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My research interests revolve around two main themes. The first of these relates to the use of geochemistry to interpret the origins of sediments and sedimentary rocks. I began my research career using rare earth elements to interpret sediment provenance in active tectonic settings, and this has now expanded to include other trace elements, and also to investigate situations where the provenance signal is overwritten, for example by traces of volcanic ash from pyroclastic eruptions. The second theme involves the interpretation of sedimentary processes and geomorphology, to understand sediment transport at the present time and in the recent past. Much of this work has been applied to monitoring beach processes on Staten Island, which is important in understanding, and potentially predicting, the response of beaches to storm events. It also includes work on monitoring microplastic pollution in the marine environment around Staten Island, and the interpretation of fluvioglacial sediments.
My research interests revolve around two main themes. The first of these relates to the use of geochemistry to interpret the origins of sediments and sedimentary rocks. I began my research career using rare earth elements to interpret sediment provenance in active tectonic settings, and this has now expanded to include other trace elements, and also to investigate situations where the provenance signal is overwritten, for example by traces of volcanic ash from pyroclastic eruptions. The second theme involves the interpretation of sedimentary processes and geomorphology, to understand sediment transport at the present time and in the recent past. Much of this work has been applied to monitoring beach processes on Staten Island, which is important in understanding, and potentially predicting, the response of beaches to storm events. It also includes work on monitoring microplastic pollution in the marine environment around Staten Island, and the interpretation of fluvioglacial sediments.
Geochemistry and origin of sedimentary rocks deposited in the Newark Basin, NJ
Geochemistry and origin of sedimentary rocks deposited in the Newark Basin, NJ
The Newark Basin in New Jersey formed at a divergent plate boundary, with the development of a continental rift basin during the late Triassic representing the start of opening of the North Atlantic. My work here involves an outcrop of rock deposited during the early stages of rifting, which was exposed during recent construction. This provided an opportunity to study the primary and secondary sedimentary structures of a previously hidden part of the Stockton Formation. The geochemistry of the samples helps to determine the source of the sediment, and also assists with the interpretation of soft sediment mobilization structures. Despite its small size, this outcrop provides strong evidence for varying rates of basin subsidence, with rocks deposited during more rapid subsidence also showing secondary structures associated with major earthquakes. Additionally, one sample had a trace element signature that is suggestive of a volcanic ash, as did another sample from a nearby outcrop.
Related publications
Related publications
Alexander, J. L., *Thatcher, S. T., *Tobon, J. and *Rivelli, V. (2024) Evidence for subsidence rate variation in the Newark Basin and its influence on the deposition of fluvial sediments of the Stockton Formation. The Depositional Record, 11, 637–653, Article link
*Tobon, J. and Alexander, J. L. (2023) A suspected volcanic ash uncovered by trace element chemistry of sediments in the Newark Basin. Geological Society of America Abstracts with Programs. 55, (6), Article link
Alexander, J. L., *Tobon, J., *Thatcher S. and *Rivelli V. (2022) Geochemical evidence for the origin of Triassic fluvial sediments and their remobilization during intrusion of the Palisades Sill. Geological Society of America Abstracts with Programs. 54, (5), Article link
Alexander, J. L., *Thatcher, S. T. and *Rivelli, V. (2018) Geochemical variation in metasedimentary rocks adjacent to the Palisades Sill – metamorphic influence or original sediment composition? GSA Abstracts with Programs, 50 (2), Article link
*Current or former undergraduate student
Provenance of sedimentary and volcaniclastic rocks on the Boso Peninsula, Japan
Provenance of sedimentary and volcaniclastic rocks on the Boso Peninsula, Japan
The Boso Peninsula in Japan, was a marine basin at a convergent margin during the Miocene, receiving hemipelagic muds, punctuated by deposits from pyroclastic eruptions (ash and tuff) and turbidity currents. The geochemistry of the sediments generally illustrates their changing provenance over time from intermediate towards mafic, due to the uplift of the Mineoka Mountain Range. However, some samples have anomalous trace element signatures that do not match the provenance interpretation based on major elements. In sandy layers, the sand component dominates the major element signature, while the mud component strongly influences the trace element signature. In a few mudrock samples, there appear to be traces of volcanic ash, and this material dominates the trace element signature over the background mudrock.
Related publications
Related publications
Alexander, J. L., Pickering, K. T. and Bailey, E. H. (in prep) Interpreting provenance changes through time using whole rock geochemistry: insights from a Miocene forearc basin, Boso peninsula, Japan.
Alexander, J. L., Pickering, K. T., Bailey, E. H. and *Hajdarevic, M. (2023) Interpreting provenance changes through time in a Miocene marine basin, Boso Peninsula, Japan. Geological Society of America Abstracts with Programs. 55, (6), Article link
*Former undergraduate student
Geochemistry of accretionary wedge sediments
Geochemistry of accretionary wedge sediments
My work on the provenance of sediments in active tectonic settings began with accretionary wedge sediments collected during the Ocean Drilling Program (ODP) from the Nankai Trough, Cascadia, Barbados and Costa Rica. The provenance of these sediments may be interpreted using major and trace element chemistry, corroborated with knowledge of the paleogeography and likely sediment sources. While the overall results show provenance signatures expected for the settings, there are some variations and anomalies related to specific sediment sources and their temporal variation. Additionally, accretionary wedge sediments will ultimately be subducted, and the data compiled from these locations will add to the global database of subducting sediment chemistry. This is important for scientists who work on the recycling of subducted materials and their influence on melting and volcanism at convergent plate margins.
Related publications
Related publications
Alexander J. L, *Atkinson A., Pickering K. T. and Bailey E. H. (in prep) Provenance interpretation of accretionary wedge sediments using trace element chemistry and their contribution to element cycling in subduction zones.
Alexander, J. L. (2022) Are provenance interpretations from major, trace and rare earth element data accurate? Results from four active margins. Geological Society of America Abstracts with Programs, 54 (3), Article link
*Former MS student
Tracing volcanic ashes by their geochemical signature
Tracing volcanic ashes by their geochemical signature
The fact that trace element signatures from provenance have been “overwritten” by volcanic ash at two of the locations I have studied has inspired me to follow this line of research further. There is some discussion in the geochemical community of how accurate this technique is for identifying volcanic ashes in general, and also whether individual ashes can be traced geographically by their unique trace element signature. An ideal opportunity to answer these questions has been provided by the recent IODP cruise to the Hellenic Volcanic Arc. I currently have some PSC-CUNY funding to sample the cores, and plan to add to the work done by the shipboard scientists by analyzing the geochemistry of sediments containing volcanic ash and potentially recognizing traces of ash because of their similar trace element signatures. Doing this work on ashes that have been correlated to specific eruptions will potentially prove that the trace element signatures are characteristic of the specific ash. If this can be established, the opportunity to apply this technique in other environments and locations will be a source for future funding. A secondary goal for the Hellenic Volcanic Arc sediments is to again use geochemistry to assist with provenance interpretation of these marine sediments. The dataset created will also supplement records of the geochemistry of subducting sediments, adding to the global database mentioned above. The Hellenic Volcanic Arc is part of a subduction zone with little previous published data, and which is not yet represented in the commonly used global databases.
Staten Island beach morphology and processes
Staten Island beach morphology and processes
The beaches on Staten Island’s eastern shore were shown to be vulnerable to storm surge during Hurricane Sandy, with severe inundation into adjacent neighborhoods, so it is important to understand the reasons for this vulnerability to mitigate future storm events. The Army Corps of Engineers plan construct a seawall in this area, so a baseline understanding of the nature and movement of sand on the beach will be necessary to interpret any changes resulting from the construction. A preliminary survey in summer 2018 suggested that this shoreline is reflective - i.e. one that changes little over the course of a year, but which is vulnerable to erosion during major storm event. I am currently testing the hypothesis that this is a reflective shoreline by completing regular field surveys over the course of a year. Field surveys are complete, but sample and data analysis are still in progress. Analysis of the sediment grain size distribution and its variation during the year will assist with interpreting the movement of sand on the beach, both by natural processes and human intervention. The data collected may be used to make predictions about future shoreline responses to storm events and sea level rise.
Related publications
Related publications
Alexander, J. L., *Reiszel, J. and *Acevedo, A. (2024) Understanding current beach processes to interpret future change – Interactions between natural and anthropogenic influences. (NH13E-2322) presented at AGU24, 9-13 Dec, 2024, Article link
*Acevedo, A., Alexander, J. L., *Reiszel, J. and Thatcher, S. T. (2023) Coastal vulnerability and resistance: A yearlong study of Staten Island beaches. Geological Society of America Abstracts with Programs. 55, (6), Article link
*Reiszel, J., Alexander, J. L. and *Acevedo, A. (2023) Assessing the stability of Staten Island’s eastern shore: A sediment analysis. Geological Society of America Abstracts with Programs. 55, (6), Article link
Alexander, J. L., *Acevedo, A. and *Reiszel, J. (2022) Understanding the vulnerability of Staten Island’s eastern coastline from a beach morphology perspective. Field Guide and Proceedings Geological Association of New Jersey, Thirty Eighth Annual Meeting, 33 – 43, Article link
Alexander, J. L., and *Avilla Sanchez, J. (2019) Staten Island beach morphology - implications for shoreline response to storm events. GSA Abstracts with Programs, 51 (1), Article link
*Former undergraduate student
Staten Island fluvioglacial sediments
Staten Island fluvioglacial sediments
This study focuses on an area of fluvioglacial cross-bedded sands and massive gravels on Staten Island. It has been used by previous investigators to determine the age and origin of sediments to the north of the terminal moraine, however these studies have resulted in different interpretations, either Late Miocene Pensauken Formation or Pleistocene outwash deposits. My goal is to use a detailed analysis of sediments from two outcrops that were exposed by construction about a decade apart. Combining the data from the two sites, we see an approximately 3.5 m thick sequence of sands and gravels with abundant cross-bedding, interpreted as fluvioglacial outwash, based on detailed logging of the beds, grain size analysis and pebble composition. This sequence directly overlies the Cretaceous Raritan Formation at the first location and is capped by Wisconsinan glacial till at the second location. Based on this work, the most likely origin of these sediments is pre-Wisconsinan glacial outwash, however it is possible that any future exposure during construction could provide further evidence to contradict this interpretation.
Related publications
Related publications
Alexander J. L., *Thatcher, S. T., and *Rivelli, V. (in prep) Origin and age of fluvioglacial sediments on Staten Island NY and implications for meltwater flow.
Alexander, J. L., *Rivelli, V. and *Thatcher, S. T. (2024) Interpreting the glacial history of Staten Island, NY from small, temporary exposures. Abstract (EP13B-1343) presented at AGU24, 9-13 Dec, 2024, Article link
Alexander, J. L., *Thatcher, S., *Rivelli, V. and *Bond, V. (2014) Origin and age of fluvial sediments, Charleston, Staten Island. GSA Abstracts with Programs, 46 (2), 45, Article link
*Former undergraduate student
Microplastic in the marine environment around Staten Island
Microplastic in the marine environment around Staten Island
During the beach surveys described above, we noticed the presence of many colorful “sand” grains in our samples, which led to my interest in studying these microplastics, at a time when the field was in its infancy. With the help of several undergraduate and MS students, we worked to develop a method of separating these particles from beach sands. This work was suspended during Covid, and is slowly starting up again with some new students and the recent purchase of an FT-IR to analyze the composition of the microplastics.
Related publications
Related publications
Alexander, J. L., *Chen, T. T., *Fiero, A., +Vaserman, E., Lindo-Atichati, D., #Callaghan, R., *Kominoski, S. and Kozyra, M. (2020) Developing a reliable method for separating microplastics from a variety of beach sediments. Geological Society of America Abstracts with Programs, 52 (2), Article link
Desai M., Seijo-Ellis G. G., Lindo-Atichati D., Jalon-Rojas I., Alexander J. L., Montero P. and Miro M. (2020) Influence of microfiber properties and environmental processes on their dispersal in estuaries. AGU Ocean Sciences Meeting, February 2020, Article link
Former *undergraduate, +high school, #MS students
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