov.

  • (i) slide 32708, 11,978.5 ft, O44/1, FM 1574;

  • (j) slide 32592, 11,965.0 ft, M47/4, FM 1575;

  • (k) slide 32707, 11,977.5 ft, G39/0, FM 1576;

  • (l) slide 32708, 11,978.5 ft, G45/3, FM 1577;

  • (m) slide 32592, 11,965.0 ft, U41/0, FM 1578.

  • (n-o) Laevolancis chibrikovae sp. nov.

  • (n) slide 32707, 11,977.5 ft, Q43/3, FM 1579;

  • (o) Holotype slide 32592, 11,965 ft, U45/4, FM 1580.

Plate 3:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a) Laevolancis chibrikovae sp. nov. slide 32708, 11,978.5 ft, F45/3, FM 1581.

  • (b-e) Laevolancis divellomedia (Chibrikova 1959) Burgess and Richardson, 1991.

  • (b) slide 32707, 11,977.5 ft, G44/4, FM 1582;

  • (c) slide 32707, 11,977.5 ft, Q37/1-2, FM 1583;

  • (d) slide 32708, 11,978.5 ft, L46/2-4, FM 1584;

  • (e) slide 32707, 11,977.5 ft, R42/3, FM 1585.

  • (f) Pachytetras rugosa Hagström 1997. Slide 32708, 11,978.5 ft, F40/3, FM 1586.

  • (g) Pseudodyadospora laevigata Johnson 1985. Slide 32708, 11,978.5 ft, J47/0, FM 1587.

  • (h-i) Pseudodyadospora petasus Wellman and Richardson, 1993.

  • (h) slide 32708, 11,978.5 ft, O39/1, FM 1588;

  • (i) slide 32708, 11,978.5 ft, P55/0, FM 1589.

  • (j-k) Rimosotetras problematica Burgess, 1991.

  • (j) slide 32583, 11,908.0 ft, J36/2, FM 1590;

  • (k) slide 32707, 11,977.5 ft, W42/4, FM 1591.

  • (l-m) Rugosphaera tuscarorensis Strother and Traverse, 1979.

  • (l) slide 32707, 11,977.5 ft, Q41/2, FM 1592;

  • (m) slide 32587, 11,911.6 ft, S38/1, FM 1593.

  • (n) Segestrepora laevigata Burgess 1991. Slide 32708, 11,978.5 ft, Q46/3, FM 1594.

  • (o-p) Segestrespora membranifera (Johnson, 1985) Burgess, 1991.

  • (o) slide 32592, 11,965.0 ft, G45/3, FM 1595;

  • (p) slide 32708, 11,978.5 ft, Z45/2, FM 1596.

  • (q) Segestrespora rugosa (Johnson, 1985) Burgess, 1991. Slide 32592, 11,965.0 ft, U46/2, FM 1597.

Plate 3:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a) Laevolancis chibrikovae sp. nov. slide 32708, 11,978.5 ft, F45/3, FM 1581.

  • (b-e) Laevolancis divellomedia (Chibrikova 1959) Burgess and Richardson, 1991.

  • (b) slide 32707, 11,977.5 ft, G44/4, FM 1582;

  • (c) slide 32707, 11,977.5 ft, Q37/1-2, FM 1583;

  • (d) slide 32708, 11,978.5 ft, L46/2-4, FM 1584;

  • (e) slide 32707, 11,977.5 ft, R42/3, FM 1585.

  • (f) Pachytetras rugosa Hagström 1997. Slide 32708, 11,978.5 ft, F40/3, FM 1586.

  • (g) Pseudodyadospora laevigata Johnson 1985. Slide 32708, 11,978.5 ft, J47/0, FM 1587.

  • (h-i) Pseudodyadospora petasus Wellman and Richardson, 1993.

  • (h) slide 32708, 11,978.5 ft, O39/1, FM 1588;

  • (i) slide 32708, 11,978.5 ft, P55/0, FM 1589.

  • (j-k) Rimosotetras problematica Burgess, 1991.

  • (j) slide 32583, 11,908.0 ft, J36/2, FM 1590;

  • (k) slide 32707, 11,977.5 ft, W42/4, FM 1591.

  • (l-m) Rugosphaera tuscarorensis Strother and Traverse, 1979.

  • (l) slide 32707, 11,977.5 ft, Q41/2, FM 1592;

  • (m) slide 32587, 11,911.6 ft, S38/1, FM 1593.

  • (n) Segestrepora laevigata Burgess 1991. Slide 32708, 11,978.5 ft, Q46/3, FM 1594.

  • (o-p) Segestrespora membranifera (Johnson, 1985) Burgess, 1991.

  • (o) slide 32592, 11,965.0 ft, G45/3, FM 1595;

  • (p) slide 32708, 11,978.5 ft, Z45/2, FM 1596.

  • (q) Segestrespora rugosa (Johnson, 1985) Burgess, 1991. Slide 32592, 11,965.0 ft, U46/2, FM 1597.

Plate 4:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Spahaerasaccus glabellus gen. and sp. nov.

  • (a) Holotype slide 32592, 11,965.0 ft, K39/0, FM 1598;

  • (b) slide 32707, 11,977.5 ft, G40/1, FM 1599.

  • (c-d) Tetrahedraletes medinensis Strother and Traverse emend. Wellman and Richardson, 1993.

  • (c) slide 32587, 11,911.6 ft, K39/2-4, FM 1600;

  • (d) slide 32587, 11,911.6 ft, M39/2-4, FM 1601.

  • (e-f) Velatitetras laevigata Burgess, 1991.

  • (e) slide 32587, 11,911.6 ft, L35/3-4, FM 1602;

  • (f) slide 32587, 11,911.6 ft, D43/1-3, FM 1603.

  • (g-h) Velatitetras retimembrana (Miller and Eames, 1982) Wellman and Richardson, 1996.

  • (g) slide 32593, 11,969.0 ft, W47/0, FM 1604;

  • (h) slide 32587, 11,911.6 ft, P38/3-4, FM 1605.

  • (i-j) Velatitetras rugosa (Strother and Traverse, 1979) Steemans, Le Hérissé and Bozdogan, 1996.

  • (i) slide 32583, 11,908.0 ft, S39/4, FM 1606.

  • (j) Velatitetras sp. slide 32708, 11,978.5 ft, X46/1-3, FM 1607.

  • (k-l) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (k) slide 32583, 11,908.0 ft, M39/0, FM 1608;

  • (l) Holotype slide 32707, 11,977.5 ft, P38/1, FM 1609.

Plate 4:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Spahaerasaccus glabellus gen. and sp. nov.

  • (a) Holotype slide 32592, 11,965.0 ft, K39/0, FM 1598;

  • (b) slide 32707, 11,977.5 ft, G40/1, FM 1599.

  • (c-d) Tetrahedraletes medinensis Strother and Traverse emend. Wellman and Richardson, 1993.

  • (c) slide 32587, 11,911.6 ft, K39/2-4, FM 1600;

  • (d) slide 32587, 11,911.6 ft, M39/2-4, FM 1601.

  • (e-f) Velatitetras laevigata Burgess, 1991.

  • (e) slide 32587, 11,911.6 ft, L35/3-4, FM 1602;

  • (f) slide 32587, 11,911.6 ft, D43/1-3, FM 1603.

  • (g-h) Velatitetras retimembrana (Miller and Eames, 1982) Wellman and Richardson, 1996.

  • (g) slide 32593, 11,969.0 ft, W47/0, FM 1604;

  • (h) slide 32587, 11,911.6 ft, P38/3-4, FM 1605.

  • (i-j) Velatitetras rugosa (Strother and Traverse, 1979) Steemans, Le Hérissé and Bozdogan, 1996.

  • (i) slide 32583, 11,908.0 ft, S39/4, FM 1606.

  • (j) Velatitetras sp. slide 32708, 11,978.5 ft, X46/1-3, FM 1607.

  • (k-l) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (k) slide 32583, 11,908.0 ft, M39/0, FM 1608;

  • (l) Holotype slide 32707, 11,977.5 ft, P38/1, FM 1609.

Plate 5:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (a) slide 32590, 11,944.5 ft, L43/3, FM 1610;

  • (b) slide 32708, 11,978.5 ft, J55/2, FM 1611.

  • (c-d) Morphon Ambitisporites avitus Hoffmeister, 1959 sensu Steemans, Le Hérissé and Bozdogan, 1996.

  • (c) slide 32708, 11,978.5 ft, O44/2, FM 1612;

  • (d) slide 32708, 11,978.5 ft, F42/0, FM 1613.

  • (e-f) Crowned monad.

  • (e) slide 32707, 11,977.5 ft, R46/3, FM 1614;

  • (f) slide 32592, 11,965.0 ft, H45/0, FM 1615.

  • (g-h) Genus A sp. A.

  • (g) slide 32707, 11,977.5 ft, S41/1, FM 1616;

  • (h) slide 32708, 11,978.5 ft, Y56/1, FM 1617.

  • (i) Micrornamented dyads in cluster. Slide 32593, 11,969 ft, J35/4, FM 1618.

  • (j-k) Micrornamented monad.

  • (j) slide 32707, 11,977.5 ft, T45/3, FM 1619;

  • (k) slide 32587, 11,911.6 ft, K40/2-4, FM 1620.

  • (l) Micrornamented tetrad. Slide 32707, 11,977.5 ft, L40/3, FM 1621.

  • (m) Tetrad sp. Slide 32592, 11,965.0 ft, E49/1, FM 1622.

  • (n) Monad type. Slide 32707, 11,977.5 ft, U43/4, FM 1623.

Plate 5:

All spores at magnification x 1,100. Figured material is housed in the Palaeontological Collections of the Natural History Museum, London. Well names and sample depths are followed by England Finder co-ordinates and Museum Collection Number.

  • (a-b) Vestidusdyadus qalibahinus gen. and sp. nov.

  • (a) slide 32590, 11,944.5 ft, L43/3, FM 1610;

  • (b) slide 32708, 11,978.5 ft, J55/2, FM 1611.

  • (c-d) Morphon Ambitisporites avitus Hoffmeister, 1959 sensu Steemans, Le Hérissé and Bozdogan, 1996.

  • (c) slide 32708, 11,978.5 ft, O44/2, FM 1612;

  • (d) slide 32708, 11,978.5 ft, F42/0, FM 1613.

  • (e-f) Crowned monad.

  • (e) slide 32707, 11,977.5 ft, R46/3, FM 1614;

  • (f) slide 32592, 11,965.0 ft, H45/0, FM 1615.

  • (g-h) Genus A sp. A.

  • (g) slide 32707, 11,977.5 ft, S41/1, FM 1616;

  • (h) slide 32708, 11,978.5 ft, Y56/1, FM 1617.

  • (i) Micrornamented dyads in cluster. Slide 32593, 11,969 ft, J35/4, FM 1618.

  • (j-k) Micrornamented monad.

  • (j) slide 32707, 11,977.5 ft, T45/3, FM 1619;

  • (k) slide 32587, 11,911.6 ft, K40/2-4, FM 1620.

  • (l) Micrornamented tetrad. Slide 32707, 11,977.5 ft, L40/3, FM 1621.

  • (m) Tetrad sp. Slide 32592, 11,965.0 ft, E49/1, FM 1622.

  • (n) Monad type. Slide 32707, 11,977.5 ft, U43/4, FM 1623.

Figure 2:

Intercalibrated correlations between the biostratigraphic scale I established in Libya and UK, the biostratigraphic scale II established in Turkey, the chitinozoans biostratigraphic scale (Paris et al., 1995), and the biostratigraphic scale III established in Saudi Arabia and on the basis of the literature.

Figure 2:

Intercalibrated correlations between the biostratigraphic scale I established in Libya and UK, the biostratigraphic scale II established in Turkey, the chitinozoans biostratigraphic scale (Paris et al., 1995), and the biostratigraphic scale III established in Saudi Arabia and on the basis of the literature.

Figure 3:

Stratigraphic distribution of the cryptospores/spores from the Nuayyim-2 borehole. Chitinozoan biozones (Paris et al., 1995). (A) Downwards or upwards known extension of the naked cryptospores; (B) range of the naked cryptospores in the Nuayyim-2 borehole; (C) downwards or upwards known extension of the cryptospores enclosed within an envelope; (D) range of the cryptospores enclosed within an envelope in the Nuayyim-2 borehole; (E) downwards or upwards known extension of the trilete spores; and (F) range of the trilete spores in the Nuayyim-2 borehole.

Figure 3:

Stratigraphic distribution of the cryptospores/spores from the Nuayyim-2 borehole. Chitinozoan biozones (Paris et al., 1995). (A) Downwards or upwards known extension of the naked cryptospores; (B) range of the naked cryptospores in the Nuayyim-2 borehole; (C) downwards or upwards known extension of the cryptospores enclosed within an envelope; (D) range of the cryptospores enclosed within an envelope in the Nuayyim-2 borehole; (E) downwards or upwards known extension of the trilete spores; and (F) range of the trilete spores in the Nuayyim-2 borehole.

Figure 4:

Palaeogeographical map at the Llandovery (Scotese and McKerrow, 1990). Localities where cryptsopores/trilete spores are described. (1) Ashgill, Kentucky, USA (Gray, 1985; Gray, 1988); Ashgill, Illinois, USA (Strother, 1991); Llandovery, Pennsylvania, USA (Johnson, 1985; Strother and Traverse, 1979); Llandovery, New York, USA (Miller and Eames, 1982); Llandovery, Virginia, USA (Pratt et al., 1978); (2) Llandovery, Ontario, Canada (Eley and Legault, 1988); (3) Llandovery, Anticosti Island, Quebec, Canada (Duffield, 1985); (4) Caradoc, Southern Britain, UK (Wellman, 1996); Ashgill and Llandovery, Wales, UK (Burgess, 1991); (5) Llandovery, Norway (Smelror, 1987); (6) Ashgill or Llandovery, Belgium (Steemans, unpublished); (7) Bohêmia, Czeckia (Vavrdova, 1984; Vavrdova, 1988, 1989); (8) Llandovery, Libya (Gray et al., 1982); Ashgill-Llandovery, Libya (Richardson, 1988); (9) Ashgill, Bulgaria (Lakova et al., 1992); (10) Ashgill, Tarim, China (Wang et al., 1997); (11) Ashgill, Turkey (Steemans et al., 1996); (12) Llandovery, Saudi Arabia (the present study; Wellman et al., this volume); (13) Llandovery, Brazil (Melo, 1997; Melo and Steemans, 1997; and Steemans unpublished); (14) Llandovery, Paraguay (Gray et al., 1992); Llandovery, Paraguay (Pereira and Steemans, unpublished data); (15) latest Ordovician-earliest Llandovery, South Africa (Gray et al., 1986); and (16) latest Ordovician-earliest Llandovery, Australia (Foster and Williams, 1991).

Figure 4:

Palaeogeographical map at the Llandovery (Scotese and McKerrow, 1990). Localities where cryptsopores/trilete spores are described. (1) Ashgill, Kentucky, USA (Gray, 1985; Gray, 1988); Ashgill, Illinois, USA (Strother, 1991); Llandovery, Pennsylvania, USA (Johnson, 1985; Strother and Traverse, 1979); Llandovery, New York, USA (Miller and Eames, 1982); Llandovery, Virginia, USA (Pratt et al., 1978); (2) Llandovery, Ontario, Canada (Eley and Legault, 1988); (3) Llandovery, Anticosti Island, Quebec, Canada (Duffield, 1985); (4) Caradoc, Southern Britain, UK (Wellman, 1996); Ashgill and Llandovery, Wales, UK (Burgess, 1991); (5) Llandovery, Norway (Smelror, 1987); (6) Ashgill or Llandovery, Belgium (Steemans, unpublished); (7) Bohêmia, Czeckia (Vavrdova, 1984; Vavrdova, 1988, 1989); (8) Llandovery, Libya (Gray et al., 1982); Ashgill-Llandovery, Libya (Richardson, 1988); (9) Ashgill, Bulgaria (Lakova et al., 1992); (10) Ashgill, Tarim, China (Wang et al., 1997); (11) Ashgill, Turkey (Steemans et al., 1996); (12) Llandovery, Saudi Arabia (the present study; Wellman et al., this volume); (13) Llandovery, Brazil (Melo, 1997; Melo and Steemans, 1997; and Steemans unpublished); (14) Llandovery, Paraguay (Gray et al., 1992); Llandovery, Paraguay (Pereira and Steemans, unpublished data); (15) latest Ordovician-earliest Llandovery, South Africa (Gray et al., 1986); and (16) latest Ordovician-earliest Llandovery, Australia (Foster and Williams, 1991).

Contents

GeoRef

References

REFERENCES

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