Limestone tal-Belt ta' Malta:
Il-gżejjer Maltin huma komposti kollha minn limestone. Madwar 30 sa 5 miljun sena ilu, sedimenti karbonati tal-ħajja marina (bħall-qoxra, ċkejken, u koralli) ġew depożitati fuq qiegħ il-baħar antik f'Malta tal-lum u parti mill-Afrika tal-Lvant. Minħabba żvilupp tektoniku, l-gżejjer li jidhru llum ġew issemmew fuq is-suq. Ġeoloġi li studjaw il-limestone Malti ħabbtu li hemm ħames subkategori ta' limestone li jinstabu fil-gżira. Dawn is-subtipi jikkontengjaw kollha prinċipalment karbonat tal-kalċju. Il-karbonat tal-kalċju huwa kompost abjad li jiffurma madwar 5% tal-ffiha tal-Art. Huwa mitlub f'ġebla sedimentarja (bħal-limestone) u huwa estremament sensibbli għall-inqasbiet tal-mija. Ħafna mill-fortifikazzjonijiet li ġew mibnija mill-Kavallieri ta' San Ġwann huma mfassra minn limestone.
Tafoni:
Ligħa qrib il-punt ta' ħarsien tal-Port il-Kbir, tista' tara mħabbra tal-limestone bl-imqassar tafoni fih. It-tafoni huma ftit fornijiet mudellati fuq wiċċ ta' saqaf ta' ġebla li jinxtebu minn ħafna xagħar tal-inqasbiet. It-tqassir tal-ħajja tafoni jitratta ħafna l-ġeblin sedimentarji, bħal ġebla tas-sabbun u l-limestone. Jistgħu jidhru bħal għandna il-qasam ta' spuża u jistgħu jiġu mfassra f'ambjenti aridi.
Ġeologi jemmnu li it-tafoni jistgħu jinfużjaw taħt l-influenza tat-tliet tipi ta' inqasbiet: inqasbiet mekkaniki, kimiċi, jew bijoloġiċi. L-inqasbiet mekkaniki huma l-proċess ta' degħa tal-ġebla minħabba proċessi fiżiċi (bħal ilma, n-nofs, u ħafna aktar). Meta l-għalab fil-klimi polari jiffriża, jista' jespandi u jirrikjedi stress fuq il-ġebla madwaru. Dan il-proċess, magħruf bħala abrasjoni tal-ħalib, jista' jaħrab forom żgħar u jwassal għal qamar fuq wiċċ il-ġebla. F'żoni qrib ir-rieda tal-milgħuba, ilma eċċezziva tista' twaqqaf l-inqasbiet tal-minerali f'ġebla li tikkonteniet klay. Dan il-proċess ta' twaqqif tal-minerali jista' jwassal għal fraġmentazzjoni u inqasbiet tal-ġebla. F'ċirkostanzi rari, il-forom ta' tafoni jistgħu jkunu viżibbli. L-inqasbiet kimiċi huma id-dissoluzzjoni tal-ġebla minħabba reazzjonijiet kimiċi. L-inqasbiet tal-kristall tal-melħ huma wieħed mill-tipi ta' inqasbiet kimiċi li jistgħu jinħoloq tafoni. Dan il-proċess jiġri meta ilma bl-isqof li tikkontenih melħ mtejba tiġi l fuq wiċċ ta' ġebla li tikkontenih kwantitajiet għoljin ta' karbonat tal-kalċju (bħal l-limestone). Il-melħ jista' jiddissolvi dan il-kompound permezz ta' proċess kimiċi, li jnaqqas il-wiċċ tal-ġebla u jforza kixxin/grooves ta' ġebla li twaqqfet mill-inqasbiet. It-tafoni li jinstabu qrib it-tieqa huma spiss imwasslin minn brunita tal-baħar fil-arja. L-inqasbiet bijoloġiċi huma meta organiżmi bħal pjaneti jew fungi jinżammu taħt xi wiċċ ta' ġebla u jimtlaqqu acidu. Dan il-proċess bjoċċemiku jista' jiddissolvi l-ġebla.
**Dan l-EarthCache mhux f'lokazzjoni direttament fuq il-punt ta' ħarsien, iżda huwa qribu. Sħoħ il-miżuri ta' logħob li ġejjin billokazzjoni tat-tiġrija tal-limestone fil-post.**
Mistoqsijiet:
- Ixxerex il-limestone għal network ta' fornijiet tafoni. Huma jidhru tendenti li jkunu ċirkuļari, ellittiki, jew poligonal?
- Bbażat fuq l-osservazzjonijiet tiegħek fil-GZ u dak li ktibt fil-deskrizzjoni, liema tip ta' inqasba (mekkanika, kimiċa, jew bijoloġika) jqassam li qed jikkawża l-iżvilupp tat-tafoni fil-GZ?
- Tixtri l-testura fiċ-ċekiċiet tafoni. Tixtieq li l-fornijiet tafoni itejbu aktar skur, aktar ħalq, jew l-istess bħala l-ġebla ġenitur (limestone)?
- Dan huwa taħdit meħtieġ. Jekk jogħġbok għażżel ritratt tiegħek, tal-GPS tiegħek, jew oġġett personali li jidher li żżurta din il-post. Jekk jogħġbok poġġih fil-log tiegħek.
Sorċijiet:
https://www.nps.gov/articles/tafoni.htm
https://education.nationalgeographic.org/resource/weathering/#:~:text=Mechanical%20Weathering%20Mechanical%20weathering%2C%20also,cracks%20and%20crevices%20in%20rock
https://onepetro.org/ARMAUSRMS/proceedings-abstract/ARMA88/All-ARMA88/ARMA-88-0017/129948
https://era.org.mt/topic/maltese-geology/
Limestone of Malta:
The Maltese islands are composed entirely of limestone. About 30 to 5 million years ago, carbonate sediments of marine life (such as shells, echinoderms, and corals) were deposited on an ancient sea bed in present-day Malta and portions of North Africa. Due to tectonic uplift, the islands visible today are pushed to the surface. Geologists that have examined Maltese limestone have noticed that five subcategories of limestone are found on the island. These subtypes all contain mostly calcium carbonate. Calcium carbonate is a white compound that makes up about 5% of the Earth’s surface. It is found in sedimentary rock (like limestone) and is highly susceptible to weathering. Many of the fortifications created by the Knights of St. John are carved out of limestone.
Tafoni:
Next to the viewpoint of the Grand Harbor, you can observe a specimen of limestone with tafoni divots in it. Tafoni are small, rounded openings in a rock face created by weathering. Tafoni weathering commonly occurs in sedimentary rocks, such as sandstone and limestone. They can appear sponge-like and can be created in arid environments.
Geologists believe that tafoni can form under the influence of the three types of weathering: mechanical, chemical, or biological. Mechanical weathering is the wearing away of rock due to physical processes (like water, wind, etc.) When ice in polar climates freezes, it can expand and put stress on the surrounding rock. This process, known as ice abrasion, can carve out small holes and cause flaking on the rock face. In areas near floodplains, excessive water can cause mineral swelling in clay-containing rock. Mineral swelling can lead to fragmentation and weathering of the rock. In rare circumstances, tafoni holes may be visible. Chemical weathering is the disintegration of rock due to chemical reactions. Salt crystal weathering is a type of chemical weathering that can create tafoni. This process occurs when moisture containing dissolved salts lands on a rock surface containing high amounts of calcium carbonate (like limestone). The salts can dissolve this compound through a chemical process, which weakens the rock face and forms pockets/grooves of weathered rock. Tafoni found near coastlines is often created due to sea spray in the air. Biological weathering is when organisms like plants or fungi break down a rock face and weather it. Lichens and moss can attach to the surface of a rock and release acids. This biochemical process can dissolve rock.
**This EarthCache is not located directly at the viewpoint, although it is close to it. Complete the following logging tasks by locating the limestone brick at the site**
Logging Tasks:
- Search the limestone for a network of tafoni holes. Do they tend to appear circular, elliptical, or polygonal?
- Based on your observations at the GZ and what you’ve learned in the description, what type of weathering (mechanical, chemical, or biological) seems to be causing tafoni development at the GZ?
- Feel the texture inside of the tafoni divots. Do the tafoni feel rougher, smoother, or the same as the parent rock (limestone)?
- This is a required photo task. Please provide a photo of yourself, your GPS, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://www.nps.gov/articles/tafoni.htm
https://education.nationalgeographic.org/resource/weathering/#:~:text=Mechanical%20Weathering%20Mechanical%20weathering%2C%20also,cracks%20and%20crevices%20in%20rock
https://onepetro.org/ARMAUSRMS/proceedings-abstract/ARMA88/All-ARMA88/ARMA-88-0017/129948
https://era.org.mt/topic/maltese-geology/
| We have earned GSA's highest level: |
 |
