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The charophyte flora from Socotra Island, Indian Ocean, studied for the first time from streams waterbodies that distributed at the northern part of the Island. The recognized charophyte taxa were taxonomically investigated, and four dominant species belonging to family Characeae are identified as Chara braunii, C. globularis, C. hispida and Lamprothamnium papulosum. These taxa are reported as a new record for algal flora of Socotra Island. A brief account of the environment where the charophytes were found is provided, as a first evaluation of the ecological requirements of Indian charophytes. A taxonomically diverse of charophyte assemblage and ecological variables explain abiotic features of biotope as shallow (max 1.3 m), alkaline fresh (pH 7.5–8.4), slightly saline, and moderate eutrophic.

Arabia is an important potential pathway for the dispersal of Homo sapiens (“out of Africa”). Yet, because of its arid to hyper-arid climate humans could only migrate across southern Arabia during pluvial periods when environmental conditions were favorable. However, knowledge on the timing of Arabian pluvial periods prior to the Holocene is mainly based on a single and possibly incomplete speleothem record from Hoti Cave in Northern Oman. Additional terrestrial records from the Arabian Peninsula are needed to confirm the Hoti Cave record. Here we present a new speleothem record from Mukalla Cave in southern Yemen. The Mukalla Cave and Hoti Cave records clearly reveal that speleothems growth occurred solely during peak interglacial periods, corresponding to Marine Isotope Stages (MIS) 1 (early to mid-Holocene), 5.1, 5.3, 5.5 (Eemian), 7.1, 7.5 and 9. Of these humid periods, highest precipitation occurred during MIS 5.5 and lowest during early to middle Holocene.

Africa and the Middle East consist of a rich geodiversity, which is regrettably not well known by the public. This is due partly to limited research and studies undertaken in geoheritage and geoconservation in these parts of world, especially those with the intent to explore, inventory and valorize such inherent geodiversity. With the aim to improve this situation, the African Geoparks Network (AGN) was created to increase the awareness of the local population and decision makers regarding the need for sustainable use and management of geoheritage in particular for the benefit of local socio-economic sustainable development targets through the promotion of both geotourism and the creation of unique geoparks.

A new stratigraphy for bimodal Oligocene flood volcanism that forms the volcanic plateau of northern Yemen is presented based on detailed field observations, petrography and geochemical correlations. The >1 km thick volcanic pile is divided into three phases of volcanism: a main basaltic stage (31 to 29.7 Ma), a main silicic stage (29.7 to 29.5 Ma), and a stage of upper bimodal volcanism (29.5 to 27.7 Ma). Eight large-volume silicic pyroclastic eruptive units are traceable throughout northern Yemen, and some units can be correlated with silicic eruptive units in the Ethiopian Traps and to tephra layers in the Indian Ocean. The silicic units comprise pyroclastic density current and fall deposits and a caldera-collapse breccia, and they display textures that unequivocally identify them as primary pyroclastic deposits: basal vitrophyres, eutaxitic fabrics, glass shards, vitroclastic ash matrices and accretionary lapilli. Individual pyroclastic eruptions have preserved on-land volumes of up to ∼850 km3. The largest units have associated co-ignimbrite plume ash fall deposits with dispersal areas >1×107 km2 and estimated maximum total volumes of up to 5,000 km3, which provide accurate and precisely dated marker horizons that can be used to link litho-, bio- and magnetostratigraphy studies. There is a marked change in eruption style of silicic units with time, from initial large-volume explosive pyroclastic eruptions producing ignimbrites and near-globally distributed tuffs, to smaller volume (

A combined paleomagnetic and Ar-40/Ar-39 study was carried out along eight stratigraphically overlapping sections in the Oligocene Afro-Arabian flood volcanic province in Yemen (73 sites). The composite section covers the entire volcanic stratigraphy in the sampling region and represents five polarity zones that are correlated to the geomagnetic polarity time scale based on Ar-40/Ar-39 ages from this and previous studies. The resulting magnetostratigraphy is similar to that of the conjugate margin in Ethiopia. The earliest basaltic volcanism took place in a reverse polarity chron that appears to correspond to C11r, while the massive rhyolitic ignimbrite eruptions correlated to ash layers in Oligocene Indian Ocean sediment 2700 km away from the Afro-Arabian traps, appear to have taken place during magnetochron C11n. The youngest ignimbrite was emplaced during magnetochron C9n. Both 40Ar/39Ar and paleornagnetic data suggest rapid < 1 Ma eruption of the basal basalt units and punctuated eruption of the upper silicic units over a duration potentially as long as 3 Ma with interspersed eruptive hiatuses. Eruption of the basal basalts may have preceded the Oi2 cooling event. The paleornagnetic pole lambda=74.2 degrees N, phi=249.1 degrees E (A95=3.6 degrees; N=48) is supported by a positive reversal test. Paleosecular variation, estimated as the angular standard deviation of the VGP distribution 14.2 degrees+2.3 degrees/-1.7 degrees, is close to expected, suggesting that the paleornagnetic pole represents a time-averaged field. The pole is in excellent accord with the paleornagnetic poles obtained from the Ethiopian part of the Afro-Arabian province, after closure of the Red Sea. By analyzing Afro-Arabian paleomagnetic data in conjunction with contemporaneous paleomagnetic poles available from different latitudes we argue that the Oligocene paleomagnetic field was dominated by the axial dipole with insignificant non-dipole field contributions. (Less)

Widespread silicic pyroclastic eruptions of the Oligocene Afro-Arabian flood volcanic province (ignimbrites and airfall tuffs) produced up to 20% of the total flood volcanic stratigraphy (>6×104 km3). Volumes of individual ignimbrites and tuffs exposed on land range from ∼150 to >2000 km3 and eight major units (15–100 m thick) were erupted in 500 km distant); and (b) to two deep sea ash layers sampled by ODP Leg 115 in the Indian Ocean ∼2700 km to the southeast. This correlation is based on whole rock analyses of silicic units for isotope ratios (Pb, Nd) and rare earth element compositions, in conjunction with novel in situ Pb isotope laser ablation multicollector inductively coupled plasma mass spectroscopy analysis of groundmass and glass shards. Compositional diversity preserved on the scale of individual ash shards in these deep sea tephra layers record chemical heterogeneity present in the silicic magma chambers that is not evident in the welded on-land deposits. Ages of the ash layers can be established by correlation to precisely dated on-land ignimbrites, and current evidence suggests that while these eruptions may have exacerbated already changing climatic conditions, they both marginally post-date the Oi2 global cooling anomaly.

High-resolution oxygen isotope (δ18O) profiles of Holocene stalagmites from four caves in Northern and Southern Oman and Yemen (Socotra) provide detailed information on fluctuations in precipitation along a latitudinal transect from 12°N to 23°N. δ18O values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the ITCZ and dynamics of the Indian summer monsoon (ISM). During the early Holocene rapidly decreasing δ18O values indicate a rapid northward displacement in the mean latitudinal position of the summer ITCZ and the associated ISM rainfall belt, with decadal- to centennial-scale changes in monsoon precipitation correlating well with high-latitude temperature variations recorded in Greenland ice cores. During the middle to late Holocene the summer ITCZ continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation, a trend, which is also recorded in other monsoon records from the Indian and East Asian monsoon domains. Importantly, there is no evidence for an abrupt middle Holocene weakening in monsoon precipitation. Although abrupt monsoon events are apparent in all monsoon records, they are short-lived and clearly superimposed on the long-term trend of decreasing monsoon precipitation. For the late Holocene there is an anti-correlation between ISM precipitation in Oman and inter-monsoon (spring/autumn) precipitation on Socotra, revealing a possible long-term change in the duration of the summer monsoon season since at least 4.5 ka BP. Together with the progressive shortening of the ISM season, gradual southward retreat of the mean summer ITCZ and weakening of the ISM, the total amount of precipitation decreased in those areas located at the northern fringe of the Indian and Asian monsoon domains, but increased in areas closer to the equator.

Oxygen-isotope ratios of a stalagmite from Socotra Island in the Indian Ocean provide a record of changes in monsoon precipitation and climate for the time period from 42 to 55 thousand years before the present. The pattern of precipitation bears a striking resemblance to the oxygen-isotope record from Greenland ice cores, with increased tropical precipitation associated with warm periods in the high northern latitudes. The largest change, at the onset of interstadial 12, occurred very rapidly, in about 25 years. The chronology of the events found in our record requires a reevaluation of previously published time scales for climate events during this period.

The tectonic evolution of the southeastern margin of the Red Sea Rift in western Yemen has been investigated using a multi-disciplinary field study of an east-west transect between Al Hudaydah and Sana9a. Slow subsidence of up to 1 km occurred over the area during a 100 m.y. period before rifting. There was a major episode of flood volcanism between ca. 30 and 20 Ma, and important extensional faulting began after the eruption of the volcanic rocks and ceased before middle to late Miocene sediments and volcanic rocks were deposited unconformably on top of rotated fault blocks on the coastal Tihama Plain. Surface uplift has produced the Yemen highlands, whose highest peak reaches an elevation of 3660 m. This is attributed to plume heating and eruption of >3000 m of volcanic rocks. Apatite fission-track ages indicate early to middle Miocene exhumational cooling ages, postdating the major volcanic phase and contemporaneous with rifting. Volcanism was accompanied by emplacement of subvertical dike swarms, which generally strike north-northwest to northwest, broadly parallel to the Red Sea coastline. Major faults indicate northeast-southwest-directed extension. Large granitic sheets and plutons (up to 25 km wide) intruded the volcanic rocks. Approximately 30 km of extension has taken place across a 75-km-wide zone (β = 1.7) in 6-8 m.y. The relative timing of volcanism followed by extension and uplift does not fit conventional models of passive or active rifting. We suggest that the proto-Red Sea Rift was caused by regional plate stresses that exploited lithospheric weakening caused by the Afar plume. Appreciable doming only occurred after the main episode of volcanism, which suggests that magmas extruded before maximum thermal expansion of the lithosphere took place.

This paper analyses new field and radiometric age data on the timing of extension, sedimentation and magmatism related to the opening of the Red Sea. The first evidence of widespread extension is found in synsedimentary fissures in the fluviatile to shallow marine Tawilah Formation of Cretaceous to early Tertiary age. The first indication of magmatism is the eruption of alkaline basalts (43.5–21.2 Ma) on to marine and non-marine sandstones of lower to middle Tertiary age. The lack of an angular unconformity at the sediment-basalt contact, over a period of 25 Myr, corroborates a diachronous relationship between the Tawilah sandstones and the Yemen Volcanics. These data also indicate that the onset of volcanism in Yemen was in the Eocene, as is the case in Ethiopia and Saudi Arabia. A passive rifting model is supported by early extension and sedimentation followed by syn- and post-tectonic magmatism.

The behaviour of the lithosphere prior to rifting and rift- related volcanism in the southern Red Sea area is recorded in the stratigraphy underlying the Yemen Volcanic Group. The Medj-zir Formation is dated as Paleocene to Oligocene in age and is the upper part of the Cretaceous to Paleogene Tawilah Group of Yemen. The Medj-zir Formation is well exposed over a large area of western Yemen, forming a unit which varies in thickness from 30–60 m in the west to 60–75 m in the east. The Yemen Volcanic Group overlies the Medj-zir with a sharp, but conformable boundary. The lowest volcanics are dated as 30–32 Ma. The Medj-zir Formation consists of clastic and subordinate carbonate facies which indicate deposition in fluvial, shallow marine and lacustrine-lagoonal environments. Three members are recognized: the basal Zijan Member comprises fluvial facies and shallow marine sandstones and mudstones; the Kura Member is made up of fluvial channel and overbank facies, the latter including well-developed ferruginous paleosols; the Lahima Member, at the top, is fine-grained, including gastropod-rich limestones deposited in a lacustrine or brackish lagoonal environment. These facies and transitions between them represent deposition in a coastal plain to shallow marine shelf setting which was subjected to minor fluctuations in sea level. It is noteworthy that there are no angular unconformities or erosional hiatuses within the Medj- zir Formation anywhere in western Yemen. Deposition- al hiatuses of unknown duration are represented by well-developed paleosols indicating long periods of tectonic stability. The contact with the overlying volcanics is conformable in all examined sections and there are no volcanic horizons or clasts in the Medj-zir Formation.

Tertiary synrift deposits along the northern margin of the Gulf of Aden, Republic of Yemen, provide new information on the controls on deposition and stratigraphic relationships during the transition from continental to marine rift sedimentation. Intracontinental rifting in the region commenced in the Oligocene, developing into a marine extensional margin in the Miocene. The outcropping part of a small subbasin at Wadi Hiru, west of Mukalla, contains carbonate platform, alluvial-fan, fan-delta, and raised-beach deposits that record the development of the rift margin. The spatial relationships between carbonate and clastic units, their location adjacent to rift-border faults, and timing of sea-level changes indicate that tectonics was the overriding control on relative sea-level change . Accommodation space created by fault movement and the morphology of older sediment bodies dictated the three-dimensional architecture of carbonate platforms and clastic fans. Fault movements are documented by changes in clast provenance in fanglomerates. Rift-parallel and rift-perpendicular faults formed a trap-door configuration that controlled long-lived pathways of terrigenous clastic supply throughout rifting. Five local depositional sequences, bounded by erosion surfaces, are recognized. Sequences have a distinct tectonic signature in the form of sequence boundaries overlain by thick fanglomerates followed by transgressive and highstand carbonates. Two of these sequences were dated using 87Sr/86Sr isotope dating. The relative sea-level curve derived from thi study bears little relationship to published "eustatic" curves.