The radiolarian age and petrographic composition of a block of the Lower Jurassic volcaniclastic breccia and chert of the Mamonia Complex, SW Cyprus

An exceptional exposure of volcaniclastic breccia intercalated with radiolarian cherts and limestones was studied which constitutes a unique block within the Upper Cretaceous Mamonia Mélange in the Akamas Peninsula of southwestern Cyprus. This breccia, represents the lower part of the sedimentary cover of the Upper Triassic Phasoula Formation volcanics. The breccia mainly consists of clasts of metabasalts, diabases, metagabbros, hyaloclastites and quartz-albite-chlorite-epidote aggregates, which have been metamorphosed at greenschist facies, and subordinate siltstones. The thin-bedded cherts intercalated between breccia levels, yielded radiolarian assemblages, which indicate an Early Jurassic age (Sinemurian to Pliensbachian) for the sequence.

The Dhiarizos Group consists of the following sub-units: the Phasoula Formation (Upper Triassic basic volcanics with interlayers of limestones and cherts) (SWARBRICK & ROBERTSON, 1980;BRAGIN, 2007;2010), the Loutra tis Aphroditis Formation (Upper Triassic lava breccias and volcaniclastic breccias with interlayers of volcaniclastic siltstones and radiolarian mudstones) (SWARBRICK & ROBERTSON, 1980), the Petra tou Romiou Formation (detached blocks of Upper Triassic reefal limestones) (HENSON et al., 1949;SWARBRICK & ROBERTSON, 1980;MARTINI et al., 2009), and the Mavrokolympos Formation (Jurassic to Cretaceous alternating layers of limestones, cherts, mudstones, siltstones and calcilutites) (SWARBRICK & ROBERT-SON, 1980). The sedimentary interlayers within and above the Phasoula and Loutra tis Aphroditis formations are referred to as the Kholetria Member and are represented by chert-limestone alternations (SWARBRICK & ROBERTSON, 1980). Furthermore, the greenschist-to amphibolite-facies metamorphic rocks are termed the Ayia Varvara Formation (metasediments and metavolcanics of various Dhiarizos lithologies, metamorphosed during the Cretaceous) (MALPAS et al., 1992;CHAN et al., 2007;. For the purposes of this study, field work was conducted in the southwestern part of the Akamas Peninsula (Fig. 2). This area is characterized by the extensive distribution of the Ayios Photios Group lithologies and the Mamonia Mélange. Furthermore, seve-  ral big blocks of the Dhiarizos Group (mainly the Phasoula Formation) are also observed within the Mamonia Mélange. These blocks are mainly composed of basic volcanics commonly with interbeds of limestone and radiolarian chert. One of these blocks is composed of sedimentary-volcaniclastic breccia consisting mainly of fragments of basalts, diabases and gabbro, with interlayers of limestones and cherts that yield abundant radiolarian assemblages.
This roughly rounded block is located 2.5 km east-northeast of the northern Lara Bay (Fig. 2) and has an extent of 270 x 200 m, with an elongated axis along a SW -NE direction (Fig. 3, Fig.  4A, B). The studied breccia block is in tectonic contact with the surrounding matrix of the Mamonia Mélange, that yields numerous small blocks of Lower Cretaceous Akamas Sandstone of the Episkopi Formation (SWARBRICK & ROBERTSON, 1980) (Fig. 4C), Upper Triassic limestones of the Petra tou Romiou Formation or the Kholetria Member (SWARBRICK & ROBERTSON, 1980), as well as basic volcanics of the Upper Triassic Phasoula Formation. The matrix of the mélange consists of reddish-grey to brownish-grey mudstones and siltstones. Furthermore, another, smaller block of similar breccia was identified near the NW boundary of the studied breccia block (Fig. 3,. From the detailed survey of the large breccia block, from the northwestern boundary (point 18-18, coordinates 34⁰ 58' 22,4'' N, 32⁰ 20' 13,4'' E) towards its southern edge coordinates 34⁰ 58' 17,5'' N,32⁰ 20' 19,9'' E) (Fig. 3,4,5,6), various individual units of the block were recognized and described: 1. Greenish-grey hard cemented breccia mainly consisting of small (3-5 up to 15-20 cm in size) diabase and subordinate metagabbro clasts in a coarse-grained to gravelly matrix of the same composition. The thickness of the unit is 50 m.
2. Greenish-grey and reddish-brown hard cemented breccia of metabasalt, diabase and metagabbro clasts with rare small fragments of red recrystallized limestone in a coarse-grained to gravelly matrix of metabasalt, diabase and metagabbro. Lenses (1-2 m thick) of breccia within a pinkish matrix of highly brecciated limestone, occur in the upper part of the unit. The thickness of the unit is 100 m. 3. Pink to greenish-brown hard cemented breccia of diabase and metabasalt clasts within a matrix of highly brecciated pink to white limestone (Fig. 4F). The thickness of the unit is 4 m. 4. Greenish-grey hard cemented breccia with lenses (1,5 m thick) of breccia within a matrix of highly brecciated pink to white limestone (Fig. 4E). The thickness of the unit is 20 m. 5. White to pink, hard, thin-bedded recrystallized limestones with calcite veins (Fig. 5F). The thickness of the unit is 2 m. 6. Greenish-grey hard cemented breccia consisting of metabasalt, diabase and metagabbro fragments and blocks (Fig. 4G, H) in a coarse-grained to gravelly matrix of the same composition. The thickness of the unit is 5 m. 7. Brick-red and crimson-red, thin-bedded radiolarian cherts ( Fig. 5D) with interbeds (0,5 -1 m) of pink and white hard recrystallized limestones (Fig. 5E). The thickness of the unit is 20 m. 8. Greenish-grey to reddish-brown, hard cemented breccia consisting of diabase and metagabbro fragments and blocks as well as rare fragments of siltstones in a coarsegrained to gravelly matrix of the metabasalt, metagabbro and diabases. The thickness of the unit is 5 m. 9. Brick-red, thin-bedded radiolarian cherts intercalated with red cherty mudstones. Interbeds (up to 1 m) of dark-  greenish-grey breccia with fragments of metabasalt and metagabbro and lenses of pink recrystallized brecciated limestone are observed in the middle part of this unit. The contact between the chert and breccia layers is clearly sedimentary (Fig. 5A-C). The thickness of the unit is 5 m. 10. Dark-greenish-grey hard cemented breccia composed of unsorted diabase and metabasalt fragments in a coarsegrained to gravelly matrix of the same composition (Fig.  4D). The thickness of the unit is 6 m. It is herein assumed that this fragmentary section is the lower part of the sedimentary cover of the Upper Triassic volcanics of the Dhiarizos Group, which consists of breccia, while the upper part of the succession is characterized by the presence of limestone and radiolarian chert layers that become more and more abundant towards the top.

MATERIALS AND METHODS
Twenty-five samples of various rock types including metavolcanics, limestones and cherts were collected during fieldwork in 2018 and 2019. The petrography of the acquired rock samples was studied in standard thin-sections using a light microscope Olympus BS51. Radiolarians were extracted from chert samples using diluted (5%) hydrofluoric acid (HF) for twelve (12) hours and the residues were rinsed with water and dried. The residues were studied using a light microscope LOMO-MBS-10. The microfos- A -Red radiolarian cherts and white limestones in direct contact with breccia (units 9 and 10); B -Sedimentary contact between breccia and radiolarian chert. Small lense of breccia within radiolarian cherts (unit 9); C -radiolarian cherts, a fault is visible in the left side of the photograph (unit 9); D -radiolarian cherts and bed of limestone (unit 7); E -strongly brecciated white to pink limestone (unit 7); F -thin-bedded tectonized and brecciated pink to white limestone (unit 5). sils were collected, mounted, studied in detail and photographed with scanning electron microscopes: TESCAN 2300 in the Geological Institute RAS, Moscow, and TESCAN VEGA-II XMU in the Palaeontological Institute RAS, Moscow. Thin sections and radiolarian assemblages are stored in the Geological Institute RAS, Moscow, Russia.

Breccia with carbonate matrix
The breccia consists of metabasalt, diabase and metagabbro blocks and clasts that are irregularly shaped, sub-angular and poorly sorted. These rock fragments vary from a few centimetres to 10-15, rarely 20-30 cm in size. The matrix is represented by micritic limestone or recrystallized calcite.

Breccia clasts
Metabasalts are represented by amygdaloidal aphyric, plagioclase-and clinopyroxene-plagioclase porphyric varieties ( Fig.   7A, B, 8A, B). Phenocrysts of clinopyroxene are represented by short-prismatic crystals (0.4-0.9 mm) and are partly replaced by amphibole. Phenocrysts of plagioclase are tabular and often elongated tabular zoned crystals (0.2 mm); plagioclase is completely altered pseudomorphs of albite, epidote group mineral and chlorite creating a very fine-grained aggregate. The groundmass exhibits hyalopilitic and intersertal textures. The intersertal groundmass is composed of altered plagioclase, altered pyroxene and opaque minerals; the hyalopilitic groundmass is composed of elongated, needle-shaped, often skeletal plagioclase and altered glass replaced by a black opaque substance. Diabase (Fig. 7C) is composed of pseudomorphs after the alteration of plagioclase and pyroxene crystals, Fe-Ti oxides, quartz and micrographic intergrowths of quartz with feldspar. Plagioclase pseudomorphs are nearly euhedral in form, elongated tabular grains of a microcrystalline aggregate of epidote, colourless chlorite and albite in cores or rims. Pyroxene pseudomorphs are nearly euhedral and anhedral grains, represented by light-green to colourless amphibole with tiny inclusions of titanite. Fe-Ti oxides, which are abundant in the rock, comprise euhedral crystals with lacy edges. Minor quartz (<1%) and its intergrowths with feldspar (<1%) fill interstices. The rock texture is doleritic.

Carbonate matrix
The matrix is represented mainly by pink to white micritic limestone which is often strongly brecciated and cut by calcite veins (Fig. 8A, B). This matrix yields small non-sorted clasts of metabasalts and chlorite (formed supposedly after volcanic glass). Sometimes, the matrix is represented by highly recrystallized calcite. There is no visible layering of the matrix. Rare epidote group minerals are present in the carbonate matrix between clasts (Fig. 7B).

Breccia with sandstone-gravel matrix
This type of breccia is composed of metabasalt, diabase and metagabbro blocks, altered volcanic glass, quartz-albite-chlorite-epidote aggregates and rarely siltstone clasts. Blocks and clasts are irregularly shaped, sub-rounded and poorly sorted rock fragments from predominantly few centimetres up to 20-30 cm in size. The matrix is represented by sandstone-gravel that has the same composition with the large (both rock and mineral debris) clasts.

Breccia clasts
Metabasalts and diabase are represented by the same lithologies as clasts of the breccia with carbonate matrix. Metagabbro (Fig. 7D) is composed of clinopyroxene, pseudomorphs after the alteration of plagioclase and an accessory opaque mineral. Clinopyroxene is preserved only in relicts and is largely replaced by green to light-yellow amphibole with lamellae of an opaque mineral (<100 µm in size) and chlorite with interference in a blue colour. Plagioclase pseudomorphs form euhedral tabular grains, composed of a microcrystalline aggregate of albite, an epidote group mineral and chlorite. The opaque mineral is anhedral. Metagabbro is a fine-to medium-grained rock exhibiting a primary hypidiomorphic-granular texture.
Some clasts exhibit no primary textures. Intensively fractured clasts of presumably altered volcanic glass (Fig. 7E) consist of pale-green and colourless chlorite with minor hydrogarnet and fine-to medium-grained aggregates of quartz, albitite, epidote group mineral and chlorite which are produced from an unidentified rock.  Siltstone clasts (sample 18-15-2, unit 10, Fig. 7F-H) are composed of quartz and feldspar (albite). The supporting matrix is composed of chlorite and an epidote group mineral. Thin fractures are filled by carbonate minerals.

Sandstone-gravel matrix
Sandstone-gravel matrix is represented by the same lithologies as in the blocks and clasts. The matrix exhibits no layering or sorting. Occasional veins of calcite are present.

Limestone and radiolarian chert beds and lenses within the breccia succession
Limestones and radiolarian cherts form interbeds and lenses within the breccia. Limestones are represented by micrites which are commonly brecciated, and sometimes contain recrystallized radiolarian remains. Stylolites and fractures filled by calcite are common; these fractures are commonly confined to limestone clasts (Fig. 8C, D).

RADIOLARIAN ASSEMBLAGE AND AGE OF BRECCIA
Abundant radiolarians are present in the chert beds of the upper part of the studied section (Plate 1, 2, localities 18-15 and 18-16). The systematic composition of the radiolarian assemblages re-  4); B -limestone with clast of plagioclase porphyry metabasalt with intersertal groundmass (sample 18-17-5, unit 4); C, D -brecciated micritic limestones with relics of radiolarians (sample 18-15-1, unit 9); E -red radiolarian chert with moderately preserved radiolarians (sample 18-15-7, unit 9); F -dark-red radiolarian chert with abundant, moderately to poorly preserved radiolarians (sample 18-6-6, unit 7). covered from units 7 and 9 (Fig. 6) is similar ( Table 1). The presence of several characteristic taxa within the radiolarian assemblages is used to determine the age of the radiolarian cherts ( Fig. 9). Primary attention was given to well-preserved radiolarians determined to the species level useful for dating. Taxa described in open nomenclature are of secondary importance.

Bagotum maudence PESSAGNO & WHALEN is present in
Bipedis hannai WHALEN & CARTER, 1998 is known from the lower Hettangian -lower Sinemurian of Canada , from the lower Sinemurian of the Philippines (YEH & CHENG, 1998) and from the Hettangian -Sinemurian of Turkey (TEKIN, 2002). The known range of the species is Hettangian -lower Sinemurian, but it needs additional study because it is proven by macrofossils only in Haida Gwaii, British Columbia, Canada .
Bipedis japonicus GORIČAN et al., 2006 was firstly reported from the Hettangian to the Pliensbachian of Japan (HORI, 1990). It was documented later in the lower Pliensbachian of Canada (CARTER et al., 2010). Due to the absence of macrofossils in the Lower Jurassic chert sequences of Japan, we can state that the range is from the Hettangian to Pliensbachian under question.
Pantanellium sixi WHALEN & CARTER, 1998 is known from the upper Sinemurian of Canada . This species is known from only one region, and its stratigraphic range needs additional study.
Udalia primaeva WHALEN & CARTER, 1998 is present in the Hettangian and lower Sinemurian of Canada  and from the Hettangian to the Sinemurian of Turkey (TEKIN, 2002). The range of this species needs additional study.
Certain contradictions between the stratigraphic ranges of the radiolarian taxa are observed. For example, the last appearance data of Bipedis hannai WHALEN & CARTER is upper Sinemurian, whereas the first appearance data of Katroma ninstintsi CARTER and Paronaella grahamensis CARTER are lower Pliensbachian. The age determination of this assemblage as it is, is estimated with caution as Sinemurian-Pliensbachian.

Sample 18-15-8
Only three species are represented here, two of them were determined in open nomenclature (Fig. 9 (YEH & CHENG). Their presence confirmed the Early Jurassic age of the sample, but did not allow more detailed dating.
Canoptum? megathelus CORDEY is present in the Lower Jurassic of Canada (CORDEY, 1998). The stratigraphic importance of this species is poorly known.
Charlottea weedensis WHALEN & CARTER, 1998 was previously reported from the Hettangian and lower Sinemurian of Canada , from the Middle Jurassic (Bathonian) of Oregon (YEH, 2009), and from the Hettangian -Sinemurian of Turkey (TEKIN, 2002). It seems that this species has a broad stratigraphic range -from the Hettangian to the Bathonian.
Gorgansium morganense PESSAGNO & BLOME is known from the lower Pliensbachian of British Columbia (CARTER et al., 2010) and Oregon (PESSAGNO & BLOME, 1982;YEH, 1987). The stratigraphic range is questionable, because this species is studied only in two regions of North America.
As a result, we have for this sample clear contradictions between the stratigraphic ranges of the determined samples. For example, the LAD of Bipedis hannai and Pantanellium sixi is the upper Sinemurian, while the FAD for Gorgansium morganense, Katroma ninstintsi, and Paronaella grahamensis is the lower Pliensbachian. The presence of such contradictions in both of the two most diverse assemblages may be explained by the insufficient current knowledge of the Lower Jurassic radiolarian stratigraphic ranges and occurrences that need more detailed study. The age of this assemblage can be estimated only with caution as a broad range -Sinemurian to Pliensbachian.
We cannot currently give a more precise age, but the presen ce of Lower Jurassic radiolarian chert layers in this breccia represents a significant discovery for the stratigraphy of the Dhiarizos Group, as previously a large hiatus (the Lower Jurassic and part of the Middle Jurassic) had been recorded in the typical sections of the Mamonia Complex (BRAGIN & KRYLOV, 1996, 1999. It should be noted that the Lower Jurassic radiolarian cherts are relatively rare in the Mediterranean area (BAUMGARTNER et al., 2003;BORTOLOTTI et al., 2003;CHIARI et al., 2013). Similar rare Lower Jurassic cherts are observed as intercalations within ophiolitic breccia in the Old Zod Pass section of the Lesser Caucasus along the Armenian-Azerbaijan border zone (KNIPPER et al., 1987), and as a chert unit (Angelokastron Chert) covered by the Dhimaina and Potami formations (ophiolitic sandstones and breccias) at the Argolis in Greece (CHIARI et al., 2013). The Lower Jurassic cherts intercalated with micritic limestones were described and dated by TEKIN et al. (2020) in southeastern Turkey.

THE ORIGIN AND SIGNIFICANCE OF BRECCIA
The studied block of volcaniclastic breccia represents a new undescribed unit of the Dhiarizos Group. It differs from other units of the Dhiarizos Group by its composition and origin. The breccia consists of fragments of metabasalts, diabases and metagabbro with minor fragments of siltstones. The supporting matrix of the breccia can vary -from sandy consisting of grains of diabase and other igneous rocks to recrystallized micritic carbonates. Several beds of micritic limestone and radiolarian chert are present within the breccia. The presence of siltstone fragments and sedimentary contacts between the breccia, limestone and chert beds are an indication of the sedimentary origin of the breccia.
The volcaniclastic breccia is closely related with the volcanic units of the Dhiarizos Group, such as the Phasoula and Loutra tis Aphroditis formations, which could be the source of the clastic material. The breccia may have originated via underwater erosion of previously formed basic volcanics. The breccia is characterized by the irregular, poorly rounded character of the rock fragments, and by the absence of any sorting or stratification. The deposition of the breccia was probably local -along steep slopes or in narrow depressions triggered by tectonic movements. The formation of the breccia took place simultaneously with deepwater carbonate-chert sedimentation. The beds of micritic limestone and radiolarian chert within the breccia display a close affinity with the Upper Triassic -Lower Jurassic Kholetria Member of the Dhiarizos Group.
Similar Mesozoic volcaniclastic sedimentary breccias are known in various regions of the Mediterranean, either related to the upper part of plutonic and intrusive sequences of ophiolite complexes or formed within volcanic sequences (KNIPPER, 1978). The latter type is characterized by the predominance of clastic material consisting of dolerites, basalts and altered gabbro, while serpentinites are rare. These breccias can occur within or at the top of volcanic sections and they usually have sedimentary relationships with chert layers. Such breccias were studied in detail in the Ligurian Alps (GIANELLI & PRINCIPI, 1974).
Thus, the Lower Jurassic breccia in the Akamas Peninsula represents the lower part of the Dhiarizos Group sedimentary section. The presence of radiolarian cherts related with volcaniclastic breccia is of significant interest as according to many studi es the Rhaetian to Toarcian (Liassic) cherts are very rare in the Mediterranean Region, and, if present, they can be related to breccias, as in the Lesser Caucasus (KNIPPER et al., 1987) and Greece (CHIARI et al., 2013).

CONCLUSIONS
Volcaniclastic breccia of sedimentary origin, composed mainly of blocks and clasts of metabasalts, diabase and metagabbro, has been described from the Akamas Peninsula, western Cyprus.
Interbeds of radiolarian cherts within breccia yield radiolari an assemblages that allow dating of the breccia as Lower Jurassic, Sinemurian -Pliensbachian. The Triassic volcanics of the Phasoula Formation can be the source of the clastic material of the breccia.
The breccia represents a previously unknown lower part of the sedimentary cover of the Triassic volcanics (Phasoula Formation, Mamonia Complex).