GEO Research Publications

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    Holocene coral patch reef ecology and sedimentary architecture, northern Belize, Central America
    (1992-12) Mazzullo, Salvatore J.; Anderson-Underwood, K.E.; Burke, Collette D.; Bischoff William D.
    A pronounced coral zonation exists across Elmer Reef, with Montastrea annularis dominating on its crest and Acropora cervicornis occurring on its windward and leeward flanks. -from Authors
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    Environmental setting of Holocene sabellariid worm reefs, northern Belize
    (SEPM Society for Sedimentary Geology, 1992) Burke, Collette D.; Mazzullo, Salvatore J.; Bischoff, William D.; Dunn,Richard K.
    Communities of sabellariid worms (Polychaeta) occur as areally discontinuous, unlithified reefs on an irregular depositional topography of Holocene and older sediments at the mouth of the Northern River Lagoon, Belize, Central America. Based upon radiocarbon dating of peat deposits, and analyses of sediment cores, the worm reefs have flourished in the study area of at least 5100 yr. This time span corresponds with sea level rise and transgression of the northern Belize coast. Initially, worms colonized drowned levees. Once established, the worm reefs stabilized these levees so that their original orientation normal to shore line is preserved today. -from Authors
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    Stratigraphy and eruptive history of Gedemsa caldera volcano, Central Main Ethiopian Rift
    (Elsevier B.V., 2024-02) Bedassa, Gemechu; Ayalew, Dereje; Getaneh, Worash; Fontijn, Karen; Emishaw, Luelseged; Melaku, Abate A.; Tadesse, Amdemichael Z.; Demissie, Zelalem S.; Swindle, Andrew L.; Chamberlain, Katy J.
    Gedemsa caldera is a peralkaline volcanic depression located in the Central sector of the Main Ethiopian Rift. An integrated volcanological study of stratigraphic sections was carried out in order to constrain the eruptive history of Gedemsa caldera volcano (GCV), Ethiopia. Textural analyses on plagioclase crystals together with field observations shed light on magma chamber processes feeding the volcanic complex. A multi-vent eruption is ascribed to the pre-caldera volcanic products, as can be seen from the varying caldera wall sequences comprising lavas and pyroclastic deposits. At least three major caldera-forming eruptions are identified producing: 1) a lower ignimbrite, 2) extensive pumice fall and pyroclastic density current deposits, and 3) an upper ignimbrite exposed in different areas of the caldera, indicating a sector collapse. We identified 20 individual pyroclastic deposits found outside and within the caldera that erupted after the climactic caldera collapse. The most recent volcanic activity at Gedemsa is characterized by rhyolitic lava domes and pyroclastic deposits from eruptions through numerous vents aligned with WNW-ESE pre-existing cross-cutting structures. Macrocryst disequilibrium textures such as fine-scale oscillatory zoning (FOZ), sieve textures, glomerocryst, and synneusis indicate that magma reservoir is characterized by repeated magma injection, convection flows, and mixing.
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    Subsurface structural control of geothermal resources in a magmatic rift: Gravity and magnetic study of the Tulu Moye geothermal prospect, Main Ethiopian Rift
    (Frontiers Media SA, 2023-07) Nigussie, Wubamlak; Alemu, Abera; Mickus, Kevin; Keir, Derek; Demissie, Zelalem S.; Muhabaw, Yoseph; Muluneh, Ameha A.; Corti, Giacomo; Yehualaw, Esubalew
    Since the Quaternary, extension and magmatism in the Main Ethiopian Rift (MER) have been mainly focused into narrow magmatic segments that have numerous volcanic centers and caldera collapses that offer favorable conditions for the occurrence of geothermal resources. However, the subsurface structure of the volcanic systems (0-10 km) and their link to the distribution of shallow geothermal resources remain unclear. To investigate the role of subsurface structures on the occurrence of these resources, we conducted gravity and magnetic studies combined with geological constraints within the Tulu Moye Geothermal Prospect (TMGP), one of the current geothermal prospects in the central MER associated with caldera collapses. Gravity data from the Global Gravity Model plus (GGMplus 2013) and ground magnetic data transformed into residual and derivative maps reveal that shallow magmatic intrusions occur under the volcanic centers (Tulu Moye, Bora, and Bericha). Our interpretation along with recent magnetotelluric model suggests that only the intrusion beneath Tulu Moye is currently magmatically active and includes partial melt, consistent with it being a primary heat source for the geothermal system. A new caldera formation model is proposed where the TMGP hosts an older large caldera (about 25 km diameter) within which there are several smaller nested caldera systems associated with the Bora, Bericha, and Tulu Moye volcanoes. Along with existing geologic, seismic, and magnetotelluric studies, our gravity and magnetic analysis indicate the interaction between NNE-SSW (rift-parallel) and NW-SE (cross-rift) trending faults, along with shallow magmatic intrusions and caldera systems, suggesting that such a large geothermal system is possible under these conditions.
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    The significance of volcanic segments and rifts in faults characterization within the Amagmatic graben of the Afar Depression, Ethiopia
    (Elsevier Ltd, 2023-09) Demissie, Zelalem S.; Bedassa, Gemechu; Rattani, Ajita; Nigussie, Wubamlak; Kebede, Hailemichael; Muhabaw, Yoseph; Haridasan, Smitha
    The Dobi graben is a northwestern trending, continental rift situated in the East Central Block (ECB) of the Afar Depression (AD), Ethiopia. Ongoing extensional rifting in the graben is evident from the swarm of intermediate magnitude earthquakes (5.7 < Ms < 6.3) in 1989. The graben's extension occurs on steeply dipping faults, where the maximum displacement and traced fault length spans four orders of magnitude. Using a 30 m resolution Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM), we conducted a fault population analysis in the Dobi graben. We traced 953 faults and conducted a size-frequency distribution analysis has been conducted for various spatially heterogeneous structural zones. Our results show that the frequency size distribution revealed a negative exponential fitting trend, indicating strong strain distribution within the Imbrication, the Fault Termination zone, and the active axial graben floor. However, a power law size distribution dominates most first-order border faults, suggesting that the strain is localized mainly at the graben flanks. The fault displacement-length profiles demonstrate that approximately 48% of the total fault traced lengths exhibit increasing slip rates towards the southeast, while about 40% display increasing slip rates towards the northwest. These suggest that ?88% of the lateral propagation of the 953 faults in the Dobi graben is governed by the regional differential strain transfer of the Red Sea Rift (RSR) and Gulf of Aden Rift (GAR) to the central Afar. Most of the hmax/L aspect ratio of the Dobi graben's faults fits in Category II, which exhibits a constant hmax/L ratio, meaning that the hmax/L ratio increases with fault growth, presumably due to the graben's is in an active tectonic region. This implies that these faults are becoming more efficient at accommodating deformation as they grow. Additionally, the normalized average maximum displacement over maximum length (Dmax/Lmax) ratio for most faults is 0.03, which is in accord with the constant displacement length fault growth model. © 2023 Elsevier Ltd